Immunity and Immune Evasion Laboratory, Chronic Infectious and Inflammatory Diseases Research, School of Health and Biomedical Sciences, RMIT University, Bundoora, VIC 3083, Australia.
Infection & Immunity Program, Monash Biomedicine Discovery Institute and Department of Biochemistry and Molecular Biology, Monash University, Clayton, VIC 3800, Australia.
Int J Mol Sci. 2021 Aug 23;22(16):9094. doi: 10.3390/ijms22169094.
The cytoplasmic retinoic acid-inducible gene-I (RIG-I)-like receptors (RLRs) initiate interferon (IFN) production and antiviral gene expression in response to RNA virus infection. Consequently, RLR signalling is tightly regulated by both host and viral factors. Tripartite motif protein 25 (TRIM25) is an E3 ligase that ubiquitinates multiple substrates within the RLR signalling cascade, playing both ubiquitination-dependent and -independent roles in RIG-I-mediated IFN induction. However, additional regulatory roles are emerging. Here, we show a novel interaction between TRIM25 and another protein in the RLR pathway that is essential for type I IFN induction, DEAD-box helicase 3X (DDX3X). In vitro assays and knockdown studies reveal that TRIM25 ubiquitinates DDX3X at lysine 55 (K55) and that TRIM25 and DDX3X cooperatively enhance induction following RIG-I activation, but the latter is independent of TRIM25's catalytic activity. Furthermore, we found that the influenza A virus non-structural protein 1 (NS1) disrupts the TRIM25:DDX3X interaction, abrogating both TRIM25-mediated ubiquitination of DDX3X and cooperative activation of the promoter. Thus, our results reveal a new interplay between two RLR-host proteins that cooperatively enhance IFN-β production. We also uncover a new and further mechanism by which influenza A virus NS1 suppresses host antiviral defence.
细胞质视黄酸诱导基因-I (RIG-I)-样受体 (RLRs) 可识别 RNA 病毒感染，并启动干扰素 (IFN) 的产生和抗病毒基因的表达。因此，RLR 信号通路受到宿主和病毒因素的严格调控。三结构域蛋白 25 (TRIM25) 是一种 E3 连接酶，可泛素化 RLR 信号通路中的多个底物，在 RIG-I 介导的 IFN 诱导中发挥依赖和不依赖泛素化的作用。然而，新的调节作用正在出现。在这里，我们展示了 RLR 途径中的 TRIM25 和另一种对 I 型 IFN 诱导至关重要的蛋白之间的新相互作用，即 DEAD-box 解旋酶 3X (DDX3X)。体外实验和敲低研究表明，TRIM25 可在赖氨酸 55 (K55) 处泛素化 DDX3X，并且 TRIM25 和 DDX3X 在 RIG-I 激活后协同增强 IFN-β 的诱导，但后者不依赖于 TRIM25 的催化活性。此外，我们发现甲型流感病毒非结构蛋白 1 (NS1) 破坏了 TRIM25:DDX3X 相互作用，从而阻断了 TRIM25 介导的 DDX3X 泛素化和 IFN-β 启动子的协同激活。因此，我们的研究结果揭示了 RLR-宿主蛋白之间的一种新相互作用，该相互作用可协同增强 IFN-β 的产生。我们还揭示了甲型流感病毒 NS1 抑制宿主抗病毒防御的一个新的和更进一步的机制。
