Decreased BRCA1 confers tamoxifen resistance in breast cancer cells by altering estrogen receptor-coregulator interactions

J. Wen, R. Li, Y. Lu, M. A. Shupnik

Research output: Contribution to journalArticle

39 Scopus citations

Abstract

The breast cancer susceptibility gene 1 (BRCA1) is mutated in approximately 50% of hereditary breast cancers, and its expression is decreased in 30-40% of sporadic breast cancers, suggesting a general role in breast cancer development. BRCA1 physically and functionally interacts with estrogen receptor-α (ERα) and several transcriptional regulators. We investigated the relationship between cellular BRCA1 levels and tamoxifen sensitivity. Decreasing BRCA1 expression in breast cancer cells by small interfering RNA alleviated tamoxifen-mediated growth inhibition and abolished tamoxifen suppression of several endogenous ER-targeted genes. ER-stimulated transcription and cytoplasmic signaling was increased without detectable changes in ER or ER coregulator expression. Co-immunoprecipitation studies showed that with BRCA1 knockdown, tamoxifen-bound ERα was inappropriately associated with coactivators, and not effectively with corepressors. Chromatin immunoprecipitation studies demonstrated that with tamoxifen, BRCA1 knockdown did not change ERα promoter occupancy, but resulted in increased coactivator and decreased corepressor recruitment onto the endogenous cyclin D1 promoter. Our results suggest that decreased BRCA1 levels modify ERα-mediated transcription and regulation of cell proliferation in part by altering ERα-coregulator association. In the presence of tamoxifen, decreased BRCA1 expression results in increased coactivator and decreased corepressor recruitment on ER-regulated gene promoters.

Original languageEnglish (US)
Pages (from-to)575-586
Number of pages12
JournalOncogene
Volume28
Issue number4
DOIs
StatePublished - Jan 29 2009

Keywords

  • BRCA1, ERα
  • Coactivators
  • Corepressors
  • Tamoxifen resistance

ASJC Scopus subject areas

  • Molecular Biology
  • Genetics
  • Cancer Research

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