Two PKR inhibitor HCV proteins correlate with early but not sustained response to interferon

Background & Aims: The NS5A and the E2 proteins of hepatitis 0 virus (HCV)-1b can bind and inhibit in vitro the interferon (IFN)-induced cellular kinase PHR. The role of such interaction in modulating the antiviral effect of IFN is still controversial. We have analyzed the E2 and the NS5A sequences in HCV-lb-infected patients treated with IFN to assess whether and how different combinations of wild-type and mutant proteins correlated with early and long-term virological response. Methods: in 30 patients, sequences of pretreatment and on-treatment E2-PePHD and NS5A-PKR binding domain (including the putative ISDR) were analyzed in parallel by sequencing cDNA-polymerase chain reaction products and up to 25 independent clones. Results: The E2-PePHD sequence was highly conserved with a homogeneous quasispecies and was identical in 29 of 30 cases with no association with the pattern of response and no evidence of evolution during therapy. Patients with a mutated NS5A-ISDR had a higher rate of early virological response (67%) than cases with wild-type ISDR (17%). This association was lost in long-term responders (33% vs. 17%). Conclusions: Although the highly conserved E2-PePHD motif might contribute to reduce IFN responsiveness, variations within this region do not seem to play a role in modulating IFN sensitivity. The NS5A-ISDR sequence influenced the early, but not the sustained response, to IFN, suggesting that other factors may be more important for the long-term outcome of therapy.