XBP1 and cancer: UPR sensor activation is characterized by cleavage of X-box- binding protein 1 (Xbp1) mRNA (IRE1), phosphorylation of the translation initiation factor 2 α subunit (eIF2α) (PERK) and processing of ATF6 in the Golgi apparatus [6]–[12] The UPR has been implicated in a variety of diseases including cancer, metabolic, neurodegenerative and inflammatory diseases [13].