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)

We have previously found that both mitogen-activated protein kinase (MAPK)- and Rho kinase (ROCK)-related signaling pathways are necessary for the induction of pulmonary artery smooth muscle cell (SMC) proliferation by serotonin (5-hydroxytryptamine [5-HT]). In the present study, we investigated the possible additional participation of a phosphatidylinositol 3-kinase (PI3K)/serine-threonine protein kinase B (Akt)/mammalian target of rapamycin (mTOR)/p70 ribosomal S6 kinase (S6K1) pathway in this growth response. We found transient activation of Akt (Ser473) and more prolonged activation of S6K1 by 5-HT. Inhibition of PI3K with Wortmannin and LY294002 completely blocked these activations, but not that of MAPK or the ROCK substrate myosin phosphatase targeting subunit. Similarly, inhibition of MAPK and ROCK failed to block the Akt activation. Inhibition of Akt with NL-71-101 and downregulation of Akt expression with Akt small interfering RNA blocked 5-HT-induced S6K1 phosphorylation. Wortmannin, LY294002, and NL-71-101 dose-dependently inhibited 5-HT-induced SMC proliferation. 5-HT stimulated mTOR phosphorylation and the mTOR inhibitor, rapamycin, blocked activations of S6K1 and S6 ribosomal protein, and inhibited 5-HT-induced SMC proliferation. Akt phosphorylation and cell proliferation were also blocked by the antioxidants, N-acetyl-l-cysteine, Ginko biloba 501, and tiron, the reduced nicotinamide adenine dinucleotide phosphate oxidase inhibitor, diphenyleneiodonium, and the 5-HT2 receptor antagonists ketanserin and mianserin, but not by the 5-HT serotonin transporter or 5-HT 1B/1D receptor antagonists. We conclude from these studies that a parallel PI3K- and reactive oxygen species-dependent Akt/mTOR/S6K1 pathway participates independently from MAPK and Rho/ROCK in the mitogenic effect of 5-HT on pulmonary artery SMCs. From these and other studies, we postulate that independent signaling pathways leading to 5-HT-induced SMC proliferation are initiated through multiple 5-HT receptors and serotonin transporter at the cell surface.
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PMID:Serotonin-induced growth of pulmonary artery smooth muscle requires activation of phosphatidylinositol 3-kinase/serine-threonine protein kinase B/mammalian target of rapamycin/p70 ribosomal S6 kinase 1. 1619 41

The p70 S6 ribosomal protein kinase 1 (S6K) is a substrate and effector of the mammalian target of rapamycin (mTOR). The mTOR/S6K pathway is implicated in cancer and metabolic disorders. To study the molecular regulation of S6K and identify specific inhibitors, availability of active recombinant S6K and robust enzyme assays are critically needed. To date, however, expression of active recombinant S6K has not been feasible as S6K activation requires a cascade of phosphorylation events. We have compared several engineered S6K enzymes. Expression of the Flag-S6KDeltaCT(T389E) in HEK293 cells resulted in a highly active S6K that was constitutively phosphorylated on T229 in the activation-loop (T-loop). The active enzyme was readily purified in large scale by anti-Flag affinity chromatography achieving a high purity. We developed a high capacity homogeneous time-resolved fluorescence resonance energy transfer. Lance assay for measurement of substrate phosphorylation and analysis of kinetic parameters. The Michaelis constant (Km) values of S6K for ATP and the Biotin-S6 substrate peptide were determined to be 21.4+/-0.29 and 0.9+/-0.48 microM, respectively. The Lance assay was further validated with a diverse panel of literature inhibitors, in which the PKC inhibitors staurosporine, Ro-318220, and the PKA inhibitor Balanol potently inhibited S6K. Dose-response and inhibition mechanism by these inhibitors were also studied. Our data provide a new simplified strategy to achieve rapid production of active S6K and demonstrate utility of the Lance assay for S6K enzyme screen in searching for specific inhibitors.
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PMID:Identification and characterization of a constitutively T-loop phosphorylated and active recombinant S6K1: expression, purification, and enzymatic studies in a high capacity non-radioactive TR-FRET Lance assay. 1621 57

The mammalian target of rapamycin (mTOR) is a kinase responsible for mitogen-induced cell proliferation/survival signaling. Its activation in response to mitogens leads to a cell-cycle progression from G1 to S phase. mTOR controls the activation of ribosomal protein translation and the initiation of cap-dependent translation. A role of mTOR signaling pathway dysregulation in tumourigenesis is postulated. mTOR and pathways upstream of this kinase were found to be frequently upregulated in neoplastic diseases. Therefore, it is also an attractive target for antitumour therapy. Several mTOR inhibitors were developed, including rapamycin and its analogues: CCI-779, RAD001 and AP23573. After promising phase I studies, their potential clinical significance is currently under evaluation in several phase II-III trials on patients with solid tumours and some hematological malignancies.
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PMID:The mammalian target of the rapamycin (mTOR) kinase pathway: its role in tumourigenesis and targeted antitumour therapy. 1621 58

Radiocontrast media can induce vascular endothelial cell apoptosis. Apoptotic damage to the vascular endothelium is an important mechanism in vascular disease. Several growth factors with anti-apoptotic effects may help protect the vascular endothelium from apoptosis. The present study evaluated whether the radiocontrast agent iopromide induces apoptosis in human umbilical vein endothelial cells and also whether angiopoietin-1 (Ang1) protects against iopromide-induced apoptosis through the p70 S6 kinase-dependent signaling pathway. Iopromide induced apoptosis in vascular endothelial cells in a dose-dependent manner. Ang1 reduced iopromide-induced apoptosis in a dose-dependent manner. Wortmannin and LY294002, phosphatidylinositol 3'-kinase inhibitors, decreased the Ang1-induced anti-apoptotic effect. Ang1 mediates the activation of mTOR/ribosomal protein p70 S6 kinase through phosphatidylinositol-3' kinase. Wortmannin and rapamycin, an inhibitor of mTOR, suppressed Ang1-induced p70 S6 kinase phosphorylation and partially inhibited the Ang1-induced anti-apoptotic effect. These results suggest that Ang1 may protect vascular endothelial cells from iopromide-induced apoptosis through phosphatidylinositol 3'-kinase and mTOR/S6 kinase. Pretreatment with Ang1 could help maintain normal vascular endothelial cell integrity before and during systemic radiocontrast administration.
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PMID:Angiopoietin-1 reduces iopromide-induced endothelial cell apoptosis through activation of phosphatidylinositol 3'-kinase/p70 S6 kinase. 1637 78

The present study examined the effects of an acute bout of treadmill exercise on signalling through the extracellular signal-regulated kinase (ERK)1/2 and mammalian target of rapamycin (mTOR) pathways to regulatory mechanisms involved in mRNA translation in mouse gastrocnemius muscle. Briefly, C57BL/6 male mice were run at 26 m min(-1) on a treadmill for periods of 10, 20 or 30 min, then the gastrocnemius was rapidly removed and analysed for phosphorylation and/or association of protein components of signalling pathways and mRNA translation regulatory mechanisms. Repression of global mRNA translation was suggested by disaggregation of polysomes into free ribosomes, which occurred by 10 min and was sustained throughout the time course. Exercise repressed the mTOR signalling pathway, as shown by dephosphorylation of the eukaryotic initiation factor (eIF)4E-binding protein-1 (4E-BP1), enhanced association of the regulatory-associated protein of mTOR with mTOR, and increased assembly of the tuberin-hamartin complex. In contrast, exercise caused no change in phosphorylation of either Akt/PKB or tuberin. Upstream of mTOR, exercise was associated with an increase in cAMP, protein kinase A activity, and AMP-activated protein kinase phosphorylation. Simultaneously, exercise caused a rapid and sustained activation of the MEK1/2-ERK1/2-p90RSK pathway, resulting in increased phosphorylation of downstream targets including eIF4E and the ribosomal protein (rp)S6 on S235/S236. Overall, the data are consistent with exercise-induced repression of mTOR signalling and global rates of mRNA translation, accompanied perhaps by up-regulated translation of selected mRNAs through regulatory mechanisms such as eIF4E and rpS6 phosphorylation, mediated by activation of the ERK1/2 pathway.
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PMID:Exercise-induced alterations in extracellular signal-regulated kinase 1/2 and mammalian target of rapamycin (mTOR) signalling to regulatory mechanisms of mRNA translation in mouse muscle. 1660 Sep 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.
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PMID:Regulation of protein synthesis by insulin. 1654 79

An early signaling event activated by amino acids and growth factors in many cell types is the phosphorylation of the mammalian target of rapamycin (mTOR; FRAP), which is functionally linked to ribosomal protein s6 kinase (p70(s6k)), a kinase that plays a critical regulatory role in the translation of mRNAs and protein synthesis. We previously showed that intestinal cell migration, the initial event in epithelial restitution, is enhanced by l-arginine (ARG). In this study, we used amino acids as prototypic activators of mTOR and ARG, IGF-1, or serum as recognized stimulators of intestinal cell migration. We found that 1) protein synthesis is required for intestinal cell migration, 2) mTOR/p70(s6k) pathway inhibitors (rapamycin, wortmannin, and intracellular Ca(2+) chelation) inhibit cell migration, 3) ARG activates migration and mTOR/p70(s6k) (but not ERK-2) in migrating enterocytes, and 4) immunocytochemistry reveals abundant p70(s6k) staining in cytoplasm, whereas phospho-p70(s6k) is virtually all intranuclear in resting cells but redistributes to the periphery on activation by ARG. We conclude that mTOR/p70(s6k) signaling is essential to intestinal cell migration, is activated by ARG, involves both nuclear and cytoplasmic events, and may play a role in intestinal repair.
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PMID:Role of mTOR signaling in intestinal cell migration. 1671 51

Peroxisome proliferator-activated receptor-gamma (PPARgamma), a member of the nuclear receptor superfamily, is activated by several compounds including the thiazolidinediones. In addition to being a target for diabetes, PPARgamma activation state has recently been shown to modulate beta-amyloid peptide (Abeta) production in cellular models relevant to Alzheimer's disease. Here, we report the effect of troglitazone, a thiazolidinedione, in cells expressing 4-repeat tau. A 24 h treatment with troglitazone significantly reduced phosphorylation of tau at Ser202 and Ser396/404, residues of early and later stages of neurofibrillary tangle accumulation in Alzheimer's disease and other neurodegenerative disorders. Under the same experimental conditions the level of tau did not change. In our cellular model, troglitazone appeared to enhance 3'-phosphoinositide-dependent protein kinase 1 (PDK1) nuclear translocation, resulting in a decrease in cytosolic phosphorylated 70 kDa ribosomal protein kinase (p70S6) and phosphorylated mammalian target of rapamycin (mTor). Furthermore, PPARgamma transcriptional activity did not appear to be responsible for decreased phosphorylation of tau. Thus, we believe that the thiazolidinedione regulates tau phosphorylation through a PPARgamma-dependent/independent mechanism involving an Akt/glycogen synthase kinase-3(GSK-3beta)-independent signalling cascade: PDK1/p70S6K/mTor.
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PMID:Troglitazone, a peroxisome proliferator-activated receptor-gamma agonist, decreases tau phosphorylation in CHOtau4R cells. 1678 14

We tested the hypothesis that phosphorylation of S6 ribosomal protein (S6RP), a downstream target of the PI3K/Akt/mTOR pathway, is a biomarker of antibody-mediated rejection (AMR) in heart allografts. Primary cultures of human aortic and microvascular endothelial cells (EC) were treated with anti-HLA class I and class II antibodies (Ab) and cell lysates were studied for phosphorylation of S6 ribosmal protein at Serine235/236 (p-S6RP). Treatment of cultured EC with anti-class I and class II Ab stimulated S6RP phosphorylation. Immunohistochemical techniques were used to detect the level of p-S6RP in endomyocardial biopsies (n = 131) from 46 heart transplant recipients and the results were correlated with histopathological diagnosis of rejection, C4d staining, production of posttransplant anti-HLA Ab and clinical outcome. Increased phosphorylation of S6RP in endomyocardial biopsies was significantly associated with the diagnosis of AMR (p < 0.0001). No significant association between acute cellular rejection (ACR) and p-S6RP was observed. C4d staining was positively associated with both AMR and p-S6RP. Posttransplant anti-HLA class II Ab production was also significantly associated with a positive p-S6RP status in cardiac biopsies. These results indicate that p-S6RP is a useful biomarker for the diagnosis of AMR.
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PMID:Phosphorylated S6 ribosomal protein: a novel biomarker of antibody-mediated rejection in heart allografts. 1682 56

Tuberous sclerosis complex (TSC) is caused by mutations in either the TSC1 or TSC2 gene. Both genes are generally considered to act as tumor suppressors that fulfill Knudson's "two-hit hypothesis" and that function within the phosphoinositide 3-kinase-Akt-mammalian target of rapamycin (mTOR) pathway. We previously generated Tsc1(+/-) mice that are predisposed to renal cysts, which develop into cystadenomas and renal cell carcinomas. Here, we identified somatic Tsc1 mutations (second hits) in approximately 80% of cystadenomas and renal cell carcinomas, but only 31.6% of cysts from Tsc1(+/-) mice (P < 0.0003), raising the possibility that haploinsufficiency for Tsc1 plays a role in cyst formation. Consistent with this proposal, many cysts showed little or no staining for phosphorylated mTOR (53%) and phosphorylated S6 ribosomal protein (37%), whereas >90% of cystadenomas and renal cell carcinomas showed strong staining for both markers (P < 0.0005). We also sought somatic mutations in renal lesions from Tsc1(+/-) Blm(-/-) mice that have a high frequency of somatic loss of heterozygosity, thereby facilitating the detection of second hits. We also found significantly less somatic mutations in cysts as compared with cystadenomas and renal cell carcinomas from these mice (P = 0.017). Our data indicate that although activation of the mTOR pathway is an important step in Tsc-associated renal tumorigenesis, it may not be the key initiating event in this process.
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PMID:Tsc1 haploinsufficiency without mammalian target of rapamycin activation is sufficient for renal cyst formation in Tsc1+/- mice. 1691 67


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