adenosine-5--o-(3-thiotriphosphate) and Lymphoma--T-Cell

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.

Topics: Adaptor Proteins, Signal Transducing; Adenosine Triphosphate; Androstadienes; Animals; Brain Chemistry; Carrier Proteins; Cell Cycle Proteins; Cell Line; Chromones; Dithiothreitol; Enzyme Inhibitors; Eukaryotic Initiation Factors; Immunosuppressive Agents; Interleukin-2; Intracellular Signaling Peptides and Proteins; Lymphocyte Activation; Lymphoma, T-Cell; Mice; Morpholines; Phosphatidylinositol 3-Kinases; Phosphoproteins; Phosphorylation; Phosphotransferases (Alcohol Group Acceptor); Polyenes; Protein Kinases; Rats; Recombinant Fusion Proteins; Signal Transduction; Sirolimus; T-Lymphocytes; T-Lymphocytes, Cytotoxic; TOR Serine-Threonine Kinases; Tumor Cells, Cultured; Wortmannin