title: The overmethylated genes in Helicobacter pylori-infected gastric mucosa are demethylated in gastric cancers.
abstract: BACKGROUND
  The transitional-CpG sites between weakly methylated genes and densely methylated retroelements are overmethylated in the gastric mucosa infected with Helicobacter pylori (H. pylori) and they are undermethylated in the gastric cancers depending on the level of loss of heterozygosity (LOH) events. This study delineated the transitional-CpG methylation patterns of CpG-island-containing and -lacking genes in view of the retroelements.
  
  
  METHODS
  The transitional-CpG sites of eight CpG-island-containing genes and six CpG-island-lacking genes were semi-quantitatively examined by performing radioisotope-labelling methylation-specific PCR under stringent conditions. The level of LOH in the gastric cancers was estimated using the 40 microsatellite markers on eight cancer-associated chromosomes. Each gene was scored as overmethylated or undermethylated based on an intermediate level of transitional-CpG methylation common in the H. pylori-negative gastric mucosa.
  
  
  RESULTS
  The eight CpG-island genes examined were overmethylated depending on the proximity to the nearest retroelement in the H. pylori-positive gastric mucosa. The six CpG-island-lacking genes were similarly methylated in the H. pylori-positive and -negative gastric mucosa. In the gastric cancers, long transitional-CpG segments of the CpG-island genes distant from the retroelements remained overmethylated, whereas the overmethylation of short transitional-CpG segments close to the retroelements was not significant. Both the CpG-island-containing and -lacking genes tended to be decreasingly methylated in a LOH-level-dependent manner.
  
  
  CONCLUSIONS
  The overmethylated genes under the influence of retroelement methylation in the H. pylori-infected stomach are demethylated in the gastric cancers influenced by LOH.
authors.affiliation: Department of Microbiology, College of Medicine, The Catholic University of Korea, Seoul, Korea.
authors.forename: Seung-Jin
authors.initials: SJ
authors.lastname: Hong
authors.forename: Jung-Hwan
authors.initials: JH
authors.lastname: Oh
authors.forename: Eun-Jung
authors.initials: EJ
authors.lastname: Jeon
authors.forename: Ki-Ouk
authors.initials: KO
authors.lastname: Min
authors.forename: Moo-Il
authors.initials: MI
authors.lastname: Kang
authors.forename: Sang-Wook
authors.initials: SW
authors.lastname: Choi
authors.forename: Mun-Gan
authors.initials: MG
authors.lastname: Rhyu
mesh_terms: D001706:Biopsy; D004269:DNA, Bacterial / Q000235:genetics* / Q000378:metabolism; D004273:DNA, Neoplasm / Q000235:genetics* / Q000378:metabolism; D005260:Female; D005753:Gastric Mucosa / Q000378:metabolism / Q000382:microbiology* / Q000473:pathology; D016481:Helicobacter Infections / Q000382:microbiology*; D016480:Helicobacter pylori / Q000235:genetics* / Q000302:isolation & purification / Q000378:metabolism; D006801:Humans; D008297:Male; D008745:Methylation; D008875:Middle Aged; D012189:Retrospective Studies; D013274:Stomach Neoplasms / Q000235:genetics* / Q000378:metabolism / Q000473:pathology
chemical_list: D004269:DNA, Bacterial; D004273:DNA, Neoplasm