Effect of the methylenetetrahydrofolate reductase gene C677T polymorphism on C-erbB-2 methylation status and its association with cancer

Methylation abnormalities of cancer-related genes are recognized to play an important role in carcinogenesis. Methylenetetrahydrofolate reductase (MTHFR) regulates DNA methylation by affecting synthesis of S-adenosylmethionine, which is a universal methyl donor for methylation reactions. MTHFR gene polymorphisms that affect enzymatic activity may be associated with DNA methylation and cancer susceptibility. In the present study, we investigated the MTHFR C677T polymorphism in 247 cancer patients and 100 healthy subjects using PCR-RFLP, as well as the methylation status of the CpG island in the promoter region of the C-erbB-2 oncogene in 247 tumor and matched adjacent tissue samples using methylation-specific PCR. The results revealed that the methylation rate of the C-erbB-2 gene was significantly lower in the tumor tissues than in the matched adjacent tissues (43.3 vs. 69.2%, P=0.000). No correlation was observed between the methylation patterns of C-erbB-2 in tumor tissues and the clinicopathological characteristics of the patients. The frequency of the MTHFR gene 677 T allele was significantly higher in cancer patients than in the healthy subjects, and the combined variant genotypes (677CT+TT) significantly increased the risk of developing cancer (OR=1.619, 95% CI 1.012-2.588, P=0.043). Among the cancer patients, the methylation rate of the C-erbB-2 gene was higher in indi-viduals with the CC genotype than in those with the CT/TT genotype (50.0 vs. 39.4%). This difference was not significant (P=0.103). However, a significant difference was found in patients with breast cancer (P=0.008). In conclusion, the C-erbB-2 promoter CpG island was hypomethylated in cancer patients, and the MTHFR 677 CT/TT genotype increased the risk of developing the disease. Moreover, in breast cancer patients, the MTHFR gene C677T polymorphism had an effect on the methylation status of the C-erbB-2 gene.