Interferon alpha-2b inhibits negative-strand RNA and protein expression from full-length HCV1a infectious clone

We have established a T7-based model system for hepatitis C virus (HCV) 1a strain, which involves the use of a replication-defective adenovirus that carries the gene for T7 RNA polymerase and a transcription plasmid containing full-length HCV cDNA clone. To facilitate high-level expression of HCV, sub-confluent Huh7 cells were first infected with adenovirus containing the gene for the T7 RNA polymerase and then transfected with the transcription plasmid. As a negative control, part of NS5B gene of this clone was deleted which abolishes the HCV RNA-dependent RNA polymerase and prevents replication of viral RNA. This model produces high levels of structural (core, E1, E2) and nonstructural proteins (NS5), which were detected by Western blot analysis and immunofluorescence assay. Negative-strand HCV RNA was detected only in the wild-type clone in the presence of actinomycin D, and no RNA was detected with the NS5B deleted mutant control. As a practical validation of this model, we showed that IFN alpha-2b selectively inhibits negative-strand RNA synthesis by blocking at the level of protein translation. The inhibitory effect of IFN alpha-2b is not due reduction of transcription by T7 polymerase or due to intracellular degradation of HCV RNA. This in vitro model provides an efficient and reliable means of assaying negative-strand RNA, protein processing, and testing the antiviral properties of interferon.