ADAP is required for normal alphaIIbbeta3 activation by VWF/GP Ib-IX-V and other agonists.
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 alphaIIbbeta3. 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 alphaIIbbeta3 was stimulated by adhesion of ADAP+/+ murine platelets to dimeric VWF A1A2 but was significantly reduced in ADAP-/- platelets (P<.01). alphaIIbbeta3 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 alphaIIbbeta3 activation were observed in SKAP-HOM-/- platelets, which express normal ADAP levels, further implicating ADAP as a modulator of alphaIIbbeta3 function. Under shear flow conditions over a combined surface of VWF A1A2 and fibronectin to test interactions involving GP Ib-IX-V and alphaIIbbeta3, respectively, ADAP-/- platelets displayed reduced alphaIIbbeta3-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 alphaIIbbeta3 activation.
Kasirer-Friede
Ana
A
Department of Medicine, University of California San Diego, La Jolla 92093-0726, USA. akasirer@ucsd.edu
Moran
Barry
B
Nagrampa-Orje
Jennifer
J
Swanson
Ken
K
Ruggeri
Zaverio M
ZM
Schraven
Burkhart
B
Neel
Benjamin G
BG
Koretzky
Gary
G
Shattil
Sanford J
SJ
D048868:Adaptor Proteins, Signal Transducing / Q000172:deficiency / Q000502:physiology*; D000818:Animals; D005340:Fibrinogen / Q000378:metabolism; D006470:Hemorrhage; D051379:Mice; D018345:Mice, Knockout; D010973:Platelet Adhesiveness; D019039:Platelet Glycoprotein GPIIb-IIIa Complex / Q000819:agonists / Q000378:metabolism*; D019038:Platelet Glycoprotein GPIb-IX Complex / Q000378:metabolism / Q000502:physiology*; D015398:Signal Transduction; D014841:von Willebrand Factor / Q000378:metabolism / Q000502:physiology*
D048868:Adaptor Proteins, Signal Transducing; C491468:Fyb protein, mouse; D019039:Platelet Glycoprotein GPIIb-IIIa Complex; D019038:Platelet Glycoprotein GPIb-IX Complex; D014841:von Willebrand Factor; D005340:Fibrinogen