title: Regulation of tyrosine phosphorylation during the CD40-mediated rescue of Ramos-BL B cells from BCR-triggered apoptosis.
abstract: The regulation of tyrosine phosphorylation is essential for BCR-triggered cellular responses during the selection process in the germinal centres. We were interested in examining the temporal regulation of tyrosine phosphorylation following CD40 cross-linking of anti-IgM-triggered Ramos-BL B cells. CD40 co-stimulation of anti-IgM-treated Ramos-BL B cells rescued them from growth inhibition and apoptosis, even when anti-CD40 Abs were added up to 12 h after the cross-linking of the BCR. The initial up-regulation of tyrosine phosphorylation triggered by BCR cross-linking is followed by tyrosine dephosphorylation after 12 h of stimulation, coinciding with pro-caspase-3 processing and PARP cleavage. We find that CD40 co-stimulation rescues BCR-triggered Ramos-BL B cells only before the irreversible inhibition of tyrosine kinase activity after 12 h of BCR cross-linking and that this is coupled with up-regulation of tyrosine phosphorylation; thus demonstrating the importance of the late regulation of tyrosine phosphorylation for CD40-mediated rescue of Ramos-BL B cells from BCR-triggered G1 growth arrest and apoptosis.
authors.affiliation: Department of Biochemistry, University of Oxford, Oxford OX1 3QU, UK.
authors.forename: Kroum K
authors.initials: KK
authors.lastname: Hristov
authors.forename: Kirstine A
authors.initials: KA
authors.lastname: Knox
authors.forename: Vanio I
authors.initials: VI
authors.lastname: Mitev
mesh_terms: D017209:Apoptosis; D001402:B-Lymphocytes / Q000187:drug effects / Q000276:immunology*; D002051:Burkitt Lymphoma; D019013:CD40 Antigens / Q000378:metabolism*; D045744:Cell Line, Tumor; D006801:Humans; D007075:Immunoglobulin M / Q000276:immunology; D010766:Phosphorylation; D011947:Receptors, Antigen, B-Cell / Q000276:immunology*; D015398:Signal Transduction; D014443:Tyrosine / Q000378:metabolism*
chemical_list: D019013:CD40 Antigens; D007075:Immunoglobulin M; D011947:Receptors, Antigen, B-Cell; D014443:Tyrosine