title: cFLIPL prevents TRAIL-induced apoptosis of hepatocellular carcinoma cells by inhibiting the lysosomal pathway of apoptosis.
abstract: Sensitivity to TNF-related apoptosis-inducing ligand (TRAIL)-mediated apoptosis and the lysosomal pathway of cell death are features of cancer cells. However, it is unknown if TRAIL cytotoxic signaling engages the lysosomal pathway of cell death. Our aim, therefore, was to ascertain if TRAIL killing involves lysosomal permeabilization. TRAIL-induced apoptosis of hepatocellular carcinoma cells (HuH-7, Hep3B) was associated with lysosomal permeabilization, as demonstrated by redistribution of the lysosomal protease cathepsin B into the cytosol. Pharmacological and short hairpin RNA-targeted inhibition of cathepsin B reduced apoptosis. Because cellular FLICE-inhibitory protein (cFLIP) inhibits TRAIL-induced cell death and is frequently overexpressed by human cancers, the ability of cFLIP to prevent lysosomal permeabilization during TRAIL treatment was examined. Enforced long-form cFLIP (cFLIP(L)) expression reduced release of cathepsin B from lysosomes and attenuated apoptosis. cFLIP(L) overexpression was also associated with robust p42/44 MAPK activation following exposure to TRAIL. In contrast, cFLIP(L) overexpression attenuated p38 MAPK activation and had no significant effect on JNK and NF-kappaB activation. Inhibition of p42/44 MAPK by PD98059 restored TRAIL-mediated lysosomal permeabilization and apoptosis in cFLIP-overexpressing cells. In conclusion, these results demonstrate that lysosomal permeabilization contributes to TRAIL-induced apoptosis of hepatocellular carcinoma cells and suggest that cFLIP(L) cytoprotection is, in part, due to p42/44 MAPK-dependent inhibition of lysosomal breakdown.
authors.affiliation: Division of Gastroenterology and Hepatology, Mayo Clinic College of Medicine, 200 First St. SW, Rochester, MN 55905, USA.
authors.forename: Maria Eugenia
authors.initials: ME
authors.lastname: Guicciardi
authors.forename: Steven F
authors.initials: SF
authors.lastname: Bronk
authors.forename: Nathan W
authors.initials: NW
authors.lastname: Werneburg
authors.forename: Gregory J
authors.initials: GJ
authors.lastname: Gores
mesh_terms: D017209:Apoptosis / Q000187:drug effects*; D002070:Butadienes / Q000494:pharmacology; D053446:CASP8 and FADD-Like Apoptosis Regulating Protein / Q000502:physiology*; D006528:Carcinoma, Hepatocellular / Q000473:pathology*; D002403:Cathepsins / Q000378:metabolism; D045744:Cell Line, Tumor; D005419:Flavonoids; D006801:Humans; D007093:Imidazoles / Q000494:pharmacology; D008113:Liver Neoplasms / Q000473:pathology*; D008247:Lysosomes / Q000187:drug effects*; D019950:Mitogen-Activated Protein Kinase 1 / Q000502:physiology; D048052:Mitogen-Activated Protein Kinase 3 / Q000502:physiology; D009570:Nitriles / Q000494:pharmacology; D010539:Permeability / Q000187:drug effects; D021381:Protein Transport; D011725:Pyridines / Q000494:pharmacology; D053221:TNF-Related Apoptosis-Inducing Ligand / Q000037:antagonists & inhibitors*; D048051:p38 Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors
chemical_list: D002070:Butadienes; D053446:CASP8 and FADD-Like Apoptosis Regulating Protein; D005419:Flavonoids; D007093:Imidazoles; D009570:Nitriles; D011725:Pyridines; D053221:TNF-Related Apoptosis-Inducing Ligand; C505653:TNFSF10 protein, human; C113580:U 0126; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D048051:p38 Mitogen-Activated Protein Kinases; D002403:Cathepsins; C093642:SB 203580; C093973:2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one