Study the Role of Chfr in Tumorigenesis

描述（由申请人提供）：遗传物质DNA在细胞中被包装并组织成染色体。染色体数目的异常或染色体结构或组织的改变会引起包括癌症在内的人类疾病。许多有丝分裂检查点途径在细胞中进化以维持染色体稳定性。近十年来的研究强调了纺锤体组装检查点在维持染色体稳定性中的重要性。虽然纺锤体检查点在这一过程中显然起着关键作用，但在癌症中并不经常观察到纺锤体检查点组分的突变或失调，这表明肿瘤相关的不稳定性可能由其他缺陷引起。 这些缺陷之一可能是Chfr下调，这在许多类型的癌症中反复观察到。具有FHA和RING结构域的检查点蛋白（Chfr）参与早期有丝分裂检查点。它由RING结构域组成，并作为E3泛素连接酶发挥功能。在上一个资助期间，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。此外，我们发现Chfr的主要功能是调节几个关键有丝分裂蛋白的稳定性，包括Aurora A和PLK 1。我们目前的工作假设是，Chfr通常在G1，S和G2期发挥作用，但在有丝分裂中特异性下调。Chfr的功能是防止许多关键的有丝分裂调节剂在进入有丝分裂之前过早积累。在缺乏Chfr的情况下，可能由于这些Chfr底物的不合时宜的上调，细胞将经历异常的有丝分裂转变，这导致染色体不稳定性的频率较低，从而促进肿瘤发生。因此，Chfr底物的鉴定和对有丝分裂中Chfr下调的理解将揭示Chfr如何在体内正常发挥作用以防止肿瘤的发生。 我们最近确定了一个潜在的有丝分裂激酶TOPK作为Chfr底物。此外，我们证明了Chfr缺陷极大地促进了MLH 1缺陷小鼠的肿瘤发生，这表明Chfr缺陷引起的染色体不稳定性可能与错配修复缺陷引起的微卫星不稳定性协同作用，以促进肿瘤发生。基于这些初步研究，我们拟：（1）研究Chfr与TOPK在有丝分裂中的功能相互作用;（2）探讨TOPK是否平衡调控 表达对于维持染色体稳定性和肿瘤抑制至关重要;（3）确定由Chfr下调引起的染色体不稳定性是否与肿瘤起始中的错配修复缺陷协同作用。

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.