We previously showed that protein kinase C (PKC) induces phosphatidylcholine-hydrolysing phospholipase D activation in osteoblast-like MC3T3-E1 cells and that tyrosine kinase is involved in this activation. Wortmannin, a potent inhibitor of phosphatidylinositol 3-kinase, markedly enhanced the formation of choline induced by 12-O-tetradecanoylphorbol-13-acetate (TPA), an activator of PKC in MC3T3-E1 cells. The effect of wortmannin was dose-dependent between 0.1 μM and 10 μM. ML-7, an inhibitor of myosin light chain kinase, had little effect on the TPA-induced formation of choline. Genistein, an inhibitor of protein tyrosine kinases, significantly suppressed the potentiation by wortmannin. These results strongly suggest that phosphatidylinositol 3-kinase is involved in the regulation of phospholipase D activation by PKC in osteoblast-like cells. © 1995.
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