Suppression of interferon-induced antiviral activity in cells expressing hepatitis C virus proteins

To elucidate the mechanism of the persistent nature of hepatitis C virus (HCV) infection, we examined whether the expression of HCV proteins affect the antiviral activity of interferon (IFN). Antiviral activity of IFN in HepG2 cells expressing all HCV (type 1b) proteins was much lower than vector control (VC) HepG2 cells when encephalomyocarditis virus (EMCV) was used as a challenge virus. Lesser sensitivity to IFN was also observed in cells expressing NS3, NS4, and NS5 acid in cells expressing only NS5A. In contrast, HepG2 cells expressing core, E1, E2, NS2, and NS3 proteins were equally sensitive to IFN as VC cells. We then tested the antiviral activity by IFN in two human amnion-derived FL cell lines expressing NS5A from two different clones, one with an intact sequence of IFN sensitivity-determining region (ISDR) and the other with a mutated ISDR sequence. They were almost equally insensitive to IFN treatment when EMCV was challenged. HCV thus has functional protein(s), possibly NS5A, to suppress IFN-induced antiviral activity and plays an important role in virus-cell interaction and regulation of viral replication.