Glycoprotein VI oligomerization in cell lines and platelets

Berlanga, Oscar; Bori-Sanz, Teresa; James, John R.; Frampton, Jon; Davis, Simon J.; Tomlinson, Michael G.; Watson, Steve P.

doi:10.1111/j.1538-7836.2007.02449.x

Cited by 51 publications

(59 citation statements)

References 33 publications

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“…This m-Fab can therefore be used as an important diagnostic tool for determining the nature of the GPVI dimer on the surface of platelets. Jung et al [18] showed by flow cytometry that the mFab bound to platelets, indicating that a preformed dimeric conformation of the GPVI ectodomain was present at the platelet surface.These new results nicely complement the previous cellular studies showing evidence for GPVI dimerization on transfected cells or platelets [16,17]. The observation of a specific dimeric conformation of the GPVI collagen-binding domain at the platelet surface is significant, as this dimer is likely to play an important role in recognition of fibrillar collagen.…”

supporting

confidence: 77%

“…These new results nicely complement the previous cellular studies showing evidence for GPVI dimerization on transfected cells or platelets [16,17]. The observation of a specific dimeric conformation of the GPVI collagen-binding domain at the platelet surface is significant, as this dimer is likely to play an important role in recognition of fibrillar collagen.…”

supporting

confidence: 77%

“…An analysis of receptor binding sites on intact fibrillar collagen indicated that at least for collagen III, there are one or two sites per Dperiod that could support binding of a dimeric GPVI ectodomain [19]. It is certainly possible that the GPVI monomer-dimer equilibrium observed on 293T cells using BRET [16] also occurs at the platelet surface. The existence of both monomeric and dimeric receptor forms may thus allow binding to different sites along a single collagen fiber or on other types of fibrillar collagen.…”

mentioning

confidence: 99%

“…Furthermore, they carried out bioluminescence resonance energy transfer (BRET) experiments to clearly demonstrate that GPVI existed in a monomerdimer equilibrium at the cell surface. Finally, they used chemical cross-linking to provide evidence for oligomerization of GPVI on platelets, although the precise oligomeric state was not clear [16]. Subsequently, Arthur et al [17] showed that the cytoplasmic domain of GPVI undergoes disulfide cross-linking upon ligand binding.…”

mentioning

confidence: 99%

“…This difference may have been due to the absence of LAIR-1, an inhibitory collagen receptor, on the DT40 cells. Berlanga et al [16] used immunoprecipitation to show that GPVI formed dimers on transfected 293T cells and that dimerization required the GPVI extracellular region (i.e. the mucin-like stalk and the collagen-binding domain).…”

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confidence: 99%

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Direct evidence of a native GPVI dimer at the platelet surface

Herr

2009

Journal of Thrombosis and Haemostasis

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To cite this article: Herr AB. Direct evidence of a native GPVI dimer at the platelet surface. J Thromb Haemost 2009; 7: 1344-6.See also Jung SM, Tsuji K, Moroi M. Glycoprotein (GP) VI dimer as a major collagen-binding site of native platelets: direct evidence obtained with dimeric GPVI-specific Fabs This issue, pp 1347-55.Glycoprotein VI (GPVI) is an activating receptor expressed on the surface of platelets and megakaryocytes. Clustering of GPVI upon collagen binding triggers a signaling cascade that leads to platelet activation, and depletion or inhibition of GPVI on mouse or human platelets prevents arterial thrombus formation [1,2]. There is great interest in the molecular mechanism by which GPVI recognizes fibrillar collagen. One of the major unresolved questions is whether GPVI exists on the platelet surface as a monomer or dimer, and how its assembly state affects its recognition of fibrillar collagen.GPVI is a multi-chain receptor related to several immune receptors such as the IgA-specific receptor FcaRI [3]. The GPVI ectodomain recognizes several ligands, which include fibrillar collagen, collagen-related peptides (CRPs), or snake venom proteins such as convulxin [4,5]. Unlike the a 2 b 1 integrin, GPVI binds collagen with relatively low affinity [6]; furthermore, GPVI recognizes the quaternary assembly of the collagen fiber and cannot bind to acid-solubilized collagen triple helices [2]. An intriguing possibility is that GPVI forms a cell-surface dimer whose conformation is specific for the quaternary structure of fibrillar collagen.Work from several groups has provided evidence that GPVI may form a dimer that has functional significance. In 2002, Moroi and colleagues showed that a recombinant dimeric GPVI-Fc fusion protein was able to bind fibrillar collagen with moderate affinity whereas binding of monomeric GPVI (called GPVIex) was hardly detectable [6]. The very large discrepancy between the apparent affinities of monomeric and dimeric GPVI for fibrillar collagen is greater than would be expected from a simple avidity effect, suggesting the dimer may recognize a specific conformational epitope in collagen. The GPVI-Fc fusion protein has been used in physiologically relevant settings to demonstrate effective inhibition of thrombus formation, consistent with the ability of the dimeric receptor to bind fibrillar collagen with high specificity and reasonably high affinity [6][7][8][9].The crystal structure of the collagen-binding domain of GPVI was solved in 2006, revealing two receptor chains arranged back-to-back in a dimeric conformation [10]. Computational docking identified a shallow groove on the top of the N-terminal Ig-like domain as the most likely binding site for a collagen triple helix, which agreed with prior mutational results [10][11][12]. Interestingly, the geometry and spacing of the two putative binding grooves in the crystalline GPVI dimer precisely matched the known geometry and spacing of triple helices within the collagen fiber [10]. These structural data provided a plausible mec...

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supporting

confidence: 77%

supporting

confidence: 77%

mentioning

confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

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Direct evidence of a native GPVI dimer at the platelet surface

Herr

2009

Journal of Thrombosis and Haemostasis

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Signaling Chain Homooligomerization (SCHOOL) Model

Sigalov

Advances in Experimental Medicine and Biology

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Multichain immune recognitionreceptors (MIRRs) represent a family of surfacereceptors expressed on different cells of the hematopoietic system and function to transduce signals leading to a variety of biologic responses. The most intriguing and distinct structural feature ofMIRR family members is that extracellular recognition domains and intracellular signaling domains are located on separate subunits. The biochemical cascades triggered by MIRRs are understood in significant detail, however, the mechanism by which extracellular ligand binding initiates intracellular signal transduction processes is not clear and no model fully explains how MIRR signaling commences. In this Chapter, I describe a novel mechanistic model of MIRR-mediated signal transduction, the signaling chain homooligomerization (SCHOOL) model. The basic concept of this model assumes that the structural similarity of the MIRRs provides the basis for the similarity in the mechanisms ofMIRR-mediated transmembrane signaling. Within the SCHOOL model, MIRR triggering is considered to be a result of the ligand-induced interplay between (1) intrareceptor transmembrane interactions between MIRR recognition and signaling subunits that stabilize and maintain receptor integrity and (2) interreceptor homointeractions between MIRR signaling subunits that lead to the formation of oligomeric signaling structures, thus triggering the receptors and initiating the signaling cascade. Thus, the SCHOOL model is based on specific protein-protein interactions--biochemical processes that can be influenced and controlled. In this context, this plausible and easily testable model is fundamentally different from those previously suggested for particular MIRRs and has several important advantages. The basic principles oftransmembrane signaling learned from the SCHOOL model may be used in different fields of immunology and cell biology to describe, explain and predict immunological phenomena and processes mediated by structurally related but functionally different membrane receptors. Important applications of the SCHOOL model in clinical immunology, molecular pharmacology and virology are described in the Chapters 20 and 22 of this book.

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SCHOOL Model and New Targeting Strategies

Sigalov

2008

Advances in Experimental Medicine and Biology

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Protein-protein interactions play a central role in biological processes and thus are an appealing target for innovative drug design a nd development. They can be targeted bysmall molecule inhibitors, peptides and peptidomimetics, which represent an alternative to protein therapeutics that carry many disadvantages. In this chapter, I describe specific protein-protein interactions suggested by a novel model of immune signaling, the Signaling Chain HOmoOLigomerization (SCHOOL) model, to be critical for cell activation mediated by multichain immune recognition receptors (MIRRs) expressed on different cells of the hematopoietic system. Unraveling a long-standing mystery of MIRR triggering and transmembrane signaling, the SCHOOL model reveals the intrareceptor transmembrane interactions and interreceptor cytoplasmic homointeractions as universal therapeutic targets for a diverse variety of disorders mediated by immune cells. Further, assuming that the general principles underlying MIRR-mediated transmembrane signaling mechanisms are similar, the SCHOOL model can be applied to any particular receptor of the MIRR family. Thus, an important application of the SCHOOL model is that global therapeutic strategies targeting key protein-protein interactions involved in MIRR triggering and transmembrane signal transduction may be used to treat a diverse set of immune-mediated diseases. This assumes that clinical knowledge and therapeutic strategies can be transferred between seemingly disparate disorders, such as T-cell-mediated skin diseases and platelet disorders, or combined to develop novel pharmacological approaches. Intriguingly, the SCHOOL model unravels the molecular mechanisms underlying ability of different human viruses such as human immunodeficiency virus, cytomegalovirus and severe acute respiratory syndrome coronavirus to modulate and/or escape the host immune response. It also demonstrates how the lessons learned from viral pathogenesis can be used practically for rational drug design. Application of this model to platelet collagen receptor signaling has already led to the development of a novel concept of platelet inhibition and the invention of new platelet inhibitors, thus proving the suggested hypothesis and highlighting the importance and broad perspectives of the SCHOOL model in the development of new targeting strategies.

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Glycoprotein VI oligomerization in cell lines and platelets

Cited by 51 publications

References 33 publications

Direct evidence of a native GPVI dimer at the platelet surface

Direct evidence of a native GPVI dimer at the platelet surface

Signaling Chain Homooligomerization (SCHOOL) Model

SCHOOL Model and New Targeting Strategies

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