Regulation of estrogen receptor expression

Effects of bifenthrin exposure on the estrogenic and dopaminergic pathways in zebrafish embryos and juveniles

Bifenthrin is a pyrethroid insecticide used in urban and agricultural applications. Previous studies have shown that environmentally relevant (ng/L) concentrations of bifenthrin increased plasma concentrations of 17β-estradiol (E2) and altered the expression of dopaminergic pathway components. The dopaminergic neurons can indirectly regulate E2 biosynthesis, suggesting that bifenthrin may disrupt the hypothalamic-pituitary-gonadal (HPG) axis. Because embryos do not have a complete HPG axis, the hypothesis that bifenthrin impairs dopamine regulation was tested in embryonic and 1-mo-old juvenile zebrafish (Danio rerio) with exposure to measured concentrations of 0.34 and 3.1 µg/L bifenthrin for 96 h. Quantitative reverse transcriptase polymerase chain reaction was used to investigate transcripts of tyrosine hydroxylase (TH), dopamine receptor 1 (DR1) and 2A (DR2A), dopamine active transporter (DAT), estrogen receptor α (ERα), ERβ1, ERβ2, luteinizing hormone β (LHβ), follicle-stimulating hormone β (FSHβ), vitellogenin (VTG), cytochrome P450 cyp19a1a, and cyp19a1b. Levels of E2 were measured by enzyme-linked immunosorbent assay (ELISA). Dopamine and its metabolites 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) concentrations were measured by liquid chromatrography-tandem mass spectrometry (LC-MS/MS). Significant decreases in TH and DR1 transcripts and HVA levels, as well as ratios of HVA/dopamine and HVA+DOPAC/dopamine, in zebrafish embryos were observed after bifenthrin treatment. In juveniles, a significant increase in the expression of ERβ1 and the DOPAC to dopamine ratio was noted. These results show a possible antiestrogenic effect of bifenthrin in embryos, and estrogenicity in juveniles, indicating life-stage-dependent toxicity in developing fish. Environ Toxicol Chem 2018;37:236-246. © 2017 SETAC.

ESR1 is co-expressed with closely adjacent uncharacterised genes spanning a breast cancer susceptibility locus at 6q25.1

Approximately 80% of human breast carcinomas present as oestrogen receptor α-positive (ER+ve) disease, and ER status is a critical factor in treatment decision-making. Recently, single nucleotide polymorphisms (SNPs) in the region immediately upstream of the ER gene (ESR1) on 6q25.1 have been associated with breast cancer risk. Our investigation of factors associated with the level of expression of ESR1 in ER+ve tumours has revealed unexpected associations between genes in this region and ESR1 expression that are important to consider in studies of the genetic causes of breast cancer risk. RNA from tumour biopsies taken from 104 postmenopausal women before and after 2 weeks treatment with an aromatase (oestrogen synthase) inhibitor was analyzed on Illumina 48K microarrays. Multiple-testing corrected Spearman correlation revealed that three previously uncharacterized open reading frames (ORFs) located immediately upstream of ESR1, C6ORF96, C6ORF97, and C6ORF211 were highly correlated with ESR1 (Rs =  0.67, 0.64, and 0.55 respectively, FDR<1 × 10(-7)). Publicly available datasets confirmed this relationship in other groups of ER+ve tumours. DNA copy number changes did not account for the correlations. The correlations were maintained in cultured cells. An ERα antagonist did not affect the ORFs' expression or their correlation with ESR1, suggesting their transcriptional co-activation is not directly mediated by ERα. siRNA inhibition of C6ORF211 suppressed proliferation in MCF7 cells, and C6ORF211 positively correlated with a proliferation metagene in tumours. In contrast, C6ORF97 expression correlated negatively with the metagene and predicted for improved disease-free survival in a tamoxifen-treated published dataset, independently of ESR1. Our observations suggest that some of the biological effects previously attributed to ER could be mediated and/or modified by these co-expressed genes. The co-expression and function of these genes may be important influences on the recently identified relationship between SNPs in this region and breast cancer risk.

Progesterone receptor B recruits a repressor complex to a half-PRE site of the estrogen receptor alpha gene promoter

In the present study, we demonstrate that elevated levels of the progesterone receptor (PR)-B isoform in breast cancer cells induces down-regulation of estrogen receptor (ER) alpha mRNA and protein content, causing concomitant repression of the estrogen-regulated genes insulin receptor substrate 1, cyclin D1, and pS2, addressing a specific effect of PR/PR-B on ERalpha gene transcription. ERalpha gene promoter activity was drastically inhibited by PR-B overexpression. Promoter analysis revealed a transcriptionally responsive region containing a half-progesterone response element (PRE) site located at -1757 bp to -1752 bp. Mutation of the half-PRE down-regulated the effect induced by PR/PR-B overexpression. Moreover chromatin immunoprecipitation analyses revealed an increase of PR bound to the ERalpha-regulatory region encompassing the half-PRE site, and the recruitment of a corepressor complex containing nuclear receptor corepressor (NCoR) but not silencing mediator of retinoid and thyroid hormone receptor and DAX1, concomitantly with hypoacetylation of histone H4 and displacement of RNA polymerase II. Furthermore, NCoR ablation studies demonstrated the crucial involvement of NCoR in the down-regulatory effects due to PR-B overexpression on ERalpha protein and mRNA. We also demonstrated that the ERalpha regulation observed in MCF-7 cells depended on PR-B expression because PR-B knockdown partially abrogates the feedback inhibition of ERalpha levels after estrogenic stimulus. Our study provides evidence for a mechanism by which overexpressed PR-B is able to actively repress ERalpha gene expression.

Crosstalk between the estrogen receptor and the HER tyrosine kinase receptor family: molecular mechanism and clinical implications for endocrine therapy resistance

Breast cancer evolution and tumor progression are governed by the complex interactions between steroid receptor [estrogen receptor (ER) and progesterone receptor] and growth factor receptor signaling. In recent years, the field of cancer therapy has witnessed the emergence of multiple strategies targeting these specific cancer pathways and key molecules (ER and growth factor receptors) to arrest tumor growth and achieve tumor eradication; treatment success, however, has varied and both de novo (up front) and acquired resistance have proven a challenge. Recent studies of ER biology have revealed new insights into ER action in breast cancer and have highlighted the role of an intimate crosstalk between the ER and HER family signaling pathways as a fundamental contributor to the development of resistance to endocrine therapies against the ER pathway. The aim of this review article is to summarize the current knowledge on mechanisms of resistance of breast cancer cells to endocrine therapies due to the crosstalk between the ER and the HER growth factor receptor signaling pathways and to explore new available therapeutic strategies that could prolong duration of response and circumvent endocrine resistant tumor growth.

Proteomic analysis of MCF-7 breast cancer cell line exposed to mitogenic concentration of 17β-estradiol

Estrogens are powerful mitogens that play a critical role in the onset of breast cancer and its progression. About two-thirds of all breast cancers are estrogen receptor (ER)+ at the time of diagnosis, and the ER expression is the determinant of a tumor phenotype associated with hormone responsiveness. The molecular basis of the relationship between ER expression, (anti)hormonal responsiveness, and breast cancer prognosis is still unknown. To identify the proteins affected by the presence of the hormone we used 2-D-PAGE-based bottom-up proteomics for the study of the proteome of MCF-7 cells of estrogen-responsive breast carcinoma exposed to a mitogenic concentration of 17beta-estradiol (E2) for 12, 18, 24, and 30 h. Differential expression analysis showed significant changes for 12 proteins. These include ezrin-radixin-moesin-binding phosphoprotein of 50 kDa which was previously shown to be directly regulated by E2. Expression profiles of other proteins already implicated in the progression of breast cancer, such as stathmin, calreticulin, heat shock 71 kDa, alpha-enolase are also described. Moreover, it is observed that different unexpected proteins, translation factors, and energetic metabolism enzymes are also influenced by the presence of the hormone.

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.

Reciprocal regulation of extracellular matrix proteins and ovarian steroid activity in the mammary gland

Despite the critical importance of ovarian steroids in the treatment of breast cancer, little is known about the acquisition or loss of estrogen and progesterone responsiveness in either the normal or neoplastic mammary gland. This review focuses on the interactions among mammary stroma-derived extracellular matrix (ECM) proteins, integrins and ovarian hormone-dependent proliferation in normal and neoplastic mammary cells both in vivo and in vitro. In vitro studies show that fibronectin is required for progesterone-induced proliferation of normal mammary epithelial cells and that specific ECM proteins also regulate interactions between growth factors and ovarian hormones. Studies with human breast cancer cell lines have shown that laminin inhibits estrogen-induced proliferation and estrogen-response-element-mediated transcription in vitro and also inhibits estrogen-induced proliferation in vivo. Reciprocally, ovarian steroids regulate the expression of ECM proteins and their cellular receptors, integrins, during mammary gland development in vivo. The fibronectin-specific integrin, alpha5beta1 is regulated by ovarian steroids and its expression is positively correlated with developmental stages of peak proliferation. These studies suggest that the coordinated regulation of ovarian hormone responsiveness and ECM/integrin expression may be critical to normal mammary gland development and breast cancer growth and progression.

Development and characterization of a tamoxifen-resistant breast carcinoma xenograft

A human tamoxifen-resistant mammary carcinoma, MaCa 3366/TAM, originating from a sensitive parental xenograft 3366 was successfully established by treatment of tumour-bearing nude mice with 1-50 mg kg(-1) tamoxifen for 3 years during routine passaging. Both tumours did not differ significantly in OR- and PR-positivity, however, when compared with the sensitive tumour line, the mean OR content of the TAM-resistant subline is slightly lower. An OR-upregulation following withdrawal of oestradiol treatment was observed in the parental tumours but not in the resistant xenografts. Following long-term treatment with tamoxifen, the histological pattern of the breast carcinoma changed. The more differentiated structures being apparent after treatment with 17beta-oestradiol in the original 3366 tumour were not induced in the resistant line. Tamoxifen failed to induce a tumour growth inhibition in comparison to the tamoxifen-sensitive line. The pure anti-oestrogen, ICI 182 780, revealed cross-resistance. Sequence analysis of the hormone-binding domain of the OR of both lines showed no differences, suggesting that either mutations in other regions of the OR are involved in the TAM-resistance phenotype or that mechanisms outside of this protein induced this phenotype. Oestrogen and anti-oestrogen regulate pS2 and cathepsin D expression in 3366 tumours as in the human breast cancer cell line MCF-7. The resistant 3366/TAM tumours have lost this regulation. The established breast cancer xenografts 3366 and 3366/TAM offer the possibility of investigating mechanisms of anti-oestrogen resistance in an in vivo situation. They can be used to test novel approaches to prevent, or to overcome, this resistance in a clinically related manner.

Oestrogen receptor and its potential role in breast cancer development

The first studies of oestrogen receptor (ER) focused on measurements of levels in breast cancers and relationship to hormonal response, but the introduction of antibodies which can be used on fixed tissue has meant that ER can be studied in detail in normal and precancerous tissue. Cloning and sequencing of ER has resulted in more detailed understanding of structure and function, with the identification of variant forms in both tumours and normal, followed by the discovery that ER has two forms, the classical ER-alpha and ER-beta. Analyses of both forms in normal and preneoplastic breast will be important for our understanding of the role of ER in the development of breast cancer and its possible prevention.

Modulation of glucose transport in fetal rat lung: a sexual dimorphism

Male fetuses exhibit delayed lung maturation and surfactant production in comparison with female fetuses. This delay may be related to sex hormone effects: estrogen enhances and androgens delay lung development. The uptake of glucose, an important precursor for surfactant synthesis, may be differently affected by estrogen and androgens. In these studies we determined the effects of these two hormones on glucose transport (glucose uptake, glucose transporter [Glut] 1 protein, and mRNA) and hexokinase activity in lung tissue of fetal rats. On Day 20 of gestation (term = 21.5 d) lung tissue was harvested from female and male fetal rats, minced into explants, and cultured for 24 h. Basal glucose uptake, measured in the absence of sex hormones, was 37% higher (P < 0.05) in female compared with male lungs. Explants were washed and cultured for an additional 3 h or 24 h in either estradiol or dihydrotestosterone (DHT) at 0, 1, 10, or 100 nM. Twenty-four-hour treatment with estradiol in both male and female explants increase 2-deoxyglucose uptake, Glut 1 protein, and mRNA levels (P < 0.05). However, explants from male fetuses were not as responsive to estradiol treatment as were those from females (P < 0.05). Treatment for 24 h with DHT decreased 2-deoxyglucose uptake, Glut 1 protein, and mRNA levels in females and males (P < 0.05). There was no difference in response between females and males. Short-term incubation (3 h) with sex hormones had no effect on glucose uptake. However, 3-h treatment with estradiol did increase Glut 1 mRNA levels (P < 0.05). Hexokinase activity was not affected by estradiol or DHT treatment. These findings indicate that estradiol and DHT differentially regulate glucose uptake in fetal rat lung tissue. This regulation of substrate supply (glucose) by estradiol and DHT may be another mechanism for the sexual dimorphism observed in lung development and surfactant synthesis.

Increased expression of estrogen-receptor exon-5-deletion variant in relapse tissues of human breast cancer

A substantial percentage (30-70%) of human breast carcinomas that initially respond to endocrine therapy acquire resistance during the treatment. Many patients with tumor progression despite treatment with anti-estrogen tamoxifen show continued expression of estrogen receptors (ER) and/or progesterone receptors (PgR) in the relapse tissue. This indicates that, in these tumors, mechanisms other than loss of ER expression are responsible for treatment failure. We have investigated the occurrence and frequency of the exon-5-deletion variant (d5) of ER in human breast-cancer biopsies and in normal tissues. In all normal and tumor tissues tested, both wild-type (wt) and d5 were detected, indicating that expression of the d5 variant is a naturally occurring polymorphism. However, the primary tumors of patients who relapse within 15 months (n = 13) express higher ratios of d5 than do those of patients with no relapse during the same period (p = 0.4, n = 19), though this difference is statistically not significant. A significant increase in the expression level of d5 was determined in relapse as compared with the respective primary tumor (p = 0.02). These data indicate that increased expression of the ER exon-5-deletion variant in relapse tissues might be due to clonal selection of cells resistant to anti-estrogen treatment.

Phytoestrogen concentration determines effects on DNA synthesis in human breast cancer cells

Thirteen isoflavonoids, flavonoids, and lignans, including some known phytoestrogens, were evaluated for their effects on DNA synthesis in estrogen-dependent (MCF-7) and -independent (MDA-MB-231) human breast cancer cells. Treatment for 24 hours with most of the compounds at 20-80 microM sharply inhibited DNA synthesis in MDA-MB-231 cells. In MCF-7 cells, on the other hand, biphasic effects were seen. At 0.1-10 microM, coumestrol, genistein, biochanin A, apigenin, luteolin, kaempferol, and enterolactone induced DNA synthesis 150-235% and, at 20-90 microM, inhibited DNA synthesis by 50%. Treatment of MCF-7 cells for 10 days with genistein or coumestrol showed continuous stimulation of DNA synthesis at low concentrations. Time-course experiments with genistein in MCF-7 cells showed effects to be reversed by 48-hour withdrawal of genistein at most concentrations. Induction of DNA synthesis in MCF-7 cells, but not in MDA-MB-231 cells, is consistent with an estrogenic effect of these compounds. Inhibition of estrogen-dependent and -independent breast cancer cells at high concentrations suggests additional mechanisms independent of the estrogen receptor. The current focus on the role of phytoestrogens in cancer prevention must take into account the biphasic effects observed in this study, showing inhibition of DNA synthesis at high concentrations but induction at concentrations close to probable levels in humans.

Estrogen receptor status of breast cancer: a marker of different stages of tumor or different entities of the disease?

Breast cancer can be divided into two types according to the estrogen receptor (ER) level of the tumor: ER-positive and ER-negative. Two hypotheses have been raised about the relationship between ER-positive and ER-negative breast tumors. One hypothesis considers ER status as an indicator of a different stage of the disease. The other regards ER-positive and ER-negative tumors as different entities. For both etiological and biological studies of breast cancer it is important to know which hypothesis is correct. In this paper, we review evidence for and against each hypothesis and suggest issues to be addressed in future studies.