Investigation of interferon-α response by a single amino acid substitution of nonstructural protein 5A in hepatitis C virus-infected patients.

The therapeutic efficacy of interferon (IFN) for the hepatitis C is closely related with mutations in interferon sensitivity determining region or V3 domain of the hepatitis C virus (HCV) nonstructural protein 5A (NS5A). However, the relationship between alanine aminotransferase (ALT) normalization and the NS5A variability remains unclear. To clarify these features of NS5A, we examined the genetic variability of the patients' NS5A from 33 HCV genotype 1b-infected patients: 11 sustained virological response (SVR), 11 end-of-treatment response (ETR) with normal ALT (<40 IU/L), and 11 non-response (NR) with abnormal ALT (>40 IU/L) after IFN treatment for >24 weeks. The amino acid in position 2378 (followed by HCV-J prototype strain) with alanine (A2378) before IFN treatment was frequent in both SVR and ETR after IFN treatment, whereas that with threonine (T2378) was significant in NR. Moreover, substitution of threonine for alanine in HCV subgenomic replicon showed a 3- to 4-fold reduction of IFN transactivation and replication even in the presence of IFN, suggesting an IFN-resistant phenotype. These observations suggest that a single amino acid in position 2378 of NS5A plays important roles for both ALT normalization and IFN response in HCV-1b infected patients.