A Novel Oncogenic Role for Cdc20 Implications in Adult T Cell Leukemia Treatment

描述（由申请人提供）：已在多种人类癌症中观察到Cdc 20的过表达或超活化。在成人T细胞白血病（ATL）患者中，病毒癌蛋白Tax部分通过激活APCCdc 20（一种关键的M期驱动因子）促进细胞转化，以增强增殖，并如本研究中所提出的，逃避凋亡。该提案的目的是揭示APCCdc 20泛素E3连接酶复合物在允许癌细胞逃避化疗药物诱导的细胞凋亡中的新的致癌作用，从而促进白血病发生并赋予多药耐药性。我的初步数据显示，当Cdc 20最活跃时，促凋亡蛋白Bim的蛋白水平在M期较低。此外，Bim蛋白丰度，但不是mRNA水平显着升高，在多个细胞系内源Cdc 20耗尽后。进一步的研究表明，Cdc 20直接结合Bim，并促进其泛素化和随后的26 S蛋白酶体降解。引人注目的是，Bim表达在Cdc 20活性升高的人T细胞嗜酸性病毒I型（HTLV-I）感染的T细胞系中显著低，并且这些细胞始终对各种抗有丝分裂剂和DNA损伤剂具有抗性。在这个提议中，我假设Cdc 20依赖性抑制Bim是ATL细胞逃避凋亡的关键，特别是在治疗药物的挑战下。因此，抑制Cdc 20活性或引入BH 3-模拟试剂可以在体外和体内使ATL细胞对常规化疗药物敏感。在这个提议中，我计划：1）将APCCdc 20表征为负调节Bim稳定性的上游E3连接酶; 2）确定APCCdc 20激活在抑制细胞凋亡中的生理作用; 3）确定靶向抑制Cdc 20或引入BH 3模拟物是否抑制ATL或其他Cdc 20过表达癌症（包括头颈癌）的体内发展。我职业生涯的长期目标是应用分子和细胞生物学的见解来理解在人类恶性肿瘤发展中重要的失调蛋白水解途径的生理意义，并寻找适当的药物靶点。这个K99/R 00奖将为我提供受保护的时间来追求这个提案的新假设，获得新的技能来执行实验和解决问题。此外，该奖项将使我能够专注于独立开展基础和转化研究，并培养未来的年轻科学家。

DESCRIPTION (provided by applicant): Overexpression or hyper-activation of Cdc20 has been observed in a variety of human cancers. In adult T-cell leukemia (ATL) patients, the viral oncoprotein Tax promotes cellular transformation in part through activating APCCdc20, a critical M phase driver, to enhance proliferation, and as proposed in this study, to evade apoptosis. The goal of this proposal is to uncover a novel oncogenic role of the APCCdc20 ubiquitin E3 ligase complex in allowing cancer cells to evade chemotherapeutic agents-induced cellular apoptosis, thereby promoting leukemia-genesis and conferring multidrug resistance. My preliminary data showed that the protein levels of the pro-apoptotic protein, Bim, were low in M phase when Cdc20 is most active. Moreover, Bim protein abundance but not mRNA level was significantly elevated in multiple cell lines after depletion of endogenous Cdc20. Further studies revealed that Cdc20 directly binds to Bim and promotes its ubiquitination and subsequent degradation by the 26S proteasome. Strikingly, Bim expression is remarkably low in Human T-cell Lymphotropic Virus type I (HTLV-I)-infected T cell lines with elevated Cdc20 activity, and consistently, these cells are resistant to various anti-mitotic and DNA damage agents. In this proposal, I hypothesize that Cdc20- dependent repression of Bim is critical for ATL cells to evade apoptosis, especially under the challenge of therapeutic drugs. Therefore, inhibiting Cdc20 activity or introducing BH3-mimetic reagents could sensitize ATL cells to conventional chemotherapeutic drugs both in vitro and in vivo. In this proposal, I plan to: 1) Characterize APCCdc20 as an upstream E3 ligase that negatively regulates Bim stability; 2) Determine the physiological role of APCCdc20 activation in suppressing apoptosis; 3) Determine whether targeted inhibition of Cdc20 or introducing BH3-mimetic suppresses the development of ATL or other Cdc20-overexpressing cancer including head and neck cancer in vivo. The long-term goals of my career are to apply the insights of molecular and cellular biology to understand the physiological significance of deregulated proteolytic pathways that are important in the development of human malignancies, and to search for proper druggable targets. This K99/R00 award will provide protected time for me to pursue the novel hypotheses of this proposal, obtain new skill sets to execute experiments and solve problems. In addition, the award will allow me to focus my efforts on independently conducting basic and translational research, and to train future young scientists.