Phosphorylation status and function of p53 are inversely related to protein kinase C activation

The role of phosphorylation in the regulation of p53 protein function is li ttle understood We have addressed the role of protein kinase C (PKC) in the phosphorylation. Exposure to the protein kinase inhibitor, 1-(5-isoquinoli nesulfonyl) -2-methylpiperazine dihydrochloride (H7) increased the phosphor ylation of wild type p53 protein, whereas exposure to the tumor promoter ph orbol ester, 12-O-retradecanoyl-phorbol-13-acetate (TPA), decreased it in v ivo following 3 hours incubation with mouse epidermal JB6 cells. Exposure t o the c-AMP dependent protein kinase (PKA) activator, forskolin, did not de crease the phosphorylation of p53 protein. In the transient transfection/lu ciferase reporter transactivation assay,H7 modestly increased the mouse dou ble minute (MDM) 2 reporter transactivation activity of p53 protein after 2 4 hours treatment, and TPA completely blocked it. These results suggest tha t the accelerated phosphorylation of wild type p53 protein is inversely rel ated to PKC activation, and that p53 phosphorylation may have some relation to transcription factor function.