High Mobility Group Protein Box 1 Promotes Hepatitis C Virus Replication

Hepatitis C virus (HCV) HCV is an enveloped, positive-strand RNA virus, and causes serious liver diseases such as chronic hepatitis, cirrhosis, and hepatocellular carcinoma. A protective vaccine is not yet available and therapeutic options are still limited. It is reported that many host factors may be implicated in the pathogenesis of HCV-related diseases, such as La antigen and poly(C)-binding protein 2 (PCBP2), and so on.High-mobility-group box 1 (HMGB1), a nonhistone chromosomal protein, belongs to the family of the high-mobility-group (HMG) nuclear proteins. HMGB1 is composed of two homologous DNA-binding domains and a highly negatively charged C-terminal domain. It has reported that HMGB1, in addition to DNA binding, can also bind to both double-stranded and single-stranded immunogenic RNAs and functions as a universal sensor for nucleic acid-mediated innate immune responses. Although a recent study suggested that HMGBlreleased from virusinfected cells could block HCV infection, but the role of intracellular HMGB1 in HCV replication and/or translation is still unclear.In this study, we investigated HMGB1 functions in HCV replication and translation. We found that the level of HCV RNA and protein was significantly increased or reduced when we conducted HMGB1 overexpression or knockdown, respectively, in HCV-infected cells. Next, we tested the impact of HMGB 1 on HCV translation activity using both the HCV bicistronic plasmid system (pRL-HL) and the HCV IRES RNA reporter system. The results indicated that HMGB1 is not required for viral protein translation. Immuno-fluorescence localization revealed HMGB1 translocation from nuclear to cytoplasm after HCV infection. Co-immunoprecipitation and RNA binding protein co-immunoprecipitation showed that HMGB1 bound to HCV positive-strand RNA during HCV infection. Further studies demonstrated that the HMGB1 A box binds to the SL4 of HCV 5'UTR, which facilitates HCV RNA replication. These data suggest that HMGB1 is an HCV RNA-binding protein and serves as a proviral factor to promote HCV infection.