Requirements for Protein Synthesis and Calcium for Stimulation of Prostaglandin Synthesis in Cultured Rat Liver Cells by Tumor Promoters1

The tumor promoters, 12-O-tetradecanoylphorbol-IS-acetate (TPA), phorbol-12,13-didecanoate, teleocidin, and dihydroteleocidin, at nw levels, but not the non-tumor-promoting 4«-phorbol12,13-didecanoate even at ¡Mconcentrations, stimulated arachidonic acid metabolism in cultured rat liver cells. These liver cells synthesize primarily prostaglandin I2 [measured as its nonenzymatic hydrolytic product, 6-keto-prostaglandin F1«(PGF1o)].The production of 6-keto-PGFi„increased with time of incubation with TPA and was essentially complete in 4 hr. Cycloheximide, at nw levels, blocked the TPA-stimulated 6-keto-PGF1a produc tion in a dose-dependent manner; this inhibition was related to inhibition of protein synthesis. Chelation of Ca2+ by ethyleneglycol-bis(/8-aminoethyl ether)-A/,A/'-tetraacetic acid, treatment of the cells with the Ca2+ channel blocker, nifedipine, or inhibition of intracellular Ca2+ mobilization by 8-(diethylamine)octyl-3,4,5trimethoxybenzoate hydrochloride also inhibited TPA-stimulated 6-keto-PGF1a production. The steroidal antiinflammatory drug, dexamethasone, a potent in vivo inhibitor of tumor promotion, was an inhibitor of 6-keto-PGF1n stimulation by TPA.