G Protein-coupled Estrogen Receptor Activation Research Articles

The G protein-coupled estrogen receptor (GPER/GPR30) may serve as a prognostic marker in early-stage cervical cancer.

Estrogen signalling is transmitted via various receptors and multiple intracellular signalling pathways. Estrogen receptor alpha (ERα)-mediated transcription of target genes has been demonstrated to be closely linked to human papilloma virus (HPV)-induced carcinogenesis in case of cervical cancer. So far, the role of non-genomic estrogen signals in cervical cancer, e.g. transmitted by the G protein-coupled estrogen receptor (GPER) remains to be rather elusive. Today's knowledge on the role of GPER in cervical cancer is sparse and-to the best of our knowledge-GPER has not been investigated in context with clinicopathological parameters or prognosis of cervical cancer. Therefore, the current study investigated whether GPER is expressed in cervical cancer tissue. Further, GPER was correlated to clinicopathological parameters, tissue markers of cervical carcinogenesis and to patient overall and recurrence-free survival. Cervical cancer tissue was collected from 156 patients during surgery between 1993 and 2002. GPER immunostaining was performed on all the cases and correlated to clinicopathological data. More than half of all patients were diagnosed at advanced stage (FIGO II-IV 93/156; 59.6%) of disease. The large majority of patients presented with tumours of intermediate or high grade (G2-3 140/152, 92.1%). 22 cervical cancer-related deaths (22/156, 14.1%) were documented during the follow-up period. GPER was detected in various subcellular staining patterns. In 129/156 (82.7%) cases GPER was expressed in the tumour cell cytoplasm (GPERcyt). GPER immunopositivity at the cell membrane (GPERmem) was found in 114/156 (73.1%) cases. While co-occurrence of both membrane and cytoplasmic staining (GPERcyt+GPERmem) was detected in the majority of tissue samples (101/156; 64.7%), only few cases (14/156, 9.0%) were classified as not expressing GPER at all. GPERcyt was positively correlated with tumour grade. Statistical associations of GPER and both p16 and p53 were detected. Finally, immunopositivity of GPERcyt was predictive for favourable overall as well as recurrence-free survival in cervical cancer of early stage (FIGO I). This retrospective study reports GPERcyt to be associated with improved overall and recurrence-free survival in early-stage cervical cancer. Further investigations are needed thus to determine whether this observation may be of clinical impact. Interestingly, Raloxifene-a GPER-activating selective estrogen receptor modulator-has recently been demonstrated to be preventive for cervical cancer relapse in mice. Whether this effect is only reliant on raloxifene blocking ERα or may also be related to activation of GPER remains to be determined.

Abstract 041: New Evidence for G Protein-coupled Estrogen Receptor as a Natriuretic Factor

Premenopausal women have a lower risk of cardiovascular and renal diseases compared to age-matched men. This protection includes fewer salt-dependent complications. We have shown that female rats have a more robust natriuretic capacity compared to males in response to increased dietary salt. The novel estrogen receptor, G protein-coupled estrogen receptor (GPER), is a membrane-bound receptor linked to acute signaling pathways. GPER activation elicits protective effects throughout the cardiovascular system. However, its role in sodium handling is not defined. We hypothesized that activation of GPER in the renal medulla stimulates sodium excretion. In female Sprague Dawley (SD) rats, isosmotic saline was infused into the renal medullary interstitium (500 μl/h) during a 60-80 min equilibration period and 20 min baseline urine collection period. This was followed by infusion of the GPER agonist G1 (50 pmol/kg/min) or vehicle into the renal medulla for two further 20 min periods. Compared with vehicle, G1 significantly increased urinary sodium excretion and urine flow (from 0.5 ± 0.1 to 0.9 ± 0.2 μmol/min and from 5.3±1.1 to 8.3±1.6 μl/min, respectively, n=6, p<0.05). Urinary potassium excretion and mean arterial pressure remained unchanged during the experiments (0.5 ± 0.1 vs. 0.4 ± 0.1 μmol/min and 108.6 ± 3.4 vs. 107.2 ± 5.1 mmHg, respectively, n=6). Immunohistochemical analysis of GPER revealed more predominant staining in both inner and outer renal medulla in female SD rats, compared to males. GPER appears to be predominantly expressed in interstitial cells. These data reveal that renal medullary GPER plays an important role in renal sodium handling and may account for the enhanced ability to handle increased dietary salt in females. Funded by AHA 15POST25090329 to EYG and P01 HL136267 to DMP

GPER Agonist G1 Attenuates Neuroinflammation and Dopaminergic Neurodegeneration in Parkinson Disease

Objective: Epidemiological studies have shown that women of reproductive age have much less possibility of developing Parkinson disease (PD) than men. The beneficial effect of estrogen also has been well-described in both culture and animal models of PD. G protein-coupled estrogen receptor (GPER) is a membrane-associated estrogen receptor, and displayed a neuroprotective role in a mouse model of PD. Since GPER is highly expressed in microglia, we speculate that GPER mediates the neuroprotective function of estradiol through suppressing the neuroinflammation of PD. Methods: We investigated the effects of GPER agonist G1 and GPER antagonist G15 on the neurodegeneration of dopaminergic neuron, the activation of microglia, and the production of IL-1β, TNF-α, and IL-6 in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced animal model of parkinsonism. Furthermore, we confirmed the effects of GPER activation on the production of IL-1β, TNF-α, and IL-6 in an in vitro MPP+ model in BV2 microglial cells. Results: After 12-day treatment with G1, mice showed an increase in the number of tyrosine hydroxylase-immunoreactive cells, reduced activation of microglia, and the abatement of proinflammatory cytokines, and the anti-inflammatory effect of G1 was abolished by G15. Meanwhile, in vitro studies demonstrated that GPER activation also reduced the release of proinflammatory cytokines from BV2 microglial cells after MPP+ stimulation. Conclusion: Our data suggest that GPER mediates the anti-neuroinflammatory effect of estrogen in experimental PD progression.

Abstract 3084: Therapeutic implications of sex hormone signaling in melanoma

Abstract Female gender, early age of first birth, and multiparity are associated with less aggressive melanoma; however, the mechanisms underlying the apparent clinical benefit are undefined. Previously we reported that 17β-estradiol drives melanocyte differentiation through G-protein coupled estrogen receptor (GPER), a nonclassical sex hormone receptor. Here, we use genetically-defined human skin xenograft melanoma to show that pregnancy antagonizes oncogenic BRAF and inhibits melanomagenesis. Transient GPER activation drives stable melanocyte differentiation that persists after removal of the activating ligand. Consistent with this, brief exposure of melanoma cells to GPER agonists prior to xenografting inhibited subsequent tumor growth. Systemic treatment with GPER agonists cooperated with PD-1 blockade in melanoma bearing mice to greatly prolong survival longer than that observed with either agent alone. The combination of differentiation-based therapies with immunotherapy may have significant therapeutic benefit for melanoma. Citation Format: Christopher Natale, Junqian Zhang, Ankit Dahal, Todd Ridky. Therapeutic implications of sex hormone signaling in melanoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 3084. doi:10.1158/1538-7445.AM2017-3084

Epigenetic down regulation of G protein-coupled estrogen receptor (GPER) functions as a tumor suppressor in colorectal cancer

BackgroundEstrogenic signals are suggested to have protection roles in the development of colorectal cancer (CRC). The G protein-coupled estrogen receptor (GPER) has been reported to mediate non-genomic effects of estrogen in hormone related cancers except CRC. Its expression and functions in CRC were investigated.MethodsThe expression of GPER and its associations with clinicopathological features were examined. The mechanisms were further investigated using cells, mouse xenograft models, and clinical human samples.ResultsGPER was significantly (p < 0.01) down regulated in CRC tissues compared with their matched adjacent normal tissues in our two cohorts and three independent investigations from Oncomine database. Patients whose tumors expressing less (n = 36) GPER showed significant (p < 0.01) poorer survival rate as compared with those with greater levels of GPER (n = 54). Promoter methylation and histone H3 deacetylation were involved in the down regulation of GPER in CRC cell lines and clinical tissues. Activation of GPER by its specific agonist G-1 inhibited proliferation, induced cell cycle arrest, mitochondrial-related apoptosis and endoplasmic reticulum (ER) stress of CRC cells. The upregulation of reactive oxygen species (ROS) induced sustained ERK1/2 activation participated in G-1 induced cell growth arrest. Further, G-1 can inhibit the phosphorylation, nuclear localization, and transcriptional activities of NF-κB via both canonical IKKα/ IκBα pathways and phosphorylation of GSK-3β. Xenograft model based on HCT-116 cells confirmed that G-1 can suppress the in vivo progression of CRC.ConclusionsEpigenetic down regulation of GPER acts as a tumor suppressor in colorectal cancer and its specific activation might be a potential approach for CRC treatment.

GPER activation is effective in protecting against inflammation-induced nigral dopaminergic loss and motor function impairment

Increasing evidence suggest that excessive inflammatory responses from overactivated microglia play a critical role in Parkinson’s disease (PD), contributing to, or exacerbating, nigral dopaminergic (DA) degeneration. Recent results from our group and others demonstrated that selective activation of G protein-coupled estrogen receptor (GPER) with the agonist G1 can protect DA neurons from 1-methyl-4-phenylpyridinium (MPP+) and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) neurotoxins. However, it is not known whether modulation of microglial responses is one of the mechanisms by which G1 exerts its DA neuroprotective effects. We analyzed, in the N9 microglial cell line, the effect of G1 on microglial activation induced by lipopolysaccharide (LPS) exposure. The results revealed that G1 significantly decrease phagocytic activity, expression of inducible nitric oxide synthase (iNOS) and release of nitric oxide (NO) induced by LPS. To determine the relevance of this anti-inflammatory effect to the protection of nigral DA cells, the effect of G1 was analyzed in male mice injected unilaterally in the substantia nigra (SN) with LPS. Although G1 treatment did not decrease LPS-induced increase of ionized calcium binding adaptor molecule 1 (iba-1) positive cells it significantly reduced interleukin-1beta (IL-1β), cluster of differentiation 68 (CD68) and iNOS mRNA levels, and totally inhibited nigral DA cell loss and, as a consequence, protected the motor function. In summary, our findings demonstrated that the G1 agonist is able to modulate microglial responses and to protect DA neurons and motor functions against a lesion induced by an inflammatory insult. Since G1 lacks the feminizing effects associated with agonists of the classical estrogen receptors (ERs), the use of G1 to selectively activate the GPER may be a promising strategy for the development of new therapeutics for the treatment of PD and other neuroinflammatory diseases.

Oxabicycloheptene Sulfonate Protects Against β-Amyloid-induced Toxicity by Activation of PI3K/Akt and ERK Signaling Pathways Via GPER1 in C6 Cells.

Oxabicycloheptene sulfonate (OBHS) is a novel bicyclic core selective estrogen receptor modulator (SERM) with estrogen receptor (ER) antagonistic-activity and anti-inflammatory activity. However, little is known about protective action of OBHS on neurodegenerative disorders. In the present study, OBHS demonstrated a remarkably protective effect against amyloid beta (Aβ) induced cytotoxicity via G-protein-coupled estrogen receptor 1 (GPER1) in rat astroglial cell line (C6). The C6 cell death induced by Aβ was decreased by OBHS (1μM) treatment for 45min. This rapid protective action was blocked by GPER1 specific antagonist or siRNA knockdown. Inhibitors of phosphatidylinositol 3-kinase (PI3k)/Akt and extracellular signal-regulated kinase (ERK) activation also exhibited similar effects as GPER1 antagonist in blocking the protective effects of OBHS. Moreover, the expression of anti-apoptotic protein Bcl-2 was also increased by OBHS as a consequence of the activation of GPER1-PI3K/Akt and ERK pathways. Additionally, the phenyl sulfonate moiety of OBHS played a vital role in producing GPER1's agonist property according to the molecular docking analysis. These findings suggest that OBHS provide protection directed at enhancing glial cell survival through the activation of GPER1, which, in turn, offers a novel insight into the molecular mechanisms behind the potential application of OBHS in treating Alzheimer's disease (AD).

Activation of GPER (G protein‐coupled estrogen receptor) increases Gs activity via forming a plasma membrane complex with AKAP/SAP97

Evidence suggest that G protein‐coupled estrogen receptor (GPER) is emerging as a therapeutic target in cardiovascular diseases. Activation of GPER elicits many cardiovascular protective effects, including lowering blood pressure, reducing ischemia/reperfusion‐induced cardiac infarct size and decreasing the process of atherosclerosis in animal models. However, the understanding of the mechanisms underlying GPER‐mediated actions is still limited. The objective of this study is to test the hypothesis that activation of GPER by selective agonist G‐1 increases Gs activation by forming a plasma membrane complex with AKAP/SAP97. Isometric tension studies, Gs activity assays, immunoprecipitation studies and Western blots were performed by using porcine coronary arteries, primary cultured porcine coronary artery smooth muscle cells (PCASMCs) and HA‐tagged GPER gene stably transfected HEK293 cells (GPER‐HEK293). First, we measured the Gs activity in both GPER‐HEK293 cells and PCASMCs with selective GPER agonist G‐1 (1 μM); and observed that treatment with G‐1 significantly elevated the Gs‐GTP level. Next, we explored the association of GPER with Gs in immunoprecipitation studies of both GPER‐HEK293 cells and PCASMCs. Similar to Gs activity assays, activation of GPER with G‐1 promoted the association of activated GPER with Gs, and it was in a concentration dependent manner in PCASMCs. We further observed effects of GPER activation on cAMP production in PCASMCs and demonstrated that G‐1 significantly stimulated cAMP production. Last, we investigated the interaction of both Protein Kinase A‐anchoring Protein (AKAP5) and membrane‐associated guanylate kinase SAP97 to GPER by applying FMP‐API‐1 (100 μM) in isometric tension studies to disrupt the interaction between AKAPs and PKA, and detecting AKAP and SAP97 in immunoprecipitation studies in PCASMCs. Pretreatment with FMP‐API‐1 attenuated G‐1‐induced relaxation (10 – 3,000 nM) of endothelium‐denuded coronary arteries preconstricted with PGF2α (1 μM). In immunoprecipitation studies, G‐1 clearly enhanced the interaction of both AKAP5 and SAP97 to GPER. Therefore, we conclude that activation of GPER with G‐1 stimulates the production of cAMP, which is due to GPER coupling to Gs via forming a plasma membrane signaling complex with AKAP/SAP97.Support or Funding InformationAHA, Diversity of G Protein

G Protein-Coupled Estrogen Receptor 1 Regulates Human Neutrophil Functions

Background: The role of estrogens in immune functioning is relatively well known under both physiological and pathological conditions. Neutrophils are the most abundant circulating leukocytes in humans, and their abundance and function are regulated by estrogens, since they express estrogen receptors (ERs). Traditionally, estrogens were thought to act via classical nuclear ERs, namely ERα and ERβ. However, it was observed that some estrogens induced biological effects only minutes after their application. This rapid, “nongenomic” effect of estrogens is mediated by a membrane-anchored receptor called G protein-coupled estrogen receptor 1 (GPER1). Nevertheless, the expression and role of GPER1 in the immune system has not been exhaustively studied, and its relevance in neutrophil functions remains unknown. Methods: Human neutrophils were incubated in vitro with 10-100 µ<smlcap>M</smlcap> of the GPER1-specific agonist G1 alone or in combination with lipopolysaccharide. GPER1 expression and subcellular localization, respiratory burst, life span, gene expression profile, and cell signaling pathways involved were then analyzed in stimulated neutrophils. Results: Human neutrophils express a functional GPER1 which regulates their functions through cAMP/protein kinase A/cAMP response element-binding protein, p38 mitogen-activated protein kinase, and extracellular regulated MAPK signaling pathways. Thus, GPER1 activation in vitro increases the respiratory burst of neutrophils, extends their life span, and drastically alters their gene expression profile. Conclusions: Our results demonstrate that GPER1 activation promotes the polarization of human neutrophils towards a proinflammatory phenotype and point to GPER1 as a potential therapeutic target in immune diseases where neutrophils play a key role.

NHERF1 inhibits proliferation of triple-negative breast cancer cells by suppressing GPER signaling.

G protein-coupled estrogen receptor (GPER) signaling is activated in triple-negative breast cancer (TNBC); however, the detailed mechanisms of its regulation remain unclear. The present study aimed to elucidate the molecular mechanisms involved in GPER activation in TNBC. In MDA-MB-231 cells, a TNBC cell line, NHERF1 interaction with GPER was verified by co-immunoprecipitation and immunofluorescent staining assays. Overexpression of NHERF1 in MDA-MB-231 cells inhibited GPER-mediated proliferation and phosphorylation of ERK1/2 and Akt. Furthermore, NHERF1 expression levels were negatively correlated with the gene signatures of GPER activation, ERK1/2 and Akt signaling, and cell proliferation in early stage of TNBC tumors from the TCGA data set. Taken together, NHERF1 inhibited the activation of GPER-mediated signaling and suppressed the proliferation of triple-negative breast cancer cells. Loss of NHERF1 expression may play a pivotal role in the early stage of TNBC carcinogenesis.

The Androgen Receptor Promotes Cellular Proliferation by Suppression of G-Protein Coupled Estrogen Receptor Signaling in Triple-Negative Breast Cancer

Background/Aims: The targeted therapy for triple-negative breast cancer (TNBC) is still challenging due to poor understanding on its molecular etiology. The androgen receptor (AR) has recently emerged as a prognostic and treatment-predictive marker in breast cancer. However, the role of AR in TNBC remained elusive. Methods: Immunohistochemistry (IHC) was used to detect AR and G-protein coupled estrogen receptor (GPER) expression in tissue microarrays of 165 TNBC patients. Microarray analysis of mRNAs was performed to identify downstream regulators of AR. TNBC cells were cultured with dihydrotestosterone (DHT) alone or in combination with AR knockdown performed with AR shRNA. Cell viability and colony formation were assessed. Western blotting and qRT-PCR were used to examine protein and mRNA expression, respectively. The potential mechanism of AR-mediated GPER suppression was identified by Chromatin immunoprecipitation (ChIP) assay. AR and GPER expressions were also assessed in nude mouse xenografts by IHC. Results: IHC staining showed that the expression of AR was positively associated with tumor size, lymph node metastasis and high-grade tumor in TNBC patients. AR activation triggered by DHT suppressed GPER expression, to promote cell growth of TNBC. G-1, a GPER agonist, inhibited DHT-stimulated proliferation. Further experiments illustrated that AR suppressed GPER activation via binding directly to the promoter of GPER. Moreover, a negative correlation between AR and GPER was observed in MDA-MB-231 tumor cell xenografts and TNBC patient samples. Conclusions: The suppression of GPER via AR may be involved in the positive actions towards the TNBC progression, making it a promising therapeutic target for TNBC treatment.

Activation of GPER suppresses migration and angiogenesis of triple negative breast cancer via inhibition of NF-κB/IL-6 signals

Triple-negative breast cancer (TNBC) is characterized by high vascularity and frequent metastasis. Here, we found that activation of G protein-coupled estrogen receptor (GPER) by its specific agonist G-1 can significantly inhibit interleukin 6 (IL-6) and vascular endothelial growth factor A (VEGF-A). TNBC tissue microarrays from 100 TNBC patients revealed GPER is negatively associated with IL-6 levels and higher grade and stage. Activation of GPER or anti-IL-6 antibody can inhibit both in vitro tube formation of human umbilical vein endothelial cells (HUVECs) and migration of TNBC cells. While recombinant IL-6 supplementary can significantly reverse the inhibitory effects of G-1, suggesting the essential role of IL-6 in G-1 induced suppression of angiogenesis and invasiveness of TNBC cells. G-1 treatment decreased the phosphorylation, nuclear localization, transcriptional activities of NF-κB and suppressed its binding with IL-6 promoter. BAY11-7028, the inhibitor of NF-κB, can mimic the effect of G-1 to suppression of IL-6 and VEGF-A. While over expression of p65 can attenuate the inhibitory effects of G-1 on IL-6 and VEGF expression. The suppression of IL-6 by G-1 can further inhibit HIF-1α and STAT3 signals in TNBC cells by inhibition their expression, phosphorylation and/or nuclear localization. Moreover, G-1 also inhibited the in vivo NF-κB/IL-6 signals and angiogenesis and metastasis of MDA-MB-231 xenograft tumors. In conclusion, our study demonstrated that activation of GPER can suppress migration and angiogenesis of TNBC via inhibition of NF-κB/IL-6 signals, therefore it maybe act as an important target for TNBC treatment.

Activation of GPER ameliorates experimental pulmonary hypertension in male rats

RationalePulmonary hypertension (PH) is characterized by pulmonary vascular remodeling that leads to pulmonary congestion, uncompensated right-ventricle (RV) failure, and premature death. Preclinical studies have demonstrated that the G protein-coupled estrogen receptor (GPER) is cardioprotective in male rats and that its activation elicits vascular relaxation in rats of either sex. ObjectivesTo study the effects of GPER on the cardiopulmonary system by the administration of its selective agonist G1 in male rats with monocrotaline (MCT)-induced PH. MethodsRats received a single intraperitoneal injection of MCT (60mg/kg) for PH induction. Experimental groups were as follows: control, MCT+vehicle, and MCT+G1 (400μg/kg/daysubcutaneous). Animals (n=5pergroup) were treated with vehicle or G1 for 14days after disease onset. Measurements and Main ResultsActivation of GPER attenuated exercise intolerance and reduced RV overload in PH rats. Rats with PH exhibited echocardiographic alterations, such as reduced pulmonary flow, RV hypertrophy, and left-ventricle dysfunction, by the end of protocol. G1 treatment reversed these PH-related abnormalities of cardiopulmonary function and structure, in part by promoting pulmonary endothelial nitric oxide synthesis, Ca2+ handling regulation and reduction of inflammation in cardiomyocytes, and a decrease of collagen deposition by acting in pulmonary and cardiac fibroblasts. ConclusionsG1 was effective to reverse PH-induced RV dysfunction and exercise intolerance in male rats, a finding that have important implications for ongoing clinical evaluation of new cardioprotective and vasodilator drugs for the treatment of the disease.

Extent of Vascular Remodeling Is Dependent on the Balance Between Estrogen Receptor α and G-Protein-Coupled Estrogen Receptor.

Estrogens are important regulators of cardiovascular function. Some of estrogen's cardiovascular effects are mediated by a G-protein-coupled receptor mechanism, namely, G-protein-coupled estrogen receptor (GPER). Estradiol-mediated regulation of vascular cell programmed cell death reflects the balance of the opposing actions of GPER versus estrogen receptor α (ERα). However, the significance of these opposing actions on the regulation of vascular smooth muscle cell proliferation or migration in vitro is unclear, and the significance in vivo is unknown. To determine the effects of GPER activation in vitro, we studied rat aortic vascular smooth muscle cells maintained in primary culture. GPER was reintroduced using adenoviral gene transfer. Both estradiol and G1, a GPER agonist, inhibited both proliferation and cell migration effects that were blocked by the GPER antagonist, G15. To determine the importance of the GPER-ERα balance in regulating vascular remodeling in a rat model of carotid ligation, we studied the effects of upregulation of GPER expression versus downregulation of ERα. Reintroduction of GPER significantly attenuated the extent of medial hypertrophy and attenuated the extent of CD45 labeling. Downregulation of ERα expression comparably attenuated the extent of medial hypertrophy and inflammation after carotid ligation. These studies demonstrate that the balance between GPER and ERα regulates vascular remodeling. Receptor-specific modulation of estrogen's effects may be an important new approach in modifying vascular remodeling in both acute settings like vascular injury and perhaps in longer term regulation like in hypertension.

Relaxant Effects of the Selective Estrogen Receptor Modulator, Bazedoxifene, and Estrogen Receptor Agonists in Isolated Rabbit Basilar Artery.

We have previously shown that the selective estrogen receptor modulator, bazedoxifene, improves the consequences of ischemic stroke. Now we aimed to characterize the effects and mechanisms of action of bazedoxifene in cerebral arteries. Male rabbit isolated basilar arteries were used for isometric tension recording and quantitative polymerase chain reaction. Bazedoxifene relaxed cerebral arteries, as 17-β-estradiol, 4,4',4″-(4-propyl-[1H]-pyrazole-1,3,5-triyl)trisphenol [estrogen receptor (ER) α agonist], and G1 [G protein-coupled ER (GPER) agonist] did it (4,4',4″-(4-propyl-[1H]-pyrazole-1,3,5-triyl)trisphenol > bazedoxifene = G1 > 17-β-estradiol). 2,3-Bis(4-hydroxyphenyl)-propionitrile (ERβ agonist) had no effect. Expression profile of genes encoding for ERα (ESR1), ERβ (ESR2), and GPER was GPER > ESR1 > ESR2. As to the endothelial mechanisms, endothelium removal, N-nitro-L-arginine methyl ester, and indomethacin, did not modify the relaxant responses to bazedoxifene. As to the K channels, both a high-K medium and the Kv blocker, 4-aminopyridine, inhibited the bazedoxifene-induced relaxations, whereas tetraethylammonium (nonselective K channel blocker), glibenclamide (selective KATP blocker) or iberiotoxin (selective KCa blocker) were without effect. Bazedoxifene also inhibited both Ca- and Bay K8644-elicited contractions. Therefore, bazedoxifene induces endothelium-independent relaxations of cerebral arteries through (1) activation of GPER and ERα receptors; (2) increase of K conductance through Kv channels; and (3) inhibition of Ca entry through L-type Ca channels. Such a profile is compatible with the beneficial effects of estrogenic compounds (eg, SERMs) on vascular function and, specifically, that concerning the brain. Therefore, bazedoxifene could be useful in the treatment of cerebral disorders in which the cerebrovascular function is compromised (eg, stroke).

G protein-coupled estrogen receptor deficiency accelerates liver tumorigenesis by enhancing inflammation and fibrosis

G protein-coupled estrogen receptor (GPER) is a novel estrogen-binding receptor involved in many pathological conditions, including cancer. In this study, we investigated the effect of GPER on hepatocellular carcinoma (HCC). Our data show GPER knockout in a diethylnitrosamine (DEN)-induced mouse tumor model significantly accelerated liver tumorigenesis, accompanied by enhanced immune cell infiltration, fibrosis, and the production of inflammatory factors, such as interleukin-6 (IL-6). We further delineated the function of GPER in macrophages and hepatic stellate cells (HSCs). Treatment with the selective GPER agonist, G-1, decreased the expression of IL-6 in bone marrow-derived macrophages, which was abrogated upon deficiency of GPER. In a HSC line (LX2), G-1 treatment downregulated the expression of α-smooth muscle actin. In addition, both GPER mRNA and protein levels were significantly lower in HCC compared with matched non-tumor tissues. However, modulating GPER expression did not affect the viability and proliferation of hepatoma cells in vitro. Together our results indicate that GPER protects against HCC tumorigenesis through regulating inflammatory responses rather than directly acting on tumor cells. Therefore, GPER activation may be a potential strategy for prevention and treatment of HCC.

Abstract 115: Post-ischemic Estrogen Administration Protects the Myocardium Against Ischemia/Reperfusion Injury by Reducing Mitochondrial Protein Ubiquitination, Acetylation and Calpain10 Levels and Inhibition of the mPTP Opening via GPER1 Activation

Introduction: We recently found in isolated perfused hearts that acute pre-ischemic estrogen-induced cardioprotection against ischemia/reperfusion injury is mainly mediated via G protein-coupled estrogen receptor1 (GPER1) activation but not through classical estrogen receptors: alpha (ERα) and beta (ERβ). Hypothesis: We investigated whether acute post-ischemic estrogen (PI-E2) treatment can also induce cardioprotective effects via GPER1 activation in the intact animal subjected to ischemia/reperfusion injury. Methods: Male and ovariectomized female Sprague-Dawley rats were anesthetized with ketamine (80 mg/kg i.p.) and xylazine (8 mg/kg i.p.). Hearts were subjected to 35 min of the left anterior descending (LAD) artery occlusion, followed by 180 min reperfusion. An E2 bolus (50 mg/kg body weight) or PBS (same volume) was applied via the femoral vein 5 min before reperfusion and a GPER1 antagonist, G15, was given 10 min before E2. Area at risk (AAR) was identified using Evans Blue dye and myocardial infarct size assessed by TTC staining method. Mitochondria calcium retention capacity (CRC) required to induce mitochondrial permeability transition pore (mPTP) opening was assessed after 10 min reperfusion. Expression of ubiquitinated, acetylated, as well as calpains 1 and 10 proteins was measured by Western Blot in mitochondrial and cytosolic fractions. Results: We found that PI-E2 treatment reduced myocardial infarct size normalized to the AAR or the whole LV and improved mitochondrial CRC. PI-E2 treatment reduced mitochondrial protein acetylation, ubiquitination, and decreased calpain10 levels in mitochondrial but not in cytosolic fractions as compared to control, respectively. Interestingly, all these effects of E2 were abolished by addition of G15. Conclusion: Acute post-ischemic GPER1 activation by E2 induces cardioprotection against ischemia/reperfusion injury. PI-E2 effects through GPER1 involve the reduction of the levels of mitochondrial protein acetylation, ubiquitination, and calpain10. These PI-E2-GPER1 effects lead to inhibition of the mPTP opening.

Abstract 267: Activation of a Novel Estrogen Receptor Ameliorates Experimental Pulmonary Hypertension in Male Rats

Introduction: Pulmonary arterial hypertension (PAH) is characterized by pulmonary vascular remodeling that leads to uncompensated RV failure, and premature death. Preclinical studies have demonstrated that activation of the G protein-coupled estrogen receptor (GPER) is cardioprotective in male rats, and that a selective agonist G1, elicits vascular relaxation in rats of either sex. This work investigated the effects of G1 in male rats with monocrotaline (MCT)-induced PAH. Methods and Results: Male Wistar rats received a single intraperitoneal injection of MCT (60 mg/kg) for PAH induction. Experimental groups were: control, MCT + vehicle, and MCT + G1 (400 μg/kg/day s.c.). Animals were treated with vehicle or G1 for 14 days after the onset of disease (n = 5 per group). Treadmill test and transthoracic echocardiography were performed to access exercise capacity and cardiac function, respectively. RV systolic pressure (RVSP) and mean arterial pressure (MAP) were measured. Time to exhaustion in the treadmill (s) was reduced from 1042.0 ± 66.4 to 188.0 ± 53.1 (MCT + vehicle) and recovered to 809.4 ± 61.5 after G1 treatment. Pulmonary acceleration time (PAT) (ms) was reduced from 44.7 ± 1.4 to 24.7 ± 1.2 in MCT + vehicle group and restored to 41.8 ± 1.0 in MCT + G1 group. RVSP (mmHg) was increased from 24.6 ± 0.6 to 41.1 ± 1.4 (MCT + vehicle) and was reduced to 27.5 ± 0.7 (MCT + G1). MAP (mmHg) was reduced from 100.9 ± 1.1 to 77.1 ± 2.4 (MCT + vehicle), indicating HF induced by the RV dysfunction, and G1 normalized it to 92.4 ± 1.4. G1 decreased pulmonary vascular remodeling and normalized endothelial nitric oxide enzyme levels in lungs from PAH rats. PLB/SERCA2a ratio increased, as a sign of contractility dysfunction, in PAH rats and tumor necrosis factor alpha upregulation was significantly correlated with these Ca 2+ handling proteins impairment. Activation of GPER beneficially reduced PLB/SERCA2a ratio and TNF-α levels in RV tissue of MCT-induced PAH rats. Conclusions: G1 was effective to reverse PAH-induced RV dysfunction and exercise intolerance in male rats, a finding that may have important implications for ongoing clinical evaluation of new drugs for the treatment of the disease.

NHERF1, a novel GPER associated protein, increases stability and activation of GPER in ER-positive breast cancer.

G protein-coupled estrogen receptor (GPER) plays an important role in mediating the effects of estradiol. High levels of GPER have been implicated to associate with the malignant progress of invasive breast cancer (IBC). However, the mechanisms by which GPER protein levels were regulated remain unclear. In this study, PDZ protein Na+/H+ exchanger regulatory factor (NHERF1) was found to interact with GPER in breast cancer cells. This interaction was mediated by the PDZ2 domain of NHERF1 and the carboxyl terminal PDZ binding motif of GPER. NHERF1 was demonstrated to facilitate GPER expression at post-transcriptional level and improve GPER protein stability by inhibiting the receptor degradation via ubiquitin-proteasome pathway in a GPER/NHERF1 interaction-dependent manner. In addition, GPER protein levels are positively associated with NHERF1 protein levels in a panel of estrogen receptor (ER)-positive breast cancer cells. Furthermore, analysis of clinical IBC data from The Cancer Genome Atlas (TCGA) showed no significant difference in GPER mRNA levels between ER-positive IBC and normal breast tissues. However, gene set enrichment analysis (GSEA) showed that GPER signaling is ultra-activated in ER-positive IBC when compared with normal and its activation is positively associated with NHERF1 mRNA levels. Taken together, our findings identify NHERF1 as a new binding partner for GPER and its overexpression promotes protein stability and activation of GPER in ER-positive IBC. Our data indicate that regulation of GPER stability by NHERF1 may contribute to GPER-mediated carcinogenesis in ER-positive IBC.

G protein-coupled estrogen receptor enhances melanogenesis via cAMP-protein kinase (PKA) by upregulating microphthalmia-related transcription factor-tyrosinase in melanoma

ObjectiveThis study investigated the role and mechanism of action of G protein-coupled estrogen receptor (GPER) in melanogenesis. MethodsGPER expression was detected in the A375 human melanoma cell line and B16 mouse melanoma cell line. Cell proliferation, melanin content, tyrosinase (TYR) activity, cyclic adenosine monophosphate (cAMP) level, and TYR and microphthalmia-related transcription factor (MITF) expression were measured. GPER activation was altered by agonist and antagonist treatment and its expression was downregulated by gene silencing. Estradiol-induced melanin synthesis and the activation of related signaling pathways were suppressed by inhibiting GPER via antagonist treatment. The relationship between GPER and TYR was evaluated in clinical chloasma samples by immunohistochemistry. ResultsUpregulation of GPER in A375 cells promoted melanogenesis, favored as indicated by increases in TYR and MITF expression and TYR activity. GPER activated melanin production via the cAMP-protein kinase (PK) A pathway, suggesting that GPER plays an important role in estrogen-induced melanin synthesis. The effect of GPER activation on cAMP-MITF-TYR signaling was also demonstrated in B16 cells. A significant association was observed between GPER and TYR expression in chloasma skin lesions relative to normal skin. ConclusionGPER enhances melanin synthesis via cAMP-PKA-MITF-TYR signaling and modulates the effects of estrogen in melanogenesis. GPER is therefore a potential drug target for chloasma treatment.