ERN1 and glioblastoma: Unlike in HEK293 cells, IRE1α was not active in glioblastoma under hypoxia as demonstrated by the absence of XBP1s mRNA (a downstream product of the active-IRE1α RNase domain) and by the decrease in phosphorylated IRE1α (necessary for the activation of its kinase activity) (Fig. 1c–e).