Abstract 1851: Estradiol-inducible dependence receptor UNC5a restricts estrogen receptor activity and imparts estradiol dependence to breast cancer cells
Authors: Bhat-Nakshatri Poornima , Anjanappa Manjushree , Hao Yangyang , Edenberg Howard , Liu Yunlong , Nakshatri Harikrishna 
Published: August 2015

Abstract
Signaling by Dependence Receptors (DRs) is a new paradigm in cell signaling and recently has been recognized to play a major role in cancers. DRs are cell surface receptors that function as tumor suppressors or induce apoptosis when disengaged from their ligands. In the presence of ligands, these receptors transmit proliferation, migratory, and anti-apoptotic signals thus creating a cellular state that is dependent on ligands for survival. This study was focused on regulation of their expression in breast cancer. We observed that UNC5a, a DR, and its ligand Netrin-1 (NTN1) are estradiol (E2)-inducible depending on cell types. Since E2 and its receptor estrogen receptor alpha (ERα) are major signaling hubs in ERα-positive breast cancers, we examined the function of UNC5a in ERα-positive breast cancer cells. Knockdown of UNC5a resulted in deregulated expression of E2-regulated genes, E2-independent and anti-estrogen-resistant growth in vitro, and E2-indpendent tumor formation in xenograft models. RNA-seq analyses of parental and UNC5a knockdown cells with or without E2 treatment revealed ∼ 10-fold increase in number of E2-regulated genes in UNC5a knockdown cells compared with parental cells. The basal expression of E2-inducible anti-apoptotic BCL-2 was elevated &gt;30-fold at mRNA and/or protein levels in UNC5a knockdown cells compared with vector control cells. In addition, UNC5a knockdown resulted in aberrant NF-κB signaling, which is typically under negative regulation by ERα:E2. Furthermore, UNC5a knockdown cells showed elevated expression of p63, a p53 family transcription factor that promotes breast epithelial stem cell maintenance and basal-like breast cancer. Consistent with the known role of NF-κB and p63 in cancer stem cells, UNC5a-knockdown cells displayed cancer stem cell phenotype as evident from ∼3-fold increase in the number of CD44+/CD24+ and CD44+/EpCAM+ subpopulation compared with parental cells. Overall, our results suggest that E2 induces UNC5a expression as a negative regulatory loop to restrict or fine tune ERα:E2 signaling and maintain luminal phenotype. Loss or mutation of UNC5a, as observed frequently in cancer, could lead to unrestricted E2:ERα signaling and anti-estrogen resistant growth while simultaneously enabling ERα-positive luminal breast cancer cells to acquire basal-like and cancer stem cell-like features.
This work is supported by grants from the Susan G. Komen for the Cure (SAC110025 to HN)
Citation Format: Poornima Bhat-Nakshatri, Manjushree Anjanappa, Yangyang Hao, Howard Edenberg, Yunlong Liu, Harikrishna Nakshatri. Estradiol-inducible dependence receptor UNC5a restricts estrogen receptor activity and imparts estradiol dependence to breast cancer cells. [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 1851. doi:10.1158/1538-7445.AM2015-1851