Modulation of phorbol ester-associated events in epidermal cells by linoleate and arachidonate

To elucidate the events elicited by the skin tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA), which are modulated by linoleic acid (LA) and arachidonic acid (AA), the activity of these fatty acids in cultured mouse epidermal cells was compared. Approximately 94% of either exogenous radiolabelled fatty acid was incorporated into the total phospholipid pool over 15 h. The relative distribution among the phospholipid classes differed, however, such that approximately 70% of phospholipid-associated [14C]-LA was found in phosphatidylcholine, compared to approximately 30% for [14C]AA. Phosphatidylethanolamine and phosphatidylinositol/phosphatidylserine contained 17 and 13% of the phospholipid [14C]LA, and 34 and 30% of [14C]AA, respectively. Prostaglandin (PG) E2 production was low but similar in unstimulated cultures prelabelled with either [14C]LA or [14C]AA. However, in cultures treated with TPA (1.6 microM), [14C]AA-prelabelling resulted in approximately three times the amount of [14C]PGE2 compared with cultures prelabelled with [14C]LA. Cultured cells were found to contain significant delta 6 desaturase activity, which may enable conversion of LA to AA, and thus may account for the observed PGE2 production from [14C]LA treated cells. AA-Supplemented (1.6 microM) cultures supported approximately twice the induction of ornithine decarboxylase activity by TPA compared with cultures treated with 1.8 microM LA. Activation of partially purified protein kinase C was similar for either fatty acid tested over a 10-300 microM dose range. Overall, the results suggest that LA does not have the same biological activity as AA with regard to several TPA-associated events known to be important in skin tumor promotion.(ABSTRACT TRUNCATED AT 250 WORDS)