Bile salt-induced hepatocyte apoptosis involves epidermal growth factor receptor-dependent CD95 tyrosine phosphorylation.
OBJECTIVE
Hydrophobic bile acids induce CD95-dependent hepatocyte apoptosis.


METHODS
The mechanisms of bile acid-induced CD95 activation were studied in 24-hour cultured rat hepatocytes, in situ-perfused rat livers, and livers from bile duct-ligated rats.


RESULTS
Within 1 minute, the proapoptotic bile salts taurolithocholate-3-sulfate and glycochenodeoxycholate induced oxidative stress and EGF receptor (EGF-R) tyrosine phosphorylation followed by rapid c-Jun-N-terminal kinase (JNK) activation. Thereafter, EGF-R associated with CD95 with subsequent CD95 tyrosine phosphorylation, CD95 membrane targeting, and death-inducing signal complex (DISC) formation. All of these responses were also triggered by taurochenodeoxycholate except that DISC formation only occurred in the presence of phosphatidylinositol 3-kinase inhibitors. No activation of EGF-R or CD95 was observed with tauroursodeoxycholate or taurocholate. Taurolithocholate-3-sulfate-induced EGF-R phosphorylation was sensitive to N-acetylcysteine (NAC) and genistein, whereas CD95/EGF-R association was inhibited by NAC, JNK, or protein kinase C inhibition but not by AG1478. However, the latter compound as well as NAC, genistein, inhibition of JNK, or protein kinase C inhibited CD95 tyrosine phosphorylation, membrane trafficking, and DISC formation.


CONCLUSIONS
Induction of apoptosis by hydrophobic bile salts involves EGF-R activation and EGF-R-dependent CD95 tyrosine phosphorylation, which triggers CD95 membrane targeting and Fas-associated death domain/caspase-8 recruitment. The latter step is apparently also controlled by phosphatidylinositol 3-kinase.
Reinehr
Roland
R
Clinic for Gastroenterology, Hepatology and Infectiology, Heinrich-Heine-University, Düesseldorf, Germany.
Graf
Dirk
D
Häussinger
Dieter
D
D000818:Animals; D017209:Apoptosis / Q000187:drug effects*; D001647:Bile Acids and Salts / Q000633:toxicity*; D002462:Cell Membrane / Q000378:metabolism; D066246:ErbB Receptors / Q000502:physiology*; D022781:Hepatocytes / Q000187:drug effects* / Q000502:physiology; D048031:JNK Mitogen-Activated Protein Kinases; D008297:Male; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D018384:Oxidative Stress; D010766:Phosphorylation; D021381:Protein Transport / Q000187:drug effects; D051381:Rats; D017208:Rats, Wistar; D014443:Tyrosine / Q000378:metabolism; D019014:fas Receptor / Q000378:metabolism*
D001647:Bile Acids and Salts; D019014:fas Receptor; D014443:Tyrosine; D066246:ErbB Receptors; D048031:JNK Mitogen-Activated Protein Kinases; D020928:Mitogen-Activated Protein Kinases