Basic fibroblast growth factor stimulates phosphatidylcholine-hydrolyzing phospholipase D in osteoblast-like cells

We examined the effect of basic fibroblast growth factor (bFGF) on the activation of phosphatidylcholine-hydrolyzing phospholipase D in osteoblast-like MC3T3-E1 cells. bFGF stimulated both the formations of choline (EC50 was 30 ng/ml) and inositol phosphates (EC50 was 10 ng/ml). Calphostin C, an inhibitor of protein kinase C (PKC), had little effect on the bFGF-induced formation of choline. bFGF stimulated the formation of choline also in PKC down regulated cells. Genistein and methyl 2,5-dihydroxycinnamate, inhibitors of protein tyrosine kinases, significantly suppressed the bFGF-induced formation of choline. Sodium orthovanadate, an inhibitor of protein tyrosine phosphatases, enhanced the bFGF-induced formation of choline. In vitro kinase assay for FGF receptors revealed that FGF receptor 1 and 2 were autophosphorylated after FGF stimulation. bFGF dose-dependently stimulated DNA synthesis of these cells. These results strongly suggest that bFGF activates phosphatidylcholine-hydrolyzing phospholipase D through the activation of tyrosine kinase, but independently of PKC activated by phosphoinositide hydrolysis in osteoblast-like cells.