Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
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.
 ...
PMID:Activation of mRNA translation in rat cardiac myocytes by insulin involves multiple rapamycin-sensitive steps. 1074 98

Skeletal muscle is composed of multinucleated fibres, formed after the differentiation and fusion of myoblast precursors. Skeletal muscle atrophy and hypertrophy refer to changes in the diameter of these pre-existing muscle fibres. The prevention of atrophy would provide an obvious clinical benefit; insulin-like growth factor 1 (IGF-1) is a promising anti-atrophy agent because of its ability to promote hypertrophy. However, the signalling pathways by which IGF-1 promotes hypertrophy remain unclear, with roles suggested for both the calcineurin/NFAT (nuclear factor of activated T cells) pathway and the PtdIns-3-OH kinase (PI(3)K)/Akt pathway. Here we employ a battery of approaches to examine these pathways during the hypertrophic response of cultured myotubes to IGF-1. We report that Akt promotes hypertrophy by activating downstream signalling pathways previously implicated in activating protein synthesis: the pathways downstream of mammalian target of rapamycin (mTOR) and the pathway activated by phosphorylating and thereby inhibiting glycogen synthase kinase 3 (GSK3). In contrast, in addition to demonstrating that calcineurin does not mediate IGF-1-induced hypertrophy, we show that IGF-1 unexpectedly acts via Akt to antagonize calcineurin signalling during myotube hypertrophy.
 ...
PMID:Mediation of IGF-1-induced skeletal myotube hypertrophy by PI(3)K/Akt/mTOR and PI(3)K/Akt/GSK3 pathways. 1171 22

The mTOR inhibitor rapamycin induces G1 cell cycle accumulation and p53-independent apoptosis of the human rhabdomyosarcoma cell line Rh1. Insulin-like growth factor I (IGF-I) and insulin, but not epidermal growth factor or platelet-derived growth factor, completely prevented apoptosis of this cell line. Because the Ras-Erk1-Erk2 and phosphatidylinositol 3'-kinase (PI3K)-Akt pathways are implicated in the survival of various cancer cells, we determined whether protection from rapamycin-induced apoptosis by IGF-I requires one or both of these pathways. Despite the blocking of Ras-Erk signaling by the addition of PD 98059 (a MEK1 inhibitor) or by the overexpression of dominant-negative RasN17, IGF-I completely prevented rapamycin-induced death. Inhibition of Ras signaling did not prevent Akt activation by IGF-I. To determine the role of the PI3K-Akt pathway in rescuing cells from apoptosis caused by rapamycin, cells expressing dominant-negative Akt were tested. This mutant protein inhibited IGF-I-induced phosphorylation of Akt and blocked phosphorylation of glycogen synthase kinase 3. The prevention of rapamycin-induced apoptosis by IGF-I was not inhibited by expression of dominant-negative Akt either alone or under conditions in which LY 294002 inhibited PI3K signaling. Furthermore, IGF-I prevented rapamycin-induced apoptosis when the Ras-Erk1-Erk2 and PI3K-Akt pathways were blocked simultaneously. Similar experiments in a second rhabdomyosarcoma cell line, Rh30, using pharmacological inhibitors of PI3K or MEK1, alone or in combination, failed to block IGF-I rescue from rapamycin-induced apoptosis. Therefore, we conclude that a novel pathway(s) is responsible for the IGF-I-mediated protection against rapamycin-induced apoptosis in these rhabdomyosarcoma cells.
 ...
PMID:Insulin-like growth factor I-mediated protection from rapamycin-induced apoptosis is independent of Ras-Erk1-Erk2 and phosphatidylinositol 3'-kinase-Akt signaling pathways. 1254 89

The molecular mechanisms underlying the pathogenesis of the malignant Hodgkin's/Reed-Sternberg (HRS) cells of Hodgkin's lymphoma (HL) are largely unknown. This study investigates the contribution of phosphatidyl-inositide 3 kinase (PI3-kinase) and demonstrates that Akt, a substrate of PI3-kinase, is constitutively activated in HL-derived cell lines. Several downstream effectors of Akt signalling, including glycogen synthase kinase 3 (GSK-3) alpha and beta and mTOR substrates 4E-BP1 and p70 S6 kinase, were also phosphorylated in HL cells. The mTOR inhibitor, rapamycin, inhibited phosphorylation of these proteins. Furthermore, LY294002 inhibited phosphorylation of p70 S6 kinase and 4E-BP1, suggesting that the phosphorylation of p70 S6 kinase and 4E-BP1 in HL cells is PI3-kinase dependent. Importantly, HRS cells of primary tumour samples not only expressed high levels of activated Akt but also displayed phosphorylation of downstream targets of Akt activation including GSK-3, 4E-BP1, and p70 S6 Kinase. Inhibition of PI3-kinase and mTOR showed only modest effects on cell survival at the lower serum concentrations. However, rapamycin and doxorubicin acted synergistically to reduce HL cell survival. A combination of rapamycin and chemotherapy should be investigated in the treatment of HL.
 ...
PMID:Constitutive activation of phosphatidyl-inositide 3 kinase contributes to the survival of Hodgkin's lymphoma cells through a mechanism involving Akt kinase and mTOR. 1571 59

To examine the molecular mechanisms by which plasma amino acid elevation impairs insulin action, we studied seven healthy men twice in random order during infusion of an amino acid mixture or saline (total plasma amino acid approximately 6 vs. approximately 2 mmol/l). Somatostatin-insulin-glucose clamps created conditions of low peripheral hyperinsulinemia ( approximately 100 pmol/l, 0-180 min) and prandial-like peripheral hyperinsulinemia ( approximately 430 pmol/l, 180-360 min). At low peripheral hyperinsulinemia, endogenous glucose production (EGP) did not change during amino acid infusion but decreased by approximately 70% during saline infusion (EGP(150-180 min) 11 +/- 1 vs. 3 +/- 1 mumol . kg(-1) . min(-1), P = 0.001). Prandial-like peripheral hyperinsulinemia completely suppressed EGP during both protocols, whereas whole-body rate of glucose disappearance (R(d)) was approximately 33% lower during amino acid infusion (R(d) (330-360 min) 50 +/- 4 vs. 75 +/- 6 mumol . kg(-1) . min(-1), P = 0.002) indicating insulin resistance. In skeletal muscle biopsies taken before and after prandial-like peripheral hyperinsulinemia, plasma amino acid elevation markedly increased the ability of insulin to activate S6 kinase 1 compared with saline infusion ( approximately 3.7- vs. approximately 1.9-fold over baseline). Furthermore, amino acid infusion increased the inhibitory insulin receptor substrate-1 phosphorylation at Ser312 and Ser636/639 and decreased insulin-induced phosphoinositide 3-kinase activity. However, plasma amino acid elevation failed to reduce insulin-induced Akt/protein kinase B and glycogen synthase kinase 3alpha phosphorylation. In conclusion, amino acids impair 1) insulin-mediated suppression of glucose production and 2) insulin-stimulated glucose disposal in skeletal muscle. Our results suggest that overactivation of the mammalian target of rapamycin/S6 kinase 1 pathway and inhibitory serine phosphorylation of insulin receptor substrate-1 underlie the impairment of insulin action in amino acid-infused humans.
 ...
PMID:Overactivation of S6 kinase 1 as a cause of human insulin resistance during increased amino acid availability. 1612 57

BCAAs (leucine, isoleucine, and valine), particularly leucine, have anabolic effects on protein metabolism by increasing the rate of protein synthesis and decreasing the rate of protein degradation in resting human muscle. Also, during recovery from endurance exercise, BCAAs were found to have anabolic effects in human muscle. These effects are likely to be mediated through changes in signaling pathways controlling protein synthesis. This involves phosphorylation of the mammalian target of rapamycin (mTOR) and sequential activation of 70-kD S6 protein kinase (p70 S6 kinase) and the eukaryotic initiation factor 4E-binding protein 1. Activation of p70 S6 kinase, and subsequent phopsphorylation of the ribosomal protein S6, is associated with enhanced translation of specific mRNAs. When BCAAs were supplied to subjects during and after one session of quadriceps muscle resistance exercise, an increase in mTOR, p70 S6 kinase, and S6 phosphorylation was found in the recovery period after the exercise with no effect of BCAAs on Akt or glycogen synthase kinase 3 (GSK-3) phosphorylation. Exercise without BCAA intake led to a partial phosphorylation of p70 S6 kinase without activating the enzyme, a decrease in Akt phosphorylation, and no change in GSK-3. It has previously been shown that leucine infusion increases p70 S6 kinase phosphorylation in an Akt-independent manner in resting subjects; however, a relation between mTOR and p70 S6 kinase has not been reported previously. The results suggest that BCAAs activate mTOR and p70 S6 kinase in human muscle in the recovery period after exercise and that GSK-3 is not involved in the anabolic action of BCAAs on human muscle.
 ...
PMID:Branched-chain amino acids activate key enzymes in protein synthesis after physical exercise. 1636 96

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.
 ...
PMID:Regulation of protein synthesis by insulin. 1654 79

Zinc (Zn) is an essential trace element that functions in cellular signaling. The mammalian target of rapamycin (mTOR) regulates the initiation of protein synthesis. The objective of this study was to determine whether Zn could stimulate protein phosphorylation in the mTOR pathway in vivo. Mice (C57BL/6J, n = 30) were fed Zn marginal diets (ZM, 5 mg/kg) for 4 weeks, followed by fasting (F) and/or refeeding with ZM or Zn supplemental (300 mg/kg, ZS) diets for 3 or 6 h. Plasma insulin was greater (P < 0.05) in refed animals as compared to F animals. Protein phosphorylation was detected using multiplex analysis and Western blotting. Multiplex analysis indicated greater (P < 0.05) p70 S6 kinase (p70S6K) and glycogen synthase kinase 3 (GSK-3 alpha/beta) phosphorylation in livers from 6-h refed ZS animals as compared to F animals. Western blots indicated increased (P < 0.05) Akt (Ser 473) phosphorylation in skeletal muscle from animals refed ZS diets for 3 and 6 h as compared to F animals. The ZS diet affected phosphorylation of GSK-3 (alpha/beta) in liver, as 3-h ZS refed animals had greater (P < 0.01) phosphorylation than F animals. These findings indicate that Zn may contribute to the initiation of protein synthesis as a signaling molecule in vivo.
 ...
PMID:Effect of supplemental dietary zinc on the mammalian target of rapamycin (mTOR) signaling pathway in skeletal muscle and liver from post-absorptive mice. 1784 32

The specificities of 65 compounds reported to be relatively specific inhibitors of protein kinases have been profiled against a panel of 70-80 protein kinases. On the basis of this information, the effects of compounds that we have studied in cells and other data in the literature, we recommend the use of the following small-molecule inhibitors: SB 203580/SB202190 and BIRB 0796 to be used in parallel to assess the physiological roles of p38 MAPK (mitogen-activated protein kinase) isoforms, PI-103 and wortmannin to be used in parallel to inhibit phosphatidylinositol (phosphoinositide) 3-kinases, PP1 or PP2 to be used in parallel with Src-I1 (Src inhibitor-1) to inhibit Src family members; PD 184352 or PD 0325901 to inhibit MKK1 (MAPK kinase-1) or MKK1 plus MKK5, Akt-I-1/2 to inhibit the activation of PKB (protein kinase B/Akt), rapamycin to inhibit TORC1 [mTOR (mammalian target of rapamycin)-raptor (regulatory associated protein of mTOR) complex], CT 99021 to inhibit GSK3 (glycogen synthase kinase 3), BI-D1870 and SL0101 or FMK (fluoromethylketone) to be used in parallel to inhibit RSK (ribosomal S6 kinase), D4476 to inhibit CK1 (casein kinase 1), VX680 to inhibit Aurora kinases, and roscovitine as a pan-CDK (cyclin-dependent kinase) inhibitor. We have also identified harmine as a potent and specific inhibitor of DYRK1A (dual-specificity tyrosine-phosphorylated and -regulated kinase 1A) in vitro. The results have further emphasized the need for considerable caution in using small-molecule inhibitors of protein kinases to assess the physiological roles of these enzymes. Despite being used widely, many of the compounds that we analysed were too non-specific for useful conclusions to be made, other than to exclude the involvement of particular protein kinases in cellular processes.
 ...
PMID:The selectivity of protein kinase inhibitors: a further update. 1785 Feb 14

Rictor is an essential component of mTOR (mammalian target of rapamycin) complex 2 (mTORC2), a kinase complex that phosphorylates Akt at Ser473 upon activation of phosphatidylinositol 3-kinase (PI-3 kinase). Since little is known about the role of either rictor or mTORC2 in PI-3 kinase-mediated physiological processes in adult animals, we generated muscle-specific rictor knockout mice. Muscle from male rictor knockout mice exhibited decreased insulin-stimulated glucose uptake, and the mice showed glucose intolerance. In muscle lacking rictor, the phosphorylation of Akt at Ser473 was reduced dramatically in response to insulin. Furthermore, insulin-stimulated phosphorylation of the Akt substrate AS160 at Thr642 was reduced in rictor knockout muscle, indicating a defect in insulin signaling to stimulate glucose transport. However, the phosphorylation of Akt at Thr308 was normal and sufficient to mediate the phosphorylation of glycogen synthase kinase 3 (GSK-3). Basal glycogen synthase activity in muscle lacking rictor was increased to that of insulin-stimulated controls. Consistent with this, we observed a decrease in basal levels of phosphorylated glycogen synthase at a GSK-3/protein phosphatase 1 (PP1)-regulated site in rictor knockout muscle. This change in glycogen synthase phosphorylation was associated with an increase in the catalytic activity of glycogen-associated PP1 but not increased GSK-3 inactivation. Thus, rictor in muscle tissue contributes to glucose homeostasis by positively regulating insulin-stimulated glucose uptake and negatively regulating basal glycogen synthase activity.
 ...
PMID:Muscle-specific deletion of rictor impairs insulin-stimulated glucose transport and enhances Basal glycogen synthase activity. 1796 79


1 2 3 4 Next >>