von Willebrand factor mediates platelet spreading through glycoprotein Ib and alpha(IIb)beta3 in the presence of botrocetin and ristocetin, respectively.
BACKGROUND
von Willebrand factor (VWF) plays a critical role in the process of hemostasis by mediating flow-dependent adhesion and spreading of platelets on exposed extracellular matrix proteins following vascular injury. To accomplish this, VWF binds to two distinct platelet receptors: glycoprotein (GP)Ib-IX-V and integrin alpha(IIb)beta3.


OBJECTIVE
To evaluate the ability of GPIb and alpha(IIb)beta3 to mediate platelet adhesion and lamellipodia formation on immobilized VWF in the presence of the biochemical modulators, ristocetin and botrocetin.


RESULTS
In the presence of botrocetin and inhibitors of adenosine diphosphate (ADP) and thromboxane A2 (TxA2), VWF is able to support formation of lamellipodia through a GPIb-dependent mechanism that is independent of alpha(IIb)beta3 and PI3-kinase. Lamellipodia formation under these conditions is incomplete. In marked contrast, in the presence of ristocetin, VWF stimulates formation of fully spread lamellipodia through a pathway that is dependent upon alpha(IIb)beta3 and PI3-kinase. Furthermore, alpha(IIb)beta3 also supports platelet spreading on VWF alone, but only in the absence of inhibitors of ADP and TxA2. The localization of filamentous actin and the Arp2/3 complex in platelets on VWF in the presence of botrocetin and ristocetin are distinct, yielding disparate lamellipodium kinetic signatures. Interestingly, botrocetin significantly enhances platelet adhesion to VWF under flow in whole blood in an alpha(IIb)beta3-independent manner, while ristocetin augments washed platelet adhesion and spreading to VWF under flow in an alpha(IIb)beta3-dependent manner.


CONCLUSIONS
These observations demonstrate that VWF is able to induce lamellipodia formation through distinct receptors, and has important consequences for investigation of the role of VWF-GPIb interactions in the context of platelet regulation.
McCarty
O J T
OJ
Centre for Cardiovascular Sciences, University of Birmingham, Birmingham, UK. mccartyo@ohsu.edu
Calaminus
S D J
SD
Berndt
M C
MC
Machesky
L M
LM
Watson
S P
SP
D008841:Actin Cytoskeleton / Q000378:metabolism; D000818:Animals; D001569:Benzodiazepines / Q000494:pharmacology; D001792:Blood Platelets / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D003435:Crotalid Venoms / Q000494:pharmacology; D003599:Cytoskeleton; D006801:Humans; D066298:In Vitro Techniques; D051379:Mice; D018345:Mice, Knockout; D009479:Neuropeptides / Q000235:genetics; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010880:Piperidines / Q000494:pharmacology; D010973:Platelet Adhesiveness / Q000187:drug effects / Q000502:physiology*; D010975:Platelet Aggregation Inhibitors / Q000494:pharmacology; D019039:Platelet Glycoprotein GPIIb-IIIa Complex / Q000037:antagonists & inhibitors / Q000378:metabolism*; D019038:Platelet Glycoprotein GPIb-IX Complex / Q000378:metabolism*; D011554:Pseudopodia / Q000187:drug effects / Q000378:metabolism*; D012310:Ristocetin / Q000494:pharmacology; D015398:Signal Transduction; D020744:rac GTP-Binding Proteins / Q000235:genetics; D020830:rac1 GTP-Binding Protein; D019061:src-Family Kinases / Q000378:metabolism; D014841:von Willebrand Factor / Q000378:metabolism*; D000097766:RAC2 GTP-Binding Protein
D001569:Benzodiazepines; D003435:Crotalid Venoms; D009479:Neuropeptides; D019869:Phosphatidylinositol 3-Kinases; D010880:Piperidines; D010975:Platelet Aggregation Inhibitors; D019039:Platelet Glycoprotein GPIIb-IIIa Complex; D019038:Platelet Glycoprotein GPIb-IX Complex; D012310:Ristocetin; D020744:rac GTP-Binding Proteins; D020830:rac1 GTP-Binding Protein; D019061:src-Family Kinases; D014841:von Willebrand Factor; D000097766:RAC2 GTP-Binding Protein; C484602:Rac1 protein, mouse; C030961:botrocetin; C412702:lotrafiban