Minireview: Extranuclear steroid receptors: roles in modulation of cell functions

Hormone signaling requirements for the conversion of non-mammary mouse cells to mammary cell fate(s) in vivo

Mammotropic hormones and growth factors play a very important role in mammary growth and differentiation. Here, hormones including Estrogen, Progesterone, Prolactin, their cognate receptors, and the growth factor Amphiregulin, are tested with respect to their roles in signaling non-mammary cells from the mouse to redirect to mammary epithelial cell fate(s). This was done in the context of glandular regeneration in pubertal athymic female mice. Our previous studies demonstrated that mammary stem cell niches are recapitulated during gland regeneration in vivo. During this process, cells of exogenous origin cooperate with mammary epithelial cells to form mammary stem cell niches and thus respond to normal developmental signals. In all cases tested with the possible exception of estrogen receptor alpha (ER-α), hormone signaling is dispensable for non-mammary cells to undertake mammary epithelial cell fate(s), proliferate, and contribute progeny to chimeric mammary outgrowths. Importantly, redirected non-mammary cell progeny, regardless of their source, have the ability to self-renew and contribute offspring to secondary mammary outgrowths derived from transplanted chimeric mammary fragments; thus suggesting that some of these cells are capable of mammary stem cell/progenitor functions.

Emerging roles of GPER in diabetes and atherosclerosis

The G protein-coupled estrogen receptor (GPER) is a 7-transmembrane receptor implicated in rapid estrogen signaling. Originally cloned from vascular endothelial cells, GPER plays a central role in the regulation of vascular tone and cell growth as well as lipid and glucose homeostasis. This review highlights our knowledge of the physiological and pathophysiological functions of GPER in the pancreas, peripheral and immune tissues, and the arterial vasculature. Recent findings on its roles in obesity, diabetes, and atherosclerosis, including GPER-dependent regulation of lipid metabolism and inflammation, are presented. The therapeutic potential of targeting GPER-dependent pathways in chronic diseases such as coronary artery disease and diabetes and in the context of menopause is also discussed.

Membrane steroid receptor-mediated action of soy isoflavones: tip of the iceberg

Soy isoflavone's (genistein and daidzein in particular) biological significance has been thoroughly studied for decades, so we started from the premise that refreshed investigation approach in this field should consider identification of their new molecular targets. In addition to recently described epigenetic aspects of polyphenole action, the cell membrane constituents-mediated effects of soy isoflavones are worthy of special attention. Accordingly, the expanding concept of membrane steroid receptors and rapid signaling from the cell surface may include the prominent role of these steroid-like compounds. It was observed that daidzein strongly interacts with membrane estrogen receptors in adrenal medullary cells. At low doses, daidzein was found to stimulate catecholamine synthesis through extracellular signal-regulated kinase 1/2 or protein kinase A pathways, but at high doses, it inhibited catecholamine synthesis and secretion induced by acetylcholine. Keeping in mind that catecholamine excess can contribute to the cardiovascular pathologies and that catecholamine lack may lead to depression, daidzein application promises to have a wide range of therapeutic effects. On the other hand, it was shown in vitro that genistein inhibits LNCaP prostate cancer cells invasiveness by decreasing the membrane fluidity along with immobilization of the androgen receptor containing membrane lipid rafts, with down regulation of the androgen receptors and Akt signaling. These data are promising in development of the molecular pharmacotherapy pertinent to balanced soy isoflavone treatment of cardiovascular, psychiatric, and steroid-related malignant diseases.

Molecular signature of rapid estrogen regulation of synaptic connectivity and cognition

There is now a growing appreciation that estrogens are capable of rapidly activating a number of signaling cascades within the central nervous system. In addition, there are an increasing number of studies reporting that 17β-estradiol, the major biologically active estrogen, can modulate cognition within a rapid time frame. Here we review recent studies that have begun to uncover the molecular and cellular framework which contributes to estrogens ability to rapidly modulate cognition. We first describe the mechanisms by which estrogen receptors (ERs) can couple to intracellular signaling cascades, either directly, or via the transactivation of other receptors. Subsequently, we review the evidence that estrogen can rapidly modulate both neuronal function and structure in the hippocampus and the cortex. Finally, we will discuss how estrogens may influence cognitive function through the modulation of neuronal structure, and the implications this may have on the treatment of a range of brain disorders.

Nuclear receptors and endocrine disruptors in fetal and neonatal testes: a gapped landscape

During the last decades, many studies reported that male reproductive disorders are increasing among humans. It is currently acknowledged that these abnormalities can result from fetal exposure to environmental chemicals that are progressively becoming more concentrated and widespread in our environment. Among the chemicals present in the environment (air, water, food, and many consumer products), several can act as endocrine disrupting compounds (EDCs), thus interfering with the endocrine system. Phthalates, bisphenol A (BPA), and diethylstilbestrol (DES) have been largely incriminated, particularly during the fetal and neonatal period, due to their estrogenic and/or anti-androgenic properties. Indeed, many epidemiological and experimental studies have highlighted their deleterious impact on fetal and neonatal testis development. As EDCs can affect many different genomic and non-genomic pathways, the mechanisms underlying the adverse effects of EDC exposure are difficult to elucidate. Using literature data and results from our laboratory, in the present review, we discuss the role of classical nuclear receptors (genomic pathway) in the fetal and neonatal testis response to EDC exposure, particularly to phthalates, BPA, and DES. Among the nuclear receptors, we focused on some of the most likely candidates, such as peroxisome-proliferator activated receptor (PPAR), androgen receptor (AR), estrogen receptors (ERα and β), liver X receptors (LXR), and small heterodimer partner (SHP). First, we describe the expression and potential functions (based on data from studies using receptor agonists and mouse knockout models) of these nuclear receptors in the developing testis. Then, for each EDC studied, we summarize the main evidences indicating that the reprotoxic effect of each EDC under study is mediated through a specific nuclear receptor(s). We also point-out the involvement of other receptors and nuclear receptor-independent pathways.

Interplay between steroid signalling and microRNAs: implications for hormone-dependent cancers

Hormones are key drivers of cancer development. To date, interest has largely been focussed on the classical model of hormonal gene regulation, but there is increasing evidence for a role of hormone signalling pathways in post-translational regulation of gene expression. In particular, a complex and dynamic network of bi-directional interactions with microRNAs (miRs) at all stages of biogenesis and during target gene repression is emerging. miRs, which act mainly by negatively regulating gene expression through association with 3'-UTRs of mRNA species, are increasingly understood to be important in development, normal physiology and pathogenesis. Given recent demonstrations of altered miR profiles in a diverse range of cancers, their ability to function as oncogenes or tumour suppressors, and hormonal regulation of miRs, understanding mechanisms by which miRs are generated and regulated is vitally important. miRs are transcribed by RNA polymerase II and then processed in the nucleus by the Drosha-containing Microprocessor complex and in the cytoplasm by Dicer, before mature miRs are incorporated into the RNA-induced silencing complex. It is increasingly evident that multiple cellular signalling pathways converge upon the miR biogenesis cascade, adding further layers of regulatory complexity to modulate miR maturation. This review summarises recent advances in identification of novel components and regulators of the Microprocessor and Dicer complexes, with particular emphasis on the role of hormone signalling pathways in regulating their activity. Understanding hormone regulation of miR production and how this is perturbed in cancer are critical for the development of miR-based therapeutics and biomarkers.

GPER-targeted, 99mTc-labeled, nonsteroidal ligands demonstrate selective tumor imaging and in vivo estrogen binding

Our understanding of estrogen (17β-estradiol, E2) receptor biology has evolved in recent years with the discovery and characterization of a 7-transmembrane-spanning G protein-coupled estrogen receptor (GPER/GPR30) and the development of GPER-selective functional chemical probes. GPER is highly expressed in certain breast, endometrial, and ovarian cancers, establishing the importance of noninvasive methods to evaluate GPER expression in vivo. Here, we developed (99m)Tc-labeled GPER ligands to demonstrate the in vivo status of GPER as an estrogen receptor (ER) and for GPER visualization in whole animals. A series of (99m)Tc(I)-labeled nonsteroidal tetrahydro-3H-cyclopenta[c]quinolone derivatives was synthesized utilizing pyridin-2-yl hydrazine and picolylamine chelates. Radioligand receptor binding studies revealed binding affinities in the 10 to 30 nmol/L range. Cell signaling assays previously demonstrated that derivatives retaining a ketone functionality displayed agonist properties, whereas those lacking such a hydrogen bond acceptor were antagonists. In vivo biodistribution and imaging studies performed on mice bearing human endometrial and breast cancer cell xenografts yielded significant tumor uptake (0.4-1.1%ID/g). Blocking studies revealed specific uptake in multiple organs (adrenals, uterus, and mammary tissue), as well as tumor uptake with similar levels of competition by E2 and G-1, a GPER-selective agonist. In conclusion, we synthesized and evaluated a series of first-generation (99m)Tc-labeled GPER-specific radioligands, demonstrating GPER as an estrogen-binding receptor for the first time in vivo using competitive binding principles, and establishing the utility of such ligands as tumor imaging agents. These results warrant further investigation into the role of GPER in estrogen-mediated carcinogenesis and as a target for diagnostic/therapeutic/image-guided drug delivery.

IMPLICATIONS

These studies provide a molecular basis to evaluate GPER expression and function as an ER through in vivo imaging.

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.

Estrogens and aging skin

Estrogen deficiency following menopause results in atrophic skin changes and acceleration of skin aging. Estrogens significantly modulate skin physiology, targeting keratinocytes, fibroblasts, melanocytes, hair follicles and sebaceous glands, and improve angiogenesis, wound healing and immune responses. Estrogen insufficiency decreases defense against oxidative stress; skin becomes thinner with less collagen, decreased elasticity, increased wrinkling, increased dryness and reduced vascularity. Its protective function becomes compromised and aging is associated with impaired wound healing, hair loss, pigmentary changes and skin cancer.

 

Skin aging can be significantly delayed by the administration of estrogen. This paper reviews estrogen effects on human skin and the mechanisms by which estrogens can alleviate the changes due to aging. The relevance of estrogen replacement, selective estrogen receptor modulators (SERMs) and phytoestrogens as therapies for diminishing skin aging is highlighted. Understanding estrogen signaling in skin will provide a basis for interventions in aging pathologies.

Cyclin D1 integrates estrogen-mediated DNA damage repair signaling

The cyclin D1 gene encodes the regulatory subunit of a holoenyzme that phosphorylates the retinoblastoma protein (pRb) and nuclear respiratory factor (NRF1) proteins. The abundance of cyclin D1 determines estrogen-dependent gene expression in the mammary gland of mice. Using estradiol (E2) and an E2-dendrimer conjugate that is excluded from the nucleus, we demonstrate that E2 delays the DNA damage response (DDR) via an extranuclear mechanism. The E2-induced DDR required extranuclear cyclin D1, which bound ERα at the cytoplasmic membrane and augmented AKT phosphorylation (Ser473) and γH2AX foci formation. In the nucleus, E2 inhibited, whereas cyclin D1 enhanced homology-directed DNA repair. Cyclin D1 was recruited to γH2AX foci by E2 and induced Rad51 expression. Cyclin D1 governs an essential role in the E2-dependent DNA damage response via a novel extranuclear function. The dissociable cytoplasmic function to delay the E2-mediated DDR together with the nuclear enhancement of DNA repair uncovers a novel extranuclear function of cyclin D1 that may contribute to the role of E2 in breast tumorigenesis.

Dissection of estrogen receptor alpha signaling pathways in osteoblasts using RNA-sequencing

The effects of 17-β-estradiol in osteoblasts are primarily mediated by the nuclear transcription factors, estrogen receptor (ER)α and ERβ. ERs function through three general modes of action: DNA-binding dependent through estrogen response elements (EREs; designated nuclear ERE signaling); nuclear signaling via protein-protein interactions to other transcription factors (nuclear non-ERE signaling); and extra-nuclear signaling (membrane-bound functions of ERs). Identification of the specific transcriptional signatures regulated by each of these modes of action should contribute to an enhanced understanding of estrogen signaling in osteoblasts. To achieve this goal, we utilized specific mutations of ERα that eliminate the ability of the receptor to signal through a specific mode of action. The non-classical ERα knock-in (NERKI) mutation is incapable of signaling through direct DNA binding to EREs and the nuclear only ERα (NOER) mutation eliminates all membrane-localized signaling. Comparison of the gene expression patterns elicited by these mutations with the wild-type ERα (WT) pattern provides mode-specific data concerning transcriptional regulation by ERα. We expressed these constructs in the ER-negative osteoblastic cell line hFOB (−/+ estrogen) and performed global RNA-sequencing. Using a series of pair-wise comparisons, we generated three lists of genes that were regulated either by the nuclear ERE-dependent, nuclear ERE-independent, or extra-nuclear actions of ERα. Pathway and gene ontology analyses revealed that genes regulated through the nuclear ERE and nuclear non-ERE pathways were largely involved in transcriptional regulation, whereas genes regulated through extra-nuclear mechanisms are involved in cytoplasmic signaling transduction pathways. We also intersected our data with genes linked to bone density and fractures from a recent genome-wide association study and found 25 of 72 genes (35%) regulated by estrogen. These data provide a comprehensive list of genes and pathways targeted by these specific modes of ERα action and suggest that “mode-specific” ligands could be developed to modulate specific ERα functionality in bone.

Bisphenol A promotes human prostate stem-progenitor cell self-renewal and increases in vivo carcinogenesis in human prostate epithelium

Previous studies in rodent models have shown that early-life exposure to bisphenol A (BPA) reprograms the prostate and enhances its susceptibility to hormonal carcinogenesis with aging. To determine whether the human prostate is similarly sensitive to BPA, the current study used human prostate epithelial stem-like cells cultured from prostates of young, disease-free donors. Similar to estradiol-17β (E2), BPA increased stem-progenitor cell self-renewal and expression of stem-related genes in a dose-dependent manner. Further, 10 nM BPA and E2 possessed equimolar membrane-initiated signaling with robust induction of p-Akt and p-Erk at 15 minutes. To assess in vivo carcinogenicity, human prostate stem-progenitor cells combined with rat mesenchyme were grown as renal grafts in nude mice, forming normal human prostate epithelium at 1 month. Developmental BPA exposure was achieved through oral administration of 100 or 250 μg BPA/kg body weight to hosts for 2 weeks after grafting, producing free BPA levels of 0.39 and 1.35 ng/mL serum, respectively. Carcinogenesis was driven by testosterone plus E2 treatment for 2 to 4 months to model rising E2 levels in aging men. The incidence of high-grade prostate intraepithelial neoplasia and adenocarcinoma markedly increased from 13% in oil-fed controls to 33% to 36% in grafts exposed in vivo to BPA (P < .05). Continuous developmental BPA exposure through in vitro (200 nM) plus in vivo (250 μg/kg body weight) treatments increased high-grade prostate intraepithelial neoplasia/cancer incidence to 45% (P < .01). Together, the present findings demonstrate that human prostate stem-progenitor cells are direct BPA targets and that developmental exposure to BPA at low doses increases hormone-dependent cancer risk in the human prostate epithelium.

Estrogen receptor 1 gene (TA)n polymorphism is associated with lone atrial fibrillation in men

Aim

To determine the association between the number of thymine-adenine (TA)n dinucleotide repeats in the promoter region of the gene coding for the estrogen receptor alpha (ESR1) and the prevalence of lone atrial fibrillation (AF) in men.

Methods

We conducted a case-control study involving 89 men with lone AF and 166 healthy male controls. The ESR1 genotype was established by polymerase chain reaction and capillary electrophoresis. To assess the association of ESR1 genotype with AF, logistic regression models were built with AF as outcome.

Results

Men with lone AF had significantly greater number of (TA)n repeats of single alleles than controls (mean ± standard deviation, 19.2 ± 4.2 vs 18 ± 4.3, P = 0.010). After adjustment for other factors, a unit-increase in (TA)n repeat number was associated with a significantly greater likelihood of AF (odds ratio 1.069; 95% confidence interval 1.024-1.116, P = 0.002).

Conclusions

Our results indicate that a greater number of (TA)n repeats in the promoter region of ESR1 is associated with a significantly increased likelihood of lone atrial fibrillation in men.

Measuring selective estrogen receptor modulator (SERM)-membrane interactions with second harmonic generation

The interaction of selective estrogen receptor modulators (SERMs) with lipid membranes has been measured at clinically relevant serum concentrations using the label-free technique of second harmonic generation (SHG). The SERMs investigated in this study include raloxifene, tamoxifen, and the tamoxifen metabolites 4-hydroxytamoxifen, N-desmethyltamoxifen, and endoxifen. Equilibrium association constants (Ka) were measured for SERMs using varying lipid compositions to examine how lipid phase, packing density, and cholesterol content impact SERM-membrane interactions. Membrane-binding properties of tamoxifen and its metabolites were compared on the basis of hydroxyl group substitution and amine ionization to elucidate how the degree of drug ionization impacts membrane partitioning. SERM-membrane interactions were probed under multiple pH conditions, and drug adsorption was observed to vary with the concentration of soluble neutral species. The agreement between Ka values derived from SHG measurements of the interactions between SERMs and artificial cell membranes and independent observations of the SERMs efficacy from clinical studies suggests that quantifying membrane adsorption properties may be important for understanding SERM action in vivo.

Understanding response and resistance to oestrogen deprivation in ER-positive breast cancer

Oestrogens (E) and oestrogen receptor alpha (ERα) play fundamental roles in the development and progression of more than three-quarters of breast cancers (BC). The ability to influence the natural history of BC by hormonal manipulation is well established and endocrine therapies represent the cornerstone of systemic management for women with ERα-positive disease. Endocrine agents abrogate oestrogenic signalling through distinct and incompletely overlapping mechanisms, either impeding the transcriptional activity of ERα or diminishing E-synthesis. In post-menopausal women, E-production is chiefly attributable to the enzymatic conversion of androgens in extra-gonadal tissues by the cytochrome P-450 superfamily member aromatase. Greater understanding of steroid biosynthesis has underpinned rational drug design and pharmacological development of potent and specific aromatase inhibitors (AIs). Contemporary agents induce profound E-suppression in post-menopausal women and are first-line neo-adjuvant, adjuvant and metastatic therapies, with greater efficacy and tolerability than tamoxifen. The principal qualifier for endocrine treatment, including AIs, remains ERα expression. However, it is increasingly apparent that ERα expression is not synonymous with sensitivity to treatment and insufficient to account for the considerable heterogeneity of response. Better predictive biomarkers of de novo resistance are required to improve patient selection and identify those poor-responders who may benefit from alternative or additional systemic treatment from the outset. Among patients who do respond well initially, many relapse during their clinical course and there is also an unmet need for biomarkers of acquired resistance. The majority of women who relapse on AIs continue to express functional ERα which remains a legitimate target for second-line endocrine therapy. Understanding and overcoming acquired resistance to AIs requires a greater appreciation of ERα biology and the mechanisms though which E-dependence can be subverted. In this article, we review the impact of therapeutic E-deprivation on the natural history of ERα-positive breast cancer. Consideration is given to established and emerging biomarkers and/or determinants of response and resistance to E-deprivation. In vitro and in vivo evidence of the molecular mechanisms underpinning the transition from sensitivity to resistance are reviewed in the context of current models of ERα activity and their potential translational relevance.

Influence of estradiol administration on estrogen receptors of nasal mucosa: an experimental study on guinea pigs

INTRODUCTION

Some clinical trials revealed a correlation between increased serum estrogen and nasal symptoms or inflammatory changes in nasal mucosa. Estrogen receptors tend to be controlled by a negative feedback, to avoid a deleterious stimulus over several body functions while in hyperestrogenic periods. This study proposes a hypothesis where mechanisms regulating expression of estradiol receptors in nasal mucosa are absent in some patients, and their concentration remains steady even in periods of high serum hormonal concentration, potentially leading to local estrogenic symptoms in nasal mucosa.

STUDY DESIGN

This was an experimental prospective study.

AIM

To determine whether estrogen levels induce the reduction of the number of estrogen receptors in the nasal mucosa.

METHODS

In the present study, 30 adult male guinea pigs were subjected to a biopsy of the middle nasal turbinate and received 0.5 mL of estradiol cypionate intraperitoneally for 30 consecutive days. Afterwards, samples from contralateral middle turbinate were obtained. Immunohistochemical analysis of estrogen receptors were performed pre- and post-treatment.

RESULTS

The post-treatment group showed reduction of receptor expression when compared to the pre-treatment group. (p = 5.2726-5).

CONCLUSION

A reduction in the expression of the nasal estrogen receptor was observed after 30 days of estradiol administration.

Paxillin and steroid signaling: from frog to human

Paxillin is a well-characterized cytoplasmic adaptor protein that is known to play important roles in cytoskeletal rearrangement, cell adhesion, and cell motility. In addition to its structural functions, paxillin has more recently been shown to function as a regulator of cell division-mediating steroid-triggered meiosis in oocytes as well as steroid- and growth factor-induced proliferation in prostate and breast cancer. Paxillin mediates these processes through a conserved pathway that involves both extranuclear (nongenomic) and nuclear (genomic) steroid signaling, as well as both cytoplasmic and nuclear kinase signaling. In fact, paxillin appears to serve as a critical liaison between extranuclear and nuclear signaling in response to multiple stimuli, making it a fascinating molecule to study when trying to determine how growth signals from the membrane lead to important proliferative changes in the nucleus. This chapter outlines recent advances in understanding how paxillin regulates both steroid and growth factor signaling, focusing on the conserved nature of its actions from a frog germ cell to a human cancer cell.

Nitric oxide as a mediator of estrogen effects in osteocytes

Postmenopausal osteoporosis due to estrogen deficiency is a major health problem, and available therapies rely largely on the inhibition of bone resorption, because estrogen replacement is associated with risks. Estrogen promotes bone health in large part by increasing osteocyte survival, but the molecular mechanisms involved are only partly understood. We showed that estradiol stimulates nitric oxide (NO) production in osteocytes, leading to increased cGMP synthesis and activation of cGMP-dependent protein kinases (PKGs). Moreover, we found that 17β-estradiol protects osteocytes against apoptosis via the NO/cGMP signaling pathway: type II PKG mediates estradiol-induced activation of the prosurvival kinases Erk and Akt, whereas type I PKG contributes to prosurvival signaling by directly phosphorylating and inactivating the cell death protein BAD. Preclinical data support an important role of NO in bone biology, and clinical trials suggest that NO donors may prevent bone loss in postmenopausal women. Our data provide novel insights into estrogen signaling through the NO/cGMP/PKG pathway and a rationale for using NO donors and other cGMP-elevating agents for treating postmenopausal osteoporosis.

Cognition, mood, and physiological concentrations of sex hormones in the early and late postmenopause

Variations in the hormonal milieu after menopause may influence neural processes concerned with cognition, cognitive aging, and mood, but findings are inconsistent. In particular, cognitive effects of estradiol may vary with time since menopause, but this prediction has not been assessed directly using serum hormone concentrations. We studied 643 healthy postmenopausal women not using hormone therapy who were recruited into early (<6 y after menopause) and late (10+ y after menopause) groups. Women were administered a comprehensive neuropsychological battery and assessed with the Center for Epidemiologic Studies Depression Scale. They provided serum for free estradiol, estrone, progesterone, free testosterone, and sex hormone binding globulin measurements. Cognitive outcomes were standardized composite measures of verbal episodic memory, executive functions, and global cognition. Covariate-adjusted linear regression analyses were conducted for each hormone separately and after adjustment for other hormone levels. Endogenous sex steroid levels were unassociated with cognitive composites, but sex hormone binding globulin was positively associated with verbal memory. Results for early and late groups did not differ significantly, although progesterone concentrations were significantly positively associated with verbal memory and global cognition in early group women. Hormone concentrations were not significantly related to mood. Results fail to support the hypothesis that temporal proximity to menopause modifies the relation between endogenous serum levels of estradiol and verbal memory, executive functions, or global cognition. Physiological variations in endogenous postmenopausal levels of sex steroid hormones are not substantially related to these aspects of cognition or mood; positive associations for progesterone and sex hormone binding globulin merit additional study.

G-protein oestrogen receptor 1: trials and tribulations of a membrane oestrogen receptor

Oestrogens are now recognised to be able to initiate rapid, fast responses, in addition to their classical, longer-term actions. There is a growing appreciation of the potential implications of this mode of action for oestrogenic signalling in both neuronal and non-neuronal systems. As such, much effort has been made to determine the mechanisms that are critical for transducing these rapid effects into cellular responses. Recently, an orphan G-protein-coupled receptor (GPCR), termed GPR30, was identified as an oestrogen-sensitive receptor in cancer cells. This receptor, now term G-protein oestrogen receptor 1 (GPER1) has been the subject of many investigations, and a role for this receptor in the nervous system is now emerging. In this review, we highlight some of the more recent advances in our understanding of the distribution and subcellular localisation of this receptor in the brain, as well as some of the evidence for the potential role that this receptor may play in the brain. We then discuss some of the controversies surrounding the pharmacology of this receptor, and attempt to reconcile these by suggesting that the 'agonist-specific coupling' model of GPCR function may provide a potential explanation for some of the divergent reports of GPER1 pharmacology.

Temporal and concentration-dependent effects of oestradiol on neural pathways mediating sexual receptivity

The acceptance of oestradiol signalling through receptors found in the cell membrane, as well as, the nucleus, has provided for a re-examination of the timing and location of the actions of oestradiol on neural circuits mediating sexual receptivity (lordosis). Oestradiol membrane signalling involves the transactivation of metabotrophic glutamate receptors (mGluRs) that transduce steroid information through protein kinase C signalling cascades producing rapid activation of lordosis-regulating circuits. It has been known for some time that oestradiol initially produces an inhibition of the medial preoptic nucleus. We have demonstrated that underlying this inhibition is oestradiol acting in the arcuate nucleus to induce β-endorphin release, which inhibits the medial preoptic nucleus through a μ-opioid receptor mechanism. This transient inhibition is relieved by either subsequent progesterone treatment or longer exposure to higher doses of oestradiol to facilitate lordosis behaviour. We review recent findings about oestradiol membrane signalling inducing dendritic spine formation in the arcuate nucleus that is critical for oestradiol induction of sexual receptivity. Moreover, we discuss the evidence that, in addition to oestrogen receptor α, several other putative membrane oestrogen receptors facilitate lordosis behaviour through regulation of the arcuate nucleus. These include the GRP30 and the STX activated Gq-mER. Finally, we report on the importance of GABA acting at GABAB receptors for oestradiol membrane signalling that regulates lordosis circuit activation and sexual receptivity.

Revisiting the roles of progesterone and allopregnanolone in the nervous system: resurgence of the progesterone receptors

Progesterone is commonly considered as a female reproductive hormone and is well-known for its role in pregnancy. It is less well appreciated that progesterone and its metabolite allopregnanolone are also male hormones, as they are produced in both sexes by the adrenal glands. In addition, they are synthesized within the nervous system. Progesterone and allopregnanolone are associated with adaptation to stress, and increased production of progesterone within the brain may be part of the response of neural cells to injury. Progesterone receptors (PR) are widely distributed throughout the brain, but their study has been mainly limited to the hypothalamus and reproductive functions, and the extra-hypothalamic receptors have been neglected. This lack of information about brain functions of PR is unexpected, as the protective and trophic effects of progesterone are much investigated, and as the therapeutic potential of progesterone as a neuroprotective and promyelinating agent is currently being assessed in clinical trials. The little attention devoted to the brain functions of PR may relate to the widely accepted assumption that non-reproductive actions of progesterone may be mainly mediated by allopregnanolone, which does not bind to PR, but acts as a potent positive modulator of γ-aminobutyric acid type A (GABA(A) receptors. The aim of this review is to critically discuss effects of progesterone on the nervous system via PR, and of allopregnanolone via its modulation of GABA(A) receptors, with main focus on the brain.

Activation of membrane estrogen receptors attenuates opioid receptor-like1 receptor-mediated antinociception via an ERK-dependent non-genomic mechanism

To our knowledge, the present data are the first to demonstrate that activation of membrane estrogen receptors (mERs) abolishes opioid receptor-like 1 (ORL1) receptor-mediated analgesia via extracellular signal-regulated kinase (ERK)-dependent non-genomic mechanisms. Estrogen was shown previously to both attenuate ORL1-mediated antinociception and down-regulate the ORL1 gene expression. The present study investigated whether non-genomic mechanisms contribute to estrogen-induced attenuation of ORL1-mediated antinociception by the mERs GPR30, Gq-coupled mER, ERα, and ERβ. E2BSA [β-estradiol-6-(O-carboxymethyl)oxime: bovine serum albumin] (0.5mM), a membrane impermeant analog of estradiol, injected intrathecally immediately prior to orphanin FQ (OFQ;10 nmol), the endogenous ligand for the ORL1 receptor, abolished OFQ's antinociceptive effect in both male and ovariectomized (OVX) female rats, assessed using the heat-induced tail-flick assay. This effect was not altered by protein synthesis inhibitor, anisomycin (125 μg), given intrathecally 15 min prior to E2BSA and OFQ. Intrathecal application of selective receptor agonists permitted the relative contributions of various estrogen receptors in mediating this blockade of the antinociceptive response of OFQ. Activation of GPR30, Gq-mER, ERα, but not ERβ abolished ORL1-mediated antinociception in males and OVX females. E2BSA produced a parallel and significant increase in the phosphorylation of ERK 2 only in OVX females, and pre-treatment with MEK/ERK 1/2 inhibitor, U0126 (10 μg), blocked the mER-mediated abolition of ORL1-mediated antinociception in OVX females. Taken together, the data are consistent with the interpretations that mER activation attenuates ORL1-mediated antinociception through a non-genomic, ERK 2-dependent mechanism in females.

Insights into rapid modulation of neuroplasticity by brain estrogens

Converging evidence from cellular, electrophysiological, anatomic, and behavioral studies suggests that the remodeling of synapse structure and function is a critical component of cognition. This modulation of neuroplasticity can be achieved through the actions of numerous extracellular signals. Moreover, it is thought that it is the integration of different extracellular signals regulation of neuroplasticity that greatly influences cognitive function. One group of signals that exerts powerful effects on multiple neurologic processes is estrogens. Classically, estrogens have been described to exert their effects over a period of hours to days. However, there is now increasing evidence that estrogens can rapidly influence multiple behaviors, including those that require forebrain neural circuitry. Moreover, these effects are found in both sexes. Critically, it is now emerging that the modulation of cognition by rapid estrogenic signaling is achieved by activation of specific signaling cascades and regulation of synapse structure and function, cumulating in the rewiring of neural circuits. The importance of understanding the rapid effects of estrogens on forebrain function and circuitry is further emphasized as investigations continue to consider the potential of estrogenic-based therapies for neuropathologies. This review focuses on how estrogens can rapidly influence cognition and the emerging mechanisms that underlie these effects. We discuss the potential sources and the biosynthesis of estrogens within the brain and the consequences of rapid estrogenic-signaling on the remodeling of neural circuits. Furthermore, we argue that estrogens act via distinct signaling pathways to modulate synapse structure and function in a manner that may vary with cell type, developmental stage, and sex. Finally, we present a model in which the coordination of rapid estrogenic-signaling and activity-dependent stimuli can result in long-lasting changes in neural circuits, contributing to cognition, with potential relevance for the development of novel estrogenic-based therapies for neurodevelopmental or neurodegenerative disorders.

Estrogen replacement therapy and asthma

A growing body of clinical and experimental evidence indicates that female sex hormones, particularly estrogen, have significant effects on normal airway function as well as on respiratory disorders, such as asthma. These effects are very complex and are exerted at several levels, directly on airway reactivity or indirectly through regulation of the immune and inflammatory responses in the lung. They can have relevant clinical implications not only according to the phases of the reproductive life in women, but also in relation to the therapeutical administration of estrogen, as in the case of menopausal hormone therapy. Clinical evidence suggests that administration of estrogen to menopausal women is associated with increased rates of newly diagnosed asthma. Conversely, functional studies show that estrogen can improve objective indexes of respiratory functionality.

Molecular effects of ER alpha- and beta-selective agonists on regulation of energy homeostasis in obese female Wistar rats

The molecular mechanisms underlying the effects of selective ER subtype activation on lipogenesis, adipogenesis, lipid utilization and storage as well as glucose metabolism are currently largely unknown and were analyzed in female OVX Wistar rats on a high-fat diet. Rats received estradiol (E2), ER subtype-selective agonists (Alpha and Beta), and genistein (Gen) for 10 weeks. In adipose tissue, treatment with E2, Alpha, and Beta significantly decreased lipogenic (SREBP-1c, FAS) and adipogenic genes (LPL, PPAR gamma). In liver and skeletal muscle of E2-, Alpha-, Beta-, and Gen-treated animals, lipogenesis and triglyceride accumulation were significantly reduced. Increased hepatic and muscular PPAR gamma mRNA expression was observed in untreated, Beta- and Gen-treated animals, which correlates with increased hepatic glucose uptake. However, only untreated animals showed impaired insulin sensitivity compared to all other groups. Therefore, PPAR gamma up-regulation in untreated animals suggests a compensatory mechanism, probably due to increased triglyceride accumulation in non-adipose tissues. Beta- and Gen-treated animals may benefit from the anabolic potency of ER beta that ameliorates lipid and glucose utilization in muscle. Activation of either ER subtype reduces fat enrichment and improves insulin sensitivity. Depending on the investigated tissue, different molecular pathways seem to be involved.

In silico methods in the discovery of endocrine disrupting chemicals

The prevalence of sex hormone-dependent cancers, reproductive problems, obesity, and cardiovascular complications has risen especially in the Western world. It has been suggested, that the exposure to various endocrine disrupting chemicals (EDCs) contributes to the development and progression of these diseases. EDCs can interfere with various proteins: nuclear steroid hormone receptors, such as estrogen-, androgen-, glucocorticoid- and mineralocorticoid receptors (ER, AR, GR, MR), and enzymes that are involved in steroid hormone synthesis and metabolism, for example hydroxysteroid dehydrogenases (HSDs). Numerous chemicals are known as endocrine disruptors. However, the mechanism of action for most of these EDCs is still unknown. It is exhaustive and time consuming to test in vitro all chemicals - potential EDCs - used in industry, agriculture or as food preservatives against their effects on the endocrine system. Computational methods, such as virtual screening, quantitative structure activity relationships and docking, are already well recognized and used in drug development. The same methods could also aid the research on EDCs. So far, the computational methods in the search of EDCs have been retrospective. There are, however, some prospective studies reporting the use of in silico methods: five studies reporting the identification of previously unknown 17β-HSD3 inhibitors, MR agonists, and ER antagonists/agonists. This review provides an overview of case studies and in silico methods that are used in the search of EDCs. This article is part of a Special Issue entitled 'CSR 2013'.

Sex differences in the physiology of eating

Hypothalamic-pituitary-gonadal (HPG) axis function fundamentally affects the physiology of eating. We review sex differences in the physiological and pathophysiological controls of amounts eaten in rats, mice, monkeys, and humans. These controls result from interactions among genetic effects, organizational effects of reproductive hormones (i.e., permanent early developmental effects), and activational effects of these hormones (i.e., effects dependent on hormone levels). Male-female sex differences in the physiology of eating involve both organizational and activational effects of androgens and estrogens. An activational effect of estrogens decreases eating 1) during the periovulatory period of the ovarian cycle in rats, mice, monkeys, and women and 2) tonically between puberty and reproductive senescence or ovariectomy in rats and monkeys, sometimes in mice, and possibly in women. Estrogens acting on estrogen receptor-α (ERα) in the caudal medial nucleus of the solitary tract appear to mediate these effects in rats. Androgens, prolactin, and other reproductive hormones also affect eating in rats. Sex differences in eating are mediated by alterations in orosensory capacity and hedonics, gastric mechanoreception, ghrelin, CCK, glucagon-like peptide-1 (GLP-1), glucagon, insulin, amylin, apolipoprotein A-IV, fatty-acid oxidation, and leptin. The control of eating by central neurochemical signaling via serotonin, MSH, neuropeptide Y, Agouti-related peptide (AgRP), melanin-concentrating hormone, and dopamine is modulated by HPG function. Finally, sex differences in the physiology of eating may contribute to human obesity, anorexia nervosa, and binge eating. The variety and physiological importance of what has been learned so far warrant intensifying basic, translational, and clinical research on sex differences in eating.

Cyclin D1 determines estrogen signaling in the mammary gland in vivo

The CCND1 gene, which is frequently overexpressed in cancers, encodes the regulatory subunit of a holoenzyme that phosphorylates the retinoblastoma protein. Although it is known that cyclin D1 regulates estrogen receptor (ER)α transactivation using heterologous reporter systems, the in vivo biological significance of cyclin D1 to estrogen-dependent signaling, and the molecular mechanisms by which cyclin D1 is involved, are yet to be elucidated. Herein, genome-wide expression profiling conducted of 17β-estradiol-treated castrated virgin mice deleted of the Ccnd1 gene demonstrated that cyclin D1 determines estrogen-dependent gene expression for 88% of estrogen-responsive genes in vivo. In addition, expression profiling of 17β-estradiol-stimulated cyclin D1 small interfering RNA treated MCF7 cells shows cyclin D1 is required for estrogen-mediated gene expression in vitro. Genome-wide chromatin immunoprecipitation-Seq analysis revealed a cyclin D1-DNA bound form associated with genes that were regulated by estrogen in a cyclin D1-dependent manner. The cyclin D1-dependent estrogen signaling pathways identified in vivo were highly enriched for extracellular membrane-associated growth factor receptors (epidermal growth factor receptor, ErbB3, and EphB3) and their ligands (amphiregulin, encoded by AREG gene), and matrix metalloproteinase. The AREG protein, a pivotal ligand for epidermal growth factor receptors to promote cellular proliferation, was induced by cyclin D1 via the AREG promoter. Chromatin immunoprecipitation analysis demonstrated the recruitment of cyclin D1 to the breast cancer 1 (Brca1)/ERα binding site of the Areg gene. Cyclin D1 genetic deletion demonstrated the in vivo requirement for cyclin D1 in assembling the estrogen-dependent amplified in breast cancer 1-associated multiprotein complex. The current studies define a requirement for cyclin D1 in estrogen-dependent signaling modules governing growth factor receptor and ligand expression in vivo and reveal a noncanonical function of cyclin D1 at ERα target gene promoters. Cyclin D1 mediates the convergence of ERα and growth factor signaling at a common cis-element of growth factor genes.

Bisphenol A at concentrations relevant to human exposure enhances histamine and cysteinyl leukotriene release from bone marrow-derived mast cells

Bisphenol A (BPA), a monomer of polycarbonate plastics and epoxide resin, acts as an endocrine-active compound and has been shown to enhance the inflammatory response to allergen challenge. Previous reports in rodents have demonstrated that perinatal BPA exposure alters airway inflammation following sensitization and challenge to ovalbumin in juvenile and adult offspring. Additionally, a high concentration of BPA has been shown to enhance mediator release in mast cell lines. This study aimed to determine if short-term BPA exposure, at levels relevant to human exposure, enhances mast cell release of histamine and cysteinyl leukotrienes (CysLTs). Primary murine bone marrow-derived mast cells (BMMC) produced from the femurs of female C57BL/6 mice were stimulated with BPA or estradiol (E2) in vitro. It was observed that both BPA and E2 increased BMMC histamine release over a range of nanomolar concentrations (1-1000 nM). The estrogen receptor (ER) antagonist ICI 182,780 partially blocked the ability of E2, but not BPA, to elevate histamine release. BPA also increased CysLT release, which was not abrogated by ER inhibition. It was also observed that the ability of BPA to enhance histamine and CysLT release was inhibited by blocking the extracellular signal-regulated kinase (ERK) pathway with U0126 or by chelating extracellular calcium (Ca(2+)) using EGTA. In summary, these experiments are the first to demonstrate that acute BPA exposure enhances mast cell histamine and CysLT release in vitro--an effect that is not dependent on an ER-mediated mechanism. Instead, BPA-induced mast cell histamine and CysLT release may be mediated, in part, by the ERK pathway and extracellular Ca(2+) concentrations. These data suggest that exposure to BPA at levels relevant to human exposure may provoke an acute inflammatory response in atopic individuals via enhanced mast cell activation.

Interaction of JAK with steroid receptor function

The function of steroid receptors is not only regulated by steroid hormones, but also by multiple cellular signaling cascades activated by membrane-bound receptors which are stimulated by growth factors or cytokines. Cross-talk between JAK and steroid receptors plays a central role in the regulation of a multitude of physiological processes and aberrant signaling is involved in the development of numerous diseases including cancer. In this review we provide a brief summary of the knowledge of interactions between JAK and the function of steroid receptors in normal cells and tissues and in diseases.

Evidence for gating roles of protein kinase A and protein kinase C in estradiol-induced luteinizing hormone receptor (lhcgr) expression in zebrafish ovarian follicle cells

Estradiol (E2) stimulates luteinizing hormone receptor (lhcgr) expression in zebrafish follicle cells via nuclear estrogen receptors (nERs) that are likely expressed on the membrane, and lhcgr responds to E2 in a biphasic manner during 24-h treatment. These observations raise an interesting question on the signaling mechanism underlying E2 regulation, in particular the biphasic response of lhcgr expression. In the present study, we demonstrated that E2 regulation of lhcgr was significantly influenced by the activity of cAMP-PKA pathway. Activation of cAMP-PKA pathway by forskolin or db-cAMP suppressed E2-stimulated lhcgr expression in short-term (3 h) but enhanced its effect in long-term (24 h), suggesting differential roles of PKA at these two phases of lhcgr response. PKA inhibitor H89 showed reversed effects. In contrast, PKC pathway had consistent permissive effect on E2-induced lhcgr expression as evidenced by strong inhibition of E2 effect by PKC inhibitors GF109203X and Ro-31-8220 at both 3 and 24 h. One of the mechanisms by which PKA and PKC gated E2 effect might be through regulating nERs, particularly esr2a. Despite the strong influence of PKA and PKC, our data did not suggest direct mediating roles for these two pathways in E2 stimulation of lhcgr expression; yet they likely play critical gating roles in E2 signal transduction. As a follow-up study to our previous report on E2 regulation of gonadotropin receptors in the zebrafish ovary, the present study provides further evidence for the involvement of classical intracellular signal transduction pathways in E2 stimulation of lhcgr expression in the follicle cells.

Targeted genome-wide methylation and gene expression analyses reveal signaling pathways involved in ovarian dysfunction after developmental EDC exposure in rats

Transient exposure to methoxychlor (MXC), an environmental endocrine-disrupting chemical, during fetal and neonatal stages causes ovarian dysfunction in pubertal, adult, and aging animals. Adult animals have reduced number of ovulations and abnormal follicular composition associated with altered gene expression and DNA methylation patterns. To test the hypothesis that the ovarian epigenomic changes induced by MXC are detectable following the exposure period, leading to altered gene expression by adulthood, we conducted a targeted genome-wide methylation study using Nimblegen 3x720K CpG Island Plus RefSeq Promoter Arrays. Control (vehicle), low-dose MXC (20 μg/kg/day), or high-dose MXC (100 mg/kg/day) treatments were administered between Embryonic Day 19 and Postnatal Day (PND) 7. Ovaries were collected at PND 7 immediately after exposure or at adulthood, PND 60. Array hybridizations were conducted with genomic DNA after methylated DNA immunoprecipitation and the array data were analyzed. DNA methylation events were functionally annotated, and candidate loci common to all the treatments or unique to some treatments were identified. Specific loci encoding signaling molecules such as the regulatory subunit p85 of phosphoinositide-3-kinase, insulin-like growth factor-1 receptor, Harvey rat sarcoma viral oncogene, insulin receptor, and forkhead box protein O3 were identified to be hypermethylated in MXC-treated ovaries at PND 7 and/or PND 60. Examination of gene expression changes with TaqMan low-density arrays revealed that nearly 25% of the genes that were assayed were downregulated. These data demonstrate that key molecules in specific signaling pathways such as PTEN signaling, IGF-1 signaling, or rapid estrogen signaling are epigenetically altered in MXC-exposed ovaries, which is associated with ovarian dysfunction and female infertility.

Effects of estradiol on the endocytic transport of vitamin D carrier protein in hepatocytes

BACKGROUND

The possible modulation of receptor-mediated endocytosis (RME) by sex steroids is not well understood, especially in terms of the different receptor-ligand systems and cell types that may exhibit such regulation. The main objective of the current study was to examine the short-term effects of 17β-estradiol (E2) on RME of an extracellular carrier protein for calciferols, vitamin D-binding protein (DBP).

METHODS

Murine male and female primary hepatocytes were treated for 30min in the absence (controls) or presence of Ε2 (1μM). Labeled DBP was then added, and its endocytosis was measured after an incubation of 10min at 37°C using standard ELISA techniques. To obtain further insight into potential molecular mechanisms, fulvestrant and 17α-ethinyl estradiol (EE) were also analyzed. And as part of comparative analyses, a second nutrient carrier protein, vitamin A-binding protein (RBP), was also analyzed.

RESULTS

The results provide the first evidence for an estradiol-dependent stimulation of DBP endocytosis (p<0.05 relative to controls without Ε2). This stimulation, however, was only observed in female hepatocytes. Uptake of RBP was enhanced to a similar extent as DBP by estradiol. In normal (non-estradiol treated) male and female hepatocytes such changes in DBP or RBP endocytosis were not observed. Both fulvestrant and EE exhibited a significant (p<0.05), but incomplete, inhibition of Ε2-dependent stimulation of endocytosis.

CONCLUSIONS

The results provide novel evidence for Ε2 effects on endocytic transport; and for gender-related differences in E2-enhanced transport. These Ε2 effects may be partly dependent on estrogen receptors; but possible, additional or alternative mechanisms are also proposed.

GENERAL SIGNIFICANCE

Endocytic transport is a fundamental function whose regulation has implications for cell signaling, growth, survival, differentiation, and death. This study helps delineate a possible endocrine regulatory pathway involving modulation of endocytosis by a steroid hormone. It also provides a potential, new relation between different hormonal regulators, e.g., estradiol effects on cellular assimilation of calciferols.

17β-Estradiol and 17α-estradiol induce rapid changes in cytoskeletal organization in cultured oligodendrocytes

Dramatic changes in the cytoskeleton and the morphology of oligodendrocytes (OLs) occur during various stages of the myelination process. OLs in culture produce large membrane sheets containing cytoskeletal veins of microtubules and actin filaments. We recently showed that estrogen receptors (ER) related to ERα/β were expressed in the membrane sheets of mature OLs in culture. Ligation of these or other membrane ERs in OLs with both 17β- and 17α-estradiol mediated rapid non-genomic signaling. Here, we show that estrogens also mediate rapid non-genomic remodeling of the cytoskeleton in mature OLs in culture. 17β-Estradiol caused a rapid loss of microtubules and the actin cytoskeleton in the OL membrane sheets. It also increased phosphorylation of the actin filament-severing protein cofilin, thus inactivating it. Staining for actin barbed ends with rhodamine-actin showed that it decreased the amount of actin barbed ends. 17α-Estradiol, on the other hand, increased the percentage of cells with abundant staining of actin filaments and actin barbed ends, suggesting that it stabilized and/or increased the dynamics of the actin cytoskeleton. The specific ERα and ERβ agonists, 4,4',4″-(4-propyl-(1H)-pyrazole-1,3,5-triyl) trisphenol (PPT) and diarylpropionitrile 2,3-bis(4-hydroxy-phenyl)-propionitrile (DPN), respectively, also caused the rapid phosphorylation of cofilin. Estrogen-induced phosphorylation of cofilin was inhibited by Y-27632, a specific inhibitor of the Rho-associated protein serine/threonine kinase (ROCK). The Rho/ROCK/cofilin pathway is therefore implicated in actin rearrangement via estrogen ligation of membrane ERs, which may include forms of ERα and ERβ. These results indicate a role for estrogens in modulation of the cytoskeleton in mature OLs, and thus in various processes required for myelinogenesis.

DHEA metabolites activate estrogen receptors alpha and beta

Dehydroepiandrosterone (DHEA) levels were reported to associate with increased breast cancer risk in postmenopausal women, but some carcinogen-induced rat mammary tumor studies question this claim. The purpose of this study was to determine how DHEA and its metabolites affect estrogen receptors α or β (ERα or ERβ)-regulated gene transcription and cell proliferation. In transiently transfected HEK-293 cells, androstenediol, DHEA, and DHEA-S activated ERα. In ERβ transfected HepG2 cells, androstenedione, DHEA, androstenediol, and 7-oxo DHEA stimulated reporter activity. ER antagonists ICI 182,780 (fulvestrant) and 4-hydroxytamoxifen, general P450 inhibitor miconazole, and aromatase inhibitor exemestane inhibited activation by DHEA or metabolites in transfected cells. ERβ-selective antagonist R,R-THC (R,R-cis-diethyl tetrahydrochrysene) inhibited DHEA and DHEA metabolite transcriptional activity in ERβ-transfected cells. Expression of endogenous estrogen-regulated genes: pS2, progesterone receptor, cathepsin D1, and nuclear respiratory factor-1 was increased by DHEA and its metabolites in an ER-subtype, gene, and cell-specific manner. DHEA metabolites, but not DHEA, competed with 17β-estradiol for ERα and ERβ binding and stimulated MCF-7 cell proliferation, demonstrating that DHEA metabolites interact directly with ERα and ERβin vitro, modulating estrogen target genes in vivo.

Enhanced expression of G-protein coupled estrogen receptor (GPER/GPR30) in lung cancer

Background

G-protein-coupled estrogen receptor (GPER/GPR30) was reported to bind 17β-estradiol (E₂), tamoxifen, and ICI 182,780 (fulvestrant) and promotes activation of epidermal growth factor receptor (EGFR)-mediated signaling in breast, endometrial and thyroid cancer cells. Although lung adenocarcinomas express estrogen receptors α and β (ERα and ERβ), the expression of GPER in lung cancer has not been investigated. The purpose of this study was to examine the expression of GPER in lung cancer.

Methods

The expression patterns of GPER in various lung cancer lines and lung tumors were investigated using standard quantitative real time PCR (at mRNA levels), Western blot and immunohistochemistry (IHC) methods (at protein levels). The expression of GPER was scored and the pairwise comparisons (cancer vs adjacent tissues as well as cancer vs normal lung tissues) were performed.

Results

Analysis by real-time PCR and Western blotting revealed a significantly higher expression of GPER at both mRNA and protein levels in human non small cell lung cancer cell (NSCLC) lines relative to immortalized normal lung bronchial epithelial cells (HBECs). The virally immortalized human small airway epithelial cell line HPL1D showed higher expression than HBECs and similar expression to NSCLC cells. Immunohistochemical analysis of tissue sections of murine lung adenomas as well as human lung adenocarcinomas, squamous cell carcinomas and non-small cell lung carcinomas showed consistently higher expression of GPER in the tumor relative to the surrounding non-tumor tissue.

Conclusion

The results from this study demonstrate increased GPER expression in lung cancer cells and tumors compared to normal lung. Further evaluation of the function and regulation of GPER will be necessary to determine if GPER is a marker of lung cancer progression.

Mechanisms underlying the interactions between rapid estrogenic and BDNF control of synaptic connectivity

The effects of the steroid hormone 17β-estradiol and the neurotrophin brain-derived neurotrophic factor (BDNF) on neuronal physiology have been well investigated. Numerous studies have demonstrated that each signal can exert powerful influences on the structure and function of synapses, and specifically on dendritic spines, both within short and long time frames. Moreover, it has been suggested that BDNF is required for the long-term, or genomic, actions of 17β-estradiol on dendritic spines, via its ability to regulate the expression of neurotrophins. Here we focus on the acute, or rapid effects, of 17β-estradiol and BDNF, and their ability to activate specific signalling cascades, resulting in alterations in dendritic spine morphology. We first review recent literature describing the mechanisms by which 17β-estradiol activates these pathways, and the resulting alterations in dendritic spine number. We then describe the molecular mechanisms underlying acute modulation of dendritic spine morphology by BDNF. Finally, we consider how this new evidence may suggest that the temporal interactions of 17β-estradiol and BDNF can occur more rapidly than previously reported. Building on these new data, we propose a novel model for the interactions of this steroid and neurotrophin, whereby rapid, non-genomic 17β-estradiol and acute BDNF signal in a co-operative manner, resulting in dendritic spine formation and subsequent stabilization in support of synapse and circuit plasticity. This extended hypothesis suggests an additional mechanism by which these two signals may modulate dendritic spines in a time-specific manner.

Tuning the properties and functions of 17β-estradiol-polysaccharide conjugates in thin films: impact of sample history

In addition to its role in the regulation of sex-related processes, 17β-estradiol (E2) participates in the prevention and treatment of cardiovascular diseases via nongenomic pathways mediated by estrogen receptors (ER-α) located in the cell membrane. To achieve specific nongenomic activity of E2, we linked E2 (4.4 mol %) to chitosan-phosphorylcholine (CH-PC) (20 mol % PC). Injections of ER-α solutions (5 to 100 nmol L(-1)) over rehydrated CH-PC-E2 thin films led to permanent adsorption of ER-α to the film surface, as detected by quartz crystal microbalance with dissipation (QCM-D). However, ER-α did not bind onto CH-PC-E2 films formed in situ and never dried. X-ray photoelectron spectroscopy (XPS) analysis of spin-cast CH-PC-E2 films revealed significant E2 enrichment of the topmost section of the film, attributed to the preferential migration of E2 toward the film/air interface upon drying. Mechanical analysis of CH-PC-E2 films in the frequency domain probed by QCM-D indicated that rehydrated films behave as an entangled network with junction points formed by self-assembly of hydrophobic E2 moieties and by ion pairing among PC groups, whereas films formed in situ are entangled polymer solutions with temporary junctions. The structural analysis presented offers useful guidelines for the study of amphiphilic biomacromolecules designed for therapeutic use as thin films.

Tyrosine phosphorylation of estradiol receptor by Src regulates its hormone-dependent nuclear export and cell cycle progression in breast cancer cells

We report that in breast cancer cells, tyrosine phosphorylation of the estradiol receptor alpha (ERalpha) by Src regulates cytoplasmic localization of the receptor and DNA synthesis. Inhibition of Src or use of a peptide mimicking the ERalpha p-Tyr537 sequence abolishes ERalpha tyrosine phosphorylation and traps the receptor in nuclei of estradiol-treated MCF-7 cells. An ERalpha mutant carrying a mutation of Tyr537 to phenylalanine (ER537F) persistently localizes in nuclei of various cell types. In contrast with ERalpha wt, ER537F does not associate with Ran and its interaction with Crm1 is insensitive to estradiol. Thus, independently of estradiol, ER537F is retained in nuclei, where it entangles FKHR-driving cell cycle arrest. Chromatin immunoprecipitation analysis reveals that overexpression of ER537F in breast cancer cells enhances FKHR interaction with cyclin D1 promoter. This mutant also counteracts cell transformation by the activated forms of Src or PI3-K. In conclusion, in addition to regulating receptor localization, ERalpha phosphorylation by Src is required for hormone responsiveness of DNA synthesis in breast cancer cells.

The organizational and aromatization hypotheses apply to rapid, nonclassical hormone action: neonatal masculinization eliminates rapid estradiol action in female hippocampal neurons

Early exposure to the steroid sex hormone testosterone and its estrogen metabolite estradiol masculinize neural tissue during a developmental critical period. Many aspects of neuron anatomy and physiology are permanently altered, including later sensitivity to estradiol. Although it is well established that early hormone exposure alters neuronal responsiveness regarding classical estradiol actions (i.e. acting via nuclear estrogen receptors), it has not yet been determined whether it also alters neuronal processing of nonclassical estrogen receptor signaling, including the actions of membrane-associated estrogen receptors. Hence, we tested whether membrane estrogen receptor regulation of cAMP response element binding protein (CREB) phosphorylation observed in female (but not male) hippocampal pyramidal neurons is due to the lack of androgen and/or estrogen exposure in females during this critical period. Female rat neonates on postnatal d 0 and 1 were systemically injected with one of four compounds: vehicle, testosterone, the nonaromatizable androgen dihydrotestosterone, or estradiol. On postnatal d 2, primary hippocampal neuron cultures were generated from these animals. After 8-9 d in culture, we assessed whether estradiol affected CREB phosphorylation. Neurons from female neonates exposed to testosterone lacked estradiol signaling to CREB. In contrast, dihydrotestosterone injections of female neonates did not disrupt estradiol regulation of CREB. Estradiol injections of female neonates, however, eliminated estradiol signaling to CREB. These findings indicate that testosterone aromatization to estradiol leads to a masculinization/defeminization process whereby hippocampal neurons fail to exhibit rapid estradiol signaling to CREB. Broadly, these findings extend the organizational and aromatization hypotheses to rapid, nonclassical hormone action.

Rapid control of male typical behaviors by brain-derived estrogens

Beside their genomic mode of action, estrogens also activate a variety of cellular signaling pathways through non-genomic mechanisms. Until recently, little was known regarding the functional significance of such actions in males and the mechanisms that control local estrogen concentration with a spatial and time resolution compatible with these non-genomic actions had rarely been examined. Here, we review evidence that estrogens rapidly modulate a variety of behaviors in male vertebrates. Then, we present in vitro work supporting the existence of a control mechanism of local brain estrogen synthesis by aromatase along with in vivo evidence that rapid changes in aromatase activity also occur in a region-specific manner in response to changes in the social or environmental context. Finally, we suggest that the brain estrogen provision may also play a significant role in females. Together these data bolster the hypothesis that brain-derived estrogens should be considered as neuromodulators.

Structural and mechanistic insights into bisphenols action provide guidelines for risk assessment and discovery of bisphenol A substitutes

Bisphenol A (BPA) is an industrial compound and a well known endocrine-disrupting chemical with estrogenic activity. The widespread exposure of individuals to BPA is suspected to affect a variety of physiological functions, including reproduction, development, and metabolism. Here we report that the mechanisms by which BPA and two congeners, bisphenol AF and bisphenol C (BPC), bind to and activate estrogen receptors (ER) α and β differ from that used by 17β-estradiol. We show that bisphenols act as partial agonists of ERs by activating the N-terminal activation function 1 regardless of their effect on the C-terminal activation function 2, which ranges from weak agonism (with BPA) to antagonism (with BPC). Crystallographic analysis of the interaction between bisphenols and ERs reveals two discrete binding modes, reflecting the different activities of compounds on ERs. BPA and 17β-estradiol bind to ERs in a similar fashion, whereas, with a phenol ring pointing toward the activation helix H12, the orientation of BPC accounts for the marked antagonist character of this compound. Based on structural data, we developed a protocol for in silico evaluation of the interaction between bisphenols and ERs or other members of the nuclear hormone receptor family, such as estrogen-related receptor γ and androgen receptor, which are two known main targets of bisphenols. Overall, this study provides a wealth of tools and information that could be used for the development of BPA substitutes devoid of nuclear hormone receptor-mediated activity and more generally for environmental risk assessment.

Dissecting rapid estrogen signaling with conjugates

Hypothesizing that rapid estrogen signaling could be modulated from different estrogen receptors with unique localization patterns, a number of groups have attempted to design drug conjugates that target or restrict compounds to specific subcellular compartments. This article will briefly discuss the history of using conjugates to dissect rapid estrogen signaling and different strategies to attempt to target estrogens and antiestrogens to different locations. It will also detail some of the potential issues that can arise with different types of conjugates, using examples drawn from the authors' own work.

Transcriptomine, a web resource for nuclear receptor signaling transcriptomes

The nuclear receptor (NR) superfamily of ligand-regulated transcription factors directs ligand- and tissue-specific transcriptomes in myriad developmental, metabolic, immunological, and reproductive processes. The NR signaling field has generated a wealth of genome-wide expression data points, but due to deficits in their accessibility, annotation, and integration, the full potential of these studies has not yet been realized. We searched public gene expression databases and MEDLINE for global transcriptomic datasets relevant to NRs, their ligands, and coregulators. We carried out extensive, deep reannotation of the datasets using controlled vocabularies for RNA Source and regulating molecule and resolved disparate gene identifiers to official gene symbols to facilitate comparison of fold changes and their significance across multiple datasets. We assembled these data points into a database, Transcriptomine (http://www.nursa.org/transcriptomine), that allows for multiple, menu-driven querying strategies of this transcriptomic "superdataset," including single and multiple genes, Gene Ontology terms, disease terms, and uploaded custom gene lists. Experimental variables such as regulating molecule, RNA Source, as well as fold-change and P value cutoff values can be modified, and full data records can be either browsed or downloaded for downstream analysis. We demonstrate the utility of Transcriptomine as a hypothesis generation and validation tool using in silico and experimental use cases. Our resource empowers users to instantly and routinely mine the collective biology of millions of previously disparate transcriptomic data points. By incorporating future transcriptome-wide datasets in the NR signaling field, we anticipate Transcriptomine developing into a powerful resource for the NR- and other signal transduction research communities.