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Query: UNIPROT:P42345 (mTOR)
 26,049 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The mammalian target of rapamycin (mTOR) integrates nutrient and mitogen signals to regulate cell growth (increased cell mass and cell size) and cell division. The immunosuppressive drug rapamycin inhibits cell cycle progression via inhibition of mTOR; however, the signaling pathways by which mTOR regulates cell cycle progression have remained poorly defined. Here we demonstrate that restoration of mTOR signaling (by using a rapamycin-resistant mutant of mTOR) rescues rapamycin-inhibited G(1)-phase progression, and restoration of signaling along the mTOR-dependent S6K1 or 4E-BP1/eukaryotic translation initiation factor 4E (eIF4E) pathways provides partial rescue. Furthermore, interfering RNA-mediated reduction of S6K1 expression or overexpression of mTOR-insensitive 4E-BP1 isoforms that block eIF4E activity inhibit G(1)-phase progression individually and additively. Thus, the activities of both the S6K1 and 4E-BP1/eIF4E pathways are required for and independently mediate mTOR-dependent G(1)-phase progression. In addition, overexpression of constitutively active mutants of S6K1 or wild-type eIF4E accelerates serum-stimulated G(1)-phase progression, and stable expression of wild-type S6K1 confers a proliferative advantage in low-serum-containing media, suggesting that the activity of each of these pathways is limiting for cell proliferation. These data demonstrate that, as for the regulation of cell growth and cell size, the S6K1 and 4E-BP1/eIF4E pathways each represent critical mediators of mTOR-dependent cell cycle control.
Mol Cell Biol 2004 Jan
PMID:mTOR controls cell cycle progression through its cell growth effectors S6K1 and 4E-BP1/eukaryotic translation initiation factor 4E. 1467 56

Arsenite is ubiquitous in the environment, particularly in the form of contaminated water. Although this metal is a known human carcinogen, its exact mechanism of action remains unclear. P70S6K1 phosphorylates the ribosomal 40S protein leading to increased protein translation, and is an important regulator of cell growth and proliferation. Hypoxia inducible factor-1 (HIF-1) is a basic helix-loop-helix transcription factor composed of two subunits, HIF-1alpha and HIF-1beta. HIF-1 activates the transcription of a number of genes that mediate angiogenesis and tumor formation. In this study we demonstrated that arsenite treatment increased levels of p70S6K1 phosphorylation and p70S6K1 activity in a PI3K and mTOR sensitive manner. We have also shown that arsenite specifically induces HIF-1alpha, but not HIF-1beta, protein levels in prostate cancer cells in a mTOR-dependent manner.
Mol Cell Biochem 2004 Jan
PMID:Arsenite induces p70S6K1 activation and HIF-1alpha expression in prostate cancer cells. 1497 42

The genes encoding microtubule-associated protein 2 (MAP2), and the alpha subunit of calcium/calmodulin-dependent protein kinase II (alphaCaMKII), are members of a small number of genes whose expression is increased in hippocampal neurones during the intermediate phase of long-term potentiation (LTP)-a phase dependent on mRNA translation but not on gene transcription. However, the intracellular signalling pathways which mediate these increases in expression are largely unknown. Organotypic slice cultures of rat hippocampus were exposed to either forskolin (to elevate cAMP levels), A23187 (to increase intracellular Ca(2+) levels) or the corresponding vehicle. The levels of immunoreactive (ir-) MAP2 were increased 4 h after forskolin treatment, but were unaffected by A23187 treatment. Conversely, the levels of ir-alphaCaMKII were increased 4 h after A23187 treatment, but were unaffected by forskolin. The regulation of the expression of these proteins was the same in the CA3 region as in the CA1 and dentate gyrus of the hippocampus. While rapamycin reduced the basal levels of ir-MAP2, it did not affect the ability of either forskolin or A23187 to enhance ir-MAP2 or ir-alphaCaMKII levels. These results suggest that cAMP and Ca(2+) differentially modulate the expression of these two plasticity-related genes, and that translational enhancement via the mammalian target of rapamycin kinase is not involved in these effects.
Brain Res Mol Brain Res 2004 Mar 17
PMID:Differential regulation of MAP2 and alphaCamKII expression in hippocampal neurones by forskolin and calcium ionophore treatment. 1499 11

Amino acids, especially branched-chain amino acids such as l-Leucine, have been revealed to regulate activation of p70 S6 kinase and phosphorylation of 4E-BP1 through mTOR signaling pathway. In this study, we showed that a cationic amino acid, l-Arginine, also activated this signaling pathway in a rapamycin-sensitive manner in rat intestinal epithelial cells, and this l-Arginine-induced amino acid signal transduction involved the cationic amino acid transport system. The manner of l-Arginine- and l-Leucine-induced activation of p70 S6 kinase depended on the stimulation time and the concentration of each amino acid, which suggested that the mechanism of this amino acid signal acceptance might be saturable. l-Arginine and l-Leucine induced activation of p70 S6 kinase and phosphorylation of 4E-BP1 in a rapamycin-sensitive manner, which suggested the involvement of mTOR signaling pathway in these effects. l-Arginine-induced activation of p70 S6 kinase was inhibited by NG-Methyl-L-Arginine (NMMA) and L-N5-(1-Iminoethyl) Ornithine (NIO), inhibitors of nitric oxide synthase (NOS) which also block cationic amino acid transporters, system y(+). However, l-Leucine-induced activation of p70 S6 kinase was not affected with treatment of NOS inhibitors. In conclusion, l-Arginine regulates p70 S6 kinase activity and phosphorylation of 4E-BP1 through mTOR signaling pathway, which involves system y(+), cationic amino acid transporters.
Int J Mol Med 2004 Apr
PMID:Arginine and Leucine regulate p70 S6 kinase and 4E-BP1 in intestinal epithelial cells. 1501 Aug 53

Growth factors and hormones activate global and selective protein translation by phosphorylation and therefore activation of p70 S6 kinase through a wortmannin-sensitive phosphoinositide-3 kinase (PI-3K) antiapoptotic pathway and a rapamycin-sensitive signalling pathway of mTOR. Here we demonstrate that the phosphorylation of 40S ribosomal protein S6, a physiological substrate p70 S6 kinase, was highly increased by growth-stimulation of the cytolytic T cells (CTLL2) with interleukin 2 (IL2), which was accompanied with the increased phosphorylation of p70 S6K. The activity of p70 S6K and phosphorylation of the S6 protein was completely blocked by rapamycin and significantly decreased upon treatment of the cells with wortmannin, indicating an involvement of the PI-3K pathway in concert with the signalling pathway of mTOR in IL2-dependent phos-phorylation of ribosomal protein S6. The phosphorylation and activity of PKB/Akt in IL2-stimulated CTLL2 cells were rapamycin-insensitive and reduced upon wortmannin treatment of the cells, confirming a requirement for PI-3K for Akt activity. The data support the hypothesis that Akt may act downstream to PI-3K and upstream to mTOR in an IL2-mediated signal transduction pathway that controls phosphorylation of the regulatory protein S6 in CTLL2 cells.
Int J Mol Med 2004 Apr
PMID:IL2-dependent phosphorylation of 40S ribosomal protein S6 is controlled by PI-3K/mTOR signalling in CTLL2 cells. 1501 Aug 63

Eukaryotic elongation factor 2 (eEF2) kinase is an unusual calcium- and calmodulin-dependent protein kinase that is regulated by insulin through the rapamycin-sensitive mTOR pathway. Here we show that insulin decreases the ability of eEF2 kinase to bind calmodulin in a rapamycin-sensitive manner. We identify a novel phosphorylation site in eEF2 kinase (Ser78) that is located immediately next to its calmodulin-binding motif. Phosphorylation of this site is increased by insulin in a rapamycin-sensitive fashion. Regulation of the phosphorylation of Ser78 also requires amino acids and the protein kinase phosphoinositide-dependent kinase 1. Mutation of this site to alanine strongly attenuates the effects of insulin and rapamycin both on the binding of calmodulin to eEF2 kinase and on eEF2 kinase activity. Phosphorylation of Ser78 is thus likely to link insulin and mTOR signaling to the control of eEF2 phosphorylation and chain elongation. This site is not a target for known kinases in the mTOR pathway, e.g., the S6 kinases, implying that it is phosphorylated by a novel mTOR-linked protein kinase that serves to couple hormones and amino acids to the control of translation elongation. eEF2 kinase is thus a target for mTOR signaling independently of previously known downstream components of the pathway.
Mol Cell Biol 2004 Apr
PMID:A novel mTOR-regulated phosphorylation site in elongation factor 2 kinase modulates the activity of the kinase and its binding to calmodulin. 1502 86

Neointima formation, the leading cause of restenosis, is caused by proliferation of coronary artery smooth muscle cells (CASMCs) and is associated with infiltration by monocytes. Rapamycin inhibits neointima formation after stent implantation in humans. It reduces proliferation by its effects on mammalian target of rapamycin (mTOR) kinase. In this study, we investigated the expression of mTOR in human neointima and the effect of rapamycin on global transcriptional events controlling CASMC phenotype. In neointimal CASMCs, mTOR exhibited increased phosphorylation and was translocated to the nucleus compared with control. Comparative gene expression analysis of CASMCs treated with rapamycin (100 ng/ml) revealed down-regulation of the transcription factor E2F-1, a key regulator of G(1)/S-phase entry, and of various retinoblastoma protein/E2F-1-regulated genes. In addition, we found changes in the expression of genes associated with replication, apoptosis, and extracellular matrix formation. Furthermore, rapamycin decreased the gene expression of endothelial monocyte-activating polypeptide-II (EMAP-II). This decrease of EMAP-II expression was reflected in a reduced adhesiveness of CASMCs for monocytic cells. Addition of EMAP-II counteracted the antiadhesive effect of rapamycin. Therefore, EMAP-II may comprise a mechanism of rapamycin-mediated reduction of the proinflammatory activation of CASMCs. The effects reported here of rapamycin on the down-regulation of genes involved in cell cycle progression, apoptosis, proliferation, and extracellular matrix formation in CASMCs provide an explanation of how rapamycin reduces CASMC proliferation. In addition, rapamycin may contribute to a reduction of inflammatory responses by reducing the adhesiveness of CASMC, a mechanism suggested to be mediated by the production and release of EMAP II.
Mol Pharmacol 2004 Apr
PMID:Rapamycin effects transcriptional programs in smooth muscle cells controlling proliferative and inflammatory properties. 1504 17

Activation of 40S ribosomal protein S6 kinases (S6Ks) is mediated by anabolic signals triggered by hormones, growth factors, and nutrients. Stimulation by any of these agents is inhibited by the bacterial macrolide rapamycin, which binds to and inactivates the mammalian target of rapamycin, an S6K kinase. In mammals, two genes encoding homologous S6Ks, S6K1 and S6K2, have been identified. Here we show that mice deficient for S6K1 or S6K2 are born at the expected Mendelian ratio. Compared to wild-type mice, S6K1(-/-) mice are significantly smaller, whereas S6K2(-/-) mice tend to be slightly larger. However, mice lacking both genes showed a sharp reduction in viability due to perinatal lethality. Analysis of S6 phosphorylation in the cytoplasm and nucleoli of cells derived from the distinct S6K genotypes suggests that both kinases are required for full S6 phosphorylation but that S6K2 may be more prevalent in contributing to this response. Despite the impairment of S6 phosphorylation in cells from S6K1(-/-)/S6K2(-/-) mice, cell cycle progression and the translation of 5'-terminal oligopyrimidine mRNAs were still modulated by mitogens in a rapamycin-dependent manner. Thus, the absence of S6K1 and S6K2 profoundly impairs animal viability but does not seem to affect the proliferative responses of these cell types. Unexpectedly, in S6K1(-/-)/S6K2(-/-) cells, S6 phosphorylation persisted at serines 235 and 236, the first two sites phosphorylated in response to mitogens. In these cells, as well as in rapamycin-treated wild-type, S6K1(-/-), and S6K2(-/-) cells, this step was catalyzed by a mitogen-activated protein kinase (MAPK)-dependent kinase, most likely p90rsk. These data reveal a redundancy between the S6K and the MAPK pathways in mediating early S6 phosphorylation in response to mitogens.
Mol Cell Biol 2004 Apr
PMID:S6K1(-/-)/S6K2(-/-) mice exhibit perinatal lethality and rapamycin-sensitive 5'-terminal oligopyrimidine mRNA translation and reveal a mitogen-activated protein kinase-dependent S6 kinase pathway. 1506 Jan 35

Previous studies have shown that the synthesis and stability of milk protein mRNAs are regulated by lactogenic hormones. We demonstrate here in cultured mouse mammary epithelial cells (CID 9) that insulin plus prolactin also synergistically increases the rate of milk protein mRNA translation. Insulin alone stimulates synthesis of both milk and nonmilk proteins, whereas prolactin alone has no effect, but insulin plus prolactin selectively stimulate synthesis of milk proteins more than insulin alone. The increase in beta-casein mRNA translation is also reflected in a shift to larger polysomes, indicating an effect on translational initiation. Inhibitors of the phosphatidylinositol 3-kinase, mammalian target of rapamycin, and MAPK pathways block insulin-stimulated total protein and beta-casein synthesis but not the synergistic stimulation. Conversely, cordycepin abolishes synergistic stimulation of protein synthesis without affecting insulin-stimulated translation. The poly(A) tract of beta-casein mRNA progressively increases from approximately 20 to about 200 A residues over 30 min of treatment with insulin plus prolactin. The 3'-untranslated region of beta-casein mRNA containing an unaltered cytoplasmic polyadenylation element is sufficient for the translational enhancement and mRNA-specific polyadenylation, based on transient transfection of cells with a reporter construct. Insulin and prolactin stimulate cytoplasmic polyadenylation element binding protein phosphorylation with no increase of cytoplasmic poly(A) polymerase activity.
Mol Endocrinol 2004 Jul
PMID:Insulin and prolactin synergistically stimulate beta-casein messenger ribonucleic acid translation by cytoplasmic polyadenylation. 1507 Oct 91

Increased airway smooth muscle in airway remodeling results from myocyte proliferation and hypertrophy. Skeletal and vascular smooth muscle hypertrophy is induced by phosphatidylinositide-3 kinase (PI(3) kinase) via mammalian target of rapamycin (mTOR) and p70S6 kinase (p70S6K). We tested the hypothesis that this pathway regulates contractile protein accumulation in cultured canine airway myocytes acquiring an elongated contractile phenotype in serum-free culture. In vitro assays revealed a sustained activation of PI(3) kinase and p70S6K during serum deprivation up to 12 d, with concomitant accumulation of SM22 and smooth muscle myosin heavy chain (smMHC) proteins. Immunocytochemistry revealed that activation of PI3K/mTOR/p70S6K occurred almost exclusively in myocytes that acquire the contractile phenotype. Inhibition of PI(3) kinase or mTOR with LY294002 or rapamycin blocked p70S6K activation, prevented formation of large elongated contractile phenotype myocytes, and blocked accumulation of SM22 and smMHC. Inhibition of MEK had no effect. Steady-state mRNA abundance for SM22 and smMHC was unaffected by blocking p70S6K activation. These studies provide primary evidence that PI(3) kinase and mTOR activate p70S6K in airway myocytes leading to the accumulation of contractile apparatus proteins, differentiation, and growth of large, elongated contractile phenotype airway smooth muscle cells.
Am J Respir Cell Mol Biol 2004 Sep
PMID:Phophatidylinositol-3 kinase/mammalian target of rapamycin/p70S6K regulates contractile protein accumulation in airway myocyte differentiation. 1510 62


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