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.

Tissue-specific regulation of protein synthesis by insulin and free fatty acids

2003 ◽  
Vol 285 (4) ◽  
pp. E754-E762 ◽  
Author(s):  
Stephen J. Crozier ◽  
Joshua C. Anthony ◽  
Charles M. Schworer ◽  
Ali K. Reiter ◽  
Tracy G. Anthony ◽  
...  
Keyword(s):  
Protein Synthesis ◽  
Translational Control ◽  
Mammalian Target Of Rapamycin ◽  
Diabetic Rats ◽  
Mtor Signaling ◽  
Initiation Factor ◽  
Energy Status ◽  
Cellular Energy ◽  
Specific Regulation ◽  
Induced Changes

The purpose of the study described herein was to investigate how the mammalian target of rapamycin (mTOR)-signaling pathway and eukaryotic initiation factor 2B (eIF2B) activity, both having key roles in the translational control of protein synthesis in skeletal muscle, are regulated in cardiac muscle of rats in response to two different models of altered free fatty acid (FFA) and insulin availability. Protein synthetic rates were reduced in both gastrocnemius and heart of 3-day diabetic rats. The reduction was associated with diminished mTOR-mediated signaling and eIF2B activity in the gastrocnemius but only with diminished mTOR signaling in the heart. In response to the combination of acute hypoinsulinemia and hypolipidemia induced by administration of niacin, protein synthetic rates were also diminished in both gastrocnemius and heart. The niacin-induced changes were associated with diminished mTOR signaling and eIF2B activity in the heart but only with decreased mTOR signaling in the gastrocnemius. In the heart, mTOR signaling and eIF2B activity correlated with cellular energy status and/or redox potential. Thus FFAs may contribute to the translational control of protein synthesis in the heart but not in the gastrocnemius. In contrast, insulin, but not FFAs, is required for the maintenance of protein synthesis in the gastrocnemius.

β-Oxidation of free fatty acids is required to maintain translational control of protein synthesis in heart

2002 ◽  
Vol 283 (6) ◽  
pp. E1144-E1150 ◽  
Author(s):  
Stephen J. Crozier ◽  
Douglas R. Bolster ◽  
Ali K. Reiter ◽  
Scot R. Kimball ◽  
Leonard S. Jefferson
Keyword(s):  
Fatty Acids ◽  
Protein Synthesis ◽  
Free Fatty Acids ◽  
Translation Initiation ◽  
Translational Control ◽  
Mrna Translation ◽  
Nucleotide Exchange ◽  
Energy Status ◽  
Α Subunit

The study described herein investigated the role of free fatty acids (FFAs) in the maintenance of protein synthesis in vivo in rat cardiac and skeletal muscle. Suppression of FFA β-oxidation by methyl palmoxirate caused a marked reduction in protein synthesis in the heart. The effect on protein synthesis was mediated in part by changes in the function of eukaryotic initiation factors (eIFs) involved in the initiation of mRNA translation. The guanine nucleotide exchange activity of eIF2B was repressed, phosphorylation of the α-subunit of eIF2 was enhanced, and phosphorylation of eIF4E-binding protein-1 and ribosomal protein S6 kinase was reduced. Similar changes in protein synthesis and translation initiation were not observed in the gastrocnemius following treatment with methyl palmoxirate. In heart, repressed β-oxidation of FFA correlated, as demarcated by changes in the ATP/AMP ratio and phosphorylation of AMP-activated kinase, with alterations in the energy status of the tissue. Therefore, the activation state of signal transduction pathways that are responsive to cellular energy stress represents one mechanism whereby translation initiation may be regulated in cardiac muscle.

scholarly journals A UV-Induced Mutation in Neurospora That Affects Translational Regulation in Response to Arginine

Genetics ◽  
1996 ◽  
Vol 142 (1) ◽  
pp. 117-127 ◽  
Author(s):  
Michael Freitag ◽  
Nelima Dighde ◽  
Matthew S Sachs
Keyword(s):  
Translational Control ◽  
Translational Regulation ◽  
Fusion Gene ◽  
Mrna Translation ◽  
Small Subunit ◽  
Upstream Open Reading Frame ◽  
Control Mechanisms ◽  
Carbamoyl Phosphate ◽  
Altered Expression ◽  
Reading Frame

The Neurospora crmsu arg-2 gene encodes the small subunit of arginine-specific carbamoyl phosphate synthetase. The levels of arg-2 mRNA and mRNA translation are negatively regulated by arginine. An upstream open reading frame (uORF) in the transcript’s 5′ region has been implicated in arginine-specific control. An arg-2-hph fusion gene encoding hygromycin phosphotransferase conferred arginine-regulated resistance to hygromycin when introduced into N. crassa. We used an arg-2-hph strain to select for UV-induced mutants that grew in the presence of hygromycin and arginine, and we isolated 46 mutants that had either of two phenotypes. One phenotype indicated altered expression of both arg-2-hph and urg-2 genes; the other, altered expression of urg-2-hph but not arg-2. One of the latter mutations, which was genetically closely linked to arg-2-hph, was recovered from the 5′ region of the arg-2-hph gene using PCR. Sequence analyses and transformation experiments revealed a mutation at uORF codon 12 (Asp to Asn) that abrogated negative regulation. Examination of the distribution of ribosomes on arg-2-hph transcripts showed that loss of regulation had a translational component, indicating the uORF sequence was important for Arg-specific translational control. Comparisons with other uORFS suggest common elements in translational control mechanisms.

4E-BP1 and S6K1: translational integration sites for nutritional and hormonal information in muscle

2000 ◽  
Vol 279 (4) ◽  
pp. E715-E729 ◽  
Author(s):  
O. Jameel Shah ◽  
Joshua C. Anthony ◽  
Scot R. Kimball ◽  
Leonard S. Jefferson
Keyword(s):  
Translational Control ◽  
Mrna Translation ◽  
Cellular Protein ◽  
Initiation Factor ◽  
Translational Repressor ◽  
Initiation Factors ◽  
Initiation Phase ◽  
Eukaryotic Initiation Factor 4E ◽  
Integration Sites ◽  
A Site

Maintenance of cellular protein stores in skeletal muscle depends on a tightly regulated synthesis-degradation equilibrium that is conditionally modulated under an extensive range of physiological and pathophysiological circumstances. Recent studies have established the initiation phase of mRNA translation as a pivotal site of regulation for global rates of protein synthesis, as well as a site through which the synthesis of specific proteins is controlled. The protein synthetic pathway is exquisitely sensitive to the availability of hormones and nutrients and employs a comprehensive integrative strategy to interpret the information provided by hormonal and nutritional cues. The translational repressor, eukaryotic initiation factor 4E binding protein 1 (4E-BP1), and the 70-kDa ribosomal protein S6 kinase (S6K1) have emerged as important components of this strategy, and together they coordinate the behavior of both eukaryotic initiation factors and the ribosome. This review discusses the role of 4E-BP1 and S6K1 in translational control and outlines the mechanisms through which hormones and nutrients effect changes in mRNA translation through the influence of these translational effectors.

Molecular Regulation of Energy Balance

2019 ◽  
Author(s):  
D. Grahame Hardie ◽  
A. Mark Evans
Keyword(s):  
Energy Balance ◽  
Energy Homeostasis ◽  
Adenine Nucleotides ◽  
Kinase Domain ◽  
Cellular Level ◽  
Whole Body ◽  
Energy Status ◽  
Α Subunit ◽  
Cellular Energy ◽  
Synthetic Drugs

AMP-activated protein kinase (AMPK) is a sensor of cellular energy status that monitors the levels of AMP and ADP relative to ATP. If increases in AMP:ATP and/or ADP:ATP ratios are detected (indicating a reduction in cellular energy status), AMPK is activated by the canonical mechanism involving both allosteric activation and enhanced net phosphorylation at Thr172 on the catalytic subunit. Once activated, AMPK phosphorylates dozens of downstream targets, thus switching on catabolic pathways that generate ATP and switching off anabolic pathways and other energy-consuming processes. AMPK can also be activated by non-canonical mechanisms, triggered either by glucose starvation by a mechanism independent of changes in adenine nucleotides, or by increases in intracellular Ca2+ in response to hormones, mediated by the alternate upstream kinase CaMKK2. AMPK is expressed in almost all eukaryotic cells, including neurons, as heterotrimeric complexes comprising a catalytic α subunit and regulatory β and γ subunits. The α subunits contain the kinase domain and regulatory regions that interact with the other two subunits. The β subunits contain a domain that, with the small lobe of the kinase domain on the α subunit, forms the “ADaM” site that binds synthetic drugs that are potent allosteric activators of AMPK, while the γ subunits contain the binding sites for the classical regulatory nucleotides, AMP, ADP, and ATP. Although much undoubtedly remains to be discovered about the roles of AMPK in the nervous system, emerging evidence has confirmed the proposal that, in addition to its universal functions in regulating energy balance at the cellular level, AMPK also has cell- and circuit-specific roles at the whole-body level, particularly in energy homeostasis. These roles are mediated by phosphorylation of neural-specific targets such as ion channels, distinct from the targets by which AMPK regulates general, cell-autonomous energy balance. Examples of these cell- and circuit-specific functions discussed in this review include roles in the hypothalamus in balancing energy intake (feeding) and energy expenditure (thermogenesis), and its role in the brainstem, where it supports the hypoxic ventilatory response (breathing), increasing the supply of oxygen to the tissues during systemic hypoxia.

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.

Upregulation of eIF4E in Nucleophosmin 1 (NPM1) Haploinsufficient Cells Alters CCAAT Enhancer Binding Protein Alpha (C/EBPα) Activity: Implications for MDS and AML

Blood ◽  
2011 ◽  
Vol 118 (21) ◽  
pp. 2432-2432
Author(s):  
Nirmalee Abayasekara ◽  
Michelle Levine ◽  
Niccolo Bolli ◽  
Hong Sun ◽  
Matthew Silver ◽  
...  
Keyword(s):  
Gene Expression ◽  
Translation Initiation ◽  
Translational Control ◽  
Conflicts Of Interest ◽  
Mrna Translation ◽  
Dominant Negative ◽  
Full Length ◽  
Initiation Factor ◽  
Specific Gene ◽  
Specific Gene Expression

Abstract Abstract 2432 NPM1, is a highly conserved, ubiquitous nucleolar phosphoprotein that belongs to the nucleoplasmin family of nuclear chaperones. NPM1−/− mice die at mid-gestation (E11.5) from anemia, underscoring the gene's role in embryonic development. NPM1 is one of the most frequently mutated genes in AML. Mutations in NPM1 are found in 50% of normal karyotype AML patients, and mutant NPM1 (NPMc+) is aberrantly located in the cytoplasm of leukemic blasts in about 35% of all AML patients. Furthermore, NPM1 maps to a region on chromosome 5q that is the target of deletions in both de novo and therapy-associated human MDS. NPM1 thus acts as a haploinsufficient tumor suppressor in the hematological compartment, although the mechanism of its contribution to dysmyelopoiesis remains unknown. NPM-1+/− mice develop a hematological syndrome similar to that observed in human MDS, and develop AML over time. The NPM1 deficient model therefore provides a platform to interrogate the molecular basis of MDS. We identified nucleophosmin (NPM1) in a screen for protein binding partners of C/EBPα. C/EBPα is a single exon gene, but is expressed as two isoforms that arise by alternate translation start sites to yield a full length C/EBPα p42 and a truncated dominant negative C/EBPα p30 isoform. Translational control of isoform expression is orchestrated by a conserved upstream open reading frame (uORF) in the 5' untranslated region (5'UTR) and modulated by the translation initiation factors eIF4E and eIF2. We generated factor-dependent myeloid cell lines from the bone marrow of Npm1+/+ and Npm1+/− mice. These lines are IL-3-dependent and inducible toward neutrophil maturation with GM-CSF and/ or all- trans retinoic acid (ATRA). Neutrophils derived from MNPM1+/− cells display defective neutrophil-specific gene expression, including a cassette of C/EBPα-dependent genes. These observations led us to postulate that myeloid abnormalities in NPM1 deficiency reflect an aberrant NPM1-C/EBPα axis. We show that NPM1 haploinsufficiency upregulates eIF4E (eukaryotic initiation factor 4E) (but not eIF2), which binds the mRNA-Cap (m7-GTP) as part of the mRNA translation initiation complex, eIF4F. Increased eIF4E is observed in about 30% of all malignancies. Initial increased eIF4E levels in MNPM+/− cells likely reflect transcriptional activation by the oncoprotein c-Myc, protein levels of which are also elevated in MNPM1+/− cells. We propose that increased eIF4E then induces increased C/EBPαp30 translation. C/EBPαp30 is a dominant negative inhibitor of full length C/EBPαp42 activity and disrupts normal neutrophil development. Furthermore, we demonstrate that C/EBPαp30 but not C/EBPαp42, activates the eIF4E promoter. We propose a positive feedback loop, wherein increased C/EBPαp30 induced by eIF4E further increases the expression of eIF4E. Our data suggest that NPM1 deficiency modulates neutrophil-specific gene expression by altering C/EBPα. We propose an aberrant feed-forward mechanism that increases levels of both eIF4E and C/EBPαp30 and likely contributes to MDS associated with NPM1 deficiency. Disclosures: No relevant conflicts of interest to declare.

scholarly journals Repression of ferritin light chain translation by human eIF3

2018 ◽  
Author(s):  
Mia C. Pulos-Holmes ◽  
Daniel N. Srole ◽  
Amy S. Y. Lee ◽  
Maria G. Juarez ◽  
David T. McSwiggen ◽  
...  
Keyword(s):  
Light Chain ◽  
Translational Control ◽  
Association Studies ◽  
Regulatory Protein ◽  
Mrna Translation ◽  
Translation Initiation Factor ◽  
Initiation Factor ◽  
Genome Wide Association Studies ◽  
Nucleotide Polymorphisms ◽  
Direct Role

AbstractA central problem in human biology remains the discovery of causal molecular links between mutations identified in genome-wide association studies (GWAS) and their corresponding disease traits. This challenge is magnified for variants residing in non-coding regions of the genome. Single-nucleotide polymorphisms (SNPs) in the 5’ untranslated region (5’-UTR) of the ferritin light chain (FTL) gene that cause hyperferritinemia are thought to disrupt translation repression by altering iron regulatory protein (IRP) interactions with theFTLmRNA 5’-UTR. Here, we show that human eukaryotic translation initiation factor 3 (eIF3) acts as a distinct repressor ofFTLmRNA translation, and eIF3-mediatedFTLrepression is disrupted by a subset of SNPs inFTLthat cause hyperferritinemia. These results identify a direct role for eIF3-mediated translational control in a specific human disease.

Skeletal muscle eEF2 and 4EBP1 phosphorylation during endurance exercise is dependent on intensity and muscle fiber type

2009 ◽  
Vol 296 (2) ◽  
pp. R326-R333 ◽  
Author(s):  
Adam J. Rose ◽  
Bruno Bisiani ◽  
Bodil Vistisen ◽  
Bente Kiens ◽  
Erik A. Richter
Keyword(s):  
Skeletal Muscle ◽  
Protein Synthesis ◽  
Exercise Intensity ◽  
Muscle Protein ◽  
Muscle Protein Synthesis ◽  
Fiber Type ◽  
Mrna Translation ◽  
Initiation Factor ◽  
Type I ◽  
Α Subunit

Protein synthesis in skeletal muscle is known to decrease during exercise, and it has been suggested that this may depend on the magnitude of the relative metabolic stress within the contracting muscle. To examine the mechanisms behind this, the effect of exercise intensity on skeletal muscle eukaryotic elongation factor 2 (eEF2) and eukaryotic initiation factor 4E binding protein 1 (4EBP1) phosphorylation, key components in the mRNA translation machinery, were examined together with AMP-activated protein kinase (AMPK) in healthy young men. Skeletal muscle eEF2 phosphorylation at Thr56 increased during exercise but was not influenced by exercise intensity, and was lower than rest 30 min after exercise. On the other hand, 4EBP1 phosphorylation at Thr37/46 decreased during exercise, and this decrease was greater at higher exercise intensities and was similar to rest 30 min after exercise. AMPK activity, as indexed by AMPK α-subunit phosphorylation at Thr172 and phosphorylation of the AMPK substrate ACCβ at Ser221, was higher with higher exercise intensities, and these indices were higher than rest after high-intensity exercise only. Using immunohistochemistry, it was shown that the increase in skeletal muscle eEF2 Thr56 phosphorylation was restricted to type I myofibers. Taken together, these data suggest that the depression of skeletal muscle protein synthesis with endurance-type exercise may be regulated at both initiation (i.e., 4EBP1) and elongation (i.e., eEF2) steps, with eEF2 phosphorylation contributing at all exercise intensities but 4EBP1 dephosphorylation contributing to a greater extent at high vs. low exercise intensities.

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