Bile salt-induced apoptosis of hepatocytes involves activation of protein kinase C.
Toxic bile salts induce hepatocyte apoptosis, a model relevant to liver injury during cholestasis. However, the signaling mechanisms culminating in bile salt-induced apoptosis remain unclear. Because protein kinase C (PKC) is activated by bile salts in hepatocytes and causes apoptosis in other cells, we tested the hypothesis that bile salt-induced hepatocyte apoptosis is mediated by PKC. The PKC inhibitors chelerythrine and Gö-6976 reduced, whereas a PKC agonist, phorbol 12-myristate 13-acetate (PMA), increased glycochenodeoxycholate (GCDC)-induced hepatocyte apoptosis. Membrane-associated total PKC activity was increased in GCDC-treated hepatocytes. Quantitative immunoblot analysis demonstrated membrane translocation of PKC-alpha, PKC-delta, and PKC-epsilon to hepatocyte membranes after administration of GCDC. Direct activation of PKC-alpha and PKC-delta by GCDC was also demonstrated using recombinant, baculovirus-expressed PKC isoforms in a medium of defined lipid composition. Chelerythrine and Gö-6976 reduced, whereas PMA enhanced, cathepsin B activity during treatment of hepatocytes with GCDC, demonstrating coupling of PKC activity to the protease effector mechanisms of apoptosis. In conclusion, our data suggest for the first time that PKC-dependent signaling pathways play a critical role in bile salt-induced hepatocyte apoptosis.
Jones
B A
BA
Center for Basic Research in Digestive Diseases, Mayo Clinic, Rochester, Minnesota, USA.
Rao
Y P
YP
Stravitz
R T
RT
Gores
G J
GJ
D000818:Animals; D017209:Apoptosis; D001647:Bile Acids and Salts / Q000494:pharmacology*; D001692:Biological Transport; D002478:Cells, Cultured; D010450:Endopeptidases / Q000378:metabolism; D004789:Enzyme Activation / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005999:Glycochenodeoxycholic Acid / Q000494:pharmacology; D007527:Isoenzymes / Q000378:metabolism; D008099:Liver / Q000166:cytology / Q000187:drug effects* / Q000201:enzymology*; D010749:Phosphoprotein Phosphatases / Q000037:antagonists & inhibitors; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000378:metabolism*; D051381:Rats
D001647:Bile Acids and Salts; D004791:Enzyme Inhibitors; D007527:Isoenzymes; D005999:Glycochenodeoxycholic Acid; D011493:Protein Kinase C; D010749:Phosphoprotein Phosphatases; D010450:Endopeptidases