The G Protein-Coupled Receptor GPR30 Inhibits Proliferation of Estrogen Receptor-Positive Breast Cancer Cells

The G protein-coupled receptor GPR30 binds 17 beta-estradiol (E-2) yet differs from classic estrogen receptors (ER alpha and ER beta). GPR30 can mediate E-2-induced nongenomic signaling, but its role in ER alpha-positive breast cancer remains unclear. Gene expression microarray data from five cohorts comprising 1,250 breast carcinomas showed an association between increased GPR30 expression and ER alpha-positive status. We therefore examined GPR30 in estrogenic activities in ER-positive MCF-7 breast cancer cells using G-1 and diethylstilbestrol (DES), ligands that selectively activate GPR30 and ER, respectively, and small interfering RNAs. In expression studies, E-2 and DES, but not G-1, transiently downregulated both ER and GPR30, indicating that this was ER mediated. In Ca2+ mobilization studies, GPR30, but not ER alpha, mediated E-2-induced Ca2+ responses because E-2, 4-hydroxytamoxifen (activates GPR30), and G-1, but not DES, elicited cytosolic Ca2+ increases not only in MCF-7 cells but also in ER-negative SKBr3 cells. Additionally, in MCF-7 cells, GPR30 depletion blocked E-2-induced and G-1-induced Ca2+ mobilization, but ER alpha depletion did not. Interestingly, GPR30-coupled Ca2+ responses were sustained and inositol triphosphate receptor mediated in ER-positive MCF-7 cells but transitory and ryanodine receptor mediated in ER-negative SKBr3 cells. Proliferation studies involving GPR30 depletion indicated that the role of GPR30 was to promote SKBr3 cell growth but reduce MCF-7 cell growth. Supporting this, G-1 profoundly inhibited MCF-7 cell growth, potentially via p53 and p21 induction. Further, flow cytometry showed that G-1 blocked MCF-7 cell cycle progression at the G(1) phase. Thus, GPR30 antagonizes growth of ER alpha-positive breast cancer and may represent a new target to combat this disease. Cancer Res; 70(3); 1184-94. (C) 2010 AACR.