The Rap GTPases regulate integrin-mediated adhesion, cell spreading, actin polymerization, and Pyk2 tyrosine phosphorylation in B lymphocytes.
Integrin-mediated adhesion plays an important role in B cell development and activation. Signaling initiated by antigens, chemokines, or phorbol esters can rapidly convert integrins to an activated adhesion-competent state. The binding of integrins to their ligands can then induce actin-dependent cell spreading, which can facilitate cell-cell adhesion or cell migration on extracellular matrices. The signaling pathways involved in integrin activation and post-adhesion events in B cells are not completely understood. We have previously shown that anti-Ig antibodies, the chemokine stromal cell-derived factor-1 (SDF-1; CXCL12), and phorbol esters activate the Rap1 and Rap2 GTPases in B cells and that Rap activation is essential for SDF-1-induced B cell migration (McLeod, S. J., Li, A. H. Y., Lee, R. L., Burgess, A. E., and Gold, M. R. (2002) J. Immunol. 169, 1365-1371; Christian, S. L., Lee, R. L., McLeod, S. J., Burgess, A. E., Li, A. H. Y., Dang-Lawson, M., Lin, K. B. L., and Gold, M. R. (2003) J. Biol. Chem. 278, 41756-41767). We show here that preventing Rap activation by expressing Rap-specific GTPase-activating protein II (RapGAPII) significantly decreased lymphocyte function-associated antigen-1- and alpha(4) integrin-dependent binding of murine B cell lines to purified adhesion molecules and to other cells. Conversely, augmenting Rap activation by expressing a constitutively active form of Rap2 enhanced B cell adhesion, showing for the first time that Rap2 can promote integrin activation. We also show that blocking Rap activation inhibited anti-Ig-induced cell spreading and phorbol ester-induced actin polymerization as well as anti-Ig- and SDF-1-induced phosphorylation of Pyk2, a tyrosine kinase involved in morphological changes and chemokine-induced B cell migration. Thus, the Rap GTPases regulate integrin-mediated B cell adhesion as well as processes that control B cell morphology and migration.
McLeod
Sarah J
SJ
Department of Microbiology and Immunology, University of British Columbia, 6174 University Boulevard, Vancouver, BC V6T 1Z3, Canada.
Shum
Andrew J
AJ
Lee
Rosaline L
RL
Takei
Fumio
F
Gold
Michael R
MR
D000199:Actins / Q000378:metabolism*; D000818:Animals; D001402:B-Lymphocytes / Q000378:metabolism*; D001854:Bone Marrow Cells / Q000166:cytology; D002448:Cell Adhesion; D002455:Cell Division; D002460:Cell Line; D002465:Cell Movement; D018076:DNA, Complementary / Q000378:metabolism; D004789:Enzyme Activation; D005434:Flow Cytometry; D051418:Focal Adhesion Kinase 2; D005822:Genetic Vectors; D016023:Integrins / Q000378:metabolism*; D018799:Intercellular Adhesion Molecule-1 / Q000378:metabolism; D008214:Lymphocytes / Q000378:metabolism; D051379:Mice; D009068:Movement; D010703:Phorbol Esters / Q000378:metabolism; D010766:Phosphorylation; D011505:Protein-Tyrosine Kinases / Q000378:metabolism*; D015398:Signal Transduction; D017154:Stromal Cells; D013997:Time Factors; D014443:Tyrosine / Q000378:metabolism; D019010:Vascular Cell Adhesion Molecule-1 / Q000378:metabolism; D020668:rap GTP-Binding Proteins / Q000378:metabolism / Q000502:physiology*
D000199:Actins; D018076:DNA, Complementary; D016023:Integrins; D010703:Phorbol Esters; D019010:Vascular Cell Adhesion Molecule-1; D018799:Intercellular Adhesion Molecule-1; D014443:Tyrosine; D011505:Protein-Tyrosine Kinases; D051418:Focal Adhesion Kinase 2; C496053:Ptk2b protein, mouse; C492137:Rap2a protein, mouse; D020668:rap GTP-Binding Proteins