Activation of phosphatidylinositol-3 kinase by ligation of the interleukin-7 receptor is dependent on protein tyrosine kinase activity.
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.
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Division of Immunology/Allergy, University of Toronto, Hospital for Sick Children, ON.
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Roifman
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D015703:Antigens, CD / Q000032:analysis / Q000096:biosynthesis; D001402:B-Lymphocytes / Q000187:drug effects / Q000276:immunology / Q000378:metabolism*; D015153:Blotting, Western; D002396:Catechols / Q000494:pharmacology; D002460:Cell Line; D002478:Cells, Cultured; D002648:Child; D004305:Dose-Response Relationship, Drug; D004789:Enzyme Activation; D006801:Humans; D015851:Interleukin-7 / Q000494:pharmacology*; D007700:Kinetics; D009570:Nitriles / Q000494:pharmacology; D019869:Phosphatidylinositol 3-Kinases; D010750:Phosphoproteins / Q000302:isolation & purification / Q000378:metabolism; D010766:Phosphorylation; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000378:metabolism*; D019000:Phosphotyrosine; D054198:Precursor Cell Lymphoblastic Leukemia-Lymphoma; D011505:Protein-Tyrosine Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D018123:Receptors, Interleukin / Q000378:metabolism*; D020395:Receptors, Interleukin-7; D011994:Recombinant Proteins / Q000494:pharmacology; D013601:T-Lymphocytes / Q000187:drug effects / Q000276:immunology / Q000378:metabolism*; D013950:Thymus Gland; D014407:Tumor Cells, Cultured; D014443:Tyrosine / Q000031:analogs & derivatives / Q000032:analysis / Q000378:metabolism; D020032:Tyrphostins
D015703:Antigens, CD; D002396:Catechols; D015851:Interleukin-7; D009570:Nitriles; D010750:Phosphoproteins; D018123:Receptors, Interleukin; D020395:Receptors, Interleukin-7; D011994:Recombinant Proteins; D020032:Tyrphostins; C060152:tyrphostin 47; D019000:Phosphotyrosine; D014443:Tyrosine; D019869:Phosphatidylinositol 3-Kinases; D017853:Phosphotransferases (Alcohol Group Acceptor); D011505:Protein-Tyrosine Kinases