title: Dual role of the actin cytoskeleton in regulating cell adhesion mediated by the integrin lymphocyte function-associated molecule-1.
abstract: Intracellular signals are required to activate the leukocyte-specific adhesion receptor lymphocyte function-associated molecule-1 (LFA-1; CD11a/CD18) to bind its ligand, intracellular adhesion molecule-1 (ICAM-1). In this study, we investigated the role of the cytoskeleton in LFA-1 activation and demonstrate that filamentous actin (F-actin) can both enhance and inhibit LFA-1-mediated adhesion, depending on the distribution of LFA-1 on the cell surface. We observed that LFA-1 is already clustered on the cell surface of interleukin-2/phytohemagglutinin-activated lymphocytes. These cells bind strongly ICAM-1 and disruption of the actin cytoskeleton inhibits adhesion. In contrast to interleukin-2/phytohemagglutinin-activated peripheral blood lymphocytes, resting lymphocytes, which display a homogenous cell surface distribution of LFA-1, respond poorly to intracellular signals to bind ICAM-1, unless the actin cytoskeleton is disrupted. On resting peripheral blood lymphocytes, uncoupling of LFA-1 from the actin cytoskeleton induces clustering of LFA-1 and this, along with induction of a high-affinity form of LFA-1, via "inside-out" signaling, results in enhanced binding to ICAM-1, which is dependent on intact intermediate filaments, microtubules, and metabolic energy. We hypothesize that linkage of LFA-1 to cytoskeletal elements prevents movement of LFA-1 over the cell surface, thus inhibiting clustering and strong ligand binding. Release from these cytoskeletal elements allows lateral movement and activation of LFA-1, resulting in ligand binding and "outside-in" signaling, that subsequently stimulates actin polymerization and stabilizes cell adhesion.
authors.affiliation: Department of Tumor Immunology, University Hospital Nijmegen St. Radboud, The Netherlands.
authors.forename: M
authors.initials: M
authors.lastname: Lub
authors.forename: Y
authors.initials: Y
authors.lastname: van Kooyk
authors.forename: S J
authors.initials: SJ
authors.lastname: van Vliet
authors.forename: C G
authors.initials: CG
authors.lastname: Figdor
mesh_terms: D008841:Actin Cytoskeleton / Q000378:metabolism; D000199:Actins / Q000502:physiology*; D000818:Animals; D002448:Cell Adhesion / Q000502:physiology*; D015638:Cytochalasin D / Q000494:pharmacology; D003599:Cytoskeleton / Q000502:physiology*; D005347:Fibroblasts; D006801:Humans; D018799:Intercellular Adhesion Molecule-1 / Q000378:metabolism; D007382:Intermediate Filaments / Q000378:metabolism; D007739:L Cells; D007962:Leukocytes / Q000378:metabolism; D016169:Lymphocyte Function-Associated Antigen-1 / Q000502:physiology*; D008545:Melanoma; D051379:Mice; D008870:Microtubules / Q000378:metabolism; D011485:Protein Binding; D014407:Tumor Cells, Cultured
chemical_list: D000199:Actins; D016169:Lymphocyte Function-Associated Antigen-1; D018799:Intercellular Adhesion Molecule-1; D015638:Cytochalasin D