Benzo[a]pyrene diol epoxide suppresses retinoic acid receptor-beta2 expression by recruiting DNA (cytosine-5-)-methyltransferase 3A

Mol Cancer. 2010 Apr 28:9:93. doi: 10.1186/1476-4598-9-93.

Abstract

Tobacco smoke is an important risk factor for various human cancers, including esophageal cancer. How benzo [a]pyrene diol epoxide (BPDE), a carcinogen present in tobacco smoke as well as in environmental pollution, induces esophageal carcinogenesis has yet to be defined. In this study, we investigated the molecular mechanism responsible for BPDE-suppressed expression of retinoic acid receptor-beta2 (RAR-beta2) in esophageal cancer cells. We treated esophageal cancer cells with BPDE before performing methylation-specific polymerase chain reaction (MSP) to find that BPDE induced methylation of the RAR-beta2 gene promoter. We then performed chromatin immunoprecipitation (ChIP) assays to find that BPDE recruited genes of the methylation machinery into the RAR-beta2 gene promoter. We found that BPDE recruited DNA (cytosine-5-)-methyltransferase 3 alpha (DNMT3A), but not beta (DNMT3B), in a time-dependent manner to methylate the RAR-beta2 gene promoter, which we confirmed by reverse transcription-polymerase chain reaction (RT-PCR) analysis of the reduced RAR-beta2 expression in these BPDE-treated esophageal cancer cell lines. However, BPDE did not significantly change DNMT3A expression, but it slightly reduced DNMT3B expression. DNA methylase inhibitor 5-aza-2'-deoxycytidine (5-Aza) and DNMT3A small hairpin RNA (shRNA) vector antagonized the effects of BPDE on RAR-beta2 expressions. Transient transfection of the DNMT3A shRNA vector also antagonized BPDE's effects on expression of RAR-beta2, c-Jun, phosphorylated extracellular signal-regulated protein kinases 1/2 (ERK1/2), and cyclooxygenase-2 (COX-2), suggesting a possible therapeutic effect. The results of this study form the link between the esophageal cancer risk factor BPDE and the reduced RAR-beta2 expression.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • 7,8-Dihydro-7,8-dihydroxybenzo(a)pyrene 9,10-oxide / toxicity*
  • Blotting, Northern
  • Blotting, Western
  • Carcinogens / toxicity*
  • Cell Line, Tumor
  • Chromatin Immunoprecipitation
  • DNA (Cytosine-5-)-Methyltransferases / genetics
  • DNA (Cytosine-5-)-Methyltransferases / metabolism*
  • DNA Methylation
  • DNA Methyltransferase 3A
  • DNA Methyltransferase 3B
  • Esophageal Neoplasms / genetics
  • Esophageal Neoplasms / metabolism*
  • Gene Expression / drug effects*
  • Humans
  • Promoter Regions, Genetic
  • Receptors, Retinoic Acid / biosynthesis*
  • Receptors, Retinoic Acid / genetics
  • Reverse Transcriptase Polymerase Chain Reaction
  • Transfection

Substances

  • Carcinogens
  • DNMT3A protein, human
  • Receptors, Retinoic Acid
  • retinoic acid receptor beta
  • 7,8-Dihydro-7,8-dihydroxybenzo(a)pyrene 9,10-oxide
  • DNA (Cytosine-5-)-Methyltransferases
  • DNA Methyltransferase 3A