Methylation status of six tumor-associated genes in Japanese patients with ulcerative colitis

Abstract

It has been recognized that patients with longstanding ulcerative colitis (UC) have an increased risk of colorectal cancer. The major carcinogenic molecular pathways that lead to sporadic colorectal cancer, namely chromosomal instability, microsatellite instability, and hypermethylation, are also believed to correlate with the developing of colitis associated colorectal cancer (CAC). We detected the methylation status of promoter regions of estrogen receptor gene (ER), TP53, p14, p16, p21 and hMLH1 in rectal inflammatory mucosa of patients with UC, and investigated the association between DNA methylation rate and the clinical manifestations. Enrolled in the study were 36 Japanese patients with UC, including 20 cases of male and 16 cases of female. The average age was 40.4±9.6 years old, and the clinical duration was 9.1±4.8 years. A total of 51 specimens, including 38 biopsies at inflammatory mucosa from the rectum and 13 at normal mucosa from the terminal ileum were obtained during colonoscopic examinations. DNA extraction and methylation specific polymerase chain reaction were performed to detect the methylation in promoter CpG islands of the above six genes. The results showed that methylation rate of ER promoter in the rectal inflammatory mucosa was significant higher than that in the controls (76.3% vs 46.2%, p=0.0251). The methylation rate of ER was also remarkably higher in the longstanding patients (90.9% in those longer than 7 years, 57.1% in the shorter, p=0.0175). Methylation rates in promoters of p14 and p16 in inflammatory mucosa were higher than those in the controls, respectively, but the differences were not of statistic significance. Meanwhile, methylation in TP53 promoter was found in only one case and p21 and hMLH1 methylation were negative in all cases. In addition, significant association was found between p14 methylation and patient's age, however, no significant association was found in methylation rates of ER, p14 and p16 to gender, inflammatory degree or extension of colitis. These results suggests that methylation in promoter regions of ER, p14 and pl6 may play a role in the development of mucosal inflammation in chronic UC, and methylation analysis of ER in rectal mucosa may be useful on the identification of UC patients at high risk of carcinogenesis. In addition, our experiments also prove that inflamed rectal mucosa, unlike normal colorectal mucosa, demonstrates significant abnormalities in DNA methylation even before any histological evidence of neoplastic transformation.