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  • Title: Negative feedback loop of BRCA1-BARD1 ubiquitin ligase on estrogen receptor alpha stability and activity antagonized by cancer-associated isoform of BARD1.
    Author: Dizin E, Irminger-Finger I.
    Journal: Int J Biochem Cell Biol; 2010 May; 42(5):693-700. PubMed ID: 20060929.
    Abstract:
    Estrogen is involved in breast cancer risk, which is increased for BRCA1 mutation carriers, suggesting a role for BRCA1 in estrogen signaling. BRCA1 exerts its function through forming an E3 ubiquitin ligase with BARD1. We report that the estrogen receptor alpha is a target of the BRCA1-BARD1 ubiquitin ligase in vivo. BRCA1 and BARD1 are required for estrogen receptor alpha ubiquitination and degradation, and repression of either one leads to ERalpha accumulation, suggesting a feedback loop between BRCA1-BARD1 and estrogen receptor alpha, since BRCA1 and BARD1 are induced by estrogen receptor alpha. While the ubiquitin ligase activity maps to the N-terminal RING finger domains of BRCA1 and BARD1, we demonstrate that the BARD1 C-terminus is important for target recognition. Furthermore, a BARD1 isoform lacking the RING domain binds and stabilizes estrogen receptor alpha. Thus deficiencies of BRCA1 or BARD1 and/or upregulation of BARD1 isoforms lead to estrogen receptor alpha upregulation, providing a functional link between BRCA1 deficiency, estrogen signaling, and tumorigenesis.
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