title: The nucleolar size is associated to the methylation status of ribosomal DNA in breast carcinomas.
abstract: BACKGROUND
  There is a body of evidence that shows a link between tumorigenesis and ribosome biogenesis. The precursor of mature 18S, 28S and 5.8S ribosomal RNAs is transcribed from the ribosomal DNA gene (rDNA), which exists as 300-400 copies in the human diploid genome. Approximately one half of these copies are epigenetically silenced, but the exact role of epigenetic regulation on ribosome biogenesis is not completely understood. In this study we analyzed the methylation profiles of the rDNA promoter and of the 5' regions of 18S and 28S in breast cancer.
  
  
  METHODS
  We analyzed rDNA methylation in 68 breast cancer tissues of which the normal counterpart was partially available (45/68 samples) using the MassARRAY EpiTYPER assay, a sensitive and quantitative method with single base resolution.
  
  
  RESULTS
  We found that rDNA locus tended to be hypermethylated in tumor compared to matched normal breast tissues and that the DNA methylation level of several CpG units within the rDNA locus was associated to nuclear grade and to nucleolar size of tumor tissues. In addition we identified a subgroup of samples in which large nucleoli were associated with very limited or absent rDNA hypermethylation in tumor respect to matched normal tissue.
  
  
  CONCLUSIONS
  In conclusion, we suggest that rDNA is an important target of epigenetic regulation in breast tumors and that rDNA methylation level is associated to nucleolar size.
authors.forename: Maria Giulia
authors.initials: MG
authors.lastname: Bacalini
authors.forename: Annalisa
authors.initials: A
authors.lastname: Pacilli
authors.forename: Cristina
authors.initials: C
authors.lastname: Giuliani
authors.forename: Marianna
authors.initials: M
authors.lastname: Penzo
authors.forename: Davide
authors.initials: D
authors.lastname: Treré
authors.forename: Chiara
authors.initials: C
authors.lastname: Pirazzini
authors.forename: Stefano
authors.initials: S
authors.lastname: Salvioli
authors.forename: Claudio
authors.initials: C
authors.lastname: Franceschi
authors.affiliation: Department of Experimental, Diagnostic and Specialty Medicine, University of Bologna, Bologna, Italy. lorenzo.montanaro@unibo.it.
authors.forename: Lorenzo
authors.initials: L
authors.lastname: Montanaro
authors.forename: Paolo
authors.initials: P
authors.lastname: Garagnani
mesh_terms: D000368:Aged; D001943:Breast Neoplasms / Q000235:genetics* / Q000473:pathology; D002277:Carcinoma / Q000235:genetics* / Q000473:pathology; D002466:Cell Nucleolus / Q000235:genetics / Q000648:ultrastructure; D018899:CpG Islands / Q000235:genetics; D019175:DNA Methylation / Q000235:genetics*; D004275:DNA, Ribosomal / Q000235:genetics*; D044127:Epigenesis, Genetic; D005260:Female; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D008875:Middle Aged; D011401:Promoter Regions, Genetic; D012337:RNA, Ribosomal, 18S / Q000235:genetics; D012339:RNA, Ribosomal, 28S / Q000235:genetics
chemical_list: D004275:DNA, Ribosomal; D012337:RNA, Ribosomal, 18S; D012339:RNA, Ribosomal, 28S