Phospholipid dependence of membrane-bound phospholipase A(2) in ras-transformed NIH 3T3 fibroblasts

Although the activation of phospholipase A(2) (PLA(2)) in ms-transformed ce lls has been well documented, the mechanisms underlying this activation are poorly understood. In this study we tried to elucidate whether the membran e phospholipid composition and physical state influence the activity of mem brane-associated PLA(2) in ras-transformed fibroblasts. For this purpose me mbranes from non-transfected and ms-transfected NM 3T3 fibroblasts were enr iched with different phospholipids by the aid of partially purified lipid t ransfer protein. The results showed that of all tested phospholipids only p hosphatidylcholine (PC) increased PLA(2) activity in the control cells, whe reas in their transformed counterparts both PC and phosphatidic acid (PA) i nduced such effect. Further we investigated whether the activatory effect w as due only to the polar head of these phospholipids, or if it was also rel ated to their acyl chain composition. The results demonstrated that the ara chidonic acid-containing PC and PA molecules induced a more pronounced incr ease of membrane-associated PLA(2) activity in ras-transformed cells compar ed to the corresponding palmitate stearate- or oleate- containing molecular species. However, we did not observe any specific effect of the phospholip id fatty acid composition in non-transformed NM 3T3 fibroblasts. In ras-tra nsformed cells incubated with increasing concentrations of arachidonic acid , PLA(2) activity was altered in parallel with the changes of the cellular content of this fatty acid. The role of phosphatidic and arachidonic acids as specific activators of PLA(2) in ras-transformed cells is discussed with respect to their possible role in the signal transduction pathways as well as in the processes of malignant transformation of cells. (C) Societe fran caise de biochimie et biologie moleculaire / Elsevier, Paris.