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Small self-RNA generated by RNase L amplifies antiviral innate immunity


Antiviral innate immunity is initiated in response to RNA molecules that are produced in virus-infected cells1. These RNAs activate signalling cascades that activate the genes that encode α- and β-interferon (IFN). Signalling occurs through the interaction of the RNAs with either of two pathogen recognition receptors, retinoic acid-inducible gene-I (RIG-I, also known as DDX58) and melanoma differentiation associated gene-5 (MDA5, also known as IFIH1), which contain amino-terminal caspase activation and recruitment domains (CARD) and carboxy-terminal DExD/H Box RNA helicase motifs2,3,4,5. RIG-I and MDA5 interact with another CARD protein, interferon-β promotor stimulator protein-1 (IPS-1, also known as MAVS, VISA and Cardif), in the mitochondrial membrane, which relays the signal through the transcription factors interferon regulatory factor 3 (IRF-3) and nuclear factor (NF)-κB to the IFN-β gene6,7,8,9,10. Although the signalling pathway is well understood, the origin of the RNA molecules that initiate these processes is not. Here we show that activation of the antiviral endoribonuclease, RNase L11, by 2′,5′-linked oligoadenylate (2-5A)12 produces small RNA cleavage products from self-RNA that initiate IFN production. Accordingly, mouse embryonic fibroblasts lacking RNase L were resistant to the induction of IFN-β expression in response to 2-5A, dsRNA or viral infection. Single-stranded regions of RNA are cleaved 3′ of UpUp and UpAp sequences by RNase L during viral infections, resulting in small, often duplex, RNAs13,14. We show that small self-RNAs produced by the action of RNase L on cellular RNA induce IFN-β expression and that the signalling involves RIG-I, MDA5 and IPS-1. Mice lacking RNase L produce significantly less IFN-β during viral infections than infected wild-type mice. Furthermore, activation of RNase L with 2-5A in vivo induced the expression of IFN-β in wild-type but not RNase L-deficient mice. Our results indicate that RNase L has an essential role in the innate antiviral immune response that relieves the requirement for direct sensing of non-self RNA.

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Figure 1: Involvement of RNase L in induction of IFN-β expression by 2-5A, dsRNA or viral infection.
Figure 2: 2-5A induces transcriptional activation of the IFN-β promoter.
Figure 3: Cleavage of cellular RNA by RNase L produces small RNAs that activate the IFN-β gene.
Figure 4: RNase L contributes to induction of IFN-β by virus or 2-5A in vivo.

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We thank M. Diamond and M. Colonna (St Louis, Missouri, USA) for the Mda5–/– MEFs, S. Akira (Osaka, Japan) for Ips1–/– and Rig-i–/– cells, M. David (San Diego, California, USA) for IRF3 antibodies, C.M. Rice (New York, New York, USA) for Huh7 and Huh7.5 cells, I.M. Kerr (London, UK) for EMCV, P.J. Sims (Rochester, New York, USA) for discussions, and (all from Cleveland, Ohio, USA) G. Sen for Sendai virus, J. Paranjape for cell line preparations and RNA chip analysis, B.K. Jha for RNase L, B.K. Jha, C. Thakur and Z. Novince for preparing 2-5A, and S. Shelby for technical assistance with mice. These studies were supported by grants from the NIH to R.H.S. and M.G. and by a grant from the Burroughs Wellcome Fund to M.G.

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Correspondence to Robert H. Silverman.

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Malathi, K., Dong, B., Gale, M. et al. Small self-RNA generated by RNase L amplifies antiviral innate immunity. Nature 448, 816–819 (2007).

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