Abstract 3465: p53 status as a determinant of estrogen receptor beta function in breast cancer

While the importance of estrogen receptor alpha (ERα) in breast cancer is well documented, role of estrogen receptor beta (ERβ) still remains elusive. Whether ERβ is an oncogenic or a tumor suppressor protein in breast cancer remains controversial. ERβ levels are high in ERα negative cancers including triple-negative breast cancer (TNBCs). Recent reports including the Cancer Genome Atlas (TCGA) show that about 80% of TNBC express mutant p53 (mut-p53) and it is the most predominant driver mutant in these cancers. Importantly, in addition to losing tumor suppressor activity, mut-p53 gains oncogenic functions, and therefore, has a major role in driving the cancer process. We tested the hypothesis that p53 status in breast cancer will have an important role in determining function of ERβ. We report that ERβ directly binds to p53 in human breast cancer cells. Using glutathione-S-transferase (GST)-pull down and co-imunoprecipitation assays, we have delineated the domains of both proteins that are required for the ERβ-p53 interaction. The DNA binding domain (DBD) along with the hinge domain of ERβ and the C-terminal regulatory domain of p53 are essential for the interaction. Using the highly sensitive proximity ligation assay (PLA), we show ERβ-p53 interaction in situ in breast cancer cells expressing either wt- or mut-p53. Surprisingly, we found that ERβ has opposite functions depending on the wt/mut status of p53. A combination of proliferation and apoptosis assays, RNAi technology, quantitative chromatin immunoprecipitation (qChIP), and quantitative real-time PCR (qRT-PCR) showed that in the context of the wt-p53, ERβ is pro-proliferative, whereas in the context of mut-p53, ERβ is anti-proliferative. ERβ binds wt-p53 and inhibits its transcriptional function. On the other hand, ERβ binds and sequesters mut-p53 from mut-p53−p73 complex leading to reactivation of tumor suppressor p73. Consistent with findings in cell culture models, combination of immunohistochemistry (IHC) and PLA in TNBC patient tissue microarray (TMA) representing 130 tumors followed by correlative analysis of linked patient tumor characteristics obtained from RPCI clinical data network showed that p53 status is an important determinant of ERβ function. For example, ERβ along with mut-p53 has negative effect on tumor growth, whereas ERβ in the wt-p53 context has opposite effect. Our finding that ERβ elicits opposite functions dependent on p53 status provides an important insight into the mechanism underlying the context-dependent function of ERβ and provides an explanation to the controversial reports on pro- versus anti-tumorigenic role of ERβ. These data would have significant clinical implications in targeting ERβ and mutant p53 signaling pathways for diagnostic, prognostic, and therapeutic purposes especially in ERα negative cancers such as triple negative breast cancer. Note: This abstract was not presented at the meeting. Citation Format: Gokul M. Das, Utpal K. Mukhopadhyay, Sanjay Bansal, Nadi Wickramasekera, Rajesh Medisetty, Wendy M. Swetzig, Austin Miller, Jianmin Wang, Chetan Oturkar, Alka Mukhopadhyay, Santhi Konduri. p53 status as a determinant of estrogen receptor beta function in breast cancer. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 3465. doi:10.1158/1538-7445.AM2015-3465