Zinc-dependent interaction between JAB1 and Pre-S₂ mutant large surface antigen of hepatitis B virus and its implications for viral hepatocarcinogenesis

Chronic hepatitis B virus (HBV) infection is a major cause of hepatocellular carcinoma (HCC) worldwide. The pre-S₂ mutant large HBV surface protein (Δ2 LHBS), which contains an in-frame deletion of approximately 17 amino acids in LHBS, is highly associated with risks and prognoses of HBV-induced HCC. It was previously reported that Δ2 LHBS interacts with the Jun activation domain-binding protein 1 (JAB1), a zinc metalloprotease. This promotes the degradation of the cell cycle regulator p27^Kip1 and is believed to be the major mechanism for Δ2 LHBS-induced HCC. In this study, it was found that the interaction between JAB1 and Δ2 LHBS is facilitated by divalent metal Zn²⁺ ions. The binding of JAB1 to Δ2 LHBS requires the JAB1/CSN5 MPN metalloenzyme (JAMM) motif and residue H138 that binds to Zn²⁺ ions in JAB1. Isothermal titration calorimetry showed that Δ2 LHBS binds directly to Zn²⁺ ions in a two-site binding mode. Residues H71 and H116 in Δ2 LHBS, which also contact Zn²⁺ ions, are also indispensable for Δ2 LHBS-mediated p27^Kip1 degradation in human HuH7 cells. These results suggest that developing drugs that interrupt interactions between Δ2 LHBS and JAB1 can be used to mitigate Δ2 LHBS-associated risks for HCC.