A human cellular noncoding RNA activates the antiviral protein 2′–5′-oligoadenylate synthetase 1

Brenda M Calderon,Graeme L Conn

doi:10.1074/jbc.ra118.004747

Abstract

The 2'-5'-oligoadenylate synthetase (OAS) family of enzymes sense cytosolic dsRNA, a potent signal of viral infection. In response to dsRNA binding, OAS proteins synthesize the second messenger 2'-5'-linked oligoadenylate that activates the latent ribonuclease L (RNase L). RNase L-mediated degradation of viral and cellular RNAs effectively halts viral replication and further stimulates innate immune responses by inducing type I interferon. The OAS/RNase L pathway is therefore central in innate immune recognition and promotion of antiviral host responses. However, the potential for specific RNA sequences or structures to drive OAS1 activation and the molecular mechanisms by which they act are not currently fully understood. Moreover, the cellular regulators of OAS activity are not well defined. Here, we demonstrate that the human cellular noncoding RNA 886 (nc886) activates OAS1 both in vitro and in human A549 cells. We show that a unique structure present only in one of the two structural conformers adopted by nc886 drives potent OAS1 activation. In contrast, the conformer lacking this unique structure activated OAS1 only very weakly. We also found that formation of this OAS1-activating structural motif depends on the nucleotides in the apical-most loop of nc886 and the adjacent helix. These findings identify a cellular RNA capable of activating the OAS/RNase L pathway in human cells and illustrate the importance of structural elements, and their context, in potentiating OAS1 activity.

Highlights

The 2؅–5؅-oligoadenylate synthetase (OAS) family of enzymes sense cytosolic double-stranded RNA (dsRNA), a potent signal of viral infection
We show that a unique structure present only in one of the two structural conformers adopted by nc886 drives potent OAS1 activation
In OAS3, the catalytically inactive N-terminal OAS domain serves as a dsRNA-binding module, whereas its third C-terminal OAS domain carries out 2Ј–5Ј-linked oligoadenylate (2–5A) synthesis

Summary

Introduction

The 2؅–5؅-oligoadenylate synthetase (OAS) family of enzymes sense cytosolic dsRNA, a potent signal of viral infection. In response to dsRNA binding, OAS proteins synthesize the second messenger 2؅–5؅-linked oligoadenylate that activates the latent ribonuclease L (RNase L). We found that formation of this OAS1-activating structural motif depends on the nucleotides in the apical-most loop of nc886 and the adjacent helix These findings identify a cellular RNA capable of activating the OAS/RNase L pathway in human cells and illustrate the importance of structural elements, and their context, in potentiating OAS1 activity. Accumulation of double-stranded RNA (dsRNA) in the cell cytoplasm is a potent signal of viral infection and is detected by PRRs, including Toll-like receptors 3, 7, and 8; dsRNA-activated protein kinase (PKR); and the retinoic acid-inducible gene I (RIG-I)-like and 2Ј–5Ј-oligoadenylate synthetase (OAS) families of enzymes [3, 4]. More recent evidence suggests that OAS/RNase L–mediated translational arrest arises, in part, via specific cleavage of cellular tRNAs (tRNA) and Y RNAs [17]

Results

Discussion

Conclusion