Mutations in nonstructural protein 5A gene and response to interferon in hepatitis C virus genotype 2 infection

Abstract

An association has been reported between mutations in the amino acid residues 2209-2248 of the nonstructural protein 5A (NS5A) gene (interferon-sensitivity determining region [ISDR]) and interferon efficacy in hepatitis C virus (HCV)-1b infection. This relationship was analyzed in chronic HCV-2 infection. Forty patients with HCV-2a and 35 with HCV-2b were treated with interferon alfa for 6 months with a total dose of 468 to 860 million units. Pretreatment NS5A sequences were determined by direct sequencing. A higher complete and sustained response rate was observed in HCV-2a than in HCV-2b (70% vs. 34%; P ‫؍‬ .003). Serum HCV-RNA levels were lower in complete responders than nonresponders in HCV-2a (P ‫؍‬ .049) and HCV-2b (P ‫؍‬ .02). The number of amino acid mutations was greater in complete responders than nonresponders in NS5A2193- The current primary therapy for chronic hepatitis C is parenteral administration of type 1 interferons (interferon alfa and beta), while the rate of sustained and complete responses with virus eradication is obtained in only up to 30% of the patients. 1-3 To date, hepatitis C virus (HCV) is classified into at least 9 major genotypes and more than 30 subtypes. 4,5 In Japan, about 70% of the patients with chronic hepatitis C are infected with HCV genotype 1b (HCV-1b), and the rest are infected with HCV genotype 2 (HCV-2) 6 (25% with HCV-2a and 5% with HCV-2b). While the complete response is as low as 10% to 20% in HCV-1b infection, it is considered more than 60% in HCV-2 infection in Japan. [7][8][9][10][11][12] Such differences in interferon efficacy among various HCV genotypes suggest that a certain kind of genetic change of the virus could affect the sensitivity to interferon.We recently identified a region that is associated with the response to interferon in HCV-1b genomes in Japan. 13 An increase in the number of amino acid changes in the nonstructural protein 5A gene (NS5A) (NS5A2209-2248, interferon sensitivity determining region [ISDR]) makes HCV more sensitive to interferon. 14 However, the mechanism of the different response to interferon therapy among patients with HCV-2 infection is still unclear. Some studies suggested that a lower viral load is associated with the good response to interferon in HCV-1b or non-1b, 12,15 the mechanism of which is still unknown. In previous studies, interferon effect and pretreatment viral load were also associated with the mutations in ISDR in HCV-1b. 13,16 Thus, the relation between NS5A structure and interferon effect or viral load in HCV genotypes other than HCV-1b is of great interest.Several studies that focused on biological functions of NS5A revealed some aspects of its properties. In particular, Gale et al. 17 suggested that the NS5A protein inhibits an RNA-dependent protein kinase (PKR), which plays a major role in the viral protection by inhibiting viral protein translation. The NS5A protein of HCV-1b and -1a forms a complex with the PKR and inhibits the phosphorylation of eukaryotic translation initiation factor-2 (eIF-2). Mor...

Activation of the Ras/Raf/MEK Pathway Facilitates Hepatitis C Virus Replication via Attenuation of the Interferon-JAK-STAT Pathway

“…Previous studies explored the mechanism by which HCV accomplishes this feat, such as disruption of the IFN-␣/␤ production pathway, e.g., the disruption of retinoic acid-inducible gene I (RIG-I) signaling (20) and blockade of IRF3 phosphorylation (21) by the NS3/4A protein. The IFN-␣/␤ resistance may also be a result of sequence variation, e.g., mutations within the IFN-␣ sensitivity-determining region (ISDR) of the NS5A protein (18,47) or within the hypervariable region 1 (HVR1) of the E2 protein (11). Direct inhibition of antiviral IFNstimulated genes (ISGs) is also possible, such as the interaction between the E2 protein and the phosphorylation homology domain (PePHD) of protein kinase R (PKR), whose kinase activity is abolished as a result (65).…”

Coevolution of the Hepatitis C Virus Polyprotein Sites in Patients on Combined Pegylated Interferon and Ribavirin Therapy

“…Analysis of HCV 1b sequences showed an association between the number of ISDR mutations and the response to the IFN therapy (92). However, studies of HCV genotype 2b and 3a did not find such a relation between SVR and NS5A variability (8,89). Additionally, no binding between PKR and the genotype 3a NS5A from the IFN-resistant HCV strains was observed in vitro (20).…”

Epistatic connectivity among HCV genomic sites as a genetic marker of interferon resistance

“…The number of mutations in ISDR was found to correlate with response to IFN therapy [29][30][31], thus suggesting that ISDR may be used as a genetic marker of IFN resistance. However, these findings were refuted in other studies [32,33]. Castelain and colleagues [34] observed no binding between PKR and the genotype 3a NS5A from IFNresistant HCV strains.…”

“…Changes in mutation rates corresponding to IFN response were observed in some regions of the HCV genome, including E2 [40,41], NS5A [31,36], P7 [39] and NS2 [42]. However, no strong linkage between the HCV genetic diversity and IFN/RBV sensitivity has been detected [29,32,33,36,38]. All these observations indicate a complex association between HCV genetic variability and response to IFN/RBV treatment.…”