Korea Zoonosis Research Institute, Department of Bioactive Material Science and Genetic Engineering Research Institute, Chonbuk National University, Jeonju 54531, Republic of Korea.
Center for Convergent Research of Emerging Virus Infection, Korea Research Institute of Chemical Technology, Yuseong, Daejeon 34114, Republic of Korea.
J Microbiol Biotechnol. 2019 Oct 28;29(10):1665-1674. doi: 10.4014/jmb.1909.09017.
Zika virus (ZIKV) is a mosquito-transmitted, emerging Flavivirus that causes Guillain-Barré syndrome and microcephaly in adults and fetuses, respectively. Since ZIKV was first isolated in 1947, severe outbreaks have occurred at various places worldwide, including Yap Island in 2007, French Polynesia in 2013, and Brazil in 2015. Although incidences of ZIKV infection and dissemination have drastically increased, the mechanisms underlying the pathogenesis of ZIKV have not been sufficiently studied. In addition, despite extensive research, the exact roles of individual ZIKV genes in the viral evasion of the host innate immune responses remain elusive. Besides, it is still possible that more than one ZIKV-encoded protein may negatively affect type I interferon (IFN) induction. Hence, in this study, we aimed to determine the modulations of the IFN promoter activity, induced by the MDA5/RIG-I signaling pathway, by over-expressing individual ZIKV genes. Our results show that two nonstructural proteins, NS2A and NS4A, significantly down-regulated the promoter activity of IFN-β by inhibiting multiple signaling molecules involved in the activation of IFN-β. Interestingly, while NS2A suppressed both full-length and constitutively active RIG-I, NS4A had inhibitory activity only on full-length RIG-I. In addition, while NS2A inhibited all forms of IRF3 (full-length, regulatory domain-deficient, and constitutively active), NS4A could not inhibit constitutively active IRF3-5D. Taken together, our results showed that NS2A and NS4A play major roles as antagonists of MDA5/RIG-I-mediated IFN-β induction and more importantly, these two viral proteins seem to inhibit induction of the type I IFN responses in differential mechanisms. We believe this study expands our understanding regarding the mechanisms via which ZIKV controls the innate immune responses in cells and may pave the way to development of ZIKV-specific therapeutics.
寨卡病毒（ZIKV）是一种通过蚊子传播的新兴黄病毒，分别导致成人吉兰-巴雷综合征和胎儿小头畸形。自 1947 年首次分离出寨卡病毒以来，世界各地都发生了严重的疫情，包括 2007 年的雅浦岛、2013 年的法属波利尼西亚和 2015 年的巴西。尽管寨卡病毒感染和传播的发生率急剧增加，但寨卡病毒发病机制的机制尚未得到充分研究。此外，尽管进行了广泛的研究，但个别寨卡病毒基因在病毒逃避宿主先天免疫反应中的确切作用仍然难以捉摸。此外，可能有不止一种寨卡病毒编码蛋白可能会对 I 型干扰素（IFN）的诱导产生负面影响。因此，在这项研究中，我们旨在通过过表达单个寨卡病毒基因来确定 MDA5/RIG-I 信号通路诱导的 IFN 启动子活性的调节。我们的结果表明，两种非结构蛋白 NS2A 和 NS4A 通过抑制 IFN-β激活所涉及的多种信号分子，显著下调 IFN-β 的启动子活性。有趣的是，虽然 NS2A 抑制全长和组成性激活的 RIG-I，但 NS4A 仅对全长 RIG-I 具有抑制活性。此外，虽然 NS2A 抑制所有形式的 IRF3（全长、调节域缺失和组成性激活），但 NS4A 不能抑制组成性激活的 IRF3-5D。总之，我们的结果表明 NS2A 和 NS4A 作为 MDA5/RIG-I 介导的 IFN-β诱导的拮抗剂发挥主要作用，更重要的是，这两种病毒蛋白似乎以不同的机制抑制 I 型 IFN 反应的诱导。我们相信这项研究扩展了我们对寨卡病毒控制细胞固有免疫反应的机制的理解，并可能为寨卡病毒特异性治疗方法的开发铺平道路。
