Coordinate regulation of estrogen-mediated fibronectin matrix assembly and epidermal growth factor receptor transactivation by the G protein-coupled receptor, GPR30

Exploring associations between estrogen and gene candidates identified by coronary artery disease genome-wide association studies

Introduction

Coronary artery disease (CAD) is the leading cause of death around the world, with epidemiological sex and gender differences in prevalence, pathophysiology and outcomes. It has been hypothesized that sex steroids, like estrogen, may contribute to these sex differences. There is a relatively large genetic component to developing CAD, with heritability estimates ranging between 40%-60%. In the last two decades, genome-wide association studies (GWAS) have contributed substantially to advancing the understanding of genetic candidates contributing to CAD. The aim of this study was to determine if genes discovered in CAD GWASs are affected by estrogen via direct modulation or indirect down-stream targets.

Methods

A scoping review was conducted using MEDLINE and EMBASE for studies of atherosclerotic coronary artery disease and a genome-wide association study (GWAS) design. Analysis was limited to candidate genes with corresponding single nucleotide polymorphisms (SNPs) surpassing genome-wide significance and had been mapped to genes by study authors. The number of studies that conducted sex-stratified analyses with significant genes were quantified. A literature search of the final gene lists was done to examine any evidence suggesting estrogen may modulate the genes and/or gene products.

Results

There were 60 eligible CAD GWASs meeting inclusion criteria for data extraction. Of these 60, only 36 had genome-wide significant SNPs reported, and only 3 of these had significant SNPs from sex-stratified analyses mapped to genes. From these 36 studies, a total of 61 genes were curated, of which 26 genes (43%) were found to have modulation by estrogen. All 26 were discovered in studies that adjusted for sex. 12/26 genes were also discovered in studies that conducted sex-stratified analyses. 12/26 genes were classified as having a role in lipid synthesis, metabolism and/or lipoprotein mechanisms, while 11/26 were classified as having a role in vascular integrity, and 3/26 were classified as having a role in thrombosis.

Discussion

This study provides further evidence of the relationship between estrogen, genetic risk and the development of CAD. More sex-stratified research will need to be conducted to further characterize estrogen's relation to sex differences in the pathology and progression of CAD.

Current progress and prospects for G protein-coupled estrogen receptor in triple-negative breast cancer

Triple-negative breast cancer (TNBC) is a biologically and clinically heterogeneous disease. The G protein-coupled estrogen receptor (GPER) plays a crucial role in mediating the effect of estrogen and estrogen-like compounds in TNBC cells. Compared with other subtypes, GPER has a higher expression in TNBC. The GPER mechanisms have been thoroughly characterized and analyzed in estrogen receptor α (ERα) positive breast cancer, but not in TNBC. Our previous work revealed that a higher expression of GPER mRNA indicates a better prognosis for ERα-positive breast cancer; however, its effects in TNBC differ. Whether GPER could serve as a predictive prognostic marker or therapeutic target for TNBC remains unclear. In this review, we provide a detailed introduction to the subcellular localization of GPER, the different effects of various ligands, and the interactions between GPER and closely associated factors in TNBC. We focused on the internal molecular mechanisms specific to TNBC and thoroughly explored the role of GPER in promoting tumor development. We also discussed the interaction of GPER with specific cytokines and chemokines, and the relationship between GPER and immune evasion. Additionally, we discussed the feasibility of using GPER as a therapeutic target in the context of existing studies. This comprehensive review highlights the effects of GPER on TNBC, providing a framework and directions for future research.

Relaxed fibronectin: a potential novel target for imaging endometriotic lesions

BACKGROUND

Endometriosis is characterized by the ectopic occurrence of endometrial tissue. Though considered benign, endometriotic lesions possess tumor-like properties such as tissue invasion and remodeling of the extracellular matrix. One major clinical hurdle concerning endometriosis is its diagnosis. The diagnostic modalities ultrasound and MRI are often unable to detect all lesions, and a clear correlation between imaging and clinical symptoms is still controversial. Therefore, it was our aim to identify a potential target to image active endometriotic lesions.

RESULTS

For our studies, we employed the preclinical radiotracer [111In]In-FnBPA5, which specifically binds to relaxed fibronectin-an extracellular matrix protein with key functions in homeostasis that has been implicated in the pathogenesis of diseases such as cancer and fibrosis. We employed this tracer in biodistribution as well as SPECT/CT studies in mice and conducted immunohistochemical stainings on mouse uterine tissue as well as on patient-derived endometriosis tissue. In biodistribution and SPECT/CT studies using the radiotracer [111In]In-FnBPA5, we found that radiotracer uptake in the myometrium varies with the estrous cycle of the mouse, leading to higher uptake of [111In]In-FnBPA5 during estrogen-dependent phases, which indicates an increased abundance of relaxed fibronectin when estrogen levels are high. Finally, immunohistochemical analysis of patient samples demonstrated that there is preferential relaxation of fibronectin in the proximity of the endometriotic stroma.

CONCLUSION

Estrous cycle stages characterized by high estrogen levels result in a higher abundance of relaxed fibronectin in the murine myometrium. This finding together with a first proof-of-concept study employing human endometriosis tissues suggests that relaxed fibronectin could be a potential target for the development of a diagnostic radiotracer targeting endometriotic lesions. With [111In]In-FnBPA5, the matching targeting molecule is in preclinical development.

In silico design and cell-based evaluation of two dual anti breast cancer compounds targeting Bcl-2 and GPER

According to WHO statistics, breast cancer (BC) disease represents about 2.3 million diagnosed and 685,000 deaths globally. Regarding histological classification of BC, the Estrogen (ER) and Progesterone (PR) receptors negative-expression cancer, named Triple-Negative BC (TNBC), represents the most aggressive type of this disease, making it a challenge for drug discovery. In this context, our research group, applying a well-established Virtual Screening (VS) protocol, in addition to docking and molecular dynamics simulations studies, yielded two ligands identified as 6 and 37 which were chemically synthesized and evaluated on MCF-7 and MDA-MB-231 cancer cell lines. Strikingly, 37 assayed on MDA-MB-231 (a TNBC cell model) depicted an outstanding value of 18.66 μM much lower than 65.67 μM yielded by Gossypol Bcl-2 inhibitor whose main disadvantage is to produce multiple toxic effects. Highlighted above, enforce the premise of the computational tools to find new therapeutic options against the most aggressive forms of breast cancer, as the results herein showed.

The G Protein-Coupled Estrogen Receptor (GPER): A Critical Therapeutic Target for Cancer

Estrogens have been implicated in the pathogenesis of various cancers, with increasing concern regarding the overall rising incidence of disease and exposure to environmental estrogens. Estrogens, both endogenous and environmental, manifest their actions through intracellular and plasma membrane receptors, named ERα, ERβ, and GPER. Collectively, they act to promote a broad transcriptional response that is mediated through multiple regulatory enhancers, including estrogen response elements (EREs), serum response elements (SREs), and cyclic AMP response elements (CREs). Yet, the design and rational assignment of antiestrogen therapy for breast cancer has strictly relied upon an endogenous estrogen-ER binary rubric that does not account for environmental estrogens or GPER. New endocrine therapies have focused on the development of drugs that degrade ER via ER complex destabilization or direct enzymatic ubiquitination. However, these new approaches do not broadly treat all cancer-involved receptors, including GPER. The latter is concerning since GPER is directly associated with tumor size, distant metastases, cancer stem cell activity, and endocrine resistance, indicating the importance of targeting this receptor to achieve a more complete therapeutic response. This review focuses on the critical importance and value of GPER-targeted therapeutics as part of a more holistic approach to the treatment of estrogen-driven malignancies.

Modulation of JAK-STAT Signaling by LNK: A Forgotten Oncogenic Pathway in Hormone Receptor-Positive Breast Cancer

Breast cancer remains the most frequently diagnosed cancer in women worldwide. Tumors that express hormone receptors account for 75% of all cases. Understanding alternative signaling cascades is important for finding new therapeutic targets for hormone receptor-positive breast cancer patients. JAK-STAT signaling is commonly activated in hormone receptor-positive breast tumors, inducing inflammation, proliferation, migration, and treatment resistance in cancer cells. In hormone receptor-positive breast cancer, the JAK-STAT cascade is stimulated by hormones and cytokines, such as prolactin and IL-6. In normal cells, JAK-STAT is inhibited by the action of the adaptor protein, LNK. However, the role of LNK in breast tumors is not fully understood. This review compiles published reports on the expression and activation of the JAK-STAT pathway by IL-6 and prolactin and potential inhibition of the cascade by LNK in hormone receptor-positive breast cancer. Additionally, it includes analyses of available datasets to determine the level of expression of LNK and various members of the JAK-STAT family for the purpose of establishing associations between expression and clinical outcomes. Together, experimental evidence and in silico studies provide a better understanding of the potential implications of the JAK-STAT-LNK loop in hormone receptor-positive breast cancer progression.

G protein-coupled estrogen receptor: a promising therapeutic target for aldosterone-induced hypertension

Aldosterone is one of the most essential hormones synthesized by the adrenal gland because it regulates water and electrolyte balance. G protein-coupled estrogen receptor (GPER) is a newly discovered aldosterone receptor, which is proposed to mediate the non-genomic pathways of aldosterone while the hormone simultaneously interacts with mineralocorticoid receptor. In contrast to its cardio-protective role in postmenopausal women via its interaction with estrogen, GPER seems to trigger vasoconstriction effects and can further induce water and sodium retention in the presence of aldosterone, indicating two entirely different binding sites and effects for estrogen and aldosterone. Accumulating evidence also points to a role of aldosterone in mediating hypertension and its risk factors via the interaction with GPER. Therefore, with this review, we aimed to summarize the research on these interactions to help (1) elucidate the role of GPER activated by aldosterone in the blood vessels, heart, and kidney; (2) compare the non-genomic actions between aldosterone and estrogen mediated by GPER; and (3) address the potential of GPER as a new promising therapeutic target for aldosterone-induced hypertension.

Phytoestrogens, novel dietary supplements for breast cancer

While endocrine therapy is considered as an effective way to treat breast cancer, it still faces many challenges, such as drug resistance and individual discrepancy. Therefore, novel preventive and therapeutic modalities are still in great demand to decrease the incidence and mortality rate of breast cancer. Numerous studies suggested that G protein-coupled estrogen receptor (GPER), a membrane estrogen receptor, is a potential target for breast cancer prevention and treatment. It was also shown that not only endogenous estrogens can activate GPERs, but many phytoestrogens can also function as selective estrogen receptor modulators (SERMs) to interact GPERs. In this review, we discussed the possible mechanisms of GPERs pathways and shed a light of developing novel phytoestrogens based dietary supplements against breast cancers.

Comparative G-Protein-Coupled Estrogen Receptor (GPER) Systems in Diabetic and Cancer Conditions: A Review

For many patients, diabetes Mellitus and Malignancy are frequently encountered comorbidities. Diabetes affects approximately 10.5% of the global population, while malignancy accounts for 29.4 million cases each year. These troubling statistics indicate that current treatment approaches for these diseases are insufficient. Alternative therapeutic strategies that consider unique signaling pathways in diabetic and malignancy patients could provide improved therapeutic outcomes. The G-protein-coupled estrogen receptor (GPER) is receiving attention for its role in disease pathogenesis and treatment outcomes. This review aims to critically examine GPER' s comparative role in diabetes mellitus and malignancy, identify research gaps that need to be filled, and highlight GPER's potential as a therapeutic target for diabetes and malignancy management. There is a scarcity of data on GPER expression patterns in diabetic models; however, for diabetes mellitus, altered expression of transport and signaling proteins has been linked to GPER signaling. In contrast, GPER expression in various malignancy types appears to be complex and debatable at the moment. Current data show inconclusive patterns of GPER expression in various malignancies, with some indicating upregulation and others demonstrating downregulation. Further research should be conducted to investigate GPER expression patterns and their relationship with signaling pathways in diabetes mellitus and various malignancies. We conclude that GPER has therapeutic potential for chronic diseases such as diabetes mellitus and malignancy.

Modulatory Effects of Estradiol and Its Mixtures with Ligands of GPER and PPAR on MAPK and PI3K/Akt Signaling Pathways and Tumorigenic Factors in Mouse Testis Explants and Mouse Tumor Leydig Cells

The present study was designed to evaluate how estradiol alone or in combination with G protein-coupled estrogen receptor (GPER) agonists and GPER and peroxisome proliferator-activated receptor (PPAR) antagonists alter the expression of tumor growth factor β (TGF-β), cyclooxygenase-2 (COX-2), hypoxia inducible factor 1-alpha (HIF-1α), and vascular endothelial growth factor (VEGF) in mouse testis explants and MA-10 mouse tumor Leydig cells. In order to define the hormone-associated signaling pathway, the expression of MAPK and PI3K/Akt was also examined. Tissue explants and cells were treated with estradiol as well as GPER agonist (ICI 182,780), GPER antagonist (G-15), PPARα antagonist (GW6471), and PPARγ antagonist (T00709072) in various combinations. First, we showed that in testis explants GPER and PPARα expressions were activated by the GPER agonist and estradiol (either alone or in mixtures), whereas PPARγ expression was activated only by GPER agonist. Second, increased TGF-β expression and decreased COX-2 expression were found in all experimental groups of testicular explants and MA-10 cells, except for up-regulated COX-2 expression in estradiol-treated cells, compared to respective controls. Third, estradiol treatment led to elevated expression of HIF-1α and VEGF, while their lower levels versus control were noted in the remaining groups of explants. Finally, we demonstrated the up-regulation of MAPK and PI3Kp85/Akt expressions in estradiol-treated groups of both ex vivo and in vitro models, whereas estradiol in mixtures with compounds of agonistic or antagonistic properties either up-regulated or down-regulated signaling kinase expression levels. Our results suggest that a balanced estrogen level and its action together with proper GPER and PPAR signaling play a key role in the maintenance of testis homeostasis. Moreover, changes in TGF-β and COX-2 expressions (that disrupted estrogen pathway) as well as disturbed GPER-PPAR signaling observed after estradiol treatment may be involved in testicular tumorigenesis.

G protein-coupled estrogen receptor 1: a novel target to treat cardiovascular disease in a sex-specific manner?

As an agonist of the classical nuclear receptors, estrogen receptor-α and -β (NR3A1/2), estrogen has been assumed to inhibit the development of cardiovascular disease in premenopausal women. Indeed, reduced levels of estrogen after menopause are believed to contribute to accelerated morbidity and mortality rates in women. However, estrogen replacement therapy has variable effects on cardiovascular risk in postmenopausal women, including increased serious adverse events. Interestingly, preclinical studies have shown that selective activation of the novel membrane-associated G protein-coupled estrogen receptor, GPER, can promote cardiovascular protection. These benefits are more evident in ovariectomised than intact females or in males. It is therefore possible that selective targeting of the GPER in postmenopausal women could provide cardiovascular protection with fewer adverse effects that are caused by conventional 'receptor non-specific' estrogen replacement therapy. This review describes new data regarding the merits of targeting GPER to treat cardiovascular disease with a focus on sex differences.

Therapeutic Perspectives on the Modulation of G-Protein Coupled Estrogen Receptor, GPER, Function

Estrogens exert their physiological and pathophysiological effects via cellular receptors, named ERα, ERβ, and G-protein coupled estrogen receptor (GPER). Estrogen-regulated physiology is tightly controlled by factors that regulate estrogen bioavailability and receptor sensitivity, while disruption of these control mechanisms can result in loss of reproductive function, cancer, cardiovascular and neurodegenerative disease, obesity, insulin resistance, endometriosis, and systemic lupus erythematosus. Restoration of estrogen physiology by modulating estrogen bioavailability or receptor activity is an effective approach for treating these pathological conditions. Therapeutic interventions that block estrogen action are employed effectively for the treatment of breast and prostate cancer as well as for precocious puberty and anovulatory infertility. Theoretically, treatments that block estrogen biosynthesis should prevent estrogen action at ERs and GPER, although drug resistance and ligand-independent receptor activation may still occur. In addition, blockade of estrogen biosynthesis does not prevent activation of estrogen receptors by naturally occurring or man-made exogenous estrogens. A more complicated scenario is provided by anti-estrogen drugs that antagonize ERs since these drugs function as GPER agonists. Based upon its association with metabolic dysregulation and advanced cancer, GPER represents a therapeutic target with promise for the treatment of several critical health concerns facing Western society. Selective ligands that specifically target GPER have been developed and may soon serve as pharmacological agents for treating human disease. Here, we review current forms of estrogen therapy and the implications that GPER holds for these therapies. We also discuss existing GPER targeted drugs, additional approaches towards developing GPER-targeted therapies and how these therapies may complement existing modalities of estrogen-targeted therapy.

Continuous Exposure of Breast Cancer Cells to Tamoxifen Upregulates GPER-1 and Increases Cell Proliferation

GPER-1 is a novel membrane sited G protein-coupled estrogen receptor. Clinical studies have shown that patients suffering an estrogen receptor α (ERα)/GPER-1 positive, breast cancer have a lower survival rate than those who have developed ERα-positive/GPER-1 negative tumors. Moreover, absence of GPER-1 improves the prognosis of patients treated with tamoxifen, the most used selective estrogen receptor modulator to treat ERα-positive breast cancer. MCF-7 breast cancer cells were continuously treated with 1,000 nM tamoxifen for 7 days to investigate its effect on GPER-1 protein expression, cell proliferation and intracellular [Ca2+]i mobilization, a key signaling pathway. Breast cancer cells continuously treated with tamoxifen, exhibited a robust [Ca2+]i mobilization after stimulation with 1,000 nM tamoxifen, a response that was blunted by preincubation of cells with G15, a commercial GPER-1 antagonist. Continuously treated cells also displayed a high [Ca2+]i mobilization in response to a commercial GPER-1 agonist (G1) and to estrogen, in a magnitude that doubled the response observed in untreated cells and was almost completely abolished by G15. Proliferation of cells continuously treated with tamoxifen and stimulated with 2,000 nM tamoxifen, was also higher than that observed in untreated cells in a degree that was approximately 90% attributable to GPER-1. Finally, prolonged tamoxifen treatment did not increase ERα expression, but did overexpress the kinin B1 receptor, another GPCR, which we have previously shown is highly expressed in breast tumors and increases proliferation of breast cancer cells. Although we cannot fully extrapolate the results obtained in vitro to the patients, our results shed some light on the occurrence of drug resistance in breast cancer patients who are ERα/GPER-1 positive, have been treated with tamoxifen and display low survival rate. Overexpression of kinin B1 receptor may explain the increased proliferative response observed in breast tumors under continuous treatment with tamoxifen.

Estradiol/GPER affects the integrity of mammary duct-like structures in vitro

High estrogen concentration leads to an inflammatory reaction in the mammary gland tissue in vivo; however, the detailed mechanism underlying its specific effects on the breast duct has not been fully clarified. We used 3D-cultured MCF-10A acini as a breast duct model and demonstrated various deleterious effects of 17-β estradiol (E2), including the destruction of the basement membrane surrounding the acini, abnormal adhesion between cells, and cell death via apoptosis and pyroptosis. Moreover, we clarified the mechanism underlying these phenomena: E2 binds to GPER in MCF-10A cells and stimulates matrix metalloproteinase 3 (MMP-3) and interleukin-1β (IL-1β) secretion via JNK and p38 MAPK signaling pathways. IL-1β activates the IL-1R1 signaling pathway and induces continuous MMP-3 and IL-1β secretion. Collectively, our novel findings reveal an important molecular mechanism underlying the effects of E2 on the integrity of duct-like structures in vitro. Thus, E2 may act as a trigger for ductal carcinoma transition in situ.

G Protein-Coupled Estrogen Receptor: A Potential Therapeutic Target in Cancer

The G protein-coupled estrogen receptor (GPER) is a seven-transmembrane-domain receptor that mediates non-genomic estrogen related signaling. After ligand activation, GPER triggers multiple downstream pathways that exert diverse biological effects on the regulation of cell growth, migration and programmed cell death in a variety of tissues. A significant correlation between GPER and the progression of multiple cancers has likewise been reported. Therefore, a better understanding of the role GPER plays in cancer biology may lead to the identification of novel therapeutic targets, especially among estrogen-related cancers. Here, we review cell signaling and detail the functions of GPER in malignancies.

Stabilization of MORC2 by estrogen and antiestrogens through GPER1- PRKACA-CMA pathway contributes to estrogen-induced proliferation and endocrine resistance of breast cancer cells

Aberrant activation of estrogen signaling through three ESR (estrogen receptor) subtypes, termed ESR1/ERα, ESR2/ERβ, and GPER1 (G protein-coupled estrogen receptor 1), is implicated in breast cancer pathogenesis and progression. Antiestrogens tamoxifen (TAM) and fulvestrant (FUL) are effective for treatment of ESR1-positive breast tumors, but development of resistance represents a major clinical challenge. However, the molecular mechanisms behind these events remain largely unknown. Here, we report that 17β-estradiol (E2), TAM, and FUL stabilize MORC2 (MORC family CW-type zinc finger 2), an emerging oncoprotein in human cancer, in a GPER1-dependent manner. Mechanistically, GPER1 activates PRKACA (protein kinase cAMP-activated catalytic subunit alpha), which in turn phosphorylates MORC2 at threonine 582 (T582). Phosphorylated MORC2 decreases its interaction with HSPA8 (heat shock protein family A [Hsp70] member 8) and LAMP2A (lysosomal associated membrane protein 2A), two core components of the chaperone-mediated autophagy (CMA) machinery, thus protecting MORC2 from lysosomal degradation by CMA. Functionally, knockdown of MORC2 attenuates E2-induced cell proliferation and enhances cellular sensitivity to TAM and FUL. Moreover, introduction of wild-type MORC2, but not its phosphorylation-lacking mutant (T582A), in MORC2-depleted cells restores resistance to antiestrogens. Clinically, the phosphorylation levels of MORC2 at T582 are elevated in breast tumors from patients undergoing recurrence after TAM treatment. Together, these findings delineate a phosphorylation-dependent mechanism for MORC2 stabilization in response to estrogen and antiestrogens via blocking CMA-mediated lysosomal degradation and uncover a dual role for MORC2 in both estrogen-induced proliferation and resistance to antiestrogen therapies of breast cancer cells.

ABBREVIATIONS

4-OHT: 4-hydroxytamoxifen; Baf A1: bafilomycin A₁; CMA: chaperone-mediated autophagy; E2: 17β-estradiol; ESR: estrogen receptor; FUL: fulvestrant; GPER1: G protein-coupled estrogen receptor 1; HSPA8: heat shock protein family A (Hsp70) member 8; LAMP2A: lysosomal associated membrane protein 2A; MORC2: MORC family CW-type zinc finger 2; PRKACA: protein kinase cAMP-activated catalytic subunit alpha; TAM: tamoxifen; VCL: vinculin.

Selection of a GPER1 Ligand via Ligand-based Virtual Screening Coupled to Molecular Dynamics Simulations and Its Anti-proliferative Effects on Breast Cancer Cells

BACKGROUND

Recent reports have demonstrated the role of the G Protein-Coupled Estrogen Receptor 1 (GPER1) on the proliferation of breast cancer. The coupling of GPER1 to estrogen triggers cellular signaling pathways related to cell proliferation.

OBJECTIVE

Develop new therapeutic strategies against breast cancer.

METHOD

We performed in silico studies to explore the binding mechanism of a set of G15 /G1 analogue compounds. We included a carboxyl group instead of the acetyl group from G1 to form amides with several moieties to increase affinity on GPER1. The designed ligands were submitted to ligand-based and structure-based virtual screening to get insights into the binding mechanism of the best designed compound and phenol red on GPER1.

RESULTS

According to the in silico studies, the best molecule was named G1-PABA ((3aS,4R,9bR)-4-(6- bromobenzo[d][1,3]dioxol-5-yl)-3a,4,5,9b-tetrahydro-3H-cyclopenta[c]quinoline-8-carboxylic acid). It was synthesized and assayed in vitro in breast cancer (MCF-7 and MDA-MB-231) and normal (MCF-10A) cell lines. Experimental studies showed that the target compound was able to decrease cell proliferation, IC50 values of 15.93 µM, 52.92 µM and 32.45 µM in the MCF-7, MDA-MB-231 and MCF-10A cell lines, respectively, after 72 h of treatment. The compound showed better IC50 values without phenol red, suggesting that phenol red interfere with the G1-PABA action at GPER1, as observed through in silico studies, which is present in MCF-7 cells according to PCR studies and explains the cell proliferation effects.

CONCLUSION

Concentration-dependent inhibition of cell proliferation occurred with G1-PABA in the assayed cell lines and could be due to its action on GPER1.

G-Protein Coupled Estrogen Receptor in Breast Cancer

The G-protein coupled estrogen receptor (GPER), an alternate estrogen receptor (ER) with a structure distinct from the two canonical ERs, being ERα, and ERβ, is expressed in 50% to 60% of breast cancer tissues and has been presumed to be associated with the development of tamoxifen resistance in ERα positive breast cancer. On the other hand, triple-negative breast cancer (TNBC) constitutes 15% to 20% of breast cancers and frequently displays a more aggressive behavior. GPER is prevalent and involved in TNBC and can be a therapeutic target. However, contradictory results exist regarding the function of GPER in breast cancer, proliferative or pro-apoptotic. A better understanding of the GPER, its role in breast cancer, and the interactions with the ER and epidermal growth factor receptor will be beneficial for the disease management and prevention in the future.

GPER is involved in the functional liaison between breast tumor cells and cancer-associated fibroblasts (CAFs)

The aggressiveness of breast tumors is deeply influenced by the surrounding stroma. In this regard, the functional crosstalk between cancer cells and the tumor microenvironment has received considerable attention in recent years. Cancer-associated fibroblasts (CAFs) are active components of the tumor stroma as they play a main role in the initiation, progression, metastasis and recurrence of breast malignancy. Hence, a better understanding of the mechanisms through which host stroma may contribute to cancer development would lead to novel therapeutic approaches aimed to target both tumor cells and the adjacent microenvironment. The G protein estrogen receptor (GPER/GPR30) has been involved in estrogenic signaling in normal and malignant cells, including breast cancer. It is noteworthy that the potential of GPER to mediate stimulatory effects of estrogens has been also shown in CAFs derived from patients with breast tumors, suggesting that GPER may act at the cross-road between cancer cells and these important components of the tumor microenvironment. This review recapitulates recent findings underlying the breast tumor-promoting action of CAFs, in particular their functional liaison with breast cancer cells via GPER toward the occurrence of malignant features.

A role for G-protein coupled estrogen receptor (GPER) in estrogen-induced carcinogenesis: Dysregulated glandular homeostasis, survival and metastasis

Mechanisms of carcinogenesis by estrogen center on its mitogenic and genotoxic potential on tumor target cells. These models suggest that estrogen receptor (ER) signaling promotes expansion of the transformed population and that subsequent accumulation of somatic mutations that drive cancer progression occur via metabolic activation of cathecol estrogens or by epigenetic mechanisms. Recent findings that GPER is linked to obesity, vascular pathology and immunosuppression, key events in the development of metabolic syndrome and intra-tissular estrogen synthesis, provides an alternate view of estrogen-induced carcinogenesis. Consistent with this concept, GPER is directly associated with clinicopathological indices that predict cancer progression and poor survival in breast and gynecological cancers. Moreover, GPER manifests cell biological responses and a microenvironment conducive for tumor development and cancer progression, regulating cellular responses associated with glandular homeostasis and survival, invading surrounding tissue and attracting a vascular supply. Thus, the cellular actions attributed to GPER fit well with the known molecular mechanisms of G-protein coupled receptors, GPCRs, namely, their ability to transactivate integrins and EGF receptors and alter the interaction between glandular epithelia and their extracellular environment, affecting epithelial-to-mesenchymal transition (EMT) and allowing for tumor cell survival and dissemination. This perspective reviews the molecular and cellular responses manifested by GPER and evaluates its contribution to female reproductive cancers as diseases that progress as a result of dysregulated glandular homeostasis resulting in chronic inflammation and metastasis. This review is organized in sections as follows: I) a brief synopsis of the current state of knowledge regarding estrogen-induced carcinogenesis, II) a review of evidence from clinical and animal-based studies that support a role for GPER in cancer progression, and III) a mechanistic framework describing how GPER-mediated estrogen action may influence the tumor and its microenvironment.

The activation of G protein-coupled estrogen receptor induces relaxation via cAMP as well as potentiates contraction via EGFR transactivation in porcine coronary arteries

Estrogen exerts protective effects against cardiovascular diseases in premenopausal women, but is associated with an increased risk of both coronary heart disease and stroke in older postmenopausal women. Studies have shown that activation of the G-protein-coupled estrogen receptor 1 (GPER) can cause either relaxation or contraction of arteries. It is highly likely that these dual actions of GPER may contribute to the seemingly paradoxical effects of estrogen in regulating coronary artery function. The objective of this study was to test the hypothesis that activation of GPER enhances agonist-stimulated porcine coronary artery contraction via epidermal growth factor receptor (EGFR) transactivation and its downstream extracellular signal-regulated kinases (ERK1/2) pathway. Isometric tension studies and western blot were performed to determine the effect of GPER activation on coronary artery contraction. Our findings demonstrated that G-1 caused concentration-dependent relaxation of ET-1-induced contraction, while pretreatment of arterial rings with G-1 significantly enhanced ET-1-induced contraction. GPER antagonist, G-36, significantly inhibited both the G-1-induced relaxation effect and G-1-enhanced ET-1 contraction. Gallein, a Gβγ inhibitor, significantly increased G-1-induced relaxation, yet inhibited G-1-enhanced ET-1-mediated contraction. Similarly, inhibition of EGFR with AG1478 or inhibition of Src with phosphatase 2 further increased G-1-induced relaxation responses in coronary arteries, but decreased G-1-enhanced ET-1-induced contraction. Western blot experiments in porcine coronary artery smooth muscle cells (PCASMC) showed that G-1 increased tyrosine phosphorylation of EGFR, which was inhibited by AG-1478. Furthermore, enzyme-linked immunosorbent assays showed that the level of heparin-binding EGF (HB-EGF) released by ET-1 treatment increased two-fold; whereas pre-incubation with G-1 further increased ET-1-induced HB-EGF release to four-fold over control conditions. Lastly, the role of ERK1/2 was determined by applying the MEK inhibitor, PD98059, in isometric tension studies and detecting phospho-ERK1/2 in immunoblotting. PD98059 potentiated G-1-induced relaxation response, but blocked G-1-enhanced ET-1-induced contraction. By western blot, G-1 treatment decreased phospho-ERK1/2, however, in the presence of the adenylyl cyclase inhibitor, SQ22536, G-1 significantly increased ERK1/2 phosphorylation in PCASMC. These data demonstrate that activation of GPER induces relaxation via cAMP as well as contraction via a mechanism involving transactivation of EGFR and the phosphorylation of ERK1/2 in porcine coronary arteries.

Sodium arsenite inhibited genomic estrogen signaling but induced pERα (Ser118) via MAPK pathway in breast cancer cells

Arsenic (As) is considered a major environmental health threat worldwide due to its widespread contamination in drinking water. Recent studies reported that arsenic is a potential xenoestrogen as it interfered with the action of estrogen (E2) and estrogen receptor (ER) signaling. The present study investigated the effects of sodium arsenite (NaAsO2 ) on estrogen signaling in human breast cancer cells. The results demonstrated that NaAsO2 dose-dependently increased viability of hormone-dependent breast cancer MCF-7 and T47D cells expressing both ERα and ERβ but not hormone-independent MDA-MB-231 cells expressing ERβ. These suggested ERα contribution to NaAsO2 -stimulated breast cancer cells growth. NaAsO2 induced down-regulation of ERα but up-regulation of ERβ protein expressions in T47D cells. Moreover, NaAsO2 dose-dependently inhibited E2-induced ER transcriptional activity as it decreased E2-mediated ERE-luciferase transcription activation and PgR mRNA transcription but increased pS2 mRNA transcription. However, NaAsO2 induced both rapid and sustained activation of ERK1/2 and increased in phosphorylation of ERα at serine 118 residue, c-fos and c-myc protein expressions. These results indicated that NaAsO2 interferes the genomic estrogen-signaling pathway but induces activation of a rapid nongenomic signal transduction through ERK1/2 pathway which may contribute to its proliferative effect on hormone-dependent breast cancer cells. © 2015 Wiley Periodicals, Inc. Environ Toxicol 31: 1133-1146, 2016.

Dynamic monitoring of GPER-mediated estrogenic effects in breast cancer associated fibroblasts: An alternative role of estrogen in mammary carcinoma development

Cancer associated fibroblasts (CAFs) are crucial contributors to breast cancer development. Estrogen affects mammary stroma in both physiological and pathophysiological conditions. We show here that estrogen (G-protein coupled) receptor (GPER) could be detected by immunohistochemistry in stromal fibroblasts of primary breast cancers. The presence of GPER expression was further confirmed by immunofluorescence and quantitative PCR in CAFs isolated from primary breast cancers. Based on dynamic monitoring by real time cell analyzer (RTCA) system, 17-β-estradiol (E2) as well as GPER specific agonist G1 were observed to trigger transient cell index increasing within an hour in a dosage-dependent manner in breast CAFs. In addition, E2 and G1 stimulated intracellular calcium modulation and phosphorylation of extracellular signal-regulated kinase (ERK) 1/2 within seconds and minutes in CAFs, respectively. Moreover, E2 and G1 promoted cell proliferation of breast CAFs measured by RTCA monitoring, cell viability assay and cell cycle analysis, and this promotion could be blocked by a GPER-selective antagonist G15. Interestingly, dynamic RTCA monitoring indicated that E2 increased adhesion of resuspended cells, and microscopy confirmed that E2 stimulated cell spreading. Both the adhesion and spreading were proposed to be mediated by GPER, since G1 also stimulated these effects similar to E2, and G15 reduced them. Moreover, GPER was found to mediate migration that was increased by E2 and G1 but reduced by G15 in RTCA cell migration assay and transwell assay. Accordingly, GPER mediates not only rapid actions but also slow effects including adhesion/spreading, proliferation and migration in breast CAFs. Estrogen is likely to affect tumor associated stroma and contributes to mammary carcinoma development through CAFs.

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

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

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.

Acquisition of epithelial-mesenchymal transition phenotype in the tamoxifen-resistant breast cancer cell: a new role for G protein-coupled estrogen receptor in mediating tamoxifen resistance through cancer-associated fibroblast-derived fibronectin and β1-integrin signaling pathway in tumor cells

INTRODUCTION

Acquired tamoxifen resistance remains the major obstacle to breast cancer endocrine therapy. β1-integrin was identified as one of the target genes of G protein-coupled estrogen receptor (GPER), a novel estrogen receptor recognized as an initiator of tamoxifen resistance. Here, we investigated the role of β1-integrin in GPER-mediated tamoxifen resistance in breast cancer.

METHODS

The expression of β1-integrin and biomarkers of epithelial-mesenchymal transition were evaluated immunohistochemically in 53 specimens of metastases and paired primary tumors. The function of β1-integrin was investigated in tamoxifen-resistant (MCF-7R) subclones, derived from parental MCF-7 cells, and MCF-7R β1-integrin-silenced subclones in MTT and Transwell assays. Involved signaling pathways were identified using specific inhibitors and Western blotting analysis.

RESULTS

GPER, β1-integrin and mesenchymal biomarkers (vimentin and fibronectin) expression in metastases increased compared to the corresponding primary tumors; a close expression pattern of β1-integrin and GPER were in metastases. Increased β1-integrin expression was also confirmed in MCF-7R cells compared with MCF-7 cells. This upregulation of β1-integrin was induced by agonists of GPER and blocked by both antagonist and knockdown of it in MCF-7R cells. Moreover, the epidermal growth factor receptor/extracellular regulated protein kinase (EGFR/ERK) signaling pathway was involved in this transcriptional regulation since specific inhibitors of these kinases also reduced the GPER-induced upregulation of β1-integrin. Interestingly, silencing of β1-integrin partially rescued the sensitivity of MCF-7R cells to tamoxifen and the α5β1-integrin subunit is probably responsible for this phenomenon. Importantly, the cell migration and epithelial-mesenchymal transition induced by cancer-associated fibroblasts, or the product of cancer-associated fibroblasts, fibronectin, were reduced by knockdown of β1-integrin in MCF-7R cells. In addition, the downstream kinases of β1-integrin including focal adhesion kinase, Src and AKT were activated in MCF-7R cells and may be involved in the interaction between cancer cells and cancer-associated fibroblasts.

CONCLUSIONS

GPER/EGFR/ERK signaling upregulates β1-integrin expression and activates downstream kinases, which contributes to cancer-associated fibroblast-induced cell migration and epithelial-mesenchymal transition, in MCF-7R cells. GPER probably contributes to tamoxifen resistance via interaction with the tumor microenvironment in a β1-integrin-dependent pattern. Thus, β1-integrin may be a potential target to improve anti-hormone therapy responses in breast cancer patients.

Relocalisation and activation of integrins induced rapidly by oestrogen via G-protein-coupled receptor 30 in mouse blastocysts

Integrins are the dominant and final adhesion molecules in the attachment process between the blastocysts and endometrium. It is necessary for oestrogen to rapidly activate mouse blastocysts so that they attach to the endometrial epithelium. Our previous study suggested that oestrogen can rapidly induce an increase in intracellular calcium in mouse blastocysts via G-protein-coupled receptor 30 (GPR30). Thus, we deduced that integrins may be involved in GPR30 mediation of the fast effect of oestrogen on mouse blastocysts in implantation. To prove our hypothesis, we used immunofluorescence staining and in vitro coculture of mouse blastocysts and endometrial epithelial cell line (EECs), Ishikawa cells, in the present study. We found that αv and β1 integrin clustered in mouse blastocysts, and that β3 integrin was relocalised to the apical membrane of blastocyst cells when embryos were treated with 1 μM 17β-estradiol (E2), 1 μM E2 conjugated to bovine serum albumin (E2-BSA) and 1 μM G-1, a specific GPR30 agonist, for 30 min respectively, whereas pretreatment with 1 μM G15, a specific GPR30 antagonist, and 5 μM 1,2-Bis(2-aminophenoxy)ethane-N,N,N'',N''-tetraacetic acid tetrakis (acetoxymethyl ester)(BAPTA/AM), a cellular Ca2+ chelator, blocked the localisation of integrins induced by oestrogen via GPR30 in mouse blastocyst cells. E2, E2-BSA and G-1 increased the fibronectin (FN)-binding activity of integrins in blastocysts, whereas G15 and BAPTA/AM blocked the activation of integrins induced by oestrogen via GPR30 in mouse blastocysts. Inhibition of integrins by Arg-Gly-Asp peptide in blastocysts resulted in their failure to adhere to EECs in vitro, even if oestrogen or G-1 was provided. Together, the results indicate the fast effect of oestrogen via the GPR30 membrane receptor further induces relocalisation and activation of integrins in mouse blastocysts, which play important roles in the adhesion of blastocysts to EECs.

Role of G protein-coupled orphan receptors in intestinal inflammation: novel targets in inflammatory bowel diseases

A large number of proteins were classified into the family of G protein-coupled receptors (GPCRs). Based on their characteristic serpentine domain, they are called 7 TM receptors. Presently, their ligands and physiological functions remain unknown. In this review, we summarize what is known on these receptors and discuss the potential use of these orphan GPCRs (GPRs) in the induction or maintenance of remission in inflammatory bowel diseases. We focus on GPRs 30, 41, 43, 55, 119, and 120, where scientific evidence supports a potential role in intestinal inflammation.

Antihistamines modulate the integrin signaling pathway in h9c2 rat cardiomyocytes: Possible association with cardiotoxicity

The identification of biomarkers for toxicity prediction is crucial for drug development and safety evaluation. The selective and specific biomarkers for antihistamines-induced cardiotoxicity is not well identified yet. In order to evaluate the mechanism of the life-threatening effects caused by antihistamines, we used DNA microarrays to analyze genomic profiles in H9C2 rat cardiomyocytes that were treated with antihistamines. The gene expression profiles from drug-treated cells revealed changes in the integrin signaling pathway, suggesting that cardiac arrhythmias induced by antihistamine treatment may be mediated by changes in integrin-mediated signaling. It has been reported that integrin plays a role in QT prolongation that may induce cardiac arrhythmia. These results indicate that the integrin-mediated signaling pathway induced by antihistamines is involved in various biological mechanisms that lead to cardiac QT prolongation. Therefore, we suggest that genomic profiling of antihistamine-treated cardiomyocytes has the potential to reveal the mechanism of adverse drug reactions, and this signal pathway is applicable to prediction of in vitro cardiotoxicity induced by antihistamines as a biomarker candidate.

Is oestrogen an important player in melanoma progression?

The oestrogen-dependent regulation of cell behaviour is realised by stimulation of specific oestrogen receptors. The classical oestrogen receptors ERα and ERβ are transcription factors, and they modulate expression of hormonally regulated genes, while the third one, GPER, is thought to be responsible for the observed rapid, non-genomic cellular response. Oestrogen dependency is attributed to a number of cancers, including breast, ovarian and endometrial cancer; however, there is still growing evidence that melanoma should also be cited as a hormonally dependent tumour. This comes from the observations of gender-related differences in melanoma progression and reports concerning the history of the malignant course of melanomas during pregnancy. Although, the observations of oestrogen regulation of melanoma progression are controversial, the effect of oestrogen should not be neglected, as the skin possesses its own hormonal microenvironment. This aspect of melanoma progression should be taken under careful consideration as it may offer new therapeutic possibilities.

The G protein-coupled estrogen receptor-1, GPER-1, promotes fibrillogenesis via a Shc-dependent pathway resulting in anchorage-independent growth

The G protein-coupled estrogen receptor-1, GPER-1, coordinates fibronectin (FN) matrix assembly and release of heparan-bound epidermal growth factor (HB-EGF). This mechanism of action results in the recruitment of FN-engaged integrin α5β1 to fibrillar adhesions and the formation of integrin α5β1-Shc adaptor protein complexes. Here, we show that GPER-1 stimulation of murine 4 T1 or human SKBR3 breast cancer cells with 17β-estradiol (E2β) promotes the formation of focal adhesions and actin stress fibers and results in increased cellular adhesion and haptotaxis on FN, but not collagen. These actions are also induced by the xenoestrogen, bisphenol A, and the estrogen receptor (ER) antagonist, ICI 182, 780, but not the inactive stereoisomer, 17α-estradiol (E2α). In addition, we show that GPER-1 stimulation of breast cancer cells allows for FN-dependent, anchorage-independent growth and FN fibril formation in "hanging drop" assays, indicating that these GPER-1-mediated actions occur independently of adhesion to solid substrata. Stable expression of Shc mutant Y317F lacking its primary tyrosyl phosphorylation site disrupts E2β-induced focal adhesion and actin stress fiber formation and abolishes E2β-enhanced haptotaxis on FN and anchorage-dependent growth. Collectively, these data demonstrate that E2β action via GPER-1 enhances cellular adhesivity and FN matrix assembly and allows for anchorage-independent growth, cellular events that may allow for cellular survival, and tumor progression.

G protein-coupled estrogen receptor regulates mammary tumorigenesis and metastasis

The role of 17β-estradiol (E2) in breast cancer development and tumor growth has traditionally been attributed exclusively to the activation of estrogen receptor-α (ERα). Although targeted inhibition of ERα is a successful approach for patients with ERα(+) breast cancer, many patients fail to respond or become resistant to anti-estrogen therapy. The discovery of the G protein-coupled estrogen receptor (GPER) suggested an additional mechanism through which E2 could exert its effects in breast cancer. Studies have demonstrated clinical correlations between GPER expression in human breast tumor specimens and increased tumor size, distant metastasis, and recurrence, as well as established a proliferative role for GPER in vitro; however, direct in vivo evidence has been lacking. To this end, a GPER-null mutation [GPER knockout (KO)] was introduced, through interbreeding, into a widely used transgenic mouse model of mammary tumorigenesis [MMTV-PyMT (PyMT)]. Early tumor development, assessed by the extent of hyperplasia and proliferation, was not different between GPER wild-type/PyMT (WT/PyMT) and those mice harboring the GPER-null mutation (KO/PyMT). However, by 12 to 13 weeks of age, tumors from KO/PyMT mice were smaller with decreased proliferation compared with those from WT/PyMT mice. Furthermore, tumors from the KO/PyMT mice were of histologically lower grade compared with tumors from their WT counterparts, suggesting less aggressive tumors in the KO/PyMT mice. Finally, KO/PyMT mice displayed dramatically fewer lung metastases compared with WT/PyMT mice. Combined, these data provide the first in vivo evidence that GPER plays a critical role in breast tumor growth and distant metastasis.

IMPLICATIONS

This is the first description of a role for the novel estrogen receptor GPER in breast tumorigenesis and metastasis, demonstrating that it represents a new target in breast cancer diagnosis, prognosis, and therapy.

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.

Transcriptomics of the fetal hypothalamic response to brachiocephalic occlusion and estradiol treatment

Estradiol (E2) is a well-known modulator of fetal neuroendocrine activity and has been proposed as a critical endocrine signal readying the fetus for birth and postnatal life. To investigate the modulatory role of E2 on fetal stress responsiveness and the response of the fetal brain to asphyxic stress, we subjected chronically catheterized fetal sheep to a transient (10 min) brachiocephalic artery occlusion (BCO) or sham occlusion. Half of the fetuses received subcutaneous pellets that increased plasma E2 concentrations within the physiological range. Hypothalamic mRNA was analyzed using the Agilent 8x15k ovine array (019921), processed and annotated as previously reported by our laboratory. Analysis of the data by ANOVA revealed that E2 differentially regulated (DR) 561 genes, and BCO DR 894 genes compared with control and E2+BCO DR 1,153 genes compared with BCO alone (all P < 0.05). E2 upregulated epigenetic pathways and downregulated local steroid biosynthesis but did not significantly involve genes known to directly respond to the estrogen receptor. Brachiocephalic occlusion upregulated kinase pathways as well as genes associated with lymphocyte infiltration into the brain and downregulated neuropeptide synthesis. E2 upregulated immune- and apoptosis-related pathways after BCO and reduced kinase and epigenetic pathway responses to the BCO. Responses to BCO are different from responses to hypoxic hypoxia suggesting that mechanisms of responses to these two forms of brain hypoxia are distinct. We conclude that cerebral ischemia caused by BCO might stimulate lymphocyte infiltration into the brain and that this response appears to be modified by estradiol.

Anatomical location and redistribution of G protein-coupled estrogen receptor-1 during the estrus cycle in mouse kidney and specific binding to estrogens but not aldosterone

Prior studies have linked renoprotective effects of estrogens to G-protein-coupled estrogen receptor-1 (GPER-1) and suggest that aldosterone may also activate GPER-1. Here, the role of GPER-1 in murine renal tissue was further evaluated by examining its anatomical distribution, subcellular distribution and steroid binding specificity. Dual immunofluorescent staining using position-specific markers showed that GPER-1 immunoreactivity primarily resides in distal convoluted tubules and the Loop of Henle (stained with Tamm-Horsfall Protein-1). Lower GPER-1 expression was observed in proximal convoluted tubules marked with megalin, and GPER-1 was not detected in collecting ducts. Plasma membrane fractions prepared from whole kidney tissue or HEK293 cells expressing recombinant human GPER-1 (HEK-GPER-1) displayed high-affinity, specific [(3)H]-17β-estradiol ([(3)H]-E2) binding, but no specific [(3)H]-aldosterone binding. In contrast, cytosolic preparations exhibited specific binding to [(3)H]-aldosterone but not to [(3)H]-E2, consistent with the subcellular distribution of GPER-1 and mineralocorticoid receptor (MR) in these preparations. Aldosterone and MR antagonists, spironolactone and eplerenone, failed to compete for specific [(3)H]-E2 binding to membranes of HEK-GPER-1 cells. Furthermore, aldosterone did not increase [(35)S]-GTP-γS binding to membranes of HEK-GPER-1 cells, indicating that it is not involved in G protein signaling mediated through GPER-1. During the secretory phases of the estrus cycle, GPER-1 is upregulated on cortical epithelia and localized to the basolateral surface during proestrus and redistributed intracellularly during estrus. GPER-1 is down-modulated during luteal phases of the estrus cycle with significantly less receptor on the surface of renal epithelia. Our results demonstrate that GPER-1 is associated with specific estrogen binding and not aldosterone binding and that GPER-1 expression is modulated during the estrus cycle which may suggest a physiological role for GPER-1 in the kidney during reproduction.

Expression and prognostic significance of fibronectin and matrix metalloproteases in breast cancer metastasis

AIMS

Fibronectin (FN) has attracted interest in cancer research, owing to its role in tumour progression. The aims of this study were to investigate the expression and clinical relevance of FN in breast cancer, and to explore its relationship with the expression of matrix metalloproteases (MMPs) and their inhibitors (TIMPs).

METHODS AND RESULTS

An immunohistochemical study was performed using tumours from 110 breast cancer patients, with tissue arrays and specific antibodies against FN, MMP-7, MMP-9, MMP-11, TIMP-1, and TIMP-2. The results indicated that FN expression was related to tumour size, histological grade, and MMP-9 expression. Tumours with high FN expression by tumour cells were significantly associated with a higher probability of metastasis, poorer overall survival, and expression of MMP-7, MMP-9, MMP-11, TIMP-1 and TIMP-2 by mononuclear inflammatory cells (MICs). In addition, the combination of FN expression by tumour cells and MMP-11 by MICs was strongly associated with distant metastasis development.

CONCLUSIONS

Breast carcinomas with distant metastasis frequently have tumour cells expressing intracellular FN. There is a strong association between FN expression by tumour cells and MMP or TIMP expression by stromal MICs, and this may represent crosstalk that is of prognostic relevance in breast cancer.

G-protein oestrogen receptor 1: trials and tribulations of a membrane oestrogen receptor

Oestrogens are now recognised to be able to initiate rapid, fast responses, in addition to their classical, longer-term actions. There is a growing appreciation of the potential implications of this mode of action for oestrogenic signalling in both neuronal and non-neuronal systems. As such, much effort has been made to determine the mechanisms that are critical for transducing these rapid effects into cellular responses. Recently, an orphan G-protein-coupled receptor (GPCR), termed GPR30, was identified as an oestrogen-sensitive receptor in cancer cells. This receptor, now term G-protein oestrogen receptor 1 (GPER1) has been the subject of many investigations, and a role for this receptor in the nervous system is now emerging. In this review, we highlight some of the more recent advances in our understanding of the distribution and subcellular localisation of this receptor in the brain, as well as some of the evidence for the potential role that this receptor may play in the brain. We then discuss some of the controversies surrounding the pharmacology of this receptor, and attempt to reconcile these by suggesting that the 'agonist-specific coupling' model of GPCR function may provide a potential explanation for some of the divergent reports of GPER1 pharmacology.

Cross-talk between GPER and growth factor signaling

G protein-coupled receptors (GPCRs) and growth factor receptors mediate multiple physio-pathological responses to a diverse array of extracellular stimuli. In this regard, it has been largely demonstrated that GPCRs and growth factor receptors generate a multifaceted signaling network, which triggers relevant biological effects in normal and cancer cells. For instance, some GPCRs transactivate the epidermal growth factor receptor (EGFR), which stimulates diverse transduction pathways leading to gene expression changes, cell migration, survival and proliferation. Moreover, it has been reported that a functional interaction between growth factor receptors and steroid hormones like estrogens is involved in the growth of many types of tumors as well as in the resistance to endocrine therapy. This review highlights recent findings on the cross-talk between a member of the GPCR family, the G protein-coupled estrogen receptor 1 (GPER, formerly known as GPR30) and two main growth factor receptors like EGFR and insulin-like growth factor-I receptor (IGF-IR). The biological implications of the functional interaction between these important mediators of cell responses particularly in cancer are discussed. This article is part of a Special Issue entitled 'CSR 2013'.

Vasoconstriction induced by G1, a G-protein-coupled oestrogen receptor1 (GPER-1) agonist, in the isolated perfused rat kidney

Vascular effects of the G protein-coupled oestrogen receptor1 (GPER-1) agonist, G1 (10(-7)-5×10(-6) M), the main oestrogenic hormone, 17β-estradiol (10(-9)-10(-4) M), the NR3A1 agonist, PPT (10(-8)-10(-5) M), the NR3A2 agonist DPN (10(-8)-10(-5) M), and the classical oestrogen receptor blocker but also a GPER agonist, ICI-182780 (10(-8)-3×10(-6) M), were investigated on the perfusion pressure in the isolated rat kidney. To seek cellular mechanisms involved in GPER-1-induced signalling we tested several compounds including the inhibitors of Rho-kinase (ROCK) (Y-27632), tyrosine kinase (genistein), p38MAPK (SB203580), p44/42MAPK (PD98059), protein kinase C (PKC) (GF109203X), Jun-kinase (JNK) (SP600125), phosphatidylinositol-3-kinase (PI3K) (LY294002), Ca(2+) channels (nifedipine), GPER-1 (G15) and epidermal growth factor (EGF) receptor kinase (AG-1478). Moreover, the effect of saponin (50mg/ml) that was used for endothelium removal was explored on G1-elicited vascular action. G1, 17β-estradiol and ICI-182780 but not PPT and DPN induced vasoconstrictions in basal renal perfusion pressure. In contrast, G1 promoted vasodilatation when the perfusion pressure was elevated in advance by phenylephrine. G1-elicited vasoconstriction was not modified by endothelial removal; however, it was markedly inhibited by GPER-1 antagonist, G15. The vasoconstrictor response to G1 was also significantly attenuated by Y-27632, PD98059, SB203580, GF109203X, genistein, AG-1478, and nifedipine, but not LY294002 and SP600125. Western blotting indicated the expression of GPER-1 in renal artery, medulla and cortex of rat kidney. In conclusion, GPER-1 could substantially modulate vascular responses through a variety of signalling pathways including ROCK, PKC, p38 MAPK, p42/44 MAPK, tyrosine kinase, EGF receptor kinase and VOCC but not JNK or PI3K in isolated perfused rat kidney.

Mechanisms underlying the interactions between rapid estrogenic and BDNF control of synaptic connectivity

The effects of the steroid hormone 17β-estradiol and the neurotrophin brain-derived neurotrophic factor (BDNF) on neuronal physiology have been well investigated. Numerous studies have demonstrated that each signal can exert powerful influences on the structure and function of synapses, and specifically on dendritic spines, both within short and long time frames. Moreover, it has been suggested that BDNF is required for the long-term, or genomic, actions of 17β-estradiol on dendritic spines, via its ability to regulate the expression of neurotrophins. Here we focus on the acute, or rapid effects, of 17β-estradiol and BDNF, and their ability to activate specific signalling cascades, resulting in alterations in dendritic spine morphology. We first review recent literature describing the mechanisms by which 17β-estradiol activates these pathways, and the resulting alterations in dendritic spine number. We then describe the molecular mechanisms underlying acute modulation of dendritic spine morphology by BDNF. Finally, we consider how this new evidence may suggest that the temporal interactions of 17β-estradiol and BDNF can occur more rapidly than previously reported. Building on these new data, we propose a novel model for the interactions of this steroid and neurotrophin, whereby rapid, non-genomic 17β-estradiol and acute BDNF signal in a co-operative manner, resulting in dendritic spine formation and subsequent stabilization in support of synapse and circuit plasticity. This extended hypothesis suggests an additional mechanism by which these two signals may modulate dendritic spines in a time-specific manner.

Minireview: G protein-coupled estrogen receptor-1, GPER-1: its mechanism of action and role in female reproductive cancer, renal and vascular physiology

Using cDNA cloning strategies commonly employed for G protein-coupled receptors (GPCR), GPCR-30 (GPR30), was isolated from mammalian cells before knowledge of its cognate ligand. GPR30 is evolutionarily conserved throughout the vertebrates. A broad literature suggests that GPR30 is a Gs-coupled heptahelical transmembrane receptor that promotes specific binding of naturally occurring and man-made estrogens but not cortisol, progesterone, or testosterone. Its "pregenomic" signaling actions are manifested by plasma membrane-associated actions familiar to GPCR, namely, stimulation of adenylyl cyclase and Gβγ-subunit protein-dependent release of membrane-tethered heparan bound epidermal growth factor. These facts regarding its mechanism of action have led to the formal renaming of this receptor to its current functional designate, G protein-coupled estrogen receptor (ER) (GPER)-1. Further insight regarding its biochemical action and physiological functions in vertebrates is derived from receptor knockdown studies and the use of selective agonists/antagonists that discriminate GPER-1 from the nuclear steroid hormone receptors, ERα and ERβ. GPER-1-selective agents have linked GPER-1 to physiological and pathological events regulated by estrogen action, including, but not limited to, the central nervous, immune, renal, reproductive, and cardiovascular systems. Moreover, immunohistochemical studies have shown a positive association between GPER-1 expression and progression of female reproductive cancer, a relationship that is diametrically opposed from ER. Unlike ER knockout mice, GPER-1 knockout mice are fertile and show no overt reproductive anomalies. However, they do exhibit thymic atrophy, impaired glucose tolerance, and altered bone growth. Here, we discuss the role of GPER-1 in female reproductive cancers as well as renal and vascular physiology.

Estrogen effects on the brain: actions beyond the hypothalamus via novel mechanisms

From its origins in how the brain controls the endocrine system via the hypothalamus and pituitary gland, neuroendocrinology has evolved into a science that now includes hormone action on many aspects of brain function. These actions involve the whole central nervous system and not just the hypothalamus. Advances in our understanding of cellular and molecular actions of steroid hormones have gone beyond the important cell nuclear actions of steroid hormone receptors to include signaling pathways that intersect with other mediators such as neurotransmitters and neuromodulators. This has, in turn, broadened the search for and identification of steroid receptors to include nonnuclear sites in synapses, dendrites, mitochondria, and glial cells, as well as cell nuclei. The study of estrogen receptors and estrogen actions on processes related to cognition, mood, autonomic regulation, pain, and neuroprotection, among other functions, has led the way in this new view of hormone actions on the brain. In this review, we summarize past and current work in our laboratory on this topic. This exciting and growing field involving many laboratories continues to reshape our ideas and approaches to neuroendocrinology both at the bench and the bedside.

Trans-Golgi Network (TGN) as a regulatory node for β1-adrenergic receptor (β1AR) down-modulation and recycling

Receptor down-modulation is the key mechanism by which G protein-coupled receptors (GPCRs) prevent excessive receptor signaling in response to agonist stimulation. Recently, the trans-Golgi network (TGN) has been implicated as a key checkpoint for receptor endocytosis and degradation. Here, we investigated the involvement of the TGN in down-modulation of β1-adrenergic receptor in response to persistent isoprotenerol stimulation. Immunofluorescent staining showed that ~50% of endocytosed β1AR colocalized with TGN-46 at 5 h. Disruption of the TGN by brefeldin A (BFA) led to the robust accumulation of endocytosed β1AR in Rab11(+) recycling endosomes, inhibited β1AR entry into LAMP1(+) lysosomes, and as a result enhanced β1AR recycling to the plasma membrane. The lysosomotropic agent, chloroquine, arrested the majority of endocytosed β1AR in the TGN by 4 h. Immunoblot analysis showed that either disruption of the TGN or blockage of the lysosome prevented β1AR degradation. Co-expression of GFP-arrestin-3 in β1AR cells increased the endocytosis of β1AR and facilitated its entry to the TGN but inhibited recycling to the plasma membrane. Arrestin-3-induced inhibition of β1AR recycling was reversed by BFA treatment, whereas chloroquine induced the accumulation of arrestin-3 with β1AR in the TGN. These results demonstrate for the first time that the TGN acts as a checkpoint for both the recycling and down-regulation of β1AR and that arrestin-3 not only mediates β1AR endocytosis but also its recycling through the TGN.

MIBE acts as antagonist ligand of both estrogen receptor α and GPER in breast cancer cells

Introduction

The multiple biological responses to estrogens are mainly mediated by the classical estrogen receptors ERα and ERβ, which act as ligand-activated transcription factors. ERα exerts a main role in the development of breast cancer; therefore, the ER antagonist tamoxifen has been widely used although its effectiveness is limited by de novo and acquired resistance. Recently, GPR30/GPER, a member of the seven-transmembrane G protein-coupled receptor family, has been implicated in mediating the effects of estrogens in various normal and cancer cells. In particular, GPER triggered gene expression and proliferative responses induced by estrogens and even ER antagonists in hormone-sensitive tumor cells. Likewise, additional ER ligands showed the ability to bind to GPER eliciting promiscuous and, in some cases, opposite actions through the two receptors. We synthesized a novel compound (ethyl 3-[5-(2-ethoxycarbonyl-1-methylvinyloxy)-1-methyl-1H-indol-3-yl]but-2-enoate), referred to as MIBE, and investigated its properties elicited through ERα and GPER in breast cancer cells.

Methods

Molecular modeling, binding experiments and functional assays were performed in order to evaluate the biological action exerted by MIBE through ERα and GPER in MCF7 and SkBr3 breast cancer cells.

Results

MIBE displayed the ability to act as an antagonist ligand for ERα and GPER as it elicited inhibitory effects on gene transcription and growth effects by binding to both receptors in breast cancer cells. Moreover, GPER was required for epidermal growth factor receptor (EGFR) and ERK activation by EGF as ascertained by using MIBE and performing gene silencing experiments.

Conclusions

Our findings provide novel insights on the functional cross-talk between GPER and EGFR signaling. Furthermore, the exclusive antagonistic activity exerted by MIBE on ERα and GPER could represent an innovative pharmacological approach targeting breast carcinomas which express one or both receptors at the beginning and/or during tumor progression. Hence, the simultaneous inhibition of both ERα and GPER may guarantee major therapeutic benefits in respect to the use of a selective estrogen receptor antagonist.

Transcriptomic effects of di-(2-ethylhexyl)-phthalate in Syrian hamster embryo cells: an important role of early cytoskeleton disturbances in carcinogenesis?

Background

Di-(2-ethylhexyl)-phthalate (DEHP) is a commonly used plasticizer in polyvinylchloride (PVC) formulations and a potentially non-genotoxic carcinogen. The aim of this study was to identify genes whose level of expression is altered by DEHP by using a global wide-genome approach in Syrian hamster embryo (SHE) cells, a model similar to human cells regarding their responses to this type of carcinogen. With mRNA Differential Display (DD), we analysed the transcriptional regulation of SHE cells exposed to 0, 12.5, 25 and 50 μM of DEHP for 24 hrs, conditions which induced neoplastic transformation of these cells. A real-time quantitative polymerase chain reaction (qPCR) was used to confirm differential expression of genes identified by DD.

Results

Gene expression profiling showed 178 differentially-expressed fragments corresponding to 122 genes after tblastx comparisons, 79 up-regulated and 43 down-regulated. The genes of interest were involved in many biological pathways, including signal transduction, regulation of the cytoskeleton, xenobiotic metabolism, apoptosis, lipidogenesis, protein conformation, transport and cell cycle. We then focused particularly on genes involved in the regulation of the cytoskeleton, one of the processes occurring during carcinogenesis and in the early steps of neoplastic transformation. Twenty one cytoskeleton-related genes were studied by qPCR. The down-regulated genes were involved in focal adhesion or cell junction. The up-regulated genes were involved in the regulation of the actin cytoskeleton and this would suggest a role of cellular plasticity in the mechanism of chemical carcinogenesis. The gene expression changes identified in the present study were PPAR-independent.

Conclusion

This study identified a set of genes whose expression is altered by DEHP exposure in mammalian embryo cells. This is the first study that elucidates the genomic changes of DEHP involved in the organization of the cytoskeleton. The latter genes may be candidates as biomarkers predictive of early events in the multistep carcinogenic process.