PKCζ protects against UV-C-induced apoptosis by inhibiting acid sphingomyelinase-dependent ceramide production

In a recent study, we described that UV-C irradiation resulted in redox-dependent activation and relocalization of A-SMase (acid sphingomyelinase) to the external surface of raft membrane microdomains, hydrolysis of SM (sphingomyelin) associated with the plasma membrane outer leaflet, ceramide generation and apoptosis. In the present study, we have investigated the influence of PKC zeta (protein kinase C zeta), an atypical form of PKC on this pathway. This study shows that PKC zeta overexpression resulted in the abrogation of UV-C-induced A-SMase translocation and activation into the raft microdomains, lack of ceramide generation and apoptosis inhibition. Moreover, PKC zeta overexpression resulted in a decrease in UV-C-induced ROS (reactive oxygen species) production, which correlated with increased gene expression level of various antioxidant enzymes, including TRx (thioredoxin), TR (thioredoxin reductase) 1, TR2 and peroxiredoxin 1/TPx2 (thioredoxin peroxidase 2). Importantly, enforced TPx2 gene expression inhibited UV-C-induced A-SMase translocation. Finally, PKC zeta inhibition led to a significant reduction in TPx2 protein expression. Altogether, these results suggest that PKC zeta interferes with the UV-activated sphingolipid signalling pathway by regulating the TRx system. These findings may have important consequences for UV-induced carcinogenesis and resistance to phototherapy.