Center for Research in Radio-Oncology (CR2), Department of Nuclear Medicine and Radiobiology, Faculty of Medicine and Life Sciences, Université de Sherbrooke 3001, 12e Avenue Nord, Sherbrooke J1H5N4, Canada.
Mutat Res. 2010 Apr-Jun;704(1-3):101-7. doi: 10.1016/j.mrrev.2009.12.007. Epub 2010 Jan 15.
The induction of DNA interstrand cross-links by ionizing radiation has been largely ignored in favour of studies on double-strand break formation and repair. At least part of the problem is technical; it is difficult to detect and quantify interstrand cross-links when the same agent forms both cross-links and single strand breaks because the detection of interstrand cross-links generally involves a denaturation step. Our group has studied the induction of interstrand cross-links following irradiation of DNA containing bromouracil at specific sites. We found that the formation of interstrand cross-links requires the presence of a few (3-5) mismatched bases, comprising the bromouracil. In the absence of mismatched bases, no radiation-induced cross-linking was observed; however, even in the absence of bromouracil, cross-linking still occurred, albeit at a lower efficiency. Our molecular modelling studies demonstrate that the mobility of the bases in the mismatched region is essential for the cross-linking process. Thus, our hypothesis is that ionizing radiation induces DNA interstrand cross-links in non-hybridized regions of DNA. Some obvious examples of such DNA regions are replication forks, transcription bubbles and the D-loop of telomeres. However, an abundance of studies have made it clear that there must be many single-stranded regions in the genome, such as hairpins and cruciforms. For example, alpha satellite DNA, in centromere regions of human chromosomes, forms hairpins. Thus, a variety of non-B DNA structures (hairpins, slipped DNA and tetrahelical structures) exist in the genome and should be susceptible to the formation of radiation-induced interstrand cross-links. Although interstrand cross-links have thus far been virtually ignored in radiation biology, it will be worthwhile to develop methods to detect their presence following exposure of cells to biologically relevant levels of ionizing radiation, since, on a per lesions basis, they are probably more toxic than double-strand breaks.
电离辐射诱导的 DNA 链间交联在很大程度上被忽视，而倾向于研究双链断裂的形成和修复。至少部分问题是技术上的；当同一试剂形成交联和单链断裂时，很难检测和定量链间交联，因为链间交联的检测通常涉及变性步骤。我们的小组研究了含有溴尿嘧啶的 DNA 经特定部位照射后链间交联的诱导。我们发现，链间交联的形成需要存在几个（3-5）个错配碱基，包括溴尿嘧啶。在没有错配碱基的情况下，没有观察到辐射诱导的交联；然而，即使没有溴尿嘧啶，交联仍然发生，尽管效率较低。我们的分子建模研究表明，错配区域中碱基的迁移性对于交联过程至关重要。因此，我们的假设是，电离辐射会在 DNA 的非杂交区域诱导 DNA 链间交联。这种 DNA 区域的一些明显例子是复制叉、转录泡和端粒的 D 环。然而，大量研究已经清楚地表明，基因组中必须有许多单链区域，如发夹和十字形。例如，人染色体着丝粒区域的α卫星 DNA 形成发夹。因此，各种非 B DNA 结构（发夹、滑链和四链体结构）存在于基因组中，应该容易受到辐射诱导的链间交联的形成。尽管迄今为止，链间交联在放射生物学中几乎被忽视，但开发在细胞暴露于生物相关水平的电离辐射后检测其存在的方法将是值得的，因为从每个损伤的基础上看，它们可能比双链断裂更具毒性。
