Estrogen receptor α is a putative substrate for the BRCA1 ubiquitin ligase

Abstract

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.breast cancer ͉ ubiquitylation ͉ ubiquitination ͉ steroid hormone receptor T he breast cancer suppressor protein, BRCA1, is essential for early development and associated with a number of cellular processes including cell proliferation, cell cycle progression, apoptosis, and DNA repair/recombination. Inheritance of a single mutation in BRCA1 increases a woman's lifetime risk of developing breast cancer from 1 in 9 to greater than 1 in 2 (1). Additionally, in sporadic nonfamilial cases of breast cancer, BRCA1 expression is significantly reduced, indicating loss of BRCA1 at the protein or mRNA level (2, 3). Therefore, BRCA1 inactivation either through mutation or repression of gene expression is implicated in all forms of breast cancer development.The only known enzymatic activity associated with BRCA1 is its activity as a ubiquitin protein ligase (4). Attachment of ubiquitin to substrates is a versatile method of regulation involved in practically all aspects of cell biology. Substrate ubiquitination involves several steps and a well-known trio of enzymes called ubiquitin activating (E1), ubiquitin conjugating (E2), and ubiquitin ligase (E3). The E3 activity of BRCA1 has been localized to the N-terminal RING domain and depends on heterodimerization with the RING domain of BARD1 (5). Importantly, all BRCA1 cancer-predisposing mutations within the RING domain are observed to eliminate the BRCA1/ BARD1 E3 activity both in vitro and in vivo (5-7). This strongly suggests a link between the tumor suppressor function of BRCA1 and its E3 activity. The ultimate fate of a ubiquitinated substrate depends on both the number of ubiquitins linked in a chain and the ubiquitin chain topology (8). BRCA1/BARD1 has been observed to monoubiquitinate proteins as well as build Lys-6-linked polyubiquitin chains. Lys-6-linked chains are recognized by the 26S proteasome for deubiquitination rather than degradation (9), suggesting ubiquitinat...

Phosphorylation by p38 Mitogen-Activated Protein Kinase Promotes Estrogen ReceptorαTurnover and Functional Activity via the SCFSkp2Proteasomal Complex

“…For instance, the cullin regulation of the ER␣ protein was previously reported to be mediated through S118 in ER␣ (8). ER␣ has also been shown to be ubiquitinated at K302 by BRCA1/ BARD1, a ubiquitin ligase (15,35), although the effect of this on ER␣ stability was not reported. Nephew and associates also reported previously that lysines 302 and 303 in ER␣ impact receptor interactions with the E3-ubiquitin ligase CHIP and the proteasome-mediated degradation of the receptor (6,17).…”

RETRACTED ARTICLE: Regulation of estrogen receptor signaling in breast carcinogenesis and breast cancer therapy

“…2). [152], E6-associated protein (e6AP) [153], RING finger protein 147 (RNF147, also named estrogen-responsive finger protein (EFP)) [154], SPOP [155], CHIP [156][157][158] and BRCA1/BARD1 [126,159] regulate ERα proteasomal degradation (Fig. 2).…”

“…The BRCA1/BARD1 complex has been observed to monoubiquitinate and polyubiquitinate proteins. ERα has also been shown to be a substrate for BRCA1/BARD1 in vitro and in vivo [126,159,163]. BRCA1/BARD1 monoubiquitinates ERα at Lys302, which is a residue located at the C-terminal ligand binding domain.…”

Calmodulin, a regulatory partner of the estrogen receptor alpha in breast cancer cells

“…acetylation (Wang et al, 2001) and mono-ubiquitination (Eakin et al, 2007;Heine, Parvin, 2007); S 305 : phosphorylation by PAK-1and/or PKA (Wang et al, 2002;Zwart et al, 2007)) suggests a complementary regulatory control of CaM at this level.…”

“…When bound to BARD-1, BRCA-1 indeed provokes the mono-ubiquitination of Lys-302 and 303 in ERα (Eakin et al, 2007). Inasmuch as these residues are implicated in the (Seielstad et al, 1995), frequently recorded in breast cancer samples (Maaroufi et al, 2000), is likely to withdraw ERα from the action of repressors like BRCA-1, the oligomeric nature of ERα maintaining such cleaved receptors in a compact structure still able to mediate transcription (Kraus et al, 1995).…”