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)

The immunosuppressant, rapamycin, inhibits cell growth by interfering with the function of a novel kinase, termed mammalian target of rapamycin (mTOR). The putative catalytic domain of mTOR is similar to those of mammalian and yeast phosphatidylinositol (PI) 3-kinases. This study demonstrates that mTOR is a component of a cytokine-triggered protein kinase cascade leading to the phosphorylation of the eukaryotic initiation factor-4E (eIF-4E) binding protein, PHAS-1, in activated T lymphocytes. This event promotes G1 phase progression by stimulating eIF-4E-dependent translation initiation. A mutant YAC-1 T lymphoma cell line, which was selected for resistance to the growth-inhibitory action of rapamycin, was correspondingly resistant to the suppressive effect of this drug on PHAS-1 phosphorylation. In contrast, the PI 3-kinase inhibitor, wortmannin, reduced the phosphorylation of PHAS-1 in both rapamycin-sensitive and -resistant T cells. At similar drug concentrations (0.1-1 microM), wortmannin irreversibly inhibited the serine-specific autokinase activity of mTOR. The autokinase activity of mTOR was also sensitive to the structurally distinct PI 3-kinase inhibitor, LY294002, at concentrations (1-30 microM) nearly identical to those required for inhibition of the lipid kinase activity of the mammalian p85-p110 heterodimer. These studies indicate that the signaling functions of mTOR, and potentially those of other high molecular weight PI 3-kinase homologs, are directly affected by cellular treatment with wortmannin or LY294002.
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PMID:Direct inhibition of the signaling functions of the mammalian target of rapamycin by the phosphoinositide 3-kinase inhibitors, wortmannin and LY294002. 889 71

The role of the mammalian target of rapamycin (mTOR) was investigated in insulin responsive cell lines. mTOR was expressed at high levels in insulin responsive cell types and in 3T3-L1 cells mTOR expression levels increased dramatically as cells differentiated from fibroblasts into insulin responsive adipocytes. mTOR localized to membrane fractions in all cells tested and in 3T3-L1 adipocytes mTOR was specifically localized to microsomal membranes. Protein kinase activity directed towards mTOR was tightly associated with mTOR immunoprecipitates and this kinase activity was inhibited by FKBP12-rapamycin indicating it was due to an autokinase activity present in mTOR. The mTOR autokinase and the protein kinase activity of the p110 alpha isoform of PI 3-kinase shared several notable similarities; (a) both were maximally active in the presence of Mn2+ but also showed significant activity in the presence of Mg2+ (b) neither were inhibited by the presence of non-ionic detergent and (c) both were inhibited by wortmannin and LY294002, known inhibitors of the PI 3-kinase lipid kinase activity. These data taken together indicate the autokinase activity lay in the PI 3-kinase homology domain. In summary mTOR is a membrane anchored protein kinase that is active in conditions encountered in vivo and the fact it is highly expressed in insulin responsive cell types is consistent with a role in insulin signalling.
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PMID:Expression, enzyme activity, and subcellular localization of mammalian target of rapamycin in insulin-responsive cells. 943 72

Phosphatidylinositol (PI) 3-kinase is required for G1 to S phase cell cycle progression stimulated by a variety of growth factors and is implicated in the activation of several downstream effectors, including p70(S6K). However, the molecular mechanisms by which PI 3-kinase is engaged in activation of the cell cycle machinery are not well understood. Here we report that the expression of a dominant negative (DN) form of either the p110alpha catalytic or the p85 regulatory subunit of heterodimeric PI 3-kinase strongly inhibited epidermal growth factor (EGF)-induced upregulation of cyclin D1 protein in NIH 3T3(M17) fibroblasts. The PI 3-kinase inhibitors LY294002 and wortmannin completely abrogated increases in both mRNA and protein levels of cyclin D1 and phosphorylation of pRb, inducing G1 arrest in EGF-stimulated cells. By contrast, rapamycin, which potently suppressed p70(S6K) activity throughout the G1 phase, had little inhibitory effect, if any, on either of these events. PI 3-kinase, but not rapamycin-sensitive pathways, was also indispensable for upregulation of cyclin D1 mRNA and protein by other mitogens in NIH 3T3 (M17) cells and in wild-type NIH 3T3 cells as well. We also found that an enforced expression of wild-type p110 was sufficient to induce cyclin D1 protein expression in growth factor-deprived NIH 3T3(M17) cells. The p110 induction of cyclin D1 in quiescent cells was strongly inhibited by coexpression of either of the PI 3-kinase DN forms, and by LY294002, but was independent of the Ras-MEK-ERK pathway. Unlike mitogen stimulation, the p110 induction of cyclin D1 was sensitive to rapamycin. These results indicate that the catalytic activity of PI 3-kinase is necessary, and could also be sufficient, for upregulation of cyclin D1, with mTOR signaling being differentially required depending upon cellular conditions.
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PMID:Cyclin D1 expression mediated by phosphatidylinositol 3-kinase through mTOR-p70(S6K)-independent signaling in growth factor-stimulated NIH 3T3 fibroblasts. 989 Oct 68

Stem cell factor (SCF)/c-kit plays an important role in the regulation of hematopoiesis, melanogenesis, and spermatogenesis. In the testis, the SCF/c-kit system is believed to regulate germ cell proliferation, meiosis, and apoptosis. Studies with type A spermatogonia in vivo and in vitro have indicated that SCF induces DNA synthesis and proliferation. However, the signaling pathway for this function of SCF/c-kit has not been elucidated. We now demonstrate that SCF activates phosphoinositide 3-kinase (PI3-K) and p70 S6 kinase (p70S6K) and that rapamycin, a FRAP/mammalian target of rapamycin-dependent inhibitor of p70S6K, completely inhibited bromodeoxyuridine incorporation induced by SCF in primary cultures of spermatogonia. SCF induced cyclin D3 expression and phosphorylation of the retinoblastoma protein through a pathway that is sensitive to both wortmannin and rapamycin. Furthermore, AKT, but not protein kinase C-zeta, is used by SCF/c-kit/PI3-K to activate p70S6K. Dominant negative AKT-K179M completely abolished p70S6K phosphorylation induced by the constitutively active PI3-K catalytic subunit p110. Constitutively active v-AKT highly phosphorylated p70S6K, which was totally inhibited by rapamycin. Thus, SCF/c-kit uses a rapamycin-sensitive PI3-K/AKT/p70S6K/cyclin D3 pathway to promote spermatogonial cell proliferation.
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PMID:Stem cell factor/c-kit up-regulates cyclin D3 and promotes cell cycle progression via the phosphoinositide 3-kinase/p70 S6 kinase pathway in spermatogonia. 1084 22

To develop novel mechanism-based preventive approaches for lung cancer, we examined the effect of oral consumption of a human achievable dose of pomegranate fruit extract (PFE) on growth, progression, angiogenesis, and signaling pathways in two mouse lung tumor protocols. Benzo(a)pyrene [B(a)P] and N-nitroso-tris-chloroethylurea (NTCU) were used to induce lung tumors, and PFE was given in drinking water to A/J mice. Lung tumor yield was examined on the 84th day and 140 days after B(a)P dosing and 240 days after NTCU treatment. Mice treated with PFE and exposed to B(a)P and NTCU had statistically significant lower lung tumor multiplicities than mice treated with carcinogens only. Tumor reduction was 53.9% and 61.6% in the B(a)P + PFE group at 84 and 140 days, respectively, compared with the B(a)P group. The NTCU + PFE group had 65.9% tumor reduction compared with the NTCU group at 240 days. Immunoblot analysis and immunohistochemistry were used to determine effect on cell survival pathways and markers of cellular proliferation and angiogenesis. PFE treatment caused inhibition of (a) activation of nuclear factor-kappaB and IkappaBalpha kinase, (b) degradation and phosphorylation of IkappaBalpha, (c) phosphorylation of mitogen-activated protein kinases (extracellular signal-regulated kinase 1/2, c-Jun NH(2)-terminal kinase 1/2, and p38), (d) phosphatidylinositol 3-kinase (p85 and p110), (e) phosphorylation of Akt at Thr(308), (f) activation of mammalian target of rapamycin signaling, (g) phosphorylation of c-met, and (h) markers of cell proliferation (Ki-67 and proliferating cell nuclear antigen) and angiogenesis (inducible nitric oxide synthase, CD31, and vascular endothelial growth factor) in lungs of B(a)P- and NTCU-treated mice. Thus, our data show that PFE significantly inhibits lung tumorigenesis in A/J mice and merits investigation as a chemopreventive agent for human lung cancer.
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PMID:Oral consumption of pomegranate fruit extract inhibits growth and progression of primary lung tumors in mice. 1738 58

Phosphatidylinositol 3-kinase (PI3K) signalling plays a pivotal role in intracellular signal transduction pathways involved in cell growth, cellular transformation, and tumourigenesis. PI3K is overexpressed in many human cancers, including endometrial carcinomas, one of the most common female genital tract malignancies. Here, we used small interfering RNA (siRNA) targeted to PI3K p110-beta to determine whether inhibition of the beta isoform could be a potential therapeutic target for endometrial carcinoma. In this study, treatment of HEC-1B endometrial cancer cells with PI3K p110-beta-specific siRNA resulted in increased apoptosis and decreased tumour cell proliferation. Depletion of PI3K p110-beta decreased the protein levels of AKT1, AKT2, pAKT, and mTOR-downstream targets of PI3K. Knock-down of PI3K p110-beta by siRNA also induced decreased expression of cyclin E and Bcl-2, suggesting that PI3K p110-beta stimulates tumour growth, at least in part by regulating cyclin E and Bcl-2. Thus, our results indicate that siRNA-mediated gene silencing of PI3K p110-beta may be a useful therapeutic strategy for endometrial cancers overexpressing PI3K p110-beta.
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PMID:Targeted RNA interference of phosphatidylinositol 3-kinase p110-beta induces apoptosis and proliferation arrest in endometrial carcinoma cells. 1742 68

2-Deoxyglucose (2-DG), which has been shown to inhibit mammary carcinogenesis, was used as a metabolic probe to investigate effects of limiting energy availability (reduced cellular ATP) on patterns of proteins' phosphorylation that play a role in the development of cancer. Experiments were conducted using a human breast cancer cell line, MDA-MB-468, and 1-methyl-1-nitrosourea-induced rat model for mammary carcinogenesis. Under in vitro conditions in which cellular ATP concentration decreased rapidly with increasing 2-DG in a dose and time dependent manner, levels of phosphorylated mammalian target of rapamycin (P-mTOR) decreased in parallel to decreases in ATP concentration. Concomitantly, phosphorylation of two upstream regulators of mTOR, AMP-activated protein kinase (AMPK) and Akt/protein kinase B were increased and decreased, respectively, with increased levels of phosphorylated acetyl-CoA carboxylase as an indicator of AMPK activation. Levels of insulin like growth factor 1-receptor and phosphoinositide-3 kinase p110 alpha were also reduced. Similar effects were observed in mammary carcinomas in vivo at concentration of 0.03% (w/w) dietary 2-DG that inhibited carcinogenesis. In vitro, downregulation of mTOR was accompanied by decreases in phosphorylation of two of mTOR's targets, 70-kDa ribosomal protein S6 kinase and eukaryote initiation factor 4E binding protein 1. Glucose treatment reversed 2-DG effects. When cells were transfected with dominant-negative AMPK alpha 2, effects of 2-DG on mTOR and its downstream effectors were diminished, providing evidence of a link between AMPK and mTOR when energy availability was limited. This work indicates that AMPK, Akt, and mTOR are candidate targets for efforts to inhibit the carcinogenic process by limiting energy availability.
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PMID:Modulation of the activities of AMP-activated protein kinase, protein kinase B, and mammalian target of rapamycin by limiting energy availability with 2-deoxyglucose. 1824 80

Acquisition of a transformed phenotype involves deregulation of several signal transduction pathways contributing to unconstrained cell growth. Understanding the interplay of different cancer-related signaling pathways is important for development of efficacious multitargeted anticancer drugs. The small molecule 9-aminoacridine (9AA) and its derivative, the antimalaria drug quinacrine, have selective toxicity for tumor cells and can simultaneously suppress nuclear factor-kappaB (NF-kappaB) and activate p53 signaling. To investigate the mechanism underlying these drug activities, we used a combination of two-dimensional protein separation by gel electrophoresis and mass spectrometry to identify proteins whose expression is altered in tumor cells by 9AA treatment. We found that 9AA treatment results in selective downregulation of a specific catalytic subunit of the phosphoinositide 3-kinase (PI3K) family, p110 gamma. Further exploration of this observation demonstrated that the mechanism of action of 9AA involves inhibition of the prosurvival AKT/mammalian target of rapamycin (mTOR) pathway that lies downstream of PI3K. p110 gamma translation appears to be regulated by mTOR and feeds back to further modulate mTOR and AKT, thereby impacting the p53 and NF-kappaB pathways as well. These results reveal functional interplay among the PI3K/AKT/mTOR, p53 and NF-kappaB pathways that are frequently deregulated in cancer and suggest that their simultaneous targeting by a single small molecule such as 9AA could result in efficacious and selective killing of transformed cells.
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PMID:9-Aminoacridine-based anticancer drugs target the PI3K/AKT/mTOR, NF-kappaB and p53 pathways. 1913 16

The PI3K/Akt/mTOR signaling pathway is critical for cellular growth and survival in skeletal muscle, and is activated in response to growth factors such as insulin-like growth factor-I (IGF-I). We found that in C2C12 myoblasts, deficiency of PI3K p110 catalytic subunits or Akt isoforms had distinct effects on phosphorylation of mTOR and p70S6K. siRNA-mediated knockdown of PI3K p110alpha, p110beta, and simultaneous knockdown of p110alpha and p110beta resulted in increased basal and IGF-I-stimulated phosphorylation of mTOR S2448 and p70S6K T389; however, phosphorylation of S6 was reduced in p110beta-deficient cells, possibly due to reductions in total S6 protein. We found that IGF-I-stimulated Akt1 activity was enhanced in Akt2- or Akt3-deficient cells, and that knockdown of individual Akt isoforms increased mTOR/p70S6K activation in an isoform-specific fashion. Conversely, levels of IGF-I-stimulated p70S6K phosphorylation in cells simultaneously deficient in both Akt1 and Akt3 were increased beyond those seen with loss of any single Akt isoform, suggesting an alternate, Akt-independent mechanism that activates mTOR/p70S6K. Our results collectively suggest that mTOR/p70S6K is activated in a PI3K/Akt-dependent manner, but that in the absence of p110alpha or Akt, alternate pathway(s) may mediate activation of mTOR/p70S6K in C2C12 myoblasts.
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PMID:Effects of PI3K catalytic subunit and Akt isoform deficiency on mTOR and p70S6K activation in myoblasts. 1979 71

Fragile X syndrome, the most common form of inherited mental retardation and leading genetic cause of autism, is caused by transcriptional silencing of the Fmr1 gene. The fragile X mental retardation protein (FMRP), the gene product of Fmr1, is an RNA binding protein that negatively regulates translation in neurons. The Fmr1 knock-out mouse, a model of fragile X syndrome, exhibits cognitive deficits and exaggerated metabotropic glutamate receptor (mGluR)-dependent long-term depression at CA1 synapses. However, the molecular mechanisms that link loss of function of FMRP to aberrant synaptic plasticity remain unclear. The mammalian target of rapamycin (mTOR) signaling cascade controls initiation of cap-dependent translation and is under control of mGluRs. Here we show that mTOR phosphorylation and activity are elevated in hippocampus of juvenile Fmr1 knock-out mice by four functional readouts: (1) association of mTOR with regulatory associated protein of mTOR; (2) mTOR kinase activity; (3) phosphorylation of mTOR downstream targets S6 kinase and 4E-binding protein; and (4) formation of eukaryotic initiation factor complex 4F, a critical first step in cap-dependent translation. Consistent with this, mGluR long-term depression at CA1 synapses of FMRP-deficient mice is exaggerated and rapamycin insensitive. We further show that the p110 subunit of the upstream kinase phosphatidylinositol 3-kinase (PI3K) and its upstream activator PI3K enhancer PIKE, predicted targets of FMRP, are upregulated in knock-out mice. Elevated mTOR signaling may provide a functional link between overactivation of group I mGluRs and aberrant synaptic plasticity in the fragile X mouse, mechanisms relevant to impaired cognition in fragile X syndrome.
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PMID:Dysregulation of mTOR signaling in fragile X syndrome. 2050 79


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