Expression of human DNA methyltransferase 1 in colorectal cancer tissues and their corresponding distant normal tissues

Background and aim DNA methylation plays an important role during colorectal cancer (CRC) carcinogenesis. DNA methyltransferase 1 (DNMT1) is responsible for maintaining DNA methylation. We addressed the significance of DNMT1 expression in CRC. Materials and methods We measured the expression of DNMT1 in CRC tissues and in their corresponding distal normal colorectal mucosa using reverse transcriptase-polymerase chain reaction and immunohistochemical analysis. Results The mean +/- SD of DNMT1 mRNA in CRC tissues was 1.04 +/- 0.36, which was significantly higher than that in their corresponding distal normal colorectal mucosa (0.58 +/- 0.44, P < 0.05). Fifty-eight out of 77 (75.3%) CRC tissues and only 30 out of 77 (39%) corresponding distant normal colorectal mucosa showed immunoreactivity (P < 0.001). We also found that the immunoreactivity of DNMT1 was higher in mucosa adjacent to cancer than in corresponding normal colorectal mucosa; high immunoreactivity was significantly correlated with poor differentiation in CRC tissues (P=0.008). No significant associations were found between DNMT1 immunoreactivity and the following variables: age, sex, locations of cancer, Duke's phase, and the presence of lymph-node metastasis. Conclusion These findings suggested that DNMT1 was associated with the malignant phenotype, and dysregulation of DNMT1 expression was present in tumor cells of CRC.