Identification of essential transcription factors for adequate DNA damage response after benzo(a)pyrene and aflatoxin B1 exposure by combining transcriptomics with functional genomics

Evelyn Smit, Terezinha Souza, Danyel G. J. Jennen, Jos C. S. Kleinjans, Twan van den Beucken*

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review

20 Citations (Web of Science)

Abstract

DNA damage mediates widespread changes in transcription through activation or repression of transcription factors (TFs). However, the consequences of regulating specific TFs for the outcome of the DNA repair process remain incompletely understood. Here, we combined transcriptomics and TF binding prediction with functional genomics to identify TFs essential for adequate DNA repair in HepG2 liver cells after a non-cytotoxic dose of carcinogens benzo(a)pyrene (BaP) (2 [mu M) and aflatoxin B1 (AFB1) (5 mu M). BaP and AFB1 induced a largely common transcriptional response, mediated by similar TFs. A lentiviral shRNA screen knocking down the top31 identified TFs, was performed to determine their effect on DNA repair by assessing phosphorylation of H2AX (gamma-H2AX). In addition to the top candidate p53, we identified several other interesting TFs that modulated gamma-H2AX after BaP and AFB1 treatment. Validation studies confirmed the role of p53 in reducing y-H2AX formation and DNA breaks measured by COMET assay after BaP and AFB1 exposure. Expression of the cell cycle inhibitor p21 was profoundly impaired upon p53 knock down. In addition, the expression of 2 genes involved in nucleotide exchange repair, DDB2 and XPC was significantly reduced in p53 knock down cells. Although p63 knock down affected DNA damage upon BaP treatment this was not associated with altered expression of DDB2 or XPC. Finally, knock down of ARNT reduced y-H2AX in response to BaP, which was associated with reduced CYP1A1 expression. Importantly, our results suggest a new role for ARNT and its dimerization partner AHR in the occurrence of H2AX phosphorylation after AFB1 treatment.

These data show that modulation of TF activity impacts on the repair of BaP- and AFB1-induced DNA damage. Our study also demonstrates the potential of combining functional genomics with genome-wide expression analysis to identify yet unknown causal relationships, thereby aiding in the interpretation of complex biological systems.

Original languageEnglish
Pages (from-to)74-82
Number of pages9
JournalToxicology
Volume390
DOIs
Publication statusPublished - 1 Sep 2017

Keywords

  • Gene expression
  • Aflatoxin B1
  • Benzo(a)pyrene
  • shRNA screen
  • Transcription factor
  • NUCLEOTIDE EXCISION-REPAIR
  • GENE-EXPRESSION PROFILE
  • HEPG2 CELLS
  • H2AX PHOSPHORYLATION
  • EPITHELIAL-CELLS
  • HISTONE H2AX
  • HUMAN LIVER
  • P53 FAMILY
  • IN-VIVO
  • GENOTOXICITY

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