title: Hypermethylation of genomic 3.3-kb repeats is frequent event in HPV-positive cervical cancer.
abstract: BACKGROUND
  Large-scale screening methods are widely used to reveal cancer-specific DNA methylation markers. We previously identified non-satellite 3.3-kb repeats associated with facioscapulohumeral muscular dystrophy (FSHD) as hypermethylated in cervical cancer in genome-wide screening. To determine whether hypermethylation of 3.3-kb repeats is a tumor-specific event and to evaluate frequency of this event in tumors, we investigated the 3.3-kb repeat methylation status in human papilloma virus (HPV)-positive cervical tumors, cancer cell lines, and normal cervical tissues. Open reading frames encoding DUX family proteins are contained within some 3.3-kb repeat units. The DUX mRNA expression profile was also studied in these tissues.
  
  
  METHODS
  The methylation status of 3.3-kb repeats was evaluated by Southern blot hybridization and bisulfite genomic sequencing. The expression of DUX mRNA was analyzed by RT-PCR and specificity of PCR products was confirmed by sequencing analysis.
  
  
  RESULTS
  Hypermethylation of 3.3-kb repeats relative to normal tissues was revealed for the first time in more than 50% (18/34) of cervical tumors and in 4 HPV-positive cervical cancer cell lines. Hypermethylation of 3.3-kb repeats was observed in tumors concurrently with or independently of hypomethylation of classical satellite 2 sequences (Sat2) that were hypomethylated in 75% (15/20) of cervical tumors. We have revealed the presence of transcripts highly homologous to DUX4 and DUX10 genes in normal tissues and down-regulation of transcripts in 68% of tumors with and without 3.3-kb repeats hypermethylation.
  
  
  CONCLUSIONS
  Our results demonstrate that hypermethylation rather than hypomethylation of 3.3-kb repeats is the predominant event in HPV-associated cervical cancer and provide new insight into the epigenetic changes of repetitive DNA elements in carcinogenesis.
authors.affiliation: Laboratory of Molecular Biology of Viruses, Institute of Carcinogenesis, NN Blokhin Cancer Research Center, Russian Academy of Medical Sciences, Moscow, Russia. akatar@yandex.ru
authors.forename: Alexey N
authors.initials: AN
authors.lastname: Katargin
authors.forename: Larissa S
authors.initials: LS
authors.lastname: Pavlova
authors.forename: Fjodor L
authors.initials: FL
authors.lastname: Kisseljov
authors.forename: Natalia P
authors.initials: NP
authors.lastname: Kisseljova