POU5F1 and glioblastoma: A recent study revealed that HIF-2α regulates Oct4 directly upstream and binds hypoxic regulatory elements in the promoter of murine Oct4, which is a stem cell regulatory protein; this is not the case for HIF-1α.39 HIF-2α may have a specific function in glioblastoma stem cells: it was shown to be selectively expressed in the CD133+ subpopulation of glioblastoma cells, whereas HIF-1α expression is widespread among both tumorigenic and nontumorigenic cells.40