Fibrinogen Is a Ligand for Integrin α5β1 on Endothelial Cells

doi:10.1074/jbc.272.8.5360

Fibrinogen Is a Ligand for Integrin α₅β₁ on Endothelial Cells*

^‡ Joseph J. Jacobs Center for Thrombosis and Vascular Biology, Department of Molecular Cardiology, The Cleveland Clinic Foundation, Cleveland, Ohio 44195 and the
^§ Department of Dermatology, State University of New York, Stony Brook, New York 11794-8165

^¶ To whom correspondence should be addressed:
Joseph J. Jacobs Center for Thrombosis and Vascular Biology/FF20, The Cleveland Clinic Foundation, 9500 Euclid Ave., Cleveland, Ohio 44195.
Tel.: 216-445-8200; Fax: 216-445-8204.

Abstract

Previous studies have shown that fibrinogen can associate with endothelial cells via an Arg-Gly-Asp (RGD) recognition specificity. In the present study, we have characterized the specificity of fibrinogen binding to endothelial cells under different cation conditions. Fibrinogen binding to suspended endothelial cells was selectively supported by Mn²⁺ and was suppressed by Ca²⁺. The Mn²⁺-supported interaction was completely inhibited by RGD peptides but not by α_vβ₃ blocking monoclonal antibodies. In contrast, the interaction was completely blocked by two α₅β₁ monoclonal antibodies. This interaction was not mediated by fibronectin bound to the integrin; could be demonstrated with purified α₅β₁; and also was observed with a second α₅β₁-bearing cell type, platelets. The binding of fibrinogen to α₅β₁ on endothelial cells in the presence of Mn²⁺ was time-dependent, specific, saturable, and of high affinity (K_d = 65 nM). By employing anti-peptide monoclonal antibodies, the carboxyl-terminal RGD sequence at Aα 572-574 was implicated in fibrinogen recognition by α₅β₁. Two circumstances were identified in which α₅β₁ interacted with fibrinogen in the presence of Ca²⁺: when the receptor was activated with monoclonal antibody (8A2) or when the fibrinogen was presented as an immobilized substratum. These results identify fibrinogen as a ligand for α₅β₁ on endothelial and other cells, an interaction which may have broad biological implications.

Footnotes

↵* This work was supported by National Institutes of Health Grants HL-38292 and HL-54924. 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.
↵¹ The abbreviations used are:

EC

endothelial cells

BSA

bovine serum albumin

Fg

fibrinogen

Fn

fibronectin

HUVEC

human umbilical vein endothelial cells

mAb

monoclonal antibody

RGD

Arg-Gly-Asp.
- Received June 6, 1996.
- Revision received December 10, 1996.