INCREASED CONCENTRATIONS OF PHOSPHATIDATE, DIACYLGLYCEROL AND CERAMIDE IN RAS-TRANSFORMED AND TYROSINE KINASE (FPS)-TRANSFORMED FIBROBLASTS

Concentrations of the bioactive lipids, phosphatidate and diacylglycer ol, increased with time in culture in ras- and tyrosine kinase (fps)-t ransformed fibroblasts but not in control fibroblasts, On Day 3, diacy lglycerol and phosphatidate concentrations were about 3.3- and 5.5-fol d higher respectively in the Pas-transformed compared to control fibro blasts. These concentrations in fps-transformed fibroblasts were incre ased about twofold. The changes in phosphatidate and diacylglycerol re sulted from enhanced phospholipid turnover rather than from synthesis de novo, The increased ratio of phosphatidate to diacylglycerol is exp lained by decreased activities of two distinct phosphatidate phosphohy drolases and increased diacylglycerol kinase in Pas-transformed fibrob lasts. Ceramide concentrations were about 2.5- and threefold higher in the fps- and ras-transformed cells respectively on Day 3 compared to the controls, Incubating control fibroblasts from Days 1 to 3 with pho sphatidylcholine-specific phospholipase C increased diacylglycerol, ph osphatidate and ceramide concentrations, and decreased Mg2+-independen t-phosphatidate phosphohydrolase activity, 8-(4-chlorophenylthio)-cAMP had a cytostatic effect in Pas-transformed cells, it decreased the co ncentrations of phosphatidate and diacylglycerol, but increased that o f ceramide, The consequences of increased ceramide and phosphatidate c oncentrations in Pas-transformed cells are discussed in relation to si gnal transduction, cell division and the transformed phenotype.