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

ABSTRACT: 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.

ORGANISM(S): Homo sapiens

PROVIDER: GSE134929 | GEO | 2020/07/22

REPOSITORIES: GEO

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Project description:Oral administration of nucleotide analogues and injection of interferon-alpha (IFNalpha) are used to achieve immediate suppression in replication of hepatitis B virus (HBV). Nucleotide analogs and IFNalpha inhibit viral polymerase activity and cause long-term eradication of the virus at least in part through removing covalently closed circular DNA (cccDNA) via induction of the APOBEC3 deaminases family of molecules, respectively. This study aimed to explore whether the orally administrable low molecular weight agent CDM-3008 (RO8191), which mimics IFNalpha through the binding to IFNalpha receptor 2 (IFNAR2) and the activation of the JAK/STAT pathway, can suppress HBV replication and reduce cccDNA levels. In primary cultured human hepatocytes, HBV DNA levels as well as cccDNA levels were decreased after CDM-3008-treatment in a dose-dependent manner with a half-maximal inhibitory concentration (IC50) value of 0.1 micro M, and this was accompanied by significant reductions in both HBeAg and HBsAg levels in the cell culture medium. Using a microarray we comprehensively analyzed and compared changes in gene (mRNA) expression in CDM-3008- and IFNalpha-treated primary cultured human hepatocytes. As reported previously, CDM-3008 mimicked the induction of　molecules that participate in the interferon signaling pathway. OAS1 and ISG20 mRNA expression was similarly enhanced by both CDM-3008 and IFNalpha. Thus, CDM-3008 could suppress pgRNA expression to show anti-HBV activity. APOBEC3F and 3G mRNA expression was induced by CDM-3008 and IFNalpha treatment suggesting that cccDNA could be degraded through induced APOBEC3 family proteins. Finally, we identified the genes whose expression was specifically enhanced in CDM-3008-treated cells compared to IFNalpha-treated cells. The expression of SOCS1, SOCS2, SOCS3, and CISH, which inhibit STAT activation, was enhanced in CDM-3008-treated cells suggesting that a feedback inhibition of the JAK/STAT pathway was enhanced in CDM-3008-treated cells compared to IFNalpha-treated cells. In addition, CDM-3008 showed an additive effect with entecavir on inhibition of HBV replication. In summary, CDM-3008 showed anti-HBV activity through activation of the JAK/STAT pathway, inducing the expression of interferon-stimulated genes (ISGs), with greater feedback inhibition than IFNalpha.

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

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