The susceptibility to Fas-induced apoptosis in normal enterocytes is regulated on the level of cIAP1 and 2.
Various members of the tumor necrosis factor receptor superfamily are implicated in the regulation of enterocyte apoptosis. Previously, we observed that human intestinal epithelial cells are rather unsusceptible to Fas-induced apoptosis. In the present study we analyzed these protective mechanisms in the human intestinal epithelial cell line HIEC, focusing on antiapoptotic molecules of the IAP family which block apoptosis at the level of the caspase cascade. HIEC expressed all key molecules required to trigger Fas-induced apoptosis. However, no apoptosis occurred after activation of Fas, whereas an upregulation of antiapoptotic cIAP1 and 2 was observed. Suppression of this upregulation with the proteasome inhibitor MG132 or the protein synthesis inhibitor cycloheximide highly sensitized HIEC toward Fas-induced apoptosis. Western blot analyses revealed that both inhibitors potently suppressed endogenously produced cIAP1 and 2. No effect was observed on XIAP expression. These data indicate that enterocytes are particularly protected against Fas-induced apoptosis on the level of executionary caspases.
Ruemmele
F M
FM
Laboratory of Intestinal Immunology, University of Bonn, Bonn, Germany. frankruemmele@uni-bonn.de
Beaulieu
J F
JF
O'Connell
J
J
Bennett
M W
MW
Seidman
E G
EG
Lentze
M J
MJ
D048868:Adaptor Proteins, Signal Transducing; D017209:Apoptosis / Q000187:drug effects / Q000235:genetics / Q000502:physiology*; D053446:CASP8 and FADD-Like Apoptosis Regulating Protein; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism; D053148:Caspase 3; D053181:Caspase 8; D053453:Caspase 9; D020169:Caspases / Q000235:genetics / Q000378:metabolism; D002460:Cell Line; D003513:Cycloheximide / Q000494:pharmacology; D015536:Down-Regulation; D020895:Enterocytes / Q000166:cytology* / Q000378:metabolism*; D053200:Fas-Associated Death Domain Protein; D006801:Humans; D051034:Inhibitor of Apoptosis Proteins; D047908:Intracellular Signaling Peptides and Proteins; D007976:Leupeptins / Q000494:pharmacology; D016328:NF-kappa B / Q000378:metabolism; D011506:Proteins / Q000378:metabolism*; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D044767:Ubiquitin-Protein Ligases; D015854:Up-Regulation; D019014:fas Receptor / Q000235:genetics / Q000378:metabolism*
D048868:Adaptor Proteins, Signal Transducing; D053446:CASP8 and FADD-Like Apoptosis Regulating Protein; C506386:CFLAR protein, human; D002352:Carrier Proteins; C505533:FADD protein, human; D053200:Fas-Associated Death Domain Protein; D051034:Inhibitor of Apoptosis Proteins; D047908:Intracellular Signaling Peptides and Proteins; D007976:Leupeptins; D016328:NF-kappa B; D011506:Proteins; D012333:RNA, Messenger; D019014:fas Receptor; D003513:Cycloheximide; C494833:BIRC2 protein, human; D044767:Ubiquitin-Protein Ligases; C505407:CASP3 protein, human; C505530:CASP8 protein, human; C506433:CASP9 protein, human; D053148:Caspase 3; D053181:Caspase 8; D053453:Caspase 9; D020169:Caspases; C072553:benzyloxycarbonylleucyl-leucyl-leucine aldehyde