Selective effects of TPA and IL-1 on protein phosphorylation in murine thymocytes

Protein kinase C activity was demonstrated in murine thymocytes and the effects of TPA and IL-1 on this enzyme were studied. TPA, but not IL-1, could substitute for diacylglycerol in protein kinase C activation. Although TPA and IL-1 are both potent comitogens for murine thymocytes they markedly differ in their effects on protein phosphorylation and protein kinase C activation. Treatment of intact thymocytes with TPA resulted in a marked increase in the phosphorylation of an endogenous protein with Mr approximately 44,000. Enhanced phosphorylation of this protein was also observed when protein kinase C was activated in thymocyte extracts. In contrast to TPA, IL-1 neither induced phosphorylation of the 44,000-Da protein nor activated protein kinase C. The data suggests that protein kinase C does not mediate the comitogenic effect of IL-1 in murine thymocytes.