Identification of ISG20 as the nuclease involved in interferon-induced decline of hepatitis B virus cccDNA. Identification of ISG20 as the nuclease involved in interferon-induced decline of hepatitis B virus cccDNA

Hepatitis B virus (HBV) persists by depositing a covalently closed circular DNA (cccDNA) in the nucleus that cannot be targeted by available antivirals. Cytokine treatments can purge cccDNA from the nucleus of infected cells by APOBEC3-mediated deamination. cccDNA levels in HBV-infected cells were not reduced by overexpression of APOBEC3A alone, but only after simultaneous addition of interferon. This indicated the need of an additional, interferon-induced factor (ISG). Microarray analysis identified ISG20 as the only nuclease located to the nucleus induced by type I and II interferons. ISG20 was confirmed to be expressed in acute, self-limiting but not in chronic hepatitis B in human livers. ISG20 knockdown abolished the interferon-induced loss of cccDNA, and co-expression of ISG20 and APOBEC3A was sufficient to diminish cccDNA without further treatment. To conclude, nucleolar ISG20 was identified as the nuclease contributing to interferon-induced purging of HBV cccDNA, opening new avenues for antiviral targeting. Overall design: Transcriptional profiles of HBV infected HepaRG cells expressing A3A in presence of Interferon Alpha were compared with HepaRG cells expressing A3A without Interferon Alpha.