DEREGULATION OF CELLULAR IKB KINASES BY HTLV1 TAX

人类T细胞白血病病毒1型(HTLV1)是成人T细胞白血病的病原体，成人T细胞白血病是一种由活化的CD4T淋巴细胞引起的侵袭性且通常无法治疗的恶性肿瘤。HTLV1编码的Tax癌蛋白能有效地诱导转录因子NF-kappaB的组成性核表达，在正常的生长信号转导过程中表现出快速而短暂的生物学活性。尽管先前的研究表明这种病毒/宿主的相互作用在HTLV1介导的细胞转化中起关键作用，但Tax对宿主NF-kappaB途径的作用机制尚不清楚。申请人的实验室最近发现，HTLV1 Tax通过涉及核因子-kappaB的细胞质抑制物IkappaBalpha的位点特异性磷酸化、泛素化和降解的一系列过程来触发NF-kappaB的诱导。为了启动这种IkappaBalpha靶向功能，Tax结合并持久激活一个多蛋白IkappaB激酶复合体(IKK)。与之形成鲜明对比的是，诱导核因子-kappaB的促炎细胞因子刺激的是短暂的而不是持久的ikk反应。这项拨款申请的中心假设是，税收导向的IKK激活是导致HTLV1感染的T细胞中IkappaBalpha崩溃和不适当的结构性核输入的关键酶检查点。因此，提出了一个高度集成的研究计划来阐明HTLV1的确切机制。TAX激活了IKK催化活性的持续功能表达。为了实现这一总体目标，将结合免疫学、生化和遗传学的方法来确定(I)HTLV1感染的T细胞中Tax/IKK复合体的稳定性、大小分布和亚基组成，(Ii)这些病理性Tax/IKK复合体形成的分子机制，以及(Iii)细胞蛋白激酶和磷酸酶在Tax导向的IKK激活中的功能作用。这项拟议的研究不仅将描绘出Tax如何在物理上影响多蛋白IKK信号转导装置，而且还将在分子水平上描绘这种病理性病毒/宿主相互作用的整个功能结构。反过来，识别这些在TAX/IKK轴中缺失的重要环节将导致开发HTLV1相关疾病的治疗控制的创新策略。

Human T-cell leukemia virus type 1 (HTLV1) is the etiologic agent of adult T-cell leukemia, an aggressive and often untreatable malignancy of activated CD4+ T lymphocytes. The Tax oncoprotein encoded by HTLV1 potently induces the constitutive nuclear expression of transcription factor NF-kappaB, which exhibits a rapid but transient pattern of biologic activity during normal growth-signal transduction. Although prior investigations have indicated that this viral/host interaction is pivotal for HTLV1-mediated cellular transformation, the pathologic mechanism of Tax action on the host NF-kappaB pathway remains unclear. The applicant's laboratory has recently discovered that HTLV1 Tax triggers NF-kappaB induction via a sequential process involving site-specific phosphorylation, ubiquitination, and degradation of IkappaBalpha, a cytoplasmic inhibitor of NF-kappaB. To initiate this IkappaBalpha targeting function, Tax binds to and persistently activates a multiprotein IkappaB kinase complex (IKK). In sharp contrast, pro-inflammatory cytokines that induce NF-kappaB stimulate a transient rather than persistent IKK response. The central hypothesis of this grant application is that Tax-directed IKK activation is the crucial enzymatic checkpoint leading to IkappaBalpha breakdown and the inappropriate constitutive nuclear import of NF-kappaB in HTLV1-infected T cells. Accordingly, a highly-integrated research program is proposed to elucidate the precise mechanism by which HTLV1. Tax activates the persistent functional expression of IKK catalytic activity. To achieve this overall objective, a combination of immunological, biochemical, and genetic approaches will be used to determine (i) the stability, size distribution, and subunit composition of Tax/IKK complexes in HTLV1-infected T cells, (ii) the molecular mechanism responsible for the formation of these pathologic Tax/IKK complexes, and (iii) the functional role of cellular protein kinases and phosphatases in Tax-directed IKK activation. This proposed investigation will delineate not only how Tax impinges physically on the multiprotein IKK signal transduction apparatus but also the entire functional architecture of this pathologic viral/host interaction at the molecular level. In turn, identification of these important missing links in the Tax/IKK axis will lead to the development of innovative strategies for the therapeutic control of HTLV1-associated diseases.