Accumulation of DNA methylation is associated with tumor stage in gastric cancer.
BACKGROUND
The authors purpose in this study was to clarify the difference in terms of clinicopathologic features between gastric cancer (GC) with high numbers of DNA methylated genes and CpG island methylator phenotype (CIMP)-positive GC as originally defined.


METHODS
We analyzed DNA methylation of 12 tumor-related genes (hMLH1, MGMT, p16(INK4a), CDH1, RAR-beta, HLTF, RIZ1, TM, FLNc, LOX, HRASLS, HAND1) in 75 samples of GC from 75 patients, 25 samples of corresponding nonneoplastic mucosa from 25 patients, and 10 samples of normal gastric mucosa from 10 healthy young individuals by methylation-specific polymerase chain reaction (PCR) and bisulfite PCR. We also investigated CIMP status by examining the methylation of five MINT loci and p53 mutation status by PCR single-strand conformation polymorphism. We measured levels of expression of mRNAs for these 12 genes by quantitative reverse transcription PCR in 50 GC specimens.


RESULTS
The average number of methylated genes per tumor was 4.83. DNA methylation of each gene was correlated with low expression of the respective mRNA. High methylation (GC with 5 or more methylated genes) was detected in 39 (52.0%) of 75 GCs. Twenty-nine (37.8%) of 75 GCs were CIMP-positive. DNA methylation of each of the 12 genes was observed more frequently in the high-methylation group than in the low-methylation group. Methylation of 6 specific genes occurred more frequently in CIMP-positive GC than in CIMP-negative GC. Methylation of the remaining 6 genes was not correlated with CIMP-status. High methylation was found more frequently in Stage III/IV GC (26 of 40 cases, 65.0%) than in Stage I/II GC (13 of 35 cases, 37.1%, P = 0.029).CONCLUSIONS.These findings indicate that GCs with higher numbers of methylated genes have more distinct DNA methylation profiles than the originally defined CIMP-positive GCs. DNA methylation of tumor-related genes accumulates in conjunction with tumor progression.
Department of Molecular Pathology, Graduate School of Biomedical Sciences, Hiroshima University, Kasumi 1-2-3, Minami-ku, Hiroshima 734-8551, Japan.
Naohide
N
Oue
Yoshitsugu
Y
Mitani
Junichi
J
Motoshita
Shunji
S
Matsumura
Kazuhiro
K
Yoshida
Hiroki
H
Kuniyasu
Hirofumi
H
Nakayama
Wataru
W
Yasui
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D016022:Case-Control Studies; D018899:CpG Islands; D019175:DNA Methylation; D018450:Disease Progression; D005260:Female; D005753:Gastric Mucosa / Q000378:metabolism / Q000473:pathology; D015972:Gene Expression Regulation, Neoplastic; D020868:Gene Silencing; D016147:Genes, Tumor Suppressor; D016158:Genes, p53 / Q000502:physiology; D006801:Humans; D007414:Intestinal Neoplasms / Q000235:genetics / Q000473:pathology; D008297:Male; D008679:Metaplasia / Q000235:genetics / Q000473:pathology; D008875:Middle Aged; D009367:Neoplasm Staging; D010641:Phenotype; D016133:Polymerase Chain Reaction; D018807:Polymorphism, Single-Stranded Conformational; D011401:Promoter Regions, Genetic / Q000235:genetics; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D012189:Retrospective Studies; D013274:Stomach Neoplasms / Q000235:genetics* / Q000378:metabolism; D014158:Transcription, Genetic
D012333:RNA, Messenger