title: Ligand-induced Epitope Masking: DISSOCIATION OF INTEGRIN α5β1-FIBRONECTIN COMPLEXES ONLY BY MONOCLONAL ANTIBODIES WITH AN ALLOSTERIC MODE OF ACTION.
abstract: We previously demonstrated that Arg-Gly-Asp (RGD)-containing ligand-mimetic inhibitors of integrins are unable to dissociate pre-formed integrin-fibronectin complexes (IFCs). These observations suggested that amino acid residues involved in integrin-fibronectin binding become obscured in the ligand-occupied state. Because the epitopes of some function-blocking anti-integrin monoclonal antibodies (mAbs) lie near the ligand-binding pocket, it follows that the epitopes of these mAbs may become shielded in the ligand-occupied state. Here, we tested whether function-blocking mAbs directed against α5β1 can interact with the integrin after it forms a complex with an RGD-containing fragment of fibronectin. We showed that the anti-α5 subunit mAbs JBS5, SNAKA52, 16, and P1D6 failed to disrupt IFCs and hence appeared unable to bind to the ligand-occupied state. In contrast, the allosteric anti-β1 subunit mAbs 13, 4B4, and AIIB2 could dissociate IFCs and therefore were able to interact with the ligand-bound state. However, another class of function-blocking anti-β1 mAbs, exemplified by Lia1/2, could not disrupt IFCs. This second class of mAbs was also distinguished from 13, 4B4, and AIIB2 by their ability to induce homotypic cell aggregation. Although the epitope of Lia1/2 was closely overlapping with those of 13, 4B4, and AIIB2, it appeared to lie closer to the ligand-binding pocket. A new model of the α5β1-fibronectin complex supports our hypothesis that the epitopes of mAbs that fail to bind to the ligand-occupied state lie within, or very close to, the integrin-fibronectin interface. Importantly, our findings imply that the efficacy of some therapeutic anti-integrin mAbs could be limited by epitope masking.
authors.affiliation: From the Biomolecular Analysis Core Facility and.
authors.forename: A Paul
authors.initials: AP
authors.lastname: Mould
authors.affiliation: Wellcome Trust Centre for Cell-Matrix Research, Faculty of Life Sciences, University of Manchester, Manchester M13 9PT, United Kingdom.
authors.forename: Janet A
authors.initials: JA
authors.lastname: Askari
authors.affiliation: the Edinburgh Cancer Research UK Centre, Institute of Genetics and Molecular Medicine, University of Edinburgh, Edinburgh EH4 2XR, Scotland, United Kingdom, and.
authors.forename: Adam
authors.initials: A
authors.lastname: Byron
authors.affiliation: the Department of Vascular Biology, VB-1, The Scripps Research Institute, La Jolla, California 92037.
authors.forename: Yoshikazu
authors.initials: Y
authors.lastname: Takada
authors.affiliation: From the Biomolecular Analysis Core Facility and.
authors.forename: Thomas A
authors.initials: TA
authors.lastname: Jowitt
authors.affiliation: Wellcome Trust Centre for Cell-Matrix Research, Faculty of Life Sciences, University of Manchester, Manchester M13 9PT, United Kingdom, martin.humphries@manchester.ac.uk.
authors.forename: Martin J
authors.initials: MJ
authors.lastname: Humphries
mesh_terms: D000494:Allosteric Regulation / Q000276:immunology; D058846:Antibodies, Monoclonal, Murine-Derived / Q000737:chemistry* / Q000276:immunology; D000939:Epitopes / Q000737:chemistry* / Q000235:genetics / Q000276:immunology; D005353:Fibronectins / Q000737:chemistry* / Q000235:genetics / Q000276:immunology; D006801:Humans; D039081:Integrin alpha5beta1 / Q000737:chemistry* / Q000235:genetics / Q000276:immunology; D019169:Jurkat Cells; D008958:Models, Molecular; D009842:Oligopeptides / Q000737:chemistry* / Q000235:genetics / Q000276:immunology
chemical_list: D058846:Antibodies, Monoclonal, Murine-Derived; D000939:Epitopes; D005353:Fibronectins; D039081:Integrin alpha5beta1; D009842:Oligopeptides; C047981:arginyl-glycyl-aspartic acid
keywords: allosteric regulation; antibody; cell adhesion; epitope masking; fibronectin; integrin; therapeutics