Protein kinase R-like ER kinase (PERK), inositol-requiring enzyme 1a (IRE1a), and activating transcription factor-6 (ATF6) are three proteins that mediate the ER stress response.276–278 X-box binding protein 1 (XBP1) is a key transcription factor in the IRE1a signaling branch and is spliced by endoribonuclease and IRE1a to regulate protein folding, trafficking, and secretion, thus enhancing cell survival and ER homeostasis under ER stress.279 Researchers found that most PATs are upregulated in GBM. Here, XBP1 is linked to glioblastoma.