RNA Viruses Section, Laboratory of Infectious Diseases, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland, United States of America.
PLoS One. 2012;7(2):e28382. doi: 10.1371/journal.pone.0028382. Epub 2012 Feb 15.
Interferons (IFNs) play a crucial role in the antiviral immune response. Whereas the C proteins of wild-type human parainfluenza virus type 1 (WT HPIV1) inhibit both IFN-β induction and signaling, a HPIV1 mutant encoding a single amino acid substitution (F170S) in the C proteins is unable to block either host response. Here, signaling downstream of the type 1 IFN receptor was examined in Vero cells to define at what stage WT HPIV1 can block, and F170S HPIV1 fails to block, IFN signaling. WT HPIV1 inhibited phosphorylation of both Stat1 and Stat2, and this inhibition was only slightly reduced for F170S HPIV1. Degradation of Stat1 or Stat2 was not observed. The HPIV1 C proteins were found to accumulate in the perinuclear space, often forming large granules, and co-localized with Stat1 and the cation-independent mannose 6-phosphate receptor (M6PR) that is a marker for late endosomes. Upon stimulation with IFN-β, both the WT and F170S C proteins remained in the perinuclear space, but only the WT C proteins prevented Stat1 translocation to the nucleus. In addition, WT HPIV1 C proteins, but not F170S C proteins, co-immunoprecipitated both phosphorylated and unphosphorylated Stat1. Our findings suggest that the WT HPIV1 C proteins form a stable complex with Stat1 in perinuclear granules that co-localize with M6PR, and that this direct interaction between the WT HPIV1 C proteins and Stat1 is the basis for the ability of HPIV1 to inhibit IFN signaling. The F170S mutation in HPIV1 C did not prevent perinuclear co-localization with Stat1, but apparently weakened this interaction such that, upon IFN stimulation, Stat1 was translocated to the nucleus to induce an antiviral response.
干扰素（IFNs）在抗病毒免疫反应中起着至关重要的作用。野生型人副流感病毒 1（WT HPIV1）的 C 蛋白既抑制 IFN-β的诱导，也抑制其信号转导，而 C 蛋白中单个氨基酸（F170S）取代的 HPIV1 突变体则不能阻断这两种宿主反应。在这里，在 Vero 细胞中检查了 I 型 IFN 受体下游的信号转导，以确定 WT HPIV1 可以在哪个阶段阻断，以及 F170S HPIV1 无法阻断 IFN 信号转导。WT HPIV1 抑制了 Stat1 和 Stat2 的磷酸化，而 F170S HPIV1 的抑制作用略有降低。未观察到 Stat1 或 Stat2 的降解。发现 HPIV1 C 蛋白在核周空间中积累，通常形成大颗粒，并与 Stat1 和阳离子非依赖性甘露糖 6-磷酸受体（M6PR）共定位，M6PR 是晚期内体的标志物。用 IFN-β刺激后，WT 和 F170S C 蛋白均留在核周空间，但只有 WT C 蛋白阻止了 Stat1 向核内易位。此外，WT HPIV1 C 蛋白，但不是 F170S C 蛋白，与磷酸化和非磷酸化的 Stat1 共免疫沉淀。我们的研究结果表明，WT HPIV1 C 蛋白在核周颗粒中与 Stat1 形成稳定的复合物，该复合物与 M6PR 共定位，WT HPIV1 C 蛋白与 Stat1 之间的这种直接相互作用是 HPIV1 抑制 IFN 信号转导的基础。HPIV1 C 中的 F170S 突变并没有阻止与 Stat1 的核周共定位，但显然削弱了这种相互作用，使得在 IFN 刺激下，Stat1 易位到细胞核以诱导抗病毒反应。
