HSP70 Promotes HBV Secretion By Binding To HBV PreS1 Domain

Objective: Hepatitis B virus(HBV)infection is the most common viral infection in the world.Various liver diseases caused by HBV infection are life-threatening global health problems.The preS1 domain on HBV large envelope proteins(LHBs)is one of the most important structures of the virus and is exposed to the outermost layer of the virus.In this study,preS1 was used as a bait protein to capture HSP70,which was specifically bound to it,and the relationship between the two was analyzed.Methods: In order to verify the interaction between preS1 and HSP70,tests were performed using immunofluorescence(IF)and co-immunoprecipitation(co-IP).To detect the level of HSP70 in the blood for 50 cases with chronic hepatitis B(CHB)patients was compared with that with 50 healthy people by ELISA.To analyze the relationship between PreS1 and HSP70,HepG2 cells line transfected with HBV 1.1 plasmid、HepG2.2.15 cells line stably expressing HBV genome and HepG2-NTCP cells line infected with HBV were detected the expression level of HSP70.To examine the effect of HSP70 on HBV,qRT-PCR was used to count HBV DNA copies in cell culture supernatant.In order to further explore the influence of HSP70 on HBV Dane particles,particle gel assays were performed to test HBV quantity in the supernatant.Results: IF confirmed the colocalization of preS1 and HSP70 in the cytoplasm,and co-IP also verified the specific binding of the two.ELISA testing of clinical specimens found that HSP70 levels in CHB patients’ blood were significantly increased(t = 2.328,p = 0.022).Cell experiments also proved that HBV expression can up-regulate HSP70 expression at the mRNA and protein levels.QRT-PCR revealed that the number of HBV DNA copies were increased in culture supernatants in HSP70 overexpressing cell lines.Although ELISA detected the expression of HBV surface antigen(HBsAg)and HBV e antigen(HBeAg)in the supernatants was not affected,however,HBV Dane particles were also increased in the supernatant.Conclusion: The preS1 domain of HBV LHBs can interact with HSP70,and the former promotes the expression of the latter;in turn,HSP70 also facilitates the secretion of HBV Dane particles in a replication-independent manner.