Hepatitis B virus polymerase inhibits RIG-I- and Toll-like receptor 3-mediated beta interferon induction in human hepatocytes through interference with interferon regulatory factor 3 activation and dampening of the interaction between TBK1/IKKϵ and DDX3

Hepatitis B virus (HBV) infection remains one of the most serious health problems worldwide. Whilst studies have shown that HBV impairs interferon (IFN) production from dendritic cells in chronic hepatitis B patients, it remains unknown whether HBV inhibits IFN production in human hepatocytes. Using transient transfection assays in a primary human hepatocyte cell line (PH5CH8), this study demonstrated that HBV polymerase inhibits IFN-β promoter activity induced by Newcastle disease virus, Sendai virus or poly(I : C) in a dose-dependent manner, whilst ectopic expression of the HBV core and X proteins had no effect on IFN-β promoter activity. In addition, HBV polymerase blocked cellular IFN- β expression and consequent antiviral immunity revealed by an infection protection assay. Furthermore, overexpression of key molecules on the IFN- β induction axis, together with HBV polymerase, resulted in a block of IFN-β promoter activity triggered by RIG-I, IPS-1, TRIF, TBK1 and IKKϵ, but not by an IFN regulatory factor 3 dominant-positive mutant (IRF3-5D), suggesting that HBV polymerase prevents IFN- β expression at the TBK1/IKKϵ level. Further studies showed that HBV polymerase inhibited phosphorylation, dimerization and nuclear translocation of IRF3, in response to Sendai virus infection. Finally, it was shown that HBV polymerase-mediated dampening of the interaction between TBK1/IKKϵ and DDX3 may be involved in the inhibitory effect on IFN- β induction. Taken together, these findings reveal a novel role of HBV polymerase in HBV counteraction of IFN- β production in human hepatocytes.