The receptor activator of NFkB (RANK)-RANK ligand (RANKL) pathway, pivotal regulator of bone remodeling, has emerged as a major mediator of progesterone-driven breast cancer (BC) carcinogenesis. RANK expression is particularly elevated in triple negative BC and has been associated with aggressiveness and poor prognosis. This study addressed the impact of elevated RANK expression in estrogen receptor (ER)-positive BC.
In silico analysis of RANK (TNFRSF11A) expression was performed in the TCGA BC cohort. ER+HER2- cell lines overexpressing RANK were obtained by lentiviral transduction and standard assays were used for gene expression and phenotype evaluation. In vivo tumor growth was measured in orthotopic xenografts or after tail vein inoculation. Comparisons between two groups were performed using unpaired t-test. Survival analyzes used the Kaplan–Meier method and log-rank test.
RANK expression was higher in ER- breast tumors (p < 0.001); and associated with decreased 5-year overall survival (HR = 2.12 (1.16-3.87), p = 0.012). However, 5% of ER+ tumors were found to express RANK within the ER- 75%Q range. ER+ cell lines overexpressing RANK (MCF-7OE and T47DOE) were characterized by hyper activation of downstream pathways; upregulation of mesenchymal and stem cell phenotype. In silico, elevated RANK expression in ER+ tumors was significantly correlated with mesenchymal and stemness-related genes. In vivo, MCF-7OE xenografts were consistently smaller in comparison with parental ones. However, tail vein inoculation showed that MCF-7 and MCF-7OE cells where identically metastatic in the lungs and skeleton, and animals harboring MCF-7OE cells had more circulating tumor cells.
Our data shows for the first time that RANK expression in ER+ BC is not unneglectable, and may impact on the tumor progression, particularly in the metastatic setting.
Instituto de Medicina Molecular.
This project was funded by National Funds (FCT-MEC), under the research project PTDC/MED-ONC/28636/2017. IG is supported by FCT grant SFRH/BD/139178/2018.
S. Casimiro: Research support: Amgen. L. Costa: Research support, advisory board: Amgen. All other authors have declared no conflicts of interest.