Targeted deletion of the genes encoding NTH1 and NEIL1 DNA N-glycosylases reveals the existence of novel carcinogenic oxidative damage to DNA.
Targeted deletion of the genes encoding NTH1 and NEIL1 DNA N-glycosylases reveals the existence of novel carcinogenic oxidative damage to DNA.
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DOI：
10.1016/j.dnarep.2009.03.001
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发表时间：
2009-07-04
期刊：
影响因子：
3.8
通讯作者：
Teebor GW
中科院分区：
文献类型：
--
作者：
Chan MK;Ocampo-Hafalla MT;Vartanian V;Jaruga P;Kirkali G;Koenig KL;Brown S;Lloyd RS;Dizdaroglu M;Teebor GW
我们已经产生了一个菌株的小鼠缺乏两个DNA N-糖基化酶的碱基切除修复（BER），NTH 1和NEIL 1，同源的细菌Nth（内切核酸酶3）和Nei（内切核酸酶8）。虽然这些酶从DNA中去除几个氧化的碱基，但它们不能去除众所周知的鸟嘌呤的致癌氧化产物：7，8-二氢-8-氧代鸟嘌呤（8-OH-Gua），其被另一种DNA N-糖基化酶OGG 1去除。Nth 1 −/− Neil 1 −/−小鼠发生肺和肝细胞肿瘤的发生率远远高于单一敲除Nth 1 −/−和Neil 1 −/−小鼠。肺肿瘤仅在其DNA的K-ras密码子12中含有激活的GGT→GAT转换。这种转变与病理相似的肺肿瘤的K-ras密码子12中激活的GGT→GTT颠换形成鲜明对比，后者出现在缺乏OGG 1和第二种DNA N-糖基化酶MUTY的小鼠中。为了表征基因敲除小鼠的生化表型，从分离自对照、单基因敲除小鼠和双基因敲除小鼠的三种组织中分析氧化DNA碱基损伤的含量。8-OH-Gua含量在各基因型间无显著差异。相反，在Neil 1 −/−和Neil 1 −/− Nth 1 −/−小鼠的部分但非全部组织中，分别源自腺嘌呤和鸟嘌呤的4，6-二氨基-5-甲酰胺基嘧啶（FapyAde）和2，6-二氨基-4-羟基-5-甲酰胺基嘧啶（FapyGua）的含量增加。我们的Nth 1 −/− Neil 1 −/−小鼠中肿瘤的高发病率以及其肺肿瘤K-ras基因中激活突变的性质，首次揭示了对DNA的诱变和致癌氧化损伤的存在，而不是8-OH-Gua。
We have generated a strain of mice lacking two DNA N-glycosylases of base excision repair (BER), NTH1 and NEIL1, homologs of bacterial Nth (endonuclease three) and Nei (endonuclease eight). Although these enzymes remove several oxidized bases from DNA, they do not remove the well-known carcinogenic oxidation product of guanine: 7,8-dihydro-8-oxoguanine (8-OH-Gua), which is removed by another DNA N-glycosylase, OGG1. The Nth1−/−Neil1−/− mice developed pulmonary and hepatocellular tumors in much higher incidence than either of the single knockouts, Nth1−/− and Neil1−/−. The pulmonary tumors contained, exclusively, activating GGT→GAT transitions in codon 12 of K-ras of their DNA. Such transitions contrast sharply with the activating GGT→GTT transversions in codon 12 of K-ras of the pathologically similar pulmonary tumors, which arose in mice lacking OGG1 and a second DNA N-glycosylase, MUTY. To characterize the biochemical phenotype of the knockout mice, the content of oxidative DNA base damage was analyzed from three tissues isolated from control, single and double knockout mice. The content of 8-OH-Gua was indistinguishable among all genotypes. In contrast, the content of 4,6-diamino-5-formamidopyrimidine (FapyAde) and 2,6-diamino-4-hydroxy-5-formamidopyrimidine (FapyGua) derived from adenine and guanine, respectively, were increased in some but not all tissues of Neil1−/− and Neil1−/−Nth1−/− mice. The high incidence of tumors in our Nth1−/−Neil1−/− mice together with the nature of the activating mutation in the K-ras gene of their pulmonary tumors, reveal for the first time, the existence of mutagenic and carcinogenic oxidative damage to DNA which is not 8-OH-Gua.