Mutation and methylation of hMLH1 in gastric carcinomas with microsatellite instability.
OBJECTIVE
To appraise the correlation of mutation and methylation of hMSH1 with microsatellite instability (MSI) in gastric cancers.


METHODS
Mutation of hMLH1 was detected by Two-dimensional electrophoresis (Two-D) and DNA sequencing; Methylation of hMLH1 promoter was measured with methylation-specific PCR; MSI was analyzed by PCR-based methods.


RESULTS
Sixty-eight cases of sporadic gastric carcinoma were studied for mutation and methylation of hMLH1 promoter and MSI. Three mutations were found, two of them were caused by a single bp substitution and one was caused by a 2 bp substitution, which displayed similar Two-D band pattern. Methylation of hMLH1 promoter was detected in 11(16.2 %) gastric cancer. By using five MSI markers, MSI in at least one locus was detected in 17/68(25 %) of the tumors analyzed. Three hMLH1 mutations were all detected in MSI-H (>=2 loci, n=8), but no mutation was found in MSI-L (only one locus, n=9) or MSS (tumor lacking MSI or stable, n=51). Methylation frequency of hMLH1 in MSI-H (87.5 %, 7/8) was significantly higher than that in MSI-L (11.1 %, 1/9) or MSS (5.9 %, 3/51) (P<0.01-0.001), but no difference was found between MSI-L and MSS (P>0.05).


CONCLUSIONS
Both mutation and methylation of hMLH1 are involved in the MSI pathway but not related to the LOH pathway in gastric carcinogenesis.
Fang
Dian-Chun
DC
Southwest Hospital, Third Military Medical University, Chongqing 400038, China. fangdianchun@hotmail.com
Wang
Rong-Quan
RQ
Yang
Shi-Ming
SM
Yang
Jian-Ming
JM
Liu
Hai-Feng
HF
Peng
Gui-Yong
GY
Xiao
Tian-Li
TL
Luo
Yuan-Hui
YH
D048868:Adaptor Proteins, Signal Transducing; D020137:Base Pair Mismatch / Q000235:genetics; D001483:Base Sequence; D002352:Carrier Proteins; D019175:DNA Methylation; D017931:DNA Primers; D004273:DNA, Neoplasm / Q000235:genetics* / Q000302:isolation & purification; D005091:Exons; D006801:Humans; D018895:Microsatellite Repeats; D000070957:MutL Protein Homolog 1; D009154:Mutation; D009363:Neoplasm Proteins / Q000235:genetics*; D009687:Nuclear Proteins; D016133:Polymerase Chain Reaction; D011401:Promoter Regions, Genetic; D013274:Stomach Neoplasms / Q000235:genetics* / Q000473:pathology / Q000601:surgery
D048868:Adaptor Proteins, Signal Transducing; D002352:Carrier Proteins; D017931:DNA Primers; D004273:DNA, Neoplasm; C501486:MLH1 protein, human; D009363:Neoplasm Proteins; D009687:Nuclear Proteins; D000070957:MutL Protein Homolog 1