Oestrogen receptor splice variants in the pathogenesis of disease

Selective Estrogen receptor degraders (SERDs) for the treatment of breast cancer: An overview

Discovery of SERDs has changed the direction of anticancer research, as more than 70% of breast cancer cases are estrogen receptor positive (ER+). Therapies such as selective estrogen receptor modulators (SERM) and aromatase inhibitors (AI's) have been effective, but due to endocrine resistance, SERDs are now considered essential therapeutics for the treatment of ER+ breast cancer. The present review deliberates the pathophysiology of SERDs from the literature covering various molecules in clinical trials. Estrogen receptors active sites distinguishing characteristics and interactions with currently available FDA-approved drugs have also been discussed. Designing strategy of previously reported SERDs, their SAR analysis, in silico, and the biological efficacy have also been summarized along with appropriate examples.

Estrogen Receptor Alpha Splice Variants, Post-Translational Modifications, and Their Physiological Functions

The importance of estrogenic signaling for a broad spectrum of biological processes, including reproduction, cancer development, energy metabolism, memory and learning, and so on, has been well documented. Among reported estrogen receptors, estrogen receptor alpha (ERα) has been known to be a major mediator of cellular estrogenic signaling. Accumulating evidence has shown that the regulations of ERα gene transcription, splicing, and expression across the tissues are highly complex. The ERα promoter region is composed of multiple leader exons and 5′-untranslated region (5′-UTR) exons. Differential splicing results in multiple ERα proteins with different molecular weights and functional domains. Furthermore, various post-translational modifications (PTMs) further impact ERα cellular localization, ligand affinity, and therefore functionality. These splicing isoforms and PTMs are differentially expressed in a tissue-specific manner, mediate certain aspects of ERα signaling, and may work even antagonistically against the full-length ERα. The fundamental understanding of the ERα splicing isoforms in normal physiology is limited and association studies of the splicing isoforms and the PTMs are scarce. This review aims to summarize the functional diversity of these ERα variants and the PTMs in normal physiological processes, particularly as studied in transgenic mouse models.

The Co-Expression of Estrogen Receptors ERα, ERβ, and GPER in Endometrial Cancer

Estrogens have important roles in endometrial cancer (EC) and exert biological effects through the classical estrogen receptors (ERs) ERα and ERβ, and the G-protein-coupled ER, GPER. So far, the co-expression of these three types of ERs has not been studied in EC. We investigated ERα, ERβ, GPER mRNA and protein levels, and their intracellular protein distributions in EC tissue and in adjacent control endometrial tissue. Compared to control endometrial tissue, immunoreactivity for ERα in EC tissue was weaker for nuclei with minor, but unchanged, cytoplasmic staining; mRNA and protein levels showed decreased patterns for ERα in EC tissue. For ERβ, across both tissue types, the immunoreactivity was unchanged for nuclei and cytoplasm, although EC tissues again showed lower mRNA and protein levels compared to adjacent control endometrial tissue. The immunoreactivity of GPER as well as mRNA levels of GPER were unchanged across cancer and control endometrial tissues, while protein levels were lower in EC tissue. Statistically significant correlations of estrogen receptor α (ESR1) versus estrogen receptor β (ESR2) and GPER variant 3,4 versus ESR1 and ESR2 was seen at the mRNA level. At the protein level studied with Western blotting, there was significant correlation of ERα versus GPER, and ERβ versus GPER. While in clinical practice the expression of ERα is routinely tested in EC tissue, ERβ and GPER need to be further studied to examine their potential as prognostic markers, provided that specific and validated antibodies are available.

Hypomorphism of a Novel Long ERα Isoform Causes Severe Reproductive Dysfunctions in Female Mice

Estrogen receptor alpha (ERα)-mediated estrogen signaling plays a pivotal role in both reproductive and nonreproductive functions. Transcriptional regulation of the ERα gene is highly complex, with multiple transcript variants being differentially produced across the tissues. However, tissue-specific variation and physiological specificity of the ERα variants are not yet fully understood. In an attempt to generate a Cre-dependently restorable ERα-null mouse for functional genetic studies, we unexpectedly produced ERα hypomorphic mice with biased downregulation of a previously unappreciated long ERα isoform that is enriched in the female reproductive organs (uterus and ovaries) and the pituitary but minimally expressed in the brain. Female homozygous mutant mice were capable of pregnancy but displayed irregular estrus cycle and rarely kept newborn pups alive. No significant morphological and pathological changes in reproductive system or disruption of body weight homeostasis were seen in female homozygous mutant mice. Collectively, our results define a tissue-specific enriched long ERα isoform and its preferential role in female reproductive function rather than body weight homeostasis.

Dysregulation of splicing variants and spliceosome components in breast cancer

The dysregulation of the splicing process has emerged as a novel hallmark of metabolic and tumor pathologies. In breast cancer (BCa), which represents the most diagnosed cancer type among women worldwide, the generation and/or dysregulation of several oncogenic splicing variants have been described. This is the case of the splicing variants of HER2, ER, BRCA1, or the recently identified by our group, In1-ghrelin and SST5TMD4, which exhibit oncogenic roles, increasing the malignancy, poor prognosis, and resistance to treatment of BCa. This altered expression of oncogenic splicing variants has been closely linked with the dysregulation of the elements belonging to the macromolecular machinery that controls the splicing process (spliceosome components and the associated splicing factors). In this review, we compile the current knowledge demonstrating the altered expression of splicing variants and spliceosomal components in BCa, showing the existence of a growing body of evidence supporting the close implication of the alteration in the splicing process in mammary tumorigenesis.

Estradiol Signaling at the Heart of Folliculogenesis: Its Potential Deregulation in Human Ovarian Pathologies

Estradiol (E2) is a major hormone controlling women fertility, in particular folliculogenesis. This steroid, which is locally produced by granulosa cells (GC) within ovarian follicles, controls the development and selection of dominant preovulatory follicles. E2 effects rely on a complex set of nuclear and extra-nuclear signal transduction pathways principally triggered by its nuclear receptors, ERα and ERβ. These transcription factors are differentially expressed within follicles, with ERβ being the predominant ER in GC. Several ERβ splice isoforms have been identified and display specific structural features, which greatly complicates the nature of ERβ-mediated E2 signaling. This review aims at providing a concise overview of the main actions of E2 during follicular growth, maturation, and selection in human. It also describes the current understanding of the various roles of ERβ splice isoforms, especially their influence on cell fate. We finally discuss how E2 signaling deregulation could participate in two ovarian pathogeneses characterized by either a follicular arrest, as in polycystic ovary syndrome, or an excess of GC survival and proliferation, leading to granulosa cell tumors. This review emphasizes the need for further research to better understand the molecular basis of E2 signaling throughout folliculogenesis and to improve the efficiency of ovarian-related disease therapies.

Molecular intrinsic versus clinical subtyping in breast cancer: A comprehensive review

Breast cancer is a heterogeneous disease manifesting diversity at the molecular, histological and clinical level. The development of breast cancer classification was centered on informing clinical decisions. The current approach to the classification of breast cancer, which categorizes this disease into clinical subtypes based on the detection of estrogen receptor, progesterone receptor, human epidermal growth factor receptor 2, and proliferation marker Ki67, is not ideal. This is manifested as a heterogeneity of therapeutic responses and outcomes within the clinical subtypes. The newer classification model, based on gene expression profiling (intrinsic subtyping) informs about transcriptional responses downstream from IHC single markers, revealing deeper appreciation for the disease heterogeneity and capturing tumor biology in a more comprehensive way than an expression of a single protein or gene alone. While accumulating evidences suggest that intrinsic subtypes provide clinically relevant information beyond clinical surrogates, it is imperative to establish whether the current conventional immunohistochemistry-based clinical subtyping approach could be improved by gene expression profiling and if this approach has a potential to translate into clinical practice.

Health benefits attributed to 17α-estradiol, a lifespan-extending compound, are mediated through estrogen receptor α

Metabolic dysfunction underlies several chronic diseases, many of which are exacerbated by obesity. Dietary interventions can reverse metabolic declines and slow aging, although compliance issues remain paramount. 17α-estradiol treatment improves metabolic parameters and slows aging in male mice. The mechanisms by which 17α-estradiol elicits these benefits remain unresolved. Herein, we show that 17α-estradiol elicits similar genomic binding and transcriptional activation through estrogen receptor α (ERα) to that of 17β-estradiol. In addition, we show that the ablation of ERα completely attenuates the beneficial metabolic effects of 17α-E2 in male mice. Our findings suggest that 17α-E2 may act through the liver and hypothalamus to improve metabolic parameters in male mice. Lastly, we also determined that 17α-E2 improves metabolic parameters in male rats, thereby proving that the beneficial effects of 17α-E2 are not limited to mice. Collectively, these studies suggest ERα may be a drug target for mitigating chronic diseases in male mammals.

Estrogen Receptors and Ubiquitin Proteasome System: Mutual Regulation

This review provides information on the structure of estrogen receptors (ERs), their localization and functions in mammalian cells. Additionally, the structure of proteasomes and mechanisms of protein ubiquitination and cleavage are described. According to the modern concept, the ubiquitin proteasome system (UPS) is involved in the regulation of the activity of ERs in several ways. First, UPS performs the ubiquitination of ERs with a change in their functional activity. Second, UPS degrades ERs and their transcriptional regulators. Third, UPS affects the expression of ER genes. In addition, the opportunity of the regulation of proteasome functioning by ERs—in particular, the expression of immune proteasomes—is discussed. Understanding the complex mechanisms underlying the regulation of ERs and proteasomes has great prospects for the development of new therapeutic agents that can make a significant contribution to the treatment of diseases associated with the impaired function of these biomolecules.

Sex, Gender, and Sex Hormones in Pulmonary Hypertension and Right Ventricular Failure

Pulmonary hypertension (PH) encompasses a syndrome of diseases that are characterized by elevated pulmonary artery pressure and pulmonary vascular remodeling and that frequently lead to right ventricular (RV) failure and death. Several types of PH exhibit sexually dimorphic features in disease penetrance, presentation, and progression. Most sexually dimorphic features in PH have been described in pulmonary arterial hypertension (PAH), a devastating and progressive pulmonary vasculopathy with a 3-year survival rate <60%. While patient registries show that women are more susceptible to development of PAH, female PAH patients display better RV function and increased survival compared to their male counterparts, a phenomenon referred to as the "estrogen paradox" or "estrogen puzzle" of PAH. Recent advances in the field have demonstrated that multiple sex hormones, receptors, and metabolites play a role in the estrogen puzzle and that the effects of hormone signaling may be time and compartment specific. While the underlying physiological mechanisms are complex, unraveling the estrogen puzzle may reveal novel therapeutic strategies to treat and reverse the effects of PAH/PH. In this article, we (i) review PH classification and pathophysiology; (ii) discuss sex/gender differences observed in patients and animal models; (iii) review sex hormone synthesis and metabolism; (iv) review in detail the scientific literature of sex hormone signaling in PAH/PH, particularly estrogen-, testosterone-, progesterone-, and dehydroepiandrosterone (DHEA)-mediated effects in the pulmonary vasculature and RV; (v) discuss hormone-independent variables contributing to sexually dimorphic disease presentation; and (vi) identify knowledge gaps and pathways forward. © 2020 American Physiological Society. Compr Physiol 10:125-170, 2020.

Correlations between exposure to deoxynivalenol and zearalenone and the immunohistochemical expression of estrogen receptors in the intestinal epithelium and the mRNA expression of selected colonic enzymes in pre-pubertal gilts

Plant-based materials used in the production of pig feed are very often contaminated with deoxynivalenol and zearalenone. Daily intake of small amounts of these mycotoxins with feed induces various subclinical states in gilts and influences different biological processes. The aim of this preclinical study was to determine the correlation between monotonic doses of zearalenone and deoxynivalenol (40 μg/kg body weight and 12 μg/kg body weight, respectively, administered over a period of 42 days) and the immunohistochemical expression of estrogen receptors in the intestinal tract and the mRNA expression of selected colonic enzymes. The immunohistochemical expression of estrogen receptor alpha was observed in the colon, but its intensity varied in different weeks of exposure. A minor increase in estrogen receptor beta expression was noted only in the colon, whereas the expression of cytochrome P450 1A1 enzyme mRNA and mRNA isoform of the glutathione S-transferase π gene decreased. The observed correlations suggest that the risk of loss of control over the biotransformation and biological activity of the parent compounds in distal intestinal mucosa is delayed.

Aberrant alternative splicing in breast cancer

Alternative splicing is critical for human gene expression regulation, which plays a determined role in expanding the diversity of functional proteins. Importantly, alternative splicing is a hallmark of cancer and a potential target for cancer therapeutics. Based on the statistical data, breast cancer is one of the top leading causes of cancer-related deaths in women worldwide. Strikingly, alternative splicing is closely associated with breast cancer development. Here, we seek to provide a general review of the relationship between alternative splicing and breast cancer. We introduce the process of alternative splicing and its regulatory role in cancers. In addition, we highlight the functions of aberrant alternative splicing and mutations of splicing factors in breast cancer progression. Moreover, we discuss the role of alternative splicing in cancer drug resistance and the potential of being targets for cancer therapeutics.

Estrogen receptor variants in ER-positive basal-type breast cancers responding to therapy like ER-negative breast cancers

Immunohistochemically ER-positive HER2-negative (ER+HER2−) breast cancers are classified clinically as Luminal-type. We showed previously that molecular subtyping using the 80-gene signature (80-GS) reclassified a subset of ER+HER2− tumors to molecular Basal-type. We report here that molecular reclassification is associated with expression of dominant-negative ER variants and evaluate response to neoadjuvant therapy and outcome in the prospective neoadjuvant NBRST study (NCT01479101). The 80-GS reclassified 91 of 694 (13.1%) immunohistochemically Luminal-type tumors to molecular Basal-type. Importantly, all 91 discordant tumors were classified as high-risk, whereas only 66.9% of ER+/Luminal-type tumors were classified at high-risk for disease recurrence (i.e., Luminal B) (P < 0.001). ER variant mRNA (ER∆3, ER∆7, and ERα-36) analysis performed on 84 ER+/Basal tumors and 48 ER+/Luminal B control tumors revealed that total ER mRNA was significantly lower in ER+/Basal tumors. The relative expression of ER∆7/total ER was significantly higher in ER+/Basal tumors compared to ER+/Luminal B tumors (P < 0.001). ER+/Basal patients had similar pathological complete response (pCR) rates following neoadjuvant chemotherapy as ER−/Basal patients (34.3 vs. 37.6%), and much higher than ER+/Luminal A or B patients (2.3 and 5.8%, respectively). Furthermore, 3-year distant metastasis-free interval (DMFI) for ER+/Basal patients was 65.8%, significantly lower than 96.3 and 88.9% for ER+/Luminal A and B patients, respectively, (log-rank P < 0.001). Significantly lower total ER mRNA and increased relative ER∆7 dominant-negative variant expression provides a rationale why ER+/Basal breast cancers are molecularly ER-negative. Identification of this substantial subset of patients is clinically relevant because of the higher pCR rate to neoadjuvant chemotherapy and correlation with clinical outcome.

Sex hormone-binding globulin provides a novel entry pathway for estradiol and influences subsequent signaling in lymphocytes via membrane receptor

The complex effects of estradiol on non-reproductive tissues/cells, including lymphoid tissues and immunocytes, have increasingly been explored. However, the role of sex hormone binding globulin (SHBG) in the regulation of these genomic and non-genomic actions of estradiol is controversial. Moreover, the expression of SHBG and its internalization by potential receptors, as well as the influence of SHBG on estradiol uptake and signaling in lymphocytes has remained unexplored. Here, we found that human and mouse T cells expressed SHBG intrinsically. In addition, B lymphoid cell lines as well as both primary B and T lymphocytes bound and internalized external SHBG, and the amount of plasma membrane-bound SHBG decreased in B cells of pregnant compared to non-pregnant women. As potential mediators of this process, SHBG receptor candidates expressed by lymphocytes were identified in silico, including estrogen receptor (ER) alpha. Furthermore, cell surface-bound SHBG was detected in close proximity to membrane ERs while highly colocalizing with lipid rafts. The SHBG-membrane ER interaction was found functional since SHBG promoted estradiol uptake by lymphocytes and subsequently influenced Erk1/2 phosphorylation. In conclusion, the SHBG-SHBG receptor-membrane ER complex participates in the rapid estradiol signaling in lymphocytes, and this pathway may be altered in B cells in pregnant women.

Pathways to Endocrine Therapy Resistance in Breast Cancer

Breast cancers with positive expression of Estrogen Receptor (ER+) are treated with anti-hormone/endocrine therapy which targets the activity of the receptor, the half-life of the receptor or the availability of estrogen. This has significantly decreased mortality in women with ER+ breast cancer, however, about 25-30% of treated women run the risk or recurrence due to either intrinsic or acquired resistance to endocrine therapies. While ER itself is a predictor of response to such therapies, there exists a need to find more biomarkers and novel targets to treat resistant tumors. In this review, we summarize the known mechanisms and describe the ability of genomics in unraveling rare mutations and gene rearrangements that may impact the development of resistance and therefore treatment of ER+ breast cancer in the near future.

The evolving role of receptors as predictive biomarkers for metastatic breast cancer

INTRODUCTION

In breast cancer, estrogen receptor (ER) and human epidermal growth factor receptor 2 (HER2) are essential biomarkers to predict response to endocrine and anti-HER2 therapies, respectively. In metastatic breast cancer, the use of these receptors and targeted therapies present additional challenges: temporal heterogeneity, together with limited sampling methodologies, hinders receptor status assessment, and the constant evolution of the disease invariably leads to resistance to treatment. Areas covered: This review summarizes the genomic abnormalities in ER and HER2, such as mutations, amplifications, translocations, and alternative splicing, emerging as novel biomarkers that provide an insight into underlying mechanisms of resistance and hold potential predictive value to inform treatment selection. We also describe how liquid biopsies for sampling of circulating markers and ultrasensitive detection technologies have emerged which complement ongoing efforts for biomarker discovery and analysis. Expert commentary: While evidence suggests that genomic aberrations in ER and HER2 could contribute to meeting the pressing need for better predictive biomarkers, efforts need to be made to standardize assessment methods and better understand the resistance mechanisms these markers denote. Taking advantage of emerging technologies, research in upcoming years should include prospective trials incorporating these predictors into the study design to validate their potential clinical value.

HMGA1a induces alternative splicing of estrogen receptor alpha in MCF-7 human breast cancer cells

The high-mobility group A protein 1a (HMGA1a) protein is known as an oncogene whose expression level in cancer tissue correlates with the malignant potential, and known as a component of senescence-related structures connecting it to tumor suppressor networks in fibroblasts. HMGA1 protein binds to DNA, but recent studies have shown it exerts novel functions through RNA-binding. Our previous studies have shown that sequence-specific RNA-binding of HMGA1a induces exon-skipping of Presenilin-2 exon 5 in sporadic Alzheimer disease. Here we show that HMGA1a induced exon-skipping of the estrogen receptor alpha (ERα) gene and increased ERα46 mRNA expression in MCF-7 breast cancer cells. An RNA-decoy of HMGA1a efficiently blocked this event and reduced ERα46 protein expression. Blockage of HMGA1a RNA-binding property consequently induced cell growth through reduced ERα46 expression in MCF-7 cells and increased sensitivity to tamoxifen in the tamoxifen-resistant cell line, MCF-7/TAMR1. Stable expression of an HMGA1a RNA-decoy in MCF-7 cells exhibited decreased ERα46 protein expression and increased estrogen-dependent tumor growth when these cells were implanted in nude mice. These results show HMGA1a is involved in alternative splicing of the ERα gene and related to estrogen-related growth as well as tamoxifen sensitivity in MCF-7 breast cancer cells.

Structural and functional characteristics of oestrogen receptor β splice variants: Implications for the ageing brain

Oestrogen receptor (ER)β is a multifunctional nuclear receptor that mediates the actions of oestrogenic compounds. Despite its well defined role in mediating the actions of oestrogens, a substantial body of evidence demonstrates that ERβ has a broad range of physiological functions independent of those normally attributed to oestrogen signalling. These functions can partly be achieved by the activity of several alternatively spliced isoforms that have been identified for ERβ. This short review describes structural differences between the ERβ splice variants that are known to be translated into proteins. Moreover, we discuss how these alternative structures contribute to functional differences in the context of both healthy and pathological conditions. Our review also describes the principal factors that regulate alternative RNA splicing. The alternatively spliced isoforms of ERβ are differentially expressed according to brain region, age and hormonal milieu, emphasising the likelihood that there are precise cell-specific mechanisms regulating ERβ alternative splicing. However, despite these correlative data, the molecular factors regulating alternative ERβ splicing in the brain remain unknown. We also review the basic mechanisms that regulate alternative RNA splicing and use that framework to make logical predictions about ERβ alternative splicing in the brain.

Reduced alternative splicing of estrogen receptor alpha in the endometrium of women with endometriosis

Endometriosis is a condition which involves the presence of uterine stroma and glands outside of the uterine cavity and represents one of the most prevalent disorders of the female reproductive tract. The key symptom of endometriosis is pain, including dysmenorrhea, deep dyspareunia, and chronic pelvic pain. As such, endometriosis has significant economic consequences within the healthcare system and can influence the daily quality of life in affected patients. However, the pathophysiology of this disease and the mechanisms in which this condition generates pain are very unclear. This study, involving 30 women with endometriosis and 28 controls without endometriosis, aimed to investigate relative levels of estrogen receptor alpha (ERα) splice variants in the endometrium of women with and without endometriosis and investigate potential links to the severity of pain. Wild type (wt)-ERα was dominantly expressed in human endometrium while the expression of ERα-del.4, ERα-del.7, and ERα-del.3,4 was significantly reduced in endometriosis patients compared with healthy patients (p < 0.05). Furthermore, the relative ratios of wtERα:ERα-del.4, and wtERα:ERα-del.3,4 were associated with the severity of pain in endometriosis patients (p < 0.05). Consequently, analyzing differences in the relative levels of four types of ERα splice variant in the endometrium of patients with endometriosis may help in the development of endometriosis-targeted treatment and the development of appropriate therapies.

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

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

Estrogen receptor mutations and splice variants determined in liquid biopsies from metastatic breast cancer patients

Mutations and splice variants in the estrogen receptor (ER) gene, ESR1, may yield endocrine resistance in metastatic breast cancer (MBC) patients. These putative endocrine resistance markers are likely to emerge during treatment, and therefore, its detection in liquid biopsies, such as circulating tumor cells (CTCs) and cell‐free DNA (cfDNA), is of great interest. This research aimed to determine whether ESR1 mutations and splice variants occur more frequently in CTCs of MBC patients progressing on endocrine treatment. In addition, the presence of ESR1 mutations was evaluated in matched cfDNA and compared to CTCs. CellSearch‐enriched CTC fractions (≥5/7.5 mL) of two MBC cohorts were evaluated, namely (a) patients starting first‐line endocrine therapy (n = 43, baseline cohort) and (b) patients progressing on any line of endocrine therapy (n = 40, progressing cohort). ESR1 hotspot mutations (D538G and Y537S/N/C) were evaluated in CTC‐enriched DNA using digital PCR and compared with matched cfDNA (n = 18 baseline cohort; n = 26 progressing cohort). Expression of ESR1 full‐length and 4 of its splice variants (∆5, ∆7, 36 kDa, and 46 kDa) was evaluated in CTC‐enriched mRNA. It was observed that in the CTCs, the ESR1 mutations were not enriched in the progressing cohort (8%), when compared with the baseline cohort (5%) (P = 0.66). In the cfDNA, however, ESR1 mutations were more prevalent in the progressing cohort (42%) than in the baseline cohort (11%) (P = 0.04). Three of the same mutations were observed in both CTCs and cfDNA, 1 mutation in CTCs only, and 11 in cfDNA only. Only the ∆5 ESR1 splice variant was CTC‐specific expressed, but was not enriched in the progressing cohort. In conclusion, sensitivity for detecting ESR1 mutations in CTC‐enriched fractions was lower than for cfDNA. ESR1 mutations detected in cfDNA, rarely present at the start of first‐line endocrine therapy, were enriched at progression, strongly suggesting a role in conferring endocrine resistance in MBC.

Estrogen receptor mutations and splice variants determined in liquid biopsies from metastatic breast cancer patients

Mutations and splice variants in the estrogen receptor (ER) gene, ESR1, may yield endocrine resistance in metastatic breast cancer (MBC) patients. These putative endocrine resistance markers are likely to emerge during treatment, and therefore, its detection in liquid biopsies, such as circulating tumor cells (CTCs) and cell-free DNA (cfDNA), is of great interest. This research aimed to determine whether ESR1 mutations and splice variants occur more frequently in CTCs of MBC patients progressing on endocrine treatment. In addition, the presence of ESR1 mutations was evaluated in matched cfDNA and compared to CTCs. CellSearch-enriched CTC fractions (≥5/7.5 mL) of two MBC cohorts were evaluated, namely (a) patients starting first-line endocrine therapy (n = 43, baseline cohort) and (b) patients progressing on any line of endocrine therapy (n = 40, progressing cohort). ESR1 hotspot mutations (D538G and Y537S/N/C) were evaluated in CTC-enriched DNA using digital PCR and compared with matched cfDNA (n = 18 baseline cohort; n = 26 progressing cohort). Expression of ESR1 full-length and 4 of its splice variants (∆5, ∆7, 36 kDa, and 46 kDa) was evaluated in CTC-enriched mRNA. It was observed that in the CTCs, the ESR1 mutations were not enriched in the progressing cohort (8%), when compared with the baseline cohort (5%) (P = 0.66). In the cfDNA, however, ESR1 mutations were more prevalent in the progressing cohort (42%) than in the baseline cohort (11%) (P = 0.04). Three of the same mutations were observed in both CTCs and cfDNA, 1 mutation in CTCs only, and 11 in cfDNA only. Only the ∆5 ESR1 splice variant was CTC-specific expressed, but was not enriched in the progressing cohort. In conclusion, sensitivity for detecting ESR1 mutations in CTC-enriched fractions was lower than for cfDNA. ESR1 mutations detected in cfDNA, rarely present at the start of first-line endocrine therapy, were enriched at progression, strongly suggesting a role in conferring endocrine resistance in MBC.

In vivo xenoestrogenic actions of cadmium and arsenic in anterior pituitary and uterus

Cadmium (Cd) and arsenic (iAs) are toxic metals ubiquitously present in the environment. Both pollutants exert nonmonotonic dose responses, being mostly cytotoxic at high concentrations but mimicking estrogen (E2) effects at low doses. Xenoestrogenic activity of Cd and iAs has been demonstrated in different hormone-dependent tumor cell lines; however, their actions in vivo remain largely unknown. Here, we investigated whether in vivo administration of low doses of Cd and iAs through drinking water would display xenoestrogenic effects in the anterior pituitary gland and uterus of ovariectomized rats. Cd (1ppm) and iAs (0.1ppm) exposure increased the wet weight of anterior pituitary gland and uterus and induced proestrus- and estrus-like vaginal smears. Both metals stimulate cell proliferation of these tissues as they increased the expression of proliferation markers. More importantly, they augmented soluble guanylyl cyclase α1 subunit expression, which has been linked to hormone-dependent tumor progression. Also, Cd and iAs modified protein levels of full-length estrogen receptor α and its truncated variants in an E2-like manner. Anterior pituitary hormone secretion was differentially affected by both metals. Luteinizing hormone synthesis and release were strongly diminished after Cd exposure and only mildly reduced by iAs. Both metals were able to increase prolactin synthesis, although only iAs augmented serum prolactin levels. This study shows for the first time that Cd and iAs exert strong xenoestrogenic effects on anterior pituitary gland at low doses. The differences between Cd and iAs E2-like behavior indicate that other Cd- and iAs-specific mechanisms could be involved. Altogether, these results contribute to the knowledge of reproductive disorders associated with Cd and iAs environmental contamination.

Estrogen receptor beta expression and prognosis of diffuse large B cell lymphoma

OBJECTIVES

Estrogen receptor beta (ERβ)-selective agonists inhibited B cell lymphoma growth in animal models. However, a recent study found that higher ERβ expression in tissue from diffuse large B cell lymphoma (DLBCL) patients indicated a poorer survival. This study aimed to determine the ERβ expression in DLBCL tissue using immunohistochemistry and correlate with clinical outcomes.

METHODS

Diagnostic tissues from newly diagnosed adult DLBCL patients treated with Rituximab-Cyclophosphamide/Doxorubicin/Vincristine/Prednisolone were counted for ERβ1-expressing cells. Nodal lymphoma (N = 41) was analyzed separately from extra-nodal DLBCL (N = 31).

RESULTS

On immunohistochemistry, ERβ1 was expressed in 73.6% of cases with the median expressing cells of 20%. For nodal lymphoma, high ERβ expression (≥25%) was associated with poorer event free survival (EFS) independent of the international prognostic index with the adjusted hazard ratio (HR) of 2.49 (95% Confidence interval (CI) 1.03-6.00, P = 0.042). On the contrary, high ERβ expression (≥25%) was associated with superior outcomes in extra-nodal DLBCL with the adjusted HR of 0.25 (95% CI 0.09-0.75, P = 0.013) for EFS and adjusted HR of 0.29 (95% CI 0.10-0.85, P = 0.024) for overall survival in multivariate analyses.

CONCLUSION

ERβ1 protein expression represented opposite prognostic factors in nodal vs. extra-nodal DLBCL.

Estrogen receptor expression in chronic hepatitis C and hepatocellular carcinoma pathogenesis

AIM

To investigate gender-specific liver estrogen receptor (ER) expression in normal subjects and patients with hepatitis C virus (HCV)-related cirrhosis and hepatocellular carcinoma (HCC).

METHODS

Liver tissues from normal donors and patients diagnosed with HCV-related cirrhosis and HCV-related HCC were obtained from the NIH Liver Tissue and Cell Distribution System. The expression of ER subtypes, ERα and ERβ, were evaluated by Western blotting and real-time RT-PCR. The subcellular distribution of ERα and ERβ was further determined in nuclear and cytoplasmic tissue lysates along with the expression of inflammatory [activated NF-κB and IκB-kinase (IKK)] and oncogenic (cyclin D1) markers by Western blotting and immunohistochemistry. The expression of ERα and ERβ was correlated with the expression of activated NF-κB, activated IKK and cyclin D1 by Spearman’s correlation.

RESULTS

Both ER subtypes were expressed in normal livers but male livers showed significantly higher expression of ERα than females (P < 0.05). We observed significantly higher mRNA expression of ERα in HCV-related HCC liver tissues as compared to normals (P < 0.05) and ERβ in livers of HCV-related cirrhosis and HCV-related HCC subjects (P < 0.05). At the protein level, there was a significantly higher expression of nuclear ERα in livers of HCV-related HCC patients and nuclear ERβ in HCV-related cirrhosis patients as compared to normals (P < 0.05). Furthermore, we observed a significantly higher expression of phosphorylated NF-κB and cyclin D1 in diseased livers (P < 0.05). There was a positive correlation between the expression of nuclear ER subtypes and nuclear cyclin D1 and a negative correlation between cytoplasmic ER subtypes and cytoplasmic phosphorylated IKK in HCV-related HCC livers. These findings suggest that dysregulated expression of ER subtypes following chronic HCV-infection may contribute to the progression of HCV-related cirrhosis to HCV-related HCC.

CONCLUSION

Gender differences were observed in ERα expression in normal livers. Alterations in ER subtype expression observed in diseased livers may influence gender-related disparity in HCV-related pathogenesis.

Complete knockout of estrogen receptor alpha is not directly protective in murine lupus

Systemic lupus erythematosus (SLE) is a chronic and potentially severe autoimmune disease that disproportionately affects women. Despite a known role for hormonal factors impacting autoimmunity and disease pathogenesis, the specific mechanisms of action remain poorly understood. Our laboratory previously backcrossed "estrogen receptor alpha knockout (ERαKO)" mice onto the NZM2410 lupus prone background to generate NZM/ERαKO mice. This original ERαKO mouse, developed in the mid-1990s and utilized in hundreds of published studies, is not in fact ERα null. They express an N-terminally truncated ERα, and are considered a functional KO. They have physiologic deficiencies including infertility due to disruption of a critical activation domain (AF-1) at the N terminus of ERα, required for most classic estrogen (E2) actions. We demonstrated that female NZM/ERαKO mice had significantly less renal disease and significantly prolonged survival compared to WT littermates despite similar serum levels of autoantibodies and glomerular immune complex deposition. Herein, we present results of experiments using a lupus prone true ERα-/- mice (deletional KO mice on the NZM2410 background), surprisingly finding that these animals were not protected if they were ovariectomized, suggesting that another hormonal component confers protection, possibly testosterone, rather than the absence of the full-length ERα.

Characterization of rodent constitutively active estrogen receptor α variants and their constitutive transactivation mechanisms

Estrogen receptor α (ERα) mRNAs exhibit remarkable heterogeneity owing to complicated alternative splicing. Some encode C-terminally-truncated ERα proteins, which display ligand-independent transactivation or dominant-negative activity. We previously characterized C-terminally-truncated ERα mRNA variants with cryptic sequences in humans and mice, and demonstrated that helices in the ligand-binding domains (LBDs) of ERα variants contribute to ligand-independent transcriptional activity. However, existence of non-conventional coding exons and generation of constitutively active ERα variants have remained to be examined in rats. To comparatively analyze modular organization and splicing profiles of the ERα genes, the range of C-terminally-truncated ERα variants was explored in rats and mice using rapid amplification of cDNA ends and RT-PCR cloning. Furthermore, their functions were determined in transiently transfected cells using expression constructs and luciferase reporter assays. Multiple cryptic exons and C-terminally-truncated ERα variant mRNAs were identified in rats and mice. Naturally occurring and artificially truncated variants/constructs lacking helix 5 potentially exhibited gain-of-function in transfected cells. Although cryptic exons and splicing profiles were poorly conserved among humans, mice, and rats, constitutively active variants were generated from the ERα genes. Moreover, the primary mechanism of ligand-independent activation by C-terminally-truncated ERα variants is C-terminus to helix 5 deletion in the LBD. This comparative study documented the complexity of ERα genes, mRNAs, and proteins, and further determined the underlying structural basis of ligand-independent activation by C-terminally-truncated ERα variants.

The single nucleotide variant rs12722489 determines differential estrogen receptor binding and enhancer properties of an IL2RA intronic region

We studied functional effect of rs12722489 single nucleotide polymorphism located in the first intron of human IL2RA gene on transcriptional regulation. This polymorphism is associated with multiple autoimmune conditions (rheumatoid arthritis, multiple sclerosis, Crohn's disease, and ulcerative colitis). Analysis in silico suggested significant difference in the affinity of estrogen receptor (ER) binding site between alternative allelic variants, with stronger predicted affinity for the risk (G) allele. Electrophoretic mobility shift assay showed that purified human ERα bound only G variant of a 32-bp genomic sequence containing rs12722489. Chromatin immunoprecipitation demonstrated that endogenous human ERα interacted with rs12722489 genomic region in vivo and DNA pull-down assay confirmed differential allelic binding of amplified 189-bp genomic fragments containing rs12722489 with endogenous human ERα. In a luciferase reporter assay, a kilobase-long genomic segment containing G but not A allele of rs12722489 demonstrated enhancer properties in MT-2 cell line, an HTLV-1 transformed human cell line with a regulatory T cell phenotype.

Intrinsic ubiquitin E3 ligase activity of histone acetyltransferase Hbo1 for estrogen receptor α

Estrogen receptors (ER) are important transcription factors to relay signals from estrogen and to regulate proliferation of some of breast cancers. The cycling of estrogen-induced DNA binding and ubiquitin-linked proteolysis of ER potentiates ER-mediated transcription. Indeed, several transcriptional coactivators for ER-dependent transcription ubiquitinate ER. Histone acetyltransferase (HAT) Hbo1/KAT7/MYST2, involved in global histone acetylation, DNA replication, transcription, and cellular proliferation, promotes proteasome-dependent degradation of ERα through ubiquitination. However, molecular mechanism for ubiquitination of ERα by Hbo1 is unknown. Here we report the intrinsic ubiquitin E3 ligase activity of Hbo1 toward the ERα. The ligand, estradiol-17β, inhibited E3 ligase activity of Hbo1 for ERα in vitro, whereas hyperactive ERα mutants from metastatic breast cancers resistant to hormonal therapy, were better substrates for ERα ubiquitination by Hbo1. Hbo1 knock-down caused increase in ERα expression. Hbo1 is another ERα coactivator that ubiquitinates ERα.

Activity of Zearalenone in the Porcine Intestinal Tract

This study demonstrates that low doses (somewhat above the No Observed Adverse Effect Level, NOAEL) of the mycoestrogen zearalenone (ZEN) and its metabolites display multispecificity towards various biological targets in gilts. The observed responses in gilts were surprising. The presence of ZEN and zearalenols (ZELs) did not evoke a response in the porcine gastrointestinal tract, which was attributed to dietary tolerance. Lymphocyte proliferation was intensified in jejunal mesenteric lymph nodes, and lymphocyte counts increased in the jejunal epithelium with time of exposure. In the distal digestive tract, fecal bacterial counts decreased, the activity of fecal bacterial enzymes and lactic acid bacteria increased, and cecal water was characterized by higher genotoxicity. The accompanying hyperestrogenism led to changes in mRNA activity of selected enzymes (cytochrome P450, hydroxysteroid dehydrogenases, nitric oxide synthases) and receptors (estrogen and progesterone receptors), and it stimulated post-translational modifications which play an important role in non-genomic mechanisms of signal transmission. Hyperestrogenism influences the regulation of the host's steroid hormones (estron, estradiol and progesteron), it affects the virulence of bacterial genes encoding bacterial hydroxysteroid dehydrogenases (HSDs), and it participates in detoxification processes by slowing down intestinal activity, provoking energy deficits and promoting antiporter activity at the level of enterocytes. In most cases, hyperestrogenism fulfils all of the above roles. The results of this study indicate that low doses of ZEN alleviate inflammatory processes in the digestive system, in particular in the proximal and distal intestinal tract, and increase body weight gains in gilts.

Changes in the metabolic profile and body weight of pre-pubertal gilts during prolonged monotonic exposure to low doses of zearalenone and deoxynivalenol

The aim of this study was to determine whether exposure to low doses of ZEN + DON induces changes in serum biochemical and hematological parameters in pre-pubertal gilts. In the evaluated groups, minor but statistically significant changes were noted in selected serum biochemical parameters, including glucose, total cholesterol, ALT, AST, AP, total bilirubin, P_in, Fe, K and Cl, and in hematological parameters, including WBC, eosinophils, basophils, monocytes, Ht, Hb, MCHC, HDW and PLT. A statistical analysis of the results revealed significant differences between groups in the values of WBC, eosinophils, basophils, Hb, Ht, PLT, glucose, ALT, AP, total bilirubin, Fe and K. Change trends were noted mainly in weeks II and V-VI. An analysis of the metabolic profile of pre-pubertal gilts exposed to ZEN + DON indicates that homeostasis and biotransformation of ZEN + DON can be toned down at the expense of the animals' energy reserves. Body weight gains were lower in group E, and BW gains were not observed in weeks II and VI. The activity levels of gilts decreased in the first weeks of exposure (I and II), but the drop was minimized by a compensatory effect, or in the last two weeks of exposure due to nutrient deficiency or insufficient supply of protein and energy with feed and feed additives, which decreased BW gains. Low doses of mycotoxins induce completely different changes in the metabolic test than higher doses. The above can probably be attributed to: (i) a negative compensatory effect, (ii) initiation of adaptive mechanisms and stimulation of the immune system, probably due to the allergizing properties of mycotoxins, (iii) excessive loss of energy and protein due to more effective feed utilization, or (iv) involvement in detoxification processes which leads to fatigue. Depending on the body's energy stores, the above processes tend to tone down the biotransformation of low doses of the examined mycotoxins but in the present study, the BW of gilts did not increase under exposure to a combination of ZEN + DON.

Risk assessment for changes in the metabolic profile and body weights of pre-pubertal gilts during long-term monotonic exposure to low doses of zearalenone (ZEN)

The aim of the study was to examine whether the process of exposure to low doses of ZEN generates changes in the hematological and biochemical image of blood serum. During the experiment, pre-pubertal gilts (up to 25kg) were administered per os ZEN at a dose of 40μg/kg BW (Group E, n=18) or placebo (Group C, n=21) on a daily basis for 42days. Blood samples for investigation were collected seven times at intervals of one week. In the experimental groups, slight but statistically significant changes in the values of selected biochemical blood indices such as glucose, ALT, P_in, total protein and Fe, or in hematological indices such as RBC, MCV, PLT, WBC, basophils, eosinophils and monocytes were observed. Based on statistical analysis between the groups, differences in the values of WBC, basophils, peroxidase negative cells, Hb, Ht, MCV, HDW, glucose, ALT, AP, total protein, iron or potassium were found. In Group E, decreasing trends in the values of PLT and glucose, and increasing trends in the values of total protein, P_in, Na and Cl were found. The described situations occurred during the last three weeks of exposure. Low levels of exposure to ZEN lead to completely different changes in the metabolic profile than those resulting from higher doses of the toxin. The stimulatory effect of mycotoxins, observed in initial stages of exposure, is eliminated when the compensatory response and adaptive mechanisms are triggered, and due to excessive loss of energy, which may point to more efficient feed utilization and/or detoxification processes. The values of body weight gain obtained in Group E were monotonically higher in four out of the six investigated weeks of exposure. The above changes were accompanied by a decrease in glucose concentrations and higher total protein levels (a rising tendency), which could have affected the rate of body weight gain.

The G protein-coupled estrogen receptor as a modulator of neoplastic transformation

Estrogens play a crucial role in the regulation of physiological and pathophysiological processes. These hormones act through specific receptors, most notably the canonical estrogen receptors α and β (ERα and ERβ) and their truncated forms as well as the G protein-coupled estrogen receptor (GPER). Several studies have shown that GPER is expressed in many normal and cancer cells, including those of the breast, endometrium, ovary, testis and lung. Hormonal imbalance is one possible cause of cancer development. An accumulating body of evidence indicates that GPER is involved in the regulation of cancer cell proliferation, migration and invasion, it may act as a mediator of microRNA, and is believed to modulate the inflammation associated with neoplastic transformation. Furthermore, used in various treatment regimens anti-estrogens such as tamoxifen, raloxifen and fulvestrant (ICI 182.780), antagonists/modulators of canonical estrogen receptors, were found to be GPER agonists. This review presents the current knowledge about the potential role of GPER in neoplastic transformation.

Adaptive Significance of ERα Splice Variants in Killifish (Fundulus heteroclitus) Resident in an Estrogenic Environment

The possibility that chronic, multigenerational exposure to environmental estrogens selects for adaptive hormone-response phenotypes is a critical unanswered question. Embryos/larvae of killifish from an estrogenic-polluted environment (New Bedford Harbor, MA [NBH]) compared with those from a reference site overexpress estrogen receptor alpha (ERα) mRNA but are hyporesponsive to estradiol. Analysis of ERα mRNAs in the two populations revealed differences in splicing of the gene encoding ERα (esr1). Here we tested the transactivation functions of four differentially expressed ERα mRNAs and tracked their association with the hyporesponsive phenotype for three generations after transfer of NBH parents to a clean environment. Deletion variants ERαΔ6 and ERαΔ6-8 were specific to NBH killifish, had dominant negative functions in an in vitro reporter assay, and were heritable. Morpholino-mediated induction of ERαΔ6 mRNA in zebrafish embryos verified its role as a dominant negative ER on natural estrogen-responsive promoters. Alternate long (ERαL) and short (ERαS) 5'-variants were similar transcriptionally but differed in estrogen responsiveness (ERαS ≫ ERαL). ERαS accounted for high total ERα expression in first generation (F1) NBH embryos/larvae but this trait was abolished by transfer to clean water. By contrast, the hyporesponsive phenotype of F1 NBH embryos/larvae persisted after long-term laboratory holding but reverted to a normal or hyper-responsive phenotype after two or three generations, suggesting the acquisition of physiological or biochemical traits that compensate for ongoing expression of negative-acting ERαΔ6 and ERαΔ6-8 isoforms. We conclude that a heritable change in the pattern of alternative splicing of ERα pre-mRNA is part of a genetic adaptive response to estrogens in a polluted environment.

Human C-terminally truncated ERα variants resulting from the use of alternative exons in the ligand-binding domain

The nuclear receptor genes contain alternative internal and terminal exons, with alternative exon incorporation yielding mRNA variants that encode various receptor types, including some with C-terminal truncation that exhibit constitutive activation or dominant-negative transcriptional transactivation. However, C-terminally truncated estrogen receptor α (ERα) variants with alternative sequences have rarely been reported in humans. Therefore, we assessed human ERα genomic organization and alternative splicing profiles, and identified both alternative exons and C-terminally truncated ERα variants. These naturally occurring C-terminally truncated ERα proteins were localized in the nuclei of transfected cells. In addition, ERαi45c and ERαΔ5 variants exhibited constitutive transactivation of an estrogen responsive element-driven promoter in transfected cells. We manufactured expression vectors encoding artificially truncated ERα constructs and evaluated their transactivation abilities to establish mechanisms determining the constitutive activity and dominant-negative properties of truncated variants. Lack of the region encoded in exon 8 eliminated basal and ligand-induced transcriptional transactivation. The C-terminally truncated ERα variants/constructs containing the helices 5 in their ligand-binding domains did not exhibit constitutive transactivation. Furthermore, we demonstrated that truncation from C-termini to helices 5 in the variant ligand-binding domains was required for constitutive activation and found that the remnant regions of the ligand-binding domains and variant-specific sequences influenced transcriptional transactivation efficiency. In conclusion, we elucidated the structural and functional features of novel C-terminally truncated ERα variants and revealed the mechanisms underlying constitutive transactivation by C-terminally truncated nuclear receptor variants.

Interplay of estrogen receptors and FOXA factors in the liver cancer

Liver cancer is the fifth most common cancer in human with male dominance. Sexual dimorphism of liver cancer is conserved from rodents to humans, which was firstly found in mice in late 1930s and female mice were resistant to liver cancer. Sex hormones were found to affect the incidence of liver cancer in rodents. Estrogen receptor alpha (ERα)-mediated estrogen signaling or androgen receptor-mediated androgen signaling prevents or promotes the growth of rodent liver tumors, respectively. Forkhead box protein A (Foxa) factors, Foxa1 and Foxa2, also known as pioneer transcription factors in liver specification, are essential for both estrogen and androgen signaling by acting as central regulators of sexual dimorphism in liver cancer. This review mainly focuses on the interplay between ERα and FOXA factors in liver cancer, and summarizes recent breakthrough studies in elucidating the mechanisms of sexual dimorphism in liver cancer.

The Effect of Low Monotonic Doses of Zearalenone on Selected Reproductive Tissues in Pre-Pubertal Female Dogs--A Review

The growing interest in toxic substances combined with advancements in biological sciences has shed a new light on the problem of mycotoxins contaminating feeds and foods. An interdisciplinary approach was developed by identifying dose-response relationships in key research concepts, including the low dose theory of estrogen-like compounds, hormesis, NOAEL dose, compensatory response and/or food tolerance, and effects of exposure to undesirable substances. The above considerations increased the researchers’ interest in risk evaluation, namely: (i) clinical symptoms associated with long-term, daily exposure to low doses of a toxic compound; and (ii) dysfunctions at cellular or tissue level that do not produce clinical symptoms. Research advancements facilitate the extrapolation of results and promote the use of novel tools for evaluating the risk of exposure, for example exposure to zearalenone in pre-pubertal female dogs. The arguments presented in this paper suggest that low doses of zearalenone in commercial feeds stimulate metabolic processes and increase weight gains. Those processes are accompanied by lower proliferation rates in the ovaries, neoangiogenesis and vasodilation in the ovaries and the uterus, changes in the steroid hormone profile, and changes in the activity of hydroxysteroid dehydrogenases. All of the above changes result from exogenous hyperestrogenizm.

ERα36--Another piece of the estrogen puzzle

Although the nuclear action of estrogen receptors (ER) is a well-known fact, evidence supporting membrane estrogen receptors is steadily accumulating. New ER variants of unrecognized function have been discovered. ERα is a product of the ESR1 gene. It serves not only as a template for the full-length 66kDa protein, but also for smaller isoforms which exist as independent receptors. The recently discovered ERα36 (36kDa), consisting of 310 amino acids of total 595 ERα66 protein residues, is an example of that group. The transcription initiation site is identified in the first intron of the ESR1 gene. C-Terminal 27 amino acids are encoded by previously unknown exon 9. The presence of this unique C-terminal sequence creates an opportunity for the production of selective antibodies. ERα36 has been shown to have a high affinity to the cell membrane and as much as 90% of the protein can be bound with it. Post-translational palmitoylation is suspected to play a crucial role in ERα36 anchoring to the cell membrane. In silico analysis suggests the existence of a potential transmembrane domain in ERα36. ERα36 was found in most cells of animals at various ages, but its exact physiological function remains to be fully elucidated. It seems that cells traditionally considered as being deprived of ER are able to respond to hormonal stimulation via the ERα36 receptor. Moreover, ERα36 displays unique pharmacological properties and its action may be behind antiestrogen resistance. The use of ERα36 in cancer diagnosis gives rise to great expectations.

Estrogenic endocrine disruptors: Molecular mechanisms of action

A comprehensive summary of more than 450 estrogenic chemicals including estrogenic endocrine disruptors is provided here to understand the complex and profound impact of estrogen action. First, estrogenic chemicals are categorized by structure as well as their applications, usage and effects. Second, estrogenic signaling is examined by the molecular mechanism based on the receptors, signaling pathways, crosstalk/bypassing and autocrine/paracrine/homeostatic networks involved in the signaling. Third, evaluation of estrogen action is discussed by focusing on the technologies and protocols of the assays for assessing estrogenicity. Understanding the molecular mechanisms of estrogen action is important to assess the action of endocrine disruptors and will be used for risk management based on pathway-based toxicity testing.

Zearalenone in the Intestinal Tissues of Immature Gilts Exposed per os to Mycotoxins

Zearalenone and its metabolites, α-zearalenol and β-zearalenol, demonstrate estradiol-like activity and disrupt physiological functions in animals. This article evaluates the carryover of zearalenone and its selected metabolites from the digesta to intestinal walls (along the entire intestines) in pre-pubertal gilts exposed to low doses of zearalenone over long periods of time. The term “carryover” describes the transfer of mycotoxins from feed to edible tissues, and it was used to assess the risk of mycotoxin exposure for consumers. The experimental gilts with body weight of up to 25 kg were per os administered zearalenone at a daily dose of 40 μg/kg BW (Group E, n = 18) or placebo (Group C, n = 21) over a period of 42 days. In the first weeks of exposure, the highest values of the carryover factor were noted in the duodenum and the jejunum. In animals receiving pure zearalenone, the presence of metabolites was not determined in intestinal tissues. In the last three weeks of the experiment, very high values of the carryover factor were observed in the duodenum and the descending colon. The results of the study indicate that in animals exposed to subclinical doses of zearalenone, the carryover factor could be determined by the distribution and expression of estrogen receptor beta.

International Union of Basic and Clinical Pharmacology. XCVII. G Protein-Coupled Estrogen Receptor and Its Pharmacologic Modulators

Estrogens are critical mediators of multiple and diverse physiologic effects throughout the body in both sexes, including the reproductive, cardiovascular, endocrine, nervous, and immune systems. As such, alterations in estrogen function play important roles in many diseases and pathophysiological conditions (including cancer), exemplified by the lower prevalence of many diseases in premenopausal women. Estrogens mediate their effects through multiple cellular receptors, including the nuclear receptor family (ERα and ERβ) and the G protein-coupled receptor (GPCR) family (GPR30/G protein-coupled estrogen receptor [GPER]). Although both receptor families can initiate rapid cell signaling and transcriptional regulation, the nuclear receptors are traditionally associated with regulating gene expression, whereas GPCRs are recognized as mediating rapid cellular signaling. Estrogen-activated pathways are not only the target of multiple therapeutic agents (e.g., tamoxifen, fulvestrant, raloxifene, and aromatase inhibitors) but are also affected by a plethora of phyto- and xeno-estrogens (e.g., genistein, coumestrol, bisphenol A, dichlorodiphenyltrichloroethane). Because of the existence of multiple estrogen receptors with overlapping ligand specificities, expression patterns, and signaling pathways, the roles of the individual receptors with respect to the diverse array of endogenous and exogenous ligands have been challenging to ascertain. The identification of GPER-selective ligands however has led to a much greater understanding of the roles of this receptor in normal physiology and disease as well as its interactions with the classic estrogen receptors ERα and ERβ and their signaling pathways. In this review, we describe the history and characterization of GPER over the past 15 years focusing on the pharmacology of steroidal and nonsteroidal compounds that have been employed to unravel the biology of this most recently recognized estrogen receptor.

Estrogen and Estrogen Receptor-α-Mediated Transrepression of Bile Salt Export Pump

Among diseases unique to pregnancy, intrahepatic cholestasis of pregnancy is the most prevalent disorder with elevated serum bile acid levels. We have previously shown that estrogen 17β-estradiol (E2) transrepresses bile salt export pump (BSEP) through an interaction between estrogen receptor (ER)-α and farnesoid X receptor (FXR) and transrepression of BSEP by E2/ERα is an etiological contributing factor to intrahepatic cholestasis of pregnancy. Currently the mechanistic insights into such transrepression are not fully understood. In this study, the dynamics of coregulator recruitment to BSEP promoter after FXR activation and E2 treatment were established with quantitative chromatin immunoprecipitation assays. Coactivator peroxisome proliferator-activated receptor-γ coactivator-1 was predominantly recruited to the BSEP promoter upon FXR activation, and its recruitment was decreased by E2 treatment. Meanwhile, recruitment of nuclear receptor corepressor was markedly increased upon E2 treatment. Functional evaluation of ERα and ERβ chimeras revealed that domains AC of ERα are the determinants for ERα-specific transrepression on BSEP. Further studies with various truncated ERα proteins identified the domains in ERα responsible for ligand-dependent and ligand-independent transrepression. Truncated ERα-AD exhibited potent ligand-independent transrepressive activity, whereas ERα-CF was fully capable of transrepressing BSEP ligand dependently in vitro in Huh 7 cells and in vivo in mice. Both ERα-AD and ERα-CF proteins were associated with FXR in the coimmunoprecipitation assays. In conclusion, E2 repressed BSEP expression through diminishing peroxisome proliferator-activated receptor-γ coactivator-1 recruitment with a concurrent increase in nuclear receptor corepressor recruitment to the BSEP promoter. Domains AD and CF in ERα mediated ligand-independent and ligand-dependent transrepression on BSEP, respectively, through interacting with FXR.

Cloning of multiple ERα mRNA variants in killifish (Fundulus heteroclitus), and differential expression by tissue type, stage of reproduction, and estrogen exposure in fish from polluted and unpolluted environments

To test the hypothesis that alternative splicing could be an adaptive mechanism for populations subject to multi-generational estrogenic exposures, we compared estrogen receptor alpha (ERα) splicing variants in two populations of killifish (Fundulus heteroclitus): one resident in an estrogenic polluted environment (New Bedford Harbor, NBH, MA, USA) and one from a relatively uncontaminated reference site (Scorton Creek, SC, MA, USA). In total we identified 19 ERα variants, each with deletions of one or more coding exons. Four of the variants with potential functional relevance were analyzed by qPCR to test for population differences in expression by tissue type, site, sex, seasonal reproductive status and estrogen treatment. Significantly, a 5'-truncated short form variant (ERαS) was highly expressed in liver and ovary, and was associated with seasonal reproductive activity in SC but not NBH fish. Both ERαS and the full-length long variant (ERαL) were estrogen-inducible (ERαS>ERαL) but the induction response was lower in NBH than in SC fish. In contrast, NBH killifish were hyper-responsive to estrogen as measured by expression of two other estrogen responsive genes: vitellogenin (Vtg) and aromatase B (AroB). Most strikingly, two ERα deletion variants (Δ6 and Δ6-8), lacking ligand binding and activation function domains, were identified in a subset of NBH fish, where they were associated with reduced responsiveness to estrogen treatment. Together, these results support the hypothesis that alternative splicing of the esr1 gene of killifish could be an autoregulatory mechanism by which estrogen modulates the differential expression of ERα, and suggests a novel and adaptive mechanistic response to xenoestrogenic exposure.

Structural insights into tumor-specific chaperoning activity of gamma synuclein in protecting estrogen receptor alpha 36 and its role in tamoxifen resistance in breast cancer

This study investigates structural aspects underlying the chaperoning activity of an intrinsically disordered protein, gamma synuclein, in promoting estrogen mediated breast cancer.

The endometrial cancer cell lines Ishikawa and HEC-1A, and the control cell line HIEEC, differ in expression of estrogen biosynthetic and metabolic genes, and in androstenedione and estrone-sulfate metabolism

Estrogens have important roles in the pathogenesis of endometrial cancer. They can have carcinogenic effects through stimulation of cell proliferation or formation of DNA-damaging species. To characterize model cell lines of endometrial cancer, we determined the expression profiles of the estrogen receptors (ERs) ESR1, ESR2 and GPER, and 23 estrogen biosynthetic and metabolic genes, and investigated estrogen biosynthesis in the control HIEEC cell line and the Ishikawa and HEC-1A EC cell lines. HIEEC and Ishikawa expressed all ERs to different extents, while HEC-1A cells lacked expression of ESR1. Considering the estrogen biosynthetic and metabolic enzymes, these cells showed statistically significant different gene expression profiles for SULT2B1, HSD3B2, CYP19A1, AKR1C3, HSD17B1, HSD17B7, HSD17B12, CYP1B1, CYP3A5, COMT, SULT1A1, GSTP1 and NQO2. In these cells, E2 was formed from E1S and E1, while androstenedione was not converted to estrogens. HIEEC and Ishikawa had similar profiles of androstenedione and E1 metabolism, but hydrolysis of E1S to E1 was weaker in Ishikawa cells. HEC-1A cells were less efficient for activation of E1 into the potent E2, but metabolized androstenedione to other androgenic metabolites better than HIEEC and Ishikawa cells. This study reveals that HIEEC, Ishikawa, and HEC-1A cells can all form estrogens only via the sulfatase pathway. HIEEC, Ishikawa, and HEC-1A cells expressed all the major genes in the production of hydroxyestrogens and estrogen quinones, and in their conjugation. Significantly higher CYP1B1 mRNA levels in Ishikawa cells compared to HEC-1A cells, together with lack of UGT2B7 expression, indicate that Ishikawa cells can accumulate more toxic estrogen-3,4-quinones than HEC-1A cells, as also for HIEEC cells. This study provides further characterization of HIEEC, Ishikawa, and HEC-1A cells, and shows that they differ greatly in expression of the genes investigated and in their capacity for E2 formation, and thus they represent different in vitro models.