Laboratory of Molecular Immunobiology, Division of Biological Science, Graduate School of Science and Technology, Nara Institute of Science and Technology, Ikoma, Nara 630-0192, Japan.
Department of Immunology, Graduate School of Pharmaceutical Sciences, Hokkaido University, Sapporo, Hokkaido 060-0812, Japan.
J Immunol. 2018 Jun 1;200(11):3814-3824. doi: 10.4049/jimmunol.1701282. Epub 2018 Apr 20.
Retinoic acid-inducible gene I (RIG-I)-like receptors (RLRs), RIG-I, and melanoma differentiation-associated gene 5 (MDA5) play a critical role in inducing antiviral innate immune responses by activating IFN regulatory factor 3 (IRF3) and NF-κB, which regulates the transcription of type I IFN and inflammatory cytokines. Antiviral innate immune responses are also regulated by posttranscriptional and translational mechanisms. In this study, we identified an RNA-binding protein HuR as a regulator for RLR signaling. Overexpression of HuR, but not of other Hu members, increased IFN-β promoter activity. HuR-deficient macrophage cells exhibited decreased expression after RLR stimulation, whereas they showed normal induction after stimulation with bacterial LPS or immunostimulatory DNA. Moreover, HuR-deficient cells displayed impaired nuclear translocation of IRF3 after RLR stimulation. In HuR-deficient cells, the mRNA expression of Polo-like kinase (PLK) 2 was markedly reduced. We found that HuR bound to the 3' untranslated region of mRNA and increased its stabilization. PLK2-deficient cells also showed reduced IRF3 nuclear translocation and mRNA expression during RLR signaling. Together, these findings suggest that HuR bolsters RLR-mediated IRF3 nuclear translocation by controlling the stability of mRNA.
视黄酸诱导基因 I（RIG-I）样受体（RLRs）、RIG-I 和黑色素瘤分化相关基因 5（MDA5）通过激活干扰素调节因子 3（IRF3）和 NF-κB 发挥关键作用，从而诱导抗病毒先天免疫反应，调节 I 型干扰素和炎症细胞因子的转录。抗病毒先天免疫反应也受转录后和翻译机制的调节。在这项研究中，我们确定了 RNA 结合蛋白 HuR 是 RLR 信号的调节剂。HuR 的过表达（但不是其他 Hu 成员）增加了 IFN-β 启动子活性。RLR 刺激后，HuR 缺陷型巨噬细胞的表达减少，而刺激细菌 LPS 或免疫刺激性 DNA 后则正常诱导。此外，RLR 刺激后 HuR 缺陷型细胞中 IRF3 的核易位减少。在 HuR 缺陷型细胞中，Polo 样激酶（PLK）2 的 mRNA 表达明显减少。我们发现 HuR 与 mRNA 的 3'非翻译区结合并增加其稳定性。PLK2 缺陷型细胞在 RLR 信号转导过程中也显示出 IRF3 核易位和 mRNA 表达减少。总之，这些发现表明 HuR 通过控制 mRNA 的稳定性来增强 RLR 介导的 IRF3 核易位。
