Identification of an Interferon-Inducible Regulatory Molecule, IFI44L, for Hepatitis B Virus cccDNA in Primary Human Hepatocytes

Aim: IFN-γ, produced by cytotoxic T lymphocytes 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 associated with cccDNA amplification and IFN-γ effects using an in vitro HBV infection system exhibiting various transcription levels.
Methods: Primary human hepatocytes were infected with HBV using genomic plasmids carrying the basic core promoter double mutation A1762T/G1764A and/or the precore mutation G1896A and treated with IFN-γ, IFN-α, and entecavir (ETV). Comprehensive expression analysis and functional studies involving RNA microarray and small interfering RNA analysis were performed.
Results: The HBV infection system accurately reproduced the HBV life cycle and exhibited various transcription levels. Microarray analysis revealed 53 genes correlated with the cccDNA levels. Of the 53 genes, expression of IFN-induced protein 44-like (IFI44L) was upregulated by IFN-γ and IFN-α, but not ETV. IFI44L was associated with the anti-viral effects of IFN-γ. IFI44L negatively regulated the innate immune response and IFN-γ function that suppresses HBV transcription and propagation by inhibiting the activation of NF-κB and STAT1 pathways.
Conclusions: Using the unique in vitro HBV infection system, an IFN-inducible molecule, IFI44L, associated with cccDNA amplification, was identified. These results suggest an innovative molecular strategy for the regulation of HBV cccDNA by controlling a novel host factor IFI44L.