GTP-binding protein-stimulated phospholipase C and phospholipase D activities in ras-transformed NIH 3T3 fibroblasts

The stable GTP analog, guanosine 5'-(3-O-thiotriphosphate), GTP gamma S, stimulated both inositol trisphosphate (InsP3) and choline generation by NIH 3T3 cell membranes. Choline generation was stimulated by GTP gamma S over the dose range for activation of GTP-binding proteins. Membranes from control and c-Ha-ras- or c-Ha-ras(61 leu)-transformed cells did not differ in the extent to which GTP gamma S stimulated InsP3 or choline formation despite 5-10 fold over expression of Ras in the transformed cells. Unlike GTP gamma S, GTP did not stimulate phospholipid hydrolysis, even in membranes from cells expressing Ras61leu, a mutant protein having reduced GTPase activity. Thus there is G protein regulation of both phosphatidylcholine-specific phospholipase D and polyphosphoinositide-specific phospholipase C in NIH 3T3 cell membranes. However, the lack of difference in GTP gamma S-stimulated phospholipid metabolism between control and ras-transformed cell membranes suggests that Ras does not function as the G protein(s) that directly regulate either phospholipase.