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 p95vavand on the p85 re...

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Veröffentlicht in:Cellular immunology 1997-05, Vol.177 (2), p.119-128
Hauptverfasser: Padmore, Lauren, An, Sungkwan, Gunby, Rosalind H., Kelly, Ken, Radda, George K., Knox, Kirstine A.
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Sprache:eng
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Zusammenfassung: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 p95vavand 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 and32P 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.
ISSN:0008-8749
1090-2163
DOI:10.1006/cimm.1997.1102