2′-O-methylation within prokaryotic and eukaryotic tRNA inhibits innate immune activation by endosomal Toll-like receptors but does not affect recognition of whole organisms
2′-O-methylation within prokaryotic and eukaryotic tRNA inhibits innate immune activation by endosomal Toll-like receptors but does not affect recognition of whole organisms
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DOI：
10.1261/rna.070243.118
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发表时间：
2019-07-01
期刊：
影响因子：
4.5
通讯作者：
Eigenbrod, Tatjana
中科院分区：
文献类型：
--
作者：
Freund, Isabel;Buhl, Daniel K.;Eigenbrod, Tatjana
细菌 RNA 通过刺激人类 Toll 样受体 TLR7 和 TLR8 已成为先天免疫反应的重要激活剂。细菌 tRNA 中第 18 位（Gm18）的鸟苷 2'-O-甲基化被证明可以拮抗 tRNA 诱导的 TLR7/8 激活，表明 Gm18 作为免疫逃逸机制的潜在作用。这种修饰也发生在真核生物的 tRNA 中，但其生理免疫功能仍有待测试。因此，我们着手研究 Gm18 在原核和真核微生物、大肠杆菌和酿酒酵母以及人类细胞中的免疫调节作用。使用 RiboMethSeq 分析，我们发现大肠杆菌中的 trmH 突变、酿酒酶中的 trm3 突变以及智人中 CRISPR/Cas9 诱导的 TARBP1 敲除都会导致 tRNA 中 Gm18 的丢失。当 tRNA 制剂激活时，各个王国中 Gm18 的缺乏导致外周血单核细胞的免疫刺激增加。在大肠杆菌中，缺乏 2'-O-甲基转移酶 trmH 也增强了全细胞 RNA 的免疫刺激特性。相比之下，酵母和人类细胞中缺乏 Gm18 并不影响全 RNA 制剂的免疫刺激作用。当使用活的大肠杆菌时，尽管我们在大肠杆菌感染时检测到了明确的 TLR8/RNA 依赖性基因表达特征，但缺乏 trmH 并不影响整体免疫刺激。总之，这些结果表明，Gm18 是跨界的全局免疫抑制性 tRNA 修饰，有助于先天免疫细胞识别 tRNA，但作为个体修饰，其效力不足以调节所研究微生物的识别。
Bacterial RNA has emerged as an important activator of innate immune responses by stimulating Toll-like receptors TLR7 and TLR8 in humans. Guanosine 2'-O-methylation at position 18 (Gm18) in bacterial tRNA was shown to antagonize tRNA-induced TLR7/8 activation, suggesting a potential role of Gm18 as an immune escape mechanism. This modification also occurs in eukaryotic tRNA, yet a physiological immune function remained to be tested. We therefore set out to investigate the immune modulatory role of Gm18 in both prokaryotic and eukaryotic microorganisms, Escherichia coli and Saccharomyces cerevisiae, and in human cells. Using RiboMethSeq analysis we show that mutation of trmH in E. coli, trm3 in S. cereviase, and CRISPR/Cas9-induced knockout of TARBP1 in H. sapiens results in loss of Gm18 within tRNA. Lack of Gm18 across the kingdoms resulted in increased immunostimulation of peripheral blood mononuclear cells when activated by tRNA preparations. In E. coli, lack of 2'-O-methyltransferase trmH also enhanced immune stimulatory properties by whole cellular RNA. In contrast, lack of Gm18 in yeasts and human cells did not affect immunostimulation by whole RNA preparations. When using live E. coli bacteria, lack of trmH did not affect overall immune stimulation although we detected a defined TLR8/RNA-dependent gene expression signature upon E. coli infection. Together, these results demonstrate that Gm18 is a global immune inhibitory tRNA modification across the kingdoms and contributes to tRNA recognition by innate immune cells, but as an individual modification has insufficient potency to modulate recognition of the investigated microorganisms.