Early changes in the arachidonic acid metabolism of HeLa cells in response to the tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA) and related compounds

Abstract

In order to search for possible mediators involved in the transient radiomimetic effectiveness of TPA and related compounds early changes in the AA metabolism of HeLa cells prelabeled with 1-14C-AA have been analyzed. Maximum release of AA with different concentrations of TPA (3 X 10(-9) to 3 X 10(-5) M) was observed after 2-3 h treatment in the presence of 10% calf serum. Released AA was reincorporated by the cells after that period, a phenomenon which was largely abolished or delayed by cycloheximide. Reincorporation of released AA was observed in the presence of 10% fresh serum as well as with 0.5% BSA, and appears to be due to an induction of responsible enzyme(s) by the phorbol ester. The earliest metabolites of AA produced via the cyclooxygenase such as PGE2 and PGF2 alpha and via lipoxygenases such as 12-, and 15-hydroxyeicosatetraenoic acids appear in small amounts and after later time points. AA release exhibited a pluriphasic dose response to TPA with maxima at 3 X 10(-8) M and greater than or equal to 10(-5) M. Comparative dose response measurements with respect to AA release were established using various promoting skin mitogens which exhibited the following order of potency: TPA greater than teleocidin approximately equal to RPA greater than mezerein much greater than EPA greater than 4-O-Me-TPA. For reasons discussed it appears unlikely that AA, Prostaglandins, or hydroxyeicosatetraenoic acid products play a significant role as mediators of the radiomimetic effects of TPA in G2 of the cell cycle.