Effects of the phorbolester TPA and of the ionophore A 23187 on phospholipase A2 and C activities in the mouse epidermal cell line HEL-30

The 12-O-tetradecanoylphorbol-13-acetate (TPA)- or ionophore A 23187-induced release of 14C-arachidonic acid from prelabeled murine HEL-30 keratinocytes was studied in vitro. Starting 8 min after drug treatment, a linear increase in the arachidonic acid content in the extracellular medium was observed with a concomitant loss of label in cellular phosphatidylcholine and phosphatidylinositol, but not in phosphatidylethanolamine and phosphatidylserine. No increase in intracellular diacylglycerol and phosphatidic acid was observed. The TPA-induced arachidonic acid release was inhibited by fluocinolone acetonide. The results indicate a direct activation of phosphatidylcholine- and phosphatidylinositol-specific phospholipases A2 by TPA and A23187. Cells prelabeled with 3H-choline released choline, choline phosphate and CDP-choline upon TPA but not upon A 23187 treatment. This could indicate activation of a phospholipase C-type enzyme by the phorbol ester. However, concomitant generation of diacylglycerol and phosphatidic acid was not detected.