Endoplasmic reticulum stress and unfolded protein response machinery (UPR) (UPR)

The Endoplasmic Reticulum (ER) stress and Unfolded Protein Response (UPR) machinery is a complex signaling network that monitors and maintains protein folding quality control within the ER (Hetz et al., 2020, Nature Reviews Molecular Cell Biology). It is governed by three transmembrane sensors: Inositol-requiring enzyme 1 (IRE1), Protein kinase RNA-like ER kinase (PERK), and Activating transcription factor 6 (ATF6), which collectively coordinate a program to reduce protein influx and increase folding capacity (Walter & Ron, 2011, Science). In diseases such as cancer, the UPR is often hijacked to support tumor survival under harsh microenvironmental conditions, whereas in neurodegenerative disorders, chronic UPR activation can lead to neuronal loss (Wang & Kaufman, 2016, Nature). Therapeutic strategies involve small molecule inhibitors or activators designed to modulate these pathways, such as PERK inhibitors for oncology or chemical chaperones like 4-phenylbutyric acid for metabolic and protein-misfolding diseases (Oakes & Papa, 2015, Annual Review of Pathology). However, because the UPR is fundamental to the health of secretory tissues like the pancreas and liver, targeting this machinery presents significant challenges regarding therapeutic index and systemic safety (Hetz & Papa, 2018, Molecular Cell).

Other names

ER stress responseUnfolded protein responseUPR signaling pathwayER-associated degradation machineryProteostatic stress response

The machinery is targeted through the inhibition or activation of its primary sensors (IRE1, PERK, ATF6) to either promote cell survival by enhancing folding capacity or trigger apoptosis in diseased cells. Small molecules can act as chemical chaperones to stabilize protein conformation or as specific inhibitors of UPR-related kinases and endonucleases to modulate downstream gene expression and protein translation.