title: TIFA activates IkappaB kinase (IKK) by promoting oligomerization and ubiquitination of TRAF6.
abstract: TRAF6 (tumor necrosis factor receptor-associated factor 6) is a RING (really interesting new gene) domain ubiquitin (Ub) ligase that mediates the activation of protein kinases, such as transforming growth factor beta-activated kinase (TAK1) and IkappaB kinase (IKK), by catalyzing the formation of a unique polyubiquitin chain linked through Lys-63 of Ub. Here, we present evidence that TIFA (TRAF-interacting protein with a forkhead-associated domain, also known as T2BP) activates IKK by promoting the oligomerization and Ub ligase activity of TRAF6. We show that recombinant TIFA protein, but not TRAF6-binding-defective mutant, can activate IKK in crude cytosolic extracts. Furthermore, TIFA activates IKK in an in vitro reconstitution system consisting of purified proteins, including TRAF6, the TAK1 kinase complex, and Ub-conjugating enzyme complex Ubc13-Uev1A. Interestingly, a fraction of recombinant TIFA protein exists as high-molecular-weight oligomers, and only these oligomeric forms of TIFA can activate IKK. Importantly, TIFA induces the oligomerization and polyubiquitination of TRAF6, which leads to the activation of TAK1 and IKK through a proteasome-independent mechanism.
authors.affiliation: Department of Molecular Biology, University of Texas Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, TX 75390-9148, USA.
authors.forename: Chee-Kwee
authors.initials: CK
authors.lastname: Ea
authors.forename: Lijun
authors.initials: L
authors.lastname: Sun
authors.forename: Jun-Ichiro
authors.initials: J
authors.lastname: Inoue
authors.forename: Zhijian J
authors.initials: ZJ
authors.lastname: Chen
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000502:physiology*; D001704:Biopolymers / Q000378:metabolism*; D002474:Cell-Free System; D004789:Enzyme Activation; D006801:Humans; D051550:I-kappa B Kinase; D016328:NF-kappa B / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D048029:TNF Receptor-Associated Factor 6 / Q000378:metabolism*; D025801:Ubiquitin / Q000378:metabolism*
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D001704:Biopolymers; D016328:NF-kappa B; C446759:TIFA protein, human; D048029:TNF Receptor-Associated Factor 6; D025801:Ubiquitin; D017346:Protein Serine-Threonine Kinases; C496559:CHUK protein, human; D051550:I-kappa B Kinase; C496560:IKBKB protein, human; C496565:IKBKE protein, human