Signaling across the Platelet Adhesion Receptor Glycoprotein Ib-IX Induces αIIbβ3 Activation Both in Platelets and a Transfected Chinese Hamster Ovary Cell System

Yona Zaffran,Sylvie C Meyer,Emil Negrescu,Kumar B Reddy,Joan E.B Fox

doi:10.1074/jbc.275.22.16779

Yona Zaffran, Sylvie C Meyer + Show 3 more

Open Access

https://doi.org/10.1074/jbc.275.22.16779

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Abstract

In platelets, alpha(IIb)beta(3) exists in a form that cannot bind adhesive proteins in the plasma; although it can interact with immobilized fibrinogen it cannot interact with immobilized von Willebrand factor in the vessel wall. Soluble agonists such as thrombin convert alpha(IIb)beta(3) to a form that recognizes soluble and immobilized ligands. Attempts to reconstitute alpha(IIb)beta(3) activation in a non-hematopoietic, nucleated cell system have been unsuccessful. In the present study, we have developed a transfected Chinese hamster ovary cell model in which alpha(IIb)beta(3) activation is induced by signaling across glycoprotein (GP) Ib-IX by its ligand, von Willebrand factor. GPIb-IX activates not only the transfected alpha(IIb)beta(3) but also endogenous alpha(v)beta(3). Activation of the pathways leading to integrin activation occurred even in cells transfected with GPIb-IX lacking the domain on GPIbalpha that binds 14-3-3 or that which binds actin-binding protein. These studies demonstrate that signals induced by interaction of GPIb-IX with von Willebrand factor lead to alpha(IIb)beta(3) activation and suggest that the signaling pathways by which GPIb-IX induces alpha(IIb)beta(3) activation are different to those used by thrombin. Elucidation of these differences may provide insights into therapeutic ways in which to inhibit integrin activation in selective clinical settings.

Highlights

In platelets, ␣IIb␤3 exists in a form that cannot bind adhesive proteins in the plasma; it can interact with immobilized fibrinogen it cannot interact with immobilized von Willebrand factor in the vessel wall
GPIb-IX-induced Activation of ␣IIb␤3 Detected by Outside-in Signaling across Activated ␣IIb␤3 in Platelets—GPIb-IX can bind to vWf in the blood vessel wall but is not able to bind to vWf immobilized on glass unless a modulator such as ristocetin or botrocetin is present [25, 26]
Platelets that lacked ␣IIb␤3 adhered but showed little spreading. Both adhesion and spreading occurred even in the presence of aspirin and apyrase supporting the idea that integrin activation occurred as a direct consequence of GPIb-IX-induced signaling and was not due to ADP or thromboxane secreted from the platelet

Summary

Introduction

In platelets, ␣IIb␤3 exists in a form that cannot bind adhesive proteins in the plasma; it can interact with immobilized fibrinogen it cannot interact with immobilized von Willebrand factor in the vessel wall Soluble agonists such as thrombin convert ␣IIb␤3 to a form that recognizes soluble and immobilized ligands. Activation of the pathways leading to integrin activation occurred even in cells transfected with GPIb-IX lacking the domain on GPIb␣ that binds 14-3-3 or that which binds actin-binding protein These studies demonstrate that signals induced by interaction of GPIb-IX with von Willebrand factor lead to ␣IIb␤3 activation and suggest that the signaling pathways by which GPIb-IX induces ␣IIb␤3 activation are different to those used by thrombin. The suggestion has been made that the pathway involved in ␣IIb␤3 activation is specific for hematopoietic cells [11]

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