Chromosome instability resulting from double-strand breaks near telomeres

描述（由申请方提供）：已知哺乳动物细胞暴露于电离辐射会诱导染色体不稳定性（CIN），这会促进导致癌症的遗传变化的快速积累。我们已经证明，发生在染色体末端附近的DSB，称为端粒，可以通过引起姐妹染色单体融合，启动断裂/融合/桥（B/F/B）循环来促进CIN。B/F/B循环发生在融合的姐妹染色单体在分裂后期断裂时，因为它们的着丝粒被拉向相反的方向。因为断裂不会发生在渗出部位，一个子细胞获得一条末端有反向重复的染色体，而另一个子细胞的染色体末端缺失。然后在随后的细胞周期中重复该循环，导致进一步的基因扩增和大的末端缺失。B/F/B循环一直持续到染色体获得一个新的端粒，我们已经证明这可以通过多种机制发生。最常见的机制之一是非相互易位，这导致不稳定性转移到染色体捐赠易位由于其端粒的损失。因此，端粒附近的单个DSB可导致多条染色体的不稳定性。这项建议有两个具体目标。在第一个具体的目标，我们将解决的假设，姐妹染色单体融合导致的DBS端粒附近的非同源末端连接（NHEJ）端粒附近的缺陷，如已被证明在酵母。对于这些研究，我们将使用等基因细胞系创建测定系统，以比较NHEJ在距离端粒不同距离处发生的DSB处的效率。我们还将使用该检测系统来解决NHEJ和姐妹染色单体融合中涉及的修复蛋白的差异，这已被提出涉及微同源介导的同源重组修复。在第二个具体的目标，我们将解决的假设，p53和Rb蛋白参与复制衰老是重要的，在预防CIN由于DSB诱导的端粒丢失。此外，我们将建立一个使用绿色荧光蛋白监测B/F/B循环持续时间的遗传筛选，以鉴定可阻止B/F/B循环的其他蛋白质。这些研究很重要，因为它们将为癌症中染色体不稳定性的机制提供新的见解，并为开发预防癌细胞CIN的疗法提供新的方法。

DESCRIPTION (provided by applicant): Exposure of mammalian cells to ionizing radiation is known to induce chromosome instability (CIN), which can promote the rapid accumulation of genetic changes leading to cancer. We have demonstrated that DSBs occurring near the ends of chromosomes, called telomeres, can promote CIN by causing sister chromatid fusions that initiate breakage/fusion/bridge (B/F/B) cycles. B/F/B cycles occur when fused sister chromatids break during anaphase as their centromeres are pulled in opposite directions. Because breakage does not occur at the site effusion, one daughter cell acquires a chromosome with an inverted repeat at its end, while the other has a chromosome with a terminal deletion. This cycle is then repeated in subsequent cell cycles, resulting in further gene amplification and large terminal deletions. B/F/B cycles continue until the chromosome acquires a new telomere, which we have shown can occur by multiple mechanisms. One of the most common mechanisms is nonreciprocal translocation, which results in the transfer of instability to the chromosome donating the translocation due to the loss of its telomere. As a result, a single DSB near a telomere can result in the instability in multiple chromosomes. This proposal has two specific aims. In the first specific aim, we will address the hypothesis that sister chromatid fusions resulting from DBSs near telomeres result from a deficiency in nonhomologous end joining (NHEJ) near telomeres, as has been demonstrated in yeast. For these studies, we will create an assay system using isogenic cell lines to compare the efficiency of NHEJ at DSBs occurring at various distances from a telomere. We will also use this assay system to address differences in the repair proteins involved in NHEJ and sister chromatid fusion, which has been proposed to involve microhomology-mediated homologous recombinational repair. In the second specific aim, we will address the hypothesis that the p53 and Rb proteins involved in replicative senescence are important in preventing CIN due to DSB-induced telomere loss. In addition, we will establish a genetic screen using green fluorescent protein to monitor the duration of B/F/B cycles to identify additional proteins that can prevent B/F/B cycles. These studies are important in that they will provide new insights into mechanisms of chromosome instability in cancer and lead to new approaches for the development of therapies for preventing CIN in cancer cells.