Abstract
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.
Publication types
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Research Support, Non-U.S. Gov't
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Research Support, U.S. Gov't, P.H.S.
MeSH terms
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Adaptor Proteins, Signal Transducing
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Adenosine Triphosphate / analogs & derivatives
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Adenosine Triphosphate / pharmacology
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Androstadienes / pharmacology*
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Animals
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Brain Chemistry
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Carrier Proteins*
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Cell Cycle Proteins
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Cell Line
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Chromones / pharmacology*
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Dithiothreitol / pharmacology
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Enzyme Inhibitors / pharmacology
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Eukaryotic Initiation Factors
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Immunosuppressive Agents / pharmacology
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Interleukin-2 / pharmacology
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Intracellular Signaling Peptides and Proteins
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Lymphocyte Activation
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Lymphoma, T-Cell
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Mice
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Morpholines / pharmacology*
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Phosphatidylinositol 3-Kinases
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Phosphoproteins / metabolism*
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Phosphorylation / drug effects
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Phosphotransferases (Alcohol Group Acceptor) / antagonists & inhibitors*
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Phosphotransferases (Alcohol Group Acceptor) / genetics
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Phosphotransferases (Alcohol Group Acceptor) / isolation & purification
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Polyenes / pharmacology
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Protein Kinases*
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Rats
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Recombinant Fusion Proteins / metabolism
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Signal Transduction / drug effects
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Sirolimus
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T-Lymphocytes / immunology
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T-Lymphocytes, Cytotoxic
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TOR Serine-Threonine Kinases
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Tumor Cells, Cultured
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Wortmannin
Substances
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Adaptor Proteins, Signal Transducing
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Androstadienes
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Carrier Proteins
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Cell Cycle Proteins
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Chromones
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Eif4ebp1 protein, mouse
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Eif4ebp1 protein, rat
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Enzyme Inhibitors
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Eukaryotic Initiation Factors
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Immunosuppressive Agents
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Interleukin-2
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Intracellular Signaling Peptides and Proteins
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Morpholines
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Phosphoproteins
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Polyenes
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Recombinant Fusion Proteins
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2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one
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adenosine 5'-O-(3-thiotriphosphate)
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Adenosine Triphosphate
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Protein Kinases
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Phosphotransferases (Alcohol Group Acceptor)
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mTOR protein, mouse
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mTOR protein, rat
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TOR Serine-Threonine Kinases
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Dithiothreitol
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Sirolimus
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Wortmannin