Targeted deletion of the genes encoding NTH1 and NEIL1 DNA N-glycosylases reveals the existence of novel carcinogenic oxidative damage to DNA

Abstract

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.

Epigenetic screen of human DNA repair genes identifies aberrant promoter methylation of NEIL1 in head and neck squamous cell carcinoma

“…30 NEIL1 and NEIL1/NTH1 double knockout mice developed pulmonary and hepatocellular tumors. 31 Genetic alterations of the NEIL1 gene in human gastric cancer lead to impaired DNA glycosylase activity or a truncated protein. 32 Furthermore, NEIL1 has been shown to interact with other DNA repair genes which have been linked to cancer.…”

“…32 Furthermore, NEIL1 has been shown to interact with other DNA repair genes which have been linked to cancer. 31,33,34 The level of NEIL1 is greatly diminished in cells depleted for FANC proteins and Fanconi anemia cell lines. Expression of the NEIL1 protein partially reverses the hypersensitivity of Fanconi anemia cells to interstrand crosslinks.…”

Effects of base excision repair proteins on mutagenesis by 8-oxo-7,8-dihydroguanine (8-hydroxyguanine) paired with cytosine and adenine

“…The four DNA glycosylases each function in the suppression of mutations by 8-oxo-Gua in DNA. The overlapped recognition of 8-oxo-Gua could explain the fact that single knock-out mice deficient in OGG1, MUTYH, NTH1, and NEIL1 show few tumor phenotypes [57,[65][66][67][68][69][70][71]. In contrast, there is evidence to support the view that polymorphisms in these DNA glycosylases are associated with human carcinogenesis (reviewed in 72).…”

Oxidative DNA damage in disease—Insights gained from base excision repair glycosylase‐deficient mouse models

“…Furthermore, cell culture studies have indicated that knock down of Neil1 renders cells more sensitive to oxidative stress, such as that induced by glucose oxidase or gamma irradiation [Rosenquist et al, 2003;Maiti et al, 2008]. NEIL1-deficient mice, although initially expected to display a promutagenic phenotype, have not been found to be significantly prone to spontaneous tumor formation, although lung adenomas and hepatocellular carcinomas have been documented in about 10-20% of aged animals [Chan et al, 2009]. A potential explanation for this lack of a cancer phenotype is overlapping substrate specificity with other NEIL isoforms or with NTH1, as discussed above.…”

“…A potential explanation for this lack of a cancer phenotype is overlapping substrate specificity with other NEIL isoforms or with NTH1, as discussed above. Indeed, Neil1 2/2 ; Nth1 2/2 double knockout mice have been shown to develop spontaneous pulmonary adenomas and carcinomas after the first year of life at much higher rates than WT counterparts [Chan et al, 2009]. Additionally, Neil1 2/2 ; Nth1 2/2 mice also developed hepatocellular carcinomas at higher rates than WT or Nth1 2/2 mice [Chan et al, 2009].…”