scholarly journals Role of Translation Initiation Factor 2B in Control of Cell Survival by the Phosphatidylinositol 3-Kinase/Akt/Glycogen Synthase Kinase 3β Signaling Pathway

2002 ◽  
Vol 22 (2) ◽  
pp. 578-586 ◽  
Author(s):  
Marianna Pap ◽  
Geoffrey M. Cooper
Keyword(s):  
Protein Synthesis ◽  
Cell Survival ◽  
Signaling Pathway ◽  
Glycogen Synthase ◽  
Akt Signaling ◽  
Translation Initiation Factor ◽  
Initiation Factor ◽  
Phosphatidylinositol 3 Kinase ◽  
Gsk 3Β

ABSTRACT The phosphatidylinositol 3-kinase (PI 3-kinase)/Akt signaling pathway is an important mediator of growth factor-dependent survival of mammalian cells. A variety of targets of the Akt protein kinase have been implicated in cell survival, including the protein kinase glycogen synthase kinase 3β (GSK-3β). One of the targets of GSK-3β is translation initiation factor 2B (eIF2B), linking global regulation of protein synthesis to PI 3-kinase/Akt signaling. Because of the central role of protein synthesis, we have investigated the involvement of eIF2B, which is inhibited as a result of GSK-3β phosphorylation, in programmed cell death. We demonstrate that expression of eIF2B mutants lacking the GSK-3β phosphorylation or priming sites is sufficient to protect both Rat-1 and PC12 cells from apoptosis induced by overexpression of GSK-3β, inhibition of PI 3-kinase, or growth factor deprivation. Consistent with these effects on cell survival, expression of nonphosphorylatable eIF2B prevented inhibition of protein synthesis following treatment of cells with the PI 3-kinase inhibitor LY294002. Conversely, cycloheximide induced apoptosis of PC12 and Rat-1 cells, further indicating that protein synthesis was required for cell survival. Inhibition of translation resulting from treatment with cycloheximide led to the release of cytochrome c from mitochondria, similar to the effects of inhibition of PI 3-kinase. Expression of nonphosphorylatable eIF2B prevented cytochrome c release resulting from PI 3-kinase inhibition but did not affect cytochrome c release or apoptosis induced by cycloheximide. Regulation of translation resulting from phosphorylation of eIF2B by GSK-3β thus appears to contribute to the control of cell survival by the PI 3-kinase/Akt signaling pathway, acting upstream of mitochondrial cytochrome c release.

ANG II activates effectors of mTOR via PI3-K signaling in human coronary smooth muscle cells

2004 ◽  
Vol 287 (3) ◽  
pp. H1232-H1238 ◽  
Author(s):  
Sassan Hafizi ◽  
Xuemin Wang ◽  
Adrian H. Chester ◽  
Magdi H. Yacoub ◽  
Christopher G. Proud
Keyword(s):  
Protein Synthesis ◽  
Smooth Muscle ◽  
Smooth Muscle Cells ◽  
Signaling Pathway ◽  
Initiation Factor ◽  
Ang Ii ◽  
Eukaryotic Initiation Factor ◽  
Mtor Signaling Pathway ◽  
Phosphatidylinositol 3 Kinase ◽  
Eukaryotic Initiation Factor 4E

We have previously shown that the vasoconstrictive peptide angiotensin II (ANG II) is a hypertrophic agent for human coronary artery smooth muscle cells (cSMCs), which suggests that it plays a role in vascular wall thickening. The present study investigated the intracellular signal transduction pathways involved in the growth response of cSMCs to ANG II. The stimulation of protein synthesis by ANG II in cSMCs was blocked by the immunosuppressant rapamycin, which is an inhibitor of the mammalian target of rapamycin (mTOR) signaling pathway that includes the 70-kDa S6 kinase (p70S6k) and plays a key role in cell growth. The inhibitory effect of rapamycin was reversed by a molar excess of FK506; this indicates that both agents act through the common 12-kDa immunophilin FK506-binding protein. ANG II caused a rapid and sustained activation of p70S6k activity that paralleled its phosphorylation, and both processes were blocked by rapamycin. In addition, both of the phosphatidylinositol 3-kinase inhibitors wortmannin and LY-294002 abolished the ANG II-induced increase in protein synthesis, and wortmannin also blocked p70S6k phosphorylation. Furthermore, ANG II triggered dissociation of the translation initiation factor, eukaryotic initiation factor-4E, from its regulatory binding protein 4E-BP1, which was also inhibited by rapamycin and wortmannin. In conclusion, we have shown that ANG II activates components of the rapamycin-sensitive mTOR signaling pathway in human cSMCs and involves activation of phosphatidylinositol 3-kinase, p70S6k, and eukaryotic initiation factor-4E, which leads to activation of protein synthesis. These signaling mechanisms may mediate the growth-promoting effect of ANG II in human cSMCs.

scholarly journals Mitotic MELK-eIF4B signaling controls protein synthesis and tumor cell survival

2016 ◽  
Vol 113 (35) ◽  
pp. 9810-9815 ◽  
Author(s):  
Yubao Wang ◽  
Michael Begley ◽  
Qing Li ◽  
Hai-Tsang Huang ◽  
Ana Lako ◽  
...  
Keyword(s):  
Protein Synthesis ◽  
Cell Survival ◽  
Cancer Cells ◽  
Cancer Cell ◽  
Leucine Zipper ◽  
Apoptotic Cell ◽  
Translation Initiation Factor ◽  
Initiation Factor ◽  
Signaling Axis ◽  
Cancer Cell Survival

The protein kinase maternal and embryonic leucine zipper kinase (MELK) is critical for mitotic progression of cancer cells; however, its mechanisms of action remain largely unknown. By combined approaches of immunoprecipitation/mass spectrometry and peptide library profiling, we identified the eukaryotic translation initiation factor 4B (eIF4B) as a MELK-interacting protein during mitosis and a bona fide substrate of MELK. MELK phosphorylates eIF4B at Ser406, a modification found to be most robust in the mitotic phase of the cell cycle. We further show that the MELK–eIF4B signaling axis regulates protein synthesis during mitosis. Specifically, synthesis of myeloid cell leukemia 1 (MCL1), an antiapoptotic protein known to play a role in cancer cell survival during cell division, depends on the function of MELK-elF4B. Inactivation of MELK or eIF4B results in reduced protein synthesis of MCL1, which, in turn, induces apoptotic cell death of cancer cells. Our study thus defines a MELK–eIF4B signaling axis that regulates protein synthesis during mitosis, and consequently influences cancer cell survival.

scholarly journals ROLE OF GSK-3 IN Wnt/β-CATENIN SIGNALING PATHWAY IN OBESITY

2021 ◽  
Vol 23 (4) ◽  
pp. 775-780
Author(s):  
A. S. Kulakova ◽  
I. A. Snimshchikova ◽  
M. O. Plotnikova
Keyword(s):  
Serum Level ◽  
Wnt Signaling ◽  
Signaling Pathway ◽  
Glycogen Synthase ◽  
Wnt Signaling Pathway ◽  
Obese Patients ◽  
Healthy Individuals ◽  
Gsk 3Β ◽  
The Impact

The complexity of the adipogenesis mechanism results from the impact of multiple cues, among which an important place is held by the components of the Wnt signaling pathway. The search for potential markers of the development of diseases related to obesity aroused an interest in the study of GSK-3 (glycogen synthase kinase), β-catenin. GSK-3β is an intracellular serine / threonine kinase found in the cytoplasm, nucleus, mitochondria, synthesized in all body tissues and involved in regulating metabolic processes, cell proliferation, apoptosis etc. The first of the discovered functions of GSK-3β was the regulation of glycogen synthesis. Active GSK-3β phosphorylates and thereby inhibits glycogen synthase. As a result of the insulin binding to the cell receptor via inositol-3-phosphate, protein kinase B (Akt1) is activated, which, in turn, phosphorylates and inhibits GSK-3β. In addition, GSK-3β is involved in the regulating glucose metabolism. The most important function of GSK-3β is the inhibition of the β-catenin protein. In a resting cell, GSK-3β in complex with the APC and Axin proteins binds and phosphorylates the β-catenin transcription factor, which leads to its ubiquitination and degradation. When Wnt proteins act on the cell, the Dvl protein is activated, which, by binding to GSK-3β, releases β-catenin, preventing its degradation, however, the role of GSK3α/β in the adipocyte inflammatory response has not yet been fully investigated, therefore it seems promising to study the role of GSK-3 in the Wnt/β-catenin signaling pathway in obesityThe aim of the study was to assess the activity of the components of the Wnt signaling pathway in obese patients by measuring the serum level of GSK-3 and β-catenin. There were enrolled 32 patients with progressive forms of I-III degree obesity in the absence of diabetes mellitus. The concentration of serum GSK-3α, GSK-3β, and β-catenin was measured by enzyme-linked immunoassay. Data are presented as absolute and relative (%) number of patients; arithmetic mean; medians, 1 and 3 quartiles – Ме (Q0.25-Q0.75). Obese patients contained a 7.5-fold increased serum level of GSK-3α (785 (371-1317.5) pg/ml) compared to healthy individuals 105 (102.5-110) pg/ml, (p < 0.001), paralleled with increased amount of GSK-3β, which level in obese patients was 295 (190-695) pg/ml, which is by 18.3% higher than those in healthy individuals 241 (218.75-287.5) pg/ml, p = 0.111. Amount of GSK-3 depending on the degree of obesity tended to increase, most often coupled to decreased β-catenin level which is consistent with the literature data and can be considered as a prognostic criterion for the course of pathological processes in obesity. 

Effect of CCK and intracellular calcium to regulate eIF2B and protein synthesis in rat pancreatic acinar cells

2002 ◽  
Vol 282 (2) ◽  
pp. G267-G276 ◽  
Author(s):  
Maria Dolors Sans ◽  
Scot R. Kimball ◽  
John A. Williams
Keyword(s):  
Protein Synthesis ◽  
Glycogen Synthase ◽  
Translation Initiation Factor ◽  
Initiation Factor ◽  
Pancreatic Acinar Cells ◽  
Alternative Mechanism ◽  
Α Subunit ◽  
Eif2α Phosphorylation ◽  
A 23187 ◽  
High Concentrations

Pancreatic secretagogues enhance acinar protein synthesis at physiological concentrations and inhibit protein synthesis at high concentrations. We investigated the potential role in this process of the eukaryotic translation initiation factor (eIF)2B. Cholecystokinin (CCK) at 10–100 pM did not significantly affect eIF2B activity, which averaged 35.4 nmol guanosine 5′-diphosphate exchanged per minute per milligram protein under control conditions; higher CCK concentrations reduced eIF2B activity to 38.2% of control. Carbamylcholine chloride (Carbachol, CCh), A-23187, and thapsigargin also inhibited eIF2B and protein synthesis, whereas bombesin and the CCK analog JMV-180 were without effect. Previous studies have shown that eIF2B can be negatively regulated by glycogen synthase kinase-3 (GSK-3). However, GSK-3 activity, as assessed by phosphorylation state, was inhibited at high concentrations of CCK, an effect that should have stimulated, rather than repressed, eIF2B activity. An alternative mechanism for regulating eIF2B is through phosphorylation of the α-subunit of eIF2, which converts it into an inhibitor of eIF2B. CCK, CCh, A-23187, and thapsigargin all enhanced eIF2α phosphorylation, suggesting that eIF2B activity is regulated by eIF2α phosphorylation under these conditions. Removal of Ca2+ from the medium enhanced the inhibitory action of CCK on both protein synthesis and eIF2B activity as well as further increasing eIF2α phosphorylation. Although it is likely that other mechanisms account for the stimulation of acinar protein synthesis, these results suggest that the inhibition of acinar protein synthesis by CCK occurs as a result of depletion of Ca2+ from the endoplasmic reticulum lumen leading to phosphorylation of eIF2α and inhibition of eIF2B.

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.

scholarly journals Defects in Translational Regulation Mediated by the α Subunit of Eukaryotic Initiation Factor 2 Inhibit Antiviral Activity and Facilitate the Malignant Transformation of Human Fibroblasts

2004 ◽  
Vol 24 (5) ◽  
pp. 2025-2040 ◽  
Author(s):  
Darren J. Perkins ◽  
Glen N. Barber
Keyword(s):  
Protein Synthesis ◽  
Translation Initiation ◽  
T Antigen ◽  
Translation Initiation Factor ◽  
Initiation Factor ◽  
Eukaryotic Initiation Factor ◽  
Α Subunit ◽  
Eukaryotic Initiation Factor 2 ◽  
Initiation Factor 2

ABSTRACT Suppression of protein synthesis through phosphorylation of the translation initiation factor α subunit of eukaryotic initiation factor 2 (eIF2α) is known to occur in response to many forms of cellular stress. To further study this, we have developed novel cell lines that inducibly express FLAG-tagged versions of either the phosphomimetic eIF2α variant, eIF2α-S51D, or the phosphorylation-insensitive eIF2α-S51A. These variants showed authentic subcellular localization, were incorporated into endogenous ternary complexes, and were able to modulate overall rates of protein synthesis as well as influence cell division. However, phosphorylation of eIF2α failed to induce cell death or sensitize cells to killing by proapoptotic stimuli, though it was able to inhibit viral replication, confirming the role of eIF2α in host defense. Further, although the eIF2α-S51A variant has been shown to transform NIH 3T3 cells, it was unable to transform the murine fibroblast 3T3 L1 cell line. To therefore clarify this issue, we explored the role of eIF2α in growth control and demonstrated that the eIF2α-S51A variant is capable of collaborating with hTERT and the simian virus 40 large T antigen in the transformation of primary human kidney cells. Thus, dysregulation of translation initiation is indeed sufficient to cooperate with defined oncogenic elements and participate in the tumorigenesis of human tissue.

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