scholarly journals GCN2 phosphorylation of eIF2α activates NF-κB in response to UV irradiation

2005 ◽  
Vol 385 (2) ◽  
pp. 371-380 ◽  
Author(s):  
Hao-Yuan JIANG ◽  
Ronald C. WEK
Keyword(s):  
Uv Irradiation ◽  
Mammalian Cells ◽  
Transcriptional Control ◽  
Control Cell ◽  
Nuclear Factor Κb ◽  
Initiation Factor ◽  
Α Subunit ◽  
Eif2α Phosphorylation ◽  
Eif2α Kinase ◽  
Secondary Function

In response to UV irradiation, mammalian cells elicit a gene expression programme designed to repair damage and control cell proliferation and apoptosis. Important members of this stress response include the NF-κB (nuclear factor-κB) family. However, the mechanisms by which UV irradiation activates NF-κB are not well understood. In eukaryotes, a variety of environmental stresses are recognized and remediated by a family of protein kinases that phosphorylate the α subunit of eIF2 (eukaryotic initiation factor-2). In the present study we show that NF-κB in MEF (murine embryo fibroblast) cells is activated by UV-C and UV-B irradiation through a mechanism requiring eIF2α phosphorylation. The primary eIF2α kinase in response to UV is GCN2 (general control non-derepressible-2), with PEK/PERK (pancreatic eIF2α kinase/RNA-dependent-protein-kinase-like endoplasmic-reticulum kinase) carrying out a secondary function. Our studies indicate that lowered protein synthesis accompanying eIF2α phosphorylation, combined with eIF2α kinase-independent turnover of IκBα (inhibitor of κBα), reduces the levels of IκBα in response to UV irradiation. Release of NF-κB from the inhibitory IκBα would facilitate NF-κB entry into the nucleus and targeted transcriptional control. We also find that loss of GCN2 in MEF cells significantly enhances apoptosis in response to UV exposure similar to that measured in cells deleted for the RelA/p65 subunit of NF-κB. These results demonstrate that GCN2 is central to recognition of UV stress, and that eIF2α phosphorylation provides resistance to apoptosis in response to this environmental insult.

scholarly journals Phosphorylation of the α subunit of translation initiation factor-2 by PKR mediates protein synthesis inhibition in the mouse brain during status epilepticus

2006 ◽  
Vol 397 (1) ◽  
pp. 187-194 ◽  
Author(s):  
Larissa S. Carnevalli ◽  
Catia M. Pereira ◽  
Carolina B. Jaqueta ◽  
Viviane S. Alves ◽  
Vanessa N. Paiva ◽  
...  
Keyword(s):  
Protein Synthesis ◽  
Initiation Factor ◽  
Dependent Protein Kinase ◽  
Α Subunit ◽  
Eif2α Phosphorylation ◽  
Inhibition Of Protein Synthesis ◽  
Initiation Factor 2 ◽  
Dependent Protein ◽  
Eif2α Kinase ◽  
The Brain

In response to different cellular stresses, a family of protein kinases phosphorylates eIF2α (α subunit of eukaryotic initiation factor-2), contributing to regulation of both general and genespecific translation proposed to alleviate cellular injury or alternatively induce apoptosis. Recently, we reported eIF2α(P) (phosphorylated eIF2α) in the brain during SE (status epilepticus) induced by pilocarpine in mice, an animal model of TLE (temporal lobe epilepsy) [Carnevalli, Pereira, Longo, Jaqueta, Avedissian, Mello and Castilho (2004) Neurosci. Lett. 357, 191–194]. We show in the present study that one eIF2α kinase family member, PKR (double-stranded-RNA-dependent protein kinase), is activated in the cortex and hippocampus at 30 min of SE, reflecting the levels of eIF2α(P) in these areas. In PKR-deficient animals subjected to SE, eIF2α phosphorylation was clearly evident coincident with activation of a secondary eIF2α kinase, PEK/PERK (pancreatic eIF2α kinase/RNA-dependent-protein-kinase-like endoplasmic reticulum kinase), denoting a compensatory mechanism between the two kinases. The extent of eIF2α phosphorylation correlated with the inhibition of protein synthesis in the brain, as determined from polysome profiles. We also found that C57BL/6 mice, which enter SE upon pilocarpine administration but are more resistant to seizure-induced neuronal degeneration, showed very low levels of eIF2α(P) and no inhibition of protein synthesis during SE. These results taken together suggest that PKR-mediated phosphorylation of eIF2α contributes to inhibition of protein synthesis in the brain during SE and that sustained high levels of eIF2α phosphorylation may facilitate ensuing cell death in the most affected areas of the brain in TLE.

A critical review of translation initiation factor eIF2α kinases in plants - regulating protein synthesis during stress

2012 ◽  
Vol 39 (9) ◽  
pp. 717 ◽  
Author(s):  
Tracey M. Immanuel ◽  
David R. Greenwood ◽  
Robin M. MacDiarmid
Keyword(s):  
Protein Synthesis ◽  
Translation Initiation ◽  
Current Knowledge ◽  
Mrna Translation ◽  
Translation Initiation Factor ◽  
Initiation Factor ◽  
Α Subunit ◽  
Eif2α Phosphorylation ◽  
Phosphorylation Mechanism ◽  
Eif2α Kinase

Eukaryotic cells must cope with environmental stress. One type of general stress response is the downregulation of protein synthesis in order to conserve cellular resources. Protein synthesis is mainly regulated at the level of mRNA translation initiation and when the α subunit of eukaryotic translation initiation factor 2 (eIF2) is phosphorylated, protein synthesis is downregulated. Although eIF2 has the same translation initiation function in all eukaryotes, it is not known whether plants downregulate protein synthesis via eIF2α phosphorylation. Similarly, although there is evidence that plants possess eIF2α kinases, it is not known whether they operate in a similar manner to the well characterised mammalian and yeast eIF2α kinases. Two types of eIF2α kinases have been reported in plants, yet the full understanding of the plant eIF2α phosphorylation mechanism is still lacking. Here we review the current knowledge of the eIF2α phosphorylation mechanism within plants and discuss plant eIF2α, plant eIF2α kinase GCN2 and the data supporting and contradicting the hypothesis that a functional orthologue for the eIF2α kinase PKR, is present and functional in plants.

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

2003 ◽  
Vol 23 (16) ◽  
pp. 5651-5663 ◽  
Author(s):  
Hao-Yuan Jiang ◽  
Sheree A. Wek ◽  
Barbara C. McGrath ◽  
Donalyn Scheuner ◽  
Randal J. Kaufman ◽  
...  
Keyword(s):  
Nuclear Factor Κb ◽  
Stress Conditions ◽  
Initiation Factor ◽  
Eukaryotic Initiation Factor ◽  
Inhibitory Protein ◽  
Α Subunit ◽  
Eif2α Phosphorylation ◽  
Eukaryotic Initiation Factor 2 ◽  
Initiation Factor 2 ◽  
Stress Signals

ABSTRACT Nuclear factor κB (NF-κB) serves to coordinate the transcription of genes in response to diverse environmental stresses. In this report we show that phosphorylation of the α subunit of eukaryotic initiation factor 2 (eIF2) is fundamental to the process by which many stress signals activate NF-κB. 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 eIF2α by PEK (Perk or EIF2AK3) is essential for induction of NF-κB transcriptional activity. The mechanism by which NF-κB is activated during ER stress entails the release, but not the degradation, of the inhibitory protein IκB. During amino acid deprivation, phosphorylation of eIF2α by GCN2 (EIF2AK4) signals the activation of NF-κB. Furthermore, inhibition of general translation or transcription by cycloheximide and actinomycin D, respectively, elicits the eIF2α phosphorylation required for induction of NF-κB. Together, these studies suggest that eIF2α kinases monitor and are activated by a range of stress conditions that affect transcription and protein synthesis and assembly, and the resulting eIFα phosphorylation is central to activation of the NF-κB. The absence of NF-κB-mediated transcription and its antiapoptotic function provides an explanation for why eIF2α kinase deficiency in diseases such as Wolcott-Rallison syndrome leads to cellular apoptosis and disease.

scholarly journals The ribosomal P-stalk couples amino acid starvation to GCN2 activation in mammalian cells

eLife ◽  
2019 ◽  
Vol 8 ◽  
Author(s):  
Heather P Harding ◽  
Adriana Ordonez ◽  
Felicity Allen ◽  
Leopold Parts ◽  
Alison J Inglis ◽  
...  
Keyword(s):  
Amino Acid ◽  
Mammalian Cells ◽  
Amino Acid Starvation ◽  
Translation Initiation Factor ◽  
Initiation Factor ◽  
Eukaryotic Translation ◽  
Ribosome Stalling ◽  
Eif2α Phosphorylation ◽  
Eif2α Kinase

The eukaryotic translation initiation factor 2α (eIF2α) kinase GCN2 is activated by amino acid starvation to elicit a rectifying physiological program known as the Integrated Stress Response (ISR). A role for uncharged tRNAs as activating ligands of yeast GCN2 is supported experimentally. However, mouse GCN2 activation has recently been observed in circumstances associated with ribosome stalling with no global increase in uncharged tRNAs. We report on a mammalian CHO cell-based CRISPR-Cas9 mutagenesis screen for genes that contribute to ISR activation by amino acid starvation. Disruption of genes encoding components of the ribosome P-stalk, uL10 and P1, selectively attenuated GCN2-mediated ISR activation by amino acid starvation or interference with tRNA charging without affecting the endoplasmic reticulum unfolded protein stress-induced ISR, mediated by the related eIF2α kinase PERK. Wildtype ribosomes isolated from CHO cells, but not those with P-stalk lesions, stimulated GCN2-dependent eIF2α phosphorylation in vitro. These observations support a model whereby lack of a cognate charged tRNA exposes a latent capacity of the ribosome P-stalk to activate GCN2 in cells and help explain the emerging link between ribosome stalling and ISR activation.

scholarly journals Circadian clock control of eIF2α phosphorylation is necessary for rhythmic translation initiation

2020 ◽  
Vol 117 (20) ◽  
pp. 10935-10945 ◽  
Author(s):  
Shanta Karki ◽  
Kathrina Castillo ◽  
Zhaolan Ding ◽  
Olivia Kerr ◽  
Teresa M. Lamb ◽  
...  
Keyword(s):  
Circadian Clock ◽  
Translation Initiation ◽  
Translation Initiation Factor ◽  
Initiation Factor ◽  
Nutrient Metabolism ◽  
Eif2α Phosphorylation ◽  
Eif2α Kinase ◽  
The Impact

The circadian clock in eukaryotes controls transcriptional and posttranscriptional events, including regulation of the levels and phosphorylation state of translation factors. However, the mechanisms underlying clock control of translation initiation, and the impact of this potential regulation on rhythmic protein synthesis, were not known. We show that inhibitory phosphorylation of eIF2α (P-eIF2α), a conserved translation initiation factor, is clock controlled in Neurospora crassa, peaking during the subjective day. Cycling P-eIF2α levels required rhythmic activation of the eIF2α kinase CPC-3 (the homolog of yeast and mammalian GCN2), and rhythmic activation of CPC-3 was abolished under conditions in which the levels of charged tRNAs were altered. Clock-controlled accumulation of P-eIF2α led to reduced translation during the day in vitro and was necessary for the rhythmic synthesis of select proteins in vivo. Finally, loss of rhythmic P-eIF2α levels led to reduced linear growth rates, supporting the idea that partitioning translation to specific times of day provides a growth advantage to the organism. Together, these results reveal a fundamental mechanism by which the clock regulates rhythmic protein production, and provide key insights into how rhythmic translation, cellular energy, stress, and nutrient metabolism are linked through the levels of charged versus uncharged tRNAs.

scholarly journals Phosphorylation of Eukaryotic Initiation Factor 2 by Heme-Regulated Inhibitor Kinase-Related Protein Kinases in Schizosaccharomyces pombe Is Important for Resistance to Environmental Stresses

2002 ◽  
Vol 22 (20) ◽  
pp. 7134-7146 ◽  
Author(s):  
Ke Zhan ◽  
Krishna M. Vattem ◽  
Bettina N. Bauer ◽  
Thomas E. Dever ◽  
Jane-Jane Chen ◽  
...  
Keyword(s):  
Protein Synthesis ◽  
Schizosaccharomyces Pombe ◽  
Environmental Stresses ◽  
Initiation Factor ◽  
Eukaryotic Initiation Factor ◽  
Α Subunit ◽  
Eukaryotic Initiation Factor 2 ◽  
Initiation Factor 2 ◽  
Eif2α Kinase

ABSTRACT Protein synthesis is regulated by the phosphorylation of the α subunit of eukaryotic initiation factor 2 (eIF2α) in response to different environmental stresses. One member of the eIF2α kinase family, heme-regulated inhibitor kinase (HRI), is activated under heme-deficient conditions and blocks protein synthesis, principally globin, in mammalian erythroid cells. We identified two HRI-related kinases from Schizosaccharomyces pombe which have full-length homology with mammalian HRI. The two HRI-related kinases, named Hri1p and Hri2p, exhibit autokinase and kinase activity specific for Ser-51 of eIF2α, and both activities were inhibited in vitro by hemin, as previously described for mammalian HRI. Overexpression of Hri1p, Hri2p, or the human eIF2α kinase, double-stranded-RNA-dependent protein kinase (PKR), impeded growth of S. pombe due to elevated phosphorylation of eIF2α. Cells from strains with deletions of the hri1+ and hri2+ genes, individually or in combination, exhibited a reduced growth rate when exposed to heat shock or to arsenic compounds. Measurements of in vivo phosphorylation of eIF2α suggest that Hri1p and Hri2p differentially phosphorylate eIF2α in response to these stress conditions. These results demonstrate that HRI-related enzymes are not unique to vertebrates and suggest that these eIF2α kinases are important participants in diverse stress response pathways in some lower eukaryotes.

scholarly journals Phosphorylation of eIF2α at Serine 51 Is an Important Determinant of Cell Survival and Adaptation to Glucose Deficiency

2010 ◽  
Vol 21 (18) ◽  
pp. 3220-3231 ◽  
Author(s):  
Hala Muaddi ◽  
Mithu Majumder ◽  
Philippos Peidis ◽  
Andreas I. Papadakis ◽  
Martin Holcik ◽  
...  
Keyword(s):  
Cell Survival ◽  
Biological Response ◽  
Translation Initiation Factor ◽  
Initiation Factor ◽  
Α Subunit ◽  
Eukaryotic Translation ◽  
Life And Death ◽  
Eif2α Phosphorylation ◽  
Apoptosis Protein ◽  
Eukaryotic Translation Initiation

Various forms of stress induce pathways that converge on the phosphorylation of the alpha (α) subunit of eukaryotic translation initiation factor eIF2 at serine 51 (S51), a modification that results in a global inhibition of protein synthesis. In many cases eIF2α phosphorylation is a biological response that facilitates cells to cope with stressful environments. Glucose deficiency, an important form of stress, is associated with an induction of apoptosis. Herein, we demonstrate that eIF2α phosphorylation is a key step in maintaining a balance between the life and death of a glucose-deficient cell. That is, eIF2α phosphorylation acts as a molecular switch that shifts cells from a proapoptotic to a cytoprotective state in response to prolonged glucose deficiency. This adaptation process is associated with the timely expression of proteins and activation of pathways with significant contributions to cell survival and adaptation including the X-linked inhibitor of apoptosis protein (XIAP). We also show that among the eIF2α kinases GCN2 plays a proapoptotic role whereas PERK and PKR play a cytoprotective one in response to glucose deficiency. Our data demonstrate that eIF2α phosphorylation is a significant determinant of survival and adaptation of glucose-deficient cells with possible important implications in biological processes that interfere with glucose metabolism.

scholarly journals A Novel Function of eIF2α Kinases as Inducers of the Phosphoinositide-3 Kinase Signaling Pathway

2007 ◽  
Vol 18 (9) ◽  
pp. 3635-3644 ◽  
Author(s):  
Shirin Kazemi ◽  
Zineb Mounir ◽  
Dionissios Baltzis ◽  
Jennifer F. Raven ◽  
Shuo Wang ◽  
...  
Keyword(s):  
Protein Synthesis ◽  
Translation Initiation ◽  
Active Form ◽  
Translation Initiation Factor ◽  
Initiation Factor ◽  
Pi3k Signaling ◽  
Α Subunit ◽  
Wide Range ◽  
Eif2α Kinase ◽  
Phosphoinositide 3 Kinase

Phosphoinositide-3 kinase (PI3K) plays an important role in signal transduction in response to a wide range of cellular stimuli involved in cellular processes that promote cell proliferation and survival. Phosphorylation of the α subunit of the eukaryotic translation initiation factor eIF2 at Ser51 takes place in response to various types of environmental stress and is essential for regulation of translation initiation. Herein, we show that a conditionally active form of the eIF2α kinase PKR acts upstream of PI3K and turns on the Akt/PKB-FRAP/mTOR pathway leading to S6 and 4E-BP1 phosphorylation. Also, induction of PI3K signaling antagonizes the apoptotic and protein synthesis inhibitory effects of the conditionally active PKR. Furthermore, induction of the PI3K pathway is impaired in PKR−/− or PERK−/− mouse embryonic fibroblasts (MEFs) in response to various stimuli that activate each eIF2α kinase. Mechanistically, PI3K signaling activation is indirect and requires the inhibition of protein synthesis by eIF2α phosphorylation as demonstrated by the inactivation of endogenous eIF2α by small interfering RNA or utilization of MEFs bearing the eIF2α Ser51Ala mutation. Our data reveal a novel property of eIF2α kinases as activators of PI3K signaling and cell survival.

scholarly journals Substrate recognition determinants of human eIF2α phosphatases

2021 ◽  
Author(s):  
George Hodgson ◽  
Antonina Andreeva ◽  
Anne Bertolotti
Keyword(s):  
Mammalian Cells ◽  
Biological Significance ◽  
Translation Initiation Factor ◽  
Initiation Factor ◽  
Wild Type ◽  
Binding Region ◽  
Antagonistic Action ◽  
Catalytic Subunits ◽  
Eif2α Phosphorylation ◽  
Cellular Defence

Phosphorylation of the translation initiation factor eIF2α is a rapid and vital cellular defence against many forms of stress. In mammals, the levels of eIF2α phosphorylation are set through the antagonistic action of four protein kinases and two heterodimeric protein phosphatases. The phosphatases are composed of the catalytic subunit PP1 and one of two related non-catalytic subunits, PPP1R15A or PPP1R15B (R15A or R15B). Attempts at reconstituting recombinant holophosphatases have generated two models, one proposing that substrate recruitment requires the addition of actin, whilst the second proposes that this function is encoded by R15s. The biological relevance of actin in substrate recruitment has not been evaluated. Here we generated a series of truncation mutants and tested their properties in mammalian cells. We show that substrate recruitment is encoded by an evolutionary conserved region in R15s, R15A325-554 and R15B340-639. Actin does not bind these regions establishing that it is not required for substrate recruitment. Activity assays in cells showed that R15A325-674 and R15B340-713, encompassing the substrate-binding region and the PP1 binding-region, exhibit wild-type activity. This study identifies essential regions of R15s and demonstrates they function as substrate receptors. This work will guide the design of future structural studies with biological significance.

Sign in / Sign up

Export Citation Format

Share Document