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 single-stranded DNA that mimics transcriptionally active, APOBEC3A-deaminated 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.

中文翻译：

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干扰素诱导的持久性乙型肝炎病毒 cccDNA 形式的降解取决于 ISG20


乙型肝炎病毒 (HBV) 通过在受感染细胞的细胞核中沉积共价闭合环状 DNA (cccDNA) 来持续存在，而现有抗病毒药物无法靶向该细胞核。干扰素可以通过 APOBEC3 介导的脱氨基作用减少 HBV cccDNA。在这里，我们表明单独过表达 APOBEC3A 不足以减少 HBV cccDNA，需要用干扰素对细胞进行额外处理，表明干扰素刺激基因 (ISG) 参与 cccDNA 降解。转录组分析确定 ISG20 是唯一具有注释核酸酶活性的 I 型和 II 型干扰素诱导核蛋白。 ISG20 定位于干扰素刺激的肝细胞的核仁，富含含脱氧尿苷的单链 DNA，模拟转录活性、APOBEC3A 脱氨基的 HBV DNA。在急性自限性人类肝脏中检测到 ISG20 表达，但在慢性乙型肝炎中未检测到。ISG20 耗竭可减轻干扰素诱导的 cccDNA 丢失，与 APOBEC3A 共表达足以减少 cccDNA。总之，非溶细胞性 HBV cccDNA 下降需要脱氨酶和核酸酶的协同作用。我们的研究结果强调，ISG 可能在其抗病毒活性方面进行合作，这可能会被探索用于治疗靶向。