Regulation of protein synthesis by insulin

2006 ◽  
Vol 34 (2) ◽  
pp. 213-216 ◽  
Author(s):  
C.G. Proud
Keyword(s):  
Protein Synthesis ◽  
Translation Initiation ◽  
Ribosomal Proteins ◽  
Glycogen Synthase ◽  
Mammalian Target Of Rapamycin ◽  
Protein Translation ◽  
Initiation Factor ◽  
Translational Machinery ◽  
Phosphoinositide 3 Kinase ◽  
Eef2 Kinase

Insulin rapidly activates protein synthesis by activating components of the translational machinery including eIFs (eukaryotic initiation factors) and eEFs (eukaryotic elongation factors). In the long term, insulin also increases the cellular content of ribosomes to augment the capacity for protein synthesis. The rapid activation of protein synthesis by insulin is mediated primarily through phosphoinositide 3-kinase. This involves the activation of PKB (protein kinase B). In one case, PKB acts to phosphorylate and inactivate glycogen synthase kinase 3, which in turn phosphorylates and inhibits eIF2B. Insulin elicits the dephosphorylation and activation of eIF2B. Since eIF2B is required for recycling of eIF2, a factor required for all cytoplasmic translation initiation events, this will contribute to overall activation of protein synthesis. PKB also phosphorylates the TSC1 (tuberous sclerosis complex 1)–TSC2 complex to relieve its inhibitory action on the mTOR (mammalian target of rapamycin). Inhibition of mTOR by rapamycin markedly impairs insulin-activated protein synthesis. mTOR controls translation initiation and elongation. The cap-binding factor eIF4E can be sequestered in inactive complexes by 4E-BP1 (eIF4E-binding protein 1). Insulin elicits phosphorylation of 4E-BP1 and its release from eIF4E, allowing eIF4E to form initiation factor complexes. Insulin induces dephosphorylation and activation of eEF2 to accelerate elongation. Both effects are blocked by rapamycin. Insulin inactivates eEF2 kinase by increasing its phosphorylation at several mTOR-regulated sites. Insulin also stimulates synthesis of ribosomal proteins by promoting recruitment of their mRNAs into polyribosomes. This is inhibited by rapamycin. Several key questions remain about, for example, the mechanisms by which mTOR controls 4E-BP1 and eEF2 kinase and the control of ribosomal protein translation.

Intravenous administration of amino acids during anesthesia stimulates muscle protein synthesis and heat accumulation in the body

2006 ◽  
Vol 290 (5) ◽  
pp. E882-E888 ◽  
Author(s):  
Ippei Yamaoka ◽  
Masako Doi ◽  
Mitsuo Nakayama ◽  
Akane Ozeki ◽  
Shinji Mochizuki ◽  
...  
Keyword(s):  
Protein Synthesis ◽  
Protein Kinase ◽  
Intravenous Administration ◽  
Translation Initiation ◽  
Muscle Protein ◽  
Muscle Protein Synthesis ◽  
Mammalian Target Of Rapamycin ◽  
The Body ◽  
Initiation Factor ◽  
Heat Accumulation

The present study was conducted to determine the contribution of muscle protein synthesis to the prevention of anesthesia-induced hypothermia by intravenous administration of an amino acid (AA) mixture. We examined the changes of intraperitoneal temperature (Tcore) and the rates of protein synthesis ( Ks) and the phosphorylation states of translation initiation regulators and their upstream signaling components in skeletal muscle in conscious (Nor) or propofol-anesthetized (Ane) rats after a 3-h intravenous administration of a balanced AA mixture or saline (Sal). Compared with Sal administration, the AA mixture administration markedly attenuated the decrease in Tcore in rats during anesthesia, whereas Tcore in the Nor-AA group became slightly elevated during treatment. Stimulation of muscle protein synthesis resulting from AA administration was observed in each case, although Ks remained lower in the Ane-AA group than in the Nor-Sal group. AA administration during anesthesia significantly increased insulin concentrations to levels ∼6-fold greater than in the Nor-AA group and enhanced phosphorylation of eukaryotic initiation factor 4E-binding protein-1 (4E-BP1) and ribosomal protein S6 protein kinase relative to all other groups and treatments. The alterations in the Ane-AA group were accompanied by hyperphosphorylation of protein kinase B and the mammalian target of rapamycin (mTOR). These results suggest that administration of an AA mixture during anesthesia stimulates muscle protein synthesis via insulin-mTOR-dependent activation of translation initiation regulators caused by markedly elevated insulin and, thereby, facilitates thermal accumulation in the body.

scholarly journals Activation of mRNA translation in rat cardiac myocytes by insulin involves multiple rapamycin-sensitive steps

2000 ◽  
Vol 278 (4) ◽  
pp. H1056-H1068 ◽  
Author(s):  
Lijun Wang ◽  
Xuemin Wang ◽  
Christopher G. Proud
Keyword(s):  
Protein Synthesis ◽  
Protein Kinase ◽  
Signaling Pathways ◽  
Glycogen Synthase ◽  
Mrna Translation ◽  
Mitogen Activated Protein Kinase ◽  
Initiation Factor ◽  
Translation Factors ◽  
P70 S6k ◽  
Eef2 Kinase

Insulin acutely activates protein synthesis in ventricular cardiomyocytes from adult rats. In this study, we have established the methodology for studying the regulation of the signaling pathways and translation factors that may be involved in this response and have examined the effects of acute insulin treatment on them. Insulin rapidly activated the 70-kDa ribosomal S6 kinase (p70 S6k), and this effect was inhibited both by rapamycin and by inhibitors of phosphatidylinositol 3-kinase. The activation of p70 S6k is mediated by a signaling pathway involving the mammalian target of rapamycin (mTOR), which also modulates other translation factors. These include the eukaryotic initiation factor (eIF) 4E binding proteins (4E-BPs) and eukaryotic elongation factor 2 (eEF2). Insulin caused phosphorylation of 4E-BP1 and induced its dissociation from eIF4E, and these effects were also blocked by rapamycin. Concomitant with this, insulin increased the binding of eIF4E to eIF4G. Insulin also activated protein kinase B (PKB), which may lie upstream of p70 S6k and 4E-BP1, with the activation of the different isoforms being in the order α>β>γ. Insulin also caused inhibition of glycogen synthase kinase 3, which lies downstream of PKB, and of eEF2 kinase. The phosphorylation of eEF2 itself was also decreased by insulin, and this effect and the inactivation of eEF2 kinase were attenuated by rapamycin. The activation of overall protein synthesis by insulin in cardiomyocytes was substantially inhibited by rapamycin (but not by inhibitors of other specific signaling pathways, e.g., mitogen-activated protein kinase), showing that signaling events linked to mTOR play a major role in the control of translation by insulin in this cell type.

The Translation Initiation Factor eIF4E Is Overexpressed in Multiple Myeloma and Is Critical for Myeloma Cell Proliferation and Survival

Blood ◽  
2011 ◽  
Vol 118 (21) ◽  
pp. 1853-1853 ◽  
Author(s):  
Shirong Li ◽  
MeiHua Jin ◽  
Ailing Liu ◽  
Markus Y. Mapara ◽  
Suzanne Lentzsch
Keyword(s):  
Multiple Myeloma ◽  
Protein Synthesis ◽  
Translation Initiation ◽  
Clinical Care ◽  
Protein Translation ◽  
Translation Initiation Factor ◽  
Initiation Factor ◽  
Mrna Levels ◽  
Myeloma Cells ◽  
Rpmi 8226

Abstract Abstract 1853 Methods: The translation initiation factor eIF4E is central to protein synthesis in general, and overexpression and/or activation of eIF4E is associated with a malignant phenotype by regulating oncogenic protein translation. Several previous publications indicate that aberrant control of protein synthesis contributes to lymphoma genesis but the exact role of protein translation in multiple myeloma (MM) is less clear. Therefore, understanding the mechanisms that control protein synthesis is an emerging new research area in MM with significant potential for developing innovative therapies. The goal of this study was to determine the role and regulation of eIF4E, as well as the effects of protein translation controlling drugs in MM. Results: By western blot analysis as well as RT-PCR we found that eIF4E protein and mRNA levels are significantly elevated (up to 20 fold) in MM cell lines (H929, RPMI-8226, MM.1S and OPM2) and primary myeloma cells compared to normal plasma cells. Silencing of eIF4E gene expression in RPMI-8226 MM cells by a stable and inducible shRNA system significantly decreased viability of myeloma cells (by ∼ 43%) but not of HEK 293 suggesting a higher dependency of MM cells to protein translation. Next we evaluated different drugs including pomalidomide, rapamycin, pp242, 4EGI-1 and ribavirin, that are known to inhibit protein synthesis for their effects on protein translation in MM. By m7GTP pull down assays we evaluated the effects of the different drugs on eIF4E expression and activity. Rapamycin blocked the phosphorylation of 4EBP1 and eIF4E release, and subsequently inhibited eIF4G binding. The compound 4EGI-1 decreased the interaction between eIF4E and eIF4G. Pomalidomide decreased eIF4E protein expression. All drugs inhibited MM cell DNA synthesis measured by 3H-Thymidine incorporation. Treatment with pomalidomide (10uM), rapamycin (40nM), pp242 (10uM), 4EGI1 (50uM) or ribavirin (50uM) for 48h significantly decreased (p<0.05) proliferation by 43–62% indicating that drugs controlling protein translation inhibit MM growth. We also found that all drugs decreased expression of eIF4E dependent targets such as cyclin D1 and c-myc. Conclusion: Here we show that eIF4E, a key player in translational control, is highly expressed in MM cells and critical for MM growth and survival. Therefore our study helps to understand the function and regulatory mechanism of eIF4E in MM. Further the evaluation of drugs targeting protein translation provides the basis for the optimization of current MM treatment or to open up new strategies such as targeting protein translation in future MM therapy. Disclosures: Lentzsch: Celgene Corp: Consultancy, Research Funding; Onyx: Consultancy; Genzyme: Consultancy; prIME Oncology: Honoraria; Imedex: Honoraria; Clinical Care Options: Honoraria.

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 O-GlcNAc Cycling Enzymes Associate with the Translational Machinery and Modify Core Ribosomal Proteins

2010 ◽  
Vol 21 (12) ◽  
pp. 1922-1936 ◽  
Author(s):  
Quira Zeidan ◽  
Zihao Wang ◽  
Antonio De Maio ◽  
Gerald W. Hart
Keyword(s):  
Protein Synthesis ◽  
Posttranslational Modifications ◽  
Ribosomal Proteins ◽  
Ribosome Biogenesis ◽  
Mammalian Target Of Rapamycin ◽  
Nuclear Staining ◽  
Mtor Signaling Pathway ◽  
Translational Machinery ◽  
Translation Factors ◽  
Nucleolar Stress

Protein synthesis is globally regulated through posttranslational modifications of initiation and elongation factors. Recent high-throughput studies have identified translation factors and ribosomal proteins (RPs) as substrates for the O-GlcNAc modification. Here we determine the extent and abundance of O-GlcNAcylated proteins in translational preparations. O-GlcNAc is present on many proteins that form active polysomes. We identify twenty O-GlcNAcylated core RPs, of which eight are newly reported. We map sites of O-GlcNAc modification on four RPs (L6, L29, L32, and L36). RPS6, a component of the mammalian target of rapamycin (mTOR) signaling pathway, follows different dynamics of O-GlcNAcylation than nutrient-induced phosphorylation. We also show that both O-GlcNAc cycling enzymes OGT and OGAse strongly associate with cytosolic ribosomes. Immunofluorescence experiments demonstrate that OGAse is present uniformly throughout the nucleus, whereas OGT is excluded from the nucleolus. Moreover, nucleolar stress only alters OGAse nuclear staining, but not OGT staining. Lastly, adenovirus-mediated overexpression of OGT, but not of OGAse or GFP control, causes an accumulation of 60S subunits and 80S monosomes. Our results not only establish that O-GlcNAcylation extensively modifies RPs, but also suggest that O-GlcNAc play important roles in regulating translation and ribosome biogenesis.

Manipulation of the host translation initiation complex eIF4F by DNA viruses

2010 ◽  
Vol 38 (6) ◽  
pp. 1511-1516 ◽  
Author(s):  
Derek Walsh
Keyword(s):  
Translation Initiation ◽  
Mammalian Target Of Rapamycin ◽  
Mrna Translation ◽  
Viral Proteins ◽  
Mitogen Activated Protein Kinase ◽  
Scaffolding Protein ◽  
Initiation Factor ◽  
Viral Protein Synthesis ◽  
Dna Viruses ◽  
Translational Machinery

In the absence of their own translational machinery, all viruses must gain access to host cell ribosomes to synthesize viral proteins and replicate. Ribosome recruitment and scanning of capped host mRNAs is facilitated by the multisubunit eIF (eukaryotic initiation factor) 4F, which consists of a cap-binding protein, eIF4E and an RNA helicase, eIF4A, assembled on a large scaffolding protein, eIF4G. Although inactivated by many viruses to inhibit host translation, a growing number of DNA viruses are being found to employ diverse strategies to stimulate eIF4F activity in infected cells and maximize viral protein synthesis. These strategies include stimulation of cellular mTOR (mammalian target of rapamycin) signalling to inactivate 4E-BPs (eIF4E-binding proteins), a family of translational repressors that limit eIF4E availability and eIF4F complex formation, together with modulating the activity of the eIF4E kinase Mnk (mitogen-activated protein kinase signal-integrating kinase) in a variety of manners to regulate both host and viral mRNA translation. In some cases, specific viral proteins that mediate these signalling events have been identified, whereas others have been shown to interact with host translation initiation factors or complexes and modify their activity and/or subcellular localization. The present review outlines current understanding of the role of eIF4F in the life cycle of various DNA viruses and discusses its potential as a therapeutic target to suppress viral infection.

mTORC1 regulates the efficiency and cellular capacity for protein synthesis

2013 ◽  
Vol 41 (4) ◽  
pp. 923-926 ◽  
Author(s):  
Christopher G. Proud
Keyword(s):  
Protein Synthesis ◽  
Growth Factors ◽  
Cell Growth ◽  
Translation Initiation ◽  
Ribosomal Proteins ◽  
Mammalian Target Of Rapamycin ◽  
Rna Polymerases ◽  
Short Term ◽  
Cellular Capacity ◽  
Cell Growth And Proliferation

mTORC1 (mammalian target of rapamycin complex 1) is activated by nutrients, growth factors and certain hormones. Signalling downstream of mTORC1 promotes protein synthesis by both activating the processes of translation initiation and elongation, in the short term, and the production of new ribosomes, in the longer term. mTORC1 signalling stimulates the translation of the mRNAs encoding the ribosomal proteins, activates RNA polymerases I and III, which make the rRNAs, and promotes the processing of the precursor for the main rRNAs. Taken together, these effects allow mTORC1 signalling to drive cell growth and proliferation.

Endotoxin induces differential regulation of mTOR-dependent signaling in skeletal muscle and liver of neonatal pigs

2003 ◽  
Vol 285 (3) ◽  
pp. E637-E644 ◽  
Author(s):  
Scot R. Kimball ◽  
Renán A. Orellana ◽  
Pamela M. J. O'Connor ◽  
Agus Suryawan ◽  
Jill A. Bush ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Protein Synthesis ◽  
Translation Initiation ◽  
Critical Role ◽  
Mammalian Target Of Rapamycin ◽  
Initiation Factor ◽  
Neonatal Pigs ◽  
Ribosomal Protein S6 ◽  
Induced Changes ◽  
Mrna Binding

In the present study, differential responses of regulatory proteins involved in translation initiation in skeletal muscle and liver during sepsis were studied in neonatal pigs treated with lipopolysaccharide (LPS). LPS did not alter eukaryotic initiation factor (eIF) 2B activity in either tissue. In contrast, binding of eIF4G to eIF4E to form the active mRNA-binding complex was repressed in muscle and enhanced in liver. Phosphorylation of eIF4E-binding protein, 4E-BP1, and ribosomal protein S6 kinase, S6K1, was reduced in muscle during sepsis but increased in liver. Finally, changes in 4E-BP1 and S6K1 phosphorylation were associated with altered phosphorylation of the protein kinase mammalian target of rapamycin (mTOR). Overall, the results suggest that translation initiation in both skeletal muscle and liver is altered during neonatal sepsis by modulation of the mRNA-binding step through changes in mTOR activation. Moreover, the LPS-induced changes in factors that regulate translation initiation are more profound than previously reported changes in global rates of protein synthesis in the neonate. This finding suggests that the initiator methionyl-tRNA-rather than the mRNA-binding step in translation initiation may play a more critical role in maintaining protein synthesis rates in the neonate during sepsis.

scholarly journals Shiga Toxin 1-Induced Proinflammatory Cytokine Production Is Regulated by the Phosphatidylinositol 3-Kinase/Akt/Mammalian Target of Rapamycin Signaling Pathway

2009 ◽  
Vol 77 (9) ◽  
pp. 3919-3931 ◽  
Author(s):  
Rama P. Cherla ◽  
Sang-Yun Lee ◽  
Renée A. Mulder ◽  
Moo-Seung Lee ◽  
Vernon L. Tesh
Keyword(s):  
Translation Initiation ◽  
Shiga Toxin ◽  
Cytokine Production ◽  
Glycogen Synthase ◽  
Mammalian Target Of Rapamycin ◽  
Translation Initiation Factor ◽  
Initiation Factor ◽  
Target Of Rapamycin ◽  
Phosphatidylinositol 3 Kinase ◽  
Phosphatidylinositol 3

ABSTRACT Shiga toxin 1 (Stx1) transiently increases the expression of proinflammatory cytokines by macrophage-like THP-1 cells in vitro. Increased cytokine production is partly due to activation of the translation initiation factor eIF4E through a mitogen-activated protein kinase (MAPK)- and Mnk1-dependent pathway. eIF4E availability for translation initiation is regulated by association with eIF4E binding proteins (4E-BP). In this study, we showed that Stx1 transiently induced 4E-BP hyperphosphorylation, which may release eIF4E for translation initiation. Phosphorylation of 4E-BP at priming sites T37 and T46 was not altered by Stx1 but was transiently increased at S65, concomitant with increased cytokine expression. Using kinase inhibitors, we showed that 4E-BP phosphorylation was dependent on phosphatidylinositol 3-kinase (PI3K), Akt, and mammalian target of rapamycin (mTOR) activation but did not require MAPKs. Stx1 treatment resulted in increased levels of cytosolic Ca2+. PI3K and Akt activation led to the phosphorylation and inactivation of the positive cytokine regulator glycogen synthase kinase 3α/β (GSK-3α/β). PI3K, Akt, and mTOR inhibitors and small interfering RNA knockdown of Akt expression all increased, whereas a GSK-3α/β inhibitor decreased, Stx1-induced soluble tumor necrosis factor alpha and interleukin-1β production. Overall, these findings suggest that despite transient activation of 4E-BP, the PI3K/Akt/mTOR pathway negatively influences cytokine induction by inactivating the positive regulator GSK-3α/β.

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