Comparison of Huh6 and Huh7 cells under IFNgamma treatment

All major types of interferon (IFN) efficiently inhibit hepatitis C virus (HCV) replication in vitro and in vivo. Remarkably, HCV replication is not sensitive to IFN in the hepatoma cell line Huh6, despite an intact signaling pathway. We performed transcriptome analyses between Huh6 and Huh-7 to identify effector genes of the IFN response and thereby identified the DExD/H box helicase DDX60L as a restriction factor of HCV replication. DDX60L and its homolog DDX60 were both induced upon viral infection and IFN treatment in primary human hepatocytes. However, exclusively DDX60L knockdown increased HCV replication in Huh-7 cells, and rescued HCV replication from type II IFN as well as type I and III IFN treatment, suggesting that DDX60L is an important effector protein of the innate immune response against HCV. DDX60L had no impact on replication of hepatitis A virus (HAV), but severely impaired production of lentiviral vectors, arguing for a potential antiretroviral activity. Detection of endogenous DDX60L protein turned out to be difficult due to instability. DDX60L knockdown did not alter interferon stimulated gene (ISG) induction after IFN treatment, suggesting that it is a direct effector of the innate immune response. It most likely inhibits viral RNA replication, since we found no impact of DDX60L on translation or stability of HCV subgenomic replicons, nor additional impact on entry and assembly of infectious virus. Similar to its homolog DDX60, DDX60L had a moderate impact on retinoic acid-inducible gene I (RIG-I)-dependent activation of innate immunity arguing for additional functions in the sensing of viral RNA.

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Grünvogel O, Esser-Nobis K, Reustle A, Schult P, Müller B, Metz P, Trippler M, Windisch MP, Frese M, Binder M, Fackler O, Bartenschlager R, Ruggieri A, Lohmann V