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Mutagenic potency at the Na+/K+ ATPase locus correlates with cycle-dependent killing of 10T1/2 cells
G J Smith1, J W Grisham, K S Bentley
1Department of Pathology, School of Medicine, University of North Carolina, Chapel Hill 27599-7525.
Abstract:
Perturbation of DNA replication by chemical-DNA adducts produced by exposure to mutagenic/carcinogenic chemicals results in mutagenic or cytotoxic damage in the DNA. Demonstration of a correlation between cell cycle dependency of cytotoxicity and point mutation at the Na+/K+ ATPase gene could suggest that the two consequences of chemical exposure are caused by the same damage in the template DNA and that both are mediated through DNA replication-associated mechanisms. N-methyl-N'-nitro-N-nitrosoguanidine, N-ethyl-N'-nitro-N-nitrosoguanidine, 4-nitroquinoline-1-oxide, and benzo(a)pyrene-trans-7,8-dihydrodiol-9,10-epoxide demonstrated cell cycle-related patterns of cytotoxicity in 10T1/2 cells, with maximal cell killing produced by exposure in early S phase, and were highly efficient mutagens of the Na+/K+ ATPase gene relative to their cytotoxic potential. In contrast, methyl methanesulfonate and N-acetoxy-N-2-fluorenylacetamide were maximally cytotoxic in cell populations exposed in early G1 phase and were weak mutagens of the Na+/K+ ATPase gene at comparable levels of cytotoxicity. These data suggest that mutagenic/carcinogenic chemicals that are effective at producing mutations by misreplication kill cells by a related mechanism that may be associated with the perturbation of DNA replication.
Insights
Chemicals causing DNA damage during replication can lead to mutations or cell death. This study links cell cycle-dependent cytotoxicity and gene mutations, suggesting shared DNA replication-related mechanisms for both outcomes.
Area of Science:
- Molecular Biology
- Genetics
- Toxicology
Background:
- Chemicals can damage DNA, causing mutations and cell death.
- DNA replication is a critical process sensitive to chemical damage.
- The Na+/K+ ATPase gene is a target for studying chemical mutagenesis.
Purpose of the Study:
- To investigate the relationship between cell cycle-dependent cytotoxicity and point mutations at the Na+/K+ ATPase gene.
- To determine if chemical-induced mutagenicity and cytotoxicity share common DNA replication-associated mechanisms.
- To differentiate chemicals based on their cell cycle-specific effects on DNA damage and mutation.
Main Methods:
- Exposure of 10T1/2 cells to various mutagenic/carcinogenic chemicals at different cell cycle phases.
- Assessment of cytotoxicity and mutation frequency at the Na+/K+ ATPase gene.
- Analysis of cell cycle dependency of both cytotoxic and mutagenic effects.
Main Results:
- N-methyl-N'-nitro-N-nitrosoguanidine, N-ethyl-N'-nitro-N-nitrosoguanidine, 4-nitroquinoline-1-oxide, and benzo(a)pyrene-trans-7,8-dihydrodiol-9,10-epoxide showed cell cycle-dependent cytotoxicity, peaking in early S phase, and were potent mutagens.
- Methyl methanesulfonate and N-acetoxy-N-2-fluorenylacetamide were maximally cytotoxic in early G1 phase and weak mutagens.
- A correlation was observed between cell cycle-dependent cytotoxicity and mutation frequency for some chemicals.
Conclusions:
- Chemicals that induce mutations via misreplication may kill cells through related DNA replication-associated mechanisms.
- The cell cycle dependency of cytotoxicity and mutation suggests shared underlying DNA damage and repair pathways.
- Differential responses to chemicals based on cell cycle phase can inform about their mutagenic and cytotoxic potentials.