| Many genetic and environmental factors contribute to the development of cancer, but DNA methylation may provide a link between these influences. Genome stability and normal gene expression are largely maintained by a fixed and predetermined pattern of DNA methylation. In cancer, this idealistic balance is disrupted by a phenomenon : the hypermethylation of regulatory regions called CpG islands in some tumor suppressor genes- eg: BRCA1, hMLHl, p16INK4A, APC, VHL-which cause their inactivation. So, someone thought that CpG island hypermethylation occurs in relation to tumorigenesis or aging. Abnormal changes in the pattern of pi 6 gene promoter methylation are observed in human cancers, such as gastric carcinoma, lymphoma, prostate, breast, esophageal, lung carcinomas and so on, indicating its role in tumorigenesis. In the past studies, someone usually focused on the relationship between the status of the exon methylation and the tumorigenesis of gasric carcinoma. However, the links between the promoter CpG island methylation status of p16 gene and clinicopathological parameters has been very limited in gastric carcinomas.Recently, development of new techniques-Methylation-specific PCR (MSP) hasenabled more hypermethylation locus be studied. Compared with Southern Blotting Method and Digestion with methylat ion-sensitive enzymes followed by PCR, it can not only compensate their shortages but also possess many striking advantages: avoiding the use of restriction enzymes and resultantly problems associated with incomplete enzymatic digestion, high sensitivity and specialty and being suitable for small, heterogeneous samples. In this study, MSP was used to explore the status of the promoter 5'CpG island methylation of the p16 gene in gastric carcinomas tissues, adjacent tissues of carcinomas and normal gastric mucosa samples. The frequency of CpG island hypermethylation of p16 gene promoter and the relationship between whether the occurrence of hypermethylation and the clinicopathological features of the gastric carcinomas were discussed. Materials and MethodsThirty-two gastric carcinoma specimans were surgically removed and collected from the First Affiliated Hospital of Zhengzhou University, Henan Province People's Hospital, Henan Tumor Hospital, China. Clinical information was obtained from the medical records. The average age of the patients was 48 years old (from 23 to 69) and none of them had received radiotherapy or chemotherapy. Histologically, 7 cases were well and mediately differentiated carcinomas, 19 cases were poorly differentiated carcinomas, 6 cases were gelatinous carcinomas and signet-ring cell carcinomas. All samples were immediately frozen and stored at -80 MSP. non-denaturing PAGE and the detection to DNA sequencing of MSP products were used to detect the promoter methylation hi p!6 gene in a series of 32 gastric carcinomas, 32 adjacent carcinomatous tissues and 32 normal gastric mucosa samples, and the data was studied associating with clinicopathological factors.The data was analysized by SPSS10.0 and P value < 0.05 was taken as statistical significance.Results1. The promoter 5'CpG island methylation of p!6 gene was found in 56.25% (18/32 cases) of gastric cancer samples, 25% (8/32 cases) of adjacent carcinomatous samples and 6.25% (2/32 cases) of normal gastric mucosa5samples. The incidence of methylation of p16 gene was significantly higher in gastric carcinomas than in normal gastric mucosa (P<0.05). 2. In gastric carcinoma, the 5'CpG island methylation of p1 6 gene promoter occurred in 33.33% (2/6 cases) of well and mediately differentiated carcinomas and 57.89% (11/19 cases) of poorly differentiated carcinomas. The different rate of promoter methylation of p16 gene between well . mediately and poorly differentiated carcinomas has statistical significance3. The rate of hypermethylation with lymph-node metastasis (73.7%) was obviously higher than that without lymph-node metastasis (P<0.05).4. An increasing rate of methylation in associated with increasing depth...
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