THE MAMMALIAN UNFOLDED PROTEIN RESPONSE

TLDR

In the endoplasmic reticulum, secretory and transmembrane proteins fold and undergo post‑translational modifications, and when folding is inhibited, the unfolded protein response (UPR) is activated to restore homeostasis. This review summarizes principles of protein folding and chaperone function to elucidate UPR‑signaling mechanisms. The authors discuss mammalian UPR signal‑transduction mechanisms and how the UPR remodels cellular processes. Data show that UPR signaling influences processes such as starvation responses and differentiation, previously considered unrelated to ER function.

Abstract

▪ Abstract In the endoplasmic reticulum (ER), secretory and transmembrane proteins fold into their native conformation and undergo posttranslational modifications important for their activity and structure. When protein folding in the ER is inhibited, signal transduction pathways, which increase the biosynthetic capacity and decrease the biosynthetic burden of the ER to maintain the homeostasis of this organelle, are activated. These pathways are called the unfolded protein response (UPR). In this review, we briefly summarize principles of protein folding and molecular chaperone function important for a mechanistic understanding of UPR-signaling events. We then discuss mechanisms of signal transduction employed by the UPR in mammals and our current understanding of the remodeling of cellular processes by the UPR. Finally, we summarize data that demonstrate that UPR signaling feeds into decision making in other processes previously thought to be unrelated to ER function, e.g., eukaryotic starvation responses and differentiation programs.