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Mechanistic link between the anti‐HCV effect of interferon gamma and control of viral replication by a ras‐MAPK signaling cascade
Author(s) -
Huang Ying,
Chen Xinyi Cynthia,
Konduri Madhavi,
Fomidejda,
Lu Jin,
Jin Ling,
Kolykhalov Alexander,
Tan SengLai
Publication year - 2006
Publication title -
hepatology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 5.488
H-Index - 361
eISSN - 1527-3350
pISSN - 0270-9139
DOI - 10.1002/hep.21011
Subject(s) - replication (statistics) , viral replication , virology , mapk/erk pathway , interferon , cascade , biology , microbiology and biotechnology , signal transduction , virus , chemistry , chromatography
Abstract Interferon‐gamma (IFN‐γ) exerts potent antiviral activity in the hepatitis C virus (HCV) replicon systems. However, the mechanisms underlying the direct antiviral effect have not been determined. We found that the type II transcriptional response to IFN‐γ could be suppressed by inhibition of MEK1/2 kinase activity by MEK1/2 inhibitor U0126 in the hepatoma cell line Huh‐7. Using a bicistronic HCV replicon system expressing a luciferase reporter gene in Huh‐7 cells (RLuc‐replicon), we showed that inhibition of MEK1/2 kinase activity is sufficient to counteract the antiviral activity of IFN‐γ. Expression of a constitutive active form of Ras inhibited the luciferase activity of RLuc‐replicon, whereas a dominant‐negative mutant of Ras enhanced the reporter activity, indicating that the Ras‐MAPK pathway has a role in limiting replication of the viral RNA. Consistent with the involvement of the Ras‐MAPK pathway, treatment with epidermal growth factor suppressed HCV protein expression in the RLuc‐replicon cells, an effect that could be abolished by U0126. Inhibition of MEK1/2 kinase activity correlated with reduced phosphorylation of the HCV NS5A protein and enhanced RLuc‐replicon luciferase reporter activity, in line with recent reports that phosphorylation of NS5A negatively modulates HCV RNA replication. Finally, genetic deletion analysis in yeast supported the role of a MEK‐like kinase(s) in the regulation of NS5A phosphorylation. In conclusion, the direct anti‐HCV effect of IFN‐γ in cell culture is, at least in part, mediated through the Ras‐MAPK signaling pathway, which possibly involves a direct or indirect modulation of NS5A protein phosphorylation. (H EPATOLOGY 2006;43:81–90.)