Mechanisms of Ubiquitin-Mediated Activation of IKK

描述（由申请人提供）：转录因子NF-κ B通过信号诱导的磷酸化、泛素化和随后的抑制性蛋白IicB家族降解来调节。1 KB的磷酸化由IKK复合物进行，IKK复合物被几乎所有的NF-κ B刺激物激活，包括促炎细胞因子白细胞介素-1（IL-1）和肿瘤坏死因子（TNF）。IL-1和TNF分别通过TRAF 2和TRAF 6激活IKK。我们的实验室已经发现TRAF 2和TRAF 6是泛素连接酶，其与UbclS/UevlA一起起作用以催化通过泛素的赖氨酸-63连接的独特的多聚泛素链的合成。这种多聚泛素化通过蛋白酶体非依赖性机制介导由TAK 1、TAB 1和TAB 2（或TAB 3）组成的蛋白激酶复合物的活化。我们最近的研究表明，TAB 2和TABS通过一个专门的锌指结构域与K63多聚泛素链结合，这种结合对TAK 1的激活很重要。活化的TAK 1随后磷酸化并活化IKK。这些结果为详细研究TAK 1和IKK被泛素激活的机制奠定了基础。此外，我们的发现提出了一个问题，即泛素化是否可以激活除TAK 1和IKK以外的其他蛋白激酶。我们下一阶段研究的目标是更深入地了解泛素激活蛋白激酶的分子机制，并开始探索这种机制的潜在普遍性。具体而言，我们将致力于：1）阐明TAK 1通过泛素激活的机制; 2）定义IKK通过TAK 1和泛素激活的机制; 3）研究IKK激活的TAK 1非依赖性途径; 4）剖析TRAF 6和泛素依赖性ERK激活途径。这些研究将导致IKK激活机制的解开，这是NF-κ B研究中的一个中心问题。此外，我们的研究将有助于建立一个新的信号转导模式，其中泛素起着重要的调节作用。

DESCRIPTION (provided by applicant): The transcription factor NF-KB is regulated through signal-induced phosphorylation, ubiquitination and subsequent degradation of the IicB family of inhibitory proteins. The phosphorylation of 1KB is carried out by the IKK complex, which is activated by virtually all NF-KB stimuli including the proinflammatory cytokines interleukin-1 (IL-1) and tumor necrosis factor (TNF). IL-1 and TNF activate IKK through TRAF2 and TRAF6, respectively. Our lab has found that TRAF2 and TRAF6 are ubiquitin ligases that function together with UbclS/UevlA to catalyze the synthesis of a unique polyubiquitin chain linked through lysine-63 of ubiquitin. This polyubiquitination mediates the activation of a protein kinase complex consisting of TAK1, TAB1 and TAB2 (or TAB3), through a proteasome-independent mechanism. Our recent studies show that TAB2 and TABS bind to K63 polyubiquitin chains through a specialized zinc finger domain, and that this binding is important for TAK1 activation. The activated TAK1 subsequently phosphorylates and activates IKK. These results set the stage for a detailed study of the mechanism of TAK1 and IKK activation by ubiquitin. In addition, our finding raises the question of whether ubiquitination may activate other protein kinases besides TAK1 and IKK. The goals of our next phase of research are to have a deeper understanding of the molecular mechanism of ubiquitin activation of protein kinases, and to begin to explore the potential generality of this mechanism. Specifically, we will strive to: 1) Elucidate the mechanism of TAK1 activation by ubiquitin; 2) Define the mechanism of IKK activation by TAK1 and ubiquitin; 3) Investigate the TAK1- independent pathway of IKK activation; 4) Dissect the TRAF6- and ubiquitin-dependent pathway of ERK activation. These studies should lead to the unraveling of the IKK activation mechanism, a central question in NF-KB research. Moreover, our research should help establish a new paradigm of signal transduction in which ubiquitin plays an important regulatory role.