title: The phosphatidylinositol 3' kinase pathway is required for the survival signal of leukocyte tyrosine kinase.
abstract: Leukocyte tyrosine kinase (LTK) is a receptor tyrosine kinase which belongs to the insulin receptor superfamily and is mainly expressed in pre-B lymphocytes and neuronal tissues. Recently, we demonstrated that LTK utilizes Shc and IRS-1 as two major substrates and while both equally activate the Ras pathway, only IRS-1 suppresses apoptosis of hematopoietic cells, suggesting the existence of another unidentified signaling pathway downstream of IRS-1, which is relevant to the anti-apoptotic activity. In the present study, we found that wortmannin, a specific inhibitor of phosphatidylinositol 3' (PI3)-kinase, abolished the survival effects of LTK. Although c-Cbl is found to be phosphorylated by LTK and therefore is a second candidate linking LTK with the PI3-kinase pathway along with IRS-1, we found that the p85 subunit of PI3 kinase directly binds to tyrosine 753 of LTK, which is located within a YXXM motif, a consensus binding amino acid sequence for the SH2 domain of p85, but fails to bind to IRS-1 or c-Cbl. Ba/F3 cells which stably express the EGF receptor-LTK chimeric receptor carrying a mutation at tyrosine 753 fell into apoptotic death even in the presence of EGF, indicating that the PI3 kinase pathway is required for the survival effects of LTK.
authors.affiliation: The Third Department of Internal Medicine, Faculty of Medicine, University of Tokyo, Japan.
authors.forename: H
authors.initials: H
authors.lastname: Ueno
authors.forename: H
authors.initials: H
authors.lastname: Honda
authors.forename: T
authors.initials: T
authors.lastname: Nakamoto
authors.forename: T
authors.initials: T
authors.lastname: Yamagata
authors.forename: K
authors.initials: K
authors.lastname: Sasaki
authors.forename: K
authors.initials: K
authors.lastname: Miyagawa
authors.forename: K
authors.initials: K
authors.lastname: Mitani
authors.forename: Y
authors.initials: Y
authors.lastname: Yazaki
authors.forename: H
authors.initials: H
authors.lastname: Hirai
mesh_terms: D000730:Androstadienes / Q000494:pharmacology; D000818:Animals; D017209:Apoptosis / Q000502:physiology; D001665:Binding Sites; D002460:Cell Line; D002470:Cell Survival / Q000187:drug effects / Q000502:physiology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006801:Humans; D051379:Mice; D009154:Mutation; D019869:Phosphatidylinositol 3-Kinases; D010750:Phosphoproteins / Q000378:metabolism; D010766:Phosphorylation; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D050721:Proto-Oncogene Proteins c-cbl; D020794:Receptor Protein-Tyrosine Kinases / Q000187:drug effects / Q000378:metabolism*; D015398:Signal Transduction; D014443:Tyrosine / Q000378:metabolism; D044767:Ubiquitin-Protein Ligases; D000077191:Wortmannin
chemical_list: D000730:Androstadienes; D004791:Enzyme Inhibitors; D010750:Phosphoproteins; D011518:Proto-Oncogene Proteins; D014443:Tyrosine; D050721:Proto-Oncogene Proteins c-cbl; D044767:Ubiquitin-Protein Ligases; D019869:Phosphatidylinositol 3-Kinases; D017853:Phosphotransferases (Alcohol Group Acceptor); D020794:Receptor Protein-Tyrosine Kinases; C067419:CBL protein, human; C493849:Cbl protein, mouse; D000077191:Wortmannin