Silencing-specific methylation and single nucleotide polymorphism of hMLH1 promoter in gastric carcinomas.
OBJECTIVE
To investigate CpG methylation and single nucleotide polymorphism (SNP) of a specific promoter region of hMLH1 in primary gastric carcinoma.


METHODS
Primary gastric carcinomas (n=80), their corresponding normal mucosal samples, and gastric mucosal biopsies from normal/gastritis control patients (n=54) were used. Hypermethylation at -253 nt and -251 nt in relation with the translational start site and SNP of a silencing specific region (-339 nt-46 nt) in the hMLH1 promoter were analyzed by Bst UI-combined bisulfite assay (COBRA), denaturing high performance liquid chromatogram (DHPLC), and sequencing.


RESULTS
(A) The specific methylation at -253 nt and -251 nt was observed in 2 of 60 primary gastric carcinomas, but neither in all of the corresponding mucosa nor in normal/gastritis samples, by Bst UI-COBRA and DHPLC. (B) The hMLH1 promoter was methylated homogeneously in the xenograft of the primary gastric carcinoma with the methylated and unmethylated hMLH1. (C) The pattern of SNP at -93 nt of the hMLH1 promoter in 54 Chinese patients with gastric carcinoma was the same as that in the control patients: 51 % was A/G heteroalleles, 34 % and 15 % were A/A and G/G homoalleles, respectively.


CONCLUSIONS
Biallelic inactivation of hMLH1 by epigenetic silencing existed in human primary gastric carcinoma homogeneously. Hypermethylation of hMLH1 may play a role in the early stage of development of a few gastric carcinomas. The SNP at -93 nt is not related to the susceptibility of gastric carcinomas.
Deng
Da-Jun
DJ
Peking University Health Science Center and Beijing Institute for Cancer Research, Beijing, 100034, China. dengdajun@sina.com
Zhou
Jin
J
Zhu
Bu-Dong
BD
Ji
Jia-Fu
JF
Harper
Jeffrey C
JC
Powell
Steven M
SM
D048868:Adaptor Proteins, Signal Transducing; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002277:Carcinoma / Q000235:genetics*; D002352:Carrier Proteins; D018899:CpG Islands; D004260:DNA Repair; D005260:Female; D020868:Gene Silencing; D006801:Humans; D008297:Male; D008745:Methylation; D008875:Middle Aged; D000070957:MutL Protein Homolog 1; D009363:Neoplasm Proteins / Q000235:genetics* / Q000378:metabolism; D009687:Nuclear Proteins; D020641:Polymorphism, Single Nucleotide; D011401:Promoter Regions, Genetic; D013274:Stomach Neoplasms / Q000235:genetics*; D013447:Sulfites / Q000378:metabolism
D048868:Adaptor Proteins, Signal Transducing; D002352:Carrier Proteins; C501486:MLH1 protein, human; D009363:Neoplasm Proteins; D009687:Nuclear Proteins; D013447:Sulfites; D000070957:MutL Protein Homolog 1