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Blood, 1 February 2007, Vol. 109, No. 3, pp. 1018-1025.
Prepublished online as a Blood First Edition Paper on September 26, 2006; DOI 10.1182/blood-2006-05-022301.
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HEMOSTASIS, THROMBOSIS, AND VASCULAR BIOLOGY
ADAP is required for normal IIbß3 activation by VWF/GP Ib-IX-V and other agonists
Ana Kasirer-Friede1,
Barry Moran1,
Jennifer Nagrampa-Orje2,
Ken Swanson3,
Zaverio M. Ruggeri2,
Burkhart Schraven4,
Benjamin G. Neel3,
Gary Koretzky5, and
Sanford J. Shattil1
1 Department of Medicine, University of California San Diego, La Jolla;
2 Department of Molecular and Experimental Medicine, The Scripps Research Institute, La Jolla, CA;
3 Department of Medicine, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA;
4 Institute of Immunology, University of Magdeburg, Germany;
5 Abramson Family Cancer Research Institute and Division of Rheumatology, University of Pennsylvania, Philadelphia
Interaction between von Willebrand factor (VWF) and platelet GP Ib-IX-V is required for hemostasis, in part because intracellular signals from VWF/GP Ib-IX-V activate the ligand-binding function of integrin IIbß3. Because they also induce tyrosine phosphorylation of the ADAP adapter, we investigated ADAP's role in GP Ib-IX-V signal transduction. Fibrinogen or ligand-mimetic POW-2 Fab binding to IIbß3 was stimulated by adhesion of ADAP+/+ murine platelets to dimeric VWF A1A2 but was significantly reduced in ADAP/ platelets (P < .01). IIbß3 activation by ADP or a Par4 thrombin receptor agonist was also decreased in ADAP/ platelets. ADAP stabilized the expression of another adapter, SKAP-HOM, via interaction with the latter's SH3 domain. However, no abnormalities in IIbß3 activation were observed in SKAP-HOM/ platelets, which express normal ADAP levels, further implicating ADAP as a modulator of IIbß3 function. Under shear flow conditions over a combined surface of VWF A1A2 and fibronectin to test interactions involving GP Ib-IX-V and IIbß3, respectively, ADAP/ platelets displayed reduced IIbß3-dependent stable adhesion. Furthermore, ADAP/ mice demonstrated increased rebleeding from tail wounds. These studies establish ADAP as a component of inside-out signaling pathways that couple GP Ib-IX-V and other platelet agonist receptors to IIbß3 activation.

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