Roles of RIG-I N-terminal tandem CARD and splice variant in TRIM25-mediated antiviral signal transduction

Proc Natl Acad Sci U S A. 2008 Oct 28;105(43):16743-8. doi: 10.1073/pnas.0804947105. Epub 2008 Oct 23.


The caspase recruitment domain (CARD) of intracellular adaptors and sensors plays a critical role in the assembly of signaling complexes involved in innate host defense against pathogens and in the regulation of inflammatory responses. The cytosolic receptor retinoic acid-inducible gene-I (RIG-I) recognizes viral RNA in a 5'-triphosphate-dependent manner and initiates an antiviral signaling cascade. Upon viral infection, the N-terminal CARDs of RIG-I undergo the K(63)-linked ubiquitination induced by tripartite motif protein 25 (TRIM25), critical for the interaction of RIG-I with its downstream signaling partner MAVS/VISA/IPS-1/Cardif. Here, we demonstrate the distinct roles of RIG-I first and second CARD in TRIM25-mediated RIG-I ubiquitination: TRIM25 binds the RIG-I first CARD and subsequently ubiquitinates its second CARD. The T(55)I mutation in RIG-I first CARD abolishes TRIM25 interaction, whereas the K(172)R mutation in the second CARD eliminates polyubiquitin attachment. The necessity of the intact tandem CARD for RIG-I function is further evidenced by a RIG-I splice variant (SV) whose expression is robustly up-regulated upon viral infection. The RIG-I SV carries a short deletion (amino acids 36-80) within the first CARD and thereby loses TRIM25 binding, CARD ubiquitination, and downstream signaling ability. Furthermore, because of its robust inhibition of virus-induced RIG-I multimerization and RIG-I-MAVS signaling complex formation, this SV effectively suppresses the RIG-I-mediated IFN-beta production. This study not only elucidates the vital role of the intact tandem CARD for TRIM25-mediated RIG-I activation but also identifies the RIG-I SV as an off-switch regulator of its own signaling pathway.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • CARD Signaling Adaptor Proteins / immunology
  • Cell Line, Tumor
  • DEAD Box Protein 58
  • DEAD-box RNA Helicases / genetics
  • DEAD-box RNA Helicases / immunology*
  • DEAD-box RNA Helicases / metabolism
  • Humans
  • Immunity, Innate*
  • Mutation
  • Protein Isoforms
  • Receptors, Immunologic
  • Signal Transduction / immunology
  • Transcription Factors / metabolism*
  • Tripartite Motif Proteins
  • Ubiquitin-Protein Ligases / metabolism*
  • Ubiquitination
  • Up-Regulation / immunology


  • CARD Signaling Adaptor Proteins
  • Protein Isoforms
  • Receptors, Immunologic
  • Transcription Factors
  • Tripartite Motif Proteins
  • TRIM25 protein, human
  • Ubiquitin-Protein Ligases
  • DDX58 protein, human
  • DEAD Box Protein 58
  • DEAD-box RNA Helicases