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Use of shuttle vectors to study the molecular processing of defined carcinogen-induced DNA damage: mutagenicity of
J C Klein1, M J Bleeker, J T Lutgerink
1Division of Chemical Carcinogenesis, The Netherlands Cancer Institute, Amsterdam.
Abstract:
We developed a simian virus 40 based shuttle vector system to study the molecular consequences of distinct carcinogen-induced DNA lesions in human cells. To establish the mutagenicity of O4-ethylthymine adducts, oligonucleotides carrying a single O4-ethylthymine adduct at a unique position were ligated into the vector molecules. Following replication in HeLa cells on average 23% of the progeny molecules carried a mutation in the region of modification. The vast majority of these mutations represented single T----C transitions at the position of the modified base, most probably as a consequence of mispairing of the O4-ethylthymine residues during replication. To a minor extent the O4-ethylthymine adduct may also induce T----A transversions or double point mutations. The in vivo mutation frequency of the adduct was found to be comparable to that of a C-A mismatch at the same position, but was lower than that expected from in vitro experiments with adducted DNA templates and purified DNA polymerases.
Insights
This study shows that O4-ethylthymine DNA adducts cause mutations in human cells, primarily T to C changes. The in vivo mutation frequency was comparable to a DNA mismatch.
Area of Science:
- Molecular Biology
- Genetics
- Carcinogenesis
Background:
- Carcinogen-induced DNA damage is a key factor in cancer development.
- Understanding the mutagenic potential of specific DNA adducts is crucial for risk assessment.
Purpose of the Study:
- To investigate the mutagenicity of O4-ethylthymine adducts in human cells.
- To determine the types of mutations induced by this specific DNA lesion.
Main Methods:
- Development of a simian virus 40-based shuttle vector system.
- Ligation of oligonucleotides with a single O4-ethylthymine adduct into the vector.
- Replication of the vector in HeLa cells to analyze progeny DNA.
Main Results:
- Approximately 23% of progeny molecules carried mutations at the adduct site.
- The majority of mutations were single T to C transitions.
- Minor mutations included T to A transversions and double point mutations.
Conclusions:
- O4-ethylthymine adducts are mutagenic in vivo, primarily causing T:C transitions.
- In vivo mutagenicity is comparable to DNA mismatches but lower than in vitro predictions.