Signal Transduction Pathways Mediated by Glycoprotein Ia/IIa in Human Platelets: Comparison with Those of Glycoprotein VI

Inoue, Katsue; Satoh, Kaneo; Yatomi, Yutaka; Shin, Yongchol; Morita, Takashi

doi:10.1006/bbrc.1999.0295

Cited by 41 publications

(50 citation statements)

References 26 publications

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“…The N-terminal sequences that they determined are identical with the first 22 and 19 amino acids, respectively, of aggretin. Recently, the same group reported that the ␣ 2 subunit of ␣ 2 ␤ 1 is involved in the platelet interaction with rhodocytin and investigated some aspects of signal transduction occurring in platelets after activation with rhodocytin (20,21). The situation has been complicated by a recent report that rhodocytin does not bind to a recombinant ␣ 2 ␤ 1 complex, whereas another C. rhodostoma venom C-type lectin, rhodocetin, composed of noncovalently associated ␣-and ␤-subunits with different sequences than those of aggretin or rhodocytin, bound strongly to the recombinant complex and blocked its binding to collagen (22).…”

Section: Discussionmentioning

confidence: 99%

“…A C-type lectin from the same species, termed rhodocytin, was described later (19) with N-terminal sequences identical to those of aggretin, but it was reported to have some different properties. The mechanism of rhodocytin action on platelets was recently investigated (20,21), showing that rhodocytin interacts with the ␣ 2 -subunit of ␣ 2 ␤ 1 on the platelet surface. On the other hand, Eble et al (22) have reported that rhodocytin does not bind to a recombinant ␣ 2 ␤ 1 complex.…”

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confidence: 99%

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Aggretin, a Heterodimeric C-type Lectin from Calloselasma rhodostoma (Malayan Pit Viper), Stimulates Platelets by Binding to α2β1 Integrin and Glycoprotein Ib, Activating Syk and Phospholipase Cγ2, but Does Not Involve the Glycoprotein VI/Fc Receptor γ Chain Collagen Receptor

Navdaev

Clemetson

Polgár

et al. 2001

Journal of Biological Chemistry

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Aggretin, a potent platelet activator, was isolated from Calloselasma rhodostoma venom, and 30-amino acid N-terminal sequences of both subunits were determined. Aggretin belongs to the heterodimeric snake Ctype lectin family and is thought to activate platelets by binding to platelet glycoprotein ␣ 2 ␤ 1 . We now show that binding to glycoprotein (GP) Ib is also required. Aggretin-induced platelet activation was inhibited by a monoclonal antibody to GPIb as well as by antibodies to ␣ 2 ␤ 1 . Binding of both of these platelet receptors to aggretin was confirmed by affinity chromatography. No binding of other major platelet membrane glycoproteins, in particular GPVI, to aggretin was detected. Aggretin also activates platelets from Fc receptor ␥ chain (Fc␥)-deficient mice to a greater extent than those from normal control mice, showing that it does not use the GPVI/Fc␥ pathway. Platelets from Fc␥-deficient mice expressed fibrinogen receptors normally in response to collagen, although they did not aggregate, indicating that these platelets may partly compensate via other receptors including ␣ 2 ␤ 1 or GPIb for the lack of the Fc␥ pathway. Signaling by aggretin involves a dose-dependent lag phase followed by rapid tyrosine phosphorylation of a number of proteins. Among these are p72 SYK , p125 FAK , and PLC␥2, whereas, in comparison with collagen and convulxin, the Fc␥ subunit neither is phosphorylated nor coprecipitates with p72 SYK . This supports an independent, GPIb-and integrin-based pathway for activation of p72 SYK not involving the Fc␥ receptor.Platelet-collagen interactions are integral to primary hemostasis (1, 2). Resting platelets using several receptors adhering to subendothelium of damaged blood vessels are activated and spread to provide finally a new nonthrombogenic surface until vasculature regeneration occurs. Reversible binding between GPIb-V-IX 1 and von Willebrand factor, associated with collagen, is crucial to slow down the platelet (especially under high shear) so that it can bind more firmly via other receptors (3, 4). This mechanism strongly parallels that of the selectins in leukocyte adhesion (5). Another important receptor is the ␣ 2 ␤ 1 integrin, which is essential for anchoring the platelet to collagen in the subendothelium (6) and for linking to the platelet cytoskeleton to prevent the receptor being torn from the membrane by the forces that it has to withstand. Activation induces the release of storage granules and the expression of new receptors on the platelet surface (7) as well as changes in other receptors such as the fibrinogen receptor, ␣ IIb ␤ 3 , which is critical for spreading. Although GPIb-V-IX and ␣ 2 ␤ 1 also participate in signaling to the platelet interior (8, 9), recent studies, particularly in patients with platelet receptor deficiencies, have implicated GPVI/Fc␥ as a major collagen receptor for platelet activation (10 -12). Patients with platelets lacking any one of these receptors (GPIb-V-IX, ␣ 2 ␤ 1 , or GPVI/Fc␥) have increased bleeding times, and platelet adhesio...

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Section: Discussionmentioning

confidence: 99%

mentioning

confidence: 99%

Aggretin, a Heterodimeric C-type Lectin from Calloselasma rhodostoma (Malayan Pit Viper), Stimulates Platelets by Binding to α2β1 Integrin and Glycoprotein Ib, Activating Syk and Phospholipase Cγ2, but Does Not Involve the Glycoprotein VI/Fc Receptor γ Chain Collagen Receptor

Navdaev

Clemetson

Polgár

et al. 2001

Journal of Biological Chemistry

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“…19 The latter operates through tyrosine-phosphorylated ITAMs within the cytoplasmic domain of the FcR␥-chain dimer. 23 Despite much progress in identifying components of the signaling pathway responsible for initiating and sustaining collageninduced platelet activation, [24][25][26][27][28][29][30] virtually nothing is known about platelets were labeled to a similar extent with calcine AM (not shown). After removal of nonadherent platelets, fluorescence associated with adherent platelets was measured as described in "Materials and methods."…”

Section: Platelets Derived From Pecam-1-deficient Mice Exhibit Exaggementioning

confidence: 99%

Platelet endothelial cell adhesion molecule-1 serves as an inhibitory receptor that modulates platelet responses to collagen

Patil

Newman

2001

Blood

135

133

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Platelet responses to collagen are mediated by the combined actions of the integrin ␣ 2 ␤ 1 , which serves as a major collagenbinding receptor, and the GPVI/FcR␥-chain complex, which transmits collagen-specific activation signals into the cell interior through the action of an immunoreceptor tyrosine-based activation motif within the cytoplasmic domain of the FcR␥-chain. Despite much progress in identifying components of the signaling pathway responsible for collagen-induced platelet activation, virtually nothing is known about the regulatory elements that modulate this important hemostatic event. PECAM-1, a recently recognized member of the inhibitory receptor family, contains a functional immunoreceptor tyrosine-based inhibitory motif within its cytoplasmic domain that, when tyrosine phosphorylated, recruits and activates the protein-tyrosine phosphatase, SHP-2. To test the hypothesis that PECAM-1 functions to regulate GPVI/FcR␥-chain-mediated platelet activation, the responses of wild-type versus PECAM-1-deficient murine platelets to GPVI-specific agonists were compared. Four distinct GPVI/FcR␥-chain-dependent responses were found to be significantly exaggerated in platelets derived from PE-CAM-1-deficient mice, including Mg ؉؉ -independent adhesion to immobilized fibrillar collagen, collagen-induced platelet aggregation, platelet aggregation induced by the GPVI-specific agonist collagen-related peptide, and GPVI/FcR␥-chain-induced dense granule secretion. Together, these data provide compelling evidence that PECAM-1 modulates platelet responses to collagen, and they implicate this novel member of the inhibitory receptor family in the regulation of primary hemostasis. IntroductionPlatelet endothelial cell adhesion molecule-1 (PECAM-1, CD31) is a 130-kd member of the immunoglobulin (Ig) superfamily that is expressed on the surface of circulating platelets, endothelial cells, neutrophils, monocytes, and certain T-lymphocyte subsets. The extracellular domain of PECAM-1 is composed of 6 extracellular Ig-like homology units, 1 the amino-terminal 2 of which mediates PECAM-1-PECAM-1 homophilic interactions. 2,3 Antibodies to the extracellular domain have been shown to have profound physiologic and cell biologic effects, including delaying leukocyte transendothelial migration 4-6 and inhibiting angiogenesis. 7 The extracellular domain of PECAM-1 also serves as a portal for entry into endothelial cells of certain strains of Plasmodium falciparuminfected erythrocytes. 8,9 The PECAM-1 cytoplasmic domain also plays a key biologic role because a large number of extracellular stimuli (reviewed in Newman 10 ) have been shown to result in the phosphorylation of 2 key tyrosine residues, located at positions 663 and 686 of the cytoplasmic domain. 11 The sequence surrounding each of these 2 tyrosine residues conforms to an immunoreceptor tyrosine-based inhibitory motif (ITIM) that, when phosphorylated, provides a major docking site for the src homology 2 (SH2) domaincontaining protein tyrosine phosphatase (PTP), SHP-2. 11-14 ...

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“…Rhodocytin/Aggretin Does Not Inhibit Binding of Soluble ␣ 2 ␤ 1 Integrin to Type I Collagen-Rhodocytin or aggretin are the two names of a 29-kDa protein of C. rhodostoma venom, which induces activation and aggregation of thrombocytes (15,30). It was isolated from the snake venom according to Shin and Morita (31).…”

Section: Production and Isolation Of Recombinant Soluble Humanmentioning

confidence: 99%

α2β1 Integrin Is Not Recognized by Rhodocytin but Is the Specific, High Affinity Target of Rhodocetin, an RGD-independent Disintegrin and Potent Inhibitor of Cell Adhesion to Collagen

Eble¹,

Beermann

Hinz

et al. 2001

Journal of Biological Chemistry

116

123

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and the ¶Institut fü r Physikalische Chemie, Schlossplatz 7, Universitä t Mü nster, 48149 Mü nster, GermanyWe have recombinantly expressed a soluble form of human ␣ 2 ␤ 1 integrin that lacks the membrane-anchoring transmembrane domains as well as the cytoplasmic tails of both integrin subunits. This soluble ␣ 2 ␤ 1 integrin binds to its collagen ligands the same way as the wildtype ␣ 2 ␤ 1 integrin. Furthermore, like the wild-type form, it can be activated by manganese ions and an integrinactivating antibody. However, it does not bind to rhodocytin, a postulated agonist of ␣ 2 ␤ 1 integrin from the snake venom of Calloselasma rhodostoma, which elicits platelet aggregation. Taking advantage of the recombinantly expressed, soluble ␣ 2 ␤ 1 integrin, an inhibition assay was established in which samples can be tested for their capability to inhibit binding of soluble ␣ 2 ␤ 1 integrin to immobilized collagen. Thus, by scrutinizing the C. rhodostoma snake venom in this protein-protein interaction assay, we found a component of the snake venom that inhibits the interaction of soluble ␣ 2 ␤ 1 integrin to type I collagen efficiently. N-terminal sequences identified this inhibitor as rhodocetin, a recently published antagonist of collagen-induced platelet aggregation. We could demonstrate that its inhibitory effect bases on its strong and specific binding to ␣ 2 ␤ 1 integrin, proving that rhodocetin is a disintegrin. Standing apart from the growing group of RGD-dependent snake venom disintegrins, rhodocetin interacts with ␣ 2 ␤ 1 integrin in an RGD-independent manner. Furthermore, its native conformation, which is stabilized by disulfide bridges, is indispensibly required for its inhibitory activity. Rhodocetin does not contain any major collagenous structure despite its high affinity to ␣ 2 ␤ 1 integrin, which binds to collagenous molecules much more avidly than to noncollagenous ligands, such as laminin. Blocking ␣ 2 ␤ 1 integrin as the major collagen receptor on platelets, rhodocetin is responsible for hampering collagen-induced, ␣ 2 ␤ 1 integrin-mediated platelet activation, leading to hemorrhages and bleeding disorders of the snakebite victim. Moreover, having a widespread tissue distribution, ␣ 2 ␤ 1 integrin also mediates cell adhesion, spreading, and migration. We showed that rhodocetin is able to inhibit ␣ 2 ␤ 1 integrin-mediated adhesion of fibrosarcoma cells to type I collagen completely.Integrins are cell adhesion molecules that consist of two noncovalently associated subunits, ␣ and ␤ (for review see Refs. 1 and 2). The subfamily of integrins sharing the ␤ 1 subunit are well known receptors for extracellular matrix molecules, such as collagens, laminins, and fibronectin. The subfamily of ␤ 3 subunit containing cytoadhesins comprise the platelet integrin, ␣ IIb ␤ 3 which binds fibrinogen/fibrin (3) and the vitronectin receptor ␣ V ␤ 3 . The latter ones, along with several ␤ 1 integrin, such as the fibronectin receptor ␣ 5 ␤ 1 integrin, recognize a linear arginyl-glycyl-aspartyl sequence within their respective ...

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Signal Transduction Pathways Mediated by Glycoprotein Ia/IIa in Human Platelets: Comparison with Those of Glycoprotein VI

Cited by 41 publications

References 26 publications

Aggretin, a Heterodimeric C-type Lectin from Calloselasma rhodostoma (Malayan Pit Viper), Stimulates Platelets by Binding to α2β1 Integrin and Glycoprotein Ib, Activating Syk and Phospholipase Cγ2, but Does Not Involve the Glycoprotein VI/Fc Receptor γ Chain Collagen Receptor

Aggretin, a Heterodimeric C-type Lectin from Calloselasma rhodostoma (Malayan Pit Viper), Stimulates Platelets by Binding to α2β1 Integrin and Glycoprotein Ib, Activating Syk and Phospholipase Cγ2, but Does Not Involve the Glycoprotein VI/Fc Receptor γ Chain Collagen Receptor

Platelet endothelial cell adhesion molecule-1 serves as an inhibitory receptor that modulates platelet responses to collagen

α2β1 Integrin Is Not Recognized by Rhodocytin but Is the Specific, High Affinity Target of Rhodocetin, an RGD-independent Disintegrin and Potent Inhibitor of Cell Adhesion to Collagen

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