The Nucleocapsid Protein of Coronaviruses Acts as a Viral Suppressor of RNA Silencing in Mammalian Cells
The Nucleocapsid Protein of Coronaviruses Acts as a Viral Suppressor of RNA Silencing in Mammalian Cells
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冠状病毒的核衣壳蛋白在哺乳动物细胞中充当 RNA 沉默的病毒抑制剂。
DOI：
10.1128/jvi.01331-15
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发表时间：
2015-09-01
影响因子：
5.4
通讯作者：
Chen, Yu
中科院分区：
文献类型：
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作者：
Cui, Lei;Wang, Haiying;Chen, Yu
RNA干扰(RNAi)是真核生物转录后基因沉默的过程，在植物、线虫和昆虫中发挥抗病毒免疫的作用。然而，最近的研究提供了强有力的支持，即RNAi也在哺乳动物细胞的抗病毒机制中发挥作用。为了对抗RNAi介导的抗病毒反应，许多病毒编码RNA沉默的病毒抑制物(VSR)以促进其复制。针对植物和昆虫病毒的VSR已经得到了广泛的研究，但目前针对哺乳动物病毒的VSR还很少。我们从冠状病毒中鉴定出一种新的VSR，冠状病毒是一组具有重要医学意义的哺乳动物病毒，包括严重急性呼吸综合征冠状病毒(SARS-CoV)，并表明冠状病毒的核衣壳蛋白(N蛋白)抑制哺乳动物细胞中由短发夹RNA或小干扰RNA触发的RNAi。小鼠肝炎病毒(MHV)在冠状病毒科中与SARS-CoV关系密切，被用作冠状病毒复制模型。当N蛋白以反式方式表达时，MHV的复制增加，而Dicer1或Ago2转录本的敲除有助于MHV在哺乳动物细胞中的复制。这些结果支持这一假设，即RNAi是哺乳动物细胞抗病毒免疫反应的一部分。众所周知，IMPORTANCERNAi在从植物到无脊椎动物的抗病毒中发挥着重要的作用。然而，最近的研究提供了强有力的支持，RNAi也参与了哺乳动物细胞的抗病毒反应。在哺乳动物中，RNAi介导的抗病毒活性的一个重要迹象是，许多哺乳动物病毒编码有效的RNA沉默抑制因子。我们的结果表明，冠状病毒N蛋白可以通过其双链RNA结合活性而发挥VSR的功能。N蛋白的突变分析使我们能够找到影响VSR活性的关键残基。以MHV-A59作为冠状病毒复制模型，我们发现异位表达SARS-CoV N蛋白可以促进MHV在RNAi活跃细胞中的复制，但在RNAi缺失细胞中不能促进MHV复制。这些结果表明，冠状病毒编码的VSR在复制周期中发挥作用，并为支持RNAi介导的抗病毒反应在哺乳动物细胞中存在提供了进一步的证据。
RNA interference (RNAi) is a process of eukaryotic posttranscriptional gene silencing that functions in antiviral immunity in plants, nematodes, and insects. However, recent studies provided strong supports that RNAi also plays a role in antiviral mechanism in mammalian cells. To combat RNAi-mediated antiviral responses, many viruses encode viral suppressors of RNA silencing (VSR) to facilitate their replication. VSRs have been widely studied for plant and insect viruses, but only a few have been defined for mammalian viruses currently. We identified a novel VSR from coronaviruses, a group of medically important mammalian viruses including Severe acute respiratory syndrome coronavirus (SARS-CoV), and showed that the nucleocapsid protein (N protein) of coronaviruses suppresses RNAi triggered by either short hairpin RNAs or small interfering RNAs in mammalian cells. Mouse hepatitis virus (MHV) is closely related to SARS-CoV in the family Coronaviridae and was used as a coronavirus replication model. The replication of MHV increased when the N proteins were expressed in trans, while knockdown of Dicer1 or Ago2 transcripts facilitated the MHV replication in mammalian cells. These results support the hypothesis that RNAi is a part of the antiviral immunity responses in mammalian cells.IMPORTANCERNAi has been well known to play important antiviral roles from plants to invertebrates. However, recent studies provided strong supports that RNAi is also involved in antiviral response in mammalian cells. An important indication for RNAi-mediated antiviral activity in mammals is the fact that a number of mammalian viruses encode potent suppressors of RNA silencing. Our results demonstrate that coronavirus N protein could function as a VSR through its double-stranded RNA binding activity. Mutational analysis of N protein allowed us to find out the critical residues for the VSR activity. Using the MHV-A59 as the coronavirus replication model, we showed that ectopic expression of SARS-CoV N protein could promote MHV replication in RNAi-active cells but not in RNAi-depleted cells. These results indicate that coronaviruses encode a VSR that functions in the replication cycle and provide further evidence to support that RNAi-mediated antiviral response exists in mammalian cells.