GB virus type C NS5A sequence polymorphisms: Association with interferon susceptibility and inhibition of PKR-mediated eIF2α phosphorylation

GB virus type C (GBV-C) causes persistent infection in humans, although the mechanism by which the virus avoids clearance by the host is unknown. To determine if amino acid polymorphisms in the GB virus type C (GBV-C) NS5A and E2 proteins alter response to interferon (IFN) therapy, we studied the sequence of GBV-C NS5A and E2 obtained from people receiving IFN therapy. In addition, we expressed recombinant GBV-C NS5A protein to determine if it interferes with RNA-activated protein kinase (PKR) function in vitro. GBV-C NS5A amplified from a person whose virus was cleared by IFN therapy (IFN sensitive) demonstrated unique amino acid changes occurring in the region that aligns with the hepatitis C virus (HCV) IFN sensitivity-determining region (ISDR) compared with NS5A sequences from individuals who did not clear GBV-C (IFN resistant). There were no differences in the E2 sequences obtained from IFN-sensitive and IFN-resistant isolates. Using a yeast genetic system, IFN-resistant NS5A inhibited PKR-mediated phosphorylation of eukaryotic initiation factor 2α (eIF2α) in yeast, whereas IFN-sensitive NS5A did not inhibit PKR function. GBV-C NS5A amino acid polymorphisms appear to be involved in response to IFN therapy, and IFN-resistant GBV-C NS5A inhibited PKR-mediated eIF2α phosphorylation in a yeast genetic system, suggesting a mechanism by which GBV-C may evade clearance by naturally occurring host antiviral responses.