Inhibition of BRCA-1 expression by benzo[a]pyrene and its diol epoxide

Brandon D. Jeffy, Elizabeth U. Schultz, Ornella Selmin, Jean M. Gudas, G. Tim Bowden, Donato Romagnolo

Research output: Contribution to journalArticle

40 Scopus citations

Abstract

The objective of this study was to investigate whether polycyclic aromatic hydrocarbons (PAHs) contribute to the etiology of sporadic breast cancer by altering the expression of BRCA-1. Acute exposure to the PAH benzo[a]pyrene (B[a]P) inhibited in a time- and dose-dependent fashion cell proliferation and levels of BRCA-1 mRNA and protein in estrogen receptor (ER)-positive breast MCF-7 and ovarian BG-1 cancer cells. Moreover, the acute exposure to B[a]P abrogated estrogen induction of BRCA-1 in MCF-7 cells. The loss of BRCA-1 expression was prevented by the aromatic hydrocarbon receptor (AhR) antagonist α-naphthoflavone, suggesting participation of the AhR pathway. BRCA, 1 exon 1 a transcripts were downregulated by B[a]P faster than exon 1 b mRNA was. Long-term exposure to B[a]P (40 nM for 15 mo) lowered BRCA-1 mRNA levels in subclones of MCF-7 and BG-1 cells, whereas expression of BRCA-1 in these clones was reverted to normal levels by washing out of B[a]P. The mechanisms of BRCA-1 repression by B[a]P were further investigated by examining the effects of the halogenated aryi hydrocarbon 2,3,7,8- tetrachlorodibenzo-p-dioxin (TCDD) and the B[a]P metabolite 7r,8t-dihydroxy- 9t, 10t-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene (BPDE). While TCDD did not influence basal BRCA- 1 mRNA and protein levels at any of the doses (from 10 nM to 1 μM) tested in this study, treatment with 50 nM BPDE drastically reduced BRCA-1 mRNA levels, indicating that metabolism of B[a]P to BPDE may contribute to downregulation of BRCA-1. Conversely, ER-negative breast MDA- MB-231 and HBL-100 cancer cells were refractory to treatment with B[a]P or TCDD and expressed constant levels of BRCA-1 mRNA and protein. We conclude that B[a]P may be a risk factor in the etiology of sporadic breast cancer.

Original languageEnglish (US)
Pages (from-to)100-118
Number of pages19
JournalMolecular Carcinogenesis
Volume26
Issue number2
DOIs
StatePublished - Oct 23 1999

Keywords

  • Aromatic hydrocarbon receptor
  • BRCA-1
  • Benzo[a]pyrene
  • Sporadic breast cancer

ASJC Scopus subject areas

  • Molecular Biology
  • Cancer Research

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