Protein Kinase C Regulates FADD Recruitment and Death-inducing Signaling Complex Formation in Fas/CD95-induced Apoptosis

Abstract

Activation of protein kinase C (PKC) triggers cellular signals that inhibit Fas/CD95-induced cell death in Jurkat T-cells by poorly defined mechanisms. Previously, we have shown that one effect of PKC on Fas/CD95-dependent cell death occurs through inhibition of cell shrinkage and K+ efflux (Gómez-Angelats, M., Bortner, C. D., and Cidlowski, J. A. (2000) J. Biol. Chem. 275, 19609-19619). Here we report that PKC alters Fas/CD95 signaling from the plasma membrane to the activation of caspases by exerting a profound action on survival/cell death decisions. Specific activation of PKC with 12-O-tetradecanoylphorbol-13-acetate or bryostatin-1 induced translocation of PKC from the cytosol to the membrane and effectively inhibited cell shrinkage and cell death triggered by anti-Fas antibody in Jurkat cells. In contrast, inhibition of classical PKC isotypes with Gö6976 exacerbated the effect of Fas activation on both apoptotic volume decrease and cell death. PKC activation/inhibition did not affect anti-Fas antibody binding to the cell surface, intracellular levels of FADD (Fas-associated protein with death domain), or c-FLIP (cellular FLICE-like inhibitory protein) expression. However, processing/activation of both caspase-8 and caspase-3 and BID cleavage were markedly blocked upon PKC activation and, conversely, were augmented during PKC inhibition, suggesting a role for PKC upstream of caspase-8 processing and activation. Analysis of death-inducing signaling complex (DISC) formation was carried out to examine the influence of PKC on recruitment of both FADD and procaspase-8 to the Fas receptor. PKC activation blocked FADD recruitment and caspase-8 activation and thus DISC formation in both type I and II cells. In contrast, inhibition of classical PKCs promoted the opposite effect on the Fas pathway by rapidly increasing FADD recruitment, caspase-8 activation, and DISC formation. Together, these data show that PKC finely modulates Fas/CD95 signaling by altering the efficiency of DISC formation.