Exploration On The Relationship Between Methylenetetrahydrofolate Reductase Gene C677T Polymorphisms And Susceptibility Of Breast Cancer And Ovarian Cancer

Epidemiology and clinical evidence indicate that the deficiency of folate can increase the affectability of the tumor. Both DNA impairment and DNA methylation are thought to play an important role in the process of cell malignant transformation and folate can induce tumorigenesis by interfering the process of DNA synthesis and methylation. The abnormality of folate metabolism can induce the aberration of DNA methylation, which may reduce the efficiency of DNA repair system. Insufficient methylation of genomic DNA may cause genomic instability .MTHFR is a critical enzyme that can regulate the metabolism of folate, which can catalyze the 5,10- methylenetetrahydrofolate into the 5-methylte- trahydrofolate that can't be converted into the substrate. 5-methyltetrahy- drofolate is the main active form of the folic acid in the blood plasma and the organization. The homocysteic acid gains DNA methylation of the 5-methylte- trahydrofolate,which changes into methionin (Met).The adenylase catalyzes Met into S-adenosylmethionine (SAM).SAM as the supplier of methylium has an important function in the process of DNA methylation and nucleic acid synthesis. The common single nucleotide polymorphisms leads to the amino acid change (677C→T/Ala222Val) of MTHFR, which cause enzyme activity reducing and the thermolability. Through investingating, C677T of MTHFR that locates catalytic district of MTHFR has the polymorphism. There are three types of MTHFR C677T mutations: wild type (C/C) , heterozygous mutation (C/T) and homozygous mutation (T/T). Both homozygous and heterozygous mutations can decrease the enzyme activity and the thermolability of MTHFR. The enzyme activity of homozygous mutation (T/T) and heterozygous mutation (C/T) is respectively 30 % and 60 % of the wild type (C/C). The discrepancy of MTHFR that leads to the reduction of 5-methyltetrahydrofolate and the augmentation of the homocysteic acid(HCA) results in the dyssynthesis of the Met and finally makes DNA hypomethylation. There are many reports that point out MTHFR gene polymorphisms have relation to the susceptibility of the tumor, for instance colorectal cancer,gastric cancer,carcinoma of esophagus and so on. As far as, the study on the methylenetetrahydrofolate reductase gene C677T polymorphisms Associated with breast cancer and ovarian cancer is seldom.Objective: To investigate the frequency and distribution of MTHFR SNPs in the northeast of China and explore on the relationship between methylenetetrahydrofolate reductase(MTHFR) polymerphisms and the risk of breast cancer and ovarian cancer. Provide gene diagnosis and rational therapy for breast cancer and ovarian cancer ,Methods: 1. Obtaining gene: In this thesis, we isolated the genome DNA from 80 breast cancer, 81 ovarian cancer patients and 80 wide control. Complete MTHFR sequence was obtained according to Genbank database and a pair of specific primers was designed. Target DNA fragment were amplified by using polymerase chain reaction (PCR), which contained SNPs 677 of the MTHFR gene.2. Analysis of gene mutation: Mutation of MTHFR gene possibly produce the changes of restriction enzyme map which can be predictded according to rebase database. To determine the frequency of the SNP677 polymorphism of the MTHFR gene, we carried out a PCR-RFLP based method.3. Reclaiming sequencing and analysis: after screening, the PCR products of the homozygous mutation and wild type were reclaimed and sent for sequence. Next, the results of the sequence were analyzed by employing bioinformatics resources.4. Calculated the frequency of three gene types and allele on MTHFR in the disease groups and wide control groups using Biostatistics.Result: The difference of the genotype between the control group and breast cancer group has the statistics significance (P<0.05), so does ovarian cancer.Conclusion: The polymorphisms of C677T in the MTHFR gene may have relation with breast cancer and ovarian cancer in the population from Northeast of China .The MTHFR gene could be a predisposing gene for breast cancer and ovarian cancer in the population from Northeast of China.