Estrogen receptor-alpha detected on the plasma membrane of aldehyde-fixed GH3/B6/F10 rat pituitary tumor cells by enzyme-linked immunocytochemistry

Sex Differences in Colon Cancer: Genomic and Nongenomic Signalling of Oestrogen

Colon cancer (CRC) is a prevalent malignancy that exhibits distinct differences in incidence, prognosis, and treatment responses between males and females. These disparities have long been attributed to hormonal differences, particularly the influence of oestrogen signalling. This review aims to provide a comprehensive analysis of recent advances in our understanding of the molecular mechanisms underlying sex differences in colon cancer and the protective role of membrane and nuclear oestrogen signalling in CRC development, progression, and therapeutic interventions. We discuss the epidemiological and molecular evidence supporting sex differences in colon cancer, followed by an exploration of the impact of oestrogen in CRC through various genomic and nongenomic signalling pathways involving membrane and nuclear oestrogen receptors. Furthermore, we examine the interplay between oestrogen receptors and other signalling pathways, in particular the Wnt/β-catenin proliferative pathway and hypoxia in shaping biological sex differences and oestrogen protective actions in colon cancer. Lastly, we highlight the potential therapeutic implications of targeting oestrogen signalling in the management of colon cancer and propose future research directions to address the current gaps in our understanding of this complex phenomenon.

The emerging role of estrogen's non-nuclear signaling in the cardiovascular disease

Sexual dimorphism exists in the epidemiology of cardiovascular disease (CVD), which indicates the involvement of sexual hormones in the pathophysiology of CVD. In particular, ample evidence has demonstrated estrogen's protective effect on the cardiovascular system. While estrogen receptors, bound to estrogen, act as a transcription factor which regulates gene expressions by binding to the specific DNA sequence, a subpopulation of estrogen receptors localized at the plasma membrane induces activation of intracellular signaling, called "non-nuclear signaling" or "membrane-initiated steroid signaling of estrogen". Although the precise molecular mechanism of non-nuclear signaling as well as its physiological impact was unclear for a long time, recent development of genetically modified animal models and pathway-selective estrogen receptor stimulant bring new insights into this pathway. We review the published experimental studies on non-nuclear signaling of estrogen, and summarize its role in cardiovascular system, especially focusing on: (1) the molecular mechanism of non-nuclear signaling; (2) the design of genetically modified animals and pathway-selective stimulant of estrogen receptor.

Differential effects of vascular endothelial growth factor on glycocalyx of endothelial and tumor cells and potential targets for tumor metastasis

On the surface of every mammalian cell, there is a matrix-like glycocalyx (GCX) consisting of proteoglycans and glycosaminoglycans (GAGs). Disruption of endothelial cell (EC) GCX by a vascular endothelial growth factor (VEGF, VEGF-A₁₆₅), a tumor secretion, was found to be an early event in tumor cell (TC) metastasis across vascular barriers. However, how the TC secretion VEGF affects its own GCX is unknown. To investigate the VEGF effect on TC GCX and to elucidate the ultrastructural organization of EC and TC GCX and their alteration by VEGF, we employed super-resolution stochastic optical reconstruction microscopy to observe the spatio-chemical organizations of the heparan sulfate (HS) and hyaluronic acid (HA), two representative GAGs of GCX, on human cerebral microvascular endothelial cells (hCMEC) and malignant breast cancer cells MDA-MB-231 (MB231). We found that HS and HA have distinct organizations on hCMEC and MB231. Only HS of hCMEC is perpendicular to the cell surface, while HA of hCMEC as well as HS and HA of MB231 all lie in the same plane as the cell surface where they appear to weave into a 2D network covering the cell. We also found that VEGF significantly reduces the length and coverage of HS on hCMEC but does not change the thickness and coverage of HA on hCMEC. On the contrary, VEGF significantly enhances the coverage of HS and HA on MB231 although it does not alter the thickness. The differential effects of VEGF on the GCX of TC and that of EC may favor TC adhesion and transmigration across EC barriers for their metastasis.

Segregation of nuclear and membrane-initiated actions of estrogen receptor using genetically modified animals and pharmacological tools

Estrogen receptor alpha (ERα) and beta (ERβ) are members of the nuclear receptor superfamily, playing widespread functions in reproductive and non-reproductive tissues. Beside the canonical function of ERs as nuclear receptors, in this review, we summarize our current understanding of extra-nuclear, membrane-initiated functions of ERs with a specific focus on ERα. Over the last decade, in vivo evidence has accumulated to demonstrate the physiological relevance of this ERα membrane-initiated-signaling from mouse models to selective pharmacological tools. Finally, we discuss the perspectives and future challenges opened by the integration of extra-nuclear ERα signaling in physiology and pathology of estrogens.

Endolysosome Localization of ERα Is Involved in the Protective Effect of 17α-Estradiol against HIV-1 gp120-Induced Neuronal Injury

Neurotoxic HIV-1 viral proteins contribute to the development of HIV-associated neurocognitive disorder (HAND), the prevalence of which remains high (30-50%) with no effective treatment available. Estrogen is a known neuroprotective agent; however, the diverse mechanisms of estrogen action on the different types of estrogen receptors is not completely understood. In this study, we determined the extent to which and mechanisms by which 17α-estradiol (17αE2), a natural less-feminizing estrogen, offers neuroprotection against HIV-1 gp120-induced neuronal injury. Endolysosomes are important for neuronal function, and endolysosomal dysfunction contributes to HAND and other neurodegenerative disorders. In hippocampal neurons, estrogen receptor α (ERα) is localized to endolysosomes and 17αE2 acidifies endolysosomes. ERα knockdown or overexpressing an ERα mutant that is deficient in endolysosome localization prevents 17αE2-induced endolysosome acidification. Furthermore, 17αE2-induced increases in dendritic spine density depend on endolysosome localization of ERα. Pretreatment with 17αE2 protected against HIV-1 gp120-induced endolysosome deacidification and reductions in dendritic spines; such protective effects depended on endolysosome localization of ERα. In male HIV-1 transgenic rats, we show that 17αE2 treatment prevents the development of enlarged endolysosomes and reduction in dendritic spines. Our findings demonstrate a novel endolysosome-dependent pathway that governs the ERα-mediated neuroprotective actions of 17αE2, findings that might lead to the development of novel therapeutic strategies against HAND.SIGNIFICANCE STATEMENT Extranuclear presence of membrane-bound estrogen receptors (ERs) underlie the enhancing effect of estrogen on cognition and synaptic function. The estrogen receptor subtype ERα is present on endolysosomes and plays a critical role in the enhancing effects of 17αE2 on endolysosomes and dendritic spines. These findings provide novel insight into the neuroprotective actions of estrogen. Furthermore, 17αE2 protected against HIV-1 gp120-induced endolysosome dysfunction and reductions in dendritic spines, and these protective effects of 17αE2 were mediated via endolysosome localization of ERα. Such findings provide a rationale for developing 17αE2 as a therapeutic strategy against HIV-associated neurocognitive disorders.

The extra-nuclear interactome of the estrogen receptors: implications for physiological functions

Over the last decades, a great body of evidence has defined a novel view of the cellular mechanism of action of the steroid hormone 17β-estradiol (E2) through its estrogen receptors (i.e., ERα and ERβ). It is now clear that the E2-activated ERs work both as transcription factors and extra-nuclear plasma membrane-localized receptors. The activation of a plethora of signal transduction cascades follows the E2-dependent engagement of plasma membrane-localized ERs and is required for the coordination of gene expression, which ultimately controls the occurrence of the pleiotropic effects of E2. The definition of the molecular mechanisms by which the ERs locate at the cell surface (i.e., palmitoylation and protein association) determined the quest for understanding the specificity of the extra-nuclear E2 signaling. The use of mice models lacking the plasma membrane ERα localization unveiled that the extra-nuclear E2 signaling is operational in vivo but tissue-specific. However, the underlying molecular details for such ERs signaling diversity in the perspective of the E2 physiological functions in the different cellular contexts are still not understood. Therefore, to gain insights into the tissue specificity of the extra-nuclear E2 signaling to physiological functions, here we reviewed the known ERs extra-nuclear interactors and tried to extrapolate from available databases the ERα and ERβ extra-nuclear interactomes. Based on literature data, it is possible to conclude that by specifically binding to extra-nuclear localized proteins in different sub-cellular compartments, the ERs fine-tune their molecular activities. Moreover, we report that the context-dependent diversity of the ERs-mediated extra-nuclear E2 actions can be ascribed to the great flexibility of the physical structures of ERs and the spatial-temporal organization of the logistics of the cells (i.e., the endocytic compartments). Finally, we provide lists of proteins belonging to the potential ERα and ERβ extra-nuclear interactomes and propose that the systematic experimental definition of the ERs extra-nuclear interactomes in different tissues represents the next step for the research in the ERs field. Such characterization will be fundamental for the identification of novel druggable targets for the innovative treatment of ERs-related diseases.

Accurate assessment of estrogen receptor profiles in non-functioning pituitary adenomas using RT-digital PCR and immunohistochemistry

BACKGROUND

Non-functioning pituitary adenomas (NFPAs) are common pituitary tumors, and surgery is generally the only treatment option. Few attempts have been made to explore target molecules for the development of NFPA pharmacological treatments.

METHOD

We quantitatively assessed the expression profiles of estrogen receptor (ER) transcripts and proteins in NFPA samples, using reverse transcription-digital polymerase chain reaction (RT-dPCR) and immunohistochemistry, and further investigated the correlations between the expression levels of ER and those of downstream responsive genes. All patients had undergone surgery at the same high-volume hospital. A total of 20 patients with NFPAs were included. All patients were new-onset, and none were diagnosed with intratumoral hemorrhages or cysts.

RESULTS

NFPA samples exhibited a bimodal ESR1 expression pattern and were categorized into significantly different high- and low-ESR1 expression level groups (P < 0.05). In contrast, expression levels of ESR1 variants and ESR2 could barely be detected. Similar results were obtained through the immunohistochemical staining of NFPAs, using well-validated antibodies against ERs. The expression levels of ESR1 positively correlated with those of GREB1, an estrogen-responsive gene [correlation coefficient (r) = 0.623, P = 0.003].

CONCLUSIONS

ESR1 expression levels in NFPAs exhibited a bimodal pattern and were positively correlated with GREB1 expression levels. The accurate assessment of ER expression levels may further advance future NFPA-related research.

Characterization of a membrane-associated estrogen receptor in breast cancer cells and its contribution to hormone therapy resistance using a novel selective ligand

The estrogen receptor (ER) plays a role in the progression of hormone-dependent breast cancer and is a hormone therapy target. Estrogen acts as a transcription factor (genomic action) and also produces a quick non-genomic reaction through intracellular signaling pathways. The membrane associated ER (mER) may regulate both these signals and hormone therapy resistance. However, the details remain unclear because a reliable method to distinguish the signals induced by the estradiol (E2)-mER and E2-nuclear ER complex has not been established. In the present study, we prepared the novel ligand Qdot-6-E2, selective for mER, by coupling E2 with insoluble quantum dot nano-beads. We investigated the characteristics of mER signaling pathways and its contribution to hormone therapy resistance using different cell lines including estrogen depletion resistant (EDR) cells with different mechanisms. Qdot-6-E2 stimulated proliferation of nuclear ER-positive cells, but nuclear ER-negative cells showed no response. In addition, Qdot-6-E2 indirectly activated nuclear ER and increased mRNA expression of target genes. We confirmed that E2 was not dissociated from Qdot-6-E2 using a mammalian one-hybrid assay. We visually demonstrated that Qdot-6-E2 acts from the outside of cells. The gene expression profile induced by Qdot-6-E2-mER was different from that induced by E2-nuclear ER. The effect of anti-ER antibody, the GFP-ER fusion protein localization, and the effect of palmitoyl acyltransferase inhibitor also indicated the existence of mER. Regarding intracellular phosphorylation signaling pathways, the MAPK (Erk 1/2) and the PI3K/Akt pathways were both activated by Qdot-6-E2. In EDR cells, only nuclear ER-positive cells showed increased cell proliferation with increased localization of ERα to the membrane fraction. These findings suggested that Qdot-6-E2 reacts with ERα surrounding the cell membrane and that mER signals help the cells to survive under estrogen-depleted conditions by re-localizing the ER to use trace amounts of E2 more effectively. We expect that Qdot-6-E2 is a useful tool for studying the mER.

Extranuclear signaling by sex steroid receptors and clinical implications in breast cancer

Estrogen and progesterone play essential roles in the development and progression of breast cancer. Over 70% of breast cancers express estrogen receptors (ER) and progesterone receptors (PR), emphasizing the need for better understanding of ER and PR signaling. ER and PR are traditionally viewed as transcription factors that directly bind DNA to regulate gene networks. In addition to nuclear signaling, ER and PR mediate hormone-induced, rapid extranuclear signaling at the cell membrane or in the cytoplasm which triggers downstream signaling to regulate rapid or extended cellular responses. Specialized membrane and cytoplasmic proteins may also initiate hormone-induced extranuclear signaling. Rapid extranuclear signaling converges with its nuclear counterpart to amplify ER/PR transcription and specify gene regulatory networks. This review summarizes current understanding and updates on ER and PR extranuclear signaling. Further investigation of ER/PR extranuclear signaling may lead to development of novel targeted therapeutics for breast cancer management.

Molecular pathways involved in the transport of nuclear receptors from the nucleus to cytoplasm

Nuclear receptors (NRs) are transcription regulators that direct the expression of many genes linked to cellular processes, such as proliferation, differentiation, and apoptosis. Additionally, some cellular events are also modulated by signaling pathways induced by NRs outside of the nucleus. Hence, the subcellular transport of NRs is dynamic and is modulated by several signals, protein-protein interactions, and posttranslational modifications. Particularly, the exit of NRs from the nucleus to cytoplasm and/or other compartments is transcendental, as it is this export event, which determines their abundance in the cells' compartments, the activation or attenuation of nuclear or extranuclear pathways, and the magnitude and duration of their effects inside or outside of the nucleus. Consequently, an adequate control of the distribution of NRs is critical for homeostasis, because a deregulation in the nucleo-cytoplasmic transport of NRs could be involved in diseases including cancer as well as metabolic and vascular alterations. In this review, we investigated the pathways and molecular and biological aspects that have been described for the nuclear export of NRs so far and their functional relevance in some diseases. This information suggests that the transport of NRs out of the nucleus is a key mechanism for the identification of new therapeutic targets for alterations associated with the deregulation of the function of NRs.

Of Oestrogens and Sperm: A Review of the Roles of Oestrogens and Oestrogen Receptors in Male Reproduction

The crucial role that oestrogens play in male reproduction has been generally accepted; however, the exact mechanism of their action is not entirely clear and there is still much more to be clarified. The oestrogen response is mediated through oestrogen receptors, as well as classical oestrogen receptors’ variants, and their specific co-expression plays a critical role. The importance of oestrogen signalling in male fertility is indicated by the adverse effects of selected oestrogen-like compounds, and their interaction with oestrogen receptors was proven to cause pathologies. The aims of this review are to summarise the current knowledge on oestrogen signalling during spermatogenesis and sperm maturation and discuss the available information on oestrogen receptors and their splice variants. An overview is given of species-specific differences including in humans, along with a detailed summary of the methodology outcome, including all the genetically manipulated models available to date. This review provides coherent information on the recently discovered mechanisms of oestrogens’ and oestrogen receptors’ effects and action in both testicular somatic and germ cells, as well as in mature sperm, available for mammals, including humans.

Estrogen Receptors in Cell Membranes: Regulation and Signaling

Estrogens can stimulate the development, proliferation, migration, and survival of target cells. These biological effects are mediated through their action upon the plasma membrane estrogen receptors (ERs). ERs regulate transcriptional processes by nuclear translocation and binding to specific response elements, which leads to the regulation of gene expression. This effect is termed genomic or nuclear. However, estrogens may exert their biological activity also without direct binding to DNA and independently of gene transcription or protein synthesis. This action is called non-genomic or non-nuclear. Through non-genomic mechanisms, estrogens can modify regulatory cascades such as MAPK, P13K, and tyrosine cascade as well as membrane-associated molecules such as ion channels and G-protein-coupled receptors. The recent studies on the mechanisms of estrogen action provide an evidence that non-genomic and genomic effects converge. An example of such convergence is the potential possibility to modulate gene expression through these two independent pathways. The understanding of the plasma membrane estrogen receptors is crucial for the development of novel drugs and therapeutic protocols targeting specific receptor actions.

Nuclear receptors outside the nucleus: extranuclear signalling by steroid receptors

Steroid hormone receptors mediate numerous crucial biological processes and are classically thought to function as transcriptional regulators in the nucleus. However, it has been known for more than 50 years that steroids evoke rapid responses in many organs that cannot be explained by gene regulation. Mounting evidence indicates that most steroid receptors in fact exist in extranuclear cellular pools, including at the plasma membrane. This latter pool, when engaged by a steroid ligand, rapidly activates signals that affect various aspects of cellular biology. Research into the mechanisms of signalling instigated by extranuclear steroid receptor pools and how this extranuclear signalling is integrated with responses elicited by nuclear receptor pools provides novel understanding of steroid hormone signalling and its roles in health and disease.

Oxidative Stress and Maxi Calcium-Activated Potassium (BK) Channels

All cells contain ion channels in their outer (plasma) and inner (organelle) membranes. Ion channels, similar to other proteins, are targets of oxidative impact, which modulates ion fluxes across membranes. Subsequently, these ion currents affect electrical excitability, such as action potential discharge (in neurons, muscle, and receptor cells), alteration of the membrane resting potential, synaptic transmission, hormone secretion, muscle contraction or coordination of the cell cycle. In this chapter we summarize effects of oxidative stress and redox mechanisms on some ion channels, in particular on maxi calcium-activated potassium (BK) channels which play an outstanding role in a plethora of physiological and pathophysiological functions in almost all cells and tissues. We first elaborate on some general features of ion channel structure and function and then summarize effects of oxidative alterations of ion channels and their functional consequences.

G-protein coupled estrogen receptor (GPER) inhibits final oocyte maturation in common carp, Cyprinus carpio

GPR-30, now named as GPER (G protein-coupled estrogen receptor) was first identified as an orphan receptor and subsequently shown to be required for estrogen-mediated signaling in certain cancer cells. Later studies demonstrated that GPER has the characteristics of a high affinity estrogen membrane receptor on Atlantic croaker and zebra fish oocytes and mediates estrogen inhibition of oocyte maturation in these two distantly related teleost. To determine the broad application of these findings to other teleost, expression of GPER mRNA and its involvement in 17β-estradiol mediated inhibition of oocyte maturation in other cyprinid, Cyprinus carpio was investigated. Carp oocytes at pre-vitellogenic, late-vitellogenic and post-vitellogenic stages of development contained GPER mRNA and its transcribed protein with a maximum at late-vitellogenic oocytes. Ovarian follicular cells did not express GPER mRNA. Carp oocytes GPER mRNA was essentially identical to that found in other perciformes and cyprinid fish oocytes. Both spontaneous and 17,20β-dihydroxy-4-pregnen-3-one (17,20β-P)-induced oocyte maturation in carp was significantly decreased when they were incubated with either E2, or GPER agonist G-1. On the other hand spontaneous oocyte maturation was significantly increased when carp ovarian follicles were incubated with an aromatase inhibitor, fadrozole, GPER antagonist, G-15 and enzymatic removal of the ovarian follicle cell layers. This increase in oocyte maturation was partially reversed by co-treatment with E2. Consistent with previous findings with human and fish GPR30, E2 treatment in carp oocytes caused increase in cAMP production and simultaneously decrease in oocyte maturation, which was inhibited by the addition of 17,20β-P. The results suggest that E2 and GPER play a critical role in regulating re-entry in to meiotic cell cycle in carp oocytes.

Extranuclear estrogen receptor's roles in physiology: lessons from mouse models

Steroid receptors exist and function in multiple compartments of cells in most organs. Although the functions and nature of some of these receptors is being defined, important aspects of receptor localization and signaling to physiology and pathophysiology have been identified. In particular, extranuclear sex steroid receptors have been found in many normal cells and in epithelial tumors, where they enact signal transduction that impacts both nongenomic and genomic functions. Here, I focus on the progress made in understanding the roles of extranuclear estrogen receptors (ER) in physiology and pathophysiology. Extranuclear ER serve as a model to selectively intervene with novel receptor reagents to prevent or limit disease progression. Recent novel mouse models and membrane ER-selective agonists also provide a better understanding of receptor pool cross-talk that results in the overall integrative actions of sex steroids.

Unraveling the functions of the membrane-bound glucocorticoid receptors: first clues on origin and functional activity

Glucocorticoids (GCs) are routinely used to treat a wide range of rheumatic and other inflammatory diseases. GCs are steroidal drugs that exert their strong anti-inflammatory and immunosuppressive effects via genomic mechanisms, primarily by signaling through the cytosolic glucocorticoid receptor. In addition, rapid, nongenomic responses following GC treatment have been reported to involve signaling via the membrane-bound glucocorticoid receptor (mGR). Since an important clinical role of this receptor has been proposed, investigations regarding the origin and function of the mGR are currently performed in order to understand rapid GC signaling and to optimize treatment strategies with GCs. Here, we summarize the current knowledge on the mGR and compare these findings to results obtained for other membrane-bound receptors, such as membrane forms of the estrogen and progesterone receptors.

Non-genomic effects of xenoestrogen mixtures

Xenoestrogens (XEs) are chemicals derived from a variety of natural and anthropogenic sources that can interfere with endogenous estrogens by either mimicking or blocking their responses via non-genomic and/or genomic signaling mechanisms. Disruption of estrogens' actions through the less-studied non-genomic pathway can alter such functional end points as cell proliferation, peptide hormone release, catecholamine transport, and apoptosis, among others. Studies of potentially adverse effects due to mixtures and to low doses of endocrine-disrupting chemicals have recently become more feasible, though few so far have included actions via the non-genomic pathway. Physiologic estrogens and XEs evoke non-monotonic dose responses, with different compounds having different patterns of actions dependent on concentration and time, making mixture assessments all the more challenging. In order to understand the spectrum of toxicities and their mechanisms, future work should focus on carefully studying individual and mixture components across a range of concentrations and cellular pathways in a variety of tissue types.

17β-Estradiol stimulates the translocation of endogenous estrogen receptor α at the plasma membrane of normal anterior pituitary cells

In the present work we aimed at identifying ERα in the plasma membrane of normal anterior pituitary cells and investigated if 17β-estradiol was able to induce their subcellular redistribution. Our results show that about 8% of anterior pituitary cells expressed ERα in the plasma membrane, with the geometrical mean fluorescence intensity being increased after steroid hormone treatment. 17β-Estradiol and the selective ERα agonist PPT induced an increase of ERα expression in the plasma membrane and activated the PKCα/ERK 1/2 pathway in a time-course not compatible with genomic actions, thus supporting the notion of membrane-initiated effects. These findings suggest that 17β-estradiol stimulates the translocation of endogenous ERα to the plasma membrane, consequently modulating this ER pool and leading to cellular biological effects in normal anterior pituitary gland.

Quantitative changes in intracellular calcium and extracellular-regulated kinase activation measured in parallel in CHO cells stably expressing serotonin (5-HT) 5-HT2A or 5-HT2C receptors

Background

The serotonin (5-HT) 2A and 2C receptors (5-HT_2AR and 5-HT_2CR) are involved in a wide range of physiological and behavioral processes in the mammalian central and peripheral nervous systems. These receptors share a high degree of homology, have overlapping pharmacological profiles, and utilize many of the same and richly diverse second messenger signaling systems. We have developed quantitative assays for cells stably expressing these two receptors involving minimal cell sample manipulations that dramatically improve parallel assessments of two signaling responses: intracellular calcium (Ca_i⁺⁺) changes and activation (phosphorylation) of downstream kinases. Such profiles are needed to begin to understand the simultaneous contributions from the multiplicity of signaling cascades likely to be initiated by serotonergic ligands.

Results

We optimized the Ca_i⁺⁺ assay for stable cell lines expressing either 5-HT_2AR or 5-HT_2CR (including dye use and measurement parameters; cell density and serum requirements). We adapted a quantitative 96-well plate immunoassay for pERK in the same cell lines. Similar cell density optima and time courses were observed for 5-HT_2AR- and 5-HT_2CR-expressing cells in generating both types of signaling. Both cell lines also require serum-free preincubation for maximal agonist responses in the pERK assay. However, 5-HT_2AR-expressing cells showed significant release of Ca_i⁺⁺ in response to 5-HT stimulation even when preincubated in serum-replete medium, while the response was completely eliminated by serum in 5-HT_2CR-expressing cells. Response to another serotonergic ligand (DOI) was eliminated by serum-replete preincubation in both cells lines.

Conclusions

These data expand our knowledge of differences in ligand-stimulated signaling cascades between 5-HT_2AR and 5-HT_2CR. Our parallel assays can be applied to other cell and receptor systems for monitoring and dissecting concurrent signaling responses.

Regulation of leptin expression by 17beta-estradiol in human placental cells involves membrane associated estrogen receptor alpha

The placenta produces a wide number of molecules that play essential roles in the establishment and maintenance of pregnancy. In this context, leptin has emerged as an important player in reproduction. The synthesis of leptin in normal trophoblastic cells is regulated by different endogenous biochemical agents, but the regulation of placental leptin expression is still poorly understood. We have previously reported that 17β-estradiol (E(2)) up-regulates placental leptin expression. To improve the understanding of estrogen receptor mechanisms in regulating leptin gene expression, in the current study we examined the effect of membrane-constrained E(2) conjugate, E-BSA, on leptin expression in human placental cells. We have found that leptin expression was induced by E-BSA both in BeWo cells and human placental explants, suggesting that E(2) also exerts its effects through membrane receptors. Moreover E-BSA rapidly activated different MAPKs and AKT pathways, and these pathways were involved in E(2) induced placental leptin expression. On the other hand we demonstrated the presence of ERα associated to the plasma membrane of BeWo cells. We showed that E(2) genomic and nongenomic actions could be mediated by ERα. Supporting this idea, the downregulation of ERα level through a specific siRNA, decreased E-BSA effects on leptin expression. Taken together, these results provide new evidence of the mechanisms whereby E(2) regulates leptin expression in placenta and support the importance of leptin in placental physiology.

Breaking the cycle: An insight into the role of ERα in eukaryotic cell cycles

There have been numerous reviews written to date on estrogen receptor (ER), focusing on topics such as its role in the etiology of breast cancer, its mode of regulation, its role as a transcriptional activator and how to target it therapeutically, just to name a few. One reason for so much attention on this nuclear receptor is that it acts not only as a prognostic marker, but also as a target for therapy. However, a relatively undiscovered area in the literature regarding ER is how its activity in the presence and absence of ligand affects its role in proliferation and cell cycle transition. In this review, we provide a brief overview of ER signaling, ligand dependent and independent, genomic and non-genomic, and how these signaling events affect the role of ER in the mammalian cell cycle.

Cytoplasmic estrogen receptor in breast cancer

PURPOSE

In addition to genomic signaling, it is accepted that estrogen receptor-α (ERα) has nonnuclear signaling functions, which correlate with tamoxifen resistance in preclinical models. However, evidence for cytoplasmic ER localization in human breast tumors is less established. We sought to determine the presence and implications of nonnuclear ER in clinical specimens.

EXPERIMENTAL DESIGN

A panel of ERα-specific antibodies (SP1, MC20, F10, 60c, and 1D5) was validated by Western blot and quantitative immunofluorescent (QIF) analysis of cell lines and patient controls. Then eight retrospective cohorts collected on tissue microarrays were assessed for cytoplasmic ER. Four cohorts were from Yale (YTMA 49, 107, 130, and 128) and four others (NCI YTMA 99, South Swedish Breast Cancer Group SBII, NSABP B14, and a Vietnamese Cohort) from other sites around the world.

RESULTS

Four of the antibodies specifically recognized ER by Western and QIF analysis, showed linear increases in amounts of ER in cell line series with progressively increasing ER, and the antibodies were reproducible on YTMA 49 with Pearson correlations (r(2) values) ranging from 0.87 to 0.94. One antibody with striking cytoplasmic staining (MC20) failed validation. We found evidence for specific cytoplasmic staining with the other four antibodies across eight cohorts. The average incidence was 1.5%, ranging from 0 to 3.2%.

CONCLUSIONS

Our data show ERα is present in the cytoplasm in a number of cases using multiple antibodies while reinforcing the importance of antibody validation. In nearly 3,200 cases, cytoplasmic ER is present at very low incidence, suggesting its measurement is unlikely to be of routine clinical value.

The Effects of 17β-estradiol in Cancer are Mediated by Estrogen Receptor Signaling at the Plasma Membrane

Two different isoforms of the estrogen receptors (i.e., ERα and ERβ) mediate pleiotropic 17β-estradiol (E2)-induced cellular effects. The ERs are principally localized in the nucleus where they act by globally modifying the expression of the E2-target genes. The premise that E2 effects are exclusively mediated through the nuclear localized ERs has been rendered obsolete by research over the last 15 years demonstrating that ERα and ERβ proteins are also localized at the plasma membranes and in other extra-nuclear organelles. The E2 modulation of cancer cell proliferation represents a good example of the impact of membrane-initiated signals on E2 effects. In fact, E2 via ERα elicits rapid signals driving cancer cells to proliferation (e.g., in breast cancer cells), while E2-induced ERβ rapid signaling inhibits proliferation (e.g., in colon cancer cells). In this review we provide with an overview of the complex system of E2-induced signal transduction pathways, their impact on E2-induced cancer cell proliferation, and the participation of E2-induced membrane-initiated signals in tumor environment.

Estrogens of multiple classes and their role in mental health disease mechanisms

Gender and sex hormones can influence a variety of mental health states, including mood, cognitive development and function, and vulnerability to neurodegenerative diseases and brain damage. Functions of neuronal cells may be altered by estrogens depending upon the availability of different physiological estrogenic ligands; these ligands and their effects vary with life stages, the genetic or postgenetic regulation of receptor levels in specific tissues, or the intercession of competing nonphysiological ligands (either intentional or unintentional, beneficial to health or not). Here we review evidence for how different estrogens (physiological and environmental/dietary), acting via different estrogen receptor subtypes residing in alternative subcellular locations, influence brain functions and behavior. We also discuss the families of receptors and transporters for monoamine neurotransmitters and how they may interact with the estrogenic signaling pathways.

Signal integration through blending, bolstering and bifurcating of intracellular information

A cell's response to its environment is often determined by signaling through the actions of enzyme cascades. The ability to organize these enzymes into multiprotein complexes allows for a high degree of fidelity, efficiency and spatial precision in signaling responses.

Plasma membrane estrogen receptors

It is now firmly established that estrogen and all sex steroid receptors exist in discrete cellular pools outside the nucleus. Estrogen receptors (ER) have been localized to the plasma membrane where both ERalpha and ERbeta function in a wide variety of cells and organs. ERs have also been found in discrete cytoplasmic organelles including mitochondria and the endoplasmic reticulum. In ligand-dependent fashion, each ER pool contributes to the overall, integrated effects of estrogens producing biological outcomes. This review highlights the recent work establishing new roles and targets of membrane ER signaling. Such actions include prevention of vascular injury or cardiac hypertrophy, sexual behavior and pain perception mediated through the central nervous system, osteoblast survival, and fluid resorption in the colon.

Proliferative and anti-proliferative effects of dietary levels of phytoestrogens in rat pituitary GH3/B6/F10 cells - the involvement of rapidly activated kinases and caspases

Background

Phytoestogens are a group of lipophillic plant compounds that can have estrogenic effects in animals; both tumorigenic and anti-tumorigenic effects have been reported. Prolactin-secreting adenomas are the most prevalent form of pituitary tumors in humans and have been linked to estrogen exposures. We examined the proliferative effects of phytoestrogens on a rat pituitary tumor cell line, GH₃/B₆/F₁₀, originally subcloned from GH₃ cells based on its ability to express high levels of the membrane estrogen receptor-α.

Methods

We measured the proliferative effects of these phytoestrogens using crystal violet staining, the activation of several mitogen-activated protein kinases (MAPKs) and their downstream targets via a quantitative plate immunoassay, and caspase enzymatic activities.

Results

Four phytoestrogens (coumestrol, daidzein, genistein, and trans-resveratrol) were studied over wide concentration ranges. Except trans-resveratrol, all phytoestrogens increased GH₃/B₆/F₁₀ cell proliferation at some concentration relevant to dietary levels. All four phytoestrogens attenuated the proliferative effects of estradiol when administered simultaneously. All phytoestrogens elicited MAPK and downstream target activations, but with time course patterns that often differed from that of estradiol and each other. Using selective antagonists, we determined that MAPKs play a role in the ability of these phytoestrogens to elicit these responses. In addition, except for trans-resveratrol, a serum removal-induced extrinsic apoptotic pathway was blocked by these phytoestrogens.

Conclusion

Phytoestrogens can block physiological estrogen-induced tumor cell growth in vitro and can also stimulate growth at high dietary concentrations in the absence of endogenous estrogens; these actions are correlated with slightly different signaling response patterns. Consumption of these compounds should be considered in strategies to control endocrine tumor cell growth, such as in the pituitary.

Membrane oestrogen receptor alpha signalling to cell functions

Conservation of steroid hormone action outside the nucleus occurs from plants that make brassinosteroids to higher metazoans (primates). In plants, steroid hormone action occurs when the brassinosteroids bind a membrane tyrosine kinase receptor. Ligated receptors for all sex steroids exist at the plasma membrane and rapidly signal through G proteins to second messengers including calcium, cAMP and cGMP, activating proximal and more distal kinases. These signal cascades impact many functions of steroid hormones, responsible for the biological actions of these molecules. Support also exists for membrane-localized receptors of other members of the steroid superfamily, responding to glucocorticoids, mineralocorticoids, thyroid hormone, and vitamin D. The nature of these receptors is in some cases unclear. Steroid receptors also exist in discrete cytoplasmic organelles, most notably the mitochondria, although the functions of these receptors are poorly understood. In this review, I highlight the essential elements of the membrane oestrogen receptor alpha, noting where conserved aspects exist for other steroid receptors.

Alkylphenol xenoestrogens with varying carbon chain lengths differentially and potently activate signaling and functional responses in GH3/B6/F10 somatomammotropes

BACKGROUND

Alkylphenols varying in their side-chain lengths [ethyl-, propyl-, octyl-, and nonylphenol (EP, PP, OP, and NP, respectively)] and bisphenol A (BPA) represent a large group of structurally related xenoestrogens that have endocrine-disruptive effects. Their rapid nongenomic effects that depend on structure for cell signaling and resulting functions are unknown.

OBJECTIVES

We compared nongenomic estrogenic activities of alkylphenols with BPA and 17beta-estradiol (E(2)) in membrane estrogen receptor-alpha-enriched GH3/B6/F10 pituitary tumor cells. These actions included calcium (Ca) signaling, prolactin (PRL) release, extracellular-regulated kinase (ERK) phosphorylation, and cell proliferation.

METHODS

We imaged Ca using fura-2, measured PRL release via radioimmunoassay, detected ERK phosphorylation by fixed cell immunoassay, and estimated cell number using the crystal violet assay.

RESULTS

All compounds caused increases in Ca oscillation frequency and intracellular Ca volume at 100 fM to 1 nM concentrations, although long-chain alkylphenols were most effective. All estrogens caused rapid PRL release at concentrations as low as 1 fM to 10 pM; the potency of EP, PP, and NP exceeded that of E(2). All compounds at 1 nM produced similar increases in ERK phosphorylation, causing rapid peaks at 2.5-5 min, followed by inactivation and additional 60-min peaks (except for BPA). Dose-response patterns of ERK activation at 5 min were similar for E2, BPA, and PP, whereas EP caused larger effects. Only E2 and NP increased cell number. Some rapid estrogenic responses showed correlations with the hydrophobicity of estrogenic molecules; the more hydrophobic OP and NP were superior at Ca and cell proliferation responses, whereas the less hydrophobic EP and PP were better at ERK activations.

CONCLUSIONS

Alkylphenols are potent estrogens in evoking these nongenomic responses contributing to complex functions; their hydrophobicity can largely predict these behaviors.

Membrane estrogen receptor-alpha-mediated nongenomic actions of phytoestrogens in GH3/B6/F10 pituitary tumor cells

Background

Estradiol (E₂) mediates various intracellular signaling cascades from the plasma membrane via several estrogen receptors (ERs). The pituitary is an estrogen-responsive tissue, and we have previously reported that E₂ can activate mitogen-activated protein kinases (MAPKs) such as ERK1/2 and JNK1/2/3 in the membrane ERα (mERα)-enriched GH₃/B₆/F₁₀ rat pituitary tumor cell line. Phytoestrogens are compounds found in plants and foods such as soybeans, alfalfa sprouts, and red grapes. They are structurally similar to E₂ and share a similar mechanism of action through their binding to ERs. Phytoestrogens bind to nuclear ERs with a much lower affinity and therefore are less potent in mediating genomic responses. However, little is known about their ability to act via mERs to mediate nongenomic effects.

Methods

To investigate the activation of different nongenomic pathways, and determine the involvement of mERα, we measured prolactin (PRL) release by radio-immunoassay, MAPK activations (ERK1/2 and JNK1/2/3) via a quantitative plate immunoassay, and intracellular [Ca²⁺] by Fura-2 fluorescence imaging in cells treated with E₂ or four different phytoestrogens (coumestrol, daidzein, genistein, and trans-resveratrol).

Results

Coumesterol and daidzein increased PRL release similar to E₂ in GH₃/B₆/F₁₀ cells, while genistein and trans-resveratrol had no effect. All of these compounds except genistein activated ERK1/2 signaling at 1–10 picomolar concentrations; JNK 1/2/3 was activated by all compounds at a 100 nanomolar concentration. All compounds also caused rapid Ca²⁺ uptake, though in unique dose-dependent Ca²⁺ response patterns for several aspects of this response. A subclone of GH₃ cells expressing low levels of mERα (GH₃/B₆/D₉) did not respond to any phytoestrogen treatments for any of these responses, suggesting that these nongenomic effects were mediated via mERα.

Conclusion

Phytoestrogens were much more potent in mediating these nongenomic responses (activation of MAPKs, PRL release, and increased intracellular [Ca²⁺]) via mERα than was previously reported for genomic responses. The unique non-monotonic dose responses and variant signaling patterns caused by E₂ and all tested phytoestrogens suggest that complex and multiple signaling pathways or binding partners could be involved. By activating these different nongenomic signaling pathways, phytoestrogens could have significant physiological consequences for pituitary cell functions.

The localization and non-genomic function of the membrane-associated estrogen receptor in oligodendrocytes

There is general acceptance that the estrogen receptor can act as a transcription factor. However, estrogens can also bind to receptors that are located at the plasma membrane and stimulate rapid intracellular signaling processes. We recently showed that a membrane-associated estrogen receptor (mER) is present within myelin and at the oligodendrocyte (OL) plasma membrane. To understand the physiological function of mER in OLs, we investigated its cellular localization and involvement in rapid signaling in CG4 cells and OL primary cultures. An ERalpha was expressed along the lacy network of veins in the membrane sheets and in the perikaryon and nucleus in OLs. ERbeta was located in the nucleus, and to a lesser extent along the veins. The expression of ERalpha and ERbeta in OL membranes was confirmed by Western analysis of isolated membranes. OL membranes mainly had truncated forms of ERalpha, 53 and 50 kDa, in addition to some 65 kDa form, whereas ERbeta was a 54 kDa form. CG4 cells and OLs were pulsed with 17alpha- and 17beta-estradiol for various times and the total lysates were analyzed for phosphorylated kinases. Both 17alpha- and 17beta-estradiol elicited rapid phosphorylation of p42/44MAPK, Akt, and GSK-3beta within 8 min. This rapid signaling is consistent with estradiol ligation of a membrane form of ER. Since 17alpha-estradiol is produced at higher concentrations than 17beta-estradiol in the brain of both sexes, signaling via 17alpha-estradiol-liganded mER may have an important function in OLs.

Estrogen inhibits RANKL-stimulated osteoclastic differentiation of human monocytes through estrogen and RANKL-regulated interaction of estrogen receptor-alpha with BCAR1 and Traf6

The effects of estrogen on osteoclast survival and differentiation were studied using CD14-selected mononuclear osteoclast precursors from peripheral blood. Estradiol at approximately 1 nM reduced RANKL-dependent osteoclast differentiation by 40-50%. Osteoclast differentiation was suppressed 14 days after addition of RANKL even when estradiol was withdrawn after 18 h. In CD14+ cells apoptosis was rare and was not augmented by RANKL or by 17-beta-estradiol. Estrogen receptor-alpha (ERalpha) expression was strongly down-regulated by RANKL, whether or not estradiol was present. Mature human osteoclasts thus cannot respond to estrogen via ERalpha. However, ERalpha was present in CD14+ osteoclast progenitors, and a scaffolding protein, BCAR1, which binds ERalpha in the presence of estrogen, was abundant. Immunoprecipitation showed rapid (approximately 5 min) estrogen-dependent formation of ERalpha-BCAR1 complexes, which were increased by RANKL co-treatment. The RANKL-signaling intermediate Traf6, which regulates NF-kappaB activity, precipitated with this complex. Reduction of NF-kappaB nuclear localization occurred within 30 min of RANKL stimulation, and estradiol inhibited the phosphorylation of IkappaB in response to RANKL. Inhibition by estradiol was abolished by siRNA knockdown of BCAR1. We conclude that estrogen directly, but only partially, curtails human osteoclast formation. This effect requires BCAR1 and involves a non-genomic interaction with ERalpha.

Rapid mechanisms of glucocorticoid signaling in the Leydig cell

Stress-mediated elevations in circulating glucocorticoid levels lead to corresponding rapid declines in testosterone production by Leydig cells in the testis. In previous studies we have established that glucocorticoids act on Leydig cells directly, through the classic glucocorticoid receptor (GR), and that access to the GR is controlled prior to the GR by a metabolizing pathway mediated by the type 1 isoform of 11beta-hydroxysteroid dehydrogenase (11betaHSD1). This enzyme is bidirectional (with both oxidase and reductase activities) and in the rat testis is exclusively localized in Leydig cells where it is abundantly expressed and may catalyze the oxidative inactivation of glucocorticoids. The predominant reductase direction of 11betaHSD1 activity in liver cells is determined by an enzyme, hexose-6-phosphate dehydrogenase (H6PDH), on the luminal side of the smooth endoplasmic reticulum (SER). Generation of the pyridine nucleotide cofactor NADPH by H6PDH stimulates the reductase direction of 11betaHSD1 resulting in increased levels of active glucocorticoids in liver cells. Unlike liver cells, steroidogenic enzymes including 17beta-hydroxysteroid dehydrogenase 3 (17betaHSD3) forms the coupling with 11betaHSD1. Thus the physiological concentrations of androstenedione serve as a substrate for 17betaHSD3 utilizing NADPH to generate NADP+, which drives 11betaHSD1 in Leydig cells primarily as an oxidase; thus eliminating the adverse effects of glucocorticoids on testosterone production. At the same time 11betaHSD1 generates NADPH which promotes testosterone biosynthesis by stimulating 17betaHSD3 in a cooperative cycle. This enzymatic coupling constitutes a rapid mechanism for modulating glucocorticoid control of testosterone biosynthesis. Under stress conditions, glucocorticoids also have rapid actions to suppress cAMP formation thus to lower testosterone production.

Estradiol-induced enhancement of object memory consolidation involves hippocampal extracellular signal-regulated kinase activation and membrane-bound estrogen receptors

The extracellular signal-regulated kinase (ERK) pathway is critical for various forms of learning and memory, and is activated by the potent estrogen 17beta-estradiol (E(2)). Here, we asked whether E(2) modulates memory via ERK activation and putative membrane-bound estrogen receptors (ERs). Using ovariectomized mice, we first demonstrate that intraperitoneal injection of 0.2 mg/kg E(2) significantly increases dorsal hippocampal levels of phosphorylated ERK protein 1 h after injection. Second, we show that E(2) administered intraperitoneally (0.2 mg/kg) or via intrahippocampal infusion (5.0 microg/side) immediately after training in an object recognition task significantly enhances memory retention, and that the beneficial effect of intraperitoneal E(2) is blocked by dorsal hippocampal inhibition of ERK activation. Third, using bovine serum albumin-conjugated 17beta-estradiol (BSA-E(2)), we demonstrate that E(2) binding at membrane-bound ERs can increase dorsal hippocampal ERK activation and enhance object memory consolidation in an ERK-dependent manner. Fourth, we show that this effect is independent of nuclear ERs, but is dependent on the dorsal hippocampus. By demonstrating that E(2) enhances memory consolidation via dorsal hippocampal ERK activation, this study is the first to identify a specific molecular pathway by which E(2) modulates memory and to demonstrate a novel role for membrane-bound ERs in mediating E(2)-induced improvements in hippocampal memory consolidation.

Estrogen signaling characteristics of Atlantic croaker G protein-coupled receptor 30 (GPR30) and evidence it is involved in maintenance of oocyte meiotic arrest

Human G protein-coupled receptor 30 (GPR30) mediates estradiol-17beta (E2) activation of adenylyl cyclase in breast cancer cells and displays E2 binding typical of membrane estrogen receptors (mERs). We identified a mER in Atlantic croaker ovaries with characteristics similar to those of human GPR30. To confirm the proposed role of GPR30 as a mER in this distantly related vertebrate group, we cloned GPR30 from croaker ovaries and examined its distribution, steroid binding, and signaling characteristics. Western blot analysis showed the GPR30 protein (approximately 40 kDa) is expressed on the plasma membranes of croaker oocytes and HEK293 cells stably transfected with GPR30 cDNA. Plasma membranes prepared from croaker GPR30-transfected cells displayed high-affinity, limited-capacity, and displaceable binding specific for estrogens, characteristic of mERs. Consistent with previous findings with human GPR30, estrogen treatment of plasma membranes from both croaker ovaries and GPR30-transfected cells caused activation of a stimulatory G protein (Gs) resulting in increased cAMP production. Treatment with E2 as well as G-1, a specific GPR30 ligand, significantly reduced both spontaneous and progestin-induced maturation of both croaker and zebrafish oocytes in vitro, suggesting a possible involvement of GPR30 in maintaining oocyte meiotic arrest in these species. Injection of antisense oligonucleotides to GPR30 into zebrafish oocytes blocked the inhibitory effects of estrogen on oocyte maturation, confirming a role for GPR30 in the control of meiotic arrest. These findings further support our previous suggestion that GPR30 is a vertebrate mER. In addition, the results suggest GRP30 may play a critical role in regulating reentry into the meiotic cell cycle in fish oocytes.

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.

Sex differences in drug abuse

Sex differences are present for all of the phases of drug abuse (initiation, escalation of use, addiction, and relapse following abstinence). While there are some differences among specific classes of abused drugs, the general pattern of sex differences is the same for all drugs of abuse. Females begin regularly self-administering licit and illicit drugs of abuse at lower doses than do males, use escalates more rapidly to addiction, and females are at greater risk for relapse following abstinence. In this review, sex differences in drug abuse are discussed for humans and in animal models. The possible neuroendocrine mechanisms mediating these sex differences are discussed.

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.

Membrane-initiated actions of estrogens in neuroendocrinology: emerging principles

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.

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.

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.

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.

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.

Signaling networks from Gβ1 subunit to transcription factors and actin remodeling via a membrane-located ERβ-related protein in the rapid action of daidzein in osteoblasts

Although estrogen replacement has been the main therapy to prevent and treat osteoporosis, there are concerns about its safety. Phytoestrogens have attracted attention to their potential impacts in osteoporosis prevention and treatment. Among phytoestrogens, the isoflavone daidzein (Dz) acts on transcription via the intracellular estrogen receptors (ER), mainly ERbeta, in osteoblasts, but mimics only part of the estrogen effects. Since estradiol also exerts rapid effects in osteoblasts, we investigated the multistep processes involved in the rapid actions of low (1-100 pM) doses of daidzein. Dz bound to a membrane moiety, related to ERbeta since the calcium response to Dz was blocked by an anti-ERbeta antibody directed against the C-terminus, but not by a double-stranded siRNA specific for ERbeta. This protein was coupled to a pertussis toxin (PTX)-sensitive Gbeta1 subunit whose transducer was PLC-beta2, which triggered a rapid (5 sec) mobilization of calcium from the endoplasmic reticulum. Dz phosphorylated within 15 sec ERK1/2 whose phosphorylation involved two routes: Gbeta1/PLC-beta2/PKC/c-Raf-1/MEK1/2 and Gbeta1/PI3K/cSrc/c-Raf-1/MEK1/2 as shown using several inhibitors. Dz induced rapid (1 min) changes in the actin cytoskeleton via the two routes. The rapid (20 sec) phosphorylation of Elk-1 and CREB by Dz involved Gbeta1 and ERK1/2. All the processes were insensitive to the estradiol antagonist ICI 182,780. In conclusion, the rapid effects of Dz seem to be biologically relevant for the function of osteoblast in bone since the isoflavone activates transcription factors linked to early genes controlling cellular proliferation and differentiation, and modulates actin cytoskeleton which controls cell adhesion, division, or secretion.

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.