Schuberth-Wagner Christine, Ludwig Janos, Bruder Ann Kristin, Herzner Anna-Maria, Zillinger Thomas, Goldeck Marion, Schmidt Tobias, Schmid-Burgk Jonathan L, Kerber Romy, Wolter Steven, Stümpel Jan-Philip, Roth Andreas, Bartok Eva, Drosten Christian, Coch Christoph, Hornung Veit, Barchet Winfried, Kümmerer Beate M, Hartmann Gunther, Schlee Martin
Institute of Clinical Chemistry and Clinical Pharmacology, University Hospital, University of Bonn, 53105 Bonn, Germany.
Institute of Clinical Chemistry and Clinical Pharmacology, University Hospital, University of Bonn, 53105 Bonn, Germany; German Center for Infection Research Cologne-Bonn.
Immunity. 2015 Jul 21;43(1):41-51. doi: 10.1016/j.immuni.2015.06.015. Epub 2015 Jul 14.
The cytosolic helicase retinoic acid-inducible gene-I (RIG-I) initiates immune responses to most RNA viruses by detecting viral 5'-triphosphorylated RNA (pppRNA). Although endogenous mRNA is also 5'-triphosphorylated, backbone modifications and the 5'-ppp-linked methylguanosine ((m7)G) cap prevent immunorecognition. Here we show that the methylation status of endogenous capped mRNA at the 5'-terminal nucleotide (N1) was crucial to prevent RIG-I activation. Moreover, we identified a single conserved amino acid (H830) in the RIG-I RNA binding pocket as the mediator of steric exclusion of N1-2'O-methylated RNA. H830A alteration (RIG-I(H830A)) restored binding of N1-2'O-methylated pppRNA. Consequently, endogenous mRNA activated the RIG-I(H830A) mutant but not wild-type RIG-I. Similarly, knockdown of the endogenous N1-2'O-methyltransferase led to considerable RIG-I stimulation in the absence of exogenous stimuli. Studies involving yellow-fever-virus-encoded 2'O-methyltransferase and RIG-I(H830A) revealed that viruses exploit this mechanism to escape RIG-I. Our data reveal a new role for cap N1-2'O-methylation in RIG-I tolerance of self-RNA.
胞质解旋酶视黄酸诱导基因I（RIG-I）通过检测病毒5'-三磷酸化RNA（pppRNA）启动对大多数RNA病毒的免疫反应。尽管内源性mRNA也是5'-三磷酸化的，但主链修饰和5'-ppp连接的甲基鸟苷（（m7）G）帽可防止免疫识别。在这里，我们表明内源性加帽mRNA在5'-末端核苷酸（N1）处的甲基化状态对于防止RIG-I激活至关重要。此外，我们在RIG-I RNA结合口袋中鉴定出一个单一的保守氨基酸（H830）作为N1-2'-O-甲基化RNA空间排斥的介质。H830A改变（RIG-I（H830A））恢复了N1-2'-O-甲基化pppRNA的结合。因此，内源性mRNA激活了RIG-I（H830A）突变体，但未激活野生型RIG-I。同样，内源性N1-2'-O-甲基转移酶的敲低导致在没有外源性刺激的情况下RIG-I受到相当大的刺激。涉及黄热病病毒编码的2'-O-甲基转移酶和RIG-I（H830A）的研究表明，病毒利用这种机制逃避RIG-I。我们的数据揭示了帽N1-2'-O-甲基化在RIG-I对自身RNA耐受性中的新作用。
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