title: p16 hypermethylation during gastric carcinogenesis of Wistar rats by N-methyl-N'-nitro-N-nitrosoguanidine.
abstract: Inactivation of the tumor suppressor gene, p16 by CpG hypermethylation is a common event in various tumors including gastric carcinoma. The aim of this study is to investigate if p16 hypermethylation is an early and frequent event in gastric carcinogenesis induced by N-methyl-N'-nitro-N-nitrosoguanidine (MNNG). The frequency and timing of p16 hypermethylation during the multistep gastric carcinogenesis in Wistar rats were analyzed in various microdissected gastric lesions. The p16 methylation status and the presence of p16 protein were analyzed by methylation-specific PCR and immunohistochemistry, respectively. Results showed that p16 methylation frequency was correlated with the severity of gastric pathologic lesions, positively. For instance, p16 methylation was found in 2.7% of normal gastric epithelium (n = 36), 16.7% of chronic atrophy gastritis (n = 24), 37.5% of dysplasia (n = 24), 67.4% of gastric adenoma (n = 43), and 85.2% of gastric carcinoma (n = 27). The p16 methylation in the distal stomach epithelium was higher than that in the proximal stomach. p16 protein was expressed in all of 15 p16 unmethylated gastric epithelial samples, but not expressed in all of 12 p16 methylated samples. These results suggest that CpG island hypermethylation may account for the silencing of p16 in rat stomach and is an early event whose accumulation will finally lead to gastric carcinogenesis.
authors.affiliation: Department of Cancer Etiology, Peking University Health Science Center and Beijing Institute for Cancer Research, Da-Hong-Luo-Chang Street, Western District, Beijing 100034, China.
authors.forename: Hua
authors.initials: H
authors.lastname: Bai
authors.forename: Liankun
authors.initials: L
authors.lastname: Gu
authors.forename: Jing
authors.initials: J
authors.lastname: Zhou
authors.forename: Dajun
authors.initials: D
authors.lastname: Deng
mesh_terms: D000818:Animals; D001483:Base Sequence; D002273:Carcinogens / Q000633:toxicity*; D018899:CpG Islands; D019941:Cyclin-Dependent Kinase Inhibitor p16 / Q000235:genetics / Q000378:metabolism; D019175:DNA Methylation / Q000187:drug effects*; D004273:DNA, Neoplasm / Q000187:drug effects / Q000235:genetics; D015870:Gene Expression / Q000187:drug effects; D020868:Gene Silencing / Q000187:drug effects; D019942:Genes, p16 / Q000187:drug effects*; D008769:Methylnitronitrosoguanidine / Q000633:toxicity*; D051381:Rats; D017208:Rats, Wistar; D013274:Stomach Neoplasms / Q000139:chemically induced* / Q000235:genetics* / Q000378:metabolism / Q000473:pathology
chemical_list: D002273:Carcinogens; D019941:Cyclin-Dependent Kinase Inhibitor p16; D004273:DNA, Neoplasm; D008769:Methylnitronitrosoguanidine