[Effects of daidzein on steroid receptor coactivator-1 expression in MC3T3-E1 cells and the mechanism].

Objective: To investigate the roles of daidzein in the expressions of steroid receptor coactivator-1 (SRC-1) and nuclear receptor corepressor (NcoR) in MC3T3-E1 osteoblastic cells.

Methods: MC3T3-E1 cells were cultured in α-minimal essential medium (α-MEM) containing 2% fetal bovine serum and treated with various concentrations of daidzein (10(-9), 10(-7) and 10(-5) mol/L) or 17β-estradiol at 10(-8) mol/L for 3 d. The protein levels of SRC-1 and NcoR in MC3T3-E1 cells were determined by Western blotting. Estrogen receptor (ER) antagonist ICI182780 at 10(-7) mol/L or specific ERα antagonist methyl-piperidino-pyrazole (MPP) at 10(-6) mol/L were used to block the corresponding receptors, and then MC3T3-E1 cells were treated with daidzein at 10(-7) mol/L or 10(-5) mol/L for 3 d. SRC-1 and NcoR protein levels were detected by Western blotting.

Results: The protein levels of SRC-1 increased by 2.5 fold (P<0.05) and 2 fold (P<0.05) by 10(-7) and 10(-5) mol/L of daidzein respectively, while the NcoR levels were not significantly altered. 17β-Estradiol at dose of 10(-8) mol/L did not affect the expression of SRC-1 but decreased NcoR protein expression by 35% (P<0.05). Compared with the control, daidzein at 10(-7) and 10(-5) mol/L did not increase SRC-1 expression when ERs were blocked by antagonist ICI182780. Daidzein at 10(-7) and 10(-5) mol/L up-regulated SRC-1 by 1.8 fold (P<0.05) and 2.4 fold (P<0.05) respectively while ERα was blocked by MPP.

Conclusion: Daidzein increases protein level of SRC-1 and the ratio of SRC-1/NcoR. ERβ, instead of ERα, participates in the action of daidzein in regulating SRC-1 expression. Up-regulation of SRC-1 and increase of SRC-1/NcoR are part of the mechanism of the estrogenic effect of daidzein in improving osteogenesis.