title: Interferon-gamma inhibits interferon-alpha signalling in hepatic cells: evidence for the involvement of STAT1 induction and hyperexpression of STAT1 in chronic hepatitis C.
abstract: IFN-gamma (interferon-gamma) modulates IFN-alpha therapy in chronic hepatitis C infection; however, the underlying mechanism remains unclear. Here we demonstrate that long-term (3-6 days) but not short-term (up to 1 day) IFN-gamma treatment of human hepatoma Hep3B cells attenuates IFN-alpha activation of STAT1 (signal transducers and activators of transcription factor 1), STAT2 and STAT3, but enhances IFN-gamma and interleukin 6 activation of STATs. Prolonged exposure to IFN-gamma also significantly induces STAT1 protein expression without affecting STAT2, STAT3 and ERK (extracellular-signal-regulated kinase) 1/2 protein expression. To determine the role of STAT1 protein overexpression in regulation of IFN-alpha signalling, Hep3B cells were stably transfected with wild-type STAT1. Overexpression of STAT1 via stable transfection enhances IFN-gamma activation of STAT1, but surprisingly attenuates IFN-alpha activation of STAT1, STAT2 and STAT3 without affecting Janus kinase activation. This STAT1-mediated inhibition does not require STAT1 tyrosine phosphorylation because overexpression of dominant-negative STAT1 with a mutation on tyrosine residue 701 also blocks IFN-alpha activation of STAT1, STAT2 and STAT3. Moreover, overexpression of STAT1 blocks IFN-alpha-activated STAT2 translocation from IFN-alpha receptor 2 to IFN-alpha receptor 1, a critical step in IFN-alpha signalling activation. Finally, significantly higher levels of STAT1 protein expression, which is probably induced by IFN-gamma, are detected in the majority of hepatitis C virus-infected livers compared with healthy controls. In conclusion, long-term IFN-gamma treatment inhibits IFN-alpha-activated signals most probably, at least in part, through the induction of STAT1 protein expression, which could partly contribute to IFN-alpha treatment failure in hepatitis C patients.
authors.affiliation: Section on Liver Biology, Laboratory of Physiologic Studies, National Institute on Alcohol Abuse and Alcoholism, National Institutes of Health, 12420 Parklawn Drive, MSC 8115, Bethesda, MD 20892, USA.
authors.forename: Svetlana
authors.initials: S
authors.lastname: Radaeva
authors.forename: Barbara
authors.initials: B
authors.lastname: Jaruga
authors.forename: Won-Ho
authors.initials: WH
authors.lastname: Kim
authors.forename: Theo
authors.initials: T
authors.lastname: Heller
authors.forename: T Jake
authors.initials: TJ
authors.lastname: Liang
authors.forename: Bin
authors.initials: B
authors.lastname: Gao
mesh_terms: D000998:Antiviral Agents / Q000494:pharmacology*; D006528:Carcinoma, Hepatocellular / Q000473:pathology; D002352:Carrier Proteins / Q000096:biosynthesis / Q000235:genetics; D002453:Cell Cycle; D045744:Cell Line, Tumor / Q000187:drug effects / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D004789:Enzyme Activation / Q000187:drug effects; D005786:Gene Expression Regulation / Q000187:drug effects*; D017930:Genes, Reporter; D019698:Hepatitis C, Chronic / Q000188:drug therapy* / Q000378:metabolism; D006801:Humans; D016898:Interferon-alpha / Q000037:antagonists & inhibitors* / Q000502:physiology; D007371:Interferon-gamma / Q000494:pharmacology*; D015850:Interleukin-6 / Q000378:metabolism; D047908:Intracellular Signaling Peptides and Proteins; D053613:Janus Kinase 1; D008099:Liver / Q000187:drug effects / Q000378:metabolism*; D008103:Liver Cirrhosis / Q000378:metabolism; D008113:Liver Neoplasms / Q000473:pathology; D008565:Membrane Proteins; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D012333:RNA, Messenger / Q000096:biosynthesis; D053633:Receptor, Interferon alpha-beta; D017471:Receptors, Interferon / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000502:physiology; D012097:Repressor Proteins / Q000096:biosynthesis / Q000235:genetics; D050794:STAT1 Transcription Factor; D050795:STAT2 Transcription Factor; D050796:STAT3 Transcription Factor; D015398:Signal Transduction; D000071222:Suppressor of Cytokine Signaling 1 Protein; D050826:Suppressor of Cytokine Signaling Proteins; D053634:TYK2 Kinase; D015534:Trans-Activators / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D014162:Transfection
chemical_list: D000998:Antiviral Agents; D002352:Carrier Proteins; D004268:DNA-Binding Proteins; D016898:Interferon-alpha; D015850:Interleukin-6; D047908:Intracellular Signaling Peptides and Proteins; D008565:Membrane Proteins; D012333:RNA, Messenger; D017471:Receptors, Interferon; D011993:Recombinant Fusion Proteins; D012097:Repressor Proteins; C108944:SOCS1 protein, human; D050794:STAT1 Transcription Factor; C494079:STAT1 protein, human; D050795:STAT2 Transcription Factor; C494084:STAT2 protein, human; D050796:STAT3 Transcription Factor; C494086:STAT3 protein, human; D000071222:Suppressor of Cytokine Signaling 1 Protein; D050826:Suppressor of Cytokine Signaling Proteins; D015534:Trans-Activators; D053633:Receptor, Interferon alpha-beta; D007371:Interferon-gamma; D011505:Protein-Tyrosine Kinases; C507904:JAK1 protein, human; D053613:Janus Kinase 1; D053634:TYK2 Kinase; C070139:TYK2 protein, human