BRCA1 and FOXA1 proteins coregulate the expression of the cell cycle-dependent kinase inhibitor p27Kip1

E. A. Williamson, I. Wolf, J. O'Kelly, S. Bose, S. Tanosaki, H. P. Koeffler

Research output: Contribution to journalArticlepeer-review

65 Scopus citations


We have previously shown that the breast cancer susceptibility gene, BRCA1, can transcriptionally activate the p27Kip1 promoter. The BRCA1-responsive element was defined as a 35bp region from position -545 to -511. We next determined that within this region is also a potential binding site for the transcription factor Forkhead box (FOX)A1. RNA and protein analysis as well as immunohistochemistry showed that expression of FOXA1 correlated with the expression of the estrogen receptor in a panel of breast cancer cell lines and tissues. In transient transfection reporter assays, FOXA1 could activate the p27Kip1 promoter. Cotransfection of BRCA1 and FOXA1 resulted in a synergistic activation of the p27Kip1 promoter. Mutation of the FOXA1 DNA-binding site in the p27Kip1 promoter-luciferase construct significantly diminished the activity of FOXA1 alone or in combination with BRCA1. Cotransfection of FOXA1 and BRCA1 resulted in a greater amount of each protein compared to transfection of each expression vector alone. The half-life of FOXA1 was increased when coexpressed with BRCA1. Electrophoretic mobility shift assay analysis demonstrated that FOXA1 could bind to a wild-type oligonucleotide containing the FOXA1 binding site in the p27Kip1 promoter, but this binding was lost upon mutation of this FOXA1 binding site. The protein-DNA binding complex could be supershifted with an antibody directed against FOXA1. The activity of the p27Kip1 promoter as well as FOXA1 expression was reduced in cells treated with BRCA1 siRNA, thus silencing the expression of BRCA1 protein. In summary, we identified a FOXA1 binding site within the BRCA1-responsive element of the p27Kip1 promoter and showed that FOXA1 activated the promoter alone and in conjunction with BRCA1. Furthermore, we identified high expression of FOXA1 in breast cancer cell lines and tissues, discovered a role for BRCA1 in the regulation of p27Kip1 transcription and a possible interaction with BRCA1.

Original languageEnglish (US)
Pages (from-to)1391-1399
Number of pages9
Issue number9
StatePublished - Mar 2 2006
Externally publishedYes


  • BRCA1
  • Cell cycle regulation
  • FOXA1

ASJC Scopus subject areas

  • Genetics
  • Molecular Biology
  • Cancer Research


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