Role of Mitotic Checkpoint Defects in Mouse Tumor Models

描述（申请人提供）：生物化学和遗传学实验表明，有丝分裂检查点基因Mad2在后生动物中是有丝分裂检查点装置的重要组成部分。如果所有的染色体没有连接到有丝分裂纺锤体上，Mad2是在细胞中期到后期转变之前阻止细胞的机制的一个组成部分。功能突变的部分丧失使哺乳动物细胞在长潜伏期后易发生染色体错分离事件和肺肿瘤的发生。与低等真核生物不同，在哺乳动物细胞中，Mad2在发育和体细胞中都是必不可少的基因，这使得完全丧失功能在肿瘤进展中不太可能发生。最近的实验表明，由于肿瘤抑制因子Rb的缺失和随之而来的E2F激活而导致的Mad2过表达也可能导致染色体不稳定。在目前的建议中，我们将尝试在小鼠中模拟这些功能增益效应。初步结果表明，Mad2本身过表达可在小鼠中启动肿瘤发生，并在过表达K-ras癌基因的肿瘤易发动物中加速肿瘤发生。染色体不稳定性如何促进疾病的发生和发展将被探讨。这些实验应该允许我们进一步阐明有丝分裂检查点异常在人类疾病中的作用。

DESCRIPTION (provided by applicant): The mitotic checkpoint gene Mad2 has been shown in metazoans to be an important part of the mitotic checkpoint apparatus through biochemical and genetic experiments. Mad2 is a component of the machinery which arrests a cell prior to the metaphase to anaphase transition if all the chromosomes are not attached to the mitotic spindle apparatus. Partial loss of function mutations predisposes mammalian cells to chromosome missegregation events and lung tumor initiation in vivo after long latency. Unlike lower eukaryotes, in mammalian cells Mad2 is an essential gene both during development and in somatic cells making complete loss of function an unlikely event in tumor progression. Recent experiments indicate that overexpression of Mad2 as a result of the loss of the tumor suppressor Rb and consequent E2F activation can also lead to chromosome instability. In the current proposal, we will try to model these gain of function effects in the mouse. Preliminary results indicate that Mad2 overexpression by itself can initiate tumorigenesis in the mouse and accelerate lung tumorigenesis in tumor prone animals overexpressing the K-ras oncogene. How chromosome instability contributes to the initiation and progression of disease will be explored. These experiments should allow us to shed further light on the role of mitotic checkpoint abnormalities in human disease.