A Unique ISR Program Determines Cellular Responses to Chronic Stress

Highlights

• Protein synthesis during chronic ER stress is independent of eIF2B GEF activity

• mRNA translation during chronic ISR is mediated by an eIF3-dependent mechanism

• Coordination of transcriptional and translational reprogramming signifies chronic ISR

• ER function in chronic ISR relies on PERK-dependent translational reprograming

Summary

The integrated stress response (ISR) is a homeostatic mechanism induced by endoplasmic reticulum (ER) stress. In acute/transient ER stress, decreased global protein synthesis and increased uORF mRNA translation are followed by normalization of protein synthesis. Here, we report a dramatically different response during chronic ER stress. This chronic ISR program is characterized by persistently elevated uORF mRNA translation and concurrent gene expression reprogramming, which permits simultaneous stress sensing and proteostasis. The program includes PERK-dependent switching to an eIF3-dependent translation initiation mechanism, resulting in partial, but not complete, translational recovery, which, together with transcriptional reprogramming, selectively bolsters expression of proteins with ER functions. Coordination of transcriptional and translational reprogramming prevents ER dysfunction and inhibits “foamy cell” development, thus establishing a molecular basis for understanding human diseases associated with ER dysfunction.