BRCA1 transcriptionally regulates genes associated with the basal-like phenotype in breast cancer.
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.
Gorski
Julia J
JJ
Department of Oncology, Centre for Cancer Research and Cell Biology, Queen's University Belfast, Belfast BT9 7BL, N. Ireland, UK. j.gorski@qub.ac.uk
James
Colin R
CR
Quinn
Jennifer E
JE
Stewart
Gail E
GE
Staunton
Kieran Crosbie
KC
Buckley
Niamh E
NE
McDyer
Fionnuala A
FA
Kennedy
Richard D
RD
Wilson
Richard H
RH
Mullan
Paul B
PB
Harkin
D Paul
DP
D019313:BRCA1 Protein / Q000235:genetics*; D014408:Biomarkers, Tumor / Q000235:genetics*; D015153:Blotting, Western; D001943:Breast Neoplasms / Q000235:genetics* / Q000473:pathology; D015820:Cadherins / Q000235:genetics / Q000378:metabolism; D049109:Cell Proliferation; D047369:Chromatin Immunoprecipitation; D005260:Female; D020869:Gene Expression Profiling; D015972:Gene Expression Regulation, Neoplastic / Q000502:physiology*; D006801:Humans; D053537:Keratin-17 / Q000235:genetics / Q000378:metabolism; D053555:Keratin-5 / Q000235:genetics / Q000378:metabolism; D018295:Neoplasms, Basal Cell / Q000235:genetics* / Q000473:pathology; D020411:Oligonucleotide Array Sequence Analysis; D010641:Phenotype; D011401:Promoter Regions, Genetic; D016271:Proto-Oncogene Proteins c-myc / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics; D034741:RNA, Small Interfering / Q000494:pharmacology; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014158:Transcription, Genetic
D019313:BRCA1 Protein; C492913:BRCA1 protein, human; D014408:Biomarkers, Tumor; C512197:CDH3 protein, human; D015820:Cadherins; D053537:Keratin-17; D053555:Keratin-5; D016271:Proto-Oncogene Proteins c-myc; D012333:RNA, Messenger; D034741:RNA, Small Interfering