The Role Of Ubiquitin Specific Protease 18 In Hepatitis B Virus Infection And Its Underlying Mechanism

Background&Aims:Hepatitis B virus(HBV)infection remains as one of the major public health problems in the world.Type Ⅰ interferon(IFN),routinely used to treat patients chronically infected with HBV,plays an essential role in antiviral defense by induced expression of a few hundred interferon stimulated genes(ISGs),including ubiquitin-specific protease 18(USP18),a negative regulator of type ⅠIFN signaling.The expression level of USP18 was elevated in the pretreatment liver tissues of chronic hepatitis B(CHB)patients who did not respond to IFN treatment.However,the relationship between USP18 and HBV and the role of USP18 in persistent viral infection remain to be clarified.This study was designed to investigate the effects of USP18 on HBV infection and its potential mechaisms.Methods:The levels of wild type USP18(WT-USP18)and USP18 catalytically inactive form C64S were up-regulated by plasmids transfection followed by IFNa treatment in HepAD38 cells,respectively.Real-time PCR and ELISA were used to quantify HBV replication and protein expression.Type Ⅰ IFN signaling pathway was monitored at three levels:p-STAT1(Western Blot),IRSE activity(Dual Luciferase Assay)and ISGs expression(Real-time PCR).Co-Immunoprecipiation(CO-IP)was employed to explore the interaction between USP18 and different HBV proteins.Results:Our data demonstrated that over expression of either USP18 or USP18-C64S inactive mutant increased the intracellular viral pgRNA,total DNA,cccDNA and HBV DNA levels in the culture supernatant.Over expression of USP18 inhibited the activation of exogenous IFNa-induced type Ⅰ IFN signaling pathway.USP18 could interact with Polymerase(Pol),Large surface protein(LHBs)and Middle surface protein(MHBs)of HBV.Conclusions:USP18 stimulated HBV production independent of its protease activity.USP18 inhibited IFNa-induced type Ⅰ IFN signaling pathway.HBV polymerase,large surface protein and middle surface protein could be able to interact with USP18,although detailed outcome of these host-virus interactions remains to be further investigated.Data from this study provided new insights into the role of USP18 in host innate immune response to HBV infection.