Abstract B35: NR2F1 limits early dissemination and phenotypic plasticity of early-progressed ErbB2+ tumor cells by maintaining luminal differentiation

Abstract

Abstract Tumor cells derived from MMTV-Neu primary tumors (tumor-derived cells, TDC) are known to be able to complete all steps of the metastatic cascade. However, new evidence shows that cells derived from early stages of tumor progression (before detection of palpable tumors, ErbB2+ early-progressed tumor cells, EPTC) can disseminate and, as disseminated tumor cells (early DTCs), enter a non-proliferative state for prolonged periods at secondary organs. When EPTC are co-cultured with TDC, the tumor sphere formation capacity of the later is increased suggesting a synergistic contribution of early-progressed tumor cells to the growth of TDC. Thus, early DTCs are proposed to contribute to metastasis, but the mechanisms that would allow these cells, considered sessile and with few genetic alterations, to complete all steps of metastasis are unknown. Here we report that the orphan nuclear receptor NR2F1 is downregulated in human pre-malignant and malignant lesions and mouse ErbB2+ EPTC and TDC when compared with normal mammary tissue. In ErBb2+ EPTC further downregulation of NR2F1 activates a motile phenotype and this is coincident with the detection of circulating tumor cells (CTCs) and DTCs in lungs and bone marrow. Knock down of basal NR2F1 levels in ErBb2+ EPTC induced cell motility, loss of laminin-V deposition, β-catenin delocalization from the membrane and dramatic loss of E-cadherin junctions. Interestingly, TWIST, SMAD2, CK14 and ROR1 levels became upregulated upon NR2F1 depletion. This anti-EMT NR2F1-regulated program is ErbB2 oncogen-dependent. These results suggest that NR2F1 expression maintains epithelial identity and suppresses epithelial-mesenchymal transition (EMT), possibly by blocking WNT signaling. Knock down of NR2F1 in ErBb2+ EPTC also enhanced mammosphere formation efficiency and this was accompanied by upregulation of the pluripotency transcription factor NANOG and TWIST. These findings suggest that NR2F1 limits the spreading of ErBb2+ EPTC cells and it promotes a luminal differentiation-associated program by limiting the activation of a stem cell-like program. Our findings provide for the first time evidence that NR2F1 functions in mammary epithelial cells as a suppressor of pluripotency and dissemination during early stages of tumor progression. We propose that therapies that might restore expression of NR2F1 might limit early dissemination and the progression to metastasis of already disseminated tumor cells. Citation Format: Maria Soledad Sosa, Julie Cheung, Julio A. Aguirre-Ghiso. NR2F1 limits early dissemination and phenotypic plasticity of early-progressed ErbB2+ tumor cells by maintaining luminal differentiation. [abstract]. In: Proceedings of the AACR Special Conference on Tumor Metastasis; 2015 Nov 30-Dec 3; Austin, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(7 Suppl):Abstract nr B35.