title: Two coordinated mechanisms underlie tumor necrosis factor alpha-induced immediate and delayed IκB kinase activation.
abstract: Tumor necrosis factor alpha (TNF-α)-induced NF-κB activation has been believed to depend on TRAF2- and cIAP1-mediated RIP1 ubiquitination. However, recent findings have challenged the notion that these proteins play essential roles in NF-κB activation. Here, by assessing the kinetics and amplitude of IκB kinase (IKK) activation, we report that TNF-α-induced immediate and robust activation of IKK requires K63-linked and linearly linked ubiquitination of RIP1 and that in the absence of RIP1 expression, TRAF2 and cIAP1 cooperatively induce delayed IKK activation by recruiting LUBAC to TNFR1. Knockdown of HOIP (a component of LUBAC) in RIP1-deficient cells completely impairs the recruitment and activation of IKK but does not affect K63-linked ubiquitination of TRAF2 and recruitment of TAK1 to TNFR1, suggesting that the K63-linked ubiquitin chain is not capable of recruiting IKK in vivo. We also demonstrate that TRAF2 and cIAP1 together, but not either one alone, directly catalyze linearly linked ubiquitination of RIP1. Importantly, in embryonic hepatocytes, TNF-α activates NF-κB through a RIP1-independent pathway. Thus, our findings clarify molecular details of this important signaling mechanism by providing evidence for the existence of two phases of IKK activation: the immediate phase, induced by TRAF2/cIAP1-mediated ubiquitination of RIP1, and the delayed phase, activated by TRAF2/cIAP1-dependent recruitment of LUBAC.
authors: Department of Pathology, Carver College of Medicine, USA.
authors: Ken
authors: K
authors: Blackwell
authors: Laiqun
authors: L
authors: Zhang
authors: Lauren M
authors: LM
authors: Workman
authors: Adrian T
authors: AT
authors: Ting
authors: Kazuhiro
authors: K
authors: Iwai
authors: Hasem
authors: H
authors: Habelhah
mesh_terms: D000818:Animals; D002460:Cell Line; D004789:Enzyme Activation; D020690:GTPase-Activating Proteins / Q000378:metabolism*; D015870:Gene Expression; D005786:Gene Expression Regulation; D055786:Gene Knockout Techniques; D022781:Hepatocytes / Q000378:metabolism; D006801:Humans; D051550:I-kappa B Kinase / Q000378:metabolism*; D051034:Inhibitor of Apoptosis Proteins / Q000378:metabolism; D051379:Mice; D011485:Protein Binding; D021381:Protein Transport; D059748:Proteolysis; D047888:Receptors, Tumor Necrosis Factor, Type I / Q000378:metabolism; D015398:Signal Transduction; D047992:TNF Receptor-Associated Factor 2 / Q000378:metabolism; D048015:TNF Receptor-Associated Factor 5 / Q000378:metabolism; D014409:Tumor Necrosis Factor-alpha / Q000502:physiology*; D054875:Ubiquitination
chemical_list: D020690:GTPase-Activating Proteins; D051034:Inhibitor of Apoptosis Proteins; C490620:Ralbp1 protein, mouse; D047888:Receptors, Tumor Necrosis Factor, Type I; D047992:TNF Receptor-Associated Factor 2; D048015:TNF Receptor-Associated Factor 5; C506236:Tnfrsf1a protein, mouse; D014409:Tumor Necrosis Factor-alpha; D051550:I-kappa B Kinase