Nie Li, Xu Xiao-Xiao, Xiang Li-Xin, Shao Jian-Zhong, Chen Jiong
Laboratory of Biochemistry and Molecular Biology, School of Marine Sciences, Ningbo University, Ningbo 315211, China.
College of Life Sciences, Zhejiang University, Hangzhou 310058, China.
Int J Mol Sci. 2017 May 27;18(6):1147. doi: 10.3390/ijms18061147.
Nucleotide-binding oligomerization domain-containing protein 2 (NOD2) and retinoic acid-inducible gene I (RIG-I) are two important cytosolic pattern recognition receptors (PRRs) in the recognition of pathogen-associated molecular patterns (PAMPs), initiating innate antibacterial and antiviral signaling pathways. However, the relationship between these PRRs, especially in teleost fish models, is rarely reported. In this article, we describe the mutual regulation of zebrafish NOD2 (NOD2) and RIG-I (RIG-I) in innate immune responses. Luciferase assays were conducted to determine the activation of NF-κB and interferon signaling. Morpholino-mediated knockdown and mRNA-mediated rescue were performed to further confirm the regulatory roles between NOD2 and RIG-I. Results showed that NOD2 and RIG-I shared conserved structural hallmarks with their mammalian counterparts, and activated RIG-I signaling can induce NOD2 production. Surprisingly, NOD2-initiated signaling can also induce RIG-I expression, indicating that a mutual regulatory mechanism may exist between them. Studies conducted using HEK293T cells and zebrafish embryos showed that RIG-I could negatively regulate NOD2-activated NF-κB signaling, and NOD2 could inhibit RIG-I-induced IFN signaling. Moreover, knocking down RIG-I expression by morpholino could enhance NOD2-initiated NF-κB activation, and vice versa, which could be rescued by their corresponding mRNAs. Results revealed a mutual feedback regulatory mechanism underlying NOD2 and RIG-I signaling pathways in teleosts. This mechanism reflects the coordination between cytosolic antibacterial and antiviral PRRs in the complex network of innate immunity.
含核苷酸结合寡聚化结构域蛋白2（NOD2）和视黄酸诱导基因I（RIG-I）是识别病原体相关分子模式（PAMP）的两种重要的胞质模式识别受体（PRR），可启动先天性抗菌和抗病毒信号通路。然而，这些PRR之间的关系，尤其是在硬骨鱼模型中的关系，鲜有报道。在本文中，我们描述了斑马鱼NOD2和RIG-I在先天性免疫反应中的相互调节。进行荧光素酶测定以确定NF-κB和干扰素信号的激活。进行吗啉代介导的敲低和mRNA介导的拯救以进一步证实NOD2和RIG-I之间的调节作用。结果表明，NOD2和RIG-I与其哺乳动物对应物具有保守的结构特征，激活的RIG-I信号可诱导NOD2产生。令人惊讶的是，NOD2启动的信号也可诱导RIG-I表达，表明它们之间可能存在相互调节机制。使用HEK293T细胞和斑马鱼胚胎进行的研究表明，RIG-I可负调节NOD2激活的NF-κB信号，而NOD2可抑制RIG-I诱导的IFN信号。此外，用吗啉代敲低RIG-I表达可增强NOD2启动的NF-κB激活，反之亦然，这可通过它们相应的mRNA拯救。结果揭示了硬骨鱼中NOD2和RIG-I信号通路潜在的相互反馈调节机制。这种机制反映了先天性免疫复杂网络中胞质抗菌和抗病毒PRR之间的协调。
