Nucleoside modifications in RNA limit activation of 2'-5'-oligoadenylate synthetase and increase resistance to cleavage by RNase L

TLDR

Interferon‑induced OAS and RNase L form a 2‑5A pathway that detects viral RNA and triggers RNA cleavage, but nucleoside modifications in cellular transcripts can dampen activation of such RNA sensors. Unmodified RNA strongly activates OAS and RNase L, causing rRNA cleavage and reduced mRNA translation, whereas nucleoside‑modified RNA activates the pathway less, resists RNase L cleavage, and supports longer translation and half‑life, demonstrating that modifications suppress the 2‑5A antiviral response.

Abstract

The interferon-induced enzymes 2′-5′-oligoadenylate synthetase (OAS) and RNase L are key components of innate immunity involved in sensory and effector functions following viral infections. Upon binding target RNA, OAS is activated to produce 2′-5′-linked oligoadenylates (2-5A) that activate RNase L, which then cleaves single-stranded self and non-self RNA. Modified nucleosides that are present in cellular transcripts have been shown to suppress activation of several RNA sensors. Here, we demonstrate that in vitro transcribed, unmodified RNA activates OAS, induces RNase L-mediated ribosomal RNA (rRNA) cleavage and is rapidly cleaved by RNase L. In contrast, RNA containing modified nucleosides activates OAS less efficiently and induces limited rRNA cleavage. Nucleoside modifications also make RNA resistant to cleavage by RNase L. Examining translation in RNase L−/− cells and mice confirmed that RNase L activity reduces translation of unmodified mRNA, which is not observed with modified mRNA. Additionally, mRNA containing the nucleoside modification pseudouridine is translated longer and has an extended half-life. The observation that modified nucleosides in RNA reduce 2-5A pathway activation joins OAS and RNase L to the list of RNA sensors and effectors whose functions are limited when RNA is modified, confirming the role of nucleoside modifications in suppressing immune recognition of RNA.