Phosphorylation of specific polypeptides induced by 12-O-tetradecanoylphorbol-13-acetate in chick embryo fibroblasts.

The tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA) induces, in cultured chick embryo fibroblasts, a generalised increase of the incorporation of labelled inorganic phosphate, and stimulates the phosphorylation of at least two polypeptide bands, 26 K and 65 K. Stimulation of the phosphorylation of 26 K and 65 K occurs within minutes of the addition of TPA to the culture medium of chick embryo fibroblasts, but it can also be evidenced at later times. Removal of TPA from the culture medium causes reversion of this effect. Stimulation of the phosphorylation of 26 K is also induced by the Ca2+-ionophore A23187, but the calmodulin inhibitor trifluoperazine does not inhibit the TPA induced stimulation of polypeptide phosphorylation. Agents increasing the intracellular cAMP concentration do not stimulate the phosphorylation of 26 K and 65 K. The results obtained suggest that the phosphorylation of specific polypeptides, probably induced by TPA through a Ca2+-phospholipid dependent mechanism, may represent an early regulative event which may be relevant for the pleiotropic effect of TPA in cultured normal cells.