Translational Repression Mediates Activation of Nuclear Factor Kappa B by Phosphorylated Translation Initiation Factor 2

Abstract

ABSTRACT Numerous stressful conditions activate kinases that phosphorylate the alpha subunit of translation initiation factor 2 (eIF2α), thus attenuating mRNA translation and activating a gene expression program known as the integrated stress response. It has been noted that conditions associated with eIF2α phosphorylation, notably accumulation of unfolded proteins in the endoplasmic reticulum (ER), or ER stress, are also associated with activation of nuclear factor kappa B (NF-κB) and that eIF2α phosphorylation is required for NF-κB activation by ER stress. We have used a pharmacologically activable version of pancreatic ER kinase (PERK, an ER stress-responsive eIF2α kinase) to uncouple eIF2α phosphorylation from stress and found that phosphorylation of eIF2α is both necessary and sufficient to activate both NF-κB DNA binding and an NF-κB reporter gene. eIF2α phosphorylation-dependent NF-κB activation correlated with decreased levels of the inhibitor IκBα protein. Unlike canonical signaling pathways that promote IκBα phosphorylation and degradation, eIF2α phosphorylation did not increase phosphorylated IκBα levels or affect the stability of the protein. Pulse-chase labeling experiments indicate instead that repression of IκBα translation plays an important role in NF-κB activation in cells experiencing high levels of eIF2α phosphorylation. These studies suggest a direct role for eIF2α phosphorylation-dependent translational control in activating NF-κB during ER stress.