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.
MeSH terms
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Antiviral Agents / pharmacology*
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Carcinoma, Hepatocellular / pathology
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Carrier Proteins / biosynthesis
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Carrier Proteins / genetics
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Cell Cycle
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Cell Line, Tumor / drug effects
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Cell Line, Tumor / metabolism
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DNA-Binding Proteins / biosynthesis
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DNA-Binding Proteins / genetics
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DNA-Binding Proteins / metabolism
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DNA-Binding Proteins / physiology*
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Enzyme Activation / drug effects
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Gene Expression Regulation / drug effects*
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Genes, Reporter
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Hepatitis C, Chronic / drug therapy*
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Hepatitis C, Chronic / metabolism
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Humans
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Interferon-alpha / antagonists & inhibitors*
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Interferon-alpha / physiology
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Interferon-gamma / pharmacology*
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Interleukin-6 / metabolism
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Intracellular Signaling Peptides and Proteins*
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Janus Kinase 1
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Liver / drug effects
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Liver / metabolism*
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Liver Cirrhosis / metabolism
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Liver Neoplasms / pathology
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Membrane Proteins
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Protein-Tyrosine Kinases / metabolism
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RNA, Messenger / biosynthesis
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Receptor, Interferon alpha-beta
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Receptors, Interferon / metabolism
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Recombinant Fusion Proteins / physiology
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Repressor Proteins / biosynthesis
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Repressor Proteins / genetics
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STAT1 Transcription Factor
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STAT2 Transcription Factor
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STAT3 Transcription Factor
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Signal Transduction
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Suppressor of Cytokine Signaling 1 Protein
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Suppressor of Cytokine Signaling Proteins
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TYK2 Kinase
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Trans-Activators / biosynthesis
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Trans-Activators / genetics
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Trans-Activators / metabolism
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Trans-Activators / physiology*
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Transfection
Substances
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Antiviral Agents
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Carrier Proteins
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DNA-Binding Proteins
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Interferon-alpha
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Interleukin-6
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Intracellular Signaling Peptides and Proteins
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Membrane Proteins
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RNA, Messenger
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Receptors, Interferon
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Recombinant Fusion Proteins
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Repressor Proteins
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SOCS1 protein, human
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STAT1 Transcription Factor
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STAT1 protein, human
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STAT2 Transcription Factor
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STAT2 protein, human
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STAT3 Transcription Factor
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STAT3 protein, human
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Suppressor of Cytokine Signaling 1 Protein
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Suppressor of Cytokine Signaling Proteins
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Trans-Activators
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Receptor, Interferon alpha-beta
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Interferon-gamma
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Protein-Tyrosine Kinases
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JAK1 protein, human
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Janus Kinase 1
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TYK2 Kinase
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TYK2 protein, human