BILE SALT-INDUCED APOPTOSIS OF HEPATOCYTES INVOLVES ACTIVATION OF PROTEIN-KINASE-C

Toxic bile salts induce hepatocyte apoptosis, a model relevant to live r injury during cholestasis. However, the signaling mechanisms culmina ting in bile salt-induced apoptosis remain unclear. Because protein ki nase C (PKC) is activated by bile salts in hepatocytes and causes apop tosis in other cells, we tested the hypothesis that bile salt-induced hepatocyte apoptosis is mediated by PKC. The PKC inhibitors chelery-th rine and Go-6976 reduced, whereas a PKC agonist, phorbol 12-myristate 13-acetate (PMA), increased glycochenodeoxycholate (GCDC)-induced hepa tocyte apoptosis. Membrane-associated total PKC activity was increased in GCDC-treated hepatocytes. Quantitative immunoblot analysis demonst rated membrane translocation of PKC-alpha, PKC-delta, and PKC-epsilon to hepatocyte membranes after administration of GCDC. Direct activatio n of PKC-alpha and PKC-delta by GCDC was also demonstrated using recom binant, baculovirus-expressed PKC isoforms in a medium of defined lipi d composition. Chelery-thrine and Go-6976 reduced, whereas PMA enhance d, cathepsin B activity during treatment of hepatocytes with GCDC, dem onstrating coupling of PKC activity to the protease effector mechanism s of apoptosis. In conclusion, our data suggest for the first time tha t PKC-dependent signaling pathways play a critical role in bile salt-i nduced hepatocyte apoptosis.