Tyrosyl-DNA phosphodiesterase and oxidative DNA damage

描述（由申请人提供）：当由DNA拓扑异构酶I形成的瞬时DNA链断裂不能再连接时，拓扑异构酶通过酪氨酰键不可逆地连接到3' DNA末端。然后，该连接必须被酪氨酰-DNA磷酸二酯酶（Tdp 1）切割，以允许断裂的修复。人类Tdp 1的缺乏与遗传性脊髓小脑共济失调伴轴突神经病变（SCAN 1）有关，其临床特征与其他与氧化应激相关的共济失调相似。这些相似性，结合Tdp 1也从自由基介导的DNA链断裂的3'端去除乙醇酸部分的发现，表明Tdp 1可能参与氧化DNA损伤的修复，并且不能修复这种损伤可能导致SCAN 1中的神经元功能障碍。为了检验这些假设，将在来自SCAN 1患者的Tdp 1缺陷型淋巴母细胞样细胞中检查细胞毒性以及3 '-磷酸乙醇酸终止的DNA双链断裂的修复。端粒DNA的氧化损伤，以及端粒的结构和功能，将在正常和Tdp 1缺陷细胞进行比较。将生成常规和条件性Tdp 1敲除小鼠并进行广泛表征。这将包括在存在和不存在氧化应激的情况下评估共济失调或其他行为功能障碍的发展以及神经元凋亡。将在未处理动物和暴露于氧化应激的动物的多个部位测定肿瘤发生率，并将在易发生癌前前列腺瘤形成的小鼠中评价Tdp 1缺乏对肿瘤进展的影响。此外，将监测小鼠的加速老化迹象。这些研究旨在阐明Tdp 1缺陷导致SCAN 1的机制，也可能有助于阐明氧化应激在各种其他神经系统疾病、癌症和衰老中的作用。

DESCRIPTION (provided by applicant): When transient DNA strand breaks formed by DNA topoisomerase I fail to religate, the topoisomerase becomes irreversibly attached to the 3' DNA end via a tyrosyl linkage. This linkage must then be cleaved by tyrosyI-DNA phosphodiesterase (Tdp1) in order to allow repair of the break. Human deficiency in Tdp1 has been implicated in hereditary spinocerebellar ataxia with axonal neuropathy (SCAN1), the clinical features of which are similar to those of other ataxias associated with oxidative stress. These similarities, combined with the finding that Tdp1 also removes glycolate moieties from 3' ends of free radical-mediated DNA strand breaks, suggest that Tdp1 may be involved in repair of oxidative DNA damage, and that failure to repair such damage may lead to neuronal dysfunction in SCAN1. In order to test these hypotheses, cytotoxicity as well as repair of 3'-phosphoglycolate-terminated DNA double-strand breaks will be examined in Tdp1-deficient lymphoblastoid cells, derived from SCAN1 patients. Oxidative DNA damage to telomeric DNA, as well as telomere structure and function, will be compared in normal and Tdp1-deficient cells. Both conventional and conditional Tdp1 knockout mice will be generated and extensively characterized. This will include an assessment for the development of ataxia or other behavioral dysfunctions as well as for neuronal apoptosis both in the presence and absence of oxidative stress. Tumor incidence will be determined at a number of sites in both untreated animals and those exposed to oxidative stress, and the effects of Tdp1 deficiency on tumor progression will be evaluated in mice that are predisposed to the development of premalignant prostate neoplasia. In addition, mice will be monitored for signs of accelerated aging. These studies are intended to clarify the mechanism by which Tdp1 deficiency leads to SCAN1, and may also help elucidate the role of oxidative stress in various other neurological disorders, cancer and aging.