title: NORE1B, a candidate tumor suppressor, is epigenetically silenced in human hepatocellular carcinoma.
abstract: OBJECTIVE
  In human hepatocellular carcinoma (HCC) the ras-proto-oncogene is rarely mutated. We therefore studied the possible inactivation of the putative tumor-suppressors and ras-associating proteins, NORE1A, NORE1B, and RASSF1A in HCCs by mutation or epigenetic gene silencing through promoter-CpG hypermethylation.
  
  
  METHODS
  SSCP-analyses, sequencing, and methylation-specific PCR were performed in 28 fibrotic/cirrhotic livers and 40 HCCs.
  
  
  RESULTS
  The sequence of NORE1A/B exhibited no deviations and that of the RASSF1A gene a non-silent polymorphism ( approximately 10% of cases) and a missense mutation (one HCC). Both alterations may affect the growth-inhibiting capability of RASSF1A. Epigenetic inactivation of NORE1B was found in 62% of the HCCs and in hepatocarcinoma-cell lines due to considerable promoter-methylation of the gene. Methylation was detected also for RASSF1A in HCCs and hepatocarcinoma cell-lines. As a result, 97% of the HCCs revealed epigenetic silencing of NORE1B, RASSF1A, or both. In contrast every third fibrotic/cirrhotic liver only exhibited silencing of one or both genes.
  
  
  CONCLUSIONS
  The candidate tumor suppressor genes NORE1B and RASSF1A are epigenetically down-regulated alone in at least 62%, or in combination in 97% of the HCCs studied. This indicates a frequent and critical event in hepatocarcinogenesis, which may allow HCCs to subverse growth-control in the presence of an unaltered Ras.
authors.affiliation: Department of Medicine I, Division: Institute of Cancer Research, Medical University of Vienna, Borschkegasse 8a, A-1090 Vienna, Austria.
authors.forename: Doris
authors.initials: D
authors.lastname: Macheiner
authors.forename: Gerwin
authors.initials: G
authors.lastname: Heller
authors.forename: Sonja
authors.initials: S
authors.lastname: Kappel
authors.forename: Christoph
authors.initials: C
authors.lastname: Bichler
authors.forename: Stefan
authors.initials: S
authors.lastname: Stättner
authors.forename: Barbara
authors.initials: B
authors.lastname: Ziegler
authors.forename: Daniela
authors.initials: D
authors.lastname: Kandioler
authors.forename: Fritz
authors.initials: F
authors.lastname: Wrba
authors.forename: Rolf
authors.initials: R
authors.lastname: Schulte-Hermann
authors.forename: Sabine
authors.initials: S
authors.lastname: Zöchbauer-Müller
authors.forename: Bettina
authors.initials: B
authors.lastname: Grasl-Kraupp
mesh_terms: D048868:Adaptor Proteins, Signal Transducing; D000328:Adult; D000368:Aged; D051017:Apoptosis Regulatory Proteins; D006528:Carcinoma, Hepatocellular / Q000201:enzymology* / Q000235:genetics / Q000473:pathology; D002455:Cell Division; D045744:Cell Line, Tumor; D019175:DNA Methylation; D004273:DNA, Neoplasm / Q000235:genetics; D005260:Female; D020868:Gene Silencing; D016147:Genes, Tumor Suppressor; D005914:Globins / Q000235:genetics; D006801:Humans; D008113:Liver Neoplasms / Q000201:enzymology* / Q000235:genetics / Q000473:pathology; D008297:Male; D008875:Middle Aged; D020559:Monomeric GTP-Binding Proteins / Q000235:genetics*; D016133:Polymerase Chain Reaction; D000090063:Proto-Oncogene Mas
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D051017:Apoptosis Regulatory Proteins; D004273:DNA, Neoplasm; C000715470:MAS1 protein, human; D000090063:Proto-Oncogene Mas; C454042:RASSF5 protein, human; D005914:Globins; D020559:Monomeric GTP-Binding Proteins