Ligand-independent Activation of Steroid Receptors: New Roles for Old Players

Endocrine disrupting chemicals (EDCs) and sex steroid receptors

Sex-steroid receptors (SSRs) are essential mediators of estrogen, progestin, and androgen signaling that are critical in vast aspects of human development and multi-organ homeostasis. Dysregulation of SSR function has been implicated in numerous pathologies including cancers, obesity, Type II diabetes mellitus, neuroendocrine disorders, cardiovascular disease, hyperlipidemia, male and female infertility, and other reproductive disorders. Endocrine disrupting chemicals (EDCs) modulate SSR function in a wide variety of cell and tissues. There exists strong experimental, clinical, and epidemiological evidence that engagement of EDCs with SSRs may disrupt endogenous hormone signaling leading to physiological abnormalities that may manifest in disease. In this chapter, we discuss the molecular mechanisms by which EDCs interact with estrogen, progestin, and androgen receptors and alter SSR functions in target cells. In addition, the pathological consequences of disruption of SSR action in reproductive and other organs by EDCs is described with an emphasis on underlying mechanisms of receptors dysfunction.

SIRT1 and gynecological malignancies (Review)

Sirtuin 1 (SIRT1), a member of the sirtuin protein family, is a nicotinamide adenine dinucleotide (NAD⁺)-dependent type III histone deacetylase and mono-ADP-ribosyltransferase. SIRT1 can deacetylate histones (H1, H3, and H4) and non-histone proteins, and it is widely involved in various physiological and pathological processes in the body, including metabolism, aging, transcription, DNA damage and repair, apoptosis, cell cycle regulation, inflammation and cancer. Research has shown that SIRT1 is involved in tumorigenesis, tumor metastasis and chemotherapy resistance, but it exerts opposing effects and plays different roles in different pathogenic processes. Recent studies have demonstrated that SIRT1 may be implicated in the pathogenesis, development, treatment and prognosis of tumors; however, its role in gynecological tumors remains elusive. The aim of the present review was to summarize the pathogenic roles of SIRT1 in cancer, and to provide what is, to the best of our knowledge, the first review of recent advances involving SIRT1 in cervical cancer, endometrial cancer (EC) and ovarian cancer (OC). In addition, the critical research gaps regarding SIRT1, particularly its potential involvement in the concurrence of EC and cervical cancer and its antagonistic effect against poly(ADP-ribose) polymerase inhibitors in OC, were highlighted.

17β-estradiol binding to ERα promotes the progression of prolactinoma through estrogen-response element-induced CaBP-9k up-regulation

17β-estradiol (E2) is considered to be an important instigator of prolactinoma, and can positively regulate the expression of calbindin-D9k (CaBP-9k) which contains an estrogen responsive element (ERE) via estrogen receptors (ERs). However, the detailed mechanism of E2 in promoting CaBP-9k expression and their roles in prolactinoma progression remain unclear. Here, we aimed to characterize it. The luciferase gene reporter assay with luc-ERE transfection showed that E2 treatment significantly enhanced the transcriptional level of CaBP-9k, whereas CaBP-9k activity was reduced when GH3 and MMQ cells were treated with AZD9496, an antagonist of ERα. E2 treatment increased the protein expressions of CaBP-9k and ERα but not ERβ, whereas this effect was also abolished when cells were treated with AZD9496. Besides, immunoprecipitation (IP) and immunofluorescence assays demonstrated that CaBP-9k could directly interact with ERα not ERβ, and Chromatin IP (ChIP) assay showed that ERα could bind to ERE of the CaBP-9k promoter. Moreover, cell counting kit-8 (CCK-8) and flow cytometry assays showed that E2 treatment significantly enhanced cell viability and inhibited cell apoptosis, but these effects were all abolished when ERα was down-regulated by short hairpin RNA (shRNA) or inhibited by AZD9496, as well as CaBP-9K suppression in both GH3 and MMQ cell lines. Taken together, these findings indicated that E2 stimulation promoted prolactin cell proliferation and inhibited cell apoptosis through ERα-induced CaBP-9k up-regulation, which then accelerated the advanced progression of prolactinoma.

IFI27/ISG12 Downregulates Estrogen Receptor α Transactivation by Facilitating Its Interaction With CRM1/XPO1 in Breast Cancer Cells

The estrogen receptor alpha (ERα) is a ligand-activated transcription factor whose activity is modulated by its interaction with multiple protein complexes. In this work, we have identified the protein interferon alpha inducible protein 27 (IFI27/ISG12) as a novel ERα-associated protein. IFI27/ISG12 transcription is regulated by interferon and estradiol and its overexpression is associated to reduced overall survival in ER+ breast cancer patients but its function in mammary gland tissue remains elusive. In this study we showed that overexpression of IFI27/ISG12 in breast cancer cells attenuates ERα transactivation activity and the expression of ERα-dependent genes. Our results demonstrated that IFI27/ISG12 overexpression in MCF-7 cells reduced their proliferation rate in 2-D and 3-D cell culture assays and impaired their ability to migrate in a wound-healing assay. We show that IFI27/ISG12 downregulation of ERα transactivation activity is mediated by its ability to facilitate the interaction between ERα and CRM1/XPO1 that mediates the nuclear export of large macromolecules to the cytoplasm. IFI27/ISG12 overexpression was shown to impair the estradiol-dependent proliferation and tamoxifen-induced apoptosis in breast cancer cells. Our results suggest that IFI27/ISG12 may be an important factor in regulating ERα activity in breast cancer cells by modifying its nuclear versus cytoplasmic protein levels. We propose that IFI27/ISG12 may be a potential target of future strategies to control the growth and proliferation of ERα-positive breast cancer tumors.

Sexual Behavior and Synaptic Plasticity

Although sex drive is present in many animal species, sexual behavior is not static and, like many other behaviors, can be modified by experience. This modification relies on synaptic plasticity, a sophisticated mechanism through which neurons change how they process a given stimulus, and the neurophysiological basis of learning. This review addresses the main plastic effects of steroid sex hormones in the central nervous system (CNS) and the effects of sexual experience on the CNS, including effects on neurogenesis, intracellular signaling, gene expression, and changes in dendritic spines, as well as behavioral changes.

A Model of Glucocorticoid Receptor Interaction With Coregulators Predicts Transcriptional Regulation of Target Genes

Regulatory factors that control gene transcription in multicellular organisms are assembled in multicomponent complexes by combinatorial interactions. In this context, nuclear receptors provide well-characterized and physiologically relevant systems to study ligand-induced transcription resulting from the integration of cellular and genomic information in a cell- and gene-specific manner. Here, we developed a mathematical model describing the interactions between the glucocorticoid receptor (GR) and other components of a multifactorial regulatory complex controlling the transcription of GR-target genes, such as coregulator peptides. We support the validity of the model in relation to gene-specific GR transactivation with gene transcription data from A549 cells and in vitro real time quantification of coregulator-GR interactions. The model accurately describes and helps to interpret ligand-specific and gene-specific transcriptional regulation by the GR. The comprehensive character of the model allows future insight into the function and relative contribution of the molecular species proposed in ligand- and gene-specific transcriptional regulation.

SIRT1 and Estrogen Signaling Cooperation for Breast Cancer Onset and Progression

Breast cancer remains a significant female mortality cause. It constitutes a multifactorial disease for which research on environmental factors offers little help in predicting onset or progression. The pursuit for its foundations by analyzing hormonal changes as a motive for disease development, indicates that increased exposure to estrogens associates with increased risk. A prevalent number of breast cancer cases show dependence on the increased activity of the classic nuclear estrogen receptor (ER) for cell proliferation and survival. SIRT1 is a Type III histone deacetylase which is receiving increasing attention due to its ability to perform activities over relevant non-histone proteins and transcription factors. Interestingly, concomitant SIRT1 overexpression is commonly found in ER-positive breast cancer cases. Both proteins had been shown to directly interact, in a process related to altered intracellular signaling and aberrant transcription, then promoting tumor progression. Moreover, SIRT1 activities had been also linked to estrogenic effects through interaction with the G-protein coupled membrane bound estrogen receptor (GPER). This work aims to summarize present knowledge on the interplay between SIRT1 and ER/GPER for breast cancer onset and progression. Lastly, evidences on the ability of SIRT1 to interact with TGFß signaling, a concurrent pathway significantly involved in breast cancer progression, are reported. The potential of this research field for the development of innovative strategies in the assessment of orphan breast cancer subtypes, such as triple negative breast cancer (TNBC), is discussed.

The crossroads of breast cancer progression: insights into the modulation of major signaling pathways

Cancer is the disease with highest public health impact in developed countries. Particularly, breast cancer has the highest incidence in women worldwide and the fifth highest mortality in the globe, imposing a significant social and economic burden to society. The disease has a complex heterogeneous etiology, being associated with several risk factors that range from lifestyle to age and family history. Breast cancer is usually classified according to the site of tumor occurrence and gene expression profiling. Although mutations in a few key genes, such as BRCA1 and BRCA2, are associated with high breast cancer risk, the large majority of breast cancer cases are related to mutated genes of low penetrance, which are frequently altered in the whole population. Therefore, understanding the molecular basis of breast cancer, including the several deregulated genes and related pathways linked to this pathology, is essential to ensure advances in early tumor detection and prevention. In this review, we outline key cellular pathways whose deregulation has been associated with breast cancer, leading to alterations in cell proliferation, apoptosis, and the delicate hormonal balance of breast tissue cells. Therefore, here we describe some potential breast cancer-related nodes and signaling concepts linked to the disease, which can be positively translated into novel therapeutic approaches and predictive biomarkers.

Effects of estradiol, estrogen receptor subtype-selective agonists and genistein on glucose metabolism in leptin resistant female Zucker diabetic fatty (ZDF) rats

The leptin resistant Zucker diabetic fatty (ZDF) rats are hyperphagic and become obese, but whereas the males develop type 2 diabetes mellitus (T2DM), the females remain euglycaemic. As estrogen deficiency is known to increase the risk of developing T2DM, we evaluated the role of ER subtypes alpha and beta in the development of glucose tolerance in leptin resistant ovariectomized (OVX) ZDF rats. At least six rats per group were treated with either vehicle (OVX), 17β-estradiol (E2), ER subtype-selective agonists (Alpha and Beta), or genistein (Gen) for 17 weeks. At the end of the treatment period a glucose tolerance assay was performed and the metabolic flux of (13)C-glucose for the E2 group was investigated. OVX ZDF rats treated with E2, Alpha, Beta, and Gen tolerated the glucose significantly better than untreated controls. E2 treatment increased absorbance/flux of (13)C-glucose to metabolic relevant tissues such liver, adipose tissue, gastrocnemius, and soleus muscle. Moreover, whereas Alpha treatment markedly increased mRNA expression of GLUT4 in gastrocnemius muscle, Beta treatment resulted in the largest fiber sizes of the soleus muscle. Treatment with Gen increased both the mRNA expression of GLUT 4 and the fiber sizes in the skeletal muscle. In addition, E2 and Alpha treatment decreased food intake and body weight gain. In summary, estrogen-improved glucose absorption is mediated via different molecular mechanisms: while activation of ER alpha seems to stimulate muscular GLUT4 functionality, activation of ER beta results in a hypertrophy of muscle fibers. In addition, selective activation of ER alpha decreased food intake and body weight gain. Our data further indicate that ER subtype-selective agonists and genistein improve systemic glucose tolerance also in the absence of a functional leptin signaling pathway.

Role of RUNX2 in Breast Carcinogenesis

RUNX2 is a transcription factor playing the major role in osteogenesis, but it can be involved in DNA damage response, which is crucial for cancer transformation. RUNX2 can interact with cell cycle regulators: cyclin-dependent kinases, pRB and p21Cip1 proteins, as well as the master regulator of the cell cycle, the p53 tumor suppressor. RUNX2 is involved in many signaling pathways, including those important for estrogen signaling, which, in turn, are significant for breast carcinogenesis. RUNX2 can promote breast cancer development through Wnt and Tgfβ signaling pathways, especially in estrogen receptor (ER)-negative cases. ERα interacts directly with RUNX2 and regulates its activity. Moreover, the ERα gene has a RUNX2 binding site within its promoter. RUNX2 stimulates the expression of aromatase, an estrogen producing enzyme, increasing the level of estrogens, which in turn stimulate cell proliferation and replication errors, which can be turned into carcinogenic mutations. Exploring the role of RUNX2 in the pathogenesis of breast cancer can lead to revealing new therapeutic targets.

Tristetraprolin represses estrogen receptor α transactivation in breast cancer cells

Estrogen receptor α (ERα) mediates the effects of 17β-estradiol (E2) in normal mammary gland, and it is a key participant in breast cancer tumor development. ERα transactivation activity is mediated by the synergistic interaction of two domains designated AF1 and AF2. The function of AF2 is to recruit coactivator and corepressor proteins that allow ERα to oscillate between the roles of transcriptional activator and repressor. In contrast, the mechanism responsible for AF-1 transcriptional activity is not completely understood. In this study, we identified tristetraproline (TTP) as a novel ERα-associated protein. TTP expression in MCF7 cells repressed ERα transactivation and reduced MCF7 cell proliferation and the ability of the cells to form tumors in a mouse model. We show that TTP transcriptional activity is mediated through its recruitment to the promoter region of ERα target genes and its interaction with histone deacetylases, in particular with HDAC1. TTP expression attenuates the coactivating activity of SRC-1, suggesting that exchange between TTP and other coactivators may play an important role in fine-tuning ERα transactivation. These results indicate that TTP acts as a bona fide ERα corepressor and suggest that this protein may be a contributing factor in the development of E2-dependent tumors in breast cancer.

Does Metformin affect ER, PR, IGF-1R, β-catenin and PAX-2 expression in women with diabetes mellitus and endometrial cancer?

OBJECTIVE

Diabetes mellitus, as a risk factor for endometrial cancer (EC), causes an increase in insulin and IGF-1 concentrations in the blood serum. The increase in insulin and IGF-1 are considered mitogenic factors contributory to cancer development. Studies suggest that metformin has preventive activity, decreasing mortality and the risk of neoplasms. Since estrogen (ER), progesterone (PR) and IGF-1 (IGF-1R) receptor expression and β-catenin and PAX-2 mutations are significant in the development of endometrial cancer, it was decided to study these factors in patients with endometrial cancer and type 2 diabetes mellitus (DM2), and to establish the effects of metformin on their expression.

METHODS

The expression of ER, PR, IGF-1R, β-catenin and PAX-2 have been immunohistochemically investigated in 86 type I endometrial cancer specimens. Patients were grouped according to the presence of DM2 and the type of hypoglycemic treatment administered.

RESULTS

Comparing EC patients with DM2 and normal glycemic status, we found increased IGF-1R expression in women with DM2. A decrease in ER expression was noted in women with EC and DM2 receiving metformin as compared to women treated with insulin (p = 0.004). There was no statistically significant difference in PR, IGF-1R, β-catenin and PAX-2 expression among women receiving metformin and other hypoglycemic treatment.

CONCLUSION

Although epidemiological studies suggest the beneficial role of metformin in many human cancers, there are still few studies confirming its favorable effect on endometrial cancer. Decreased ER expression in patients receiving metformin needs further research to allow evaluation of its clinical significance.

Emerging genomic biomarkers in migraine

Migraine is a debilitating neurovascular condition classified as either migraine with aura or migraine without aura. A significant genetic basis has been implicated in migraine and has probed the role of neurotransmitters, hormones and vascular genes in this disorder. The aim of this review is to highlight the recent genetic discoveries contributing to our understanding of the complex pathogenesis of migraine. The current review will discuss the role of neurotransmitter-related genes in migraine, including the recently identified TRESK and variants of the KCNN3 gene, as well as outlining studies investigating hormone receptor genes, such as ESR1 and PGR, and vascular-related genes, including the MTHFR and NOTCH 3 genes.

ER and PR signaling nodes during mammary gland development

The ovarian hormones estrogen and progesterone orchestrate postnatal mammary gland development and are implicated in breast cancer. Most of our understanding of the molecular mechanisms of estrogen receptor (ER) and progesterone receptor (PR) signaling stems from in vitro studies with hormone receptor-positive cell lines. They have shown that ER and PR regulate gene transcription either by binding to DNA response elements directly or via other transcription factors and recruiting co-regulators. In addition they cross-talk with other signaling pathways through nongenomic mechanisms. Mouse genetics combined with tissue recombination techniques have provided insights about the action of these two hormones in vivo. It has emerged that hormones act on a subset of mammary epithelial cells and relegate biological functions to paracrine factors. With regards to hormonal signaling in breast carcinomas, global gene expression analyses have led to the identification of gene expression signatures that are characteristic of ERα-positive tumors that have stipulated functional studies of hitherto poorly understood transcription factors. Here, we highlight what has been learned about ER and PR signaling nodes in these different systems and attempt to lay out in which way the insights may converge.

Expression of estrogen receptor α and growth factors in human prolactinoma and its correlation with clinical features and gender

BACKGROUND

Many studies demonstrate that growth factors play an important role in the pathogenesis of prolactinoma induced by estrogen. The effects of estrogen are mainly mediated through its nuclear receptor (ERα); however, expression of ERα and growth factors in prolactinoma and healthy pituitary and their relationship remain obscure.

AIM

To obtain new insights regarding the expression differences of these factors and their relationship and to investigate the correlation between gender and clinical features in patients with prolactinoma.

SUBJECTS AND METHODS

A total of 21 human prolactinomas and 6 healthy human pituitaries were examined for mRNA expression of ERα, basic fibroblast growth factor (bFGF), transforming growth factor α (TGFα), TGFβ1, TGFβ3, and TGFβ receptor type II (TGFβRII) by means of real-time PCR. Patient clinical data was also analyzed.

RESULTS

Both PRL level and tumor volume of the male patient group were higher than that of the female patient group. There was a significant correlation between PRL level and tumor volume in the total patient group. Expression of ERα, bFGF, TGFα, and TGFβ3 mRNA levels of the patient group were significantly different from that of the control group. A significant correlation between ERα mRNA levels and PRL levels, tumor volume, TGFβ1 mRNA levels in the total patient group were found.

CONCLUSIONS

PRL level and tumor volume have a significant difference between genders in prolactinoma patients. ERα and some growth factors may be involved in the tumorigenesis of prolactinoma. ERα could potentially be an effective therapy target for treating prolactinoma.

Genetics of menstrual migraine: the molecular evidence

Migraine is considered to be a multifactorial disorder in which genetic, environmental, and, in the case of menstrual and menstrually related migraine, hormonal events influence the phenotype. Certainly, the role of female sex hormones in migraine has been well established, yet the mechanism behind this well-known relationship remains unclear. This review focuses on the potential role of hormonally related genes in migraine, summarizes results of candidate gene studies to date, and discusses challenges and issues involved in interpreting hormone-related gene results. In light of the molecular evidence presented, we discuss future approaches for analysis with the view to elucidate the complex genetic architecture that underlies the disorder.

Pharmacological strategies for improving the efficacy and therapeutic ratio of glucocorticoids in inflammatory lung diseases

Glucocorticoids are widely used to treat various inflammatory lung diseases. Acting via the glucocorticoid receptor (GR), they exert clinical effects predominantly by modulating gene transcription. This may be to either induce (transactivate) or repress (transrepress) gene transcription. However, certain individuals, including those who smoke, have certain asthma phenotypes, chronic obstructive pulmonary disease (COPD) or some interstitial diseases may respond poorly to the beneficial effects of glucocorticoids. In these cases, high dose, often oral or parental, glucocorticoids are typically prescribed. This generally leads to adverse effects that compromise clinical utility. There is, therefore, a need to enhance the clinical efficacy of glucocorticoids while minimizing adverse effects. In this context, a long-acting beta(2)-adrenoceptor agonist (LABA) can enhance the clinical efficacy of an inhaled corticosteroid (ICS) in asthma and COPD. Furthermore, LABAs can augment glucocorticoid-dependent gene expression and this action may account for some of the benefits of LABA/ICS combination therapies when compared to ICS given as a monotherapy. In addition to metabolic genes and other adverse effects that are induced by glucocorticoids, there are many other glucocorticoid-inducible genes that have significant anti-inflammatory potential. We therefore advocate a move away from the search for ligands of GR that dissociate transactivation from transrepression. Instead, we submit that ligands should be functionally screened by virtue of their ability to induce or repress biologically-relevant genes in target tissues. In this review, we discuss pharmacological methods by which selective GR modulators and "add-on" therapies may be exploited to improve the clinical efficacy of glucocorticoids while reducing potential adverse effects.

17β-Estradiol regulates the first steps of skeletal muscle cell differentiation via ER-α-mediated signals

17β-Estradiol (E2) mediates a wide variety of complex biological processes determining the growth and development of reproductive tract as well as nonreproductive tissues of male and female individuals. While E2 effects on the reproductive system, bone, and cardiovascular system are quite well established, less is known about how it affects the physiology of other tissues. Skeletal muscle is a tissue that is expected to be E2 responsive since both isoforms of estrogen receptor (ER-α and ER-β) are expressed. Significant sex-related differences have been described in skeletal muscle, although the role played by E2 and the mechanisms underlying it remain to be determined. Here, we demonstrate that E2 increases the glucose transporter type 4 translocation at membranes as well as the expression of well-known differentiation markers of myogenesis (i.e., myogenin and myosin heavy chain) in rat myoblast cells (L6). These E2-induced effects require rapid extranuclear signals and the presence of ER-α, whereas no contribution of IGF-I receptor has been observed. In particular, ER-α-dependent Akt activation participates in regulating the first step of myogenic differentiation. Moreover, both receptors mediate the E2-induced activation of p38, which, in turn, affects the expression of myogenin and myosin heavy chain. All together, these data indicate that E2 should be included in the list of skeletal muscle trophic factors.

Effects of the special extract ERr 731 from Rheum rhaponticum on estrogen-regulated targets in the uterotrophy model of ovariectomized rats

A recent clinical study with a two-year application of the extract ERr 731 from Rheum rhaponticum demonstrated its efficacy and potentially suggested it safety regarding unwanted endometrial side effects. The aim of the present study is to provide experimental proof for the latter observation in a preclinical experimental animal model by assessing dose-dependent effects of ERr 731 - either alone or in combination with estradiol (E2) - on growth and proliferation in the uterus of ovariectomized (ovx) rats. ERr 731 was given in a dose corresponding to human therapeutic application and additionally in three pharmacologically relevant doses. In addition to uterine wet weight, this study examines the effects of ERr 731 on the uterine mRNA expression of the proliferation marker Ki67, proliferating cell nuclear antigen (PCNA), insulin-like growth factor-1 (IGF-1), type 1 IGF receptor (IGF-1R), the two estrogen receptor (ER) subtypes alpha and beta (ERalpha and ERbeta) and the estrogen-responsive gene complement C3 (C3). ERr 731 did neither stimulate an uterotrophic response in the uterotrophic assay with ovx rats nor stimulate or modulate the expression of genes associated with proliferation. In combination with E2, ERr 731 reduced the E2-induced uterine growth stimulation. These observations were further substantiated by the expression pattern of genes related to proliferation control, in view of the fact that the E2-induced elevation of Ki67 mRNA and PCNA protein levels in the uterus were counteracted by simultaneous treatment of the animals with ERr 731. In conclusion, the experimental findings presented here provide further evidence for the safety of ERr 731 towards unwanted uterine and endometrial proliferative events in response to ERr 731 and support observations from recent clinical trials.

Notch-1 activates estrogen receptor-alpha-dependent transcription via IKKalpha in breast cancer cells

Approximately 80% of breast cancers express the estrogen receptor-alpha (ERalpha) and are treated with anti-estrogens. Resistance to these agents is a major cause of mortality. We have shown that estrogen inhibits Notch, whereas anti-estrogens or estrogen withdrawal activate Notch signaling. Combined inhibition of Notch and estrogen signaling has synergistic effects in ERalpha-positive breast cancer models. However, the mechanisms whereby Notch-1 promotes the growth of ERalpha-positive breast cancer cells are unknown. Here, we demonstrate that Notch-1 increases the transcription of ERalpha-responsive genes in the presence or absence of estrogen via a novel chromatin crosstalk mechanism. Our data support a model in which Notch-1 can activate the transcription of ERalpha-target genes via IKKalpha-dependent cooperative chromatin recruitment of Notch-CSL-MAML1 transcriptional complexes (NTC) and ERalpha, which promotes the recruitment of p300. CSL binding elements frequently occur in close proximity to estrogen-responsive elements (EREs) in the human and mouse genomes. Our observations suggest that a hitherto unknown Notch-1/ERalpha chromatin crosstalk mediates Notch signaling effects in ERalpha-positive breast cancer cells and contributes to regulate the transcriptional functions of ERalpha itself.

Androgen- and estrogen-independent regulation of copulatory behavior following castration in male B6D2F1 mice

Male reproductive behavior is highly dependent upon gonadal steroids. However, between individuals and across species, the role of gonadal steroids in male reproductive behavior is highly variable. In male B6D2F1 hybrid mice, a large proportion (about 30%) of animals demonstrate the persistence of the ejaculatory reflex long after castration. This provides a model to investigate the basis of gonadal steroid-independent male sexual behavior. Here we assessed whether non-gonadal steroids promote mating behavior in castrated mice. Castrated B6D2F1 hybrids that persisted in copulating (persistent copulators) were treated with the androgen receptor blocker, flutamide, and the aromatase enzyme inhibitor, letrozole, for 8 weeks. Other animals were treated with the estrogen receptor blocker, ICI 182,780, via continual intraventricular infusion for 2 weeks. None of these treatments eliminated persistent copulation. A motivational aspect of male sexual behavior, the preference for a receptive female over another male, was also assessed. This preference persisted after long-term castration in persistent copulators, and administration of ICI 182,780 did not influence partner preference. To assess the possibility of elevated sensitivity to sex steroids in brains of persistent copulators, we measured mRNA levels for genes that code for the estrogen receptor-alpha, androgen receptor, and aromatase enzyme in the medial preoptic area and bed nucleus of the stria terminalis. No differences in mRNA of these genes were noted in brains of persistent versus non-persistent copulators. Taken together our results suggest that non-gonadal androgens and estrogens do not maintain copulatory behavior in B6D2F1 mice which display copulatory behavior after castration.

E-cadherin mediates the aggregation of breast cancer cells induced by tamoxifen and epidermal growth factor

In the present study, we evaluated the ability of 4-hydroxytamoxifen (OHT) and epidermal growth factor (EGF) to regulate homotypic adhesion in MCF7 breast cancer cells. Our results demonstrate that OHT and EGF activate the E-cadherin promoter, increase E-cadherin mRNA and protein expression and enhance homotypic aggregation of MCF7 cells. Interestingly, an ERalpha and EGFR cross-talk is involved in the E-cadherin expression by OHT and EGF, as demonstrated by knocking down either receptor. On the basis of our findings, the well-established cross-talk between ERalpha and EGFR could be extended to the modulation of E-cadherin expression by OHT and EGF. Thus, the potential ability of tamoxifen to induce cell-cell aggregation may contribute to the biologic response of pharmacologic intervention in patients with breast cancer.

Prognostic relevance of androgen receptor detection in operable breast cancer

BACKGROUND AND OBJECTIVES

Androgen receptor (AR) is relevant for prognostication in breast cancer. Different determination methods and cut-off levels hamper interpretation and comparisons of studies. Long-term prognostic evaluation of different AR assays in patients comprising operable breast cancers is scarce.

METHODS

AR was evaluated in 120 primary tumors using the dextran-coated charcoal method (charc-AR), and quantitative immunohistochemistry (IHC) on whole sections (WS) and tissue microarrays (TMA). Nuclear and cytoplasmic-AR localization was determined, and the prognostic importance of AR assays was assessed. Comparisons and correlations with the mitotic activity index (MAI), estrogen receptor (ERalpha), progesterone receptor (PR), HER-2, and histological grade (WHO I-III) were made.

RESULTS

Nuclear-AR in WS, but not charc-AR, strongly correlated with MAI (P = 0.001). However, prognostic information appeared in univariate survival analyses only. Nuclear-AR in TMA was not prognostic. Charc-AR was independent prognostic in node positives both for relapse free survival (RFS) and breast cancer specific survival (BCSS). Both charc-AR and IHC cytoplasmic-AR provided independent prognostic survival information for BCSS in women <55 years.

CONCLUSION

Methods that can detect AR localized in the cytoplasm yield important prognostic information, and further studies in patients with operable breast cancer are warranted.

Activation of estrogen receptor-alpha by E2 or EGF induces temporally distinct patterns of large-scale chromatin modification and mRNA transcription

Estrogen receptor-alpha (ER) transcription function is regulated in a ligand-dependent (e.g., estradiol, E2) or ligand-independent (e.g., growth factors) manner. Our laboratory seeks to understand these two modes of action. Using a cell line that contains a visible prolactin enhancer/promoter array (PRL-HeLa) regulated by ER, we analyzed ER response to E2 and EGF by quantifying image-based results. Data show differential recruitment of GFP-ER to the array, with the AF1 domain playing a vital role in EGF-mediated responsiveness. Temporal analyses of large-scale chromatin dynamics, and accumulation of array-localized reporter mRNA over 24 hours showed that the EGF response consists of a single pulse of reporter mRNA accumulation concomitant with transient increase in array decondensation. Estradiol induced a novel cyclical pattern of mRNA accumulation with a sustained increase in array decondensation. Collectively, our work shows that there is a stimuli-specific pattern of large-scale chromatin modification and transcript levels by ER.

Transactivation of a growth hormone (GH) promoter-luciferase construct in canine mammary cells

The gene encoding growth hormone (GH) is expressed not only in the pituitary but also in a variety of non-pituitary tissues. In the female dog, progestins are known to stimulate GH expression in the mammary gland. In order to investigate the regulation of the GH gene expression in the mammary gland, we transfected the canine mammary tumor cell line CMT-U229 with 3 different canine GH promoter-luciferase constructs. The constructs, varying in length between 252 bp and 673 bp, were transfected followed by an incubation for 4 h, 24 h and 48 h with cAMP, all-trans-retinoic acid (RA), 3,3',5-triiodothyronine (T3), 1,25-dihydroxy-vitamin D (VitD), progesterone and EGF. Promoter activity was stimulated by cAMP, T3 and RA whereas VitD clearly inhibited gene expression. However, despite the presence of nuclear and membrane receptors for progesterone, no direct effects of progesterone on promoter activity could be demonstrated. It is concluded that progesterone alone has no direct stimulatory effect on GH transcription. This finding is discussed in relation to the slow onset of progesterone-stimulated GH release in vivo and the absence of Pit-1 in canine mammary tissue.

Loss of ERE binding activity by estrogen receptor-α alters basal and estrogen-stimulated bone-related gene expression by osteoblastic cells

Estrogen receptor (ER)-alpha can signal either via estrogen response element (ERE)-mediated pathways or via alternate pathways involving protein-protein or membrane signaling. We previously demonstrated that, as compared to wild type (WT) controls, mice expressing a mutant ER-alpha lacking the ability to bind EREs (non-classical estrogen receptor knock-in (NERKI)) display significant impairments in the skeletal response to estrogen. To elucidate the mechanism(s) underlying these in vivo deficits, we generated U2OS cells stably expressing either WT ER-alpha or the NERKI receptor. Compared to cells transfected with the control vector, stable expression of ER-alpha, even in the absence of E2, resulted in an increase in mRNA levels for alkaline phosphatase (AP, by 400%, P < 0.01) and a decrease in mRNA levels for insulin growth factor-I (IGF-I) (by 65%, P < 0.001), with no effects on collagen I (col I) or osteocalcin (OCN) mRNA levels. By contrast, stable expression of the NERKI receptor resulted in the suppression of mRNA levels for AP, col I, OCN, and IGF-I (by 62, 89, 60, and 70%, P < 0.001). While E2 increased mRNA levels of AP, OCN, col I, and IGF-I in ER-alpha cells, E2 effects in the NERKI cells on AP and OCN mRNA levels were attenuated, with a trend for E2 to inhibit col I mRNA levels. In addition, E2 had no effects on IGF-I mRNA levels in NERKI cells. Collectively, these findings indicate that ERE signaling plays a significant role in mediating effects of estrogen on osteoblastic differentiation markers and on IGF-I mRNA levels.

A Holy Grail of asthma management: toward understanding how long-acting beta(2)-adrenoceptor agonists enhance the clinical efficacy of inhaled corticosteroids

There is unequivocal evidence that the combination of an inhaled corticosteroid (ICS) -- i.e. glucocorticoid -- and an inhaled long-acting beta(2)-adrenoceptor agonist (LABA) is superior to each component administered as a monotherapy alone in the clinical management of asthma. Moreover, Calverley and colleagues (Lancet 2003, 361: 449-456; N Engl J Med 2007, 356: 775-789) reporting for the 'TRial of Inhaled STeroids ANd long-acting beta(2)-agonists (TRISTAN)' and 'TOwards a Revolution in COPD Health (TORCH)' international study groups also demonstrated the superior efficacy of LABA/ICS combination therapies over ICS alone in the clinical management of chronic obstructive pulmonary disease. This finding has been independently confirmed indicating that the therapeutic benefit of LABA/ICS combination therapies is not restricted to asthma and may be extended to other chronic inflammatory diseases of the airways. Despite the unquestionable benefit of LABA/ICS combination therapies, there is a vast gap in our understanding of how these two drugs given together deliver superior clinical efficacy. In this article, we review the history of LABA/ICS combination therapies and critically evaluate how these two classes of drugs might interact at the biochemical level to suppress pro-inflammatory responses. Understanding the molecular basis of this fundamental clinical observation is a Holy Grail of current respiratory diseases research as it could permit the rational exploitation of this effect with the development of new 'optimized' LABA/ICS combination therapies.

Overview of nomenclature of nuclear receptors

Nuclear receptor pharmacology has, to a certain extent, led the way, compared with other receptor systems, in the appreciation that ligands may exert very diverse pharmacology, based on their individual chemical structure and the allosteric changes induced in the receptor/accessory protein complex. This can lead to very selective pharmacological effects, which may not necessarily be predicted from the experience with other agonists/partial agonists/antagonists. If this is the case, then drug discovery may be back to drug-specific pharmacology (where each drug may have an original profile), rather than specific-drug pharmacology (where agents specific for a receptor have a distinct profile). As functional selectivity is indeed a crucial mechanism to be considered when going through the drug discovery development process, then initial screens using reconstituted systems may not show the appropriate pharmacology, simply because the required stoichiometry of corepressors and coactivators may not be present to select the best compounds; therefore, multiple effector systems are necessary to screen for differential activation, and, even then, screening with in vivo pathophysiological models may ultimately be required for the selection process-a massive but necessary task for pharmacologists. Thus, the characterization of nuclear receptors and their associated proteins and the ligands that interact with them will remain a challenge to pharmacologists.

Linkage of progestin and epidermal growth factor signaling: phosphorylation of progesterone receptors mediates transcriptional hypersensitivity and increased ligand-independent breast cancer cell growth

Progesterone receptor (PR) action is linked to epidermal growth factor (EGF) initiated signaling pathways at multiple levels; mitogen-activated protein kinases (MAPKs) are key mediators of this important cross-talk. Herein, we probed the effects of EGF on PR function and regulation of breast cancer cell growth. EGF stimulated rapid and transient phosphorylation of PR-B Ser294 relative to persistent phosphorylation of this site induced by the synthetic progestin, R5020. EGF induced nuclear translocation and DNA binding of unliganded wild-type, but not mutant PRs containing an Ala at position 294 (S294A). However, EGF alone induced little to no PR-B transcriptional activity; S294A PR-B was transcriptionally impaired. In contrast, pretreatment of cells with EGF (30min) significantly increased the potency and efficacy of wild-type, but not S294A PR transcriptional activity in response to progestin, and enhanced ligand-dependent downregulation of wild-type but not S294A PR. Replacement of Ser294 with aspartic acid (S294D) to mimic phosphorylation at this site decreased receptor stability and, as predicted, heightened progestin-induced transcription relative to wild-type PR-B. RT-PCR demonstrated the Ser294 phosphorylation-dependence of selected PR target genes (TGFalpha and HB-EGF). Surprisingly, PR-B expressing cells growing in soft agar were highly responsive to EGF or progestin, and this was further stimulated by the combination of both hormones. Cells expressing S294A PR exhibited reduced soft agar growth, and were also sensitive to R5020 alone, but failed to respond to EGF. These results suggest that PR Ser294 is an important "sensor" for growth factor inputs that affects PR function and breast cancer cell growth in the absence of progestin or in the presence of low or "sub-threshold" progestin concentrations. PR function likely contributes to breast cancer progression when EGFR family members or their ligands are overexpressed, a condition that predicts low abundance, but highly active and nuclear PR.

Signaling by estrogens

By regulating activities and expression levels of key signaling molecules, estrogens control mechanisms that are responsible for crucial cellular functions. Ligand binding to estrogen receptor (ER) leads to conformational changes that regulate the receptor activity, its interaction with other proteins and DNA. In the cytoplasm, receptor interactions with kinases and scaffolding molecules regulate cell signaling cascades (extranuclear/nongenomic action). In the nucleus, estrogens control a repertoire of coregulators and other auxiliary proteins that are associated with ER, which in turn determines the nature of regulated genes and level of their expression (genomic action). The combination of genomic and nongenomic actions of estrogens ultimately confers the cell-type and tissue-type selectivity. Recent studies have revealed some important new insights into the molecular mechanisms underlying ER action, which may help to explain the functional basis of existing selective ER modulators (SERMs) and provide evidence into how ER might be selectively targeted to achieve specific therapeutic goals. In this review, we will summarize some new molecular details that relate to estrogen signaling. We will also discuss some new strategies that may potentially lead to the development of functionally selective ER modulators that can separate between the beneficial, prodifferentiative effects in bone, the cardiovascular system and the CNS as well as the "detrimental," proliferative effects in reproductive tissues and organs.

Protein kinase C cross-talk with gonadotrope progesterone receptor is involved in GnRH-induced LH secretion

In the absence of progesterone (P), the anti-P at the receptor RU486 reduces basal and GnRH-stimulated LH secretion both in vivo and in vitro, demonstrating the existence of a ligand-independent activation of progesterone receptor (LIAPR). The aim of the present study was to determine which component of the intracellular LH secretory pathway activated by GnRH is responsible for LIAPR. To do this, anterior pituitary dispersed cells from female rats in proestrus, cultured in the presence of 17beta-estradiol, were incubated with activators or inhibitors of PKC, cAMP-PKA signalling pathways or intracellular calcium (Ca2+) traffic, in the presence or absence of RU486. Results showed that RU486 reduced both GnRH- and the PKC activator PMA-induced LH secretion. In GnRH-stimulated cells incubated with the PKC inhibitor BIS-I or treated with PMA "overnight", RU486 had no effect on reduced LH secretion, nor on stimulated LH secretion elicited by the Ca2+ ionophore ionomycin. Moreover, when GnRH- or PMA-treated cells were co-incubated with 1 microM of the L-type Ca2+ channel blocker nifedipine or the intracellular Ca2+ chelator BAPTA-AM, RU486 potentiated the expected inhibition of these drugs on LH secretion. Activation (forskolin, 8-Br-cAMP) or inhibition (MDL-12,330A) of the cAMP-PKA signalling cascade affected neither the GnRH- and PMA-induced increase of LH secretion nor the reduction of LH secretion due to RU486. Taken together, the data point to the existence of a Ca2+ -independent PKC-PR cross-talk mechanism as part of the intracellular signalling of GnRH-stimulated LH secretion.

The role of vascular and hormonal genes in migraine susceptibility

Migraine is a primary headache disorder that involves both genetic and environmental components. Migraine is considered to be a polygenic disorder with a number of susceptibility genes having a minor but nonetheless significant impact on susceptibility. Migraine candidate gene studies have concentrated mainly on genes involved in neurotransmitter pathways, however evidence also exists for a role for alterations in vascular and hormonal function in migraine susceptibility. We present here a mini-review of genetic studies, investigating the potential role of vascular and hormonal gene variants, and discuss how vascular and hormonal dysfunction may impact on migraine susceptibility. We propose that the potential role of vascular and hormonal genes in this disorder warrants further investigation.

The cell-specific activity of the estrogen receptor alpha may be fine-tuned by phosphorylation-induced structural gymnastics

The estrogen receptor α (ERα) regulates the transcription of target genes by recruiting coregulator proteins through several domains including the two activation functions AF1 and AF2. The contribution of the N-terminally located AF1 activity is particularly important in differentiated cells, and for ERα to integrate inputs from other signaling pathways. However, how the phosphorylation of key residues influences AF1 activity has long remained mysterious, in part because the naturally disordered AF1 domain has resisted a structural characterization. The recent discovery of two coregulators that are specific for a phosphorylated form of AF1 suggests that phosphorylation, possibly in conjunction with the subsequent binding of these coregulators, may enforce a stable structure. The binding of the "pioneer" coregulators might facilitate the subsequent recruitment of yet other coregulators. Different AF1 folds may be enabled by the combinatorial action of posttranslational modifications and coregulator binding thereby fine-tuning ERα activities in a cell- and promoter-specific fashion.

Time course of response to estradiol replacement in ovariectomized mice: brain apolipoprotein E and synaptophysin transiently increase and glial fibrillary acidic protein is suppressed

The current study examined the effect of long-term estradiol replacement in ovariectomized mice. Estradiol-17beta (E2) pellets or vehicle pellets were implanted at the time of ovariectomy (OVX) in young adult female mice. Five mice from each group were sacrificed at 5, 14, 28 and 49 days after OVX and pellet replacement. Western blotting of homogenates from somatosensory cortex, hippocampus, olfactory bulb and cerebellum was performed to obtain concentrations of glial fibrillary acidic protein (GFAP), apolipoprotein E (apoE) and synaptophysin (SYN). At 5 days after OVX, GFAP levels were not affected by E2 replacement. In contrast to GFAP, synaptophysin and apoE concentrations were significantly elevated by 15% and 25%, respectively, in the E2-replaced group compared to the vehicle-replaced group at 5 days but by 14 days concentrations were equivalent. Late in the time course of this study, at 49 days, GFAP concentrations were higher in the E2-deprived mice but did not increase in the E2-replaced group. Immunocytochemistry for GFAP confirmed this observation. Of note was that these effects occurred in all four brain regions measured. These observations suggest that estradiol is able to suppress reactive gliosis. In addition, E2 replacement in OVX mice is associated with transiently higher levels of apoE and synaptophysin.

SPBP is a phosphoserine-specific repressor of estrogen receptor alpha

Multiple signaling pathways stimulate the activity of estrogen receptor alpha (ERalpha) by direct phosphorylation within its N-terminal activation function 1 (AF1). How phosphorylation affects AF1 activity remains poorly understood. We performed a phage display screen for human proteins that are exclusively recruited to the phosphorylated form of AF1 and found the stromelysin-1 platelet-derived growth factor-responsive element-binding protein (SPBP). In a purified system, SPBP bound only the in vitro-phosphorylated form of the ERalpha AF1 or the phosphoserine mimic S118E, and the interaction domain could be mapped to a 42-amino-acid fragment of SPBP. In cells, SPBP preferentially interacted with liganded and phosphorylated ERalpha. Functionally, SPBP behaved as a repressor of activated ERalpha, which extends its previously demonstrated roles as a DNA binding transactivation factor and coactivator of other transcription factors. By targeting the phosphorylated form of AF1, SPBP may contribute to attenuating and fine-tuning ERalpha activity. A functional consequence is that SPBP inhibits the proliferation of ERalpha-dependent but not ERalpha-independent breast cancer cell lines, mirroring a reported negative correlation with the ERalpha status of breast tumors.

Is it possible docking and scoring new ligands with few experimental data? Preliminary results on estrogen receptor as a case study

Estrogens are steroid hormones playing critical roles in several physiological processes, which bind the estrogen receptors ERalpha and ERbeta. Aim of this work is to analyze, by different docking experiments, the behavior of a set of compounds, mimicking estrogens activity, in order to understand the relationship between ERalpha and such new ligands. Main goal is to verify, using a widely tested scoring software procedure applied on a set of 10 compounds, the possibility to produce new lead candidate molecules in lack of, or with few experimental data. Our preliminary results reveal the significance of HINT software as a scoring function in docking methodology and specifically, as a mean for assessing the consistency of docking solutions.

Investigation of hormone receptor genes in migraine

Migraine is a common neurological condition with a complex mode of inheritance. Steroid hormones have long been implicated in migraine, although their role remains unclear. Our investigation considered that genes involved in hormonal pathways may play a role in migraine susceptibility. We therefore investigated the androgen receptor (AR) CAG repeat, and the progesterone receptor (PR) PROGINS insert by cross-sectional association analysis. The results showed no association with the AR CAG repeat in our study group of 275 migraineurs and 275 unrelated controls. Results of the PR PROGINS analysis showed a significant difference in the same cohort, and in an independent follow-up study population of 300 migraineurs and 300 unrelated controls. Analysis of the genotypic risk groups of both populations together indicated that individuals who carried the PROGINS insert were 1.8 times more likely to suffer migraine. Interaction analysis of the PROGINS variant with our previously reported associated ESR1 594A variant showed that individuals who possessed at least one copy of both risk alleles were 3.2 times more likely to suffer migraine. Hence, variants of these steroid hormone receptor genes appear to act synergistically to increase the risk of migraine by a factor of three.

Progesterone-independent effects of human progesterone receptors (PRs) in estrogen receptor-positive breast cancer: PR isoform-specific gene regulation and tumor biology

Progesterone receptors (PRs) are prognostic markers in breast cancers irrespective of the patient's progestational status. However, there are two PR isoforms, PR-A and PR-B, that are equimolar in the normal breast but dysregulated in advanced disease. Postmenopausal, tamoxifen-treated patients with estrogen receptor (ER)-positive, PR-A-rich tumors have much faster disease recurrence than patients with PR-B-rich tumors. To study the mechanisms we engineered ER+ breast cancer cells that express each PR isoform under control of an inducible promoter. We identified 79 genes regulated by progesterone (P), mainly by PR-B, and 51 genes regulated without progesterone, mainly by PR-A. Only nine genes were regulated with and without ligand, leading to definition of three classes: I) genes regulated only by liganded PR; II) genes regulated only by unliganded PR; III) genes regulated by both. Unliganded PR-A and PR-B differentially regulate genes that coordinate extracellular signaling pathways and influence tumor cell biology. Indeed, in the absence of P, compared with ER+/PR-B+ or PR- cells, ER+, PR-A+ cells exhibit an aggressive phenotype, are more adhesive to an extracellular matrix, and are more migratory. Additionally, unliganded PR-A and PR-B both inhibit cell growth and provoke resistance to Taxol-induced apoptosis. We propose that PR-A:PR-B ratios, even in the absence of P, influence the biology and treatment response of ER+ tumors, that PR-A isoforms are functionally dominant in P-deficient states, and that PR-A rich tumors are especially aggressive.

Constitutive over expression of serine/threonine protein phosphatase 5 (PP5) augments estrogen-dependent tumor growth in mice

Serine/threonine protein phosphatase 5 (PP5) appears to play an underappreciated role in the regulation of cellular proliferation. In estrogen-responsive cells, PP5 expression is stimulated by 17 beta-estradiol, and in a variety of p53 wild-type tumor cells the suppression of PP5 expression with ISIS 15534 inhibits growth. To further explore the relationship between PP5 and the development of human cancer, here we tested the effect of elevated PP5 expression on tumor growth using a mouse xenograph model and a stable MCF-7 cell line in which the expression of wild-type PP5 was placed under the control of tetracycline-off regulated transactivator and operator plasmids. In the xenograph model a modest two fold increase in PP5 protein levels significantly enhanced the growth rate of estrogen-dependent tumors, suggesting PP5 plays a positive role in tumor development.

The estrogen receptor 1 G594A polymorphism is associated with migraine susceptibility in two independent case/control groups

Migraine is a painful and debilitating disorder with a significant genetic component. Steroid hormones, in particular estrogen, have long been considered to play a role in migraine, as variations in hormone levels are associated with migraine onset in many sufferers of the disorder. Steroid hormones mediate their activity via hormone receptors, which have a wide tissue distribution. Estrogen receptors have been localized to the brain in regions considered to be involved in migraine pathogenesis. Hence it is possible that genetic variation in the estrogen receptor gene may play a role in migraine susceptibility. This study thus examined the estrogen receptor 1 (ESRalpha) gene for a potential role in migraine pathogenesis and susceptibility. A population-based cohort of 224 migraine sufferers and 224 matched controls were genotyped for the G594A polymorphism located in exon 8 of the ESR1 gene. Statistical analysis indicated a significant difference between migraineurs and non-migraineurs in both the allele frequencies (P=0.003) and genotype distributions (P=0.008) in this sample. An independent follow-up study was then undertaken using this marker in an additional population-based cohort of 260 migraine sufferers and 260 matched controls. This resulted in a significant association between the two groups with regard to allele frequencies (P=8 x 10(-6)) and genotype distributions (P=4 x 10(-5)). Our findings support the hypothesis that genetic variation in hormone receptors, in particular the ESR1 gene, may play a role in migraine.

Progestin receptors: neuronal integrators of hormonal and environmental stimulation

Although it originally was believed that neuronal steroid hormone receptors require binding to cognate ligand for activation, more recent evidence suggests that the receptors can be activated indirectly by other compounds, such as neurotransmitters and growth factors, acting through their own membrane receptors and specific intracellular signaling pathways. For example, as is the case with facilitation of sexual behavior by progesterone, facilitation of sexual behavior by D(1)/D(5) dopamine receptor agonists is blocked by disruption of progestin receptors. Therefore, some dopamine agonists facilitate sexual behavior at least in part by a progestin receptor-dependent mechanism, as does progesterone. This "ligand-independent activation" of neuronal progestin receptors is not limited to dopamine agonists; a variety of other compounds, as well as mating stimulation, facilitate sexual receptivity by a progestin receptor-dependent process. Steroid hormone receptors also can be regulated by afferent input in another way. Various neurotransmitters upregulate or downregulate steroid hormone receptors in some neurons. This, in turn, presumably confers greater or decreased sensitivity to the particular factors that can activate the particular steroid receptor in those particular neurons. Therefore, steroid hormones are but one class of factors that can regulate and activate steroid hormone receptors. Some additional factors that activate steroid hormone receptors have been identified, as have some factors that can regulate concentrations of receptors. Relatively little is known at this time about the range of neurotransmitters, humoral factors, and intracellular signaling pathways that are involved.

Minireview: Neuronal steroid hormone receptors: they're not just for hormones anymore

The ovarian steroid hormones have numerous effects on the brain, many of which are mediated, at least in part, by interaction with intracellular steroid hormone receptors acting as regulators of transcription. These intracellular steroid hormone receptors have often been considered to be activated solely by cognate hormone. However, during the past decade, numerous studies have shown that the receptors can be activated by neurotransmitters and intracellular signaling systems, through a process that does not require hormone. Although most of these have been in vitro experiments, others have been in vivo. Evidence from a wide variety of tissues and cells suggests that steroid hormone receptors are transcription factors that can be activated by a wide variety of factors, only one of which is cognate hormone. Furthermore, ligand-independent activation of neural steroid hormone receptors, rather than being a pharmacological or in vitro curiosity, seems to be a process that occurs in the normal physiology of animals. Thinking of steroid hormone receptors only as ligand-activated proteins may constrain our thinking about the many factors that may activate the receptors and cause receptor-dependent changes in neural gene expression and neuroendocrine function.

The Focal Adhesion Protein Vinexin α Regulates the Phosphorylation and Activity of Estrogen Receptor α

Steroid receptors are transcription factors that regulate hormone-responsive genes and whose activity is controlled by their interaction with numerous other proteins. Observations reported here reveal that estrogen receptors alpha and beta (ERalpha and ERbeta), androgen receptor, and glucocorticoid receptor bind in vitro to vinexin alpha, a multiple SH3 motif-containing protein associated with the cytoskeleton. The SH3 domains are not involved in this interaction. Furthermore, we demonstrate that vinexin alpha stimulates the ligand-induced transactivation function of these receptors, although it is devoid of intrinsic transcriptional activity when tethered to DNA. In addition, the ectopic coexpression of vinexin alpha and ERalpha results in a loss of ERalpha phosphorylation on serines and the partial redistribution of vinexin alpha into the nucleus, where it colocalizes with ERalpha. These results establish a new model of transcriptional regulation where components of the cell-cell and cell-substrate adhesion complexes can regulate the phosphorylation and activity of steroid receptors.

Leptin induces, via ERK1/ERK2 signal, functional activation of estrogen receptor alpha in MCF-7 cells

Leptin is a hormone with multiple biological actions, produced predominantly by adipose tissue. In humans, plasma levels correlate with total body fat, and high concentrations occur in obese women. Among its functions, leptin is able to stimulate normal and tumor cell growth. We demonstrated that leptin induces aromatase activity in MCF-7 cells evidencing its important role in enhancing in situ estradiol production and promoting estrogen-dependent breast cancer progression. Estrogen receptor alpha (ERalpha), which plays an essential role in breast cancer development, can be transcriptionally activated in a ligand-independent manner. Taking into account that unliganded ERalpha is an effector of mitogen-activated protein kinase (MAPK) signal and that leptin is able, via Janus kinase, to activate the Ras-dependent MAPK pathway, in the present study we investigate the ability of leptin to transactivate ERalpha. We provided evidence that leptin is able to reproduce the classic features of ERalpha transactivation in a breast cancer cell line: nuclear localization, down-regulation of its mRNA and protein levels, and up-regulation of a classic estrogen-dependent gene such as pS2. Transactivation experiments with a transfected reporter gene for nuclear ER showed an activation of ERalpha either in MCF-7 or in HeLa cells. Using a dominant negative ERK2 or the MAPK inhibitor PD 98059, we showed that leptin activates the ERalpha through the MAPK pathway. The N-terminal transcriptional activation function 1 appears essential for the leptin response. Finally, it is worth noting that leptin exposure potentates also the estradiol-induced activation of ERalpha. Thus, we are able to demonstrate that the amplification of estrogen signal induced by leptin occurs through an enhancing in situ E(2) production as well as a direct functional activation of ERalpha.

Biological role of pituitary estrogen receptors ERalpha and ERbeta on progesterone receptor expression and action and on gonadotropin and prolactin secretion in the rat

Estrogen (E) is a key regulator of the synthesis and secretion of pituitary reproductive hormones [luteinizing hormone (LH), follicle-stimulating hormone (FSH) and prolactin (PRL)]. Until recently, it was thought that all biological actions of E at the pituitary were manifested through a single E receptor (R). The pituitary, like many other reproductive tissues, expresses two isoforms of ER, alpha and beta, both activated by E. The relative contribution of alpha and beta forms in E regulatory actions is largely unknown. To this end, 2-week-old ovariectomized (OVX) rats were injected over 3 days with 25 microg estradiol benzoate (EB), 1.5 mg of propylpyrazole triol (PPT), a selective ERalpha agonist, 1.5 mg of the selective ERbeta agonist diarylpropionitrile (DPN) or a combination of PPT and DPN. Controls were injected with 0.2 ml oil. At 10:00 h on the day after treatment, trunk blood was collected to determine serum concentration of LH, FSH and PRL, and pituitaries were processed for RT-PCR analysis of total (A+B) progesterone receptor (PR) mRNA, immunocytochemistry of PR and incubation. Pituitaries from each of the five groups were incubated in DMEM, with or without 20 nM of the antiprogestin at the receptor ZK299, for 3 h with: 10(-8)M 17beta-estradiol, 10(-6)M PPT, 10(-6)M DPN, PPT+DPN or medium alone, respectively, to determine LH, FSH and PRL secretion, and, when challenged with two pulses of 15 min 1 h apart of 10(-8)M gonadotropin-releasing hormone (GnRH) (GnRH self-priming). EB, PPT and PPT+DPN treatments increased PR mRNA and the number and intensity of nuclei immunoreactive (IR) for PR in gonadotropes, and reduced the number of gonadectomy cells. Like E, PPT alone or in combination with DPN stimulated PRL secretion, increased basal and GnRH-stimulated LH and FSH secretion and induced GnRH self-priming in the absence of ZK299 in the incubation medium. DPN alone had only a significant E-like effect on gonadectomy cells and IR-PR, but not on GnRH self-priming. In addition, while DPN lacked an agonistic action on peripheral tissue and serum pituitary reproductive hormones concentration, EB, PPT and PPT+DPN induced similar uterine ballooning and vaginal cornification, and increased and decreased, respectively, serum concentrations of PRL and gonadotropins. Overall, these results indicate that most of these E actions on the pituitary are exerted through the ERalpha isoform. The finding that activation of ERbeta with its selective DPN agonist had an estrogenic effect on IR-PR nuclei, but not on GnRH self-priming, a characteristic ERalpha-mediated effect of E, suggests that the biological action of E at the pituitary may involve both isoforms of ER.