Reconstitution of the RIG-I pathway reveals a signaling role of unanchored polyubiquitin chains in innate immunity

Wenwen Zeng, Lijun Sun, Xiaomo Jiang, Xiang Chen, Fajian Hou, Anirban Adhikari, Ming Xu, Zhijian J. Chen

Research output: Contribution to journalArticle

389 Scopus citations

Abstract

RIG-I detects invading viral RNA and activates the transcription factors NF-κB and IRF3 through the mitochondrial protein MAVS. Here we show that RNA bearing 5′-triphosphate strongly activates the RIG-I-IRF3 signaling cascade in a reconstituted system composed of RIG-I, mitochondria, and cytosol. Activation of RIG-I requires not only RNA but also polyubiquitin chains linked through lysine 63 (K63) of ubiquitin. RIG-I binds specifically to K63-polyubiquitin chains through its tandem CARD domains in a manner that depends on RNA and ATP. Mutations in the CARD domains that abrogate ubiquitin binding also impair RIG-I activation. Remarkably, unanchored K63-ubiquitin chains, which are not conjugated to any target protein, potently activate RIG-I. These ubiquitin chains function as an endogenous ligand of RIG-I in human cells. Our results delineate the mechanism of RIG-I activation, identify CARD domains as a ubiquitin sensor, and demonstrate that unanchored K63-polyubiquitin chains are signaling molecules in antiviral innate immunity.

Original languageEnglish (US)
Pages (from-to)315-330
Number of pages16
JournalCell
Volume141
Issue number2
DOIs
StatePublished - Apr 1 2010

Keywords

  • Cellcylce
  • Molimmuno
  • Signaling

ASJC Scopus subject areas

  • Biochemistry, Genetics and Molecular Biology(all)

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