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

Hepatitis C virus (HCV) infection in hepatocytes stimulates innate antiviral responses including the production of type III interferons (IFN-l), including IL-28A, IL28B, and IL-29 (Figure 1). However, the molecular mechanism(s) regulating the expression of IFN-l genes in HCV-infected hepatocytes remains undefined. In this study, we examined regulatory elements involved in the induction of IFN-l genes following HCV infection in hepatocytes and further determined the binding of specific transcription factor(s) to promoter regions of IFN-l genes. Our studies reveal that the regulatory portion for IL-28A, IL-28B, andIL-29 genes is localized to a 1-kb region in their respective promoters (Figure 2, 4). Notably, interferon regulatory factor (IRF)-3 and -7 are the key transcriptional factors for the induction of IL-28A and IL-28Bgenes (Figure 5, 6), whereas NFB is an additional requirement for the induction of the IL-29 gene (Figure 3). Ligation of Toll-like receptors (TLR) 3, 7, 8, and 9, which also activate IRFs and NFB, resulted in more robust production of IFN-l than that observed with HCV infection, verifying the importance of TLR pathways in IFN-l production (Figure 8). Furthermore, the addition of IFN-l 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-l and miR-122 inhibitor (miRIDIAN) (Figure 7), suggesting that such combinatorial therapies may be beneficial for the treatment of chronic HCV infection.