The hepatitis B e antigen suppresses IL-1β-mediated NF-κB activation in hepatocytes

Previous clinical studies have demonstrated an association between the hepatitis B e antigen and Toll‐like receptor (TLR) expression and signalling. Therefore, the aim of this study was to develop an in vitro assay to measure the effect of hepatitis B virus proteins, including the precore protein, on signalling mediated by members of the Toll‐like/interleukin 1 (TIR) superfamily, by measuring NF‐κB promoter activity. The basal level of NF‐κB reporter activity was measured in three hepatocyte cell lines (Huh7, HepG2 and PH5CH8) and one kidney cell line (HEK293) using a luciferase assay. All cell lines were virtually refractory to stimulation with lipopolysaccharide; however, PH5CH8 cells had a robust activation of NF‐κB in response to IL‐1β stimulation, with ∼40‐fold higher activation than the unstimulated control, a higher degree of activation than that observed in either Huh7 and HepG2, or HEK293 and HEK293‐TLR2 cells. In PH5CH8 cells transfected with pCI expression constructs and stimulated with IL‐1β, we showed that the precursor form of the precore protein, p25, inhibits NF‐κB activation by up to 30% and the cytosolic form, p22, inhibits NF‐κB activation by 70%. The core protein, p21, which shares significant homology with the precore protein except for a 10‐amino acid extension at the N‐terminus, had no effect on NF‐κB activation. We hypothesize that the inhibition of IL‐1β‐mediated NF‐κB activation by the precore protein may be a mechanism that allows the virus to persist, suggesting a role for the pool of precore protein that remains intracellular.