Study on the Role of Estrogen Receptor-Alpha in Yak-Kong and Soybean Induced Proliferation of MG-63 Human Osteoblastic Cells

ABSTRACT

Phytoestrogens, especially Yak-kong or soybean-derived isoflavones have been traditionally used as a supplement of estrogen for preventing postmenopausal osteoporosis in oriental folk medicine. In a previous study, we demonstrated that as Yak-kong and soybean increased MG-63 human osteoblastic cell proliferation, the expression of estrogen receptor alpha and beta (ERalpha ERbeta) both were increased. However, the increased level of ERalpha is much higher than that of ERbeta. To determine whether the altered level of ERalpha expression affects Yak-kong or soybean induced MG-63 cell proliferation, we established cell lines stably expressing either ERalpha or antisense ERalpha RNAs. Increased expression of ERalpha in MG-63 cells (ERalpha-MG63) enhanced Yak-kong or soybean induced proliferation which paralleled with the enhanced expression of IGF-I. Inhibition of ERalpha expression by antisense ERalpha RNAs (As-ERalpha-MG63) caused these cells to insensitize Yakkong or soybean induced proliferation and IGF-I expression. Furthermore, the comparable effects between Yak-kong and the combined treatment of genistein and daidzein at 0.5 x 10-8M, which is a concentration of these two isoflavones similar to Yak-kong at 0.001 mg/ml, on cell proliferation and IGF-I expression in ERalpha-MG63 or As-ERalpha-MG63 cells demonstrate that ERalpha plays an important, active role in MG-63 cell proliferation induced by phytoestrogens, especially Yak-kong or soybean derived isoflavones.