ERα-associated protein networks

Exploring the physiological role of the G protein-coupled estrogen receptor (GPER) and its associations with human diseases

Estrogen is a group of hormones that collaborate with the nervous system to impact the overall well-being of all genders. It influences many processes, including those occurring in the central nervous system, affecting learning and memory, and playing roles in neurodegenerative diseases and mental disorders. The hormone's action is mediated by specific receptors. Significant roles of classical estrogen receptors, ERα and ERβ, in various diseases were known since many years, but after identifying a structurally and locationally distinct receptor, the G protein-coupled estrogen receptor (GPER), its role in human physiology and pathophysiology was investigated. This review compiles GPER-related information, highlighting its impact on homeostasis and diseases, while putting special attention on functions and dysfunctions of this receptor in neurobiology and biobehavioral processes. Understanding the receptor modulation possibilities is essential for therapy, as disruptions in receptors can lead to diseases or disorders, irrespective of correct estrogen levels. We conclude that studies on the GPER receptor have the potential to develop therapies that regulate estrogen and positively impact human health.

In vitro and in silico assessment of GPER-dependent neurocytotoxicity of emerging bisphenols

To rapidly assess the toxicity of bisphenols (BPs) via the activation of G protein-coupled estrogen receptor (GPER), eight BPs action on GPER were evaluated by molecular docking and molecular dynamics (MD) simulation and then confirmed with IMR-32 cells. The target BPs significantly promoted the production of reactive oxygen species (ROS), reduced cell viability, activated the expression of apoptosis-related proteins and increased the apoptosis rate of IMR-32 cells. Intracellular Ca²⁺ level increased significantly after the treatments with bisphenol A (BPA), bisphenol E (BPE), bisphenol C (BPC) and bisphenol AP (BPAP), suggesting the activation of GPER. Moreover, the stable binding conformations between GPER and BPA, BPE, BPC and BPAP and their dynamic changes of GPER-BPs via MD simulation also suggest that these BPs may activate GPER. The interaction between bisphenol G/bisphenol P/bisphenol PH and GPER are weak, which is consistent with their low GPER activity in vitro. Notably, after the pretreatment of GPER antagonist, Ca²⁺ accumulation and ROS production induced by BPA, BPE, BPC and BPAP in IMR-32 cells were attenuated. Overall, MD simulation and in vitro results mutually verified the activation of GPER by BPs, and MD simulation can rapidly evaluate the neurocytotoxicity of BPs.

FEN1 is a prognostic biomarker for ER+ breast cancer and associated with tamoxifen resistance through the ERα/cyclin D1/Rb axis

Background

Tamoxifen is an important choice in endocrine therapy for patients with oestrogen receptor-positive (ER+) breast cancer, and disease progression-associated resistance to tamoxifen therapy is still challenging. Flap endonuclease-1 (FEN1) is used as a prognostic biomarker and is considered to participate in proliferation, migration, and drug resistance in multiple cancers, especially breast cancer, but the prognostic function of FEN1 in ER+ breast cancer, and whether FEN1 is related to tamoxifen resistance or not, remain to be explored.

Methods

On-line database Kaplan-Meier (KM) plotter, GEO datasets, and immunohistochemistry were used to analyse the prognostic value of FEN1 in ER+ breast cancer from mRNA and protein levels. Cell viability assay and colony formation assays showed the response of tamoxifen in MCF-7 and T47D cells. Microarray data with FEN1 siRNA versus control group in MCF-7 cells were analysed by Gene Set Enrichment Analysis (GSEA). The protein levels downstream of FEN1 were detected by western blot assay.

Results

ER+ breast cancer patients who received tamoxifen for adjuvant endocrine therapy with poor prognosis showed a high expression of FEN1. MCF-7 and T47D appeared resistant to tamoxifen after FEN1 over-expression and increased sensitivity to tamoxifen after FEN1 knockdown. Importantly, FEN1 over-expression could activate tamoxifen resistance through the ERα/cyclin D1/Rb axis.

Conclusions

As a biomarker of tamoxifen effectiveness, FEN1 participates in tamoxifen resistance through ERα/cyclin D1/Rb axis. In the future, reversing tamoxifen resistance by knocking-down FEN1 or by way of action as a small molecular inhibitor of FEN1 warrants further investigation.

Deregulated estrogen receptor signaling and DNA damage response in breast tumorigenesis

Carriers of BRCA1 mutations have a higher chance of developing cancers in hormone-responsive tissues like the breast, ovary and prostate, compared to other tissues. These tumors generally exhibit basal-like characters and do not express estrogen receptor (ER) or progesterone receptor (PR). Intriguingly, BRCA1 mutated breast cancers have a less favorable clinical outcome, as they will not respond to hormone therapy. BRCA1 has been reported to exhibit ligand dependent and independent transcriptional inhibition of ER-α; however, there exists a controversy on whether BRCA1 induces or inhibits ER-α expression. The mechanisms associated with resistance of BRCA1 mutated cancers to hormone therapy, as well as the tissue restriction exhibited by BRCA1 mutated tumors are still largely unknown. BRCA1 mutated tumors possess increased DNA damages and decreased genomic integrity, as BRCA1 plays a cardinal role in high fidelity DNA damage repair pathways, like homologous recombination (HR). The existence of cross regulatory signaling networks between ER-α and BRCA1 speculates a role of ER on BRCA1 dependent DDR pathways. Thus, the loss or haploinsufficiency of BRCA1 and the consequential deregulation of ER-α signaling may result in persistence of unrepaired DNA damages, eventually leading to tumorigenesis. Therefore, understanding of this cross-talk between ER-α and BRCA1, with regard to DDR, will provide critical insights to steer drug development and therapy for breast/ovarian cancers. This review discusses the mechanisms by which estrogen and ER signaling influence BRCA1 mediated DNA damage response and repair pathways in the mammalian system.

Selective Estrogen Receptor Degraders (SERDs): A Promising Strategy for Estrogen Receptor Positive Endocrine-Resistant Breast Cancer

Estrogen receptor (ER) plays important roles in gene transcription and the proliferation of ER positive breast cancers. Selective modulation of ER has been a therapeutic target for this specific type of breast cancer for more than 30 years. Selective estrogen receptor modulators (SERMs) and aromatase inhibitors (AIs) have been demonstrated to be effective therapeutic approaches for ER positive breast cancers. Unfortunately, 30-50% of ER positive tumors become resistant to SERM/AI treatment after 3-5 years. Fulvestrant, the only approved selective estrogen receptor degrader (SERD), is currently an important therapeutic approach for the treatment of endocrine-resistant breast cancers. The poor pharmacokinetic properties of fulvestrant have inspired the development of a new generation of oral SERDs to overcome drug resistance. In this review, we describe recent advances in ERα structure, functions, and mechanisms of endocrine resistance and summarize the development of oral SERDs in both academic and industrial areas.

The ERα-miR-575-p27 feedback loop regulates tamoxifen sensitivity in ER-positive Breast Cancer

Background: Breast cancer is the most common malignancy, and approximately 70% of breast cancers are estrogen receptor-α (ERα) positive. The anti-estrogen tamoxifen is a highly effective and commonly used treatment for patients with ER+ breast cancer. However, 30% of breast cancer patients fail adjuvant tamoxifen therapy and most of metastatic breast cancer patients develop tamoxifen resistance. Although increasing evidence suggests that microRNA (miRNA) dysregulation influences tamoxifen sensitivity, the mechanism of the cross-talk between miRNA and ERα signaling remains unclear. miR-575 has been reported to be involved in carcinogenesis and progression, however, the role of miR-575 in breast cancer remains limited. The aim of this study was to understand the mechanism of miR-575 in breast cancer tamoxifen resistance.

Method: RT-qPCR was employed to assess miR-575 expression in breast cancer tissues and cell lines. The association of miR-575 expression with overall survival in patients with breast cancer was evaluated with KM plotter. Additionally, the effects of miR-575 on breast cancer proliferation and tamoxifen sensitivity were investigated both in vitro and in vivo. Bioinformatic analyses and luciferase reporter assays were performed to validate CDKN1B and BRCA1 as direct targets of miR-31-5p. The ERα binding sites in the miR-575 promoter region was validated with ChIP and luciferase assays. ERα interactions with CDKN1B, cyclin D1 or BRCA1 were determined by IP analysis, and protein expression levels and localization were analyzed by western blotting and immunofluorescence, respectively.

Results: miR-575 levels were higher in ER+ breast cancer than in ER- breast cancer and patients with high miR-575 expression had a significantly poorer outcome than those with low miR-575 expression. ERα bound the miR-575 promoter to activate its transcription, and tamoxifen treatment downregulated miR-575 expression in ER+ breast cancer. Overexpression of miR-575 decreased tamoxifen sensitivity by targeting CDKN1B and BRCA1. CDKN1B and BRCA1 were both able to antagonize ERα activity by inhibiting ERα nuclear translocation and interaction with cyclin D1. Furthermore, miR-575 expression was found to be upregulated in ER+ breast cancer cell with acquired tamoxifen resistance, whereas depletion of miR-575 partially re-sensitized these cells to tamoxifen by regulation of CDKN1B.

Conclusions: Our data reveal the ERα-miR-575-CDKN1B feedback loop in ER+ breast cancer, suggesting that miR-575 can be used as a prognostic biomarker in patients with ER+ breast cancer, as well as a predictor or a promising target for tamoxifen sensitivity.

Transcriptional dysregulation of base excision repair proteins in breast cancer

Base excision repair (BER) addresses the numerous base lesions and strand breaks induced by exogenous and endogenous stressors daily. The complexity and importance of BER requires careful regulation of basal levels of these proteins and inducible responses following DNA damage. Several reports have noted the dysregulation of BER proteins and defects in BER capacity in cancer. Modulated gene and protein expression of several BER proteins, including APE1, PARP1, POL β, and XRCC1, have been observed in breast cancer. Overexpression of these factors has been associated with chemoresistance and cancer aggressiveness, but the regulatory mechanisms that drive overexpression have not been defined. Here, we review the known transcriptional regulators of these key BER proteins and examine potential mechanisms that may drive overexpression in breast cancer.

The role of G protein-coupled estrogen receptor 1 on neurological disorders

G protein-coupled estrogen receptor 1 (GPER) is a membrane-associated estrogen receptor (ER) associated with rapid estrogen-mediated effects. Over recent years GPER emerged has a potential therapeutic target to induce neuroprotection, avoiding the side effects elicited by the activation of classical ERs. The putative neuroprotection triggered by GPER selective activation was demonstrated in mood disorders, Alzheimer's disease or Parkinson's disease of male and female in vivo rodent models. In others, like ischemic stroke, the results are contradictory and currently there is no consensus on the role played by this receptor. However, it seems clear that sex is a biological variable that may impact the results. The major objective of this review is to provide an overview about the physiological effects of GPER in the brain and its putative contribution in neurodegenerative disorders, discussing the data about the signaling pathways involved, as well as, the diverse effects observed.

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.

KRAB-containing zinc finger protein ZNF496 inhibits breast cancer cell proliferation by selectively repressing ERα activity

KRAB-containing zinc finger proteins (KZNF) constitute the largest family of transcriptional regulators in humans and play critical roles in normal development and tumorigenesis. However, the function and mechanism of most KZNFs remain unclear. Here, we report that ZNF496, a KZNF family member, interacts with the DNA binding domain (DBD) of estrogen receptor alpha (ERα) via its C2H2 domain. This interaction decreases ERα binding to chromatin DNA and results in the repression of ERα transactivation, the selective suppression of ERα target genes, and ultimately in a reduction of ERα-positive cell growth in the presence of E2. An analysis of clinical data revealed that the downregulation of ZNF496 expression is observed only in ERα-positive and not in ERα-negative breast cancer tissues when compared with that in matched adjacent tissues. Lastly, we also observed that the downregulation of ZNF496 is associated with poor recurrence-free survival among patients with breast cancer. Collectively, our findings demonstrate that ZNF496 is a novel ERα-binding protein that acts as a target gene-specific ERα corepressor and inhibits the growth of ERα-positive breast cancer cells.

PARP inhibitors protect against sex- and AAG-dependent alkylation-induced neural degeneration

Alkylating agents are commonly used to treat cancer. Although base excision repair (BER) is a major pathway for repairing DNA alkylation damage, under certain conditions, the initiation of BER produces toxic repair intermediates that damage healthy tissues. The initiation of BER by the alkyladenine DNA glycosylase (AAG, a.k.a. MPG) can mediate alkylation-induced cytotoxicity in specific cells in the retina and cerebellum of male mice. Cytotoxicity in both wild-type and Aag-transgenic (AagTg) mice is abrogated in the absence of Poly(ADP-ribose) polymerase-1 (PARP1). Here, we tested whether PARP inhibitors can also prevent alkylation-induced retinal and cerebellar degeneration in male and female WT and AagTg mice. Importantly, we found that WT mice display sex-dependent alkylation-induced retinal damage (but not cerebellar damage), with WT males being more sensitive than females. Accordingly, estradiol treatment protects males against alkylation-induced retinal degeneration. In AagTg male and female mice, the alkylation-induced tissue damage in both the retina and cerebellum is exacerbated and the sex difference in the retina is abolished. PARP inhibitors, much like Parp1 gene deletion, protect against alkylation-induced AAG-dependent neuronal degeneration in WT and AagTg mice, regardless of the gender, but their efficacy in preventing alkylation-induced neuronal degeneration depends on PARP inhibitor characteristics and doses. The recent surge in the use of PARP inhibitors in combination with cancer chemotherapeutic alkylating agents might represent a powerful tool for obtaining increased therapeutic efficacy while avoiding the collateral effects of alkylating agents in healthy tissues.

Calmodulin Lobes Facilitate Dimerization and Activation of Estrogen Receptor-α

Estrogen receptor α (ER-α) is a nuclear hormone receptor that controls selected genes, thereby regulating proliferation and differentiation of target tissues, such as breast. Gene expression controlled by ER-α is modulated by Ca²⁺ via calmodulin (CaM). Here we present the NMR structure of Ca²⁺-CaM bound to two molecules of ER-α (residues 287-305). The two lobes of CaM bind to the same site on two separate ER-α molecules (residues 292, 296, 299, 302, and 303), which explains why CaM binds two molecules of ER-α in a 1:2 complex and stabilizes ER-α dimerization. Exposed glutamate residues in CaM (Glu-11, Glu-14, Glu-84, and Glu-87) form salt bridges with key lysine residues in ER-α (Lys-299, Lys-302, and Lys-303), which is likely to prevent ubiquitination at these sites and inhibit degradation of ER-α. Transfection of cells with full-length CaM slightly increased the ability of estrogen to enhance transcriptional activation by ER-α of endogenous estrogen-responsive genes. By contrast, expression of either the N- or C-lobe of CaM abrogated estrogen-stimulated transcription of the estrogen responsive genes pS2 and progesterone receptor. These data suggest that CaM-induced dimerization of ER-α is required for estrogen-stimulated transcriptional activation by the receptor. In light of the critical role of ER-α in breast carcinoma, our data suggest that small molecules that selectively disrupt the interaction of ER-α with CaM may be useful in the therapy of breast carcinoma.

Not lost in translation: Emerging clinical importance of the G protein-coupled estrogen receptor GPER

It has been 20years that the G protein-coupled estrogen receptor (GPER) was cloned as the orphan receptor GPR30 from multiple cellular sources, including vascular endothelial cells. Here, I will provide an overview of estrogen biology and the historical background leading to the discovery of rapid vascular estrogen signaling. I will also review the recent advances in the understanding of the mechanisms underlying GPER function, its role in physiology and disease, some of the currently available GPER-targeting drugs approved for clinical use such as SERMs (selective estrogen receptor modulators) and SERDs (selective estrogen receptor downregulators). Many of currently used drugs such as tamoxifen, raloxifene, or faslodex™/fulvestrant were discovered targeting GPER many years after they had been introduced to the clinics for entirely different purposes. This has important implications for the clinical use of these drugs and their modes of action, which I have termed 'reverse translational medicine'. In addition, environmental pollutants known as 'endocrine disruptors' have been found to bind to GPER. This article also discusses recent evidence in these areas as well as opportunities in translational clinical medicine and GPER research, including medical genetics, personalized medicine, prevention, and its theranostic use.

17β-Estradiol alters oxidative damage and oxidative stress response protein expression in the mouse mammary gland

Although substantial evidence has demonstrated that parity and 17β-estradiol (E2) reduce mammary carcinogenesis, it is not clear how this protection is conferred. Thus, we examined the effects of parity and E2 treatment in the mammary glands of ovariectomized 15 week-old virgin mice, 15 week-old primiparous mice, and 9 month-old retired breeders. E2 treatment significantly increased lipid peroxidation, protein carbonylation, and protein nitrosylation in the virgin mice, but not in the age-matched primiparous mice or retired breeders. Mammary gland expression of the oxidative stress response protein Cu/Zn superoxide dismutase was consistently reduced in all of the E2-treated mice regardless of parity. Expression of the oxidative stress and DNA repair protein apurinic endonuclease (Ape1) was significantly increased only in the mammary glands of the E2-treated retired breeders. These findings suggest that E2 and parity help to reduce mammary oncogenesis by maintaining the structure and function of proteins, lipids, and DNA.

Celebrating 75 years of oestradiol

Oestrogens exert important effects on the reproductive as well as many other organ systems in both men and women. The history of the discovery of oestrogens, the mechanisms of their synthesis, and their therapeutic applications are very important components of the fabric of endocrinology. These aspects provide the rationale for highlighting several key components of this story. Two investigators, Edward Doisy and Alfred Butenandt, purified and crystalized oestrone nearly simultaneously in 1929, and Doisy later discovered oestriol and oestradiol. Butenandt won the Nobel Prize for this work and Doisy's had to await his purification of vitamin K. Early investigators quickly recognized that oestrogens must be synthesized from androgens and later investigators called this process aromatization. The aromatase enzyme was then characterized, its mechanism determined, and its structure identified after successful crystallization. With the development of knock-out methodology, the precise effects of oestrogen in males and females were defined and clinical syndromes of deficiency and excess described. Their discovery ultimately led to the development of oral contraceptives, treatment of menopausal symptoms, therapies for breast cancer, and induction of fertility, among others. The history of the use of oestrogens for postmenopausal women to relieve symptoms has been characterized by cyclic periods of enthusiasm and concern. The individuals involved in these studies, the innovative thinking required, and the detailed understanding made possible by evolving biologic and molecular techniques provide many lessons for current endocrinologists.

What have we learned about GPER function in physiology and disease from knockout mice?

Estrogens, predominantly 17β-estradiol, exert diverse effects throughout the body in both normal and pathophysiology, during development and in reproductive, metabolic, endocrine, cardiovascular, nervous, musculoskeletal and immune systems. Estrogen and its receptors also play important roles in carcinogenesis and therapy, particularly for breast cancer. In addition to the classical nuclear estrogen receptors (ERα and ERβ) that traditionally mediate predominantly genomic signaling, the G protein-coupled estrogen receptor GPER has become recognized as a critical mediator of rapid signaling in response to estrogen. Mouse models, and in particular knockout (KO) mice, represent an important approach to understand the functions of receptors in normal physiology and disease. Whereas ERα KO mice display multiple significant defects in reproduction and mammary gland development, ERβ KO phenotypes are more limited, and GPER KO exhibit no reproductive deficits. However, the study of GPER KO mice over the last six years has revealed that GPER deficiency results in multiple physiological alterations including obesity, cardiovascular dysfunction, insulin resistance and glucose intolerance. In addition, the lack of estrogen-mediated effects in numerous tissues of GPER KO mice, studied in vivo or ex vivo, including those of the cardiovascular, endocrine, nervous and immune systems, reveals GPER as a genuine mediator of estrogen action. Importantly, GPER KO mice have also demonstrated roles for GPER in breast carcinogenesis and metastasis. In combination with the supporting effects of GPER-selective ligands and GPER knockdown approaches, GPER KO mice demonstrate the therapeutic potential of targeting GPER activity in diseases as diverse as obesity, diabetes, multiple sclerosis, hypertension, atherosclerosis, myocardial infarction, stroke and cancer.

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.

Gender and cell-type-specific effects of the transcription-coupled repair protein, ERCC6/CSB, on repeat expansion in a mouse model of the fragile X-related disorders

The repeat expansion diseases are human genetic disorders that arise from the expansion of a tandem-repeat tract. The Fragile X-related disorders are members of this disease group in which the repeat unit is CGG/CCG and is located in the 5′ untranslated region of the FMR1 gene. Affected individuals often show mosaicism with respect to repeat number resulting from both expansion and contraction of the repeat tract; however, the mechanism responsible for these changes in repeat number is unknown. The work from a variety of model systems suggests that transcription-coupled repair (TCR) may contribute to repeat instability in diseases resulting from CAG/CTG-repeat expansion. To test whether TCR could contribute to repeat instability in the Fragile X-related disorders, we tested the effect of mutations in Csb (Cockayne syndrome group B), a gene essential for TCR, in a knock-in mouse model of these disorders. We found that the loss of CSB affects expansions in a gender and cell-type-specific manner. Our data also show an unanticipated gender difference in instability even in Csb+/+ animals that may have implications for our understanding of the mechanism of repeat expansion in the FX mouse model and perhaps for humans as well.

PRMT2 and RORγ expression are associated with breast cancer survival outcomes

Protein arginine methyltransferases (PRMTs) methylate arginine residues on histones and target transcription factors that play critical roles in many cellular processes, including gene transcription, mRNA splicing, proliferation, and differentiation. Recent studies have linked PRMT-dependent epigenetic marks and modifications to carcinogenesis and metastasis in cancer. However, the role of PRMT2-dependent signaling in breast cancer remains obscure. We demonstrate PRMT2 mRNA expression was significantly decreased in breast cancer relative to normal breast. Gene expression profiling, Ingenuity and protein-protein interaction network analysis after PRMT2-short interfering RNA transfection into MCF-7 cells, revealed that PRMT2-dependent gene expression is involved in cell-cycle regulation and checkpoint control, chromosomal instability, DNA repair, and carcinogenesis. For example, PRMT2 depletion achieved the following: 1) increased p21 and decreased cyclinD1 expression in (several) breast cancer cell lines, 2) decreased cell migration, 3) induced an increase in nucleotide excision repair and homologous recombination DNA repair, and 4) increased the probability of distance metastasis free survival (DMFS). The expression of PRMT2 and retinoid-related orphan receptor-γ (RORγ) is inversely correlated in estrogen receptor-positive breast cancer and increased RORγ expression increases DMFS. Furthermore, we found decreased expression of the PRMT2-dependent signature is significantly associated with increased probability of DMFS. Finally, weighted gene coexpression network analysis demonstrated a significant correlation between PRMT2-dependent genes and cell-cycle checkpoint, kinetochore, and DNA repair circuits. Strikingly, these PRMT2-dependent circuits are correlated with pan-cancer metagene signatures associated with epithelial-mesenchymal transition and chromosomal instability. This study demonstrates the role and significant correlation between a histone methyltransferase (PRMT2)-dependent signature, RORγ, the cell-cycle regulation, DNA repair circuits, and breast cancer survival outcomes.

Estrogen biology: new insights into GPER function and clinical opportunities

Estrogens play an important role in the regulation of normal physiology, aging and many disease states. Although the nuclear estrogen receptors have classically been described to function as ligand-activated transcription factors mediating genomic effects in hormonally regulated tissues, more recent studies reveal that estrogens also mediate rapid signaling events traditionally associated with G protein-coupled receptors. The G protein-coupled estrogen receptor GPER (formerly GPR30) has now become recognized as a major mediator of estrogen's rapid cellular effects throughout the body. With the discovery of selective synthetic ligands for GPER, both agonists and antagonists, as well as the use of GPER knockout mice, significant advances have been made in our understanding of GPER function at the cellular, tissue and organismal levels. In many instances, the protective/beneficial effects of estrogen are mimicked by selective GPER agonism and are absent or reduced in GPER knockout mice, suggesting an essential or at least parallel role for GPER in the actions of estrogen. In this review, we will discuss recent advances and our current understanding of the role of GPER and the activity of clinically used drugs, such as SERMs and SERDs, in physiology and disease. We will also highlight novel opportunities for clinical development towards GPER-targeted therapeutics, for molecular imaging, as well as for theranostic approaches and personalized medicine.

Estrogen signaling and the DNA damage response in hormone dependent breast cancers

Estrogen is necessary for the normal growth and development of breast tissue, but high levels of estrogen are a major risk factor for breast cancer. One mechanism by which estrogen could contribute to breast cancer is via the induction of DNA damage. This perspective discusses the mechanisms by which estrogen alters the DNA damage response (DDR) and DNA repair through the regulation of key effector proteins including ATM, ATR, CHK1, BRCA1, and p53 and the feedback on estrogen receptor signaling from these proteins. We put forward the hypothesis that estrogen receptor signaling converges to suppress effective DNA repair and apoptosis in favor of proliferation. This is important in hormone-dependent breast cancer as it will affect processing of estrogen-induced DNA damage, as well as other genotoxic insults. DDR and DNA repair proteins are frequently mutated or altered in estrogen responsive breast cancer, which will further change the processing of DNA damage. Finally, the action of estrogen signaling on DNA damage is also relevant to the therapeutic setting as the suppression of a DDR by estrogen has the potential to alter the response of cancers to anti-hormone treatment or chemotherapy that induces DNA damage.

Expression of genomic functional estrogen receptor 1 in mouse sertoli cells

There is no consensus whether Sertoli cells express estrogen receptor 1 (Esr1). Reverse transcription-polymerase chain reaction, Western blot, and immunofluorescence demonstrated that mouse Sertoli cell lines, TM4, MSC-1, and 15P-1, and purified primary mouse Sertoli cells (PSCs) contained Esr1 messenger RNA and proteins. Incubation of Sertoli cells with 17β-estradiol (E2) or ESR1 agonist stimulated the expression of an estrogen responsive gene Greb1, which was prevented by ESR inhibitor or ESR1 antagonist. Overexpression of Esr1 in MSC-1 enhanced E2-induced Greb1 expression, while knockdown of Esr1 by small interfering RNA in TM4 attenuated the response. Furthermore, E2-induced Greb1 expression was abolished in the PSCs isolated from Amh-Cre/Esr1-floxed mice in which Esr1 in Sertoli cells were selectively deleted. Chromatin immunoprecipitation assays indicated that E2-induced Greb1 expression in Sertoli cells was mediated by binding of ESR1 to estrogen responsive elements. In summary, ligand-dependent nuclear ESR1 was present in mouse Sertoli cells and mediates a classical genomic action of estrogens.

IQGAP1 binds to estrogen receptor-α and modulates its function

The estrogen receptor (ER) is a steroid hormone receptor that acts as a transcription factor, modulating genes that regulate a vast range of cellular functions. IQGAP1 interacts with several signaling proteins, cytoskeletal components, and transmembrane receptors, thereby serving as a scaffold to integrate signaling pathways. Both ERα and IQGAP1 contribute to breast cancer. In this study, we report that IQGAP1 binds ERα and ERβ. In vitro analysis with pure proteins revealed a direct interaction between IQGAP1 and ERα. Investigation with multiple short fragments of each protein showed that ERα binds to the IQ domain of IQGAP1, whereas the hinge region of ERα is responsible for binding IQGAP1. In addition, IQGAP1 and ERα co-immunoprecipitated from cells, and the association was modulated by estradiol. The interaction has functional effects. Knockdown of endogenous IQGAP1 attenuated the ability of estradiol to induce transcription of the estrogen-responsive genes pS2, progesterone receptor, and cyclin D1. These data reveal that IQGAP1 binds to ERα and modulates its transcriptional function, suggesting that IQGAP1 might be a target for therapy in patients with breast carcinoma.

17β-Estradiol alters oxidative stress response protein expression and oxidative damage in the uterus

The steroid hormone 17β-estradiol (E2) has profound effects on the uterus. However, with the E2-induced increase in uterine cell proliferation and metabolism comes increased production of reactive oxygen species (ROS). We examined the expression of an interactive network of oxidative stress response proteins including thioredoxin (Trx), Cu/Zn superoxide dismutase (SOD1), apurinic endonuclease (Ape1), and protein disulfide isomerase (PDI). We demonstrated that treatment of ovariectomized C57BL/6J female mice with E2 increased the mRNA and protein levels of Trx, but decreased SOD1 and Ape1 mRNA and protein expression. In contrast, E2 treatment increased PDI protein levels but had no effect on PDI transcript levels. Interestingly, E2 treatment also increased two markers of cellular damage, lipid peroxidation and protein carbonylation. Our studies suggest that the decreased expression of SOD1 and Ape1 caused by E2 treatment may in the long term result in disruption of ROS regulation and play a role in endometrial carcinogenesis.

Noncanonical structures and their thermodynamics of DNA and RNA under molecular crowding: beyond the Watson-Crick double helix

How does molecular crowding affect the stability of nucleic acid structures inside cells? Water is the major solvent component in living cells, and the properties of water in the highly crowded media inside cells differ from that in buffered solution. As it is difficult to measure the thermodynamic behavior of nucleic acids in cells directly and quantitatively, we recently developed a cell-mimicking system using cosolutes as crowding reagents. The influences of molecular crowding on the structures and thermodynamics of various nucleic acid sequences have been reported. In this chapter, we discuss how the structures and thermodynamic properties of nucleic acids differ under various conditions such as highly crowded environments, compartment environments, and in the presence of ionic liquids, and the major determinants of the crowding effects on nucleic acids are discussed. The effects of molecular crowding on the activities of ribozymes and riboswitches on noncanonical structures of DNA- and RNA-like quadruplexes that play important roles in transcription and translation are also described.

Links between oestrogen receptor activation and proteolysis: relevance to hormone-regulated cancer therapy

Oestrogen receptor-α (ERα) is a master transcription factor that regulates cell proliferation and homeostasis in many tissues. Despite beneficial ERα functions, sustained oestrogenic exposure increases the risk and/or the progression of various cancers, including those of the breast, endometrium and ovary. Oestrogen–ERα interaction can trigger post-translational ERα modifications through crosstalk with signalling pathways to promote transcriptional activation and ubiquitin-mediated ERα proteolysis, with co-activators that have dual roles as ubiquitin ligases. These processes are reviewed herein. The elucidation of mechanisms whereby oestrogen drives both ERα transactivation and receptor proteolysis might have important therapeutic implications not only for breast cancer but also potentially for other hormone-regulated cancers.

Stability of RNA quadruplex in open reading frame determines proteolysis of human estrogen receptor α

mRNAs encodes not only information that determines amino acid sequences but also additional layers of information that regulate the translational processes. Notably, translational halt at specific position caused by rare codons or stable RNA structures is one of the potential factors regulating the protein expressions and structures. In this study, a quadruplex-forming potential (QFP) sequence derived from an open reading frame of human estrogen receptor α (hERα) mRNA was revealed to form parallel G-quadruplex and halt the translation elongation in vitro. Moreover, when the full-length hERα and variants containing synonymous mutations in the QFP sequence were expressed in cells, translation products cleaved at specific site were observed in quantities dependent on the thermodynamic stability of the G-quadruplexes. These results suggest that the G-quadruplex formation in the coding region of the hERα mRNA impacts folding and proteolysis of hERα protein by slowing down or temporarily stalling the translation elongation.

Ligand-binding dynamics rewire cellular signaling via estrogen receptor-α

Ligand-binding dynamics control allosteric signaling through the estrogen receptor-α (ERα), but the biological consequences of such dynamic binding orientations are unknown. Here, we compare a set of ER ligands having dynamic binding orientation (dynamic ligands) with a control set of isomers that are constrained to bind in a single orientation (constrained ligands). Proliferation of breast cancer cells directed by constrained ligands is associated with DNA binding, coactivator recruitment and activation of the estrogen-induced gene GREB1, reflecting a highly interconnected signaling network. In contrast, proliferation driven by dynamic ligands is associated with induction of ERα-mediated transcription in a DNA-binding domain (DBD)-dependent manner. Further, dynamic ligands displayed enhanced anti-inflammatory activity. The DBD-dependent profile was predictive of these signaling patterns in a larger diverse set of natural and synthetic ligands. Thus, ligand dynamics directs unique signaling pathways, and reveals a novel role of the DBD in allosteric control of ERα-mediated signaling.

Indole-3-carbinol disrupts estrogen receptor-alpha dependent expression of insulin-like growth factor-1 receptor and insulin receptor substrate-1 and proliferation of human breast cancer cells

We previously established that Indole-3-Carbinol (I3C), a natural hydrolysis product of glucobrassicin in cruciferous vegetables, arrests the proliferation of estrogen-dependent human breast cancer cells and induces protein degradation of Estrogen Receptor-alpha (ERα). We demonstrate in human MCF-7 breast cancer cells that I3C ablates expression of Insulin-like Growth Factor Receptor-1 (IGF1R) and Insulin Receptor Substrate-1 (IRS1), downstream effectors of the IGF1 signaling pathway. Exogenous ERα reversed the I3C mediated loss of IGF1R and IRS1 gene expression demonstrating that down-regulation of ERα is functionally linked to I3C control of IGF1R and IRS1 expression. I3C disrupted binding of endogenous ERα, but not Sp1, to ERE-Sp1 composite elements within the IGF1R/IRS1 promoters. Exogenous ERα abrogated, and combined expression of IGF1R and IRS1 attenuated, the I3C mediated cell cycle arrest. Therefore, I3C inhibits proliferation of estrogen-sensitive breast cancer cells through disruption of ERα-mediated transcription of cell signaling components within the IGF1 cascade.

Serine protease PRSS23 is upregulated by estrogen receptor α and associated with proliferation of breast cancer cells

Serine protease PRSS23 is a newly discovered protein that has been associated with tumor progression in various types of cancers. Interestingly, PRSS23 is coexpressed with estrogen receptor α (ERα), which is a prominent biomarker and therapeutic target for human breast cancer. Estrogen signaling through ERα is also known to affect cell proliferation, apoptosis, and survival, which promotes tumorigenesis by regulating the production of numerous downstream effector proteins.In the present study, we aimed to clarify the correlation between and functional implication of ERα and PRSS23 in breast cancer. Analysis of published breast cancer microarray datasets revealed that the gene expression correlation between ERα and PRSS23 is highly significant among all ERα-associated proteases in breast cancer. We then assessed PRSS23 expression in 56 primary breast cancer biopsies and 8 cancer cell lines. The results further confirmed the coexpression of PRSS23 and ERα and provided clinicopathological significance. In vitro assays in MCF-7 breast cancer cells demonstrated that PRSS23 expression is induced by 17β-estradiol-activated ERα through an interaction with an upstream promoter region of PRSS23 gene. In addition, PRSS23 knockdown may suppress estrogen-driven cell proliferation of MCF-7 cells.Our findings imply that PRSS23 might be a critical component of estrogen-mediated cell proliferation of ERα-positive breast cancer cells. In conclusion, the present study highlights the potential for PRSS23 to be a novel therapeutic target in breast cancer research.