In GBM cells without ER stress, knockdown of XBP1 did not influence VEGFA secretion (Fig. 4E, F, blue bar plots), this is because XBP1 is rarely expressed in normally cultured GBM cells without ER-stress in vitro (Fig. 3F), but it significantly blocked ER stress induced VEGFA secretion of GBM cells (Fig. 4E, F, red bar plots). Here, XBP1 is linked to glioblastoma.