Copper as a Novel Regulator of PERK

Abstract

AbstractPERK is a transmembrane kinase located on the ER with a luminal domain that senses ER stresses, such as protein misfolding, and a cytosolic kinase domain. Upon stress sensing, PERK activates and phosphorylates eIF2α to attenuate global translation while upregulating select transcripts to re-establish protein homeostasis. In a secondary phase of signaling PERK can also induce apoptosis to dispose of terminally stressed and damaged cells. Thus, the delineated bi-phasic nature of PERK signaling requires tight regulation for homeostatic function, as evidenced by dysregulation of this pathway being implicated in many diseases, including cancers and neurodegenerative conditions. Pursuant attempts to therapeutically modulate PERK and its signaling outcomes have highlighted that our understanding of the determinants of adaptive vs. mal-adaptive signaling remain ambiguous, and further delineation of PERK regulation is required. Here we report copper as a regulator of PERK kinase activity. PERK copper binding activity was confirmed by selective affinity for a copper charged resin and by ICP-MS quantification of bound copper. Mutation of the putative copper binding site, identified based on homology, abolished copper binding. Copper-binding was also determined to be necessary for kinase activity in in vitro kinase assays. Physiologic manipulation of copper availability in cells modulated PERK activity and signaling. Using this relationship, we show that copper availability determines ER stress tolerance and cell fate outcomes. This novel regulatory mechanism has broad implications for modulation of PERK activity in different diseases and disease models, and may constitute a previously unaccounted for variable in determining when PERK inhibition vs activation is therapeutically beneficial.