ATM FUNCTION DURING V(D)J RECOMBINATION

描述（由申请人提供）：编码ATM丝氨酸-苏氨酸激酶的基因突变导致共济失调毛细血管扩张症（a -t），这是一种以淋巴细胞减少和淋巴样肿瘤发生率增加为特征的疾病，易位涉及抗原受体位点，表明ATM在V(D)J重组过程中起作用。ATM激活细胞周期检查点响应DNA双链断裂（DSBs）。然而，在检查点通路中存在孤立缺陷的小鼠中，A-T的淋巴样表型并没有重现。我们已经证明，ATM可以修复V(D)J重组过程中产生的dsb，并抑制这些dsb作为染色体易位的异常分解。检查点通路和DSB修复的联合缺陷解释了A-T的一些淋巴样表型。鉴于在ATM缺陷淋巴细胞中观察到的所有V(D)J重组缺陷，我们提出ATM的部分功能是在rag介导的DNA切割后维持DSB复合物的稳定性，这是一种假设，将在Specific Aim One中直接验证。虽然ATM可以直接作用于rag介导的dsb修复，但我们预计ATM可能会磷酸化执行该功能的蛋白。在这方面，我们表明MRN复合体（Mre11， Rad50和Nbs1）， 53BP1和H2AX，它们都是ATM的靶点，在对rag介导的dsb的反应中起作用。这些蛋白如何在RAG-DSB修复的atm依赖途径中发挥作用将在特异性目标2中阐明。此外，我们将考虑RAG蛋白在V(D)J重组反应的连接步骤中可能具有atm依赖功能的可能性。重要的是，我们相信这些不同的蛋白质将以一种综合的方式在atm依赖的RAG-DSB修复途径中起作用。最后，我们将研究在atm缺陷细胞中V(D)J重组过程中产生的DNA dsb作为染色体易位异常分解的机制（Specific Aim 3）。这些目标的完成将为以下方面提供重要的新信息：1)rag介导的dsb如何修复；2) ATM在DSB修复和维持基因组稳定性中的作用；3)促进染色体易位形成的机制。

DESCRIPTION (provided by applicant): Mutations in the gene encoding the ATM serine-threonine kinase cause Ataxia Telangiectasia (A-T), a disease marked by lymphopenia and an increased incidence of lymphoid tumors with translocations involving antigen receptor loci, suggesting that ATM functions during V(D)J recombination. ATM activates cell cycle checkpoints in response to DNA double strand breaks (DSBs). However, the lymphoid phenotypes of A-T are not recapitulated in mice with isolated deficiencies in checkpoint pathways. We have demonstrated that ATM functions to repair DSBs generated during V(D)J recombination, and to suppress the aberrant resolution of these DSBs as chromosomal translocations. The combined defect in checkpoint pathways and DSB repair explains some of the lymphoid phenotypes of A-T. Given all of the defects in V(D)J recombination observed in ATM-deficient lymphocytes, we have proposed that ATM functions, in part, to maintain the stability of DSB complexes after RAG-mediated DNA cleavage, which is a hypothesis that will be directly tested in Specific Aim One. Although ATM could function directly in the repair of RAG-mediated DSBs, we expect that ATM will likely phosphorylate proteins that perform this function. In this regard we show that the MRN complex (Mre11, Rad50 and Nbs1), 53BP1 and H2AX, which are all targets of ATM, function in the response to RAG-mediated DSBs. How these proteins function in the ATM-dependent pathway of RAG-DSB repair will be elucidated in Specific Aim Two. In addition, we will consider the possibility that the RAG proteins may have ATM-dependent functions in the joining step of the V(D)J recombination reaction. Importantly, we believe that these different proteins will function in an integrated manner in the ATM-dependent RAG-DSB repair pathway. Finally, we will investigate the mechanisms by which DNA DSBs generated during V(D)J recombination in ATM-deficient cells become aberrantly resolved as chromosomal translocations (Specific Aim 3). The completion of these aims will provide important new information about: 1) how RAG-mediated DSBs are repaired; 2) how ATM functions in DSB repair and in maintaining genomic stability; and 3) the mechanisms that promote the formation of chromosomal translocations.