Effect Of Methylenetetrahydrofolate Reductase Gene C677T Polymorphism On The Methylation Status Of CpG Island In C-ERBB-2 Gene And The Association With Cancer

Objective To explore the methylation status of CpG island in the promoter region of C-erbB-2 gene in tumor and matched adjacent tissues and the expression of C-erbB-2 oncoprotein and to realize the effect of methylation status in C-erbB-2 gene promoter region on the oncoprotein expression.To investigate the effect of methylenetetrahydrofolate reductase(MTHFR) C677T gene polymorphism on C-erbB-2 methylation status and its association with cancer.Methods The methylation status of CpG island in the promoter of C-erbB-2 oncogene in 247 pathologically confirmed tumor tissues and the matched adjacent tissues were detected by the methylation specific polymerase chain reaction(MSP).The MTHFR C677T polymorphism in 247 patients with cancer and 100 healthy subjects were analyzed by the PCR-based restriction fragment length polymorphism(PCR-RFLP) method.The C-erbB-2 oncoproteins in 43 colorectal carcinoma tissues and the matched adjacent tissues were examinated by immunohistochemistry(IHC) method.Results The methylation rate of CpG island in the promoter region of the C-erbB-2 gene in tumor tissues was significantly lower than that in matched adjacent tissues(44.2%vs.74.4%,P=0.004).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 MTHFR gene 677 T allele was significantly higher in cancer patients than in 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 C-erbB-2 gene was lower in individuals with CT/TT genotype than in those with CC CT/TT genotype(39.4%vs.50.0%).This difference was not significant(P=0.103).The distribution difference of C allele and T allele was not significant between subjects with methylated and unmethylated C-erbB-2 promoter CpG island(P =0.078).However,in breast cancer,the frequency of CC genotype and C allele was significantly higher in patients with methylated C-erbB-2 promoter CpG island than that in patients with unmethylated C-erbB-2 promoter CpG island(P =0.008 and 0.007,respectively).The percentage of C-erbB-2 oncoprotein overexpression was significantly higher in 43 colorectal carcinoma tissues than that in matched adjacent tissues (67.4%vs.27.9%,P=0.000).There was no correlation of the overexpression of C-erbB-2 oncoprotein with patient age(P=0.586),sex(P=0.739),tumor localization(P=0.05),histological grade(P=0.815),lymph node metastases (P=0.594),but the C-erbB-2 oncoprotein overexpression was significantly associated with clinical stage(P=0.010).The hypomethylation of CpG island in the promoter region of the C-erbB-2 gene in colorectal carcinoma tissues was correlated with C-erbB-2 oncoprotein overexpression(P=0.03,r=0.331).Conclusion C-erbB-2 promoter CpG island was hypomethylated in tumor tissues and MTHFR 677 CT/TT genotype increased the risk of developing cancer.Moreover,in breast cancer patients,the MTHFR gene C677T polymorphism had an evident effect on the methylation status of the C-erbB-2 gene.In addition,the hypomethylation of CpG island in the promoter region of C-erbB-2 gene may be one of the important factors of C-erbB-2 oncoprotein overexpression in colorectal carcinomas and it would be a valuable marker as cancer molecular diagnosis and a therapy target.