Phosphatidylethanolamine and phosphatidylcholine are sources of diacylglycerol in ras-transformed NIH 3T3 fibroblasts

Ras-transformation of cells is accompanied by an increase of the level of d iacylglycerol (DAG), which participates in the signal transduction pathways . DAG could be generated from phospholipids either by activation of phospho lipase C or by a more complex pathway involving phospholipase D and phospha tidate phosphohydrolase. To clarify which phospholipids produce DAG and whi ch pathways are involved, we examined the DAG generating enzyme activities. using phosphatidylcholine (PC), phosphatidylethanolamine (PE) and phosphat idylinositol (PI) as substrates. The study showed that the breakdown of PC and more markedly of PE by phospholipases C and D was stimulated in membran es from ras-transformed cells. Phosphatidate phosphohydrolase activity was also elevated in oncogene-expressing cells. The increase in glycerol uptake was most pronounced in cells given PEI followed by PC. The fatty acid anal ysis revealed apparent similarities between the acyl chains of PE and DAG o nly in the transformed cells. These findings suggest that PE is a source of DAG in ras-fibroblasts but does not rule out the role of PC in DAG product ion, due to the activation of the PC-specific phospholipases C and D. (C) 1 999 Elsevier Science Ltd. All rights reserved.