Activation of an alternative death receptor-induced signaling pathway in human hepatocytes under caspase arrest.
Caspases are thought to be essential in execution of death receptor-induced apoptosis. However, recent findings suggest the existence of alternative pathways independent of caspases. We provide further evidence for such signaling in hepatocytes.


RESULTS
Death receptor-induced activation of caspases and apoptosis in primary murine hepatocytes was completely blocked in presence of 1.5 microM N-benzyloxycarbonyl-Val-Ala-Asp-(O-methyl)fluoromethylketone (zVAD-fmk). Whereas the same concentration of the inhibitor was sufficient to block TNF receptor 1-, CD95- or TRAIL receptor 1/-2-induced activation of caspases in primary human hepatocytes or HepG2 cells, complete prevention apoptotic cell death needed almost 100 microM zVAD-fmk. Under caspase-inhibitory but non-protective conditions, i.e. at 1.5 microM zVAD-fmk, various serine protease inhibitors prevented apoptosis-like cell death. Neither sole arrest of caspases nor inhibition of serine proteases alone protected human hepatocytes.


CONCLUSIONS
Human but not murine hepatocytes bear the potential to activate a permissive, serine protease inhibitor-sensitive alternative death signaling pathway under caspase-inhibitory conditions.
Dünstl
Georg
G
Biochemical Pharmacology, Faculty of Biology, University of Konstanz, Konstanz, Germany.
Weiland
Timo
T
Schlaeger
Christof
C
Nüssler
Andreas
A
Künstle
Gerald
G
Wendel
Albrecht
A
D000590:Amino Acid Chloromethyl Ketones / Q000008:administration & dosage*; D000818:Animals; D017209:Apoptosis / Q000187:drug effects / Q000502:physiology*; D051017:Apoptosis Regulatory Proteins / Q000378:metabolism; D061945:Caspase Inhibitors; D020169:Caspases / Q000378:metabolism*; D002478:Cells, Cultured; D004305:Dose-Response Relationship, Drug; D022781:Hepatocytes / Q000187:drug effects / Q000378:metabolism*; D006801:Humans; D051379:Mice; D009097:Multienzyme Complexes / Q000378:metabolism; D018384:Oxidative Stress / Q000187:drug effects / Q000502:physiology; D053218:Receptors, Death Domain / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology*; D013045:Species Specificity
D000590:Amino Acid Chloromethyl Ketones; D051017:Apoptosis Regulatory Proteins; D061945:Caspase Inhibitors; D009097:Multienzyme Complexes; D053218:Receptors, Death Domain; C096713:benzyloxycarbonylvalyl-alanyl-aspartyl fluoromethyl ketone; D020169:Caspases