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)

We report here for the first time the detection of the ribosomal p70S6 kinase (p70S6K) in a hematopoietic cell, the neutrophil, and the stimulation of its enzymatic activity by granulocyte macrophage colony-stimulating factor (GM-CSF). GM-CSF modified the Vmax of the enzyme (from 7.2 to 20.5 pmol/min/mg) and induced a time- and dose-dependent phosphorylation on p70S6K residues Thr389 and Thr421/Ser424. The immunosuppressant macrolide rapamycin caused either a decrease in intensity of phospho-Thr389 bands in Western blots, or as a downshift in the relative mobility of phospho-Thr421/Ser424 bands (consistent with the loss of phosphate), but not both simultaneously. The immunosuppressant FK506 failed to inhibit p70S6K activation, but was able to rescue the rapamycin-induced downshift, pointing to a role for the mammalian target of rapamycin (mTOR) kinase. Rapamycin also caused an inhibition (IC50 0.2 nm) of the in vitro enzymatic activity of p70S6K. However, the inhibition of activity was not complete, but only a 40-50%, indicating that neutrophil p70S6K activity has a rapamycin-resistant component. This component was totally inhibited by pre-incubating the cells with the mitogen-activated protein kinase (MAPK) kinase (MEK) inhibitor PD-98059 prior to treatment with rapamycin. This indicated that a kinase from the MEK/MAPK pathway also plays a role in p70S6K activation. Thus, GM-CSF causes the dual activation of a rapamycin-resistant, MAPK-related kinase, that targets Thr421/Ser424 S6K phosphorylation, and a rapamycin-sensitive, mTOR-related kinase, that targets Thr389, both of which are needed in cooperation to achieve full activation of neutrophil p70S6K.
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PMID:Mechanism of ribosomal p70S6 kinase activation by granulocyte macrophage colony-stimulating factor in neutrophils: cooperation of a MEK-related, THR421/SER424 kinase and a rapamycin-sensitive, m-TOR-related THR389 kinase. 1274 Mar 86

Tumor suppressor genes evolved as negative effectors of mitogen and nutrient signaling pathways, such that mutations in these genes can lead to pathological states of growth. Tuberous sclerosis (TSC) is a potentially devastating disease associated with mutations in two tumor suppressor genes, TSC1 and 2, that function as a complex to suppress signaling in the mTOR/S6K/4E-BP pathway. However, the inhibitory target of TSC1/2 and the mechanism by which it acts are unknown. Here we provide evidence that TSC1/2 is a GAP for the small GTPase Rheb and that insulin-mediated Rheb activation is PI3K dependent. Moreover, Rheb overexpression induces S6K1 phosphorylation and inhibits PKB phosphorylation, as do loss-of-function mutations in TSC1/2, but contrary to earlier reports Rheb has no effect on MAPK phosphorylation. Finally, coexpression of a human TSC2 cDNA harboring a disease-associated point mutation in the GAP domain, failed to stimulate Rheb GTPase activity or block Rheb activation of S6K1.
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PMID:Insulin activation of Rheb, a mediator of mTOR/S6K/4E-BP signaling, is inhibited by TSC1 and 2. 1282 Sep 60

Under serum-free conditions, rapamycin, an inhibitor of mammalian target of rapamycin (mTOR), induces apoptosis of cells lacking functional p53. Cells expressing wild-type p53 or p21(Cip1)arrest in G1 and remain viable. In cells lacking functional p53, rapamycin or amino acid deprivation induces rapid and sustained activation of apoptosis signal-regulating kinase 1 (ASK1), c-Jun N-terminal kinase, and elevation of phosphorylated c-Jun that results in apoptosis. This stress response depends on expression of eukaryotic initiation factor 4E binding protein 1 and is suppressed by p21(Cip1) independent of cell cycle arrest. Rapamycin induces p21(Cip1) binding to ASK1, suppressing kinase activity and attenuating cellular stress. These results suggest that inhibition of mTOR triggers a potentially lethal response that is prevented only in cells expressing p21(Cip1).
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PMID:Sustained activation of the JNK cascade and rapamycin-induced apoptosis are suppressed by p53/p21(Cip1). 1282 Sep 63

The tuberous sclerosis complex (TSC) is a genetic disorder that is caused through mutations in either one of the two tumor suppressor genes, TSC1 and TSC2, that encode hamartin and tuberin, respectively. Interaction of hamartin with tuberin forms a heterodimer that inhibits signaling by the mammalian target of rapamycin to its downstream targets: eukaryotic initiation factor 4E-binding protein 1 (4E-BP1) and ribosomal protein S6 kinase 1 (S6K1). During mitogenic sufficiency, the phosphoinositide 3-kinase (PI3K)/Akt pathway phosphorylates tuberin on Ser-939 and Thr-1462 that inhibits the tumor suppressor function of the TSC complex. Here we show that tuberin-hamartin heterodimers block protein kinase C (PKC)/MAPK- and phosphatidic acid-mediated signaling toward mammalian target of rapamycin-dependent targets. We also show that two TSC2 mutants derived from TSC patients are defective in repressing phorbol 12-myristate 13-acetate-induced 4E-BP1 phosphorylation. PKC/MAPK signaling leads to phosphorylation of tuberin at sites that overlap with and are distinct from Akt phosphorylation sites. Phosphorylation of tuberin by phorbol 12-myristate 13-acetate was reduced by treatment of cells with either bisindolylmaleimide I or UO126, inhibitors of PKC and MAPK/MEK (MAPK/ERK kinase), respectively, but not by wortmannin (an inhibitor of PI3K). This work reveals that both PI3K-independent and -dependent mechanisms modulate tuberin phosphorylation in vivo.
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PMID:Inactivation of the tuberous sclerosis complex-1 and -2 gene products occurs by phosphoinositide 3-kinase/Akt-dependent and -independent phosphorylation of tuberin. 1286 26

The T cell costimulatory receptor 4-1BB enhances cell cycle progression and proliferation of CD8(+) T cells in both an IL-2-dependent and -independent manner. In these studies, 4-1BB costimulation was shown to increase cyclin D2, D3, and E expression, and concomitantly down-regulate the expression of the cyclin-dependent kinase inhibitor p27(kip1). 4-1BB increases cyclin D2 transcription via mitogen-activated/extracellular signal-regulated kinase-1/2 and LY294002-sensitive phosphatidylinositol 3-kinase (PI3K) signaling pathways. In addition, 4-1BB up-regulates cyclin D2 translation via PI3K/Akt/mammalian target of rapamycin (mTOR) pathways, presumably triggered by IL-2/IL-2 receptor ligation. The enhanced cyclin D2 and D3 expression initiates up-regulation of cyclin E expression and down-regulation of p27(kip1). Our results suggest a role for cyclin D2, D3, and E, and p27(kip1) proteins in the 4-1BB-mediated cell cycle progression of CD8(+) T cells in vivo.
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PMID:4-1BB enhances CD8+ T cell expansion by regulating cell cycle progression through changes in expression of cyclins D and E and cyclin-dependent kinase inhibitor p27kip1. 1288 87

Regulation of the PHAS-1-eukaryotic initiation factor-4E (eIF4E) complex is the rate-limiting step in the initiation of protein synthesis. This study characterized the upstream signaling pathways that mediate ANG II-dependent phosphorylation of PHAS-1 and eIF4E in vascular smooth muscle. ANG II-dependent PHAS-1 phosphorylation was maximal at 10 min (2.47 +/- 0.3 fold vs. control). This effect was completely blocked by the specific inhibitors of phosphatidylinositol 3-kinase (PI3-kinase, LY-294002), mammalian target of rapamycin, and extracellular signal-regulated kinase 1/2 (ERK1/2, U-0126) or by a recombinant adenovirus encoding dominant-negative Akt. PHAS-1 phosphorylation was followed by dissociation of eIF4E. Increased ANG II-induced eIF4E phosphorylation was observed at 45 min (2.63 +/- 0.5 fold vs. control), was maximal at 90 min (3.38 +/- 0.3 fold vs. control), and was sustained at 2 h. This effect was blocked by inhibitors of the ERK1/2 and p38 mitogen-activated protein (MAP) kinase pathways, but not by PI3-kinase inhibition, and was dependent on PKC, intracellular Ca2+, and tyrosine kinases. Downregulation of proline-rich tyrosine kinase 2 (PYK2) by antisense oligonucleotides led to a near-complete inhibition of PHAS-1 and eIF4E phosphorylation in response to ANG II. Therefore, PYK2 represents a proximal signaling intermediate that regulates ANG II-induced vascular smooth muscle cell protein synthesis via regulation of the PHAS-1-eIF4E complex.
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PMID:A role for PYK2 in ANG II-dependent regulation of the PHAS-1-eIF4E complex by multiple signaling cascades in vascular smooth muscle. 1289 Jun 45

The cAMP pathway activates p38-MAPKs in the FRTL-5 rat thyroid cell line, contributing to the increased expression of the Na+/I- symporter (NIS) mRNA. This study investigates the cAMP-dependent expression and transcriptional activity of the p38-MAPK substrate CCAAT/enhancer-binding protein-homologous protein (CHOP). CHOP is expressed in the rat thyroid gland and in confluent PCCL3 and FRTL-5 cells. In FRTL-5 cells, TSH withdrawal induced a rapid down-regulation of CHOP that could be prevented by forskolin (Fk). Moreover, TSH and Fk were able to reinduce CHOP expression. The use of pharmacological inhibitors indicated that cAMP-induced CHOP expression was dependent on protein kinase A (PKA), mammalian target of rapamycin pathway, and reactive oxygen species. Transfection of a CHOP trans- reporting system revealed strong stimulation of the transcriptional activity of CHOP by Fk, by chlorophenylthio-cAMP, and by the catalytic subunit of PKA. CHOP transcriptional activity was significantly reduced by the p38-MAPK inhibitor SB203580, by transfection of a dominant-negative variant of p38alpha-MAPK, or by mutation of two serine residues in CHOP targeted by p38-MAPKs. Finally, cAMP-induced NIS mRNA expression was higher in FRTL-5 cells stably transfected with CHOP cDNA than in control cells. Likewise, the activity of the NIS promoter was higher in cells overexpressing CHOP than in control cells. These findings suggest that the stimulation of CHOP expression and transcriptional activity by the cAMP pathway may contribute to the regulation of genes involved in thyroid cell differentiation.
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PMID:CCAAT/enhancer-binding protein-homologous protein expression and transcriptional activity are regulated by 3',5'-cyclic adenosine monophosphate in thyroid cells. 1290 53

The molecular mechanisms that govern cell movement are the subject of intense study, as they impact biologically and medically important processes such as leukocyte chemotaxis and angiogenesis, among others. We demonstrate that leukocyte chemotaxis is prevented by the macrolide immunosuppressant rapamycin, a specific inhibitor of the mammalian target of rapamycin (mTOR)/ribosomal p70-S6 kinase (p70S6K) pathway. Both neutrophil chemotaxis and chemokinesis elicited by granulocyte-macrophage colony-stimulating factor (GM-CSF) were strongly inhibited by rapamycin with an IC(50) of 0.3 nM. Inhibition, although at a higher dose, was also observed when the chemoattractant was interleukin-8. As for the mechanism, rapamycin targeted the increase of phosphorylation of p70S6K due to GM-CSF treatment, as demonstrated with specific anti-p70S6K immunoprecipitation and subsequent immunoblotting with anti-T(421)/S(424) antibodies. Rapamycin also inhibited GM-CSF-induced actin polymerization, a hallmark of leukocyte migration. The specificity of the effect of rapamycin was confirmed by the use of the structural analog FK506, which did not have a significant effect on chemotaxis but effectively rescued rapamycin-induced p70S6K inhibition. This was expected from a competitive effect of both molecules on FK506-binding proteins (FKBP). Additionally, GM-CSF-induced chemotaxis was completely (>90%) blocked by a combination of rapamycin and the MAPK kinase (MEK) inhibitor PD-98059. In summary, the results presented here indicate for the first time that rapamycin, at sub-nanomolar concentrations, inhibits GM-CSF-induced chemotaxis and chemokinesis. This serves to underscore the relevance of the mTOR/S6K pathway in neutrophil migration.
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PMID:Rapamycin inhibits GM-CSF-induced neutrophil migration. 1293 93

Glycogen synthase kinase 3 (GSK3) is inactivated by insulin and lithium and, like insulin, Li also activates glycogen synthase (GS) via inhibition of GSK3. Li also mimics insulin's ability to stimulate glucose transport (GT), an observation that has led to the suggestion that GSK3 may coordinate hormonal increases in GT and glycogen synthesis. Here we have used Li and SB-415286, a selective GSK3 inhibitor, to establish the importance of GSK3 in the hormonal activation of GT in terms of its effect on GS in L6 myotubes and 3T3-L1 adipocytes. Insulin, Li and SB-415286 all induced a significant inhibition of GSK3, which was associated with a marked dephosphorylation and activation of GS. In L6 myotubes, SB-415286 induced a much greater activation of GS (6.8-fold) compared to that elicited by insulin (4.2-fold) or Li (4-fold). In adipocytes, insulin, Li and SB-415286 all caused a comparable activation of GS despite a substantial differentiation-linked reduction in GSK3 expression ( approximately 85%) indicating that GSK3 remains an important determinant of GS activation in fat cells. Whilst Li and SB-415286 both inhibit GSK3 in muscle and fat cells, only Li stimulated GT. This increase in GT was not sensitive to inhibitors of PI3-kinase, MAP kinase or mTOR, but was suppressed by the p38 MAP kinase inhibitor, SB-203580. Consistent with this, phosphorylation of p38 MAP kinase induced by Li correlated with its stimulatory effect on GT. Our findings support a crucial role for GSK3 in the regulation of GS, but based on the differential effects of Li and SB-415286, it is unlikely that acute inhibition of GSK3 contributes towards the rapid stimulation of GT by insulin in muscle and fat cells.
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PMID:Use of lithium and SB-415286 to explore the role of glycogen synthase kinase-3 in the regulation of glucose transport and glycogen synthase. 1295 Feb 67

Activation of 4E-binding protein 1 (4E-BP1) by growth factors regulates protein synthesis in vascular smooth muscle cells. The interaction between G protein-coupled receptors and activated 4E-BP1 is unclear. We examined phosphadityl inositol (PI) 3-kinase in angiotensin II-induced 4E-BP1 phosphorylation in cultured rat vascular smooth muscle cells. Angiotensin II time and dose dependently stimulated phosphorylation of 4E-BP1 through the angiotensin AT(1) receptor. Pretreatment with wortmannin or 2-(4-Morpholinyl)-8-phenyl-4H-1-benzopyran-4-one (LY294002), a PI 3-kinase inhibitor, suppressed angiotensin II-induced phosphorylation, but a mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinases (ERK) kinase-1 (MEK-1) inhibitor, 2'-Amino-3'-methoxyflavone (PD98059), and a p38 MAPK inhibitor, 4-(4-Fluorophenyl)-2-(4-methylsulfinylphenyl)-5-(4-pyridyl)1H-imidazole (SB203580), had no effect. With regard to the involvement of mammalian target of rapamycin (mTOR) and p70 S6 kinase, angiotensin II-induced phosphorylation was abolished by pretreatment with rapamycin, but not by tosylphenylalanine chloromethyl ketone or tosyllysine chloromethyl ketone. Ca(2+) was involved, since intracellular Ca(2+) chelation inhibited angiotensin II-induced phosphorylation while a Ca(2+) ionophore, A23187, stimulated phosphorylation. Thus, angiotensin II induces the phosphorylation of 4E-BP1 via the PI 3-kinase/mTOR pathway, but not via ERK or p70 S6 kinase.
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PMID:Phosphatidylinositol 3-kinase in angiotensin II-induced hypertrophy of vascular smooth muscle cells. 1455 83


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