Anti-APOBEC3B monoclonal antibody Made to order

Interferons (IFNs) play a major role in the control of hepatitis B virus (HBV), whether as endogenous cytokines limiting the spread of the virus during the acute phase of the infection or as drugs for the treatment of its chronic phase. However, the mechanism by which IFNs inhibit HBV replication has so far remained elusive. Here, we show that type I and II IFN treatment of human hepatocytes induces the production of APOBEC3G (A3G) and, to a lesser extent, that of APOBEC3F (A3F) and APOBEC3B (A3B) but not that of two other cytidine deaminases also endowed with anti-HBV activity, activation-induced cytidine deaminase (AID), and APOBEC1. Most importantly, we reveal that blocking A3B, A3F, and A3G by combining RNA interference and the virion infectivity factor (Vif) protein of human immunodeficiency virus does not abrogate the inhibitory effect of IFNs on HBV. We conclude that these cytidine deaminases are not essential effectors of IFN in its action against this pathogen.

Hepatitis B virus (HBV) is a partially double-stranded DNA virus that replicates by reverse transcription. We previously demonstrated that the host restriction factor-APOBEC3B (A3B) inhibited HBV replication which was dependent on its deaminase activity during reverse transcription. However, the host factors involved in the process of regulating the anti-HBV function of A3B are less known. In this research, to obtain a comprehensive understanding of the interaction networks of A3B, we conducted coimmunoprecipitation and mass spectrometry to identify A3B-interacting proteins in the presence of HBV. By this approach, we determined that DExD/H-box helicase 9 (DHX9) suppressed the anti-HBV effect of A3B, and this suppression was dependent on their interaction. Although DHX9 did not affect the deamination activity of A3B in vitro assay or the viral DNA editing of A3B in HepG2-NTCP cells that support HBV infection, it inhibited the binding of A3B with pgRNA. These data suggest that DHX9 can interact with A3B and attenuate the anti-HBV efficacy of A3B.