G protein-coupled estrogen receptor 1 (GPER 1) mediates estrogen-induced, proliferation of leiomyoma cells

G protein-coupled estrogen receptor 1 (GPER-1, formerly known as GPR30) has been proposed as the receptor for estrogen-induced, growth of leiomyomas though its precise mechanisms of action are not clear. We obtained leiomyoma cells (LC) and normal smooth muscle cells from 28 women (n=28, median age 38 years, median parity 1.0). We incubated them with 17- estradiol (E-2), after blocking, or upregulating, expression of GPER-1 with ICI182,780 (a GPER-1 agonist) and siGPR30, respectively. We evaluated the role of GPER-1 in the mitogen-activated protein kinase (MAPK) signaling pathway using Western blot analysis. We studied cell proliferation with 3-(4,5-dimethylthiazol-2-yl)2,5-diphenyl tetrazolium bromide, and, mitotic activity with phosphohistone H3 (PPH3) expression in leiomyoma, and, matched, normal, smooth muscle tissues using standard immunohistochemistry. Downregulation of GPER-1 expression with siGPR30 partially attenuated the E-2-activated MAPK signaling pathway (p<0.01). Upregulation of GPER-1 with ICI182,780 enhanced the E-2-activated MAPK signaling pathway (p<0.01). ICI182,780 enhanced E-2-induced proliferation of LC (p<0.01), while knock down of the GPER-1 gene with GPER-1 small interfering RNA partially inhibited E-2-induced cell proliferation (p<0.01). There were no significant differences in PPH3 expression between LCs and normal smooth muscle tissues (p>0.05). Neither ICI182,780 nor siGPR30 increased mitosis in LCs (p>0.05). Our results indicate that GPER-1 mediates proliferation of estrogen-induced, LC by activating the MAPK pathway, and, not by promoting mitosis.