Targeting estrogen responsive elements (EREs): design of potent transactivators for ERE-containing genes

The effect of estrogen in coronavirus disease 2019

The outcomes of coronavirus disease 2019 (COVID-19) vary between men and women. Some statistical reports have shown that men have a higher risk of developing COVID-19 and suffer from worse outcomes than females. Although there are many factors that can explain the high prevalence of COVID-19 in men, such as lifestyle habits and the different profile of comorbidities among sexes, the distinctions between male and female immune systems cannot be ignored. It has been sufficiently shown that sex differences have a critical influence on the shaping of immune response, which then leads to different pathogenesis in infectious diseases. Compared with males, females typically have a more effective innate and adaptive immune response to viral infections in COVID-19. What's more, there is a growing body of evidence showing that estrogen exerts an effect on the regulation of immune response. This article examines the effect and mechanism of estrogen on COVID-19.

CXXC5 as an unmethylated CpG dinucleotide binding protein contributes to estrogen-mediated cellular proliferation

Evidence suggests that the CXXC type zinc finger (ZF-CXXC) protein 5 (CXXC5) is a critical regulator/integrator of various signaling pathways that include the estrogen (E2)-estrogen receptor α (ERα). Due to its ZF-CXXC domain, CXXC5 is considered to be a member of the ZF-CXXC family, which binds to unmethylated CpG dinucleotides of DNA and through enzymatic activities for DNA methylation and/or chromatin modifications generates a chromatin state critical for gene expressions. Structural/functional features of CXXC5 remain largely unknown. CXXC5, suggested as transcription and/or epigenetic factor, participates in cellular proliferation, differentiation, and death. To explore the role of CXXC5 in E2-ERα mediated cellular events, we verified by generating a recombinant protein that CXXC5 is indeed an unmethylated CpG binder. We uncovered that CXXC5, although lacks a transcription activation/repression function, participates in E2-driven cellular proliferation by modulating the expression of distinct and mutual genes also regulated by E2. Furthermore, we found that the overexpression of CXXC5, which correlates with mRNA and protein levels of ERα, associates with poor prognosis in ER-positive breast cancer patients. Thus, CXXC5 as an unmethylated CpG binder contributes to E2-mediated gene expressions that result in the regulation of cellular proliferation and may contribute to ER-positive breast cancer progression.

Molecular mechanism of estrogen-estrogen receptor signaling

17β‐Estradiol (E2), as the main circulating estrogen hormone, regulates many tissue and organ functions in physiology. The effects of E2 on cells are mediated by the transcription factors and estrogen receptor (ER)α and ERβ that are encoded by distinct genes. Localized at the peri‐membrane, mitochondria, and the nucleus of cells that are dependent on estrogen target tissues, the ERs share similar, as well as distinct, regulatory potentials. Different intracellular localizations of the ERs result in dynamically integrated and finely tuned E2 signaling cascades that orchestrate cellular growth, differentiation, and death. The deregulation of E2–ER signaling plays a critical role in the initiation and progression of target tissue malignancies. A better understanding of the complex regulatory mechanisms that underlie ER actions in response to E2 therefore holds a critical trajectory for the development of novel prognostic and therapeutic approaches with substantial impacts on the systemic management of target tissue diseases.

Estradiol-Estrogen Receptor α Mediates the Expression of the CXXC5 Gene through the Estrogen Response Element-Dependent Signaling Pathway

17β-estradiol (E2), the primary circulating estrogen hormone, mediates physiological and pathophysiological functions of breast tissue mainly through estrogen receptor α (ERα). Upon binding to E2, ERα modulates the expression of target genes involved in the regulation of cellular proliferation primarily through interactions with specific DNA sequences, estrogen response elements (EREs). Our previous microarray results suggested that E2-ERα modulates CXXC5 expression. Because of the presence of a zinc-finger CXXC domain (ZF-CXXC), CXXC5 is considered to be a member of the ZF-CXXC family, which binds to non-methylated CpG dinucleotides. Although studies are limited, CXXC5 appears to participate as a transcription factor, co-regulator and/or epigenetic factor in the regulation of cellular events induced by various signaling pathways. However, how signaling pathways mediate the expression of CXXC5 is yet unclear. Due to the importance of E2-ERα signaling in breast tissue, changes in the CXXC5 transcription/synthesis could participate in E2-mediated cellular events as well. To address these issues, we initially examined the mechanism whereby E2-ERα regulates CXXC5 expression. We show here that CXXC5 is an E2-ERα responsive gene regulated by the interaction of E2-ERα with an ERE present at a region upstream of the initial translation codon of the gene.

Modulation of Estrogen Response Element-Driven Gene Expressions and Cellular Proliferation with Polar Directions by Designer Transcription Regulators

Estrogen receptor α (ERα), as a ligand-dependent transcription factor, mediates 17β-estradiol (E2) effects. ERα is a modular protein containing a DNA binding domain (DBD) and transcription activation domains (AD) located at the amino- and carboxyl-termini. The interaction of the E2-activated ERα dimer with estrogen response elements (EREs) of genes constitutes the initial step in the ERE-dependent signaling pathway necessary for alterations of cellular features. We previously constructed monomeric transcription activators, or monotransactivators, assembled from an engineered ERE-binding module (EBM) using the ERα-DBD and constitutively active ADs from other transcription factors. Monotransactivators modulated cell proliferation by activating and repressing ERE-driven gene expressions that simulate responses observed with E2-ERα. We reasoned here that integration of potent heterologous repression domains (RDs) into EBM could generate monotransrepressors that alter ERE-bearing gene expressions and cellular proliferation in directions opposite to those observed with E2-ERα or monotransactivators. Consistent with this, monotransrepressors suppressed reporter gene expressions that emulate the ERE-dependent signaling pathway. Moreover, a model monotransrepressor regulated DNA synthesis, cell cycle progression and proliferation of recombinant adenovirus infected ER-negative cells through decreasing as well as increasing gene expressions with polar directions compared with E2-ERα or monotransactivator. Our results indicate that an ‘activator’ or a ‘repressor’ possesses both transcription activating/enhancing and repressing/decreasing abilities within a chromatin context. Offering a protein engineering platform to alter signal pathway-specific gene expressions and cell growth, our approach could also be used for the development of tools for epigenetic modifications and for clinical interventions wherein multigenic de-regulations are an issue.

Ca2+ channel subunit α 1D promotes proliferation and migration of endometrial cancer cells mediated by 17β-estradiol via the G protein-coupled estrogen receptor

Calcium and calcium channels are closely related to the estrogen-induced nongenomic effect of endometrial carcinoma, but the specific role of calcium channels is unknown. This study aimed to explore the expression and the biologic effect of the L-type calcium channel in endometrial carcinoma cells and to clarify the molecular mechanism of the relationship between L-type calcium channels and estrogen. The immunohistochemical results showed that Ca(2+) channel subunit α 1D (Cav1.3) expression was high in atypical hyperplasia (1.90 ± 0.35) and endometrial carcinoma tissues (2.05 ± 0.82) but weak (0.80 ± 0.15) in benign endometrial tissues (P < 0.05). Treatment with 17β-estradiol rapidly increased Cav1.3 expression in a dose- and time-dependent manner, and 100 nM cell-impermeable β-estradiol-6-(O-carboxymethyl)oxime:bovine serum albumin also promoted Cav1.3 expression. Transfection with small interfering RNA against G protein-coupled estrogen receptor (GPER) suppressed estrogen-induced up-regulation of Cav1.3 compared with control cells and markedly reduced the estrogen-induced phosphorylation of ERK1/2 and CREB. Knocking down the Cav1.3 significantly suppressed estrogen-stimulated Ca(2+) influx, cell proliferation, and migration in endometrial cancer cells. Taken together, Cav1.3 was overexpressed in atypical hyperplasia and endometrial carcinoma, and the estrogen-induced phosphorylation of downstream molecular ERK1/2 and CREB is the result of activation of the GPER pathway. L-type channel Cav1.3 is required for estrogen-stimulated Ca(2+) influx and contributes broadly to the development of endometrial cancer. The Cav1.3 channel may be a new target for endometrial carcinoma treatment.

Molecular mechanism(s) of endocrine-disrupting chemicals and their potent oestrogenicity in diverse cells and tissues that express oestrogen receptors

Endocrine-disrupting chemicals (EDCs) are natural or synthetic compounds present in the environment which can interfere with hormone synthesis and normal physiological functions of male and female reproductive organs. Most EDCs tend to bind to steroid hormone receptors including the oestrogen receptor (ER), progesterone receptor (PR) and androgen receptor (AR). As EDCs disrupt the actions of endogenous hormones, they may induce abnormal reproduction, stimulation of cancer growth, dysfunction of neuronal and immune system. Although EDCs represent a significant public health concern, there are no standard methods to determine effect of EDCs on human beings. The mechanisms underlying adverse actions of EDC exposure are not clearly understood. In this review, we highlighted the toxicology of EDCs and its effect on human health, including reproductive development in males and females as shown in in vitro and in vivo models. In addition, this review brings attention to the toxicity of EDCs via interaction of genomic and non-genomic signalling pathways through hormone receptors.

The ligand-mediated nuclear mobility and interaction with estrogen-responsive elements of estrogen receptors are subtype specific

17β-Estradiol (E(2)) plays important roles in functions of many tissues. E(2) effects are mediated by estrogen receptor (ER) α and β. ERs regulate transcriptions through estrogen-responsive element (ERE)-dependent and ERE-independent modes of action. ER binding to ERE constitutes the basis of the ERE-dependent pathway. Direct/indirect ER interactions with transcription complexes define ERE-independent signaling. ERs share functional features. Ligand-bound ERs nevertheless induce distinct transcription profiles. Live cell imaging indicates a dynamic nature of gene expressions by highly mobile ERs. However, the relative contribution of ER mobility at the ERE-independent pathway to the overall kinetics of ER mobility remains undefined. We used fluorescent recovery after a photo-bleaching approach to assess the ligand-mediated mobilities of ERE binding-defective ERs, ER(EBD). The decrease in ERα mobility with E(2) or the selective ER modulator 4-hydroxyl-tamoxifen (4HT) was largely due to the interaction of the receptor with ERE. Thus, ERα bound to E(2) or 4HT mediates transcriptions from the ERE-independent pathway with remarkably fast kinetics that contributes fractionally to the overall motility of the receptor. The antagonist Imperial Chemical Industries 182 780 immobilized ERαs. The mobilities of ERβ and ERβ(EBD) in the presence of ligands were indistinguishable kinetically. Thus, ERβ mobility is independent of the nature of ligands and the mode of interaction with target sites. Chimeric ERs indicated that the carboxyl-termini are critical regions for subtype-specific mobility. Therefore, while ERs are highly mobile molecules interacting with target sites with fast kinetics, an indication of the hit-and-run model of transcription, they differ mechanistically to modulate transcriptions.

Telomerase in the ovary

Telomerase, an enzyme complex that binds the chromosome ends (telomeres) and maintains telomere length and integrity, is present in germ cells, proliferative granulosa cells, germline stem cells, and neoplastic cells in the ovary, but it is absent in differentiated or aged cells. Activation of telomerase in the ovary underpins both benign and malignant cell proliferation in several compartments, including the germ cells, membrana granulosa, and the ovarian surface epithelium. The difference in telomerase operation between normal and abnormal cell proliferations may lie in the mechanisms of telomerase activation in a deregulated manner. Recent studies have implicated telomerase activity in ovarian cancer as well as oogenesis and fertility. Inhibition of telomerase and the shortening of telomeres are seen in occult ovarian insufficiency. Studies of how telomerase operates and regulates ovary development may provide insight into the development of both germ cells for ovarian reproductive function and neoplastic cells in ovarian cancer. The current review summarizes the roles of telomerase in the development of oocytes and proliferation of granulosa cells during folliculogenesis and in the process of tumorigenesis. It also describes the regulation of telomerase by estrogen in the ovary.

Inositol 1,4,5-trisphosphate-induced Ca2+ signalling is involved in estradiol-induced breast cancer epithelial cell growth

Background

Ca²⁺ is a ubiquitous messenger that has been shown to be responsible for controlling numerous cellular processes including cell growth and cell death. Whereas the involvement of IP₃-induced Ca²⁺ signalling (IICS) in the physiological activity of numerous cell types is well documented, the role of IICS in cancer cells is still largely unknown. Our purpose was to characterize the role of IICS in the control of growth of the estrogen-dependent human breast cancer epithelial cell line MCF-7 and its potential regulation by 17β-estradiol (E₂).

Results

Our results show that the IP₃ receptor (IP₃R) inhibitors caffeine, 2-APB and xestospongin C (XeC) inhibited the growth of MCF-7 stimulated by 5% foetal calf serum or 10 nM E₂. Furthermore, Ca²⁺ imaging experiments showed that serum and E₂ were able to trigger, in a Ca²⁺-free medium, an elevation of internal Ca²⁺ in a 2-APB and XeC-sensitive manner. Moreover, the phospholipase C (PLC) inhibitor U-73122 was able to prevent intracellular Ca²⁺ elevation in response to serum, whereas the inactive analogue U-73343 was ineffective. Western-blotting experiments revealed that the 3 types of IP₃Rs are expressed in MCF-7 cells and that a 48 hours treatment with 10 nM E₂ elevated IP₃R3 protein expression level in an ICI-182,780 (a specific estrogen receptor antagonist)-dependent manner. Furthermore, IP₃R3 silencing by the use of specific small interfering RNA was responsible for a drastic modification of the temporal feature of IICS, independently of a modification of the sensitivity of the Ca²⁺ release process and acted to counteract the proliferative effect of 10 nM E₂.

Conclusions

Altogether, our results are in favour of a role of IICS in MCF-7 cell growth, and we hypothesize that the regulation of IP₃R3 expression by E₂ is involved in this effect.

The Arabidopsis thaliana NAC transcription factor family: structure-function relationships and determinants of ANAC019 stress signalling

TFs (transcription factors) are modular proteins minimally containing a DBD (DNA-binding domain) and a TRD (transcription regulatory domain). NAC [for NAM (no apical meristem), ATAF, CUC (cup-shaped cotyledon)] proteins comprise one of the largest plant TF families. They are key regulators of stress perception and developmental programmes, and most share an N-terminal NAC domain. On the basis of analyses of gene expression data and the phylogeny of Arabidopsis thaliana NAC TFs we systematically decipher structural and functional specificities of the conserved NAC domains and the divergent C-termini. Nine of the ten NAC domains analysed bind a previously identified conserved DNA target sequence with a CGT[GA] core, although with different affinities. Likewise, all but one of the NAC proteins analysed is dependent on the C-terminal region for transactivational activity. In silico analyses show that the NAC TRDs contain group-specific sequence motifs and are characterized by a high degree of intrinsic disorder. Furthermore, ANAC019 was identified as a new positive regulator of ABA (abscisic acid) signalling, conferring ABA hypersensitivity when ectopically expressed in plants. Interestingly, ectopic expression of the ANAC019 DBD or TRD alone also resulted in ABA hypersensitivity. Expression of stress-responsive marker genes [COR47 (cold-responsive 47), RD29b (responsive-to-desiccation 29b) and ERD11 (early-responsive-to-dehydration 11)] were also induced by full-length and truncated ANAC019. Domain-swapping experiments were used to analyse the specificity of this function. Chimaeric proteins, where the NAC domain of ANAC019 was replaced with the analogous regions from other NAC TFs, also have the ability to positively regulate ABA signalling. In contrast, replacing the ANAC019 TRD with other TRDs abolished ANAC019-mediated ABA hypersensitivity. In conclusion, our results demonstrate that the biochemical and functional specificity of NAC TFs is associated with both the DBDs and the TRDs.

Designer monotransregulators provide a basis for a transcriptional therapy for de novo endocrine-resistant breast cancer

The main circulating estrogen hormone 17beta-estradiol (E2) contributes to the initiation and progression of breast cancer. Estrogen receptors (ERs), as transcription factors, mediate the effects of E2. Ablation of the circulating E2 and/or prevention of ER functions constitute approaches for ER-positive breast cancer treatments. These modalities are, however, ineffective in de novo endocrine-resistant breast neoplasms that do not express ERs. The interaction of E2-ERs with specific DNA sequences, estrogen responsive elements (EREs), of genes constitutes one genomic pathway necessary for cellular alterations. We herein tested the prediction that specific regulation of ERE-driven genes by an engineered monomeric and constitutively active transcription factor, monotransregulator, provides a basis for the treatment of ER-negative breast cancer. Using adenovirus infected ER-negative MDA-MB-231 cells derived from a breast adenocarcinoma, we found that the monotransregulator, but not the ERE-binding defective counterpart, repressed cellular proliferation and motility, and induced apoptosis through expression of genes that required ERE interactions. Similarly, the monotransregulator suppressed the growth of ER-negative BT-549 cells derived from a breast-ductal carcinoma. Moreover, the ERE-binding monotransregulator repressed xenograft tumor growth in a nude mice model. Thus, specific regulation of genes bearing EREs could offer a therapeutic approach for de novo endocrine-resistant breast cancers.

Oestrogen, telomerase, ovarian ageing and cancer

1. Oestrogen plays an important role in ageing and ageing-related development. Lack of oestrogen prompts endocrine cell ageing of the ovary, whereas oestrogen overflow impacts on epithelial cell neoplastic development. 2. Recent studies indicate that oestrogen regulates cell proliferative fates by a mechanism of reprogramming the size of telomeres (ends of chromosomes) in the oestrogen target cells. This is achieved by upregulating the telomerase reverse transcriptase (TERT) gene in a temporal and spatial manner. 3. Currently, the relationship between oestrogen and telomerase activity in regulating productive cell development and function remains elusive. A number of lines of evidence suggest that telomerase is a downstream target of oestrogen in oestrogen-dependent reproductive ageing and neoplastic development. 4. The present minireview discusses our current understanding of the mechanisms by which telomerase maintenance of telomere homeostasis mediates oestrogen-induced ageing and tumourigenesis in the ovary under physiological and pathological conditions.

Estrogens, MSI and Lynch syndrome-associated tumors

Estrogens play a major role in the biology of hormone-responsive tissues but also in the normal physiology of various non-typical hormone-responsive tissues. In disease, estrogens have been associated with tumor development, in particular with tumors such as breast, endometrium, ovary and prostate. In this paper we will review the molecular mechanisms by which estrogens are involved in cancer development, with a special focus in Lynch syndrome related neoplasia. Further, we discuss the role estrogens might have on cell proliferation and apoptosis, how estrogens metabolites can induce DNA damage and we discuss a possible connection between estrogens and changes in DNA (hypo- and hyper) methylation. In this review we will also address the protective effect that high levels of estrogens have in MMR related neoplasias.

Genomic responses from the estrogen-responsive element-dependent signaling pathway mediated by estrogen receptor alpha are required to elicit cellular alterations

Estrogen (E2) signaling is conveyed by the transcription factors estrogen receptor (ER) alpha and beta. ERs modulate the expression of genes involved in cellular proliferation, motility, and death. The regulation of transcription by E2-ERalpha through binding to estrogen-responsive elements (EREs) in DNA constitutes the ERE-dependent signaling pathway. E2-ERalpha also modulates gene expression by interacting with transregulators bound to cognate DNA-regulatory elements, and this regulation is referred to as the ERE-independent signaling pathway. The relative importance of the ERE-independent pathway in E2-ERalpha signaling is unclear. To address this issue, we engineered an ERE-binding defective ERalpha mutant (ERalpha(EBD)) by changing residues in an alpha-helix of the protein involved in DNA binding to render the receptor functional only through the ERE-independent signaling pathway. Using recombinant adenovirus-infected ER-negative MDA-MB-231 cells derived from a breast adenocarcinoma, we found that E2-ERalpha(EBD) modulated the expression of a subset of ERalpha-responsive genes identified by microarrays and verified by quantitative PCR. However, E2-ERalpha(EBD) did not affect cell cycle progression, cellular growth, death, or motility in contrast to E2-ERalpha.ERalpha(EBD) in the presence of E2 was also ineffective in inducing phenotypic alterations in ER-negative U-2OS cells derived from an osteosarcoma. E2-ERalpha, on the other hand, effectively repressed growth in this cell line. Our findings suggest that genomic responses from the ERE-dependent signaling pathway are required for E2-ERalpha to induce alterations in cellular responses.

Do Estrogen Receptor beta Polymorphisms Play A Role in the Pharmacogenetics of Estrogen Signaling?

Estrogen hormones play critical roles in the regulation of many tissue functions. The effects of estrogens are primarily mediated by the estrogen receptors (ER) alpha and beta. ERs are ligand-activated transcription factors that regulate a complex array of genomic events that orchestrate cellular growth, differentiation and death. Although many factors contribute to their etiology, estrogens are thought to be the primary agents for the development and/or progression of target tissue malignancies. Many of the current modalities for the treatment of estrogen target tissue malignancies are based on agents with diverse pharmacology that alter or prevent ER functions by acting as estrogen competitors. Although these compounds have been successfully used in clinical settings, the efficacy of treatment shows variability. An increasing body of evidence implicates ERalpha polymorphisms as one of the contributory factors for differential responses to estrogen competitors. This review aims to highlight the recent findings on polymorphisms of the lately identified ERbeta in order to provide a functional perspective with potential pharmacogenomic implications.

Gene expression profiling reveals that the regulation of estrogen-responsive element-independent genes by 17 beta-estradiol-estrogen receptor beta is uncoupled from the induction of phenotypic changes in cell models

Estrogen hormone 17beta-estradiol (E(2)) is involved in the physiology and pathology of many tissues. E(2) information is conveyed by the transcription factors estrogen receptors (ER) alpha and beta that mediate a complex array of nuclear and non-nuclear events. The interaction of ER with specific DNA sequences, estrogen-responsive elements (EREs), constitutes a critical nuclear signaling pathway. In addition, E(2)-ER regulates transcription through interactions with transfactors bound to their cognate regulatory elements on DNA, hence the ERE-independent signaling pathway. However, the relative importance of the ERE-independent pathway in E(2)-ERbeta signaling is unclear. To address this issue, we engineered an ERE-binding defective ERbeta mutant (ERbeta(EBD)) by changing critical residues in the DNA-binding domain required for ERE binding. Biochemical and functional studies revealed that ERbeta(EBD) signaled exclusively through the ERE-independent pathway. Using the adenovirus infected ER-negative cancer cell models, we found that although E(2)-ERbeta(EBD) regulated the expression of a number of genes identified by microarrays, it was ineffective in altering cellular proliferation, motility, and death in contrast to E(2)-ERbeta. Our results indicate that genomic responses from the ERE-independent pathway to E(2)-ERbeta are not sufficient to alter the cellular phenotype. These findings suggest that the ERE-dependent pathway is a required signaling route for E(2)-ERbeta to induce cellular responses.

Oestrogen and the colon: potential mechanisms for cancer prevention

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

What are comparative studies telling us about the mechanism of ERbeta action in the ERE-dependent E2 signaling pathway?

Estrogen hormone (E2) signaling is primarily conveyed by the estrogen receptors (ER) alpha and beta. ERs are encoded by two distinct genes and share varying degrees of domain-specific structural/functional similarities. ERs mediate a complex array of nuclear and non-nuclear events critical for the homeodynamic regulation of various tissue functions. The canonical nuclear signaling involves the interaction of ERalpha and ERbeta with specific DNA sequences, the so-called estrogen responsive elements (EREs). This interaction constitutes the initial step in ERE-dependent signaling in which ERbeta is a weaker transcription factor than ERalpha in response to E2. However, it remains unclear why transactivation potencies of ER subtypes differ. Studies suggest that the amino-terminus, the least conserved structural region, of ERbeta, but not that of ERalpha, impairs the ability of the receptor to bind to ERE independent of E2. Although the impaired ERbeta-ERE interaction contributes, it is not sufficient to explain the weak transactivation potency of the receptor. It appears that the lack of transactivation ability and of the capability of the amino-terminus of ERbeta, as opposed to that of ERalpha, to functionally interact with the carboxyl-terminal hormone-dependent activation domain is also critical for the receptor-specific activity. Thus, the structurally distinct amino-termini of ERs are important determinants in defining the function of ER-subtypes in the ERE-dependent pathway. This could differentially affect the physiology and pathophysiology of E2 signaling.

New perspectives into the biological and clinical relevance of oestrogen receptors in the human breast

Oestrogen receptor (ER) is arguably the single most important biological predictive factor that exists today. In the last 10 years or so, however, our understanding of ER biology has undergone a paradigm shift following the identification of a second ER, ERbeta, with the original ER being renamed ERalpha. A number of isoforms have additionally been described, especially for ERbeta. Our knowledge of ER signalling has also increased with the recognition of accessory co-regulatory proteins, which help direct the transcriptional cascade. Here we outline these changes and discuss what biological and clinical implications these could have in the mammary gland.

Binding of estrogen receptor beta to estrogen response element in situ is independent of estradiol and impaired by its amino terminus

The functions of 17beta-estradiol (E2) are mediated by estrogen receptor (ER) alpha and beta. ERs display similar DNA- and ligand-binding properties in vitro. However, ERbeta shows lower transcriptional activity than ERalpha from the estrogen response element (ERE)-dependent signaling. We predicted that distinct amino termini contribute to differences in transcription efficacies of ERs by affecting in situ ER-ERE interactions. We used chromatin immunoprecipitation and a novel in situ ERE competition assay, which is based on the ability of ER to compete for ERE binding with a designer activator that constitutively induces transcription from an ERE-driven reporter construct. Interference of activator-mediated transcription by unliganded or liganded ERs was taken as an indication of ER-ERE interaction. Results revealed that ERs interacted with ERE similarly in the absence of E2. However, E2 enhanced the ERE binding of ERalpha but not that of ERbeta. The removal of the amino terminus increased the ERbeta-ERE interaction independent of E2. The ERbeta amino terminus also prevented E2-mediated enhancement of the chimeric ERalpha-ERE interaction. Thus, the amino terminus of ERbeta impairs the binding of ERbeta to ERE. The abrogation of ligand-dependent activation function 2 of the amino-terminally truncated ERbeta resulted in the manifestation of E2 effect on ERbeta-ERE interaction. This implies that E2-mediated enhancement of ERbeta-ERE interaction is masked by the activation function 2, whereas the intact amino terminus is a dominant region that decreases the binding of ERbeta to ERE. Thus, ERbeta-ERE interaction is independent of E2 and is impaired by its amino terminus. These findings provide an additional explanation for differences between ERalpha and ERbeta functions that could differentially affect the physiology and pathophysiology of E2 signaling.

17-β-Estradiol activates maxi-K channels through a non-genomic pathway in human breast cancer cells

We have investigated the acute effects of 17-beta-estradiol (E2) on K+ channels in MCF-7 breast epithelial cancer cells. E2 induced a rapid and irreversible augmentation of the K+ current for all membrane potentials superior to -25 mV. The effect of E2 was sensitive to Iberiotoxin, Charybdotoxin and TEA and can be elicited in the presence of the anti-estrogen ICI 182780 or be mimicked by the membrane impermeant form E2/BSA. Furthermore, E2/BSA was able to stimulate cell proliferation in a maxi-K inhibitors-sensitive manner. Thus, these results permit us to identify the maxi-K channel as the molecular target of E2 that regulates cell proliferation independently of the estrogen receptor.

Single-chain estrogen receptors (ERs) reveal that the ERalpha/beta heterodimer emulates functions of the ERalpha dimer in genomic estrogen signaling pathways

The effects of estrogens, particularly 17beta-estradiol (E2), are mediated by estrogen receptor alpha (ERalpha) and ERbeta. Upon binding to E2, ERs homo- and heterodimerize when coexpressed. The ER dimer then regulates the transcription of target genes through estrogen responsive element (ERE)-dependent and -independent pathways that constitute genomic estrogen signaling. Although ERalpha and ERbeta have similar ERE and E2 binding properties, they display different transregulatory capacities in both ERE-dependent and -independent signaling pathways. It is therefore likely that the heterodimerization provides novel functions to ERs by combining distinct properties of the contributing partners. The elucidation of the role of the ER heterodimer is critical for the understanding of physiology and pathophysiology of E2 signaling. However, differentially determining target gene responses during cosynthesis of ER subtypes is difficult, since dimers formed are a heterogeneous population of homo- and heterodimers. To circumvent the pivotal dimerization step in ER action and hence produce a homogeneous ER heterodimer population, we utilized a genetic fusion strategy. We joined the cDNAs of ERalpha and/or ERbeta to produce single-chain ERs to simulate the ER homo- and heterodimers. The fusion ERs interacted with ERE and E2 in a manner similar to that observed with the ER dimers. The homofusion receptors mimicked the functions of the parent ER dimers in the ERE-dependent and -independent pathways in transfected mammalian cells, whereas heterofusion receptors emulated the transregulatory properties of the ERalpha dimer. These results suggest that ERalpha is the functionally dominant partner in the ERalpha/beta heterodimer.