ARACHIDONIC-ACID, A GROWTH SIGNAL IN MURINE P815 MASTOCYTOMA-CELLS

Evidence is presented that inducing P815 murine mastocytoma cells to g row with serum activates a Ca2-stimulated phospholipase A2 and the rap id release of arachidonic acid by the cells. Slower growth was also ma intained by arachidonic acid or its immediate precursors or by diacylg lycerols when bovine serum albumin replaced the serum. Together, arach idonic acid and 1-oleoyl-2-acetylglycerol stimulated growth at the sam e rate as 10% serum consistent with a role for both arachidonic acid a nd protein kinase C in the response to serum. Arresting cell growth wi th N6,O2'-dibutyryladenosine 3',5'-cyclic phosphate and theophylline i nhibited the release of arachidonic acid in response to serum, suggest ing that cyclic AMP prevents phospholipase activation as one of its pl eiotypic effects on growth. Attempts to demonstrate metabolism of [H-3 ]arachidonic acid to eicosanoids in serum-treated P815 cells by high-p erformance liquid chromatography or thin layer chromatography were uns uccessful, with the major products being phospholipids and triacylglyc erol. Incubating digitonin-permeabilized P815 cells with [gamma-P-32]A TP and arachidonic acid rapidly increased the phosphorylation of some proteins in the cells, especially the M(r) 135,000 and M(r) 44,000 pro teins which were considerably more phosphorylated than the rest. Phosp horylation of these proteins was not prevented by several inhibitors o f protein kinase C, nor was it increased by diacylglycerols or phorbol ester, suggesting that arachidonic acid activates a growth-related pr otein kinase other than protein kinase C in P815 cells. The possibilit y that some polyunsaturated fatty acids may promote tumor cell growth by stimulating protein phosphorylation is considered.