help button home button Endocrine Society Endocrine Reviews
HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS

Endocrine Reviews, doi:10.1210/er.2005-0021
This Article
Right arrow Abstract Freely available
Right arrow Full Text (PDF)
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Right arrow Citation Map
Services
Right arrow Email this article to a friend
Right arrow Similar articles in this journal
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Right arrow Request Copyright Permission
Citing Articles
Right arrow Citing Articles via HighWire
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Vasudevan, N.
Right arrow Articles by Pfaff, D. W.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Vasudevan, N.
Right arrow Articles by Pfaff, D. W.
Endocrine Reviews 28 (1): 1-19
Copyright © 2007 by The Endocrine Society

Membrane-Initiated Actions of Estrogens in Neuroendocrinology: Emerging Principles

Nandini Vasudevan and Donald W. Pfaff

Department of Biology (N.V.), Pennsylvania State University, University Park, Pennsylvania 16802; and Laboratory of Neurobiology and Behavior (D.W.P.), The Rockefeller University, New York, New York 10021

Correspondence: Address all correspondence and requests for reprints to: Dr. Nandini Vasudevan, 208 Mueller Laboratory, Department of Biology, Pennsylvania State University, University Park, Pennsylvania 16802. E-mail: nuv1{at}psu.edu


    Abstract
 Top
 Abstract
 I. Introduction
 II. Estrogens Signal via...
 III. Membrane-Initiated Hormone...
 IV. The Signal Transduction...
 V. Convergence of the...
 VI. Initiation of Membrane...
 VII. Summary and Future...
 References
 
Hormonal ligands for the nuclear receptor superfamily have at least two interacting mechanisms of action: 1) classical transcriptional regulation of target genes (genomic mechanisms); and 2) nongenomic actions that are initiated at the cell membrane, which could impact transcription. Although transcriptional mechanisms are increasingly well understood, membrane-initiated actions of these ligands are incompletely understood. Historically, this has led to a considerable divergence of thought in the molecular endocrine field.

We have attempted to uncover principles of hormone action that are relevant to membrane-initiated actions of estrogens. There is evidence that the membrane-limited actions of hormones, particularly estrogens, involve the rapid activation of kinases and the release of calcium. Membrane actions of estrogens, which activate these rapid signaling cascades, can also potentiate nuclear transcription. These signaling cascades may occur in parallel or in series but subsequently converge at the level of modification of transcriptionally relevant molecules such as nuclear receptors and/or coactivators. In addition, other hormones or neurotransmitters may also activate cascades to crosstalk with estrogen receptor-mediated transcription. The idea of synergistic coupling between membrane-initiated and genomic actions of hormones fundamentally revises the paradigms of cell signaling in neuroendocrinology.

I. Introduction
II. Estrogens Signal via Both Genomic and Nongenomic Modes
A. The genomic mode of estrogen action
B. Membrane-initiated (nongenomic) actions of estrogens: the use of membrane-limited conjugates as an experimental probe in neural cells
C. Membrane-initiated (nongenomic) actions of estrogens in neural cells

III. Membrane-Initiated Hormone Actions Potentiate Their Transcriptional Actions
A. Coupling of the membrane-initiated actions of estrogen to transcription: the consequence for reproductive behavior
B. Coupling of membrane-initiated actions of estrogens to transcription in nonreproductive functions
C. The coupling of membrane-initiated actions to transcription is studied in vitro by using a two-pulse transcriptional paradigm in cell culture

IV. The Signal Transduction Cascades Initiated by Estrogens at the Membrane May Occur in Parallel or in Series
A. Membrane-initiated actions of estrogens may also occur in parallel or in series in the MCF-7 breast carcinoma cell line

V. Convergence of the Membrane-Initiated Actions of Hormones to Transcription Involves Protein-Protein Interactions, Protein Translocation, and Protein Phosphorylation
A. Coupling to transcription via stabilization or dimerization of molecules relevant to transcription
B. Coupling to transcription via the physical movement of molecules into the nucleus
C. Coupling to transcription via phosphorylation of molecules relevant to transcription

VI. Initiation of Membrane-Initiated Actions at the Membrane Involves Both Classical "Nuclear Receptors" and Other Proteins
A. The membrane estrogen receptor could be a novel protein in some cell types
B. The membrane estrogen receptor is the classical ER in other cell types
C. Do different cell types have different receptors?

VII. Summary and Future Directions


    I. Introduction
 Top
 Abstract
 I. Introduction
 II. Estrogens Signal via...
 III. Membrane-Initiated Hormone...
 IV. The Signal Transduction...
 V. Convergence of the...
 VI. Initiation of Membrane...
 VII. Summary and Future...
 References
 
ESTROGENS ARE IMPORTANT endocrine effectors of reproduction (1, 2, 3). They also play an important and sometimes permissive role in liver and cardiovascular physiology, neuronal growth and differentiation, neuroprotection, cognition, and regulation of mood (4, 5, 6, 7). They are ligands for estrogen receptors (ERs) {alpha} and ß, members of the nuclear receptor superfamily. These isoforms, have a modular "domain" structure, a characteristic that they share with other members of the nuclear receptor superfamily (8, 9, 10, 11, 12). The molecular mechanisms by which estrogens change the response of target tissues can be broadly divided into two categories: 1) genomic actions, and 2) nongenomic actions. The focus of this review is the interplay between both of these mechanisms with respect to transcription, particularly in the central nervous system (CNS). Each of the principles of estrogen action, stated as a section heading, is elaborated upon in that section.


    II. Estrogens Signal via Both Genomic and Nongenomic Modes
 Top
 Abstract
 I. Introduction
 II. Estrogens Signal via...
 III. Membrane-Initiated Hormone...
 IV. The Signal Transduction...
 V. Convergence of the...
 VI. Initiation of Membrane...
 VII. Summary and Future...
 References
 
A. The genomic mode of estrogen action
Genomic actions are those wherein the ER exerts transcriptional effects via interaction with estrogens (see Ref. 12 and references therein). In the absence of estrogens, the ER in various target tissues is associated with heat-shock proteins in a transcriptionally inactive state (13). Binding of 17ß-estradiol, the natural endogenous ligand, or a similar agonist molecule induces a conformational change in the ER, promoting ER homodimerization and subsequent nuclear translocation. In the nucleus, the ER acts as a ligand-dependent transcription factor, binding estrogen response elements (EREs) regulating gene transcription (9, 10, 11, 14) (12). This mechanism is of importance in pathological states such as hormone-dependent breast cancers (15, 16, 17). Therapy that prevents hormone binding to ER{alpha} can decrease cell proliferation, whereas the presence of 17ß-estradiol can increase the proliferation rate (14). In the CNS, the focus of this review, several genes are also regulated in this manner by estrogen-bound ER{alpha}. For example, in ER{alpha} knockout mice, estrogen cannot induce the progesterone receptor (PR) gene in the hippocampus, indicating that genomic effects on this important estrogen-marker gene required the ER{alpha} (18). Increased transcription of neurotrophins such as brain-derived neurotrophic factor (BDNF) and their high-affinity receptors (19, 20, 21), the oxytocin-oxytocin receptor genes (22, 23, 24), the preproenkephalin gene (25, 26, 27), the antiapoptotic genes such as Bcl-2 (28, 29), are important in neuroprotection (7), neurodevelopment (30), and reproductive behaviors driven by estrogens (1, 31, 32). Generally, cellular signaling cascades activated by estrogens and other hormones were thought not only to be disparate from classical genomic actions (33, 34, 35, 36) but also to lead to fewer or less important phenotypes.

B. Membrane-initiated (nongenomic) actions of estrogens: the use of membrane-limited conjugates as an experimental probe in neural cells
First reported in 1967 by Szego and Davis (37), acute 17ß-estradiol administration could increase cAMP in the uterus of ovariectomized mice within 15 sec, in stark contrast to the slower genomic actions of estrogens, which take hours for final changes in protein expression to occur, after transcriptional regulation. Nongenomic actions of estrogens can therefore be defined as rapid (milliseconds to minutes) effects, generally initiated at the plasma membrane by 17ß-estradiol, resulting in the activation of signal transduction pathways, including calcium flux, within target cells. The nature of the receptor that binds 17ß-estradiol at the plasma membrane is immaterial to this definition. Studies that attempt to conclusively demonstrate membrane-initiated estrogen effects that are confined to the membrane often utilize membrane-limited estrogen conjugates, such as E2-BSA (17ß-estradiol linked to BSA) (38) or E2-HRP (17ß-estradiol linked to horseradish peroxidase) to separate membrane-initiated actions of these conjugates from effects that arise from the steroid inside the cell. These compounds consist of 17ß-estradiol molecules (32–38 moles of 17ß-estradiol/BSA conjugated to the BSA molecule at a specific site, such as to the sixth carbon via an oxime linkage [17ß-estradiol-6-O-carboxymethyloxime-BSA (E2–6-BSA)], to the 17th carbon [1,3,5, (10)-estratrien-3,17ß-diol 17-hemisuccinate-BSA (E2–17-BSA)] or to the third carbon (39). In the immortalized GT-1 cell line, both 17ß-estradiol and E2–6-BSA increase cAMP (40). Similarly, in primary cultures of neostriatal neurons, both 17ß-estradiol and E2–6-BSA reduce calcium currents (41). Although most studies have used one or sometimes several of these compounds to mimic a membrane-limited action for 17ß-estradiol, several caveats should be noted regarding the use of these conjugates. There has been considerable controversy over the possible release of free 17ß-estradiol from membrane-limited conjugates and the possibility of endocytosis of the conjugate itself with the subsequent release of free 17ß-estradiol into cells. Stevis et al. (42) demonstrated that both E2–6-BSA and E2–17-BSA had free, presumably genomically active, 17ß-estradiol in the preparation as measured by RIA and required filtration to remove the free 17ß-estradiol. This suggests that, in some studies, signal transduction pathways that were thought to have been initiated at the membrane might have been initiated within the cell by free 17ß-estradiol present in the unfiltered E2-BSA preparation. In addition, the activity of E2-BSA conjugates has not always paralleled the activity of free 17ß-estradiol itself. For example, E2-BSA devoid of free 17ß-estradiol (achieved by filtration) did not bind either ER{alpha} or ERß or to an ERE under in vitro conditions where 17ß-estradiol did bind both ER isoforms and the ERE (42). In the SK-N-SH neuroblastoma cell line, filtered E2-BSA induced MAPK, whereas free 17ß-estradiol did not do so (42). This suggests that the E2-BSA binding conformation to the ER differs from that of 17ß-estradiol with a subsequent change in the ability of the receptor to bind or transactivate genes that are regulated by EREs. This could result in artifactual results, i.e., nonphysiological activation of rapid signal transduction pathways, with E2-BSA if ER{alpha} or ERß acts as the membrane ER.

Within neurons, studies from Susan Wray’s laboratory also show functional differences between different E2-BSA conjugates in the activation of the protein kinase A (PKA) pathway and calcium flux. Although both 17ß-estradiol and filtered E2–17-BSA increased intracellular Ca2+ levels in GnRH-positive cells in nasal explants, the transcription inhibitor, 5,6-dichloro-1-ß-D-ribobenzimidazole (DRB) could abrogate the 17ß-estradiol-mediated increase but not the E2–17-BSA increase in calcium in explants (43). In a primary culture of GnRH neurons, E2–6-BSA did not increase cAMP response element (CRE) binding protein (CREB) phosphorylation although 17ß-estradiol did so (44). This suggests that the mode of conjugation of the 17ß-estradiol moiety to BSA may allow different conjugates to contact different membrane ERs, i.e., different proteins. Alternatively, binding of free 17ß-estradiol and E2-BSA conjugates to the same receptor protein could lead to differences in protein conformation, which presumably lead to differences in calcium flux. All of these studies using filtered E2-BSA conjugates and 17ß-estradiol demonstrate that different signal transduction pathways could be activated by different E2-BSA conjugates or 17ß-estradiol, depending on cell type. One implication is that different cell types possess varied combinations of proteins capable of binding E2-BSA and/or free 17ß-estradiol. Recently, the Katzenellenbogen laboratory has synthesized estrogen dendrimer conjugates that are stable, do not seem to leach free 17ß-estradiol, and do not enter the nucleus of breast carcinoma cells to conduct genomic actions. They do not induce transcription of endogenous genes and can activate the ERK pathway rapidly at 2 min after treatment at levels similar to free 17ß-estradiol (45). These studies underscore the importance of using free 17ß-estradiol (the endogenous ER ligand) as a comparison to the artificial conjugate, E2-BSA in all studies. If the actions of the artificial conjugate, E2-BSA, and 17ß-estradiol are comparable, the E2-BSA preparation should preferably have been filtered and demonstrated to possess no transcriptional activity to conclude a true nongenomic, membrane-initiated effect. Unfiltered E2-BSA could show effects similar to 17ß-estradiol due to the presence of free 17ß-estradiol in the preparation. It should be noted that very few studies, particularly those before 2000, have explicitly shown that the E2-BSA preparation used in the study has no free 17ß-estradiol or no genomic activity.

What, therefore, could be considered a nongenomic effect? If filtered E2-BSA is not used in the study, an acute application of 17ß-estradiol that activates classically nongenomic effects (i.e., kinase activation or calcium flux) in a short time frame could also be considered to be a membrane-initiated action of estrogen. However, calcium flux could also be regulated nongenomically by 17ß-estradiol acting directly on intracellular calcium stores, apart from being initiated at the membrane. Similarly, kinase activation could also be a result of stabilization or localization; these processes may be nongenomically activated by estrogens but may not be plasma membrane-initiated.

C. Membrane-initiated (nongenomic) actions of estrogens in neural cells
In this review, we will discuss nongenomic actions of estrogens in the CNS only when they occur in physiologically relevant contexts, which will also be described to lend perspective to these actions. In the CNS, membrane-initiated actions of estrogens have been observed predominantly in the context of reproduction, neuroprotection, and neurotrophism, all of which are also affected significantly by the genomic actions of estrogens.

1. Nongenomic actions play a dominant role in the estrogen effect on neuronal excitability.
Estrogens have a rapid effect on neuronal excitability; this has been typically studied using neurons from the hypothalamus relevant to reproductive physiology, such as those that produce GnRH or neurons in the ventromedial hypothalamus (VMH) that control reproductive behavior or lordosis. In hypothalamic slice cultures from ovariectomized guinea pigs, 17ß-estradiol could uncouple the µ-opioid receptor in pro-opiomelanocortin (POMC) neurons and the {gamma}-aminobutyric acid (GABA) (B) receptors from dopaminergic neurons from the small conductance, G protein-coupled inwardly rectifying K+ channels (GIRK), resulting in lower efficacy of µ-opioid and GABA agonists activation of these channels and lower hyperpolarization of these cells (46). This increase in 17ß-estradiol-mediated excitation is blocked by a variety of inhibitors to intracellular signaling cascades, such as phospholipase C, PKA, and protein kinase C (PKC) (46, 47). The uncoupling effect can be mimicked by membrane impermeant E2-BSA and the selective ER modulators, raloxifene and 4-hydroxytamoxifen (48). The inhibitor data, along with the blockade of uncoupling by an ER antagonist, ICI 182,780, suggest that the ER is G protein-coupled in hypothalamic neurons (36). An alternate explanation could be that the ER is required intracellularly for this effect, whereas the rapid signaling cascades are activated independently by a membrane ER (mER) coupled to a G protein. Qiu et al. (49) have proposed a model whereby a G{alpha}q coupled ER at the membrane initiates this signaling cascade of enzymes, which appear to be arranged in series. Using subtractive hybridization and microarray analysis, Malyala et al. (50, 51) showed that estrogen altered the mRNA levels for a number of neurotransmitter receptors and synaptic vesicle release molecules [e.g., GABA (B) R2 subunit and synaptobrevin] as well as for enzymes in rapid signaling cascades [i.e., phosphotidylinositol-3-kinase (PI3K) p55{gamma}, gec-1, Rab 11a GTPase]. Hence, these molecules could be regulated at the level of enzyme activation by rapid, membrane-initiated mechanisms and at the level of transcription by genomic mechanisms. However, at least some part of the effect of 17ß-estradiol on neuronal excitability is solely rapid and membrane-initiated, as evidenced by both the short time scales of application and the data that cycloheximide use in hypothalamic slices could not block the uncoupling of µ-opioid receptors to the GIRK channels (52). Contrary to the evidence that a G{alpha}q receptor may increase excitability in the arcuate nucleus, in CA1 hippocampal neurons, this could be attributed to a G{alpha}s receptor that is activated rapidly by estrogens. 17ß-Estradiol as well as E2-BSA rapidly potentiated kainate-induced currents via PKA activation initiated by a G{alpha}s receptor (53). This was preserved in both wild-type and ER{alpha} knockout mice, suggesting that the classical ER was not required for the increase in excitability in CA1 hippocampal cells in response to kainate (54). The increase in neuronal excitability by estrogens is a scenario where nongenomic effects of estrogens are probably dominant over genomic effects.

2. Effects of estrogen on neuroprotection involve the activation of kinases, calcium flux, and the induction of genes.
Estrogen-mediated neuroprotection against various agents such as ischemia, glutamate, and N-methyl-D-aspartate (NMDA)-mediated excitotoxicity and degenerative diseases such as Parkinson’s and Alzheimer’s disease (5, 55) has attracted intense interest. A majority of this work stems from the finding that intact female rats had lower mortality and better neuronal survival than male rats after middle cerebral artery occlusion (MCAO) but that this effect was eliminated by ovariectomy (56). Administration of 17ß-estradiol, but not progesterone, to ovariectomized female rats (57, 58, 59), aged reproductively senescent rats (60), and male rats (61) reduced infarct volumes after MCAO. In general, to achieve neuroprotection against excitotoxicity and ß-amyloid-mediated toxicity in neurons, estrogens regulate molecules that are involved in programmed cell death and inflammation in a multifaceted manner using both genomic and membrane-initiated modes of action. Central to neuroprotection in hippocampal neurons and in NT2 cells is the up-regulation by 17ß-estradiol of the antiapoptotic genes Bcl-2 and Bcl-XL (28, 62, 63) and the down-regulation of Nip2, an inhibitor of Bcl-2 (64), as well as the activation of PI3K and the downstream substrate, protein kinase B (Akt/PKB) (65, 66). In addition, 17ß-estradiol induction of Bcl-2 mRNA has been shown to require IGF-I receptor activation (67); ER{alpha} is abundantly coexpressed with IGF-I receptor in female rat brain (68). Because both 17ß-estradiol and ER{alpha} are needed, presumably ligand-dependent transcription by the ER{alpha} is needed. However, the requirement for IGF-I receptor activation is less clear; it is possible that the downstream signaling events from the IGF-I receptor, i.e., MAPK, and Akt kinase activation are needed for Bcl-2 induction. Indeed, in PC12 cells, estrogen-mediated Akt/PKB activation induces Bcl-2 mRNA via the phosphorylation of the CREB and the subsequent binding of this protein to the CRE in the Bcl-2 promoter (69). Recently, Wu et al. (29) have reported that calcium influx mediated by rapid regulation of L-type calcium channels by 17ß-estradiol is critical in initiating a src/ERK signaling cascade that also results in enhanced Bcl-2 expression in cultured rat hippocampal neurons. Mendez et al. (70) have proposed a hypothetical model for IGF-ER interaction in the brain that is relevant to neuroprotection. On activation of the IGF-IR by IGF, the ER{alpha} associates with the receptor at the plasma membrane and activates PI3K via interaction with the p85 subunit of PI3K (70). Regulation of the downstream Akt/PKB target, glycogen synthase 3ß (GSK-3ß), by 17ß-estradiol results in a decrease in phosphorylated Tau protein in the rat hippocampus, providing protection against Alzheimer’s disease (71). However, it is not clear whether the dynamics of this model is similar with ligand-free ER{alpha} or ligand-bound ER{alpha} or how the activation of GSK-3ß decreases Tau protein.

Rapid activation of both PKB and MAPK, and to a lesser extent PKC, by estrogens has also been shown to be important in neuroprotection in a number of neuronal cell types and against different types of insults. In the rat retina, rapid activation of the PI3K pathway is important in estrogen-mediated protection against light-induced photoreceptor degeneration (72). 17ß-Estradiol also rapidly activates p44/p42 MAPK in cortical slices (73, 74) and in hippocampal neurites (75). In the rat hippocampus, rapid induction of MAPK by estrogens protects against quinoline-induced toxicity (76, 77), whereas in hippocampal primary culture as well as in SK-N-MC neuroblastoma cells, phosphorylation of the MAPK ERK 1/2 by estrogens leads to enhanced secretion of ß-amyloid precursor protein (sAPP) (78). In primary rat cortical neurons, application of 17ß-estradiol or a membrane-limited E2-BSA conjugate rapidly stimulated the release of sAPP{alpha}, whereas PKC inhibitors, added in addition to estrogens, block this effect (79). This secreted product decreases the generation of the ß-amyloid protein itself, which is a dominant neurotoxic component in the plaques of Alzheimer’s patients. Exogenous 17ß-estradiol treatment did not confer neuroprotection against MCAO in PKC{gamma} knockout mice, suggesting that this PKC isoform mediates neuroprotection by 17ß-estradiol against ischemia (80). Although these studies show that both 17ß-estradiol-activated MAPK and Akt pathways appear to be necessary for neuroprotection, alone they are not sufficient. Although Bcl-2 transcription appears dependent on rapid signaling pathways, not all genes involved in neuroprotection may be so dependent, and not all signal transduction cascades may affect transcription. In addition, the relative contribution of membrane-initiated vs. genomic actions in neuroprotection is unclear.

3. Effects of estrogen on dendritic spines involve both nongenomic and genomic actions.
17ß-Estradiol also increases the growth of dendritic spines, modulating synaptic plasticity, in several hormone-responsive brain areas such as the VMH (81), hippocampus, and amygdala (82) via both genomic and membrane-initiated mechanisms. Estrogen-mediated development of spines in rat hippocampal cultures is dependent on rapid NMDA receptor activation (83) via c-src, which in turn may be activated by 17ß-estradiol binding a putative membrane ER (4). Similar to the scenario in midbrain dopaminergic neurons, PKA activation and phospho-CREB (pCREB) increases are also required for 17ß-estradiol-induced spine increase in rat hippocampal primary cultures (84, 85). Estrogen-induced pCREB in the rat hippocampus, which occurs as early as 1 h after addition of 17ß-estradiol, requires calmodulin kinase (CaMK)II and MAPK signaling but is less dependent on PKB (86). However, the longer time frame of inhibitor addition in this study does not allow conclusive confirmation of a rapid or membrane-limited effect of estrogen on these pathways, although it is highly probable, based on the signaling pathways activated. In female mice, administration of 17ß-estradiol for 1 h increased pCREB immunoreactivity in the VMH and medial preoptic area, whereas in male mice, pCREB was increased in the CA1 field of the hippocampus and in the medial septum (87). In cultured rat hippocampal neurons, 17ß-estradiol administration increased MAPK-dependent CREB activation in as little as 3 min (88 ). In differentiated NG108–15 neuroblastoma cells, Akt/PKB activation by 17ß-estradiol increased protein synthesis of PSD-95, a major component of spines, through phosphorylation of the elongation factor, 4E-BP1; this is clearly a nongenomic effect because PSD-95 mRNA does not appear to be regulated by estrogen in this system. Estrogen-induced stabilization and maintenance of spines may also depend on the decrease of GABA inhibition exerted by interneurons on CA1 pyramidal neurons (4, 89) via decrease in glutamate decarboxylase content in interneurons by 17ß-estradiol. Such a GABA decrease could also increase BDNF synthesis by solely genomic mechanisms such as transcriptional up-regulation of BDNF mRNA via a noncanonical ERE (20) in hippocampal pyramidal cells. A more controversial model for 17ß-estradiol-mediated increase in BDNF levels proposes that membrane ER signaling results in BDNF translation in giant mossy fiber boutons, which in turn synapse on CA3 pyramidal neurons (90, 91). In differentiating midbrain dopaminergic neurons, 17ß-estradiol rapidly (within 30 min) activates the PI3K/Akt signaling cascade (92); both this pathway and estrogen-induced PKA are important in neurite outgrowth in these neurons (93). Blockade of PKA or NMDA receptor or BDNF abrogates the effect of estrogens on spines in hippocampal neurons, suggesting that all of these pathways are needed for spine formation and stabilization. Alternatively, these could be part of a single pathway that leads to spine formation; hence, decreasing the levels of one molecule in the pathway could decrease the number of spines dramatically. Because all of these studies, with the exception of studies that involve pCREB and the PKA signaling pathway (86), use application of free 17ß-estradiol on longer time scales than is traditional for membrane-initiated actions, it is impossible to conclusively rule out transcriptional genomic actions of 17ß-estradiol on these molecules. However, the requirement for the activation of several kinases suggests that nongenomic pathways are important in dendritic spine growth, in concert with genomic effects of estrogens.

The data in these studies suggest that the PI3K/PKB pathway may be predominant in neuroprotection, whereas the PKA pathway could be more important in neurotrophism. Both signal transduction pathways, initiated by G protein-coupled membrane receptors, affect neuronal excitability in the hypothalamus and hippocampus.


    III. Membrane-Initiated Hormone Actions Potentiate Their Transcriptional Actions
 Top
 Abstract
 I. Introduction
 II. Estrogens Signal via...
 III. Membrane-Initiated Hormone...
 IV. The Signal Transduction...
 V. Convergence of the...
 VI. Initiation of Membrane...
 VII. Summary and Future...
 References
 
The hypothesis that rapid signaling cascades initiated at the membrane by estrogens can lead to changes in transcription from ERE-containing genes is inspired by the fact that reproductive behavior or lordosis in female mammals is dependent on gene expression in discrete brain areas as well as kinase activation and changes in neuronal excitability by estrogens. Hence, this is a good model system to study the interaction between rapid and slow actions of estrogens.

A. Coupling of the membrane-initiated actions of estrogen to transcription: the consequence for reproductive behavior
The estrogen control of female reproductive behavior or lordosis (32) presents a scenario for the interplay between membrane-initiated signal transduction mechanisms and the classical genomic mode of transcription. In the VMH, estrogen imposes hormonal dependence on neurons that control descending efferents to the muscles in the lower back that allow for the arching of the back, a posture characteristic of lordosis (32, 94, 95). Genes transcriptionally regulated by estrogen that may play a role in approach and sex behaviors in rodents include the PR; the oxytocin receptor and its ligand, oxytocin; the preproenkephalin peptides; and the {alpha}1b-adrenergic and muscarinic receptors (96, 97).

In support of the idea that membrane-initiated actions play a role in rodent lordosis behavior, second messengers in kinase cascades can potentiate lordosis. For example, phorbol esters (PKC activators) infused into the midbrain central gray could facilitate lordosis (98), whereas PKC inhibitors could reduce lordosis behavior (95). Dibutryl cAMP and 8-bromo cAMP infused into the VMH could reduce the inhibition mediated by serotonin (99), suggesting that the coupling of the serotonin receptor to PKA inhibition has physiological relevance. Antagonists to protein kinases or to G protein-coupled receptors (GPCRs) reduce lordosis behavior, suggesting that activation of kinase cascades is permissive to lordosis. Infusion of PI3K or MAPK inhibitors into the VMH during estrogen priming of ovariectomized rats attenuates lordosis (100). In addition, IGF receptor antagonists block lordosis induction by estrogen in female rats (100, 101), whereas {delta}-opioid receptor agonists infused into the VMH, but not into the medial preoptic area, can increase lordosis in female rats already primed with estrogen and progesterone (102). In the VMH, estrogen increase in neuronal excitability is thought to be relevant to lordosis behavior in rodents (103, 104). Similar to the effects of estrogen on POMC and dopamine neurons (see Section II.C), in VMH slices, acute 17ß-estradiol administration (10 min) can potentiate the neuronal excitation caused by both histamine and NMDA, two neurotransmitters that act via GPCRs and ligand-gated ion channels, respectively (105). This suggests that 17ß-estradiol can influence two different transduction pathways to achieve a final effect, i.e., increase in depolarization of neurons. Because it appears that both genomic and membrane-initiated actions of estrogen are possibly important in lordosis behavior, we initially hypothesized that membrane-initiated actions of estrogen impacting signal transduction cascades could regulate gene transcription, also induced by estrogen (106).

B. Coupling of membrane-initiated actions of estrogens to transcription in nonreproductive functions
Apart from lordosis behavior, the above hypothesis also has roots in neuronal and non-neuronal cell culture studies which show that estrogen-induced gene transcription is indeed influenced by signaling molecules. In the human neuroblastoma cell line, SK-N-SH, a membrane-limited estrogen conjugate (E2-BSA) can induce the c-fos gene via MAPK kinase and MAPK, demonstrating a mechanism by which genes possessing non-ERE promoters might still be induced by estrogen (107). In the same cell line, E2-BSA could induce the neurotensin gene, an effect blocked by PKA inhibitors. E2-BSA alone did not induce transcription from the consensus ERE (108); presumably, there was no free 17ß-estradiol in this preparation. In the MCF-7 breast carcinoma cell line, PR mRNA is induced by both estrogen and PKA activators (109), whereas the estrogen up-regulation of cyclin D1 has been reported to be through the CRE (110). The levels of estrogen-regulated mitogenic proteins, cyclin D1 and c-myc, can be decreased by inhibition of MAPK and PI3K (111). Inhibitors to PI3K, dominant-negative Akt mutants, and a selective ErbB2 inhibitor can decrease the up-regulation of ER{alpha} mRNA by estrogen (autoregulation) in MCF-7 cells (112, 113). In endothelial cells, inhibitors for PI3K or the use of dominant-negative constructs to PI3K also block estrogen-induced cyclo-oxygenase-2 (114). An inhibitor of PKC could decrease transcriptional potentiation by E2-BSA of ER{alpha}-mediated transcription from a consensus ERE in MCF-7 cells (115). These studies show that a number of estrogen-induced genes or estrogen-induced promoters can be regulated by second messenger pathways.

C. The coupling of membrane-initiated actions to transcription is studied in vitro by using a two-pulse transcriptional paradigm in cell culture
A "proof of concept" result for the hypothesis that transcription can be influenced by kinase cascades was first demonstrated in a neuroblastoma cell line, SK-N-BE(2)C, which is devoid of endogenous ER{alpha} or ERß isoforms and has been used previously as a model for estrogen action in the brain upon the transient or stable transfection with ER{alpha} (116, 117). This cell line has been studied extensively for the effects of both µ- and {delta}-opioid (118, 119) receptors, demonstrating that GPCR-mediated receptor effects are possible in this cell line.

The use of a novel transcriptional two-pulse hormonal administration paradigm in cell culture as a tool to study transcriptional potentiation was inspired by earlier studies where discontinuous, pulsatile estrogen administration is effective in achieving cellular division and behavior. In a pioneering study, Harris and Gorski (120) showed that a discontinuous schedule of estrogen administration can induce uterine cell division. Discontinuous schedules of two 1-h pulses of estradiol benzoate (EB) with an interpulse interval of 6 h are as effective in inducing both lordosis and the PR in the VMH of female rats 48 h after the first EB administration as a continuous administration of EB for 48 h (121). It is possible that in the first pulse, estrogen may initiate kinase cascades (rapid membrane-initiated actions) that may potentiate genomic transcriptional actions in the second pulse.

To separate the membrane-initiated actions of estrogen from the genomic slower actions of estrogen in this cell line, estrogens added in the first 20-min pulse can initiate signaling from the membrane, whereas 17ß-estradiol in the second 2-h pulse promotes genomic action on a consensus ERE-linked reporter in neuroblastoma cells. We cannot completely rule out membrane actions in the second pulse because free 17ß-estradiol also has the ability to act at membrane sites. To initiate signaling cascades solely at the membrane, a membrane-impermeable estrogen conjugate, E2-BSA, filtered (42) to remove free 17ß-estradiol, was applied in the first pulse. Despite controversy over the possible leaching of free 17ß-estradiol into cells (122) (see Section II.B), we have shown that continuous administration of E2-BSA for 24 h to transfected SK-N-BE(2)C cells does not increase transcription above basal levels from a consensus ERE-based reporter gene (123). In addition, Taguchi et al. (124) showed that E2-BSA possessed the ability to bind to the ER at membrane sites.

In these initial experiments, nanomolar concentrations of E2-BSA can potentiate transcription from a transfected consensus ERE-driven luciferase gene in neuroblastoma cells induced by a second 2-h pulse of 10–9 M 17ß-estradiol (E2-BSA-mediated transcriptional potentiation) (106) (Fig. 1Go). E2-BSA can hence substitute for 17ß-estradiol in the first pulse. A lower level of transcription (albeit higher than control) is seen with vehicle in the first pulse, followed by the addition of 17ß-estradiol in the second longer pulse. A "reverse" pulse paradigm where 17ß-estradiol is given in the first pulse followed by E2-BSA in the second pulse does not potentiate transcription, demonstrating that preliminary membrane effects are both sufficient and essential for later transcriptional effects (106). To pinpoint specific kinases that play a role in E2-BSA transcriptional potentiation, specific inhibitors in the first pulse along with E2-BSA or in the second pulse with 17ß-estradiol were used. This strategy demonstrated that PKA and PKC may play a role in E2-BSA-mediated transcriptional potentiation because the PKC and PKA inhibitors chelerythrine and Sp-cAMPs in the first pulse reduce the level of transcription but do not interfere with potentiation when added in the second pulse. On the other hand, the calcium chelator BAPTA-AM blocks E2-BSA-mediated transcriptional potentiation when added either in the first pulse along with E2-BSA or in the second pulse with 17ß-estradiol, suggesting that calcium is important in both the membrane-initiated and genomic actions of estrogen (106). Using selective inhibitors, we have also provided evidence (125) that the entry of calcium via N-type voltage-gated calcium channels is important in both genomic and membrane-initiated actions of estrogens, whereas the ryanodine receptor, which modulates intracellular stores of calcium, is important in coupling membrane-initiated actions of estrogen initiated at the membrane to transcription.


Figure 1
View larger version (18K):
[in this window]
[in a new window]

 
FIG. 1. E2-BSA (10–9 M) potentiates transcription mediated by 17ß-estradiol (10–9 M) in the second pulse. SK-N-BE (2 )C neuroblastoma cells are cotransfected using Effectene reagent (QIAGEN Inc., Valencia, CA) with pGL2-TATA-Inr-Luc (reporter; 3xereluc) (200 ng), pSG-hER{alpha} (80 ng), pSV-ßgal (80 ng) (Promega, Madison, WI), and pBSKII+ (Stratagene, La Jolla, CA) to a total of 400 ng/well. Twenty-four hours after transfection, a two-pulse regimen is initiated with both pulses separated by a hormone-free 4-h interval. Results (n = at least 4 per treatment group in duplicate experiments) are analyzed using one-way ANOVA followed by Student-Newman-Keuls post hoc test (Prism Software Corp., Irvine, CA) to compare normalized luciferase activity between treatment groups (106 ). E2-BSA (10–9 M) was given for 20 min in the first pulse, and 17ß-estradiol (10–9 M) was given in the second pulse for a duration of 2 h (106 ). Test of "potentiation" hypothesis: E2-BSA given in the first pulse was followed by 17ß-estradiol in the second pulse (far right bar). Results (n = 4 per treatment group from replicate experiments) are represented as mean + SEM. *, P < 0.05 compared with all other treatment groups; #, P < 0.05 compared with the vehicle group (106 ).

 

    IV. The Signal Transduction Cascades Initiated by Estrogens at the Membrane May Occur in Parallel or in Series
 Top
 Abstract
 I. Introduction
 II. Estrogens Signal via...
 III. Membrane-Initiated Hormone...
 IV. The Signal Transduction...
 V. Convergence of the...
 VI. Initiation of Membrane...
 VII. Summary and Future...
 References
 
The experimental strategy using inhibitors to different kinase cascades and calcium channels resulted in several kinases being implicated in E2-BSA-mediated transcriptional potentiation. Presumably, all these kinases are activated by estrogens acting at the membrane of neuroblastoma cells. In addition, our data (unpublished) with dominant-negative and constitutively active G{alpha} mutants demonstrate that the membrane ER in this cell line may be coupled to G{alpha}q. Attempting to present signaling hierarchies in this cell line, models (126) were constructed taking into account both the signaling cascades elucidated by us and previous work from Martin Kelly’s laboratory which suggests that PKC activation of PKA via adenylyl cyclase (signaling in series) underlies the modulation of the SK channel in the guinea pig arcuate nucleus by estrogen (47, 49, 50, 51). Qiu et al. (49) have also suggested that estrogen can modulate µ-opioid and GABA activity in the arcuate nucleus via an ER coupled to G{alpha}q. What is the role for calcium in our paradigm? The absolute importance of calcium is shown by the use of BAPTA-AM; this calcium chelator abrogates all transcription when added in either the first pulse with E2-BSA or in the second pulse with 17ß-estradiol. In the mouse hippocampus, administration of EB for 30 min activates CaMKII in a time- and dose-dependent manner (127), whereas CamKIV is an estrogen target in the rat medial amygdala (128). However, our data (unpublished) using inhibitors indicate that CaMKII is not important in E2-BSA-mediated potentiation of transcription in neuroblastoma cells. PKC activation by calcium is yet another possibility. In addition, calcium is important in the stabilization of the ER{alpha} in MCF-7 human breast cells (129) and may be a point of convergence for all the kinase cascades. The ability of all other single kinase inhibitors to reduce, but not totally negate, the E2-BSA-mediated transcriptional potentiation suggests that transcription is a sum of signaling from several kinase cascades. This implies that signal transduction pathways may originate in parallel from a single signal at the membrane. However, it is also possible that some of these kinases could be needed to maintain the cell in a basal responsive state or be permissive, but not essential, to the membrane-initiated actions of estrogens.

A. Membrane-initiated actions of estrogens may also occur in parallel or in series in the MCF-7 breast carcinoma cell line
Based on our data, it is probable that a guiding principle of estrogen action is to activate several membrane-initiated kinase cascades in a single neuronal cell type. Is this borne out by data in other cell types? Addition of estrogens results in proliferation in breast cancer, typified by the response in the MCF-7 cell line. MCF-7 cells also respond to estrogens with rapid activation of the MAPK/ERK pathway (130) via incompletely understood mechanisms. A number of studies point to different modes of MAPK activation by estrogens. For example, addition of an antibody to the heregulin receptor or depletion of heregulin from the conditioned media of MCF-7 attenuates estrogen-mediated ERK activation, suggesting that estrogen induction of growth factors plays an autocrine/paracrine role in ERK activation and hence, cell proliferation (131). In addition, inhibition of PKC{delta} and Ras signaling also blocks MAPK activation (131), implying an upstream role for these molecules. In tamoxifen-resistant cells with equivalent levels of ER{alpha} as wild-type MCF-7 cells, the ERK activation appears to be mediated via TGF{alpha} and increased levels of epidermal growth factor (EGF) receptors (132). Liganded ER can also activate MAPK in MCF-7 cells via a rise in calcium from intracellular calcium stores (74). Because growth factor signaling to MAPK pathways involves the adaptor protein Shc, a similar pathway was proposed and demonstrated for estrogenic activation of MAPK. Shc binding to liganded ER{alpha} in the cytosol of breast cancer cells leads to association with the IGF receptor and subsequent activation of MAPK via the Grb2-Sos-Ras-Raf pathway (130, 133). Physical association with the p85 subunit of PI3K (130, 133, 134) as well as with Src (134) has also been demonstrated with the ER{alpha} in MCF-7 cells; inhibition of PI3K activity using the inhibitor LY294002 abrogates estrogen-induced Akt/PKB and Src activation (134). The transcriptional up-regulation of macrophage inhibitory cytokine-1 by PKB prolongs estrogen-induced phosphorylation of ERK (135). Membrane-limited E2-BSA activates PKC rapidly in MCF-7, independently of ER{alpha} or ERß, and recurrent tumors have higher levels of PKC (136). Furthermore, in MCF-7 cells, estrogen-induced PI3K activates the atypical PKC{zeta}, which in turn activates the src/Ras/MAPK signaling cascade (137). Other PKC isoforms have also been associated with proliferation in MCF-7 cells. For example, overexpression of PKC{delta} allows tamoxifen-sensitive MCF-7 lines to acquire tamoxifen resistance (138). In contrast, stable transfection of PKC{alpha} is accompanied by ER{alpha} down-regulation and elevated basal AP-1 activity (139). An early study also reported that transfection of this cell line with PKA or treatment with 8-bromo-cAMP could increase the agonist activity of tamoxifen on a consensus ERE-based reporter construct to about 20–75% of the level obtained with 17ß-estradiol (140). Conversely, melanin inhibited ER{alpha} transactivation by inhibiting forskolin-induced and estrogen-induced cAMP increases (141).

How can these data be resolved? First, these data imply that several kinases, i.e., MAPK, PI3K, PKA, and PKC, can be activated rapidly by estrogens, possibly via the ER{alpha}, in MCF-7 cells. This is similar to the data seen with neuroblastoma cells (see Section III). Hence, it is probable that several kinases coordinately influence gene regulation in several target cell types to achieve a final phenotype.

Finally, how proliferation of the MCF-7 cell line, i.e., the final phenotype, is affected by the membrane-initiated activation of kinases is still unclear. Long-term estrogen-deprived MCF-7 cells (the LTED lines), which mimic tamoxifen resistance, show hyperphosphorylation of ERK, whereas both MAPK/ERK kinase (MEK) and PI3K inhibitors could decrease proliferation (142). However, PI3K and MEK inhibitors do not decrease c-myc and c-fos expression although hyperphosphorylated retinoblastoma and cyclin D1 proteins decrease, suggesting that rapid signaling cascades are permissive to cell cycle progression but not to mitogenesis via the immediate early genes myc and fos (143, 144). These studies strongly imply that estrogen-regulated rapid signal transduction cascades, that is, membrane-initiated actions are relevant to the final outcome in breast cancer cells, i.e., proliferation.

We note that for full potentiation of a transcriptional effect of estrogens by a membrane-initiated action, the data using kinase activators suggest that more than one signal transduction system is sufficient, but the data with kinase inhibitors also imply that more than one signal transduction system is necessary. How can this be? If a particular kinase cascade is "sufficient," how can another one be "necessary"? If several signal transduction systems in parallel maintain a basal state of transcriptional readiness, ablating any one of them lowers that basal state such that a genomic action of 17ß-estradiol is ineffective in potentiating transcription. Conversely, if any one of the transduction systems involved is highly activated, it can substitute for the membrane-initiated action of 17ß-estradiol in potentiating the later, genomic action. This idea, therefore, postulates the existence of a transcription threshold for genes.


    V. Convergence of the Membrane-Initiated Actions of Hormones to Transcription Involves Protein-Protein Interactions, Protein Translocation, and Protein Phosphorylation
 Top
 Abstract
 I. Introduction
 II. Estrogens Signal via...
 III. Membrane-Initiated Hormone...
 IV. The Signal Transduction...
 V. Convergence of the...
 VI. Initiation of Membrane...
 VII. Summary and Future...
 References
 
Most early studies have treated membrane-initiated actions as disparate from the genomic actions of hormones encompassing and culminating at kinase activation or calcium increases, both of which have cytosolic substrates (34, 145, 146). Other studies, have examined the effect of growth factor receptor ligands, notably IGF and EGF, on ligand-independent activation of the ER (Refs. 130 and 147, 148, 149 and references therein). Such activation is particularly important in hormone therapy-resistant cancers; combined targeting to both the ER and growth factor pathways, therefore, has therapeutic significance (150). Another subset of studies has involved the role of the classical ERs in rapid, membrane-initiated actions, particularly in breast cancer (130, 133, 151, 152) and cardiovascular physiology (114, 153, 154, 155, 156, 157, 158, 159). However, how the ligand at the membrane can regulate transcription in the nucleus is unclear if the same ligand, i.e., 17ß-estradiol has the ability to signal at both membrane and nucleus and if membrane-initiated rapid actions by the ligand influence transcription on EREs by ligand-dependent nuclear receptor action. For estrogen-regulated genes, one can mechanistically envision such coupling from membrane to nucleus at various intersecting levels such as 1) stability of the ER (protein-protein interactions); 2) nuclear translocation of the ER; and 3) modification of proteins important for transcription. Some of these aspects, especially for genes that do not contain EREs in their promoters, have been recently reviewed by Bjornstrom and Sjoberg (160).

A. Coupling to transcription via stabilization or dimerization of molecules relevant to transcription
Heat shock proteins (hsp 70/90) are important for proper folding, maturation, and translocation of the steroid hormone receptors (13, 161). There are a few studies that report estrogenic regulation of the heat shock chaperones. 17ß-Estradiol and bisphenol A act via the ER in uterine tissue to increase hsp90 and hsp72 mRNA via PKC (162, 163). In the CNS, estrogens and androgens protect neurons from ß-amyloid toxicity by increasing the levels of hsp70; microinjection of hsp70 blocked the toxicity of added intracellular ß-amyloid peptide (iamyloidß1–42) (164), suggesting a role in neuroprotection. However, it is not clear whether 17ß-estradiol can regulate these proteins to enhance transcription driven by the ER.

The stability of the ER{alpha} has important consequences for function. The autologous down-regulation of ER{alpha} and subsequent proteolysis by the 26S proteasome is thought to be required for efficient transactivation from the consensus ERE (165). In MCF-7 cells, PKC can enhance proteasome degradation of ligand bound and ligand free ER{alpha}, whereas PKA, PI3K, and MAPK impede degradation. On the other hand, in pituitary tumor cells, PKA increases transactivation mediated by 17ß-estradiol-liganded ER{alpha} from a consensus ERE while protecting the ER{alpha} from estrogen-induced degradation. This suggests that 17ß-estradiol increases transcription, partly by autologous down-regulation of the ER{alpha}, whereas PKA could increase transcription by stabilizing the ER{alpha} (166). The relevance of ER{alpha} degradation is, however, controversial. For example, proteolysis is not required for ER{alpha}-mediated induction of the prolactin gene or for proliferation in anterior pituitary lactotrope cells, demonstrating different requirements for the stability of ER{alpha}, depending on the ERE (167).

B. Coupling to transcription via the physical movement of molecules into the nucleus
17ß-Estradiol can also regulate the translocation of the ER, possibly via kinase cascades. PKC{delta} activation, via GSK-3 results in nuclear translocation of the ER{alpha} with a concomitant increase in transcription (168). In endometrial adenocarcinoma, estrogenic up-regulation of p38MAPK, in turn, increases ER{alpha} phosphorylation on Thr311; mutation of this site inhibits nuclear localization as well as the interaction with coactivators (169). In human vascular smooth muscle cells, the MAPK phosphorylation of the ER{alpha} on Ser118 and nuclear translocation could also be ligand-independent (170).

C. Coupling to transcription via phosphorylation of molecules relevant to transcription
Our inhibitor studies strongly suggest that kinases such as PKA, PKC, PI3K, and MEK are activated during rapid exposure to either membrane-impermeable estrogen (E2-BSA) or T3 (see Section VII.A) at the membrane in neuroblastoma cells. Phosphorylation of molecules relevant to transcription, for example, the ER{alpha} itself, by these kinases could provide a simple coupling mechanism between events at the membrane and transcriptional events in the nucleus. Endogenous ER has a basal level of phosphorylation that is enhanced by physiological concentrations of estrogen at amino acid Tyr537 and at serines at positions 104, 106, 118, 154, and 167 in the activation function (AF)-1 N-terminal domain (171, 172). Estrogen-induced phosphorylation occurs via kinase activation. PKA can phosphorylate the ER at serines 236, 305, 338, and S518 (173). In contrast, PKC phosphorylation of the ER may be at Ser118 in the AF-1 domain (174). PI3K-activated PKB has been shown to phosphorylate ER{alpha} on Ser167 in vitro (175, 176). MAPK phosphorylation of ER{alpha} occurs on Ser118 in vivo as well as in vitro (174, 177, 178). How phosphorylation affects ER{alpha} function is less clear. PKA phosphorylation at Ser236 in the DNA binding domain increases dimerization of the ER (179). A second PKA phosphorylation site at Ser305 in the ER{alpha} blocks acetylation of the ER{alpha} at the proximal Lys303 site, enhancing transcriptional ability (180). Mutations at the Ser118 and Ser167 sites decrease transcription in fibroblast and epithelial cells, suggesting that these sites were critical for transcription (174, 178, 181, 182, 183, 184). In vivo, MAPK-mediated phosphorylation (185) of Ser167 occurs via the ribosomal S6 kinase (184), whereas in vitro, Ser167 is phosphorylated by both Akt and casein kinase II (113, 176, 186). Phosphorylation on Ser305 also increases transcription from the cyclin D1 gene in breast cancer (187). This is possibly because phosphorylation of nuclear receptors appears to enhance interaction with coactivators (188). In support of this idea, Ser118 phosphorylation in the AF-1 domain facilitates the interaction of the ERß with the steroid receptor coactivator 1 (SRC-1), hence increasing the transcription rate (189). Table 1Go presents a list of ER{alpha} phosphorylation sites and their possible impact on ER{alpha} function. The stoichiometry and the sites of ER{alpha} phosphorylation, however, vary depending on the cell type, presumably due to the tissue-specific differences in kinase and phosphatase activities (177). Translocation of the receptor may also be affected by kinase-induced phosphorylation. Blocking MAPK causes loss of phosphorylation on Ser294 and nuclear accumulation of PR-B and prevents ligand-dependent degradation of the receptor. In turn, this decreases transcriptional activation (190).


View this table:
[in this window]
[in a new window]

 
TABLE 1. Phosphorylation sites on ER{alpha} and the impact of phosphorylation on function

 
Other molecules may also be kinase targets. In COS-1 cells, PKA and subsequent MAPK activation results in an enhanced phosphorylation of SRC-1 leading to an increased transactivation by the chicken PR (191). MAPK activation of amplified in breast cancer (AIB1), a coactivator enhanced in breast cancer, stimulates the recruitment of p300 and increased estrogen-dependent ER transactivation (192). Furthermore, Bert O’Malley’s group has provided evidence that various kinases differentially phosphorylate SRC-3/AIB1, leading to selective binding to downstream transcription factors (193). In MCF-7 cells, Ishikawa cells, and HEK293 cells, p38MAPK stimulated transcription by both ER{alpha} and ERß, leading to cell proliferation. The p38MAP stimulated transcription by the phosphorylation of a p160 coactivator, GRIP1 (194). In addition, rapid 17ß-estradiol treatment could induce the phosphorylation of SRC-3 by direct interaction between the ER{alpha} and SRC-3 outside the nucleus (195). Hence, the combination of a specific coactivator and another transcription factor could depend on the phosphorylation state of the coactivator molecule itself (196).

As is evident, none of these processes need to be mutually exclusive. Extracellular signals (exemplified in our paradigm by E2-BSA) may initially converge on a molecule, for example, the ER{alpha}, using multiple molecular mechanisms such as translocation, phosphorylation, and stabilization. This initial convergence may lead to molecular activation, which may, in turn, impact divergent molecular processes within cells to achieve a final differentiated response to the signal. Conceivably, in neurons, the "activated" ER could enhance transcription, excitability due to effects on ion channels, and neurotransmitter release. Alternatively, the extracellular signal may activate several molecules, all of which converge on a single molecular process. For example, in our paradigm, if phosphorylation activated downstream transcription factors such as CREB binding protein (CBP), coactivators such as SRC-1 and SRC-3, and the ER{alpha}, transcription would be greatly enhanced, and amplification of the original extracellular signal would be achieved.


    VI. Initiation of Membrane-Initiated Actions at the Membrane Involves Both Classical "Nuclear Receptors" and Other Proteins
 Top
 Abstract
 I. Introduction
 II. Estrogens Signal via...
 III. Membrane-Initiated Hormone...
 IV. The Signal Transduction...
 V. Convergence of the...
 VI. Initiation of Membrane...
 VII. Summary and Future...
 References
 
A. The membrane estrogen receptor could be a novel protein in some cell types
The elucidation of the mER has generated enormous interest and effort (34, 146, 197, 198, 199) because knowledge of a mER can lead to dissection of membrane-initiated signal transduction pathways activated by estrogens (200). Any protein that is a candidate mER should bind 17ß-estradiol with specificity and saturability and be present at the plasma membrane of the cell to initiate rapid membrane-initiated action. Over the years, there have been conflicting reports on the mER in different cell types, predominantly based on the application of ER antagonists, such as ICI and immunocytochemistry. ICI, a pure ER{alpha} and ERß antagonist, was unable to block the ability of E2-BSA to activate PKC rapidly in chondrocytes (201) or MAPK in rat hippocampus (77), suggesting a novel membrane receptor for estrogen. In the neocortex, a novel, high-affinity mER, called ER-X, which supports MAPK phosphorylation by estrogens, has been reported (202). A novel G{alpha}q protein-coupled mER agonist, STX, can attenuate the weight gain seen in hypoestrogenic animals. This is similar to the attenuation seen with 17ß-estradiol and occurs in double (ER{alpha}–/–, ERß–/–) knockout mice (203), suggesting that a novel protein may be present at the membrane in the CNS. The identity of this receptor and its location at the membrane remains to be elucidated. This group has also previously used an ER{alpha}/ß antagonist, ICI 164,384, which blocked the ability of 17ß-estradiol to rapidly uncouple the µ-opioid receptor from an inwardly rectifying K+ channel (204); however, in this study, ICI 164,384 could not block the same response induced by STX (203). This suggests that the depolarization induced by 17ß-estradiol and by STX has differential requirements for the presence of the classical ER. In pancreatic ß-cells, binding of the membrane limited E2-HRP to the membrane can be competed by dopamine and norepinephrine, suggesting a common catecholaminergic receptor. However, the ability of norepinephrine to induce Ca2+ oscillations in these cells was unchanged by the addition of 100 nM 17ß-estradiol, which should saturate the common membrane receptor, if any (33, 205). Hence, the functional relevance of such a receptor is unclear. A novel mER has been suggested on the basis of competition binding in the GT1–7 cell line, wherein the binding of E2-HRP conjugate was competed by 17ß-estradiol but not by ICI 182,780 or 4-hydroxytamoxifen (206). The rapid reduction by 17ß-estradiol of the Ca2+ transients induced by acetylcholine in these cells may involve a protein kinase G phosphorylation of the inositol triphosphate receptor that modifies Ca2+ release from the endoplasmic reticulum (207). However, the GT1–7 cell line, has been shown by others (40) to possess the classical ER{alpha} at membrane sites. It is unclear how these conflicting data can be resolved. Is it possible that membrane-initiated signaling by 17ß-estradiol in the same cell line may involve more than one type of mER?

In fish, where membrane-initiated actions of progesterone are required for oocyte maturation, the membrane PR is a novel protein coupling to Gi/Go proteins (208, 209). Recently, an orphan GPCR, GPR30, has been identified as a membrane ER in SKBR3 breast carcinoma cells based on high-affinity binding, membrane localization, and modest levels of adenylyl cyclase activation upon estrogen addition, showing that the GPR30 can couple to G{alpha}s (210). In SKBR3 cells that express no classical ER, GPR30 is absolutely required for 17ß-estradiol activation of adenylyl cyclase. This is the first report of a mER structurally unrelated to the classical ER. In addition, binding of ICI compounds, 17ß-estradiol and 17{alpha}-estradiol, occurs with equal affinity to the GPR30 (210). On the other hand, Revankar et al. (211) have reported that the GPR30 protein is uniquely localized to the endoplasmic reticulum and may serve as an intracellular ER that increases calcium in response to 17ß-estradiol. However, they have also shown that GPR30-transfected SKBR3 cells can increase PIP2 concentrations, supporting the idea that GPR30 can increase nongenomic signaling in response to 17ß-estradiol (211). However, another laboratory has reported that ERK activation and cAMP accumulation in response to 17ß-estradiol is abrogated in ER{alpha}/GPR30+ SKBR3 cells. This may be due to differences in the parameters (fluorescence localization vs. enzymatic activity) (212) measured in these two studies. The localization of GPR30 and its functional relevance in other cell types, perhaps using a selective, recently synthesized agonist, G-1 (213), remains to be elucidated.

B. The membrane estrogen receptor is the classical ER in other cell types
Several reports support the notion that a classical ER may be tethered to the membrane (reviewed in Ref. 154). The E2-BSA activation of MAPK in Rat-2 fibroblasts (214) and endothelial cells (215) and the interaction between ER{alpha} and G{alpha}i in IC-21 macrophages (216) can be blocked by ICI compounds, which antagonize both ER{alpha} and ERß. ICI 182,780 can also block CaMKII activation in the hippocampus by EB (127). In astrocytes, E2-BSA can cause rapid calcium flux that can be blocked by ICI 182,780 (217). The existence of ER at the membrane has also been inferred from functional signaling studies, combined with inhibitor studies. In immortalized GT-1 cells, picomolar concentrations of 17ß-estradiol could inhibit cAMP levels, whereas nanomolar concentrations of 17ß-estradiol could augment cAMP levels. In addition, these effects could be blocked by ICI 182,780 and pertussis toxin, implying that the ER was coupled to a G{alpha}i protein in GT-1 cells (40). Qiu et al. (49) have, on the basis of phospholipase C signaling by 17ß-estradiol in POMC and dopamine neurons, proposed a model whereby a G{alpha}q coupled receptor at the plasma membrane may rapidly activate signaling cascades in series (see Section II.C). Signaling in these cells was also blocked by ICI 182,780 (48, 49). Functionally, the lack of ER{alpha} or ERß in double ER knockout mice abrogated the rapid ERK phosphorylation by estrogens in the medial preoptic nucleus (218), suggesting that the ER is required for rapid, nongenomic actions. Also, endothelial cells from double ER knockout mice, compared with wild-type mice, did not support PI3K, cAMP, and ERK phosphorylation or bind 17ß-estradiol (212). These studies demonstrate that classical ERs that mediate genomic actions may also mediate nongenomic actions, but they do not mean that the ER is at the plasma membrane. Using immunocytochemistry, numerous studies have shown that ER{alpha} is at the plasma membrane. In Chinese hamster ovary (CHO) cells, overexpressed ER{alpha} gives rise to a single transcript with functional protein expression in both nuclear and membrane fractions (219). Endothelial cells, a major estrogen target cell with relevance to cardiovascular protection, from the ER{alpha}–/–,ERß–/– mouse do not show membrane ER{alpha} (220). Anti-ER{alpha} antibodies on fetal rat hippocampal neurons reveal abundant staining at the neurites by confocal microscopy (221). In rat pituitary tumor cells, antisense oligodeoxynucleotide to ER{alpha} mRNA reduces the staining obtained with specific, high-affinity antibodies at the membrane of fixed, nonpermeabilized cells (222). In addition, plasma membrane fractions from MCF-7 cells that express the ER{alpha} show that the protein at the membrane that binds 17ß-estradiol is the classical ER{alpha} (212).

How do nuclear receptors attach to the plasma membrane despite a lack of standard transmembrane structure (215) and hydrophobicity? ER{alpha} can physically interact with membrane proteins, allowing anchorage to the membrane or to the vicinity of the membrane. Furthermore, the ER may also be present in specialized plasma membrane structures such as caveolae and lipid rafts that possess several signaling enzymes to form a organized signaling module (157) coupled to G{alpha}i (223). Indeed, data obtained using E2-BSA do not rule out the possibility that this compound can enter and bind ER{alpha} in caveolae. Western blotting and mass spectroscopy show caveolin-1 in isolated oligodendrocyte plasma membrane colocalizing with an ERß-like molecule (224). In endothelial cells, ER{alpha} associates with the p85 subunit of PI3K in caveolae, mediating PI3K/Akt activation of nitric oxide synthase (NOS) (155, 158). Similarly, ERß in caveolae activates NOS (156), possibly via the rapid activation of MAPK (225). Localization of ER{alpha} to the membrane appears to be dependent on Ser522; mutation of this residue abrogates membrane localization in caveolae in CHO cells and adenylyl cyclase activation but supports transcription (226), suggesting that the amino acid residues required for membrane-initiated action and genomic action may be different. In breast cancer and endothelial cells, ER{alpha} exists at the membrane as dimers, in association with caveolin-1 in caveolae (227), and can support adenylyl cyclase and PI3K signaling. NOS activation in endothelial cells was, however, not dependent on dimerization because an ER{alpha} deficient in dimerization (ER{alpha}L511R) could still activate NOS (159). Moreover, despite presence at the plasma membrane, nuclear localization signal mutants could not activate ERK, whereas DNA binding mutants of the ER{alpha} could not activate ligand-dependent PI3K binding to ER{alpha} (159). Hence, the functional relevance of membrane localization to signaling in endothelial cells is not clear. In addition, palmitoylation supports ER{alpha} attachment to the membrane and interaction with caveolin in HeLa and HepG2 cells, whereas addition of ligand decreases interaction of the receptor with caveolin (228), suggesting a classical desensitization mechanism. In MCF-7 cells, ER{alpha} can physically bind the p85 subunit of PI3K at the membrane (229, 230) as well as the Shc protein via the AF-1 domain and can drive the formation of a Shc-Grb2-SOS signaling complex (130). In addition, a novel scaffold protein called MNAR (modulator of nongenomic action of ER) can interact with c-src using its PXXP motif while interacting with the ER using the LXXXL motifs, demonstrating an "adapter" function (231, 232). Using an adapter protein to anchor at the membrane does not, however, make the ER{alpha} an intrinsic membrane protein. However, work from Cheryl Watson’s group (151) has implicated ER{alpha} at the membrane in MCF-7 cells. Using immunopanning with specific ER{alpha} antibodies, MCF-7 cells were separated by flow cytometry into high mER{alpha} and low mER{alpha} populations (151). Immunopanning suggests that the antibody binding site on the ER{alpha} is available to the antibody at the surface of cells. It is difficult to reconcile this data to the previously stated data on MCF-7 cells, which show tethering of ER{alpha} to the inner plasma membrane. One possibility is that a very small proportion of cells may have small amounts of ER{alpha} at the surface, whereas a greater number of cells in a given cell type may have ER{alpha} tethered to the membrane, although the basis of this differential distribution would be difficult to rationalize. Apart from the idea that a small fraction of endogenous cellular ER{alpha} is permanently anchored to the membrane, a small pool of nuclear ER may dynamically shuttle to the membrane. This possibility has been demonstrated by an ER{alpha} artificially tethered to the plasma membrane with a rhodopsin fusion protein that can shuttle to the nucleus to increase transcription in 293 cells (233). In MDA-MB-231 breast cells stably transfected with either wild-type ER{alpha} or myristoylated ER{alpha} lacking the nuclear localization signal, the myristoylated ER{alpha} shows membrane localization but is not down-regulated by 17ß-estradiol, as is the case for wild-type ER{alpha}. In addition, compared with the WT ER{alpha}, the myristoylated protein cannot up-regulate the transcription of estrogen reporter genes on exposure to 17ß-estradiol (234).

Functionally, the presence of ER at the membrane may have physiological consequences that need to be studied in more detail. In MCF-7 variants sorted for higher ER{alpha} localization to the membrane, estrogenic induction of adenylyl cyclase is correlated with lower proliferation (151). In Xenopus laevis oocytes, MNAR contributes to meiotic arrest because reduction of MNAR mRNA increased liganded androgen receptor-driven MAPK activation and oocyte maturation (235). In the CNS, differentiation of midbrain dopaminergic neurons appears to be due to membrane-attached ER{alpha} in astrocytes (236).

C. Do different cell types have different receptors?
The wealth of studies demonstrating novel proteins as the mER or the classical nuclear receptor, the ER{alpha}, as a candidate mER suggest that different cell types may possess different mERs. None of the novel proteins that are mER candidates (i.e., ER-X or GPR30) show any homology to the novel membrane PR, cloned from sea trout ovaries (209), indicating that, unlike the classical nuclear receptor superfamily, there may not be a parallel "membrane receptor superfamily". It is also possible that different molecules may "moonlight" as the mER either temporally or for distinct functional roles in a single cell type. Additionally, the domains required for ER function at the membrane could be cell specific, depending on the molecule that the ER may be tethered to in that cell type. These ideas about the nature of membrane receptors for hormones remain to be clarified.


    VII. Summary and Future Directions
 Top
 Abstract
 I. Introduction
 II. Estrogens Signal via...
 III. Membrane-Initiated Hormone...
 IV. The Signal Transduction...
 V. Convergence of the...
 VI. Initiation of Membrane...
 VII. Summary and Future...
 References
 
Data from other laboratories and ours suggest that both kinases and calcium flux appear to be important in E2-BSA-mediated actions on transcription in neurons. Several different, parallel pathways can couple signal transduction cascades to transcription in the nucleus (Fig. 2Go). For example, ligand-independent transcription (which is not the focus of this review) results from activation of growth factor receptors at the membrane and subsequent ERK activation. In addition, binding of cognate ligands to membrane receptors such as the mER or a novel protein that acts as the mER can activate kinase cascades which, in turn, can facilitate transcription from either EREs or other enhancer elements (reviewed in Ref. 160).


Figure 2
View larger version (31K):
[in this window]
[in a new window]

 
FIG. 2. Parallel pathways that integrate signals at the membrane to transcription in the nucleus in neuroblastoma cells. 17ß-Estradiol ({Delta}) binds to a G{alpha}q-coupled membrane ER. This initiates several kinase cascades (PKA, PKB, MEK, PKC) and Ca2+ flux. Kinases modify the ER bound to the ligand or another transcriptionally relevant molecule, such as the coactivators, SRC-3. The modified ER can translocate to the nucleus where it enhances transcription via the ERE in gene promoters. In contrast, the ER can also be activated by growth factors (ligand-independent mechanisms) via the MEK pathway. In addition, the activation of kinase cascades by membrane-limited estrogens can also result in increased transcription from non-ERE containing promoters. In this figure, a promoter with a CRE is shown; this can be bound by CREB protein, which in turn is activated by PKA. GF-R, Growth-factor receptor.

 
Because initiation of kinase activation from the plasma membrane by estrogens is an emerging story, several questions remain. E2-BSA and E2-HRP have been the only membrane-limited probes used until the synthesis of an estrogen-dendrimer conjugate. Their specificity has not always been demonstrated in all studies, and their uses in vivo have been particularly limited. The use of the estrogen-dendrimer conjugate, synthesized in Dr. John Katzenellenbogen’s laboratory, should help to clarify membrane-limited effects.

Are several kinases activated rapidly by membrane-limited estrogens to regulate transcription from a coordinate set of genes? The transcription of this set of genes would then change the physiology of the cell in response to the stimulus at the membrane. The next step would be to elucidate all kinase and other rapid signal transduction pathways that contribute to transcription and investigate whether they are absolutely necessary to transcriptional regulation. Most studies tend to look at a single kinase or a single rapid signal transduction pathway without considering the crosstalk that is inherent in these pathways. Detailed pathway profiling in response to brief administration of estrogens that is relevant to transcription as well as a physiological end point, e.g., reproduction or neuroprotection, is the next step in these studies. Models of rapid signaling pathways could then be generated for each physiological scenario affected by estrogens.

What are the molecular mechanisms by which membrane-initiated actions influence transcription for cognate ligands? Is there a point of convergence for kinase cascades? Mechanistic studies on how rapid signal transduction pathways affect estrogen-driven physiology are the next step. Phosphorylation of the ER or other key transcriptionally relevant molecules could be key coupling events and act as a point of convergence for membrane-initiated kinase cascades and transcription in the nucleus. Recently, O’Malley’s group showed that the phosphorylation of SRC-3 by 17ß-estradiol can occur in the presence of a transcriptionally inactive ER{alpha} in the cytoplasm. This suggests that SRC-3 can be phosphorylated in an extranuclear location by interaction with ER{alpha} (195). Another critical area for study is the importance of phosphorylation of transcriptionally relevant molecules. For the ER{alpha}, for example, there is little consensus on the effects of phosphorylation on transcription (177), and this needs to be studied in detail. SRC-3 phosphorylation occurs on six different sites; stimulus specificity could be encoded by different combinations of phosphorylation sites (196). Phosphorylation of nontranscriptional targets, e.g., ion channels or intracellular Ca2+ receptors, could also represent a point of convergence of rapid signaling cascades. Apart from phosphorylation, other processes such as stabilization of transcriptionally relevant molecules, methylation of promoters, or control of proteolytic degradation could also be important. The relative contributions of these molecular targets to the final phenotype are ripe for exploration in the context of nuclear receptor action in the CNS.

What are all the various physiological processes that can be influenced by these molecular mechanisms? Much of the classical studies that involve membrane actions of estrogens in the CNS have been inspired by estrogen’s control of reproductive physiology and behavior. Which genes that are relevant for lordosis behavior in rodents or other nonreproductive functions are impacted by the membrane-initiated actions of estrogens? Uncovering these genes will be important to understand behaviors driven by estrogen.

Because membrane-initiated signal transduction events can potentiate transcription by estrogens, it is obvious that other extracellular signals that impact these pathways may have an effect of transcription. Crosstalk between growth factor receptors and the ER has been studied and reviewed extensively, especially in the context of cell proliferation in cancers (see Refs. 130 and 147, 148, 149 and references therein). In the neuroendocrine context, EGF has been shown to selectively activate ER{alpha}-dependent, but not PR-dependent lordosis behavior in a ligand-independent fashion (101). In addition, dopamine receptor D1 agonists increase lordosis behavior in Sprague Dawley rats; this effect is dependent on intact D5 receptors in the VMH (237) and the PR (238). How specificity is maintained during such ligand-independent crosstalk remains to be studied. In neuroblastoma cells, T3, the genomically more active form of the hormone, via thyroid hormone receptor (TR) {alpha}1 or TRß1 potentiates ER{alpha}-mediated transcription from a consensus ERE-driven luciferase reporter compared with a single 17ß-estradiol pulse, similar to the potentiation caused by E2-BSA, via activation of MAPK signaling. Phosphorylation of ER{alpha} on serine residues 118 and 167 and the presence of 17ß-estradiol is also important in T3-mediated transcriptional potentiation (125). This is an example of ligand-dependent crosstalk between estrogens and thyroid hormone that may play roles in mood and cognition (239, 240, 241, 242, 243); this remains to be elucidated in a physiological scenario.

The novel idea that genomic transcription by hormones, i.e., ligand-dependent transcription at hormone response elements, can be affected by membrane-initiated signal transduction events initiated by cognate or noncognate ligands is a paradigm shift in nuclear receptor biology.


    Acknowledgments
 
We thank Dr. Lee Ming Kow (Laboratory of Neurobiology and Behavior, The Rockefeller University), and Dr. V. P. Nair and Dr. Alexander Punnoose (Department of Physics, City College of New York, City University of New York) for helpful discussions during the course of this work.


    Footnotes
 
Disclosure Statement: The authors have nothing to disclose.

First Published Online October 3, 2006

Abbreviations: AF, Activation function; BDNF, brain-derived neurotrophic factor; CaMK, calmodulin kinase; CNS, central nervous system; CRE, cAMP response element; CREB, CRE binding protein; E2–6-BSA, 17ß-estradiol-6-O-carboxymethyloxime-BSA; E2–17-BSA, 1,3,5, (10)-estratrien-3,17ß-diol 17-hemisuccinate-BSA; E2-BSA, 17ß-estradiol linked to BSA; E2-HRP, 17ß-estradiol linked to horseradish peroxidase; EB, estradiol benzoate; EGF, epidermal growth factor; ER, estrogen receptor; ERE, estrogen response elements; GABA, {gamma}-aminobutyric acid; GPCR, G protein-coupled receptor; GSK, glycogen synthase kinase; hsp, heat shock protein; MCAO, middle cerebral artery occlusion; MEK, MAPK/ERK kinase; mER, membrane ER; MNAR, modulator of nongenomic action of ER; NMDA, N-methyl-D-aspartate; NOS, nitric oxide synthase; pCREB, phospho-CREB; PI3K, phosphotidylinositol-3-kinase; PKA, protein kinase A; PKB, protein kinase B; PKC, protein kinase C; POMC, pro-opiomelanocortin; PR, progesterone receptor; SRC, steroid receptor coactivator; VMH, ventromedial hypothalamus.


    References
 Top
 Abstract
 I. Introduction
 II. Estrogens Signal via...
 III. Membrane-Initiated Hormone...
 IV. The Signal Transduction...
 V. Convergence of the...
 VI. Initiation of Membrane...
 VII. Summary and Future...
 References
 

  1. Pfaff DW, McCarthy M, Schwartz-Giblin S, Kow LM 1994 Female reproductive behavior. In: Knobil E, Neill J, eds. The physiology of reproduction. New York: Raven; 107–220
  2. Pfaff D 1997 Hormones, genes, and behavior. Proc Natl Acad Sci USA 94:14213–14216[Abstract/Free Full Text]
  3. Knobil E, Neill J 1999 Encyclopedia of reproduction. San Diego: Academic Press
  4. Brinton RD 2001 Cellular and molecular mechanisms of estrogen regulation of memory function and neuroprotection against Alzheimer’s disease: recent insights and remaining challenges. Learn Mem 8:121–133[Abstract/Free Full Text]
  5. Brinton RD 2005 Investigative models for determining hormone therapy-induced outcomes in brain: evidence in support of a healthy cell bias of estrogen action. Ann NY Acad Sci 1052:57–74[CrossRef][Medline]
  6. Lee SJ, McEwen BS 2001 Neurotrophic and neuroprotective actions of estrogens and their therapeutic implications. Annu Rev Pharmacol Toxicol 41:569–591
  7. Maggi A, Ciana P, Belcredito S, Vegeto E 2004 Estrogens in the nervous system: mechanisms and nonreproductive functions. Annu Rev Physiol 66:291–313[CrossRef][Medline]
  8. Muramatsu M, Inoue S 2000 Estrogen receptors: how do they control reproductive and non-reproductive functions? Biochem Biophys Res Commun 270:1–10[CrossRef][Medline]
  9. Osborne CK, Zhao H, Fuqua SA 2000 Selective estrogen receptor modulators: structure, function, and clinical use. J Clin Oncol 18:3172–3186[Abstract/Free Full Text]
  10. Klinge CM 2000 Estrogen receptor interaction with co-activators and co-repressors. Steroids 65:227–251[CrossRef][Medline]
  11. Enmark E, Gustafsson JA 1999 Oestrogen receptors—an overview. J Intern Med 246:133–138[CrossRef][Medline]
  12. Nilsson S, Makela S, Treuter E, Tujague M, Thomsen J, Andersson G, Enmark E, Pettersson K, Warner M, Gustafsson J 2001 Mechanisms of estrogen action. Physiol Rev 81:1535–1565[Abstract/Free Full Text]
  13. DeFranco DB, Ramakrishnan C, Tang Y 1998 Molecular chaperones and subcellular trafficking of steroid receptors. J Steroid Biochem Mol Biol 65:51–58[CrossRef][Medline]
  14. Robertson JF 2002 Estrogen receptor downregulators: new antihormonal therapy for advanced breast cancer. Clin Ther 24(Suppl A):A17–A30
  15. Thomas T, Gallo MA, Thomas TJ 2004 Estrogen receptors as targets for drug development for breast cancer, osteoporosis and cardiovascular diseases. Curr Cancer Drug Targets 4:483–499[CrossRef][Medline]
  16. Hanstein B, Djahansouzi S, Dall P, Beckmann MW, Bender HG 2004 Insights into the molecular biology of the estrogen receptor define novel therapeutic targets for breast cancer. Eur J Endocrinol 150:243–255[Abstract]
  17. Howell SJ, Johnston SR, Howell A 2004 The use of selective estrogen receptor modulators and selective estrogen receptor down-regulators in breast cancer. Best Pract Res Clin Endocrinol Metab 18:47–66[CrossRef][Medline]
  18. Alves SE, McEwen BS, Hayashi S, Korach KS, Pfaff DW, Ogawa S 2000 Estrogen-regulated progestin receptors are found in the midbrain raphe but not hippocampus of estrogen receptor {alpha} (ER {alpha}) gene-disrupted mice. J Comp Neurol 427:185–195[CrossRef][Medline]
  19. Miranda RC, Sohrabji F, Toran-Allerand D 1994 Interactions of estrogen with the neurotrophins and their receptors during neural development. Horm Behav 28:367–375[CrossRef][Medline]
  20. Sohrabji F, Miranda R, Toran-Allerand C 1995 Identification of a putative estrogen response element in the gene encoding brain-derived neurotrophic factor. Proc Natl Acad Sci USA 92:11110–11114[Abstract/Free Full Text]
  21. Toran-Allerand CD 1996 The estrogen/neurotrophin connection during neural development: is co-localization of estrogen receptors with the neurotrophins and their receptors biologically relevant? Dev Neurosci 18:36–48[Medline]
  22. Quinones-Jenab V, Jenab S, Ogawa S, Adan RA, Burbach JP, Pfaff DW 1997 Effects of estrogen on oxytocin receptor messenger ribonucleic acid expression in the uterus, pituitary, and forebrain of the female rat. Neuroendocrinology 65:9–17[CrossRef][Medline]
  23. Bale TL, Davis AM, Auger AP, Dorsa DM, McCarthy MM 2001 CNS region-specific oxytocin receptor expression: importance in regulation of anxiety and sex behavior. J Neurosci 21:2546–2552[Abstract/Free Full Text]
  24. McCarthy M, Chung S, Ogawa S, Kow L-M, Pfaff D 1991 Behavioral effects of oxytocin: is there a unifying principle? In: Jard S, Ramison J, eds. Vasopressin. Montrouge, France: Colloque INSERM/John Libbey Eurotext Ltd.; 195–212
  25. Holland K, Norell A, Micevych P 1997 Interaction of thyroxine and estrogen on the expression of estrogen receptor {alpha}, cholecystokinin, and preproenkephalin messenger ribonucleic acid in the limbic-hypothalamic circuit. Endocrinology 139:1221–1230
  26. Sinchak K, Eckersell C, Quezada V, Norell A, Micevych P 2000 Preproenkephalin mRNA levels are regulated by acute stress and estrogen stimulation. Physiol Behav 69:425–432[CrossRef][Medline]
  27. Priest CA, Eckersell CB, Micevych PE 1995 Estrogen regulates preproenkephalin-A mRNA levels in the rat ventromedial nucleus: temporal and cellular aspects. Mol Brain Res 28:251–262[Medline]
  28. Zhao L, Wu TW, Brinton RD 2004 Estrogen receptor subtypes {alpha} and ß contribute to neuroprotection and increased Bcl-2 expression in primary hippocampal neurons. Brain Res 1010:22–34[CrossRef][Medline]
  29. Wu TW, Wang JM, Chen S, Brinton RD 2005 17ß-Estradiol induced Ca2+ influx via L-type calcium channels activates the Src/ERK/cyclic-AMP response element binding protein signal pathway and BCL-2 expression in rat hippocampal neurons: a potential initiation mechanism for estrogen-induced neuroprotection. Neuroscience 135:59–72[CrossRef][Medline]
  30. Ciana P, Ghisletti S, Mussi P, Eberini I, Vegeto E, Maggi A 2003 Estrogen receptor {alpha}, a molecular switch converting transforming growth factor-{alpha}-mediated proliferation into differentiation in neuroblastoma cells. J Biol Chem 278:31737–31744[Abstract/Free Full Text]
  31. Pfaff DW, Schwartz-Giblin S 1988 Cellular mechanisms of female reproductive behaviors. In: Knobil E, Neill J, eds. The physiology of reproduction. New York: Raven Press; 1487–1569
  32. Pfaff D 1999 Lordosis. In: Knobil E, Neill J, eds. Encyclopedia of reproduction. San Diego: Academic Press; 1074–1075
  33. Nadal A, Ropero AB, Fuentes E, Soria B 2001 The plasma membrane estrogen receptor: nuclear or unclear? Trends Pharmacol Sci 22:597–599[CrossRef][Medline]
  34. Cato AC, Nestl A, Mink S 2002 Rapid actions of steroid receptors in cellular signaling pathways. Sci STKE 2002:RE9
  35. Moss RL, Gu Q, Wong M 1997 Estrogen: nontranscriptional signaling pathway. Recent Prog Horm Res 52:1–37[Medline]
  36. Kelly MJ, Levin ER 2001 Rapid actions of plasma membrane estrogen receptors. Trends Endocrinol Metab 12:152–156[CrossRef][Medline]
  37. Szego CM, Davis JS 1967 Adenosine 3',5'-monophosphate in rat uterus: acute elevation by estrogen. Proc Natl Acad Sci USA 58:1711–1718[Free Full Text]
  38. Zheng J, Ali A, Ramirez VD 1996 Steroids conjugated to bovine serum albumin as tools to demonstrate specific steroid neuronal membrane binding sites. J Psychiatry Neurosci 21:187–197[Medline]
  39. Somponpun S, Sladek CD 2002 Role of estrogen receptor-ß in regulation of vasopressin and oxytocin release in vitro. Endocrinology 143:2899–2904[Abstract/Free Full Text]
  40. Navarro CE, Abdul Saeed S, Murdock C, Martinez-Fuentes AJ, Arora KK, Krsmanovic LZ, Catt KJ 2003 Regulation of cyclic adenosine 3',5'-monophosphate signaling and pulsatile neurosecretion by Gi-coupled plasma membrane estrogen receptors in immortalized gonadotropin-releasing hormone neurons. Mol Endocrinol 17:1792–1804[CrossRef][Medline]
  41. Mermelstein P, Becker J, Surmeier D 1996 Estrogen reduces calcium currents in rat neostriatal neurons via a membrane receptor. J Neurosci 16:595–604[Abstract/Free Full Text]
  42. Stevis PE, Deecher DC, Suhadolnik L, Mallis LM, Frail DE 1999 Differential effects of estradiol and estradiol-BSA conjugates. Endocrinology 140:5455–5458[Abstract/Free Full Text]
  43. Temple JL, Wray S 2005 Bovine serum albumin-estrogen compounds differentially alter gonadotropin-releasing hormone-1 neuronal activity. Endocrinology 146:558–563[Abstract/Free Full Text]
  44. Abraham IM, Han SK, Todman MG, Korach KS, Herbison AE 2003 Estrogen receptor ß mediates rapid estrogen actions on gonadotropin-releasing hormone neurons in vivo. J Neurosci 23:5771–5777[Abstract/Free Full Text]
  45. Harrington WR, Kim SH, Funk CC, Madak-Erdogan Z, Schiff R, Katzenellenbogen JA, Katzenellenbogen BS 2005 Estrogen dendrimer conjugates that preferentially activate extranuclear, non-genomic versus genomic pathways of estrogen action. Mol Endocrinol 20:491–502
  46. Kelly MJ, Ronnekleiv OK, Ibrahim N, Lagrange AH, Wagner EJ 2002 Estrogen modulation of K(+) channel activity in hypothalamic neurons involved in the control of the reproductive axis. Steroids 67:447–456[CrossRef][Medline]
  47. Kelly MJ, Qiu J, Wagner EJ, Ronnekleiv OK 2002 Rapid effects of estrogen on G protein-coupled receptor activation of potassium channels in the central nervous system (CNS). J Steroid Biochem Mol Biol 83:187–193[CrossRef][Medline]
  48. Kelly MJ, Qiu J, Ronnekleiv OK 2003 Estrogen modulation of G-protein-coupled receptor activation of potassium channels in the central nervous system. Ann NY Acad Sci 1007:6–16[CrossRef][Medline]
  49. Qiu J, Bosch MA, Tobias SC, Grandy DK, Scanlan TS, Ronnekleiv OK, Kelly MJ 2003 Rapid signaling of estrogen in hypothalamic neurons involves a novel G-protein-coupled estrogen receptor that activates protein kinase C. J Neurosci 23:9529–9540[Abstract/Free Full Text]
  50. Malyala A, Kelly MJ, Ronnekleiv OK 2005 Estrogen modulation of hypothalamic neurons: activation of multiple signaling pathways and gene expression changes. Steroids 70:397–406[CrossRef][Medline]
  51. Malyala A, Pattee P, Nagalla SR, Kelly MJ, Ronnekleiv OK 2004 Suppression subtractive hybridization and microarray identification of estrogen-regulated hypothalamic genes. Neurochem Res 29:1189–1200[CrossRef][Medline]
  52. Kelly MJ, Lagrange AH, Wagner EJ, Ronnekleiv OK 1999 Rapid effects of estrogen to modulate G protein-coupled receptors via activation of protein kinase A and protein kinase C pathways. Steroids 64:64–75[CrossRef][Medline]
  53. Gu Q, Moss RL 1998 Novel mechanism for non-genomic action of 17 ß-oestradiol on kainate-induced currents in isolated rat CA1 hippocampal neurones. J Physiol 506:745–754[Abstract/Free Full Text]
  54. Gu Q, Moss RL 1996 17ß-Estradiol potentiates kainate-induced currents via activation of the cAMP cascade. J Neurosci 16:3620–3629[Abstract/Free Full Text]
  55. Brinton RD 2004 Impact of estrogen therapy on Alzheimer’s disease: a fork in the road? CNS Drugs 18:405–422[CrossRef][Medline]
  56. Alkayed NJ, Harukuni I, Kimes AS, London ED, Traystman RJ, Hurn PD 1998 Gender-linked brain injury in experimental stroke. Stroke 29:159–165; discussion, 166[Abstract/Free Full Text]
  57. Dubal DB, Kashon ML, Pettigrew LC, Ren JM, Finklestein SP, Rau SW, Wise PM 1998 Estradiol protects against ischemic injury. J Cereb Blood Flow Metab 18:1253–1258[CrossRef][Medline]
  58. Zhang YQ, Shi J, Rajakumar G, Day AL, Simpkins JW 1998 Effects of gender and estradiol treatment on focal brain ischemia. Brain Res 784:321–324[CrossRef][Medline]
  59. Simpkins JW, Rajakumar G, Zhang YQ, Simpkins CE, Greenwald D, Yu CJ, Bodor N, Day AL 1997 Estrogens may reduce mortality and ischemic damage caused by middle cerebral artery occlusion in the female rat. J Neurosurg 87:724–730[Medline]
  60. Alkayed NJ, Murphy SJ, Traystman RJ, Hurn PD, Miller VM 2000 Neuroprotective effects of female gonadal steroids in reproductively senescent female rats. Stroke 31:161–168[Abstract/Free Full Text]
  61. Toung TJ, Traystman RJ, Hurn PD 1998 Estrogen-mediated neuroprotection after experimental stroke in male rats. Stroke 29:1666–1670[Abstract/Free Full Text]
  62. Gollapudi L, Oblinger MM 1999 Stable transfection of PC12 cells with estrogen receptor (ER{alpha}): protective effects of estrogen on cell survival after serum deprivation. J Neurosci Res 56:99–108[CrossRef][Medline]
  63. Garcia-Segura LM, Cardona-Gomez P, Naftolin F, Chowen JA 1998 Estradiol upregulates Bcl-2 expression in adult brain neurons. Neuroreport 9:593–597[Medline]
  64. Garnier M, Di Lorenzo D, Albertini A, Maggi A 1997 Identification of estrogen-responsive genes in neuroblastoma SK-ER3 cells. J Neurosci 17:4591–4599[Abstract/Free Full Text]
  65. Wilson ME, Liu Y, Wise PM 2002 Estradiol enhances Akt activation in cortical explant cultures following neuronal injury. Brain Res Mol Brain Res 102:48–54[Medline]
  66. Singh M 2001 Ovarian hormones elicit phosphorylation of Akt and extracellular-signal regulated kinase in explants of the cerebral cortex. Endocrine 14:407–415[CrossRef][Medline]
  67. Cardona-Gomez GP, Mendez P, DonCarlos LL, Azcoitia I, Garcia-Segura LM 2002 Interactions of estrogen and insulin-like growth factor-I in the brain: molecular mechanisms and functional implications. J Steroid Biochem Mol Biol 83:211–217[CrossRef][Medline]
  68. Cardona-Gomez GP, DonCarlos L, Garcia-Segura LM 2000 Insulin-like growth factor I receptors and estrogen receptors colocalize in female rat brain. Neuroscience 99:751–760[CrossRef][Medline]
  69. Pugazhenthi S, Nesterova A, Sable C, Heidenreich KA, Boxer LM, Heasley LE, Reusch JE 2000 Akt/protein kinase B up-regulates Bcl-2 expression through cAMP-response element-binding protein. J Biol Chem 275:10761–10766[Abstract/Free Full Text]
  70. Mendez P, Cardona-Gomez GP, Garcia-Segura LM 2005 Interactions of insulin-like growth factor-I and estrogen in the brain. Adv Exp Med Biol 567:285–303[Medline]
  71. Cardona-Gomez P, Perez M, Avila J, Garcia-Segura LM, Wandosell F 2004 Estradiol inhibits GSK3 and regulates interaction of estrogen receptors, GSK3, and ß-catenin in the hippocampus. Mol Cell Neurosci 25:363–373[CrossRef][Medline]
  72. Yu X, Rajala RV, McGinnis JF, Li F, Anderson RE, Yan X, Li S, Elias RV, Knapp RR, Zhou X, Cao W 2004 Involvement of insulin/phosphoinositide 3-kinase/Akt signal pathway in 17 ß-estradiol-mediated neuroprotection. J Biol Chem 279:13086–13094[Abstract/Free Full Text]
  73. Singh M, Setalo Jr G, Guan X, Warren M, Toran-Allerand CD 1999 Estrogen-induced activation of mitogen-activated protein kinase in cerebral cortical explants: convergence of estrogen and neurotrophin signaling pathways. J Neurosci 19:1179–1188[Abstract/Free Full Text]
  74. Improta-Brears T, Whorton AR, Codazzi F, York JD, Meyer T, McDonnell DP 1999 Estrogen-induced activation of mitogen-activated protein kinase requires mobilization of intracellular calcium. Proc Natl Acad Sci USA 96:4686–4691[Abstract/Free Full Text]
  75. Xu Y, Traystman RJ, Hurn PD, Wang MM 2003 Neurite-localized estrogen receptor-{alpha} mediates rapid signaling by estrogen. J Neurosci Res 74:1–11[CrossRef][Medline]
  76. Kuroki Y, Fukushima K, Kanda Y, Mizuno K, Watanabe Y 2001 Neuroprotection by estrogen via extracellular signal-regulated kinase against quinolinic acid-induced cell death in the rat hippocampus. Eur J Neurosci 13:472–476[CrossRef][Medline]
  77. Kuroki Y, Fukushima K, Kanda Y, Mizuno K, Watanabe Y 2000 Putative membrane-bound estrogen receptors possibly stimulate mitogen-activated protein kinase in the rat hippocampus. Eur J Pharmacol 400:205–209[CrossRef][Medline]
  78. Manthey D, Heck S, Engert S, Behl C 2001 Estrogen induces a rapid secretion of amyloid ß precursor protein via the mitogen-activated protein kinase pathway. Eur J Biochem 268:4285–4291[Medline]
  79. Zhang S, Huang Y, Zhu YC, Yao T 2005 Estrogen stimulates release of secreted amyloid precursor protein from primary rat cortical neurons via protein kinase C pathway. Acta Pharmacol Sin 26:171–176[CrossRef][Medline]
  80. Hayashi S, Ueyama T, Kajimoto T, Yagi K, Kohmura E, Saito N 2005 Involvement of {gamma} protein kinase C in estrogen-induced neuroprotection against focal brain ischemia through G protein-coupled estrogen receptor. J Neurochem 93:883–891[CrossRef][Medline]
  81. Flanagan-Cato LM, Calizo LH, Daniels D 2001 The synaptic organization of VMH neurons that mediate the effects of estrogen on sexual behavior. Horm Behav 40:178–182[CrossRef][Medline]
  82. Cooke BM, Woolley CS 2005 Gonadal hormone modulation of dendrites in the mammalian CNS. J Neurobiol 64:34–46[CrossRef][Medline]
  83. Murphy DD, Segal M 1996 Regulation of dendritic spine density in cultured rat hippocampal neurons by steroid hormones. J Neurosci 16:4059–4068[Abstract/Free Full Text]
  84. Murphy DD, Segal M 1997 Morphological plasticity of dendritic spines in central neurons is mediated by activation of cAMP response element binding protein. Proc Natl Acad Sci USA 94:1482–1487[Abstract/Free Full Text]
  85. Segal M, Murphy DD 1998 CREB activation mediates plasticity in cultured hippocampal neurons. Neural Plast 6:1–7[Medline]
  86. Lee SJ, Campomanes CR, Sikat PT, Greenfield AT, Allen PB, McEwen BS 2004 Estrogen induces phosphorylation of cyclic AMP response element binding (pCREB) in primary hippocampal cells in a time-dependent manner. Neuroscience 124:549–560[CrossRef][Medline]
  87. Abraham IM, Herbison AE 2005 Major sex differences in non-genomic estrogen actions on intracellular signaling in mouse brain in vivo. Neuroscience 131:945–951[CrossRef][Medline]
  88. Boulware MI, Weick JP, Becklund BR, Kuo SP, Groth RD, Mermelstein PG 2005 Estradiol activates group I and II metabotropic glutamate receptor signaling, leading to opposing influences on cAMP response element-binding protein. J Neurosci 25:5066–5078[Abstract/Free Full Text]
  89. Murphy DD, Cole NB, Greenberger V, Segal M 1998 Estradiol increases dendritic spine density by reducing GABA neurotransmission in hippocampal neurons. J Neurosci 18:2550–2559[Abstract/Free Full Text]
  90. Scharfman HE, Maclusky NJ 2005 Similarities between actions of estrogen and BDNF in the hippocampus: coincidence or clue? Trends Neurosci 28:79–85[CrossRef][Medline]
  91. Scharfman HE, Mercurio TC, Goodman JH, Wilson MA, MacLusky NJ 2003 Hippocampal excitability increases during the estrous cycle in the rat: a potential role for brain-derived neurotrophic factor. J Neurosci 23:11641–11652[Abstract/Free Full Text]
  92. Ivanova T, Mendez P, Garcia-Segura LM, Beyer C 2002 Rapid stimulation of the PI3-kinase/Akt signalling pathway in developing midbrain neurones by oestrogen. J Neuroendocrinol 14:73–79[CrossRef][Medline]
  93. Beyer C, Karolczak M 2000 Estrogenic stimulation of neurite growth in midbrain dopaminergic neurons depends on cAMP/protein kinase A signalling. J Neurosci Res 59:107–116[CrossRef][Medline]
  94. Pfaff D 1998 Hormonal and environmental control of lordosis behavior: neural and molecular mechanisms. Eur J Neurosci 10:330[Medline]
  95. Kow LM, Pfaff DW 1998 Mapping of neural and signal transduction pathways for lordosis in the search for estrogen actions on the central nervous system. Behav Brain Res 92:169–180[CrossRef][Medline]
  96. Mong J, Krebs CJ, Pfaff DW 2002 Perspective: microarrays and differential display PCR-tools for studying transcript levels of genes in neuroendocrine systems. Endocrinology 143:2002–2006[Abstract/Free Full Text]
  97. Mong J, Easton A, Kow LM, Pfaff D 2003 Neural, hormonal and genetic mechanisms for the activation of brain and behavior. Eur J Pharmacol 480:229–231[CrossRef][Medline]
  98. Mobbs CV, Rothfeld JM, Saluja R, Pfaff DW 1989 Phorbol esters and forskolin infused into midbrain central gray facilitate lordosis. Pharmacol Biochem Behav 34:665–667[CrossRef][Medline]
  99. Uphouse L, Maswood S, Jackson A 2000 Factors elevating cAMP attenuate the effects of 8-OH-DPAT on lordosis behavior. Pharmacol Biochem Behav 66:383–388[CrossRef][Medline]
  100. Etgen AM, Acosta-Martinez M 2003 Participation of growth factor signal transduction pathways in estradiol facilitation of female reproductive behavior. Endocrinology 144:3828–3835[Abstract/Free Full Text]
  101. Apostolakis EM, Garai J, Lohmann JE, Clark JH, O’Malley BW 2000 Epidermal growth factor activates reproductive behavior independent of ovarian steroids in female rodents. Mol Endocrinol 14:1086–1098[Abstract/Free Full Text]
  102. Acosta-Martinez M, Etgen AM 2002 The role of {delta}-opioid receptors in estrogen facilitation of lordosis behavior. Behav Brain Res 136:93–102[CrossRef][Medline]
  103. Kow L-M, Pfaff D 1985 Estrogen effects on neuronal responsiveness to electrical and neurotransmitter stimulation: an in vitro study on the ventromedial nucleus of the hypothalamus. Brain Res 347:1- 10:45–50
  104. Kow L, Mobbs C, Pfaff D 1994 Roles of second-messenger systems and neuronal activity in the regulation of lordosis by neurotransmitters, neuropeptides, and estrogen: a review. Neurosci Biobehav Rev 18:251–268[CrossRef][Medline]
  105. Kow LM, Easton A, Pfaff DW 2005 Acute estrogen potentiates excitatory responses of neurons in rat hypothalamic ventromedial nucleus. Brain Res 1043:124–131[CrossRef][Medline]
  106. Vasudevan N, Kow LM, Pfaff DW 2001 Early membrane estrogenic effects required for full expression of slower genomic actions in a nerve cell line. Proc Natl Acad Sci USA 98:12267–12271[Abstract/Free Full Text]
  107. Watters JJ, Campbell JS, Cunningham MJ, Krebs EG, Dorsa DM 1997 Rapid membrane effects of steroids in neuroblastoma cells: effects of estrogen on mitogen activated protein kinase signalling cascade and c-fos immediate early gene transcription. Endocrinology 138:4030–4033[Abstract/Free Full Text]
  108. Watters JJ, Dorsa DM 1998 Transcriptional effects of estrogen on neuronal neurotensin gene expression involve cAMP/protein kinase A dependent mechanisms. J Neurosci 18:6672–6680[Abstract/Free Full Text]
  109. Cho H, Aronica SM, Katzenellenbogen BS 1994 Regulation of progesterone receptor gene expression in MCF-7 breast cancer cells: a comparison of the effects of cyclic adenosine 3',5'-monophosphate, estradiol, insulin-like growth factor-I, and serum factors. Endocrinology 134:658–664[Abstract/Free Full Text]
  110. Sabbah M, Courilleau D, Mester J, Redeuilh G 1999 Estrogen induction of the cyclin D1 promoter: involvement of a cAMP response-like element. Proc Natl Acad Sci USA 96:11217–11222[Abstract/Free Full Text]
  111. Mawson A, Lai A, Carroll JS, Sergio CM, Mitchell CJ, Sarcevic B 2005 Estrogen and insulin/IGF-1 cooperatively stimulate cell cycle progression in MCF-7 breast cancer cells through differential regulation of c-Myc and cyclin D1. Mol Cell Endocrinol 229:161–173[CrossRef][Medline]
  112. Stoica GE, Franke TF, Moroni M, Mueller S, Morgan E, Iann MC, Winder AD, Reiter R, Wellstein A, Martin MB, Stoica A 2003 Effect of estradiol on estrogen receptor-{alpha} gene expression and activity can be modulated by the ErbB2/PI 3-K/Akt pathway. Oncogene 22:7998–8011[CrossRef][Medline]
  113. Martin MB, Franke TF, Stoica GE, Chambon P, Katzenellenbogen BS, Stoica BA, McLemore MS, Olivo SE, Stoica A 2000 A role for Akt in mediating the estrogenic functions of epidermal growth factor and insulin-like growth factor I. Endocrinology 141:4503–4511[Abstract/Free Full Text]
  114. Pedram A, Razandi M, Aitkenhead M, Hughes CC, Levin ER 2002 Integration of the non-genomic and genomic actions of estrogen. Membrane-initiated signaling by steroid to transcription and cell biology. J Biol Chem 277:50768–50775[Abstract/Free Full Text]
  115. Devidze N, Mong JA, Jasnow AM, Kow LM, Pfaff DW 2005 Sex and estrogenic effects on coexpression of mRNAs in single ventromedial hypothalamic neurons. Proc Natl Acad Sci USA 102:14446–14451[Abstract/Free Full Text]
  116. Agrati P, Garnier M, Patrone C, Pollio G, Santagati S, Vegeto E, Maggi A 1997 SK-ER3 neuroblastoma cells as a model for the study of estrogen influence on neural cells. Brain Res Bull 44:519–523[CrossRef][Medline]
  117. Patrone C, Gianazza E, Santagati S, Agrati P, Maggi A 1998 Divergent pathways regulate ligand-independent activation of ER {alpha} in SK-N-BE2C neuroblastoma and COS-1 renal carcinoma cells. Mol Endocrinol 12:835–841[Abstract/Free Full Text]
  118. Allouche S, Polastron J, Hasbi A, Homburger V, Jauzac P 1999 Differential G-protein activation by alkaloid and peptide opioid agonists in the human neuroblastoma cell line SK-N-BE. Biochem J 342:71–78
  119. Allouche S, Roussel M, Marie N, Jauzac P 1999 Differential desensitization of human {delta}-opioid receptors by peptide and alkaloid agonists. Eur J Pharmacol 371:235–240[CrossRef][Medline]
  120. Harris J, Gorski J 1978 Evidence for a discontinuous requirement for estrogen in stimulation of deoxyribonucleic acid synthesis in the immature rat uterus. Endocrinology 103:240–245[Abstract/Free Full Text]
  121. Parsons B, McEwen B, Pfaff D 1982 A discontinuous schedule of estradiol treatment is sufficient to activate progesterone-facilitated feminine sexual behavior and to increase cytosol receptors for progestins in the hypothalamus of the rat. Endocrinology 110:613–619[Abstract/Free Full Text]
  122. Binder M 1984 Oestradiol-BSA conjugates for receptor histochemistry: problems of stability and interactions with cytosol. Histochem J 16:1003–1023[CrossRef][Medline]
  123. Vasudevan N, Pfaff DW 2005 Molecular mechanisms of crosstalk between thyroid hormones and estrogens. Curr Opin Endocrinol Diabetes 12:381–388[CrossRef]
  124. Taguchi Y, Koslowski M, Bodenner DL 2004 Binding of estrogen receptor with estrogen conjugated to bovine serum albumin (BSA). Nucl Recept 2:5[CrossRef][Medline]
  125. Zhao X, Lorenc H, Stephenson H, Wang YJ, Witherspoon D, Katzenellenbogen B, Pfaff D, Vasudevan N 2005 Thyroid hormone can increase estrogen-mediated transcription from a consensus estrogen response element in neuroblastoma cells. Proc Natl Acad Sci USA 102:4890–4895[Abstract/Free Full Text]
  126. Vasudevan N, Kow LM, Pfaff D 2005 Integration of steroid hormone initiated membrane action to genomic function in the brain. Steroids 70:388–396[CrossRef][Medline]
  127. Sawai T, Bernier F, Fukushima T, Hashimoto T, Ogura H, Nishizawa Y 2002 Estrogen induces a rapid increase of calcium-calmodulin-dependent protein kinase II activity in the hippocampus. Brain Res 950:308–311[CrossRef][Medline]
  128. Zhou J, Cohen RS, Pandey SC 2001 Estrogen affects the expression of Ca2+/calmodulin-dependent protein kinase IV in amygdala. Neuroreport 12:2987–2990[CrossRef][Medline]
  129. Li Z, Joyal JL, Sacks DB 2001 Calmodulin enhances the stability of the estrogen receptor. J Biol Chem 276:17354–17360[Abstract/Free Full Text]
  130. Song RX, McPherson RA, Adam L, Bao Y, Shupnik M, Kumar R, Santen RJ 2002 Linkage of rapid estrogen action to MAPK activation by ER{alpha}-Shc association and Shc pathway activation. Mol Endocrinol 16:116–127[Abstract/Free Full Text]
  131. Keshamouni VG, Mattingly RR, Reddy KB 2002 Mechanism of 17-ß-estradiol-induced Erk1/2 activation in breast cancer cells. A role for HER2 AND PKC-{delta}. J Biol Chem 277:22558–22565[Abstract/Free Full Text]
  132. Hutcheson IR, Knowlden JM, Madden TA, Barrow D, Gee JM, Wakeling AE, Nicholson RI 2003 Oestrogen receptor-mediated modulation of the EGFR/MAPK pathway in tamoxifen-resistant MCF-7 cells. Breast Cancer Res Treat 81:81–93[CrossRef][Medline]
  133. Zhang Z, Kumar R, Santen RJ, Song RX 2004 The role of adapter protein Shc in estrogen non-genomic action. Steroids 69:523–529[CrossRef][Medline]
  134. Castoria G, Migliaccio A, Bilancio A, Di Domenico M, de Falco A, Lombardi M, Fiorentino R, Varricchio L, Barone MV, Auricchio F 2001 PI3-kinase in concert with Src promotes the S-phase entry of oestradiol-stimulated MCF-7 cells. EMBO J 20:6050–6059[CrossRef][Medline]
  135. Wollmann W, Goodman ML, Bhat-Nakshatri P, Kishimoto H, Goulet Jr RJ, Mehrotra S, Morimiya A, Badve S, Nakshatri H 2005 The macrophage inhibitory cytokine integrates AKT/PKB and MAP kinase signaling pathways in breast cancer cells. Carcinogenesis 26:900–907[Abstract/Free Full Text]
  136. Boyan BD, Sylvia VL, Frambach T, Lohmann CH, Dietl J, Dean DD, Schwartz Z 2003 Estrogen-dependent rapid activation of protein kinase C in estrogen receptor-positive MCF-7 breast cancer cells and estrogen receptor-negative HCC38 cells is membrane-mediated and inhibited by tamoxifen. Endocrinology 144:1812–1824[Abstract/Free Full Text]
  137. Castoria G, Migliaccio A, Di Domenico M, Lombardi M, de Falco A, Varricchio L, Bilancio A, Barone MV, Auricchio F 2004 Role of atypical protein kinase C in estradiol-triggered G1/S progression of MCF-7 cells. Mol Cell Biol 24:7643–7653[Abstract/Free Full Text]
  138. Nabha SM, Glaros S, Hong M, Lykkesfeldt AE, Schiff R, Osborne K, Reddy KB 2005 Upregulation of PKC-{delta} contributes to antiestrogen resistance in mammary tumor cells. Oncogene 24:3166–3176[CrossRef][Medline]
  139. Tonetti DA, Chisamore MJ, Grdina W, Schurz H, Jordan VC 2000 Stable transfection of protein kinase C {alpha} cDNA in hormone-dependent breast cancer cell lines. Br J Cancer 83:782–791[CrossRef][Medline]
  140. Fujimoto N, Katzenellenbogen BS 1994 Alteration in the agonist/antagonist balance of antiestrogens by activation of protein kinase A signaling pathways in breast cancer cells: antiestrogen selectivity and promoter dependence. Mol Endocrinol 8:296–304[Abstract/Free Full Text]
  141. Kiefer T, Ram PT, Yuan L, Hill SM 2002 Melatonin inhibits estrogen receptor transactivation and cAMP levels in breast cancer cells. Breast Cancer Res Treat 71:37–45[CrossRef][Medline]
  142. Martin LA, Farmer I, Johnston SR, Ali S, Marshall C, Dowsett M 2003 Enhanced estrogen receptor (ER) {alpha}, ERBB2, and MAPK signal transduction pathways operate during the adaptation of MCF-7 cells to long term estrogen deprivation. J Biol Chem 278:30458–30468[Abstract/Free Full Text]
  143. Gaben AM, Saucier C, Bedin M, Redeuilh G, Mester J 2004 Mitogenic activity of estrogens in human breast cancer cells does not rely on direct induction of mitogen-activated protein kinase/extracellularly regulated kinase or phosphatidylinositol 3-kinase. Mol Endocrinol 18:2700–2713[Abstract/Free Full Text]
  144. Lobenhofer EK, Huper G, Iglehart JD, Marks JR 2000 Inhibition of mitogen-activated protein kinase and phosphatidylinositol 3-kinase activity in MCF-7 cells prevents estrogen-induced mitogenesis. Cell Growth Differ 11:99–110[Abstract/Free Full Text]
  145. Coleman KM, Smith CL 2001 Intracellular signaling pathways: nongenomic actions of estrogens and ligand-independent activation of estrogen receptors. Front Biosci 6:D1379–D1391
  146. Falkenstein E, Wehling M 2000 Nongenomically initiated steroid actions. Eur J Clin Invest 30:51–54
  147. Shupnik MA 2004 Crosstalk between steroid receptors and the c-Src-receptor tyrosine kinase pathways: implications for cell proliferation. Oncogene 23:7979–7989[CrossRef][Medline]
  148. Sabnis GJ, Jelovac D, Long B, Brodie A 2005 The role of growth factor receptor pathways in human breast cancer cells adapted to long-term estrogen deprivation. Cancer Res 65:3903–3910[Abstract/Free Full Text]
  149. Pietras RJ, Marquez DC, Chen HW, Tsai E, Weinberg O, Fishbein M 2005 Estrogen and growth factor receptor interactions in human breast and non-small cell lung cancer cells. Steroids 70:372–381[CrossRef][Medline]
  150. Stabile LP, Lyker JS, Gubish CT, Zhang W, Grandis JR, Siegfried JM 2005 Combined targeting of the estrogen receptor and the epidermal growth factor receptor in non-small cell lung cancer shows enhanced antiproliferative effects. Cancer Res 65:1459–1470[Abstract/Free Full Text]
  151. Zivadinovic D, Gametchu B, Watson CS 2005 Membrane estrogen receptor-{alpha} levels in MCF-7 breast cancer cells predict cAMP and proliferation responses. Breast Cancer Res 7:R101–R112
  152. Zivadinovic D, Watson CS 2005 Membrane estrogen receptor-{alpha} levels predict estrogen-induced ERK1/2 activation in MCF-7 cells. Breast Cancer Res 7:R130–R144
  153. Razandi M, Pedram A, Levin ER 2000 Plasma membrane estrogen receptors signal to antiapoptosis in breast cancer. Mol Endocrinol 14:1434–1447[Abstract/Free Full Text]
  154. Levin ER 2005 Integration of the extranuclear and nuclear actions of estrogen. Mol Endocrinol 19:1951–1959[Abstract/Free Full Text]
  155. Haynes MP, Sinha D, Russell KS, Collinge M, Fulton D, Morales-Ruiz M, Sessa WC, Bender JR 2000 Membrane estrogen receptor engagement activates endothelial nitric oxide synthase via the PI3-kinase-Akt pathway in human endothelial cells. Circ Res 87:677–682[Abstract/Free Full Text]
  156. Chambliss KL, Yuhanna IS, Anderson RG, Mendelsohn ME, Shaul PW 2002 ERß has nongenomic action in caveolae. Mol Endocrinol 16:938–946[Abstract/Free Full Text]
  157. Chambliss KL, Yuhanna IS, Mineo C, Liu P, German Z, Sherman TS, Mendelsohn ME, Anderson RG, Shaul PW 2000 Estrogen receptor {alpha} and endothelial nitric oxide synthase are organized into a functional signaling module in caveolae. Circ Res 87:E44–E52
  158. Chen Z, Yuhanna IS, Galcheva-Gargova Z, Karas RH, Mendelsohn ME, Shaul PW 1999 Estrogen receptor {alpha} mediates the nongenomic activation of endothelial nitric oxide synthase by estrogen. J Clin Invest 103:401–406[Medline]
  159. Chambliss KL, Simon L, Yuhanna IS, Mineo C, Shaul PW 2005 Dissecting the basis of nongenomic activation of endothelial nitric oxide synthase by estradiol: role of ER{alpha} domains with known nuclear functions. Mol Endocrinol 19:277–289[Abstract/Free Full Text]
  160. Bjornstrom L, Sjoberg M 2005 Mechanisms of estrogen receptor signaling: convergence of genomic and nongenomic actions on target genes. Mol Endocrinol 19:833–842[Abstract/Free Full Text]
  161. Pratt WB, Toft DO 1997 Steroid receptor interactions with heat shock protein and immunophilin chaperones. Endocr Rev 18:306–360[Abstract/Free Full Text]
  162. Papaconstantinou AD, Goering PL, Umbreit TH, Brown KM 2003 Regulation of uterine hsp90{alpha}, hsp72 and HSF-1 transcription in B6C3F1 mice by ß-estradiol and bisphenol A: involvement of the estrogen receptor and protein kinase C. Toxicol Lett 144:257–270[CrossRef][Medline]
  163. Papaconstantinou AD, Fisher BR, Umbreit TH, Brown KM 2002 Increases in mouse uterine heat shock protein levels are a sensitive and specific response to uterotrophic agents. Environ Health Perspect 110:1207–1212[Medline]
  164. Zhang Y, Champagne N, Beitel LK, Goodyer CG, Trifiro M, LeBlanc A 2004 Estrogen and androgen protection of human neurons against intracellular amyloid ß1–42 toxicity through heat shock protein 70. J Neurosci 24:5315–5321[Abstract/Free Full Text]
  165. Alarid ET, Bakopoulos N, Solodin N 1999 Proteasome-mediated proteolysis of estrogen receptor: a novel component in autologous down-regulation. Mol Endocrinol 13:1522–1534[Abstract/Free Full Text]
  166. Tsai HW, Katzenellenbogen JA, Katzenellenbogen BS, Shupnik MA 2004 Protein kinase A activation of estrogen receptor {alpha} transcription does not require proteasome activity and protects the receptor from ligand-mediated degradation. Endocrinology 145:2730–2738[Abstract/Free Full Text]
  167. Alarid ET, Preisler-Mashek MT, Solodin NM 2003 Thyroid hormone is an inhibitor of estrogen-induced degradation of estrogen receptor-{alpha} protein: estrogen-dependent proteolysis is not essential for receptor transactivation function in the pituitary. Endocrinology 144:3469–3476[Abstract/Free Full Text]
  168. De Servi B, Hermani A, Medunjanin S, Mayer D 2005 Impact of PKC{delta} on estrogen receptor localization and activity in breast cancer cells. Oncogene 24:4946–4955[CrossRef][Medline]
  169. Lee H, Bai W 2002 Regulation of estrogen receptor nuclear export by ligand-induced and p38-mediated receptor phosphorylation. Mol Cell Biol 22:5835–5845[Abstract/Free Full Text]
  170. Lu Q, Ebling H, Mittler J, Baur WE, Karas RH 2002 MAP kinase mediates growth factor-induced nuclear translocation of estrogen receptor {alpha}. FEBS Lett 516:1–8[CrossRef][Medline]
  171. Arnold SF, Obourn JD, Jaffe H, Notides AC 1995 Phosphorylation of the human estrogen receptor on tyrosine 537 in vivo and by src family tyrosine kinases in vitro. Mol Endocrinol 9:24–33[Abstract/Free Full Text]
  172. LeGoff P, Montano MM, Schodin DJ, Katzenellenbogen BS 1994 Phosphorylation of the human estrogen receptor. Identification of hormone-regulated sites and examination of their influence on transcriptional activity. J Biol Chem 269:4458–4466[Abstract/Free Full Text]
  173. Lazennec G, Thomas JA, Katzenellenbogen BS 2001 Involvement of cyclic AMP response element binding protein (CREB) and estrogen receptor phosphorylation in the synergistic activation of the estrogen receptor by estradiol and protein kinase activators. J Steroid Biochem Mol Biol 77:193–203[CrossRef][Medline]
  174. Joel PB, Traish AM, Lannigan DA 1995 Estradiol and phorbol ester cause phosphorylation of serine 118 in the human estrogen receptor. Mol Endocrinol 9:1041–1052[Abstract/Free Full Text]
  175. Sun M, Paciga JE, Feldman RI, Yuan Z, Coppola D, Lu YY, Shelley SA, Nicosia SV, Cheng JQ 2001 Phosphatidylinositol-3-OH kinase (PI3K)/AKT2, activated in breast cancer, regulates and is induced by estrogen receptor {alpha} (ER{alpha}) via interaction between ER{alpha} and PI3K. Cancer Res 61:5985–5991[Abstract/Free Full Text]
  176. Campbell RA, Bhat-Nakshatri P, Patel NM, Constantinidou D, Ali S, Nakshatri H 2001 Phosphatidylinositol 3-kinase/AKT-mediated activation of estrogen receptor {alpha}: a new model for anti-estrogen resistance. J Biol Chem 276:9817–9824[Abstract/Free Full Text]
  177. Lannigan DA 2003 Estrogen receptor phosphorylation. Steroids 68:1–9[CrossRef][Medline]
  178. Kato S, Endoh H, Masuhiro Y, Kitamoto T, Uchiyama S, Sasaki H, Masushige S, Gotoh Y, Nishida E, Kawashima H 1995 Activation of the estrogen receptor through phosphorylation by mitogen-activated protein kinase. Science 270:1491–1494[Abstract/Free Full Text]
  179. Chen D, Pace PE, Coombes RC, Ali S 1999 Phosphorylation of human estrogen receptor {alpha} by protein kinase A regulates dimerization. Mol Cell Biol 19:1002–1015[Abstract/Free Full Text]
  180. Cui Y, Zhang M, Pestell R, Curran EM, Welshons WV, Fuqua SA 2004 Phosphorylation of estrogen receptor {alpha} blocks its acetylation and regulates estrogen sensitivity. Cancer Res 64:9199–9208[Abstract/Free Full Text]
  181. Bunone G, Briand PA, Miksicek RJ, Picard D 1996 Activation of the unliganded estrogen receptor by EGF involves the MAP kinase pathway and direct phosphorylation. EMBO J 15:2174–2183[Medline]
  182. Joel PB, Traish AM, Lannigan DA 1998 Estradiol-induced phosphorylation of serine 118 in the estrogen receptor is independent of p42/p44 mitogen-activated protein kinase. J Biol Chem 273:13317–13323[Abstract/Free Full Text]
  183. Clark DE, Poteet-Smith CE, Smith JA, Lannigan DA 2001 Rsk2 allosterically activates estrogen receptor {alpha} by docking to the hormone-binding domain. EMBO J 20:3484–3494[CrossRef][Medline]
  184. Joel PB, Smith J, Sturgill TW, Fisher TL, Blenis J, Lannigan DA 1998 pp90rsk1 Regulates estrogen receptor-mediated transcription through phosphorylation of Ser-167. Mol Cell Biol 18:1978–1984[Abstract/Free Full Text]
  185. Arnold SF, Obourn JD, Jaffe H, Notides AC 1994 Serine 167 is the major estradiol-induced phosphorylation site on the human estrogen receptor. Mol Endocrinol 8:1208–1214[Abstract/Free Full Text]
  186. Arnold SF, Obourn JD, Jaffe H, Notides AC 1995 Phosphorylation of the human estrogen receptor by mitogen-activated protein kinase and casein kinase II: consequence on DNA binding. J Steroid Biochem Mol Biol 55:163–172[CrossRef][Medline]
  187. Balasenthil S, Barnes CJ, Rayala SK, Kumar R 2004 Estrogen receptor activation at serine 305 is sufficient to upregulate cyclin D1 in breast cancer cells. FEBS Lett 567:243–247[CrossRef][Medline]
  188. Lavinsky RM, Jepsen K, Heinzel T, Torchia J, Mullen TM, Schiff R, Del-Rio AL, Ricote M, Ngo S, Gemsch J, Hilsenbeck SG, Osborne CK, Glass CK, Rosenfeld MG, Rose DW 1998 Diverse signaling pathways modulate nuclear receptor recruitment of N-CoR and SMRT complexes. Proc Natl Acad Sci USA 95:2920–2925[Abstract/Free Full Text]
  189. Tremblay A, Tremblay GB, Labrie F, Giguere V 1999 Ligand-independent recruitment of SRC-1 to estrogen receptor ß through phosphorylation of activation function AF-1. Mol Cell 3:513–519[CrossRef][Medline]
  190. Qiu M, Olsen A, Faivre E, Horwitz KB, Lange CA 2003 Mitogen-activated protein kinase regulates nuclear association of human progesterone receptors. Mol Endocrinol 17:628–642[Abstract/Free Full Text]
  191. Rowan BG, Garrison N, Weigel NL, O’Malley BW 2000 8-Bromo-cyclic AMP induces phosphorylation of two sites in SRC-1 that facilitate ligand-independent activation of the chicken progesterone receptor and are critical for functional cooperation between SRC-1 and CREB binding protein. Mol Cell Biol 23:8720–8730
  192. Font de Mora J, Brown M 2000 AIB1 is a conduit for kinase-mediated growth factor signaling to the estrogen receptor. Mol Cell Biol 20:5041–5047[Abstract/Free Full Text]
  193. Wu RC, Qin J, Yi P, Wong J, Tsai SY, Tsai MJ, O’Malley BW 2004 Selective phosphorylations of the SRC-3/AIB1 coactivator integrate genomic responses to multiple cellular signaling pathways. Mol Cell 15:937–949[CrossRef][Medline]
  194. Frigo DE, Basu A, Nierth-Simpson EN, Weldon CB, Dugan CM, Elliott S, Collins-Burow BM, Salvo VA, Zhu Y, Melnik LI, Lopez GN, Kushner PJ, Curiel TJ, Rowan BG, McLachlan JA, Burow ME 2006 p38 Mitogen-activated protein kinase stimulates estrogen-mediated transcription and proliferation through the phosphorylation and potentiation of the p160 coactivator glucocorticoid receptor-interacting protein 1. Mol Endocrinol 20:971–983[Abstract/Free Full Text]
  195. Zheng FF, Wu RC, Smith CL, O’Malley BW 2005 Rapid estrogen-induced phosphorylation of the SRC-3 coactivator occurs in an extranuclear complex containing estrogen receptor. Mol Cell Biol 25:8273–8284[Abstract/Free Full Text]
  196. O’Malley BW 2005 A life-long search for the molecular pathways of steroid hormone action. Mol Endocrinol 19:1402–1411[Abstract/Free Full Text]
  197. Watson CS, Pappas TC, Gametchu B 1995 The other estrogen receptor in the plasma membrane: implications for the actions of environmental estrogens. Environ Health Perspect 103(Suppl 7):41–50
  198. Watson CS, Gametchu B 1999 Membrane-initiated steroid actions and the proteins that mediate them. Proc Soc Exp Biol Med 220:9–19[CrossRef][Medline]
  199. Watson CS, Campbell CH, Gametchu B 2002 The dynamic and elusive membrane estrogen receptor-{alpha}. Steroids 67:429–437[CrossRef][Medline]
  200. Warner M, Gustafsson JA 2006 Nongenomic effects of estrogen: why all the uncertainty? Steroids 71:91–95[CrossRef][Medline]
  201. Sylvia VL, Walton J, Lopez D, Dean DD, Boyan BD, Schwartz Z 2001 17-ß Estradiol-BSA conjugates and 17ß estradiol regulates growth plate chondrocytes by common membrane associated mechanisms involving PKC dependent and independent signal transduction. J Cell Biochem 81:413–429[CrossRef][Medline]
  202. Toran-Allerand CD, Guan X, MacLusky NJ, Horvath TL, Diano S, Singh M, Connolly Jr ES, Nethrapalli IS, Tinnikov AA 2002 ER-X: a novel, plasma membrane-associated, putative estrogen receptor that is regulated during development and after ischemic brain injury. J Neurosci 22:8391–8401[Abstract/Free Full Text]
  203. Qiu J, Bosch MA, Tobias SC, Krust A, Graham SM, Murphy SJ, Korach KS, Chambon P, Scanlan TS, Ronnekleiv OK, Kelly MJ 2006 A G-protein-coupled estrogen receptor is involved in hypothalamic control of energy homeostasis. J Neurosci 26:5649–5655[Abstract/Free Full Text]
  204. Lagrange A, Ronnekleiv O, Kelly M 1997 Modulation of G protein-coupled receptors by an estrogen receptor that activates protein kinase A. Mol Pharmacol 51:605–612[Abstract/Free Full Text]
  205. Nadal A, Ropero AB, Laribi O, Maillet M, Fuentes E, Soria B 2000 Nongenomic actions of estrogens and xenoestrogens by binding at a plasma membrane receptor unrelated to estrogen receptor {alpha} and estrogen receptor ß. Proc Natl Acad Sci USA 97:11603–11608[Abstract/Free Full Text]
  206. Morales A, Diaz M, Ropero AB, Nadal A, Alonso R 2003 Estradiol modulates acetylcholine-induced Ca2+ signals in LHRH-releasing GT1–7 cells through a membrane binding site. Eur J Neurosci 18:2505–2514[CrossRef][Medline]
  207. Morales A, Diaz M, Guelmes P, Marin R, Alonso R 2005 Rapid modulatory effect of estradiol on acetylcholine-induced Ca2+ signal is mediated through cyclic-GMP cascade in LHRH-releasing GT1–7 cells. Eur J Neurosci 22:2207–2215[CrossRef][Medline]
  208. Zhu Y, Bond J, Thomas P 2003 Identification, classification, and partial characterization of genes in humans and other vertebrates homologous to a fish membrane progestin receptor. Proc Natl Acad Sci USA 100:2237–2242[Abstract/Free Full Text]
  209. Zhu Y, Rice CD, Pang Y, Pace M, Thomas P 2003 Cloning, expression, and characterization of a membrane progestin receptor and evidence it is an intermediary in meiotic maturation of fish oocytes. Proc Natl Acad Sci USA 100:2231–2236[Abstract/Free Full Text]
  210. Thomas P, Pang Y, Filardo EJ, Dong J 2005 Identity of an estrogen membrane receptor coupled to a G protein in human breast cancer cells. Endocrinology 146:624–632[Medline]
  211. Revankar CM, Cimino DF, Sklar LA, Arterburn JB, Prossnitz ER 2005 A transmembrane intracellular estrogen receptor mediates rapid cell signaling. Science 307:1625–1630[Abstract/Free Full Text]
  212. Pedram A, Razandi M, Levin ER 2006 Nature of functional estrogen receptors at the plasma membrane. Mol Endocrinol 20:1996–2009[Abstract/Free Full Text]
  213. Bologa CG, Revankar CM, Young SM, Edwards BS, Arterburn JB, Kiselyov AS, Parker MA, Tkachenko SE, Savchuck NP, Sklar LA, Oprea TI, Prossnitz ER 2006 Virtual and biomolecular screening converge on a selective agonist for GPR30. Nat Chem Biol 2:207–212[CrossRef][Medline]
  214. Wade CB, Robinson S, Shapiro RA, Dorsa DM 2001 Estrogen receptor {alpha} and ER ß exhibit unique pharmacological properties when coupled to activation of the mitogen-activated protein kinase pathway. Endocrinology 142:2336–2342[Abstract/Free Full Text]
  215. Russell KS, Haynes MP, Sinha D, Clerisme E, Bender JR 2000 Human vascular endothelial cells contain membrane binding sites for estradiol, which mediate rapid intracellular signaling. Proc Natl Acad Sci USA 97:5930–5935[Abstract/Free Full Text]
  216. Wyckoff MH, Chambliss KL, Mineo C, Yuhanna IS, Mendelsohn ME, Mumby SM, Shaul PW 2001 Plasma membrane estrogen receptors are coupled to eNOS through G{alpha}i. J Biol Chem 276:27071–27076[Abstract/Free Full Text]
  217. Chaban VV, Lakhter AJ, Micevych P 2004 A membrane estrogen receptor mediates intracellular calcium release in astrocytes. Endocrinology 145:3788–3795[Abstract/Free Full Text]
  218. Abraham IM, Todman MG, Korach KS, Herbison AE 2004 Critical in vivo roles for classical estrogen receptors in rapid estrogen actions on intracellular signaling in mouse brain. Endocrinology 145:3055–3061[CrossRef][Medline]
  219. Razandi M, Pedram A, Greene GL, Levin ER 1999 Cell membrane and nuclear estrogen receptor (ERs) originate from a single transcript: studies of ER{alpha} and ERß expressed in Chinese hamster ovary cells. Mol Endocrinol 13:307–319[Abstract/Free Full Text]
  220. Razandi M, Pedram A, Merchenthaler I, Greene GL, Levin ER 2004 Plasma membrane estrogen receptors exist and function as dimers. Mol Endocrinol 18:2854–2865[Abstract/Free Full Text]
  221. Clarke CH, Norfleet AM, Clarke MS, Watson CS, Cunningham KA, Thomas ML 2000 Perimembrane localization of the estrogen receptor {alpha} protein in neuronal processes of cultured hippocampal neurons. Neuroendocrinology 71:34–42[CrossRef][Medline]
  222. Norfleet AM, Thomas ML, Gametchu B, Watson CS 1999 Estrogen receptor-{alpha} detected on the plasma membrane of aldehyde-fixed GH3/B6/F10 rat pituitary tumor cells by enzyme-linked immunocytochemistry. Endocrinology 140:3805–3814[Abstract/Free Full Text]
  223. Chambliss KL, Shaul PW 2002 Estrogen modulation of endothelial nitric oxide synthase. Endocr Rev 23:665–686[Abstract/Free Full Text]
  224. Arvanitis DN, Wang H, Bagshaw RD, Callahan JW, Boggs JM 2004 Membrane-associated estrogen receptor and caveolin-1 are present in central nervous system myelin and oligodendrocyte plasma membranes. J Neurosci Res 75:603–613[CrossRef][Medline]
  225. Mendelsohn ME 2000 Nongenomic, ER-mediated activation of endothelial nitric oxide synthase: how does it work? What does it mean? Circ Res 87:956–960[Abstract/Free Full Text]
  226. Razandi M, Alton G, Pedram A, Ghonshani S, Webb P, Levin ER 2003 Identification of a structural determinant necessary for the localization and function of estrogen receptor {alpha} at the plasma membrane. Mol Cell Biol 23:1633–1646[Abstract/Free Full Text]
  227. Razandi M, Oh P, Pedram A, Schnitzer J, Levin ER 2002 ERs associate with and regulate the production of caveolin: implications for signaling and cellular actions. Mol Endocrinol 16:100–115[Abstract/Free Full Text]
  228. Acconcia F, Ascenzi P, Bocedi A, Spisni E, Tomasi V, Trentalance A, Visca P, Marino M 2005 Palmitoylation-dependent estrogen receptor {alpha} membrane localization: regulation by 17ß-estradiol. Mol Biol Cell 16:231–237[Abstract/Free Full Text]
  229. Pozo-Guisado E, Lorenzo-Benayas MJ, Fernandez-Salguero PM 2004 Resveratrol modulates the phosphoinositide 3-kinase pathway through an estrogen receptor {alpha}-dependent mechanism: relevance in cell proliferation. Int J Cancer 109:167–173[CrossRef][Medline]
  230. Simoncini T, Hafezi-Moghadam A, Brazil DP, Ley K, Chin WW, Liao JK 2000 Interaction of oestrogen receptor with the regulatory subunit of phosphatidylinositol-3-OH kinase. Nature 407:538–541[CrossRef][Medline]
  231. Wong CW, McNally C, Nickbarg E, Komm BS, Cheskis BJ 2002 Estrogen receptor-interacting protein that modulates its nongenomic activity-crosstalk with Src/Erk phosphorylation cascade. Proc Natl Acad Sci USA 99:14783–14788[Abstract/Free Full Text]
  232. Barletta F, Wong CW, McNally C, Komm BS, Katzenellenbogen B, Cheskis BJ 2004 Characterization of the interactions of estrogen receptor and MNAR in the activation of cSrc. Mol Endocrinol 18:1096–1108[Abstract/Free Full Text]
  233. Xu Y, Traystman RJ, Hurn PD, Wang MM 2004 Membrane restraint of estrogen receptor {alpha} enhances estrogen-dependent nuclear localization and genomic function. Mol Endocrinol 18:86–96[Abstract/Free Full Text]
  234. Rai D, Frolova A, Frasor J, Carpenter AE, Katzenellenbogen BS 2005 Distinctive actions of membrane-targeted versus nuclear localized estrogen receptors in breast cancer cells. Mol Endocrinol 19:1606–1617[Abstract/Free Full Text]
  235. Haas D, White SN, Lutz LB, Rasar M, Hammes SR 2005 The modulator of nongenomic actions of the estrogen receptor (MNAR) regulates transcription-independent androgen receptor-mediated signaling: evidence that MNAR participates in G protein-regulated meiosis in Xenopus laevis oocytes. Mol Endocrinol 19:2035–2046[Abstract/Free Full Text]
  236. Pawlak J, Karolczak M, Krust A, Chambon P, Beyer C 2005 Estrogen receptor-{alpha} is associated with the plasma membrane of astrocytes and coupled to the MAP/Src-kinase pathway. Glia 50:270–275[CrossRef][Medline]
  237. Apostolakis EM, Garai J, Fox C, Smith CL, Watson SJ, Clark JH, O’Malley BW 1996 Dopaminergic regulation of progesterone receptors: brain D5 dopamine receptors mediate induction of lordosis by D1-like agonists in rats. J Neurosci 16:4823–4834[Abstract/Free Full Text]
  238. Mani SK, Allen JM, Lydon JP, Mulac-Jericevic B, Blaustein JD, DeMayo FJ, Conneely O, O’Malley BW 1996 Dopamine requires the unoccupied progesterone receptor to induce sexual behavior in mice. Mol Endocrinol 10:1728–1737[Abstract/Free Full Text]
  239. Henderson V 1997 Estrogen, cognition, and a woman’s risk of Alzheimer’s disease. Am J Med 103:11S–18S[CrossRef][Medline]
  240. Bauer M, Whybrow PC 2001 Thyroid hormone, neural tissue and mood modulation. World J Biol Psychiatry 2:59–69[Medline]
  241. Bauer M, Whybrow PC 2003 Thyroid hormone and mood modulation: new insights from functional brain imaging techniques. Curr Psychiatry Rep 5:163–165[Medline]
  242. Pinkerton JV, Henderson VW 2005 Estrogen and cognition, with a focus on Alzheimer’s disease. Semin Reprod Med 23:172–179[CrossRef][Medline]
  243. Kragie L 1993 Neuropsychiatric implications of thyroid hormone and benzodiazepine interactions. Endocr Res 19:1–32[Medline]
  244. Rogatsky I, Trowbridge JM, Garabedian MJ 1999 Potentiation of human estrogen receptor {alpha} transcriptional activation through phosphorylation of serines 104 and 106 by the cyclin A-CDK2 complex. J Biol Chem 274:22296–22302[Abstract/Free Full Text]
  245. Medunjanin S, Hermani A, De Servi B, Grisouard J, Rincke G, Mayer D 2005 Glycogen synthase kinase-3 interacts with and phosphorylates estrogen receptor {alpha} and is involved in the regulation of receptor activity. J Biol Chem 280:33006–33014[Abstract/Free Full Text]
  246. Chen D, Riedl T, Washbrook E, Pace PE, Coombes RC, Egly JM, Ali S 2000 Activation of estrogen receptor {alpha} by S118 phosphorylation involves a ligand-dependent interaction with TFIIH and participation of CDK7. Mol Cell 6:127–137[CrossRef][Medline]
  247. Aronica SM, Katzenellenbogen BS 1993 Stimulation of estrogen receptor-mediated transcription and alteration in the phosphorylation state of the rat uterine estrogen receptor by estrogen, cyclic adenosine monophosphate, and insulin-like growth factor-I. Mol Endocrinol 7:743–752[Abstract/Free Full Text]



This article has been cited by other articles:


Home page
Mol. Endocrinol.Home page
S. J. Lee, C. Chae, and M. M. Wang
p150/Glued Modifies Nuclear Estrogen Receptor Function
Mol. Endocrinol., May 1, 2009; 23(5): 620 - 629.
[Abstract] [Full Text] [PDF]


Home page
EndocrinologyHome page
S. Xu, Y. Cheng, J. R. Keast, and P. B. Osborne
17{beta}-Estradiol Activates Estrogen Receptor {beta}-Signalling and Inhibits Transient Receptor Potential Vanilloid Receptor 1 Activation by Capsaicin in Adult Rat Nociceptor Neurons
Endocrinology, November 1, 2008; 149(11): 5540 - 5548.
[Abstract] [Full Text] [PDF]


Home page
Am. J. Physiol. Regul. Integr. Comp. Physiol.Home page
S. Deurveilher, E. M. Cumyn, T. Peers, B. Rusak, and K. Semba
Estradiol replacement enhances sleep deprivation-induced c-Fos immunoreactivity in forebrain arousal regions of ovariectomized rats
Am J Physiol Regulatory Integrative Comp Physiol, October 1, 2008; 295(4): R1328 - R1340.
[Abstract] [Full Text] [PDF]


Home page
GENES CELLSHome page
A. P. Kouzmenko, K.-i. Takeyama, Y. Kawasaki, T. Akiyama, and S. Kato
Ligand-dependent interaction between estrogen receptor alpha and adenomatous polyposis coli.
Genes Cells, July 1, 2008; 13(7): 723 - 730.
[Abstract] [Full Text] [PDF]


Home page
Anesth. Analg.Home page
R. Raju and I. H. Chaudry
Sex Steroids/Receptor Antagonist: Their Use as Adjuncts After Trauma-Hemorrhage for Improving Immune/Cardiovascular Responses and for Decreasing Mortality from Subsequent Sepsis
Anesth. Analg., July 1, 2008; 107(1): 159 - 166.
[Abstract] [Full Text] [PDF]


Home page
J. Neurosci.Home page
D. Titolo, C. M. Mayer, S. S. Dhillon, F. Cai, and D. D. Belsham
Estrogen Facilitates both Phosphatidylinositol 3-Kinase/Akt and ERK1/2 Mitogen-Activated Protein Kinase Membrane Signaling Required for Long-Term Neuropeptide Y Transcriptional Regulation in Clonal, Immortalized Neurons
J. Neurosci., June 18, 2008; 28(25): 6473 - 6482.
[Abstract] [Full Text] [PDF]


Home page
Pharmacol. Rev.Home page
V. M. Miller and S. P. Duckles
Vascular Actions of Estrogens: Functional Implications
Pharmacol. Rev., June 1, 2008; 60(2): 210 - 241.
[Abstract] [Full Text] [PDF]


Home page
J. Biol. Chem.Home page
P. Hu, H. K. Kinyamu, L. Wang, J. Martin, T. K. Archer, and C. Teng
Estrogen Induces Estrogen-related Receptor {alpha} Gene Expression and Chromatin Structural Changes in Estrogen Receptor (ER)-positive and ER-negative Breast Cancer Cells
J. Biol. Chem., March 14, 2008; 283(11): 6752 - 6763.
[Abstract] [Full Text] [PDF]


Home page
Endocr. Rev.Home page
S. R. Hammes and E. R. Levin
Extranuclear Steroid Receptors: Nature and Actions
Endocr. Rev., December 1, 2007; 28(7): 726 - 741.
[Abstract] [Full Text] [PDF]


Home page
J EndocrinolHome page
A. Morales, M. Gonzalez, R. Marin, M. Diaz, and R. Alonso
Estrogen inhibition of norepinephrine responsiveness is initiated at the plasma membrane of GnRH-producing GT1-7 cells
J. Endocrinol., July 1, 2007; 194(1): 193 - 200.
[Abstract] [Full Text] [PDF]


This Article
Right arrow Abstract Freely available
Right arrow Full Text (PDF)
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Right arrow Citation Map
Services
Right arrow Email this article to a friend
Right arrow Similar articles in this journal
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Right arrow Request Copyright Permission
Citing Articles
Right arrow Citing Articles via HighWire
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Vasudevan, N.
Right arrow Articles by Pfaff, D. W.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Vasudevan, N.
Right arrow Articles by Pfaff, D. W.


HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS
Endocrinology Endocrine Reviews J. Clin. End. & Metab.
Molecular Endocrinology Recent Prog. Horm. Res. All Endocrine Journals