Hufnagl Antonia, Herr Lisa, Friedrich Thomas, Durante Marco, Taucher-Scholz Gisela, Scholz Michael
GSI Helmholtzzentrum für Schwerionenforschung (GSI), Department of Biophysics, Darmstadt, Germany.
GSI Helmholtzzentrum für Schwerionenforschung (GSI), Department of Biophysics, Darmstadt, Germany; Technische Universität Darmstadt, Darmstadt, Germany.
DNA Repair (Amst). 2015 Mar;27:28-39. doi: 10.1016/j.dnarep.2015.01.002. Epub 2015 Jan 17.
The different DNA damage repair pathways like homologous recombination (HR) and non-homologous end joining (NHEJ) have been linked to the variation of radiosensitivity throughout the cell cycle. However, no attempts have been made to test the various hypotheses derived from these studies in a quantitative way e.g. by using modeling approaches. Here we present the first modeling approach that allows predicting the cell cycle dependent radiosensitivity of repair proficient as well as of repair deficient cell lines after photon irradiation based on a small set of parameters and assumptions. A key element of the model is the classification of DNA damage according to its complexity on the level of chromatin loops of about 2Mbp size. Isolated DSB (iDSB), characterized by a single DSB within a chromatin loop, are distinguished from clustered DSB (cDSB), characterized by two or more DSB within a chromatin loop. The class of iDSB is further subdivided into two sub-classes, characterized by the replication status of the corresponding chromatin loop. For iDSB in replicated loops that are in close contact, error-free homologous recombination is assumed to be effective; in unreplicated loops or in replicated loops that have already been separated, iDSB are assumed to be repaired by error-prone non-homologous end joining. cDSB are assumed not to be repairable effectively by neither HR nor NHEJ. Assigning empirically derived lethalities to these three damage classes and pathways, we demonstrate that the model is able to accurately reproduce cell cycle dependent survival probabilities. Notably, the relevant parameters are derived solely from two survival curves for normal, repair proficient cells in G1 and late-S phase. Based on a comparison of model predictions with a large data set reported in the literature, we show that the lethality values for wild type cells are simultaneously predictive for the cell cycle dependent variation of sensitivity observed for HR-deficient and NHEJ-deficient cells.
不同的DNA损伤修复途径，如同源重组（HR）和非同源末端连接（NHEJ），已被证明与整个细胞周期中放射敏感性的变化有关。然而，尚未有人尝试以定量方式检验从这些研究中得出的各种假设，例如通过使用建模方法。在此，我们提出了第一种建模方法，该方法能够基于一小组参数和假设，预测光子照射后修复功能正常以及修复功能缺陷的细胞系的细胞周期依赖性放射敏感性。该模型的一个关键要素是根据DNA损伤在约2Mbp大小的染色质环水平上的复杂性对其进行分类。孤立的双链断裂（iDSB），其特征是在一个染色质环内有单个双链断裂，与成簇的双链断裂（cDSB）相区分，成簇的双链断裂的特征是在一个染色质环内有两个或更多双链断裂。iDSB类别进一步细分为两个子类别，其特征是相应染色质环的复制状态。对于紧密接触的复制环中的iDSB，假定无错的同源重组是有效的；在未复制的环或已经分离的复制环中，iDSB假定通过易出错的非同源末端连接进行修复。cDSB假定既不能被HR也不能被NHEJ有效修复。通过将经验得出的致死率分配给这三种损伤类别和途径，我们证明该模型能够准确再现细胞周期依赖性存活概率。值得注意的是，相关参数仅来自于G1期和S期后期正常、修复功能正常细胞的两条存活曲线。基于将模型预测与文献中报道的大量数据集进行比较，我们表明野生型细胞的致死率值同时可预测HR缺陷和NHEJ缺陷细胞中观察到的细胞周期依赖性敏感性变化。
