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Methylation tolerance in mismatch repair proficient cells with low MSH2 protein level
1Division of Molecular Biology, The Netherlands Cancer Institute, Plesmanlaan 121, 1066 CX, Amsterdam, The Netherlands.
Abstract:
Loss of DNA mismatch repair has been found in tumors associated with the familial cancer predisposition syndrome HNPCC (hereditary non-polyposis colorectal cancer) and a subset of sporadic cancers. MSH2 deficiency abolishes the action of the mismatch repair system, resulting in a phenotype which is characterized by an increased accumulation of base substitutions and frameshifts, enhanced recombination between homologous but non-identical DNA sequences, and tolerance to the cytotoxic effects of methylating agents. In this study we describe an embryonic stem cell line in which the level of MSH2 protein is 10-fold reduced compared to that in wild-type cells. Remarkably, these MSH2-low cells were as resistant to killing by methylating agents as cells completely lacking MSH2, while they had retained almost maximal mismatch repair capacity as judged from their anti-mutagenic and anti-recombinogenic capacity and the absence of microsatellite instability. In contrast, MSH2-low cells were highly sensitive to methylation-damage induced mutagenesis. Thus, 10-fold reduced MSH2 protein levels render cells resistant to the toxic and highly sensitive to the mutagenic effects of methylating agents. This condition is not manifested by microsatellite instability and may have implications for both the etiology and treatment of cancer.
Insights
Reduced MSH2 protein levels in cells confer resistance to methylating agent toxicity but increase sensitivity to their mutagenic effects. This mismatch repair deficiency phenotype lacks microsatellite instability, impacting cancer etiology and treatment.
Area of Science:
- Molecular Biology
- Genetics
- Cancer Research
Background:
- DNA mismatch repair (MMR) deficiency is implicated in hereditary non-polyposis colorectal cancer (HNPCC) and sporadic cancers.
- MSH2 protein is crucial for MMR; its deficiency leads to increased mutations, recombination, and resistance to methylating agents.
Purpose of the Study:
- To investigate the effects of a 10-fold reduction in MSH2 protein levels on cellular response to methylating agents.
- To characterize the mismatch repair capacity and mutational phenotype of MSH2-low cells.
Main Methods:
- Generation of a mouse embryonic stem cell line with a 10-fold reduction in MSH2 protein.
- Assessment of cellular resistance and sensitivity to methylating agents.
- Evaluation of mismatch repair capacity via anti-mutagenic and anti-recombinogenic assays.
- Analysis of microsatellite instability.
Main Results:
- MSH2-low cells exhibited resistance to methylating agent cytotoxicity, similar to cells lacking MSH2 entirely.
- These cells retained significant mismatch repair capacity, showing anti-mutagenic and anti-recombinogenic properties without microsatellite instability.
- Conversely, MSH2-low cells demonstrated heightened sensitivity to mutagenesis induced by methylating agents.
Conclusions:
- A 10-fold decrease in MSH2 protein confers resistance to methylating agent toxicity while increasing susceptibility to their mutagenic effects.
- This specific MMR deficiency phenotype, lacking microsatellite instability, has potential implications for understanding cancer development and therapeutic strategies.