Mechanisms of HTLV-I Tax-mediated NF-kB activation

描述(申请人提供)：人类T细胞白血病病毒I型(HTLV-I)与成人T细胞白血病(ATL)的发生有关，ATL是一种侵袭性的CD4+T细胞恶性肿瘤。Tax是一种由HTLV-I基因组编码的癌蛋白，调节病毒和细胞基因的表达。Tax促进细胞转化，部分是通过激活核因子-kB/Rel转录因子家族。Tax需要NF-kB使原代T细胞永生化，而HTLV-I转化的细胞依赖于NF-kB生存，从而为研究Tax激活NF-kB的机制提供了强有力的理论基础。TAX通过促进持久的IKB激酶(IKK)激活来激活核因子-kB，尽管其机制尚不清楚。我们的支持性研究表明，多泛素化是核因子-kB的税收激活的关键翻译后调节因子。核因子-kB的税收激活与泛素依赖的IKK重新定位到高尔基体有关。Tax通过Lys 63连接的泛素链进行泛素化，需要泛素结合酶UBC13来实现Tax泛素化和核因子-kB的激活。税收的泛素化不会促进其降解，而是调节其与IKK调节亚单位IKKg的相互作用。此外，我们还确定，TAX相互作用的细胞蛋白TAX1BP1是细胞因子介导的NF-kB信号的关键负调控因子，它是泛素编辑酶A20的一个重要亚基。我们假设税收靶向TAX1BP1作为促进持续的NF-kB激活机制的一部分。在这项提案中，我们将进一步研究泛素化如何调节税收和IKK进入高尔基体的靶向。我们还将进一步划定监管税收泛素化的要求和宿主因素的认定。最后，我们将确定Tax用来灭活TAX1BP1和A20泛素编辑复合体的机制。我们的目标将通过完成以下具体目标来实现：(1)确定税收介导的IKK重新定位的机制；(2)研究税收泛素化和核因子-kB激活的分子决定因素；(3)确定与TAX1BP1结合在核因子-kB激活中的作用。这些研究将阐明逆转录病毒癌蛋白如何篡改宿主泛素化/去泛素化机制，以持续激活促进细胞转化的转录因子。

DESCRIPTION (provided by applicant): Human T cell leukemia virus type I (HTLV-I) is linked to the genesis of adult T cell leukemia (ATL), an aggressive CD4+ T cell malignancy. Tax is an oncoprotein encoded by the HTLV-I genome that regulates viral and cellular gene expression. Tax promotes cell transformation, in part, by activating the NF-kB/Rel transcription factor family. Tax requires NF-kB for the immortalization of primary T cells and HTLV-I transformed cells are dependent on NF-kB for their survival, thereby providing a strong rationale for studying the mechanisms used by Tax to activate NF-kB. Tax activates NF-kB by promoting persistent IkB kinase (IKK) activation although the mechanisms are poorly understood. Our supporting studies indicate that polyubiquitination is a key post- translational regulator of Tax activation of NF-kB. Tax activation of NF-kB correlates with ubiquitin-dependent relocalization of IKK to the Golgi apparatus. Tax is polyubiquitinated via Lys 63-linked ubiquitin chains and requires the ubiquitin conjugating enzyme Ubc13 for Tax ubiquitination and NF-kB activation. Ubiquitination of Tax does not promote its degradation, but rather regulates its interaction with the IKK regulatory subunit IKKg. In addition, we have determined that the Tax interacting cellular protein TAX1BP1 is a key negative regulator of cytokine-mediated NF-kB signaling by functioning as an essential subunit for the ubiquitin-editing enzyme A20. We hypothesize that Tax targets TAX1BP1 as part of a mechanism to promote persistent NF-kB activation. In this proposal, we will further investigate how ubiquitination regulates the targeting of Tax and IKK into the Golgi. We will also further delineate the requirements and the identification of host factors regulating Tax ubiquitination. Finally, we will determine the mechanisms used by Tax to inactivate TAX1BP1 and the A20 ubiquitin-editing complex. Our objectives for this proposal will be satisfied by completion of the following specific aims: (1) Determine the mechanisms of Tax-mediated relocalization of IKK; (2) investigate the molecular determinants of Tax ubiquitination and NF-kB activation and (3) determine the role of Tax binding to TAX1BP1 in NF-kB activation. These studies will shed light on how a retroviral oncoprotein usurps host ubiquitination/deubiquitination machinery to persistently activate transcription factors that promote cell transformation.