Both tumor cells and endothelial cells express CXCR4, and to distinguish whether tumor cell-CXCR4 function is required for tumor growth, we depleted CXCR4 by shRNA-mediated knock-down in U87 glioblastoma cells that had also been engineered to express a fusion protein of firefly luciferase and eGFP (shCXCR4-U87-Luc). This evidence concerns the gene CXCR4 and glioblastoma.