| Gastric cardia adenocarcinoma (GCA) is one of the most common malignant digestive diseases in northern China. A remarkable epidemiological characteristic for GCA is its very similar geographic distribution with esophageal squamous cell carcinoma (SCC). In contrast to the strikingly decline of incidence of distal gastric cancer around the world in the past two decades, the incidence of GCA, especially in America and Europe, increased dramatically. The incidence of gastric-esophageal-junction cancer has increased to 6-folds with a increasing speed of 20% annually, one of the fastest increasing malignant diseases. The reason is not clear yet. There are several differences between GCA and distal gastric cancer in respect of epidemiology, risk factors, histogenesis and clinical characteristics. However, the mechanism of gastric cardia carcinogenesis is largely not known. Aberrant methylation of DNA has been described as an alternative mechanism of gene inactivation besides mutation and deletion, and plays a key role in the carcinogenesis. The hypermethylation of promoter of suppressor genes has been recognized as one of important mechanisms for gene inactivation in many kinds of malignant tumors. P15 gene is a candidate tumor suppressor gene. As cell cycle regulator, it is another inhibitor of cycle-dependent kinase CDK4 and CDK6 (CDKI) besides P16 gene. The aberrantmethylation of P15 gene promoter has been found to be relative with tumorigenesis of many cancers, such as acute lymphocytic leukemia, stomach cancer, colorectal cancer, and even esophageal carcinoma. However, the relationship of hypermethyaltion of P15 gene and GCA has not been reported yet. Recent study by us and other laboratories indicated that lateration of P53-Rb pathway is one of important molecular events in esophageal carcinogenesis, including the P53 mutation, Rb LOH, and aberrant methylation of P15, P14, P16, etc. Our hypothesis is that there may be similar risk factors and molecular changes involved in esophageal and gastric cardia carcinogenesis on subjects in Henan, the high incidence area for both SCC and GCA because of their similar geographic distribution. Thus, to further understand the molecular mechanism of GCA and provide molecular clues for possible similar risks factors involved in both GCA and SCC, the present study was undertaken to detected the methylation status of P15 gene promoter in GCA and related precancerous lesions from the patients at High-incidence area for both GCA and SCC in Henan, and to characterize the changes of P15 methylation in multistage carcinogenesis of GCA and clinicopathiological patterns.Materials and Methods:Fifty-two primary GCA speciments (43 males and 9 females, with a ratio of 4.8:1, 35 to 76 of age, with a mean age +SD of 59.83 + 8.61 years old.), together with their adjacent tissues. All the patients were from Yaochun, Linzhou, a well-recognized high-risk area for both GCA and SCC in Henan. All the speciments were identified by pathological examination. Of the 52 tumor cases, 19 were poorly differentiated, 30 moderately differentiated, and 3 well differentiated. Adjacent tissues include 9 cases with normal gastric cardia epithelium (NOR), 17 with chronic superficial gastritis (CSG), 8 with chronic atrophic gastritis (CAG), 18 with dysplisa (DYS). We also examinated the lymph nodes of the speciments. All the patients had not received either chemotherapy or radiotherapy before surgery. Genomic DNA was extracted from tissues using protocols provided by Gentra Puregene DNA purification kit. The DNA was modified by bisulfite reaction using the CpGenomeTM DNA modify kit. Modified DNA was amplified by methylation -special PCR (MSP) procedure to analyze the status of methylation. The x2 test, Nonparametric statistics test and Fisher's Exact Test were used for the statistics, P<0.05 was considered significiant.Results:1 In 52 GCA cases, the methylation rate of the promoter of P15 gene in tumor tissues was 30.8% (16/52), with 4 cases (7.7%) were Hemi-methylation; the methylation rate in ad...
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