Transcriptional regulation of IFN-λ genes in Hepatitis C virus-infected hepatocytes via IRF-3·IRF-7·NF-κB complex

Hepatitis C virus (HCV) infection in hepatocytes stimulates innate antiviral responses including the production of type III interferons (IFN-λ), including IL-28A, IL-28B, and IL-29. However, the molecular mechanism(s) regulating the expression of IFN-λ genes in HCV-infected hepatocytes remains undefined. In this study, we examined regulatory elements involved in the induction of IFN-λ genes following HCV infection in hepatocytes and further determined the binding of specific transcription factor(s) to promoter regions of IFN-λ genes. Our studies reveal that the regulatory portion for IL-28A, IL-28B, and IL-29 genes is localized to a 1-kb region in their respective promoters. Notably, interferon regulatory factor (IRF)-3 and -7 are the key transcriptional factors for the induction of IL-28A and IL-28B genes, whereas NF-κB is an additional requirement for the induction of the IL-29 gene. Ligation of Toll-like receptors (TLR) 3, 7, 8, and 9, which also activate IRFs and NF-κB, resulted in more robust production of IFN-λ than that observed with HCV infection, verifying the importance of TLR pathways in IFN-λ production. Furthermore, the addition of IFN-λ to HCV-infected hepatocytes decreased viral replication and produced a concurrent reduction in microRNA-122 (miR-122). The decrease in viral replication was enhanced by the co-administration of IFN-λ and miR-122 inhibitor (miRIDIAN), suggesting that such combinatorial therapies may be beneficial for the treatment of chronic HCV infection.