Repair-induced DNA double strand breaks after ultraviolet-light and either aphidocolin or 1-beta-D-arabinofuranosylcytosine/hydroxyurea.
Repair-induced DNA double strand breaks after ultraviolet-light and either aphidocolin or 1-beta-D-arabinofuranosylcytosine/hydroxyurea.
复制标题
紫外线和阿菲多霉素或 1-β-D-阿拉伯呋喃糖基胞嘧啶/羟基脲后，修复诱导的 DNA 双链断裂。
作者：
M. O. Bradley;V. I. Taylor
我们最近发现，紫外线照射后发生的DNA修复过程诱导正常人成纤维细胞（IMR-90）的DNA双链断裂（DSB），但不诱导着色性干皮病A组细胞的DNA双链断裂。我们称这些病变为“修复诱导的双链断裂”（RDSB），因为它们只发生在切除修复能力的细胞中。在这项工作中，我们询问这些RDSB是否在低紫外线剂量下发生在IMR-90细胞中，以及RDSB本身是否可修复。我们推断，通过在紫外线照射后用羟基脲/阿糖胞苷或aphidocolin抑制核苷酸聚合来保持切除-修复诱导的缺口开放，应该使我们能够回答这些问题。结果表明，当存在修复抑制剂时，低至2.5 J.m-2的紫外光在修复孵育期间诱导RDSB。这表明出现高病变频率的“热点”，这些区域的重叠切除将产生RDSB。如果没有修复抑制剂，这种RDSB的频率会低得多;但即使是一个未修复的RDSB也可能具有深远的生物学效应。通过在RDSB孵育后从培养基中去除蚜毒素，我们能够测试这些损伤的修复性。结果表明，RDSB仅部分可修复，在24小时内有15%至40%的断裂未修复。由于病变是部分可修复的，因此它们不应总是引起毒性，并且可能涉及与人类肿瘤相关的诸如突变、转化和染色体或染色单体类型畸变的过程。
We recently showed that the DNA repair processes occurring after u.v. light induce double strand breaks (DSBs) in the DNA of normal human fibroblast (IMR-90) but not of xeroderma pigmentosum group A cells. We call these lesions 'repair-induced double strand breaks' (RDSBs), since they only occur in excision repair competent cells. In this work, we asked whether these RDSBs occur in IMR-90 cells at low u.v. doses and whether the RDSBs are themselves repairable. We reasoned that holding open the excision-repair induced gaps by inhibiting nucleotide polymerization after u.v. light with hydroxyurea/ara C or aphidocolin should allow us to answer these questions. The results show that as little as 2.5 J.m-2 of u.v. light induces RDSBs during repair incubation when repair inhibitors are present. This suggests that 'hot spots' of high lesion frequency occur and the overlapping excision in these areas will produce RDSBs. Without repair inhibitors, the frequency of such RDSBs will be much lower; but even one unrepaired RDSB is likely to have profound biological effects. By removing aphidocolin from the medium after incubation of RDSBs, we were able to test the repairability of these lesions. The results show that RDSBs are only partially repairable with between 15 and 40% of the breaks unrepaired at 24 h. Because the lesions are partially repairable they should not always cause toxicity and may be involved in processes such as mutation, transformation, and chromosome or chromatid type aberrations of the sort associated with human tumors.