Yu T, MacPhail S H, Banáth J P, Klokov D, Olive P L
Medical Biophysics Department, British Columbia Cancer Research Centre, 675 W. 10th Ave., Vancouver, BC, Canada V5Z 1L3.
DNA Repair (Amst). 2006 Aug 13;5(8):935-46. doi: 10.1016/j.dnarep.2006.05.040. Epub 2006 Jun 30.
Microscopically visible gammaH2AX foci signify the presence of DNA double-strand breaks (dsbs) in irradiated cells. However, large foci are also observed in untreated tumour cells, and high numbers reduce the sensitivity for detecting drug or radiation-induced DNA breaks. SW756 cervical carcinoma cells that express about 50 gammaH2AX foci per cell (i.e., equivalent to the number of breaks produced by about 2Gy) showed similar numbers of dsbs as C33A cells that exhibit fewer than three foci per cell. The possibility that differences in numbers of these endogenous foci could be explained by genomic instability perhaps related to misrepair was examined. For 17cell lines selected from the panel of NCI-60 tumor cells previously characterized for karyotypic complexity [A.V. Roschke, G. Tonon, K.S. Gehlhaus, N. McTyre, K.J. Bussey, S. Lababidi, D.A. Scudiero, J.N. Weinstein, I.R. Kirsch, Karyotypic complexity of the NCI-60 drug-screening panel, Cancer Res. 63 (2003) 8634-8647], there was a significant trend (r=0.6) for cell lines with greater numbers of structural or numerical chromosomal rearrangements to show a higher background expression of gammaH2AX. Moreover, cells from this panel with wild-type p53 showed a significantly lower background level of gammaH2AX than cells with mutant p53. To confirm the importance of p53 expression, endogenous and radiation-induced gammaH2AX expression were analyzed using four isogenic SKOV3 cell lines varying in p53 function. Again, higher gammaH2AX expression was found in SKOV3 cell lines expressing mutant p53 compared to wild-type p53. HFL-1 primary lung fibroblasts showed a progressive increase in gammaH2AX as they moved towards senescence, confirming the importance of telomere instability in the development of at least some gammaH2AX foci. Therefore, the explanation for high endogenous levels of gammaH2AX in some tumor cells appears to be multifactorial and may be best described as a consequence of chromatin instability.
显微镜下可见的γH2AX病灶表明受辐照细胞中存在DNA双链断裂（dsbs）。然而，在未经处理的肿瘤细胞中也观察到大型病灶，并且大量病灶会降低检测药物或辐射诱导的DNA断裂的灵敏度。SW756宫颈癌细胞每个细胞表达约50个γH2AX病灶（即相当于约2Gy产生的断裂数量），其显示的dsbs数量与C33A细胞相似，C33A细胞每个细胞显示少于三个病灶。研究了这些内源性病灶数量差异是否可以由可能与错配修复相关的基因组不稳定性来解释。从先前已针对核型复杂性进行表征的NCI-60肿瘤细胞组中选择的17种细胞系[A.V. Roschke、G. Tonon、K.S. Gehlhaus、N. McTyre、K.J. Bussey、S. Lababidi、D.A. Scudiero、J.N. Weinstein、I.R. Kirsch，NCI-60药物筛选组的核型复杂性，《癌症研究》63（2003年）8634 - 8647]，具有更多结构或数量染色体重排的细胞系显示出更高的γH2AX背景表达，存在显著趋势（r = 0.6）。此外，该组中具有野生型p53的细胞显示出的γH2AX背景水平明显低于具有突变型p53的细胞。为了证实p53表达的重要性，使用四种p53功能不同的同基因SKOV3细胞系分析了内源性和辐射诱导的γH2AX表达。同样，与野生型p53相比，在表达突变型p53的SKOV3细胞系中发现了更高的γH2AX表达。HFL-1原代肺成纤维细胞在走向衰老时γH2AX逐渐增加，证实了端粒不稳定性在至少一些γH2AX病灶形成中的重要性。因此，一些肿瘤细胞中γH2AX内源性水平高的解释似乎是多因素的，并且最好将其描述为染色质不稳定性的结果。
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