Studies of Lymphoma Suppression and DNA Repair

描述(申请人提供)：电离辐射(IR)，由地球上的某些矿物产生，对人类的环境健康构成重大危害，因为它会导致DNA双链断裂(DSB)，这是一种剧毒的DNA损伤，通常会导致基因组不稳定和癌症。众所周知，DSB上的染色体易位可以促进淋巴瘤的发展。然而，对IR和淋巴瘤抑制诱导的修复DNA双链断裂的调控机制的认识仍然存在很大差距。含有泛素结合酶的BIR重复序列(Bruce)是一种具有嵌合泛素蛋白结合酶(E2)和连接酶(E3)活性的保守蛋白质，可催化泛素对蛋白质的翻译后修饰。直到最近，布鲁斯只被证明参与了细胞凋亡抑制、胞质分裂和小鼠胚胎发育。最近，我们的初步研究首次表明，Bruce是淋巴瘤的抑制者和DNA修复途径中的调节蛋白。特别是，我们观察到Bruce小鼠对淋巴瘤敏感，Bruce灭活的细胞在电离辐射后表现出基因组不稳定和未修复的DSB。我们还观察到，Bruce通过调节IR后早期DNA损伤信号蛋白和下游修复蛋白在DSB位置的积累，在DNA修复级联反应的上游发挥作用。此外，Bruce与人类健康有很强的相关性，因为Bruce基因表达水平的降低与人类淋巴瘤有关，也与淋巴瘤患者的低生存率相关。基于这些发现，我们假设Bruce通过促进DNA DSB修复来抑制染色体异常和淋巴肿大。我们提出了两个目的来验证这一假设：(1)确定在我们的杂合子BRUCEWT/C突变小鼠中发生的淋巴瘤的染色体易位，以及它们是否是由于淋巴细胞中程序性和/或一般DSB的受损修复所致。我们还将通过分析人类淋巴瘤组织阵列来确定Bruce蛋白水平降低是否与淋巴瘤的发生有关。(2)确定Bruce调控修复蛋白进入DSB位点的机制及其在同源重组(HR)和非同源末端连接(NHEJ，经典和替代)DSB修复途径中的意义。这项拟议的工作意义重大，因为它将是布鲁斯是淋巴瘤抑制因子和DNA修复调节蛋白的第一个迹象。这项工作也具有创新性，因为它从未预料到，甚至没有猜测，抗凋亡蛋白Bruce可以调节DNA修复和肿瘤抑制。它通过将布鲁斯置于当前泛素调控途径的上游，挑战了当前的泛素范式。这些结果有望为开发能够调节Bruce水平和/或活性的新型药物奠定基础，以创新地干预淋巴瘤和其他由DNA修复缺陷引起的相关疾病。

DESCRIPTION (provided by applicant): Ionizing radiation (IR), produced by certain minerals in the Earth, represents a major environmental health hazard to man because it causes DNA double-strand breaks (DSBs), highly toxic DNA lesions that often result in genome instability and cancer. It is well established that chromosomal translocations at DSBs can promote lymphoma development. However, there still remains a significant gap in the knowledge of regulatory mechanisms of the repair DNA DSBs induced by IR and lymphoma suppression. The BIR repeat containing ubiquitin-conjugating enzyme (BRUCE) is a conserved protein with chimeric ubiquitin-protein conjugase (E2) and ligase (E3) activities that catalyze post-translational modification of proteins by ubiquitin. Until recently, BRUCE has only been shown to be involved in apoptosis inhibition, cytokinesis, and mouse embryogenesis. Recently, our preliminary studies provide the first indication that BRUCE is a suppressor of lymphoma and a regulatory protein in DNA-repair pathways. In particular, we observed that BRUCE mice are susceptible to lymphomas, and that cells with BRUCE inactivated display genomic instabilities and unrepaired DSBs following ionizing radiation. We also observed that BRUCE acts at a step upstream in DNA-repair cascade by regulating the accumulation, at the site of the DSB, of early DNA-damage signaling proteins and downstream repair proteins following IR. Furthermore, BRUCE has strong relevance to human health in that a reduction in the level of BRUCE gene expression is associated with human lymphomas and also correlates with low survival of lymphoma patients. Based on these findings, we hypothesize that BRUCE suppresses chromosomal abnormalities and lymphomagenesis by promoting DNA DSB repair. We propose two aims to test this hypothesis: (1) To determine chromosomal translocations in lymphomas developed in our heterozygous BRUCEWT/C mutant mice, and whether they are resulted from compromised repair of programmed and/or general DSBs in lymphocytes. We will also determine whether reduced levels of BRUCE protein are associated with lymphoma development by analyzing human lymphoma tissue array. (2) To determine the mechanism by which BRUCE regulates access of repair proteins to the sites of DSB and its implication in DSB-repair pathways of homologous recombination (HR) and non-homologous end joining (NHEJ, both classic and alternative). This proposed work is significant because it will be the first indication that BRUCE is a suppressor of lymphoma and a regulatory protein in DNA repair. This work is also innovative because it has never been expected or even speculated that BRUCE, an anti-apoptosis protein, could regulate DNA repair and tumor suppression. It challenges the current ubiquitin paradigm by placing BRUCE upstream of the current ubiquitin regulatory pathway. These results are expected to lay the groundwork for developing novel agents capable of modulating the level and/or the activity of BRUCE for innovative intervention of lymphoma other related diseases resulting from faulty DNA repair.