Using in vitro mismatch repair (MMR) assay, we have identified 3 of 22 esop
hageal cancer cell lines exhibiting reduced MMR activity. By means of gel-s
hift assay, decreased binding ability to GT mismatch and CA loop was observ
ed in these 3 cell lines. However, we could not find any mutations in the h
MSH2, hMSH3 and hMSH6 genes, the protein products of which exhibit mismatch
binding activity in human cells. In addition, when using antibodies agains
t 5 MMR-related proteins (hMSH2, hMSH1, hMSH6, hPMS2 and hMLH1), no aberran
t expression was detected in any of them. When we examined 9 microsatellite
loci in endogenous genomic DNA, these 3 esophageal cancer cell lines, defi
cient in MMR, did not exhibit microsatellite instability. However, when we
examined the repetitious sequence on exogenous plasmid DNA which was introd
uced into these 3 esophageal cancer cells, the results suggested that MMR d
eficiency in esophageal cancer cells could result in moderate instability o
f the exogenous sequence. (C) 2001 Wiley-Liss, Inc.