Keratin–protein kinase C interaction in reactive oxygen species-induced hepatic cell death through mitochondrial signaling

Keratins (Ks), the intermediate filament (IF) proteins of epithelia, constitute at least 20 cytoskeletal proteins subdivided into type I (K9-20) and type II (K1-K8) and expressed as type I/type II pairs in a cell differentiation manner. Hepatocyte IFs are made only of K8/K18, the hallmark of simple epithelial cells. We have shown previously that a K8/K18 loss leads to a modulation of apoptosis in Fas-stimulated mouse hepatocytes. Here we report that K8-knockout mouse hepatocytes and K8-knockdown H4-II-E-C3 (shK8b1) rat hepatoma cells were much more resistant than their K8/K18-containing counterparts, wild-type hepatocytes, and H4ev hepatoma cells, in response to excess H2O2 or tert-butyl hydroperoxide, a ROS generator. While excess H2O2 altered glutathione (GSH) and ROS levels in H4ev versus shK8b1 cells, the differential death response was largely GSH level independent. Assessment of key cell death features revealed that hepatic cells exposed to H2O2 die through a mitochondrial involvement. Similarly, administration of the GSH depletor L-buthionine-sulfoximine to generate mitochondrial ROS-sensitized H4-II-E-C3 cells but not shK8b1 cells to death. Treatment with protein kinase C (PKC) inhibitors yielded a resistance of H2O2-treated H4-II-E-C3 cells comparable to that of nontreated shK8b1 cells, which in turn were not affected by the treatment. In addition, this differential death response was associated with altered PKCδ activation and surface-membrane/mitochondria distribution in H2O2-treated shK8b1 cells. Together, these results point to a key regulatory function for K8/K18 in ROS-induced mitochondria-mediated death through PKCδ involvement in hepatic cells.