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Immunity. 2012 Jun 29;36(6):959-73. doi: 10.1016/j.immuni.2012.03.022. Epub 2012 Jun 14.

Ubiquitin-induced oligomerization of the RNA sensors RIG-I and MDA5 activates antiviral innate immune response.

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  • 1Department of Molecular Biology, University of Texas Southwestern Medical Center, Dallas, TX 75390-9148, USA.

Abstract

RIG-I and MDA5 detect viral RNA in the cytoplasm and activate signaling cascades leading to the production of type-I interferons. RIG-I is activated through sequential binding of viral RNA and unanchored lysine-63 (K63) polyubiquitin chains, but how polyubiquitin activates RIG-I and whether MDA5 is activated through a similar mechanism remain unresolved. Here, we showed that the CARD domains of MDA5 bound to K63 polyubiquitin and that this binding was essential for MDA5 to activate the transcription factor IRF3. Mutations of conserved residues in MDA5 and RIG-I that disrupt their ubiquitin binding also abrogated their ability to activate IRF3. Polyubiquitin binding induced the formation of a large complex consisting of four RIG-I and four ubiquitin chains. This hetero-tetrameric complex was highly potent in activating the antiviral signaling cascades. These results suggest a unified mechanism of RIG-I and MDA5 activation and reveal a unique mechanism by which ubiquitin regulates cell signaling and immune response.

Copyright © 2012 Elsevier Inc. All rights reserved.

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PMID:
22705106
[PubMed - indexed for MEDLINE]
PMCID:
PMC3412146
Free PMC Article

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