Analysis of MSH3 in endometrial cancers with defective DNA mismatch repair.
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.


CONCLUSIONS
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.
Swisher
E M
EM
Department of Obstetrics and Gynecology, Washington University School of Medicine, St. Louis, Missouri 63110, USA.
Mutch
D G
DG
Herzog
T J
TJ
Rader
J S
JS
Kowalski
L D
LD
Elbendary
A
A
Goodfellow
P J
PJ
D015139:Blotting, Southern; D019175:DNA Methylation; D004252:DNA Mutational Analysis; D004260:DNA Repair / Q000235:genetics*; D016889:Endometrial Neoplasms / Q000235:genetics*; D005260:Female; D006801:Humans; D019656:Loss of Heterozygosity; D018895:Microsatellite Repeats; D018807:Polymorphism, Single-Stranded Conformational; D011401:Promoter Regions, Genetic; D015183:Restriction Mapping