VLA-4 (alpha(4)beta(1)) engagement defines a novel activation pathway for beta(2) integrin-dependent leukocyte adhesion involving the urokinase receptor.
During acute inflammatory processes, beta(2) and beta(1) integrins sequentially mediate leukocyte recruitment into extravascular tissues. We studied the influence of VLA-4 (very late antigen-4) (alpha(4)beta(1)) engagement on beta(2) integrin activation-dependent cell-to-cell adhesion. Ligation of VLA-4 by the soluble chimera fusion product vascular cell adhesion molecule-1 (VCAM-1)-Fc or by 2 anti-CD29 (beta(1) chain) monoclonal antibodies (mAb) rapidly induced adhesion of myelomonocytic cells (HL60, U937) to human umbilical vein endothelial cells (HUVECs). Cell adhesion was mediated via beta(2) integrin (LFA-1 and Mac-1) activation: induced adhesion to HUVECs was inhibited by blocking mAbs anti-CD18 (70%-90%), anti-CD11a (50%-60%), or anti-CD11b (60%-70%). Adhesion to immobilized ligands of beta(2) integrins (intercellular adhesion molecule-1 [ICAM-1], fibrinogen, keyhole limpet hemocyanin) as well as to ICAM-1-transfected Chinese hamster ovary cells, but not to ligands of beta(1) integrins (VCAM-1, fibronectin, laminin, and collagen), was augmented. VCAM-1-Fc binding provoked the expression of the activation-dependent epitope CBRM1/5 of Mac-1 on leukocytes. Clustering of VLA-4 through dimeric VCAM-1-Fc was required for beta(2) integrin activation and induction of cell adhesion, whereas monovalent VCAM-1 or Fab fragments of anti-beta(1) integrin mAb were ineffective. Activation of beta(2) integrins by alpha(4)beta(1) integrin ligation (VCAM-1-Fc or anti-beta(1) mAb) required the presence of urokinase receptor (uPAR) on leukocytic cells, because the removal of uPAR from the cell surface by phosphatidylinositol-specific phospholipase C reduced cell adhesion to less than 40%. Adhesion was reconstituted when soluble recombinant uPAR was allowed to reassociate with the cells. Finally, VLA-4 engagement by VCAM-1-Fc or anti-beta(1) integrin mAb induced uPAR-dependent adhesion to immobilized vitronectin as well. These results elucidate a novel activation pathway of beta(2) integrin-dependent cell-to-cell adhesion that requires alpha(4)beta(1) integrin ligation for initiation and uPAR as activation transducer. (Blood. 2000;96:506-513)
May
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AE
Deutsches Herzzentrum und 1. Medizinische Klinik des Klinikums Rechts der Isar, Technische Universität, D-80636 München, Germany. may@dhm.mhn.de
Neumann
F J
FJ
Schömig
A
A
Preissner
K T
KT
D000911:Antibodies, Monoclonal; D018821:CD18 Antigens / Q000276:immunology / Q000378:metabolism / Q000502:physiology*; D002448:Cell Adhesion; D004730:Endothelium, Vascular / Q000166:cytology; D006801:Humans; D039041:Integrin alpha4beta1; D016023:Integrins / Q000502:physiology*; D007962:Leukocytes / Q000502:physiology*; D016169:Lymphocyte Function-Associated Antigen-1 / Q000502:physiology; D016177:Macrophage-1 Antigen / Q000502:physiology; D011956:Receptors, Cell Surface / Q000502:physiology*; D011961:Receptors, Fc / Q000502:physiology; D016201:Receptors, Lymphocyte Homing / Q000502:physiology*; D055293:Receptors, Urokinase Plasminogen Activator; D014407:Tumor Cells, Cultured; D014471:Umbilical Veins; D019010:Vascular Cell Adhesion Molecule-1 / Q000276:immunology / Q000378:metabolism
D000911:Antibodies, Monoclonal; D018821:CD18 Antigens; D039041:Integrin alpha4beta1; D016023:Integrins; D016169:Lymphocyte Function-Associated Antigen-1; D016177:Macrophage-1 Antigen; C524898:PLAUR protein, human; D011956:Receptors, Cell Surface; D011961:Receptors, Fc; D016201:Receptors, Lymphocyte Homing; D055293:Receptors, Urokinase Plasminogen Activator; D019010:Vascular Cell Adhesion Molecule-1