The G protein-coupled receptor GPR30 inhibits human urothelial cell proliferation

Role of orphan G-protein coupled receptors in tissue ischemia: A comprehensive review

Ischemic events lead to many diseases and deaths worldwide. Ischemia/reperfusion (I/R) occurs due to reduced blood circulation in tissues followed by blood reflow. Reoxygenation of ischemic tissues is characterized by oxidative stress, inflammation, energy distress, and endoplasmic reticulum stress. There are still no adequate clinical protocols or pharmacological approaches to address the consequences of I/R damage. G protein-coupled receptors (GPCRs) are important therapeutic targets. They compose a large family of seven transmembrane-spanning proteins that are involved in many biological functions. Orphan GPCRs are a large subgroup of these receptors expressed in different organs. In the present review, we summarized the literature regarding the role of orphan GPCRs in I/R in different organs. We focused on the effect of these receptors on modulating cellular and molecular processes underlying ischemia including apoptosis, inflammation, and autophagy. The study showed that GPR3, GPR4, GPR17, GPR30, GPR31, GPR35, GPR37, GPR39, GPR55, GPR65, GPR68, GPR75, GPR81, and GPR91 are involved in ischemic events, mainly in the brain and heart. These receptors offer new possibilities for treating I/R injuries in the body.

Bisphenols A and S Alter the Bioenergetics and Behaviours of Normal Urothelial and Bladder Cancer Cells

Bisphenol A (BPA) and bisphenol S (BPS) are used in the production of plastics. These endocrine disruptors can be released into the environment and food, resulting in the continuous exposure of humans to bisphenols (BPs). The bladder urothelium is chronically exposed to BPA and BPS due to their presence in human urine samples. BPA and BPS exposure has been linked to cancer progression, especially for hormone-dependent cancers. However, the bladder is not recognized as a hormone-dependent tissue. Still, the presence of hormone receptors on the urothelium and their role in bladder cancer initiation and progression suggest that BPs could impact bladder cancer development. The effects of chronic exposure to BPA and BPS for 72 h on the bioenergetics (glycolysis and mitochondrial respiration), proliferation and migration of normal urothelial cells and non-invasive and invasive bladder cancer cells were evaluated. The results demonstrate that chronic exposure to BPs decreased urothelial cells' energy metabolism and properties while increasing them for bladder cancer cells. These findings suggest that exposure to BPA and BPS could promote bladder cancer development with a potential clinical impact on bladder cancer progression. Further studies using 3D models would help to understand the clinical consequences of this exposure.

Role of estrogen receptors in health and disease

Estrogen receptors (ERs) regulate multiple complex physiological processes in humans. Abnormal ER signaling may result in various disorders, including reproductive system-related disorders (endometriosis, and breast, ovarian, and prostate cancer), bone-related abnormalities, lung cancer, cardiovascular disease, gastrointestinal disease, urogenital tract disease, neurodegenerative disorders, and cutaneous melanoma. ER alpha (ERα), ER beta (ERβ), and novel G-protein-coupled estrogen receptor 1 (GPER1) have been identified as the most prominent ERs. This review provides an overview of ERα, ERβ, and GPER1, as well as their functions in health and disease. Furthermore, the potential clinical applications and challenges are discussed.

SMG9 Serves as an Oncogene to Promote the Tumor Progression via EMT and Wnt/β-Catenin Signaling Pathway in Hepatocellular Carcinoma

Background/Aims: SMG9 participates in the nonsense-mediated mRNA decay process that degrades mRNA harboring nonsense mutations introduced either at the level of transcription or RNA processing. However, little is known about the role of SMG9 in hepatocellular carcinoma (HCC). The objective of this research was to clarify the effects of SMG9 expression on HCC progression.

Methods: Microarray data were acquired from NCBI Gene Expression Omnibus (GEO) and The Cancer Genome Atlas (TCGA) database to bioinformatically analyze the differential expression of SMG9 between HCC patients and normal controls. SMG9 mRNA level was measured in sixteen sets of fresh tumor tissues and adjacent non-cancerous liver tissues (ANLTs) via reverse transcription-quantitative polymerase chain reaction (RT-qPCR). SMG9 protein expression was analyzed in ninety-five sets of paired formalin-fixed and paraffin-embedded tissue specimens by immunohistochemistry (IHC). In addition, clinicopathological features of SMG9 in HCC were checked. For in vitro studies, small interfering RNA (siRNA) was used to silence SMG9 expression for exploring biological functions and underlying mechanisms of SMG9 in SMMC-7721 and HepG2.

Results: We found that SMG9 was upregulated in HCC tissues and SMG9 levels were closely related to TNM stage, tumor number and tumor size. Cox regression and Kaplan–Meier proportional hazards analyses showed that high expression of SMG9 was associated with poor patient survival. Furthermore, proliferation, apoptosis resistance, migration and invasion of both SMMC-7721 and HepG2 cells were suppressed by SMG9 inhibition. In addition, EMT and the Wnt/β-catenin signaling pathway were involved in SMG9-mediated HCC progression.

Conclusions: SMG9 may serve as a potential novel prognostic biomarker and therapeutic target in HCC patients.

The Role of Estrogen Receptors in Urothelial Cancer

Epidemiological data have indicated that there are some sex-related differences in bladder cancer. Indeed, the incidence of bladder cancer in men has been substantially higher than that in women throughout the world, while women tend to have higher stage disease and poorer prognosis. These gender disparities have prompted to investigate sex hormones and their cognitive receptors in bladder cancer. Specifically, estrogen receptors, including estrogen receptor-α and estrogen receptor-β, have been shown to contribute to urothelial carcinogenesis and cancer progression, as well as to modulating chemosensitivity in bladder cancer, although conflicting findings exist. Meanwhile, immunohistochemical studies in surgical specimens have assessed the expression of estrogen receptors and related proteins as well as its associations with clinicopathologic features of bladder cancer and patient outcomes. This review article summarizes and discusses available data indicating that estrogen receptor signaling plays an important role in urothelial cancer.

G protein-coupled estrogen receptor-1 agonist induces chemotherapeutic effect via ER stress signaling in gastric cancer

G protein-coupled estrogen receptor (GPER) is known to play an important role in hormone-associated cancers. G-1, a novel synthetic GPER agonist, has been reported to exhibit anti-carcinogenic properties. However, the chemotherapeutic mechanism of GPER is yet unclear. Here, we evaluated GPER expression in human gastric cancer tissues and cells. We found that G-1 treatment attenuates GPER expression in gastric cancer. GPER expression increased G-1-induced antitumor effects in mouse xenograft model. We analyzed the effects of knockdown/overexpression of GPER on G-1-induced cell death in cancer cells. Increased GPER expression in human gastric cancer cells increased G-1-induced cell death via increased levels of cleaved caspase-3, -9, and cleaved poly ADP-ribose polymerase. Interestingly, during G-1-induced cell death, GPER mRNA and protein expression was attenuated and associated with ER stress-induced expression of PERK, ATF-4, GRP-78, and CHOP. Furthermore, PERK-dependent induction of ER stress activation increased G-1-induced cell death, whereas PERK silencing decreased cell death and increased drug sensitivity. Taken together, the data suggest that the induction of ER stress via GPER expression may increase G-1-induced cell death in gastric cancer cells. These results may contribute to a new paradigm shift in gastric cancer therapy.

Does GPER Really Function as a G Protein-Coupled Estrogen Receptor in vivo?

Estrogen can elicit pleiotropic cellular responses via a diversity of estrogen receptors (ERs)-mediated genomic and rapid non-genomic mechanisms. Unlike the genomic responses, where the classical nuclear ERα and ERβ act as transcriptional factors following estrogen binding to regulate gene transcription in estrogen target tissues, the non-genomic cellular responses to estrogen are believed to start at the plasma membrane, leading to rapid activation of second messengers-triggered cytoplasmic signal transduction cascades. The recently acknowledged ER, GPR30 or GPER, was discovered in human breast cancer cells two decades ago and subsequently in many other cells. Since its discovery, it has been claimed that estrogen, ER antagonist fulvestrant, as well as some estrogenic compounds can directly bind to GPER, and therefore initiate the non-genomic cellular responses. Various recently developed genetic tools as well as chemical ligands greatly facilitated research aimed at determining the physiological roles of GPER in different tissues. However, there is still lack of evidence that GPER plays a significant role in mediating endogenous estrogen action in vivo. This review summarizes current knowledge about GPER, including its tissue expression and cellular localization, with emphasis on the research findings elucidating its role in health and disease. Understanding the role of GPER in estrogen signaling will provide opportunities for the development of new therapeutic strategies to strengthen the benefits of estrogen while limiting the potential side effects.

Estrogen receptor alpha differentially modulates host immunity in the bladder and kidney in response to urinary tract infection

The protective role of endogenous estrogen against Urinary Tract Infection (UTI) is well recognized, but the involvement of estrogen receptors (ERs) in modulating immunity in the urinary tract during UTI pathogenesis has not been investigated. The current study investigates the role of ERα in modulating immune responses and UTI outcome. Mice were pre-treated with either ERα agonist, propyl-pyrazole-triol (PPT), or ERα antagonist, methyl-piperidino-pyrazole (MPP), before experimental UTI. The UTI outcome was determined by checking the bacterial load, CD55 and TNFα expression in the bladder and kidney tissues. We observed opposite effects of PPT and MPP treatment on bacterial clearance in bladder versus kidney. PPT significantly reduced bacterial load (P < 0.05) only in the kidney, with minimal changes in CD55 and TNFα levels. In contrast, MPP showed remarkable bacterial clearance only in the bladder that corresponded with reduced CD55 and TNFα expression. MPP treatment in uninfected state induced a significant increase in TNFα production (P < 0.05) in the bladder, but not in the kidney. Our results suggest a protective role of ERα in the kidney. However, protection in the bladder may be mediated via other ER subtypes that may be involved in boosting the local immune responses. Drugs targeting specific ERs in bladder may serve as an adjunct treatment for boosting immune responses in the urogenital tract for efficient bacterial clearance.

The activation of the G protein-coupled estrogen receptor (GPER) inhibits the proliferation of mouse melanoma K1735-M2 cells

The activation of the G protein-coupled estrogen receptor (GPER) by its specific agonist G-1 inhibits prostate cancer and 17β-estradiol-stimulated breast cancer cell proliferation. Tamoxifen (TAM), which also activates the GPER, decreases melanoma cell proliferation, but its action mechanism remains controversial. Here we investigated the expression and the effects of GPER activation by G-1, TAM and its key metabolite endoxifen (EDX) on melanoma cells. Mouse melanoma K1735-M2 cells expressed GPER and G-1 reduced cell biomass, and the number of viable cells, without increasing cell death. Rather, G-1 decreased cell division by blocking cell cycle progression in G2. Likewise, TAM and EDX exhibited an antiproliferative activity in melanoma cells due to decreased cell division. Both G-1 and the antiestrogens showed a trend to decrease the levels of phosphorylated ERK 1/2 after 1 h treatment, although only EDX, the most potent antiproliferative antiestrogen, induced significant effects. Importantly, the targeting of GPER with siRNA abolished the cytostatic activity of both G-1 and antiestrogens, suggesting that the antitumor actions of antiestrogens in melanoma cells involve GPER activation. Our results unveil a new target for melanoma therapy and identify GPER as a key mediator of antiestrogen antiproliferative effects, which may contribute to select the patients that benefit from an antiestrogen-containing regimen.

The membrane-type estrogen receptor G-protein-coupled estrogen receptor suppresses lipopolysaccharide-induced interleukin 6 via inhibition of nuclear factor-kappa B pathway in murine macrophage cells

The female sex hormone estrogen exerts anti-inflammatory effects. The G-protein-coupled estrogen receptor (GPER) has been recently identified as a novel membrane-type estrogen receptor that can mediate non-genomic estrogenic effects on many cell types. We previously demonstrated that GPER inhibits tumor necrosis factor alpha-induced expression of interleukin 6 (IL-6) through repression of nuclear factor-kappa B (NF-κB) promoter activity using human breast cancer cells. Although several reports have indicated that GPER suppresses Toll-like receptor-induced inflammatory cytokine expression in macrophages, the molecular mechanisms of the inhibition of cytokine production via GPER remain poorly understood. In the present study, we examined GPER-mediated inhibition of IL-6 expression induced by lipopolysaccharide (LPS) stimulation in a mouse macrophage cell line. We found that the GPER agonist G-1 inhibited LPS-induced IL-6 expression in macrophage cells, and this inhibition was due to the repression of NF-κB promoter activity by GPER. G-1 treatment also decreased the phosphorylation of inhibitor of κB kinases. Among the mitogen-activated protein kinases, the phosphorylation of c-jun N-terminal kinase (JNK) was increased by G-1. These findings delineate the novel mechanism of the inhibition of LPS-induced IL-6 through GPER-activated JNK-mediated negative regulation of the NF-κB pathway in murine macrophage cells, which links anti-inflammatory effects to estrogen.

Role of GPR30 in estrogen-induced prostate epithelial apoptosis and benign prostatic hyperplasia

Several studies have implicated estrogen and the estrogen receptor (ER) in the pathogenesis of benign prostatic hyperplasia (BPH); however, the mechanism underlying this effect remains elusive. In the present study, we demonstrated that estrogen (17β-estradiol, or E2)-induced activation of the G protein-coupled receptor 30 (GPR30) triggered Ca²⁺ release from the endoplasmic reticulum, increased the mitochondrial Ca²⁺ concentration, and thus induced prostate epithelial cell (PEC) apoptosis. Both E2 and the GPR30-specific agonist G1 induced a transient intracellular Ca²⁺ release in PECs via the phospholipase C (PLC)-inositol 1, 4, 5-triphosphate (IP₃) pathway, and this was abolished by treatment with the GPR30 antagonist G15. The release of cytochrome c and activation of caspase-3 in response to GPR30 activation were observed. Data generated from the analysis of animal models and human clinical samples indicate that treatment with the GPR30 agonist relieves testosterone propionate (TP)-induced prostatic epithelial hyperplasia, and that the abundance of GPR30 is negatively associated with prostate volume. On the basis of these results, we propose a novel regulatory mechanism whereby estrogen induces the apoptosis of PECs via GPR30 activation. Inhibition of this activation is predicted to lead to abnormal PEC accumulation, and to thereby contribute to BPH pathogenesis.

Activation of G protein-coupled estrogen receptor 1 mimics, but does not mediate, the anti-proliferative action of estradiol on pituitary lactotrophs in primary culture

Estrogen binds to nuclear estrogen receptors (ERs) to modulate transcription of target genes in estrogen-responsive cells. However, recent studies have shown that estrogen also binds to cytoplasmic membrane ERs to modulate protein kinase signaling cascades, leading to non-genomic actions. We investigated whether either nuclear or membrane ERs, including G protein-coupled estrogen receptor 1 (Gper1), mediate the inhibitory action of estrogen on insulin-like growth factor-1 (IGF-1)-induced proliferation of pituitary lactotrophs in primary culture. The cytoplasmic membrane-impermeable bovine serum albumin-conjugated estradiol (BSA-E2) at 1 nM, an equimolar concentration at which 17β-estradiol (E2) exerts anti-proliferative effects, did not inhibit IGF-1-induced lactotroph proliferation. In contrast, diethylstilbestrol, which is known to selectively activate nuclear ERs but not membrane ERs, inhibited IGF-1-induced proliferation and modulated mRNA expression of estrogen-responsive genes to a similar degree as E2. Activation of Gper1 by its agonist G-1 inhibited IGF-1-induced proliferation in a dose-dependent manner, but it had little effect on modulation of mRNA expression of estrogen-responsive genes. However, blockade of Gper1 by its antagonist G-15 did not affect the inhibitory action of E2 on IGF-1-induced proliferation. Here, we demonstrate that E2 inhibition of lactotroph proliferation is due to nuclear ER-mediated genomic action. Our results suggest that activation of Gper1 mimics, but does not mediate, the anti-proliferative action of E2 on lactotrophs.

Activation of GPR30 stimulates GTP-binding of Gαi1 protein to sustain activation of Erk1/2 in inhibition of prostate cancer cell growth and modulates metastatic properties

Previously, we reported that GPR30 activation by the receptor-specific, non-estrogenic ligand G-1 inhibited in vitro and in vivo growth of prostate cancer (PCa) cells via sustained Erk1/2 activation. Mechanism underlying the sustained Erk1/2 activation for PCa cell growth inhibition remains unclear. Here we report that G-1, through GPR30, activated Gαi1 proteins to sustain Erk1/2 activation but failed to activate adenylyl cyclase (AC) for cAMP production in PCa cells. The chemical-induced activation of AC-cAMP-PKA signaling attenuated Erk1/2 activity and blocked the cell growth inhibitory effects of G-1. Furthermore, PCa predominantly expressed Gαi1 proteins. Silencing of Gαi1 expression blocked the inhibitory effects of G-1 on PCa cell growth. By gene expression profiling, GPR30 activation by G-1 interfered expression of cell cycle regulators and machinery elements to modulate PCa cell growth and the RACGAP1 interactome to control metastatic properties. In this regard, we demonstrated that G-1 inhibited PCa cell migration and invasion with reduced formations of filopodia and stress fibers through a GPR30-dependent pathway. Taken together, our findings revealed the underlying mechanism for sustaining Erk1/2 activation upon GPR30 activation by G-1 in PCa cells and the GPR30-mediated pathways in controlling PCa cell growth and metastatic properties.

Importance of Estrogenic Signaling and Its Mediated Receptors in Prostate Cancer

Prostate cancer (PCa) treatment was first established by Huggins and Hodges in 1941, primarily described as androgen deprivation via interference of testicular androgen production. The disease remains incurable with relapse of hormone-refractory cancer after treatments. Epidemiological and clinical studies disclosed the importance of estrogens in PCa. Discovery of estrogen receptor ERβ prompted direct estrogenic actions, in conjunction with ERα, on PCa cells. Mechanistically, ERs upon ligand binding transactivate target genes at consensus genomic sites via interactions with various transcriptional co-regulators to mold estrogenic signaling. With animal models, Noble revealed estrogen dependencies of PCa, providing insight into potential uses of antiestrogens in the treatment. Subsequently, various clinical trials were conducted and molecular and functional consequences of antiestrogen treatment in PCa were delineated. Besides, estrogens can also trigger rapid non-genomic signaling responses initiated at the plasma membrane, at least partially via an orphan G-protein-coupled receptor GPR30. Activation of GPR30 significantly inhibited in vitro and in vivo PCa cell growth and the underlying mechanism was elucidated. Currently, molecular networks of estrogenic and antiestrogenic signaling via ERα, ERβ and GPR30 in PCa have not been fully deciphered. This crucial information could be beneficial to further developments of effective estrogen- and antiestrogen-based therapy for PCa patients.

The G-protein coupled estrogen receptor, GPER: The inside and inside-out story

GPER possesses structural and functional characteristics shared by members of the G-protein-coupled receptor (GPCR) superfamily, the largest class of plasma membrane receptors. This newly appreciated estrogen receptor is localized predominately within intracellular membranes in most, but not all, cell types and its surface expression is modulated by steroid hormones and during tissue injury. An intracellular staining pattern is not unique among GPCRs, which employ a diverse array of molecular mechanisms that restrict cell surface expression and effectively regulating receptor binding and activation. The finding that GPER displays an intracellular predisposition has created some confusion as the estrogen-inducible transcription factors, ERα and ERβ, also reside intracellularly, and has led to complex suggestions of receptor interaction. GPER undergoes constitutive retrograde trafficking from the plasma membrane to the endoplasmic reticulum and recent studies indicate its interaction with PDZ binding proteins that sort transmembrane receptors to synaptosomes and endosomes. Genetic targeting and selective ligand approaches as well as cell models that express GPER in the absence of ERs clearly supports GPER as a bonafide "stand alone" receptor. Here, the molecular details that regulate GPER action, its cell biological activities and its implicated roles in physiological and pathological processes are reviewed.

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.

Roles of ERβ and GPR30 in Proliferative Response of Human Bladder Cancer Cell to Estrogen

Bladder cancer belongs to one of the most common cancers and is a leading cause of deaths in our society. Urothelial carcinoma of the bladder (UCB) is the main type of this cancer, and the estrogen receptors in UCB remain to be studied. Our experiment aimed to investigate the possible biological effect of 17β-estradiol on human bladder-derived T24 carcinoma cells and to indicate its related mechanisms. T24 cells were treated with various doses of 17β-estradiol, and cell proliferation was detected using MTT assays. 17β-estradiol promoted T24 cell proliferation independent of ERβ/GPR30-regulated EGFR-MAPK pathway, while it inhibited cell growth via GPR30. Furthermore, the expression levels of downstream genes (c-FOS, BCL-2, and CYCLIN D1) were increased by 17β-estradiol and this effect was independently associated with activity of the EGFR-MAPK pathway. The two estrogen receptors might be potential therapeutic targets for the treatment of bladder cancer.

Activation of GPR30 inhibits cardiac fibroblast proliferation

The incidence of left ventricular diastolic dysfunction significantly increases in postmenopausal women suggesting the association between estrogen loss and diastolic dysfunction. The in vivo activation of G protein-coupled estrogen receptor (GPR30) attenuates the adverse effects of estrogen loss on cardiac fibrosis and diastolic dysfunction in mRen2.Lewis rats. This study was designed to address the effects of GPR30 on cardiac fibroblast proliferation in rats. The expression of GPR30 in cardiac fibroblasts isolated from adult Sprague-Dawley rats was confirmed by RT-PCR, Western blot analysis, and immunofluorescence staining. Results from BrdU incorporation assays, cell counting, carboxyfluorescein diacetate succinimidyl ester labeling in conjunction with flow cytometry, and Ki-67 staining showed that treatment with G1, a specific agonist of GPR30, inhibited cardiac fibroblast proliferation in a dose-dependent manner, which was associated with decreases in CDK1 and cyclin B1 protein expressions. In the GPR30-KO cells, BrdU incorporation, and CDK1 and cyclin B1 expressions significantly increased when compared to GPR30-intact cells. G1 had no effect on BrdU incorporation, CDK1 and cyclin B1 mRNA levels in GPR30-KO cells. In vivo studies showed increases in CDK1 and cyclin B1 mRNA levels, Ki-67-positive cells, and the immunohistochemistry staining of vimentin, a fibroblast marker, in the left ventricles from ovariectomized mRen2.Lewis rats versus hearts from ovary-intact littermates; 2 weeks of G1 treatment attenuated these adverse effects of estrogen loss. This study demonstrates that GPR30 is expressed in rat cardiac fibroblasts, and activation of GPR30 limits proliferation of these cells likely via suppression of the cell cycle proteins, cyclin B1, and CDK1.

GPR30 decreases cardiac chymase/angiotensin II by inhibiting local mast cell number

Chronic activation of the novel estrogen receptor GPR30 by its agonist G1 mitigates the adverse effects of estrogen (E2) loss on cardiac structure and function. Using the ovariectomized (OVX) mRen2.Lewis rat, an E2-sensitive model of diastolic dysfunction, we found that E2 status is inversely correlated with local cardiac angiotensin II (Ang II) levels, likely via Ang I/chymase-mediated production. Since chymase is released from cardiac mast cells during stress (e.g., volume/pressure overload, inflammation), we hypothesized that GPR30-related cardioprotection after E2 loss might occur through its opposing actions on cardiac mast cell proliferation and chymase production. Using real-time quantitative PCR, immunohistochemistry, and immunoblot analysis, we found mast cell number, chymase expression, and cardiac Ang II levels were significantly increased in the hearts of OVX-compared to ovary-intact mRen2.Lewis rats and the GPR30 agonist G1 (50 mg/kg/day, s.c.) administered for 2 weeks limited the adverse effects of estrogen loss. In vitro studies revealed that GPR30 receptors are expressed in the RBL-2H3 mast cell line and G1 inhibits serum-induced cell proliferation in a dose-dependent manner, as determined by cell counting, BrdU incorporation assay, and Ki-67 staining. Using specific antagonists to estrogen receptors, blockage of GPR30, but not ERα or ERβ, attenuated the inhibitory effects of estrogen on BrdU incorporation in RBL-2H3 cells. Further study of the mechanism underlying the effect on cell proliferation showed that G1 inhibits cyclin-dependent kinase 1 (CDK1) mRNA and protein expression in RBL-2H3 cells in a dose-dependent manner.

Regulation of local steroidogenesis in the brain and in prostate cancer: lessons learned from interdisciplinary collaboration

Sex steroids play critical roles in the regulation of the brain and many other organs. Traditionally, researchers have focused on sex steroid signaling that involves travel from the gonads via the circulation to intracellular receptors in target tissues. This classic concept has been challenged, however, by the growing number of cases in which steroids are synthesized locally and act locally within diverse tissues. For example, the brain and prostate carcinoma were previously considered targets of gonadal sex steroids, but under certain circumstances, these tissues can upregulate their steroidogenic potential, particularly when circulating sex steroid concentrations are low. We review some of the similarities and differences between local sex steroid synthesis in the brain and prostate cancer. We also share five lessons that we have learned during the course of our interdisciplinary collaboration, which brought together neuroendocrinologists and cancer biologists. These lessons have important implications for future research in both fields.

The activation of G protein-coupled receptor 30 (GPR30) inhibits proliferation of estrogen receptor-negative breast cancer cells in vitro and in vivo

There is an urgent clinical need for safe and effective treatment agents and therapy targets for estrogen receptor negative (ER−) breast cancer. G protein-coupled receptor 30 (GPR30), which mediates non-genomic signaling of estrogen to regulate cell growth, is highly expressed in ER− breast cancer cells. We here showed that activation of GPR30 by the receptor-specific agonist G-1 inhibited the growth of ER− breast cancer cells in vitro. Treatment of ER− breast cancer cells with G-1 resulted in G2/M-phase arrest, downregulation of G2-checkpoint regulator cyclin B, and induction of mitochondrial-related apoptosis. The G-1 treatment increased expression of p53 and its phosphorylation levels at Serine 15, promoted its nuclear translocation, and inhibited its ubiquitylation, which mediated the growth arrest effects on cell proliferation. Further, the G-1 induced sustained activation and nuclear translocation of ERK1/2, which was mediated by GPR30/epidermal growth factor receptor (EGFR) signals, also mediated its inhibition effects of G-1. With extensive use of siRNA-knockdown experiments and inhibitors, we found that upregulation of p21 by the cross-talk of GPR30/EGFR and p53 was also involved in G-1-induced cell growth arrest. In vivo experiments showed that G-1 treatment significantly suppressed the growth of SkBr3 xenograft tumors and increased the survival rate, associated with proliferation suppression and upregulation of p53, p21 while downregulation of cyclin B. The discovery of multiple signal pathways mediated the suppression effects of G-1 makes it a promising candidate drug and lays the foundation for future development of GPR30-based therapies for ER− breast cancer treatment.

G-protein-coupled estrogen receptor as a new therapeutic target for treating coronary artery disease

Coronary heart disease (CHD) continues to be the greatest mortality risk factor in the developed world. Estrogens are recognized to have great therapeutic potential to treat CHD and other cardiovascular diseases; however, a significant array of potentially debilitating side effects continues to limit their use. Moreover, recent clinical trials have indicated that long-term postmenopausal estrogen therapy may actually be detrimental to cardiovascular health. An exciting new development is the finding that the more recently discovered G-protein-coupled estrogen receptor (GPER) is expressed in coronary arteries-both in coronary endothelium and in smooth muscle within the vascular wall. Accumulating evidence indicates that GPER activation dilates coronary arteries and can also inhibit the proliferation and migration of coronary smooth muscle cells. Thus, selective GPER activation has the potential to increase coronary blood flow and possibly limit the debilitating consequences of coronary atherosclerotic disease. This review will highlight what is currently known regarding the impact of GPER activation on coronary arteries and the potential signaling mechanisms stimulated by GPER agonists in these vessels. A thorough understanding of GPER function in coronary arteries may promote the development of new therapies that would help alleviate CHD, while limiting the potentially dangerous side effects of estrogen therapy.

GPER functions as a tumor suppressor in MCF-7 and SK-BR-3 breast cancer cells

PURPOSE

The orphan, membrane-bound estrogen receptor (GPER) is expressed at high levels in a large fraction of breast cancer patients, and its expression is favorable for patients' survival. We investigated the role of GPER as a potential tumor suppressor in MCF-7 and SK-BR-3 breast cancer cells.

METHODS

The effect of GPER agonist G-1 in cell culture was used to determine whether GPER inhibit cell growth. The methylation status of GPER promoter was investigated by methylation-specific PCR.

RESULTS

GPER-specific agonist G-1 inhibited breast cancer cell proliferation in concentration-dependent manner via induction of the cell cycle arrest in M-phase, enhanced phosphorylation of histone 3 and cell apoptosis. Analysis of the methylation status of the GPER promoter in MCF-7 and SK-BR-3 cells revealed that GPER expression is regulated by epigenetic mechanisms and GPER expression is inactivated by promoter methylation. Overall, our results are consistent with our recent findings in triple-negative breast cancer cells, and the cell surface expression of GPER makes it an excellent potential therapeutic target for non-triple-negative breast cancer.

A novel estrogen receptor GPER mediates proliferation induced by 17β-estradiol and selective GPER agonist G-1 in estrogen receptor α (ERα)-negative ovarian cancer cells

G protein-coupled estrogen receptor (GPER) is recently identified as a membrane-associated estrogen receptor that mediates non-genomic effects of estrogen. Our previous immunohistochemistry study found an association between GPER and the proliferation of epithelial ovarian cancer. However, the contributions and mechanisms of GPER in the proliferation of ovarian cancers are not clear. We have examined the role of GPER in estrogen receptor α (ERα)-negative/GPER positive OVCAR5 ovarian cancer cell line. MTT assay was used to detect cell proliferation. BrdU incorporation assay was used to measure the cells in S-phase. Protein expression of marker genes of proliferation, cell cycle and apoptosis were examined by Western blot. The results showed that 17β-estradiol and selective GPER agonist G-1 stimulated the proliferation of OVCAR5 cells and increased the cells in S-phase. Both ligands upregulated the protein levels of c-fos and cyclin D1. Small interfering RNA targeting GPER or G protein inhibitor pertussin toxin (PTX) inhibited basal cell proliferation and attenuated 17β-estradiol- or G-1-induced cell proliferation. GPER mediated cell growth was also associated with the apoptosis of OVCAR5 cells. These findings suggest that GPER has an important function in the proliferation of ovarian cancer cells lacking ERα. GPER might be a promising therapeutic target in ovarian cancer.

Oleuropein and hydroxytyrosol activate GPER/ GPR30-dependent pathways leading to apoptosis of ER-negative SKBR3 breast cancer cells

SCOPE

We have previously demonstrated that oleuropein (OL) and hydroxytyrosol (HT) reduce 17β-estradiol-mediated proliferation in MCF-7 breast cancer (BC) cells without affecting the classical genomic action of estrogen receptor (ER), but activating instead the ERK1/2 pathway. Here, we hypothesized that this inhibition could be mediated by a G-protein-coupled receptor named GPER/GPR30. Using the ER-negative and GPER-positive SKBR3 BC cells as experimental model, we investigated the effects of OL and HT on GPER-mediated activation of downstream pathways.

METHODS AND RESULTS

Docking simulations and ligand-binding studies evidenced that OL and HT are able to bind GPER. MTT cell proliferation assays revealed that both phenols reduced SKBR3 cell growth; this effect was abolished silencing GPER. Focusing on OL and HT GPER-mediated pathways, using Western blot analysis we showed a sustained ERK1/2 activation triggering an intrinsic apoptotic pathway.

CONCLUSION

Showing that OL and HT work as GPER inverse agonists in ER-negative and GPER-positive SKBR3 BC cells, we provide novel insights into the potential of these two molecules as tools in the therapy of this subtype of BC.

Role of oestrogen receptors in bladder cancer development

Early studies documented the existence of sexual dimorphism in bladder cancer occurrence and progression, with a greater bladder cancer incidence in males than females. However, the progression of bladder cancer after diagnosis is much quicker in females than males. These findings can be explained by the effects of female hormones (predominantly oestrogens) and their binding receptors, including oestrogen receptor 1 (ESR1; also known as ERα), oestrogen receptor 2 (ESR2; also known as ERβ), and GPR30 protein on bladder cancer incidence and progression. Results from studies using various in vitro cell lines and in vivo mouse models demonstrate differential roles of oestrogen receptors in cancer initiation and progression. ERα suppresses bladder cancer initiation and invasion, whereas ERβ promotes bladder cancer initiation and progression. Mechanistic studies suggest that ERα and ERβ exert these effects via modulation of the AKT pathway and DNA replication complex, respectively. Targeting these signalling pathways--for example, with ERα agonists, ERβ antagonists, or selective oestrogen receptor modulators such as 4-[2-phenyl-5,7-bis(trifluoromethyl)pyrazolo[1,5-a]pyrimidin-3-yl]phenol (also known as PHTPP)--could lead to the development of new therapeutic approaches for controlling bladder cancer progression.

Urothelial signaling

The urothelium, which lines the inner surface of the renal pelvis, the ureters, and the urinary bladder, not only forms a high-resistance barrier to ion, solute and water flux, and pathogens, but also functions as an integral part of a sensory web which receives, amplifies, and transmits information about its external milieu. Urothelial cells have the ability to sense changes in their extracellular environment, and respond to chemical, mechanical and thermal stimuli by releasing various factors such as ATP, nitric oxide, and acetylcholine. They express a variety of receptors and ion channels, including P2X3 purinergic receptors, nicotinic and muscarinic receptors, and TRP channels, which all have been implicated in urothelial-neuronal interactions, and involved in signals that via components in the underlying lamina propria, such as interstitial cells, can be amplified and conveyed to nerves, detrusor muscle cells, and ultimately the central nervous system. The specialized anatomy of the urothelium and underlying structures, and the possible communication mechanisms from urothelial cells to various cell types within the bladder wall are described. Changes in the urothelium/lamina propria ("mucosa") produced by different bladder disorders are discussed, as well as the mucosa as a target for therapeutic interventions.

GPER: a novel target for non-genomic estrogen action in the cardiovascular system

A key to harnessing the enormous therapeutic potential of estrogens is understanding the diversity of estrogen receptors and their signaling mechanisms. In addition to the classic nuclear estrogen receptors (i.e., ERα and ERβ), over the past decade a novel G-protein-coupled estrogen receptor (GPER) has been discovered in cancer and other cell types. More recently, this non-genomic signaling mechanism has been found in blood vessels, and mediates vasodilatory responses to estrogen and estrogen-like agents; however, downstream signaling events involved acute estrogen action remain unclear. The purpose of this review is to discuss the latest knowledge concerning GPER modulation of cardiovascular function, with a particular emphasis upon how activation of this receptor could mediate acute estrogen effects in the heart and blood vessels (i.e., vascular tone, cell growth and differentiation, apoptosis, endothelial function, myocardial protection). Understanding the role of GPER in estrogen signaling may help resolve some of the controversies associated with estrogen and cardiovascular function. Moreover, a more thorough understanding of GPER function could also open significant opportunities for the development of new pharmacological strategies that would provide the cardiovascular benefits of estrogen while limiting the potentially dangerous side effects.

Interplay of estrogen receptors and GPR30 for the regulation of early membrane initiated transcriptional effects: A pharmacological approach

Estrogens exert their effect through ERα and ERβ intracellular transcription factors and rapid, usually membrane-initiated receptors, influencing cytosolic signaling and transcription. The nature of extranuclear estrogen elements has not been elucidated so far; classical or alternatively transcribed ER isoforms (ERα36, ERα46) anchored to the plasma membrane and GPR30 (GPER1) have been reported to exert early estrogen actions. Here, we used E2-BSA, an impermeable estradiol analog for a transcriptome analysis in four GREP1 positive breast cancer cell lines with different estrogen receptor profiles (T47D, MCF-7, MDA-MB-231 and SKBR3) in order to evaluate GPER1 transcriptional effects. Early effects of E2-BSA were assayed after 3h of incubation, in the absence/presence of ICI182,780 (ER-inhibitor) or G15 (GREP1-specific inhibitor). E2-BSA specifically modified 277-549 transcripts in the different cell lines. Two different clusters of transcripts could be identified: (1) the majority of transcripts were inhibited by both ICI182,780 and G15, suggesting an interaction of E2-BSA with a common ER-related element, or a direct ER-GPER1 interaction; (2) a small number of G15-only modified transcripts, in two cell lines (T47D and SKBR3 cells), indicative of specific GPER1-related effects. The latter transcripts were significantly related to pathways including FOXA2/FOXA3 transcription factor networks, RNA-Polymerases Transcription Regulation and lipid metabolism, while ICI/G15 inhibited transcripts affected pathways related to apoptosis, erythropoietin signaling, metabolic effects through the citric acid cycle, IL-4 and IL-5 mediated events and homologous DNA recombination. Finally, we review the current literature of GPER1 actions, in view of our results of ER-dependent and independent GPER1-modified pathways.

Estrogen receptor α and β in esophageal squamous cell carcinoma

A gender difference has been reported in the morbidity of esophageal squamous cell carcinoma (ESCC). Estrogens have been proposed to play a role in this difference but the details have not yet been clarified. Therefore, in the present study, we examined the status of estrogen receptor (ER)α and ERβ in 90 Japanese ESCC patients. ERα and ERβ immunoreactivity was detected in the nuclei of ESCC cells (41.1 and 97.8%, respectively). There was a significant positive association between the ERβ H score and histological differentiation (P = 0.0403), TNM-pM (LYM) (P = 0.00164) and Ki67/MIB1 LI of carcinoma cells (P = 0.0497, r = 0.207). In addition, the ERβ status of carcinoma cells was significantly correlated with unfavorable clinical outcome of the patients. Multivariate analysis further revealed the ERβ status in carcinoma cells as an independent unfavorable prognostic factor of these patients. We further examined the effects of estrogen treatment on ESCC cell line (ECGI-10) transfected with ERα or ERβ in vitro. The number of ECGI-10 transfected with ERβ was increased by estradiol or ERβ specific agonist but estradiol did not exert any effect upon the cell number of ECGI-10 transfected with ERα. In summary, the results of the present study clearly demonstrate that the status of ERβ in ESCC was closely associated with the unfavorable prognosis, possibly through altering cell proliferation of carcinoma cells.

GPR30, the non-classical membrane G protein related estrogen receptor, is overexpressed in human seminoma and promotes seminoma cell proliferation

BACKGROUND

Testicular germ cell tumours are the most frequent cancer of young men with an increasing incidence all over the world. Pathogenesis and reasons of this increase remain unknown but epidemiological and clinical data have suggested that fetal exposure to environmental endocrine disruptors (EEDs) with estrogenic effects, could participate to testicular germ cell carcinogenesis. However, these EEDs (like bisphenol A) are often weak ligands for classical nuclear estrogen receptors. Several research groups recently showed that the non classical membrane G-protein coupled estrogen receptor (GPER/GPR30) mediates the effects of estrogens and several xenoestrogens through rapid non genomic activation of signal transduction pathways in various human estrogen dependent cancer cells (breast, ovary, endometrium). The aim of this study was to demonstrate that GPER was overexpressed in testicular tumours and was able to trigger JKT-1 seminoma cell proliferation.

RESULTS

We report here for the first time a complete morphological and functional characterization of GPER in normal and malignant human testicular germ cells. In normal adult human testes, GPER was expressed by somatic (Sertoli cells) and germ cells (spermatogonia and spermatocytes). GPER was exclusively overexpressed in seminomas, the most frequent testicular germ cell cancer, localized at the cell membrane and triggered a proliferative effect on JKT-1 cells in vitro, which was completely abolished by G15 (a GPER selective antagonist) and by siRNA invalidation.

CONCLUSION

These results demonstrate that GPER is expressed by human normal adult testicular germ cells, specifically overexpressed in seminoma tumours and able to trigger seminoma cell proliferation in vitro. It should therefore be considered rather than classical ERs when xeno-estrogens or other endocrine disruptors are assessed in testicular germ cell cancers. It may also represent a prognosis marker and/or a therapeutic target for seminomas.

The G protein-coupled oestrogen receptor 1 agonist G-1 disrupts endothelial cell microtubule structure in a receptor-independent manner

The G protein-coupled oestrogen receptor GPER1, also known as GPR30, has been implicated in oestrogen signalling, but the physiological importance of GPER1 is not fully understood. The GPER1 agonist G-1 has become an important tool to assess GPER1-mediated cellular effects. Here, we report that this substance, besides acting via GPER1, affects the microtubule network in endothelial cells. Treatment with G-1 (3 μM) for 24 h reduced DNA synthesis by about 60 % in mouse microvascular endothelial bEnd.3 cells. Treatment with 3 μM G-1 prevented outgrowth of primary endothelial cells from mouse aortic explants embedded in Matrigel. Treatment with G-1 (0.3-3 μM) for 24 h disrupted bEnd.3 cell and HUVEC microtubule structure in a concentration-dependent manner as assessed by laser-scanning confocal immunofluorescence microscopy. G-1-induced (3 μM) disruption of microtubule was observed also after acute (3 and 6 h) treatment and in the presence of the protein synthesis inhibitor cycloheximide. Disruption of microtubules by 3 μM G-1 was observed in aortic smooth muscle cells obtained from both GPER1 knockout and wild-type mice, suggesting that G-1 influences microtubules through a mechanism independent of GPER1. G-1 dose dependently (10-50 μM) stimulated microtubule assembly in vitro. On the other hand, microtubules appeared normal in the presence of 10-50 μM G-1 as determined by electron microscopy. We suggest that G-1-promoted endothelial cell anti-proliferation is due in part to alteration of microtubule organization through a mechanism independent of GPER1. This G-1-promoted mechanism may be used to block unwanted endothelial cell proliferation and angiogenesis such as that observed in, e.g. cancer.

The G protein-coupled estrogen receptor 1 (GPER/GPR30) does not predict survival in patients with ovarian cancer

Background

Even though ovarian tumors are not generally considered estrogen-sensitive, estrogens may still have an impact on ovarian tumor progression. The recently identified trans-membrane estrogen receptor GPER is involved in rapid estrogen signaling. Furthermore, it binds selective estrogen receptor modulators with agonistic effect, which could explain tamoxifen controversies.

Methods

GPER mRNA was assayed with quantitative real-time PCR (qPCR) in 42 primary ovarian tumors and 7 ovarian cancer cell lines. ERα and ERβ mRNA were analyzed for comparison. GPER protein was semi-quantified with densitometric scanning of Western blots and its tissue distribution analyzed with immunohistochemistry (IHC) in 40 ovarian tumors. In addition, IHC was evaluated in a tissue microarray (TMA) of 150 primary malignant ovarian tumors.

Results

All tumor samples contained GPER mRNA. The content of mRNA was not different between benign and malignant tumors, but one third of malignant samples over-expressed GPER mRNA. The content of ERα mRNA was higher in malignant than in benign tumors, whereas ERβ mRNA was higher in benign than in malignant tumors. GPER mRNA was detected in all seven ovarian cancer cell lines with highest levels in TOV21G and TOV112D cells. Similar expression pattern was seen for ERβ mRNA. Western blot demonstrated GPER protein in all tumor samples. Semi-quantification showed no difference between benign and malignant tumors, but about one third of malignant samples over-expressed GPER protein. GPER staining was localized mainly in epithelial cells. In the TMA study we found no correlation between GPER staining and clinical stage, histological grade or patient survival.

Conclusions

GPER mRNA as well as GPER protein is present in both benign and malignant ovarian tumor tissue. About one third of malignant tumors over-expressed both GPER mRNA and protein. This, however, correlated neither with histological or clinical parameters nor with patient survival.

The role of cadmium and nickel in estrogen receptor signaling and breast cancer: metalloestrogens or not?

During the past half-century, incidences of breast cancer have increased globally. Various factors--genetic and environmental--have been implicated in the initiation and progression of this disease. One potential environmental risk factor that has not received a lot of attention is the exposure to heavy metals. While several mechanisms have been put forth describing how high concentrations of heavy metals play a role in carcinogenesis, it is unclear whether chronic, low-level exposure to certain heavy metals (i.e., cadmium and nickel) can directly result in the development and progression of cancer. Cadmium and nickel have been hypothesized to play a role in breast cancer development by acting as metalloestrogens--metals that bind to estrogen receptors and mimic the actions of estrogen. Since the lifetime exposure to estrogen is a well-established risk factor for breast cancer, anything that mimics its activity will likely contribute to the etiology of the disease. However, heavy metals, depending on their concentration, are capable of binding to a variety of proteins and may exert their toxicities by disrupting multiple cellular functions, complicating the analysis of whether heavy metal-induced carcinogenesis is mediated by the estrogen receptor. The purpose of this review is to discuss the various epidemiological, in vivo, and in vitro studies that show a link between the heavy metals, cadmium and nickel, and breast cancer development. We will particularly focus on the studies that test whether these two metals act as metalloestrogens in order to assess the strength of the data supporting this hypothesis.

Identification of a GPER/GPR30 antagonist with improved estrogen receptor counterselectivity

GPER/GPR30 is a seven-transmembrane G protein-coupled estrogen receptor that regulates many aspects of mammalian biology and physiology. We have previously described both a GPER-selective agonist G-1 and antagonist G15 based on a tetrahydro-3H-cyclopenta[c]quinoline scaffold. The antagonist lacks an ethanone moiety that likely forms important hydrogen bonds involved in receptor activation. Computational docking studies suggested that the lack of the ethanone substituent in G15 could minimize key steric conflicts, present in G-1, that limit binding within the ERα ligand binding pocket. In this report, we identify low-affinity cross-reactivity of the GPER antagonist G15 to the classical estrogen receptor ERα. To generate an antagonist with enhanced selectivity, we therefore synthesized an isosteric G-1 derivative, G36, containing an isopropyl moiety in place of the ethanone moiety. We demonstrate that G36 shows decreased binding and activation of ERα, while maintaining its antagonist profile towards GPER. G36 selectively inhibits estrogen-mediated activation of PI3K by GPER but not ERα. It also inhibits estrogen- and G-1-mediated calcium mobilization as well as ERK1/2 activation, with no effect on EGF-mediated ERK1/2 activation. Similar to G15, G36 inhibits estrogen- and G-1-stimulated proliferation of uterine epithelial cells in vivo. The identification of G36 as a GPER antagonist with improved ER counterselectivity represents a significant step towards the development of new highly selective therapeutics for cancer and other diseases.

The GPER1 agonist G-1 attenuates endothelial cell proliferation by inhibiting DNA synthesis and accumulating cells in the S and G2 phases of the cell cycle

G protein-coupled receptor 30 (GPR30) or G protein-coupled estrogen receptor 1 (GPER1) is expressed in the vasculature, but the importance of vascular GPER1 remains to be clarified. Here we investigate effects of the GPER1 agonist G-1 on endothelial cell proliferation using mouse microvascular endothelial bEnd.3 cells. The bEnd.3 cells express mRNA for GPER1. The bEnd.3 cells expressed both ERα and ERβ immunoreactivities. Treatment with G-1 reduced DNA synthesis and cell number with IC(50) values of about 2 μM. GPER1 siRNA prevented G-1-induced attenuation of DNA synthesis. G-1 accumulated cells in S and G2 phases of the cell cycle, suggesting that G-1 blocks transition between G2 and M. G-1 had no effect on DNA synthesis in COS-7 cells only weakly expressing GPER1 mRNA. 17β-Estradiol had no effect on DNA synthesis in physiological concentrations (nM). The ER blocker ICI182780 reduced DNA synthesis with similar potency as G-1. Treatment with the ERK/MAP kinase inhibitor PD98059 had no effect on G-1-induced attenuation of DNA synthesis. G-1- induced antiproliferation was observed not only in bEnd.3 cells but also in human umbilical vein endothelial cells and HMEC-1 endothelial cells. We conclude that the GPER1 agonist G-1 attenuates endothelial cell proliferation via inhibition of DNA synthesis and by accumulation of cells in S and G2.

Discovery of selective probes and antagonists for G-protein-coupled receptors FPR/FPRL1 and GPR30

Recent technological advances in flow cytometry provide a versatile platform for high throughput screening of compound libraries coupled with high-content biological testing and drug discovery. The G protein-coupled receptors (GPCRs) constitute the largest class of signaling molecules in the human genome with frequent roles in disease pathogenesis, yet many examples of orphan receptors with unknown ligands remain. The complex biology and potential for drug discovery within this class provide strong incentives for chemical biology approaches seeking to develop small molecule probes to facilitate elucidation of mechanistic pathways and enable specific manipulation of the activity of individual receptors. We have initiated small molecule probe development projects targeting two distinct families of GPCRs: the formylpeptide receptors (FPR/FPRL1) and G protein-coupled estrogen receptor (GPR30). In each case the assay for compound screening involved the development of an appropriate small molecule fluorescent probe, and the flow cytometry platform provided inherently biological rich assays that enhanced the process of identification and optimization of novel antagonists. The contributions of cheminformatics analysis tools, virtual screening, and synthetic chemistry in synergy with the biomolecular screening program have yielded valuable new chemical probes with high binding affinity, selectivity for the targeted receptor, and potent antagonist activity. This review describes the discovery of novel small molecule antagonists of FPR and FPRL1, and GPR30, and the associated characterization process involving secondary assays, cell based and in vivo studies to define the selectivity and activity of the resulting chemical probes.

Influence of charge on cell permeability and tumor imaging of GPR30-targeted 111in-labeled nonsteroidal imaging agents

Recent clinical studies implicate the role of G protein-coupled estrogen receptor, GPR30, in aggressive forms of breast, ovarian, and endometrial cancers. However, the functional role of GPR30 at cellular and molecular levels remains less clear and controversial, particularly its subcellular location. The primary objective of this study was to develop radiolabeled neutral and charged GPR30-targeted nonsteroidal analogues to understand the influence of ligand charge on cell binding, cellular permeability, and in vivo tumor imaging. Therefore, we developed a series of GPR30-targeted (111/113)In(III)-labeled analogues using macrocyclic and acyclic polyamino-polycarboxylate chelate designs that would render either a net negative or neutral charge. In vitro biological evaluations were performed to determine the role of negatively charged analogues on receptor binding and activation using calcium mobilization and phosphoinositide 3-kinase assays. In vivo evaluations were performed on GPR30-expressing human endometrial Hec50 tumor-bearing mice to characterize the biodistribution and potential application of GPR30-targeted imaging agents for translational research. In vitro functional assays revealed an effect of charge, such that only the neutral analogue activated GPR30-mediated rapid signaling pathways. These observations are consistent with expectations for initial rates of membrane permeability and suggest an intracellular rather than the cell surface location of functional receptor. In vivo studies revealed receptor-mediated uptake of the radiotracer in target organs and tumors; however, further structural modifications will be required for the development of future generations of GPR30-targeted imaging agents with enhanced metabolic properties and decreased nonspecific localization to the intestines.

Highly efficient synthesis and characterization of the GPR30-selective agonist G-1 and related tetrahydroquinoline analogs

The GPR30 agonist probe G-1 and structural analogs were efficiently synthesized using multicomponent or stepwise Sc(III)-catalyzed aza-Diels-Alder cyclization. Optimization of solvent and reaction temperature provided enhanced endo-diastereoselectivity.

Synthesis and characterization of iodinated tetrahydroquinolines targeting the G protein-coupled estrogen receptor GPR30

A series of iodo-substituted tetrahydro-3H-cyclopenta[c]quinolines was synthesized as potential targeted imaging agents for the G protein-coupled estrogen receptor GPR30. The affinity and specificity of binding to GPR30 versus the classical estrogen receptors ER alpha/beta and functional responses associated with ligand-binding were determined. Selected iodo-substituted tetrahydro-3H-cyclopenta[c]quinolines exhibited IC(50) values lower than 20 nM in competitive binding studies with GPR30-expressing human endometrial cancer cells. These compounds functioned as antagonists of GPR30 and blocked estrogen-induced PI3K activation and calcium mobilization. The tributylstannyl precursors of selected compounds were radiolabeled with (125)I using the iodogen method. In vivo biodistribution studies in female ovariectomized athymic (NCr) nu/nu mice bearing GPR30-expressing human endometrial tumors revealed GPR30-mediated uptake of the radiotracer ligands in tumor, adrenal, and reproductive organs. Biodistribution and quantitative SPECT/CT studies revealed structurally related differences in the pharmacokinetic profiles, target tissue uptake, and metabolism of the radiolabeled compounds as well as differences in susceptibility to deiodination. The high lipophilicity of the compounds adversely affects the in vivo biodistribution and clearance of these radioligands and suggests that further optimization of this parameter may lead to improved targeting characteristics.

Activation of GPR30 inhibits the growth of prostate cancer cells through sustained activation of Erk1/2, c-jun/c-fos-dependent upregulation of p21, and induction of G(2) cell-cycle arrest

G-protein-coupled receptor-30 (GPR30) shows estrogen-binding affinity and mediates non-genomic signaling of estrogen to regulate cell growth. We here showed for the first time, in contrast to the reported promoting action of GPR30 on the growth of breast and ovarian cancer cells, that activation of GPR30 by the receptor-specific, non-estrogenic ligand G-1 inhibited the growth of androgen-dependent and androgen-independent prostate cancer (PCa) cells in vitro and PC-3 xenografts in vivo. However, G-1 elicited no growth or histological changes in the prostates of intact mice and did not inhibit growth in quiescent BPH-1, an immortalized benign prostatic epithelial cell line. Treatment of PC-3 cells with G-1 induced cell-cycle arrest at the G(2) phase and reduced the expression of G(2)-checkpoint regulators (cyclin-A2, cyclin-B1, cdc25c, and cdc2) and phosphorylation of their common transcriptional regulator NF-YA in PC-3 cells. With extensive use of siRNA-knockdown experiments and the MEK inhibitor PD98059 in this study, we dissected the mechanism underlying G-1-induced inhibition of PC-3 cell growth, which was mediated through GPR30, followed by sustained activation of Erk1/2 and a c-jun/c-fos-dependent upregulation of p21, resulting in the arrest of PC-3 growth at the G(2) phase. The discovery of this signaling pathway lays the foundation for future development of GPR30-based therapies for PCa.

Beyond neurons: Involvement of urothelial and glial cells in bladder function

AIM

The urothelium, or epithelial lining of the lower urinary tract (LUT), is likely to play an important role in bladder function by actively communicating with bladder nerves, smooth muscle, and cells of the immune and inflammatory systems. Recent evidence supports the importance of non-neuronal cells that may extend to both the peripheral and central processes of the neurons that transmit normal and nociceptive signals from the urinary bladder. Using cats diagnosed with a naturally occurring syndrome termed feline interstitial cystitis (FIC), we investigated whether changes in physiologic parameters occur within 3 cell types associated with sensory transduction in the urinary bladder: 1) the urothelium, 2) identified bladder dorsal root ganglion (DRG) neurons and 3) grey matter astrocytes in the lumbosacral (S1) spinal cord. As estrogen fluctuations may modulate the severity of many chronic pelvic pain syndromes, we also examined whether 17beta-estradiol (E2) alters cell signaling in rat urothelial cells.

RESULTS

We have identified an increase in nerve growth factor (NGF) and substance P (SP) in urothelium from FIC cats over that seen in urothelium from unaffected (control) bladders. The elevated NGF expression by FIC urothelium is a possible cause for the increased cell body size of DRG neurons from cats with FIC, reported in this study. At the level of the spinal cord, astrocytic GFAP immuno-intensity was significantly elevated and there was evidence for co-expression of the primitive intermediate filament, nestin (both indicative of a reactive state) in regions of the FIC S1 cord (superficial and deep dorsal horn, central canal and laminae V-VIl) that receive input from pelvic afferents. Finally, we find that E2 triggers an estrus-modifiable activation of p38 MAPK in rat urothelial cells. There were cyclic variations with E2-mediated elevation of p38 MAPK at both diestrus and estrus, and inhibition of p38 MAPK in proestrous urothelial cells.

CONCLUSION

Though urothelial cells are often viewed as bystanders in the processing of visceral sensation, these and other findings support the view that these cells function as primary transducers of some physical and chemical stimuli. In addition, the pronounced activation of spinal cord astrocytes in an animal model for bladder pain syndrome (BPS) may play an important role in the pain syndrome and open up new potential approaches for drug intervention.

In vivo functions of GPR30/GPER-1, a membrane receptor for estrogen: from discovery to functions in vivo

G protein-coupled receptor 30/G protein-coupled estrogen receptor-1 (GPR30/GPER-1) was reported as a novel membrane receptor for estrogen in 2005. However, the research on GPR30 has produced conflicting reports with regard to its intracellular localization, the tissue distribution of its expression, and some its functions. Recently, in addition to the finding of G-1, a GPR30 agonist, GPR30 KO mice have been produced in laboratories, and this has significantly increased the confidence in the data. In this review, the intrinsic appearance of GPR30 is approached based mainly on data obtained in vivo.

GPR30 and estrogen receptor expression: new insights into hormone dependence of inflammatory breast cancer

GPR30 is a novel G protein-coupled estrogen receptor (ER) associated with metastases in breast cancer (BC) and poor survival in endometrial and ovarian tumors. The association of GPR30 expression with inflammatory breast cancer (IBC), an aggressive and commonly hormone-independent form of BC, has not been studied. GPR30, ER, progesterone receptor (PR), epidermal growth factor receptor (EGFR), and HER-2 expression were assessed by immunohistochemistry (and FISH for HER-2) in 88 primary IBCs. GPR30 expression was correlated with patient overall survival (OS), disease-free survival (DFS), pathologic variables, and other biomarkers. GPR30 expression was found in 69% of IBC cases. ER, PR, HER-2, and EGFR were found in 43, 35, 39, and 34% of IBC cases, respectively. GPR30 expression correlated inversely with ER expression (P = 0.02). Co-expression of ER and GPR30 was found in 24% of IBC samples; 19% expressed only ER and 46% expressed only GPR30. Univariate analysis showed no association between GPR30 expression and OS or DFS. However, co-expression of ER and GPR30 was associated with improved OS (P < 0.03) and marginally with DFS (P < 0.06); the absence of both ER and GPR30 was associated with worse OS and DFS (P = 0.03 for both). Multivariate analysis identified ER as an independent prognostic factor of OS (P = 0.008) and DFS (P = 0.02). The majority of IBC tumors are GPR30-positive, suggesting that estrogen signaling may be active in ER-negative IBC patients. These findings suggest potential new therapeutic targets for IBC such as novel endocrine agents or direct modulation of GPR30.

Importance of extranuclear estrogen receptor-alpha and membrane G protein-coupled estrogen receptor in pancreatic islet survival

OBJECTIVE

We showed that 17beta-estradiol (E(2)) favors pancreatic beta-cell survival via the estrogen receptor-alpha (ERalpha) in mice. E(2) activates nuclear estrogen receptors via an estrogen response element (ERE). E(2) also activates nongenomic signals via an extranuclear form of ERalpha and the G protein-coupled estrogen receptor (GPER). We studied the contribution of estrogen receptors to islet survival.

RESEARCH DESIGN AND METHODS

We used mice and islets deficient in estrogen receptor-alpha (alphaERKO(-/-)), estrogen receptor-beta (betaERKO(-/-)), estrogen receptor-alpha and estrogen receptor-beta (alphabetaERKO(-/-)), and GPER (GPERKO(-/-)); a mouse lacking ERalpha binding to the ERE; and human islets. These mice and islets were studied in combination with receptor-specific pharmacological probes.

RESULTS

We show that ERalpha protection of islet survival is ERE independent and that E(2) favors islet survival through extranuclear and membrane estrogen receptor signaling. We show that ERbeta plays a minor cytoprotective role compared to ERalpha. Accordingly, betaERKO(-/-) mice are mildly predisposed to streptozotocin-induced islet apoptosis. However, combined elimination of ERalpha and ERbeta in mice does not synergize to provoke islet apoptosis. In alphabetaERKO(-/-) mice and their islets, E(2) partially prevents apoptosis suggesting that an alternative pathway compensates for ERalpha/ERbeta deficiency. We find that E(2) protection of islet survival is reproduced by a membrane-impermeant E(2) formulation and a selective GPER agonist. Accordingly, GPERKO(-/-) mice are susceptible to streptozotocin-induced insulin deficiency.

CONCLUSIONS

E(2) protects beta-cell survival through ERalpha and ERbeta via ERE-independent, extra-nuclear mechanisms, as well as GPER-dependent mechanisms. The present study adds a novel dimension to estrogen biology in beta-cells and identifies GPER as a target to protect islet survival.