Cellular signal transduction system in prostaglandin-stimulated osteoblast-like MC3T3-E1 cells : Phospholipid turnover and protein tyrosine phosphorylation

点击翻译按钮获取中文摘要

The combination of beta-glycerophosphate and ascorbic acid increased alkaline phosphate (ALP) activity, a maraker for osteoblastic differentiation, in clonal osteoblast like cell line MC3T3-E1. The increase was detected as 24 hours after the addition of these agents to growth medium and reached almost maximal level at 5 days of culture. Although increase in intracellular cyclic AMP level is known to induce osteoblastic acell differentiation, these treatment did not cause significant increase in cyclic AMP.Treatment of beta-glycerophsphate and ascorbic acid suppressed activaaton of phosphoinositide-specific phospholipase C (PI-PLC) and phospholipase D (PLD) in response to prostaglandin F_<2alpha> (PGF_<2alpha>) by 20-30% and 15%, respectively. Western blot analyzes with subtype-specific PI-PLC antibodies revealed that in cells treated for 5 days with these differentiation inducers, the levels of PI-PLCbeta1 and PI-PLCbeta3 decreased to 37% and 67% compared to those of undifferentiated control cells, respectively. However, the level of PLC_<gamma>1 and those of protein kinase C isozymes (alpha, beta1, beta2, delta, epsilon, rheta, zeta) remained unaltered. PGF_<2alpha> also stimulated protein tyrosine phosphorilations and activation of mitogen-activated protein (MAP) kinases. These responses were not affected by differentiation induceres. These results suggest that the suppressed expression of PI-PLCbeta1 and PI-PLCbeta3 are closely related to osteoblast cell differentiation.