Nongenomic Effects Of Estrogen Research Articles

G-Protein-Coupled Estrogen Receptor Enhances the Stemness of Triple-Negative Breast Cancer Cells and Promotes Malignant Characteristics

G-protein coupled estrogen receptor (GPER) is a transmembrane receptor that mediates non-genomic effects of estrogen. This study aimed to investigate the role of GPER in the stemness formation and malignancies in triple negative breast cancer (TNBC) cells. Spheroids of MDA-MB-468 cells were induced by mammosphere culture, and the proportion of the CD44+ /CD24−/low stem cell subpopulation was detected. Malignant characteristics, expression of GPER and stemness-related markers, and tumorigenesis in a xenograft assay were compared between the mammospheres and adherent cultured cells. The impacts of 17β-estradiol (E2) and the GPER-specific antagonist G15 were studied in in vitro assays. The proportion of the CD44+ /CD24−/low subpopulation was increased in the mammospheres of MDA-MB-468 cells, which also showed higher expression of GPER and stemness-related markers than adherent cultured cells. The abilities of spherical colonies to proliferate, invade, and form colonies in soft agar were enhanced. Spherical cells exhibited stronger tumorigenesis ability than adherent cells in the xenograft assay. E2 treatment enhanced tumorigenicity of both adherent and spherical cells. Spherical cells treated with E2 had stronger proliferation, invasion, and colony formation abilities than other groups. Pretreatment with G15 effectively blocked the stimulation by E2. In conclusion, the expression of GPER in TNBC cells is positively related to stemness and malignant features.

A novel transcript variant of human G-protein coupled estrogen receptor.

The G-protein coupled estrogen receptor (GPER) mediates short-term non-genomic effects of estrogen in diverse cell types and tissues. According to the NCBI nucleotide database, three variants of GPER are known. They are NM_001505.2 (GPER-v2), NM_001039966.1 (GPER-v3), and NM_001098201.1 (GPER-v4). Investigations on GPER expression are key to understand its physiological and pathological roles. However, most studies on GPER mRNA expression have considered total GPER mRNA expression regardless of the individual variants. The present study is motivated by a novel transcript observed in the UCSC Genome Browser (uc010ksd.1), which is annotated as GPER. The novel variant is similar to the known transcriptvariants of GPER in terms of the protein-coding sequence and the 3'UTR. However, it has a unique 5'UTR, which distinguishes it from other GPER variants. Using primers specific for uc010ksd.1, we have performed RT-PCR to show that the novel GPER transcript (hereafter referred to as GPER-v5) is expressed in human cancer cell lines, such as MCF-7, SW-620, COLO-205, and HT-29. Preliminary evidences indicate that GPER-v5 is a novel GPER mRNA variant. The expression of GPER-v5 in primary cells and tissues should be investigated before probing into its role and relevance in physiological and pathological conditions.

Estrogen Receptors in Nonfunctioning Pituitary Neuroendocrine Tumors: Review on Expression and Gonadotroph Functions.

Estrogen (17β-estradiol or E2) is a crucial regulator of the synthesis and secretion of pituitary reproductive hormones luteinizing hormone, follicle-stimulating hormone, and prolactin. In this review, we summarize the role of estrogen receptors in nonfunctioning pituitary neuroendocrine tumors (NF-Pitnets), focusing on immunoexpression and gonadotroph cell proliferation and apoptosis. Gonadotroph tumors are the most common subtype of NF-Pitnets. Two major estrogen receptor (ER) isoforms expressed in the pituitary are estrogen receptor alpha (ERα) and estrogen receptor beta (ERβ). Overall, estrogen actions are mostly exerted through the ERα isoform on the pituitary. The G protein–coupled estrogen receptor (GPER) located at the plasma membrane may contribute to nongenomic effects of estrogen. Nuclear immunoreactivity for ERα and ERβ was highest among gonadotroph and null cell tumors. Silent corticotroph tumors are the least immunoreactive for both receptors. A significantly elevated ERα expression was observed in macroadenomas compared with microadenomas. ERα and ERβ may act in opposite directions to regulate the Slug-E-cadherin pathway and to affect invasiveness of NF-Pitnets. In the cellular pathway, ERs regulate estrogen-induced proliferation and differentiation and impact several signaling pathways including the MAPK and PI3K/Akt pathway. Estrogen was the first-discovered inducer of pituitary tumor transforming gene 1 that was abundantly expressed in NF-Pitnets. ERα can be a potential biomarker for predicting tumor size and invasiveness as well as therapeutic target for NF-Pitnets. Selective estrogen receptor modulators or antiestrogen may represent as an alternative choice for the treatment of NF-Pitnets.

Down-regulation of ER-α36 mRNA in serum exosomes of the patients with hepatocellular carcinoma.

Down-regulation of ER-α36 mRNA in serum exosomes of the patients with hepatocellular carcinoma.

Non-genomic Effects of Estrogen on Cell Homeostasis and Remodeling With Special Focus on Cardiac Ischemia/Reperfusion Injury.

This review takes into consideration the main mechanisms involved in cellular remodeling following an ischemic injury, with special focus on the possible role played by non-genomic estrogen effects. Sex differences have also been considered. In fact, cardiac ischemic events induce damage to different cellular components of the heart, such as cardiomyocytes, vascular cells, endothelial cells, and cardiac fibroblasts. The ability of the cardiovascular system to counteract an ischemic insult is orchestrated by these cell types and is carried out thanks to a number of complex molecular pathways, including genomic (slow) or non-genomic (fast) effects of estrogen. These pathways are probably responsible for differences observed between the two sexes. Literature suggests that male and female hearts, and, more in general, cardiovascular system cells, show significant differences in many parameters under both physiological and pathological conditions. In particular, many experimental studies dealing with sex differences in the cardiovascular system suggest a higher ability of females to respond to environmental insults in comparison with males. For instance, as cells from females are more effective in counteracting the ischemia/reperfusion injury if compared with males, a role for estrogen in this sex disparity has been hypothesized. However, the possible involvement of estrogen-dependent non-genomic effects on the cardiovascular system is still under debate. Further experimental studies, including sex-specific studies, are needed in order to shed further light on this matter.

G-Protein-Coupled Estrogen Receptor (GPER)-Specific Agonist G1 Induces ER Stress Leading to Cell Death in MCF-7 Cells.

The G-protein-coupled estrogen receptor (GPER) mediates rapid non-genomic effects of estrogen. Although GPER is able to induce proliferation, it is down-regulated in breast, ovarian and colorectal cancer. During cancer progression, high expression levels of GPER are favorable for patients’ survival. The GPER-specific agonist G1 leads to an inhibition of cell proliferation and an elevated level of intracellular calcium (Ca2+). The purpose of this study is to elucidate the mechanism of G1-induced cell death by focusing on the connection between G1-induced Ca2+ depletion and endoplasmic reticulum (ER) stress in the estrogen receptor positive breast cancer cell line MCF-7. We found that G1-induced ER Ca2+ efflux led to the activation of the unfolded protein response (UPR), indicated by the phosphorylation of IRE1α and PERK and the cleavage of ATF6. The pro-survival UPR signaling was activated via up-regulation of the ER chaperon protein GRP78 and translational attenuation indicated by eIF2-α phosphorylation. However, the accompanying pro-death UPR signaling is profoundly activated and responsible for ER stress-induced cell death. Mechanistically, PERK-phosphorylation-induced JNK-phosphorylation and IRE1α-phosphorylation, which further triggered CAMKII-phosphorylation, are both implicated in G1-induced cell death. Our study indicates that loss of ER Ca2+ is responsible for G1-induced cell death via the pro-death UPR signaling.

Estrogen Signaling in ERα-Negative Breast Cancer: ERβ and GPER.

Estrogen receptors are important regulators of the growth of breast tumors. Three different receptors for estrogens have been identified in breast tumors, two nuclear receptors, ERα and ERβ, and a G-protein coupled estrogen receptor 1 (GPER) that initiates non-genomic effects of estrogens in the cytosol. Recent findings show that the stimulation of cytoplasmic ERα and ERβ also triggers non-genomic signaling pathways. The treatment of breast cancer with anti-estrogens depends on the presence of ERα. About 40% of all breast cancers, however, do not express ERα. One subgroup of these tumors overexpress Her-2, another important group is designated as triple-negative breast cancer, as they neither express ERα, nor progesterone receptors, nor do they overexpress Her-2. This review addresses the signaling of ERβ and GPER in ERα-negative breast tumors. In addition to the well-established EGF-receptor transactivation pathways of GPER, more recent findings of GPER-dependent activation of FOXO3a, the Hippo-pathway, and HOTAIR-activation are summarized.

Activation of GPER suppresses the malignancy of osteosarcoma cells via down regulation of IL-6 and IL-8

Estrogenic signals can regulate the progression of osteosarcoma (OS) via classic estrogen receptor α/β (ERα/β). G protein-coupled estrogen receptor (GPER) can mediate the non-genomic effects of estrogen and regulate the progression of various cancers. Our present study revealed that the expression of GPER in OS cells and tissues was lower than that in their corresponding controls. Activation of GPER via its specific agonist G-1 can decrease the proliferation, migration, and invasion of OS cells. By screening the expression of cytokines involved in the progression of OS, we found that activation of GPER can inhibit the expression of interleukin-6 (IL-6) and IL-8 in OS cells. Recombinant IL-6 (rIL-6) or rIL-8 can attenuate G-1 suppressed migration of OS cells. Mechanically, activation of GPER can rapidly decease the phosphorylation and nuclear translocation of NF-κB in OS cells. While over expression of p65 significantly attenuated G-1 induced down regulation of IL-6/IL-8. Further, G-1 can decrease the activation of p38-MAPK, which can further shorten the half-life of IL-8 mRNA. Collectively, we revealed that GPER can suppress the migration and invasion of OS cells via inhibition of IL-6 and IL-8. It suggested that GPER might be a potential therapy target for OS treatment.

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.

17-β-estradiol Decreases Neutrophil Superoxide Production through Rac1.

Neutrophil granulocytes form the biggest free radical producing system of the human body. The importance of this system in atherosclerotic plaque formation and other free radical mediated disorders is confirmed by both in vivo and in vitro studies. Estrogen's effect on free radical production involves multiple estrogen receptors and occurs both on transcriptional and on protein phosphorylational level. Estrogen decreases the superoxide production of neutrophil granulocytes in such a short time frame it is unlikely to be mediated by transcription regulation. We investigated the underlying mechanism through which the mentioned estrogen effect takes place using an immunabsorption-based method. Phosphorylation data of 43 different messenger proteins were used for pathway analysis. The newly identified pathway involved largely second messengers from previously described non-genomic estrogen effects and affected superoxide production via Rac1 - an important regulator of free radical production and chemotaxis. Selective inhibition of the participating second messengers altered superoxide production in the predicted direction confirming that this pathway is at least partly responsible for the effect of 17-β-estradiol on chemoattractant induced superoxide production.

GPER Mediates Non-Genomic Effects of Estrogen.

Estrogens are important modulators of a broad spectrum of physiological functions in humans. However, despite their beneficial actions, a number of lines of evidence correlate the sustained exposure to exogenous estrogen with increased risk of the onset of various cancers. Mainly these steroid hormones induce their effects by binding and activating estrogen receptors (ERα and ERβ). These receptors belong to the family of ligand-regulated transcription factors, and upon activation they regulate the expression of different target genes by binding directly to specific DNA sequences. On the other hand, in recent years it has become clear that the G protein-coupled estrogen receptor 30 (GPR30/GPER) is able to mediate non-genomic action of estrogens in different cell contexts. In particular, GPER has been shown to specifically bind estrogens, and in turn to functionally cross-react with diverse cell signaling systems such as the epidermal growth factor receptor (EGFR) pathway, the Notch signaling pathway and the mitogen-activated protein kinases (MAPK) pathway. In this chapter we will present some of the different experimental techniques currently used to demonstrate the functional role of GPER in mediating non-genomic actions of estrogens, such as the dual luciferase assay, assessment of the involvement of GPER in the stimulation of cell migration in breast cancer cell lines and in cancer-associated fibroblasts, and chromatin immunoprecipitation assay. Overall, the experimental procedures described herein represent key instruments for assessing the biological role of GPER in mediating non-genomic signals of estrogen.

GPR30 Mediates the Fast Effect of Estrogen on Mouse Blastocyst and its Role in Implantation.

Our previous work demonstrated that estrogen could rapidly increase intracellular Ca(2+) in dormant mouse blastocysts. The purpose of the present study is to investigate the physiological relevance of G protein-coupled receptor 30 (GPR30) in the fast effect of estrogen on mouse blastocyst and in embryo implantation. We used reverse transcription-polymerase chain reaction, immunofluorescence, embryo coculture with Ishikawa uterine epithelial cell line, and embryo transfer technology to detect the expression of GPR30 in mouse embryos and the nongenomic effects of estrogen via GPR30 on blastocyst. We found that GPR30 is expressed in the mouse blastocyst, and its location is mostly consistent with the binding site of estrogen. Both estrogen and GPR30-specific agonist G-1 rapidly increase the intracellular Ca(2+) and phospholipase C activation in blastocyst cells, while GPR30-specific antagonist G-15 blocked this effect of estrogen. The pretreatment of G-15 on blastocysts lead to a lower attachment rate and implantation rate. Our data collectively suggested that GPR30 can mediate the fast effect of estrogen on blastocysts and play an important role in embryo implantation.

Estrogen regulates Hippo signaling via GPER in breast cancer.

The G protein-coupled estrogen receptor (GPER) mediates both the genomic and nongenomic effects of estrogen and has been implicated in breast cancer development. Here, we compared GPER expression in cancerous tissue and adjacent normal tissue in patients with invasive ductal carcinoma (IDC) of the breast and determined that GPER is highly upregulated in cancerous cells. Additionally, our studies revealed that GPER stimulation activates yes-associated protein 1 (YAP) and transcriptional coactivator with a PDZ-binding domain (TAZ), 2 homologous transcription coactivators and key effectors of the Hippo tumor suppressor pathway, via the Gαq-11, PLCβ/PKC, and Rho/ROCK signaling pathways. TAZ was required for GPER-induced gene transcription, breast cancer cell proliferation and migration, and tumor growth. Moreover, TAZ expression positively correlated with GPER expression in human IDC specimens. Together, our results suggest that the Hippo/YAP/TAZ pathway is a key downstream signaling branch of GPER and plays a critical role in breast tumorigenesis.

Nongenomic effects of estrogen on extracellular signal-regulated kinases through initiating transient calcium flux in endometrial cancer

To study the mechanism on extracellular signal-regulate kinases (ERK) signal transduction by calcium influx initiated by combination of estrogen with calcium channels or estrogen receptor in endometrial cancer cell Ishikawa. Confocal test was used to determine the relative calcium mobilization by stimulation of estrodiol together with and without the inhibition of ICI182780 and nifedipine. Western-blotting was used to detect the protein expression of phosphorylated ERK1/2 (P-ERK1/2) in the same condition. The transient calcium flux initiated by 17β-estrodiol (E2) and a membrane-impermeable conjugate of estrogen and bovine serum albumin (E2-BSA), and the calcium mobilization could be inhibited by ICI182780 and nifedipine in 1 min. In Ishikawa cells, phosphorylation of ERK1/2 was stimulated by E2, and the phosphorylation could not be inhibited by E2 after the combination with ICI182780 in 5 min and in 30 min. The phosphorylation also could not be inhibited by E2-BSA after the combination with nifedipine in 5 min, but in 30 min the phosphorylation was decreased. The phosphorylation of ERK by E2-BSA was decreased by the combination with nifedipine in 30 min. The transient calcium flux initiated by estrogen has an effect on the activation of ERK signal pathway in endometrial carcinoma cells.

Selective G-Protein Estrogen Receptor (GPER) Activation Triggers Anti-Multiple Myeloma Activity and Synergizes with MiR-29b-Inducing Drugs

Multiple myeloma (MM) is a plasma cell malignancy which remains incurable despite novel therapeutic approaches targeting both myeloma cells and their bone marrow milieu (BMM). MM cells express estrogen receptors (ER) belonging to both α and β isotypes and selective ER modulators or pure anti-estrogens have demonstrated therapeutic activity against this malignancy. GPER, formerly known as GPR30, is an orphan membrane-associated ER previously described to mediate non-genomic effects of estrogens and whose involvement in the pathophysiology of solid tumors is currently emerging. Here, we studied the expression pattern of GPER and the biological effects triggered by GPER activation using the synthetic compound G-1 ((±)-1-[(3aR*,4S*,9bS*)-4-(6-Bromo-1,3-benzodioxol-5-yl)-3a,4,5,9b-tetrahydro-3H cyclopenta[c]quinolin-8-yl] ethanone), a selective GPER agonist (Tocris). We detected GPER expression in 9 out of 9 MM cell lines either at mRNA and protein level, as assessed by qRT-PCR and western blotting, respectively. By analysis of our microarray dataset based on plasma cells from 4 normal donors, 11 MGUS, 133 MM and 9 plasma cell leukemias (PCLs), we observed that GPER mRNA levels progressively declined during MM progression, since lower levels were found in PCL and MM samples as compared to healthy controls or MGUS. Interestingly, adhesion of MM cells to bone marrow stromal cells (BMSCs) reduced GPER mRNA levels, supporting a potential role of the BMM in regulating GPER expression. To address the relevance of GPER in modulating MM cell proliferation and/or death mechanisms, first we tested the GPER agonist G-1 in vitro. We found that G-1 inhibited, in a dose-dependent manner, proliferation of IL-6 dependent (INA-6) and independent (MM1R, MM1S, U266, RPMI-8226, NCI-H929, OPM2) MM cell lines, with an IC50 ranging from 2 to 5 microM, while did not affect the survival of peripheral blood mononuclear cells from healthy donors. G-1 treatment caused cell cycle arrest by increasing cells in G0 phase; moreover, it induced a significant and dose-dependent apoptotic cell death in all MM cell lines tested, as assessed by Annexin V/7AAD staining and western blot analysis of active caspases 3, 7 and 9. G-1 promoted the expression of autophagic markers like Beclin-1 and LC3A/B, the cytosolic punctate pattern of LC3B and down-regulated p62/SQSTM-1 expression, indicating functional involvement of GPER in autophagy. Moreover, GPER transduced rapid non-genomic signaling through MAPKs, since G-1-mediated GPER activation triggered phosphorylation of ERK1/2 already after 15’ treatment in MM1S and U266 cells. Importantly, i.p. injection of G-1 (2mg/kg) in SCID mice significantly reduced the growth of subcutaneous MM1S xenografts, as compared to vehicle-treated animals.We next evaluated whether G-1-induced effects could be associated to modulation of miRNA levels in MM cells. Indeed, we found that G-1 up-regulated the tumor suppressor miR-29b; this effect was likely a consequence of the down-regulation of the miR-29b transcriptional inhibitor Sp1, whose mRNA and protein levels were reduced after G-1 treatment. Consistently, an inverse correlation between GPER and Sp1 mRNA levels in MM patient plasma cells could be gathered from our microarray dataset. In addition, miR-29b canonical targets, like CDK6 and MCL-1, were down-regulated at protein level in G-1-treated MM cell lines.Finally, we demonstrated that G-1 synergizes with established miR-29b-inducing compounds, like bortezomib and vorinostat, in the inhibition of MM cell survival.Taken together, our results indicate that the GPER agonist G-1 is a novel powerful anti-tumor compound enriching the repertoire of investigative anti-MM agents, and further strengthen the role of miR-29b as effector of anti-MM drugs. DisclosuresNo relevant conflicts of interest to declare.

Identification of G protein‐coupled estrogen receptor in human and pig spermatozoa

Estrogens are known to influence functional properties of mammalian spermatozoa inducing rapid responses through the classical estrogen receptors (ERα and ERβ). Recently, the G protein-coupled estrogen receptor (GPER) has been identified as mediator of fast non-genomic estrogen effects in different cells. This work investigated the expression of GPER in human and pig spermatozoa using immunofluorescence, Western blot analysis and RT-PCR. GPER was found to be confined to the mid-piece of human sperm cells, whereas it was detected in the acrosomal region, the equatorial segment and the mid-piece of pig spermatozoa. Furthermore, in the male gametes of both species, the immunoblots of sperm extracts revealed a band at ~42 kDa, consistent with the GPER molecular weight, and RT-PCR detected the GPER transcripts. This is the first report demonstrating the expression of GPER in human and pig mature sperm cells and evidencing its species-specific cellular localization.

Nongenomic effects of estrogen mediate the dose‐related myocardial oxidative stress and dysfunction caused by acute ethanol in female rats (652.19)

Acute ethanol lowers blood pressure (BP) and cardiac output in proestrus and after chronic estrogen (E2) replacement in ovariectomized (OVX) female rats. However, whether rapid nongenomic effects of E2 mediate these hemodynamic effects of ethanol remained unanswered. To test this hypothesis, we investigated the effect of ethanol (0.5, 1 or 1.5 g/kg; i.v.) on left ventricular (LV) function and oxidative markers in OVX rats pretreated 30 min earlier with 1 μg/kg E2 (OVXE2) or vehicle (OVX) and in proestrus sham‐operated (SO) rats. In SO rats, ethanol caused significant and dose‐ related reductions in BP, rate of rise in LV pressure (LV dP/dtmax), and LV developed pressure (LVDP). The ethanol effects disappeared in OVX rats and were restored in OVXE2 rats suggesting rapid estrogen receptor signaling mediates the detrimental LV effects of ethanol. The E2‐dependent LV dysfunction caused by ethanol was associated with higher LV: (i) generation of reactive oxygen species, (ii) expression of the malondialdehyde and 4‐hydroxynonenal protein adducts, (iii) Akt and ERK1/2, and (iv) catalase activity. Collectively, it is concluded that rapid estrogen receptor signaling is implicated in the cellular events that lead to the generation of aldehyde protein adducts and Akt/ERK1/2 phosphorylation, which ultimately mediate the estrogen‐dependent LV oxidative stress and dysfunction caused by ethanol in female rats. Grant Funding Source: Supported by NIAAA [2R01 AA014441‐07]

Expression pattern of G protein-coupled receptor 30 in human seminiferous tubular cells

The role of estrogens in male reproductive physiology has been intensively studied over the last few years. Yet, the involvement of their specific receptors has long been a matter of debate. The selective testicular expression of the classic nuclear estrogen receptors (ERα and ERβ) argues in favor of ER-specific functions in the spermatogenic event. Recently, the existence of a G protein-coupled estrogen receptor (GPR30) mediating non-genomic effects of estrogens has also been described. However, little is known about the specific testicular expression pattern of GPR30, as well as on its participation in the control of male reproductive function.Herein, by means of immunohistochemical and molecular biology techniques (RT-PCR and Western blot), we aimed to present the first exhaustive evaluation of GPR30 expression in non-neoplastic human testicular cells. Indeed, we were able to demonstrate that GPR30 was expressed in human testicular tissue and that the staining pattern was consistent with its cytoplasmic localization. Additionally, by using cultured human Sertoli cells (SCs) and isolated haploid and diploid germ cells fractions, we confirmed that GPR30 is expressed in SCs and diploid germ cells but not in haploid germ cells. This specific expression pattern suggests a role for GPR30 in spermatogenesis.

Aldosterone's Rapid, Nongenomic Effects Are Mediated by Striatin: A Modulator of Aldosterone's Effect on Estrogen Action

The cellular responses to steroids are mediated by 2 general mechanisms: genomic and rapid/nongenomic effects. Identification of the mechanisms underlying aldosterone (ALDO)'s rapid vs their genomic actions is difficult to study, and these mechanisms are not clearly understood. Recent data suggest that striatin is a mediator of nongenomic effects of estrogen. We explored the hypothesis that striatin is an intermediary of the rapid/nongenomic effects of ALDO and that striatin serves as a novel link between the actions of the mineralocorticoid and estrogen receptors. In human and mouse endothelial cells, ALDO promoted an increase in phosphorylated extracellular signal-regulated protein kinases 1/2 (pERK) that peaked at 15 minutes. In addition, we found that striatin is a critical intermediary in this process, because reducing striatin levels with small interfering RNA (siRNA) technology prevented the rise in pERK levels. In contrast, reducing striatin did not significantly affect 2 well-characterized genomic responses to ALDO. Down-regulation of striatin with siRNA produced similar effects on estrogen's actions, reducing nongenomic, but not some genomic, actions. ALDO, but not estrogen, increased striatin levels. When endothelial cells were pretreated with ALDO, the rapid/nongenomic response to estrogen on phosphorylated endothelial nitric oxide synthase (peNOS) was enhanced and accelerated significantly. Importantly, pretreatment with estrogen did not enhance ALDO's nongenomic response on pERK. In conclusion, our results indicate that striatin is a novel mediator for both ALDO's and estrogen's rapid and nongenomic mechanisms of action on pERK and phosphorylated eNOS, respectively, thereby suggesting a unique level of interactions between the mineralocorticoid receptor and the estrogen receptor in the cardiovascular system.

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

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