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Analysis of MSH3 in endometrial cancers with defective DNA mismatch repair
E M Swisher1, D G Mutch, T J Herzog
1Department of Obstetrics and Gynecology, Washington University School of Medicine, St. Louis, Missouri 63110, USA.
Objective:
To clarify the origin of defective mismatch repair (MMR) in sporadic endometrial cancers with microsatellite instability (MSI), a thorough mutation analysis was performed on the human mismatch repair gene MSH3.
Methods:
Twenty-eight MSI-positive endometrial cancers were investigated for mutations in the human mismatch repair gene MSH3 using single-strand conformation variant (SSCV) analysis of all 24 exons. All variants were sequenced. Loss of heterozygosity was investigated at all MSH3 polymorphisms discovered. A subset of tumors were investigated for methylation of the 5' promoter region of MSH3 using Southern blot hybridization.
Results:
An identical single-base deletion (delta A) predicted to result in a truncated proteins was discovered in six tumors (21.4%). This deletion occurs in a string of eight consecutive adenosine residues (A8). Because simple repeat sequences are unstable in cells with defective MMR, the observed mutation may be an effect, rather than a cause, of MSI. Evidence of inactivation of the second MSH3 allele in tumors with the delta A mutation would strongly support a causal role for these MSH3 mutations. However, there was no evidence of a second mutation, loss of sequences, or methylation of the promoter region in any of the tumors with the delta A mutation.
Conclusion:
Although the delta A mutation is a frequent event in sporadic MSI-positive endometrial cancers, it may not be causally associated with defective DNA MMR.
Insights
A frequent MSH3 gene mutation (delta A) was found in endometrial cancers with microsatellite instability (MSI). However, this mutation may be an effect, not the cause, of defective DNA mismatch repair (MMR).
Area of Science:
- Oncology
- Genetics
- Molecular Biology
Background:
- Sporadic endometrial cancers often exhibit microsatellite instability (MSI).
- The role of the MSH3 gene in defective DNA mismatch repair (MMR) in these cancers is unclear.
Purpose of the Study:
- To investigate mutations in the MSH3 gene as a potential cause of defective MMR in MSI-positive endometrial cancers.
- To analyze the MSH3 gene for mutations and assess their association with MSI in endometrial tumors.
Main Methods:
- Mutation analysis of all 24 exons of the MSH3 gene using single-strand conformation variant (SSCV) analysis in 28 MSI-positive endometrial cancers.
- Sequencing of identified variants, investigation of loss of heterozygosity at MSH3 polymorphisms, and analysis of MSH3 promoter methylation via Southern blot hybridization.
Main Results:
- A single-base deletion (delta A) in a polyadenosine tract (A8) was identified in 21.4% of tumors, potentially leading to a truncated MSH3 protein.
- The delta A mutation occurred in a simple repeat sequence, suggesting it might be a consequence, not a cause, of MSI.
- No evidence of a second MSH3 allele inactivation (mutation, deletion, or methylation) was found in tumors with the delta A mutation.
Conclusions:
- The delta A mutation in the MSH3 gene is a common finding in sporadic MSI-positive endometrial cancers.
- Despite its frequency, the delta A mutation may not be the primary cause of defective DNA mismatch repair in these cancers.
- Further research is needed to fully elucidate the role of MSH3 in endometrial cancer development and MSI.