title: CD28 engagement promotes actin polymerization through the activation of the small Rho GTPase Cdc42 in human T cells.
abstract: Engagement of the costimulatory molecule CD28 is an important step in the optimal activation of T cells. Nevertheless, the specific role of CD28 in the formation of the immunological synapse and cytoskeletal changes that occur upon TCR/CD3 complex engagement is still poorly understood. Using Ab-coated surfaces, we show that CD28 engagement in the absence of any other signal induced the formation of cytoplasmic elongations enriched in filamentous actin (F-actin), in this work called filopodia or microspikes. Such structures were specific for engagement of CD28 on mAb-coated surfaces because they could not be observed in surfaces coated with either poly(L-lysine) or anti-CD3 mAb. The signaling pathway coupling CD28 to cytoskeletal rearrangements required Src-related kinase activity and promoted Vav phosphorylation and Cdc42 activation independently of the zeta-chain-associated kinase (ZAP-70). CD28-induced filopodia required Cdc42 GTPase activity, but not the related Rho GTPase Rac1. Moreover, Cdc42 colocalized to areas of increased F-actin. Our results support a specific role for the activation of the small Rho GTPase Cdc42 in the actin reorganization mediated by CD28 in human T cells.
authors.affiliation: Laboratory of Lymphocyte Biology, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, MD 20892, USA. lfontana@niaid.nih.gov
authors.forename: Laura Inés
authors.initials: LI
authors.lastname: Salazar-Fontana
authors.forename: Valarie
authors.initials: V
authors.lastname: Barr
authors.forename: Lawrence E
authors.initials: LE
authors.lastname: Samelson
authors.forename: Barbara E
authors.initials: BE
authors.lastname: Bierer
mesh_terms: D000199:Actins / Q000378:metabolism*; D000328:Adult; D000911:Antibodies, Monoclonal / Q000378:metabolism; D018106:CD28 Antigens / Q000276:immunology / Q000378:metabolism / Q000502:physiology*; D002460:Cell Line; D002999:Clone Cells; D003432:Cross-Linking Reagents / Q000378:metabolism; D004789:Enzyme Activation / Q000276:immunology; D006801:Humans; D019169:Jurkat Cells; D019860:Lymphocyte Specific Protein Tyrosine Kinase p56(lck) / Q000502:physiology; D015513:Oncogene Proteins / Q000378:metabolism; D010766:Phosphorylation; D011505:Protein-Tyrosine Kinases / Q000502:physiology; D011518:Proto-Oncogene Proteins / Q000502:physiology; D051076:Proto-Oncogene Proteins c-fyn; D051567:Proto-Oncogene Proteins c-vav; D011554:Pseudopodia / Q000378:metabolism / Q000502:physiology; D013601:T-Lymphocytes / Q000166:cytology / Q000201:enzymology / Q000276:immunology* / Q000378:metabolism*; D015854:Up-Regulation / Q000276:immunology*; D051746:ZAP-70 Protein-Tyrosine Kinase; D020764:cdc42 GTP-Binding Protein / Q000378:metabolism* / Q000502:physiology
chemical_list: D000199:Actins; D000911:Antibodies, Monoclonal; D018106:CD28 Antigens; D003432:Cross-Linking Reagents; D015513:Oncogene Proteins; D011518:Proto-Oncogene Proteins; D051567:Proto-Oncogene Proteins c-vav; C496618:VAV1 protein, human; D011505:Protein-Tyrosine Kinases; C494957:FYN protein, human; D019860:Lymphocyte Specific Protein Tyrosine Kinase p56(lck); D051076:Proto-Oncogene Proteins c-fyn; D051746:ZAP-70 Protein-Tyrosine Kinase; C497261:ZAP70 protein, human; D020764:cdc42 GTP-Binding Protein