Heme-Reversible Impairment of CYP2B1/2 Induction in Heme-Depleted Rat Hepatocytes in Primary Culture: Translational Control by a Hepatic α-Subunit of the Eukaryotic Initiation Factor Kinase?

2005 ◽  
Vol 314 (1) ◽  
pp. 128-138 ◽  
Author(s):  
Xing-Mei Han ◽  
Gene Lee ◽  
Colleen Hefner ◽  
Jacquelyn J. Maher ◽  
Maria Almira Correia
Keyword(s):  
Primary Culture ◽  
Translational Control ◽  
Rat Hepatocytes ◽  
Initiation Factor ◽  
Eukaryotic Initiation Factor ◽  
Α Subunit

scholarly journals Pancreatic eukaryotic initiation factor-2α kinase (PEK) homologues in humans, Drosophila melanogaster and Caenorhabditis elegans that mediate translational control in response to endoplasmic reticulum stress

2000 ◽  
Vol 346 (2) ◽  
pp. 281-293 ◽  
Author(s):  
Ruchira SOOD ◽  
Amy C. PORTER ◽  
Kun MA ◽  
Lawrence A. QUILLIAM ◽  
Ronald C. WEK
Keyword(s):  
Endoplasmic Reticulum ◽  
Drosophila Melanogaster ◽  
Caenorhabditis Elegans ◽  
Er Stress ◽  
Translational Control ◽  
Mammalian Cells ◽  
Transmembrane Protein ◽  
Initiation Factor ◽  
Eukaryotic Initiation Factor ◽  
Α Subunit

In response to different cellular stresses, a family of protein kinases regulates translation by phosphorylation of the α subunit of eukaryotic initiation factor-2 (eIF-2α). Recently, we identified a new family member, pancreatic eIF-2α kinase (PEK) from rat pancreas. PEK, also referred to as RNA-dependent protein kinase (PKR)-like endoplasmic reticulum (ER) kinase (PERK) is a transmembrane protein implicated in translational control in response to stresses that impair protein folding in the ER. In this study, we identified and characterized PEK homologues from humans, Drosophila melanogaster and Caenorhabditis elegans. Expression of human PEK mRNA was found in over 50 different tissues examined, with highest levels in secretory tissues. In mammalian cells subjected to ER stress, we found that elevated eIF-2α phosphorylation was coincident with increased PEK autophosphorylation and eIF-2α kinase activity. Activation of PEK was abolished by deletion of PEK N-terminal sequences located in the ER lumen. To address the role of C. elegans PEK in translational control, we expressed this kinase in yeast and found that it inhibits growth by hyperphosphorylation of eIF-2α and inhibition of eIF-2B. Furthermore, we found that vaccinia virus K3L protein, an inhibitor of the eIF-2α kinase PKR involved in an anti-viral defence pathway, also reduced PEK activity. These results suggest that decreased translation initiation by PEK during ER stress may provide the cell with an opportunity to remedy the folding problem prior to introducing newly synthesized proteins into the secretory pathway.

scholarly journals A Mammalian Homologue of GCN2 Protein Kinase Important for Translational Control by Phosphorylation of Eukaryotic Initiation Factor-2α

Genetics ◽  
2000 ◽  
Vol 154 (2) ◽  
pp. 787-801 ◽  
Author(s):  
Ruchira Sood ◽  
Amy C Porter ◽  
DeAnne Olsen ◽  
Douglas R Cavener ◽  
Ronald C Wek
Keyword(s):  
Amino Acid ◽  
Translational Control ◽  
Catalytic Domain ◽  
Trna Synthetase ◽  
Initiation Factor ◽  
Eukaryotic Initiation Factor ◽  
Α Subunit ◽  
Amino Terminal ◽  
Kinase Catalytic Domain ◽  
Mouse Tissues

Abstract A family of protein kinases regulates translation in response to different cellular stresses by phosphorylation of the α subunit of eukaryotic initiation factor-2 (eIF-2α). In yeast, an eIF-2α kinase, GCN2, functions in translational control in response to amino acid starvation. It is thought that uncharged tRNA that accumulates during amino acid limitation binds to sequences in GCN2 homologous to histidyl-tRNA synthetase (HisRS) enzymes, leading to enhanced kinase catalytic activity. Given that starvation for amino acids also stimulates phosphorylation of eIF-2α in mammalian cells, we searched for and identified a GCN2 homologue in mice. We cloned three different cDNAs encoding mouse GCN2 isoforms, derived from a single gene, that vary in their amino-terminal sequences. Like their yeast counterpart, the mouse GCN2 isoforms contain HisRS-related sequences juxtaposed to the kinase catalytic domain. While GCN2 mRNA was found in all mouse tissues examined, the isoforms appear to be differentially expressed. Mouse GCN2 expressed in yeast was found to inhibit growth by hyperphosphorylation of eIF-2α, requiring both the kinase catalytic domain and the HisRS-related sequences. Additionally, lysates prepared from yeast expressing mGCN2 were found to phosphorylate recombinant eIF-2α substrate. Mouse GCN2 activity in both the in vivo and in vitro assays required the presence of serine-51, the known regulatory phosphorylation site in eIF-2α. Together, our studies identify a new mammalian eIF-2α kinase, GCN2, that can mediate translational control.

scholarly journals eIF2B as a Target for Viral Evasion of PKR-Mediated Translation Inhibition

mBio ◽  
2020 ◽  
Vol 11 (4) ◽  
Author(s):  
Jennifer Deborah Wuerth ◽  
Matthias Habjan ◽  
Markus Kainulainen ◽  
Besim Berisha ◽  
Damien Bertheloot ◽  
...  
Keyword(s):  
Protein Synthesis ◽  
Protein Kinase ◽  
Nonstructural Protein ◽  
Mrna Translation ◽  
Translation Initiation Factor ◽  
Initiation Factor ◽  
Mammalian Host ◽  
Eukaryotic Initiation Factor ◽  
Α Subunit ◽  
Immune Factor

ABSTRACT RNA-activated protein kinase (PKR) is a major innate immune factor that senses viral double-stranded RNA (dsRNA) and phosphorylates eukaryotic initiation factor (eIF) 2α. Phosphorylation of the α subunit converts the eIF2αβγ complex into a stoichiometric inhibitor of eukaryotic initiation factor eIF2B, thus halting mRNA translation. To escape this protein synthesis shutoff, viruses have evolved countermechanisms such as dsRNA sequestration, eIF-independent translation by an internal ribosome binding site, degradation of PKR, or dephosphorylation of PKR or of phospho-eIF2α. Here, we report that sandfly fever Sicilian phlebovirus (SFSV) confers such a resistance without interfering with PKR activation or eIF2α phosphorylation. Rather, SFSV expresses a nonstructural protein termed NSs that strongly binds to eIF2B. Although NSs still allows phospho-eIF2α binding to eIF2B, protein synthesis and virus replication are unhindered. Hence, SFSV encodes a unique PKR antagonist that acts by rendering eIF2B resistant to the inhibitory action of bound phospho-eIF2α. IMPORTANCE RNA-activated protein kinase (PKR) is one of the most powerful antiviral defense factors of the mammalian host. PKR acts by phosphorylating mRNA translation initiation factor eIF2α, thereby converting it from a cofactor to an inhibitor of mRNA translation that strongly binds to initiation factor eIF2B. To sustain synthesis of their proteins, viruses are known to counteract this on the level of PKR or eIF2α or by circumventing initiation factor-dependent translation altogether. Here, we report a different PKR escape strategy executed by sandfly fever Sicilian virus (SFSV), a member of the increasingly important group of phleboviruses. We found that the nonstructural protein NSs of SFSV binds to eIF2B and protects it from inactivation by PKR-generated phospho-eIF2α. Protein synthesis is hence maintained and the virus can replicate despite ongoing full-fledged PKR signaling in the infected cells. Thus, SFSV has evolved a unique strategy to escape the powerful antiviral PKR.

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 Modulation of the Eukaryotic Initiation Factor 2 α-Subunit Kinase PERK by Tyrosine Phosphorylation

2007 ◽  
Vol 283 (1) ◽  
pp. 469-475 ◽  
Author(s):  
Qiaozhu Su ◽  
Shuo Wang ◽  
Hong Qing Gao ◽  
Shirin Kazemi ◽  
Heather P. Harding ◽  
...  
Keyword(s):  
Tyrosine Phosphorylation ◽  
Initiation Factor ◽  
Eukaryotic Initiation Factor ◽  
Α Subunit ◽  
Eukaryotic Initiation Factor 2 ◽  
Initiation Factor 2

Cellular energy status modulates translational control mechanisms in ischemic-reperfused rat hearts

2005 ◽  
Vol 289 (3) ◽  
pp. H1242-H1250 ◽  
Author(s):  
Stephen J. Crozier ◽  
Thomas C. Vary ◽  
Scot R. Kimball ◽  
Leonard S. Jefferson
Keyword(s):  
Translational Control ◽  
Mrna Translation ◽  
Initiation Factor ◽  
Control Mechanisms ◽  
Energy Status ◽  
Α Subunit ◽  
Energy Substrate ◽  
Cellular Energy ◽  
Rat Hearts ◽  
Induced Changes

Mechanisms regulating ischemia and reperfusion (I/R)-induced changes in mRNA translation in the heart are poorly defined, as are the factors that initiate these changes. Because cellular energy status affects mRNA translation under physiological conditions, it is plausible that I/R-induced changes in translation may in part be a result of altered cellular energy status. Therefore, the purpose of the studies described herein was to compare the effects of I/R with those of altered energy substrate availability on biomarkers of mRNA translation in the heart. Isolated adult rat hearts were perfused with glucose or a combination of glucose plus palmitate, and effects of I/R on various biomarkers of translation were subsequently analyzed. When compared with hearts perfused with glucose plus palmitate, hearts perfused with glucose alone exhibited increased phosphorylation of eukaryotic elongation factor (eEF)2, the α-subunit of eukaryotic initiation factor (eIF)2, and AMP-activated protein kinase (AMPK), and these hearts also exhibited enhanced association of eIF4E with eIF4E binding protein (4E-BP)1. Regardless of the energy substrate composition of the buffer, phosphorylation of eEF2 and AMPK was greater than control values after ischemia. Phosphorylation of eIF2α and eIF4E and the association of eIF4E with 4E-BP1 were also greater than control values after ischemia but only in hearts perfused with glucose plus palmitate. Reperfusion reversed the ischemia-induced increase in eEF2 phosphorylation in hearts perfused with glucose and reversed ischemia-induced changes in eIF4E, eEF2, and AMPK phosphorylation in hearts perfused with glucose plus palmitate. Because many ischemia-induced changes in mRNA translation are mimicked by the removal of a metabolic substrate under normal perfusion conditions, the results suggest that cellular energy status represents an important modulator of I/R-induced changes in mRNA translation.

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