Absence of a radiation-induced first-cycle G1-S arrest in p53+ human tumor cells synchronized by mitotic selection.
Absence of a radiation-induced first-cycle G1-S arrest in p53+ human tumor cells synchronized by mitotic selection.
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发表时间：
1998-05
期刊：
影响因子：
11.2
通讯作者：
H. Nagasawa;Peter C. Keng;Carl G. Maki;Yongjia Yu;John B. Little
中科院分区：
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作者：
H. Nagasawa;Peter C. Keng;Carl G. Maki;Yongjia Yu;John B. Little
众所周知，正常人二倍体成纤维细胞在暴露于电离辐射后在细胞周期的G1期经历显著的p53依赖性停滞。然而，在人类肿瘤细胞系中G1期阻滞的存在和程度一直存在争议，特别是在来自实体瘤并在指数生长期间照射的细胞中。为了更精确地研究这个问题，我们通过有丝分裂选择使细胞同步化，并在任何所述的G1检查点之前的非常早期的G1中照射它们。通过放射自显影测量累积标记指数和流式细胞术分析来监测细胞从G1期进入S期的进展。检查了三种不同的被证实表达正常p53功能的人肿瘤细胞系，即，来源于结肠腺癌（RKO）、乳腺癌（MCF-7）和鳞状细胞癌（SCC 61）的细胞系。在4-8戈伊照射后，从G1期到S期的进展有短暂的延迟，持续约2小时，并且在三种细胞系中的两种（RKO和MCF-7）中，一小部分细胞（5-8%）从未进入第一个S期。虽然没有证据表明G1期阻滞延长，但在所有三种细胞系中均观察到预期的G2期延迟。当辐射的RKO细胞在下一次有丝分裂时被灭活时，约30%的细胞没有进入第二个S期。后一项发现与先前关于辐射诱导哺乳动物细胞生殖失败的动力学报告一致。这些结果表明，来自表达正常p53的人实体瘤的细胞可能对辐射的反应与正常细胞在G1检查点控制方面完全不同。
It is well known that normal human diploid fibroblasts undergo a significant, p53-dependent arrest in the G1 phase of the cell cycle after exposure to ionizing radiation. The presence and magnitude of a G1 arrest in human tumor cell lines, however, has been controversial, particularly in cells derived from solid tumors and irradiated during exponential growth. To examine this question more precisely, we synchronized cells by mitotic selection and irradiated them in very early G1 prior to any of the described G1 checkpoints. Progression of cells from G1 into the S phase was monitored by autoradiographic measurement of cumulative labeling indices and by flow cytometric analysis. Three different human tumor cell lines confirmed as expressing normal p53 function were examined, i.e., lines derived from an adenocarcinoma of the colon (RKO), a breast cancer (MCF-7), and a squamous cell carcinoma (SCC61). Following irradiation with 4-8 Gy, there was a transient delay in progression from G1 into S phase, lasting approximately 2 h, and in two of the three cell lines (RKO and MCF-7), a small fraction of cells (5-8%) never entered the first S phase. Although there was no evidence for a prolonged G1 arrest, the expected G2 delay was observed in all three cell lines. When irradiated RKO cells were resynchronized at the next mitosis, approximately 30% of the cells did not enter the second S phase. This latter finding is consistent with earlier reports on the kinetics of radiation-induced reproductive failure in mammalian cells. These results indicate that cells derived from human solid tumors that express normal p53 may respond to irradiation quite differently than do normal cells in terms of G1 checkpoint control.