De-ubiquitination and ubiquitin ligase domains of A20 downregulate NF-kappaB signalling.
NF-kappaB transcription factors mediate the effects of pro-inflammatory cytokines such as tumour necrosis factor-alpha and interleukin-1beta. Failure to downregulate NF-kappaB transcriptional activity results in chronic inflammation and cell death, as observed in A20-deficient mice. A20 is a potent inhibitor of NF-kappaB signalling, but its mechanism of action is unknown. Here we show that A20 downregulates NF-kappaB signalling through the cooperative activity of its two ubiquitin-editing domains. The amino-terminal domain of A20, which is a de-ubiquitinating (DUB) enzyme of the OTU (ovarian tumour) family, removes lysine-63 (K63)-linked ubiquitin chains from receptor interacting protein (RIP), an essential mediator of the proximal TNF receptor 1 (TNFR1) signalling complex. The carboxy-terminal domain of A20, composed of seven C2/C2 zinc fingers, then functions as a ubiquitin ligase by polyubiquitinating RIP with K48-linked ubiquitin chains, thereby targeting RIP for proteasomal degradation. Here we define a novel ubiquitin ligase domain and identify two sequential mechanisms by which A20 downregulates NF-kappaB signalling. We also provide an example of a protein containing separate ubiquitin ligase and DUB domains, both of which participate in mediating a distinct regulatory effect.
Wertz
Ingrid E
IE
Department of Molecular Oncology, School of Medicine, University of California, Davis, Davis, California 95616, USA.
O'Rourke
Karen M
KM
Zhou
Honglin
H
Eby
Michael
M
Aravind
L
L
Seshagiri
Somasekar
S
Wu
Ping
P
Wiesmann
Christian
C
Baker
Rohan
R
Boone
David L
DL
Ma
Averil
A
Koonin
Eugene V
EV
Dixit
Vishva M
VM
D002460:Cell Line; D004268:DNA-Binding Proteins; D015536:Down-Regulation; D006367:HeLa Cells; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins; D016328:NF-kappa B / Q000378:metabolism*; D009687:Nuclear Proteins; D017434:Protein Structure, Tertiary; D011506:Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D034741:RNA, Small Interfering / Q000235:genetics / Q000378:metabolism; D053422:Receptor-Interacting Protein Serine-Threonine Kinases; D015398:Signal Transduction; D047992:TNF Receptor-Associated Factor 2; D000072598:Tumor Necrosis Factor alpha-Induced Protein 3; D025801:Ubiquitin / Q000378:metabolism*; D044763:Ubiquitin-Conjugating Enzymes / Q000378:metabolism; D044767:Ubiquitin-Protein Ligases / Q000378:metabolism*
D004268:DNA-Binding Proteins; D047908:Intracellular Signaling Peptides and Proteins; D016328:NF-kappa B; D009687:Nuclear Proteins; D011506:Proteins; D034741:RNA, Small Interfering; D047992:TNF Receptor-Associated Factor 2; D025801:Ubiquitin; D044763:Ubiquitin-Conjugating Enzymes; D044767:Ubiquitin-Protein Ligases; C506249:RIPK1 protein, human; D053422:Receptor-Interacting Protein Serine-Threonine Kinases; C076529:TNFAIP3 protein, human; D000072598:Tumor Necrosis Factor alpha-Induced Protein 3