title: B cell antigen receptor-induced Rac1 activation and Rac1-dependent spreading are impaired in transitional immature B cells due to levels of membrane cholesterol.
abstract: The BCR-triggered responses of mature and transitional immature B cells differ at both the biochemical and functional level. In this study, we show that in mature B cells, BCR signaling triggers Vav phosphorylation and Rac1 activation. Furthermore, we demonstrate that although downstream actin-dependent BCR capping is independent of Rac1 activation, actin-dependent membrane ruffling and cell spreading are Rac1-dependent processes. In contrast, BCR-induced Vav phosphorylation and Rac1 activation is impaired in transitional immature B cells, resulting in defects in actin polymerization-dependent spreading and membrane ruffling while Rac1-independent BCR capping remains intact. Because transitional immature murine B cells maintain lower steady-state levels of plasma membrane cholesterol, we augmented their levels to that of mature B cells and found that BCR-induced Rac1 activation and Rac1-dependent membrane ruffling and cell spreading were restored. These studies provide a direct link between B cell cholesterol levels and downstream cellular signaling processes.
authors: Department of Pathology and Laboratory Medicine, School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA.
authors: Randall J
authors: RJ
authors: Brezski
authors: John G
authors: JG
authors: Monroe
mesh_terms: D000818:Animals; D000906:Antibodies / Q000276:immunology; D001402:B-Lymphocytes / Q000166:cytology* / Q000276:immunology / Q000378:metabolism*; D002454:Cell Differentiation; D002462:Cell Membrane / Q000378:metabolism*; D002478:Cells, Cultured; D002784:Cholesterol / Q000378:metabolism*; D004789:Enzyme Activation; D048031:JNK Mitogen-Activated Protein Kinases / Q000378:metabolism; D051379:Mice; D008807:Mice, Inbred BALB C; D010641:Phenotype; D051567:Proto-Oncogene Proteins c-vav / Q000378:metabolism; D011947:Receptors, Antigen, B-Cell / Q000276:immunology / Q000378:metabolism*; D015398:Signal Transduction; D020830:rac1 GTP-Binding Protein / Q000378:metabolism*
chemical_list: D000906:Antibodies; D051567:Proto-Oncogene Proteins c-vav; D011947:Receptors, Antigen, B-Cell; D002784:Cholesterol; D048031:JNK Mitogen-Activated Protein Kinases; D020830:rac1 GTP-Binding Protein