G15, a GPR30 antagonist, induces apoptosis and autophagy in human oral squamous carcinoma cells

The Role of Estrogen and Estrogen Receptors in Head and Neck Tumors

Head and neck squamous cell carcinoma (HNSCC) is the most common histological form of head and neck tumors (HNTs), which originate from the epithelium of the lips and oral cavity, pharynx, larynx, salivary glands, nasal cavity, and sinuses. The main risk factors include consumption of tobacco in all forms and alcohol, as well as infections with high-risk human papillomaviruses or the Epstein-Barr virus. Regardless of the etiological agent, the risk of developing different types of HNTs is from two to more than six times higher in males than in females. The reason for such disparities probably lies in a combination of both biological and psychosocial factors. Therefore, it is hypothesized that exposure to female sex hormones, primarily estrogen, provides women with protection against the formation and metastasis of HNTs. In this review, we synthesized available knowledge on the role of estrogen and estrogen receptors (ERs) in the development and progression of HNTs, with special emphasis on membrane ERs, which are much less studied. We can summarize that in addition to epidemiologic studies unequivocally pointing to the protective effect of estrogen in women, an increased expression of both nuclear ERs, ERα, and ERβ, and membrane ERs, ERα36, GPER1, and NaV1.2, was present in different types of HNSCC, for which anti-estrogens could be used as an effective therapeutic approach.

Oestrogen receptor-independent actions of oestrogen in cancer

Oestrogen, the primary female sex hormone, plays a significant role in tumourigenesis. The major pathway for oestrogen is via binding to its receptor [oestrogen receptor (ERα or β)], followed by nuclear translocation and transcriptional regulation of target genes. Almost 70% of breast tumours are ER + , and endocrine therapies with selective ER modulators (tamoxifen) have been successfully applied. As many as 25% of tamoxifen-treated patients experience disease relapse within 5 years upon completion of chemotherapy. In such cases, the ER-independent oestrogen actions provide a plausible explanation for the resistance, as well as expands the existing horizon of available drug targets. ER-independent oestrogen signalling occurs via one of the following pathways: signalling through membrane receptors, oxidative catabolism giving rise to genotoxic metabolites, effects on mitochondria and redox balance, and induction of inflammatory cytokines. The current review focuses on the non-classical oestrogen signalling, its role in cancer, and its clinical significance.

Activation of G-Protein-Coupled Estrogen Receptor 1 (GPER1) Reduces Progression of Vulvar Carcinoma Cells

Whether G protein-coupled estrogen receptor 1 (GPER1) is tumor-promoting or tumor-suppressive depends in part on tumor entity. Little is known about the function of GPER1 in vulvar carcinoma. In this work, we aim to clarify what role GPER1 plays in vulvar cancer, tumor-promoting or tumor-suppressive. Localization of GPER1 in A431 and CAL-39 vulvar carcinoma cells was examined by immunofluorescence. Using a tissue microarray of vulvar neoplasias, the correlation between GPER1 expression and grade of malignancy was investigated. A431 and CAL-39 cells were treated either with GPER1 agonist G1 or antagonist G36. Proliferation was quantified by BrdU assay and viability examined using Resazurin assay. Morphological changes were analyzed by microscopy and measured using ImageJ. Cell migration was analyzed by gap closure assay. Clonogenic potential was tested by colony and sphere formation. Expression of estrogen receptors was examined by Western blot. GPER1 was found consistently expressed in vulvar neoplasia tissues. The immune-reactive score was found to be significantly higher in tissue samples of lymph node metastases and neoplasias with grade 3. In A431 and CAL-39 vulvar carcinoma cells, GPER1 expression was mainly found in the cytoplasm and nuclei. Treatment of A431 and CAL-39 cells with GPER1 agonist G1 resulted in a decrease in proliferation and migration. In addition, colony formation and tumor sphere formation were reduced. Furthermore, morphological signs of necrosis and reduction in cell viability after G1 treatment were observed. The GPER1 antagonist G36 did not have significant effects on vulvar carcinoma cells. Neither agonist G1 nor antagonist G36 treatment resulted in altered expression of estrogen receptors. Activation of GPER1 with GPER1 agonist G1 reduces the tumorigenic potential of the vulvar carcinoma cells. It can be deduced from this that GPER1 appears to have a tumor-suppressive effect in vulvar carcinoma.

Environmental-relevant bisphenol A exposure promotes ovarian cancer stemness by regulating microRNA biogenesis

Bisphenol A (BPA) is a ubiquitous environmental xenobiotic impacting millions of people worldwide. BPA has long been proposed to promote ovarian carcinogenesis, but the detrimental mechanistic target remains unclear. Cancer stem cells (CSCs) are considered as the trigger of tumour initiation and progression. Here, we show for the first time that nanomolar (environmentally relevant) concentration of BPA can markedly increase the formation and expansion of ovarian CSCs concomitant. This effect is observed in both oestrogen receptor (ER)-positive and ER-defective ovarian cancer cells, suggesting that is independent of the classical ERs. Rather, the signal is mediated through alternative ER G-protein-coupled receptor 30 (GPR30), but not oestrogen-related receptor α and γ. Moreover, we report a novel role of BPA in the regulation of Exportin-5 that led to dysregulation of microRNA biogenesis through miR-21. The use of GPR30 siRNA or antagonist to inhibit GPR30 expression or activity, respectively, resulted in significant inhibition of ovarian CSCs. Similarly, the CSCs phenotype can be reversed by expression of Exportin-5 siRNA. These results identify for the first time non-classical ER and microRNA dysregulation as novel mediators of low, physiological levels of BPA function in CSCs that may underlie its significant tumour-promoting properties in ovarian cancer.

Inhibition of GPR30 sensitized gefitinib to NSCLC cells via regulation of epithelial-mesenchymal transition

Introduction: G-protein coupled receptor 30 (GPR30) is associated with cell metastasis and drug resistance in many different cancer cells. The present study aimed to reveal the sensitivity of GPR30 to gefitinib in non-small cell lung cancer (NSCLC) cells.Methods: Cell viability and proliferation were detected using cell counting kit 8 and 5-ethynyl-2'-deoxyuridine assays, respectively. Western blotting and quantitative real-time reverse transcription PCR were used to detect GPR30 or epithelial-mesenchyme transition (EMT)-related mRNA and protein expression.Results: The results showed that GPR30 expression is associated with gefitinib sensitivity. G15, as a GPR30 antagonist, reduced GPR30 expression. We chose the maximum concentration of G15 with minimal cytotoxicity to detect cell viability after combined treatment with gefitinib in NSCLC cells, which indicated that G15 could increase sensitivity to gefitinib. However, the effect of G15 on gefitinib sensitivity disappeared after treatment with a small interfering RNA targeting GPR30. Further research showed that G15 or GPR30 siRNA treatment could upregulate E-cadherin and downregulate vimentin levels.Conclusion: Taken together, these data suggested that G15 could enhance NSCLC sensitivity to gefitinib by inhibition of GPR30 and EMT.

G protein-coupled receptor 30 mediates cell proliferation of goat mammary epithelial cells via MEK/ERK&PI3K/AKT signaling pathway

The mammary gland of mammals possesses the specific function of synthesizing, secreting, and delivering milk. Notably, mammary epithelial cells are considered to be central to control the expansion and remodeling of mammary gland into a milk-secretory organ. And the biological function of mammary gland is mainly regulated by the endocrine system, especially for estrogen. G protein-coupled receptor 30 (GPR30), an estrogen membrane receptor, mediates estrogen-induced functions of physiology and pathophysiology. However, the relationship between estrogen/GPR30 signaling and proliferation of goat mammary epithelial cells (gMECs) is still unclear. Herein, estrogen promoted cell proliferation than control, as evidence by upregulation of cell numbers, BrdU-positive cell counts, and cell viability. Of note, these activities were all obviously reduced by treatment with GPR30 antagonist G15, yet GPR30 agonist G1 increased cell proliferation than control. Further, GPR30 silencing inhibited cell proliferation than negative control. This inhibition was accompanied by a G2/M phase arrest and downregulation of cell cycle regulators. Meanwhile, estrogen increased the phosphorylation of ERK1/2 and AKT. Further, the protein level of p-ERK1/2 and p-AKT was enhanced by GPR30 agonist G1 but inhibited by GPR30 antagonist G15 and GPR30 silencing. Importantly, MEK inhibitor and PI3K inhibitor decreased the expression of cell cycle regulators, and repressed estrogen-induced and G1-driven promotion of cell proliferation, suggesting that estrogen regulated cell proliferation of gMECs through mechanisms involving cell cycle, dependent of GPR30 and MEK/ERK and PI3K/AKT signaling pathway. This may provide a strong theoretical basis for researching estrogen sustained-release drugs promoting breast development and improving lactation performance.Abbreviations: gMECs, goat mammary epithelial cells; E2, 17β-estradiol; GPR30, G protein-coupled receptor 30; shRNA, small hairpin RNA; CDK, cyclin-dependent kinase; PI3K, phosphatidylinositol 3-kinase; AKT, proteinkinase B; MAPK, mitogen-activated protein kinase; MEK, mitogen-activated protein kinase kinase; ERK1/2, extracellular signal-regulated kinase 1/2.

The G-Protein–Coupled Estrogen Receptor Agonist G-1 Inhibits Proliferation and Causes Apoptosis in Leukemia Cell Lines of T Lineage

The G-protein–coupled estrogen receptor (GPER) mediates non-genomic action of estrogen. Due to its differential expression in some tumors as compared to the original healthy tissues, the GPER has been proposed as a therapeutic target. Accordingly, the non-steroidal GPER agonist G-1, which has often demonstrated marked cytotoxicity in experimental models, has been suggested as a novel anticancer agent for several sensitive tumors. We recently revealed that cell lines derived from acute T-cell (query) lymphoblastic leukemia (T-ALL) express the GPER. Here, we address the question whether G-1 is cytotoxic to T-ALL. We have shown that G-1 causes an early rise of intracellular Ca²⁺, arrests the cell cycle in G2/M, reduces viability, and provokes apoptosis in T-ALL cell lines. Importantly, G-1 caused destabilization and depolymerization of microtubules. We assume that it is a disturbance of the cytoskeleton that causes G-1 cytotoxic and cytostatic effects in our model. The observed cytotoxic effects, apparently, were not triggered by the interaction of G-1 with the GPER as pre-incubation with the highly selective GPER antagonist G-36 was ineffective in preventing the cytotoxicity of G-1. However, G-36 prevented the intracellular Ca²⁺ rise provoked by G-1. Finally, G-1 showed only a moderate negative effect on the activation of non-leukemic CD4⁺ lymphocytes. We suggest G-1 as a potential antileukemic drug.

Berberine Inhibits MDA-MB-231 Cells as an Agonist of G Protein-Coupled Estrogen Receptor 1

G protein-coupled estrogen receptor 1 (GPER1) is a potential therapeutic target for treating triple-negative breast cancers (TNBC). However, modulators for GPER1 that can be used to treat TNBC have not appeared. Berberine (BBR) is a bioactive isoquinoline alkaloid with high oral safety. In recent years, BBR has shown an inhibitory effect on TNBC tumors such as MDA-MB-231, but the molecular target remains unclear, which hinders related clinical research. Our work proved that BBR is a modulator of GPER1 that can inhibit cell viability, migration, and autophagy of MDA-MB-231 cells. The inhibitory effect of BBR on MDA-MB-231 cells has a dependence on estrogen levels. Although BBR promoted the proteasome, which is a major factor in the degradation of GPER1, it could still induce the protein level of GPER1. Correspondingly, the transcription of cellular communication network factor 2 (CCN2) was promoted. BBR could bind to GPER1 directly and change the secondary structure of GPER1, as in the case of 17β-estradiol (E2). In addition, BBR induced not only a high degree of co-localization of GPER1 and microtubule-associated protein 1 light chain 3 (MAP1LC3), but also the accumulation of sequestosome 1 (SQSTM1/p62) by the inhibition of the nuclear translocation of the nuclear factor-kappa B (NF-κB) subunit (RELA/p65), which indicates NF-κB inhibition and anti-cancer effects. This result proved that the promotional effect of BBR on the GPER1/NF-κB pathway was closely related to its inhibitory effect on autophagy, which may serve as a new mechanism by which to explain the inhibitory effect of BBR on MDA-MB-231 cells and expand our understanding of the function of both BBR and GPER1.

HPTE-Induced Embryonic Thymocyte Death and Alteration of Differentiation Is Not Rescued by ERα or GPER Inhibition but Is Exacerbated by Concurrent TCR Signaling

Organochlorine pesticides, such as DDT, methoxychlor, and their metabolites, have been characterized as endocrine disrupting chemicals (EDCs); suggesting that their modes of action involve interaction with or abrogation of endogenous endocrine function. This study examined whether embryonic thymocyte death and alteration of differentiation induced by the primary metabolite of methoxychlor, HPTE, rely upon estrogen receptor binding and concurrent T cell receptor signaling. Estrogen receptor inhibition of ERα or GPER did not rescue embryonic thymocyte death induced by HPTE or the model estrogen diethylstilbestrol (DES). Moreover, adverse effects induced by HPTE or DES were worsened by concurrent TCR and CD2 differentiation signaling, compared with EDC exposure post-signaling. Together, these data suggest that HPTE- and DES-induced adverse effects on embryonic thymocytes do not rely solely on ER alpha or GPER but may require both. These results also provide evidence of a potential collaborative signaling mechanism between TCR and estrogen receptors to mediate adverse effects on embryonic thymocytes, as well as highlight a window of sensitivity that modulates EDC exposure severity.

Novel Autophagy-Related Gene Signature Investigation for Patients With Oral Squamous Cell Carcinoma

The correlation between autophagy defects and oral squamous cell carcinoma (OSCC) has been previously studied, but only based on a limited number of autophagy-related genes in cell lines or animal models. The aim of the present study was to analyze differentially expressed autophagy-related genes through The Cancer Genome Atlas (TCGA) database to explore enriched pathways and potential biological function. Based on TCGA database, a signature composed of four autophagy-related genes (CDKN2A, NKX2-3, NRG3, and FADD) was established by using multivariate Cox regression models and two Gene Expression Omnibus datasets were applied for external validation. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analyses were performed to study the function of autophagy-related genes and their pathways. The most significant GO and KEGG pathways were enriched in several key pathways that were related to the progression of autophagy and OSCC. Furthermore, a prognostic risk score was constructed based on the four genes; patients were then divided into two groups (i.e., high risk and low risk) in terms of the median of risk score. Prognosis of the two groups and results showed that patients at the low-risk group had a much better prognosis than those at the high-risk group, regardless of whether they were in the training datasets or validation datasets. Multivariate Cox regression results indicated that the risk score of the autophagy-related gene signatures could greatly predict the prognosis of patients after controlling for several clinical covariates. The findings of the present study revealed that autophagy-related gene signatures play an important role in OSCC and are potential prognostic biomarkers and therapeutic targets.

G Protein-Coupled Estrogen Receptor Mediates Cell Proliferation through the cAMP/PKA/CREB Pathway in Murine Bone Marrow Mesenchymal Stem Cells

Estrogen is an important hormone to regulate skeletal physiology via estrogen receptors. The traditional estrogen receptors are ascribed to two nuclear estrogen receptors (ERs), ERα and ERβ. Moreover, G protein-coupled estrogen receptor-1 (GPER-1) was reported as a membrane receptor for estrogen in recent years. However, whether GPER-1 regulated osteogenic cell biology on skeletal system is still unclear. GPER-1 is expressed in growth plate abundantly before puberty but decreased abruptly since the very late stage of puberty in humans. It indicates GPER-1 might play an important role in skeletal growth regulation. GPER-1 expression has been confirmed in osteoblasts, osteocytes and chondrocytes, but its expression in mesenchymal stem cells (MSCs) has not been confirmed. In this study, we hypothesized that GPER-1 is expressed in bone MSCs (BMSC) and enhances BMSC proliferation. The cultured tibiae of neonatal rat and murine BMSCs were tested in our study. GPER-1-specific agonist (G-1) and antagonist (G-15), and GPER-1 siRNA (siGPER-1) were used to evaluate the downstream signaling pathway and cell proliferation. Our results revealed BrdU-positive cell counts were higher in cultured tibiae in the G-1 group. The G-1 also enhanced the cell viability and proliferation, whereas G-15 and siGPER-1 reduced these activities. The cAMP and phosphorylation of CREB were enhanced by G-1 but inhibited by G-15. We further demonstrated that GPER-1 mediates BMSC proliferation via the cAMP/PKA/p-CREB pathway and subsequently upregulates cell cycle regulators, cyclin D1/cyclin-dependent kinase (CDK) 6 and cyclin E1/CDK2 complex. The present study is the first to report that GPER-1 mediates BMSC proliferation. This finding indicates that GPER-1 mediated signaling positively regulates BMSC proliferation and may provide novel insights into addressing estrogen-mediated bone development.

Effects of ICI 182,780, an ERα and ERβ antagonist, and G-1, a GPER agonist, on autophagy in breast cancer cells

Objective

To investigate if ICI 182,780 (fulvestrant), a selective estrogen receptor alpha/beta (ERα/ERβ) antagonist, and G-1, a selective G-protein-coupled receptor (GPER) agonist, can potentially induce autophagy in breast cancer cell lines MCF-7 and SKBr3, and how G-1 affects cell viability.

Methods

Cell viability in MCF-7 and SKBr3 cells was assessed by the MTT assay. To investigate the autophagy flux, MCF-7 cells were transfected with GFP-LC3, a marker of autophagosomes, and analyzed by real-time fluorescence microscopy. MCF-7 and SKBr3 cells were incubated with acridine orange for staining of acidic vesicular organelles and analyzed by flow cytometry as an indicator of autophagy.

Results

Regarding cell viability in MCF-7 cells, ICI 182,780 and rapamycin, after 48 hours, led to decreased cell proliferation whereas G-1 did not change viability over the same period. The data showed that neither ICI 182,780 nor G-1 led to increased GFP-LC3 puncta in MCF-7 cells over the 4-hour observation period. The cytometry assay showed that ICI 182,780 led to a higher number of acidic vesicular organelles in MCF-7 cells. G-1, in turn, did not have this effect in any of the cell lines. In contrast, ICI 182,780 and G-1 did not decrease cell viability of SKBr3 cells or induce formation of acidic vesicular organelles, which corresponds to the final step of the autophagy process in this cell line.

Conclusion

The effect of ICI 182,780 on increasing acidic vesicular organelles in estrogen receptor-positive breast cancer cells appears to be associated with its inhibitory effect on estrogen receptors, and GPER does notseem to be involved. Understanding these mechanisms may guide further investigations of these receptors’ involvement in cellular processes of breast cancer resistance.

G Protein-Coupled Receptor 30 Mediates the Anticancer Effects Induced by Eicosapentaenoic Acid in Ovarian Cancer Cells

Purpose

While numerous epidemiological studies have indicated that omega-3 polyunsaturated fatty acids have anticancer properties in various cancers, the effects and mechanisms of eicosapentaenoic acid (EPA) in ovarian cancer cell growth are poorly understood.

Materials and Methods

ES2 ovarian clear cell carcinoma cells and SKOV3 adenocarcinoma cells were treated with palmitic acid or EPA, followed by flow cytometry and cell counting to measure apoptosis and proliferation, respectively. A modified protein lipid overlay assay was used to further verify whether EPA was a ligand of G protein–coupled receptor 30 (GPR30) in ES2 cells. The levels of apoptosis-related genes, phosphorylated AKT, and phosphorylated ERK1/2 were detected to explore the underlying mechanism. Finally, inhibitory effect of EPA on tumor growth via GPR30 was determined in vitro and in vivo.

Results

EPA suppressed ES2 ovarian clear cell carcinoma cells growth via GPR30, a novel EPA receptor, by inducing apoptosis. As a ligand of GPR30, EPA activated the GPR30-cAMP–protein kinase A signaling pathway. When GPR30 was suppressed by siRNA or its inhibitor G15, the antiproliferative action of EPA was impaired. Furthermore, EPA inhibited tumor growth by blocking the activation of AKT and ERK. In the mouse xenograft model, EPA decreased tumor volume and weight through GPR30 by blocking tumor cell proliferation.

Conclusion

These results confirm that EPA is a tumor suppressor in human ovarian clear cell carcinoma cells and functions through a novel fatty acid receptor, GPR30, indicating a mechanistic linkage between omega-3 fatty acids and cancers.

Autophagy modulators for the treatment of oral and esophageal squamous cell carcinomas

Oral squamous cell carcinomas (OSCC) and esophageal squamous cell carcinomas (ESCC) exhibit a survival rate of less than 60% and 40%, respectively. Late-stage diagnosis and lack of effective treatment strategies make both OSCC and ESCC a significant health burden. Autophagy, a lysosome-dependent catabolic process, involves the degradation of intracellular components to maintain cell homeostasis. Targeting autophagy has been highlighted as a feasible therapeutic strategy with clinical utility in cancer treatment, although its associated regulatory mechanisms remain elusive. The detection of relevant biomarkers in biological fluids has been anticipated to facilitate early diagnosis and/or prognosis for these tumors. In this context, recent studies have indicated the presence of specific proteins and small RNAs, detectable in circulating plasma and serum, as biomarkers. Interestingly, the interplay between biomarkers (eg, exosomal microRNAs) and autophagic processes could be exploited in the quest for targeted and more effective therapies for OSCC and ESCC. In this review, we give an overview of the available biomarkers and innovative targeted therapeutic strategies, including the application of autophagy modulators in OSCC and ESCC. Additionally, we provide a viewpoint on the state of the art and on future therapeutic perspectives combining the early detection of relevant biomarkers with drug discovery for the treatment of OSCC and ESCC.

Estrogen receptor subtype agonist activation in human cutaneous squamous cell carcinoma cells modulates expression of CD55 and Cyclin D1

Clinical studies indicate gender bias in cutaneous squamous cell carcinoma (cSCC) incidence with worse prognosis observed in males than in females, suggesting estrogen-mediated protection. In contrast, recent clinical population studies show risk of cSCC by use of oral contraceptives, thus raising controversy. However, animal studies indicate a protective role of estrogen and estrogen receptor (ER)s in cSCC. Currently we have a poor understanding of ERs that are expressed in human cSCC cells and their possible role in malignant transformation. The focus of current study was to determine ER subtype specific expression on cSCC A431 cells and investigate if ER agonist based activation modulates tumor markers CD55 and Cyclin D1 in the cells. ERα, ERβ and G protein-coupled receptor (GPR30) subtype expression at mRNA and protein level was determined in human cSCC A431 cells by reverse transcription-quantitative polymerase chain reaction (RT-qPCR) and Western blotting, respectively. The localization of ER subtypes was determined by confocal microscopy. ER subtype agonist based activation on A431 cells was performed to investigate their role in modulating mRNA and protein expression of tumor markers CD55 and Cyclin D1. A431 cells differentially expressed all three ER subtypes- ERα, ERβ and GPR30 with GPR30 expression being the highest. Confocal studies confirmed that all three ER subtypes were expressed in the cytoplasm and ERα and ERβ lacked nuclear expression. Agonist based activation of both ERα and GPR30 significantly upregulated Cyclin D1 and CD55 expression. Blocking of GPR30 led to significantly downregulation of both Cyclin D1 and CD55 expression. In contrast to ERα and GPR30, ERβ activation significantly downregulated CD55 expression. Taken together, here we demonstrate for the first time that all three ERs- ERα, ERβ and GPR30 are expressed in human A431 cSCC cells and further ER agonist based activation modulates the expression of tumor markers CD55 and Cyclin D1.

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.

Targeting GPER1 to suppress autophagy as a male-specific therapeutic strategy for iron-induced striatal injury

The functional outcome of intracerebral hemorrhage (ICH) in young male patients are poor than in premenopausal women. After ICH, ferrous iron accumulation causes a higher level of oxidative injury associated with autophagic cell death in striatum of male mice than in females. In rodent model of ferrous citrate (FC)-infusion that simulates iron accumulation after ICH, female endogenous estradiol (E₂) suppresses autophagy via estrogen receptor α (ERα) and contributes to less injury severity. Moreover, E₂ implantation diminished the FC-induced autophagic cell death and injury in males, whose ERα in the striatum is less than females. Since, no sex difference of ERβ was observed in striatum, we delineated whether ERα and G-protein-coupled estrogen receptor 1 (GPER1) mediate the suppressions of FC-induced autophagy and oxidative injury by E₂ in a sex-dimorphic manner. The results showed that the ratio of constitutive GPER1 to ERα in striatum is higher in males than in females. The GPER1 and ERα predominantly mediated suppressive effects of E₂ on FC-induced autophagy in males and antioxidant effect of E₂ in females, respectively. This finding opens the prospect of a male-specific therapeutic strategy targeting GPER1 for autophagy suppression in patients suffering from iron overload after hemorrhage.

Raloxifene decreases cell viability and migratory potential in prostate cancer cells (LNCaP) with GPR30/GPER1 involvement

OBJECTIVES

This study evaluated raloxifene (ral) effects on LNCaP prostate tumour cells modulating the activity of GPER1/GPR30 receptors.

METHODS

LNCaP cells were submitted for 40/120 min and 12 h to the following treatments: C: RPMI + DMSO; R: RPMI + Ral; G: RPMI + Ral + G15 (GPER1 antagonist). Trypan blue staining measured cell viability. Migratory potential (12 h) was measured by transwell migration test in translucent inserts, which were then stained with DAPI and analysed under a fluorescence microscope for quantification. Cells from 40- and 120-min treatments were subjected to protein extraction to the study of AKT, pAKT, ERK, pERK, ERβ and SIRT1.

KEY FINDINGS

There is a reduction in cellular viability in R compared to C at all evaluated times, and an increased cell viability in G when compared to R; cell viability was similar in C and G in all times studied. The migration assay demonstrated a significant decrease in migration potential of tumour cells in R compared to C and G. Ral treatment reduced pERK expression and increased pAKT in the treated groups after 40 min, pointing out to an antiproliferative and apoptotic effect in the GPER1-controlled rapid-effect pathways.

CONCLUSIONS

Raloxifene was able to modulate GPER1 in LNCaP prostate tumour cells, decreasing cell viability and their migratory potential.

G Protein-Coupled Estrogen Receptor 1 Inhibits Angiotensin II-Induced Cardiomyocyte Hypertrophy via the Regulation of PI3K-Akt-mTOR Signalling and Autophagy

Estrogen has been demonstrated to protect the heart against cardiac remodelling and heart failure in women. G protein-coupled estrogen receptor 1 (GPER1) is a recently discovered estrogen receptor (ER) that is expressed in various tissues. However, the mechanisms by which estrogen protects the heart, especially the roles played by ERs, are not clear. In this study, we explored the effect of GPER1 activation on angiotensin II (Ang II)-induced cardiomyocyte hypertrophy and the involved signalling pathways and mechanisms. Our data demonstrated that GPER1 is expressed in cardiomyocytes, a GPER1 agonist, G1, attenuated Ang II-induced cardiomyocyte hypertrophy and downregulated the mRNA expression levels of atrial natriuretic factor (ANF) and brain natriuretic peptide (BNP). Bioinformatics analysis revealed that five proteins, including RAP1gap, might be the key proteins involved in the attenuation of Ang II-induced cardiomyocyte hypertrophy by GPER1. G1 increased the protein level of p-Akt, p-70S6K1 and p-mTOR but decreased p-4EBP1 expression. All these effects were inhibited by either G15 (a GPER1 antagonist) or MK2206 (an inhibitor of Akt). Autophagy analysis showed that the LC3II/LC3I ratio was increased in Ang II-treated cells, and the increase was inhibited by G1 treatment. The effect of G1 on autophagy was blocked by treatment with G15, rapamycin, and MK2206. These results suggest that GPER1 activation attenuates Ang II-induced cardiomyocyte hypertrophy by upregulating the PI3K-Akt-mTOR signalling pathway and inhibiting autophagy.

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.

Regulation of sex hormone receptors in sexual dimorphism of human cancers

Gender differences in the incidences of cancers have been found in almost all human cancers. However, the mechanisms that underlie gender disparities in most human cancer types have been under-investigated. Here, we provide a comprehensive overview of potential mechanisms underlying sexual dimorphism of each cancer regarding sex hormone signaling. Fully addressing the mechanisms of sexual dimorphism in human cancers will greatly benefit current development of precision medicine. Our discussions of potential mechanisms underlying sexual dimorphism in each cancer will be instructive for future cancer research on gender disparities.

How does estrogen work on autophagy?

Macroautophagy/autophagy is vital for intracellular quality control and homeostasis. Therefore, careful regulation of autophagy is very important. In the past 10 years, a number of studies have reported that estrogenic effectors affect autophagy. However, some results, especially those regarding the modulatory effect of 17β-estradiol (E2) on autophagy seem inconsistent. Moreover, several clinical trials are already in place combining both autophagy inducers and autophagy inhibitors with endocrine therapies for breast cancer. Not all patients experience benefit, which further confuses and complicates our understanding of the main effects of autophagy in estrogen-related cancer. In view of the importance of the crosstalk between estrogen signaling and autophagy, this review summarizes the estrogenic effectors reported to affect autophagy, subcellular distribution and translocation of estrogen receptors, autophagy-targeted transcription factors (TFs), miRNAs, and histone modifications regulated by E2. Upon stimulation with estrogen, there will always be opposing functional actions, which might occur between different receptors, receptors on TFs, TFs on autophagy genes, or even histone modifications on transcription. The huge signaling network downstream of estrogen can promote autophagy and reduce overstimulated autophagy at the same time, which allows autophagy to be regulated by estrogen in a restricted range. To help understand how the estrogenic regulation of autophagy affects cell fate, a hypothetical model is presented here. Finally, we discuss some exciting new directions in the field. We hope this might help to better understand the multiple associations between estrogen and autophagy, the pathogenic mechanisms of many estrogen-related diseases, and to design novel and efficacious therapeutics. Abbreviations: AP-1, activator protein-1; HATs, histone acetyltransferases; HDAC, histone deacetylases; HOTAIR, HOX transcript antisense RNA.

Steroid and Xenobiotic Receptor Signalling in Apoptosis and Autophagy of the Nervous System

Apoptosis and autophagy are involved in neural development and in the response of the nervous system to a variety of insults. Apoptosis is responsible for cell elimination, whereas autophagy can eliminate the cells or keep them alive, even in conditions lacking trophic factors. Therefore, both processes may function synergistically or antagonistically. Steroid and xenobiotic receptors are regulators of apoptosis and autophagy; however, their actions in various pathologies are complex. In general, the estrogen (ER), progesterone (PR), and mineralocorticoid (MR) receptors mediate anti-apoptotic signalling, whereas the androgen (AR) and glucocorticoid (GR) receptors participate in pro-apoptotic pathways. ER-mediated neuroprotection is attributed to estrogen and selective ER modulators in apoptosis- and autophagy-related neurodegenerative diseases, such as Alzheimer’s and Parkinson’s diseases, stroke, multiple sclerosis, and retinopathies. PR activation appeared particularly effective in treating traumatic brain and spinal cord injuries and ischemic stroke. Except for in the retina, activated GR is engaged in neuronal cell death, whereas MR signalling appeared to be associated with neuroprotection. In addition to steroid receptors, the aryl hydrocarbon receptor (AHR) mediates the induction and propagation of apoptosis, whereas the peroxisome proliferator-activated receptors (PPARs) inhibit this programmed cell death. Most of the retinoid X receptor-related xenobiotic receptors stimulate apoptotic processes that accompany neural pathologies. Among the possible therapeutic strategies based on targeting apoptosis via steroid and xenobiotic receptors, the most promising are the selective modulators of the ER, AR, AHR, PPARγ agonists, flavonoids, and miRNAs. The prospective therapies to overcome neuronal cell death by targeting autophagy via steroid and xenobiotic receptors are much less recognized.

Autophagy analysis in oral carcinogenesis

OBJECTIVE

The aim of this study was to evaluate the levels of autophagy in oral leukoplakia and squamous cell carcinoma and to correlate with clinical pathological features, as well as, the evolution of these lesions.

METHODOLOGY

7 Normal oral mucosa, 51 oral leukoplakias, and 120 oral squamous cell carcinomas (OSCC) were included in the study. Histological sections of the mucosa and leukoplakias were evaluated throughout their length, while the carcinomas were evaluated using Tissue Microarray. After the immunohistochemical technique, LC3-II positive cells were quantified in the different epithelial layers of the mucosa and leukoplakias and in the microarrays of the squamous cell carcinomas. The correlation between positive cells with the different clinical-pathological variables and with the evolution of the lesions was tested using the t test, ANOVA, and Kaplan-Meier survival analysis.

RESULTS

We observed increased levels of autophagy in the oral squamous cell carcinomas (p<0.001) in relation to the other groups, but without any association with poorer evolution or survival of these patients. Among the leukoplakias, we observed a higher percentage of positive cells in the intermediate layer of the dysplastic leukoplakias (p=0.0319) and in the basal layer of lesions with poorer evolution (p=0.0133).

CONCLUSION

The levels of autophagy increased during the process of oral carcinogenesis and are correlated with poorer behavior of the leukoplakias.

FTY720 Induces Autophagy-Associated Apoptosis in Human Oral Squamous Carcinoma Cells, in Part, through a Reactive Oxygen Species/Mcl-1-Dependent Mechanism

In this study, we interrogated the mechanism by which the immunosuppressant FTY720 mediates anticancer effects in oral squamous cell carcinoma (OSCC) cells. FTY720 differentially suppressed the viability of the OSCC cell lines SCC4, SCC25, and SCC2095 with IC₅₀ values of 6.1, 6.3, and 4.5 μM, respectively. This antiproliferative effect was attributable to the ability of FTY720 to induce caspase-dependent apoptosis. Mechanistic evidence suggests that FTY720-induced apoptosis was associated with its ability to inhibit Akt-NF-κB signaling, to facilitate the proteasomal degradation of the antiapoptotic protein Mcl-1, and to increase reactive oxygen species (ROS) generation. Both overexpression of Mcl-1 and inhibition of ROS partially protected cells from FTY720-induced caspase-9 activation, PARP cleavage and cytotoxicity. In addition, FTY720 induced autophagy in OSCC cells, as manifested by LC3B-II conversion, decreased p62 expression, and accumulation of autophagosomes. Inhibition of autophagy by bafilomycin A1 protected cells from FTY720-induced apoptosis. Together, these findings suggest an intricate interplay between autophagy and apoptosis in mediating the tumor-suppressive effect in OSCC cells, which underlies the translational potential of FTY720 in fostering new therapeutic strategies for OSCC.

Autophagy and its implication in human oral diseases

Macroautophagy/autophagy is a conserved lysosomal degradation process essential for cell physiology and human health. By regulating apoptosis, inflammation, pathogen clearance, immune response and other cellular processes, autophagy acts as a modulator of pathogenesis and is a potential therapeutic target in diverse diseases. With regard to oral disease, autophagy can be problematic either when it is activated or impaired, because this process is involved in diverse functions, depending on the specific disease and its level of progression. In particular, activated autophagy functions as a cytoprotective mechanism under environmental stress conditions, which regulates tumor growth and mediates resistance to anticancer treatment in established tumors. During infections and inflammation, activated autophagy selectively delivers microbial antigens to the immune systems, and is therefore connected to the elimination of intracellular pathogens. Impaired autophagy contributes to oxidative stress, genomic instability, chronic tissue damage, inflammation and tumorigenesis, and is involved in aberrant bacterial clearance and immune priming. Hence, substantial progress in the study of autophagy provides new insights into the pathogenesis of oral diseases. This review outlines the mechanisms of autophagy, and highlights the emerging roles of this process in oral cancer, periapical lesions, periodontal diseases, and oral candidiasis.

Estrogens, Neuroinflammation, and Neurodegeneration

Inflammatory activation of microglia is a hallmark of several disorders of the central nervous system. In addition to protecting the brain against inflammatory insults, microglia are neuroprotective and play a significant role in maintaining neuronal connectivity, but the prolongation of an inflammatory status may limit the beneficial functions of these immune cells. The finding that estrogen receptors are present in monocyte-derived cells and that estrogens prevent and control the inflammatory response raise the question of the role that this sex steroid plays in the manifestation and progression of pathologies that have a clear sex difference in prevalence, such as multiple sclerosis, Parkinson's disease, and Alzheimer's disease. The present review aims to provide a critical review of the current literature on the actions of estrogen in microglia and on the involvement of estrogen receptors in the manifestation of selected neurological disorders. This current understanding highlights a research area that should be expanded to identify appropriate replacement therapies to slow the progression of such diseases.

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.

Function of G-Protein-Coupled Estrogen Receptor-1 in Reproductive System Tumors

The G-protein-coupled estrogen receptor-1 (GPER-1), also known as GPR30, is a novel estrogen receptor mediating estrogen receptor signaling in multiple cell types. The progress of estrogen-related cancer is promoted by GPER-1 activation through mitogen-activated protein kinases (MAPK), phosphoinositide 3-kinase (PI3K), and phospholipase C (PLC) signaling pathways. However, this promoting effect of GPER-1 is nonclassic estrogen receptor (ER) dependent manner. In addition, clinical evidences revealed that GPER-1 is associated with estrogen resistance in estrogen-related cancer patients. These give a hint that GPER-1 may be a novel therapeutic target for the estrogen-related cancers. However, preclinical studies also found that GPER-1 activation of its special agonist G-1 inhibits cancer cell proliferation. This review aims to summarize the characteristics and complex functions of GPER-1 in cancers.

The role of autophagy in squamous cell carcinoma of the head and neck

Half a million new head and neck cancers are diagnosed each year worldwide. Although traditionally thought to be triggered by alcohol and smoking abuse, there is a growing subset of oropharyngeal cancers driven by the oncogenic human papilloma virus (HPV). Despite advances in both surgical and non-surgical treatment strategies, survival rates have remained relatively static emphasising the need for novel therapeutic approaches. Autophagy, the principal catabolic process for the lysosomal--mediated breakdown of cellular products is a hot topic in cancer medicine. Increasing evidence points towards the prognostic significance of autophagy biomarkers in solid tumours as well as strategies through which to harness autophagy modulation to promote tumour cell death. However, the role of autophagy in head and neck cancers is less well defined. In the present review, we summarise the current understanding of autophagy in head and neck cancers, revealing key areas for future translational research.

A triterpenoid from wild bitter gourd inhibits breast cancer cells

The antitumor activity of 3β,7β,25-trihydroxycucurbita-5,23(E)-dien-19-al (TCD), a triterpenoid isolated from wild bitter gourd, in breast cancer cells was investigated. TCD suppressed the proliferation of MCF-7 and MDA-MB-231 breast cancer cells with IC₅₀ values at 72 h of 19 and 23 μM, respectively, via a PPARγ−independent manner. TCD induced cell apoptosis accompanied with pleiotrophic biological modulations including down-regulation of Akt-NF-κB signaling, up-regulation of p38 mitogen-activated protein kinase and p53, increased reactive oxygen species generation, inhibition of histone deacetylases protein expression, and cytoprotective autophagy. Together, these findings provided the translational value of TCD and wild bitter gourd as an antitumor agent for patients with breast cancer.

Regulation of cyclooxygenase-2 expression in rat oviductal epithelial cells: Evidence for involvement of GPR30/Src kinase-mediated EGFR signaling

The oviduct plays a crucial role in female reproduction by regulating gamete transport, providing a specific microenvironment for fertilization and early embryonic development. Cyclooxygenase (COX)-derived prostaglandins play essential role in carrying out these oviduct-specific functions. Estrogen upregulates COX-2 expression in rat oviduct; however, the mechanisms responsible for regulation of COX-2 expression in rat oviductal epithelial cells (OECs) remain unclear. In the present study, we proposed that estrogen induces COX-2 expression via G-protein coupled receptor i.e., GPR30 in OECs. To investigate this hypothesis, we examined the effects of E2-BSA, ICI 182,780, GPR30 agonist and GPR30 antagonist on COX-2 expression and explored potential signaling pathway leading to COX-2 expression. Co-localization experiments revealed GPR30 to be primarily located in the peri-nuclear space, which was also the site of E2-BSA-fluorescein isothiocyanate (E2-BSA-FITC) binding. The E2-BSA induced-COX-2 and prostaglandin release were subjected to regulation by both EGFR and PI3K signaling as inhibitors of c-Src kinase (PP2), EGFR (EGFR inhibitor) and PI-3 kinase (LY294002) attenuated E2-BSA mediated effect. These results suggest that EGFR transactivation leading to activation of PI-3K/Akt pathway participates in COX-2 expression in rat OECs. Interestingly, E2-BSA induced COX-2 expression and subsequent prostaglandin release were abolished by NF-κB inhibitor. In addition, E2-BSA induced the nuclear translocation of p65-NF-κB and up-regulated the NF-κB promoter activity in rat OECs. Taken together, results demonstrated that E2-BSA induced the COX-2 expression and consequent PGE2 and PGF2α release in rat OECs. These effects are mediated through GPR30-derived EGFR transactivation and PI-3K/Akt cascade leading to NF-κB activation.

Efficacy of quercetin against chemically induced murine oral squamous cell carcinoma

Oral squamous cell carcinoma (OSCC) is the most common form of head and neck cancer, and oxidative damage is associated with the development of OSCCs. Antioxidants have therefore been proposed for use as chemoprotective agents against different types of cancer. In the present study, the effect of the antioxidant quercetin, administered at doses of 10 and 100 mg/kg/day, was investigated in an experimental murine model of 4-nitroquinoline 1-oxide (4-NQO)-induced carcinogenesis. The survival of the treated animals, the plasmatic levels of reduced glutathione and the type and severity of lesions (according the International Histological Classification of Tumors and Bryne's Multifactorial Grading System for the Invasive Tumor Front) were assessed. Additionally, the organization of the extracellular matrix was analyzed by carbohydrate and collagen histochemistry, and immunohistochemistry was used to assess the expression of the tumor markers proliferating cell nuclear antigen and mutated p53. The results indicate that, despite the promising effect of quercetin in other studies, this drug is ineffective as a chemoprotective agent against 4-NQO-induced OSCC in mice at the assayed doses.

Deciphering the GPER/GPR30-agonist and antagonists interactions using molecular modeling studies, molecular dynamics, and docking simulations

The G-protein coupled estrogen receptor 1 GPER/GPR30 is a transmembrane seven-helix (7TM) receptor involved in the growth and proliferation of breast cancer. Due to the absence of a crystal structure of GPER/GPR30, in this work, molecular modeling studies have been carried out to build a three-dimensional structure, which was subsequently refined by molecular dynamics (MD) simulations (up to 120 ns). Furthermore, we explored GPER/GPR30's molecular recognition properties by using reported agonist ligands (G1, estradiol (E2), tamoxifen, and fulvestrant) and the antagonist ligands (G15 and G36) in subsequent docking studies. Our results identified the E2 binding site on GPER/GPR30, as well as other receptor cavities for accepting large volume ligands, through GPER/GPR30 π-π, hydrophobic, and hydrogen bond interactions. Snapshots of the MD trajectory at 14 and 70 ns showed almost identical binding motifs for G1 and G15. It was also observed that C107 interacts with the acetyl oxygen of G1 (at 14 ns) and that at 70 ns the residue E275 interacts with the acetyl group and with the oxygen from the other agonist whereas the isopropyl group of G36 is oriented toward Met141, suggesting that both C107 and E275 could be involved in the protein activation. This contribution suggest that GPER1 has great structural changes which explain its great capacity to accept diverse ligands, and also, the same ligand could be recognized in different binding pose according to GPER structural conformations.

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.