Ubiquitin-induced oligomerization of the RNA sensors RIG-I and MDA5 activates antiviral innate immune response.
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.
Department of Molecular Biology, University of Texas Southwestern Medical Center, Dallas, TX 75390-9148, USA.
Xiaomo
X
Jiang
Lisa N
LN
Kinch
Chad A
CA
Brautigam
Xiang
X
Chen
Fenghe
F
Du
Nick V
NV
Grishin
Zhijian J
ZJ
Chen
D000818:Animals; D002474:Cell-Free System; D000071457:DEAD Box Protein 58; D053487:DEAD-box RNA Helicases / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D004686:Encephalomyocarditis virus / Q000235:genetics / Q000502:physiology*; D005347:Fibroblasts / Q000378:metabolism / Q000821:virology; D057809:HEK293 Cells / Q000378:metabolism / Q000821:virology; D006801:Humans; D050838:Interferon Regulatory Factor-3 / Q000378:metabolism; D000072640:Interferon-Induced Helicase, IFIH1; D016899:Interferon-beta / Q000096:biosynthesis / Q000235:genetics; D051379:Mice; D046912:Multiprotein Complexes; D016297:Mutagenesis, Site-Directed; D025821:Polyubiquitin / Q000378:metabolism*; D011485:Protein Binding; D025941:Protein Interaction Mapping; D011499:Protein Processing, Post-Translational; D017434:Protein Structure, Tertiary; D012367:RNA, Viral / Q000378:metabolism; D011971:Receptors, Immunologic; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000502:physiology; D015398:Signal Transduction / Q000502:physiology; D013329:Structure-Activity Relationship; D054875:Ubiquitination
C494232:IRF3 protein, human; D050838:Interferon Regulatory Factor-3; C494233:Irf3 protein, mouse; D046912:Multiprotein Complexes; D012367:RNA, Viral; D011971:Receptors, Immunologic; D011993:Recombinant Fusion Proteins; D025821:Polyubiquitin; D016899:Interferon-beta; C452820:RIGI protein, human; C452815:IFIH1 protein, human; D000071457:DEAD Box Protein 58; D053487:DEAD-box RNA Helicases; D000072640:Interferon-Induced Helicase, IFIH1