Hepatocyte Host Factor IFI44L Regulates the Innate and Acquired Immune Responses to Hepatitis B Virus

Objective: Curing hepatitis B requires the complete elimination of covalently closed circular DNA (cccDNA). Interferon (IFN)-γ is produced by cytotoxic T lymphocytes and has noncytolytic antiviral potential; however, elimination of cccDNA could not be achieved. To enhance the regulatory effect of IFN-γ, we comprehensively analyzed the host factors that associated with cccDNA amplification and IFN-γ effects using the in vitro HBV infection system that exhibits various transcription levels. Design: Primary human hepatocytes were infected with HBV using genomic plasmids carrying the basic core promoter 1762/1764 and/or the precore 1896 mutation and treated with IFN-γ, IFN-α, and entecavir. Comprehensive expression analysis and functional studies were performed to analyze the host factors related to the cccDNA regulation using RNA microarray and siRNA analysis. Results: HBV infection system accurately reproduced the HBV life cycle and exhibited various transcription levels. Microarray analysis revealed that 53 genes increased depending on the cccDNA levels. Of 53 genes, the expression of IFN-induced protein 44-like (IFI44L) was the most upregulated by IFN-γ and IFN-α but not entecavir, and associated with the anti-viral effects of IFN-γ. siRNA analysis revealed that IFI44L negatively regulates the innate immune response and IFN-γ function to suppress HBV transcription and propagation by inhibiting the activation of NF-κB and STAT1 pathways. To develop an in vitro HBV infection assay system that exhibits various transcription levels, HBV clones of genotype C2 with basal core promoter (BCP) 1762/1764 and/or precore 1896 mutations (wt/wt; Low transcription, wt/mu; Medium t., mu/mu; High t.) were applied. HBV plasmids were transiently transfected into HepG2 cells and the supernatant was added to the medium of PXB cells and treated with IFN-γ, IFN-α, and entecavir (ETV). Comprehensive expression analysis was performed to analyze the host factors related to the cccDNA regulation using RNA microarray.