Protein kinase C delta is essential for etoposide-induced apoptosis in salivary gland acinar cells

We have previously shown that parotid C5 salivary acinar cells undergo apop tosis in response to etoposide treatment as indicated by alterations in cel l morphology, caspase-3 activation, DNA fragmentation, sustained activation of c-Jun N-terminal kinase, and inactivation of extracellular regulated ki nases 1 and 2, Here we report that apoptosis results in the caspase-depende nt cleavage of protein kinase C-delta (PKC delta) to a 40-kDa fragment, the appearance of which correlates with a 9-fold increase in PKC delta activit y. To understand the function of activated PKC delta in apoptosis, we have used the PKC delta-specific inhibitor, rottlerin, Pretreatment of parotid C 5 cells with rottlerin prior to the addition of etoposide blocks the appear ance of the apoptotic morphology, the sustained activation of c-Jun N-termi nal kinase, and inactivation of extracellular regulated kinases 1 and 2, In hibition of PKC delta also partially inhibits caspase-3 activation and DNA fragmentation. Immunoblot analysis shows that the PKC delta cleavage produc t does not accumulate in parotid C5 cells treated with rottlerin and etopos ide together, suggesting that the catalytic activity of PKC delta may be re quired for cleavage. PKC alpha and PKC beta 1 activities also increase duri ng etoposide-induced apoptosis, Inhibition of these two isoforms with Go697 6 slightly suppresses the apoptotic morphology, caspase-3 activation, and D NA fragmentation, but has no effect on the sustained activation of c-Jun N- terminal kinase or inactivation of extracellular regulated kinase 1 and 2, These data demonstrate that activation of PKC delta is an integral and esse ntial part of the apoptotic program in parotid C5 cells and that specific a ctivated isoforms of PKC may have distinct functions in cell death.