The unfolded protein response (UPR) signaling pathway is a cellular stress response initiated by BiP/GRP78, a central regulator of ER processes including protein biogenesis, signal transduction, and calcium homeostasis [1–5]. In the resting state, BiP/GRP78 is associated with ER stress transducers such as inositol-requiring kinase 1a (IRE1a), protein kinase RNA-like endoplasmic reticulum kinase (PERK), and activating transcription factor 6 (ATF6).