ag-213 and Precursor-Cell-Lymphoblastic-Leukemia-Lymphoma

Ligation of the interleukin-7 receptor (IL-7R) results in a rapid phosphorylation of tyrosine residues on multiple substrates. In addition, we have recently shown that the IL-7R mediates activation of phosphatidylinositol-3 (PI-3) kinase. Because PI-3 kinase activity can be immunoprecipitated with antiphosphotyrosine antibodies in most receptor systems studied, it has been examined that either PI-3 kinase or an associated protein become tyrosine-phosphorylated after ligand binding. We studied here the possibility that PI-3 kinase, which is directly linked to mitogenic responses in growth factor receptors, is tyrosine-phosphorylated after stimulation of the IL-7R. Using anti-p85 alpha or anti-p85 beta antibodies raised against the p85 subunit of PI-3 kinase for immunoprecipitation and subsequent blotting with antiphosphotyrosine clearly shows that IL-7-stimulated human precursor cells contain both p85 alpha and p85 beta proteins phosphorylated on tyrosine residues. Specific protein tyrosine kinase inhibitors such as tyrphostin AG-490 block total cell lysate phosphorylation and tyrosine phosphorylation on p85. Similar concentrations of this inhibitor also block in vitro and in vivo PI-3 kinase activity suggesting that this enzyme activation is dependent on the phosphorylation event of p85. In addition, AG-490 blocks IL-7-mediated proliferation in a dose-dependent manner, suggesting a link between the early events of PI-3 kinase phosphorylation and activation with IL-7R-induced cell growth.

Topics: Antigens, CD; B-Lymphocytes; Blotting, Western; Catechols; Cell Line; Cells, Cultured; Child; Dose-Response Relationship, Drug; Enzyme Activation; Humans; Interleukin-7; Kinetics; Nitriles; Phosphatidylinositol 3-Kinases; Phosphoproteins; Phosphorylation; Phosphotransferases (Alcohol Group Acceptor); Phosphotyrosine; Precursor Cell Lymphoblastic Leukemia-Lymphoma; Protein-Tyrosine Kinases; Receptors, Interleukin; Receptors, Interleukin-7; Recombinant Proteins; T-Lymphocytes; Thymus Gland; Tumor Cells, Cultured; Tyrosine; Tyrphostins