The arenaviruses Lassa virus (LASV), Junín virus (JUNV), and Machupo virus (MACV) can cause severe and fatal diseases in humans. Although these pathogens are closely related, the host immune responses to these virus infections differ remarkably, with direct implications for viral pathogenesis. LASV infection is immunosuppressive, with a very low-level interferon response. In contrast, JUNV and MACV infections stimulate a robust interferon (IFN) response in a retinoic acid-inducible gene I (RIG-I)-dependent manner and readily activate protein kinase R (PKR), a known host double-stranded RNA (dsRNA) sensor. In response to infection with RNA viruses, host nonself RNA sensors recognize virus-derived dsRNA as danger signals and initiate innate immune responses. Arenavirus nucleoproteins (NPs) contain a highly conserved exoribonuclease (ExoN) motif, through which LASV NP has been shown to degrade virus-derived immunostimulatory dsRNA in biochemical assays. In this study, we for the first time present evidence that LASV restricts dsRNA accumulation during infection. Although JUNV and MACV NPs also have the ExoN motif, dsRNA readily accumulated in infected cells and often colocalized with dsRNA sensors. Moreover, LASV coinfection diminished the accumulation of dsRNA and the IFN response in JUNV-infected cells. The disruption of LASV NP ExoN with a mutation led to dsRNA accumulation and impaired LASV replication in minigenome systems. Importantly, both LASV NP and RNA polymerase L protein were required to diminish the accumulation of dsRNA and the IFN response in JUNV infection. For the first time, we discovered a collaboration between LASV NP ExoN and L protein in limiting dsRNA accumulation. Our new findings provide mechanistic insights into the differential host innate immune responses to highly pathogenic arenavirus infections.IMPORTANCE Arenavirus NPs contain a highly conserved DEDDh ExoN motif, through which LASV NP degrades virus-derived, immunostimulatory dsRNA in biochemical assays to eliminate the danger signal and inhibit the innate immune response. Nevertheless, the function of NP ExoN in arenavirus infection remains to be defined. In this study, we discovered that LASV potently restricts dsRNA accumulation during infection and minigenome replication. In contrast, although the NPs of JUNV and MACV also harbor the ExoN motif, dsRNA readily formed during JUNV and MACV infections, accompanied by IFN and PKR responses. Interestingly, LASV NP alone was not sufficient to limit dsRNA accumulation. Instead, both LASV NP and L protein were required to restrict immunostimulatory dsRNA accumulation. Our findings provide novel and important insights into the mechanism for the distinct innate immune response to these highly pathogenic arenaviruses and open new directions for future studies.

中文翻译：

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拉沙病毒（而非高致病性新大陆沙粒病毒）在感染过程中限制免疫刺激双链 RNA 的积累。


沙粒病毒拉沙病毒 (LASV)、胡宁病毒 (JUNV) 和马丘波病毒 (MACV) 可引起人类严重和致命的疾病。尽管这些病原体密切相关，但宿主对这些病毒感染的免疫反应却显着不同，这对病毒发病机制有直接影响。 LASV 感染具有免疫抑制作用，干扰素反应水平非常低。相比之下，JUNV 和 MACV 感染以视黄酸诱导基因 I (RIG-I) 依赖性方式刺激强干扰素 (IFN) 反应，并容易激活蛋白激酶 R (PKR)，这是一种已知的宿主双链 RNA (dsRNA) ） 传感器。为了应对 RNA 病毒感染，宿主非自身 RNA 传感器将病毒衍生的 dsRNA 识别为危险信号并启动先天免疫反应。沙粒病毒核蛋白 (NP) 含有高度保守的核糖核酸外切酶 (ExoN) 基序，在生化测定中，LASV NP 已被证明可以通过该基序降解病毒衍生的免疫刺激性 dsRNA。在这项研究中，我们首次提出 LASV 在感染过程中限制 dsRNA 积累的证据。尽管 JUNV 和 MACV NP 也具有 ExoN 基序，但 dsRNA 很容易在受感染的细胞中积累，并且通常与 dsRNA 传感器共定位。此外，LASV 共感染减少了 JUNV 感染细胞中 dsRNA 的积累和 IFN 反应。 LASV NP ExoN 突变的破坏导致 dsRNA 积累并损害小基因组系统中的 LASV 复制。重要的是，LASV NP 和 RNA 聚合酶 L 蛋白都需要减少 dsRNA 的积累和 JUNV 感染中的 IFN 反应。我们首次发现 LASV NP ExoN 和 L 蛋白在限制 dsRNA 积累方面的协同作用。 我们的新发现提供了对高致病性沙粒病毒感染的不同宿主先天免疫反应的机制见解。 重要性 沙粒病毒 NP 含有高度保守的 DEDDh ExoN 基序，LASV NP 通过该基序在生化测定中降解病毒衍生的免疫刺激性 dsRNA，以消除危险信号和抑制先天免疫反应。然而，NP ExoN 在沙粒病毒感染中的功能仍有待确定。在这项研究中，我们发现 LASV 有效限制感染和小基因组复制过程中 dsRNA 的积累。相比之下，虽然JUNV和MACV的NP也含有ExoN基序，但在JUNV和MACV感染期间很容易形成dsRNA，并伴有IFN和PKR反应。有趣的是，单独的 LASV NP 不足以限制 dsRNA 的积累。相反，LASV NP 和 L 蛋白都需要限制免疫刺激性 dsRNA 的积累。我们的研究结果为这些高致病性沙粒病毒的独特先天免疫反应机制提供了新颖且重要的见解，并为未来的研究开辟了新的方向。