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Platelet Integrin (platelet + integrin)
Selected AbstractsThe ,3 integrin cytoplasmic tail: protein scaffold and control freakJOURNAL OF THROMBOSIS AND HAEMOSTASIS, Issue 2009S. J. SHATTIL Summary., Platelet integrin ,IIb,3 plays an essential role in thrombus formation through interactions with adhesive ligands. Successful parenteral blockade of these interactions has validated ,IIb,3 as a therapeutic target in cardiovascular medicine. However, oral ,IIb,3 antagonists have not been successful and there is an unmet need for more effective anti-platelet drugs. Growing evidence points to the cytoplasmic tails of ,IIb and ,3, and the ,3 tail in particular, as scaffolds for intracellular proteins that mediate inside-out signaling and regulate ,IIb,3 affinity for ligands. Intracellular protein interactions with the integrin cytoplasmic tails also regulate outside-in signals to the actin cytoskeleton. Here we focus on recent studies that illustrate the relevance of the ,3 cytoplasmic tail as a regulatory scaffold in vivo. We speculate that this scaffold or its interacting proteins may serve as therapeutic targets for the development of future anti-thrombotic drugs. [source] Platelet integrin ,IIb,3: activation mechanismsJOURNAL OF THROMBOSIS AND HAEMOSTASIS, Issue 7 2007Y.-Q. MA Summary., Integrin ,IIb,3 plays a critical role in platelet aggregation, a central response in hemostasis and thrombosis. This function of ,IIb,3 depends upon a transition from a resting to an activated state such that it acquires the capacity to bind soluble ligands. Diverse platelet agonists alter the cytoplasmic domain of ,IIb,3 and initiate a conformational change that traverses the transmembrane region and ultimately triggers rearrangements in the extracellular domain to permit ligand binding. The membrane-proximal regions of ,IIb and ,3 cytoplasmic tails, together with the transmembrane segments of the subunits, contact each other to form a complex which restrains the integrin in the resting state. It is unclasping of this complex that induces integrin activation. This clasping/unclasping process is influenced by multiple cytoplasmic tail binding partners. Among them, talin appears to be a critical trigger of ,IIb,3 activation, but other binding partners, which function as activators or suppressors, are likely to act as co-regulators of integrin activation. [source] Critical role of ADP interaction with P2Y12 receptor in the maintenance of ,IIb,3 activation: association with Rap1B activationJOURNAL OF THROMBOSIS AND HAEMOSTASIS, Issue 6 2006T. KAMAE Summary.,Objective:,Platelet integrin ,IIb,3 plays a crucial role in platelet aggregation, and the affinity of ,IIb,3 for fibrinogen is dynamically regulated. Employing modified ligand-binding assays, we analyzed the mechanism by which ,IIb,3 maintains its high-affinity state. Methods and results:,Washed platelets adjusted to 50 × 103 ,L,1 were stimulated with 0.2 U mL,1 thrombin or 5 ,m U46619 under static conditions. After the completion of ,IIb,3 activation and granule secretion, different kinds of antagonists were added to the activated platelets. The activated ,IIb,3 was then detected by fluorescein isothiocyanate (FITC)-labeled PAC1. The addition of 1 ,m AR-C69931MX (a P2Y12 antagonist) or 1 mm A3P5P (a P2Y1 antagonist) disrupted the sustained ,IIb,3 activation by ,92% and ,38%, respectively, without inhibiting CD62P or CD63 expression. Dilution of the platelet preparation to 500 ,L,1 also disrupted the sustained ,IIb,3 activation, and the disruption by such dilution was abrogated by the addition of exogenous adenosine 5,-diphosphate (ADP) in a dose-dependent fashion. The amounts of ADP released from activated platelets determined by high-performance liquid chromatography were compatible with the amounts of exogenous ADP required for the restoration. We next examined the effects of antagonists on protein kinase C (PKC) and Rap1B activation induced by 0.2 U mL,1 thrombin. Thrombin induced long-lasting PKC and Rap1B activation. AR-C69931MX markedly inhibited Rap1B activation without inhibiting PKC activation. Conclusions:,Our data indicate that the continuous interaction between released ADP and P2Y12 is critical for the maintenance of ,IIb,3 activation. [source] Involvement of the ,3 E749ATSTFTN756 region in stabilizing integrin ,IIb,3 -ligand interactionJOURNAL OF THROMBOSIS AND HAEMOSTASIS, Issue 10 2003P. E. M. H. Litjens Summary., Platelet integrin ,IIb,3 must be activated via intracellular mechanisms before it binds soluble ligands, and it is thought to be activated at its extracellular site by surface-bound ligands. Integrin activation is associated with rearrangement of the cytoskeleton and phosphorylation of proteins that become localized in focal contacts. In these processes, the cytoplasmic tail of the ,-subunit plays a central role. We introduced peptides homologous to the E749ATSTFTN756 domain (E,N peptide) and the T755NITYRGT762 domain (T,T peptide) of ,3 in streptolysin O-permeabilized platelets and analyzed the initial interaction with soluble fibronectin, fibrinogen and PAC-1 after stimulation with thrombin. E,N peptide left the initial binding of fibronectin intact but interfered with stable receptor occupancy. E,N peptide also inhibited fibrinogen binding, thereby reducing the formation of large aggregates. Strikingly, E,N peptide did not disturb the binding of PAC-1, which is known to reflect activation of the integrin. E,N peptide also inhibited tyrosine phosphorylation of focal adhesion kinase, a response known to be dependent on ,IIb,3. T,T peptide did not affect these processes. In a model for outside-in integrin activation, E,N peptide disrupted the binding of CHO cells expressing ,IIb,3 to surface-bound ligand. Again, T,T peptide had no effect. We conclude that the E749ATSTFTN756 region of the ,3 -tail stabilizes the binding of soluble and surface-bound ligand to integrin ,IIb,3 via a mechanism that involves the phosphorylation of FAK. [source] Diversity of Glanzmann thrombasthenia in southern India: 10 novel mutations identified among 15 unrelated patientsJOURNAL OF THROMBOSIS AND HAEMOSTASIS, Issue 8 2006E. J. R. NELSON Summary.,Background: Glanzmann thrombasthenia (GT) is a congenital bleeding disorder caused by either a lack or dysfunction of the platelet integrin ,IIb,3. Objectives: To determine the molecular basis of GT in patients from southern India. Patients: Fifteen unrelated patients whose diagnosis was consistent with GT were evaluated. Results: Platelet surface expression of ,IIb,3 was < 10%, 10%,50%, and > 50% of controls in five, nine, and one patient(s), respectively. Immunoblotting of the platelet lysates showed no ,IIb in 14 patients, and no ,3 in 10 patients, although severely reduced in four patients. Platelet fibrinogen was undetectable in 13 patients, and severely reduced in one patient. One patient showed normal surface ,IIb,3 expression, and normal ,IIb, ,3 and fibrinogen levels in the lysate. Ten novel candidate disease-causing mutations were identified in 11 patients. The missense mutations included Gly128Ser, Ser287Leu, Gly357Ser, Arg520Trp, Leu799Arg in ,IIb, and Cys575Gly in ,3. We have already shown that Gly128Ser, Ser287Leu, and Gly357Ser mutations variably affect ,IIb,3 surface expression. The Cys575Gly mutation may disrupt the disulphide link with Cys586 to cause the GT phenotype. The molecular pathology of the other missense mutations is not clear. Two nonsense mutations, Trp-16Stop and Glu715Stop in ,IIb, and a 7-bp deletion (330-336TCCCCAG) in ,3 are predicted to result in truncated proteins. An IVS15(,1)G , A mutation in ,IIb induced a cryptic splice site as confirmed by reverse transcription-polymerase chain reaction (RT-PCR) analysis. Thirteen polymorphisms were also identified (five in ,IIb and eight in ,3), among which five were novel. Conclusions: While identifying a significant number of novel mutations causing GT, this study confirms the genetic heterogeneity of the disorder in southern India. [source] The regulation of integrin-linked kinase in human platelets: evidence for involvement in the regulation of integrin ,2,1JOURNAL OF THROMBOSIS AND HAEMOSTASIS, Issue 8 2004J. M. Stevens Summary.,Background: Activation of the platelet integrin ,2,1 is closely regulated due to the high thrombogenicity of its ligand. As a ,1 interacting kinase, ILK represents a candidate intracellular regulator of ,2,1 in human platelets. Objectives We investigated the regulation of ILK in human platelets and the role of ILK in regulating ,2,1 activation in HEL cells, a megakaryocytic cell line. Methods: An in-vitro kinase assay was used to determine the effect of platelet agonists on ILK kinase activity together with the contribution of PI3K and PKC on ILK activation. Interaction of ILK with ,1 -integrin subunits was investigated by coimmunoprecipitation and the role of ILK in regulating ,2,1 function assessed by overexpression studies in HEL cells. Results: We report that collagen and thrombin modulate ILK kinase activity in human platelets in an aggregation-independent manner. Furthermore, ILK activity is dually regulated by PI3K and PKC in thrombin-stimulated platelets and regulated by PI3K in collagen-stimulated cells. ILK associates with the ,1 -integrin subunits immunoprecipitated from platelet cell lysates, an association which increased upon collagen stimulation. Overexpression of ILK in HEL cells enhanced ,2,1 -mediated adhesion whereas overexpression of kinase-dead ILK reduced adhesion, indicating a role for this kinase in the positive regulation of ,2,1. Conclusions: Our findings that ILK regulates ,2,1 in HEL cells, is activated in platelets and associates with ,1 -integrins, raise the possibility that it may play a key role in adhesion events upon agonist stimulation of platelets. [source] Dynamic Aspects Of Platelet Adhesion Under FlowCLINICAL AND EXPERIMENTAL PHARMACOLOGY AND PHYSIOLOGY, Issue 5-6 2001Sacha M Dopheide SUMMARY 1. Cell,cell and cell,matrix adhesive interactions are critical for a wide range of physiological processes, including embryogenesis, inflammation, immunity and haemostasis. 2. The ability of circulating blood cells, such as platelets and leucocytes, to adhere to sites of vascular injury is complicated by the presence of blood flow, which imposes hydrodynamic forces on adhesion contacts. 3. To overcome this problem, platelets and leucocytes have evolved specific adhesion receptors with unique biomechanical properties that enable these cells to adhere to the vessel wall under flow conditions. 4. Platelet adhesion in the normal circulation appears to be a multiple-step process involving an initial reversible interaction between the platelet adhesion receptor glycoprotein Ib-IX-V and the vascular adhesion protein von Willebrand factor. Once tethered to the vessel wall, platelets form irreversible adhesion contacts through the binding of one or more platelet integrins to specific subendothelial matrix proteins. 5. There is now a wealth of evidence demonstrating that these receptors not only mediate platelet adhesion, but also transduce signals leading to platelet activation. 6. In the present review, we will briefly discuss the current understanding of the specific roles of individual platelet receptors in supporting the haemostatic function of platelets and discuss mechanisms by which these receptors induce platelet activation. [source] | ||||||||||