Allio T, Donner E M, Preston R J
Chemical Industry Institute of Toxicology, Research Triangle Park, NC 27709, USA.
Mutat Res. 2000 Feb 14;447(2):227-37. doi: 10.1016/s0027-5107(99)00212-2.
Previous studies have shown that p53 is involved in the repair of bleomycin-induced DNA damage, and that the frequency of bleomycin-induced chromatid aberrations is elevated in G(2)-treated p53 null transgenic mouse embryo fibroblasts (MEF) as compared to isogenic controls. To further characterize p53-mediated DNA repair, we studied the effect of p53 status on the ability of the DNA repair inhibitor 1-ss-D-arabinofuranosylcytosine (AraC) to sensitize MEF to bleomycin-induced chromatid aberrations. Both p53+/+ and p53-/- MEF were treated in G(2) with 0 to 7.5 microg/ml bleomycin in the presence or absence of AraC (5x10(-5) M). The frequency of bleomycin-induced chromatid aberrations was significantly higher in p53-/- cells than wild-type cells in the absence of AraC. AraC treatment significantly increased the frequency of bleomycin-induced chromatid aberrations in p53+/+ MEF to the levels in p53-/- (no AraC) but had no effect in p53-/- MEF. These results suggest that an AraC-sensitive DNA repair component is altered or absent in p53-/- cells. Similar results were observed in p53-mutant WTK1 and wild-type TK6 human lymphoblast cells exposed to 0 to 3 microg/ml bleomycin in G(2). However, AraC did cause a small increase in bleomycin sensitivity in WTK1 cells. This difference from the p53-/- MEF response may be due to differences in p53-mutant phenotype. To determine whether mutation of p53 alters DNA replication fidelity, p53+/+ and p53-/- MEF were exposed to 0 to 1 microg/ml mitomycin C (MMC). MMC did not induce chromosome aberrations in either cell line treated in G(2) but did with the same effectiveness in both cell lines treated in S-phase. Thus, p53 deficiency does not affect DNA replication fidelity or the repair of MMC-induced DNA damage.
先前的研究表明，p53参与博来霉素诱导的DNA损伤修复，与同基因对照相比，在经G(2)处理的p53基因敲除转基因小鼠胚胎成纤维细胞（MEF）中，博来霉素诱导的染色单体畸变频率升高。为了进一步表征p53介导的DNA修复，我们研究了p53状态对DNA修复抑制剂1-β-D-阿拉伯呋喃糖基胞嘧啶（AraC）使MEF对博来霉素诱导的染色单体畸变敏感的能力的影响。在存在或不存在AraC（5×10⁻⁵ M）的情况下，将p53+/+和p53⁻/⁻ MEF在G(2)期用0至7.5 μg/ml博来霉素处理。在不存在AraC的情况下，p53⁻/⁻细胞中博来霉素诱导的染色单体畸变频率显著高于野生型细胞。AraC处理使p53+/+ MEF中博来霉素诱导的染色单体畸变频率显著增加至p53⁻/⁻（无AraC）时的水平，但对p53⁻/⁻ MEF没有影响。这些结果表明，p53⁻/⁻细胞中一个对AraC敏感的DNA修复成分发生改变或缺失。在G(2)期暴露于0至3 μg/ml博来霉素的p53突变型WTK1和野生型TK6人淋巴母细胞中观察到类似结果。然而，AraC确实使WTK1细胞对博来霉素的敏感性略有增加。与p53⁻/⁻ MEF反应的这种差异可能是由于p53突变表型的差异。为了确定p53突变是否改变DNA复制保真度，将p53+/+和p53⁻/⁻ MEF暴露于0至1 μg/ml丝裂霉素C（MMC）。MMC在G(2)期处理的两种细胞系中均未诱导染色体畸变，但在S期处理的两种细胞系中诱导效果相同。因此，p53缺陷不影响DNA复制保真度或MMC诱导的DNA损伤修复。
