Expression of G protein-coupled oestrogen receptor in melanoma and in pregnancy-associated melanoma

Advances in immune regulation of the G protein-coupled estrogen receptor

Estrogen and related receptors have been shown to have a significant impact on human development, reproduction, metabolism and immune regulation and to play a critical role in tumor development and treatment. Traditionally, the nuclear estrogen receptors (nERs) ERα and ERβ have been thought to be involved in mediating the estrogenic effects. However, our group and others have previously demonstrated that the G protein-coupled estrogen receptor (GPER) is the third independent ER, and estrogen signaling mediated by GPER is known to play an important role in normal physiology and a variety of abnormal diseases. Interestingly, recent studies have progressively revealed GPER involvement in the maintenance of the normal immune system, abnormal immune diseases, and inflammatory lesions, which may be of significant clinical value primarily in the immunotherapy of tumors. In this article, we review current advances in GPER-related immunomodulators and provide a theoretical basis and potential clinical targets to ameliorate immune-related diseases and immunotherapy for tumors.

A Narrative Review of the Role of Estrogen (Receptors) in Melanoma

In this narrative review, we attempt to provide an overview of the evidence regarding the role of estrogen (receptors) in cutaneous melanoma (CM). We reviewed 68 studies and 4 systematic reviews and meta-analyses published from 2002 up to and including 2022. The prevailing presence of estrogen receptor β (ERβ) instead of estrogen receptor α (ERα) in CM is notable, with ERβ potentially playing a protective role and being less frequently detected in progressive cases. While men with CM generally experience a less favorable prognosis, this distinction may become negligible with advancing age. The role of oral contraceptives (OC) and hormone replacement therapy (HRT) in CM remains controversial. However, recent studies tend to associate the use of these exogenous hormones with a heightened risk of CM, mostly only when using estrogen therapy and not in combination with progesterone. On the contrary, the majority of studies find no substantial influence of in vitro fertilization (IVF) treatment on CM risk. Reproductive factors, including younger age at first childbirth, higher parity, and shorter reproductive life, show conflicting evidence, with some studies suggesting a lower CM risk. We suggest an important role for estrogens in CM. More research is needed, but the integration of estrogens and targeting the estrogen receptors in melanoma therapy holds promise for future developments in the field.

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.

Analysis of human GPER expression in normal tissues and select cancers using immunohistochemistry

GPER (G protein-coupled estrogen receptor) has been reported to play roles in several areas of physiology including cancer, metabolic disorders, and cardiovascular disease. However, the understanding of where this receptor is expressed in human tissue is limited due to limited available tools and methodologies that can reliably detect GPER protein. Recently, a highly specific monoclonal antibody against GPER (20H15L21) was developed and is suitable for immunohistochemistry. Using this antibody, we show that GPER protein expression varies markedly between normal human tissue, and also among cancer tissue. As GPER is an emerging therapeutic target for cancer and other diseases, this new understanding of GPER distribution will likely be helpful in design and interpretation of ongoing and future GPER research.

Therapeutic Potential of Nitric Oxide‒Releasing Selective Estrogen Receptor Modulators in Malignant Melanoma

Malignant melanoma has a steadily increasing incidence, but treatment options are still limited, and the prognosis for patients, especially for men, is poor. To investigate whether targeting estrogen receptor (ER) signaling is a valid therapeutic approach, we retrospectively analyzed ER gene expression profiles in 448 patients with melanoma. High ERα gene (ESR1) expression was associated with improved overall survival (hazard ratio = 0.881; 95% confidence interval = 0.793-0.979; P = 0.018) and increased with tumor stage, whereas ERβ gene (ESR2) expression did not change with tumor progression. This seemingly protective function of ERα led us to speculate that specific targeting of ERβ has a therapeutic benefit in malignant melanoma. An ERβ-selective ER modulator with nitric oxide‒releasing moiety (nitric oxide‒releasing selective ER modulator 4d [NO-SERM 4d]) significantly reduced the prometastatic behavior of two melanoma cell lines (A2058 and MEL-JUSO). Epithelial‒mesenchymal transition in melanoma is consistent with a switch from E- to N-cadherin expression, mediating the invasive phenotype. NO-SERM 4d reduced N-cadherin expression and impaired spheroid formation in A2058 cells. In addition, the growth of A2058 spheroids was significantly reduced, confirming the antitumorigenic potential of NO-SERM 4d. Targeting ERβ signaling combined with targeted nitric oxide release represents a promising therapeutic approach in malignant melanoma that has the potential to prevent metastatic spread and reduce tumor growth.

G-Protein-Coupled Estrogen Receptor Expression in Rat Uterine Artery Is Increased by Pregnancy and Induces Dilation in a Ca2+ and ERK1/2 Dependent Manner

Increasing levels of estrogens across gestation are partly responsible for the physiological adaptations of the maternal vasculature to pregnancy. The G protein-coupled estrogen receptor (GPER) mediates acute vasorelaxing effects in the uterine vasculature, which may contribute to the regulation of uteroplacental blood flow. The aim of this study was to investigate whether GPER expression and vasorelaxation may occur following pregnancy. Elucidation of the functional signalling involved was also investigated. Radial uterine and third-order mesenteric arteries were isolated from non-pregnant (NP) and pregnant rats (P). GPER mRNA levels were determined and—concentration–response curve to the GPER-specific agonist, G1 (10−10–10−6 M), was assessed in arteries pre-constricted with phenylephrine. In uterine arteries, GPER mRNA expression was significantly increased and vasorelaxation to G1 was significantly enhanced in P compared with NP rats. Meanwhile, in mesenteric arteries, there was a similar order of magnitude in NP and P rats. Inhibition of L-type calcium channels and extracellular signal-regulated kinases 1/2 significantly reduced vasorelaxation triggered by G1 in uterine arteries. Increased GPER expression and GPER-mediated vasorelaxation are associated with the advancement of gestation in uterine arteries. The modulation of GPER is exclusive to uterine arteries, thus suggesting a physiological contribution of GPER toward the regulation of uteroplacental blood flow during pregnancy.

Role of estrogen receptors in health and disease

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

Molecular Proof of a Clinical Concept: Expression of Estrogen Alpha-, Beta-Receptors and G Protein-Coupled Estrogen Receptor 1 (GPER) in Histologically Assessed Common Nevi, Dysplastic Nevi and Melanomas

Background and Objectives: Epidemiologic data show significant differences in melanoma incidence and outcomes between sexes. The role of hormonal receptors in the pathogenesis of melanocytic lesions remains unclear, thus we performed this study aiming to assess estrogen receptors expression in different melanocytic lesions. Materials and Methods: We performed a cross-sectional study that included 73 consecutively excised melanocytic lesions. Estrogen receptor alpha (ERα), beta (ERβ), and G-protein coupled estrogen receptor (GPER) expression was analyzed in melanocytes and keratinocytes of common nevi, dysplastic nevi, melanoma, healthy skin margin, and in sebaceous and sweat gland cells. Results: ERβ expression was higher in dysplastic nevi margin melanocytes compared to common nevi (p = 0.046) and in dysplastic nevi keratinocytes compared to melanoma keratinocytes (p = 0.021). ERβ expression was significantly higher in margin melanocytes compared to melanoma melanocytes (p = 0.009). No difference in ERβ expression was shown between melanocytes of three types of lesions. GPER expression was higher in nuclei and cytoplasm of dysplastic nevi (p = 0.02 and p = 0.036 respectively) and at the margin compared to melanoma. GPER expression was lower in sebaceous glands of tissue surrounding common nevi (p = 0.025) compared to dysplastic nevi. GPER expression was higher in skin margin tissue melanocytes (p = 0.016 nuclear, p = 0.029 cytoplasmic) compared to melanoma melanocytes. There were no differences in ERα expression between the melanocytic lesions. Conclusion: Further large-scale studies are warranted to investigate the potential role of ERβ and GPER in the pathogenesis of melanocytic lesions.

Environmental Estrogens and Their Biological Effects through GPER Mediated Signal Pathways

Many environmental chemicals have been found to exert estrogenic effects in cells and experimental animals by activating nuclear receptors such as estrogen receptors and estrogen-related receptors. These compounds include bisphenols, pesticides, polybrominated diphenyl ethers (PBDEs), organophosphate flame retardants, phthalates and metalloestrogens. G protein-coupled estrogen receptor (GPER) exists widely in numerous cells/tissues of human and other vertebrates. A number of studies have demonstrated that GPER plays a vital role in mediating the estrogenic effects of environmental pollutants. Even at very low concentrations, these chemicals may activate GPER pathways, thus affect many aspects of cellular functions including proliferation, metastasis and apoptosis, resulting in cancer progression, cardiovascular disorders, and reproductive dysfunction. This review summarized the environmental occurrence and human exposure levels of these pollutants, and integrated current experimental evidence toward revealing the underlying mechanisms of pollutant-induced cellular dysfunction via GPER. The GPER mediated rapid non-genomic actions play an important role in the process leading to the adverse effects observed in experimental animals and even in human beings.

Sex and Gender Disparities in Melanoma

Worldwide, the total incidence of cutaneous melanoma is higher in men than in women, with some differences related to ethnicity and age and, above all, sex and gender. Differences exist in respect to the anatomic localization of melanoma, in that it is more frequent on the trunk in men and on the lower limbs in women. A debated issue is if-and to what extent-melanoma development can be attributed to gender-specific behaviors or to biologically intrinsic differences. In the search for factors responsible for the divergences, a pivotal role of sex hormones has been observed, although conflicting results indicate the involvement of other mechanisms. The presence on the X chromosome of numerous miRNAs and coding genes playing immunological roles represents another important factor, whose relevance can be even increased by the incomplete X chromosome random inactivation. Considering the known advantages of the female immune system, a different cancer immune surveillance efficacy was suggested to explain some sex disparities. Indeed, the complexity of this picture emerged when the recently developed immunotherapies unexpectedly showed better improvements in men than in women. Altogether, these data support the necessity of further studies, which consider enrolling a balanced number of men and women in clinical trials to better understand the differences and obtain actual gender-equitable healthcare.

Estrogen Receptors and Melanoma: A Review

In the last three decades cutaneous melanoma has been widely investigated as a steroid hormone-sensitive cancer. Following this hypothesis, many epidemiological studies have investigated the relationship between estrogens and melanoma. No evidence to date has supported this association due to the great complexity of genetic, external and environmental factors underlying the development of this cancer. Molecular mechanisms through which estrogen and their receptor exert a role in melanoma genesis are still under investigation with new studies increasingly focusing on the discovery of new molecular targets for therapeutic treatments.

Downregulation of G Protein-Coupled Estrogen Receptor (GPER) is Associated with Reduced Prognosis in Patients with Gastric Cancer

BACKGROUND This study is aimed to investigate the prognostic significance of the expression of G protein-coupled estrogen receptor (GPER) in gastric cancer tissue using bioinformatics data and immunohistochemistry. MATERIAL AND METHODS Expression of GPER mRNA in gastric cancer tissues and normal adjacent tissues was investigated using data from The Cancer Genome Atlas (TCGA), the Gene Expression Omnibus (GEO), and Oncomine database. Kaplan-Meier Plotter identified the association between GPER mRNA and prognosis. Correlation between GPER mRNA and DNA methylation used the cBioPortal for Cancer Genomics and the MethHC website. Genes co-expressed with GPER were identified from The Cancer Genome Atlas Stomach Adenocarcinoma (TCGA-STAD) underwent FunRich analysis. Immunohistochemistry and Western blot evaluated GPER protein expression in tissue microarrays (TMAs) and gastric cancer cell lines. RESULTS GPER mRNA and protein levels were significantly lower in gastric cancer tissue and cells lined when compared with normal tissues and cells. The results from GSE15459 showed that patients with low levels of GPER mRNA had a reduced overall survival (OS) (P=0.013) and disease-free survival (DFS) (P=0.019). A negative correlation (r=-0.611) between GPER mRNA and DNA methylation was found using the cBioPortal and MethHC. Co-expressed epithelial-mesenchymal transformation (EMT) genes were enriched with GPER (P<0.0001). Cox regression analysis showed that GPER protein expression was an independent prognostic factor (P=0.035) CONCLUSIONS Downregulation of GPER predicts poor prognosis in gastric cancer. GPER may act as a tumor suppressor through the regulation of EMT in gastric cancer.

Activation of G protein-coupled estrogen receptor signaling inhibits melanoma and improves response to immune checkpoint blockade

Female sex and history of prior pregnancies are associated with favorable melanoma outcomes. Here, we show that much of the melanoma protective effect likely results from estrogen signaling through the G protein-coupled estrogen receptor (GPER) on melanocytes. Selective GPER activation in primary melanocytes and melanoma cells induced long-term changes that maintained a more differentiated cell state as defined by increased expression of well-established melanocyte differentiation antigens, increased pigment production, decreased proliferative capacity, and decreased expression of the oncodriver and stem cell marker c-Myc. GPER signaling also rendered melanoma cells more vulnerable to immunotherapy. Systemically delivered GPER agonist was well tolerated, and cooperated with immune checkpoint blockade in melanoma-bearing mice to dramatically extend survival, with up to half of mice clearing their tumor. Complete responses were associated with immune memory that protected against tumor rechallenge. GPER may be a useful, pharmacologically accessible target for melanoma.