Fig. 5.

HIF1α-PDGFD-PDGFRα pathway controls constitutive activation of AKT in GBM cells. A PDGF-PDGFRα signaling relays the activation of downstream pathways of AKT and ERK independent of EGFR activation. Overnight serum-starved U251 cells were treated with 50 ng/ml each of growth factors as indicated for 10 min in the absence or presence of 30 min pretreatment with 100 ng/ml of PDGFR inhibitor AG1296 (PI), or 100 ng/ml EGFR inhibitor AG1478 (EI), before being lysed for Western blot. B HIF1α-PDGF-D-PDGFRα axis is required for a constitutive AKT activation. Serum-starved WT or KO U251 cells were treated with 50 ng/ml of PDGF-AA or PDGF-DD for 10 min before being lysed for Western blot. C,D,E Ectopic expression of PDGFRα (C) or HIF1α (D) in HIF1A-KO cells restored AKT activation (C,D) and the cell growth and invasion (E). HIF1A-KO U251 cells were transduced with lentiviruses of PDGFRα or HIF1α-PPN to establish stable cells expressing them for Western blot (D) and invasive assay (E). Representative experiments are shown from three independent experiments