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Articles by E. M. Rosen
Total Records ( 3 ) for E. M. Rosen
  P Katiyar , Y Ma , A Riegel , S Fan and E. M. Rosen

Previously, we reported that BRCA1 inhibits progesterone receptor (PR) activity and blocks progesterone-stimulated gene expression and cell proliferation. In the present manuscript, we studied the mechanism of BRCA1 inhibition of PR activity, using c-Myc as a model progesterone-regulated promoter. Here, we found that BRCA1 has little or no effect on PR ligand-binding affinity. However, BRCA1 overexpression inhibited the R5020-induced recruitment of PR to the c-Myc and mouse mammary tumor virus progesterone response elements (PREs) and blocked R5020-stimulated c-Myc expression, whereas BRCA1 underexpression did the opposite. In EMSAs, BRCA1 overexpression blocked the R5020-induced complex formation between PR and several radiolabeled PRE-containing oligonucleotides, and in vitro-translated BRCA1 blocked the interaction of full-length PR-A or a fragment containing the DNA-binding domain of PR with a radiolabeled PRE oligonucleotide. In further studies, BRCA1 overexpression inhibited the recruitment of coactivators (steroid receptor coactivator 1 and amplified in breast cancer 1) and enhanced the recruitment of a corepressor (histone deacetylase 1) to the c-Myc PRE, whereas BRCA1 knockdown increased the abundance of AIB1 and decreased the abundance of HDAC1 at the c-Myc PRE. These findings suggest that BRCA1 inhibits progestin-stimulated PR activity, in part, by preventing PR from binding to the PRE and by promoting the formation of a corepressor complex rather than a coactivator complex.

  Y Ma , S Fan , C Hu , Q Meng , S. A Fuqua , R. G Pestell , Y. A Tomita and E. M. Rosen

Inherited mutations of the breast cancer susceptibility gene BRCA1 confer a high risk for breast cancer development. The 300RXKK and 266KXK motifs have been identified previously as sites for acetylation of the estrogen receptor- (ER-), and 302K was also found to be a site for BRCA1-mediated mono-ubiquitination of ER- in vitro. Here we show that ER- proteins with single or double lysine mutations of these motifs (including K303R, a cancer-associated mutant) are resistant to inhibition by BRCA1, even though the mutant ER- proteins retain the ability to bind to BRCA1. We also found that BRCA1 overexpression reduced and knockdown increased the level of acetylated wild-type ER-, without changing the total ER- protein level. Increased acetylation of ER- due to BRCA1 small interfering RNA was dependent upon phosphatidylinositol 3-kinase/Akt signaling and on up-regulation of the coactivator p300. In addition, using an in vitro acetylation assay, we found that in vitro-translated wild-type BRCA1 but not a cancer-associated point mutant (C61G) inhibited p300-mediated acetylation of ER-. Furthermore, BRCA1 overexpression increased the levels of mono-ubiquitinated ER- protein, and a BRCA1 mutant that is defective for ubiquitin ligase activity but retains other BRCA1 functions (I26A) did not ubiquitinate ER- or repress its activity in vivo. Finally, ER- proteins with mutations of the 300RXKK or 266KXK motifs showed modest or no BRCA1-induced ubiquitination. We propose a model in which BRCA1 represses ER- activity, in part, by regulating the relative degree of acetylation vs. ubiquitination of ER-.

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