CDC25 PHOSPHATASES IN CELL CYCLE CONTROL AND CANCER

描述（由申请人提供）：Cdc 25磷酸酶通过激活Cdks正向调节细胞周期。在哺乳动物中，存在三个家族成员，分别表示为Cdc 25 A、Cdc 25 B和Cdc 25 C。目前尚不清楚为什么高等真核生物编码三个Cdc 25，而酵母细胞则只编码一个。产生可缺失Cdc 25 A的小鼠。此外，产生了缺乏Cdc 25 B、Cdc 25 C或两者的小鼠，并且也可以有条件地缺失Cdc 25 A。这些小鼠将用于确定Cdc 25家族成员对成体细胞周期的贡献。该提案的另一个目标是利用高通量和分子成像策略来鉴定Cdc 25 A的新型调节剂。Cdc 25 A在整个细胞周期中起作用以调节细胞周期转换，并且Cdc 25 A在几种癌症中过量产生。Cdc 25 A的活性、稳定性以及与其他蛋白质的相互作用受可逆磷酸化的调节。因此，确定调节Cdc 25 A的蛋白激酶将提供对Cdc 25 A在正常和应激条件下如何调节以及导致Cdc 25 A过度生产的途径在人类癌症中脱轨的见解。最后，实验提出了研究一种新的调节途径，涉及ATR，Chk 1和PP 2A和Chk 1和Cdc 25 A之间的相互作用在小鼠中进行调查。除了推进我们对基本细胞周期原理的理解外，这些研究也具有临床影响。例如，Cdc 25 A和Cdc 25 B在许多人类癌症中过量产生，并且正在努力开发可用于治疗人类癌症的Cdc 25抑制剂。在Cdc 25抑制剂进入临床之前，需要评估Cdc 25抑制的细胞毒性。本研究计划中的基因敲除研究将评估成年小鼠中Cdc 25家族成员丢失的影响，并可能预测患者对整体与个体Cdc 25抑制的反应。目前用于治疗癌症患者的另一种策略是将联合收割机DNA损伤剂与诱导Cdc 25 A积累的药物组合。在临床前模型中，这种策略诱导检查点绕过和p53缺陷细胞的优先杀伤。Chk 1抑制剂UCN-01正在I期和II期临床试验中与DNA损伤剂一起进行测试。因此，在我们的研究过程中鉴定的PP 2A/Chk 1通路的新型激酶和/或调节剂是潜在的可药用靶标。靶向这些途径的组分的抑制剂可以替代上述联合治疗中的Chk 1抑制剂。希望这些抑制剂可能比Chk 1抑制剂诱导更少的基因组不稳定性。公共卫生相关性：实验提出充分解剖PP 2A/Chk 1/Cdc 25 A调节途径的分子基础，并在小鼠中的Cdc 25磷酸酶的功能特征。从拟议的研究中获得的信息预计不仅会增强我们对哺乳动物细胞周期控制基本原理的理解，而且还将直接影响未来的癌症治疗策略。

DESCRIPTION (provided by applicant): The Cdc25 phosphatases positively regulate the cell cycle by activating Cdks. In mammals, three family members, denoted Cdc25A, Cdc25B, and Cdc25C, exist. It is unclear why higher eukaryotic organisms encode three Cdc25s while yeast cells survive with one. Mice that can be deleted for Cdc25A were generated. In addition, mice lacking Cdc25B, Cdc25C or both and that can also be conditionally deleted for Cdc25A were generated. These mice will be used to determine the contributions made by Cdc25 family members to adult cell cycles. Another goal of this proposal is to utilize high throughput and molecular imaging strategies to identify novel regulators of Cdc25A. Cdc25A functions throughout the cell cycle to regulate cell cycle transitions and Cdc25A is overproduced in several cancers. Cdc25A activity, stability and interactions with other proteins are regulated by reversible phosphorylation. Thus, identifying the protein kinases that regulate Cdc25A will provide insight into how Cdc25A is regulated under normal and stressed conditions and what pathways leading to Cdc25A overproduction are derailed in human cancers. Finally, experiments are proposed to study a novel regulatory pathway involving ATR, Chk1 and PP2A and to investigate interactions between Chk1 and Cdc25A in mice. In addition to advancing our understanding of basic cell cycle principles, these studies have clinical impact as well. For example, Cdc25A and Cdc25B are overproduced in many human cancers and efforts are underway to develop Cdc25 inhibitors that can be used to treat human cancers. The cytotoxicity of Cdc25 inhibition needs to be assessed before Cdc25 inhibitors can proceed to the clinic. The gene knockout studies proposed in this grant will assess effects of loss of Cdc25 family members in adult mice and may predict how patients will respond to global versus individual Cdc25 inhibition. Another strategy that is currently being used to treat cancer patients is to combine DNA damaging agents with drugs that induce Cdc25A accumulation. In preclinical models, this strategy induces checkpoint bypass and preferential killing of p53-deficient cells. The Chk1 inhibitor UCN-01 is being tested with DNA damaging agents in Phase I and II clinical trials. Thus, the novel kinases and/or regulators of the PP2A/Chk1 pathway identified in the course of our studies are potential druggable targets. Inhibitors that target components of these pathways could substitute for Chk1 inhibitors in the combination therapy described above. The hope is that these inhibitors may induce less genome instability than Chk1 inhibitors. PUBLIC HEALTH RELEVANCE: Experiments are proposed to fully dissect the molecular underpinnings of the PP2A/Chk1/Cdc25A regulatory pathway and to functionally characterize the Cdc25 phosphatases in mice. The information gained from the proposed studies is expected not only to enhance our understanding of basic principles of cell cycle control in mammals but is also expected to directly impact future therapeutic strategies for cancer treatment.