Inhibition of the protein kinase C pathway promotes anti-CD95-induced apoptosis in Jurkat T cells

The role of the basal activity of the serine/threonine protein kinase,protein kinase C (PKC) in the regulation of anti-CD95-induced apoptosis inJurkat T cells was investigated. The PKC-specific inhibitor GF 109203X andthe proposed cPKC-specific inhibitor Go 6976, in a concentration-dependentmanner, increased the percentage of cells undergoing apoptosis induced byanti-CD95 mAb as demonstrated by propidium iodide (PI) staining, TUNELassay and DNA fragmentation by gel electrophoresis. Furthermore, Go 6976and GF 109203X abrogated phorbol myristate acetate-induced inhibition ofanti-CD95-induced apoptosis. To examine the molecular mechanism by whichPKC modulates anti-CD95-induced apoptosis, the effects of Go 6976 on knowneffector and regulatory molecules of cell death were studied. Increasedrecruitment of cells undergoing apoptosis was associated with enhancedanti-CD95-induced proteolytic cleavage of the most receptor-proximalcysteine protease caspase-8, subsequent cleavage and activation of themachinery protease caspase-3, and cleavage of the caspase substratesDNA-dependent protein kinase catalytic subunit, poly-(ADP-ribose)polymerase and lamin B1. CD95 and FADD protein levels in Jurkat T cellswere not altered by Go 6976 treatment. In addition, Go 6976 did not alterprotein levels and subcellular distribution of the anti-apoptotic moleculesBcl-2 and Bcl-xL. These data suggest indirectly that basal PKC activityacts at an early stage in the anti-CD95-induced caspase pathway toattenuate subsequent activation of downstream effector molecules andassociated apoptosis in Jurkat T cells.