EDN1 and central nervous system cancer: Hypoxia promotes high expression levels of circRNA 101491 (circ-101491) in the extracellular region of glioma cells, whereas activation of the circRNA 101491/miRNA 125b-5p/endothelin 1 (circ-101491/miR-125b-5p/EDN1) axis is associated with the malignant progression of glioma (53).