title: DNA methylation of genes linked with retinoid signaling in gastric carcinoma: expression of the retinoid acid receptor beta, cellular retinol-binding protein 1, and tazarotene-induced gene 1 genes is associated with DNA methylation.
abstract: BACKGROUND
  Hypermethylation of CpG islands has been associated with silencing of various tumor suppressor genes, and the retinoid acid receptor beta (RARbeta), cellular retinol-binding protein 1 (CRBP1), and tazarotene-induced gene 1 (TIG1) genes have been associated with retinoic acid signaling. To the authors' knowledge, little is known regarding the involvement of these three genes in gastric carcinoma (GC). In this study, the authors investigated the methylation status of these genes and analyzed the role of their DNA methylation in GC.
  
  
  METHODS
  DNA methylation of 3 retinoic acid-associated genes was analyzed in 42 samples of GC from 42 patients and in 8 GC cell lines by methylation-specific polymerase chain reaction (PCR) analysis. The mRNA expression levels for these three genes were measured by quantitative reverse transcription-PCR.
  
  
  RESULTS
  In 7 of 8 GC cell lines, the CRBP1 gene was hypermethylated, and CRBP1 transcription was inactive. In 6 of 8 GC cell lines, the TIG1 gene was hypermethylated, and TIG1 transcription was inactive. Treatment with demethylating agent 5-aza-2'-deoxycytidine restored both CRBP1 and TIG1 transcription. DNA methylation of the RARbeta, CRBP1, and TIG1 genes was detected in 15 of 42 GC samples (36%), 14 of 42 GC samples (33%), and 4 of 42 GC samples (10%), respectively, and in 6 of 30 samples (20%), 0 of 30 samples (0%), and 1 of 30 samples (3%) of corresponding nonneoplastic mucosa. None of the 10 normal gastric mucosa samples from young, healthy individuals demonstrated hypermethylation of any of these genes. DNA methylation of each gene was associated significantly with low mRNA expression of the respective gene. Twenty-four of 42 GC samples (57%) demonstrated hypermethylation of at least 1 of the 3 genes. However, no significant, concordant hypermethylation of these genes was observed.
  
  
  CONCLUSIONS
  The results suggested that gastric carcinogenesis involves transcriptional inactivation by aberrant DNA methylation of genes related to retinoid signaling.
authors.affiliation: Department of Molecular Pathology, Hiroshima University Graduate School of Biomedical Sciences, Kasumi, Hiroshima, Japan.
authors.forename: Mariko
authors.initials: M
authors.lastname: Shutoh
authors.forename: Naohide
authors.initials: N
authors.lastname: Oue
authors.forename: Phyu Phyu
authors.initials: PP
authors.lastname: Aung
authors.forename: Tsuyoshi
authors.initials: T
authors.lastname: Noguchi
authors.forename: Kazuya
authors.initials: K
authors.lastname: Kuraoka
authors.forename: Hirofumi
authors.initials: H
authors.lastname: Nakayama
authors.forename: Katsunobu
authors.initials: K
authors.lastname: Kawahara
authors.forename: Wataru
authors.initials: W
authors.lastname: Yasui
mesh_terms: D000230:Adenocarcinoma / Q000235:genetics / Q000473:pathology; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001374:Azacitidine / Q000494:pharmacology; D018196:Carcinoma, Adenosquamous / Q000235:genetics / Q000473:pathology; D019175:DNA Methylation; D005260:Female; D005753:Gastric Mucosa / Q000378:metabolism / Q000473:pathology; D015972:Gene Expression Regulation, Neoplastic; D020868:Gene Silencing; D016147:Genes, Tumor Suppressor; D006801:Humans; D007414:Intestinal Neoplasms / Q000235:genetics / Q000473:pathology; D008297:Male; D008565:Membrane Proteins / Q000235:genetics* / Q000378:metabolism; D008679:Metaplasia / Q000235:genetics / Q000473:pathology; D008875:Middle Aged; D011401:Promoter Regions, Genetic / Q000235:genetics; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D018168:Receptors, Retinoic Acid / Q000235:genetics* / Q000378:metabolism; D012176:Retinoids / Q000494:pharmacology*; D012177:Retinol-Binding Proteins / Q000235:genetics* / Q000378:metabolism; D054840:Retinol-Binding Proteins, Cellular; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction; D013274:Stomach Neoplasms / Q000235:genetics* / Q000473:pathology; D014158:Transcription, Genetic; D014407:Tumor Cells, Cultured
chemical_list: D008565:Membrane Proteins; C452562:RARRES1 protein, human; C518456:RBP1 protein, human; D012333:RNA, Messenger; D018168:Receptors, Retinoic Acid; D012176:Retinoids; D012177:Retinol-Binding Proteins; D054840:Retinol-Binding Proteins, Cellular; C082925:retinoic acid receptor beta; D001374:Azacitidine