Estradiol-regulated Dependence Receptor UNC5A Restricts Estradiol Signaling and Luminal to Basal Transition and Metastasis of Breast Cancer

Estrogen receptor alpha (ERa)-positive breast cancers, while initially being responsive, eventually develop resistance to ERa targeted therapies through ERa-dependent and ERa-independent mechanisms. Through functional genomic studies we report heretofore unrecognized role for the axon guidance dependence receptor UNC5A in fine-tuning estradiol (E2) and anti-estrogen response. Knockdown of the estradiol-inducible UNC5A caused unrestricted ERa signaling as evident from deregulated E2-regulated gene expression and E2-independent tumorigenesis accompanied with multi-organ metastatic spread in xenograft models. UNC5A-knockdown cells displayed luminal/basal hybrid phenotype characterized by elevated expression of basal/stem cell enriched ?Np63 and ITGA6 (CD49f), anti-apoptotic BCL2, and the lymphangiogenic factor NTN4 but lower expression of luminal/alveolar differentiation-associated factor ELF5 while maintaining functional ERa. Thus, UNC5A is a new regulator of ERa with a tumor/metastasis suppressive activity. Significance: ERa signaling network plays a significant role in ~70% of breast cancers. While the signaling molecules that partner with ERa to augment E2-dependent signaling and promote breast cancer progression have been well studied, negative feedback proteins that attenuate ERa signaling and their contribution to breast cancer progression are yet to be identified. This study reports E2-inducible UNC5A as a critical attenuator of ERa signaling and its reduced expression in primary breast cancer is associated with poor outcome. UNC5A potentially controls ERa signaling by restricting PI3K/AKT:ERa crosstalk needed for E2-independent activity while simultaneously maintaining ERa-dependent luminal differentiation program. These findings have important implications in developing strategies to combat anti-estrogen resistance and to improve clinical utility of PI3K/AKT inhibitors. Overall design: UNC5A expression was knocked down in MCF-7 and T47D cells by shRNA and stable cells expressing shRNA were generated. The vector expressing cells served as controls (pLKO). Cells were treated with vehicle (ethanol) or estradiol (0.1 nM) for three hours. Total RNA was prepared using RNAeasy kit from Qiagen and subjected to RNA-seq