Moreover, knockdown of PDGFR-α, and to a greater extent, PDGFR-β, induced re-expression of VEGFR-2 expression in glioma-CM-treated ECs (Fig. 3c), suggesting that PDGF/PDGFR is critical for glioma-CM-induced VEGFR-2 down-expression in ECs. This evidence concerns the gene KDR and central nervous system cancer.