CD40-triggered protein tyrosine phosphorylation on Vav and on phosphatidylinositol 3-kinase correlates with survival of the Ramos-Burkitt lymphoma B cell line.
Signals transduced through CD40 rescue cells of the Ramos-Burkitt lymphoma (Ramos-BL) B cell line from surface immunoglobulin M (sIgM)-triggered growth arrest and apoptosis. This study investigates whether protein tyrosine kinase (PTK) activity and tyrosine phosphorylation on p95(vav) and on the p85 regulatory subunit of phosphatidylinositol 3-kinase (PI3 kinase) play a role in the regulation of Ramos-BL B cell survival. The PTK inhibitor herbimycin A (HA) triggers significant growth arrest prior to apoptosis from the G1-phase of the cell cycle, indicating that tyrosine phosphorylation of key proteins is critical for Ramos-BL cell cycle progression and survival. Indeed, signals transduced through CD40 fail to rescue Ramos-BL B cells from HA-triggered growth arrest and apoptosis. Since Vav and PI3 kinase are intimately involved in the regulation of cellular growth, their tyrosine phosphorylation status was determined in unstimulated and anti-IgM- and anti-CD40-treated Ramos-BL B cells: Vav and p85 are devoid of tyrosine-phosphorylated epitopes in control cells whereas p85, but not Vav, is significantly phosphorylated following ligation of sIgM and anti-CD40 triggers tyrosine phosphorylation on both proteins. Thus, tyrosine-phosphorylated Vav may be a critical effector of CD40-mediated survival. As tyrosine-phosphorylated PI3 kinase is common to both sIgM-triggered death and CD40-triggered survival pathways, its lipid kinase activity was correlated with tyrosine phosphorylation on p85: Ramos-BL B cells exhibit high basal levels of PI3 kinase activity, determined by immunoprecipitation with anti-p85 and 32P incorporation into phosphatidylinositol, which is not significantly affected by stimulation with anti-IgM but which is elevated by 36 +/- 2.9% following ligation of CD40. Thus, tyrosine phosphorylation on p85 correlates with the CD40-triggered increase in PI3 kinase activity but not with basal levels nor with sIgM-triggered levels of enzymatic activity: these data suggest the presence of different PI3 kinase isoforms or the existence of multiple regulatory pathways for the same PI3 kinase isotype in Ramos-BL B cells.
Padmore
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Department of Biochemistry, University of Oxford, United Kingdom.
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Gunby
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Kelly
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Knox
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D001402:B-Lymphocytes / Q000166:cytology / Q000187:drug effects; D016227:Benzoquinones; D002051:Burkitt Lymphoma / Q000378:metabolism / Q000473:pathology*; D019013:CD40 Antigens / Q000502:physiology*; D018797:Cell Cycle Proteins; D002675:Child, Preschool; D004791:Enzyme Inhibitors / Q000494:pharmacology; D016193:G1 Phase / Q000187:drug effects; D006801:Humans; D007075:Immunoglobulin M / Q000276:immunology; D047029:Lactams, Macrocyclic; D008297:Male; D009363:Neoplasm Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism*; D014066:Palatine Tonsil / Q000473:pathology; D019869:Phosphatidylinositol 3-Kinases; D010766:Phosphorylation; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000037:antagonists & inhibitors / Q000378:metabolism*; D011499:Protein Processing, Post-Translational; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D051567:Proto-Oncogene Proteins c-vav; D011809:Quinones / Q000494:pharmacology; D017828:Rifabutin / Q000031:analogs & derivatives; D014407:Tumor Cells, Cultured
D016227:Benzoquinones; D019013:CD40 Antigens; D018797:Cell Cycle Proteins; D004791:Enzyme Inhibitors; D007075:Immunoglobulin M; D047029:Lactams, Macrocyclic; D009363:Neoplasm Proteins; D011518:Proto-Oncogene Proteins; D051567:Proto-Oncogene Proteins c-vav; D011809:Quinones; C496618:VAV1 protein, human; C033027:secretory IgM; D017828:Rifabutin; C020754:herbimycin; D019869:Phosphatidylinositol 3-Kinases; D017853:Phosphotransferases (Alcohol Group Acceptor)