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Microsatellite instability, mismatch repair deficiency, and genetic defects in human cancer cell lines
J C Boyer1, A Umar, J I Risinger
1Laboratory of Molecular Genetics, National Institute of Environmental Health Sciences, Research Triangle Park, North Carolina 27709, USA.
Abstract:
The instability of short repetitive sequences in tumor DNA can result from defective repair of replication errors due to mutations in any of several genes required for mismatch repair. Understanding this repair pathway and how defects lead to cancer is being facilitated by genetic and biochemical studies of tumor cell lines. In the present study, we describe the mismatch repair status of extracts of 22 tumor cell lines derived from several tissue types. Ten were found to be defective in strand-specific mismatch repair, including cell lines from tumors of the colon, ovary, endometrium, and prostate. The repair defects were independent of whether the signal for strand specificity, a nick, was 5' or 3' to the mismatch. All 10 defective cell lines exhibited microsatellite instability. Repair activity was restored to 9 of these 10 extracts by adding a second defective extract made from cell lines having known mutations in either the hMSH2 or hMLH1 genes. Subsequent analyses revealed mutations in hMSH2 (4 lines) and hMLH1 (5 lines) that could explain the observed microsatellite instability and repair defects. Overall, this study strengthens the correlation between microsatellite instability and defective mismatch repair and the suggestion that diminuition in mismatch repair activity is a step in carcinogenesis common to several types of cancer. It also provides an extensive panel of repair-proficient and repair-deficient cell lines for future studies of mismatch repair.
Insights
Defective DNA mismatch repair, crucial for correcting replication errors, leads to microsatellite instability in various cancers. This study identified specific gene mutations (hMSH2, hMLH1) causing these defects, offering insights into carcinogenesis.
Area of Science:
- Molecular Biology
- Genetics
- Oncology
Background:
- DNA mismatch repair corrects replication errors, preventing mutations.
- Defects in mismatch repair are linked to cancer development.
- Microsatellite instability is a hallmark of defective mismatch repair.
Purpose of the Study:
- To assess the mismatch repair status of 22 tumor cell lines.
- To identify genetic mutations causing mismatch repair deficiencies.
- To correlate microsatellite instability with specific gene defects.
Main Methods:
- Biochemical assays on tumor cell extracts to assess mismatch repair activity.
- Complementation assays using extracts from cell lines with known mutations (hMSH2, hMLH1).
- Genetic sequencing to identify mutations in mismatch repair genes.
Main Results:
- Ten of 22 tumor cell lines showed defective strand-specific mismatch repair.
- All 10 defective cell lines exhibited microsatellite instability.
- Mutations in hMSH2 (4 lines) and hMLH1 (5 lines) were identified, explaining the observed defects.
Conclusions:
- Defective mismatch repair, indicated by microsatellite instability, is a common step in carcinogenesis across multiple cancer types.
- Specific mutations in hMSH2 and hMLH1 are significant contributors to mismatch repair deficiency.
- This study provides a valuable panel of cell lines for future research on DNA repair mechanisms.