Amino Acid Substitutions In Interferon Sensitivity Determining Region Research Articles

Interferon sensitivity-determining region of hepatitis C virus influences virus production and interferon signaling.

The number of amino acid substitutions in the interferon (IFN) sensitivity-determining region (ISDR) of hepatitis C virus (HCV) NS5A is a strong predictor for the outcome of IFN-based treatment. To assess the involvement of ISDR in the HCV life cycle and to clarify the molecular mechanisms influencing IFN susceptibility, we used recombinant JFH-1 viruses with NS5A of the genotype 1b Con1 strain (JFH1/5ACon1) and with NS5A ISDR containing 7 amino acid substitutions (JFH1/5ACon1/i-7mut), and compared the virus propagation and the induction of interferon-stimulated genes (ISGs). By transfecting RNAs of these strains into HuH-7-derived cells, we found that the efficiency of infectious virus production of JFH1/5ACon1/i-7mut was attenuated compared with JFH1/5ACon1. After transfecting full-length HCV RNA into HepaRG cells, the mRNA expression of ISGs was sufficiently induced by IFN treatment in JFH1/5ACon1/i-7mut-transfected but not in JFH1/5ACon1-transfected cells. These data suggested that the NS5A-mediated inhibition of ISG induction was deteriorated by amino acid substitutions in the ISDR. In conclusion, using recombinant JFH-1 viruses, we demonstrated that HCV NS5A is associated with infectious virus production and the inhibition of IFN signaling, and amino acid substitutions in the NS5A ISDR deteriorate these functions. These observations explain the strain-specific evasion of IFN signaling by HCV.

A mutation in the interferon sensitivity‐determining region is associated with responsiveness to interferon‐ribavirin combination therapy in chronic hepatitis patients infected with a Japan‐specific subtype of hepatitis C virus genotype 1b

The interferon sensitivity-determining region (ISDR) is useful as a predictive marker of the response to interferon (IFN) therapy for chronic hepatitis patients with a Japan-specific subtype (J-type) of hepatitis C virus (HCV) genotype 1b. This marker is not useful for predicting responsiveness of a worldwide subtype (W-type) of HCV 1b, which could explain the restricted usefulness of this system only to Japan. In the present study, we examined the predictive value of the ISDR for ribavirin combination therapy. A total of 79 patients with HCV 1b comprising 35 patients with J-type and 44 patients with W-type were treated with IFN in combination with ribavirin for more than 48 weeks. Mutations in the ISDR were detected more frequently often seen in J-type HCV 1b than in W-type; however, the sustained virological response (SVR) rate for the combination therapy was similar between the two subtypes. Multivariate analysis revealed that factors associated with SVR were IFN dose and the number of amino acid substitutions in ISDR but not with subtypes J and W. The correlation between the number of substitutions in ISDR and responses to IFN-ribavirin combination therapy was restricted to patients with J-type HCV 1b. The ISDR is a useful predictive marker for response to IFN-ribavirin combination therapy in J-type HCV.

Fluctuations of hepatitis C virus load are not related to amino acid substitutions in hypervariable region 1 and interferon sensitivity determining region.

Hepatitis C virus (HCV) load is one of the most important predictive factors of response to interferon treatment. However, little is known about the mode and determinants of viremia. The mode of viremia was investigated in 78 patients with chronic HCV genotype 1b infection during 1-2 years follow up. Virus load, determined by a branched chain DNA amplification assay, was stable in 73 of 78 (93.6%) patients, whereas 5 (6.4%) showed marked fluctuation (from undetectable level to more than 10 Meq/ml) in viral titer. To study the mechanisms mediating fluctuations in viral titer, amino acid sequences of two regions were examined; hypervariable region (HVR) 1 and the interferon sensitivity determining region (ISDR). Multiple amino acid substitutions were observed in HVR 1 but no relationship was evident between substitutions and virus titers. In contrast, no amino acid substitutions were observed in the ISDR in any patients with stable virus titer during a follow-up period of 12-24 months (7-24 samples) or in one patient who was observed for 15 years. Interestingly, multiple amino acid substitutions in the ISDR appeared in only two of the five patients with marked titer fluctuation, when the virus decreased markedly. Alanine aminotransferase levels in these five patients correlated with viral load. The data suggest that amino acid substitutions in HVR1 and ISDR are not essential for changes in viral titer. Possible mechanisms of fluctuations of viral titer and amino acid substitutions in the ISDR accompanying marked reductions in viral load are discussed.