To investigate this further, we cultured glioblastoma cells U87 and U251 under both normal (20% O2) and hypoxic (1% O2) conditions for 24 hours and found that under normal culture conditions, the expression levels of HIF-1α protein in U87 and U251 cells exceeded those observed in the control cell line HA1800. This evidence concerns the gene HIF1A and glioblastoma.