Related Experiment Videos
Selection for genome instability by DNA damage in human cells: unstable microsatellites and their consequences for
1Imperial Cancer Research Fund, Clare Hall Laboratories, Hertsfordsbire, United Kingdom. hampson@icrf.icnet.uk
Abstract:
The emergence of tumour cells resistant to chemotherapeutic treatment is a major confounding factor in anticancer treatment. Many chemotherapeutic drugs are DNA damaging agents. Resistance to DNA damage can be acquired via a plethora of different mechanisms, including, surprisingly, loss of DNA mismatch repair activity. The DNA mismatch repair system acts after DNA replication and corrects non-Watson-Crick base pairs and other replication errors. Human cells lacking mismatch repair activity have high spontaneous mutation rates. Frequent frameshift mutations in repetitive DNA sequences are characteristically associated with the defect. This hypermutability at repetitive sequences is termed microsatellite instability. DNA mismatch repair defects underlie a predisposition to cancer and are associated with a significant fraction of apparently sporadic cancer cases. In contrast to many other neoplasms, gross genetic aberrations are rare in cells from tumours with microsatellite instability. In these mismatch repair-defective tumours, certain genes that would normally hinder tumour development are frequently found to be inactivated by frameshift mutations in repetitive DNA tracts within their coding sequences. This implies that the small-scale genome alterations characteristic of mismatch repair defects can act as a driving force in tumour development.
Insights
Loss of DNA mismatch repair activity surprisingly leads to chemotherapy resistance in cancer. This defect causes microsatellite instability, driving tumor development through frameshift mutations.
Area of Science:
- Molecular Biology
- Genetics
- Oncology
Background:
- Chemotherapy resistance is a significant challenge in cancer treatment.
- Many anticancer drugs function by damaging DNA.
- Mechanisms of resistance include defects in DNA repair pathways.
Purpose of the Study:
- To investigate the role of DNA mismatch repair (MMR) deficiency in acquired resistance to DNA-damaging chemotherapeutic agents.
- To elucidate the link between MMR defects, microsatellite instability, and tumor development.
Main Methods:
- Analysis of DNA mismatch repair activity in chemotherapeutic-resistant tumor cells.
- Characterization of mutation types, focusing on repetitive DNA sequences.
- Examination of gene inactivation via frameshift mutations in MMR-defective tumors.
Main Results:
- Loss of DNA mismatch repair activity confers resistance to DNA-damaging chemotherapy.
- MMR-deficient cells exhibit high spontaneous mutation rates, particularly frameshift mutations in repetitive sequences (microsatellite instability).
- In MMR-defective tumors, inactivation of tumor suppressor genes by frameshift mutations is a common mechanism of tumor development.
Conclusions:
- Microsatellite instability arising from DNA mismatch repair defects can be a primary driver of tumorigenesis.
- Understanding MMR deficiency is crucial for developing effective anticancer strategies and overcoming treatment resistance.