Institut für Immunologie, Philipps-Universität Marburg, BMFZ, Hans-Meerwein-Straße 2, 35043 Marburg, Germany.
Institut für Medizinische Mikrobiologie und Krankenhaushygiene, Medizinische Hochschule Hannover, Carl Neuberg Straße 1, 30625 Hannover, Germany.
Nucleic Acids Res. 2020 Oct 9;48(18):10397-10412. doi: 10.1093/nar/gkaa739.
The RNA helicase RIG-I plays a key role in sensing pathogen-derived RNA. Double-stranded RNA structures bearing 5'-tri- or diphosphates are commonly referred to as activating RIG-I ligands. However, endogenous RNA fragments generated during viral infection via RNase L also activate RIG-I. Of note, RNase-digested RNA fragments bear a 5'-hydroxyl group and a 2',3'-cyclic phosphate. How endogenous RNA fragments activate RIG-I despite the lack of 5'-phosphorylation has not been elucidated. Here we describe an endogenous RIG-I ligand (eRL) that is derived from the internal transcribed spacer 2 region (ITS2) of the 45S ribosomal RNA after partial RNase A digestion in vitro, RNase A protein transfection or RNase L activation. The immunostimulatory property of the eRL is dependent on 2',3'-cyclic phosphate and its sequence is characterized by a G-quadruplex containing sequence motif mediating guanosine-5'-triphosphate (GTP) binding. In summary, RNase generated self-RNA fragments with 2',3'-cyclic phosphate function as nucleotide-5'-triphosphate binding aptamers activating RIG-I.
RNA 解旋酶 RIG-I 在识别病原体衍生的 RNA 方面发挥着关键作用。带有 5'-三磷酸或二磷酸的双链 RNA 结构通常被称为激活 RIG-I 的配体。然而，病毒感染过程中通过 RNase L 产生的内源性 RNA 片段也会激活 RIG-I。值得注意的是，RNase 消化的 RNA 片段带有 5'-羟基和 2'、3'-环状磷酸基团。尽管缺乏 5'-磷酸化，但内源性 RNA 片段如何激活 RIG-I 尚未阐明。在这里，我们描述了一种内源性 RIG-I 配体（eRL），它源自 45S 核糖体 RNA 的内部转录间隔区 2 区域（ITS2），在体外经 RNase A 部分消化、RNase A 蛋白转染或 RNase L 激活后产生。eRL 的免疫刺激特性依赖于 2'、3'-环状磷酸基团，其序列的特征是含有 G-四链体的序列基序，介导鸟苷-5'-三磷酸（GTP）结合。总之，带有 2'、3'-环状磷酸基团的 RNase 产生的自身 RNA 片段可作为核苷酸 5'-三磷酸结合适体激活 RIG-I。
