Auto-regulation of the estrogen receptor promoter

Estrogenic endocrine disruptor exposure directly impacts erectile function

Erectile dysfunction (ED) is an extremely prevalent condition which significantly impacts quality of life. The rapid increase of ED in recent decades suggests the existence of unidentified environmental risk factors contributing to this condition. Endocrine Disrupting Chemicals (EDCs) are one likely candidate, given that development and function of the erectile tissues are hormonally dependent. We use the estrogenic-EDC diethylstilbestrol (DES) to model how widespread estrogenic-EDC exposure may impact erectile function in humans. Here we show that male mice chronically exposed to DES exhibit abnormal contractility of the erectile tissue, indicative of ED. The treatment did not affect systemic testosterone production yet significantly increased estrogen receptor α (Esr1) expression in the primary erectile tissue, suggesting EDCs directly impact erectile function. In response, we isolated the erectile tissue from mice and briefly incubated them with the estrogenic-EDCs DES or genistein (a phytoestrogen). These acute-direct exposures similarly caused a significant reduction in erectile tissue contractility, again indicative of ED. Overall, these findings demonstrate a direct link between estrogenic EDCs and erectile dysfunction and show that both chronic and acute estrogenic exposures are likely risk factors for this condition.

Unraveling non-genetic heterogeneity in cancer with dynamical models and computational tools

Individual cells within an otherwise genetically homogenous population constantly undergo fluctuations in their molecular state, giving rise to non-genetic heterogeneity. Such diversity is being increasingly implicated in cancer therapy resistance and metastasis. Identifying the origins of non-genetic heterogeneity is therefore crucial for making clinical breakthroughs. We discuss with examples how dynamical models and computational tools have provided critical multiscale insights into the nature and consequences of non-genetic heterogeneity in cancer. We demonstrate how mechanistic modeling has been pivotal in establishing key concepts underlying non-genetic diversity at various biological scales, from population dynamics to gene regulatory networks. We discuss advances in single-cell longitudinal profiling techniques to reveal patterns of non-genetic heterogeneity, highlighting the ongoing efforts and challenges in statistical frameworks to robustly interpret such multimodal datasets. Moving forward, we stress the need for data-driven statistical and mechanistically motivated dynamical frameworks to come together to develop predictive cancer models and inform therapeutic strategies.

Estrogen Acts Through Estrogen Receptor-β to Promote Mannan-Induced Psoriasis-Like Skin Inflammation

Sex-bias is more obvious in several autoimmune disorders, but not in psoriasis. However, estrogen levels fluctuate during puberty, menstrual cycle, pregnancy, and menopause, which are related to variations in psoriasis symptoms observed in female patients. Estrogen has disease promoting or ameliorating functions based on the type of immune responses and tissues involved. To investigate the effects of estrogen on psoriasis, at first, we developed an innate immunity dependent mannan-induced psoriasis model, which showed a clear female preponderance in disease severity in several mouse strains. Next, we investigated the effects of endogenous and exogenous estrogen using ovariectomy and sham operated mice. 17-β-estradiol (E2) alone promoted the skin inflammation and it also significantly enhanced mannan-induced skin inflammation. We also observed a prominent estrogen receptor-β (ER-β) expression in the skin samples, especially on keratinocytes. Subsequently, we confirmed the effects of E2 on psoriasis using ER-β antagonist (PHTPP) and agonist (DPN). In addition, estrogen was found to affect the expression of certain genes (vgll3 and cebpb), microRNAs (miR146a and miR21), and immune cells (DCs and γδ T cells) as well as chemokines (CCL5 and CXCL10) and cytokines (TNF-α, IL-6, IL-22, IL-23, and IL-17 family), which promoted the skin inflammation. Thus, we demonstrate a pathogenic role for 17-β-estradiol in promoting skin inflammation, which should be considered while designing new treatment strategies for psoriasis patients.

Positive Regulation of Estrogen Receptor Alpha in Breast Tumorigenesis

Estrogen receptor alpha (ERα, NR3A1) contributes through its expression in different tissues to a spectrum of physiological processes, including reproductive system development and physiology, bone mass maintenance, as well as cardiovascular and central nervous system functions. It is also one of the main drivers of tumorigenesis in breast and uterine cancer and can be targeted by several types of hormonal therapies. ERα is expressed in a subset of luminal cells corresponding to less than 10% of normal mammary epithelial cells and in over 70% of breast tumors (ER+ tumors), but the basis for its selective expression in normal or cancer tissues remains incompletely understood. The mapping of alternative promoters and regulatory elements has delineated the complex genomic structure of the ESR1 gene and shed light on the mechanistic basis for the tissue-specific regulation of ESR1 expression. However, much remains to be uncovered to better understand how ESR1 expression is regulated in breast cancer. This review recapitulates the current body of knowledge on the structure of the ESR1 gene and the complex mechanisms controlling its expression in breast tumors. In particular, we discuss the impact of genetic alterations, chromatin modifications, and enhanced expression of other luminal transcription regulators on ESR1 expression in tumor cells.

Previous estradiol treatment during midlife maintains transcriptional regulation of memory-related proteins by ERα in the hippocampus in a rat model of menopause

Previous midlife estradiol treatment, like continuous treatment, improves memory and results in lasting increases in hippocampal levels of estrogen receptor (ER) α and ER-dependent transcription in ovariectomized rodents. We hypothesized that previous and continuous midlife estradiol act to specifically increase levels of nuclear ERα, resulting in transcriptional regulation of proteins that mediate estrogen effects on memory. Ovariectomized middle-aged rats received estradiol or vehicle capsule implants. After 40 days, rats initially receiving vehicle received another vehicle capsule (ovariectomized controls). Rats initially receiving estradiol received either another estradiol (continuous estradiol) or a vehicle (previous estradiol) capsule. One month later, hippocampi were dissected and processed. Continuous and previous estradiol increased levels of nuclear, but not membrane or cytosolic ERα and had no effect on Esr1. Continuous and previous estradiol impacted gene expression and/or protein levels of mediators of estrogenic action on memory including ChAT, BDNF, and PSD-95. Findings demonstrate a long-lasting role for hippocampal ERα as a transcriptional regulator of memory following termination of previous estradiol treatment in a rat model of menopause.

A mechanistic model captures the emergence and implications of non-genetic heterogeneity and reversible drug resistance in ER+ breast cancer cells

Resistance to anti-estrogen therapy is an unsolved clinical challenge in successfully treating ER+ breast cancer patients. Recent studies have demonstrated the role of non-genetic (i.e. phenotypic) adaptations in tolerating drug treatments; however, the mechanisms and dynamics of such non-genetic adaptation remain elusive. Here, we investigate coupled dynamics of epithelial–mesenchymal transition (EMT) in breast cancer cells and emergence of reversible drug resistance. Our mechanism-based model for underlying regulatory network reveals that these two axes can drive one another, thus enabling non-genetic heterogeneity in a cell population by allowing for six co-existing phenotypes: epithelial-sensitive, mesenchymal-resistant, hybrid E/M-sensitive, hybrid E/M-resistant, mesenchymal-sensitive and epithelial-resistant, with the first two ones being most dominant. Next, in a population dynamics framework, we exemplify the implications of phenotypic plasticity (both drug-induced and intrinsic stochastic switching) and/or non-genetic heterogeneity in promoting population survival in a mixture of sensitive and resistant cells, even in the absence of any cell–cell cooperation. Finally, we propose the potential therapeutic use of mesenchymal–epithelial transition inducers besides canonical anti-estrogen therapy to limit the emergence of reversible drug resistance. Our results offer mechanistic insights into empirical observations on EMT and drug resistance and illustrate how such dynamical insights can be exploited for better therapeutic designs.

An overview of Betacoronaviruses-associated severe respiratory syndromes, focusing on sex-type-specific immune responses

Emerging beta-coronaviruses (β-CoVs), including Severe Acute Respiratory Syndrome CoV-1 (SARS-CoV-1), Middle East Respiratory Syndrome-CoV (MERS-CoV), and Severe Acute Respiratory Syndrome CoV-2 (SARS-CoV-2, the cause of COVID19) are responsible for acute respiratory illnesses in human. The epidemiological features of the SARS, MERS, and new COVID-19 have revealed sex-dependent variations in the infection, frequency, treatment, and fatality rates of these syndromes. Females are likely less susceptible to viral infections, perhaps due to their steroid hormone levels, the impact of X-linked genes, and the sex-based immune responses. Although mostly inactive, the X chromosome makes the female's immune system more robust. The extra immune-regulatory genes of the X chromosome are associated with lower levels of viral load and decreased infection rate. Moreover, a higher titer of the antibodies and their longer blood circulation half-life are involved in a more durable immune protection in females. The activation rate of the immune cells and the production of TLR7 and IFN are more prominent in females. Although the bi-allelic expression of the immune regulatory genes can sometimes lead to autoimmune reactions, the higher titer of TLR7 in females is further associated with a stronger anti-viral immune response. Considering these sex-related differences and the similarities between the SARS, MERS, and COVID-19, we will discuss them in immune responses against the β-CoVs-associated syndromes. We aim to provide information on sex-based disease susceptibility and response. A better understanding of the evasion strategies of pathogens and the host immune responses can provide worthful insights into immunotherapy, and vaccine development approaches.

A novel function of R-spondin1 in regulating estrogen receptor expression independent of Wnt/β-catenin signaling

R-spondin1 (Rspo1) has been featured as a Wnt agonist, serving as a potent niche factor for stem cells in many tissues. Here we unveil a novel role of Rspo1 in promoting estrogen receptor alpha (Esr1) expression, hence regulating the output of steroid hormone signaling in the mouse mammary gland. This action of Rspo1 relies on the receptor Lgr4 and intracellular cAMP-PKA signaling, yet is independent of Wnt/β-catenin signaling. These mechanisms were reinforced by genetic evidence. Luminal cells-specific knockout of Rspo1 results in decreased Esr1 expression and reduced mammary side branches. In contrast, luminal cells-specific knockout of Wnt4, while attenuating basal cell Wnt/β-catenin signaling activities, enhances Esr1 expression. Our data reveal a novel Wnt-independent role of Rspo1, in which Rspo1 acts as a bona fide GPCR activator eliciting intracellular cAMP signaling. The identification of Rspo1-ERα signaling axis may have a broad implication in estrogen-associated diseases.

The Eleanor ncRNAs activate the topological domain of the ESR1 locus to balance against apoptosis

MCF7 cells acquire estrogen-independent proliferation after long-term estrogen deprivation (LTED), which recapitulates endocrine therapy resistance. LTED cells can become primed for apoptosis, but the underlying mechanism is largely unknown. We previously reported that Eleanor non-coding RNAs (ncRNAs) upregulate the ESR1 gene in LTED cells. Here, we show that Eleanors delineate the topologically associating domain (TAD) of the ESR1 locus in the active nuclear compartment of LTED cells. The TAD interacts with another transcriptionally active TAD, which is 42.9 Mb away from ESR1 and contains a gene encoding the apoptotic transcription factor FOXO3. Inhibition of a promoter-associated Eleanor suppresses all genes inside the Eleanor TAD and the long-range interaction between the two TADs, but keeps FOXO3 active to facilitate apoptosis in LTED cells. These data indicate a role of ncRNAs in chromatin domain regulation, which may underlie the apoptosis-prone nature of therapy-resistant breast cancer cells and could be good therapeutic targets.

Long term estrogen deprivation can result in apoptosis in breast cancer cells. Here, the authors show that this apoptosis is induced by the long-range chromatin interaction of loci containing the ESR1 and FOXO3 genes, resulting in FOXO3-mediated apoptosis.

Estrogen receptors and sex hormone binding globulin in neuronal cells and tissue

Estrogens exert a critical influence on neuronal tissues and cells. As demonstrated in many clinical studies, estrogens are neuroprotective to the extent that they improve prognosis for women with neurodegenerative diseases. Unfortunately, we still do not know exactly how these effects are mediated. Fifty years ago the first estrogen receptor was found, but since then many other new pathways of estrogen action have been identified. This review describes several of these pathways of estrogen effects and provides some conclusions and correlations about these as determined by recent studies with nerve growth factor differentiated rat pheochromocytoma cell line.

p21-activated kinase group II small compound inhibitor GNE-2861 perturbs estrogen receptor alpha signaling and restores tamoxifen-sensitivity in breast cancer cells

Estrogen receptor alpha (ERα) is highly expressed in most breast cancers. Consequently, ERα modulators, such as tamoxifen, are successful in breast cancer treatment, although tamoxifen resistance is commonly observed. While tamoxifen resistance may be caused by altered ERα signaling, the molecular mechanisms regulating ERα signaling and tamoxifen resistance are not entirely clear. Here, we found that PAK4 expression was consistently correlated to poor patient outcome in endocrine treated and tamoxifen-only treated breast cancer patients. Importantly, while PAK4 overexpression promoted tamoxifen resistance in MCF-7 human breast cancer cells, pharmacological treatment with a group II PAK (PAK4, 5, 6) inhibitor, GNE-2861, sensitized tamoxifen resistant MCF-7/LCC2 breast cancer cells to tamoxifen. Mechanistically, we identified a regulatory positive feedback loop, where ERα bound to the PAK4 gene, thereby promoting PAK4 expression, while PAK4 in turn stabilized the ERα protein, activated ERα transcriptional activity and ERα target gene expression. Further, PAK4 phosphorylated ERα-Ser305, a phosphorylation event needed for the PAK4 activation of ERα-dependent transcription. In conclusion, PAK4 may be a suitable target for perturbing ERα signaling and tamoxifen resistance in breast cancer patients.

Epigenetic regulation of estrogen receptor α contributes to age-related differences in transcription across the hippocampal regions CA1 and CA3

The expression of estrogen receptor alpha (ERα) varies across brain regions and changes with age and according to the previous history of estradiol exposure. ERα is regulated by a number of mechanisms including the level of mRNA (Esr1) expression. For this study, we took advantage of regional differences in hippocampal ERα expression to investigate DNA ERα promoter methylation at CpG dinucleotide sites as a potential epigenetic mechanism for regulating gene expression. Young and aged female Fischer 344 rats were ovariectomized, and Esr1 expression and ERα promoter methylation were examined in hippocampal regions CA1 and CA3, either 3 or 14 weeks following surgery. The results indicate that reduced Esr1 expression in region CA1 relative to CA3 was associated with an increase in DNA methylation in region CA1, particularly for the first CpG site. Additionally, differential methylation of distal CpG sites, 11-17, was associated with altered Esr1 expression during aging or following long-term hormone deprivation. The results support the idea that methylation of site 1 may be the primary regulatory region for cross-regional patterns in ERα expression, while distal sites are modifiable across the life span and may act as a feedback mechanism for ERα activity.

Hormonal Modulation of Dendritic Cells Differentiation, Maturation and Function: Implications for the Initiation and Progress of Systemic Autoimmunity

Hormonal homeostasis is crucial for keeping a competent and healthy immune function. Several hormones can modulate the function of various immune cells such as dendritic cells (DCs) by influencing the initiation of the immune response and the maintenance of peripheral tolerance to self-antigens. Hormones, such as estrogens, prolactin, progesterone and glucocorticoids may profoundly affect DCs differentiation, maturation and function leading to either a pro-inflammatory or an anti-inflammatory (or tolerogenic) phenotype. If not properly regulated, these processes can contribute to the pathogenesis of autoimmune disease. An unbalanced hormonal status may affect the production of pro-inflammatory cytokines, the expression of activating/inhibitory receptors and co-stimulatory molecules on conventional and plasmacytoid DCs (pDCs), conferring susceptibility to develop autoimmunity. Estrogen receptor (ER)-α signaling in conventional DCs can promote IFN-α and IL-6 production and induce the expression of CD40, CD86 and MHCII molecules. Furthermore, estrogen modulates the pDCs response to Toll-like receptor ligands enhancing T cell priming. During lupus pathogenesis, ER-α deficiency decreased the expression of MHC II on pDCs from the spleen. In contrast, estradiol administration to lupus-prone female mice increased the expression of co-stimulatory molecules, enhanced the immunogenicity and produced large amounts of IL-6, IL-12 and TNF-α by bone marrow-derived DCs. These data suggest that estradiol/ER signaling may play an active role during lupus pathology. Similarly, understanding hormonal modulation of DCs may favor the design of new therapeutic strategies based on autologous tolerogenic DCs transfer, especially in sex-biased systemic autoimmune diseases. In this review, we discuss recent data relative to the role of different hormones (estrogen, prolactin, progesterone and glucocorticoids) in DC function during systemic autoimmune pathogenesis.

17α-Estradiol Alleviates Age-related Metabolic and Inflammatory Dysfunction in Male Mice Without Inducing Feminization

Aging is associated with visceral adiposity, metabolic disorders, and chronic low-grade inflammation. 17α-estradiol (17α-E2), a naturally occurring enantiomer of 17β-estradiol (17β-E2), extends life span in male mice through unresolved mechanisms. We tested whether 17α-E2 could alleviate age-related metabolic dysfunction and inflammation. 17α-E2 reduced body mass, visceral adiposity, and ectopic lipid deposition without decreasing lean mass. These declines were associated with reductions in energy intake due to the activation of hypothalamic anorexigenic pathways and direct effects of 17α-E2 on nutrient-sensing pathways in visceral adipose tissue. 17α-E2 did not alter energy expenditure or excretion. Fasting glucose, insulin, and glycosylated hemoglobin were also reduced by 17α-E2, and hyperinsulinemic-euglycemic clamps revealed improvements in peripheral glucose disposal and hepatic glucose production. Inflammatory mediators in visceral adipose tissue and the circulation were reduced by 17α-E2. 17α-E2 increased AMPKα and reduced mTOR complex 1 activity in visceral adipose tissue but not in liver or quadriceps muscle, which is in contrast to the generalized systemic effects of caloric restriction. These beneficial phenotypic changes occurred in the absence of feminization or cardiac dysfunction, two commonly observed deleterious effects of exogenous estrogen administration. Thus, 17α-E2 holds potential as a novel therapeutic for alleviating age-related metabolic dysfunction through tissue-specific effects.

Hypoxia Represses ER-α Expression and Inhibits Estrogen-Induced Regulation of Ca2+-Activated K+ Channel Activity and Myogenic Tone in Ovine Uterine Arteries: Causal Role of DNA Methylation

Previous in vivo study demonstrated that chronic hypoxia during gestation was associated with estrogen receptor-α (ER-α) gene repression in ovine uterine arteries. Yet, it remains undetermined whether hypoxia had a direct effect and if DNA methylation played a causal role in hypoxia-mediated ER-α gene repression. Thus, this study tested the hypothesis that prolonged hypoxia has a direct effect and increases promoter methylation resulting in ER-α gene repression and inhibition of estrogen-mediated adaptation of uterine vascular tone. Uterine arteries isolated from nonpregnant and pregnant sheep were treated ex vivo with 21.0% O2 and 10.5% O2 for 48 hours. Hypoxia significantly increased ER-α promoter methylation at both specificity protein-1 and upstream stimulatory factor binding sites, decreased specificity protein-1 and upstream stimulatory factor binding to the promoter, and suppressed ER-α expression in uterine arteries of pregnant animals. Of importance, the effects of hypoxia were blocked by a methylation inhibitor 5-aza-2'-deoxycytidine. In addition, hypoxia abrogated steroid hormone-mediated increase in ER-α expression and inhibited the hormone-induced increase in large-conductance Ca(2+)-activated K(+) channel activity and decrease in myogenic tone in uterine arteries of nonpregnant animals, which were reversed by 5-aza-2'-deoxycytidine. The results provide novel evidence of a direct effect of hypoxia on heightened promoter methylation that plays a causal role in ER-α gene repression and ablation of steroid hormone-mediated adaptation of uterine arterial large conductance Ca(2+)-activated K(+) channel activity and myogenic tone in pregnancy.

Sex differences in immune responses to infectious diseases

PURPOSE

The influence of sex hormones is recognized to account for the susceptibility and distinct outcomes of diverse infectious diseases.

METHODS

This review discusses several variables including differences in behavior and exposure to pathogens, genetic, and immunological factors.

CONCLUSION

Understanding sex-based differences in immunity during different infectious diseases is crucial in order to provide optimal disease management for both sexes.

A cluster of noncoding RNAs activates the ESR1 locus during breast cancer adaptation

Estrogen receptor-α (ER)-positive breast cancer cells undergo hormone-independent proliferation after deprivation of oestrogen, leading to endocrine therapy resistance. Up-regulation of the ER gene (ESR1) is critical for this process, but the underlying mechanisms remain unclear. Here we show that the combination of transcriptome and fluorescence in situ hybridization analyses revealed that oestrogen deprivation induced a cluster of noncoding RNAs that defined a large chromatin domain containing the ESR1 locus. We termed these RNAs as Eleanors (ESR1 locus enhancing and activating noncoding RNAs). Eleanors were present in ER-positive breast cancer tissues and localized at the transcriptionally active ESR1 locus to form RNA foci. Depletion of one Eleanor, upstream (u)-Eleanor, impaired cell growth and transcription of intragenic Eleanors and ESR1 mRNA, indicating that Eleanors cis-activate the ESR1 gene. Eleanor-mediated gene activation represents a new type of locus control mechanism and plays an essential role in the adaptation of breast cancer cells.

Estrogen-receptor-positive breast cancer cells undergo hormone-independent proliferation after long-term oestrogen deprivation and become resistant to endocrine therapies. Here, the authors report a cluster of noncoding RNAs important for this adaptation process.

Estrogen receptors regulate innate immune cells and signaling pathways

Humans show strong sex differences in immunity to infection and autoimmunity, suggesting sex hormones modulate immune responses. Indeed, receptors for estrogens (ER) regulate cells and pathways in the innate and adaptive immune system, as well as immune cell development. ERs are ligand-dependent transcription factors that mediate long-range chromatin interactions and form complexes at gene regulatory elements, thus promoting epigenetic changes and transcription. ERs also participate in membrane-initiated steroid signaling to generate rapid responses. Estradiol and ER activity show profound dose- and context-dependent effects on innate immune signaling pathways and myeloid cell development. While estradiol most often promotes the production of type I interferon, innate pathways leading to pro-inflammatory cytokine production may be enhanced or dampened by ER activity. Regulation of innate immune cells and signaling by ERs may contribute to the reported sex differences in innate immune pathways. Here we review the recent literature and highlight several molecular mechanisms by which ERs regulate the development or functional responses of innate immune cells.

Gene expression profile of the neonatal female mouse brain after administration of testosterone propionate

INTRODUCTION

Clinical care decisions for peripubertal adolescents with gender dysphoria (GD) should be made carefully. Furthermore, the identification of biomarkers is very important for rapid and accurate diagnosis of GD in young people.

AIM

The aim of this study was to investigate gene expression profiles during masculinization of the neonatal female mouse brain by testosterone and to identify biomarkers related to GD.

METHODS

Microarray analysis was performed using RNAs extracted from the brains of neonatal mice treated by intraperitoneal injection of testosterone propionate during the sexual determination period. Sequence motif enrichment analysis for sex hormone receptor responsive elements was performed for the flanking regions of genes that showed significant expression changes following administration of testosterone propionate.

MAIN OUTCOME MEASURES

We revealed a gene set with marked changes in expression during brain masculinization of neonatal female mice following administration of testosterone propionate.

RESULTS

We identified 334 genes that showed differential expression in the masculinized neonatal female brain after testosterone propionate treatment. Interestingly, most of these genes are not reported to be expressed in a sexually dimorphic manner. Moreover, sequence motif enrichment analysis suggested that masculinization of the neonatal female brain by testosterone was controlled more by estrogen receptors than androgen receptors.

CONCLUSIONS

Differences in genes that are expressed differentially following administration of testosterone injection from known sexually dimorphic genes suggest that many GD-related genes are upregulated during female brain masculinization. The gene set identified in this study provides a basis to better understand the mechanisms of GD and delineate its associated biomarkers.

Estrogen receptors regulate the estrous behavior induced by progestins, peptides, and prostaglandin E2

The role of classical estrogen receptors (ERs) in priming female reproductive behavior has been studied previously; however, the participation of this receptor during activation of estrous behavior has not been extensively studied. The purpose of this work was to test the possibility that the facilitation of lordosis behavior in estrogen-primed rats by progesterone (P) and its 5α- and 5β-reduced metabolites, gonadotropin-releasing hormone (GnRH), leptin, prostaglandin E2 (PGE2) and vagino-cervical stimulation (VCS) involves interactions with classical ERs by using the selective ER modulator, tamoxifen. To further assess the role of ERs, we also explored the effects of the pure ER antagonist, ICI182780 (ICI), on estrous behavior induced by P and GnRH. Ovariectomized, estrogen-primed rats (5μg estradiol benzoate 40h earlier) were injected intraventricularly with the above-mentioned compounds, or they received VCS. All compounds and VCS effectively facilitated estrous behavior when tested at 60, 120 or 240min after infusion or application of VCS. Intraventricular infusion of tamoxifen (5μg), 30min before, significantly attenuated estrous behaviors induced in estradiol-primed rats by P, most of its 5α- and 5β-reduced metabolites, GnRH, and PGE2, but not by VCS. Although there was a trend for reduction, tamoxifen did not significantly decrease lordosis in females treated with 5β-pregnan-3,20-dione. ICI also inhibited lordosis behavior induced by P and GnRH at some testing intervals. These results suggest that activation of classical ERs participates in the triggering effects on estrous behavior induced by agents with different chemical structures that do not bind directly to ERs.

Support of a bi-faceted role of estrogen receptor β (ERβ) in ERα-positive breast cancer cells

The expression of estrogen receptor α (ERα) in breast cancer identifies patients most likely to respond to endocrine treatment. The second ER, ERβ, is also expressed in breast tumors, but its function and therapeutic potential need further study. Although in vitro studies have established that ERβ opposes transcriptional and proliferative functions of ERα, several clinical studies report its correlation with proliferative markers and poorer prognosis. The data demonstrate that ERβ opposes ERα are primarily based on transient expression of ERβ. Here, we explored the functions of constitutively expressed ERβ in ERα-positive breast cancer lines MCF7 and T47D. We found that ERβ, under these conditions heterodimerized with ERα in the presence and absence of 17β-estradiol, and induced genome-wide transcriptional changes. Widespread anti-ERα signaling was, however, not observed and ERβ was not antiproliferative. Tamoxifen antagonized proliferation and ER-mediated gene regulation both in the presence and absence of ERβ. In conclusion, ERβ's role in cells adapted to its expression appears to differ from its role in cells with transient expression. Our study is important because it provides a deeper understanding of ERβ's role in breast tumors that coexpress both receptors and supports an emerging bi-faceted role of ERβ.

The proteasome inhibitor bortezomib induces an inhibitory chromatin environment at a distal enhancer of the estrogen receptor-α gene

Expression of the estrogen receptor-α (ERα) gene, ESR1, is a clinical biomarker used to predict therapeutic outcome of breast cancer. Hence, there is significant interest in understanding the mechanisms regulating ESR1 gene expression. Proteasome activity is increased in cancer and we previously showed that proteasome inhibition leads to loss of ESR1 gene expression in breast cancer cells. Expression of ESR1 mRNA in breast cancer cells is controlled predominantly through a proximal promoter within ∼400 base pair (bp) of the transcription start site (TSS). Here, we show that loss of ESR1 gene expression induced by the proteasome inhibitor bortezomib is associated with inactivation of a distal enhancer located 150 kilobases (kb) from the TSS. Chromatin immunoprecipitation assays reveal several bortezomib-induced changes at the distal site including decreased occupancy of three critical transcription factors, GATA3, FOXA1, and AP2γ. Bortezomib treatment also resulted in decreased histone H3 and H4 acetylation and decreased occupancy of histone acetyltransferase, p300. These data suggest a mechanism to explain proteasome inhibitor-induced loss of ESR1 mRNA expression that highlights the importance of the chromatin environment at the −150 kb distal enhancer in regulation of basal expression of ESR1 in breast cancer cells.

Modulation of estrogen receptor alpha activity and expression during breast cancer progression

Seventy percent of breast tumors express the estrogen receptor (ER), which is generally considered to predict a better outcome relative to ER-negative tumors, as they often respond to antiestrogen therapies. During cancer progression, mammary tumors can escape from estrogen control, resulting in the acquisition of invasive properties and resistance to treatment. ER expression is a dynamic phenomenon and is finely regulated at numerous levels, including the gene, mRNA, and protein levels. As a consequence, many molecular mechanisms have been implicated in modulating ER activity and estrogen signaling in mammary cancer. In fact, one-third of ER-positive breast cancer cells do not respond to first-line endocrine therapies, and a large subset of relapsing tumors retain ER expression. Increased knowledge of these mechanisms has led to the development of better prognostic methods and targeted therapies for patients; however, additional research is still needed to improve patient survival. In this chapter, we focus on the signaling pathways leading to changes in or loss of ER activity in breast cancer progression.

Estrogen receptor-α, RBCK1, and protein kinase C β 1 cooperate to regulate estrogen receptor-α gene expression

Estrogen receptor α (ERα) is initially overexpressed in two-thirds of all breast cancers and is involved in its development and proliferation. We previously reported that the RanBP-type and C3HC4-type zinc finger containing 1 (RBCK1) interacts with the ERα promoter and that RBCK1 expression positively correlates with ERα levels, expression of ERα downstream target genes, and proliferation of breast cancer cells. Based on this, and that RBCK1 positively correlates with ERα expression in breast cancer samples, we propose RBCK1 as a potential therapeutic target in breast cancer acting as a modulator of ERα expression. To further explore this, the molecular mechanism by which RBCK1 regulates ERα expression has to be defined. Here, we show that ERα, RBCK1, and the RBCK1-interacting protein protein kinase C β 1 (PKCβ(I)) co-occupy a previously identified ERα binding region in the proximal ERα promoter. We describe a number of mechanistic details of this complex including that RBCK1 recruitment to the ERα promoter B is facilitated by ERα, which in turn facilitates PKCβ(I) recruitment and PKCβ(I)-dependent histone modifications. Furthermore, ERα regulation of its own mRNA expression is facilitated by RBCK1 recruitment, suggesting an ERα coactivator function of RBCK1. The interaction between RBCK1 and ERα was dependent on the E3 ubiquitin ligase domain of RBCK1 and the activating function-1 domain of ERα. The ligand-binding function of ERα does not influence the interaction with RBCK1. In summary, our data provide insight into the molecular mechanism by which ERα expression is modulated in breast cancer cells.

Progression of mouse skin carcinogenesis is associated with increased ERα levels and is repressed by a dominant negative form of ERα

Estrogen receptors (ER), namely ERα and ERβ, are hormone-activated transcription factors with an important role in carcinogenesis. In the present study, we aimed at elucidating the implication of ERα in skin cancer, using chemically-induced mouse skin tumours, as well as cell lines representing distinct stages of mouse skin oncogenesis. First, using immunohistochemical staining we showed that ERα is markedly increased in aggressive mouse skin tumours in vivo as compared to the papilloma tumours, whereas ERβ levels are low and become even lower in the aggressive spindle tumours of carcinogen-treated mice. Then, using the multistage mouse skin carcinogenesis model, we showed that ERα gradually increases during promotion and progression stages of mouse skin carcinogenesis, peaking at the most aggressive stage, whereas ERβ levels only slightly change throughout skin carcinogenesis. Stable transfection of the aggressive, spindle CarB cells with a dominant negative form of ERα (dnERα) resulted in reduced ERα levels and reduced binding to estrogen responsive elements (ERE)-containing sequences. We characterized two highly conserved EREs on the mouse ERα promoter through which dnERα decreased endogenous ERα levels. The dnERα-transfected CarB cells presented altered protein levels of cytoskeletal and cell adhesion molecules, slower growth rate and impaired anchorage-independent growth in vitro, whereas they gave smaller tumours with extended latency period of tumour onset in vivo. Our findings suggest an implication of ERα in the aggressiveness of spindle mouse skin cancer cells, possibly through regulation of genes affecting cell shape and adhesion, and they also provide hints for the effective targeting of spindle cancer cells by dnERα.

Common classification schemes for PCB congeners and the gene expression of CYP17, CYP19, ESR1 and ESR2

BACKGROUND

Reliable techniques to measure polychlorinated biphenyl (PCB) congeners make the clearer definition of their effects on human health possible. Given that PCBs are classified as endocrine disrupters, we sought to explore the expression of some key genes involved in sex steroid metabolism.

OBJECTIVES

To examine common classification schemes of PCB congeners and determine whether exposure to groups classified by mechanism of action alter the gene expression (GE) of CYP17, CYP19, and ESR1 and ESR2.

METHODS

GE and exposure to various classifications of lipid-adjusted PCB congeners were examined in 139 daughters of the Michigan Fisheaters' Cohort. Using mixed models analyses and adjusting for age, menopausal status, and current use of oral contraceptives and hormone replacement therapy, GE data were regressed on exposure to PCB congener groupings based on mechanism of action.

RESULTS

Three novel findings are elucidated: first, that up-regulation of CYP19 expression is associated with exposure to PCB groupings containing dioxin-like, potentially anti-estrogenic, immunotoxic congeners, including PCB IUPAC #74, #105, #118, #138, #156, #157, #158, #167, and #170 from this cohort. Second, that exposure to similar congeners (PCB IUPAC #105, #156, #157, #158, and #167 in this cohort) but using a classification based solely on hormonal mechanisms of action is associated with increased expression of ESR2. Third, that increased expression of CYP17 is of borderline significance when associated with exposure to PCB IUPAC #118, #138, and #156.

CONCLUSIONS

These findings are both counter-intuitive and intriguing. Rather than exhibiting anti-estrogenic effects alone, they suggest that these congeners up-regulate the major enzyme involved in estrogen synthesis and tend to confirm previous findings of links between AhR and ER signaling pathways. Replication of these findings, expansion of the number of genes examined, exploration of mixtures of environmental chemicals, and subsequent study of health outcomes in a larger cohort are future priorities.

Regulation of estrogen receptor α N-terminus conformation and function by peptidyl prolyl isomerase Pin1

Estrogen receptor alpha (ERα), a key driver of growth in the majority of breast cancers, contains an unstructured transactivation domain (AF1) in its N terminus that is a convergence point for growth factor and hormonal activation. This domain is controlled by phosphorylation, but how phosphorylation impacts AF1 structure and function is unclear. We found that serine 118 (S118) phosphorylation of the ERα AF1 region in response to estrogen (agonist), tamoxifen (antagonist), and growth factors results in recruitment of the peptidyl prolyl cis/trans isomerase Pin1. Phosphorylation of S118 is critical for Pin1 binding, and mutation of S118 to alanine prevents this association. Importantly, Pin1 isomerizes the serine118-proline119 bond from a cis to trans isomer, with a concomitant increase in AF1 transcriptional activity. Pin1 overexpression promotes ligand-independent and tamoxifen-inducible activity of ERα and growth of tamoxifen-resistant breast cancer cells. Pin1 expression correlates with proliferation in ERα-positive rat mammary tumors. These results establish phosphorylation-coupled proline isomerization as a mechanism modulating AF1 functional activity and provide insight into the role of a conformational switch in the functional regulation of the intrinsically disordered transactivation domain of ERα.

Identification of novel targets for breast cancer by exploring gene switches on a genome scale

BACKGROUND

An important feature that emerges from analyzing gene regulatory networks is the "switch-like behavior" or "bistability", a dynamic feature of a particular gene to preferentially toggle between two steady-states. The state of gene switches plays pivotal roles in cell fate decision, but identifying switches has been difficult. Therefore a challenge confronting the field is to be able to systematically identify gene switches.

RESULTS

We propose a top-down mining approach to exploring gene switches on a genome-scale level. Theoretical analysis, proof-of-concept examples, and experimental studies demonstrate the ability of our mining approach to identify bistable genes by sampling across a variety of different conditions. Applying the approach to human breast cancer data identified genes that show bimodality within the cancer samples, such as estrogen receptor (ER) and ERBB2, as well as genes that show bimodality between cancer and non-cancer samples, where tumor-associated calcium signal transducer 2 (TACSTD2) is uncovered. We further suggest a likely transcription factor that regulates TACSTD2.

CONCLUSIONS

Our mining approach demonstrates that one can capitalize on genome-wide expression profiling to capture dynamic properties of a complex network. To the best of our knowledge, this is the first attempt in applying mining approaches to explore gene switches on a genome-scale, and the identification of TACSTD2 demonstrates that single cell-level bistability can be predicted from microarray data. Experimental confirmation of the computational results suggest TACSTD2 could be a potential biomarker and attractive candidate for drug therapy against both ER+ and ER- subtypes of breast cancer, including the triple negative subtype.

Resveratrol, through NF-Y/p53/Sin3/HDAC1 complex phosphorylation, inhibits estrogen receptor alpha gene expression via p38MAPK/CK2 signaling in human breast cancer cells

Agents to counteract acquired resistance to hormonal therapy for breast cancer would substantially enhance the long-term benefits of hormonal therapy. In the present study, we demonstrate how resveratrol (Res) inhibits human breast cancer cell proliferation, including MCF-7 tamoxifen-resistant cells (IC(50) values for viability were in the 30-45 μM range). We show that Res, through p38(MAPK) phosphorylation, causes induction of p53, which recruits at the estrogen receptor α (ERα) proximal promoter, leading to an inhibition of ERα expression in terms of mRNA and protein content. These events appear specifically p53 dependent, since they are drastically abrogated with p53-targeting siRNA. Coimmunoprecipitation assay showed specific interaction between p53, the Sin3A corepressor, and histone deacetylase 1 (HDAC1), which was phosphorylated. The enhancement of the tripartite complex p53/Sin3A/HDAC1, together with NF-Y on Res treatment, was confirmed by chromatin immunoprecipitation analyses, with a concomitant release of Sp1 and RNA polymerase II, thereby inhibiting the cell transcriptional machinery. The persistence of such effects in MCF-7 tamoxifen-resistant cells at a higher extent than parental MCF-7 cells addresses how Res may be considered a useful pharmacological tool to be exploited in the adjuvant settings for treatment of breast cancer developing hormonal resistance.

Kinome screening for regulators of the estrogen receptor identifies LMTK3 as a new therapeutic target in breast cancer

Therapies targeting estrogen receptor α (ERα, encoded by ESR1) have transformed the treatment of breast cancer. However, large numbers of women relapse, highlighting the need for the discovery of new regulatory targets modulating ERα pathways. An siRNA screen identified kinases whose silencing alters the estrogen response including those previously implicated in regulating ERα activity (such as mitogen-activated protein kinase and AKT). Among the most potent regulators was lemur tyrosine kinase-3 (LMTK3), for which a role has not previously been assigned. In contrast to other modulators of ERα activity, LMTK3 seems to have been subject to Darwinian positive selection, a noteworthy result given the unique susceptibility of humans to ERα+ breast cancer. LMTK3 acts by decreasing the activity of protein kinase C (PKC) and the phosphorylation of AKT (Ser473), thereby increasing binding of forkhead box O3 (FOXO3) to the ESR1 promoter. LMTK3 phosphorylated ERα, protecting it from proteasomal degradation in vitro. Silencing of LMTK3 reduced tumor volume in an orthotopic mouse model and abrogated proliferation of ERα+ but not ERα- cells, indicative of its role in ERα activity. In human cancers, LMTK3 abundance and intronic polymorphisms were significantly associated with disease-free and overall survival and predicted response to endocrine therapies. These findings yield insights into the natural history of breast cancer in humans and reveal LMTK3 as a new therapeutic target.

Modulation of steroid hormone receptor activity

Classical steroid hormones (SHs) - estrogens, androgens, progestins, glucocorticoids and mineralocorticoids - play critical roles in the regulation of reproduction, metabolism and cancer. SHs act via their cognate steroid hormone receptors (SHRs) in multiple target tissues throughout the body, exerting their physiological effects through nuclear receptor (NR)-mediated gene transcription. Since SHRs are the mediators of steroid hormone signalling in cells, regulation of their expression and function is critical for appropriate physiological responses to SHs. Cells regulate SHRs by determining the cellular concentration of SHR proteins in the cell and by tightly regulating their activity through post-translational modifications and interactions with coactivator protein complexes. In this chapter we will examine each of these regulatory mechanisms and assess their functional impact on the activity of SHRs.

Repression of ESR1 through actions of estrogen receptor alpha and Sin3A at the proximal promoter

Gene expression results from the coordinated actions of transcription factor proteins and coregulators. Estrogen receptor alpha (ERalpha) is a ligand-activated transcription factor that can both activate and repress the expression of genes. Activation of transcription by estrogen-bound ERalpha has been studied in detail, as has antagonist-induced repression, such as that which occurs by tamoxifen. How estrogen-bound ERalpha represses gene transcription remains unclear. In this report, we identify a new mechanism of estrogen-induced transcriptional repression by using the ERalpha gene, ESR1. Upon estrogen treatment, ERalpha is recruited to two sites on ESR1, one distal (ENH1) and the other at the proximal (A) promoter. Coactivator proteins, namely, p300 and AIB1, are found at both ERalpha-binding sites. However, recruitment of the Sin3A repressor, loss of RNA polymerase II, and changes in histone modifications occur only at the A promoter. Reduction of Sin3A expression by RNA interference specifically inhibits estrogen-induced repression of ESR1. Furthermore, an estrogen-responsive interaction between Sin3A and ERalpha is identified. These data support a model of repression wherein actions of ERalpha and Sin3A at the proximal promoter can overcome activating signals at distal or proximal sites and ultimately decrease gene expression.

Nuclear factor-kappaB regulates estrogen receptor-alpha transcription in the human heart

Estrogen receptor (ER)-mediated effects have been associated with the modulation of myocardial hypertrophy in animal models and in humans, but the regulation of ER expression in the human heart has not yet been analyzed. In various cell lines and tissues, multiple human estrogen receptor alpha (hERalpha) mRNA isoforms are transcribed from distinct promoters and differ in their 5'-untranslated regions. Using PCR-based strategies, we show that in the human heart the ERalpha mRNA is transcribed from multiple promoters, namely, A, B, C, and F, of which the F-promoter is most frequently used variant. Transient transfection reporter assays in a human cardiac myocyte cell line (AC16) with F-promoter deletion constructs demonstrated a negative regulatory region within this promoter. Site-directed mutagenesis and electrophoretic mobility shift assays indicated that NF-kappaB binds to this region. An inhibition of NF-kappaB activity by parthenolide significantly increased the transcriptional activity of the F-promoter. Increasing NF-kappaB expression by tumor necrosis factor-alpha reduced the expression of ERalpha, indicating that the NF-kappaB pathway inhibits expression of ERalpha in human cardiomyocytes. Finally, 17beta-estradiol induced the transcriptional activity of hERalpha promoters A, B, C, and F. In conclusion, inflammatory stimuli suppress hERalpha expression via activation and subsequent binding of NF-kappaB to the ERalpha F-promoter, and 17beta-estradiol/hERalpha may antagonize the inhibitory effect of NF-kappaB. This suggests interplay between estrogen/estrogen receptors and the pro-hypertrophic and inflammatory responses to NF-kappaB.

Dioxin increases the interaction between aryl hydrocarbon receptor and estrogen receptor alpha at human promoters

Recent studies have shown that activated aryl hydrocarbon receptor (AHR) induced the recruitment of estrogen receptor-alpha (ERalpha) to AHR-regulated genes and that AHR is recruited to ERalpha-regulated genes. However, these findings were limited to a small number of well-characterized AHR- or ERalpha-responsive genes with little knowledge of what was occurring at other genomic regions. In this study, we showed using chromatin immunoprecipitation followed by hybridization to promoter focused microarrays (ChIP-chip) that 2,3,7,8-tetrachlorodibenzo-p-dioxin treatment significantly increased the overlap of genomic regions bound by both AHR and ERalpha. Conventional and sequential ChIPs confirmed the recruitment of AHR and ERalpha to many of the identified regions. Transcription factor binding site analysis revealed an overrepresentation of aryl hydrocarbon receptor response elements in regions bound by both AHR and ERalpha, suggesting that AHR was the important factor determining the recruitment of ERalpha to these regions. RNA interference-mediated knockdown of AHR confirmed its requirement for the recruitment of ERalpha to some, but not all, of the shared regions. Our findings demonstrate not only that dioxin induces the recruitment of ERalpha to AHR target genes but also that AHR is recruited to estrogen-responsive regions in a gene-specific manner, suggesting that AHR utilizes both of these mechanisms to modulate estrogen-dependent signaling.

Estradiol regulates expression of estrogen receptor ERalpha46 in human macrophages

Background

Monocytes and macrophages are key innate immune effector cells that produce cytokines and chemokines upon activation. We and others have shown that 17β-estradiol (E2) has a direct role in the modulation of monocyte and macrophage immune function. However, relatively little is known about the ability of E2 to regulate isoform expression of estrogen receptors (ERs) in these cells.

Methodology/Principal Findings

In this study, we quantify expression of ERα and ERβ in human monocytes and macrophages. We also show for the first time that the N-terminal truncated ERα variant, ERα46, is expressed in both cell types. Promoter utilization studies reveal that transcription of ERα in both cell types occurs from upstream promoters E and F. Treatment with E2 induces ERα expression in macrophages but has no effect on ERβ levels in either cell type. During monocyte-to-macrophage differentiation, ERα is upregulated in a time-dependent manner. Previous studies by our group demonstrated that E2 treatment attenuates production of the chemokine CXCL8 in an ER-dependent manner. We now show that ERα expression levels parallel the ability of E2 to suppress CXCL8 production.

Conclusions/Significance

This work demonstrates for the first time that human macrophages predominantly express the truncated ER variant ERαp46, which is estradiol-inducible. This is mediated through usage of the ERα F promoter. Alternative promoter usage may account for tissue and cell type-specific differences in estradiol-induced effects on gene expression. These studies signify the importance of ERα expression and regulation in the ability of E2 to modulate innate immune responses.

Krüppel-Like Factor 9 Is a Negative Regulator of Ligand-Dependent Estrogen Receptor α Signaling in Ishikawa Endometrial Adenocarcinoma Cells

Estrogen and progesterone, acting through their respective receptors and other nuclear proteins, exhibit opposing activities in target cells. We previously reported that Krüppel-like factor 9 (KLF9) cooperates with progesterone receptor (PR) to facilitate P-dependent gene transcription in uterine epithelial cells. Here we evaluated whether KLF9 may further support PR function by directly opposing estrogen receptor (ER) signaling. Using human Ishikawa endometrial epithelial cells, we showed that 17β-estradiol (E2)-dependent down-regulation of ERα expression was reversed by a small interfering RNA to KLF9. Transcription assays with the E2-sensitive 4× estrogen-responsive element-thymidine kinase-promoter-luciferase reporter gene demonstrated inhibition of ligand-dependent ERα transactivation with ectopic KLF9 expression. E2 induced PR-A/B and PR-B isoform expression in the absence of effects on KLF9 levels. Addition of KLF9 small interfering RNA augmented E2 induction of PR-A/B while abrogating that of PR-B, indicating selective E2-mediated inhibition of PR-A by KLF9. Chromatin immunoprecipitation of the ERα minimal promoter demonstrated KLF9 promotion of E2-dependent ERα association to a region containing functional GC-rich motifs. KLF9 inhibited the recruitment of the ERα coactivator specificity protein 1 (Sp1) to the PR proximal promoter region containing a half-estrogen responsive element and GC-rich sites, but had no effect on Sp1 association to the PR distal promoter region containing GC-rich sequences. In vivo association of KLF9 and Sp1, but not of ERα with KLF9 or Sp1, was observed in control and E2-treated cells. Our data identify KLF9 as a transcriptional repressor of ERα signaling and suggest that it may function at the node of PR and ER genomic pathways to influence cell proliferation.

Molecular basis for estrogen receptor alpha deficiency in BRCA1-linked breast cancer

BACKGROUND

BRCA1-mutant breast tumors are typically estrogen receptor alpha (ER alpha) negative, whereas most sporadic tumors express wild-type BRCA1 and are ER alpha positive. We examined a possible mechanism for the observed ER alpha-negative phenotype of BRCA1-mutant tumors.

METHODS

We used a breast cancer disease-specific microarray to identify transcripts that were differentially expressed between paraffin-embedded samples of 17 BRCA1-mutant and 14 sporadic breast tumors. We measured the mRNA levels of estrogen receptor 1 (ESR1) (the gene encoding ER alpha), which was differentially expressed in the tumor samples, by quantitative polymerase chain reaction. Regulation of ESR1 mRNA and ER alpha protein expression was assessed in human breast cancer HCC1937 cells that were stably reconstituted with wild-type BRCA1 expression construct and in human breast cancer T47D and MCF-7 cells transiently transfected with BRCA1-specific short-interfering RNA (siRNA). Chromatin immunoprecipitation assays were performed to determine if BRCA1 binds the ESR1 promoter and to identify other interacting proteins. Sensitivity to the antiestrogen drug fulvestrant was examined in T47D and MCF-7 cells transfected with BRCA1-specific siRNA. All statistical tests were two-sided.

RESULTS

Mean ESR1 gene expression was 5.4-fold lower in BRCA1-mutant tumors than in sporadic tumors (95% confidence interval [CI] = 2.6-fold to 40.1-fold, P = .0019). The transcription factor Oct-1 recruited BRCA1 to the ESR1 promoter, and both BRCA1 and Oct-1 were required for ER alpha expression. BRCA1-depleted breast cancer cells expressing exogenous ER alpha were more sensitive to fulvestrant than BRCA1-depleted cells transfected with empty vector (T47D cells, the mean concentration of fulvestrant that inhibited the growth of 40% of the cells [IC40] for empty vector versus ER alpha: >10(-5) versus 8.0 x 10(-9) M [95% CI = 3.1 x 10(-10) to 3.2 x 10(-6) M]; MCF-7 cells, mean IC40 for empty vector versus ER alpha: >10(-5) versus 4.9 x 10(-8) M [95% CI = 2.0 x 10(-9) to 3.9 x 10(-6) M]).

CONCLUSIONS

BRCA1 alters the response of breast cancer cells to antiestrogen therapy by directly modulating ER alpha expression.

Positive Cross-Regulatory Loop Ties GATA-3 to Estrogen Receptor α Expression in Breast Cancer

The transcription factor GATA-3 is required for normal mammary gland development, and its expression is highly correlated with estrogen receptor alpha (ER alpha) in human breast tumors. However, the functional role of GATA-3 in ER alpha-positive breast cancers is yet to be established. Here, we show that GATA-3 is required for estradiol stimulation of cell cycle progression in breast cancer cells. The role of GATA-3 in estradiol signaling requires the direct positive regulation of the expression of the ER alpha gene itself by GATA-3. GATA-3 binds to two cis-regulatory elements located within the ER alpha gene, and this is required for RNA polymerase II recruitment to ER alpha promoters. Reciprocally, ER alpha directly stimulates the transcription of the GATA-3 gene, indicating that these two factors are involved in a positive cross-regulatory loop. Moreover, GATA-3 and ER alpha regulate their own expression in breast cancer cells. Hence, this transcriptional coregulatory mechanism accounts for the robust coexpression of GATA-3 and ER alpha in human breast cancers. In addition, these results highlight the crucial role of GATA-3 for the response of ER alpha-positive breast cancers to estradiol. Moreover, they identify GATA-3 as a critical component of the master cell-type-specific transcriptional network including ER alpha and FoxA1 that dictates the phenotype of hormone-dependent breast cancer.

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

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

Osteocytes use estrogen receptor alpha to respond to strain but their ERalpha content is regulated by estrogen

The role of mechanical strain and estrogen status in regulating ERalpha levels in bone cells was studied in female rats. OVX is associated with decreased ERalpha protein expression/osteocyte, whereas habitual strain and artificial loading has only a small but positive effect, except on the ulna's medial surface, where artificial loading stimulates reversal of resorption to formation.

INTRODUCTION

Osteoporosis is the most widespread failure of bones' ability to match their architectural strength to their habitual load bearing. In men and women, the severity of bone loss is associated with bioavailability of estrogen. This association could result from the estrogen receptor (ER) involvement in bone cells' adaptive response to loading.

MATERIALS AND METHODS

In vivo semiquantitative analysis of the amount of ERalpha protein per osteocyte was performed in immuno-cytochemically stained sections from control and loaded rat ulna, as well as tibias of ovariectomy (OVX) and sham-operated female rats. In vitro, the effect of exogenous estrogen (10(-8) M) and mechanical strain (3400 microepsilon, 1 Hz, 600 cycles) on the expression of ERalpha mRNA levels was assessed in ROS 17/2.8 cells in monolayers using real-time PCR and ER promoter activity. ERalpha translocation in response to exogenous estrogen and mechanical strain was assessed in both ROS 17/2.8 and MLO-Y4 cells.

RESULTS

More than 90 percent of tibial osteocytes express ERalpha, the level/osteocyte being higher in cortical than cancellous bone. OVX is associated with decreased ERalpha protein expression/osteocyte, whereas in the ulna habitual strain and that caused by artificial loading had only a small but positive effect, except on the medial surface, where loading stimulates reversal of resorption to formation. In unstimulated osteocytes and osteoblasts in situ, and osteocyte-like and osteoblast-like cells in vitro, ERalpha is predominantly cytoplasmic. In vitro, both strain and estrogen stimulate transient ERalpha translocation to the nucleus and transient changes in ERalpha mRNA. Strain but not estrogen also induces discrete membrane localization of ERalpha.

CONCLUSIONS

Bone cells' responses to both strain and estrogen involve ERalpha, but only estrogen regulates its cellular concentration. This is consistent with the hypothesis that bone loss associated with estrogen deficiency is a consequence of reduction in ERalpha number/activity associated with lower estrogen concentration reducing the effectiveness of bone cells' anabolic response to strain.

Altered target gene regulation controlled by estrogen receptor-alpha concentration

Estrogen receptor-alpha (ERalpha) is a transcriptional activator whose concentration is tightly regulated by the cellular environment. In breast tumors of postmenopausal women, elevated receptor concentrations can be associated with negative clinical outcomes, yet it remains poorly understood how such high levels impact ERalpha function. We previously demonstrated that high nuclear concentrations of ERalpha in breast cancer cells bypass the requirement for ligand and are sufficient to activate transcription and accelerate proliferation. Here, we extended those studies and asked whether the transcriptional targets and activation mechanism are similar or different from that of estrogen-stimulated ERalpha. We found that at elevated levels, ERalpha activated, but could not repress, known estrogen-responsive genes. Moreover, the set of activated genes was expanded to include the uterine-restricted target gene, complement component 3. The activation mechanism of ERalpha under these conditions depends both on activation function-1 and residues in the proximal region of the ligand-binding domain. Mutations of aspartate 351 and leucine 372 can inhibit ERalpha transcriptional activity gained at high concentrations and discriminate concentration-inducible ERalpha function from that induced by estrogen. Moreover, we demonstrate that at high levels, ERalpha stimulates transcription without recruiting steroid receptor coactivator-3 and without interference by a Gal4-receptor interaction domain box fusion protein containing LxxLL motifs, further distinguishing this mode of regulation from known activation mechanisms. Together these results demonstrate that the concentration of receptor in breast cancer cells can influence the pattern of target gene expression through a noncanonical activation mechanism.

Cloning and characterization of the 5'-flanking region of the rat estrogen receptor beta gene

In the rat, estrogen receptor (ER) beta is preferentially expressed in the ovary and the prostate gland where it is transcriptionally regulated by testosterone. A single 5'-end of rERbeta cDNA was identified in these tissues by the 5'-RACE analysis in the present study. The transcription starting site was predicted at -335 from the translation starting signal (ATG), and a 640bp section of the 5'-flanking region of the gene was cloned. Luciferase reporter assays revealed this region to be responsible for cell-specific promoter activity and successive deletion analyses indicated that only 98bp were sufficient for basic promoter activity as well as for testosterone-dependent transcription. The sequence of the determined region found to demonstrate high homology with the mouse ERbeta promoter with more than 80% identity between positions -1 and -550. The rat region of -30/-110 also showed good homology with 69% identity to corresponding section of the human promoter. Putative cis-acting elements, USF/Arnt and AML1a, were found in common in the promoter regions of three species. The present study thus demonstrated the 5'-flanking region of the rERbeta gene to be a functional promoter.

Regulation of the estrogen receptor alpha minimal promoter by Sp1, USF-1 and ERalpha

The exact molecular mechanisms regulating estrogen receptor alpha (ERalpha) expression in breast tumors are unclear, but studies suggest that they are partly at the level of transcription. We have focused on the transcription factors that regulate the ERalpha minimal promoter, which we have previously shown to reside within the first 245 bp of the 5'-flanking region of the gene. Within this region are several elements essential for full ERalpha promoter transcriptional activity, including a GC box and an imperfect E box. In earlier studies we demonstrated an essential function for the Sp1 family of transcription factors in the regulation of ERalpha expression. We have now identified both USF-1 and ERalpha itself as components of a multi-protein complex of transcription factors that interacts at the ERalpha minimal promoter and is essential for its full transcriptional activity. Electrophoretic mobility shift assays demonstrated that Sp1 and USF-1, but not ERalpha, bind directly to the ERalpha minimal promoter. We showed by GST pull-down assays that ERalpha is able to interact in vitro with USF-1, suggesting, in addition to a possible interaction between ERalpha and Sp1, a mechanism whereby ERalpha is able to interact with the protein complex. Combined exogenous expression of the components of the complex in MCF-7 breast cancer cells resulted in a synergistic effect on transactivation of the ERalpha minimal promoter, suggesting that the importance of the protein complex is in the interactions among the components. Based upon these findings, we propose a possible model for transcription from the ERalpha minimal promoter.

The Ah receptor inhibits estrogen-induced estrogen receptor β in breast cancer cells

We have studied the effect of the aryl hydrocarbon receptor ligand 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on estrogen receptor (ER) beta gene expression in the human breast cancer cell line, T47D. TCDD inhibited 17beta-estradiol (E2)-induced up-regulation of both ER beta wild type and ER beta cx mRNA. Cycloheximide pre-treatment had no inhibitory effect, and the estimated half-life of ER beta mRNA of about 33 min was not changed by any hormone administration. Chromatin immunoprecipitation experiments showed recruitment of ER alpha to the ER beta promoter. Gel mobility shift experiments revealed an E2-induced protein binding to a half site estrogen response element in the ER beta promoter, and TCDD reduced that binding. These results show that ER alpha regulates the expression of its own heterodimerization partner, ER beta, in T47D cells. TCDD, an anti-estrogenic compound, inhibits ER alpha-mediated induction of ER beta mRNA. These findings add to our understanding of cross talk between dioxin and estrogen signaling in human cells.

SAFB2, a new scaffold attachment factor homolog and estrogen receptor corepressor

We have characterized previously the nuclear matrix protein/scaffold attachment factor (SAFB) as an estrogen receptor corepressor and as a potential tumor suppressor gene in breast cancer. A search of the human genome for other potential SAFB family members revealed that KIAA00138 (now designated as SAFB2) has high homology to SAFB (now designated as SAFB1). SAFB1 and SAFB2 are mapped adjacent to each other on chromosome 19p13.3 and are arranged in a bidirectional divergent configuration (head to head), being separated by a short (<500 bp) GC-rich intergenic region that can function as a bidirectional promoter. SAFB1 and SAFB2 share common functions but also have unique properties. As shown previously for SAFB1, SAFB2 functions as an estrogen receptor corepressor, and its overexpression results in inhibition of proliferation. SAFB1 and SAFB2 interact directly through a C-terminal domain, resulting in additive repression activity. They are coexpressed in a number of tissues, but unlike SAFB1, which is exclusively nuclear, SAFB2 is found in the cytoplasm as well as the nucleus. Consistent with its cytoplasmic localization, we detected an interaction between SAFB2 and vinexin, a protein involved in linking signaling to the cytoskeleton. Our findings suggest that evolutionary duplication of the SAFB gene has allowed it to retain crucial functions, but also to gain novel functions in the cytoplasm and/or nucleus.