title: Downregulation of homologous recombination DNA repair genes by HDAC inhibition in prostate cancer is mediated through the E2F1 transcription factor.
abstract: BACKGROUND
  Histone deacetylase inhibitors (HDACis) re-express silenced tumor suppressor genes and are currently undergoing clinical trials. Although HDACis have been known to induce gene expression, an equal number of genes are downregulated upon HDAC inhibition. The mechanism behind this downregulation remains unclear. Here we provide evidence that several DNA repair genes are downregulated by HDAC inhibition and provide a mechanism involving the E2F1 transcription factor in the process.
  
  
  RESULTS
  Applying Analysis of Functional Annotation (AFA) on microarray data of prostate cancer cells treated with HDACis, we found a number of genes of the DNA damage response and repair pathways are downregulated by HDACis. AFA revealed enrichment of homologous recombination (HR) DNA repair genes of the BRCA1 pathway, as well as genes regulated by the E2F1 transcription factor. Prostate cancer cells demonstrated a decreased DNA repair capacity and an increased sensitization to chemical- and radio-DNA damaging agents upon HDAC inhibition. Recruitment of key HR repair proteins to the site of DNA damage, as well as HR repair capacity was compromised upon HDACi treatment. Based on our AFA data, we hypothesized that the E2F transcription factors may play a role in the downregulation of key repair genes upon HDAC inhibition in prostate cancer cells. ChIP analysis and luciferase assays reveal that the downregulation of key repair genes is mediated through decreased recruitment of the E2F1 transcription factor and not through active repression by repressive E2Fs.
  
  
  CONCLUSIONS
  Our study indicates that several genes in the DNA repair pathway are affected upon HDAC inhibition. Downregulation of the repair genes is on account of a decrease in amount and promoter recruitment of the E2F1 transcription factor. Since HDAC inhibition affects several pathways that could potentially have an impact on DNA repair, compromised DNA repair upon HDAC inhibition could also be attributed to several other pathways besides the ones investigated in this study. However, our study does provide insights into the mechanism that governs downregulation of HR DNA repair genes upon HDAC inhibition, which can lead to rationale usage of HDACis in the clinics.
authors.affiliation: Prostate Cancer Program, The Sidney Kimmel Comprehensive Cancer Center at Johns Hopkins, Johns Hopkins University School of Medicine, Baltimore, Maryland, United States of America. kachhsu@jhmi.edu
authors.forename: Sushant K
authors.initials: SK
authors.lastname: Kachhap
authors.forename: Nadine
authors.initials: N
authors.lastname: Rosmus
authors.forename: Spencer J
authors.initials: SJ
authors.lastname: Collis
authors.forename: Madeleine S Q
authors.initials: MS
authors.lastname: Kortenhorst
authors.forename: Michel D
authors.initials: MD
authors.lastname: Wissing
authors.forename: Mohammad
authors.initials: M
authors.lastname: Hedayati
authors.forename: Shabana
authors.initials: S
authors.lastname: Shabbeer
authors.forename: Janet
authors.initials: J
authors.lastname: Mendonca
authors.forename: Justin
authors.initials: J
authors.lastname: Deangelis
authors.forename: Luigi
authors.initials: L
authors.lastname: Marchionni
authors.forename: Jianqing
authors.initials: J
authors.lastname: Lin
authors.forename: Naseruddin
authors.initials: N
authors.lastname: Höti
authors.forename: Johan W R
authors.initials: JW
authors.lastname: Nortier
authors.forename: Theodore L
authors.initials: TL
authors.lastname: DeWeese
authors.forename: Hans
authors.initials: H
authors.lastname: Hammers
authors.forename: Michael A
authors.initials: MA
authors.lastname: Carducci
mesh_terms: D045744:Cell Line, Tumor; D047369:Chromatin Immunoprecipitation; D020552:Comet Assay; D004249:DNA Damage; D004260:DNA Repair / Q000235:genetics*; D015536:Down-Regulation / Q000502:physiology*; D050687:E2F1 Transcription Factor / Q000502:physiology*; D005455:Fluorescent Antibody Technique; D006655:Histone Deacetylases / Q000378:metabolism*; D006801:Humans; D008297:Male; D020411:Oligonucleotide Array Sequence Analysis; D016133:Polymerase Chain Reaction; D011471:Prostatic Neoplasms / Q000201:enzymology / Q000235:genetics*; D011995:Recombination, Genetic
chemical_list: D050687:E2F1 Transcription Factor; C493753:E2F1 protein, human; D006655:Histone Deacetylases