Doherty Sharon C, McKeown Stephanie R, McKelvey-Martin Valerie, Downes C Stephen, Atala Anthony, Yoo James J, Simpson Dennis A, Kaufmann William K
Cancer and Ageing Research Group, School of Biomedical Sciences, University of Ulster, Coleraine, Northern Ireland.
J Natl Cancer Inst. 2003 Dec 17;95(24):1859-68. doi: 10.1093/jnci/djg120.
Cell cycle checkpoints function to maintain genetic stability by providing additional time for repair of DNA damage and completion of events that are necessary for accurate cell division. Some checkpoints, such as the DNA damage G1 checkpoint, are dependent on p53, whereas other checkpoints, such as the decatenation G(2) checkpoint, are not. Because bladder transitional cell carcinomas (TCCs) often contain numerous chromosomal aberrations and appear to have highly unstable genomes, we analyzed cell cycle checkpoint functions in a panel of TCC lines.
Cell cycle arrest was induced in normal human fibroblasts (NHF1-hTERT) and normal human uroepithelial cells (HUCs), and TCC lines and checkpoint functions were quantified using flow cytometry and fluorescence microscopy. The inducers and checkpoints were ionizing radiation (i.e., DNA damage) (G1 and G2 checkpoints), the mitotic inhibitor colcemid (polyploidy checkpoint), or the topoisomerase II catalytic inhibitor ICRF-193 (decatenation G2 checkpoint). Four of the five TCC lines expressed mutant p53.
HUCs had an effective G1 checkpoint response to ionizing radiation, with 68% of cells inhibited from moving from G1 into S phase. By contrast, G1 checkpoint function was severely attenuated (<15% inhibition) in three of the five TCC lines and moderately attenuated (<50% inhibition) in the other two lines. NHF1-hTERT had an effective polyploidy checkpoint response, but three of five TCC lines were defective in this checkpoint. HUCs had effective ionizing radiation and decatenation G2 checkpoint responses. All TCC lines had a relatively effective G2 checkpoint response to DNA damage, although the responses of two of the TCC lines were moderately attenuated relative to HUCs. All TCC lines had a severe defect in the decatenation G2 checkpoint response.
Bladder TCC lines have defective cell cycle checkpoint functions, suggesting that the p53-independent decatenation G2 checkpoint may cooperate with the p53-dependent G1 checkpoints to preserve chromosomal stability and suppress bladder carcinogenesis.
细胞周期检查点通过为DNA损伤修复和准确细胞分裂所需事件的完成提供额外时间来维持遗传稳定性。一些检查点，如DNA损伤G1检查点，依赖于p53，而其他检查点，如解连环G2检查点，则不依赖p53。由于膀胱移行细胞癌（TCC）通常含有大量染色体畸变，且似乎具有高度不稳定的基因组，我们分析了一组TCC细胞系中的细胞周期检查点功能。
在正常人成纤维细胞（NHF1-hTERT）和正常人尿路上皮细胞（HUC）中诱导细胞周期停滞，并使用流式细胞术和荧光显微镜对TCC细胞系和检查点功能进行定量分析。诱导剂和检查点分别为电离辐射（即DNA损伤）（G1和G2检查点）、有丝分裂抑制剂秋水仙酰胺（多倍体检查点）或拓扑异构酶II催化抑制剂ICRF-193（解连环G2检查点）。五个TCC细胞系中有四个表达突变型p53。
HUC对电离辐射有有效的G1检查点反应，68%的细胞被抑制从G1期进入S期。相比之下，五个TCC细胞系中有三个的G1检查点功能严重减弱（抑制率<15%），另外两个细胞系的G1检查点功能中度减弱（抑制率<50%）。NHF1-hTERT有有效的多倍体检查点反应，但五个TCC细胞系中有三个在该检查点存在缺陷。HUC有有效的电离辐射和解连环G2检查点反应。所有TCC细胞系对DNA损伤都有相对有效的G2检查点反应，尽管其中两个TCC细胞系的反应相对于HUC有所中度减弱。所有TCC细胞系在解连环G2检查点反应方面都存在严重缺陷。
膀胱TCC细胞系的细胞周期检查点功能存在缺陷，提示不依赖p53的解连环G2检查点可能与依赖p53的G1检查点协同作用，以维持染色体稳定性并抑制膀胱癌发生。
