The Mechanisms Of NLRX1 And Sam68 Regulating Hepatitis C Virus Replication

HCV is an important human pathogen and more than 170 million people are infected by HCV worldwide.It causes health problems such as chronic hepatitis,liver cirrhosis,and even hepatocellular carcinoma.There is no effective vaccine for HCV.HCV is a positive sense,single-stranded RNA virus that encodes three structural proteins and seven non-structural proteins.After HCV infects human cells,it is regulated by the host's innate immune response and host factors.Upon viral invasion,pattern recognition receptors RIG-I-like receptors identify the pathogen-associated molecular patterns(PAMPs).RIG-I and MDA5 undergo conformational changes to activate the downstream adaptor protein MAVS,which resides on the mitochondrial outer membrane.MAVS recruits and activates IRF3 and NF-kB,eventually inducing the production of type I interferon(IFN),type III IFN and other antiviral cytokines.Our study showed that HCV induced the expression of NLRX1 protein in human hepatocytes.Overexpression of NLRX1 enhanced HCV replication,and silencing of NLRX1 inhibited HCV replication and viral protein accumulation.The mRNA level of type I IFN,type III IFN and downstream IFN-stimulated genes(ISGs)increased significantly in stable NLRX1-silenced cells under HCV infection.Further studies showed that NLRX1 bound to the adaptor protein MAVS and then induced the polyubiquitination of MAVS.Further studies demonstrated that NLRX1 interacted with PCBP2 and promoted the K48-linked polyubiquitination of MAVS.NLRX1 also negatively regulates innate immune response to other RNA viruses.In addition,we found that HCV infection induces the translocation of Sam68 from the nucleus to the cytoplasm,and Sam68 binds to the SL2 of HCV 5'UTR,promoting viral replication.In summary,NLRX1 promotes the ubiquitination and degradation of MAVS by recruiting PCBP2,ultimately inhibiting innate immune response to HCV infection and promoting persistent HCV infection.Sam68 promotes HCV replication by direct targeting of viral genomic RNA.This study identify two host proteins NLRX1 and Sam68 in regulation of HCV replication in the host cells through controlling innate immune response and directly targeting HCV genomic RNA respectively.This study provides interesting insights into understanding the regulatory mechanisms of viralinfection by host factors.It also provides a new way to develop potential vaccine for HCV.