DEFECTIVE PHOSPHOLIPASE-D ACTIVATION IN KI-RAS-TRANSFORMED NIH3T3 CELLS - EVIDENCE FOR DOWNSTREAM EFFECTOR OF PLC-GAMMA-1 IN PDGF-MEDIATED SIGNAL-TRANSDUCTION

Platelet-derived growth factor (PDGF), a potent mitogen for fibroblasts and many other cell types, was used to examine phosphatidylcholine-speific phospholipase D (PLD), phosphoinositide-specific phospholipase C (PI-PLC) and tyrosine phosphorylation in NIH3T3 fibroblast and its Ki-ms-transformed derivative, DT. When cells prelabeled with [H-3] myristic acid were stimulated by 10 and 50 ng/ml of PDGF in presence of 0.3% butanol, formation of phosphatidylbutanol (PtdBut) was increased three to six fold in NIH3T3 fibroblasts whereas it was marginal in DT cells, Myo-[H-3]inositol-labeled cells showed higher inositol phosphate production in nontransformed control fibroblasts, indicating higher phospholipase C activity compared to the transformed DT cells. PDGF caused increase in tyrosine phosphorylation of a group of proteins with 110-130 kDa, PLC-gamma l and PDGF receptor in NIH3T3 cells. There was no significant increase in tyrosine phosphorylation in both PDGF receptor and PLC-gamma l in DT cells. These results suggest that PLD acts as a downstream effector molecule of PLC-gamma l in the PDGF-mediated Signal transduction pathway. (C) 1995 Academic Press, Inc.