Mechanisms of Ubiquitin-Mediated Activation of IKK

描述（由申请人提供）：转录因子NF-KB通过信号诱导的抑制蛋白IicB家族的磷酸化、泛素化和随后的降解来调节。1KB的磷酸化是由IKK复合物完成的，IKK复合物被几乎所有NF-KB刺激激活，包括促炎细胞因子白介素-1 （IL-1）和肿瘤坏死因子（TNF）。IL-1和TNF分别通过TRAF2和TRAF6激活IKK。我们的实验室发现TRAF2和TRAF6是泛素连接酶，它们与UbclS/UevlA一起作用，催化合成一个独特的泛素链，通过泛素的赖氨酸-63连接。这种多泛素化通过蛋白酶体不依赖的机制介导由TAK1、TAB1和TAB2（或TAB3）组成的蛋白激酶复合物的激活。我们最近的研究表明，TAB2和TABS通过一个特殊的锌指结构域结合到K63多泛素链上，这种结合对TAK1的激活很重要。活化的TAK1随后磷酸化并激活IKK。这些结果为详细研究泛素激活TAK1和IKK的机制奠定了基础。此外，我们的发现提出了泛素化是否可以激活除TAK1和IKK之外的其他蛋白激酶的问题。我们下一阶段的研究目标是更深入地了解泛素活化蛋白激酶的分子机制，并开始探索这一机制的潜在普遍性。具体而言，我们将努力：1)阐明TAK1被泛素激活的机制；2)明确TAK1和泛素激活IKK的机制；3)研究不依赖TAK1的IKK激活途径；4)剖析TRAF6-和泛素依赖的ERK激活途径。这些研究将导致IKK激活机制的解开，这是NF-KB研究的一个核心问题。此外，我们的研究应该有助于建立一个新的信号转导范式，其中泛素发挥重要的调节作用。

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.