de Vries A, Dollé M E, Broekhof J L, Muller J J, Kroese E D, van Kreijl C F, Capel P J, Vijg J, van Steeg H
University of Utrecht, Department of Immunology, The Netherlands.
Carcinogenesis. 1997 Dec;18(12):2327-32. doi: 10.1093/carcin/18.12.2327.
We were interested to study the relationship between DNA lesions, DNA repair, mutation fixation, and tumour development. Therefore, mice harbouring lacZ reporter genes and being either wild-type or defective in the DNA excision repair gene XPA, were treated with the genotoxic carcinogen benzo[a]pyrene at an oral dose of 13 mg/kg b.w. (3 times/week). At different time points, i.e. 1, 5, 9 or 13 weeks after start of the oral administration, levels of BPDE-N2-dG adducts (the major formed DNA adduct by benzo[a]pyrene in mice), and lacZ mutation frequencies were measured both in target (spleen) and non-target (lung and liver) tissues. Both in wild-type and XPA-deficient mice, benzo[a]pyrene treatment resulted in increased BPDE-N2-dG adduct levels in all three tissues analysed. In XPA-deficient mice, BPDE-N2-dG adduct levels still increased up to 13 weeks of oral benzo[a]pyrene treatment, whereas in DNA repair proficient mice steady-state levels were reached after 5 weeks of treatment. After 13 weeks, the BPDE-N2-dG adduct levels observed in XPA-/- mice, were 2- to 3-fold higher than the steady state levels observed in XPA+/+ mice in the same tissues. Mutation frequencies in the lacZ reporter gene were the same in wild-type and XPA-deficient mice that were treated with the solvent only. Oral benzo[a]pyrene treatment resulted in an increase in mutation frequency in the lacZ marker gene in all three tissues, but this increase was most profound in the spleen. After 13 weeks of treatment, a 7-fold increase in lacZ mutation frequency was detected in the spleen of wild-type mice as compared to mutation frequencies in control mice. At the same time point, a 15-fold increase in lacZ mutation frequency was observed in the spleen of XPA-deficient mice. The data presented here show, that a defect in NER mainly results in enhanced mutation frequencies in lymphocytic cells after oral treatment with the genotoxic compound benzo[a]pyrene. Interestingly, as we established in a previously performed carcinogenicity assay, the same oral treatment with benzo[a]pyrene induced lymphomas residing in the spleen of XPA-deficient mice.
我们对研究DNA损伤、DNA修复、突变固定与肿瘤发生之间的关系感兴趣。因此，携带lacZ报告基因且DNA切除修复基因XPA为野生型或有缺陷的小鼠，以13mg/kg体重的口服剂量（每周3次）给予基因毒性致癌物苯并[a]芘。在不同时间点，即口服给药开始后的1、5、9或13周，在靶组织（脾脏）和非靶组织（肺和肝脏）中测量BPDE-N2-dG加合物（苯并[a]芘在小鼠中形成的主要DNA加合物）水平和lacZ突变频率。在野生型和XPA缺陷型小鼠中，苯并[a]芘处理均导致所分析的所有三种组织中BPDE-N2-dG加合物水平升高。在XPA缺陷型小鼠中，口服苯并[a]芘处理至13周时，BPDE-N2-dG加合物水平仍在升高，而在DNA修复功能正常的小鼠中，处理5周后达到稳态水平。13周后，在XPA-/-小鼠中观察到的BPDE-N2-dG加合物水平比在相同组织的XPA+/+小鼠中观察到的稳态水平高2至3倍。仅用溶剂处理的野生型和XPA缺陷型小鼠中，lacZ报告基因的突变频率相同。口服苯并[a]芘处理导致所有三种组织中lacZ标记基因的突变频率增加，但在脾脏中这种增加最为显著。处理13周后，与对照小鼠的突变频率相比，野生型小鼠脾脏中的lacZ突变频率增加了七倍。在同一时间点，XPA缺陷型小鼠脾脏中的lacZ突变频率增加了15倍。此处呈现的数据表明，NER缺陷主要导致在用基因毒性化合物苯并[a]芘口服处理后淋巴细胞中的突变频率增加。有趣的是，正如我们在先前进行的致癌性试验中所确定的，相同的苯并[a]芘口服处理诱导了XPA缺陷型小鼠脾脏中的淋巴瘤。
