Pharmacologic IRE1/XBP1s Activation Confers Targeted ER Proteostasis Reprogramming

Activation of the IRE1/XBP1s signaling arm of the unfolded protein response (UPR) is a promising strategy to correct defects in endoplasmic reticulum (ER) proteostasis implicated in diverse diseases. However, no pharmacologic activators of this pathway identified to date are suitable for ER proteostasis remodeling through selective activation of IRE1/XBP1s signaling. Here, we use high-throughput screening to identify non-toxic compounds that induce ER proteostasis remodeling through IRE1/XBP1s activation. We employ transcriptional profiling to stringently confirm that our prioritized compounds selectively activate IRE1/XBP1s signaling without activating other cellular stress-responsive signaling pathways. Furthermore, we demonstrate that our compounds improve ER proteostasis of destabilized variants of amyloid precursor protein (APP) through an IRE1-dependent mechanism and reduce APP-associated mitochondrial toxicity in cellular models. These results establish highly-selective IRE1 activating compounds that can be widely employed to define the functional importance of IRE1/XBP1s activity for ER proteostasis regulation in the context of health and disease. Overall design: Comparisons of the transcriptomes of HEK293T cells treated with DMSO or identified IRE1/XBP1s activating compounds IXA1, IXA4, IXA6, or global UPR activator thapsigargin (Tg)