Study DNA repair in preventing MDS and AML after radiation and benzene exposure

描述(申请人提供)：骨髓增生异常综合征(MDS)是一组以血细胞功能障碍为特征的疾病，可发展为急性髓系白血病(AML)。目前，MDS发展和进展为AML的病因尚不清楚，也没有治愈方法(确诊时的中位生存期不到5年)。然而，DNA损伤和突变似乎在造血干细胞(HSC)的启动缺陷中发挥了关键作用。在支持方面，患有某些DNA修复缺陷综合征的人，包括范科尼贫血(FA)和布卢姆综合征(BS)，表现出MDS。有趣的是，FA和BS是机械相关的，因为BS蛋白与FA途径中的蛋白质结合，并且都通过同源重组(HR)途径影响DNA双链断裂(DSB)的修复。此外，一些DNA损伤剂似乎使人们容易患上MDS/AML，包括辐射和苯。这两种物质都会导致染色体异常和HR修复？--辐射诱导的双链断裂。此外，另一种DSB修复途径，非同源末端连接(NHEJ)可能通过促进染色体易位而促进MDS/AML的进展。因此，DNA损伤和DNA修复似乎是MDS/AML病因学中不可或缺的因素。这项提议是两个实验室之间的合作，这两个实验室在MDS/AML(Rebel博士的实验室)和DNA损伤/修复(Hasty博士的实验室)方面拥有专业知识。Rebel博士在CREBBP基因缺陷的小鼠模型中研究了MDS/AML。CREBBP是一种转录辅活化子，CREBBP缺陷小鼠总是随着年龄的增长而发展为MDS，通常进展为AML。重要的是，这些小鼠在修复辐射诱导的DNA断裂方面存在缺陷，并在胎肝细胞中表现出较高的突变水平。因此，Rebel博士对CREBBP缺陷小鼠的分析支持了对患者的观察，即DNA损伤和DNA修复缺陷是MDS/AML的致病因素。因此，假设全功能HR对于抑制MDS/AML对引起DSB的基因毒素至关重要，而NHEJ则产生导致MDS/AML的染色体易位。针对这一假设，本文提出了两个具体的目标。CREBBP缺陷的小鼠胚胎干细胞(特异性目标1)和小鼠(目标2)将被研究修复辐射和苯诱导的DNA损伤的动力学，以及MDS的发展和向AML的进展。预计这将使人们更好地了解DNA损伤/修复在疾病进展中所起的作用，这些基因毒素对包括造血干细胞在内的各种骨髓细胞的影响，以及暴露在危险环境中的时间(胚胎发育与成人)。因此，这一建议的结果将阐明MDS/AML的病理生物学。 公共卫生相关性：骨髓增生异常综合征(MDS)是一种白血病前期骨髓疾病，可能进展为急性髓系白血病(AML)。遗传不稳定可能促进这种疾病的每个阶段，启动事件发生在HSC中；因此，已知的导致遗传不稳定的环境基因毒素和DNA修复缺陷可能导致MDS/AML。这项建议的目的是阐明DNA修复和基因组不稳定在这种鲜为人知的疾病的病因学中所起的作用。

DESCRIPTION (provided by applicant): Myelodysplastic syndrome (MDS) is a group of disorders characterized by dysfunctional blood cells that can progress to acute myeloid leukemia (AML). At this time the etiology of MDS development and progression to AML is not understood and there is no cure (median survival at time of diagnosis is less than 5 years). Yet, DNA damage and mutations appear to play a key role with the initiating defect in a hematopoietic stem cell (HSC). In support, people with certain DNA repair defective syndromes including Fanconi anemia (FA) and Bloom syndrome (BS) exhibit MDS. Interestingly, FA and BS are mechanistically related since the BS protein associates with proteins in the FA pathway and since both influence the repair of DNA double-strand breaks (DSBs) through the homologous recombination (HR) pathway. In addition, some DNA damaging agents appear to predispose people to MDS/AML including ?-radiation and benzene. Both of these agents cause chromosomal abnormalities and HR repairs ?-radiation-induced DSBs. Furthermore, another DSB repair pathway, nonhomologous end joining (NHEJ) may enable the progression of MDS/AML by facilitating chromosomal translocations. Thus, DNA damage and DNA repair appear to be integral factors in the etiology of MDS/AML. This proposal is a collaboration between two labs with expertise in MDS/AML, (Dr. Rebel's lab) and DNA damage/repair (Dr. Hasty's lab). Dr. Rebel has studied MDS/AML in a Crebbp-deficient mouse model. Crebbp is a transcriptional coactivator and Crebbp-deficient mice invariably develop MDS with age that often progress to AML. Importantly, these mice are defective for repairing ?-radiation-induced DNA breaks and exhibit elevated mutation levels in fetal liver cells. Thus, Dr. Rebel's analysis on Crebbp-deficient mice support observations made on patients that DNA damage and defects in DNA repair are causal factors in MDS/AML. Therefore, the hypothesis is that fully functional HR is critical for suppressing MDS/AML in response to genotoxins that cause DSBs while NHEJ generates chromosomal translocations that cause MDS/AML. Two specific aims are presented to address the hypothesis. Crebbp-deficient mouse embryonic stem (ES) cells (Specific Aim 1) and mice (aim 2) will be investigated for the dynamics of repairing ?-radiation- and benzene-induced DNA lesions and the development of MDS and progression to AML. It is anticipated that this will lead to a better understanding of the role that DNA damage/repair plays in disease progression, the impact these genotoxins have on a variety of bone marrow cells including HSCs and vulnerable times of exposure (embryonic development vs. adult). Thus, results from this proposal will elucidate the pathobiology of MDS/AML. PUBLIC HEALTH RELEVANCE: Myelodysplastic syndrome (MDS) is a pre-leukemic bone marrow disorder that may progress to acute myeloid leukemia (AML). Genetic instability likely facilitates each stage of this disease with the initiating event occurring in a HSC; therefore, environmental genotoxins and defective DNA repair that are known to cause genetic instability could enable MDS/AML. The goal of this proposal is to elucidate the role DNA repair and genomic instability play in the etiology of this poorly understood disease.