RIG-I ATPase activity and discrimination of self-RNA versus non-self-RNA.
Many RNA viruses are detected by retinoic acid-inducible gene i (RIG-I), a cytoplasmic sensor that triggers an antiviral response upon binding non-self-RNA that contains a stretch of double-stranded RNA (dsRNA) bearing a base-paired 5' ppp nucleotide. To gain insight into how RIG-I discriminates between self-RNA and non-self-RNA, we used duplexes whose complementary bottom strand contained both ribo- and deoxynucleotides. These duplexes were examined for their binding to RIG-I and their relative abilities to stimulate ATPase activity, to induce RIG-I dimerization on the duplex, and to induce beta interferon (IFN-β) expression. We show that the chemical nature of the bottom strand is not critical for RIG-I binding. However, two key ribonucleotides, at positions 2 and 5 on the bottom strand, are minimally required for the RIG-I ATPase activity, which is necessary but not sufficient for IFN-β stimulation. We find that duplexes with shorter stretches of dsRNA, as model self-RNAs, bind less stably to RIG-I but nevertheless have an enhanced ability to stimulate the ATPase. Moreover, ATPase activity promotes RIG-I recycling on RIG-I/dsRNA complexes. Since pseudo-self-RNAs bind to RIG-I less stably, they are preferentially recycled by ATP hydrolysis that weakens the helicase domain binding of dsRNA. Our results suggest that one function of the ATPase is to restrict RIG-I signaling to its interaction with non-self-RNA. A model of how this discrimination occurs as a function of dsRNA length is presented.


OBJECTIVE
The innate immune response to pathogens is based on the discrimination between self-RNA and non-self-RNA. The main determinants of this detection for RNA viruses are specific pathogen-associated molecular patterns (PAMPs) of RNA, which are detected by dedicated cytoplasmic pattern recognition receptors (PRRs). RIG-I is a PRR that specifically detects short viral dsRNAs amid a sea of cellular RNAs. Here we study the determinants of this discrimination and how RIG-I ATPase activity, the only enzymatic activity of this sensor, contributes to its activation in a manner restricted to its interaction with non-self-RNAs. We also show how the innate immune response evolves during infection via IFN expression, from a state in which discrimination of self-RNA from non-self-RNA is most important to one in which this discrimination is sacrificed for the effectiveness of the antiviral response.
Department of Microbiology and Molecular Medicine, Faculty of Medicine, University of Geneva, Geneva, Switzerland.
Stéphanie
S
Anchisi
Department of Microbiology and Molecular Medicine, Faculty of Medicine, University of Geneva, Geneva, Switzerland.
Jessica
J
Guerra
Department of Microbiology and Molecular Medicine, Faculty of Medicine, University of Geneva, Geneva, Switzerland dominique.garcin@unige.ch.
Dominique
D
Garcin
D000251:Adenosine Triphosphatases / Q000378:metabolism*; D000071457:DEAD Box Protein 58; D053487:DEAD-box RNA Helicases / Q000378:metabolism*; D015870:Gene Expression; D016899:Interferon-beta / Q000096:biosynthesis; D011485:Protein Binding; D055503:Protein Multimerization; D012313:RNA / Q000378:metabolism*; D012330:RNA, Double-Stranded / Q000378:metabolism; D011971:Receptors, Immunologic; D013379:Substrate Specificity
D012330:RNA, Double-Stranded; D011971:Receptors, Immunologic; D012313:RNA; D016899:Interferon-beta; D000251:Adenosine Triphosphatases; C452820:RIGI protein, human; D000071457:DEAD Box Protein 58; D053487:DEAD-box RNA Helicases