scholarly journals A decrease in cellular energy status stimulates PERK-dependent eIF2α phosphorylation and regulates protein synthesis in pancreatic β-cells

2008 ◽  
Vol 410 (3) ◽  
pp. 485-493 ◽  
Author(s):  
Edith Gomez ◽  
Mike L. Powell ◽  
Alan Bevington ◽  
Terence P. Herbert
Keyword(s):  
Endoplasmic Reticulum ◽  
Protein Synthesis ◽  
Dominant Negative ◽  
Initiation Factor ◽  
Energy Status ◽  
Β Cells ◽  
Pancreatic Β Cells ◽  
Eif2α Phosphorylation ◽  
Truncation Mutant ◽  
Inducible Protein

In the present study, we demonstrate that, in pancreatic β-cells, eIF2α (eukaryotic initiation factor 2α) phosphorylation in response to a decrease in glucose concentration is primarily mediated by the activation of PERK [PKR (protein kinase RNA activated)-like endoplasmic reticulum kinase]. We provide evidence that this increase in PERK activity is evoked by a decrease in the energy status of the cell via a potentially novel mechanism that is independent of IRE1 (inositol requiring enzyme 1) activation and the accumulation of unfolded nascent proteins within the endoplasmic reticulum. The inhibition of eIF2α phosphorylation in glucose-deprived cells by the overexpression of dominant-negative PERK or an N-terminal truncation mutant of GADD34 (growth-arrest and DNA-damage-inducible protein 34) leads to a 53% increase in the rate of total protein synthesis. Polysome analysis revealed that this coincides with an increase in the amplitude but not the number of ribosomes per mRNA, indicating that eIF2α dephosphorylation mobilizes hitherto untranslated mRNAs on to polysomes. In summary, we show that PERK is activated at low glucose concentrations in response to a decrease in energy status and that this plays an important role in glucose-regulated protein synthesis in pancreatic β-cells.

scholarly journals The selective recruitment of mRNA to the ER and an increase in initiation are important for glucose-stimulated proinsulin synthesis in pancreatic β-cells

2005 ◽  
Vol 391 (2) ◽  
pp. 291-300 ◽  
Author(s):  
Isabel C. Greenman ◽  
Edith Gomez ◽  
Claire E. J. Moore ◽  
Terence P. Herbert
Keyword(s):  
Endoplasmic Reticulum ◽  
Protein Synthesis ◽  
Regulatory Mechanism ◽  
De Novo ◽  
Secretory Protein ◽  
Secretory Proteins ◽  
Β Cells ◽  
Pancreatic Β Cells ◽  
Large Pool ◽  
Proinsulin Synthesis

Glucose acutely stimulates proinsulin synthesis in pancreatic β-cells through a poorly understood post-transcriptional mechanism. In the present study, we demonstrate in pancreatic β-cells that glucose stimulates the recruitment of ribosome-associated proinsulin mRNA, located in the cytoplasm, to the ER (endoplasmic reticulum), the site of proinsulin synthesis, and that this plays an important role in glucose-stimulated proinsulin synthesis. Interestingly, glucose has greater stimulatory effect on the recruitment of proinsulin mRNA to the ER compared with other mRNAs encoding secretory proteins. This, as far as we are aware, is the first example whereby mRNAs encoding secretory proteins are selectively recruited to the ER and provides a novel regulatory mechanism for secretory protein synthesis. Contrary to previous reports, and importantly in understanding the mechanism by which glucose stimulates proinsulin synthesis, we demonstrate that there is no large pool of ‘free’ proinsulin mRNA in the cytoplasm and that glucose does not increase the rate of de novo initiation on the proinsulin mRNA. However, we show that glucose does stimulate the rate of ribosome recruitment on to ribosome-associated proinsulin mRNA. In conclusion, our results provide evidence that the selective recruitment of proinsulin mRNA to the ER, together with increases in the rate of initiation are important mediators of glucose-stimulated proinsulin synthesis in pancreatic β-cells.

scholarly journals Pharmacological brake-release of mRNA translation enhances cognitive memory

eLife ◽  
2013 ◽  
Vol 2 ◽  
Author(s):  
Carmela Sidrauski ◽  
Diego Acosta-Alvear ◽  
Arkady Khoutorsky ◽  
Punitha Vedantham ◽  
Brian R Hearn ◽  
...  
Keyword(s):  
Endoplasmic Reticulum ◽  
Protein Synthesis ◽  
Memory Consolidation ◽  
Cognitive Disorders ◽  
Mrna Translation ◽  
Initiation Factor ◽  
Α Subunit ◽  
Eif2α Phosphorylation ◽  
Initiation Factor 2 ◽  
A Cell

Phosphorylation of the α-subunit of initiation factor 2 (eIF2) controls protein synthesis by a conserved mechanism. In metazoa, distinct stress conditions activate different eIF2α kinases (PERK, PKR, GCN2, and HRI) that converge on phosphorylating a unique serine in eIF2α. This collection of signaling pathways is termed the ‘integrated stress response’ (ISR). eIF2α phosphorylation diminishes protein synthesis, while allowing preferential translation of some mRNAs. Starting with a cell-based screen for inhibitors of PERK signaling, we identified a small molecule, named ISRIB, that potently (IC50 = 5 nM) reverses the effects of eIF2α phosphorylation. ISRIB reduces the viability of cells subjected to PERK-activation by chronic endoplasmic reticulum stress. eIF2α phosphorylation is implicated in memory consolidation. Remarkably, ISRIB-treated mice display significant enhancement in spatial and fear-associated learning. Thus, memory consolidation is inherently limited by the ISR, and ISRIB releases this brake. As such, ISRIB promises to contribute to our understanding and treatment of cognitive disorders.

scholarly journals Regulation of Protein Synthesis by Hypoxia via Activation of the Endoplasmic Reticulum Kinase PERK and Phosphorylation of the Translation Initiation Factor eIF2α

2002 ◽  
Vol 22 (21) ◽  
pp. 7405-7416 ◽  
Author(s):  
Constantinos Koumenis ◽  
Christine Naczki ◽  
Marianne Koritzinsky ◽  
Sally Rastani ◽  
Alan Diehl ◽  
...  
Keyword(s):  
Endoplasmic Reticulum ◽  
Protein Synthesis ◽  
Translation Initiation ◽  
Prolonged Exposure ◽  
Response To Therapy ◽  
Dominant Negative ◽  
Translation Initiation Factor ◽  
Initiation Factor ◽  
Hypoxic Stress ◽  
Wild Type

ABSTRACT Hypoxia profoundly influences tumor development and response to therapy. While progress has been made in identifying individual gene products whose synthesis is altered under hypoxia, little is known about the mechanism by which hypoxia induces a global downregulation of protein synthesis. A critical step in the regulation of protein synthesis in response to stress is the phosphorylation of translation initiation factor eIF2α on Ser51, which leads to inhibition of new protein synthesis. Here we report that exposure of human diploid fibroblasts and transformed cells to hypoxia led to phosphorylation of eIF2α, a modification that was readily reversed upon reoxygenation. Expression of a transdominant, nonphosphorylatable mutant allele of eIF2α attenuated the repression of protein synthesis under hypoxia. The endoplasmic reticulum (ER)-resident eIF2α kinase PERK was hyperphosphorylated upon hypoxic stress, and overexpression of wild-type PERK increased the levels of hypoxia-induced phosphorylation of eIF2α. Cells stably expressing a dominant-negative PERK allele and mouse embryonic fibroblasts with a homozygous deletion of PERK exhibited attenuated phosphorylation of eIF2α and reduced inhibition of protein synthesis in response to hypoxia. PERK−/− mouse embryo fibroblasts failed to phosphorylate eIF2α and exhibited lower survival after prolonged exposure to hypoxia than did wild-type fibroblasts. These results indicate that adaptation of cells to hypoxic stress requires activation of PERK and phosphorylation of eIF2α and suggest that the mechanism of hypoxia-induced translational attenuation may be linked to ER stress and the unfolded-protein response.

scholarly journals PERK Activation at Low Glucose Concentration Is Mediated by SERCA Pump Inhibition and Confers Preemptive Cytoprotection to Pancreatic β-Cells

2011 ◽  
Vol 25 (2) ◽  
pp. 315-326 ◽  
Author(s):  
Claire E. Moore ◽  
Omotola Omikorede ◽  
Edith Gomez ◽  
Gary B. Willars ◽  
Terence P. Herbert
Keyword(s):  
Glucose Concentration ◽  
Cell Function ◽  
Initiation Factor ◽  
Eukaryotic Initiation Factor ◽  
Energy Status ◽  
Β Cells ◽  
Β Cell ◽  
Pancreatic Β Cells ◽  
Β Cell Function ◽  
Low Glucose

Abstract Protein kinase R-like ER kinase (PERK) is activated at physiologically low glucose concentrations in pancreatic β-cells. However, the molecular mechanisms by which PERK is activated under these conditions and its role in β-cell function are poorly understood. In this report, we investigated, in dispersed rat islets of Langerhans and mouse insulinoma-6 (MIN6) cells, the relationship between extracellular glucose concentration, the free endoplasmic reticulum (ER) calcium concentration ([Ca2+]ER) measured directly using an ER targeted fluorescence resonance energy transfer-based calcium sensor, and the activation of PERK. We found that a decrease in glucose concentration leads to a concentration-dependent reduction in [Ca2+]ER that parallels the activation of PERK and the phosphorylation of its substrate eukaryotic initiation factor-2α. We provide evidence that this decrease in [Ca2+]ER is caused by a decrease in sarcoplasmic/ER Ca2+-ATPase pump activity mediated by a reduction in the energy status of the cell. Importantly, we also report that PERK-dependent eukaryotic initiation factor-2α phosphorylation at low glucose concentration plays a significant role in 1) the regulation of both proinsulin and global protein synthesis, 2) cell viability, and 3) conferring preemptive cytoprotection against ER stress. Taken together, these results provide evidence that a decrease in the ATP/energy status of the cell in response to a decrease in glucose concentration results in sarcoplasmic/ER Ca2+-ATPase pump inhibition, the efflux of Ca2+ from the ER, and the activation of PERK, which plays an important role in both pancreatic β-cell function and survival.

scholarly journals Differential regulation of the endoplasmic reticulum stress response in pancreatic β-cells exposed to long-chain saturated and monounsaturated fatty acids

2008 ◽  
Vol 197 (3) ◽  
pp. 553-563 ◽  
Author(s):  
Eleftheria Diakogiannaki ◽  
Hannah J Welters ◽  
Noel G Morgan
Keyword(s):  
Fatty Acids ◽  
Endoplasmic Reticulum ◽  
Stress Response ◽  
Er Stress ◽  
Initiation Factor ◽  
Β Cells ◽  
Pancreatic Β Cells ◽  
Er Stress Response ◽  
Stress Pathway ◽  
Long Chain

Exposure of pancreatic β-cells to long-chain fatty acids leads to the activation of some components of the endoplasmic reticulum (ER) stress pathway and this mechanism may underlie the ability of certain fatty acids to promote β-cell death. We have studied ER stress in BRIN-BD11 β-cells exposed to either the saturated fatty acid palmitate (C16:0) or the monounsaturated palmitoleate (C16:1). Palmitate (0.025–0.25 mM) induced the expression of various markers of the RNA-dependent protein kinase-like ER eukaryotic initiation factor 2α (eIF2α) kinase (PERK)-dependent pathway of ER stress (phospho-eIF2α; ATF4, activating transcription factor 4 and C/EBP homologous protein (CHOP-10)) although it failed to promote the expression of the ER chaperone GRP78. By contrast, palmitoleate did not induce any markers of the ER stress pathway even at concentrations as high as 1 mM. When palmitate and palmitoleate were added in combination, a marked attenuation of the ER stress response occurred. Under these conditions, the levels of phospho-eIF2α, ATF4 and CHOP-10 were reduced to less than those found in control cells. Palmitoleate also attenuated the ER stress response to the protein glycosylation inhibitor, tunicamycin, and improved the viability of the cells exposed to this agent. Exposure of the BRIN-BD11 cells to the protein phosphatase inhibitor, salubrinal, in the absence of fatty acids resulted in increased eIF2α phosphorylation but this was abolished by co-incubation with palmitoleate. We conclude that saturated fatty acids activate components of the PERK-dependent ER stress pathway in β-cells, ultimately leading to increased apoptosis. This effect is antagonised by monounsaturates that may exert their anti-apoptotic actions by regulating the activity of one or more kinase enzymes involved in mediating the phosphorylation of eIF2α.

scholarly journals Endoplasmic reticulum stress and eIF2α phosphorylation: The Achilles heel of pancreatic β cells

2017 ◽  
Vol 6 (9) ◽  
pp. 1024-1039 ◽  
Author(s):  
Miriam Cnop ◽  
Sanna Toivonen ◽  
Mariana Igoillo-Esteve ◽  
Paraskevi Salpea
Keyword(s):  
Endoplasmic Reticulum ◽  
Endoplasmic Reticulum Stress ◽  
Β Cells ◽  
Pancreatic Β Cells ◽  
Eif2α Phosphorylation

scholarly journals Mitochondrial–Endoplasmic Reticulum Interplay: A Lifelong On–Off Relationship?

Contact ◽  
2019 ◽  
Vol 2 ◽  
pp. 251525641986122 ◽  
Author(s):  
Corina T. Madreiter-Sokolowski ◽  
Roland M. Malli ◽  
Wolfgang F. Graier
Keyword(s):  
Endoplasmic Reticulum ◽  
Adenosine Triphosphate ◽  
Therapeutic Strategies ◽  
Mitochondrial Activity ◽  
Β Cells ◽  
Pancreatic Β Cells ◽  
Potential Target ◽  
Pathological Conditions ◽  
Elevated Glucose ◽  
Stimulation Of

This article comments recent publications that highlight an intriguing importance of specific settings in the interaction between the mitochondria and the endoplasmic reticulum to ensure cell-specific functions like the responsiveness to elevated glucose in pancreatic β-cells. Hence, alterations of the mitochondria–endoplasmic reticulum communications under various pathological conditions like aging or cancer often come with enhanced Ca2+ transfer that, in turn, yields stimulation of basal mitochondrial activity to meet the increasing adenosine triphosphate demand of the very cell. Such observations identify mitochondria-associated membranes as potential target for new therapeutic strategies against aging or cancer.

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