Department of Cardiology, Respiratory Medicine and Nephrology, Hirosaki University Graduate School of Medicine, Hirosaki, Japan.
J Virol. 2012 Dec;86(23):12760-9. doi: 10.1128/JVI.01881-12. Epub 2012 Sep 12.
Upon viral infection, pattern recognition receptors sense viral nucleic acids, leading to the production of type I interferons (IFNs), which initiate antiviral activities. Type I IFNs bind to their cognate receptor, IFNAR, resulting in the activation of signal-transducing activators of transcription 1 (STAT1). Thus, it has long been thought that double-stranded RNA (dsRNA)-induced STAT1 phosphorylation is mediated by the transactivation of type I IFN signaling. Foreign RNA, such as viral RNA, in cells is sensed by the cytoplasmic sensors retinoic acid-inducible gene I (RIG-I) and melanoma differentiation-associated gene 5 (MDA-5). In this study, we explored the molecular mechanism responsible for STAT1 phosphorylation in response to the sensing of dsRNA by cytosolic RNA sensors. Polyinosinic-poly(C) [poly(I:C)], a synthetic dsRNA that is sensed by both RIG-I and MDA-5, induces STAT1 phosphorylation. We found that the poly(I:C)-induced initial phosphorylation of STAT1 is dependent on the RIG-I pathway and that MDA-5 is not involved in STAT1 phosphorylation. Furthermore, pretreatment of the cells with neutralizing antibody targeting the IFN receptor suppressed the initial STAT1 phosphorylation in response to poly(I:C), suggesting that this initial phosphorylation event is predominantly type I IFN dependent. In contrast, neither the known RIG-I pathway nor type I IFN is involved in the late phosphorylation of STAT1. In addition, poly(I:C) stimulated STAT1 phosphorylation in type I IFN receptor-deficient U5A cells with delayed kinetics. Collectively, our study provides evidence of a comprehensive regulatory mechanism in which dsRNA induces STAT1 phosphorylation, indicating the importance of STAT1 in maintaining very tight regulation of the innate immune system.
病毒感染后，模式识别受体识别病毒核酸，导致 I 型干扰素（IFN）的产生，从而启动抗病毒活性。I 型 IFN 与它们的同源受体 IFNAR 结合，导致转录激活因子 1（STAT1）的激活。因此，长期以来，人们一直认为双链 RNA（dsRNA）诱导的 STAT1 磷酸化是通过 I 型 IFN 信号的转激活来介导的。细胞内的外来 RNA，如病毒 RNA，被细胞质传感器视黄酸诱导基因 I（RIG-I）和黑色素瘤分化相关基因 5（MDA-5）识别。在这项研究中，我们探讨了细胞溶质 RNA 传感器识别 dsRNA 时导致 STAT1 磷酸化的分子机制。多聚肌苷酸-多聚胞苷酸[poly(I:C)]是一种被 RIG-I 和 MDA-5 都识别的合成 dsRNA，它诱导 STAT1 磷酸化。我们发现，poly(I:C)诱导的 STAT1 的初始磷酸化依赖于 RIG-I 途径，而 MDA-5 不参与 STAT1 磷酸化。此外，用针对 IFN 受体的中和抗体预处理细胞可抑制 poly(I:C)引起的初始 STAT1 磷酸化，表明这一初始磷酸化事件主要依赖于 I 型 IFN。相反，无论是已知的 RIG-I 途径还是 I 型 IFN 都不参与 STAT1 的晚期磷酸化。此外，poly(I:C)以延迟的动力学刺激 I 型 IFN 受体缺陷型 U5A 细胞中 STAT1 的磷酸化。总之，我们的研究提供了 dsRNA 诱导 STAT1 磷酸化的综合调控机制的证据，表明 STAT1 在维持先天免疫系统的严格调控中具有重要作用。
