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Preferential DNA damage and poor repair determine ras gene mutational hotspot in human cancer
Zhaohui Feng1, Wenwei Hu, James X Chen
1Department of Environmental Medicine, New York University School of Medicine, Tuxedo 10987, USA.
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.
Conclusion:
These findings link the human cancer mutational hotspot at codon 12 of K-ras to preferential DNA damage and poor repair.
Insights
Mutations in the K-ras gene at codon 12 are common in human cancers. This study found that carcinogens preferentially damage this K-ras codon and DNA repair is less efficient, linking damage to cancer mutations.
Area of Science:
- Molecular biology
- Cancer research
- Genetics
Background:
- Ras gene mutations are prevalent in human cancers.
- Mutations at specific codons (12, 13, 61) activate oncogenic function.
- Codon 12 mutations in K-ras are the most frequent in human cancers.
Purpose of the Study:
- To investigate if codon 12 of human K-ras is susceptible to carcinogen-induced DNA damage.
- To determine if carcinogen-DNA adducts at codon 12 are repaired less efficiently.
- To examine tobacco smoke carcinogen-induced DNA damage in human cells.
Main Methods:
- Utilized the UvrABC nuclease incision method combined with ligation-mediated polymerase chain reaction.
- Mapped DNA adduct distribution induced by benzo[a]pyrene diol epoxide (BPDE) and other bulky carcinogens in H-ras, N-ras, and K-ras genes (exons 1-2).
- Analyzed BPDE-DNA adduct repair efficiency in these three genes.
Main Results:
- Codons 12 and 14 of K-ras were identified as hotspots for carcinogen-DNA adduct formation.
- BPDE-DNA adducts at K-ras codon 14 were repaired nearly twice as fast as those at codon 12.
- While BPDE-DNA adducts formed at codon 12 of H-ras and N-ras, these were not hotspots, and repair rates showed no substantial difference.
Conclusions:
- The study links the human cancer mutational hotspot at K-ras codon 12 to preferential DNA damage.
- Findings suggest that poor DNA repair efficiency at K-ras codon 12 contributes to its high mutation rate in cancer.