Stimulatory effect of genistein and daidzein on protein synthesis in osteoblastic MC3T3-E1 cells: Activation of aminoacyl-tRNA synthetase

The effect of genistein and daidzein on protein synthesis in osteoblastic M C3T3-E1 cells in vitro was investigated to determine a cellular mechanism b y which the isoflavones stimulate bone formation. Cells were cultured for 4 8 h in alpha -minimal essential medium containing either vehicle, genistein (10(-7)-10(-5) M) or daidzein (10(-7)-10(-5) M). The 5,500 g supernatant o f cell homogenate was used for assay of protein synthesis with [H-3]leucine incorporation in vitro. The culture with genistein or daidzein caused a si gnificant elevation of protein synthesis in the cell homogenate. The effect of genistein (10(-5) M) or daidzein (10(-5) M) in elevating protein synthe sis was significantly prevented, when cells were cultured for 48 h in a med ium containing either actinomycin D (10(-7) M) or cycloheximide (10(-6) M) in the absence or presence of isoflavones. Moreover, when genistein (10(-7) -10(-5) M) or daidzein (10(-6) and 10(-5) M) was added to the reaction mixt ure containing the cell homogenate obtained from osteoblastic cells culture d without isoflavone, protein synthesis was significantly raised. This incr ease was markedly blocked by the addition of cycloheximide (10(-7) M). In a ddition, [H-3]leucyl-tRNA synthetase activity in the cytosol of osteoblasti c cells was significantly increased by the addition of genistein (10(-6) an d 10(-5) M) or daidzein (10(-5) M) into the enzyme reaction mixture. The pr esent study demonstrates that genistein or daidzein can stimulate protein s ynthesis in osteoblastic MC3T3-E1 cells. The isoflavones may have a stimula tory effect on osteoblastic bone formation due to increasing protein synthe sis.