Interleukin-1 and TRAF6-dependent activation of TAK1 in the absence of TAB2 and TAB3.

Interleukin-1 (IL-1) signaling induces the formation of Lys63-linked ubiquitin (K63-Ub) chains, which are thought to activate the 'master' protein kinase TGFβ-activated kinase 1 (TAK1) by interacting with its TAK1-binding 2 (TAB2) and TAB3 subunits. Here, we report that IL-1β can also activate the TAB1-TAK1 heterodimer present in TAB2/TAB3 double knockout (DKO) IL-1 receptor-expressing cells. The IL-1β-dependent activation of the TAB1-TAK1 heterodimer in TAB2/3 DKO cells is required for the expression and E3 ligase activity of tumor necrosis factor receptor-associated factor 6 (TRAF6) and is reduced by the small interfering RNA (siRNA) knockdown of ubiquitin conjugating 13 (Ubc13), an E2-conjugating enzyme that directs the formation of K63-Ub chains. IL-1β signaling was restored to TAB1/2/3 triple KO cells by the re-expression of either TAB1 or TAB2, but not by an ubiquitin binding-defective mutant of TAB2. We conclude that IL-1β can induce the activation of TAK1 in two ways, only one of which requires the binding of K63-Ub chains to TAB2/3. The early IL-1β-stimulated, TAK1-dependent activation of p38α mitogen-activated protein (MAP) kinase and the canonical IκB kinase (IKK) complex, as well as the NF-κB-dependent transcription of immediate early genes, was similar in TAB2/3 DKO cells and TAB2/3-expressing cells. However, in contrast with TAB2/3-expressing cells, IL-1β signaling was transient in TAB2/3 DKO cells, and the activation of c-Jun N-terminal kinase 1 (JNK1), JNK2 and p38γ was greatly reduced at all times. These observations indicate a role for TAB2/3 in directing the TAK1-dependent activation of MAP kinase kinases that switch on JNK1/2 and p38γ MAP kinases. These observations and the transient activation of the TAB1-TAK1 heterodimer may explain why IL-1β-dependent IL-8 mRNA formation was abolished in TAB2/3 DKO cells.

Zhang J ，Macartney T ，Peggie M ，Cohen P ... -  《-》

Roles for TAB1 in regulating the IL-1-dependent phosphorylation of the TAB3 regulatory subunit and activity of the TAK1 complex.

Mendoza H ，Campbell DG ，Burness K ，Hastie J ，Ronkina N ，Shim JH ，Arthur JS ，Davis RJ ，Gaestel M ，Johnson GL ，Ghosh S ，Cohen P ... -  《-》

TAK1-dependent signaling requires functional interaction with TAB2/TAB3.

Besse A ，Lamothe B ，Campos AD ，Webster WK ，Maddineni U ，Lin SC ，Wu H ，Darnay BG ... -  《-》

Phosphoinositide-dependent kinase-1 inhibits TRAF6 ubiquitination by interrupting the formation of TAK1-TAB2 complex in TLR4 signaling.

Phosphoinositide-dependent protein kinase 1 (PDK1) plays a key role in the phosphoinositide 3-kinase (PI3K)-PDK1-Akt pathway that induces cell survival and cardiovascular protections through anti-apoptosis, vasodilation, anti-inflammation, and anti-oxidative stress activities. Although several reports have proposed the negative role of PDK1 in Toll-like receptor 4 (TLR4) signaling, the molecular mechanism is still unknown. Here we show that PDK1 inhibits tumor necrosis factor (TNF) receptor-associated factor 6 (TRAF6) ubiquitination by interrupting the complex between transforming growth factor beta-activated kinase 1 (TAK1) and TAK1 binding protein 2 (TAB2), which negatively regulates TAK1 activity. The overexpression of PDK1 in 293/TLR4 cells resulted in suppressions of nuclear factor kappa B (NF-κB) activation and production of proinflammatory cytokines including interleukin (IL)-6 and TNF-α in response to lipopolysaccharide stimulation. Conversely, THP-1 human monocytes transiently cultured in low glucose medium displayed down-regulated PDK1 expression, and significantly enhanced TLR4-mediated signaling for the activation of NF-κB, demonstrating a negative role of PDK1. Biochemical studies revealed that PDK1 significantly interacted with TAK1, resulting in the inhibition of the association of TAB2 with TAK1, which led to the attenuation of TRAF6 ubiquitination. Moreover, PDK1-knockdown THP-1 cells displayed enhancement of downstream signals, activation of NF-κB, and increased production of pro-inflammatory cytokines IL-6, IL-1β, and TNF-α, which potentially led to the up-regulation of NF-κB-dependent genes in response to TLR4 stimulation. Collectively, the results demonstrate that PDK1 inhibits the formation of the TAK1-TAB2-TRAF6 complex and leads to the inhibition of TRAF6 ubiquitination, which negatively regulates the TLR4-mediated signaling for NF-κB activation.

Moon G ，Kim J ，Min Y ，Wi SM ，Shim JH ，Chun E ，Lee KY ... -  《-》

TAB2 and TAB3 activate the NF-kappaB pathway through binding to polyubiquitin chains.

Kanayama A ，Seth RB ，Sun L ，Ea CK ，Hong M ，Shaito A ，Chiu YH ，Deng L ，Chen ZJ ... -  《MOLECULAR CELL》