Location-specific epigenetic regulation of the metallothionein 3 gene in esophageal adenocarcinomas

PLoS One. 2011;6(7):e22009. doi: 10.1371/journal.pone.0022009. Epub 2011 Jul 19.

Abstract

Background: Metallothionein 3 (MT3) maintains intracellular metal homeostasis and protects against reactive oxygen species (ROS)-induced DNA damage. In this study, we investigated the epigenetic alterations and gene expression of the MT3 gene in esophageal adenocarcinomas (EACs).

Methods and results: Using quantitative bisulfite pyrosequencing, we detected unique DNA methylation profiles in the MT3 promoter region. The CpG nucleotides from -372 to -306 from the transcription start site (TSS) were highly methylated in tumor (n = 64) and normal samples (n = 51), whereas CpG nucleotides closest to the TSS (-4 and +3) remained unmethylated in all normal and most tumor samples. Conversely, CpG nucleotides in two regions (from -139 to -49 and +296 to +344) were significantly hypermethylated in EACs as compared to normal samples [FDR<0.001, -log10(FDR)>3.0]. The DNA methylation levels from -127 to -8 CpG sites showed the strongest correlation with MT3 gene expression (r = -0.4, P<0.0001). Moreover, the DNA hypermethylation from -127 to -8 CpG sites significantly correlated with advanced tumor stages and lymph node metastasis (P = 0.005 and P = 0.0313, respectively). The ChIP analysis demonstrated a more repressive histone modification (H3K9me2) and less active histone modifications (H3K4me2, H3K9ace) in OE33 cells than in FLO-1 cells; concordant with the presence of higher DNA methylation levels and silencing of MT3 expression in OE33 as compared to FLO-1 cells. Treatment of OE33 cells with 5-Aza-deoxycitidine restored MT3 expression with demethylation of its promoter region and reversal of the histone modifications towards active histone marks.

Conclusion: In summary, EACs are characterized by frequent epigenetic silencing of MT3. The choice of specific regions in the CpG island is a critical step in determining the functional role and prognostic value of DNA methylation in cancer cells.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Adenocarcinoma / genetics*
  • Adenocarcinoma / pathology
  • Adult
  • Aged
  • Aged, 80 and over
  • Azacitidine / pharmacology
  • Cell Line, Tumor
  • CpG Islands / genetics
  • DNA Methylation / drug effects
  • Down-Regulation / drug effects
  • Down-Regulation / genetics
  • Epigenesis, Genetic* / drug effects
  • Esophageal Neoplasms / genetics*
  • Esophageal Neoplasms / pathology
  • Gene Expression Regulation, Neoplastic* / drug effects
  • Genes, Neoplasm / genetics*
  • Histones / metabolism
  • Humans
  • Lymphatic Metastasis / genetics
  • Middle Aged
  • Neoplasm Staging
  • Nerve Tissue Proteins / genetics*
  • Promoter Regions, Genetic / genetics
  • Protein Processing, Post-Translational / drug effects
  • Repressor Proteins / metabolism

Substances

  • Histones
  • Nerve Tissue Proteins
  • Repressor Proteins
  • growth inhibitory factor
  • Azacitidine