The association between methylenetetrahydrofolate reductase polymorphism and promoter methylation in proximal colon cancer.
BACKGROUND
Methylenetetrahydrofolate reductase (MTHFR) plays a critical role in folate metabolism, which is an important pathway of the methyl donor for DNA methylation. The MTHFR gene has genetic variants (C667T and A1298C), which cause reduced enzyme activity. Impaired folate metabolism by these genetic variants of MTHFR could change the methylation pattern of DNA including promoter hypermethylation, which has been frequently observed in cancer. In this study, we compared the MTHFR genotypes and haplotype to the features of colorectal cancer focusing on the promoter methylation of tumor DNA.


METHODS
Genomic DNA was isolated from 194 colorectal cancer tissues and subjected to MTHFR genotyping by PCR-based restriction fragment length polymorphism analysis. The MTHFR haplotype was determined by combination of C667T and A1298C genotype and classified into 2 groups, high (H-haplotype) or low (L-haplotype) enzymatic activity of MTHFR. The methylation level of tumor suppressor genes (CDKN2A, hMLH1, ARF and TIMP3) was measured by a fluorescence-based, real-time methylation specific PCR method.


RESULTS
There was no significant association of the clinicopathological features with either C667T genotype, A1298C genotype or haplotype of MTHFR. The methylation level of CDKN2A was higher in cancer with the L-haplotype of MTHFR than in that with the H-haplotype when cancers of proximal origin were considered (p=0.029). hMLH1 methylation also tended to be higher in proximal colon cancers of MTHFR L-haplotype (p=0.059). In addition, the proximal colon cancers showing CpG island methylator phenotype (CIMP) were significantly more frequent in L-haplotype than in H-haplotype.


CONCLUSIONS
These results suggest that the haplotype with low enzymatic activity of MTHFR is linked with promoter hypermethylation and consequently modifies the risk of CIMP(+) proximal colon cancer development in the Japanese people. The relationship between MTHFR polymorphism and DNA methylation in the Japanese is contrary to the previous results in Caucasians. Further study is needed focusing on ethnic variations in the relationships among MTHFR polymorphism, DNA methylation and the development of CIMP(+) colorectal cancer.
Oyama
Kaeko
K
Department of Surgery, Kanazawa University School of Medicine, 13-1 Takaramachi, Kanazawa 920-8641, Japan.
Kawakami
Kazuyuki
K
Maeda
Kazuya
K
Ishiguro
Kaname
K
Watanabe
Go
G
D048868:Adaptor Proteins, Signal Transducing; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002352:Carrier Proteins; D003110:Colonic Neoplasms / Q000201:enzymology* / Q000235:genetics*; D019175:DNA Methylation; D005260:Female; D019942:Genes, p16; D006239:Haplotypes; D006801:Humans; D008297:Male; D042965:Methylenetetrahydrofolate Reductase (NADPH2) / Q000235:genetics*; D008875:Middle Aged; D000070957:MutL Protein Homolog 1; D009363:Neoplasm Proteins / Q000235:genetics; D009687:Nuclear Proteins; D011110:Polymorphism, Genetic; D011401:Promoter Regions, Genetic; D019717:Tissue Inhibitor of Metalloproteinase-3; D019714:Tissue Inhibitor of Metalloproteinases / Q000235:genetics; D025803:Tumor Suppressor Protein p14ARF / Q000235:genetics
D048868:Adaptor Proteins, Signal Transducing; D002352:Carrier Proteins; C501486:MLH1 protein, human; D009363:Neoplasm Proteins; D009687:Nuclear Proteins; C088390:TIMP3 protein, human; D019717:Tissue Inhibitor of Metalloproteinase-3; D019714:Tissue Inhibitor of Metalloproteinases; D025803:Tumor Suppressor Protein p14ARF; D042965:Methylenetetrahydrofolate Reductase (NADPH2); D000070957:MutL Protein Homolog 1