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A single amino acid substitution in MSH5 results in DNA alkylation tolerance
1Department of Microbiology and Immunology, University of Saskatchewan, 107 Wiggins Road, Saskatoon, SK, Canada S7N 5E5.
Abstract:
DNA alkylation tolerance is a major concern in cancer chemotherapy. It has been suggested that mutations in DNA mismatch repair genes may result in alkylation tolerance. This alkylation tolerant phenotype is often manifested in cells lacking an O(6)-methylguanine DNA methyltransferase (MTase) activity. However, deletion of each mismatch repair gene in the MTase mutant of a model eukaryotic yeast does not result in alkylation tolerance. We previously isolated an alkylation tolerant mutant and mapped the mutation to MSH5. Here we present evidence that a single point mutation that results in a Y823H amino acid substitution, but not deletion, of the MSH5 gene is responsible for tolerance to killing by DNA alkylating agents. We also find that other preexisting amino acid variations may also enhance alkylation tolerance in the above mutation background. Since MSH5 encodes a protein homologous to DNA mismatch recognition proteins, mismatch repair genes are frequently mutated in cancers cells and, like mismatch repair genes, MSH5 is highly conserved from yeast to human, this observation suggests novel mechanisms of chemotherapeutic drug resistance that may occur in certain human cancer patients.
Insights
A specific mutation in the MSH5 gene, not its deletion, confers DNA alkylation tolerance. This finding suggests new mechanisms for chemotherapy drug resistance in cancer patients.
Area of Science:
- Molecular Biology
- Genetics
- Cancer Research
Background:
- DNA alkylation is a significant challenge in cancer chemotherapy.
- Mutations in DNA mismatch repair genes are hypothesized to cause alkylation tolerance.
- Cells lacking O(6)-methylguanine DNA methyltransferase (MTase) activity often exhibit an alkylation-tolerant phenotype.
Purpose of the Study:
- To investigate the genetic basis of DNA alkylation tolerance.
- To determine the role of the MSH5 gene in DNA alkylation tolerance.
- To explore novel mechanisms of chemotherapeutic drug resistance.
Main Methods:
- Isolation and characterization of an alkylation-tolerant yeast mutant.
- Genetic mapping of the mutation to the MSH5 gene.
- Analysis of the effect of point mutations versus gene deletion in MSH5.
Main Results:
- A single point mutation (Y823H) in the MSH5 gene, not its deletion, confers tolerance to DNA alkylating agents.
- Preexisting amino acid variations can enhance alkylation tolerance in the presence of the MSH5 Y823H mutation.
- This contrasts with the lack of alkylation tolerance observed upon deletion of mismatch repair genes in MTase-mutant yeast.
Conclusions:
- The MSH5 gene plays a critical role in DNA alkylation tolerance.
- Specific point mutations in MSH5, rather than gene deletion, are responsible for this phenotype.
- This discovery suggests novel mechanisms of chemotherapeutic drug resistance in human cancer patients, particularly those with MSH5 variations.
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