Competitive binding of vascular cell adhesion molecule-1 and the HepII/IIICS domain of fibronectin to the integrin alpha 4 beta 1

• Published in: The Journal of biological chemistry Vol. 269; no. 6; pp. 4005 - 4011
• Main Authors: Makarem, R, Newham, P, Askari, J A, Green, L J, Clements, J, Edwards, M, Humphries, M J, Mould, A P
• Format: Journal Article
• Language: English
• Published: United States American Society for Biochemistry and Molecular Biology 11.02.1994
• Subjects: Amino Acid Sequence; Binding Sites; Binding, Competitive; Cell Adhesion; Cell Adhesion Molecules - metabolism; Fibronectins - metabolism; Humans; In Vitro Techniques; Integrin alpha4beta1; Integrins - metabolism; Kinetics; Ligands; Molecular Sequence Data; Peptides - chemistry; Peptides - metabolism; Protein Binding; Receptors, Fibronectin - metabolism; Vascular Cell Adhesion Molecule-1
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1016/S0021-9258(17)41734-0

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.