Unfolded protein response (UPR) signaling machinery (UPR)

The Unfolded Protein Response (UPR) signaling machinery is a complex network of signal transduction pathways designed to maintain protein folding homeostasis within the endoplasmic reticulum (ER) (Hetz et al., 2020, Nature Reviews Molecular Cell Biology). It is primarily governed by three ER-resident transmembrane sensors: Inositol-requiring enzyme 1 (IRE1), Protein kinase RNA-like endoplasmic reticulum kinase (PERK), and Activating transcription factor 6 (ATF6) (Wang & Kaufman, 2016, Frontiers in Endocrinology). Under conditions of ER stress, such as nutrient deprivation or high secretory demand, these sensors activate downstream effectors to expand ER capacity, reduce protein translation, and enhance protein degradation. However, if the stress is chronic or irremediable, the UPR shifts from a pro-survival to a pro-apoptotic program, often mediated by the transcription factor CHOP (Oakes, 2020, American Journal of Pathology). This machinery is a critical therapeutic target in oncology, where cancer cells exploit UPR signaling to survive hypoxia and nutrient deprivation, and in neurodegenerative diseases, where chronic ER stress contributes to neuronal loss. Pharmacological modulation of the UPR includes the use of small-molecule inhibitors of IRE1alpha or PERK, as well as chemical chaperones like 4-phenylbutyric acid that alleviate the underlying protein folding burden (Hetz & Papa, 2018, Molecular Cell).

Other names

Endoplasmic reticulum stress pathwayER stress responseUPR pathwayIntegrated stress response (ISR)

Small molecule inhibition of the kinase or RNase domains of UPR sensors (IRE1, PERK), modulation of the integrated stress response (ISR) via eIF2alpha, and chemical chaperoning to stabilize protein folding (Hetz & Papa, 2018, Molecular Cell).