Estrogen Hormone Biology

Estrogen-Receptor Expression and Function in Female Reproductive Disease

Estrogen receptors (ER) include ER alpha, ER beta and new membrane receptor G protein-coupled receptor 30 (GPR30). Estrogen receptors are key receptors to maintain ovarian granulosa cell differentiation, follicle and oocyte growth and development, and ovulation function. The abnormal functions of estrogen, its receptors, and estradiol synthesis-related enzymes are closely related to clinical reproductive endocrine diseases, such as polycystic ovary syndrome (PCOS) and endometriosis (EMS). At present, hormone therapy is the main treatment for ovarian-related diseases, and a stable hormone environment is established by regulating ovarian function. In recent years, some estrogen-related drugs have made great progress, such as clomiphene, which is a nonsteroidal antiestrogen drug in clinical application. This article elaborates on the regulatory role of estrogen and its nuclear receptors and membrane receptors in oocyte development, especially female reproductive diseases related to the abnormal expression of estrogen and its receptors. We also highlighted the latest advances of treatment strategy for these diseases and the application of related targeted small molecule drugs in clinical research and treatment, so as to provide reference for the treatment of female reproductive diseases.

ESR1 mutations: a new biomarker in breast cancer

Introduction: In hormone receptor-positive breast cancer, ESR1 mutations have emerged as a key mechanism of resistance to endocrine therapy. Areas covered: Here, we review currently available data on ESR1 mutations, regarding their functional impact, prevalence at different stages (and according to the material used: tissue-based analysis vs. liquid biopsy), prognostic impact and predictive value of resistance to aromatase inhibitors. Possible strategies to overcome this resistance by using selective estrogen receptor downregulators (such as fulvestrant) are also discussed. Expert opinion: ESR1 mutation detection will probably become a prognostic and predictive biomarker in the future, used in clinical practice for hormone-receptor breast cancer, especially in the metastatic setting. In the future, we should expect to assess ESR1 mutations, using liquid biopsy (by digital-PCR or next-generation sequencing), in the same way as other prognostic or predictive biomarkers, such as EGFR mutations in lung cancer, and possibly even have targeted-therapies against these mutations.

History of Estrogen: Its Purification, Structure, Synthesis, Biologic Actions, and Clinical Implications

This mini-review summarizes key points from the Clark Sawin Memorial Lecture on the History of Estrogen delivered at Endo 2018 and focuses on the rationales and motivation leading to various discoveries and their clinical applications. During the classical period of antiquity, incisive clinical observations uncovered important findings; however, extensive anatomical dissections to solidify proof were generally lacking. Initiation of the experimental approach followed later, influenced by Claude Bernard's treatise "An Introduction to the Study of Experimental Medicine." With this approach, investigators began to explore the function of the ovaries and their "internal secretions" and, after intensive investigations for several years, purified various estrogens. Clinical therapies for hot flashes, osteoporosis, and dysmenorrhea were quickly developed and, later, methods of hormonal contraception. Sophisticated biochemical methods revealed the mechanisms of estrogen synthesis through the enzyme aromatase and, after discovery of the estrogen receptors, their specific biologic actions. Molecular techniques facilitated understanding of the specific transcriptional and translational events requiring estrogen. This body of knowledge led to methods to prevent and treat hormone-dependent neoplasms as well as a variety of other estrogen-related conditions. More recently, the role of estrogen in men was uncovered by prismatic examples of estrogen deficiency in male patients and by knockout of the estrogen receptor and aromatase in animals. As studies became more extensive, the effects of estrogen on nearly every organ were described. We conclude that the history of estrogen illustrates the role of intellectual reasoning, motivation, and serendipity in advancing knowledge about this important sex steroid.

Neonatal genistein exposure disrupts ovarian and uterine development in the mouse by inhibiting cellular proliferation

Soy-based formula contains high concentrations of the isoflavone genistein. Genistein possesses estrogenic and tyrosine kinase inhibitory activity and interferes with cellular proliferation and development. To date, the acute and chronic effects of genistein on ovarian and uterine development have not been fully elucidated. In this study, mice at postnatal day 1 were subcutaneously injected with 100 mg/kg genistein for 10 consecutive days, and then their ovaries and uteri were collected on days 10, 21, and 90. Histological evaluation was performed after hematoxylin and eosin staining. The proliferating activity was indicated by the proliferating indicator protein Ki67. Results showed that the subcutaneous injection of genistein to neonatal mice induced the formation of multi-oocyte follicles and delayed the primordial follicle assembly in the ovaries. Genistein significantly enlarged the cross-sectional area of the uterine cavity and wall and disrupted the regularity between the uterine stroma and myometrium. Genistein exposure inhibited proliferative activity because fewer Ki67-positive nuclei were detected in ovarian and uterine cell populations than in the control. Furthermore, most ovaries from adult mice given neonatal genistein were without corpora lutea, and there appeared to be cystic follicles and hypertrophy of the theca, and cortical and medullary layers. Considering the high concentration of isoflavone in soy-based infant formulas and livestock feed, we suggest that the use of isoflavone-rich diets in humans and livestock receive closer examination.

Estrogen receptor signaling mechanisms

The primary female sex hormones, estrogens, are responsible for the control of functions of the female reproductive system, as well as the development of secondary sexual characteristics that appear during puberty and sexual maturity. Estrogens exert their actions by binding to specific receptors, the estrogen receptors (ERs), which in turn activate transcriptional processes and/or signaling events that result in the control of gene expression. These actions can be mediated by direct binding of estrogen receptor complexes to specific sequences in gene promoters (genomic effects), or by mechanisms that do not involve direct binding to DNA (non-genomic effects). Whether acting via direct nuclear effects, indirect non-nuclear actions, or a combination of both, the effects of estrogens on gene expression are controlled by highly regulated complex mechanisms. In this chapter, we summarize the knowledge gained in the past 60years since the discovery of the estrogen receptors on the mechanisms governing estrogen-mediated gene expression. We provide an overview of estrogen biosynthesis, and we describe the main mechanisms by which the female sex hormone controls gene transcription in different tissues and cell types. Specifically, we address the molecular events governing regulation of gene expression via the nuclear estrogen receptors (ERα, and ERβ) and the membrane estrogen receptor (GPER1). We also describe mechanisms of cross-talk between signaling cascades activated by both nuclear and membrane estrogen receptors. Finally, we discuss natural compounds that are able to target specific estrogen receptors and their implications for human health and medical therapeutics.

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

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

Lymph/angiogenesis contributes to sex differences in lung cancer through oestrogen receptor alpha signalling

Oestrogen signalling pathways are emerging targets for lung cancer therapy. Unravelling the contribution of oestrogens in lung cancer development is a pre-requisite to support the development of sex-based treatments and identify patients who could potentially benefit from anti-oestrogen treatments. In this study, we highlight the contribution of lymphatic and blood endothelia in the sex-dependent modulation of lung cancer. The orthotopic graft of syngeneic lung cancer cells into immunocompetent mice showed that lung tumours grow faster in female mice than in males. Moreover, oestradiol (E2) promoted tumour development, increased lymph/angiogenesis and VEGFA and bFGF levels in lung tumours of females through an oestrogen receptor (ER) alpha-dependent pathway. Furthermore, while treatment with ERb antagonist was inefficient, ERa antagonist (MPP) and tamoxifen decreased lung tumour volumes, altered blood and lymphatic vasculature and reduced VEGFA and bFGF levels in females, but not in males. Finally, the quantification of lymphatic and blood vasculature of lung adenocarcinoma biopsies from patients aged between 35 and 55 years revealed more extensive lymphangiogenesis and angiogenesis in tumour samples issued from women than from men. In conclusion, our findings highlight an E2/ERa-dependent modulation of lymphatic and blood vascular components of lung tumour microenvironment. Our study has potential clinical implication in a personalised medicine perspective by pointing to the importance of oestrogen status or supplementation on lung cancer development that should be considered to adapt therapeutic strategies.

Understanding Obesity as a Risk Factor for Uterine Tumors Using Drosophila

Multiple large-scale epidemiological studies have identified obesity as an important risk factor for a variety of human cancers, particularly cancers of the uterus, gallbladder, kidney, liver, colon, and ovary, but there is much uncertainty regarding how obesity increases the cancer risks. Given that obesity has been consistently identified as a major risk factor for uterine tumors, the most common malignancies of the female reproductive system, we use uterine tumors as a pathological context to survey the relevant literature and propose a novel hypothesis: chronic downregulation of the cyclin-dependent kinase 8 (CDK8) module, composed of CDK8 (or its paralog CDK19), Cyclin C, MED12 (or MED12L), and MED13 (or MED13L), by elevated insulin or insulin-like growth factor signaling in obese women may increase the chances to dysregulate the activities of transcription factors regulated by the CDK8 module, thereby increasing the risk of uterine tumors. Although we focus on endometrial cancer and uterine leiomyomas (or fibroids), two major forms of uterine tumors, our model may offer additional insights into how obesity increases the risk of other types of cancers and diseases. To illustrate the power of model organisms for studying human diseases, here we place more emphasis on the findings obtained from Drosophila melanogaster.

The promiscuous estrogen receptor: Evolution of physiological estrogens and response to phytochemicals and endocrine disruptors

Many actions of estradiol (E2), the principal physiological estrogen in vertebrates, are mediated by estrogen receptor-α (ERα) and ERβ. An important physiological feature of vertebrate ERs is their promiscuous response to several physiological steroids, including estradiol (E2), Δ⁵-androstenediol, 5α-androstanediol, and 27-hydroxycholesterol. A novel structural characteristic of Δ⁵-androstenediol, 5α-androstanediol, and 27-hydroxycholesterol is the presence of a C19 methyl group, which precludes the presence of an aromatic A ring with a C3 phenolic group that is a defining property of E2. The structural diversity of these estrogens can explain the response of the ER to synthetic chemicals such as bisphenol A and DDT, which disrupt estrogen physiology in vertebrates, and the estrogenic activity of a variety of plant-derived chemicals such as genistein, coumestrol, and resveratrol. Diversity in the A ring of physiological estrogens also expands potential structures of industrial chemicals that can act as endocrine disruptors. Compared to E2, synthesis of 27-hydroxycholesterol and Δ⁵-androstenediol is simpler, leading us, based on parsimony, to propose that one or both of these steroids or a related metabolite was a physiological estrogen early in the evolution of the ER, with E2 assuming this role later as the canonical estrogen. In addition to the well-studied role of the ER in reproductive physiology, the ER also is an important transcription factor in non-reproductive tissues such as the cardiovascular system, kidney, bone, and brain. Some of these ER actions in non-reproductive tissues appeared early in vertebrate evolution, long before the emergence of mammals.

Estrogen Receptors: New Directions in the New Millennium

Nineteen years have passed since our previous review in this journal in 1999 regarding estrogen receptors. At that time, we described the current assessments of the physiological activities of estrogen and estrogen receptors. Since that time there has been an explosion of progress in our understanding of details of estrogen receptor-mediated processes from the molecular and cellular level to the whole organism. In this review we discuss the basic understanding of estrogen signaling and then elaborate on the progress and current understanding of estrogen receptor actions that have developed using new models and continuing clinical studies.

Mechanisms for estrogen receptor expression in human cancer

Estrogen is a steroid hormone that has critical roles in reproductive development, bone homeostasis, cardiovascular remodeling and brain functions. However, estrogen also promotes mammary, ovarian and endometrial tumorigenesis. Estrogen antagonists and drugs that reduce estrogen biosynthesis have become highly successful therapeutic agents for breast cancer patients. The effects of estrogen are largely mediated by estrogen receptor (ER) α and ERβ, which are members of the nuclear receptor superfamily of transcription factors. The mechanisms underlying the aberrant expression of ER in breast cancer and other types of human tumors are complex, involving considerable alternative splicing of ERα and ERβ, transcription factors, epigenetic and post-transcriptional regulation of ER expression. Elucidation of mechanisms for ER expression may not only help understand cancer progression and evolution, but also shed light on overcoming endocrine therapy resistance. Herein, we review the complex mechanisms for regulating ER expression in human cancer.

Beyond the Antioxidant Activity of Dietary Polyphenols in Cancer: the Modulation of Estrogen Receptors (ERs) Signaling

The potential "health benefits" of dietary polyphenols have been ascribed to their direct antioxidant activity and their impact on the regulation of cell and tissue redox balance. However, because of the relative poor bioavailability of many of these compounds, their effects could not be easily explained by the antioxidant action, which may occur only at high circulating and tissue concentrations. Therefore, many efforts have been put forward to clarify the molecular mechanisms underlining the biological effect of polyphenols in physiological and pathological conditions. Polyphenols' bioavailability, metabolism, and their effects on enzyme, membrane, and/or nuclear receptors and intracellular transduction mechanisms may define the overall impact of these compounds on cancer risk and progression, which is still debated and not yet clarified. Polyphenols are able to bind to estrogen receptor α (ERα) and β (ERβ), and therefore induce biological effects in human cells through mimicking or inhibiting the action of endogenous estrogens, even at low concentrations. In this work, the role and effects of food-contained polyphenols in hormone-related cancers will be reviewed, mainly focusing on the different polyphenols' mechanisms of action with particular attention on their estrogen receptor-based effects, and on the consequences of such processes on tumor progression and development.

Knockdown of CREB1 promotes apoptosis and decreases estradiol synthesis in mouse granulosa cells

Cyclic AMP response element-binding protein 1 (CREB1), a member of the CREB family, is known to be involved in follicular growth, ovulation, and ovarian disease. However, the physiological function of CREB1 in mouse granulosa cells (mGCs) remains lagerly unknown. The aim of this study was to determine the role of CREB1 in mGCs by knocking down CREB1 expression. CREB1 knock-down in mGCs at the mRNA and protein levels, was confirmed by quantitative real-time polymerase chain reaction and western blot. Results of enzyme linked immunosorbent assay revealed that CREB1 knockdown significantly decreased the concentrations of estradiol (E2) and progesterone (P4) in mGCs. Furthermore, the CREB1 knockdown in mGCs promoted cell proliferation and apoptosis, and arrested the cell cycle in S-phase. To elucidate the regulatory mechanism underlying the effects of CREB1 knockdown on steroid synthesis, cell cycle, and apoptosis, we measured the protein expression levels of several related genes in mGCs knocked down CREB1. When CREB1 was knocked down, the expression of Cyp1b1 and Cyp19a1, which encode steroidogenic enzymes, was down-regulated; the expression of the cell cycle factors CyclinA1, CyclinB1, and CyclinD2 were significantly decreased. Among apoptosis-related genes, Bcl-2 was down-regulated, whereas Bax and cleaved Caspase3 were upregulated. Moreover, CREB1 knockdown significantly decreased expression level of Has2, Ptgs2, and Igfbp4, which are essential genes for folliculogenesis in mGCs. Taken together, these findings suggested that CREB1 might be a key regulator of mGCs through regulating steroid synthesis, cell proliferation, cell cycle, apoptosis, and other regulators of folliculogenesis.

Cholesterol and Its Metabolites in Tumor Growth: Therapeutic Potential of Statins in Cancer Treatment

Cholesterol is essential for cell function and viability. It is a component of the plasma membrane and lipid rafts and is a precursor for bile acids, steroid hormones, and Vitamin D. As a ligand for estrogen-related receptor alpha (ESRRA), cholesterol becomes a signaling molecule. Furthermore, cholesterol-derived oxysterols activate liver X receptors (LXRs) or estrogen receptors (ERs). Several studies performed in cancer cells reveal that cholesterol synthesis is enhanced compared to normal cells. Additionally, high serum cholesterol levels are associated with increased risk for many cancers, but thus far, clinical trials with 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors (statins) have had mixed results. Statins inhibit cholesterol synthesis within cells through the inhibition of HMG-CoA reductase, the rate-limiting enzyme in the mevalonate and cholesterol synthetic pathway. Many downstream products of mevalonate have a role in cell proliferation, since they are required for maintenance of membrane integrity; signaling, as some proteins to be active must undergo prenylation; protein synthesis, as isopentenyladenine is an essential substrate for the modification of certain tRNAs; and cell-cycle progression. In this review starting from recent acquired findings on the role that cholesterol and its metabolites fulfill in the contest of cancer cells, we discuss the results of studies focused to investigate the use of statins in order to prevent cancer growth and metastasis.

Xenografted tissue models for the study of human endometrial biology

The human endometrium undergoes extensive morphological, biochemical and molecular changes under the influence of female sex steroid hormones. Besides the fact that estrogen stimulates endometrial cell proliferation and progesterone inhibits this proliferation and induces differentiation, there is limited knowledge about precise molecular mechanisms underlying human endometrial biology. The importance of paracrine signaling in endometrial physiology explains why in vitro culture of endometrial cells has been challenging. Researchers, therefore, have developed alternative experimental in vivo models for the study of endometrial biology. The objective of this review is to summarize the recent developments and work on these in vivo endometrial research models. The in vivo recombinant tissue models in which wild-type endometrial cells are combined with endometrial cells from a gene-targeted mouse strain followed by xenografting to host mice have been critical in confirming the significance of paracrine signaling between the epithelium and stroma in the growth regulation of the endometrium. Additionally, these studies have uncovered differences between the mouse and human, emphasizing the need for the development of experimental models specifically of the human endometrium. Recently, xenotransplants of human endometrial fragments into the subcutaneous space of host mice and endometrial xenografts of dissociated and recombined epithelial and stromal cells beneath the kidney capsule of immunodeficient host mice have proven to be highly promising tools for in vivo research of endometrial functions. For the first time, the latter approach provides an immense opportunity for the application of genome engineering, such as targeted ablation of endometrial genes for example by using CRISPR/CAS9 system. This research will begin to elucidate the functional role of specific genes in this complex tissue. Another advantage of xenotransplantation and xenograft models of the human endometrium is their use to investigate endometrial effects of new compounds and drugs without needing to give them to women. Underpinning the molecular mechanisms underlying endometrial functions is critical to ultimately advance our understanding of endometrial pathophysiology and develop targeted therapies to prevent and cure endometrial pathologies as well as enhance endometrial function when it is desired for fertility.

Nuclear receptors in neural stem/progenitor cell homeostasis

In the central nervous system, embryonic and adult neural stem/progenitor cells (NSCs) generate the enormous variety and huge numbers of neuronal and glial cells that provide structural and functional support in the brain and spinal cord. Over the last decades, nuclear receptors and their natural ligands have emerged as critical regulators of NSC homeostasis during embryonic development and adult life. Furthermore, substantial progress has been achieved towards elucidating the molecular mechanisms of nuclear receptors action in proliferative and differentiation capacities of NSCs. Aberrant expression or function of nuclear receptors in NSCs also contributes to the pathogenesis of various nervous system diseases. Here, we review recent advances in our understanding of the regulatory roles of steroid, non-steroid, and orphan nuclear receptors in NSC fate decisions. These studies establish nuclear receptors as key therapeutic targets in brain diseases.