Membrane estrogen receptors identified by multiple antibody labeling and impeded-ligand binding

Estrogen-mediated protection in myocardial ischemia-reperfusion injury

Before menopause, a woman has a relatively low risk for developing cardiovascular disease. After menopause, however, the risk increases nearly twofold and cardiovascular disease remains the number one cause of death among women. Observational trials and studies in animal models of cardiovascular disease suggested that females have reduced injury after myocardial ischemia and reperfusion injury. However, two large clinical trials, the women's health initiative (WHI) and the heart estrogen and progestin replacement study (HERS), found an increase in cardiovascular incidences in women taking hormone replacement therapy. The discrepancy between these data highlights the need for further research on the mechanism of estrogen in the cardiovascular system. Animal studies have demonstrated protective effects by endogenous estrogen (gender differences) and also by the administration of exogenous estrogen. In vivo studies suggest a possible anti-inflammatory mechanism of estrogen. Exogenous estrogen has been shown to have anti-oxidant activities. Pre-treatment with estrogen prior to myocardial ischemia and reperfusion causes a decrease in neutrophil infiltration into the irreversibly injured myocardium, decrease in C-reactive protein expression, and deposition of the membrane attack complex. This review will summarize the protection afforded by estrogen as well as discuss several possible mechanisms of protection for exogenous estrogen administration.

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

It is established that increases in neuropeptide Y (NPY) expression are associated with hyperphagia and obesity. These effects can be reversed by estrogen, a recognized anorexigen. We found that 17beta-estradiol (E(2)) regulates biphasic NPY gene expression in a clonal, immortalized hypothalamic cell line, N-38, through estrogen receptor (ER) action at the level of the NPY promoter. However, rapid, nongenomic actions of estrogen, linked to the phosphatidylinositol 3-kinase (PI3-K)/Akt and ERK1/2 mitogen-activated protein kinase (MAPK) pathways, may also play a role. We therefore examined the changes in the phosphorylation status of Akt, ERK1/2, and cAMP response element-binding protein (CREB) after treatment with 10 nm E(2) in the N-38 neurons and found activation of these signaling proteins within 5-30 min. We also demonstrated possible cross talk between the estrogen-activated PI3-K/Akt and MAPK/extracellular signal-regulated kinase pathways using pharmacological inhibitors. We find that only ERalpha is involved in the early signaling events using the ERalpha agonist 4,4',4''-(4-propyl-[1H]-pyrazole-1,3,5-triyl)trisphenol and the ERbeta agonist 2,3-bis(4-hydroxyphenyl)-propionitrile. Furthermore, we can detect colocalization of ERalpha and caveolin-1, a membrane-associated signaling protein. Remarkably, we find that the membrane-mediated events are critical for the long-term estrogen-mediated repression of NPY gene expression that can be mapped to within -97 bp of the NPY promoter. To link the early signaling events to downstream effectors, we detected induction of c-fos and inactivation of MSK-1 by estrogen and binding of CREB to this minimal promoter region. These observations suggest that rapid estrogen-mediated signaling is mediated by ERalpha, and the signal transduction events potentiate the genomic actions of estrogen on NPY gene expression in the N-38 NPY neurons.

Nongenomic actions of estradiol compared with estrone and estriol in pituitary tumor cell signaling and proliferation

Physiological estrogens, including estrone (E(1)), estradiol (E(2)), and estriol (E(3)), fluctuate with life stage, suggesting specific roles for them in biological and disease processes. We compared their nongenomic signaling and functional actions in GH3/B6/F10 rat pituitary tumor cells. All hormones caused prolactin release at 1 min; the lowest effective concentrations were 10(-11) M E(2), 10(-10) M E(1), and 10(-7) M E(3). All estrogens increased the oscillation frequency of calcium (Ca) spikes, with the same time delay (approximately 200 s) at all levels (10(-15) to 10(-9) M). At some concentrations, E(1) and E(3) provoked more Ca-responding cells than E(2). The amplitude and volume of Ca peaks were elevated by all hormones at > or = 10(-15) M. All hormones caused cell proliferation, with the lowest effective concentrations of E(2) (10(-15) M) > E(1) (10(-12) M) > E(3) (10(-10) M); E(2) caused higher maximal cell numbers at most concentrations. All estrogens caused oscillating extracellular-regulated kinase (ERK) activations, with relative potencies of E(1) and E(2) > E(3). All estrogens were ineffective in activation of ERKs or causing proliferation in a subline expressing low levels of membrane estrogen receptor-alpha. Dose-response patterns were frequently nonmonotonic. Therefore, the hormones E(1) and E(3), which have been designated "weak" estrogens in genomic actions, are strong estrogens in the nongenomic signaling pathways and functional responses in the pituitary.

Pancreatic insulin content regulation by the estrogen receptor ER alpha

The function of pancreatic beta-cells is the synthesis and release of insulin, the main hormone involved in blood glucose homeostasis. Estrogen receptors, ER alpha and ER beta, are important molecules involved in glucose metabolism, yet their role in pancreatic beta-cell physiology is still greatly unknown. In this report we show that both ER alpha and ER beta are present in pancreatic beta-cells. Long term exposure to physiological concentrations of 17beta-estradiol (E2) increased beta-cell insulin content, insulin gene expression and insulin release, yet pancreatic beta-cell mass was unaltered. The up-regulation of pancreatic beta-cell insulin content was imitated by environmentally relevant doses of the widespread endocrine disruptor Bisphenol-A (BPA). The use of ER alpha and ER beta agonists as well as ER alphaKO and ER betaKO mice suggests that the estrogen receptor involved is ER alpha. The up-regulation of pancreatic insulin content by ER alpha activation involves ERK1/2. These data may be important to explain the actions of E2 and environmental estrogens in endocrine pancreatic function and blood glucose homeostasis.

Oestrogen and the colon: potential mechanisms for cancer prevention

The role of oestrogen in oncogenesis has been examined extensively, especially in the context of breast cancer, and receptor modulators are an integral part of targeted treatment in this disease. The role of oestrogen signalling in colonic carcinoma is poorly understood. Men are more susceptible than women to colon cancer. Furthermore, hormone-replacement therapy affords an additive protective effect for postmenopausal women, and when these women do develop cancer, they typically have less aggressive disease. The discovery of a second oestrogen receptor (ERbeta) and its over expression in healthy human colon coupled with reduced expression in colon cancer suggests that this receptor might be involved. The underlying mechanism, however, remains largely unknown. In this Review, we discuss the various hypotheses presented in the published literature. We examine the cellular and molecular mechanisms through which oestrogen is purported to exert its protective influence, and we review the evidence available to support these claims.

Non-nuclear actions of estrogen: new targets for prevention and treatment of cardiovascular disease

Gender-based differences in the incidence of hypertensive and coronary artery disease, the development of atherosclerosis, and myocardial remodeling after infarction are attributable to the indirect effect of estrogen on risk factor profiles, such as cholesterol levels, glucose metabolism, and insulin levels. More recent evidence, however, suggests that activated estrogen receptor (ER) mediates signaling cascades that culminate in direct protective effects such as vasodilation, inhibition of response to vessel injury, limiting myocardial injury after infarction, and attenuating cardiac hypertrophy. Although the ER is usually thought of as a ligand-dependent transcription factor, it can also rapidly mobilize signals at the plasma membrane and in the cytoplasm. Thus, a greater understanding of ER function and regulation may lead to the development of highly specific therapeutics that mediate the prevention and treatment of cardiovascular diseases.

17 Beta-estradiol (E2) plus tumor necrosis factor-alpha induces a distorted maturation of human monocyte-derived dendritic cells and promotes their capacity to initiate T-helper 2 responses

There is growing evidence that 17 beta-estradiol (E2) modulates immune function. Recent studies indicated that certain effects of E2 on in vivo immune function are not a result of a direct action on T cells, but rather an indirect action on antigen-presenting cells. This study demonstrates that the pregnancy-associated doses of E2 plus tumor necrosis factor-alpha (TauNuF alpha) induce distorted maturation of human dendritic cells (DCs) that result in an increased capacity to induce T helper (Th) 2 responses. E2 did not affect the expression of human leukocyte antigen class II and costimulatory molecules by DCs, but elicited the ability of DC to produce CC chemokine ligand 1, which can attract CCR8-expressing Th2 cells and regulatory T cells. In addition, E2/TNF alpha-matured DCs increased the production of IL-10 relative to the IL-12p70 on CD40 ligation, thereby inducing naive T-cell differentiation into a Th2. Moreover, the increased concentration of E2 in the route of maturation did indeed further enhance Th2 deviation. The dominant Th2 deviation was induced at a high E2 concentration typical during pregnancy. These findings demonstrate that the high physiological levels of E2 may be an important endogenous component for regulating the DC function and skewing the immune response toward Th2.

Key developments in endocrine disrupter research and human health

Environmental etiologies involving exposures to chemicals that mimic endogenous hormones are proposed for a number of adverse human health effects, including infertility, abnormal prenatal and childhood development, and reproductive cancers (National Research Council, 1999; World Health Organization, 2002). Endocrine disrupters represent a significant area of environmental research with important implications for human health. This article provides an overview of some of the key developments in this field that may enhance our ability to assess the human health risks posed by exposure to endocrine disrupters. Advances in methodologies of hazard identification (toxicogenomics, transcriptomics, proteomics, metabolomics, bioinformatics) are discussed, as well as epigenetics and emerging biological endpoints.

Estrogen induces rapid translocation of estrogen receptor beta, but not estrogen receptor alpha, to the neuronal plasma membrane

Estrogen receptors can activate transcription in the nucleus, and activate rapid signal transduction cascades in the cytosol. Multiple reports identify estrogen receptors at the plasma membrane, while others document the dynamic responses of estrogen receptor to ligand binding. However, the function and identity of membrane estrogen receptors remain controversial. We have used confocal microscopy and cell fractionation on the murine hippocampus-derived HT22 cell line and rat primary cortical neurons transfected with estrogen receptor-green fluorescent protein constructs to address the membrane localization of these receptors. We observe translocation of estrogen receptor beta (beta) to the plasma membrane 5 min after exposure to 17beta-estradiol, whereas estrogen receptor alpha (alpha) localization remains unchanged. Membrane localization of estrogen receptor beta is transient, selective for 17beta-estradiol, and is not blocked by ICI182,780. Inhibition of the mitogen-activated protein kinase pathway does not block estrogen-mediated estrogen receptor beta membrane translocation, and in fact prolongs membrane localization. These data suggest that while both estrogen receptor alpha and estrogen receptor beta can be present at the neuronal membrane, their presence is differentially regulated.

Oestrogen receptor alpha and beta in female rat pituitary cells: an immunochemical study

Estradiol is a critical factor in the anterior pituitary secretory activity of mammalian females. Previous reports have demonstrated the presence of oestrogen receptor alpha (ERalpha) and beta (ERbeta) in specific anterior pituitary cells from ovariectomized rats, as well as in the whole anterior pituitary at particular stages of the rat oestrous cycle. However, the ERalpha and ERbeta distribution patterns in specific hormone producing cells of the anterior pituitary during the oestrous cycle remain to be clarified. The purpose of this study was to determine the cellular and subcellular distribution of both ER-subtypes during the rat oestrous cycle, using immunochemistry at light- and electron-microscope levels. ERalpha-immunoreactive (ir) cells mainly corresponded to PRL-ir cells and, to a lesser extent, to TSH-, FSH- and GH-ir cells. ERbeta-ir cells corresponded to a few GH-, PRL- and FSH-ir cells, whichever the phase of the cycle. ERalpha-ir was found either in the cytoplasm and/or the nucleus, depending on the phase of the oestrous cycle, while ERbeta-ir was always detected in the cytoplasm. Both ER-subtypes were immunoreactives inside the rough endoplasmic reticulum (RER), secretory vesicles (SV) and free in the cytosol. The highest number of ERalpha-ir cells was consistently found at pro-oestrus midday and the lowest at metaoestrous, while the number of ERbeta-ir cells was low in all stages of the cycle. These results indicate that the genomic actions of oestrogen in the anterior pituitary cells during the oestrous cycle are mediated by ERalpha. However, the localization of ERalpha and ERbeta in the RER and SV suggest a different translational and/or post-translational pathway, which could be involved in non-genomic mechanisms.

Extranuclear steroid receptors: nature and actions

Rapid effects of steroid hormones result from the actions of specific receptors localized most often to the plasma membrane. Fast-acting membrane-initiated steroid signaling (MISS) leads to the modification of existing proteins and cell behaviors. Rapid steroid-triggered signaling through calcium, amine release, and kinase activation also impacts the regulation of gene expression by steroids, sometimes requiring integration with nuclear steroid receptor function. In this and other ways, the integration of all steroid actions in the cell coordinates outcomes such as cell fate, proliferation, differentiation, and migration. The nature of the receptors is of intense interest, and significant data suggest that extranuclear and nuclear steroid receptor pools are the same proteins. Insights regarding the structural determinants for membrane localization and function, as well as the nature of interactions with G proteins and other signaling molecules in confined areas of the membrane, have led to a fuller understanding of how steroid receptors effect rapid actions. Increasingly, the relevance of rapid signaling for the in vivo functions of steroid hormones has been established. Examples include steroid effects on reproductive organ development and function, cardiovascular responsiveness, and cancer biology. However, although great strides have been made, much remains to be understood concerning the integration of extranuclear and nuclear receptor functions to organ biology. In this review, we highlight the significant progress that has been made in these areas.

Nongenomic actions of low concentration estrogens and xenoestrogens on multiple tissues

Nongenomic estrogenic mechanisms offer an opportunity to explain the conundrum of environmental estrogen and plant estrogen effects on cells and animals at the very low concentrations which are prevalent in our environments and diets. Heretofore the actions of these compounds have not been adequately accounted for by laboratory tests utilizing assays for actions only via the genomic pathway of steroid action and the nuclear forms of estrogen receptor alpha and beta. Membrane versions of these receptors, and the newly described GPR30 (7TMER) receptor protein provide explanations for the more potent actions of xenoestrogens. The effects of estrogens on many tissues demand a comprehensive assessment of the receptors, receptor levels, and mechanisms that might be involved, to determine which of these estrogen mimetic compounds are harmful and which might even be used therapeutically, depending upon the life stage at which we are exposed to them.

Estrogen receptors outside the nucleus in breast cancer

The estrogen receptor (ER) is the single most powerful predictor of breast cancer prognosis as well as an important contributor to the biology of carcinogenesis. In addition, endocrine therapy targeting ER directly (SERMS) or indirectly (aromatase inhibitors) forms the mainstay of adjuant therapy. Traditionally, human tumors are scored for the amount and presence of ER. However, this has centered on the population of ER found in the transformed epithelial cell nucleus. Over the last 40 years, it has been appreciated that additional cellular ER pools exist, in cytoplasm and at the plasma membrane. In this review, we discuss the important functions of extra-nuclear ER in breast cancer, including integration of function with nuclear ER.

Tamoxifen-induced rapid death of MCF-7 breast cancer cells is mediated via extracellularly signal-regulated kinase signaling and can be abrogated by estrogen

Tamoxifen (Tam) is widely used in chemotherapy of breast cancer. It inhibits proliferation and induces apoptosis of breast cancer cells by estrogen receptor (ER)-dependent modulation of gene expression. In addition, recent reports have shown that Tam also has nongenomic effects. We previously reported induction of a rapid mitochondrial death program in breast cancer cells at pharmacological concentrations of Tam. Here we studied the upstream signaling events leading to mitochondrial disruption by Tam. We observed that 5 mum Tam rapidly induced sustained activation of ERK1/2 in ER-positive breast cancer cell lines (MCF-7 and T47D) and that PD98059 (inhibitor of ERK activation) was able to protect MCF-7 cells against Tam-induced death. These data suggest that activation of ERK has a primary role in the acute death response of the cells. In addition, inhibition of epidermal growth factor receptor (EGFR) opposed both Tam-induced ERK1/2 phosphorylation and cell death, which suggests that EGFR-associated mechanisms are involved in Tam-induced death. ERK1/2 phosphorylation was associated with a prolonged nuclear localization of ERK1/2 as determined by fluorescence microscopy with ERK2-green fluorescent protein construct. 17beta-Estradiol was shown to exert a different kind of temporal pattern of ERK nuclear localization in comparison with Tam. Moreover, 17beta-estradiol was found to oppose the rapid effects of Tam in MCF-7 and T47D cells but not in MDA-MB-231 cells, which implies a role for estrogen receptors in the protective effect of estrogen. The pure antiestrogen ICI182780 could not, however, prevent Tam-induced ERK1/2 phosphorylation, suggesting that the Tam-induced rapid cell death is primarily ER-independent or mediated by ICI182780 insensitive nongenomic mechanisms.

In vitro molecular mechanisms of bisphenol A action

Bisphenol A (BPA, 2,2-bis (4-hydroxyphenyl) propane; CAS# 80-05-7) is a chemical used primarily in the manufacture of polycarbonate plastic, epoxy resins and as a non-polymer additive to other plastics. Recent evidence has demonstrated that human and wildlife populations are exposed to levels of BPA which cause adverse reproductive and developmental effects in a number of different wildlife species and laboratory animal models. However, there are major uncertainties surrounding the spectrum of BPA's mechanisms of action, the tissue-specific impacts of exposures, and the critical windows of susceptibility during which target tissues are sensitive to BPA exposures. As a foundation to address some of those uncertainties, this review was prepared by the "In vitro" expert sub-panel assembled during the "Bisphenol A: An Examination of the Relevance of Ecological, In vitro and Laboratory Animal Studies for Assessing Risks to Human Health" workshop held in Chapel Hill, NC, Nov 28-29, 2006. The specific charge of this expert panel was to review and assess the strength of the published literature pertaining to the mechanisms of BPA action. The resulting document is a detailed review of published studies that have focused on the mechanistic basis of BPA action in diverse experimental models and an assessment of the strength of the evidence regarding the published BPA research.

Estrogen and raloxifene inhibit the monocytic chemoattractant protein-1-induced migration of human monocytic cells via nongenomic estrogen receptor alpha

OBJECTIVE

To investigate the effects of estradiol (E2) and raloxifene on the migration of human monocytic THP-1 cells to endothelium.

DESIGN

A prospective comparative study. THP-1 cells, a human acute monocytic leukemia cell line, were used for the study. Migration assays were performed using transwell inserts. THP-1 cells were exposed to E2 or raloxifene in the presence of monocytic chemoattractant protein-1 (MCP-1), a major chemoattractant for monocytes. The cells were transfected with small interfering RNA (siRNA) against estrogen receptor (ER) alpha and ERbeta for gene silencing. ER expression was evaluated by Western blot analysis.

RESULTS

MCP-1 induced the migration of the cells for 90 minutes. The addition of E2 or raloxifene significantly inhibited the MCP-1-induced migration for 90 minutes. Preincubation of THP-1 cells with an ER antagonist, ICI 182780, significantly attenuated the inhibitory effects of E2 and raloxifene. Whereas transfection with siRNA of ERalpha significantly attenuated the inhibition by E2 of MCP-1-induced monocyte migration, transfection with control siRNA or siRNA of ERbeta had no effect on the rapid inhibitory action of E2. Moreover, preincubation of THP-1 cells with a transcriptional inhibitor, actinomycin D, had no effect on the rapid inhibitory action of E2.

CONCLUSIONS

Our findings suggest that both E2 and raloxifene inhibited the MCP-1-induced monocyte migration through nongenomic ERalpha. This result may explain one of the antiatherosclerotic effects of E2 and raloxifene on vasculature.

17-Beta-estradiol-mediated activation of extracellular-signal regulated kinase, phosphatidylinositol 3-kinase/protein kinase B-Akt and N-methyl-D-aspartate receptor phosphorylation in cortical synaptoneurosomes

In addition to its well-known activational mechanism, the steroid hormone 17-beta-estradiol (E2) has been shown to rapidly activate various signal transduction pathways that could participate in estrogen-mediated regulation of synaptic plasticity. Although the mechanisms underlying these effects are not clearly understood, it has been repeatedly suggested that they involve a plasma membrane receptor which has direct links to several intracellular signaling cascades. To further address the question of whether E2 acts directly at the synapse and through membrane-bound receptors, we studied the effects of E2 and of ligands of estrogen receptors on various signaling pathways in cortical synaptoneurosomes. Our results demonstrate that E2 elicits N-methyl-D-aspartate receptor phosphorylation and activates the extracellular signal-regulated kinase and the phosphatidylinositol 3-kinase/Akt signal transduction pathways in this cortical membrane preparation. Furthermore, we provide evidence for the presence of a membrane-bound estrogen receptor responsible for these effects in cortical synaptoneurosomes. Our study demonstrates that E2 directly acts at cortical synapses, and that synaptoneurosomes provide a useful system to investigate the mechanisms by which E2 regulates synaptic transmission and plasticity.

The complete nuclear estrogen receptor family in the rainbow trout: discovery of the novel ERalpha2 and both ERbeta isoforms

Estrogen hormones interact with cellular ERs to exert their biological effects in vertebrate animals. Similar to other animals, fishes have two distinct ER subtypes, ERalpha (NR3A1) and ERbeta (NR3A2). The ERbeta subtype is found as two different isoforms in several fish species because of a gene duplication event. Although predicted, two different isoforms of ERalpha have not been demonstrated in any fish species. In the rainbow trout (Oncorhynchus mykiss), the only ER described is an isoform of the ERalpha subtype (i.e. ERalpha1, NR3A1a). The purpose of this study was to determine whether the gene for the other ERalpha isoform, ERalpha2 (i.e., NR3A1b), exists in the rainbow trout. A RT-PCR and cloning strategy, followed by screening a rainbow trout BAC library yielded a unique DNA sequence coding for 558 amino acids. The deduced amino acid sequence had a 75.4% overall similarity to ERalpha1. Both the rainbow trout ERbeta subtypes, ERbeta1 [NR3A2a] and ERbeta2, [NR3A2b] which were previously unknown in this species, were also sequenced as part of this study, and the amino acid sequences were found to be very different from the ERalphas (approximately 40% similarity). ERbeta1 and ERbeta2 had 594 and 604 amino acids, respectively, and had 57.6% sequence similarity when compared to one another. This information provides what we expect to be the first complete nuclear ER gene family in a fish. A comprehensive phylogenetic analysis with all other known fish ER gene sequences was undertaken to understand the evolution of fish ERs. The results show a single ERalpha subtype clade, with the closest relative to rainbow trout ERalpha2 being rainbow trout ERalpha1, suggesting a recent, unique duplication event to create these two isoforms. For the ERbeta subtype there are two distinct subclades, one represented by the ERbeta1 isoform and the other by the ERbeta2 isoform. The rainbow trout ERbeta1 and ERbeta2 are not closely associated with each other, but instead fall into their respective ERbeta subclades with other known fish species. Real-time RT-PCR was used to measure the mRNA levels of all four ER isoforms (ERalpha1, ERalpha2, ERbeta1, and ERbeta2) in stomach, spleen, heart, brain, pituitary, muscle, anterior kidney, posterior kidney, liver, gill, testis and ovary samples from rainbow trout. The mRNAs for each of the four ERs were detected in every tissue examined. The liver tended to have the highest ER mRNA levels along with the testes, while the lowest levels were generally found in the stomach or heart. The nuclear ERs have a significant and ubiquitous distribution in the rainbow trout providing the potential for complex interactions that involve the functioning of many organ systems.

Effect of estrogens on skin aging and the potential role of SERMs

In humans, structural and functional changes attributable to aging are more visibly evident in the skin than in any other organ. Estrogens have significant effects on skin physiology and modulate epidermal keratinocytes, dermal fibroblasts and melanocytes, in addition to skin appendages including the hair follicle and the sebaceous gland. Importantly, skin aging can be significantly delayed by the administration of estrogen. This paper reviews the effects of estrogens on skin and the mechanisms by which estrogens can alleviate the changes due to aging that occur in human skin. The relevance of estrogen replacement therapy (HRT) in postmenopausal women and the potential value of selective estrogen receptor modulators (SERMs) as a therapy for diminishing skin aging are also highlighted.

Implants of estradiol conjugated to bovine serum albumin in the male rat medial preoptic area promote copulatory behavior

The expression of mating behavior in male rats is dependent on estrogen-responsive neurons in the medial preoptic area (MPO). Previous reports showed that mating is attenuated if the aromatization of testosterone to estradiol (E2) is blocked in the MPO and that mating is maintained by MPO E2 implants. However, the mechanisms by which E2 exerts its action are not fully understood. It had been thought that E2 acted exclusively by binding to nuclear estrogen receptors to exert it effects; however, recent reports suggest that E2 also binds to membrane-associated receptors activating downstream intracellular cascade responses. In this study, we aimed to determine if an action of E2 at the cell surface is sufficient to support mating behavior. Therefore, either vehicle, E2, or E2 conjugated to bovine serum albumin (BSA-E2: a complex of E2 and a large protein that will not cross the plasma membrane, thereby restricting the action of E2 to cell surface signaling) was chronically administered bilaterally to the MPO of castrated, dihydrotestosterone-treated male rats. Mating behavior was supported by MPO BSA-E2 implants, suggesting that E2 operates in the MPO via a cell surface mechanism to facilitate male rat mating behavior.

Xenoestrogens are potent activators of nongenomic estrogenic responses

Studies of the nuclear transcriptional regulatory activities of non-physiological estrogens have not explained their actions in mediating endocrine disruption in animals and humans at the low concentrations widespread in the environment. However, xenoestrogens have rarely been tested for their ability to participate in the plethora of nongenomic steroid signaling pathways elucidated over the last several years. Here we review what is known about such responses in comparison to our recent evidence that xenoestrogens can rapidly and potently elicit signaling through nongenomic pathways culminating in functional endpoints. Both estradiol (E(2)) and compounds representing various classes of xenoestrogens (diethylstilbestrol, coumestrol, bisphenol A, DDE, nonylphenol, endosulfan, and dieldrin) act via a membrane version of the estrogen receptor-alpha on pituitary cells, and can provoke Ca(2+) influx via L-type channels, leading to prolactin (PRL) secretion. These hormones and mimetics can also cause the oscillating activation of extracellular regulated kinases (ERKs). However, individual estrogen mimetics differ in their potency and temporal phasing of these activations compared to each other and to E(2). It is perhaps in these ways that they disrupt some endocrine functions when acting in combination with physiological estrogens. Our quantitative assays allow comparison of these outcomes for each mimetic, and let us build a detailed picture of alternative signaling pathway usage. Such an understanding should allow us to determine the estrogenic or antiestrogenic potential of different types of xenoestrogens, and help us to develop strategies for preventing xenoestrogenic disruption of estrogen action in many tissues.

Estradiol effects on the dopamine transporter - protein levels, subcellular location, and function

Background

The effects of estrogens on dopamine (DA) transport may have important implications for the increased incidence of neurological disorders in women during life stages when hormonal fluctuations are prevalent, e.g. during menarche, reproductive cycling, pregnancy, and peri-menopause.

Results

The activity of the DA transporter (DAT) was measured by the specific uptake of ³H-DA. We found that low concentrations (10^-14 to 10^-8 M) of 17β-estradiol (E₂) inhibit uptake via the DAT in PC12 cells over 30 minutes, with significant inhibition taking place due to E₂ exposure during only the last five minutes of the uptake period. Such rapid action suggests a non-genomic, membrane-initiated estrogenic response mechanism. DAT and estrogen receptor-α (ERα) were elevated in cell extracts by a 20 ng/ml 2 day NGFβ treatment, while ERβ was not. DAT, ERα and ERβ were also detectable on the plasma membrane of unpermeabilized cells by immunocytochemical staining and by a fixed cell, quantitative antibody (Ab)-based plate assay. In addition, PC12 cells contained RNA coding for the alternative membrane ER GPR30; therefore, all 3 ER subtypes are candidates for mediating the rapid nongenomic actions of E₂. At cell densities above 15,000 cells per well, the E₂-induced inhibition of transport was reversed. Uptake activity oscillated with time after a 10 nM E₂ treatment; in a slower room temperature assay, inhibition peaked at 9 min, while uptake activity increased at 3 and 20–30 min. Using an Ab recognizing the second extracellular loop of DAT (accessible only on the outside of unpermeabilized cells), our immunoassay measured membrane vs. intracellular/nonvesicular DAT; both were found to decline over a 5–60 min E₂ treatment, though immunoblot analyses demonstrated no total cellular loss of protein.

Conclusion

Our results suggest that physiological levels of E₂ may act to sequester DAT in intracellular compartments where the transporter's second extramembrane loop is inaccessible (inside vesicles) and that rapid estrogenic actions on this differentiated neuronal cell type may be regulated via membrane ERs of several types.

Regulation of estrogen receptor alpha by estradiol in pregnant and estradiol treated rats

Estrogens play an important role in tissue metabolism through specific regulation of several intracellular pathways. We studied ERalpha regulation in muscle and adipose tissue from pregnant and estradiol treated rats. In both groups, we identified three different ERalpha inmunoreactive proteins (80, 67 and 46 kDa) using total protein extracts. Because it has been showed that estrogens are able to promote rapid effects in several cellular models, we looked for three ERalpha-related proteins at plasma membrane. In skeletal muscle of both groups, we positively identified the three ERalpha-related isoforms in plasma membrane, but in adipose tissue from pregnant we were not able to identify ERalpha67, and in estradiol treated animals ERalpha80 was absent. Taking together, our results showed a tissue-specific regulation of whole-cell ERalpha-related proteins and ERalpha located at plasma membrane, which should be involved in non-genomic actions of 17beta-estradiol. The role of the three ERalpha inmunoreactive proteins is unknown, however, seems probably related to rapid activation of signalling pathways.

Rapid endocrine disruption: environmental estrogen actions triggered outside the nucleus

An exogenous substance is defined as an endocrine disrupter chemical (EDC) if it alters the function of the endocrine system provoking adverse health effects. Environmental estrogens are the most studied EDCs. They follow the same mechanisms of action as the gonadal hormone 17beta-estradiol. Up to now, the estrogenicity of environmental estrogenic pollutants has been based on the property of these compounds to bind to estrogen receptors (ERs), either ERalpha or ERbeta, and to act subsequently as transcription factors when binding to the estrogen response element (ERE) in the DNA. All the estrogenic bioassays currently used are based on this mechanism of action. New evidence indicates that the definition of estrogenicity for a chemical should take into account other estrogen receptors as well as new signaling pathways. These include the activation of additional transcription factors as well as the action of xenoestrogens through estrogen receptors located outside the nucleus: in the plasma membrane, mitochondria and probably the cytosol. Therefore, new estrogenic bioassays should be developed to include the novel concept of rapid endocrine disruption.

Estrogen and the development and protection of nigrostriatal dopaminergic neurons: concerted action of a multitude of signals, protective molecules, and growth factors

The nigrostriatal dopamine system comprises the dopaminergic neurons located in the ventral midbrain, their axonal connections to the forebrain, and their direct cellular target cells in the striatal complex, i.e. GABAergic neurons. The major function of the nigrostriatal dopaminergic unit is the coordination and fine tuning of motor functions at the extrapyramidal level. Numerous biologically active factors including different types of growth factors (neurotrophins, members of the TGFbeta family, IGFs) and peptide/steroid hormones have been identified in the past to be implicated in the regulation of developmental aspects of this neural system. Some of these developmentally active determinants have in addition been found to play a crucial role in the mediation of neuroprotection concerning dopaminergic neurons. Estrogen was identified as such a compound interfering with embryonic neuronal differentiation and cell survival. The physiological mechanisms underlying these effects are very complex and include interactions with other developmental signals (growth factors), inflammatory processes as well as apoptotic events, but also require the activation of nonneuronal cells such as astrocytes. It appears that estrogen is assuming control over or at least influences a multitude of developmental and protective cellular mechanisms rather than taking over the part of a singular protagonist.

Aging of Brain: Role of Estrogen

The brain undergoes many structural and functional changes during aging. Some of these changes are regulated by estrogens which act mainly through their intracellular receptors, estrogen receptor ERalpha and ERbeta. The expression of these receptors is regulated by several factors including their own ligand estrogen, and others such as growth hormone and thyroid hormone. The levels of these factors decrease during aging which in turn influence estrogen signaling leading to alterations in brain functions. In the present paper, we review the effects of aging on brain structure and function, and estrogen action and signaling during brain aging. The findings suggest key role of estrogen in the maintenance of brain functions during aging.

Effects of short- and long-term estrogen and progesterone replacement on behavioral responses and c-fos mRNA levels in female rats after acute cocaine administration

It is well established that there are estrous cycle differences in cocaine-induced behavioral activity, implicating fluctuations in levels of estrogen and progesterone throughout the cycle in these alterations in behavior. However, the mechanisms by which steroids alter cocaine-induced behavioral responses have yet to be determined. The aim of this study was to determine whether short- or long-term estrogen and progesterone administration differentially alters behavioral responses to cocaine. Estrogen (50 microg) was administered 30 min or 48 h before cocaine (15 mg/kg, i.p.) administration; progesterone (500 microg) was administered 30 min or 24 h before cocaine. Short-term estrogen replacement decreased cocaine-induced ambulations. Short-term progesterone decreased rearing, whereas long-term progesterone decreased ambulations. Although cocaine increased levels of c-fos mRNA, none of the estrogen or progesterone replacement paradigms affected this measure. Because long-term estrogen replacement has been shown to have no effect on locomotor activity after acute cocaine administration, our observations suggest that short-term estrogen may underlie behavioral alterations. These findings suggest that after acute cocaine administration, while estrogen may activate only membrane receptors to alter behavioral responses to cocaine, progesterone activates both nuclear and membrane receptors.

The Isoflavone Equol Mediates Rapid Vascular Relaxation

We recently reported that soy isoflavones increase gene expression of endothelial nitric-oxide synthase (eNOS) and antioxidant defense enzymes, resulting in improved endothelial function and lower blood pressure in vivo. In this study, we establish that equol (1-100 nM) causes acute endothelium- and nitric oxide (NO)-dependent relaxation of aortic rings and rapidly (2 min) activates eNOS in human aortic and umbilical vein endothelial cells. Intracellular Ca2+ and cyclic AMP levels were unaffected by treatment (100 nM, 2 min) with equol, daidzein, or genistein. Rapid phosphorylation of ERK1/2, protein kinase B/Akt, and eNOS serine 1177 by equol was paralleled by association of eNOS with heat shock protein 90 (Hsp90) and NO synthesis in human umbilical vein endothelial cells, expressing estrogen receptors (ER)alpha and ERbeta. Inhibition of phosphatidylinositol 3-kinase and ERK1/2 inhibited eNOS activity, whereas pertussis toxin and the ER antagonists ICI 182,750 and tamoxifen had negligible effects. Our findings provide the first evidence that nutritionally relevant plasma concentrations of equol (and other soy protein isoflavones) rapidly stimulate phosphorylation of ERK1/2 and phosphatidylinositol 3-kinase/Akt, leading to the activation of NOS and increased NO production at resting cytosolic Ca2+ levels. Identification of the nongenomic mechanisms by which equol mediates vascular relaxation provides a basis for evaluating potential benefits of equol in the treatment of postmenopausal women and patients at risk of cardiovascular disease.

Structure-function relationship of estrogen receptor alpha and beta: impact on human health

17Beta-estradiol (E2) controls many aspects of human physiology, including development, reproduction and homeostasis, through regulation of the transcriptional activity of its cognate receptors (ERs). The crystal structures of ERs with agonists and antagonists and the use of transgenic animals have revealed much about how hormone binding influences ER conformation(s) and how this conformation(s), in turn, influences the interaction of ERs with co-activators or co-repressors and hence determines ER binding to DNA and cellular outcomes. This information has helped to shed light on the connection between E2 and the development or progression of numerous diseases. Current therapeutic strategy in the treatment of E2-related pathologies relies on the modulation of ER trancriptional activity by anti-estrogens; however, data accumulated during the last five years reveal that ER activities are not only restricted to the nucleus. ERs are very mobile proteins continuously shuttling between protein targets located within various cellular compartments (e.g., membrane, nucleus). This allows E2 to generate different and synergic signal transduction pathways (i.e., non-genomic and genomic) which provide plasticity for cell response to E2. Understanding the structural basis and the molecular mechanisms by which ER transduce E2 signals in target cells will allow to create new pharmacologic therapies aimed at the treatment of a variety of human diseases affecting the cardiovascular system, the reproductive system, the skeletal system, the nervous system, the mammary gland, and many others.

Dehydroepiandrosterone inhibits intracellular calcium release in beta-cells by a plasma membrane-dependent mechanism

Both dehydroepiandrosterone (DHEA) and DHEA sulfate (DHEAS) affect glucose stimulated insulin secretion, though their cellular mechanisms of action are not well characterized. We tested the hypothesis that human physiological concentrations of DHEA alter insulin secretion by an action initiated at the plasma membrane of beta-cells. DHEA alone had no effect on intracellular calcium concentration ([Ca(2+)](i)) in a rat beta-cell line (INS-1). However, it caused an immediate and dose-dependent inhibition of carbachol-induced Ca(2+) release from intracellular stores, with a 25% inhibition at zero. One nanometer DHEA. DHEA also inhibited the Ca(2+) mobilizing effect of bombesin (29% decrease), but did not inhibit the influx of extracellular Ca(2+) evoked by glyburide (100 microM) or glucose (15 mM). The steroids (androstenedione, 17-alpha-hydroxypregnenolone, and DHEAS) had no inhibitory effect on carbachol-induced intracellular Ca(2+) release. The action of DHEA depended on a signal initiated at the plasma membrane, since membrane impermeant DHEA-BSA complexes also inhibited the carbachol effect on [Ca(2+)](i) (39% decrease). The inhibition of carbachol-induced Ca(2+) release by DHEA was blocked by pertussis toxin (PTX). DHEA also inhibited the carbachol induction of phosphoinositide generation, with a maximal inhibition at 0.1 nM DHEA. Furthermore, DHEA inhibited insulin secretion induced by carbachol in INS-1 cells by 25%, and in human pancreatic islets by 53%. Taken together, this is the first report showing that human physiological concentrations of DHEA decrease agonist-induced Ca(2+) release by a rapid, non-genomic mechanism in INS-1 cells. Furthermore, these data provide evidence consistent with the existence of a specific plasma membrane DHEA receptor, mediating this signal transduction pathway by pertussis toxin-sensitive G-proteins.

Novel mechanisms for estrogen-induced neuroprotection

Estrogens are gonadal steroid hormones that are present in the circulation of both males and females and that can no longer be considered within the strict confines of reproductive function. In fact, the bone, the cardiovascular system, and extrahypothalamic regions of the brain are now well-established targets of estrogens. Among the numerous aspects of brain function regulated by estrogens are their effects on mood, cognitive function, and neuronal viability. Here, we review the supporting evidence for estrogens as neuroprotective agents and summarize the various mechanisms that may be involved in this effect, focusing particularly on the mitochondria as an important target. On the basis of this evidence, we discuss the clinical applicability of estrogens in treating various age-related disorders, including Alzheimer disease and stroke, and identify the caveats that must be considered.

Nature of functional estrogen receptors at the plasma membrane

Although rapid signaling by estrogen at the plasma membrane is established, it is controversial as to the nature of the receptor protein. Estrogen may bind membrane proteins comparable to classical nuclear estrogen receptors (ERs), but some studies identify nonclassical receptors, such as G protein-coupled receptor (GPR)30. We took several approaches to define membrane-localized estrogen-binding proteins. In endothelial cells (ECs) from ERalpha/ERbeta combined-deleted mice, estradiol (E2) failed to specifically bind, and did not activate cAMP, ERK, or phosphatidyinositol 3-kinase or stimulate DNA synthesis. This is in contrast to wild-type ECs, indicating the lack of any functional estrogen-binding proteins in ERalpha/ERbeta combined-deleted ECs. To directly determine the identity of membrane and nuclear-localized ER, we isolated subcellular receptor pools from MCF7 cells. Putative ER proteins were trypsin digested and subjected to tandem array mass spectrometry. The output analysis identified membrane and nuclear E2-binding proteins as classical human ERalpha. We also determined whether GPR30 plays any role in E2 rapid actions. MCF7 (ER and GPR30 positive) and SKBR-3 (ER negative, GPR30 positive) cells were incubated with E2. Only MCF7 responded with significantly increased signaling. In MCF7, the response to E2 was not different in cells transfected with small interfering RNA to green fluorescent protein or GPR30. In contrast, interfering RNA to ERalpha or ER inhibition prevented rapid signaling and resulting biology in MCF7. In breast cancer and ECs, nuclear and membrane ERs are the same proteins. Furthermore, classical ERs mediate rapid signals induced by E2 in these cells.

Multiple pathways transmit neuroprotective effects of gonadal steroids

Numerous preclinical studies suggest that gonadal steroids, particularly estrogen, may be neuroprotective against insult or disease progression. This paper reviews the mechanisms contributing to estrogen-mediated neuroprotection. Rapid signaling pathways, such as MAPK, PI3K, Akt, and PKC, are required for estrogen's ability to provide neuroprotection. These rapid signaling pathways converge on genomic pathways to modulate transcription of E2-responsive genes via ERE-dependent and ERE-independent mechanisms. It is clear that both rapid signaling and transcription are important for estrogen's neuroprotective effects. A mechanistic understanding of estrogen-mediated neuroprotection is crucial for the development of therapeutic interventions that enhance quality of life without deleterious side effects.

S-palmitoylation modulates estrogen receptor alpha localization and functions

17beta-Estradiol (E2) acts as a chemical messenger in target tissues inducing both slow nuclear and rapid extra-nuclear responses. E2 binds to its cognate nuclear receptors (ER) resulting in the activation of target gene transcription in the nucleus. In addition to these genomic effects, E2 modulates cell functions through rapid non-genomic actions. Stimulation of G-proteins, Ca(2+) influx, inositol phosphate generation as well as phospholipase C, ERK/MAPK, and PI3K/AKT activation all occur within seconds to minutes after E2 binding to a small population of ERalpha located at the plasma membrane. The great impact of these rapid signals on cell physiology renders central the knowledge of the structural bases and mechanisms that mediate extra-nuclear signaling by E2. Several laboratories, including our own, have recently elucidated the structural requirements for localization and function of plasma membrane ERalpha. This review summarizes the molecular mechanisms of E2-induced rapid non-genomic actions relevant for cell functions, highlighting the role of lipid modification (i.e., palmitoylation) in the ERalpha localization to and residence at the plasma membrane.

Biology of estrogens in skin: implications for skin aging

Estrogens have a profound influence on skin. The relative hypoestrogenism that accompanies menopause exacerbates the deleterious effects of both intrinsic and environmental aging. Estrogens clearly have a key role in skin aging homeostasis as evidenced by the accelerated decline in skin appearance seen in the perimenopausal years. Estrogens improve skin in many ways. Among these, they increase collagen content and skin thickness and improve skin moisture. However, despite the knowledge that estrogens have such important effects on skin, the cellular and subcellular sites and mechanisms of estrogen action are still poorly understood. Estrogen receptors (ERs) have been detected in skin, and recent studies suggest that estrogens exert their effect in skin through the same molecular pathways used in other non-reproductive tissues. Although systemic hormone replacement therapy (HRT) has been used for many years, recent trials have reported a significant increased risk of breast cancer and other pathologies with this treatment. This has led to reconsider the risks and benefits of HRT. For this reason, systemic HRT cannot be recommended today to treat skin aging. Currently, intensive research is conducted to develop new drugs called selective ER modulators (SERMs). These drugs exert mixed estrogenic and antiestrogenic effects depending on the tissue and cell type. One might expect in the future such a drug targeting specifically the skin without systemic side effects.

Integration of membrane and nuclear estrogen receptor signaling

The classical mechanism of estradiol (E2) action is mediated by the nuclear estrogen receptors ERalpha and ERbeta, which function as ligand-dependent transcription factors that regulate transcription of target genes containing the consensus estrogen response element (ERE) in their promoter regions. However, accumulating evidence indicates that E2 can also exert its actions through a unique membrane estrogen receptor (mER). Upon activation of the mER, various signaling pathways (i.e. Ca(2+), cAMP, protein kinase cascades) are rapidly activated and ultimately influence downstream transcription factors. Some target genes of the mER pathway may be activated independently of the nuclear estrogen receptor (nER). Additionally, it has been shown that classical nER action can be modulated by mER-initiated signaling through phosphorylation of nER and its coactivators, and by induction of third messengers (i.e. cyclin D1 and c-fos). Based on current evidence, we propose a model for E2 action integrating distinct membrane receptor and nuclear receptor signaling. This membrane receptor-nuclear receptor interaction is likely to exist for other hormones. Steroid hormones and other hormones acting through hormone receptors in the steroid receptor superfamily (i.e. thyroid hormones) also activate many of the same intracellular signaling cascades, which provides the basis for extensive crosstalk networks between hormones. The model proposed serves as a framework to investigate the diverse actions of hormones and endocrine disrupting chemicals (EDCs).

Estrogen and tamoxifen induce cytoskeletal remodeling and migration in endometrial cancer cells

Much research effort has been directed toward understanding how estrogen [17beta-estradiol (E2)] regulates cell proliferation and motility through the rapid, direct activation of cytoplasmic signaling cascades (i.e. nongenomic signaling). Cell migration is critical to cancer cell invasion and metastasis and involves dynamic filamentous actin cytoskeletal remodeling and disassembly of focal adhesion sites. Although estrogen is recognized to induce cell migration in some model systems, very little information is available regarding the underlying pathways and potential influence of selective estrogen receptor modulators such as 4-hydroxytamoxifen on these processes. Using the human endometrial cancer cell lines Hec 1A and Hec 1B as model systems, we have investigated the effects of E2 and Tam on endometrial nongenomic signaling, cytoskeletal remodeling, and cell motility. Results indicate that both E2 and Tam triggered rapid activation of ERK1/2, c-Src, and focal adhesion kinase signaling pathways and filamentous actin cytoskeletal changes. These changes included dissolution of stress fibers, dynamic actin accumulation at the cell periphery, and formation of lamellipodia, filopodia, and membrane spikes. Longer treatments with either agent induced cell migration in wound healing and Boyden chamber assays. Agent-induced cytoskeletal remodeling and cell migration were blocked by a Src inhibitor. These findings define cytoskeletal remodeling and cell migration as processes regulated by E2 and 4-hydroxytamoxifen nongenomic signaling in endometrial cancer. This new information may serve as the foundation for the development of new clinical therapeutic strategies.

Estrogen receptors in membrane lipid rafts and signal transduction in breast cancer

Regulation of breast cancer growth by estrogen is mediated by estrogen receptors (ER) in nuclear and extranuclear compartments. We assessed the structure and functions of extranuclear ER that initiate downstream signaling to the nucleus. ER, including full-length 66-kDa ER and a 46-kDa ER splice variant, are enriched in lipid rafts from MCF-7 cells with (MCF-7/HER-2) or without (MCF-7/PAR) HER-2 gene overexpression and co-localize with HER-1 and HER-2 growth factor receptors, as well as with lipid raft marker flotillin-2. In contrast, ER-negative MCF-7 cells do not express nuclear or lipid raft ER. ER knockdown with siRNA also elicits a marked loss of ER in MCF-7 cell rafts. In MCF-7/PAR cells, estrogen enhances ER association with membrane rafts and induces rapid phosphorylation of nuclear receptor coactivator AIB1, actions not detected in ER-negative cells. Thus, nuclear and lipid raft ER derive from the same transcript, and extranuclear ER co-localizes with HER receptors in membrane signaling domains that modulate downstream nuclear events leading to cell growth.

Alternative estrogen receptors homologous to classical receptor α in murine neural tissues

Although it is widely accepted the existence of putative estrogen receptors (ERs) localized at extranuclear domains in the brain, their molecular identity is still unclear. We have previously demonstrated in a murine septal cell line the existence of a membrane-related ER (mER) that participates in estrogen-mediated neuroprotection. To investigate the molecular structure of mER, we have used a battery of antibodies raised against different domains of the classical ERalpha to immunoblot with plasma membrane fractions from septal SN56 and hippocampal HT22 cell lines, and microsomal fractions of mouse septal and hippocampal tissues. The results confirmed that mER is the homologue of its intracellular counterpart ERalpha, suggesting the possibility that both nuclear and extranuclear receptors may share a common origin.

Altered subcellular distribution of estrogen receptor alpha is implicated in estradiol-induced dual regulation of insulin signaling in 3T3-L1 adipocytes

We investigated the mechanisms by which estrogen alters insulin signaling in 3T3-L1 adipocytes. Treatment with 17beta-estradiol (E2) did not affect insulin-induced tyrosine phosphorylation of insulin receptor. E2 enhanced insulin-induced tyrosine phosphorylation of insulin receptor substrate-1 (IRS-1), IRS-1/p85 association, phosphorylation of Akt, and 2-deoxyglucose uptake at 10(-8) m, but inhibited these effects at 10(-5) m. A concentration of 10(-5) m E2 enhanced insulin-induced phosphorylation of IRS-1 at Ser(307), which was abolished by treatment with a c-Jun NH(2)-terminal kinase inhibitor. In addition, the effect of E2 was abrogated by pretreatment with a specific estrogen receptor antagonist, ICI182,780. Membrane-impermeable E2, E2-BSA, did not affect the insulin-induced phosphorylation of Akt at 10(-8) m, but inhibited it at 10(-5) m. Furthermore, E2 decreased the amount of estrogen receptor alpha at the plasma membrane at 10(-8) m, but increased it at 10(-5) m. In contrast, the subcellular distribution of estrogen receptor beta was not altered by the treatment. These results indicate that E2 affects the metabolic action of insulin in a concentration-specific manner, that high concentrations of E2 inhibit insulin signaling by modulating phosphorylation of IRS-1 at Ser(307) via a c-Jun NH(2)-terminal kinase-dependent pathway, and that the subcellular redistribution of estrogen receptor alpha in response to E2 may explain the dual effect of E2.

Identification of estrogen receptor ligands leading to activation of non-genomic signaling pathways while exhibiting only weak transcriptional activity

Estrogen receptors (ERs) stimulate genomic effects by acting as nuclear transcription factors as well as non-genomic effects by activating distinct cytoplasmic protein kinase cascades. Non-genomic effects have been implicated in numerous cellular processes, such as proliferation, differentiation, apoptosis and vasorelaxation. To exploit non-genomic effects mediated by ERalpha for novel hormone replacement regimens, we screened a focused library of steroid receptor ligands to identify compounds exhibiting properties different from estradiol, i.e. substances that selectively stimulate non-genomic signal transduction pathways while exhibiting low genomic activities. Treatment of breast cancer cells and osteosarcoma cells with estradiol, estren, substance A and substance B led to non-genomic activation of Akt (protein kinase B) and extracellular signal-regulated kinase 1/2 (ERK1/2) signaling cascades mediated by Src (Rous Sarcoma Virus, non-receptor tyrosine kinase) and phosphatidylinositol-3-kinase (PI3K) stimulation. Such compounds leading to prominent Akt/ERK activation but exhibiting only weak genomic properties were applied in vasorelaxation assays, modeling physiological non-genomic ER responses. As expected from PI3K and Src activation data, substances were as effective as estradiol in mediating vasorelaxation. We assume that these pathway-selective estrogen receptor ligands may serve as potent lead structures for novel hormone replacement strategies exhibiting lesser side effects than the existing treatment paradigms.

Effects of estrogen in the male rat medial amygdala: infusion of an aromatase inhibitor lowers mating and bovine serum albumin-conjugated estradiol implants do not promote mating

In male rats, copulatory behavior depends on estrogen-responsive neurons located in brain areas known to be crucial for mating. Blocking the aromatization of testosterone (T) to estradiol (E(2)) either throughout the brain or within the medial preoptic area (MPO) reduces mating, whereas E(2) treatment of either the MPO or the medial amygdala (MEA) maintains sexual behavior. The effects of T aromatization in the MEA have received less attention; therefore, 2 studies were done to further elucidate the effects of E(2) in the MEA. In experiment 1, gonadally intact male rats that showed robust mating behavior were administered chronic fadrozole, a nonsteroidal aromatase inhibitor, to the MEA to stop the conversion of T to E(2) and then paired with receptive females. Infusion of fadrozole to the MEA significantly lowered mating behavior in experimental males compared to vehicle-infused control males. To further investigate the mechanism by which E(2) acts in the MEA, in experiment 2, E(2) conjugated to bovine serum albumin (BSA-E(2): a complex of E(2 )and a large protein that does not cross the plasma membrane, thereby restricting the action of E(2) to cell-surface signaling) was chronically administered bilaterally to the MEA of castrated, dihydrotestosterone-treated males. This treatment did not maintain mating behavior. These studies show that E(2) acts in the MEA to promote male sexual behavior and suggest an intercellular mechanism of E(2) action.

Steering estrogen signals from the plasma membrane to the nucleus: Two sides of the coin

Estrogen mediate its biological effects through its association with estrogen receptors (ERs). They also regulate the expression of a variety of genes involved in distinct physiological processes, including development, metabolism, and reproduction. In addition, emerging data suggest that the estrogen-estrogen receptor complex can also function as a cytoplasmic signaling molecule and may influence processes such as cardiovascular protection, bone preservation, neuroprotection, and proliferation of various cell types. Such extranuclear or nongenomic signaling pathways are rapid and supposedly independent of transcription. A recent exciting finding was that G-coupled membrane protein receptor, GPR30, an alternative to the classical ERs, is also involved in the rapid signaling of estrogen through its direct association with estrogen. These new findings combined with the recent advances in the cytoplasmic functions of proline, glutamic acid, luecine rich protein 1 (PELP1), and metastatic tumor antigen 1 short form (MTA1s) have opened a new spectrum and raised several new concerns in the field of estrogen biology and put the attention to unveil many unknown mechanistic actions of estrogen in cellular physiology. In this review, we briefly summarize what is currently known of the cellular mechanisms and physiology of estrogen's nongenomic actions in various cellular systems used by ERs.

Estrogen signaling multiple pathways to impact gene transcription

Steroid hormones exert profound effects on cell growth, development, differentiation, and homeostasis. Their effects are mediated through specific intracellular steroid receptors that act via multiple mechanisms. Among others, the action mechanism starting upon 17beta-estradiol (E2) binds to its receptors (ER) is considered a paradigmatic example of how steroid hormones function. Ligand-activated ER dimerizes and translocates in the nucleus where it recognizes specific hormone response elements located in or near promoter DNA regions of target genes. Behind the classical genomic mechanism shared with other steroid hormones, E2 also modulates gene expression by a second indirect mechanism that involves the interaction of ER with other transcription factors which, in turn, bind their cognate DNA elements. In this case, ER modulates the activities of transcription factors such as the activator protein (AP)-1, nuclear factor-kappaB (NF-kappaB) and stimulating protein-1 (Sp-1), by stabilizing DNA-protein complexes and/or recruiting co-activators. In addition, E2 binding to ER may also exert rapid actions that start with the activation of a variety of signal transduction pathways (e.g. ERK/MAPK, p38/MAPK, PI3K/AKT, PLC/PKC). The debate about the contribution of different ER-mediated signaling pathways to coordinate the expression of specific sets of genes is still open. This review will focus on the recent knowledge about the mechanism by which ERs regulate the expression of target genes and the emerging field of integration of membrane and nuclear receptor signaling, giving examples of the ways by which the genomic and non-genomic actions of ERs on target genes converge.