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 protein kinase mammalian target of rapamycin (mTOR) is well established as a key regulator of skeletal muscle size. In this study, we determined that the stress responsive gene REDD2 (regulated in development and DNA damage responses 2) is a negative regulator of mTOR signaling and is expressed predominantly in skeletal muscle. Overexpression of REDD2 in muscle cells significantly inhibited basal mTOR signaling and diminished the response of mTOR to leucine addition or mechanical stretch. The inhibitory function of REDD2 on mTOR signaling seems to be mediated downstream or independent of Akt signaling and upstream of Rheb (Ras homolog enriched in brain). Knock down of tuberous sclerosis complex 2 (TSC2) using small interfering (si)RNA potently activated mTOR signaling and was sufficient to rescue REDD2 inhibition of mTOR activity, suggesting that REDD2 functions by modulating TSC2 function. Immunoprecipitation assays demonstrated that REDD2 does not directly interact with either TSC1 or TSC2. However, we found that REDD2 forms a complex with 14-3-3 protein and that increasing expression of REDD2 acts to competitively dissociate TSC2 from 14-3-3 and inhibits mTOR signaling. These findings demonstrate that REDD2 is a skeletal muscle specific inhibitory modulator of mTOR signaling and identify TSC2 and 14-3-3 as key molecular links between REDD2 and mTOR function.
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PMID:REDD2 is enriched in skeletal muscle and inhibits mTOR signaling in response to leucine and stretch. 1912 61

Akt/PKB (protein kinase B) both regulates and is regulated by the TSC (tuberous sclerosis complex) 1-TSC2 complex. Downstream of PI3K (phosphoinositide 3-kinase), Akt phosphorylates TSC2 directly on multiple sites. Although the molecular mechanism is not well understood, these phosphorylation events relieve the inhibitory effects of the TSC1-TSC2 complex on Rheb and mTORC1 [mTOR (mammalian target of rapamycin) complex] 1, thereby activating mTORC1 in response to growth factors. Through negative-feedback mechanisms, mTORC1 activity inhibits growth factor stimulation of PI3K. This is particularly evident in cells and tumours lacking the TSC1-TSC2 complex, where Akt signalling is severely attenuated due, at least in part, to constitutive activation of mTORC1. An additional level of complexity in the relationship between Akt and the TSC1-TSC2 complex has recently been uncovered. The growth-factor-stimulated kinase activity of mTORC2 [also known as the mTOR-rictor (rapamycin-insensitive companion of mTOR) complex], which normally enhances Akt signalling by phosphorylating its hydrophobic motif (Ser(473)), was found to be defective in cells lacking the TSC1-TSC2 complex. This effect on mTORC2 can be separated from the inhibitory effects of the TSC1-TSC2 complex on Rheb and mTORC1. The present review discusses our current understanding of the increasingly complex functional interactions between Akt, the TSC1-TSC2 complex and mTOR, which are fundamentally important players in a large variety of human diseases.
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PMID:A complex interplay between Akt, TSC2 and the two mTOR complexes. 1914 35

The signalling function of mTOR complex 1 is activated by Rheb-GTP, which controls the catalytic competence of the mTOR (mammalian target of rapamycin) kinase domain by an incompletely understood mechanism. Rheb can bind directly to the mTOR kinase domain, and association with inactive nucleotide-deficient Rheb mutants traps mTOR in a catalytically inactive state. Nevertheless, Rheb-GTP targets other than mTOR, such as FKBP38 (FK506-binding protein 38) and/or PLD1 (phospholipase D(1)), may also contribute to mTOR activation. Once activated, the mTOR catalytic domain phosphorylates substrates only when they are bound to raptor (regulatory associated protein of mTOR), a separate polypeptide within the complex. The mechanism of insulin/nutrient stimulation of mTOR complex 1 signalling, in addition to Rheb-GTP activation of the mTOR catalytic function, also involves a stable modification of the configuration of mTORC1 (mTOR complex 1) that increases access of substrates to their binding site on the raptor polypeptide. The mechanism underlying this second step in the activation of mTORC1 is unknown.
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PMID:Activation of mTORC1 in two steps: Rheb-GTP activation of catalytic function and increased binding of substrates to raptor. 1914 36

Failure in the regulation of mTOR (mammalian target of rapamycin) appears to be critical to the pathogenesis of the inherited disorder tuberous sclerosis and the related lung disease LAM (lymphangioleiomyomatosis). Both diseases are caused by mutations of TSC1 or TSC2 (TSC is tuberous sclerosis complex) that impair GAP (GTPase-activating protein) activity of the TSC1-TSC2 complex for Rheb, leading to inappropriate activity of signalling downstream of mTORC1 (mTOR complex 1). mTOR inhibitors are already used in a variety of clinical settings including as immunosuppressants, anticancer agents and antiproliferative agents in drug-eluting coronary artery stents. They also represent candidate therapies directed to the underlying molecular pathology in tuberous sclerosis and LAM. Phase I/II clinical trials of the mTORC1 inhibitor rapamycin have demonstrated reduction in size of tuberous-sclerosis- and LAM-associated renal tumours (angiomyolipomas) and some evidence for reversible improvement in lung function in patients with LAM. A case series of tuberous-sclerosis-associated brain tumours were also reported to shrink during rapamycin therapy. An important, although variable, feature of the tuberous sclerosis phenotype is learning difficulty. Recent studies in mouse models carrying heterozygous Tsc2 mutations demonstrated improvement in memory and learning deficits following treatment with rapamycin. These promising pre-clinical and early human trials are being followed by larger-scale randomized control trials of mTOR inhibitors for treatment of renal, lung and brain manifestations of TSC1- and TSC2-associated disease.
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PMID:Therapeutic targeting of mTOR in tuberous sclerosis. 1914 43

Tuberous sclerosis complex 2 (TSC2), whose gene is frequently mutated in tuberous sclerosis, increases the guanosine triphosphatase (GTPase) activity of the small heterotrimeric GTP-binding protein (G protein) Rheb, thus resulting in the decreased activity of the mammalian target of rapamycin (mTOR), the master regulator of cell growth. Here, we describe the development of a nuclear magnetic resonance (NMR)-based, quantitative, real-time assay to explore the molecular mechanism of the intrinsic and TSC2-catalyzed GTPase activity of Rheb. We confirmed that TSC2 accelerated GTP hydrolysis by Rheb 50-fold through an "asparagine-thumb" mechanism to substitute for the nonfunctional "catalytic" glutamine of Rheb and we determined that catalysis was enthalpy driven. Most, but not all, of the disease-associated GTPase-activating protein (GAP) domain mutants of TSC2 that we examined affected its enzymatic activity. This method can now be applied to study the function and regulation of other GTPases.
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PMID:Characterization of the intrinsic and TSC2-GAP-regulated GTPase activity of Rheb by real-time NMR. 1917 17

Astrocytes in the CNS respond to tissue damage by becoming reactive. They migrate, undergo hypertrophy, and form a glial scar that inhibits axon regeneration. Therefore, limiting astrocytic responses represents a potential therapeutic strategy to improve functional recovery. It was recently shown that the epidermal growth factor (EGF) receptor is upregulated in astrocytes after injury and promotes their transformation into reactive astrocytes. Furthermore, EGF receptor inhibitors were shown to enhance axon regeneration in the injured optic nerve and promote recovery after spinal cord injury. However, the signaling pathways involved were not elucidated. Here we show that in cultures of adult spinal cord astrocytes EGF activates the mTOR pathway, a key regulator of astrocyte physiology. This occurs through Akt-mediated phosphorylation of the GTPase-activating protein Tuberin, which inhibits Tuberin's ability to inactivate the small GTPase Rheb. Indeed, we found that Rheb is required for EGF-dependent mTOR activation in spinal cord astrocytes, whereas the Ras-MAP kinase pathway does not appear to be involved. Moreover, astrocyte growth and EGF-dependent chemoattraction were inhibited by the mTOR-selective drug rapamycin. We also detected elevated levels of activated EGF receptor and mTOR signaling in reactive astrocytes in vivo in an ischemic model of spinal cord injury. Furthermore, increased Rheb expression likely contributes to mTOR activation in the injured spinal cord. Interestingly, injured rats treated with rapamycin showed reduced signs of reactive gliosis, suggesting that rapamycin could be used to harness astrocytic responses in the damaged nervous system to promote an environment more permissive to axon regeneration.
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PMID:The Rheb-mTOR pathway is upregulated in reactive astrocytes of the injured spinal cord. 1917 18

Rapamycin and its derivatives represent a unique set of pharmaceutical agents being employed across a broad range of therapeutic indications including organ transplantation, cardiovascular disease, the treatment of harmartomas, and cancer. In cancer this family of drugs is unique as it exploits tumor-associated changes in cell metabolism. mTOR complex 1 (mTORC1), a protein kinase complex, is the major target of rapamycin, and is a key element of evolutionarily conserved pathways that regulate cellular metabolism in response to environmental nutrients and intracellular energy status. Upstream mTOR regulatory proteins -- the TSC tumor suppressor, the Rheb proto-oncogene, the hVps34 phophatidylinositol kinase, and the Rag GTPases -- determine tumor growth, metabolism, and apoptosis susceptibility. Novel compounds that target mTOR and PI3K enzymes may further enhance the efficacy in inhibiting this pathway in a number of human pathologies, particularly cancer.
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PMID:Tubers and tumors: rapamycin therapy for benign and malignant tumors. 1923 73

The mammalian target of rapamycin (mTOR) pathway is implicated in a number of human diseases, but the pathway details are not fully understood. Here we elucidate the interactions between various proteins involved in mTOR complex 1 (mTORC1). An in vitro mTORC1 kinase assay approach was used to probe the role of the mTORC1 component Raptor and revealed that certain Raptor mutations disrupt binding to eukaryotic initiation factor 4E-binding protein 1 (4E-BP1) and prevent its subsequent phosphorylation by mTOR. Interestingly, we show that a point mutation in the highly conserved Raptor RNC domain still allows binding to mTOR but prevents Raptor association and mTOR-dependent phosphorylation of 4E-BP1, indicating that this Raptor domain facilitates substrate recognition by mTORC1. This Raptor RNC domain mutant also dominantly inhibits mTORC1 signalling to 4E-BP1, S6K1 and HIF1alpha in vivo. We further characterise the functions of the mTORC1 signalling (TOS) and RAIP motifs of 4E-BP1, which are involved in substrate recognition by Raptor and phosphorylation by mTORC1. We show that an mTOR mutant, L1460P, responds to insulin even in nutrient-deprived conditions and is resistant to inhibition by inactive RagB-RagC heterodimers that mimic nutrient withdrawal suggesting that this region of mTOR is involved in sensing the permissive amino acid input. We found that FKBP38 inhibits mTOR(L1460P), while the mTOR(E2419K) kinase domain mutant was resistant to FKBP38 inhibition. Finally, we show that activation of mTORC1 by both Rheb and RhebL1 is impaired by FKBP38. Our work demonstrates the value of an in vitro mTORC1 kinase assay to characterise cell signalling components of mTORC1 involved in recognition and phosphotransfer to mTORC1 substrates.
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PMID:Mammalian target of rapamycin complex 1-mediated phosphorylation of eukaryotic initiation factor 4E-binding protein 1 requires multiple protein-protein interactions for substrate recognition. 1927 48

Rheb G-protein plays critical roles in the TSC/Rheb/mTOR signaling pathway by activating mTORC1. The activation of mTORC1 by Rheb can be faithfully reproduced in vitro by using mTORC1 immunoprecipitated by the use of anti-raptor antibody from mammalian cells starved for nutrients. The low in vitro kinase activity against 4E-BP1 of this mTORC1 preparation is dramatically increased by the addition of recombinant Rheb. On the other hand, the addition of Rheb does not activate mTORC2 immunoprecipitated from mammalian cells by the use of anti-rictor antibody. The activation of mTORC1 is specific to Rheb, because other G-proteins such as KRas, RalA/B, and Cdc42 did not activate mTORC1. Both Rheb1 and Rheb2 activate mTORC1. In addition, the activation is dependent on the presence of bound GTP. We also find that the effector domain of Rheb is required for the mTORC1 activation. FKBP38, a recently proposed mediator of Rheb action, appears not to be involved in the Rheb-dependent activation of mTORC1 in vitro, because the preparation of mTORC1 that is devoid of FKBP38 is still activated by Rheb. The addition of Rheb results in a significant increase of binding of the substrate protein 4E-BP1 to mTORC1. PRAS40, a TOR signaling (TOS) motif-containing protein that competes with the binding of 4EBP1 to mTORC1, inhibits Rheb-induced activation of mTORC1. A preparation of mTORC1 that is devoid of raptor is not activated by Rheb. Rheb does not induce autophosphorylation of mTOR. These results suggest that Rheb induces alteration in the binding of 4E-BP1 with mTORC1 to regulate mTORC1 activation.
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PMID:Specific activation of mTORC1 by Rheb G-protein in vitro involves enhanced recruitment of its substrate protein. 1929 11

Phenethyl isothiocyanate (PEITC) is a promising cancer chemopreventive agent but the mechanism of its anticancer effect is not fully understood. We now show, for the first time, that PEITC treatment triggers Atg5-dependent autophagic and apoptotic cell death in human prostate cancer cells. Exposure of PC-3 (androgen independent, p53 null) and LNCaP (androgen responsive, wild-type p53) human prostate cancer cells to PEITC resulted in several specific features characteristic of autophagy, including appearance of membranous vacuoles, formation of acidic vesicular organelles, and cleavage and recruitment of microtubule-associated protein 1 light chain 3 (LC3) to autophagosomes. A normal human prostate epithelial cell line (PrEC) was markedly more resistant toward PEITC-mediated cleavage and recruitment of LC3 compared with prostate cancer cells. Although PEITC treatment suppressed activating phosphorylations of Akt and mammalian target of rapamycin (mTOR), which are implicated in regulation of autophagy by different stimuli, processing and recruitment of LC3 was only partially/marginally reversed by ectopic expression of constitutively active Akt or overexpression of mTOR-positive regulator Rheb. The PEITC-mediated apoptotic DNA fragmentation was significantly attenuated in the presence of a pharmacologic inhibitor of autophagy (3-methyl adenine). Transient transfection of LNCaP and PC-3 cells with Atg5-specific small interfering RNA conferred significant protection against PEITC-mediated autophagy as well as apoptotic DNA fragmentation. A xenograft model using PC-3 cells and Caenorhabditis elegans expressing a lgg-1:GFP fusion protein provided evidence for occurrence of PEITC-induced autophagy in vivo. In conclusion, the present study indicates that Atg5 plays an important role in regulation of PEITC-induced autophagic and apoptotic cell death.
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PMID:Atg5 regulates phenethyl isothiocyanate-induced autophagic and apoptotic cell death in human prostate cancer cells. 1933 71


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