title: Preferential DNA damage and poor repair determine ras gene mutational hotspot in human cancer.
abstract: BACKGROUND
  Mutations in ras genes are commonly found in human cancers and in animal models. Although mutations at codons 12, 13, and 61 of H-, N- and K-ras genes can activate their oncogenic function, mutations at codon 12 of K-ras are the most common mutations found among the three ras genes in human cancers. To investigate whether codon 12 of human K-ras is especially susceptible to carcinogens and/or whether carcinogen-DNA adducts at this codon are repaired less efficiently, we examined tobacco smoke carcinogen-induced DNA damage in normal human bronchial epithelial and fibroblast cells.
  
  
  METHODS
  We used the UvrABC nuclease incision method in combination with ligation-mediated polymerase chain reaction to map the distribution of DNA adducts induced by benzo[a]pyrene diol epoxide (BPDE) and other bulky carcinogens within exons 1 and 2 in H-ras, N-ras, and K-ras. We also analyzed BPDE-DNA adduct repair efficiency in these three genes using the same method.
  
  
  RESULTS
  Codons 12 and 14 of the K-ras gene were hotspots for carcinogen-DNA adduct formation, with little and no adduct formation at codons 13 and 61, respectively. The BPDE-DNA adducts formed at codon 14 were repaired almost twice as quickly as those formed at codon 12. There was some BPDE-DNA adduct formation at codons 12 of H-ras and N-ras, but this codon was not a hotspot. Furthermore, no substantial difference in repair rates between codon 12 and the other codons analyzed (codons 3 and 18) was observed in either the H-ras or N-ras genes.
  
  
  CONCLUSIONS
  These findings link the human cancer mutational hotspot at codon 12 of K-ras to preferential DNA damage and poor repair.
authors.affiliation: Department of Environmental Medicine, New York University School of Medicine, Tuxedo 10987, USA.
authors.forename: Zhaohui
authors.initials: Z
authors.lastname: Feng
authors.forename: Wenwei
authors.initials: W
authors.lastname: Hu
authors.forename: James X
authors.initials: JX
authors.lastname: Chen
authors.forename: Annie
authors.initials: A
authors.lastname: Pao
authors.forename: Haiying
authors.initials: H
authors.lastname: Li
authors.forename: William
authors.initials: W
authors.lastname: Rom
authors.forename: Mien-Chie
authors.initials: MC
authors.lastname: Hung
authors.forename: Moon-shong
authors.initials: MS
authors.lastname: Tang
mesh_terms: D015123:7,8-Dihydro-7,8-dihydroxybenzo(a)pyrene 9,10-oxide / Q000009:adverse effects*; D001980:Bronchi; D002273:Carcinogens / Q000009:adverse effects*; D002478:Cells, Cultured; D002874:Chromosome Mapping / Q000379:methods; D003062:Codon / Q000187:drug effects / Q000235:genetics*; D018736:DNA Adducts / Q000187:drug effects*; D004249:DNA Damage / Q000187:drug effects*; D004260:DNA Repair / Q000187:drug effects*; D004706:Endodeoxyribonucleases / Q000378:metabolism; D004847:Epithelial Cells / Q000187:drug effects; D029968:Escherichia coli Proteins; D005347:Fibroblasts / Q000187:drug effects; D011905:Genes, ras / Q000187:drug effects*; D006801:Humans; D009153:Mutagens / Q000009:adverse effects*; D009369:Neoplasms / Q000139:chemically induced / Q000235:genetics*; D017354:Point Mutation / Q000187:drug effects*; D016133:Polymerase Chain Reaction / Q000379:methods; D012907:Smoking / Q000009:adverse effects
chemical_list: D002273:Carcinogens; D003062:Codon; D018736:DNA Adducts; D029968:Escherichia coli Proteins; D009153:Mutagens; D015123:7,8-Dihydro-7,8-dihydroxybenzo(a)pyrene 9,10-oxide; D004706:Endodeoxyribonucleases; C036385:endodeoxyribonuclease uvrABC