Repression of MLH1 and MGMT genes in colon mucosa adjacent to implanted cancer in Athymic mouse

Hyperplastic mucosa adjacent to colon cancer, being a reactive change, accelerates cancer progression and its metastasis through expression of angiogenic factors (17). We investigated promoter methylation in hyperplastic mucosa adjacent to orthotopic KM12SM colon cancer in mice. In the hyperplastic mucosa adjacent to KM12SM tumors in the cecum of athymic mice, reductions in the levels of the mutL homologue 1 (MLH1) and O-6 -methyl-guanine-DNA methyltransferase (MGMT) proteins were detected by immunohistochemistry and immunoblotting. To examine the effects of growth factors and cytokines on promoter methylation and repressed expression of the MLH1 and MGMT genes, a rat intestinal epithelial cell line, IEC6, was treated with epidermal growth factor (EGF) and interleukin (IL)-15 for 35 days. Protein levels of MLH1 and MGMT were reduced in EGF- and IL-15-treated IEC6 cells. A methylation-sensitive restriction enzyme assay revealed that CpG methylation was present in the promoter regions of the MLH1 and MGMT genes in DNAs extracted from hyperplastic mucosa adjacent to KM12SM tumors. These findings suggest that promoter CpG methylation affects expression of MLH1 MGMT genes in hyperplastic mucosa adjacent to colon cancer.