SAT-309 Nuclear Receptor V-ErbA-related Protein 2 (EAR2): a Novel Driver of Breast Cancer Proliferation

Abstract Disclosure: F. Sharafath Yoosuf: None. C. Magne De: None. C.D. Clyne: None. S. Chu: None. P.J. Fuller: None. Breast cancer is the most common cancer in women, with over 2 million cases diagnosed annually worldwide. Two-thirds of breast cancers are estrogen receptor positive (ER+), and may be treated with hormone therapy such as tamoxifen, to block estrogen’s effects on residual cancer cells and reduce recurrence risk. However, ∼30% of women develop endocrine resistance or fail to respond to treatment. Limited alternative therapies exist for endocrine-resistant disease, leaving patients at higher risk of relapse. This creates an urgent need to uncover and characterize other molecular drivers of breast cancer to develop novel therapeutic strategies. Apart from steroid receptors such as the ER and progesterone receptor (PR), the role of other nuclear receptors (NR) in breast cancer remains underexplored. Our previous research investigating NR expression in breast cancer revealed that NR2F6, also known as EAR2 (V-Erb-A related protein 2), is uniquely upregulated in both ER+ and ER- breast cancers. In contrast, most other NR are universally downregulated, suggesting that EAR2 may drive breast cancer proliferation.In this study we investigated the role of EAR2 in breast cancer cell proliferation, invasion and migration using three breast cancer cell lines with modulated EAR2 expression. EAR2 was inducibly overexpressed in MCF7 cells, constitutively overexpressed in Hs578T cells and knocked down using CRISPR/Cas9 in T47D cells. Proliferation/viability were assessed using the xCELLigence Real Time Cell Analyser SP, MTS assay and Incucyte Live Cell Imaging. Cell migration was studied using the Incucyte. RNA-seq analysis was conducted using DNBSEQ technology and selected differentially expressed genes were validated using RT-qPCR. EAR2 overexpression increased proliferation while knockdown decreased proliferation and increased cell size. Migration was enhanced with EAR2 overexpression. In MCF7 cells overexpressing EAR2, highly expressed genes included GALNT16, MACROD2, GPD1 and WNT10B, of which MACROD2 is implicated in therapy-resistant breast cancers. Comparative analysis of MCF7 (EAR2 overexpression) and T47D (EAR2 knockdown) cells identified 54 common inversely regulated genes. Among these, DUSP4 and RUNX1 are implicated in early oncogenic transformation in breast cancer, while KRT8, KRT18 and KRT19 are associated with keratinization and epithelial differentiation.Our findings demonstrate that EAR2 is a novel driver of breast cancer proliferation, and may contribute to cancer progression in both ER+ and ER- subtypes. Notably, the role for EAR2 in tamoxifen resistance and its association with highly invasive, dedifferentiated tumors with poor prognosis suggest it could represent a novel, unexplored therapeutic target. Future studies are warranted to further explore EAR2’s functional role in breast cancer and its potential as a target for overcoming endocrine resistance. Presentation: Saturday, July 12, 2025