Haas-Kogan D A, Dazin P, Hu L, Deen D F, Israel A
Preuss Laboratory for Molecular Neuro-oncology, University of California, San Francisco 94143-0520, USA.
Cancer J Sci Am. 1996 Mar-Apr;2(2):114-21.
Radiation therapy, though routinely used in the treatment of patients with glioblastoma multiforme, is of limited efficacy in extending patients' lives. In this study we investigated the mechanism by which ionizing radiation causes death of glioblastoma cells in the hope of ultimately altering the intrinsic radioresistance of glioblastoma tumors.
Radiation survival in vitro was quantitated using linear quadratic and repair-saturation mathematical models. Radiation-induced apoptosis was assayed by fluorescence-activated cell sorter analysis, terminal deoxynucleotide transferase labeling technique, and chromatin morphology. Cellular distribution within the cell cycle was quantitated by dual labeling with propidium iodide and bromodeoxyuridine.
We examined whether in vitro clonogenic radioresistance of glioblastoma would reflect their susceptibility to radiation-induced apoptosis and their ability to undergo a G1 arrest--two cellular functions associated with wild-type p53 expression. We demonstrated that apoptosis contributed to the cytocidal effect of ionizing radiation on glioblastoma cells. The apoptosis observed in glioblastoma cell lines occurred in the absence of wild-type p53 expression. We identified a glioblastoma cell line expressing wild-type p53 and found that it did not exhibit radiation-induced apoptosis but rather underwent a prolonged G1 arrest not observed in any glioblastoma cell line lacking wild-type p53 expression.
Apoptosis is an important component of the lethal effect of ionizing radiation on glioblastoma cells and does not require wild-type p53 expression. Glioblastoma expressing wild-type p53 exhibited no apoptosis, even after high radiation doses, but rather underwent a prolonged G1 arrest. The observation of p53-independent apoptosis and p53-dependent Gi arrest in glioblastoma cells have important radiobiologic and clinical implications.
放射治疗虽常用于多形性胶质母细胞瘤患者的治疗，但在延长患者生命方面疗效有限。在本研究中，我们探究了电离辐射导致胶质母细胞瘤细胞死亡的机制，以期最终改变胶质母细胞瘤肿瘤固有的放射抗性。
使用线性二次模型和修复饱和数学模型对体外放射存活进行定量分析。通过荧光激活细胞分选分析、末端脱氧核苷酸转移酶标记技术和染色质形态学检测放射诱导的细胞凋亡。用碘化丙啶和溴脱氧尿苷双重标记对细胞周期内的细胞分布进行定量分析。
我们研究了胶质母细胞瘤体外克隆放射抗性是否反映其对放射诱导凋亡的敏感性以及经历G1期阻滞的能力，这两种细胞功能与野生型p53表达相关。我们证明细胞凋亡促成了电离辐射对胶质母细胞瘤细胞的杀伤作用。在胶质母细胞瘤细胞系中观察到的细胞凋亡在无野生型p53表达的情况下发生。我们鉴定出一株表达野生型p53的胶质母细胞瘤细胞系，发现它未表现出放射诱导的细胞凋亡，而是经历了长时间的G1期阻滞，这在任何缺乏野生型p53表达的胶质母细胞瘤细胞系中均未观察到。
细胞凋亡是电离辐射对胶质母细胞瘤细胞致死效应的重要组成部分，且不需要野生型p53表达。表达野生型p53的胶质母细胞瘤即使在高剂量辐射后也未表现出细胞凋亡，而是经历了长时间的G1期阻滞。在胶质母细胞瘤细胞中观察到的不依赖p53的细胞凋亡和依赖p53的G1期阻滞具有重要的放射生物学和临床意义。
