The molecular and genetic dissection of DNA damage response using cellular and animal models

DNA损伤反应途径中的关键组分如ATM、ATR、MRE 11和NBS 1的突变分别引起共济失调-毛细血管扩张症（A-T）、Seckel综合征、A-T样障碍（A-T）和奈梅亨断裂综合征（NBS）。这些疾病的主要症状重叠，包括共济失调、小头畸形、免疫缺陷、染色体不稳定和癌症易感性。为了响应DNA双链断裂（DSB），NBS 1通过其C-末端招募ATM以使DNA断裂并激活ATM，ATM进而磷酸化NBS 1和其他下游靶标。NBS 1似乎也在复制叉停止时与ATR相互作用。因此，NBS 1，ATM和ATR的相互作用被认为在DNA损伤信号传导，DNA修复，检查点和凋亡中起着至关重要的作用。然而，由于MRN复合物（NBS 1/MRE 11/RAD 50）或ATR中的无效突变导致细胞和小鼠致死的事实，这些相互作用在这些人类疾病的发病机制中的生物学意义仍然难以捉摸。在这个项目中，我们建议研究：1。NBS 1C端在NBS、A-T和A-T发病机制中的生物学功能; 2.由NBS 1调节的ATM和ATR的不同和相互依赖的功能;和3。DSB修复途径在病理发展中的作用。我们将采取以下方法：（i）产生和表征携带缺乏Atm相互作用结构域的突变型Nbs 1的小鼠和条件性Atr敲除小鼠，以研究Atm和Atr激活在淋巴和神经器官中的作用;（ii）在小鼠中构建诱导性修复测定，以测试Nbs 1、Atm或Atr在体内DSB修复途径中的作用。本研究不仅对理解A-T、A-Bst、Seckel和NBS的机制，而且对阐明体内DNA损伤反应网络具有重要意义。这些知识，今天仍然缺乏，可能有利于发展新的战略，用于治疗神经退行性疾病的组成部分和恶性这些疾病。

Mutations of key components in the DNA damage response pathways, such as ATM, ATR, MRE11 and NBS1, cause Ataxia-Telangiectasia (A-T), Seckel Syndrome, A-T Like Disorder (A-TLD) and Nijmegen Breakage Syndrome (NBS), respectively. The major symptoms overlap in these diseases ranging from ataxia, microcephaly, immunodeficiency, chromosomal instability and cancer susceptibility. In response to DNA double strand breaks (DSBs), NBS1 recruits, by its C-terminus, ATM to DNA breaks and activates ATM, which in turn phosphorylates NBS1 and other downstream targets. NBS1 seems also to interact with ATR upon replication fork stalls. The interaction of NBS1, ATM and ATR is thus proposed to play a vital role in DNA damage signalling, DNA repair, checkpoints and apoptosis. However, the biological significance of such interactions in pathogenesis of these human diseases remains elusive, due to the fact that null mutation in the MRN complex (NBS1/MRE11/RAD50) or in ATR causes cell and mice lethality. In this project we propose to study: 1. The biological functions of the C-terminus of NBS1 in the pathogenesis of NBS, A-T and A-TLD; 2. The distinct and interdependent functions of ATM and ATR that are regulated by NBS1; and 3. The role of the DSB repair pathways in pathological development. We will take the following approaches: (i) Generation and characterization of mice carrying mutant Nbs1 that lacks Atm interaction domain and of conditional Atr knockout mice to study the role of Atm and Atr activation in lymphoid and neuronal organs; (ii) Construction of an inducible repair assay in mice to test the role of Nbs1, Atm or Atr in DSB repair pathways in vivo. This study is very important, not only for the understanding of the mechanisms responsible for A-T, A-TLD, Seckel and NBS, but also for delineating the network of DNA damage response in vivo. Such knowledge, still lacking today, may facilitate the development of novel strategies for the treatment of neurodegenerative components and the malignancy of these diseas.