Many immune responses depend upon activation of NF-κB, a key transcription factor in the elicitation of a cytokine response. Here we demonstrate that N4BP1 inhibited TLR-dependent activation of NF-κB by interacting with the NF-κB signaling essential modulator (NEMO, also known as IκB kinase γ) to attenuate NEMO-NEMO dimerization or oligomerization. The UBA-like (ubiquitin associated-like) and CUE-like (ubiquitin conjugation to ER degradation) domains in N4BP1 mediated the interaction with the NEMO COZI domain. Both in vitro and in mice, N4bp1 deficiency specifically enhanced TRIF-independent (TLR2, TLR7, or TLR9-mediated), but not TRIF-dependent (TLR3 or TLR4-mediated), NF-κB activation leading to increased production of proinflammatory cytokines. In response to TLR4 or TLR3 activation, TRIF caused activation of caspase 8, which cleaved N4BP1 distal to residues D424 and D490 and abolished its inhibitory effect. N4bp1-/- mice also exhibited diminished numbers of T cells in the peripheral blood. Our work identifies N4BP1 as an inhibitory checkpoint protein that must be overcome to activate NF-κB, and a TRIF-initiated caspase 8-dependent mechanism by which this is accomplished.

中文翻译：

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N4BP1对NF-κB负调控的机制

许多免疫应答依赖于NF-κB的激活，NF-κB是引起细胞因子应答的关键转录因子。在这里，我们证明N4BP1通过与NF-κB信号必需调节剂（NEMO，也称为IκB激酶γ）相互作用来抑制NEMO-NEMO二聚化或低聚，从而抑制TLR依赖性的NF-κB活化。N4BP1中的UBA样（泛素相关样）域和CUE样（泛素与ER降解结合）域介导了与NEMO COZI域的相互作用。无论是在体外还是在小鼠中，N4bp1缺乏都会特异性增强TRIF依赖性（TLR2，TLR7或TLR9介导），而不是TRIF依赖性（TLR3或TLR4介导），NF-κB活化导致促炎细胞因子产生增加。响应TLR4或TLR3激活，TRIF导致caspase 8激活，其将N4BP1切割至残基D424和D490的远端，并消除了其抑制作用。N4bp1-/-小鼠的外周血中T细胞数量也减少。我们的工作将N4BP1识别为抑制性检查点蛋白，必须激活N4BP1才能激活NF-κB，并通过TRIF启动caspase 8依赖性机制来实现这一点。