Chromium(VI) enhances (±)-anti-7β,8α-dihydroxy-9α, 10α-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene-induced cytotoxicity and mutagenicity in mammalian cells through its inhibitory effect on nucleotide excision repair
Chromium(VI) enhances (±)-anti-7β,8α-dihydroxy-9α, 10α-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene-induced cytotoxicity and mutagenicity in mammalian cells through its inhibitory effect on nucleotide excision repair
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DOI：
10.1021/bi048560o
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发表时间：
2004-11-09
期刊：
影响因子：
2.9
通讯作者：
Tang, MS
中科院分区：
文献类型：
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作者：
Hu, WW;Feng, ZH;Tang, MS
铬(VI)[Cr(VI)]是一种普遍存在的环境污染物，对人类和实验动物都是一种众所周知的致癌物质，尽管它本身是一种微弱的诱变剂。职业性接触铬(VI)与肺癌的高发病率密切相关，但其潜在机制尚不清楚。吸烟是导致肺癌的主要原因，而烟草烟雾中的多环芳烃(PAHs)是主要的致病因素。由于人类经常同时暴露于铬(VI)和多环芳烃，因此铬(VI)和多环芳烃可能在致突变性和细胞毒性方面具有协同作用，从而导致与这两种药物接触相关的肺癌的高发病率。在这项研究中，我们通过测定铬(VI)暴露对多环芳烃的活性代谢物(+/-)-anti-7beta，8alpha-dihydroxy-9alpha，10alpha-epoxy-7，8，9，10-tetrahydrobenzo[alpha]pyrene(BPDE)诱导的中国仓鼠卵巢(CHO)细胞的细胞毒性、诱变性和DNA加合物形成的影响来验证这种可能性。利用腺嘌呤磷酸核糖基转移酶(aprt(+))-->；aprt(-)-->；正向突变试验，我们发现，虽然铬(VI)单独诱导的突变频率很低，但它大大增强了BPDE诱导的核苷酸切除修复(NER)熟练的CHO细胞的突变。铬(VI)暴露也大大增强了BPDE诱导的NER熟练细胞的杀伤作用。已知BPDE的细胞毒性和致突变性主要是由DNA加合物的形成引起的，DNA加合物被NER去除。为了验证铬(VI)对细胞毒性和致突变性的增强可能是通过抑制NER而引起的，我们使用了NER缺乏的细胞，而在这些细胞中没有观察到铬(VI)的增强作用。我们进一步发现，虽然铬(VI)暴露不改变总的BPDE-DNA加合物的形成，但它显著地抑制了NER熟练细胞中基因组DNA的BPDE-DNA加合物的修复。利用宿主细胞再激活实验，我们发现，在NER熟练的细胞中，铬(VI)暴露后，荧光素酶报告基因中BPDE-DNA加合物的修复受到极大的抑制，而在NER缺乏的细胞中则没有。综上所述，这些结果清楚地表明，铬(VI)暴露可通过抑制细胞内NER途径而大大增强多环芳烃的致突变性和细胞毒性，这可能是铬(VI)诱发人类致癌的一个重要机制。
Chromium(VI) [Cr(VI)], a ubiquitous environmental contaminant, is a well-known carcinogen to both humans and experimental animals, although it is a weak mutagen by itself. Occupational exposure to Cr(VI) is strongly associated with a high incidence of lung cancer, but the underlying mechanisms remain unclear. Tobacco smoking is the major cause of lung cancer, and polycyclic aromatic hydrocarbons (PAHs) in tobacco smoke are the major etiological agents. Since humans are frequently exposed to both Cr(VI) and PAHs, it is possible that Cr(VI) and PAHs have a synergistic effect on mutagenecity and cytotoxicity that contributes to the high incidence of lung cancer associated with exposure to both agents. In this study, we tested this possibility by determining the effect of Cr(VI) exposure on (+/-)-anti-7beta,8alpha-dihydroxy-9alpha,10alpha-epoxy-7,8,9,10-tetrahydrobenzo[alpha]pyrene (BPDE, an active metabolite of PAHs) induced cytotoxicity, mutagenicity, and DNA adduct formation in Chinese hamster ovary (CHO) cells. Using the adenine phosphoribosyltransferase (APRT(+)) --> APRT(-) --> forward mutation assay, we found that while Cr(VI) alone induced low mutation frequency, it greatly enhanced BPDE-induced mutations in nucleotide excision repair (NER)-proficient CHO cells. Cr(VI) exposure also greatly enhanced BPDE-induced killing in NER-proficient cells. It is known that the cytotoxicity and mutagenicity of BPDE are mainly caused by the formation of DNA adduct, which are removed by NER. To test the possibility that the enhancement of cytotoxicity and mutagenicity by Cr(VI) is caused by the inhibition of NER, NER-deficient cells were used, and the enhancement effects of Cr(VI) were not observed in those cells. We further found that while Cr(VI) exposure does not change the total BPDE-DNA adduct formation, it significantly inhibited the repair of BPDE-DNA adducts from genomic DNA in NER-proficient cells. Using a host cell reactivation assay, we found that the repair of BPDE-DNA adduct in a luciferase reporter gene is greatly inhibited after Cr(VI) exposure in NER-proficient cells while not in NER-deficient cells. Together these results clearly demonstrate that Cr(VI) exposure can greatly enhance the mutagenicity and cytotoxicity of PAHs by inhibiting the cellular NER pathway, and this may constitute an important mechanism for Cr(VI)induced human carcinogenesis.