Fibronectin Type III5 Repeat Contains a Novel Cell Adhesion Sequence, KLDAPT, Which Binds Activated α4β1 and α4β7 Integrins

doi:10.1074/jbc.272.40.24832

Fibronectin Type III5 Repeat Contains a Novel Cell Adhesion Sequence, KLDAPT, Which Binds Activated α4β1 and α4β7 Integrins*

From the ^‡Departamento de Inmunologı́a, Centro de Investigaciones Biológicas, CSIC, 28006 Madrid, Spain;^‖Laboratory of Cell Biology, Istituto Nazionale per la Ricerca sul Cancro, 16132 Genoa, Italy; and ^§§Departamento de Inmunologı́a y Oncologı́a, Centro Nacional de Biotecnologı́a, CSIC, 28049 Madrid, Spain

Abstract

The region of fibronectin encompassing type III repeats 4–6 contains a low affinity heparin binding domain, but its physiological significance is not clear. We have studied whether this domain is able to interact with cells as already shown for other heparin binding domains of fibronectin. A computer search based on homologies with known active sites in fibronectin revealed the sequence KLDAPT located in FN-III5. A synthetic peptide containing this sequence induced lymphoid cell adhesion upon treatment with the activating anti-β1 monoclonal antibody (mAb) TS2/16 or with Mn²⁺, indicating that KLDAPT was binding to an integrin. A recombinant fragment containing repeat III5 (FN-III5) also mediated adhesion of TS2/16/Mn²⁺-treated cells while the FN-III6 fragment did not. Soluble KLDAPT peptide inhibited cell adhesion to FN-III5 as well as to a 38-kDa fibronectin fragment and VCAM-1, two previously known ligands for α4β1 integrin. KLDAPT also competed with the binding of soluble alkaline phosphatase-coupled VCAM-Ig to Mn²⁺-treated α4β1. Furthermore, mAbs anti-α4 and anti-α4β7, but not mAbs to other integrins, inhibited cell adhesion to FN-III5 and KLDAPT. These results therefore establish a cell adhesive function for the FN-III5 repeat and show that KLDAPT is a novel fibronectin ligand for activated α4 integrins.

Footnotes

↵* This work was supported by Grants SAF94-0117 from the Comisión Interministerial de Ciencia y Tecnologı́a (CICYT), 94/0277 from Fondo de Investigaciones Sanitarias (FIS), AE00413/95 from the Comunidad Autónoma de Madrid, and BMH1-CT92–0376 from the European Union Biomed 1 Program (to A. G. P.), and partially by funds from the Associazione Italiana per la Ricerca sul Cancro (AIRC) and the Consiglio Nazionale delle Ricerche (CNR), “Progetto finalizzato: applicazioni cliniche della ricerca oncologica” (to L. Z).The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
↵§ The first two authors contributed equally to this work.
↵¶ Supported by a fellowship from Fondo de Investigaciones Sanitarias.
↵** Supported by a fellowship from Fondo de Investigaciones Sanitarias. Present address: Hospital del la Princesa, 28006 Madrid, Spain.
↵‡ Supported by a fellowship from Comisión Interministerial de Ciencia y Tecnologı́a.
↵¶¶ Present address: The Netherland Cancer Institute, 1066 CX Amsterdam, The Netherlands.
↵166 To whom correspondence should be addressed: Centro de Investigaciones Biológicas, CSIC, Velázquez 144, 28006 Madrid, Spain. Tel.: 34-1-564 4562 (ext. 4430); Fax: 34-1-562 7518; E-mail: cibgp96{at}fresno.csic.es.
↵1 The abbreviations used are: Fn, fibronectin; mAb, monoclonal antibody; KLH, keyhole limpet hemocyanin.
↵2 B. Carnemolla, A. Leprini, G. Querzé, and L. Zardi, unpublished results.
- Received April 3, 1997.
- Revision received July 14, 1997.