Posttranslational Modification of HOIP Blocks Toll-Like Receptor 4-Mediated Linear-Ubiquitin-Chain Formation.
Posttranslational Modification of HOIP Blocks Toll-Like Receptor 4-Mediated Linear-Ubiquitin-Chain Formation.
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DOI：
10.1128/mbio.01777-15
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发表时间：
2015-11-17
期刊：
影响因子：
6.4
通讯作者：
Jung JU
中科院分区：
文献类型：
--
作者：
Bowman J;Rodgers MA;Shi M;Amatya R;Hostager B;Iwai K;Gao SJ;Jung JU
线性泛素化是由线性泛素链组装复合物（LUBAC）催化的非典型翻译后修饰，包含HOIP，HOIL-1 L和Sharpin。LUBAC通过将线性泛素链连接到关键信号分子上，促进受体刺激后NF-κB活化和炎症。事实上，线性泛素化依赖性信号传导对于预防可能导致死亡的化脓性细菌感染至关重要。虽然线性泛素化对于微生物感染后的细胞内受体信号传导是必不可少的，但必须测量并停止这种反应以避免组织损伤和自身免疫。虽然LUBAC在细菌刺激后被激活，但调节LUBAC活性以响应细菌刺激的机制仍然难以捉摸。我们证明，LUBAC活性本身是通过泛素化下调，特别是催化亚基HOIP在羧基末端赖氨酸1056的泛素化。Lys 1056的泛素化动态改变HOIP构象，导致其催化活性的抑制。因此，HOIP Lys 1056-to-Arg突变不仅导致持续的LUBAC活性，而且延长了由细菌脂多糖介导的Toll样受体4（TLR 4）刺激诱导的NF-κB活化，而它对由CD 40刺激诱导的NF-κB活化没有影响。本研究描述了一种新的LUBAC介导的线性泛素化的翻译后调节，这种线性泛素化对于特异性指导TLR 4介导的NF-κB活化至关重要。蛋白质的翻译后修饰使细胞能够以严格控制的方式对感染和免疫刺激做出快速反应。具体而言，用小蛋白泛素共价修饰蛋白质对于细胞响应细菌和病毒感染而启动和终止免疫信号传导是必需的。这一过程由泛素连接酶控制，泛素连接酶本身必须受到调节以防止持续和有害的免疫信号传导。然而，人们对这一规定是如何实现的知之甚少。本文报道了一种新的泛素化事件的非典型泛素连接酶HOIP，需要终止细菌脂多糖（LPS）诱导的TLR 4免疫信号。泛素化导致HOIP连接酶经历构象变化，这阻断其酶活性并最终终止LPS诱导的TLR 4信号传导。这些发现为控制HOIP连接酶活性提供了一种新的机制，该机制对于适当调节促炎免疫应答至关重要。
Linear ubiquitination is an atypical posttranslational modification catalyzed by the linear-ubiquitin-chain assembly complex (LUBAC), containing HOIP, HOIL-1L, and Sharpin. LUBAC facilitates NF-κB activation and inflammation upon receptor stimulation by ligating linear ubiquitin chains to critical signaling molecules. Indeed, linear-ubiquitination-dependent signaling is essential to prevent pyogenic bacterial infections that can lead to death. While linear ubiquitination is essential for intracellular receptor signaling upon microbial infection, this response must be measured and stopped to avoid tissue damage and autoimmunity. While LUBAC is activated upon bacterial stimulation, the mechanisms regulating LUBAC activity in response to bacterial stimuli have remained elusive. We demonstrate that LUBAC activity itself is downregulated through ubiquitination, specifically, ubiquitination of the catalytic subunit HOIP at the carboxyl-terminal lysine 1056. Ubiquitination of Lys1056 dynamically altered HOIP conformation, resulting in the suppression of its catalytic activity. Consequently, HOIP Lys1056-to-Arg mutation led not only to persistent LUBAC activity but also to prolonged NF-κB activation induced by bacterial lipopolysaccharide-mediated Toll-like receptor 4 (TLR4) stimulation, whereas it showed no effect on NF-κB activation induced by CD40 stimulation. This study describes a novel posttranslational regulation of LUBAC-mediated linear ubiquitination that is critical for specifically directing TLR4-mediated NF-κB activation. Posttranslational modification of proteins enables cells to respond quickly to infections and immune stimuli in a tightly controlled manner. Specifically, covalent modification of proteins with the small protein ubiquitin is essential for cells to initiate and terminate immune signaling in response to bacterial and viral infection. This process is controlled by ubiquitin ligase enzymes, which themselves must be regulated to prevent persistent and deleterious immune signaling. However, how this regulation is achieved is poorly understood. This paper reports a novel ubiquitination event of the atypical ubiquitin ligase HOIP that is required to terminate bacterial lipopolysaccharide (LPS)-induced TLR4 immune signaling. Ubiquitination causes the HOIP ligase to undergo a conformational change, which blocks its enzymatic activity and ultimately terminates LPS-induced TLR4 signaling. These findings provide a new mechanism for controlling HOIP ligase activity that is vital to properly regulate a proinflammatory immune response.