title: Regulation of cell adhesion by affinity and conformational unbending of alpha4beta1 integrin.
abstract: Rapid activation of integrins in response to chemokine-induced signaling serves as a basis for leukocyte arrest on inflamed endothelium. Current models of integrin activation include increased affinity for ligand, molecular extension, and others. In this study, using real-time fluorescence resonance energy transfer to assess alpha(4)beta(1) integrin conformational unbending and fluorescent ligand binding to assess affinity, we report at least four receptor states with independent regulation of affinity and unbending. Moreover, kinetic analysis of chemokine-induced integrin conformational unbending and ligand-binding affinity revealed conditions under which the affinity change was transient whereas the unbending was sustained. In a VLA-4/VCAM-1-specific myeloid cell adhesion model system, changes in the affinity of the VLA-4-binding pocket were reflected in rapid cell aggregation and disaggregation. However, the initial rate of cell aggregation increased 9-fold upon activation, of which only 2.5-fold was attributable to the increased affinity of the binding pocket. These data show that independent regulation of affinity and conformational unbending represents a novel and fundamental mechanism for regulation of integrin-dependent adhesion in which the increased affinity appears to account primarily for the increasing lifetime of the alpha(4)beta(1) integrin/VCAM-1 bond, whereas the unbending accounts for the increased capture efficiency.
authors.affiliation: Department of Pathology and Cancer Center, University of New Mexico Health Sciences Center, Albuquerque, NM 87131, USA.
authors.forename: Alexandre
authors.initials: A
authors.lastname: Chigaev
authors.forename: Anna
authors.initials: A
authors.lastname: Waller
authors.forename: Gordon J
authors.initials: GJ
authors.lastname: Zwartz
authors.forename: Tione
authors.initials: T
authors.lastname: Buranda
authors.forename: Larry A
authors.initials: LA
authors.lastname: Sklar
mesh_terms: D000818:Animals; D002448:Cell Adhesion / Q000502:physiology; D002449:Cell Aggregation / Q000502:physiology; D045744:Cell Line, Tumor; D002465:Cell Movement / Q000502:physiology; D006801:Humans; D018836:Inflammation Mediators / Q000737:chemistry / Q000378:metabolism / Q000502:physiology; D039041:Integrin alpha4beta1 / Q000737:chemistry* / Q000378:metabolism / Q000502:physiology*; D007962:Leukocytes / Q000166:cytology / Q000378:metabolism / Q000473:pathology; D051379:Mice; D011485:Protein Binding / Q000502:physiology; D011487:Protein Conformation; D015398:Signal Transduction / Q000502:physiology; D020298:U937 Cells
chemical_list: D018836:Inflammation Mediators; D039041:Integrin alpha4beta1