Kinetic discrimination of self-non-self RNA by the ATPase activity of RIG-I and MDA5Report as inadecuate




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BMC Biology

, 13:54

First Online: 28 July 2015Received: 31 March 2015Accepted: 11 July 2015DOI: 10.1186-s12915-015-0166-9

Cite this article as: Louber, J., Brunel, J., Uchikawa, E. et al. BMC Biol 2015 13: 54. doi:10.1186-s12915-015-0166-9

Abstract

BackgroundThe cytoplasmic RIG-like receptors are responsible for the early detection of viruses and other intracellular microbes by activating the innate immune response mediated by type I interferons IFNs. RIG-I and MDA5 detect virus-specific RNA motifs with short 5′-tri-diphosphorylated, blunt-end double-stranded RNA dsRNA and >0.5–2 kb long dsRNA as canonical agonists, respectively. However, in vitro, they can bind to many RNA species, while in cells there is an activation threshold. As SF2 helicase-ATPase family members, ATP hydrolysis is dependent on co-operative RNA and ATP binding. Whereas simultaneous ATP and cognate RNA binding is sufficient to activate RIG-I by releasing autoinhibition of the signaling domains, the physiological role of the ATPase activity of RIG-I and MDA5 remains controversial.

ResultsA cross-analysis of a rationally designed panel of RNA binding and ATPase mutants and truncated receptors, using type I IFN promoter activation as readout, allows us to refine our understanding of the structure-function relationships of RIG-I and MDA5. RNA activation of RIG-I depends on multiple critical RNA binding sites in its helicase domain as confirmed by functional evidence using novel mutations. We found that RIG-I or MDA5 mutants with low ATP hydrolysis activity exhibit constitutive activity but this was fully reverted when associated with mutations preventing RNA binding to the helicase domain. We propose that the turnover kinetics of the ATPase domain enables the discrimination of self-non-self RNA by both RIG-I and MDA5. Non-cognate, possibly self, RNA binding would lead to fast ATP turnover and RNA disassociation and thus insufficient time for the caspase activation and recruitment domains CARDs to promote downstream signaling, whereas tighter cognate RNA binding provides a longer time window for downstream events to be engaged.

ConclusionsThe exquisite fine-tuning of RIG-I and MDA5 RNA-dependent ATPase activity coupled to CARD release allows a robust IFN response from a minor subset of non-self RNAs within a sea of cellular self RNAs. This avoids the eventuality of deleterious autoimmunity effects as have been recently described to arise from natural gain-of-function alleles of RIG-I and MDA5.

KeywordsRIG-I MDA5 dsRNA ATPase self from non-self AbbreviationsCARDCaspase activation and recruitment domain

chMDA5Chicken MDA5

CTDC-terminal domain

dRIG-IDuck RIG-I

dsRNADouble-stranded RNA

EMSAElectrophoretic mobility shift assay

IFNInterferon

helHelicase

hMDA5Human MDA5

hRIG-IHuman RIG-I

MAVSMitochondrial antiviral signaling

MeVMeasles virus

RLRRIG-I-like receptor

SDStandard deviation

wtWild-type

Electronic supplementary materialThe online version of this article doi:10.1186-s12915-015-0166-9 contains supplementary material, which is available to authorized users.

Jade Louber and Joanna Brunel contributed equally to this work.

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Author: Jade Louber - Joanna Brunel - Emiko Uchikawa - Stephen Cusack - Denis Gerlier

Source: https://link.springer.com/







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