Prolonged hypoxia exposure (i.e., 1% O2 for a period of 72 h) stimulated glioblastoma cells to express CD133 and the stemness markers Kruppel-like factor 4 (KLF4) and SOX2 via a hypoxia inducible factor (HIF)-1α-dependent mechanism (Fig. 2a) [130]. This evidence concerns the gene KLF4 and glioblastoma.