The E3 ubiquitin ligase TRIM25 is a key factor in the innate immune response to RNA viruses. TRIM25 has been shown to play a role in the retinoic-acid-inducible gene-1 (RIG-I) pathway, which triggers expression of type 1 interferons upon viral infection. We and others have shown that TRIM25 is an RNA-binding protein; however, the role of TRIM25 RNA-binding in the innate immune response to RNA viruses is unclear. Here, we demonstrate that influenza A virus (IAV A/PR/8/34_NS1(R38A/K41A)) infection is inhibited by TRIM25. Surprisingly, previously identified RNA-binding deficient mutant TRIM25ΔRBD and E3 ubiquitin ligase mutant TRIM25ΔRING, which lack E3 ubiquitin ligase activity, still inhibited IAV replication. Furthermore, we show that in human-derived cultured cells, activation of the RIG-I/interferon type 1 pathway mediated by either an IAV-derived 5′-triphosphate RNA or by IAV itself does not require TRIM25 activity. Additionally, we present new evidence that instead of TRIM25 directly inhibiting IAV transcription it binds and destabilizes IAV mRNAs. Finally, we show that direct tethering of TRIM25 to RNA is sufficient to downregulate the targeted RNA. In summary, our results uncover a potential mechanism that TRIM25 uses to inhibit IAV infection and regulate RNA metabolism.

中文翻译：

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TRIM25 抑制甲型流感病毒感染，使病毒 mRNA 不稳定，但对于激活 RIG-I 通路是多余的

E3 泛素连接酶 TRIM25 是对 RNA 病毒的先天免疫反应的关键因素。TRIM25 已被证明在视黄酸诱导基因 1 (RIG-I) 通路中发挥作用，该通路在病毒感染后触发 1 型干扰素的表达。我们和其他人已经证明 TRIM25 是一种 RNA 结合蛋白；然而，TRIM25 RNA 结合在对 RNA 病毒的先天免疫反应中的作用尚不清楚。在这里，我们证明了甲型流感病毒 (IAV A/PR/8/34_NS1(R38A/K41A)) 感染被 TRIM25 抑制。令人惊讶的是，先前发现的缺乏 E3 泛素连接酶活性的 RNA 结合缺陷突变体 TRIM25ΔRBD 和 E3 泛素连接酶突变体 TRIM25ΔRING 仍然抑制 IAV 复制。此外，我们表明在人源培养细胞中，由 IAV 衍生的 5'-三磷酸 RNA 或 IAV 本身介导的 RIG-I/1 型干扰素通路的激活不需要 TRIM25 活性。此外，我们提出了新的证据，表明 TRIM25 不是直接抑制 IAV 转录，而是结合并破坏 IAV mRNA 的稳定性。最后，我们表明 TRIM25 与 RNA 的直接连接足以下调目标 RNA。总之，我们的结果揭示了 TRIM25 用于抑制 IAV 感染和调节 RNA 代谢的潜在机制。