Suppressive effect of protein kinase C inhibitors on tumor cell function via phosphorylation of p53 protein in mice

We examined the role of protein kinase C (PKC) in the phosphorylation of a p53 protein. Exposure to a protein kinase inhibitor, 1-(5-isoquinolinesulfo nyl)-2-methylpiperazine dihydrochloride (H7), increased the phosphorylation of the wild type p53 protein, whereas exposure to a tumor promoter phorbol ester, 12-O-tetradecanoyl-phorbol-13-acetate (TPA), decreased it in vivo a fter incubation with mouse epidermal JB6 cells for 3h. Exposure to a cAMP d ependent protein kinase (PKA) activator, forskolin, did not decrease the ph osphorylation of p53 protein. In the transient transfection/luciferase repo rter transactivation assay, H7 slightly increased the mouse double minute ( MDM) 2 reporter transactivation activity of the p53 protein after treatment for 24h, whereas TPA completely blocked it. Exposure to H7 and a specific PKC inhibitor, bisindolylmaleimide (bis), dose-dependently reduced the lung -colonizing potential of highly metastatic B16-F10 mouse melanoma cells in syngeneic mice. These results suggest that the phosphorylation of the wild type p53 protein is inversely related to PKC activation, and also suggest t hat the phosphorylation of the p53 protein is involved in the function of i ts transcription factor. The PKC inhibitor may exhibit a potent anti-metast atic effect through the phosphorylation of wild type p53 protein and the ac tivation of its function.