Etiology of Translocations in Hematopoietic Cells

描述（由申请人提供）：我研究的长期目标是了解造血特异性发育程序对修复DNA损伤的影响，如双链断裂（dsb）和导致易位的初始分子事件，这是白血病，淋巴瘤和软组织肉瘤的标志。dsb具有高度的重组性，将两个同源DNA双链之间的信息交换提高了几个数量级；因此，哺乳动物细胞在DSB修复过程中可能存在重排的风险。染色体dsb是在暴露于辐射、烷基化剂和拓扑异构酶II （topo异构酶II）抑制剂（人类癌症治疗中的常用疗法）后产生的。包括topoII抑制剂依托泊苷在内的治疗方案与一类治疗相关的急性髓性白血病（t-AML）和染色体易位相关，涉及染色体带11q23上的混合谱系白血病（MLL）基因。t-AML和婴儿白血病中11q23 MLL断点的相似性表明新生婴儿白血病与子宫内暴露于topoII抑制剂之间存在关联。潜在的topo II抑制剂列表很广泛，目前尚不清楚这些化合物中哪些具有直接诱导临床环境中观察到的染色体易位的潜力。使用一个独特的遗传系统来确定11q23 MLL基因和共同伴侣基因的断点簇区域内dsb修复的潜力，从而导致染色体易位，该提议将(1)确定暴露于一系列topoII抑制剂引发MLL和AF9基因断点簇区域内染色体重排的潜力，类似于在临床环境中观察到的情况；(2)创建一个靶向小鼠模型，以确定体内暴露于topoII抑制剂引发MLL和AF9基因断点簇区域内染色体重排的可能性，通过骨髓和外周血中MLL-AF9基因组重排的存在来测量。这些方法在体外细胞培养和体内小鼠模型中都将为潜在致癌染色体重排和白血病发生的起始提供重要的见解。揭示易位的病因和后果可能会导致新的治疗和预防方法。公共卫生相关性：暴露于拓扑异构酶II （topoII）抑制剂与染色体易位有关，涉及染色体带11q23上的混合谱系白血病（MLL）基因，一类治疗相关性急性髓性白血病（t-AML），以及可能在子宫内暴露于topoII抑制剂后新生婴儿白血病。潜在的topo II抑制剂列表很广泛，目前尚不清楚这些化合物中哪些具有直接诱导临床环境中观察到的染色体易位的潜力。我们在体外细胞培养和体内小鼠模型中的方法将为这些致癌染色体易位和白血病发生的开始提供重要的见解，并可能导致新的治疗和预防方法。

DESCRIPTION (provided by applicant): The long-term objective of my research is to understand the influence of hematopoietic-specific developmental programs on the repair DNA damage such as double strand breaks (DSBs) and the initial molecular events that lead to translocations, which are a hallmark of leukemia, lymphoma, and soft-tissue sarcomas. DSBs are highly recombinogenic, increasing the exchange of information between two homologous DNA duplexes by several orders of magnitude; thus, mammalian cells are potentially at risk for rearrangements arising during DSB repair. Chromosomal DSBs result following exposure to irradiation, alkylating agents, and topoisomerase II (topoII) inhibitors that are common therapies in the treatment of human cancers. Treatment regimens that include the topoII inhibitor etoposide are associated with one class of therapy-related acute myeloid leukemia (t-AML) and chromosomal translocations involving the mixed lineage leukemia (MLL) gene on chromosome band 11q23. Similarity of 11q23 MLL breakpoints in t-AML and infant leukemias suggests an association between de novo infant leukemia and in utero exposure to topoII inhibitors. The list of potential topo II inhibitors is extensive, and it remains unclear which of these compounds have a direct potential to induce the chromosomal translocations observed in the clinical setting. Using a unique genetic system to determine the potential for repair of DSBs within the breakpoint cluster regions of the 11q23 MLL gene and common partner genes to result in chromosomal translocations, this proposal will (1) determine the potential for exposure to a range of topoII inhibitors to initiate chromosomal rearrangements within the breakpoint cluster region of the MLL and AF9 genes similar to those observed in the clinical setting; and (2) create a targeted mouse model to determine in vivo the potential for exposure to topoII inhibitors to initiate chromosomal rearrangements within the breakpoint cluster region of the MLL and AF9 genes as measured by the presence of MLL-AF9 genome rearrangements in bone marrow and peripheral blood. These approaches in both ex vivo cell culture and in vivo mouse models will provide significant insight into the initiation of potentially oncogenic chromosomal rearrangements and leukemogenesis. Unraveling the etiology and consequences of translocations may lead to new approaches to therapy and prevention. PUBLIC HEALTH RELEVANCE: Exposure to the topoisomerase II (topoII) inhibitors is associated with chromosomal translocations involving the mixed lineage leukemia (MLL) gene on chromosome band 11q23, one class of therapy-related acute myeloid leukemia (t-AML), and possibly de novo infant leukemias following in utero exposure to topoII inhibitors. The list of potential topo II inhibitors is extensive, and it remains unclear which of these compounds have a direct potential to induce the chromosomal translocations observed in the clinical setting. Our approaches in both ex vivo cell culture and in vivo mouse models will provide significant insight into the initiation of these oncogenic chromosomal translocations and leukemogenesis and may lead to new approaches to therapy and prevention.