Control of Viral Pathogenesis by Regulation of 2-5A Levels

干扰素（IFN）的诱导和信号传导是由病毒双链DNA引发的早期抗病毒反应。 （ds）RNA。虽然对限制病毒复制和传播至关重要，但IFN应答的过表达可能是 对人体健康有害。例如，Aicardi-Goutiéres综合征（AGS）是一种严重的神经发育障碍， 和炎症性遗传病，其特征在于宿主诱导的IFN产生和信号传导过量 self-dsRNA。因此，了解宿主如何调节自身诱导的双链RNA途径非常重要。 dsRNA以及病毒（非自身）-dsRNA。寡腺苷酸合成酶-核糖核酸酶L（OAS-RNase L）是一种 有效的抗病毒途径，严重限制了许多病毒的发病机制。在感测dsRNA时，OAS 产生2 '，5'-寡聚腺苷酸（2-5A），其激活RNase L以切割宿主和病毒单链RNA 从而限制蛋白质产生、病毒复制和传播，并导致凋亡性细胞死亡。期间 上一阶段，我们鉴定并表征了病毒和宿主编码的磷酸二酯酶（PDE）， RNA酶L激活的拮抗剂，最值得注意的是鼠冠状病毒（MHV）的PDE，NS 2，肝特异性 毒力因子我们还鉴定了OAS 3作为人类细胞中的主要抗病毒OAS。此外，我们发现， RNase L是导致人类细胞系凋亡的主要dsRNA依赖性途径， 外源dsRNA或自身dsRNA在细胞中消融表达ADAR 1，ADAR 1是一种酶， dsRNA突变后可导致AGS。然而，在理解如何激活 RNA酶L被控制以防止dsRNA的潜在破坏性作用，同时仍然保持 限制病毒复制和传播。在这个项目的继续中，我们将测试宿主 病毒有多种途径来控制2-5A的水平，其对RNase L的激活以及 RNase L的直接抗病毒以及促凋亡和促炎作用。我们将使用创新的 方法调查OAS-RNase L系统在三个互补的物种特异性系统，每个 具有独特的功能。我们将研究：1）ADAR 1亚型和宿主PDE如何调节2-5A的水平， 人类细胞，并确定哪些OAS亚型参与; 2）如何抗病毒，凋亡和炎症 RNase L的作用协同影响MHV小鼠模型中的病毒清除;以及3）OAS-RNase L如何 OAS-RNase L通路在蝙蝠中表达和激活，并且OAS-RNase L的拮抗作用的潜在机制 丝状病毒VP 35激活。这些研究的结果应该提供更好的理解如何主机 RNA酶控制自身dsRNA和2-5A的水平，以限制未感染细胞中的RNA酶L活性， 病毒感染过程中的激活以及组合的抗病毒，凋亡和促炎作用， RNA酶L在病毒清除中的作用。这些研究将使我们能够确定增强宿主细胞抵抗力的靶点， 病毒，同时最大限度地减少OAS-RNase L过度激活对宿主的威胁，最后可能有助于 确定病毒性疾病和ADAR 1突变的AGS患者的治疗策略。

Interferon (IFN) induction and signaling is an early antiviral response triggered by viral double-stranded (ds)RNA. While critical to limiting viral replication and spread, overexpression of the IFN response can be detrimental to human health. For example, Aicardi-Goutiéres syndrome (AGS) is a severe neurodevelopmental and inflammatory genetic disease, characterized by excessive IFN production and signaling induced by host self-dsRNA. Thus it is important to understand how the host regulates dsRNA pathways induced by self- dsRNA as well as viral (non self)-dsRNA. Oligoadenylate synthetase-ribonuclease L (OAS-RNase L) is a potent antiviral pathway that severely limits pathogenesis of many viruses. Upon sensing dsRNA, OASs produce 2',5'-oligoadenylates (2-5A) which activate RNase L to cleave both host and viral single-stranded RNA thereby limiting protein production, virus replication and spread, and leading to apoptotic cell death. During the last period we identified and characterized virus- and host-encoded phosphodiesterases (PDEs) as potent antagonists of RNase L activation, most notably the PDE of murine coronavirus (MHV), NS2, a liver specific virulence factor. We also identified OAS3 as the principal antiviral OAS in human cells. Moreover, we found that RNase L is the dominant dsRNA-dependent pathway leading to apoptosis in human cell lines by exogenous dsRNA or by self-dsRNA in cells ablated for expression of ADAR1, an enzyme that destabilizes dsRNA and when mutated can cause AGS. However, there is a gap in understanding how the activation of RNase L is controlled to prevent the potentially destructive effects of dsRNA while still maintaining the ability to limit viral replication and spread. In the continuation of this project, we will test the hypothesis that the host and viruses have multiple pathways to control the levels of 2-5A, its activation of RNase L and the directly antiviral as well as proapoptotic and proinflammatory effects of RNase L. We will use innovative approaches to investigate the OAS-RNase L system in three complementary species-specific systems, each with unique features. We will investigate: 1) how ADAR1 isoforms and host PDEs regulate levels of 2-5A in human cells, and determine which OAS isoforms are involved; 2) how the antiviral, apoptotic and inflammatory roles of RNase L cooperate to effect viral clearance in an MHV mouse model; and 3) how the OAS-RNase L pathway is expressed and activated in bats, and the mechanism(s) underlying antagonism of OAS-RNase L activation by filovirus VP35. Results of these studies should provide a better understanding of how host enzymes control the levels of self-dsRNA and 2-5A to limit RNase L activity in uninfected cells, while allowing activation during viral infections as well as the combined antiviral, apoptotic and proinflammatory roles of RNase L in viral clearance. These studies will allow us to identify targets that enhance host cell resistance to virus while minimizing the threat of over activation of OAS-RNase L to the host, and finally may contribute to identifying therapeutic strategies for viral diseases and for AGS patients with mutations in ADAR1.