Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P42345 (mTOR)
 26,049 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

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 alpha>beta>gamma. 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.
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PMID:Activation of mRNA translation in rat cardiac myocytes by insulin involves multiple rapamycin-sensitive steps. 1074 98

We have examined the effects of widely used stress-inducing agents on protein synthesis and on regulatory components of the translational machinery. The three stresses chosen, arsenite, hydrogen peroxide and sorbitol, exert their effects in quite different ways. Nonetheless, all three rapidly ( approximately 30 min) caused a profound inhibition of protein synthesis. In each case this was accompanied by dephosphorylation of the eukaryotic initiation factor (eIF) 4E-binding protein 1 (4E-BP1) and increased binding of this repressor protein to eIF4E. Binding of 4E-BP1 to eIF4E correlated with loss of eIF4F complexes. Sorbitol and hydrogen peroxide each caused inhibition of the 70-kDa ribosomal protein S6 kinase, while arsenite activated it. The effects of stresses on the phosphorylation of eukaryotic elongation factor 2 also differed: oxidative stress elicited a marked increase in eEF2 phosphorylation, which is expected to contribute to inhibition of translation, while the other stresses did not have this effect. Although all three proteins (4E-BP1, p70 S6 kinase and eEF2) can be regulated through the mammalian target of rapamycin (mTOR), our data imply that stresses do not interfere with mTOR function but act in different ways on these three proteins. All three stresses activate the p38 MAP kinase pathway but we were able to exclude a role for this in their effects on 4E-BP1. Our data reveal that these stress-inducing agents, which are widely used to study stress-signalling in mammalian cells, exert multiple and complex inhibitory effects on the translational machinery.
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PMID:Cellular stresses profoundly inhibit protein synthesis and modulate the states of phosphorylation of multiple translation factors. 1207 73

Acute pancreatitis (AP) has been shown in some studies to inhibit total protein synthesis in the pancreas, whereas in other studies, protein synthesis was not affected. Previous in vitro work has shown that high concentrations of cholecystokinin both inhibit protein synthesis and inhibit the activity of the guanine nucleotide exchange factor eukaryotic initiation factor (eIF)2B by increasing the phosphorylation of eIF2alpha. We therefore evaluated in C57BL/6 mice the effects of caerulein-induced AP on pancreatic protein synthesis, eIF2B activity and other protein translation regulatory mechanisms. Repetitive hourly injections of caerulein were administered at 50 microg/kg ip. Pancreatic protein synthesis was reduced 10 min after the initial caerulein administration and was further inhibited after three and five hourly injections. Caerulein inhibited the two major regulatory points of translation initiation: the activity of the guanine nucleotide exchange factor eIF2B (with an increase of eIF2alpha phosphorylation) and the formation of the eIF4F complex due, in part, to degradation of eIF4G. This inhibition was not accounted for by changes in the upstream stimulatory pathway, because caerulein activated Akt as well as phosphorylating the downstream effectors of mTOR, 4E-BP1, and ribosomal protein S6. Caerulein also decreased the phosphorylation of the eukaryotic elongation factor 2, implying that this translation factor was not inhibited in AP. Thus the inhibition of pancreatic protein synthesis in this model of AP most likely results from the inhibition of translation initiation as a result of increased eIF2alpha phosphorylation, reduction of eIF2B activity, and the inhibition of eIF4F complex formation.
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PMID:Caerulein-induced acute pancreatitis inhibits protein synthesis through effects on eIF2B and eIF4F. 1277 2

Eukaryotic elongation factor 2 (eEF2) kinase is an unusual calcium- and calmodulin-dependent protein kinase that is regulated by insulin through the rapamycin-sensitive mTOR pathway. Here we show that insulin decreases the ability of eEF2 kinase to bind calmodulin in a rapamycin-sensitive manner. We identify a novel phosphorylation site in eEF2 kinase (Ser78) that is located immediately next to its calmodulin-binding motif. Phosphorylation of this site is increased by insulin in a rapamycin-sensitive fashion. Regulation of the phosphorylation of Ser78 also requires amino acids and the protein kinase phosphoinositide-dependent kinase 1. Mutation of this site to alanine strongly attenuates the effects of insulin and rapamycin both on the binding of calmodulin to eEF2 kinase and on eEF2 kinase activity. Phosphorylation of Ser78 is thus likely to link insulin and mTOR signaling to the control of eEF2 phosphorylation and chain elongation. This site is not a target for known kinases in the mTOR pathway, e.g., the S6 kinases, implying that it is phosphorylated by a novel mTOR-linked protein kinase that serves to couple hormones and amino acids to the control of translation elongation. eEF2 kinase is thus a target for mTOR signaling independently of previously known downstream components of the pathway.
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PMID:A novel mTOR-regulated phosphorylation site in elongation factor 2 kinase modulates the activity of the kinase and its binding to calmodulin. 1502 86

While pancreatic protein synthesis and the initiation of translation are regulated by hormones and neurotransmiters, whether the elongation process is also regulated is unknown. Stimulatory doses of cholecystokinin (CCK) (100 pM), bombesin (10 nM), and carbachol (10 microM) increased elongation rates (measured as ribosomal half-transit time) in pancreatic acini in vitro. At the same time these secretagogues reduced elongation factor 2 (eEF2) phosphorylation, the main factor known to regulate elongation, and increased the phosphorylation of the eEF2 kinase. The mTOR inhibitor rapamycin reversed the dephosphorylation of eEF2 induced by CCK, as did treatment with the p38 MAPK inhibitor SB202190, the MEK inhibitor PD98059, and the phosphatase inhibitor calyculin A. Neither rapamycin, SB202190, PD98059 nor calyculin A had an effect on CCK mediated eEF2 kinase phosphorylation. Translation elongation in pancreatic acinar cells is likely regulated by eEF2 through the mTOR, p38, and MEK pathways, and modulated through PP2A.
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PMID:Regulation of translation elongation and phosphorylation of eEF2 in rat pancreatic acini. 1515 53

Amino acids positively regulate signaling through the mammalian target of rapamycin (mTOR). Recent work demonstrated the importance of the tuberous sclerosis protein TSC2 for regulation of mTOR by insulin. TSC2 contains a GTPase-activator domain that promotes hydrolysis of GTP bound to Rheb, which positively regulates mTOR signaling. Some studies have suggested that TSC2 also mediates the control of mTOR by amino acids. In cells lacking TSC2, amino acid withdrawal still results in dephosphorylation of S6K1, ribosomal protein S6, the eukaryotic initiation factor 4E-binding protein, and elongation factor-2 kinase. The effects of amino acid withdrawal are diminished by inhibiting protein synthesis or adding back amino acids. These studies demonstrate that amino acid signaling to mTOR occurs independently of TSC2 and involves additional unidentified inputs. Although TSC2 is not required for amino acid control of mTOR, amino acid withdrawal does decrease the proportion of Rheb in the active GTP-bound state. Here we also show that Rheb and mTOR form stable complexes, which are not, however, disrupted by amino acid withdrawal. Mutants of Rheb that cannot bind GTP or GDP can interact with mTOR complexes. We also show that the effects of hydrogen peroxide and sorbitol, cell stresses that impair mTOR signaling, are independent of TSC2. Finally, we show that the ability of energy depletion (which impairs mTOR signaling in TSC2+/+ cells) to increase the phosphorylation of eukaryotic elongation factor 2 is also independent of TSC2. This likely involves the phosphorylation of the elongation factor-2 kinase by the AMP-activated protein kinase.
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PMID:The tuberous sclerosis protein TSC2 is not required for the regulation of the mammalian target of rapamycin by amino acids and certain cellular stresses. 1577 76

The pathogenesis of formation of neurofibrillary tangles (NFTs) in Alzheimer's disease (AD) brains is unknown. One of the possibilities might be that translation of tau mRNA is aberrantly regulated in AD brains. In the current study, levels of various translation control elements including total and phosphorylated (p) forms of mammalian target of rapamycin (mTOR), eukaryotic initiation factor 4E binding protein 1 (4E-BP1), eukaryotic elongation factor 2 (eEF2), and eEF2 kinase were investigated in relationship with tau in homogenates of the medial temporal cortex from 20 AD and 10 control brains. We found that levels of p-mTOR (Ser2481), and p-4E-BP1 (Thr70 and Ser65) dramatically increase in AD, and are positively significantly correlated with total tau and p-tau. Levels of p-eEF2K were significantly increased, and total eEF2 significantly decreased in AD, when compared to controls. The changes of p-mTOR (2481), p-4E-BP1, and p-eEF2 were immunohistochemically confirmed to be in neurons of AD brains. This suggested that there are obvious abnormalities of elements related with translation control in AD brain and their aberrant changes may up-regulate the translation of tau mRNA, contributing to hyperphosphorylated tau accumulation in NFT-bearing neurons.
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PMID:Levels of mTOR and its downstream targets 4E-BP1, eEF2, and eEF2 kinase in relationships with tau in Alzheimer's disease brain. 1609 2

Brief glutamatergic stimulation of neurons from fetal mice, cultured in vitro for 6 days, activates the mTOR-S6 kinase, ERK1/2 and Akt pathways, to an extent approaching that elicited by brain-derived neurotrophic factor. In contrast, sustained glutamatergic stimulation inhibits ERK, Akt, and S6K. Glutamatergic activation of S6K is calcium/calmodulin-dependent and is prevented by inhibitors of calcium/calmodulin-dependent protein kinase 2, phosphatidylinositol 3-OH-kinase and by rapamycin. 2-Amino-5-phosphonovaleric acid, an inhibitor of N'-methyl-D-aspartate receptors, abolishes glutamatergic activation of ERK1/2 but not the activation of mTOR-S6K; the latter is completely abolished by inhibitors of voltage-dependent calcium channels. Added singly, dopamine gives slight, and norepinephrine a more significant, activation of ERK and S6K; both catecholeamines, however, enhance glutamatergic activation of S6K but not ERK. After 12 days in culture, the response to direct glutamatergic activation is attenuated but can be uncovered by suppression of gamma-aminobutyric acid interneurons with bicuculline in the presence of the weak K(+) channel blocker 4-aminopyridine (4-AP). This selective synaptic activation of mTOR-S6K is also resistant to APV and inhibited by Ca(2+) channel blockers and higher concentrations of glutamate. Elongation factor 2 (EF2) is phosphorylated and inhibited by the eEF2 kinase (CaM kinase III); the latter is inhibited by the S6K or Rsk. Bicuculline/4-AP or KCl-induced depolarization reduces, whereas higher concentrations of glutamate increases, EF2 phosphorylation. Thus the mTOR-S6K pathway in neurons, a critical component of the late phase of LTP, is activated by glutamatergic stimulation in a calcium/calmodulin-dependent fashion through a calcium pool controlled by postsynaptic voltage-dependent calcium channels, whereas sustained stimulation of extrasynaptic glutamate receptors is inhibitory.
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PMID:Glutamatergic regulation of the p70S6 kinase in primary mouse neurons. 1618 39

Diabetes mellitus results in chronic hyperglycemia, a serious metabolic disorder associated with a markedly increased risk of cardiovascular disease. However, the effects of high glucose (HG) on cardiac myocyte growth have not been fully clarified. In this study, the effect of glucose on cardiac myocyte growth was examined using leucine incorporation as an index of protein synthesis. High glucose (HG, 25 mmol/L) increased leucine incorporation (167% +/- 0.2% over normal glucose, n=4, P<.01) compared with a physiological glucose concentration (5.5 mmol/L, normal glucose). The HG-induced increase in leucine incorporation was time- and dose-dependent and was not due to osmotic changes because 25 mmol/L mannitol did not change leucine incorporation. High glucose also significantly reduced elongation factor 2 phosphorylation, an effect known to result in increased protein synthesis at the elongation step. Western blot analysis showed that HG-activated protein kinase B (PKB), also called Akt (PKB/Akt), at 18 hours. High glucose-induced leucine incorporation was attenuated with phosphatidylinositol 3-kinase (PI3K) inhibition using wortmannin and LY294002 and by rapamycin, a mammalian target of rapamycin (mTOR) inhibitor, 72%, 64%, and 65% (P<.05), respectively. High glucose also activated extracellular signal-regulated kinase 1/2 activity with peak stimulation at 5 minutes. In addition, PD98059, an inhibitor of mitogen-activated protein kinase kinase, attenuated HG-induced leucine incorporation. These data show for the first time that elevated glucose increases protein synthesis in cardiac myocytes. The increase appears to be mediated by activation of PI3K-PKB/Akt and/or PI3K-mTOR as well as extracellular signal-regulated kinase 1/2. These results provide new evidence for a direct effect of glucose independent of insulin on cardiac myocyte growth.
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PMID:Elevated glucose activates protein synthesis in cultured cardiac myocytes. 1625 33

Impaired overload-induced protein synthesis and growth in aged fast-twitch skeletal muscle may result from diminished responsiveness of signalling intermediates controlling protein translation. Yet, potential age-related signalling decrements have never been examined in direct parallel with impaired overload-induced muscle growth in any model. To this end, we used Western blotting to examine the contents and phosphorylation states of mammalian target of rapamycin (mTOR) and its downstream translational signalling intermediates, 70 kDa ribosomal protein S6 kinase (S6k), ribosomal protein S6 (rpS6), eukaryotic elongation factor 2 (eEF2), and eukaryotic initiation factor 4E-binding protein 1 (4E-BP1), in conjunction with impaired growth in 1 week overloaded fast-twitch plantaris muscles (via unilateral gastrocnemius ablation) of old (O; 30 months) versus young adult (YA; 8 months) male Fischer344 x Brown Norway rats. The significantly (P <or= 0.05) diminished growth (assessed by total muscle protein content) in overloaded O muscles (5.6 +/- 1.7 versus 19.3 +/- 2.9% in YA) was accompanied by significant impairments in the phosphorylation states of mTOR (Ser2448), S6k (impaired at the mTOR-specific Thr389 residue but not at Thr421/Ser424), rpS6 (Ser235/236) and 4E-BP1 (gel shift), as well as deficits in total eEF2 accretion. Moreover, in overloaded muscles across both age groups, phospho-S6k at Thr389 (but not at Thr421/Ser424), 4E-BP1 phosphorylation status, and total eEF2 accretion were all positively correlated with percentage muscle hypertrophy, and negatively correlated with the phosphorylation (Thr172) of 5'-AMP-activated protein kinase (AMPK; which inhibits translational signalling and protein synthesis in young muscle at rest). As previously published by ourselves, AMPK was hyperphosphorylated in O versus YA muscles used in the current investigation. The present results provide solid evidence that impaired overload-induced growth in aged fast-twitch muscle may partly result from multiple-level decrements in signalling pathway(s) controlling protein translation, and also provide an initial indication that AMPK hyperactivation with age may potentially lie upstream of these decrements.
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PMID:Impaired overload-induced muscle growth is associated with diminished translational signalling in aged rat fast-twitch skeletal muscle. 1662 69


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