| Objectives: To investigate the methylation status of cyclinD1, p16, p27 and Rb gene promotor(CpG island) and the expressions of their proteins in colorectal carcinogenesis. The relation between the expression of gene and DNA methylation was analysed, and the role of DNA methylation and the relation between DNA methylation and biological behavior were determined. On the basis of it, we searched the molecular markers of early diagnosis, biological characteristics and prognosis criterion in the colorectal carcinoma.Methods: Immunohistochemical staining was used to detect the expressions of cyclinD1, p16, p27 and Rb in the tissue of normal colorectal mucosa epithelium, adjacent tissue of carcinoma, colorectal adenoma and colorectal carcinoma, respectively. According to the results of Immunohistochemical staining, all cases were divided into 2 groups, and then methylation-specific PCR was used to detect the methylation status of every gene promoter.Results: 1.The immunohistochemical staining showed that there was a increased tendency of the expression of cyclinDl in colorectal carcinogenesis. For the expression of cyclinD1, compared with normal mucosa epithelium, there was a significant difference in adjacent tissue, adenoma and carcinoma (p < 0.01 or 0.05). We also observed a dramaticdifference between carcinoma and adjacent tissue, adenoma (p < 0.01 or 0.05), while there was not marked difference between adjacent tissue and adenoma (p > 0.05). There was a decreased tendency of the expressions of p16 and p27 in colorectal carcinogenisis. Their expressions were significantly reduced in adjacent tissue, adenoma and carcinoma compared with normal mucosae epithelium. There was a marked difference between carcinoma and adjacent tissue, adenoma (p < 0.01 or 0.05). For the expression of Rb, there was a depressed tendency in colorectal carcinogenisis. Compared with normal mucosae epithelium, there was a significant difference in adjacent tissue, adenoma and carcinoma (p < 0.01 or 0.05). But there was not significant difference between carcinoma and adjacent tissue, adenoma, the same as adjacent tissue and adenoma (p > 0.05). For 1 case with strangulation of colon and 2 cases accidental death, the expressions of p16, p27 and Rb were positive in normal colorectal mucosa, and the expression of cyclinD1 was negative (2 cases) and positive (1 case). 2. The results, of methylation-specific PCR indicated that there was a increased tendency of the rate of methylation of p16, p27, Rb gene promoter in colorectal carcinogenisis, and there was a descending tendency the rate of methylation of cyclinDl gene promoter. There was obviously correlativity between abnormal methylation of p16, p27, cyclinDl and their expressions, respectively (p < 0.01 or 0.05). Though there was a increased tendency of the rate of methylation of Rb gene promoter, its rate of positive was very low, and there was no correlation with the extent of methylation and the expression of Rb (p > 0.05). For 1 case with strangulation of colon and 2 cases accidental death, p16 and p27 gene was on the state of negative methylation in 3 cases, and Rbgene was on the state of negative methylation in 2 cases and on the state of partly methylation in 1 case, and cyclinD1 gene was on the state of partly methylation in 3 cases. 3. Relationship between DNA methylation and biological behavior of colorectal carcinoma shows, for the extent of methylation of p16 and cyclinDl gene, there was markedly difference in the degrees of differentiation, the depth of infiltration and the metastasis of lymph node (p<0.01 or 0.05), while the extent of methylation of p27 gene was only related to the metastasis of lymph node(p<0.01).Conclusions: Abnormal methylation of cyclinD1, p16, p27 gene promotor was main mechanism of overexpression of cyclinDl and inactivation of p16 and p27, which led to disproportion of cell proliferation cycle, and it played an important role in colorectal carcinogenesis . The abnormality of gene methylation was an important early molecular event. |
PDF Full Text Request