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Msh2 status modulates both apoptosis and mutation frequency in the murine small intestine
N J Toft1, D J Winton, J Kelly
1Cancer Research Campaign Laboratories, Department of Pathology, University Medical School, Teviot Place, Edinburgh, EH8 9AG, United Kingdom.
Abstract:
Deficiency in genes involved in DNA mismatch repair increases susceptibility to cancer, particularly of the colorectal epithelium. Using Msh2 null mice, we demonstrate that this genetic defect renders normal intestinal epithelial cells susceptible to mutation in vivo at the Dlb-1 locus. Compared with wild-type mice, Msh2-deficient animals had higher basal levels of mutation and were more sensitive to the mutagenic effects of temozolomide. Experiments using Msh2-deficient cells in vitro suggest that an element of this effect is attributable to increased clonogenicity. Indeed, we show that Msh2 plays a role in the in vivo initiation of apoptosis after treatment with temozolomide, N-methyl-N'-nitro-N-nitrosoguanidine, and cisplatin. This was not influenced by the in vivo depletion of O6-alkylguanine-DNA-alkyltransferase after administration of O6-benzylguanine. By analyzing mice mutant for both Msh2 and p53, we found that the Msh2-dependent apoptotic response was primarily mediated through a p53-dependent pathway. Msh2 also was required to signal delayed p53-independent death. Taken together, these studies characterize an in vivo Msh2-dependent apoptotic response to methylating agents and raise the possibility that Msh2 deficiency may predispose to malignancy not only through failed repair of mismatch DNA lesions but also through the failure to engage apoptosis.
Insights
Deficiency in DNA mismatch repair genes like Msh2 increases cancer risk. Msh2-deficient mice show increased mutations and impaired apoptosis, suggesting dual roles in cancer prevention.
Area of Science:
- Molecular Biology
- Genetics
- Cancer Research
Background:
- DNA mismatch repair (MMR) gene deficiencies, such as in Msh2, are linked to increased cancer susceptibility, particularly colorectal cancer.
- MMR system corrects DNA replication errors, maintaining genomic stability.
Purpose of the Study:
- To investigate the in vivo role of Msh2 in intestinal epithelial cell mutation and apoptosis.
- To determine the contribution of Msh2 to cellular responses to DNA damaging agents.
Main Methods:
- Utilized Msh2 null mice and wild-type littermates for in vivo studies.
- Assessed mutation rates at the Dlb-1 locus and sensitivity to mutagens like temozolomide.
- Examined apoptosis induction following treatment with genotoxic agents (temozolomide, N-methyl-N'-nitro-N-nitrosoguanidine, cisplatin).
- Investigated the role of p53 in Msh2-dependent apoptosis using Msh2/p53 double mutant mice.
Main Results:
- Msh2-deficient mice exhibited higher basal mutation rates and increased sensitivity to temozolomide.
- Msh2 deficiency impaired the in vivo induction of apoptosis following exposure to methylating agents and cisplatin.
- The Msh2-dependent apoptotic response was primarily mediated by p53, with a p53-independent pathway also identified for delayed cell death.
- Increased clonogenicity was observed in Msh2-deficient cells in vitro.
Conclusions:
- Msh2 plays a critical role in initiating apoptosis in response to DNA damage, particularly from methylating agents.
- Msh2 deficiency may promote malignancy through both failed DNA repair and impaired apoptotic signaling.
- These findings highlight Msh2's dual function in maintaining genomic integrity and triggering cell death pathways to prevent cancer.