HIF1A and glioblastoma: We next cultured GBM cells in 21% O2 and 1% O2 for 72 h; in both western blotting and immunofluorescence results, both HIF1α and HIF2α were highly expressed under 1% O2 conditions, while there was almost no HIF1α and HIF2α expression under 21% O2 conditions (Fig. 1C, E).