Interferon-inducible MX2 is a host restriction factor of hepatitis B virus replication

Abstract Background and Aim Noncytolytic curing of hepatitis B virus (HBV) infected hepatocytes by cytokines including type I interferons (IFNs) is of importance for resolving acute and chronic infection. However, as IFNs stimulate hundreds of genes those most relevant for HBV suppression remain largely unknown. Amongst them are the large Mx GTPases. Human MX1 (or MxA) is active against many RNA viruses while MX2 (or MxB) was recently found to restrict human immunodeficiency virus 1, hepatitis C virus, and herpesviruses. Here we investigated the anti-HBV activity of MX2. Methods Potential anti-HBV activity of MX2 and functional variants was assessed in transfected and HBV infected hepatoma cells and primary human hepatocytes, employing multiple assays to determine HBV nucleic acids as well as their synthesis and decay. The specific roles of MX2 in IFN-α inhibition of HBV transcription and replication were addressed by MX2-specific shRNA interference (RNAi). Results MX2 alone as well as IFN-α substantially inhibited HBV replication, due to significant deceleration of the synthesis and slight acceleration of the turnover of viral RNA. RNAi knock-down of MX2 significantly reduced the inhibitory effects of IFN-α. Strikingly, MX2 inhibited HBV infection by reducing covalently closed circular DNA (cccDNA), most likely by indirectly impairing relaxed circular DNA to cccDNA conversion rather than destabilizing existing cccDNA. Various mutations affecting the GTPase activity and oligomerization status reduced MX2’s anti-HBV activity. Conclusion MX2 is an important IFN-α inducible effector that decreases HBV RNA levels but can also potently inhibit HBV infection by indirectly impairing cccDNA formation. MX2 likely has the potential of therapeutic application aimed at curing HBV infection by eliminating cccDNA.