NES and glioblastoma: Moreover, we detected apelin and its receptor, the G-protein coupled receptor APLNR (APJ), in clinical glioblastoma samples in the vicinity of PECAM-labelled endothelial cells and cells positive for the stem cell markers NESTIN and SOX2 (Fig. 1E), suggesting a potential role for apelin in the tumour vascular niche (Calabrese et al., 2007).