Abstract
Cells of all mammals recognize double-stranded RNA (dsRNA) as a foreign material. In response, they release interferons (IFNs) and activate a ubiquitously expressed pseudokinase/endoribonuclease RNase L. RNase L executes regulated RNA decay and halts global translation. Here, we developed a biosensor for 2',5'-oligoadenylate (2-5A), the natural activator of RNase L. Using this biosensor, we found that 2-5A was acutely synthesized by cells in response to dsRNA sensing, which immediately triggered cellular RNA cleavage by RNase L and arrested host protein synthesis. However, translation-arrested cells still transcribed IFN-stimulated genes and secreted IFNs of types I and III (IFN-β and IFN-λ). Our data suggest that IFNs escape from the action of RNase L on translation. We propose that the 2-5A/RNase L pathway serves to rapidly and accurately suppress basal protein synthesis, preserving privileged production of defense proteins of the innate immune system.
Highlights
Cells of all mammals recognize double-stranded RNA as a foreign material
The activity of the OASs is normally low to allow for housekeeping protein synthesis, but it increases in the presence of viral or host double-stranded RNA (dsRNA) molecules [8]. 2-5A has an antiviral effect, against which some viruses have evolved 2-5A antagonist genes that are essential for infection [9,10,11,12,13,14,15,16]
Our biosensor can detect in situ 25A synthesis in mammalian cells, and it provides a heretofore missing platform for cell-based applications. These applications can range from live cell screens for modulators of innate immune responses to mechanistic analysis of dsRNA sensing, which we describe in this paper
Summary
Cells of all mammals recognize double-stranded RNA (dsRNA) as a foreign material They release interferons (IFNs) and activate a ubiquitously expressed pseudokinase/endoribonuclease RNase L. IFN production requires protein synthesis; during the innate immune response to double-stranded RNA (dsRNA), IFN production is universally accompanied by translational arrest. 2-5A binds to the ankyrin-repeat (ANK) domain of RNase L and promotes its oligomerization and the formation of a dimeric endoribonuclease active site [21,22,23] This dimer further assembles into high-order oligomers [24] that cleave viral RNAs [16, 18] and all components of the translation apparatus, including mRNAs [25], tRNAs [26], and 28S/18S rRNAs [27, 28]. The resulting action of RNase L inhibits global translation, which puts all proteins, including IFNs, at risk for arrest during a cellular response to dsRNA
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