Mendonca M S, Howard K L, Farrington D L, Desmond L A, Temples T M, Mayhugh B M, Pink J J, Boothman D A
Department of Radiation Oncology, Indiana University School of Medicine, Indianapolis 46202, USA.
Cancer Res. 1999 Aug 15;59(16):3972-9.
HeLa X human skin fibroblast hybrid cells have been developed into a model for radiation-induced neoplastic transformation of human cells. Previous studies indicate that the appearance of neoplastically transformed foci in this system is delayed for several population doublings after irradiation and appears to involve the loss of putative tumor suppressor loci on fibroblast chromosomes 11 and 14. We now show that after treatment with 7 Gy of X-rays, transformed foci initiation correlates with delayed apoptosis initiated in the progeny of the irradiated cells after 10-12 cell divisions and with reduced plating efficiency (delayed death). The cells develop classic apoptotic morphology, positive terminal deoxynucleotidyl transferase-mediated nick end labeling and phosphatidylserine (annexin V) staining, and cleavage of poly(ADP-ribose) polymerase. In addition, a delayed induction of the p53 protein and the proapoptotic Bax protein is evident over a week after radiation exposure. We propose that a delayed build-up of mitosis-dependent genomic DNA damage or a loss of genetic material over time (10-12 cell divisions postirradiation) has two relevant outcomes: (a) cell death due to the delayed induction of a p53-dependent apoptosis; and (b) neoplastic transformation of a minor subset of survivors that has lost fibroblast chromosomes 11 and 14 (tumor suppressor loci for this system) and has either evaded apoptosis or not acquired enough genetic damage to induce apoptosis. It is postulated that both phenomena result from X-ray-induced, translesion-mediated genomic instability.
HeLa与人类皮肤成纤维细胞杂交细胞已被开发成为一种人类细胞辐射诱导肿瘤转化的模型。先前的研究表明，在该系统中，肿瘤转化灶的出现会在照射后延迟几个群体倍增时间，并且似乎涉及成纤维细胞11号和14号染色体上假定的肿瘤抑制基因座的丢失。我们现在表明，用7 Gy的X射线处理后，转化灶的起始与照射后细胞后代在10 - 12次细胞分裂后启动的延迟凋亡以及降低的铺板效率（延迟死亡）相关。细胞呈现出典型的凋亡形态、阳性的末端脱氧核苷酸转移酶介导的缺口末端标记和磷脂酰丝氨酸（膜联蛋白V）染色，以及聚（ADP - 核糖）聚合酶的裂解。此外，在辐射暴露一周后，p53蛋白和促凋亡的Bax蛋白明显延迟诱导。我们提出，有丝分裂依赖性基因组DNA损伤的延迟积累或随着时间推移（照射后10 - 12次细胞分裂）遗传物质的丢失有两个相关结果：(a) 由于p53依赖性凋亡的延迟诱导导致细胞死亡；(b) 一小部分存活细胞发生肿瘤转化，这些细胞丢失了成纤维细胞11号和14号染色体（该系统的肿瘤抑制基因座），并且要么逃避了凋亡，要么没有获得足够的遗传损伤来诱导凋亡。据推测，这两种现象都是由X射线诱导的、跨损伤介导的基因组不稳定性导致的。
