This subproject is one of many research subprojects utilizing theresources provided by a Center grant funded by NIH/NCRR. The subproject andinvestigator (PI) may have received primary funding from another NIH source,and thus could be represented in other CRISP entries. The institution listed isfor the Center, which is not necessarily the institution for the investigator.The breast cancer suppressor protein, BRCA1, is a ubiquitin ligase expressed in a wide range of tissues. However, inheritance of a single BRCA1 mutation significantly increases a woman's lifetime chance of developing tissue-specific cancers in the breast and ovaries. Recently, studies have suggested this tissue specificity may be linked to inhibition of estrogen receptor (ER) transcriptional activation by BRCA1. Here, we show that ER is a putative substrate for the BRCA1/BARD1 ubiquitin ligase, suggesting a possible mechanism for regulation of ER activity by BRCA1. Our results show ER is predominantly monoubiquitinated in a reaction that involves interactions with both BRCA1 and BARD1. The regions of BRCA1/BARD1 necessary for ER ubiquitination include the RING domains and at least 241 and 170 residues of BRCA1 and BARD1, respectively. Cancer-predisposing mutations in BRCA1 are observed to abrogate ER ubiquitination. The identification of ER as a putative BRCA1/BARD1 ubiquitination substrate reveals a potential link between the loss of BRCA1/BARD1 ligase activity and tissue-specific carcinoma.
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