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.