A tumor promoter enhances the phosphorylation of polyphosphoinositides while decreasing phosphatidylinositol labelling in lymphocytes.

12-O-Tetradecanoyl-phorbol-13-acetate, a comitogen for lymphocytes, suppresses the concanavalin A-induced accumulation of 3 2P-phosphatidyl-inositol, in mouse spleen lymphocytes incubated with 3 2P-orthophosphate. The comitogenic tumor promoter does not affect the rate of de novo synthesis of phosphatidylinositol, as measured by [3H]-glycerol incorporation. Mitogen stimulates the incorporation of [3 2P]-phosphate into phosphatidylinositol, phosphatidylinositol-4-phosphate and phosphatidylinositol-4,5-bisphosphate, but the tumor promoter suppresses only the increased labelling of the phosphatidylinositol, while it enhances phosphorylation of the polyphosphoinositides.