The IRAK-1-BCL10-MALT1-TRAF6-TAK1 Cascade Mediates Signaling to NF-κB from Toll-like Receptor 4

Abstract

Our previous studies have revealed that the signaling protein BCL10 plays a major role in adaptive immunity by mediating NF-B activation in the LPS/TLR4 pathway. In this study, we show that IRAK-1 acts as the essential upstream adaptor that recruits BCL10 to the TLR4 signaling complex and mediates signaling to NF-B through the BCL10-MALT1-TRAF6-TAK1 cascade. Following dissociation from IRAK-1, BCL10 is translocated into the cytosol along with TRAF6 and TAK1, in a process bridged by a direct BCL10-Pellino2 interaction. RNA interference against MALT1 markedly reduced the level of NF-B activation stimulated by lipopolysaccharide (LPS) in macrophages, which suggests that MALT1 plays a major role in the LPS/TLR4 pathway. MALT1 interacted with BCL10 and TRAF6 to facilitate TRAF6 self-ubiquitination in the cytosol, which was strictly dependent on the dissociation of BCL10 from IRAK-1. We show that BCL10 oligomerization is a prerequisite for BCL10 function in LPS signaling to NF-B and that IRAK-1 dimerization is an important event in this process.BCL10 and MALT1 are intracellular NF-B activators that are involved in MALT 4 lymphoma translocations (1, 2). These translocations are associated with MALT tumorigenesis via constitutive NF-B activation, which provides both anti-apoptotic and proliferative signals by up-regulating the transcription of specific targets (3). BCL10 contains the caspase recruitment domain (CARD), which is involved in protein oligomerization and protein-protein associations (4), as well as the MALT1-binding sequence containing 16 amino acids.BCL10 proteins can form homo-oligomers through CARD-CARD interaction under suitable conditions. In TCR signaling, BCL10 binds to its downstream adaptor MALT1 and co-operatively activates NF-B (4 -6). Recent studies have shown that BCL10 and MALT1 mediate NF-B activation by facilitating Lys-63 polyubiquitination of NEMO, which is an essential regulatory subunit of the IKK complex (7). In this process, tumor necrosis factor receptor-associated factor 6 (TRAF6), which is a polyubiquitin ligase, fills the gap between BCL10-MALT1 and NEMO in TCR signaling (8). MALT1 binds to TRAF6 through two putative C-terminal TRAF6-binding motifs. In vitro experiments using purified MALT1, TRAF6, TGF-␤-activated kinase (TAK1), and ubiquitination enzymes, which include Ubc13/ Uev1A, allowed reconstitution of the pathway from BCL10 to IKK activation. As reported previously, BCL10 and MALT1 form oligomers that bind to TRAF6, induce TRAF6 oligomerization, and activate the ligase activity of TRAF6 to promote self-ubiquitination and polyubiquitination of NEMO. This cascade model is predicted to be responsible for TCR signaling and NF-B activation in T lymphocytes (8).Toll-like receptors (TLRs) play essential roles in innate immune recognition in mammalian species. Upon engagement of their respective ligands, TLRs stimulate the transcription of effector genes through activation of common transcription factors, which include nuclear factor-B (NF-B), activating protein 1, and activating tr...

Carrageenan-induced NFκB activation depends on distinct pathways mediated by reactive oxygen species and Hsp27 or by Bcl10

“…Bcl10 is well-recognized as a mediator of a mechanism of inflammation in immune cells [16][17][18][19]. Recent reports, including our work in human colonic epithelial cells, have also established a role for Bcl10 in an inflammatory pathway in non-immune cells, including mouse embryonic kidney cells and hepatocytes [5,8,[20][21][22].…”

A dual role for the API2 moiety in API2-MALT1-dependent NF-κB activation: heterotypic oligomerization and TRAF2 recruitment

“…Zhou et al (2004Zhou et al ( , 2005 suggest that MALT1 possesses E3 ubiquitin ligase activity and that, together with the Ubc13/MMS2 E2 enzyme complex, MALT1 directly catalyses ubiquitination of NF-kB essential modulator (NEMO), the regulatory subunit of the IKK complex, upon oligomerization. Other groups suggest that MALT1 oligomerization triggers TRAF6-dependent ubiquitination of NEMO (Sun et al, 2004;Dong et al, 2006). Further studies are required to resolve this controversy.…”

TLR-4, IL-1R and TNF-R signaling to NF-κB: variations on a common theme

“…Upon LPS stimulation, MALT1 can only be detected in the cytosolic TAK1 complexes, whereas BCL10 is also found in TLR-4 and TAK1 complexes at the membrane. In addition, no IRAK-1 can be detected in the cytosolic TAK1 complex, suggesting that BCL10 dissociates from IRAK-1 before binding to MALT1 in the cytosolic TAK1 complex [78]. Pellino-2 was also found to interact with BCL10 in both the membrane-bound and cytosolic TAK1 complex, and its knock-down inhibits the recruitment of BCL10 to the cytosolic TAK1 complex.…”

“…Upon LPS stimulation, the scaffolding protein B-cell leukemia/lymphoma 10 (BCL10) is recruited into the TLR-4 receptor complex via its interaction with IRAK-1 [78]. Furthermore, IRAK-1 oligomerization stimulates BCL10 oligomerization, which is necessary for LPS-induced NF-kB activation.…”

“…Furthermore, IRAK-1 oligomerization stimulates BCL10 oligomerization, which is necessary for LPS-induced NF-kB activation. The BCL10-interacting protein mucosa-associated lymphoid tis- [78]. LPS stimulation effectively induces BCL10-MALT1 and MALT1-TRAF6 interactions, indicating that the BCL10-MALT1-TRAF6 signaling cascade to NF-kB is not only important in T-cell receptor signaling but also in the TLR-4 pathway.…”