Studies of Lymphoma Suppression and DNA Repair

描述（由申请人提供）：地球上某些矿物质产生的电离辐射（IR）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（DSBs），这是一种高毒性DNA损伤，通常会导致基因组不稳定和癌症。dsb的染色体易位可以促进淋巴瘤的发展。然而，对于IR和淋巴瘤抑制诱导的修复DNA dsb的调控机制仍存在很大的空白。含有泛素偶联酶（BRUCE）的BIR重复序列是一种具有嵌合泛素偶联酶（E2）和连接酶（E3）活性的保守蛋白，可催化泛素对蛋白质的翻译后修饰。直到最近，BRUCE仅被证明参与细胞凋亡抑制、细胞分裂和小鼠胚胎发生。最近，我们的初步研究首次表明BRUCE是淋巴瘤的抑制因子和dna修复途径的调节蛋白。特别是，我们观察到BRUCE小鼠易患淋巴瘤，并且BRUCE灭活的细胞在电离辐射后表现出基因组不稳定性和未修复的dsb。我们还观察到，BRUCE通过调节早期dna损伤信号蛋白和IR后下游修复蛋白在DSB位点的积累，在dna修复级联的上游发挥作用。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有关。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瘤的发生。我们提出了两个目的来验证这一假设：(1)确定BRUCEWT/C杂合突变小鼠淋巴瘤的染色体易位，以及它们是否由淋巴细胞中程序性和/或一般dsb的修复受损引起。我们还将通过分析人类淋巴瘤组织阵列来确定BRUCE蛋白水平的降低是否与淋巴瘤的发展有关。(2)确定BRUCE调控修复蛋白进入DSB位点的机制及其在DSB修复途径的同源重组（HR）和非同源末端连接（NHEJ，经典和替代）中的意义。这项工作具有重要意义，因为它将首次表明BRUCE是淋巴瘤的抑制因子和DNA修复的调节蛋白。这项工作也是创新的，因为它从来没有预料到甚至推测布鲁斯，一种抗凋亡蛋白，可以调节DNA修复和肿瘤抑制。它通过将BRUCE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，用于创新性地干预由DNA修复缺陷引起的淋巴瘤和其他相关疾病。

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. PUBLIC HEALTH RELEVANCE: The proposed research is relevant to public health because the discovery of novel regulatory mechanisms for lymphoma suppression and for ionizing radiation-induced DNA damage repair are ultimately expected to improve our understanding of the pathology and etiology of lymphoma and of other malignancies in general. Therefore, the proposed work is relevant to the part of NIH's mission for opening new avenues for developing therapeutic strategies aimed at eliminating lesions that lead to the initiation, maintenance, and progression of cancer.