Endothelial protein C receptor (EPCR) is a transmembrane receptor widely expressed in endothelial cells where it exerts cytoprotective and anticoagulant activities. We have shown that it is also expressed in lung tumour cells where it promotes tumour cell survival and increases osseous prometastatic activity. However, to date the contribution of EPCR to tumourogenesis and skeletal metastasis in breast cancer remains ill defined. Lentiviral shRNA-mediated EPCR silenced (shEPCR) cells in the MDA-MB-231 derived 1833 breast cancer cell line showed unaltered growth kinetics in basal or apoptotic-induced in vitro conditions. However, EPCR silencing reduced tumour growth in an orthotopic model of mammary fat pad injection. Interestingly, intracardiac inoculation of shEPCR cells led to a substantial reduction in skeletal metastatic burden, assessed by bioluminescence imaging, and osteolytic lesions, evaluated by micro-X-Ray imaging, micro-CT scans and histological analysis. This effect was associated with a decreased skeletal tumour growth observed after intratibial inoculation of shEPCR cells as compared with control cells. Furthermore, after intra-tail injection of the murine breast cancer cell line ANV5, we found a dramatic decrease in lung metastasis in animals injected with shEPCR cells as compared with control mice, despite the similar growth kinetics of the cell lines in vitro. In vivo transcriptomic analysis identified several relevant signalling pathways differentially altered in shEPCR and control tumours. To explore the clinical relevance of these findings we carried out global expression analysis in a cohort of 286 patients. Patients with high EPCR expression levels had shorter relapse-free survival times as compared with patients with low EPCR expression levels. These data indicate that EPCR confers an in vivo protumourogenic and prometastatic phenotype to bone and lung. Monitoring EPCR could represent a clinically relevant factor in breast cancer and a potential therapeutic target.
Disclosure: The authors declared no competing interests.