The AMPK-related kinase SNARK regulates hepatitis C virus replication and pathogenesis through enhancement of TGF-β signaling

Background & Aims: Hepatitis C virus (HCV) is a major cause of chronic liver disease worldwide. The biological and therapeutic importance of host cellular cofactors for viral replication has been recently appreciated. Here we examined the roles of SNF1/AMP kinase-related kinase (SNARK) in HCV replication and pathogenesis. Methods: The JFH1 infection system and the full-length HCV replicon OR6 cell line were used. Gene expression was knocked down by siRNAs. SNARK mutants were created by site-directed mutagenesis. Intracellular mRNA levels were measured by qRT-PCR. Endogenous and overexpressed proteins were detected by Western blot analysis and immunofluorescence. Transforming growth factor (TGF)-beta signaling was monitored by a luciferase reporter construct. Liver biopsy samples from HCV-infected patients were analyzed for SNARK expression. Results: Knockdown of SNARK impaired viral replication, which was rescued by wild type SNARK but not by unphosphorylated or kinase-deficient mutants. Knockdown and overexpression studies demonstrated that SNARK promoted TGF-beta signaling in a manner dependent on both its phosphorylation and kinase activity. In turn, chronic HCV replication upregulated the expression of SNARK in patients. Further, the SNARK kinase inhibitor metformin suppressed both HCV replication and SNARK-mediated enhancement of TGF-beta signaling. Conclusions: Thus reciprocal regulation between HCV and SNARK promotes TGF-beta signaling, a major driver of hepatic fibrogenesis. These findings suggest that SNARK will be an attractive target for the design of novel host-directed antiviral and antifibrotic drugs. (C) 2013 European Association for the Study of the Liver. Published by Elsevier B.V. All rights reserved.