Integrated stress response of vertebrates is regulated by four eIF2α kinases

Abstract

The integrated stress response (ISR) is a cytoprotective pathway initiated upon phosphorylation of the eukaryotic translation initiation factor 2 (eIF2α) residue designated serine-51, which is critical for translational control in response to various stress conditions. Four eIF2α kinases, namely heme-regulated inhibitor (HRI), protein kinase R (PKR), PKR-like endoplasmic reticulum kinase, (PERK) and general control non-depressible 2 (GCN2), have been identified thus far, and they are known to be activated by heme depletion, viral infection, endoplasmic reticulum stress, and amino acid starvation, respectively. Because eIF2α is phosphorylated under various stress conditions, the existence of an additional eIF2α kinase has been suggested. To validate the existence of the unidentified eIF2α kinase, we constructed an eIF2α kinase quadruple knockout cells (4KO cells) in which the four known eIF2α kinase genes were deleted using the CRISPR/Cas9-mediated genome editing. Phosphorylation of eIF2α was completely abolished in the 4KO cells by various stress stimulations. Our data suggests that the four known eIF2α kinases are sufficient for ISR and that there are no additional eIF2α kinases in vertebrates.

Flavivirus Infection Uncouples Translation Suppression from Cellular Stress Responses

“…Of note, impairment of eIF2α phosphorylation in response to kinases other than PKR was previously reported (36, 37). Consistently, DENV and ZIKV infection blocked eIF2α phosphorylation induced by treatment with arsenite, which activates both heme-regulated eIF2α kinase (HRI) and general control nonderepressible 2 (GCN2), thapsigargin, which activates the PKR-like endoplasmic reticulum kinase (PERK), and carbonyl cyanide p -(trifluoromethoxy) phenylhydrazone (FCCP), which activates HRI (61) (see Fig. S5A to F in the supplemental material).…”

Stress Kinase GCN2 Controls the Proliferative Fitness and Trafficking of Cytotoxic T Cells Independent of Environmental Amino Acid Sensing

“…Recent studies in fibroblasts lacking all four stress kinases (GCN2, PERK, HRI and PKR) has confirmed that no other kinases phosphorylate eIF2α (Taniuchi et al, 2016). However, the phosphorylation of eIF2α is countered by the Ppp1r15a/Gadd34 phosphatase, which terminates stress kinase signaling (Tsaytler et al, 2011).…”

“…However, the phosphorylation of eIF2α is countered by the Ppp1r15a/Gadd34 phosphatase, which terminates stress kinase signaling (Tsaytler et al, 2011). We therefore isolated CD8 + T cells from GCN2 WT or GCN2 KO cells on an OTI background and measured p-Ser51 on eIF2α across time of stimulation using validated and highly specific mAbs (Taniuchi et al, 2016). We found p-Ser51 eIF2α in all samples at time zero, which may reflect stress from processing and purifying the T cells.…”

“…Using these cells reconstituted with each individual stress kinase, Taniuchi et al established that multiple signals activate GCN2, including salt, arsenic and hydrogen peroxide (Taniuchi et al, 2016). These signals may eventually impinge on the ability of cells to make enough charged tRNAs and thus activate GCN2.…”

Dysregulation of RNA Binding Protein Aggregation in Neurodegenerative Disorders

“…There are four core stress activated kinases that phosphorylate eIF2α: Protein Kinase R (PKR), PKR-like/Pancreatic Endoplasmic Reticulum kinase (PERK), Heme-Regulated Inhibitor (HRI), or General Control Non-derepressible 2 (GCN) (Taniuchi et al, 2016). PKR is activated by double stranded RNA, enabling it to respond to viral infection (Taniuchi et al, 2016).…”