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Mismatch repair processing of carcinogen-DNA adducts triggers apoptosis
1Department of Pathology and Laboratory Medicine, Markey Cancer Center, University of Kentucky Medical Center, Lexington, Kentucky 40536, USA.
Abstract:
The DNA mismatch repair pathway is well known for its role in correcting biosynthetic errors of DNA replication. We report here a novel role for mismatch repair in signaling programmed cell death in response to DNA damage induced by chemical carcinogens. Cells proficient in mismatch repair were highly sensitive to the cytotoxic effects of chemical carcinogens, while cells defective in either human MutS or MutL homologs were relatively insensitive. Since wild-type cells but not mutant cells underwent apoptosis upon treatment with chemical carcinogens, the apoptotic response is dependent on a functional mismatch repair system. By analyzing p53 expression in several pairs of cell lines, we found that the mismatch repair-dependent apoptotic response was mediated through both p53-dependent and p53-independent pathways. In vitro biochemical studies demonstrated that the human mismatch recognition proteins hMutSalpha and hMutSbeta efficiently recognized DNA damage induced by chemical carcinogens, suggesting a direct participation of mismatch repair proteins in mediating the apoptotic response. Taken together, these studies further elucidate the mechanism by which mismatch repair deficiency predisposes to cancer, i.e., the deficiency not only causes a failure to repair mismatches generated during DNA metabolism but also fails to direct damaged and mutation-prone cells to commit suicide.
Insights
The DNA mismatch repair pathway signals programmed cell death after DNA damage from carcinogens. This pathway is crucial for cancer prevention by eliminating damaged cells.
Area of Science:
- Molecular Biology
- Cell Biology
- Genetics
Background:
- The DNA mismatch repair (MMR) pathway is primarily known for correcting DNA replication errors.
- Its role in cellular responses to DNA damage beyond replication fidelity has been less understood.
Purpose of the Study:
- To investigate a novel role for the MMR pathway in programmed cell death (apoptosis).
- To determine if MMR is involved in the cellular response to DNA damage induced by chemical carcinogens.
Main Methods:
- Comparing the sensitivity of MMR-proficient and MMR-deficient cells to chemical carcinogens.
- Analyzing p53 expression in response to DNA damage.
- Conducting in vitro biochemical assays with hMutSalpha and hMutSbeta proteins.
Main Results:
- MMR-proficient cells showed high sensitivity to cytotoxic effects of chemical carcinogens, unlike MMR-deficient cells.
- Apoptosis was induced in wild-type cells but not mutant cells, indicating MMR-dependence.
- The MMR-dependent apoptotic response involved both p53-dependent and p53-independent pathways.
- Human mismatch recognition proteins (h hMutSalpha and hMutSbeta) directly recognized carcinogen-induced DNA damage.
Conclusions:
- The MMR pathway plays a critical role in signaling apoptosis in response to DNA damage from chemical carcinogens.
- MMR deficiency not only impairs DNA repair but also compromises the elimination of damaged cells, contributing to cancer predisposition.
- This highlights a dual mechanism by which MMR deficiency promotes tumorigenesis.