cFLIP-L inhibits p38 MAPK activation: an additional anti-apoptotic mechanism in bile acid-mediated apoptosis.
In cholestasis, toxic bile acids accumulate within the liver inducing hepatocyte apoptosis, which exacerbates liver injury. Although bile acids activate both death receptors and mitogen-activated kinase (MAPK) pathways, the mechanistic link between death receptor signaling and MAPK activation in bile acid apoptosis remains unclear. The aim of this study was to ascertain if MAPKs contribute to bile acid cytotoxicity. Although deoxycholate induced apoptosis and activated all three classic mediators of the MAPK pathways including JNK 1/2, p38, and p42/44, only p38 MAPK inhibition attenuated apoptosis. Suppressing FADD expression with siRNA or employing a caspase inhibitor, zVAD-fmk, did not block p38 MAPK activation suggesting its activation was not death receptor-dependent. Unexpectedly, expression of cFLIP-L in a stably transfected cell line blocked apoptosis and p38 MAPK phosphorylation. Based on these data we postulated a direct effect of cFLIP on p38 MAPK activation. The nonphosphorylated but not the phosphorylated/active form of p38 MAPK co-immunoprecipitated with cFLIP-L. In reverse immunoprecipitation experiments, cFLIP-L long but not cFLIP-S co-immunoprecipitate with p38 MAPK. In conclusion, these data suggest that cFLIP-L exerts its anti-apoptotic activity, in part, by inhibiting p38 MAPK activation, an additional anti-apoptotic effect for this protein.
Division of Gastroenterology and Hepatology, Mayo Medical School, Clinic, and Foundation, Rochester, Minnesota 55905, USA.
Annette
A
Grambihler
Hajime
H
Higuchi
Steven F
SF
Bronk
Gregory J
GJ
Gores
D048868:Adaptor Proteins, Signal Transducing; D017209:Apoptosis / Q000187:drug effects / Q000502:physiology*; D001647:Bile Acids and Salts / Q000378:metabolism*; D053446:CASP8 and FADD-Like Apoptosis Regulating Protein; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D020169:Caspases / Q000378:metabolism; D002460:Cell Line; D003840:Deoxycholic Acid / Q000378:metabolism / Q000494:pharmacology; D004789:Enzyme Activation; D053200:Fas-Associated Death Domain Protein; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D010766:Phosphorylation; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D014162:Transfection; D048051:p38 Mitogen-Activated Protein Kinases
D048868:Adaptor Proteins, Signal Transducing; D001647:Bile Acids and Salts; 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; D047908:Intracellular Signaling Peptides and Proteins; D011994:Recombinant Proteins; D003840:Deoxycholic Acid; D020928:Mitogen-Activated Protein Kinases; D048051:p38 Mitogen-Activated Protein Kinases; D020169:Caspases