Activation of PKC is sufficient to induce an apoptotic program in salivarygland acinar cells

Accumulating evidence suggests that specific isoforms of PKC may function t o promote apoptosis. We show here that activation of the conventional and n ovel isoforms of PKC with 12-O-tetradecanoyl phorbol-13-ester (TPA) induces apoptosis in salivary acinar cells as indicated by DNA fragmentation and a ctivation of caspase-3. TPA-induced DNA fragmentation, caspase-3 activation , and morphologic indicators of apoptosis, can be enhanced by pretreatment of cells with the calpain inhibitor, calpeptin, prior to the addition of TP A. Analysis of PKC isoform expression by immunoblot shows that TPA-induced downregulation of PKC alpha and PKC delta is delayed in cells pre-treated w ith calpeptin, and that this correlates with an increase of these isoforms in the membrane fraction of cells. TPA-induced apoptosis is accompanied by biphasic activation of the c-jun-N-terminal kinase (JNK) pathway and inacti vation of the extracellular regulated kinase (ERK) pathway. Expression of c onstitutively activated PKC alpha or PKC delta, but not kinase negative mut ants of these isoforms, or constitutively activated PKC epsilon, induces ap optosis in salivary acinar cells, suggesting a role for these isoforms in T PA-induced apoptosis. These studies demonstrate that activation of PKC is s ufficient for initiation of an apoptotic program in salivary acinar cells.