title: Competitive binding of vascular cell adhesion molecule-1 and the HepII/IIICS domain of fibronectin to the integrin alpha 4 beta 1.
abstract: The integrin receptor alpha 4 beta 1 binds to two different ligands, the extracellular matrix glycoprotein fibronectin and the endothelial cell surface protein vascular cell adhesion molecule-1 (VCAM-1). Using probes derived from each ligand and a variety of cell adhesion and ligand-receptor binding assays, we have investigated the relationship between the mechanisms of fibronectin and VCAM-1 interaction with alpha 4 beta 1. CS1 peptide, which represents the dominant active site from the HepII/IIICS recognition domain in fibronectin, was found to inhibit VCAM-1-dependent adhesion in three different assays: MOLT-4 T lymphoblastic leukaemia cell attachment to immobilized recombinant soluble VCAM-1 (rsVCAM-1), MOLT-4 cell attachment to monolayers of VCAM-1-transfected COS-1 cells, and A375-SM melanoma cell spreading on immobilized rs VCAM-1. Half-maximal inhibition required CS1 concentrations of 1.7-3.0 mg/ml, some 3-7-fold higher than that needed to autoinhibit adhesion to CS1-IgG conjugate. Using a more sensitive solid-phase receptor-ligand binding assay, CS1 was found to be a potent inhibitor of the binding of rsVCAM-1 to alpha 4 beta 1 (half-maximal inhibition at 13 micrograms/ml). In agreement with cell-based assays, severalfold lower concentrations of CS1 were required to inhibit binding of recombinant HepII/IIICS region of fibronectin (half-maximal inhibition at 3 micrograms/ml). VCAM-1-alpha 4 beta 1 binding was blocked not only by CS1 peptide but also by the recombinant HepII/IIICS region of fibronectin. Kinetic analysis of CS1 inhibition of VCAM-1 binding revealed that it was directly competitive in nature, indicating that VCAM-1 and fibronectin recognize either identical or spatially overlapping binding sites on alpha 4 beta 1. The implications of these results for the future design of VCAM-1 antagonists are discussed.
authors.affiliation: Department of Biochemistry and Molecular Biology, School of Biological Sciences, University of Manchester, United Kingdom.
authors.forename: R
authors.initials: R
authors.lastname: Makarem
authors.forename: P
authors.initials: P
authors.lastname: Newham
authors.forename: J A
authors.initials: JA
authors.lastname: Askari
authors.forename: L J
authors.initials: LJ
authors.lastname: Green
authors.forename: J
authors.initials: J
authors.lastname: Clements
authors.forename: M
authors.initials: M
authors.lastname: Edwards
authors.forename: M J
authors.initials: MJ
authors.lastname: Humphries
authors.forename: A P
authors.initials: AP
authors.lastname: Mould
mesh_terms: D000595:Amino Acid Sequence; D001665:Binding Sites; D001667:Binding, Competitive; D002448:Cell Adhesion; D015815:Cell Adhesion Molecules / Q000378:metabolism*; D005353:Fibronectins / Q000378:metabolism*; D006801:Humans; D066298:In Vitro Techniques; D039041:Integrin alpha4beta1; D016023:Integrins / Q000378:metabolism*; D007700:Kinetics; D008024:Ligands; D008969:Molecular Sequence Data; D010455:Peptides / Q000737:chemistry / Q000378:metabolism; D011485:Protein Binding; D017469:Receptors, Fibronectin / Q000378:metabolism*; D019010:Vascular Cell Adhesion Molecule-1
chemical_list: D015815:Cell Adhesion Molecules; D005353:Fibronectins; D039041:Integrin alpha4beta1; D016023:Integrins; D008024:Ligands; D010455:Peptides; D017469:Receptors, Fibronectin; D019010:Vascular Cell Adhesion Molecule-1