The Nuclear Receptor, RORγ, Regulates Pathways Necessary for Breast Cancer Metastasis

Abstract

We have previously reported that RORγ expression was decreased in ER-ve breast cancer, and increased expression improves clinical outcomes. However, the underlying RORγ dependent mechanisms that repress breast carcinogenesis have not been elucidated. Here we report that RORγ negatively regulates the oncogenic TGF-β/EMT and mammary stem cell (MaSC) pathways, whereas RORγ positively regulates DNA-repair. We demonstrate that RORγ expression is: (i) decreased in basal-like subtype cancers, and (ii) inversely correlated with histological grade and drivers of carcinogenesis in breast cancer cohorts. Furthermore, integration of RNA-seq and ChIP-chip data reveals that RORγ regulates the expression of many genes involved in TGF-β/EMT-signaling, DNA-repair and MaSC pathways (including the non-coding RNA, LINC00511). In accordance, pharmacological studies demonstrate that an RORγ agonist suppresses breast cancer cell viability, migration, the EMT transition (microsphere outgrowth) and mammosphere-growth. In contrast, RNA-seq demonstrates an RORγ inverse agonist induces TGF-β/EMT-signaling. These findings suggest pharmacological modulation of RORγ activity may have utility in breast cancer.

Keywords: Breast cancer; Carcinogenesis; DNA repair; EMT (epithelial–mesenchymal transition); MaSC (mammary stem cell); Metastasis; Nuclear receptor; RNA-seq; RORγ (RORC, RORgamma); Stemness; TGF-β (TGF-beta).