Dysregulation of DNA methylation induced by past arsenic treatment causes persistent genomic instability in mammalian cells

Environ Mol Mutagen. 2016 Mar;57(2):137-50. doi: 10.1002/em.21987. Epub 2015 Nov 19.

Abstract

The mechanisms by which arsenic-induced genomic instability is initiated and maintained are poorly understood. To investigate potential epigenetic mechanisms, in this study we evaluated global DNA methylation levels in V79 cells and human HaCaT keratinocytes at several time points during expanded growth of cell cultures following removal of arsenite exposures. We have found altered genomic methylation patterns that persisted up to 40 cell generations in HaCaT cells after the treatments were withdrawn. Moreover, mRNA expression levels were evaluated by RT-PCR for DNMT1, DNMT3A, DNMT3B, HMLH1, and HMSH2 genes, demonstrating that the down regulation of DNMT3A and DNMT3B genes, but not DNMT1, occurred in an arsenic dose-dependent manner, and persisted for many cell generations following removal of the arsenite, offering a plausible mechanism of persistently genotoxic arsenic action. Analyses of promoter methylation status of the DNA mismatch repair genes HMLH1 and HMSH2 show that HMSH2, but not HMLH1, was epigenetically regulated by promoter hypermethylation changes following arsenic treatment. The results reported here demonstrate that arsenic exposure promptly induces genome-wide global DNA hypomethylation, and some specific gene promoter methylation changes, that persist for many cell generations following withdrawal of arsenite, supporting the hypothesis that the cells undergo epigenetic reprogramming at both the gene and genome level that is durable over many cell generations in the absence of further arsenic treatment. These DNA methylation changes, in concert with other known epigenome alterations, are likely contributing to long-lasting arsenic-induced genomic instability that manifests in several ways, including aberrant chromosomal effects.

Keywords: DNA methylation; arsenic; genomic instability.

Publication types

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

MeSH terms

  • 5-Methylcytosine / metabolism
  • Adaptor Proteins, Signal Transducing / genetics
  • Animals
  • Arsenic / toxicity*
  • Arsenites / toxicity
  • Cells, Cultured
  • Cricetulus
  • DNA (Cytosine-5-)-Methyltransferase 1
  • DNA (Cytosine-5-)-Methyltransferases / genetics
  • DNA Methylation / drug effects*
  • Fibroblasts / drug effects
  • Genomic Instability / drug effects*
  • Keratinocytes / drug effects
  • Long Interspersed Nucleotide Elements / drug effects
  • MutL Protein Homolog 1
  • MutS Homolog 2 Protein / genetics
  • Nuclear Proteins / genetics
  • Promoter Regions, Genetic / drug effects

Substances

  • Adaptor Proteins, Signal Transducing
  • Arsenites
  • MLH1 protein, human
  • Nuclear Proteins
  • 5-Methylcytosine
  • DNA (Cytosine-5-)-Methyltransferase 1
  • DNA (Cytosine-5-)-Methyltransferases
  • DNA methyltransferase 3A
  • DNA methyltransferase 3B
  • DNMT1 protein, human
  • MSH2 protein, human
  • MutL Protein Homolog 1
  • MutS Homolog 2 Protein
  • arsenite
  • Arsenic