Oxidative stress is known to be involved in most of the aetiological factors of nasopharyngeal carcinoma (NPC). Cells that are under oxidative stress may undergo apoptosis. We have previously demonstrated that oxidative stress-induced apoptosis could be a potential mechanism mediating chromosome breakages in nasopharyngeal epithelial cells. Additionally, caspase-activated DNase (CAD) may be the vital player in mediating the chromosomal breakages during oxidative stress-induced apoptosis. Chromosomal breakage occurs during apoptosis and chromosome rearrangement. Chromosomal breakages tend to cluster in certain regions, such as matrix association region/scaffold attachment region (MAR/SAR). We hypothesised that oxidative stress-induced apoptosis may result in chromosome breaks preferentially at the MAR/SAR sites. The AF9 gene at 9p22 was targeted in this study because 9p22 is a deletion site commonly found in NPC. By using MAR/SAR recognition signature (MRS), potential MAR/SAR sites were predicted in the AF9 gene. The predicted MAR/SAR sites precisely match to the experimentally determined MAR/SARs. Hydrogen peroxide (H2O2) was used to induce apoptosis in normal nasopharyngeal epithelial cells (NP69) and NPC cells (HK1). Nested inverse polymerase chain reaction was employed to identify the AF9 gene cleavages. In the SAR region, the gene cleavage frequency of H2O2-treated cells was significantly higher than that of the non-treated cells. A few chromosomal breakages were detected within the AF9 region which was previously found to be involved in the mixed lineage leukaemia (MLL)-AF9 translocation in an acute lymphoblastic leukaemia patient. As for the non-SAR region, no significant difference in the gene cleavage frequency was found between the untreated control and H2O2-treated cells. Furthermore, H2O2-induced cleavages within the SAR region were reduced by caspase-3 inhibitor, which indirectly inhibits CAD. These results reaffirm our previous findings that oxidative stress-induced apoptosis could be one of the potential mechanisms underlying chromosome breakages in nasopharyngeal epithelial cells. MAR/SAR may play a vital role in defining the location of chromosomal breakages mediated by oxidative stress-induced apoptosis, where CAD is the major nuclease.

中文翻译：

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基质缔合区/支架附着区（MAR / SAR）序列：它通过氧化应激诱导的凋亡介导鼻咽上皮细胞染色体断裂中的重要作用。

已知氧化应激与鼻咽癌（NPC）的大多数病因有关。处于氧化应激状态的细胞可能会发生凋亡。我们以前已经证明，氧化应激诱导的细胞凋亡可能是介导鼻咽上皮细胞染色体断裂的潜在机制。此外，胱天蛋白酶激活的脱氧核糖核酸酶（CAD）可能是介导氧化应激诱导的细胞凋亡过程中染色体断裂的重要参与者。在细胞凋亡和染色体重排过程中发生染色体断裂。染色体断裂倾向于聚集在某些区域，例如基质缔合区/支架附着区（MAR / SAR）。我们假设氧化应激诱导的细胞凋亡可能会导致MAR / SAR位点的染色体断裂。由于9p22是NPC中常见的缺失位点，因此本研究靶向9p22处的AF9基因。通过使用MAR / SAR识别签名（MRS），可以在AF9基因中预测潜在的MAR / SAR位点。预测的MAR / SAR站点与实验确定的MAR / SAR精确匹配。过氧化氢（H2O2）用于诱导正常鼻咽上皮细胞（NP69）和NPC细胞（HK1）的凋亡。巢式反向聚合酶链反应用于鉴定AF9基因的切割。在SAR区域，H2O2处理的细胞的基因切割频率显着高于未处理的细胞。在AF9区域内检测到一些染色体断裂，先前发现这与急性淋巴细胞白血病患者的混合谱系白血病（MLL）-AF9易位有关。至于非SAR区域，在未处理的对照和经H 2 O 2处理的细胞之间未发现基因切割频率的显着差异。此外，caspase-3抑制剂减少了H2O2诱导的SAR区域内的裂解，该酶间接抑制了CAD。这些结果证实了我们以前的发现，即氧化应激诱导的细胞凋亡可能是鼻咽上皮细胞染色体断裂的潜在机制之一。MAR / SAR可能在确定由氧化应激诱导的细胞凋亡介导的染色体断裂的位置中起着至关重要的作用，其中CAD是主要的核酸酶。间接抑制CAD。这些结果证实了我们以前的发现，即氧化应激诱导的细胞凋亡可能是鼻咽上皮细胞染色体断裂的潜在机制之一。MAR / SAR可能在确定由氧化应激诱导的细胞凋亡介导的染色体断裂的位置中起着至关重要的作用，其中CAD是主要的核酸酶。间接抑制CAD。这些结果证实了我们以前的发现，即氧化应激诱导的细胞凋亡可能是鼻咽上皮细胞染色体断裂的潜在机制之一。MAR / SAR可能在确定由氧化应激诱导的细胞凋亡介导的染色体断裂的位置中起着至关重要的作用，其中CAD是主要的核酸酶。