The Platelet High Affinity Binding Site for Thrombin Mimics Hirudin, Modulates Thrombin-induced Platelet Activation, and Is Distinct from the Glycoprotein Ib-IX-V Complex

Hayes, Kelly L.; Tracy, Paula B.

doi:10.1074/jbc.274.2.972

Cited by 23 publications

(14 citation statements)

References 35 publications

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“…Gene targeting of PARs reduces responsiveness of platelets to thrombin (37,38). The GP Ib subunit of the GP Ib-IX-V complex is a second thrombin-binding site on platelets, providing a high-affinity binding site and thus regulating surfacebound thrombin in human platelets (39,40). Additionally, the GP V subunit is a thrombin substrate and is cleaved during thrombin-induced platelet aggregation.…”

Section: Discussionmentioning

confidence: 99%

Increased thrombin responsiveness in platelets from mice lacking glycoprotein V

Ramakrishnan

Reeves

DeGuzman

et al. 1999

Proc. Natl. Acad. Sci. U.S.A.

108

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A role for glycoprotein (GP)V in platelet function has been proposed on the basis of observations that GP V is the major thrombin substrate on intact platelets cleaved during thrombin-induced platelet aggregation, and that GP V promotes GP Ib-IX surface expression in heterologous cells. We tested the hypotheses that GP V is involved in thrombin-induced platelet activation, in GP Ib-IX expression, and in other platelet responses by generating GP V null mice. Contrary to expectations, GP V ؊͞؊ platelets were normal in size and expressed normal amounts of GP Ib-IX that was functional in von Willebrand factor binding, explaining why defects in GP V have not been observed in Bernard-Soulier syndrome, a bleeding disorder caused by a lack of functional GP Ib-IX-V. Moreover, in vitro analysis demonstrated that GP V ؊͞؊ platelets were hyperresponsive to thrombin, resulting in increased fibrinogen binding and an increased aggregation response. Consistent with these findings, GP V ؊͞؊ mice had a shorter bleeding time. These data support a role for GP V as a negative modulator of platelet activation. Furthermore, they suggest a new mechanism by which thrombin enhances platelet responsiveness independent of activation of the classical G-protein-coupled thrombin receptors. P latelet thrombosis and hemostasis are complex reactions that depend on adhesive interactions mediated by specific receptors. A major platelet complex is glycoprotein (GP) Ib-IX-V. The initial adhesion of platelets is primarily mediated by binding of platelet membrane GP Ib-IX-V to von Willebrand factor (vWf) found on damaged vessel walls (1). After adhesion, binding of other agonists such as thrombin, ADP, and collagen induce signaling events that ultimately activate the receptor function of ␣⌱⌱b␤3 for soluble fibrinogen, leading to platelet aggregation (2). Although platelet aggregates are required for normal hemostasis, they can in addition cause arterial thrombosis in atherosclerotic arteries, e.g., acute myocardial infarction and stroke, inducing ischemic complications of cardiovascular disease (3, 4).The importance of the GP Ib-IX-V complex in normal platelet function is underscored by the study of Bernard-Soulier syndrome (BSS), an inherited bleeding disorder characterized by large platelets that are defective in adhesion to damaged vessel walls (1). This genetic disorder is caused by a lack of functional GP Ib-IX-V and has been linked to defects in either GP Ib or GP IX (5). The activities mapped to the GP Ib subunit of the GP Ib-IX-V complex include vWf (6) and thrombin binding (7, 8) on the extracellular domain and actin-binding protein (9-11) and 14-3-3 (12-15) binding on the cytoplasmic domain.Several studies indicate functional activities for the GP V subunit of the GP Ib-IX-V complex. In one example, GP V has been shown to be cleaved by thrombin from the platelet surface during thrombin-mediated platelet stimulation (16), but the role of GP V cleavage in this thrombin-induced platelet response is unresolved (17). In another example, the signa...

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Section: Discussionmentioning

confidence: 99%

Increased thrombin responsiveness in platelets from mice lacking glycoprotein V

Ramakrishnan

Reeves

DeGuzman

et al. 1999

Proc. Natl. Acad. Sci. U.S.A.

108

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“…Disruption of this interaction impedes the capacity of ␣-thrombin to cleave PAR 1 and cause aggregation of platelets, suggesting that glycoprotein I␤␣ is a cofactor for PAR 1 that promotes PAR 1mediated platelet aggregation (84). Thrombin may also interact with other proteins on platelets (118).…”

Section: E Protease Binding To Other Membrane Proteins Can Facilitatmentioning

confidence: 99%

Protease-Activated Receptors: Contribution to Physiology and Disease

Ossovskaya

Bunnett

2004

Physiological Reviews

998

1,103

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Proteases acting at the surface of cells generate and destroy receptor agonists and activate and inactivate receptors, thereby making a vitally important contribution to signal transduction. Certain serine proteases that derive from the circulation (e.g., coagulation factors), inflammatory cells (e.g., mast cell and neutrophil proteases), and from multiple other sources (e.g., epithelial cells, neurons, bacteria, fungi) can cleave protease-activated receptors (PARs), a family of four G protein-coupled receptors. Cleavage within the extracellular amino terminus exposes a tethered ligand domain, which binds to and activates the receptors to initiate multiple signaling cascades. Despite this irreversible mechanism of activation, signaling by PARs is efficiently terminated by receptor desensitization (receptor phosphorylation and uncoupling from G proteins) and downregulation (receptor degradation by cell-surface and lysosomal proteases). Protease signaling in tissues depends on the generation and release of proteases, availability of cofactors, presence of protease inhibitors, and activation and inactivation of PARs. Many proteases that activate PARs are produced during tissue damage, and PARs make important contributions to tissue responses to injury, including hemostasis, repair, cell survival, inflammation, and pain. Drugs that mimic or interfere with these processes are attractive therapies: selective agonists of PARs may facilitate healing, repair, and protection, whereas protease inhibitors and PAR antagonists can impede exacerbated inflammation and pain. Major future challenges will be to understand the role of proteases and PARs in physiological control mechanisms and human diseases and to develop selective agonists and antagonists that can be used to probe function and treat disease.

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“…74 Also, one group has tentatively identified a thrombinbinding site that is thought to be independent of the 2 sites mentioned above. 75 Unactivated factor VIII circulates in association with von Willebrand factor and can bind to platelets through the von Willebrand factor-binding site on the GP Ib-IX-V complex. 76 Previous studies have shown that platelets potentiate thrombin activation of factor VIII.…”

Section: Platelet-binding Proteins Important For the Priming Stepmentioning

confidence: 99%

Platelets and Thrombin Generation

Monroe

Hoffman

Roberts

2002

ATVB

604

479

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Abstract-This review examines the evidence that platelets play a major role in localizing and controlling the burst of thrombin generation leading to fibrin clot formation. From the first functional description of platelets, it has been recognized that platelets supply factors that support the activation of prothrombin. Studies have demonstrated that on activation, the amount of one specific lipid, phosphatidylserine, is significantly increased on the outer leaflet of platelet membranes. When it was found that phosphatidylserine containing lipid extracts could be substituted for platelets in clotting assays, this suggested the possibility that changes in platelet lipid composition were necessary and sufficient to account for platelet surface thrombin generation. Because a growing body of data suggest that platelet-binding proteins provide much of the specificity for platelet thrombin generation, we review in this report data suggesting that changes in lipid composition are necessary but not sufficient to account for platelet surface regulation of thrombin generation. Also, we review data suggesting that platelets from different individuals differ in their capacity to generate thrombin, whereas platelets from a single subject support thrombin generation in a reproducible manner. Individual differences in platelet thrombin generation might be accounted for by differences in platelet-binding proteins.

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The Platelet High Affinity Binding Site for Thrombin Mimics Hirudin, Modulates Thrombin-induced Platelet Activation, and Is Distinct from the Glycoprotein Ib-IX-V Complex

Cited by 23 publications

References 35 publications

Increased thrombin responsiveness in platelets from mice lacking glycoprotein V

Increased thrombin responsiveness in platelets from mice lacking glycoprotein V

Protease-Activated Receptors: Contribution to Physiology and Disease

Platelets and Thrombin Generation

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