title: BRCA1 regulates acetylation and ubiquitination of estrogen receptor-alpha.
abstract: Inherited mutations of the breast cancer susceptibility gene BRCA1 confer a high risk for breast cancer development. The (300)RXKK and (266)KXK motifs have been identified previously as sites for acetylation of the estrogen receptor-alpha (ER-alpha), and (302)K was also found to be a site for BRCA1-mediated mono-ubiquitination of ER-alpha in vitro. Here we show that ER-alpha 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-alpha 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-alpha, without changing the total ER-alpha protein level. Increased acetylation of ER-alpha 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-alpha. Furthermore, BRCA1 overexpression increased the levels of mono-ubiquitinated ER-alpha protein, and a BRCA1 mutant that is defective for ubiquitin ligase activity but retains other BRCA1 functions (I26A) did not ubiquitinate ER-alpha or repress its activity in vivo. Finally, ER-alpha proteins with mutations of the (300)RXKK or (266)KXK motifs showed modest or no BRCA1-induced ubiquitination. We propose a model in which BRCA1 represses ER-alpha activity, in part, by regulating the relative degree of acetylation vs. ubiquitination of ER-alpha.
authors.affiliation: Department of Oncology, Lombardi Comprehensive Cancer Center, Georgetown University, Washington, DC 20057-1469, USA.
authors.forename: Yongxian
authors.initials: Y
authors.lastname: Ma
authors.forename: Saijun
authors.initials: S
authors.lastname: Fan
authors.forename: Changyan
authors.initials: C
authors.lastname: Hu
authors.forename: Qinghui
authors.initials: Q
authors.lastname: Meng
authors.forename: Suzanne A
authors.initials: SA
authors.lastname: Fuqua
authors.forename: Richard G
authors.initials: RG
authors.lastname: Pestell
authors.forename: York A
authors.initials: YA
authors.lastname: Tomita
authors.forename: Eliot M
authors.initials: EM
authors.lastname: Rosen
mesh_terms: D000107:Acetylation; D019313:BRCA1 Protein / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D001943:Breast Neoplasms; D045744:Cell Line, Tumor; D004958:Estradiol / Q000494:pharmacology; D047628:Estrogen Receptor alpha / Q000378:metabolism*; D005260:Female; D055785:Gene Knockdown Techniques; D019398:Genes, BRCA1; D017930:Genes, Reporter; D006801:Humans; D008297:Male; D009154:Mutation; D000081082:Phosphoinositide-3 Kinase Inhibitors; D011471:Prostatic Neoplasms; D011485:Protein Binding; D011499:Protein Processing, Post-Translational; D051057:Proto-Oncogene Proteins c-akt / Q000235:genetics; D034741:RNA, Small Interfering; D014162:Transfection; D054875:Ubiquitination; D050880:p300-CBP Transcription Factors / Q000235:genetics / Q000378:metabolism
chemical_list: D019313:BRCA1 Protein; D047628:Estrogen Receptor alpha; D000081082:Phosphoinositide-3 Kinase Inhibitors; D034741:RNA, Small Interfering; D004958:Estradiol; D050880:p300-CBP Transcription Factors; D051057:Proto-Oncogene Proteins c-akt