GPR30: a novel indicator of poor survival for endometrial carcinoma

Stimulating the GPR30 estrogen receptor with a novel tamoxifen analogue activates SF-1 and promotes endometrial cell proliferation

Estrogens and selective estrogen receptor (ER) modulators such as tamoxifen are known to increase uterine cell proliferation. Mounting evidence suggests that estrogen signaling is mediated not only by ERalpha and ERbeta nuclear receptors, but also by GPR30 (GPER), a seven transmembrane (7TM) receptor. Here, we report that primary human endometriotic H-38 cells express high levels of GPR30 with no detectable ERalpha or ERbeta. Using a novel tamoxifen analogue, STX, which activates GPR30 but not ERs, significant stimulation of the phosphatidylinositol 3-kinase (PI3K) and mitogen-activated protein kinase (MAPK) pathways was observed in H-38 cells and in Ishikawa endometrial cancer cells expressing GPR30; a similar effect was observed in JEG3 choriocarcinoma cells. STX treatment also increased cellular pools of phosphatidylinositol (3,4,5) triphosphate, a proposed ligand for the nuclear hormone receptor SF-1 (NR5A1). Consistent with these findings, STX, tamoxifen, and the phytoestrogen genistein were able to increase SF-1 transcription, promote Ishikawa cell proliferation, and induce the SF-1 target gene aromatase in a GPR30-dependent manner. Our findings suggest a novel signaling paradigm that is initiated by estrogen activation of the 7TM receptor GPR30, with signal transduction cascades (PI3K and MAPK) converging on nuclear hormone receptors (SF-1/LRH-1) to modulate their transcriptional output. We propose that this novel GPR30/SF-1 pathway increases local concentrations of estrogen, and together with classic ER signaling, mediate the proliferative effects of synthetic estrogens such as tamoxifen, in promoting endometriosis and endometrial cancers.

GPR30 predicts poor survival for ovarian cancer

OBJECTIVES

GPR30 is a 7-transmembrane G protein-coupled estrogen receptor that functions alongside traditional estrogen receptors to regulate cellular responses to estrogen. Recent studies suggest that GPR30 expression is linked to lower survival rates in endometrial and breast cancer. This study was conducted to evaluate GPR30 expression in ovarian tumors.

METHODS

GPR30 expression was analyzed using immunohistochemistry and archival specimens from 45 patients with ovarian tumors of low malignant potential (LMP) and 89 patients with epithelial ovarian cancer (EOC). Expression, defined as above or below the median (intensity times the percentage of positive epithelial cells) was correlated with predictors of adverse outcome and survival.

RESULTS

GPR30 expression above the median was observed more frequently in EOC than in LMP tumors (48.3% vs. 20%, p=0.002), and in EOC was associated with lower 5-year survival rates (44.2% vs. 82.6%, Log-rank p<0.001). Tumor grade and FIGO stage, the other significant predictors of survival, were used to stratify cases into "high risk" and "low risk" groups. The 5-year survival rate for "low risk" EOC (all grade 1 and Stage I/II, grade 2) was 100%. In "high risk" EOC (all grade 3 and Stage III/IV, grade 2), the difference in 5-year survival by GPR 30 expression was significant (33.3% vs. 72.4%, p=0.001).

CONCLUSIONS

The novel estrogen-responsive receptor GPR30 is preferentially expressed in "high risk" EOC and is associated with lower survival rates. Further investigation of GPR30 as a potential target for therapeutic intervention in high risk EOC is warranted.

Estrogenic G protein-coupled receptor 30 signaling is involved in regulation of endometrial carcinoma by promoting proliferation, invasion potential, and interleukin-6 secretion via the MEK/ERK mitogen-activated protein kinase pathway

The regulatory mechanism of endometrial carcinoma and the signal transduction pathways involved in hormone action are poorly defined. It has become apparent that the G protein-coupled receptor (GPR) 30 mediates the non-genomic signaling of 17beta-estradiol (E2). Here we show that GPR30 is highly expressed in endometrial cancer tissues and cancer cell lines and positively regulates cell proliferation and invasion. GPR30 expression was detected in 50 human endometrial carcinomas. The transcription level of GPR30 was significantly higher in the tissue of endometrial carcinoma than in normal endometrium (P < 0.05). Immunohistochemical assays revealed that the positive expression rate of GPR30 protein in endometrial carcinoma tissue (35/50, 70%) was statistically higher than in normal endometrium tissue (8/30, 26.67%) (chi2 = 14.16, P = 0.0002). GPR30 overexpression was correlated with high-grade endometrial carcinoma. GPR30 expression was also found in two human endometrial cancer cell lines: RL95-2 (estrogen receptor positive) and KLE (estrogen receptor negative). The roles of GPR30 in proliferative and invasive responses to E2 and G1, a non-steroidal GPR30-specific agonist, in RL95-2 and KLE cell lines were then explored. We showed that E2 and G1 could initiate the MAPK/ERK mitogen-activated protein kinase pathway in both cell lines. What's more, E2 and G1 promoted KLE and RL95-2 proliferation and stimulated matrix metalloproteinase production and activity via the GPR30-mediated MEK/ERK mitogen-activated protein kinase pathway, as well as increased interleukin-6 secretion. These findings suggest that GPR30-mediated non-genomic signaling could play an important role in endometrial cancer.

Signaling, physiological functions and clinical relevance of the G protein-coupled estrogen receptor GPER

GPR30, now named GPER1 (G protein-coupled estrogen receptor1) or GPER here, was first identified as an orphan 7-transmembrane G protein-coupled receptor by multiple laboratories using either homology cloning or differential expression and subsequently shown to be required for estrogen-mediated signaling in certain cancer cells. The actions of estrogen are extensive in the body and are thought to be mediated predominantly by classical nuclear estrogen receptors that act as transcription factors/regulators. Nevertheless, certain aspects of estrogen function remain incompatible with the generally accepted mechanisms of classical estrogen receptor action. Many recent studies have revealed that GPER contributes to some of the actions of estrogen, including rapid signaling events and rapid transcriptional activation. With the introduction of GPER-selective ligands and GPER knockout mice, the functions of GPER are becoming more clearly defined. In many cases, there appears to be a complex interplay between the two receptor systems, suggesting that estrogen-mediated physiological responses may be mediated by either receptor or a combination of both receptor types, with important medical implications.

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

Estrogen promotes changes in cytoskeletal architecture not easily attributed to the biological action of estrogen receptors, ERalpha and ERbeta. The Gs protein-coupled transmembrane receptor, GPR30, is linked to specific estrogen binding and rapid estrogen-mediated release of heparin-bound epidermal growth factor. Using marker rescue and dominant interfering mutant strategies, we show that estrogen action via GPR30 promotes fibronectin (FN) matrix assembly by human breast cancer cells. Stimulation with 17beta-estradiol or the ER antagonist, ICI 182, 780, results in the recruitment of FN-engaged integrin alpha5beta1 conformers to fibrillar adhesions and the synthesis of FN fibrils. Concurrent with this cellular response, GPR30 promotes the formation of Src-dependent, Shc-integrin alpha5beta1 complexes. Function-blocking antibodies directed against integrin alpha5beta1 or soluble Arg-Gly-Asp peptide fragments derived from FN specifically inhibited GPR30-mediated epidermal growth factor receptor transactivation. Estrogen-mediated FN matrix assembly and epidermal growth factor receptor transactivation were similarly disrupted in integrin beta1-deficient GE11 cells, whereas reintroduction of integrin beta1 into GE11 cells restored these responses. Mutant Shc (317Y/F) blocked GPR30-induced FN matrix assembly and tyrosyl phosphorylation of erbB1. Interestingly, relative to recombinant wild-type Shc, 317Y/F Shc was more readily retained in GPR30-induced integrin alpha5beta1 complexes, yet this mutant did not prevent endogenous Shc-integrin alpha5beta1 complex formation. Our results suggest that GPR30 coordinates estrogen-mediated FN matrix assembly and growth factor release in human breast cancer cells via a Shc-dependent signaling mechanism that activates integrin alpha5beta1.

Estrogenic GPR30 signalling induces proliferation and migration of breast cancer cells through CTGF

The steroid hormone oestrogen can signal through several receptors and pathways. Although the transcriptional responses mediated by the nuclear oestrogen receptors (ER) have been extensively characterized, the changes in gene expression elicited by signalling through the membrane-associated ER GPR30 have not been studied. We show here for ER-negative human breast cancer cells that the activation of GPR30 signalling by oestrogen or by hydroxytamoxifen (OHT), an ER antagonist but GPR30 agonist, induces a transcription factor network, which resembles that induced by serum in fibroblasts. The most strongly induced gene, CTGF, appears to be a target of these transcription factors. We found that the secreted factor connective tissue growth factor (CTGF) not only contributes to promote proliferation but also mediates the GPR30-induced stimulation of cell migration. These results provide a framework for understanding the physiological and pathological functions of GPR30. As the activation of GPR30 by OHT also induces CTGF in fibroblasts from breast tumour biopsies, these pathways may be involved in promoting aggressive behaviour of breast tumours in response to endogenous oestrogens or to OHT being used for endocrine therapy.

Cyr61, a member of ccn (connective tissue growth factor/cysteine-rich 61/nephroblastoma overexpressed) family, predicts survival of patients with endometrial cancer of endometrioid subtype

OBJECTIVES

It has been reported that expression of Cyr61 decreased in endometrial cancers and cancer cell lines compared with normal endometrium, and forced expression of Cyr61 could suppress the growth of human endometrial cancer cells. However, in another report, Cyr61 was immunostained in most of endometrial cancer tissues analyzed. Thus, the aim of this study was to examine the expression of Cyr61 in endometrial cancer and to correlate Cyr61 expression with cinicopathologic factors in a larger cohort.

METHODS

We used immunohistochemistry and RT-PCR to examine the expression of Cyr61 in 92 endometrial carcinomas of endometrioid subtype. We correlated the expression of Cyr61 with various clinicopathologic factors in patients with endometrioid adenocarcinoma. Survival analyses were performed by the Kaplan Meier curves and the log-rank test. Independent prognostic factors were determined by multivariate Cox regression analysis.

RESULTS

Cyr61 expression was high in 21 of 92 cases of endometrioid adenocarcinoma (22.8%). High expression of Cyr61 was related to poor survival of patients with endometrioid adenocarcinoma. Multivariate analysis including Cyr61 expression revealed that Cyr61 expression and positive lymph node metastasis (LNM) were independent prognostic factors for survival. Survival of patients with endometrioid adenocarcinoma could be stratified into three groups by combination of Cyr61 expression and positive LNM with an estimated 5-year survival rate of 96.5% for no LNM irrespective of Cyr61 expression (group A), 85.7% for positive LNM with low/moderate expression of Cyr61 (group B), and 0% for positive LNM with high expression of Cyr61 (group C)(p=0.18 for group A vs group B, p=0.008 for group B vs group C, and p<0.0001 for group A vs group C).

CONCLUSIONS

Cyr61 is highly expressed in some endometrial cancer of endometrioid subtype. Cyr61 expression and positive LNM were independent prognostic factors for patients with endometrioid adenocarcinoma. Cyr61 might be a new molecular marker to predict the prognosis of patients with endometrioid adenocarcinoma.

Significance of concurrent endometrial cancer in women with a preoperative diagnosis of atypical endometrial hyperplasia

OBJECTIVES

Our objectives were (1) to review the rate of concurrent endometrial cancer in patients with a preoperative diagnosis of atypical endometrial hyperplasia (AEH); (2) to determine the proportion of patients with concurrent endometrial cancer who have high-risk disease; and (3) to re-evaluate our surgical management of AEH.

METHODS

We performed a retrospective chart review of all patients who had surgery on the basis of a preoperative diagnosis of atypical endometrial hyperplasia between January 2001 and December 2006. Demographic data, the method of preoperative diagnosis, postoperative grade of tumour, and other postoperative findings were recorded. When applicable, this included cancer stage, lymph node status, and presence of lymphovascular space invasion. In postoperative review, patients were considered to be high risk if they had disease beyond the uterus or a combination of other risk factors.

RESULTS

Of 70 patients, 25 (35.7%) were found to have concurrent endometrial cancer. This was higher than the commonly accepted rate of 25% (P = 0.03). Of the 25 patients upgraded, 4 (16%) had high-risk cancer on final pathologic evaluation.

CONCLUSION

Simple hysterectomy in women with AEH may result in inadequate surgical management. Simple methods are required to identify patients with a preoperative diagnosis of AEH who may harbour significant cancers.

Extra-nuclear signaling of estrogen receptors

Estrogen controls multiple biological functions through binding to estrogen receptors (ERs). Traditionally, ERs have been regarded as transcription factors regulating the expression of target genes. However, growing evidence of rapid estrogen's actions in a number of tissues has been accumulating and alternative mechanisms of signal transduction have been proposed. These so called "extra-nuclear actions" do not require gene expression or protein synthesis and are independent of the nuclear localization of ERs. Indeed, some of these actions are elicited by ERs residing at or near the plasma membrane. Membrane-associated molecules such as ion channels, G proteins, the tyrosine kinase c-Src as well as growth factor receptors are modulated by liganded ERs within the membrane, leading to the activation of downstream cascades such as mitogen-activated protein kinase, phosphatidylinositol 3-OH kinase, protein kinase A, and protein kinase C. These cascades mediate some important rapid actions of estrogen, such as the activation of nitric oxide synthesis or the remodeling of actin cytoskeleton. In addition, these pathways are critical for the regulation of the expression of a number of target proteins implicated in cell proliferation, apoptosis, differentiation, movement, and homeostasis. In this manner, the extra-nuclear pathways are tightly integrated with the genomic pathways to orchestrate the full spectrum of estrogen's biological functions. The recent advancements in the characterization of the molecular basis of the extra-nuclear signaling of estrogen helps to understand the role of estrogen on human cells, and may in future turn out to be of relevance for clinical purposes.

Epidermal growth factor induces G protein-coupled receptor 30 expression in estrogen receptor-negative breast cancer cells

Different cellular receptors mediate the biological effects induced by estrogens. In addition to the classical nuclear estrogen receptors (ERs)-alpha and -beta, estrogen also signals through the seven-transmembrane G-protein-coupled receptor (GPR)-30. Using as a model system SkBr3 and BT20 breast cancer cells lacking the classical ER, the regulation of GPR30 expression by 17beta-estradiol, the selective GPR30 ligand G-1, IGF-I, and epidermal growth factor (EGF) was evaluated. Transient transfections with an expression plasmid encoding a short 5'-flanking sequence of the GPR30 gene revealed that an activator protein-1 site located within this region is required for the activating potential exhibited only by EGF. Accordingly, EGF up-regulated GPR30 protein levels, which accumulated predominantly in the intracellular compartment. The stimulatory role elicited by EGF on GPR30 expression was triggered through rapid ERK phosphorylation and c-fos induction, which was strongly recruited to the activator protein-1 site found in the short 5'-flanking sequence of the GPR30 gene. Of note, EGF activating the EGF receptor-MAPK transduction pathway stimulated a regulatory loop that subsequently engaged estrogen through GPR30 to boost the proliferation of SkBr3 and BT20 breast tumor cells. The up-regulation of GPR30 by ligand-activated EGF receptor-MAPK signaling provides new insight into the well-known estrogen and EGF cross talk, which, as largely reported, contributes to breast cancer progression. On the basis of our results, the action of EGF may include the up-regulation of GPR30 in facilitating a stimulatory role of estrogen, even in ER-negative breast tumor cells.

Gene Expression Studies Demonstrate that the K-ras/Erk MAP Kinase Signal Transduction Pathway and Other Novel Pathways Contribute to the Pathogenesis of Cumene-induced Lung Tumors

National Toxicology Program (NTP) inhalation studies demonstrated that cumene significantly increased the incidence of alveolar/bronchiolar adenomas and carcinomas in B6C3F1 mice. Cumene or isopropylbenzene is a component of crude oil used primarily in the production of phenol and acetone. The authors performed global gene expression analysis to distinguish patterns of gene regulation between cumene-induced tumors and normal lung tissue and to look for patterns based on the presence or absence of K- ras and p53 mutations in the tumors. Principal component analysis segregated the carcinomas into groups with and without K- ras mutations, but failed to separate the tumors based on p53 mutation status. Expression of genes associated with the Erk MAP kinase signaling pathway was significantly altered in carcinomas with K- ras mutations compared to tumors without K- ras mutations or normal lung. Gene expression analysis also suggested that cumene-induced carcinomas with K- ras mutations have greater malignant potential than those without mutations. In addition, significance analysis of function and expression (SAFE) demonstrated expression changes of genes regulated by histone modification in carcinomas with K- ras mutations. The gene expression analysis suggested the formation of alveolar/bronchiolar carcinomas in cumene-exposed mice typically involves mutation of K- ras, which results in increased Erk MAP kinase signaling and modification of histones.

Estrogen signaling characteristics of Atlantic croaker G protein-coupled receptor 30 (GPR30) and evidence it is involved in maintenance of oocyte meiotic arrest

Human G protein-coupled receptor 30 (GPR30) mediates estradiol-17beta (E2) activation of adenylyl cyclase in breast cancer cells and displays E2 binding typical of membrane estrogen receptors (mERs). We identified a mER in Atlantic croaker ovaries with characteristics similar to those of human GPR30. To confirm the proposed role of GPR30 as a mER in this distantly related vertebrate group, we cloned GPR30 from croaker ovaries and examined its distribution, steroid binding, and signaling characteristics. Western blot analysis showed the GPR30 protein (approximately 40 kDa) is expressed on the plasma membranes of croaker oocytes and HEK293 cells stably transfected with GPR30 cDNA. Plasma membranes prepared from croaker GPR30-transfected cells displayed high-affinity, limited-capacity, and displaceable binding specific for estrogens, characteristic of mERs. Consistent with previous findings with human GPR30, estrogen treatment of plasma membranes from both croaker ovaries and GPR30-transfected cells caused activation of a stimulatory G protein (Gs) resulting in increased cAMP production. Treatment with E2 as well as G-1, a specific GPR30 ligand, significantly reduced both spontaneous and progestin-induced maturation of both croaker and zebrafish oocytes in vitro, suggesting a possible involvement of GPR30 in maintaining oocyte meiotic arrest in these species. Injection of antisense oligonucleotides to GPR30 into zebrafish oocytes blocked the inhibitory effects of estrogen on oocyte maturation, confirming a role for GPR30 in the control of meiotic arrest. These findings further support our previous suggestion that GPR30 is a vertebrate mER. In addition, the results suggest GRP30 may play a critical role in regulating reentry into the meiotic cell cycle in fish oocytes.

Preclinical development of a neutral, estrogen receptor-targeted, tridentate 99mTc(I)-estradiol-pyridin-2-yl hydrazine derivative for imaging of breast and endometrial cancers

Breast and endometrial cancers are the most common invasive malignancies in women, with more than 217,000 new diagnoses per year in the United States. These cancers are often classified into 2 subtypes based on the expression of the classical estrogen receptor. In this study, we describe a new structural class of neutral tridentate 99mTc(I)-estradiol-pyridin-2-yl hydrazine derivatives for potential use in breast and endometrial cancer imaging.

METHODS

The 99mTc(I)-estradiol-pyridin-2-yl hydrazine derivative was synthesized via the Sonogashira cross-coupling reaction and radiolabeled via the tricarbonyl approach. Radiochemical purity was assessed by high-performance liquid chromatography. Cell-binding studies were performed with human breast adenocarcinoma MCF-7 cells. The in vivo biodistribution of the 99mTc(I) derivative was evaluated in virgin female C57BL/6 mice in defined phases of the estrous cycle. Biodistribution and SPECT/CT studies were performed with mice bearing MCF-7 and primary human endometrial tumors.

RESULTS

Radiochemical analysis demonstrated that the postpurification purity of the 99mTc(I)-estradiol-pyridin-2-yl hydrazine derivative was > or =95%, with a specific activity of 99mTc of 47.5 TBq/mmol. Cell-binding studies yielded a dissociation constant (mean +/- SEM) of 11 +/- 1.5 nM. In vivo studies revealed that receptor-mediated uptake was present in all phases of the estrous cycle in reproductive organs and mammary glands but was highest during the diestrous phase of the estrous cycle. Despite high nonspecific uptake in the liver, significant receptor-mediated uptake was observed in target tissues and estrogen receptor-expressing tumors (0.67% for MCF-7 tumors and 0.77% for endometrial tumors). Tumor uptake was reduced by approximately 50% on coinjection with 17beta-estradiol.

CONCLUSION

We have characterized a novel neutral tridentate 99mTc(I)-estradiol-pyridin-2-yl hydrazine derivative for potential use in breast and endometrial cancer imaging. This study represents the first step on a path toward the design of estrogen-based Tc-labeled tracers with improved targeting and SPECT imaging characteristics.

Estrogen signaling through the transmembrane G protein-coupled receptor GPR30

Steroids play an important role in the regulation of normal physiology and the treatment of disease. Steroid receptors have classically been described as ligand-activated transcription factors mediating long-term genomic effects in hormonally regulated tissues. It is now clear that steroids also mediate rapid signaling events traditionally associated with growth factor receptors and G protein-coupled receptors. Although evidence suggests that the classical steroid receptors are capable of mediating many of these events, more recent discoveries reveal the existence of transmembrane receptors capable of responding to steroids with cellular activation. One such receptor, GPR30, is a member of the G protein-coupled receptor superfamily and mediates estrogen-dependent kinase activation as well as transcriptional responses. In this review, we provide an overview of the evidence for the cellular and physiological actions of GPR30 in estrogen-dependent processes and discuss the relationship of GPR30 with classical estrogen receptors.

Hormonal heterogeneity of endometrial cancer

Endometrial cancer is the most common malignant tumor of the female genital tract in the developed world. Increasing evidence suggests that the majority of cases can be divided into two different types ofendometrial cancer based on clinico-pathological and molecular characteristics. Type I is associated with an endocrine milieu of estrogen predominance. These tumors are ofendometroid histology and develop from endometrial hyperplasia. They have good prognosis and are sensitive to endocrine treatment. Type II endometrial cancers are not associated with a history of unopposed estrogens and develop from the atrophic endometrium of elderly women. Mainly, they are of serous papillary or clear cell morphology, have a poor prognosis and do not react to endocrine treatment. Both types of endometrial cancer probably differ markedly with regard to the molecular mechanisms of transformation. The transition from normal endometrium to a malignant tumor is thought to involve a stepwise accumulation of alterations in cellular mechanisms leading to dysfunctional cell growth. This chapter reviews the current knowledge of the molecular mechanisms commonly associated with development of type I and type II endometrial cancer.

Endometrial Expression of Cyr61

OBJECTIVE

To compare the expression of Cyr61 in normal cycling endometrium with endometrium from women with polycystic ovarian syndrome (PCOS) and endometrial hyperplasia and adenocarcinoma.

METHODS

This is a retrospective study of 59 samples of normal and abnormal endometrium. Endometrial biopsies were obtained from normal fertile controls throughout the menstrual cycle and compared with endometrium from ovulatory and anovulatory women with PCOS and complex endometrial hyperplasia and endometrioid adenocarcinoma. Cyr61 expression was evaluated by using immunohistochemistry and reverse transcription PCR for Cyr61, estrogen receptor (ER)-alpha, a marker of cell proliferation (Ki67), and another marker of early estrogen action, cFos. Regulation of Cyr61 protein was studied in a steroid-responsive endometrial carcinoma cell line, ECC1.

RESULTS

Cyr61 protein was regulated by estrogen. In normal endometrium, Cyr61 was highest in the proliferative phase and lowest in the normal midsecretory phase. In contrast, elevated levels of Cyr61, ER-alpha, Ki67, and cFos were all found in the midsecretory endometrium of ovulatory PCOS patients, endometrial cancer patients, and hyperplasia patients.

CONCLUSION

Cyr61 is overexpressed in PCOS endometrium, reflecting a heightened responsiveness to estrogen. As a unique marker of estrogen action, Cyr61 may be an early biomarker for the development of hyperplasia or adenocarcinoma in this group of women.