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 lymp homa (Ramos-BL) B cell line from surface immunoglobulin M (sIgM)-trigg ered growth arrest and apoptosis, This study investigates whether prot ein tyrosine kinase (PTK) activity and tyrosine phosphorylation on p95 (vav) and on the p85 regulatory subunit of phosphatidylinositol 3-kina se (PI3 kinase) play a role in the regulation of Ramos-BL B cell survi val, The PTH inhibitor herbimycin A (HA) triggers significant growth a rrest prior to apoptosis from the G(1)-phase of the cell cycle, indica ting that tyrosine phosphorylation of key proteins is critical for Ram os-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-trea ted Ramos-BL B cells: Vav and p85 are devoid of tyro sine-phosphorylat ed epitopes in control cells whereas p85, but not Vav, is significantl y phosphorylated following ligation of sIgM and anti-CD40 triggers tyr osine phosphorylation on both proteins, Thus, tyro sine-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 correl ated with tyrosine phosphorylation on p85: Ramos-BL B cells exhibit hi gh basal levels of PI3 kinase activity, determined by immunoprecipitat ion with anti-p85 and P-32 incorporation into phosphatidylinositol, wh ich is not significantly affected by stimulation with anti-IgM but whi ch is elevated by 36 +/- 2.9% following ligation of CD40, Thus, tyrosi ne phosphorylation on p85 correlates with the CD40-triggered increase in PI3 kinase activity but not with basal levels nor with sIgM-trigger ed levels of enzymatic activity: these data suggest the presence of di fferent PI3 kinase isoforms or the existence of multiple regulatory pa thways for the same PI3 kinase isotype in Ramos-BL B cells. (C) 1997 A cademic Press.