Interferon‐induced degradation of the persistent hepatitis B virus cccDNA form depends on ISG20

Abstract

Hepatitis B virus (HBV) persists by depositing a covalently closed circular DNA (cccDNA) in the nucleus of infected cells that cannot be targeted by available antivirals. Interferons can diminish HBV cccDNA via APOBEC3-mediated deamination. Here, we show that overexpression of APOBEC3A alone is not sufficient to reduce HBV cccDNA that requires additional treatment of cells with interferon indicating involvement of an interferon-stimulated gene (ISG) in cccDNA degradation. Transcriptome analyses identify ISG20 as the only type I and II interferon-induced, nuclear protein with annotated nuclease activity. ISG20 localizes to nucleoli of interferon-stimulated hepatocytes and is enriched on deoxyuridine-containing singlestranded DNA that mimics transcriptionally active, APOBEC3Adeaminated HBV DNA. ISG20 expression is detected in human livers in acute, self-limiting but not in chronic hepatitis B. ISG20 depletion mitigates the interferon-induced loss of cccDNA, and co-expression with APOBEC3A is sufficient to diminish cccDNA. In conclusion, non-cytolytic HBV cccDNA decline requires the concerted action of a deaminase and a nuclease. Our findings highlight that ISGs may cooperate in their antiviral activity that may be explored for therapeutic targeting.

Concentration of Na+-taurocholate-cotransporting polypeptide expressed after in vitro-transcribed mRNA transfection determines susceptibility of hepatoma cells for hepatitis B virus

“…5 D, top) showed increasing IFNβ expression over time in poly I:C but not in IVT mRNA transfected cells. We repeated the experiment with either 1000 ng IVT mRNA or poly I:C in differentiated HepaRG, a cell line which has a functional interferon pathway 33 , also demonstrating exclusive upregulation of IFNβ in poly I:C treated cells over time (Fig. 5 D, bottom).…”

“…We here established the transfection of various cell lines with IVT mRNA as a suitable tool to study whether NTCP expression suffices to render non-hepatic cells permissive for HBV and how NTCP concentration determines the efficiency of HBV infection. IVT mRNA proved to be a powerful alternative to introduce a gene of interest into hard-to-transfect hepatoma cells or primary cells 33 . Thereby, higher transfection efficiency and protein expression levels can be achieved in differentiated HepG2 cells than using plasmid or adenoviral vectors without affecting cell viability or triggering cell-intrinsic immune responses.…”

“…One option to overcome this limitation is the repeated administration of IVT mRNA to ensure steady expression of a protein of interest. Alternatively, IVT mRNA allows introducing several components of a pathways through application of multiple mRNAs simultaneously 33 . This was shown to be a suitable alternative for reprogramming fibroblasts into induced pluripotent stem cells 26 .…”

Interferon and Hepatitis B: Current and Future Perspectives

“…These modifications are associated with reduced transcription of pgRNA and subgenomic RNAs from the cccDNA minichromosome. In addition to regulating cccDNA transcription, recent studies suggested that IFN may induce degradation of cccDNA by inducing APOBEC3A and ISG20 ( 31 , 32 ). However, it remains unclear how efficient such a mechanism is in the liver and whether cccDNAs in distinct epigenetic states are similar or differ in their sensitivity to IFN and IFN-induced antiviral factors.…”

Immunity and Viral Infections: Modulating Antiviral Response via CRISPR–Cas Systems

“…ISG20 can impair mRNA synthesis and protein translation of RNA viruses [ 83 , 84 ]. Potentially, ISG20 can also contribute to the restriction of HBV replication and degradation of HBV cccDNA by APOBEC3A [ 85 ].…”