Methylenetetrahydrorefolate reductase gene expression and folate concentration in adjacent mucosa are associated with outcome of colorectal cancer patients
Department of General Surgery, Sahlgrenska University Hospital/Östra, Göteborg, Sweden
The enzyme methylenetetrahydrofolate reductase (MTHFR) catalyses the conversion of 5, 10-methyleneTHF to 5-methylTHF which is the major circulating form of folate. 5-MethylTHF is required for DNA methylation. Abnormal DNA methylation may cause decreases or increases in the activity of the genes affected. A common mutation in MTHFR (C677T) is associated with reduced enzyme activity, resulting in decreased concentration of 5-methylTHF in the cell. Thymidylate synthase (TS) catalyzes the methylation of dUMP to dTMP with the transferred methyl group provided by 5,10-methyleneTHF. Thus, this conversion is essential for DNA synthesis and repair. Alteration in MTHFR and TS gene expression levels could affect DNA methylation and the supply of thymidine for DNA synthesis particularly in rapidly proliferating tissue such as colorectal mucosa. Normally, a balance exists between the provision of 5, 10-methyleneTHF for DNA synthesis and DNA methylation in the cells. However, when folates are limited, the balance between these pathways may be disturbed. AIM: The aim of the study was to investigate the role of MTHFR in patients with colorectal cancer. METHODS: The frequency of MTHFR polymorphism C677T was determined and gene expression levels of TS and MTHFR were quantified on ABI prism 7700 in 98 patients with colorectal cancer. Furthermore, reduced folates in the tissue were measured with a binding assay in 40 out of 98 patients. RESULTS: The genotype distribution of the examined MTHFR C677T polymorphism in the investigated group of colorectal cancer patients was 51% CC, 44% CT and 5% TT. The relative gene expression levels of MTHFR were found to be significantly lower (p < 0.0001) in carcinomas (0.53 ± 0.46) compared with adjacent mucosa (1.2 ± 0.88). However, the gene expression levels of TS were found to be significantly higher in the carcinoma compared to mucosa (p < 0.0001). A significantly longer overall survival time was found among CRC patients with Dukes’ A-C having a high level of MTHFR expression compared to those with a low level. However, no significant differences were found between these groups according to tumor-specific survival. Significantly higher folate concentrations and gene expression levels of TS were detected in the mucosa of patients with high MTHFR gene expression levels compared to the group of patients with low MTHFR expression. CONCLUSIONS: Our results suggest that normal-appearing mucosa adjacent to primary colorectal carcinomas can show altered gene expression levels of MTHFR that may affect the overall survival. Supplementation with folate may have a protective role in colorectal mucosa by enhancing the availability of 5,10-methyleneTHF.
Paper presented at the International Symposium on Predictive Oncology and Intervention Strategies; Nice, France; February 7 - 10, 2004; in poster session 797 (Manifestations of cancer).