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. 2021 Jan 14;11(1):52. doi: 10.3390/metabo11010052

Figure 1.

Figure 1

Overview of the canonical endoplasmic reticulum unfolded protein response (UPR-ER) pathways. In higher eukaryotes, upon sensing misfolded proteins by HSP-4/BiP, the three UPR-ER branches—IRE-1α, PEK-1, and ATF-6—are activated to mount distinct and collective downstream transcriptional and translational programs to promote protein folding, processing, and secretion, thereby reducing the load of misfolded proteins in the ER lumen and alleviating ER stress. Abbreviations: ATF-4: Activating Transcription Factor 4; ATF-6: Activating Transcription Factor 6; eIF2α: Eukaryotic Initiation Factor 2α; HSP-4/BiP: heat shock protein 4/ Binding immunoglobulin protein; IRE-1α: Inositol-Requiring-Enzyme 1α; PEK-1: human PERK kinase homolog; UPR: unfolded protein response; xbp-1: X-box Binding Protein homolog 1. (Figure created with Biorender.com, Toronto, ON, Canada).