title: Down-regulation of the de-ubiquitinating enzyme ubiquitin-specific protease 2 contributes to tumor necrosis factor-alpha-induced hepatocyte survival.
abstract: Tumor necrosis factor-alpha (TNFalpha) stimulation of hepatocytes induces either cell survival or apoptosis, which seems to be regulated by the ubiquitin-proteasome system. Here we investigated the role of TNFalpha-induced down-modulation of the de-ubiquitinating enzyme USP2 for hepatocyte survival. Inhibition of hepatocyte apoptosis by pre-treatment with TNFalpha (TNFalpha tolerance) was analyzed in the mouse model of galactosamine/TNFalpha-induced liver injury and in actinomycin D/TNFalpha-treated primary mouse hepatocytes. The role of USP2 for TNFalpha-induced hepatocyte survival was studied using small interference RNA or an expression clone. Injection of mice or preincubation of hepatocytes with TNFalpha caused a rapid down-regulation of hepatic USP2-41kD, the predominant USP2 isoform in the liver. In vitro an artificial knockdown of USP2 inhibited actinomycin D/TNFalpha-induced hepatocyte apoptosis, which was associated with elevated levels of the anti-apoptotic protein c-Flip(L/S) and a concomitant decrease of cellular levels of the ubiquitinligase Itch, a negative regulator of c-Flip. USP2-41kD overexpression abrogated TNFalpha tolerance in vitro, prevented accumulation of c-Flip(L/S) and resulted in elevated levels of Itch. Accordingly, c-Flip(L/S) protein levels were elevated in livers of TNFalpha-tolerant mice, which correlated to a switch from JNK and ERK to p38 signaling after galactosamine/TNF re-challenge. Our results indicate that TNFalpha-induced USP2 down-regulation is an effective cytoprotective mechanism in hepatocytes. Hence, USP2 could be a novel pharmacological target, and specific USP2 inhibitors might be potential candidates for the treatment of inflammation-related apoptotic liver damage.
authors.affiliation: Institute of Experimental and Clinical Pharmacology and Toxicology, University of Erlangen-Nuremberg, Erlangen D-91054 and the Division of Experimental Immunology and Hepatology, University Medical Center Hamburg-Eppendorf, Martinistrasse 52, Hamburg D-20246, Germany.
authors.forename: Florian
authors.initials: F
authors.lastname: Haimerl
authors.affiliation: Institute of Experimental and Clinical Pharmacology and Toxicology, University of Erlangen-Nuremberg, Erlangen D-91054 and the Division of Experimental Immunology and Hepatology, University Medical Center Hamburg-Eppendorf, Martinistrasse 52, Hamburg D-20246, Germany.
authors.forename: Annette
authors.initials: A
authors.lastname: Erhardt
authors.affiliation: Institute of Experimental and Clinical Pharmacology and Toxicology, University of Erlangen-Nuremberg, Erlangen D-91054 and the Division of Experimental Immunology and Hepatology, University Medical Center Hamburg-Eppendorf, Martinistrasse 52, Hamburg D-20246, Germany.
authors.forename: Gabriele
authors.initials: G
authors.lastname: Sass
authors.affiliation: Institute of Experimental and Clinical Pharmacology and Toxicology, University of Erlangen-Nuremberg, Erlangen D-91054 and the Division of Experimental Immunology and Hepatology, University Medical Center Hamburg-Eppendorf, Martinistrasse 52, Hamburg D-20246, Germany; Institute of Experimental and Clinical Pharmacology and Toxicology, University of Erlangen-Nuremberg, Erlangen D-91054 and the Division of Experimental Immunology and Hepatology, University Medical Center Hamburg-Eppendorf, Martinistrasse 52, Hamburg D-20246, Germany. Electronic address: g.tiegs@uke.de.
authors.forename: Gisa
authors.initials: G
authors.lastname: Tiegs
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000187:drug effects*; D053446:CASP8 and FADD-Like Apoptosis Regulating Protein / Q000378:metabolism; D002470:Cell Survival / Q000187:drug effects; D056486:Chemical and Drug Induced Liver Injury / Q000188:drug therapy / Q000201:enzymology*; D003609:Dactinomycin / Q000633:toxicity; D015536:Down-Regulation / Q000187:drug effects; D010450:Endopeptidases / Q000096:biosynthesis*; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects*; D022781:Hepatocytes / Q000201:enzymology* / Q000473:pathology; D048031:JNK Mitogen-Activated Protein Kinases / Q000378:metabolism; D008099:Liver / Q000201:enzymology / Q000473:pathology; D020935:MAP Kinase Signaling System / Q000187:drug effects; D051379:Mice; D008807:Mice, Inbred BALB C; D011500:Protein Synthesis Inhibitors / Q000633:toxicity; D034741:RNA, Small Interfering; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology*; D043222:Ubiquitin Thiolesterase; D044767:Ubiquitin-Protein Ligases / Q000378:metabolism; D064570:Ubiquitin-Specific Proteases; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism
chemical_list: D053446:CASP8 and FADD-Like Apoptosis Regulating Protein; C506387:Cflar protein, mouse; D011500:Protein Synthesis Inhibitors; D034741:RNA, Small Interfering; D014409:Tumor Necrosis Factor-alpha; D003609:Dactinomycin; C471637:Itch protein, mouse; D044767:Ubiquitin-Protein Ligases; D048031:JNK Mitogen-Activated Protein Kinases; D048051:p38 Mitogen-Activated Protein Kinases; D010450:Endopeptidases; D043222:Ubiquitin Thiolesterase; D064570:Ubiquitin-Specific Proteases; C579224:Usp2 protein, mouse