The G protein-coupled receptor GPR30 inhibits proliferation of estrogen receptor-positive breast cancer cells

The G protein-coupled receptor GPR30 binds 17β-estradiol (E ₂) yet differs from classic estrogen receptors (ERα and ERβ). GPR30 can mediate E₂-induced nongenomic signaling, but its role in ERα-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 ERα-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, E₂ 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 ERα, mediated E₂-induced Ca ²⁺ responses because E₂, 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 E₂-induced and G-1-induced C ^a2+ mobilization, but ERα 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 ERα-positive breast cancer and may represent a new target to combat this disease.