title: c-Myc activates BRCA1 gene expression through distal promoter elements in breast cancer cells.
abstract: BACKGROUND
  The BRCA1 gene plays an important role in the maintenance of genomic stability. BRCA1 inactivation contributes to breast cancer tumorigenesis. An increasing number of transcription factors have been shown to regulate BRCA1 expression. c-Myc can act as a transcriptional activator, regulating up to 15% of all genes in the human genome and results from a high throughput screen suggest that BRCA1 is one of its targets. In this report, we used cultured breast cancer cells to examine the mechanisms of transcriptional activation of BRCA1 by c-Myc.
  
  
  METHODS
  c-Myc was depleted using c-Myc-specific siRNAs in cultured breast cancer cells. BRCA1 mRNA expression and BRCA1 protein expression were determined by quantitative RT-PCR and western blot, respectively and BRCA1 promoter activities were examined under these conditions. DNA sequence analysis was conducted to search for high similarity to E boxes in the BRCA1 promoter region. The association of c-Myc with the BRCA1 promoter in vivo was tested by a chromatin immunoprecipitation assay. We investigated the function of the c-Myc binding site in the BRCA1 promoter region by a promoter assay with nucleotide substitutions in the putative E boxes. BRCA1-dependent DNA repair activities were measured by a GFP-reporter assay.
  
  
  RESULTS
  Depletion of c-Myc was found to be correlated with reduced expression levels of BRCA1 mRNA and BRCA1 protein. Depletion of c-Myc decreased BRCA1 promoter activity, while ectopically expressed c-Myc increased BRCA1 promoter activity. In the distal BRCA1 promoter, DNA sequence analysis revealed two tandem clusters with high similarity, and each cluster contained a possible c-Myc binding site. c-Myc bound to these regions in vivo. Nucleotide substitutions in the c-Myc binding sites in these regions abrogated c-Myc-dependent promoter activation. Furthermore, breast cancer cells with reduced BRCA1 expression due to depletion of c-Myc exhibited impaired DNA repair activity.
  
  
  CONCLUSIONS
  The distal BRCA1 promoter region is associated with c-Myc and contributes to BRCA1 gene activation.
authors.affiliation: Center for Clinical Cancer Genetics and Global Health, Department of Medicine, University of Chicago, Chicago, IL, USA.
authors.forename: Yinghua
authors.initials: Y
authors.lastname: Chen
authors.forename: Jinhua
authors.initials: J
authors.lastname: Xu
authors.forename: Stanley
authors.initials: S
authors.lastname: Borowicz
authors.forename: Cindy
authors.initials: C
authors.lastname: Collins
authors.forename: Dezheng
authors.initials: D
authors.lastname: Huo
authors.forename: Olufunmilayo I
authors.initials: OI
authors.lastname: Olopade
mesh_terms: D000230:Adenocarcinoma / Q000235:genetics / Q000473:pathology*; D019313:BRCA1 Protein / Q000096:biosynthesis / Q000502:physiology; D001665:Binding Sites; D001943:Breast Neoplasms / Q000235:genetics / Q000473:pathology*; D045744:Cell Line, Tumor / Q000378:metabolism; D016384:Consensus Sequence; D004260:DNA Repair / Q000235:genetics; D004273:DNA, Neoplasm / Q000235:genetics; D004274:DNA, Recombinant / Q000235:genetics; D024721:E-Box Elements / Q000235:genetics*; D005260:Female; D015972:Gene Expression Regulation, Neoplastic / Q000235:genetics*; D019398:Genes, BRCA1; D017930:Genes, Reporter; D016259:Genes, myc; D006801:Humans; D009363:Neoplasm Proteins / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology*; D011401:Promoter Regions, Genetic / Q000235:genetics*; D016271:Proto-Oncogene Proteins c-myc / Q000502:physiology*; D034622:RNA Interference; D034741:RNA, Small Interfering / Q000494:pharmacology; D017422:Sequence Analysis, DNA; D014162:Transfection
chemical_list: D019313:BRCA1 Protein; D004273:DNA, Neoplasm; D004274:DNA, Recombinant; C489427:MYC protein, human; D009363:Neoplasm Proteins; D016271:Proto-Oncogene Proteins c-myc; D034741:RNA, Small Interfering