Abstract 4599: The RING E3 ligase BCA2 is regulated by estrogen and co-expressed with estrogen receptor in breast cancer cells

Proceedings: AACR 101st Annual Meeting 2010‐‐ Apr 17‐21, 2010; Washington, DC The Breast Cancer Associated gene 2 (BCA2) protein contains a RING H2 finger and a zinc finger near the N-terminus. The presence of the RING domain allows BCA2 to function as an E3 ligase. RING finger proteins play critical roles in mediating the transfer of ubiquitin and ubiquitin-like modifiers to substrates; such modifications are pivotal in regulating protein homeostasis and basic cellular processes such as gene-transcriptional regulation. The RING domain in BCA2 is known to act as an E3 ligase in its auto-regulation, and is suspected to play a role in the modification of other proteins. In a cohort of 945 primary invasive breast cancers examined for estrogen receptor-alpha (ER) and BCA2 expression, 67% were found to be ER-positive, 74% of which also exhibited strong nuclear BCA2 protein expression (p = 0.004). In this study, we examined potential mechanism(s) underlying BCA2 and ER co-expression at transcriptional and protein levels. Estrogen-responsive and non-responsive breast cancer cell lines were used as model systems. To investigate whether BCA2 is an estrogen responsive gene, BCA2 and ER-positive T47D breast cancer cells were cultured in medium containing charcoal-stripped fetal calf serum supplemented with 10 nM and 100 nM 17β-estradiol respectively over a 72-hour time course. Northern and Western blots showed a 17β-estradiol-associated induction of BCA2 mRNA and protein within 72 hrs. Moreover, when ER is ectopically or stably expressed in ER and BCA2-negative MDA-MB-231 cells, prominent BCA2 expression is detected, suggesting that ER is responsible for induction of BCA2 transcription. To investigate a possible interaction of BCA2 and ER at a transcriptional level, bioinformatic analysis of the BCA2 promoter region revealed ER and PR binding sites as well as possible sites of general transcription factors. Together our data indicates that BCA2 is upregulated in response to estrogen and that BCA2 expression can be rescued by the introduction of ER, suggesting that ER and BCA2 may be participating in crosstalk at the transcriptional level. Further investigations into this phenomenon are necessary to determine the possibility of the development of drugs targeting BCA2 in order to manipulate ER. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 4599.