CXCR4 and glioblastoma: Hypoxia has also been reported to induce expression of C-X-C chemokine receptor type 4 (CXCR4) in GBM cells and of CXCL12 in endothelial cells, and both C-C motif chemokine receptor type 5 (CCR5) and C-C motif chemokine ligand 4 (CCL4) are positively regulated by hypoxia [69,70,71].