Snyderwine E G, Bohr V A
Laboratory of Experimental Carcinogenesis, National Cancer Institute, NIH, Bethesda, Maryland 20892.
Cancer Res. 1992 Aug 1;52(15):4183-9.
4-Nitroquinoline 1-oxide (4NQO) is a model chemical carcinogen that has often been referred to as a UV mimetic agent. Previous studies have indicated that UV-induced pyrimidine dimers are repaired preferentially and strand-specifically in actively transcribing genes. In the current study we have examined the gene-specific and strand-specific repair of 4NQO in Chinese hamster ovary B-11 cells treated with 2.5 microM 4NQO. The methodology used for detecting adducts involved the treatment of DNA from 4NQO-exposed cells with uvrABC excinuclease, which incises DNA at adduct sites, followed by denaturing gel electrophoresis of DNA, Southern hybridization, and probing for the sequence of interest. We examined the active and inactive coding regions of the DHFR gene, the active adenine phosphoribosyltransferase gene, relatively inactive c-fos oncogene, and the mitochondrial genome for 4NQO adducts. Initial 4NQO adduct levels found in these genes varied from 1.10 to 1.52 adducts/10 kilobases. Little difference in repair was found between active coding and inactive regions of the DHFR gene, or between DHFR, adenine phosphoribosyltransferase, and c-fos genes, which are transcribed at different levels. Approximately 71% of 4NQO adducts were repaired within 24 h in all gene sequences examined. During this same time period, approximately 51% of adducts were repaired from the genome overall, as determined by comparing the removal of bound radiolabeled 4NQO to total DNA. The results indicate that 4NQO adducts, unlike UV light-induced cyclobutane pyrimidine dimers (UV dimers), are not preferentially repaired in transcriptionally active genes. However, there may be regions of the genome that are not repaired with the same efficiency as the specific genes examined here. In addition, little to no difference was observed in the repair of 4NQO adducts in the transcribed and nontranscribed strands of the DHFR gene, a finding which is also in contrast to results with UV dimers. Interestingly, 4NQO adducts, unlike UV dimers, were removed from the mitochondrial genome, suggesting that repair of select lesions occurs in this organelle. Thus, there appear to be some differences in the repair pathways operating for 4NQO adducts and UV dimers, particularly with respect to gene- and strand-specific DNA repair.
4-硝基喹啉-1-氧化物（4NQO）是一种典型的化学致癌物，常被称为紫外线模拟剂。先前的研究表明，紫外线诱导的嘧啶二聚体在活跃转录基因中优先且按链特异性进行修复。在本研究中，我们检测了用2.5微摩尔4NQO处理的中国仓鼠卵巢B-11细胞中4NQO的基因特异性和链特异性修复情况。检测加合物的方法包括用uvrABC核酸内切酶处理来自4NQO处理细胞的DNA，该酶在加合物位点切割DNA，然后对DNA进行变性凝胶电泳、Southern杂交，并探测感兴趣的序列。我们检测了二氢叶酸还原酶（DHFR）基因的活性和非活性编码区、活性腺嘌呤磷酸核糖转移酶基因、相对非活性的c-fos癌基因以及线粒体基因组中的4NQO加合物。在这些基因中最初发现的4NQO加合物水平为每10千碱基1.10至1.52个加合物。在DHFR基因的活性编码区和非活性区之间，或者在转录水平不同的DHFR、腺嘌呤磷酸核糖转移酶和c-fos基因之间，未发现修复存在显著差异。在所检测的所有基因序列中，约71%的4NQO加合物在24小时内被修复。在同一时间段内，通过比较结合的放射性标记4NQO与总DNA的去除情况，确定基因组总体上约51%的加合物被修复。结果表明，与紫外线诱导的环丁烷嘧啶二聚体（UV二聚体）不同，4NQO加合物在转录活跃基因中并非优先被修复。然而，基因组中可能存在一些区域，其修复效率与这里检测的特定基因不同。此外，在DHFR基因的转录链和非转录链中，4NQO加合物的修复几乎没有差异，这一发现也与UV二聚体的结果相反。有趣的是，与UV二聚体不同，4NQO加合物从线粒体基因组中被去除，这表明该细胞器中发生了特定损伤的修复。因此，4NQO加合物和UV二聚体的修复途径似乎存在一些差异，特别是在基因和链特异性DNA修复方面。
