Analysis of aberrant methylation in DNA repair genes during malignant transformation of human bronchial epithelial cells induced by cadmium

Toxicol Sci. 2012 Feb;125(2):412-7. doi: 10.1093/toxsci/kfr320. Epub 2011 Nov 23.


Cadmium (Cd) and its compounds are well-known human carcinogens, but the mechanisms underlying the carcinogenesis are not entirely understood yet. Aberrant methylation was investigated in order to obtain insight into the DNA repair-related epigenetic mechanisms underlying CdCl(2)-induced malignant transformation of human bronchial epithelial cells (16HBE). Gene expression and DNA methylation were assessed in untreated control cells; 5th, 15th, and 35th passage of CdCl2-treated cells and tumorigenic cells (TCs) from nude mice by using high-performance liquid chromatography, real-time PCR, Western blot analysis, and methylation-specific PCR assay. During Cd-induced malignant transformation, global DNA methylation progressively increased and was associated with the overexpression of the DNA methyltransferase genes DNMT1 and DNMT3a but not DNMT3b. Expression of both the messenger RNA and proteins of the DNA repair genes (hMSH2, ERCC1, XRCC1, and hOGG1) progressively reduced and DNA damage increased with Cd-induced transformation. The promoter regions of hMSH2, ERCC1, XRCC1, and hOGG1 were heavily methylated in the 35th passage transformed cells and the TCs. The DNA demethylating agent 5-aza-2'-deoxycytidine could reverse the Cd-induced global DNA hypermethylation, DNMT hyperactivity, and the silencing of hMSH2, ERCC1, XRCC1, and hOGG1 in a time-dependent manner. The results indicate that DNMT1 and DNMT3a overexpression can result in global DNA hypermethylation and silencing of the hMSH2, ERCC1, XRCC1, and hOGG1 genes. They may partly explain the epigenetic mechanisms underlying the carcinogenesis due to Cd.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Azacitidine / analogs & derivatives
  • Azacitidine / pharmacology
  • Blotting, Western
  • Bronchi / drug effects*
  • Bronchi / enzymology
  • Bronchi / pathology
  • Cadmium Chloride / toxicity*
  • Carcinogens / toxicity*
  • Cell Line, Transformed
  • Cell Proliferation
  • Cell Transformation, Neoplastic / chemically induced*
  • Cell Transformation, Neoplastic / genetics
  • Cell Transformation, Neoplastic / metabolism
  • Cell Transformation, Neoplastic / pathology
  • Chromatography, High Pressure Liquid
  • DNA Methylation*
  • DNA Modification Methylases / antagonists & inhibitors
  • DNA Modification Methylases / metabolism*
  • DNA Repair Enzymes / genetics*
  • DNA Repair Enzymes / metabolism
  • Decitabine
  • Enzyme Inhibitors / pharmacology
  • Epithelial Cells / drug effects*
  • Epithelial Cells / enzymology
  • Epithelial Cells / pathology
  • Gene Expression Regulation, Enzymologic
  • Gene Expression Regulation, Neoplastic
  • Humans
  • Mice
  • Mice, Nude
  • Promoter Regions, Genetic
  • Real-Time Polymerase Chain Reaction
  • Time Factors


  • Carcinogens
  • Enzyme Inhibitors
  • Decitabine
  • DNA Modification Methylases
  • DNA Repair Enzymes
  • Cadmium Chloride
  • Azacitidine