Fig. 4. HIF1α/HIF2α-EGF regulated GBM malignancy via the EGFR–PI3K/AKT pathway in hypoxia.

A There was a higher expression of EGFR, PI3K, PDK1, AKT and mTOR in cells cultured in 1% O₂ than cells cultured in control conditions. B, C The cells cultured in 1% O₂ for 72 h highly expressed EGFR, PI3K, PDK1, AKT and mTOR, but there was much less expression of EGFR, PI3K, PDK1, AKT and mTOR under normoxic conditions. D Both HIF1α and HIF2α had a positive correlation with EGFR, PI3K, PDK1, AKT and mTOR. E A significant decrease in the expression of EGFR, PI3K, PDK1, AKT and mTOR in HIF1α-KO or HIF2α-KO cells. The addition of EGF into the culture medium of HIF1α-KO or HIF2α-KO cells showed an immediate recovery of the expression of EGFR, PI3K, PDK1, AKT, mTOR and HIF1α. F Adding the EGFR inhibitor (AG1478), PI3K inhibitor (Ly294002) and mTOR inhibitor (rapamycin) into the culture medium of GBM cells in 1% O₂ showed that there were no significant differences for early apoptosis; however, there were higher late and total apoptosis rates. P values were determined by the independent samples t test and one-way ANOVA.