VEGF-induced intracellular Ca2+ oscillations are weaker and do not stimulate proliferation in tumor-derived endothelial colony forming cells

Abstract

Endothelial colony forming cells (ECFCs) represent a population of truly endothelial precursors that may be mobilized from their vascular stem cell niches to promote the angiogenic switch in a growing number of solid malignancies, including breast cancer (BC). While normal ECFCs require VEGF to proliferate, tumor-associated ECFCs are seemingly insensitive to this growth factor. This phenomenon could contribute to the relative failure of anti-VEGF therapies in cancer patients. Recent work showed that the intracellular Ca2+ toolkit, which is a crucial determinant of ECFC fate and controls the pro-angiogenic program triggered by VEGF, is remodelled in tumor-associated ECFCs. Herein, we adopted an array of techniques, including Ca2+ imaging, electron microscopy, flow cytometry, real-time polymerase chain reaction, western blot analysis and functional assay to investigate whether and how VEGF uses Ca2+ signalling to control proliferation in BC-derived ECFCs (BC-ECFCs). Our results finally demonstrate for the first time that BC-ECFCs are insensitive to VEGF, which might explain at cellular and molecular level the failure of anti-VEGF therapies in BC patients, and hint at SOCE as a novel molecular target for this disease.