The recently described hepatic cell line HepaRG is the sole hepatoma cell line susceptible to hepatitis B virus (HBV) infection. It provides a unique tool for investigating some unresolved issues of the virus' biology, particularly the formation of the viral mini-chromosome believed to be responsible for the persistence of infection. In this study, we characterized the main features of HBV infection: it is restricted to a subpopulation of differentiated hepatocyte-like cells that express albumin as a functional marker and represents around 10 % of all differentiated HepaRG cells. Infection may persist for more than 100 days in cells maintained at the differentiated state. Even though infected cells continued to produce infectious viral particles, very limited or no spreading of infection was observed. Low genetic variation was also observed in the viral DNA from viruses found in the supernatant of infected cells, although this cannot explain the lack of reinfection. HBV infection of HepaRG cells appears to be a very slow process: viral replication starts at around day 8 post-infection and reaches a maximum at day 13. Analysis of viral DNA showed slow and inefficient conversion of the input relaxed circular DNA into covalently closed circular (CCC) DNA, but no further amplification. Continuous lamivudine treatment inhibited viral replication, but neither prevented viral infection nor initial formation of CCC DNA. In conclusion, HBV infection in differentiated HepaRG cells is characterized by long-term persistence without a key feature of hepadnaviruses, the so-called ‘CCC DNA amplification’ described in the duck hepatitis B model.

There is growing evidence that virus particles contain host cell proteins. These proteins may provide viruses with means to evade the immune system or with mechanisms for cell entry and release. A proteomic analysis performed on highly purified hepatitis C virus (HCV) J6/JFH virions identified the heat shock cognate protein 70 (HSC70) as part of the viral particles. These results were further validated via immunogold electron microscopy. The HSC70 interaction HPD motif was found present on the E2 envelope of the J6/JFH strain, as well as in over 50% of genotype 2 clinical HCV isolates. In addition, HSC70 was found associated with viral particles from an HCV genotype 2a–infected patient. Preincubation of HCV particles with anti‐HSC70 antibodies decreased viral infectivity. Within infected cells, colocalization of HSC70 with the HCV core and E2 proteins was observed around lipid droplets. Reduction of HSC70 expression using an RNA interference approach decreased the volume of lipid droplets as well as viral release without affecting HCV replication levels. Conclusion: These results suggest that HSC70 modulates HCV infectivity and lipid droplet–dependent virus release. (HEPATOLOGY 2009.)