TYROSINE KINASE REGULATES PHOSPHOLIPASE-D ACTIVATION AT A POINT DOWNSTREAM FROM PROTEIN-KINASE-C IN OSTEOBLAST-LIKE CELLS

It has recently been shown that the activation of protein kinase C (PK C) induces protein tyrosine phosphorylation in osteoblast-like MC3T3-E 1 cells. We previously reported that the activation of PKC stimulates phosphatidylcholine-hydrolyzing phospholipase D in these cells. In thi s study, we examined whether protein tyrosine kinase is involved in th e PKC-induced activation of phospholipase D in MC3T3-E1 cells. Geniste in, an inhibitor of protein tyrosine kinases, which by itself had litt le effect on choline formation, significantly suppressed the formation of choline induced by 12-O-tetradecanoylphorbol-13-acetate (TPA), an activator of PKC, in a dose-dependent manner. Tyrphostin, an inhibitor of protein tyrosine kinases chemically distinct from genistein, also dose-dependently suppressed the TPA-induced formation of choline. Sodi um orthovanadate, an inhibitor of protein tyrosine phosphatases, signi ficantly enhanced the TPA-induced formation of choline in a dose-depen dent manner. These results strongly suggest that protein tyrosine kina se regulates phospholipase D activity at a point downstream from PKC i n osteoblast-like cells. (C) 1995 Wiley-Liss, Inc.