Activation of the IκB Kinase Complex by TRAF6 Requires a Dimeric Ubiquitin-Conjugating Enzyme Complex and a Unique Polyubiquitin Chain

Abstract

TRAF6 is a signal transducer in the NF-kappaB pathway that activates IkappaB kinase (IKK) in response to proinflammatory cytokines. We have purified a heterodimeric protein complex that links TRAF6 to IKK activation. Peptide mass fingerprinting analysis reveals that this complex is composed of the ubiquitin conjugating enzyme Ubc13 and the Ubc-like protein Uev1A. We find that TRAF6, a RING domain protein, functions together with Ubc13/Uev1A to catalyze the synthesis of unique polyubiquitin chains linked through lysine-63 (K63) of ubiquitin. Blockade of this polyubiquitin chain synthesis, but not inhibition of the proteasome, prevents the activation of IKK by TRAF6. These results unveil a new regulatory function for ubiquitin, in which IKK is activated through the assembly of K63-linked polyubiquitin chains.

Down-Regulation of TLR9 Expression Affects the Maturation and Function of Murine Bone Marrow-Derived Dendritic Cells Induced by CpG

“…Its intracellular signaling pathway has been elucidated at the molecular level. Upon CpG binding, TLR9 associates with the adaptor molecule MyD88 to initiate CpG-dependent effects via signal transducing proteins such as members of the IL-1 receptor-associated kinase (IRAK) family, mitogen activated kinases (MAPK), or IFN regulatory factors (11)(12)(13). These events lead to the activation of nuclear factor κB (NF-κB) transcription factors, cytokine production, or expression of co-stimulatory molecules in immune cells (14).…”

Ubiquitylated Tax targets and binds the IKK signalosome at the centrosome

“…ATM-dependent ubiquitylation of IKK-g mediates NF-kB activation by genotoxic stress (Huang et al, 2003) and the deubiquitylation enzyme CYLD negatively regulates NF-kB signaling (Kovalenko et al, 2003). K63-poly-ubiquitylation of TRAF6 mediates IKK activation by interleukin-1 (Deng et al, 2000). Moreover, the recruitment of IKK-g to occupy TNF-a receptor, and IKK activation, are both dependent on K63-polyubiquitylation of the signaling intermediate RIP1 (Ea et al, 2006;Wu et al, 2006).…”

The Pellino family: IRAK E3 ligases with emerging roles in innate immune signalling

“…TRAF6 then interacts with TIFA (TRAF-interacting protein with a FHA domain), which promotes oligomerization and ubiquitylation (Box 1) of the former [11]. In this process, TRAF6 interacts with the E2 ubiquitin-conjugating heterodimer UbcH13-Uev1a, resulting in covalent attachment of Lys63-linked polyubiquitin chains to TRAF6 [12]. The IRAK1-TRAF6 complex interacts with another membrane complex consisting of TAK1 and its pre-associated proteins, TAK1-binding protein (TAB)1, TAB2 and TAB3 [13,14], through the recognition of polyubiquitin chains on TRAF6 by highly conserved zinc finger domains in TAB2 and TAB3 [15] (Figure 2).…”