Phosphorylation of the α Subunit of Eukaryotic Initiation Factor 2 Is Required for Activation of NF-κB in Response to Diverse Cellular Stresses

TLDR

NF‑κB orchestrates transcriptional responses to diverse environmental stresses. The study demonstrates that phosphorylation of eIF2α is essential for stress‑induced activation of NF‑κB. Phosphorylation of eIF2α by stress‑responsive kinases such as PERK during ER stress or GCN2 during amino‑acid deprivation triggers NF‑κB activation by releasing IκB without degrading it, and similar phosphorylation occurs upon inhibition of translation or transcription. These results show that eIF2α phosphorylation by diverse stress‑activated kinases is central to NF‑κB activation, and its loss explains the apoptosis seen in diseases such as Wolcott‑Rallison syndrome.

Abstract

Nuclear factor kappaB (NF-kappaB) serves to coordinate the transcription of genes in response to diverse environmental stresses. In this report we show that phosphorylation of the alpha subunit of eukaryotic initiation factor 2 (eIF2) is fundamental to the process by which many stress signals activate NF-kappaB. Phosphorylation of this translation factor is carried out by a family of protein kinases that each respond to distinct stress conditions. During impaired protein folding and assembly in the endoplasmic reticulum (ER), phosphorylation of eIF2alpha by PEK (Perk or EIF2AK3) is essential for induction of NF-kappaB transcriptional activity. The mechanism by which NF-kappaB is activated during ER stress entails the release, but not the degradation, of the inhibitory protein IkappaB. During amino acid deprivation, phosphorylation of eIF2alpha by GCN2 (EIF2AK4) signals the activation of NF-kappaB. Furthermore, inhibition of general translation or transcription by cycloheximide and actinomycin D, respectively, elicits the eIF2alpha phosphorylation required for induction of NF-kappaB. Together, these studies suggest that eIF2alpha kinases monitor and are activated by a range of stress conditions that affect transcription and protein synthesis and assembly, and the resulting eIFalpha phosphorylation is central to activation of the NF-kappaB. The absence of NF-kappaB-mediated transcription and its antiapoptotic function provides an explanation for why eIF2alpha kinase deficiency in diseases such as Wolcott-Rallison syndrome leads to cellular apoptosis and disease.