Department of Veterinary Biosciences, College of Veterinary Medicine, The Ohio State University, Columbus, Ohio, USA.
Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, Massachusetts, USA.
J Virol. 2021 Apr 12;95(9). doi: 10.1128/JVI.01939-20.
-Methyladenosine (mA) is the most abundant internal RNA modification catalyzed by host RNA methyltransferases. As obligate intracellular parasites, many viruses acquire mA methylation in their RNAs. However, the biological functions of viral mA methylation are poorly understood. Here, we found that viral mA methylation serves as a molecular marker for host innate immunity to discriminate self from nonself RNA and that this novel biological function of viral mA methylation is universally conserved in several families in nonsegmented negative-sense (NNS) RNA viruses. Using mA methyltransferase (METTL3) knockout cells, we produced mA-deficient virion RNAs from the representative members of the families , , and and found that these mA-deficient viral RNAs triggered significantly higher levels of type I interferon compared to the mA-sufficient viral RNAs, in a RIG-I-dependent manner. Reconstitution of the RIG-I pathway revealed that mA-deficient virion RNA induced higher expression of RIG-I, bound to RIG-I more efficiently, enhanced RIG-I ubiquitination, and facilitated RIG-I conformational rearrangement and oligomerization. Furthermore, the mA binding protein YTHDF2 is essential for suppression of the type I interferon signaling pathway, including by virion RNA. Collectively, our results suggest that several families in NNS RNA viruses acquire mA in viral RNA as a common strategy to evade host innate immunity. The nonsegmented negative-sense (NNS) RNA viruses share many common replication and gene expression strategies. There are no vaccines or antiviral drugs for many of these viruses. We found that representative members of the families , , and among the NNS RNA viruses acquire mA methylation in their genome and antigenome as a means to escape recognition by host innate immunity via a RIG-I-dependent signaling pathway. Viral RNA lacking mA methylation induces a significantly higher type I interferon response than mA-sufficient viral RNA. In addition to uncovering mA methylation as a common mechanism for many NNS RNA viruses to evade host innate immunity, this study discovered a novel strategy to enhance type I interferon responses, which may have important applications in vaccine development, as robust innate immunity will likely promote the subsequent adaptive immunity.
甲基腺苷（mA）是由宿主 RNA 甲基转移酶催化的最丰富的内源性 RNA 修饰。作为专性细胞内寄生虫，许多病毒在其 RNA 中获得 mA 甲基化。然而，病毒 mA 甲基化的生物学功能知之甚少。在这里，我们发现病毒 mA 甲基化可作为宿主固有免疫区分自身和非自身 RNA 的分子标记，并且这种病毒 mA 甲基化的新生物学功能在几种非节段负义（NNS）RNA 病毒家族中普遍保守。使用 mA 甲基转移酶（METTL3）敲除细胞，我们从家族的代表成员中产生了 mA 缺陷的病毒 RNA ， ， 和 ，并发现与 mA 充足的病毒 RNA 相比，这些 mA 缺陷的病毒 RNA 以 RIG-I 依赖性方式引发更高水平的 I 型干扰素。RIG-I 途径的重建表明，mA 缺陷的病毒 RNA 诱导更高水平的 RIG-I 表达，更有效地与 RIG-I 结合，增强 RIG-I 泛素化，并促进 RIG-I 构象重排和寡聚化。此外，mA 结合蛋白 YTHDF2 对于抑制 I 型干扰素信号通路是必需的，包括通过病毒 RNA。总之，我们的研究结果表明，NNS RNA 病毒的几个家族在病毒 RNA 中获得 mA 作为逃避宿主固有免疫的共同策略。非节段负义（NNS）RNA 病毒具有许多共同的复制和基因表达策略。其中许多病毒没有疫苗或抗病毒药物。我们发现 NNS RNA 病毒中的家族 ， ， 和 中的代表成员在其基因组和抗原基因组中获得 mA 甲基化，作为通过 RIG-I 依赖性信号通路逃避宿主固有免疫识别的一种手段。缺乏 mA 甲基化的病毒 RNA 比 mA 充足的病毒 RNA 诱导更高水平的 I 型干扰素反应。除了揭示 mA 甲基化作为许多 NNS RNA 病毒逃避宿主固有免疫的共同机制外，本研究还发现了一种增强 I 型干扰素反应的新策略，这可能在疫苗开发中具有重要应用，因为强大的固有免疫很可能会促进随后的适应性免疫。
