Garcin Dominique, Marq Jean-Baptiste, Strahle Laura, le Mercier Philippe, Kolakofsky Daniel
Department of Genetics and Microbiology, University of Geneva School of Medicine, CMU, 9 Ave de Champel, CH1211, Switzerland.
Virology. 2002 Apr 10;295(2):256-65. doi: 10.1006/viro.2001.1342.
Sendai virus infection strongly induces interferon (IFN) production and has recently been shown to interdict the subsequent IFN signaling through the Jak/Stat pathway. This anti-IFN activity of SeV is due to its "C" proteins, a nested set of four proteins (C', C, Y1, Y2) that carry out a nested set of functions in countering the innate immune response. We previously reported that all four C proteins interact with Stat1 to prevent IFN signaling through the Jak/Stat pathway. Nevertheless, only the longer C proteins reduced Stat1 levels and prevented IFN from inducing an antiviral (VSV) state, or apoptosis, in IFN-competent murine cells. Here, we investigate the mechanism by which the various C proteins differentially affect the host antiviral defenses. All four C proteins were found to physically associate with Stat1 during cell culture infections, and in vitro in the absence of other viral gene products (as evidenced by co-immunoprecipitation). In addition, the inability of a null mutant (C(F170S)) to bind Stat1 suggests that this interaction is physiologically relevant. We have also shown that the proteasomal inhibitor MG132 can prevent the C protein-induced dismantling of the antiviral (VSV) state in murine cells; thus, the turnover of Stat1 correlates with the C protein-mediated counteraction of the antiviral (VSV) state. The C protein-induced instability of Stat1 was accompanied by a clear increase in the level of mono-ubiquinated Stat1, an unexpected hallmark of protein degradation. Finally, we show that a rSeV with mutant C proteins but wild-type Y proteins (CDelta10-15, that does not counteract the endogenous antiviral (VSV) state of MEFs even though their C proteins bind Stat1 and prevent its activity) is also unable to decrease bulk Stat1 levels or to increase the level of ubiquinated Stat1.
仙台病毒感染强烈诱导干扰素（IFN）产生，并且最近已显示其通过Jak/Stat途径阻断随后的IFN信号传导。仙台病毒的这种抗IFN活性归因于其“C”蛋白，这是一组由四种蛋白（C'、C、Y1、Y2）组成的嵌套蛋白，它们在对抗先天免疫反应中发挥一系列嵌套功能。我们之前报道过，所有四种C蛋白都与Stat1相互作用，以阻止通过Jak/Stat途径的IFN信号传导。然而，只有较长的C蛋白降低了Stat1水平，并阻止IFN在具有IFN活性的鼠细胞中诱导抗病毒（VSV）状态或凋亡。在这里，我们研究了各种C蛋白对宿主抗病毒防御产生不同影响的机制。在细胞培养感染期间以及在体外不存在其他病毒基因产物的情况下（通过免疫共沉淀证明），发现所有四种C蛋白都与Stat1发生物理结合。此外，无效突变体（C(F170S)）无法结合Stat1，这表明这种相互作用具有生理相关性。我们还表明，蛋白酶体抑制剂MG132可以阻止C蛋白诱导的鼠细胞中抗病毒（VSV）状态的解除；因此，Stat1的周转与C蛋白介导的对抗病毒（VSV）状态相关。C蛋白诱导的Stat1不稳定性伴随着单泛素化Stat1水平的明显增加，这是蛋白质降解的一个意外标志。最后，我们表明，具有突变C蛋白但野生型Y蛋白的重组仙台病毒（CDelta10-15，即使其C蛋白结合Stat1并阻止其活性，也不会对抗MEF的内源性抗病毒（VSV）状态）也无法降低整体Stat1水平或增加泛素化Stat1的水平。
