Involvement of protein kinase C in macrophage activation by poly(I.C).

The expression of cytocidal activity is initiated by the interaction of macrophages with priming [e.g., interferon (IFN)] and triggering stimuli (polyinosinic-polycytidylic acid). We have shown that the triggering step can be initiated in a Ca(2+)-dependent fashion and hypothesized that protein kinase C (PKC) may couple the Ca2+ signal to the expression of a gene product, Bf, that accompanies the expression of macrophage cytocidal activity. Exposure of IFN-primed macrophages to polyinosinic-polycytidylic acid in the presence of the PKC inhibitors H-7 or sphingosine or after downregulation of PKC with phorbol myristate acetate markedly inhibited Bf synthesis. Western blots of macrophage lysates revealed the presence of the alpha-, delta-, and zeta-isozymes of PKC, and all were found to be downregulated by phorbol myristate acetate. Inhibition of PKC also prevented the increase in IFN-beta mRNA levels and partially blocked the response to IFN-beta. These data suggest that the alpha-, delta-, and zeta-isozymes of PKC are involved in signaling leading to Bf expression and that the level of involvement is restricted to the induction and response to IFN-beta.