干扰素-α诱导协同抑制肝炎病毒cccDNA转录的多种细胞蛋白。

StephenW

IFN-α Induces Multiple Cellular Proteins that Coordinately Suppress Hepadnaviral cccDNA Transcription
Junjun Cheng, Qiong Zhao, Yan Zhou, Liudi Tang, Muhammad Sheraz, Jinhong Chang, Ju-Tao Guo
DOI: 10.1128/JVI.00442-20

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ABSTRACT

Covalently closed circular (ccc) DNA of hepadnaviruses exists as an episomal minichromosome in the nucleus of infected hepatocyte and serves as the template for the transcription of viral mRNAs. It had been demonstrated by others and us that interferon alpha (IFN-α) treatment of hepatocytes induced a prolonged suppression of human and duck hepatitis B virus cccDNA transcription, which is associated with the reduction of cccDNA-associated histone modifications specifying active transcription (H3K9ac or H3K27ac), but not the histone modifications marking constitutive (H3K9me3) or facultative (H3K27me3) heterochromatin formation. In our efforts to identify IFN-induced cellular proteins that mediate the suppression of cccDNA transcription by the cytokine, we found that down-regulating the expression of signal transducer and activator of transcription 1 (STAT1), structural maintenance of chromosomes flexible hinge domain containing 1 (SMCHD1) or promyelocytic leukemia (PML) protein increased basal level of cccDNA transcription activity and partially attenuated IFN-α suppression of cccDNA transcription. On the contrary, ectopic expression of STAT1, SMCHD1 or PML significantly reduced cccDNA transcription activity. SMCHD1 is a non-canonical SMC family protein and implicated in epigenetic silencing of gene expression. PML is a component of nuclear domain 10 (ND10) and involved in suppressing the replication of many DNA viruses. Mechanistic analyses demonstrated that STAT1, SMCHD1 and PML were recruited to cccDNA minichromosomes and phenocopied the IFN-α-induced post-translational modifications of cccDNA-associated histones. We thus conclude that STAT1, SMCHD1 and PML may partly mediate the suppressive effect of IFN-α on hepadnaviral cccDNA transcription.

IMPORTANCE Pegylated IFN-alpha is the only therapeutic regimen that can induce a functional cure of chronic hepatitis B in a small, but significant fraction of treated patients. Understanding the mechanisms underlying the antiviral functions of IFN-α in hepadnaviral infection may reveal molecular targets for development of novel antiviral agents to improve the therapeutic efficacy of IFN-α. By a loss-of-function genetic screening of individual ISGs on hepadnaviral mRNAs transcribed from cccDNA, we found that down-regulating the expression of STAT1, SMCHD1 or PML significantly increased the level of viral RNAs without altering the level of cccDNA. Mechanistic analyses indicated that those cellular proteins are recruited to cccDNA minichromosomes and induce the post-translational modifications of cccDNA-associated histones similar to those induced by IFN-α treatment. We have thus identified three IFN-α-induced cellular proteins that suppress cccDNA transcription and may partly mediate IFN-α silencing of hepadnaviral cccDNA transcription.

    Copyright © 2020 American Society for Microbiology.

StephenW

干扰素-α诱导协同抑制肝炎病毒cccDNA转录的多种细胞蛋白。
程俊军，赵琼，周燕，唐六笛，穆罕默德·谢拉兹，张进宏，郭菊涛
DOI：10.1128 / JVI.00442-20

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抽象

肝炎病毒的共价闭合环状（ccc）DNA作为被感染的肝细胞核中的游离型微型染色体存在，并充当病毒mRNA转录的模板。其他人和我们已经证明，干扰素对肝细胞的干扰素（IFN-α）处理可长期抑制人和鸭乙型肝炎病毒cccDNA转录，这与cccDNA相关的组蛋白修饰减少有关，后者可修饰为主动转录（H3K9ac或H3K27ac），但不标记组蛋白修饰，表示组成性（H3K9me3）或兼性（H3K27me3）异染色质形成。在我们确定干扰素诱导的细胞因子介导cccDNA转录抑制的细胞蛋白的研究中，我们发现下调信号转导子和转录激活子1（STAT1）的表达，维持包含1个染色体的柔性铰链结构域的结构（SMCHD1）或早幼粒细胞白血病（PML）蛋白可增加cccDNA转录活性的基础水平，并部分减弱IFN-α对cccDNA转录的抑制作用。相反，STAT1，SMCHD1或PML的异位表达显着降低了cccDNA转录活性。 SMCHD1是非规范的SMC家族蛋白，与基因表达的表观遗传沉默有关。 PML是10号核域（ND10）的组成部分，参与抑制许多DNA病毒的复制。机理分析表明，STAT1，SMCHD1和PML被募集到cccDNA微型染色体上，并被表型化了IFN-α诱导的cccDNA相关组蛋白的翻译后修饰。因此，我们得出结论，STAT1，SMCHD1和PML可能部分介导IFN-α对肝炎病毒cccDNA转录的抑制作用。

重要信息聚乙二醇化的IFN-α是可在一小部分但相当一部分接受治疗的患者中诱导慢性乙肝功能治愈的唯一治疗方案。了解肝炎病毒感染中IFN-α的抗病毒功能的潜在机制可能揭示了开发新型抗病毒剂以改善IFN-α的治疗效果的分子靶标。通过从cccDNA转录的肝炎病毒mRNA上单个ISG的功能丧失基因筛选，我们发现下调STAT1，SMCHD1或PML的表达可显着增加病毒RNA的水平，而不会改变cccDNA的水平。机理分析表明，这些细胞蛋白被募集到cccDNA微染色体上，并诱导cccDNA相关组蛋白的翻译后修饰，类似于通过IFN-α处理所诱导的组蛋白。因此，我们确定了三种IFN-α诱导的细胞蛋白，它们抑制cccDNA转录，并可能部分介导肝炎病毒cccDNA转录的IFN-α沉默。

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