To see if HIF1α directly regulates the expression of PDGFRA and PDGFD in GBM, we first identified a putative hypoxia-response element (HRE) in the PDGFRA proximal promoter, and 2 HREs within intron 1 of the PDGFRA gene (Fig. 3C). This evidence concerns the gene PDGFD and glioblastoma.