Study the Role of Chfr in Tumorigenesis

描述(申请人提供)：遗传物质DNA被包装并组织成细胞中的染色体。染色体数量的异常或染色体结构或组织的变化会导致包括癌症在内的人类疾病。许多有丝分裂检查点通路在细胞中进化以维持染色体的稳定性。过去十年的研究强调了纺锤体组装检查点在维持染色体稳定性方面的重要性。尽管纺锤体检查点显然在这一过程中起着关键作用，但纺锤体检查点组件的突变或失调在癌症中并不常见，这表明肿瘤相关的不稳定性可能是其他缺陷造成的。这些缺陷之一可能是Chfr下调，这在许多类型的癌症中已经反复观察到。带有FHA和RING结构域的检查点蛋白(Chfr)参与了早期有丝分裂检查点的形成。它由一个环状结构域组成，功能类似于E3泛素连接酶。在上一次资助期间，我们建立了Chfr基因敲除小鼠，并直接证明了Chfr作为肿瘤抑制因子发挥作用。此外，我们还发现，Chfr的主要功能是调节包括Aurora A和PLK1在内的几个关键有丝分裂蛋白的稳定性。我们目前的工作假设是，Chfr正常作用于G1、S和G2期，但在有丝分裂中特别下调。Chfr的功能是防止许多关键的有丝分裂调节因子在有丝分裂进入之前过早积累。在缺乏Chfr的情况下，可能由于这些Chfr底物的不及时上调，细胞将经历异常的有丝分裂转变，导致染色体不稳定的频率较低，从而促进肿瘤的发生。因此，对CHFR底物的鉴定和对CHFR在有丝分裂中下调表达的理解将揭示CHFR在体内如何正常作用以防止肿瘤的发生。我们最近发现了一个潜在的有丝分裂激酶TOPK作为Chfr底物。此外，我们还证明了ChfR缺陷极大地促进了MLH1缺陷小鼠的肿瘤发生，提示ChfR缺陷引起的染色体不稳定可能与错配修复缺陷引起的微卫星不稳定协同促进肿瘤的发生。在这些初步研究的基础上，我们建议：(1)研究CHFR和TOPK在有丝分裂中的功能相互作用；(2)探索TOPK的平衡调控 基因表达对于维持染色体稳定和抑制肿瘤至关重要；(3)确定CHFR下调引起的染色体不稳定性是否与错配修复缺陷在肿瘤启动过程中协同作用。

DESCRIPTION (provided by applicant): The genetic material DNA is packaged and organized into chromosomes in cells. Abnormal numbers of chromosomes or changes in chromosomal structures or organizations will cause human diseases including cancers. Many mitotic checkpoint pathways are evolved in the cell to maintain chromosomal stability. Studies in the last decade have highlighted the importance of spindle assembly checkpoint in the maintenance of chromosomal stability. While spindle checkpoint clearly plays a critical role in this process, mutations or dysregulations of spindle checkpoint components are not frequently observed in cancers, suggesting that tumor-associated instability could result from other deficiencies. One of these deficiencies is likely to be Chfr downregulation, which has been repeatedly observed in many types of cancers. Checkpoint protein with FHA and RING domains (Chfr) is involved in early mitotic checkpoint. It comprises of a RING domain and functions as an E3 ubiquitin ligase. During the last funding period, we have established Chfr knockout mice and demonstrated directly that Chfr acts as tumor suppressor. In addition, we showed that the major function of Chfr is to regulate the stability of several key mitotic proteins including Aurora A and PLK1. Our current working hypothesis is that Chfr normally acts throughout G1, S and G2 phases, but is specifically downregulated in mitosis. The function of Chfr is to prevent premature accumulation of many key mitotic regulators before the entry of mitosis. In the absence of Chfr and probably due to untimely upregulation of these Chfr substrates, cells would undergo abnormal mitotic transitions, which result in low frequency of chromosomal instability and thus promote tumorigenesis. Therefore, the identification of Chfr substrates and the understanding of Chfr downregulation in mitosis will reveal how Chfr normally act to prevent tumor initiation in vivo. We recently identified a potential mitotic kinase TOPK as a Chfr substrate. In addition, we demonstrated that Chfr deficiency greatly promoted tumorigenesis in MLH1-deficient mice, suggesting that chromosomal instability caused by Chfr deficiency may synergize with microsatellite instability caused by mismatch repair deficiency to facilitate tumorigenesis. Based on these preliminary studies, we propose to: (1) Study the functional interaction between Chfr and TOPK in mitosis; (2) Explore whether balanced regulation of TOPK expression is critical for the maintenance of chromosomal stability and tumor suppression; (3) Determine whether chromosomal instability caused by Chfr downregulation cooperates with mismatch repair deficiency in tumor initiation.