Cell Cycle Regulation and Adult T Cell Leukemia

描述（由申请人提供）：HTLV-I是成人T细胞白血病/淋巴瘤（ATL）的病原体，ATL是CD4+ T细胞的恶性肿瘤，其病因与病毒反激活子/癌蛋白Tax有关。我们已经证明，Tax可以激活后期促进复合体/环体（APC/C），这是一种E3泛素连接酶，控制中期到后期的转变和有丝分裂退出。APC/C被Tax激活导致有丝分裂调节因子（包括细胞周期蛋白A、细胞周期蛋白B、securin和Skp2）的过早多泛素化和降解。Skp2是另一种E3泛素连接酶SCFSkp2的底物靶向亚基，可介导细胞周期蛋白E/A-CDK2抑制剂（CKI） p27的破坏。APC/C对Skp2的降解导致SCFSkp2失活和p27稳定。另一种CKI， p21的mRNA水平也由于启动子激活和mRNA稳定而急剧增加。p21和p27的大量增加反过来诱导细胞衰老，称为税收诱导的快速衰老（Tax-IRS）。正如预期的那样，被HTLV-1感染的HeLa和SupT1 T细胞也在衰老中停滞。相比之下，缺乏p21和p27的细胞，如HOS，在HTLV-1感染或表达Tax后逃避了Tax- irs并继续分裂。然而，他们以多核和DNA非整倍体的形式发展出戏剧性的核异常。重要的是，p27的下调和p21的错误定位在表达tax - lv -1转化的T （HTxT）细胞中很常见，并且很可能通过激活PI3K- Akt通路发生。我们的最新研究结果表明，在S/G2期间，税收引起了DNA复制许可因子Cdt1的显著积累。在最近最令人兴奋的发展中，我们发现抑制NF-？B税务激活完全废除了税务- irs。我们的发现提出了几个重要的问题：持续性NF-如何？B活化导致p21/p27上调和衰老？NF -什么?B活化位于APC/C活化和Cdt1积累的上游？由Tax诱导的Cdt1的积累是否会导致DNA再/超复制？它是否可以解释在表达Tax的细胞中所看到的戏剧性的核异常？最后，HTLV-1在SupT1和HeLa细胞中诱导的衰老样阻滞表明，HTLV-1有效感染的原代T细胞也可能发生衰老。如果是这样，那么诱导衰老的病毒是如何引起白血病的呢？html细胞系如何设法适应Tax并继续分裂？为了解决这些问题并阐明HTLV-1感染导致T细胞转化和ATL的途径，提出了三个具体目标：(1)描绘持久性NF-？a对衰老的激活；(2)探讨HTLV和税收诱导的染色体不稳定的原因和生物学效应；(3)阐明细胞适应（转化）Tax和HTLV-1的机制。

DESCRIPTION (provided by applicant): HTLV-I is the causative agent of adult T-cell leukemia/lymphoma (ATL), a malignancy of CD4+ T cells whose etiology is associated with the viral transactivator/oncoprotein, Tax. We have shown that Tax can activate the anaphase promoting complex/cyclosome (APC/C), an E3 ubiquitin ligase that controls metaphase to anaphase transition and mitotic exit. APC/C activation by Tax leads to the premature poly-ubiquitination and degradation of mitotic regulators including cyclin A, cyclin B, securin, and Skp2. Skp2 is the substrate-targeting subunit of another E3 ubiquitin ligase known as SCFSkp2, which mediates the destruction of cyclin E/A-CDK2 inhibitor (CKI), p27. The degradation of Skp2 by APC/C as induced by Tax leads to SCFSkp2 inactivation and p27 stabilization. The mRNA level of another CKI, p21, also increases sharply as a result of promoter activation and mRNA stabilization by Tax. The great surge in p21 and p27 in turn induces cellular senescence termed Tax-induced rapid senescence (Tax-IRS). As expected, HeLa and SupT1 T cells infected by HTLV-1 arrest in senescence as well. By contrast, cells deficient in p21 and p27, such as HOS, escape Tax-IRS and continue to divide after HTLV-1 infection or Tax expression. They, however, develop dramatic nuclear abnormalities in the form of multinucleation and DNA aneuploidy. Importantly, down-regulation of p27 and mis-localization of p21 are common in Tax-expressing HTLV-1-transformed T (HTxT) cells and most likely occur through activation of the PI3K- Akt pathway. Our latest results showed that Tax caused significant accumulation of the DNA replication licensing factor, Cdt1, during S/G2. In a most exciting recent development, we found that inhibition of NF-?B activation by Tax completely abrogated Tax-IRS. Our findings raise several important questions: How does persistent NF-?B activation lead to p21/p27 upregulation and senescence? Does NF-?B activation lie upstream of APC/C activation and Cdt1 accumulation? Does the accumulation of Cdt1 induced by Tax lead to DNA re/hyper-replication and can it explain the dramatic nuclear abnormalities seen in Tax-expressing cells? Finally, the senescence-like arrest induced by HTLV-1 in SupT1 and HeLa cells suggests that primary T cells productively infected by HTLV-1 likely also undergo senescence. If so, then how does a virus that induces senescence cause leukemia? How do HTxT cell lines manage to adapt to Tax and continue to divide? To address these questions and to elucidate the pathway by which HTLV-1 infection leads to T cell transformation and ATL, three specific aims are proposed: (1) to delineate the pathway leading from persistent NF-?B activation by Tax to senescence; (2) to investigate the cause and biological effects of HTLV- and Tax-induced chromosome instability; and (3) to elucidate the mechanisms by which cells become adapted to (transformed by) Tax and HTLV-1. PUBLIC HEALTH RELEVANCE: Human T-lymphotropic virus type I (HTLV-1) infects more than 20 million people world-wide. A significant percentage of infected individuals develop adult T-cell leukemia and a paralytic neurological disease known as HTLV-1-associated myelopathy/tropical spastic paraparesis. This project will elucidate the mechanism by which HTLV-1 infection affects the progression of cell division cycle and how these changes impact on the development of leukemia. The study will provide molecular insights that can lead to the development of treatment strategies for human cancer