Distinct mammalian RNA viruses trigger Dicer-mediated production of virus-derived small-interfering RNAs (vsiRNA) and encode unrelated proteins to suppress vsiRNA biogenesis. However, the mechanism and function of the mammalian RNA interference (RNAi) response are poorly understood. Here, we characterized antiviral RNAi in a mouse model of infection with Nodamura virus (NoV), a mosquito-transmissible positive-strand RNA virus encoding a known double-stranded RNA (dsRNA)-binding viral suppressor of RNAi (VSR), the B2 protein. We show that inhibition of NoV RNA replication by antiviral RNAi in mouse embryonic fibroblasts (MEFs) requires Dicer-dependent vsiRNA biogenesis and Argonaute-2 slicer activity. We found that VSR-B2 of NoV enhances viral RNA replication in wild-type but not RNAi-defective MEFs such as Argonaute-2 catalytic-dead MEFs and Dicer or Argonaute-2 knockout MEFs, indicating that VSR-B2 acts mainly by suppressing antiviral RNAi in the differentiated murine cells. Consistently, VSR-B2 expression in MEFs has no detectable effect on the induction of interferon-stimulated genes or the activation of global RNA cleavages by RNase L. Moreover, we demonstrate that NoV infection of adult mice induces production of abundant vsiRNA active to guide RNA slicing by Argonaute-2. Notably, VSR-B2 suppresses the biogenesis of both vsiRNA and the slicing-competent vsiRNA-Argonaute-2 complex without detectable inhibition of Argonaute-2 slicing guided by endogenous microRNA, which dramatically enhances viral load and promotes lethal NoV infection in adult mice either intact or defective in the signaling by type I, II, and III interferons. Together, our findings suggest that the mouse RNAi response confers essential protective antiviral immunity in both the presence and absence of the interferon response.

中文翻译：

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小鼠抗病毒RNA干扰的机制和功能。


不同的哺乳动物 RNA 病毒会触发 Dicer 介导的病毒源性小干扰 RNA (vsiRNA) 的产生，并编码无关的蛋白质以抑制 vsiRNA 的生物发生。然而，人们对哺乳动物 RNA 干扰 (RNAi) 反应的机制和功能知之甚少。在这里，我们在感染 Nodamura 病毒 (NoV) 的小鼠模型中表征了抗病毒 RNAi，Nodamura 病毒是一种蚊子传播的正链 RNA 病毒，编码已知的双链 RNA (dsRNA) 结合 RNAi 病毒抑制因子 (VSR)，即 B2蛋白质。我们发现，抗病毒 RNAi 在小鼠胚胎成纤维细胞 (MEF) 中抑制 NoV RNA 复制需要 Dicer 依赖性 vsiRNA 生物发生和 Argonaute-2 切片机活性。我们发现NoV的VSR-B2增强了野生型而非RNAi缺陷MEF（例如Argonaute-2催化死亡MEF和Dicer或Argonaute-2敲除MEF）中的病毒RNA复制，表明VSR-B2主要通过抑制抗病毒发挥作用分化的小鼠细胞中的RNAi。一致地，MEF 中的 VSR-B2 表达对干扰素刺激基因的诱导或 RNase L 激活全局 RNA 切割没有可检测到的影响。此外，我们证明成年小鼠的 NoV 感染诱导产生丰富的 vsiRNA 活性以引导 RNA由 Argonaute-2 进行切片。值得注意的是，VSR-B2 抑制了 vsiRNA 和具有切片能力的 vsiRNA-Argonaute-2 复合物的生物发生，而没有检测到内源性 microRNA 引导的 Argonaute-2 切片的抑制，这显着增加了病毒载量并促进成年小鼠中完整的致命 NoV 感染或 I、II 和 III 型干扰素的信号传导有缺陷。 总之，我们的研究结果表明，无论存在还是不存在干扰素反应，小鼠 RNAi 反应都能赋予必要的保护性抗病毒免疫力。