Suppression of apoptosis in the protein kinase Cδ null mouse in vivo

Protein kinase C (PKC) delta is an essential regulator of mitochondrial dependent apoptosis in epithelial cells. We have used the PKC delta(-/-) mouse to ask if loss of PKC delta protects salivary glands against gamma-irradiation-induced apoptosis in vivo and to explore the mechanism underlying protection from apoptosis. We show that gamma-irradiation in vivo results in a robust induction of apoptosis in the parotid glands of wild type mice, whereas apoptosis is suppressed by greater than 60% in the parotid glands of PKC delta(-/-) mice. Primary parotid cells from PKC delta(-/-) mice are defective in mitochondrial dependent apoptosis as indicated by suppression of etoposide-induced cytochrome c release, poly(ADP-ribose) polymerase cleavage, and caspase-3 activation. Notably, apoptotic responsiveness can be restored by re-introduction of PKC delta by adenoviral transduction. Etoposide and gamma-irradiation-induced activation of p53 is similar in primary parotid cells and parotid glands from PKC delta(+/+) and PKC delta(-/-) mice, indicating that PKC delta functions downstream of the DNA damage response. In contrast, activation of the c-Jun amino-terminal kinase is reduced in primary parotid cells from PKC delta(-/-) cells and in parotid C5 cells, which express a dominant inhibitory mutant of PKC delta. Similarly, c-Jun amino-terminal kinase activation is suppressed in vivo in gamma-irradiated parotid glands from PKC delta(-/-) mice. These studies indicate an essential role for PKC delta downstream of the p53 response and upstream of the c-Jun amino-terminal kinase activation in DNA damage-induced apoptosis in vivo and in vitro.