LeDoux S P, Williams B A, Hollensworth B S, Shen C, Thomale J, Rajewsky M F, Brent T P, Wilson G L
University of South Alabama, Mobile 36688, USA.
Cancer Res. 1996 Dec 15;56(24):5615-9.
Normal and malignant cells of the oligodendrocyte lineage show increased sensitivity to alkylating agents compared to astrocytes. One of the most mutagenic DNA lesions formed following exposure to alkylating agents is O6-alkylguanine. To determine whether the increased sensitivity to nitrosoureas seen in oligodendrocytes is due to decreased repair capacity for O6-alkylguanine, removal of this lesion from DNA was assessed in primary cultures of rat oligodendrocytes, astrocytes, and microglia. Glial cells were exposed to 1 mM N-methyl-N-nitrosourea for 1 h and allowed 8 or 24 h for repair. Repair was evaluated using an immunoslot blot technique and a monoclonal antibody which recognizes O6-methylguanine (O6MeGua). Astrocytes removed O6MeGua more efficiently (approximately 80% in 24 h) than either oligodendrocytes (approximately 20%) or microglia (approximately 4%). Determination of O6-alkylguanine-DNA-alkyltransferase (AT) activity revealed that astrocytes contain 0.4 pmol/mg protein, which is average by comparison to other cell types. Both oligodendrocytes and microglia exhibited very low levels of AT (oligodendrocytes, 0.08; microglia, 0.01 pmol/mg protein). These data are the first to show that within different populations of glial cells, O6MeGua adduct removal is substantially reduced in both oligodendrocytes and microglia. Rapid removal of O6MeGua in astrocytes coupled with persistence of this mutagenic lesion in oligodendrocytes following exposure of the developing central nervous system to nitrosoureas could contribute to the observed formation of oligodendrogliomas. Inefficient removal of O6MeGua in oligodendrogliomas might also account for their response to chemotherapeutic regimens involving alkylating agents such as procarbazine, lomustine, and carmustine. The lack of repair of O6MeGua in microglia suggests that primary lymphomas of the central nervous system might be sensitive to treatment with alkylating drugs whose toxicity depends on repair of this adduct.
与星形胶质细胞相比，少突胶质细胞系的正常细胞和恶性细胞对烷化剂表现出更高的敏感性。暴露于烷化剂后形成的最具致突变性的DNA损伤之一是O6-烷基鸟嘌呤。为了确定少突胶质细胞中对亚硝基脲的敏感性增加是否是由于O6-烷基鸟嘌呤的修复能力降低，在大鼠少突胶质细胞、星形胶质细胞和小胶质细胞的原代培养物中评估了从DNA中去除这种损伤的情况。将胶质细胞暴露于1 mM N-甲基-N-亚硝基脲1小时，然后给予8或24小时进行修复。使用免疫斑点印迹技术和识别O6-甲基鸟嘌呤（O6MeGua）的单克隆抗体评估修复情况。星形胶质细胞比少突胶质细胞（约20%）或小胶质细胞（约4%）更有效地去除O6MeGua（24小时内约80%）。对O6-烷基鸟嘌呤-DNA-烷基转移酶（AT）活性的测定表明，星形胶质细胞含有0.4 pmol/mg蛋白质，与其他细胞类型相比处于平均水平。少突胶质细胞和小胶质细胞均表现出非常低水平的AT（少突胶质细胞为0.08；小胶质细胞为0.01 pmol/mg蛋白质）。这些数据首次表明，在不同的胶质细胞群体中，少突胶质细胞和小胶质细胞中O6MeGua加合物的去除均显著减少。发育中的中枢神经系统暴露于亚硝基脲后，星形胶质细胞中O6MeGua的快速去除以及少突胶质细胞中这种致突变损伤的持续存在可能导致观察到的少突胶质细胞瘤的形成。少突胶质细胞瘤中O6MeGua去除效率低下也可能解释了它们对涉及烷化剂如丙卡巴肼、洛莫司汀和卡莫司汀的化疗方案的反应。小胶质细胞中O6MeGua缺乏修复表明中枢神经系统原发性淋巴瘤可能对其毒性取决于这种加合物修复的烷化药物治疗敏感。
