Vanadate-Induced Inhibition of BCR-Triggered Apoptosis is Coupled with Tyrosine Phosphorylation and Induction of G2M Growth Arrest in Ramos-BL B Cells

The regulation of the tyrosine phosphorylation of key signaling molecules by tyrosine kinases and phosphatases is essential for BCR-triggered signaling cascades during B cell selection process. We used the non-selective tyrosine phosphatase inhibitor vanadate to study the importance of the late regulation of the tyrosine phosphorylation for BCR-triggered G1 growth arrest and apoptosis in Ramos-BL B cells. Vanadate induces G2M growth arrest in a dose-dependent manner and prevents BCR-triggered apoptosis. Vanadate-induced upregulation of the tyrosine phosphorylation is concomitant with increased expression of cyclin B and inhibition of caspase-3 activation and PARP cleavage. The anti-apoptotic effect of vanadate was observed even when added up to 6 hours after the treatment of Ramos-BL B cells with anti-IgM. Vanadate increases BCR-triggered tyrosine phosphorylation of the cytosolic tyrosine phosphatases, SHP-1 and SHP-2 after 24 hours. Co-stimulation with anti-CD40 prevents anti-IgM-triggered tyrosine phosphorylation of these phosphatases and up-regulates the expression of SHP-1. We conclude that the regulation of the tyrosine phosphatase activity is indispensable for BCR-triggered execution of the apoptosis in Ramos-BL B cells.