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...

Brd2 is a novel protein kinase and plays a role in cell cycle-responsive transcription. Recent studies show that Brd2 contributes to E2F-1 regulated cell cycle progression. In this process, Brd2 exhibits scaffold or transcriptional adapter functions and mediates recruitment of both E2F-1 transcription factors and chromatin-remodelling activity to the E2F-1-resposive promoter. In the present study, we show that Brd2 is also a TBP-associated protein and a 26 amino acids peptide in the first bromodomain of Brd2 is essential for Brd2-TBP interaction. We found that serum stimulation of serum starved NIH/3T3 cells efficiently induces the formation of the Brd2-E2F-1-TBP complex in vivo. In this process, Brd2 plays a pivotal role in the recruitment of TBP into a E2F-1 transcriptional complex, as tested in overexpression assay and at the endogenous level. Furthermore, the 26 amino acid peptide that mediates Brd2-TBP interaction is proved to be critical for Brd2-dependent transactivation on E2F-1-responsive promoters, and moreover, Brd2 and E2F-1 may cooperatively participate in various serum-induced transactivation processes in Luciferase-reporter assays. Thus taken together, because Brd2 may recruit a HAT in its transactivational complex and E2F-1 has been found to stimulate transcription by recruiting acetyltransferase and cofactors GCN5, we predict that Brd2 and E2F-1 may act in a cooperative way to introduce an optimal environment for TBP binding to the TATA-element of gene promoters.