BRCA1 transcriptionally regulates genes associated with the basal-like phenotype in breast cancer

• Published in: Breast cancer research and treatment 2010-08, Vol.122 (3), p.721-731
• Main Authors: Gorski, Julia J, James, Colin R, Quinn, Jennifer E, Stewart, Gail E, Staunton, Kieran Crosbie, Buckley, Niamh E, McDyer, Fionnuala A, Kennedy, Richard D, Wilson, Richard H, Mullan, Paul B, Harkin, D. Paul
• Format: Article
• Language: English
• Subjects: Analysis; Basal-like phenotype; Biological and medical sciences; Biomarkers, Tumor - genetics; Blotting, Western; BRCA1; BRCA1 Protein - genetics; Breast cancer; breast neoplasms; Breast Neoplasms - genetics; Breast Neoplasms - pathology; Cadherins - genetics; Cadherins - metabolism; Cancer; Cancer research; Cell Proliferation; Chromatin Immunoprecipitation; Criminal investigation; Female; Gene expression; Gene Expression Profiling; Gene Expression Regulation, Neoplastic - physiology; Genes; Genetic aspects; Genetic transcription; Genotype & phenotype; Gynecology. Andrology. Obstetrics; Humans; Keratin-17 - genetics; Keratin-17 - metabolism; Keratin-5 - genetics; Keratin-5 - metabolism; Mammary gland diseases; Medical sciences; Medicine; Medicine & Public Health; Neoplasms, Basal Cell - genetics; Neoplasms, Basal Cell - pathology; Oligonucleotide Array Sequence Analysis; Oncology; Phenotype; Preclinical Study; Promoter Regions, Genetic; Proteins; Proto-Oncogene Proteins c-myc - antagonists & inhibitors; Proto-Oncogene Proteins c-myc - genetics; Proto-Oncogene Proteins c-myc - metabolism; Reverse Transcriptase Polymerase Chain Reaction; Ribonucleic acid; RNA; RNA, Messenger - genetics; RNA, Small Interfering - pharmacology; Transcription; Transcription, Genetic; Tumors
• ISSN: 0167-6806; 1573-7217
• DOI: 10.1007/s10549-009-0565-0

Expression profiling of BRCA1-deficient tumours has identified a pattern of gene expression similar to basal-like breast tumours. In this study, we examine whether a BRCA1-dependent transcriptional mechanism may underpin the link between BRCA1 and basal-like phenotype. In methods section, the mRNA and protein were harvested from a number of BRCA1 mutant and wild-type breast cancer cell lines and from matched isogenic controls. Microarray-based expression profiling was used to identify potential BRCA1-regulated transcripts. These gene targets were then validated (by in silico analysis of tumour samples) by real-time PCR and Western blot analysis. Chromatin immunoprecipitation (ChIP) assays were used to confirm recruitment of BRCA1 to specific promoters. In results, we demonstrate that functional BRCA1 represses the expression of cytokeratins 5(KRT5) and 17(KRT17) and p-Cadherin (CDH3) in HCC1937 and T47D breast cancer cell lines at both mRNA and protein level. ChIP assays demonstrate that BRCA1 is recruited to the promoters of KRT5, KRT17 and CDH3, and re-ChIP assays confirm that BRCA1 is recruited independently to form c-Myc and Sp1 complexes on the CDH3 promoter. We show that siRNA-mediated inhibition of endogenous c-Myc (and not Sp1) results in a marked increase in CDH3 expression analogous to that observed following the inhibition of endogenous BRCA1. The data provided suggest a model whereby BRCA1 and c-Myc form a repressor complex on the promoters of specific basal genes and represent a potential mechanism to explain the observed overexpression of key basal markers in BRCA1-deficient tumours.