Abstract

We have investigated the mechanisms by which the tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA) stimulates prostaglandin E2 (PGE2) formation in the rat tracheal epithelial cell line EGV-6aigT, which can be grown in serum-free medium. The addition of TPA to cells that were prelabeled with [3H]arachidonic acid did not enhance the release of [3H]arachidonic acid and/or [3H]PGE2, indicating that TPA does not stimulate phospholipase activity. The addition of exogenous arachidonic acid to cells pretreated with TPA resulted in increased PGE2 formation, compared with basal levels, indicating an elevation in prostaglandin H synthase (PHS) activity. PHS activity was maximal at 4 hr and was dependent upon the concentration of TPA. Actinomycin D and cycloheximide blocked the TPA response. The recovery of PHS activity of cells in which the existing PHS was inhibited by aspirin was enhanced by TPA treatment. TPA treatment enhanced the expression of PHS mRNA, as measured by Northern analysis. The addition of actinomycin D and cycloheximide reduced the TPA enhancement of PHS mRNA, indicating that the increase in PHS activity required de novo RNA and protein synthesis. Furthermore, pretreatment of the cells with protein kinase C inhibitors reduced the TPA-dependent stimulation of PHS activity and the expression of PHS mRNA. The data suggest that TPA-stimulated de novo synthesis of PHS is mediated by protein kinase C.