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Binding of the protein ICln to α-integrin contributes to the activation of ICl swell current. Sci Rep 2019; 9:12195. [PMID: 31434921 PMCID: PMC6704128 DOI: 10.1038/s41598-019-48496-4] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2019] [Accepted: 08/06/2019] [Indexed: 12/13/2022] Open
Abstract
IClswell is the chloride current induced by cell swelling, and plays a fundamental role in several biological processes, including the regulatory volume decrease (RVD). ICln is a highly conserved, ubiquitously expressed and multifunctional protein involved in the activation of IClswell. In platelets, ICln binds to the intracellular domain of the integrin αIIb chain, however, whether the ICln/integrin interaction plays a role in RVD is not known. Here we show that a direct molecular interaction between ICln and the integrin α-chain is not restricted to platelets and involves highly conserved amino acid motifs. Integrin α recruits ICln to the plasma membrane, thereby facilitating the activation of IClswell during hypotonicity. Perturbation of the ICln/integrin interaction prevents the transposition of ICln towards the cell surface and, in parallel, impedes the activation of IClswell. We suggest that the ICln/integrin interaction interface may represent a new molecular target enabling specific IClswell suppression in pathological conditions when this current is deregulated or plays a detrimental role.
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O’Brien KT, Golla K, Kranjc T, O’Donovan D, Allen S, Maguire P, Simpson JC, O’Connell D, Moran N, Shields DC. Computational and experimental analysis of bioactive peptide linear motifs in the integrin adhesome. PLoS One 2019; 14:e0210337. [PMID: 30689642 PMCID: PMC6349357 DOI: 10.1371/journal.pone.0210337] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2018] [Accepted: 12/20/2018] [Indexed: 12/15/2022] Open
Abstract
Therapeutic modulation of protein interactions is challenging, but short linear motifs (SLiMs) represent potential targets. Focal adhesions play a central role in adhesion by linking cells to the extracellular matrix. Integrins are central to this process, and many other intracellular proteins are components of the integrin adhesome. We applied a peptide network targeting approach to explore the intracellular modulation of integrin function in platelets. Firstly, we computed a platelet-relevant integrin adhesome, inferred via homology of known platelet proteins to adhesome components. We then computationally selected peptides from the set of platelet integrin adhesome cytoplasmic and membrane adjacent protein-protein interfaces. Motifs of interest in the intracellular component of the platelet integrin adhesome were identified using a predictor of SLiMs based on analysis of protein primary amino acid sequences (SLiMPred), a predictor of strongly conserved motifs within disordered protein regions (SLiMPrints), and information from the literature regarding protein interactions in the complex. We then synthesized peptides incorporating these motifs combined with cell penetrating factors (tat peptide and palmitylation for cytoplasmic and membrane proteins respectively). We tested for the platelet activating effects of the peptides, as well as their abilities to inhibit activation. Bioactivity testing revealed a number of peptides that modulated platelet function, including those derived from α-actinin (ACTN1) and syndecan (SDC4), binding to vinculin and syntenin respectively. Both chimeric peptide experiments and peptide combination experiments failed to identify strong effects, perhaps characterizing the adhesome as relatively robust against within-adhesome synergistic perturbation. We investigated in more detail peptides targeting vinculin. Combined experimental and computational evidence suggested a model in which the positively charged tat-derived cell penetrating part of the peptide contributes to bioactivity via stabilizing charge interactions with a region of the ACTN1 negatively charged surface. We conclude that some interactions in the integrin adhesome appear to be capable of modulation by short peptides, and may aid in the identification and characterization of target sites within the complex that may be useful for therapeutic modulation.
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Affiliation(s)
- Kevin T. O’Brien
- School of Medicine, University College Dublin, Dublin, Ireland
- Conway Institute of Biomolecular and Biomedical Research, University College Dublin, Dublin, Ireland
| | - Kalyan Golla
- Molecular and Cellular Therapeutics, Royal College of Surgeons in Ireland, Dublin, Ireland
| | - Tilen Kranjc
- Conway Institute of Biomolecular and Biomedical Research, University College Dublin, Dublin, Ireland
- School of Biology and Environment Science, University College Dublin, Dublin, Ireland
| | - Darragh O’Donovan
- Conway Institute of Biomolecular and Biomedical Research, University College Dublin, Dublin, Ireland
- School of Biomolecular and Biomedical Science, University College Dublin, Dublin, Ireland
| | - Seamus Allen
- Conway Institute of Biomolecular and Biomedical Research, University College Dublin, Dublin, Ireland
- School of Biomolecular and Biomedical Science, University College Dublin, Dublin, Ireland
| | - Patricia Maguire
- Conway Institute of Biomolecular and Biomedical Research, University College Dublin, Dublin, Ireland
- School of Biomolecular and Biomedical Science, University College Dublin, Dublin, Ireland
| | - Jeremy C. Simpson
- Conway Institute of Biomolecular and Biomedical Research, University College Dublin, Dublin, Ireland
- School of Biology and Environment Science, University College Dublin, Dublin, Ireland
| | - David O’Connell
- Conway Institute of Biomolecular and Biomedical Research, University College Dublin, Dublin, Ireland
- School of Biomolecular and Biomedical Science, University College Dublin, Dublin, Ireland
| | - Niamh Moran
- Molecular and Cellular Therapeutics, Royal College of Surgeons in Ireland, Dublin, Ireland
| | - Denis C. Shields
- School of Medicine, University College Dublin, Dublin, Ireland
- Conway Institute of Biomolecular and Biomedical Research, University College Dublin, Dublin, Ireland
- * E-mail:
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3
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Golla K, Stavropoulos I, Shields DC, Moran N. Peptides derived from cadherin juxtamembrane region inhibit platelet function. ROYAL SOCIETY OPEN SCIENCE 2018; 5:172347. [PMID: 30473799 PMCID: PMC6227957 DOI: 10.1098/rsos.172347] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 01/05/2018] [Accepted: 09/17/2018] [Indexed: 06/09/2023]
Abstract
The juxtamembrane domains (JMD) of transmembrane proteins are rich in critical peptide sequences that participate in dynamic cell signalling events. Synthetic JMD peptides derived from cadherin cell adhesion proteins have previously been shown to modulate platelet function. In this study, we aimed to develop functional bioactive agents from bioinformatically identified critical peptide sequences. We synthesized overlapping 12-15 amino acid peptides from E- and N-cadherin JMD and assessed their effect on platelet aggregation and platelet ATP secretion. Peptides derived from close to the membrane proximal region inhibit platelet function. Sequential deletion of amino acids from the N- and C-termini of the inhibitory E-cadherin peptides identified the short K756EPLLP763 motif as a critical bioactive sequence. Alanine scanning studies further identified that the di-leucine (LL) motif and positively charged lysine (K) are crucial for peptide activity. Moreover, scrambled peptides failed to show any effect on platelet activity. We conclude that peptides derived from JMD of E-cadherin provide potential lead peptides for the development of anti-thrombotic agents and to enable further understanding of the role of cadherins in platelet function.
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Affiliation(s)
- Kalyan Golla
- Molecular and Cellular Therapeutics, Royal College of Surgeons in Ireland, Dublin, Ireland
| | - Ilias Stavropoulos
- UCD Conway Institute of Biomolecular and Biomedical Research, University College Dublin, Dublin, Ireland
- School of Medicine and Medical Science, University College Dublin, Dublin, Ireland
| | - Denis C. Shields
- UCD Conway Institute of Biomolecular and Biomedical Research, University College Dublin, Dublin, Ireland
- School of Medicine and Medical Science, University College Dublin, Dublin, Ireland
| | - Niamh Moran
- Molecular and Cellular Therapeutics, Royal College of Surgeons in Ireland, Dublin, Ireland
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4
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Naik MU, Naik TU, Summer R, Naik UP. Binding of CIB1 to the αIIb tail of αIIbβ3 is required for FAK recruitment and activation in platelets. PLoS One 2017; 12:e0176602. [PMID: 28542214 PMCID: PMC5443481 DOI: 10.1371/journal.pone.0176602] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2017] [Accepted: 04/13/2017] [Indexed: 12/03/2022] Open
Abstract
Background It is believed that activation of c-Src bound to the integrin β3 subunit initiates outside-in signaling. The involvement of αIIb in outside-in signaling is poorly understood. Objectives We have previously shown that CIB1 specifically interacts with the cytoplasmic domain of αIIb and is required for αIIbβ3 outside-in signaling. Here we evaluated the role of CIB1 in regulating outside-in signaling in the absence of inside-out signaling. Methods We used αIIb cytoplasmic domain peptide and CIB1-function blocking antibody to inhibit interaction of CIB1 with αIIb subunit as well as Cib1-/- platelets to evaluate the consequence of CIB1 interaction with αIIb on outside-in signaling. Results Fibrinogen binding to αIIbβ3 results in calcium-dependent interaction of CIB1 with αIIb, which is not required for filopodia formation. Dynamic rearrangement of cytoskeleton results in CIB1-dependent recruitment of FAK to the αIIb complex and its activation. Disruption of the association of CIB1 and αIIb by incorporation of αIIb peptide or anti-CIB1 inhibited both FAK association and activation. Furthermore, FAK recruitment to the integrin complex was required for c-Src activation. Inhibition of c-Src had no effect on CIB1 accumulation with the integrin at the filopodia, suggesting that c-Src activity is not required for the formation of CIB1-αIIb-FAK complex. Conclusion Our results suggest that interaction of CIB1 with αIIb is one of the early events occurring during outside-in signaling. Furthermore, CIB1 recruits FAK to the αIIbβ3 complex at the filopodia where FAK is activated, which in turn activates c-Src, resulting in propagation of outside-in signaling leading to platelet spreading.
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Affiliation(s)
- Meghna U. Naik
- Cardeza Center for Vascular Biology, Department of Medicine, Thomas Jefferson University, Philadelphia, PA, United States of America
| | - Tejal U. Naik
- Cardeza Center for Vascular Biology, Department of Medicine, Thomas Jefferson University, Philadelphia, PA, United States of America
| | - Ross Summer
- Cardeza Center for Vascular Biology, Department of Medicine, Thomas Jefferson University, Philadelphia, PA, United States of America
| | - Ulhas P. Naik
- Cardeza Center for Vascular Biology, Department of Medicine, Thomas Jefferson University, Philadelphia, PA, United States of America
- * E-mail:
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5
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Tian X, Chang L, Ma G, Wang T, Lv M, Wang Z, Chen L, Wang Y, Gao X, Zhu Y. Delineation of Platelet Activation Pathway of Scutellarein Revealed Its Intracellular Target as Protein Kinase C. Biol Pharm Bull 2015; 39:181-91. [PMID: 26581323 DOI: 10.1248/bpb.b15-00511] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Erigeron breviscapus has been widely used in traditional Chinese medicine (TCM) and its total flavonoid component is commonly used to treat ischemic stroke, coronary heart disease, diabetes and hypertension. Scutellarin is the major ingredient of E. breviscapus and scutellarein is one of the main bioactive metabolites of scutellarin in vivo, but the latter's pharmacological activities have not been fully characterized. Provided evidence that could inhibit platelet aggregation, the effect of scutellarein on rat washed platelets and its underlying mechanisms were evaluated in our research. Scutellarein inhibited platelet adhesion and aggregation induced by multiple G protein coupled receptor agonists such as thrombin, U46619 and ADP, in a concentration-dependent manner. Furthermore, the mild effect of scutellarein on intracellular Ca(2+) mobilization and cyclic AMP (cAMP) level was observed. On the other hand, the role of scutellarein as potential protein kinase C (PKC) inhibitor was confirmed by PKC activity analysis and molecular docking. The phorbol myristate acetate-induced platelets aggregation assay with or without ADP implied that the scutellarein takes PKC(s) as its primary target(s), and acts on it in a reversible way. Finally, scutellarein as a promising agent exhibited a high inhibition effect on ADP-induced platelet aggregation among its analogues. This study clarifies the PKC-related signaling pathway involved in antiplatelet action of scutellarein, and may be beneficial for the treatment of cardiovascular diseases.
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Affiliation(s)
- Xiaoxuan Tian
- Tianjin State Key Laboratory of Modern Chinese Medicine, Tianjin University of Traditional Chinese Medicine
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6
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Bianchin A, Bell A, Chubb AJ, Doolan N, Leneghan D, Stavropoulos I, Shields DC, Mooney C. Design and evaluation of antimalarial peptides derived from prediction of short linear motifs in proteins related to erythrocyte invasion. PLoS One 2015; 10:e0127383. [PMID: 26039561 PMCID: PMC4454681 DOI: 10.1371/journal.pone.0127383] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/22/2014] [Accepted: 04/15/2015] [Indexed: 11/19/2022] Open
Abstract
The purpose of this study was to investigate the blood stage of the malaria causing parasite, Plasmodium falciparum, to predict potential protein interactions between the parasite merozoite and the host erythrocyte and design peptides that could interrupt these predicted interactions. We screened the P. falciparum and human proteomes for computationally predicted short linear motifs (SLiMs) in cytoplasmic portions of transmembrane proteins that could play roles in the invasion of the erythrocyte by the merozoite, an essential step in malarial pathogenesis. We tested thirteen peptides predicted to contain SLiMs, twelve of them palmitoylated to enhance membrane targeting, and found three that blocked parasite growth in culture by inhibiting the initiation of new infections in erythrocytes. Scrambled peptides for two of the most promising peptides suggested that their activity may be reflective of amino acid properties, in particular, positive charge. However, one peptide showed effects which were stronger than those of scrambled peptides. This was derived from human red blood cell glycophorin-B. We concluded that proteome-wide computational screening of the intracellular regions of both host and pathogen adhesion proteins provides potential lead peptides for the development of anti-malarial compounds.
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Affiliation(s)
- Alessandra Bianchin
- Conway Institute of Biomolecular and Biomedical Science, University College Dublin, Dublin, Ireland
- Complex and Adaptive Systems Laboratory, University College Dublin, Dublin, Ireland
- School of Medicine and Medical Science, University College Dublin, Dublin, Ireland
- Department of Microbiology, School of Genetics and Microbiology, Moyne Institute of Preventive Medicine, Trinity College, Dublin, Ireland
| | - Angus Bell
- Department of Microbiology, School of Genetics and Microbiology, Moyne Institute of Preventive Medicine, Trinity College, Dublin, Ireland
| | - Anthony J. Chubb
- Conway Institute of Biomolecular and Biomedical Science, University College Dublin, Dublin, Ireland
- Complex and Adaptive Systems Laboratory, University College Dublin, Dublin, Ireland
- School of Medicine and Medical Science, University College Dublin, Dublin, Ireland
| | - Nathalie Doolan
- School of Medicine and Medical Science, University College Dublin, Dublin, Ireland
| | - Darren Leneghan
- Department of Microbiology, School of Genetics and Microbiology, Moyne Institute of Preventive Medicine, Trinity College, Dublin, Ireland
| | - Ilias Stavropoulos
- Conway Institute of Biomolecular and Biomedical Science, University College Dublin, Dublin, Ireland
- Complex and Adaptive Systems Laboratory, University College Dublin, Dublin, Ireland
- School of Medicine and Medical Science, University College Dublin, Dublin, Ireland
| | - Denis C. Shields
- Conway Institute of Biomolecular and Biomedical Science, University College Dublin, Dublin, Ireland
- Complex and Adaptive Systems Laboratory, University College Dublin, Dublin, Ireland
- School of Medicine and Medical Science, University College Dublin, Dublin, Ireland
| | - Catherine Mooney
- Conway Institute of Biomolecular and Biomedical Science, University College Dublin, Dublin, Ireland
- Complex and Adaptive Systems Laboratory, University College Dublin, Dublin, Ireland
- School of Medicine and Medical Science, University College Dublin, Dublin, Ireland
- * E-mail:
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7
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Duffy FJ, O’Donovan D, Devocelle M, Moran N, O’Connell DJ, Shields DC. Virtual Screening Using Combinatorial Cyclic Peptide Libraries Reveals Protein Interfaces Readily Targetable by Cyclic Peptides. J Chem Inf Model 2015; 55:600-13. [DOI: 10.1021/ci500431q] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
Affiliation(s)
- Fergal J. Duffy
- School of Medicine and Medical
Science, ‡Complex and Adaptive Systems Laboratory, ¶Conway Institute of
Biomolecular and Biomedical Research, and §School of Biomolecular and Biomedical
Science, University College Dublin, Dublin 4, Ireland, and
- Department of Chemistry and ⊥Department of
Molecular and Cell Therapeutics, Royal College of Surgeons in Ireland, 123 St. Stephens Green, Dublin 2, Ireland
| | - Darragh O’Donovan
- School of Medicine and Medical
Science, ‡Complex and Adaptive Systems Laboratory, ¶Conway Institute of
Biomolecular and Biomedical Research, and §School of Biomolecular and Biomedical
Science, University College Dublin, Dublin 4, Ireland, and
- Department of Chemistry and ⊥Department of
Molecular and Cell Therapeutics, Royal College of Surgeons in Ireland, 123 St. Stephens Green, Dublin 2, Ireland
| | - Marc Devocelle
- School of Medicine and Medical
Science, ‡Complex and Adaptive Systems Laboratory, ¶Conway Institute of
Biomolecular and Biomedical Research, and §School of Biomolecular and Biomedical
Science, University College Dublin, Dublin 4, Ireland, and
- Department of Chemistry and ⊥Department of
Molecular and Cell Therapeutics, Royal College of Surgeons in Ireland, 123 St. Stephens Green, Dublin 2, Ireland
| | - Niamh Moran
- School of Medicine and Medical
Science, ‡Complex and Adaptive Systems Laboratory, ¶Conway Institute of
Biomolecular and Biomedical Research, and §School of Biomolecular and Biomedical
Science, University College Dublin, Dublin 4, Ireland, and
- Department of Chemistry and ⊥Department of
Molecular and Cell Therapeutics, Royal College of Surgeons in Ireland, 123 St. Stephens Green, Dublin 2, Ireland
| | - David J. O’Connell
- School of Medicine and Medical
Science, ‡Complex and Adaptive Systems Laboratory, ¶Conway Institute of
Biomolecular and Biomedical Research, and §School of Biomolecular and Biomedical
Science, University College Dublin, Dublin 4, Ireland, and
- Department of Chemistry and ⊥Department of
Molecular and Cell Therapeutics, Royal College of Surgeons in Ireland, 123 St. Stephens Green, Dublin 2, Ireland
| | - Denis C. Shields
- School of Medicine and Medical
Science, ‡Complex and Adaptive Systems Laboratory, ¶Conway Institute of
Biomolecular and Biomedical Research, and §School of Biomolecular and Biomedical
Science, University College Dublin, Dublin 4, Ireland, and
- Department of Chemistry and ⊥Department of
Molecular and Cell Therapeutics, Royal College of Surgeons in Ireland, 123 St. Stephens Green, Dublin 2, Ireland
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8
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Li X, Liu Y, Haas TA. Peptides derived from central turn motifs within integrin αIIb and αV cytoplasmic tails inhibit integrin activation. Peptides 2014; 62:38-48. [PMID: 25290158 DOI: 10.1016/j.peptides.2014.07.029] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/20/2014] [Revised: 07/07/2014] [Accepted: 07/07/2014] [Indexed: 11/16/2022]
Abstract
We previously found that peptides derived from the full length of integrin αIIb and αV cytoplasmic tails inhibited their parent integrin activation, respectively. Here we showed that the cell-permeable peptides corresponding to the conserved central turn motif within αIIb and αV cytoplasmic tails, myr-KRNRPPLEED (αIIb peptide) and myr-KRVRPPQEEQ (αV peptide), similarly inhibited both αIIb and αV integrin activation. Pre-treatment with αIIb or αV peptides inhibited Mn(2+)-activated αIIbβ3 binding to soluble fibrinogen as well as the binding of αIIbβ3-expressing Chinese Hamster Ovary cells to immobilized fibrinogen. Our turn peptides also inhibited adhesion of two breast cancer cell lines (MDA-MB-435 and MCF7) to αV ligand vitronectin. These results suggest that αIIb and αV peptides share a same mechanism in regulating integrin function. Using αIIb peptide as a model, we found that replacement of RPP with AAA significantly attenuated the inhibitory activity of αIIb peptide. Furthermore, we found that αIIb peptide specifically bound to β-tubulin in cells. Our work suggests that the central motif of α tails is an anchoring point for cytoskeletons during integrin activation and integrin-mediated cell adhesion, and its function depends on the turn structure at RPP. However, post-treatment of peptides derived from the full-length tail or from the turn motif did not reverse αIIb and αV integrin activation.
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Affiliation(s)
- Xinlei Li
- Department of Anatomy and Cell Biology, College of Medicine, University of Saskatchewan, Saskatoon, SK, Canada S7N 5E5
| | - Yongqing Liu
- Department of Anatomy and Cell Biology, College of Medicine, University of Saskatchewan, Saskatoon, SK, Canada S7N 5E5
| | - Thomas A Haas
- Department of Anatomy and Cell Biology, College of Medicine, University of Saskatchewan, Saskatoon, SK, Canada S7N 5E5.
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9
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The design and implementation of a generic lipopeptide scanning platform to enable the identification of ‘locally acting’ agonists for the apelin receptor. Bioorg Med Chem Lett 2014; 24:4871-5. [DOI: 10.1016/j.bmcl.2014.08.045] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2014] [Revised: 08/15/2014] [Accepted: 08/20/2014] [Indexed: 12/19/2022]
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10
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Stavropoulos I, Golla K, Moran N, Martin F, Shields DC. Cadherin juxtamembrane region derived peptides inhibit TGFβ1 induced gene expression. BIOARCHITECTURE 2014; 4:103-10. [PMID: 25108297 PMCID: PMC4201599 DOI: 10.4161/bioa.32143] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
Bioactive peptides in the juxtamembrane regions of proteins are involved in many signaling events. The juxtamembrane regions of cadherins were examined for the identification of bioactive regions. Several peptides spanning the cytoplasmic juxtamembrane regions of E- and N-cadherin were synthesized and assessed for the ability to influence TGFβ responses in epithelial cells at the gene expression and protein levels. Peptides from regions closer to the membrane appeared more potent inhibitors of TGFβ signaling, blocking Smad3 phosphorylation. Thus inhibiting nuclear translocation of phosphorylated Smad complexes and subsequent transcriptional activation of TGFβ signal propagating genes. The peptides demonstrated a peptide-specific potential to inhibit other TGFβ superfamily members, such as BMP4.
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Affiliation(s)
- Ilias Stavropoulos
- UCD Conway Institute of Biomolecular and Biomedical Research; University College Dublin; Dublin, Ireland; UCD Complex and Adaptive Systems Laboratory; University College Dublin; Dublin, Ireland; School of Medicine and Medical Science; University College Dublin; Dublin, Ireland
| | - Kalyan Golla
- Molecular and Cellular Therapeutics; Royal College of Surgeons in Ireland; Dublin, Ireland
| | - Niamh Moran
- Molecular and Cellular Therapeutics; Royal College of Surgeons in Ireland; Dublin, Ireland
| | - Finian Martin
- UCD Conway Institute of Biomolecular and Biomedical Research; University College Dublin; Dublin, Ireland; School of Biomolecular and Biomedical Sciences; University College Dublin; Dublin, Ireland
| | - Denis C Shields
- UCD Conway Institute of Biomolecular and Biomedical Research; University College Dublin; Dublin, Ireland; UCD Complex and Adaptive Systems Laboratory; University College Dublin; Dublin, Ireland; School of Medicine and Medical Science; University College Dublin; Dublin, Ireland
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11
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Khiari Z, Rico D, Martin-Diana AB, Barry-Ryan C. Structure elucidation of ACE-inhibitory and antithrombotic peptides isolated from mackerel skin gelatine hydrolysates. JOURNAL OF THE SCIENCE OF FOOD AND AGRICULTURE 2014; 94:1663-1671. [PMID: 24214841 DOI: 10.1002/jsfa.6476] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/15/2013] [Revised: 09/06/2013] [Accepted: 11/09/2013] [Indexed: 06/02/2023]
Abstract
BACKGROUND The fish-processing industry generates significant amounts of waste and by-products that are usually discarded. This study investigated the preparation of bioactive gelatine peptides from fish skin. Gelatine was extracted from mackerel (Scomber scombrus) skin and hydrolysed by pepsin for 1, 2, 6 and 24 h. All hydrolysates were screened for antioxidant, ACE-inhibitory and antithrombotic activities. RESULTS Gelatine peptides obtained after 24 h of hydrolysis exhibited the highest antioxidant activity (DPPH reduction ∼80%, FRAP ∼130 µmol Trolox equivalent L(-1) ). These hydrolysates had high ACE-inhibitory activity (>70%) and were able to significantly (P < 0.05) inhibit platelet aggregation by about 30%, corresponding to moderate antithrombotic activity. CONCLUSION The bioactive properties were mainly due to the presence of low-molecular-weight peptides of 337 and 423 Da.
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Affiliation(s)
- Zied Khiari
- School of Food Science and Environmental Health, Dublin Institute of Technology (DIT), Cathal Brugha Street, Dublin 1, Ireland
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12
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de Vrij EL, Vogelaar PC, Goris M, Houwertjes MC, Herwig A, Dugbartey GJ, Boerema AS, Strijkstra AM, Bouma HR, Henning RH. Platelet dynamics during natural and pharmacologically induced torpor and forced hypothermia. PLoS One 2014; 9:e93218. [PMID: 24722364 PMCID: PMC3982955 DOI: 10.1371/journal.pone.0093218] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2012] [Accepted: 03/04/2014] [Indexed: 11/20/2022] Open
Abstract
Hibernation is an energy-conserving behavior in winter characterized by two phases: torpor and arousal. During torpor, markedly reduced metabolic activity results in inactivity and decreased body temperature. Arousal periods intersperse the torpor bouts and feature increased metabolism and euthermic body temperature. Alterations in physiological parameters, such as suppression of hemostasis, are thought to allow hibernators to survive periods of torpor and arousal without organ injury. While the state of torpor is potentially procoagulant, due to low blood flow, increased viscosity, immobility, hypoxia, and low body temperature, organ injury due to thromboembolism is absent. To investigate platelet dynamics during hibernation, we measured platelet count and function during and after natural torpor, pharmacologically induced torpor and forced hypothermia. Splenectomies were performed to unravel potential storage sites of platelets during torpor. Here we show that decreasing body temperature drives thrombocytopenia during torpor in hamster with maintained functionality of circulating platelets. Interestingly, hamster platelets during torpor do not express P-selectin, but expression is induced by treatment with ADP. Platelet count rapidly restores during arousal and rewarming. Platelet dynamics in hibernation are not affected by splenectomy before or during torpor. Reversible thrombocytopenia was also induced by forced hypothermia in both hibernating (hamster) and non-hibernating (rat and mouse) species without changing platelet function. Pharmacological torpor induced by injection of 5'-AMP in mice did not induce thrombocytopenia, possibly because 5'-AMP inhibits platelet function. The rapidness of changes in the numbers of circulating platelets, as well as marginal changes in immature platelet fractions upon arousal, strongly suggest that storage-and-release underlies the reversible thrombocytopenia during natural torpor. Possibly, margination of platelets, dependent on intrinsic platelet functionality, governs clearance of circulating platelets during torpor.
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Affiliation(s)
- Edwin L. de Vrij
- Department of Clinical Pharmacy and Pharmacology, University of Groningen, University Medical Center Groningen, Groningen, The Netherlands
| | | | - Maaike Goris
- Department of Clinical Pharmacy and Pharmacology, University of Groningen, University Medical Center Groningen, Groningen, The Netherlands
| | - Martin C. Houwertjes
- Department of Anesthesiology, University of Groningen, University Medical Center Groningen, Groningen, the Netherlands
| | - Annika Herwig
- Zoological Institute, University of Hamburg, Hamburg, Germany
| | - George J. Dugbartey
- Department of Clinical Pharmacy and Pharmacology, University of Groningen, University Medical Center Groningen, Groningen, The Netherlands
| | - Ate S. Boerema
- Department of Chronobiology, University of Groningen, Center for Behaviour & Neurosciences, Groningen, The Netherlands
- Department of Molecular Neurobiology, University of Groningen, Center for Behavior & Neurosciences, Groningen, The Netherlands
- Department of Nuclear Medicine & Molecular Imaging, University of Groningen, University Medical Center Groningen, Groningen, the Netherlands
| | - Arjen M. Strijkstra
- Department of Clinical Pharmacy and Pharmacology, University of Groningen, University Medical Center Groningen, Groningen, The Netherlands
- Department of Chronobiology, University of Groningen, Center for Behaviour & Neurosciences, Groningen, The Netherlands
| | - Hjalmar R. Bouma
- Department of Clinical Pharmacy and Pharmacology, University of Groningen, University Medical Center Groningen, Groningen, The Netherlands
- Department of Rheumatology and Clinical Immunology, University of Groningen, University Medical Center Groningen, Groningen, the Netherlands
| | - Robert H. Henning
- Department of Clinical Pharmacy and Pharmacology, University of Groningen, University Medical Center Groningen, Groningen, The Netherlands
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Gkourogianni A, Egot M, Koloka V, Moussis V, Tsikaris V, Panou-Pomonis E, Sakarellos-Daitsiotis M, Bachelot-Loza C, Tsoukatos DC. Palmitoylated peptide, being derived from the carboxyl-terminal sequence of the integrin αIIbcytoplasmic domain, inhibits talin binding to αIIbβ3. Platelets 2013; 25:619-27. [DOI: 10.3109/09537104.2013.850588] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
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14
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O'Callaghan K, Kuliopulos A, Covic L. Turning receptors on and off with intracellular pepducins: new insights into G-protein-coupled receptor drug development. J Biol Chem 2012; 287:12787-96. [PMID: 22374997 DOI: 10.1074/jbc.r112.355461] [Citation(s) in RCA: 124] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
G-protein-coupled receptors (GPCRs) are a large family of remarkably versatile membrane proteins that are attractive therapeutic targets because of their involvement in a vast range of normal physiological processes and pathological diseases. Upon activation, intracellular domains of GPCRs mediate signaling to G-proteins, but these domains have yet to be effectively exploited as drug targets. Cell-penetrating lipidated peptides called pepducins target specific intracellular loops of GPCRs and have recently emerged as effective allosteric modulators of GPCR activity. The lipid moiety facilitates translocation across the plasma membrane, where pepducins then specifically modulate signaling of their cognate receptor. To date, pepducins and related lipopeptides have been shown to specifically modulate the activity of diverse GPCRs and other membrane proteins, including protease-activated receptors (PAR1, PAR2, and PAR4), chemokine receptors (CXCR1, CXCR2, and CXCR4), sphingosine 1-phosphate receptor-3 (S1P3), the melanocortin-4 receptor, the Smoothened receptor, formyl peptide receptor-2 (FPR2), the relaxin receptor (LGR7), G-proteins (Gα(q/11/o/13)), muscarinic acetylcholine receptor and vanilloid (TRPV1) channels, and the GPIIb integrin. This minireview describes recent advances made using pepducin technology in targeting diverse GPCRs and the use of pepducins in identifying potential novel drug targets.
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Affiliation(s)
- Katie O'Callaghan
- Molecular Oncology Research Institute, Tufts Medical Center, Boston, Massachusetts 02111, USA
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Sigalov AB. The SCHOOL of nature: III. From mechanistic understanding to novel therapies. SELF/NONSELF 2010; 1:192-224. [PMID: 21487477 PMCID: PMC3047783 DOI: 10.4161/self.1.3.12794] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/27/2010] [Revised: 06/10/2010] [Accepted: 06/11/2010] [Indexed: 11/19/2022]
Abstract
Protein-protein interactions play a central role in biological processes and thus represent an appealing target for innovative drug design and development. They can be targeted by small molecule inhibitors, modulatory peptides and peptidomimetics, which represent a superior alternative to protein therapeutics that carry many disadvantages. Considering that transmembrane signal transduction is an attractive process to therapeutically control multiple diseases, it is fundamentally and clinically important to mechanistically understand how signal transduction occurs. Uncovering specific protein-protein interactions critical for signal transduction, a general platform for receptor-mediated signaling, the signaling chain homooligomerization (SCHOOL) platform, suggests these interactions as universal therapeutic targets. Within the platform, the general principles of signaling are similar for a variety of functionally unrelated receptors. This suggests that global therapeutic strategies targeting key protein-protein interactions involved in receptor triggering and transmembrane signal transduction may be used to treat a diverse set of diseases. This also 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, human viruses use the SCHOOL-like strategies to modulate and/or escape the host immune response. These viral mechanisms are highly optimized over the millennia, and the lessons learned from viral pathogenesis can be used practically for rational drug design. Proof of the SCHOOL concept in the development of novel therapies for atopic dermatitis, rheumatoid arthritis, cancer, platelet disorders and other multiple indications with unmet needs opens new horizons in therapeutics.
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Raab M, Parthasarathi L, Treumann A, Moran N, Daxecker H. Differential binding of ICln in platelets to integrin-derived activating and inhibitory peptides. Biochem Biophys Res Commun 2009; 392:258-63. [PMID: 20034469 DOI: 10.1016/j.bbrc.2009.12.088] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2009] [Accepted: 12/16/2009] [Indexed: 11/17/2022]
Abstract
The capacity of platelets to form a thrombus is mediated by integrin alpha(IIb)beta(3). The cytoplasmic tail of alpha(IIb) contains a highly conserved motif, (989)KVGFFKR(995), which plays a critical role in regulating integrin activation and acts as a recognition site for various intracellular proteins, e.g. CIB1, PP1, ICln and RN181. Previously, we demonstrated that a cell-permeable integrin-derived activating (IDA) peptide, KVGFFKR, induces platelet activation, whereas an integrin-derived inhibitory (IDI) peptide, KVGAAKR, is antithrombotic. To elucidate the molecular mechanism underlying these opposite effects we investigate the affinity of known integrin alpha(IIb) binding proteins for the two immobilized peptides in dependence on the activation state of platelets by means of peptide-affinity chromatography, blotting techniques and protein:peptide docking studies. Our results provide a model for the inhibition of ICln interaction with the integrin in activated platelets by the IDI-peptide. Thus, ICln:IDI-peptide interaction profiles can have a pivotal purpose in the search for consensus pharmacophores specifically inhibiting ICln function in platelets potentially leading to the development of integrin-derived antithrombotic drugs.
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Moran N, Kenny D, O’Neill S, Harmon S, Culligan K, Kerrigan S, Meade G, Coleman L, Dunne E, Nolan E, Mckeon K, Foley O. Abstracts presented at the Ireland-UK Platelet Conference, 4–6 September, 2005, Dublin, Ireland. Platelets 2009. [DOI: 10.1080/09537100600982186] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
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18
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Reilly D, Larkin D, Devocelle M, Fitzgerald DJ, Moran N. Calreticulin-independent regulation of the platelet integrin αIIbβ3by the KVGFFKR αIIb-cytoplasmic motif. Platelets 2009; 15:43-54. [PMID: 14985176 DOI: 10.1080/09537100310001640055] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
The platelet integrin alphaIIbbeta3 alters conformation in response to platelet activation and ligand binding, although the molecular mechanisms involved are not known. We previously showed that a lipid modified peptide, corresponding to the membrane proximal 989KVGFFKR995 portion of the alphaIIb cytoplasmic tail, independently activates platelet alphaIIbbeta3. Calreticulin (CRT) is a potential integrin regulatory protein based on its interaction with the highly conserved alpha-integrin sequence KxGFFKR. We therefore examined the possible interaction of calreticulin and alphaIIbbeta3 in human platelets. We demonstrate that calreticulin in platelets is localised to the granulomere. In contrast, the known integrin-binding protein talin accumulates at the periphery of spreading platelets and colocalises with alphaIIbbeta3 during the process of adhesion. An interaction between calreticulin and alphaIIbbeta3 could not be demonstrated using co-immunoprecipitation techniques under various platelet activation states, even in the presence of covalent chemical crosslinkers. Thus, calreticulin does not functionally interact with the major integrin in human platelets. In order to identify proteins that interact with the integrin KVGFFKR motif we then used a peptide 'pull-down' assay from platelet lysates with biotinylated peptides and demonstrate that only the alphaIIb and beta3 subunits selectively and individually interact with this sequence. This interaction is divalent cation-dependent, has high-affinity, and occurs both with purified alphaIIbbeta3 complex and with electroeluted alpha and beta subunits. Thus, our data show that the conserved integrin KVGFFKR domain interacts primarily with the alpha and beta cytoplasmic tails and not with CRT in human platelets.
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Affiliation(s)
- Dermot Reilly
- Centre for Sythesis and Chemical Biology, Department of Chemistry, Royal College of Surgeons in Ireland, Dublin
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Bernard E, Parthasarathi L, Cho MK, Aylward K, Raab M, Daxecker H, O’Dushlaine CT, Shields DC, Devocelle M, Keyes T, Cosgrave L, O’Neill S, Mok KH, Moran N. Ligand switching in cell-permeable peptides: manipulation of the alpha-integrin signature motif. ACS Chem Biol 2009; 4:457-71. [PMID: 19371094 DOI: 10.1021/cb8002623] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
A synthetic cell-permeable peptide corresponding to the highly conserved alpha-integrin signature motif, Palmityl-K(989)VGFFKR(995) (Pal-FF), induces integrin activation and aggregation in human platelets. Systematic replacement of the F(992)-F(993) with amino acids of greater or lesser hydrophobicity to create Pal-KVGxxKR peptides demonstrate that hydrophobic amino acids (isoleucine, phenylalanine, tyrosine, tryptophan) are essential for agonist potency. In marked contrast, substitution with small and/or hydrophilic amino acids (glycine, alanine, serine) causes a switch in the biological activity resulting in inhibition of platelet aggregation, adhesion, ADP secretion, and thromboxane synthesis. These substituted, hydrophilic peptides are not true pharmacological antagonists, as they actively induce a phosphotyrosine signaling cascade in platelets. Singly substituted peptides (Pal-AF and Pal-FA) cause preferential retention of pro- or anti-thrombotic properties, respectively. Because the alpha-integrin signature motif is an established docking site for a number of diverse cytoplasmic proteins, we conclude that eliminating critical protein-protein interactions mediated through the hydrophobic amino acids, especially F(993), favors an anti-thrombotic pathway in platelets. Agents derived from the inhibitory peptides described in this study may represent a new therapeutic strategy for anti-platelet or anti-integrin drug development.
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Affiliation(s)
| | | | | | | | | | | | | | | | - Marc Devocelle
- Centre for Synthesis and Chemical Biology, Royal College of Surgeons in Ireland, Dublin 2, Ireland
| | - Tia Keyes
- School of Chemical Sciences, Dublin City University, Dublin 9, Ireland
| | - Lynda Cosgrave
- School of Chemical Sciences, Dublin City University, Dublin 9, Ireland
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Missirlis D, Khant H, Tirrell M. Mechanisms of peptide amphiphile internalization by SJSA-1 cells in vitro. Biochemistry 2009; 48:3304-14. [PMID: 19245247 DOI: 10.1021/bi802356k] [Citation(s) in RCA: 68] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Self-assembly of peptide amphiphiles into nanostructures makes them attractive for a variety of applications in drug and peptide delivery. We here report on the interactions of micelles composed of a palmitoylated, pro-apoptotic peptide derived from p53 tumor suppressor protein with a human cancer cell line. Characterization of self-assembly in aqueous buffered solutions revealed formation of elongated rod-like micelles above a critical micelle concentration. Our results however demonstrate that monomers instead of micelles are internalized, a finding that correlates with the dynamic nature of the assemblies and the noncovalent interactions that hold them together. Internalization is shown to occur via adsorption-mediated, energy-dependent pathways, resulting in accumulation of the material in endocytic vesicles. We conclude that palmitoylation of peptides is an efficient way to increase peptide permeability inside SJSA-1 cells and that increased micelle stability would be required for intact micelle internalization.
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Affiliation(s)
- Dimitris Missirlis
- Department of Chemical Engineering and Materials, University of California, Santa Barbara, California 93106, USA.
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Koloka V, Christofidou ED, Vaxevanelis S, Dimitriou AA, Tsikaris V, Tselepis AD, Panou-Pomonis E, Sakarellos-Daitsiotis M, Tsoukatos DC. A palmitoylated peptide, derived from the acidic carboxyl-terminal segment of the integrin alphaIIb cytoplasmic domain, inhibits platelet activation. Platelets 2009; 19:502-11. [PMID: 18979362 DOI: 10.1080/09537100802266875] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
Abstract
Platelet integrin alpha(IIb)beta(3) contains an acidic membrane distal motif, 1000LEEDDEEGE1008, in the cytoplasmic domain of the alpha(IIb) subunit. We showed that a lipid-modified peptide corresponding to the above region, palmitoyl-K-LEEDDEEGE (pal-K-1000-1008), is platelet permeable and has inhibited platelet aggregation induced by 0.4 U/ml of thrombin (IC50 = 164 microM). Moreover the peptide inhibited both Fibrinogen and PAC-1, binding to activated platelets. The non palmitoylated analog was inactive. A modified, scrambled acidic peptide (palmitoyl-K-GDDEELEEE), showed significant lower inhibitory activity than pal-K-1000-1008. A palmitoylated peptide corresponding to the membrane proximal cytoplasmic domain of alpha(IIb), 989KGVFFKR995 (pal-989-995), is known to specifically induce platelet aggregation. Pal-K-1000-1008 was an inhibitor of human washed platelet aggregation induced by pal-K-989-995 (IC50 = 15 microM). Moreover, pal-K-1000-1008 inhibited phosphorylation of ERK and FAK, two protein kinases involved in platelet activation and aggregation. Our results favour the assumption that the interaction of the membrane proximal sequence 989KGVFFKR995 of the cytoplasmic domain of alpha(IIb) with the acidic terminal 1000LEEDDEEGE1008 motif may be an important structural factor in platelet signaling, leading to platelet activation and aggregation.
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Affiliation(s)
- Vassiliki Koloka
- Sector of Organic Chemistry and Biochemistry, Department of Chemistry, University of Ioannina, Ioannina 45110, Greece
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22
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Larkin D, Treumann A, Murphy D, DeChaumont C, Kiernan A, Moran N. Compartmentalization regulates the interaction between the platelet integrin alpha IIb beta 3 and ICln. Br J Haematol 2008; 144:580-90. [PMID: 19055659 DOI: 10.1111/j.1365-2141.2008.07483.x] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The volume-regulating protein, ICln, interacts with the conserved KxGFFKR alpha-integrin signature motif. ICln is an abundant protein (4455 +/- 650 molecules/platelet) found exclusively in the soluble cytosolic fraction of unactivated platelets. In contrast, its binding partner, the platelet integrin alpha(IIb)beta(3), is present in detergent-insoluble fractions associated with membrane and cytoskeleton subcellular localizations. This study investigated factors that regulate the interaction of ICln with alpha(IIb)beta(3) during platelet activation. His-tagged recombinant ICln bound equally to purified alpha(IIb)beta(3) and to integrin from resting or activated platelets. Binding was not affected by direct integrin activation with Mn(++) or by inhibitors of integrin occupancy (abciximab, RGD). However, the capacity for interaction between integrin and recombinant ICln was slowly downregulated following prolonged platelet activation for >300 s. In parallel, ICln redistributed to membrane and cytoskeletal platelet subcellular fractions. The time-course of this redistribution preceded the downregulation of integrin binding capacity and suggests that only a short window of opportunity exists for ICln interaction with alpha(IIb)beta(3) to occur. Thus, although ICln has the inherent capacity to bind to alpha(IIb)beta(3) regardless of its activation state, it can only do so following platelet activation. Activation-dependent subcellular redistribution of ICln represents a novel, temporally-regulated mechanism for control of integrin function in platelets.
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Affiliation(s)
- Deirdre Larkin
- Molecular and Cellular Therapeutics, Royal College of Surgeons in Ireland, Dublin, Ireland
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RN181, a novel ubiquitin E3 ligase that interacts with the KVGFFKR motif of platelet integrin αIIbβ3. Biochem Biophys Res Commun 2008; 369:1088-93. [DOI: 10.1016/j.bbrc.2008.02.142] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2008] [Accepted: 02/29/2008] [Indexed: 11/18/2022]
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RGT, a synthetic peptide corresponding to the integrin beta 3 cytoplasmic C-terminal sequence, selectively inhibits outside-in signaling in human platelets by disrupting the interaction of integrin alpha IIb beta 3 with Src kinase. Blood 2008; 112:592-602. [PMID: 18398066 DOI: 10.1182/blood-2007-09-110437] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
Mutational analysis has established that the cytoplasmic tail of the integrin beta 3 subunit binds c-Src (termed as Src in this study) and is critical for bidirectional integrin signaling. Here we show in washed human platelets that a cell-permeable, myristoylated RGT peptide (myr-RGT) corresponding to the integrin beta 3 C-terminal sequence dose-dependently inhibited stable platelet adhesion and spreading on immobilized fibrinogen, and fibrin clot retraction as well. Myr-RGT also inhibited the aggregation-dependent platelet secretion and secretion-dependent second wave of platelet aggregation induced by adenosine diphosphate, ristocetin, or thrombin. Thus, myr-RGT inhibited integrin outside-in signaling. In contrast, myr-RGT had no inhibitory effect on adenosine diphosphate-induced soluble fibrinogen binding to platelets that is dependent on integrin inside-out signaling. Furthermore, the RGT peptide induced dissociation of Src from integrin beta 3 and dose-dependently inhibited the purified recombinant beta 3 cytoplasmic domain binding to Src-SH3. In addition, phosphorylation of the beta 3 cytoplasmic tyrosines, Y(747) and Y(759), was inhibited by myr-RGT. These data indicate an important role for beta 3-Src interaction in outside-in signaling. Thus, in intact human platelets, disruption of the association of Src with beta 3 and selective blockade of integrin alpha IIb beta 3 outside-in signaling by myr-RGT suggest a potential new antithrombotic strategy.
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Haas TA, Taherian A, Berry T, Ma X. Identification of residues of functional importance within the central turn motifs present in the cytoplasmic tails of integrin alphaIIb and alphaV subunits. Thromb Res 2008; 122:507-16. [PMID: 18328539 DOI: 10.1016/j.thromres.2008.01.006] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2007] [Revised: 12/17/2007] [Accepted: 01/15/2008] [Indexed: 12/24/2022]
Abstract
INTRODUCTION Previous studies demonstrated that cell-permeable alphaIIb cytoplasmic peptides can modulate the activation of alphaIIbbeta3. An integrin activation motif was mapped to its membrane proximal region and a double proline mutant peptide and receptor indicated that its central turn motif had inhibitory capacity. However, the residues critical for inhibition of alphaIIbbeta3 activation were not identified. Using central turn peptides derived from alphaIIb and alphaV, residues critical for suppression of integrin activation were identified and the importance of these residues in protein-protein interactions was assessed. MATERIALS AND METHODS Cell-permeable peptides were used to determine the capacity of the central turn peptides to suppress alphaIIbbeta3 and alphaVbeta3 activation. Far Western analysis was used to characterize the capacity of the peptides to interact with CIB1 and surface plasmon resonance was used to characterize the binding of an antibody to the cytoplasmic tails of alphaIIb and alphaV. RESULTS AND CONCLUSIONS The central turn peptide from alphaV, alphaV(993-1001), has full inhibitory capacity while that derived from alphaIIb requires additional residues located adjacent to alphaIIb(995-1003). Within these two sequences there is a switch in the position of an asparaginine and leucine residue for a valine and glutamine (alphaIIb, RNRPPLEED; alphaV, RVRPPQEEQ). This switch had a dramatic effect on their inhibitory capacity and on protein-protein interactions. The two arginine and glutamic residues, juxtapositioned at identical locations in both subunits, appeared to be important in specifying the orientation by which proteins can dock to this region in alphaIIb and alphaV.
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Affiliation(s)
- Thomas A Haas
- Department of Anatomy and Cell Biology, College of Medicine, University of Saskatchewan, Saskatoon, SK, Canada S7N 5E5.
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Abstract
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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Kargakis M, Zevgiti S, Krikorian D, Sakarellos-Daitsiotis M, Sakarellos C, Panou-Pomonis E. A palmitoyl-tailed sequential oligopeptide carrier for engineering immunogenic conjugates. Vaccine 2007; 25:6708-12. [PMID: 17692437 DOI: 10.1016/j.vaccine.2007.07.007] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/09/2007] [Revised: 06/21/2007] [Accepted: 07/09/2007] [Indexed: 11/22/2022]
Abstract
The main guideline in designing effective immunogens as vaccine candidates capable of eliciting potent and specific immune responses is to combine B/T cell epitopes and adjuvants as immunostimulators on the same carrier that links the major histocompatibility complex with T cell receptors. Aiming at contributing to the development of carriers for human usage a helicoid type sequential oligopeptide carrier, SOC(n)-II, formed by the repeating tetrapeptide unit (Aib-Lys-Aib-Gly)(n), n=2-7, elongated from the amino-terminus by the palmitoyl group, known for its adjuvanticity, is now presented. The main B cell epitope, PPGMRPP, of the Sm autoantigen against which the majority of antibodies in patients with systemic lupus erythematosus is directed, was coupled to the Lys-N(epsilon)H(2) groups of the carrier in four copies and the resulting conjugate Palm-SOC(4)-II-Sm(4) was subjected to animal immunizations without utilizing any adjuvant. The induced immune response was comparable with that produced when Ac-SOC(4)-II-Sm(4) was administered in animals following the conventional immunization protocol of complete/incomplete Freund's adjuvant. High titers of anti-Palm-SOC(4)-II-Sm(4) antibodies were generated, which recognize the priming immunogenic conjugate, as well as reconstituted Sm mimics but not the carrier alone. It is concluded that Palm-SOC(n)-II carrier is a valuable tool for engineering immunogens eliciting enhanced and specific humoral immune responses.
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Affiliation(s)
- Michael Kargakis
- Department of Chemistry, Section of Organic Chemistry and Biochemistry, University of Ioannina, 45110 Ioannina, Greece
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Liu J, Ware J, Jackson CW, Gartner TK. FcRgamma-chain-dependent alphaIIbeta3 elicited outside-in signaling. J Thromb Haemost 2007; 5:426-8. [PMID: 17105578 DOI: 10.1111/j.1538-7836.2007.02317.x] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
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29
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Edwards RJ, Moran N, Devocelle M, Kiernan A, Meade G, Signac W, Foy M, Park SDE, Dunne E, Kenny D, Shields DC. Bioinformatic discovery of novel bioactive peptides. Nat Chem Biol 2007; 3:108-12. [PMID: 17220901 DOI: 10.1038/nchembio854] [Citation(s) in RCA: 66] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2006] [Accepted: 12/12/2006] [Indexed: 12/15/2022]
Abstract
Short synthetic oligopeptides based on regions of human proteins that encompass functional motifs are versatile reagents for understanding protein signaling and interactions. They can either mimic or inhibit the parent protein's activity and have been used in drug development. Peptide studies typically either derive peptides from a single identified protein or (at the other extreme) screen random combinatorial peptides, often without knowledge of the signaling pathways targeted. Our objective was to determine whether rational bioinformatic design of oligopeptides specifically targeted to potentially signaling-rich juxtamembrane regions could identify modulators of human platelet function. High-throughput in vitro platelet function assays of palmitylated cell-permeable oligopeptides corresponding to these regions identified many agonists and antagonists of platelet function. Many bioactive peptides were from adhesion molecules, including a specific CD226-derived inhibitor of inside-out platelet signaling. Systematic screens of this nature are highly efficient tools for discovering short signaling motifs in molecular signaling pathways.
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Affiliation(s)
- Richard J Edwards
- Department of Clinical Pharmacology, Royal College of Surgeons in Ireland, 123 St. Stephen's Green, Dublin 2, Ireland
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David T, Ohlmann P, Eckly A, Moog S, Cazenave JP, Gachet C, Lanza F. Inhibition of adhesive and signaling functions of the platelet GPIb-V-IX complex by a cell penetrating GPIbalpha peptide. J Thromb Haemost 2006; 4:2645-55. [PMID: 17100656 DOI: 10.1111/j.1538-7836.2006.02198.x] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
BACKGROUND Interaction between the platelet glycoprotein (GP)Ib-V-IX complex and von Willebrand factor (VWF) is critical for initiating platelet-vessel wall contacts, particularly under high shear conditions. This interaction also plays an important role in initiating platelet activation through the generation of intracellular signals resulting in platelet shape change and integrin alpha(IIb)beta3 activation. OBJECTIVE A cell-penetrating peptide strategy was used to study the role of the intracellular domain of the GPIbalpha subunit in VWF/GPIb-V-IX-dependent adhesion and activation. METHODS Peptides of 11-13 amino acids, covering the 557-610 region, were coupled to a nine-arginine permeating tag (R9) and the effects of their cell entry on VWF-dependent responses were analyzed. RESULTS The R9alpha557 peptide corresponding to the 557-569 segment reduced platelet agglutination in response to VWF, while the other peptides had no effect. The decreased platelet agglutination appeared to be an indirect consequence of adenosine diphosphate release as a normal response was restored by apyrase or a P2Y1 receptor antagonist. A more direct effect of R9alpha557 on GPIb VWF-dependent functions was observed in adhesion studies on a VWF matrix, where it decreased platelet adhesion and profoundly inhibited filopodia formation. In addition, cell adhesion was reduced and shape change absent when Chinese hamster ovary cells expressing the GPIb-IX complex were incubated with R9alpha557. CONCLUSION This study performed in intact platelets suggests a functional role of the 557-569 domain of GPIbalpha in controlling VWF-dependent adhesion and signaling.
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Affiliation(s)
- T David
- INSERM U311, Strasbourg; EFS-Alsace, Strasbourg, France
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Aylward K, Meade G, Ahrens I, Devocelle M, Moran N. A novel functional role for the highly conserved alpha-subunit KVGFFKR motif distinct from integrin alphaIIbbeta3 activation processes. J Thromb Haemost 2006; 4:1804-12. [PMID: 16879224 DOI: 10.1111/j.1538-7836.2006.02041.x] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
BACKGROUND The highly conserved integrin alpha-subunit membrane-proximal motif KVGFFKR plays a decisive role in modulating the activation of integrin alphaIIbbeta3. Previously, we have shown that a platelet permeable palmityl (pal)-peptide with this seven amino acid sequence can directly activate alphaIIbbeta3 leading to platelet aggregation. OBJECTIVES To investigate further the role of the KVGFFKR motif in integrin alphaIIbbeta3 function. METHODS We used two sequence-specific complementary model systems, palmityl pal-peptides in platelets, and mutant alphaIIbbeta3-expressing Chinese Hamster Ovary (CHO) cell lines. RESULTS In platelets we show that the two phenylalanine amino acids in pal-KVGFFKR (pal-FF) peptide are critical for stimulating platelet aggregation. Pal-FF peptide treatment of platelets also gives rise to a tyrosine phosphorylation signal despite the presence of inhibitors of fibrinogen binding. In CHO cells, a double alanine substitution, alphaIIb(F992A, F993A)beta3, induces constitutive integrin activation but prevents actin stress fiber formation upon adhesion to fibrinogen, suggesting that alphaIIbbeta3-mediated cytoskeletal reorganization is also dependent on F992 and F993. This further highlights a critical role for the two phenylalanine residues in both of these alphaIIbbeta3-mediated processes. CONCLUSION In addition to regulating integrin alphaIIbbeta3 activation state, the KVGFFKR motif also influences cytoskeletal reorganization. This activity is critically determined by F992 and F993 within the seven amino acid sequence.
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Affiliation(s)
- K Aylward
- Department of Clinical Pharmacology, Royal College of Surgeons in Ireland, Dublin, Ireland
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Moran N, Kiernan A, Dunne E, Edwards RJ, Shields DC, Kenny D. Monitoring modulators of platelet aggregation in a microtiter plate assay. Anal Biochem 2006; 357:77-84. [PMID: 16920064 DOI: 10.1016/j.ab.2006.06.037] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2006] [Revised: 06/23/2006] [Accepted: 06/29/2006] [Indexed: 01/29/2023]
Abstract
Platelets play a central role in maintaining biological hemostasis. Inappropriate platelet activation is responsible for thrombotic diseases such as myocardial infarction and stroke. Therefore, novel agents that can inhibit platelet activation are necessary. However, assays that monitor platelet aggregation are generally time-consuming and require high volumes of blood and specialized equipment. Therefore, a medium- to high-throughput assay that can monitor platelet aggregation would be considered useful. Such an assay should be sensitive, comparable to the "gold standard" assay of platelet aggregometry, and able to monitor multiple samples simultaneously but with low assay volumes. We have developed such a microtiter assay. It can assay an average of 60 independent treatments per 60 ml blood donation and demonstrates greater sensitivity than the current gold standard assay, namely platelet aggregation in stirring conditions in a platelet aggregometer. The microtiter plate (MTP) assay can detect known inhibitors of platelet function such as indomethacin, aspirin, and ReoPro. It is highly reproducible when using standard doses of agonists such as thrombin receptor-activating peptide (20 microM) and collagen (0.19 mg/ml). Finally, the MTP assay is rapid and sensitive and can detect unknown platelet-modulating agents from a library of compounds.
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Affiliation(s)
- N Moran
- Department of Clinical Pharmacology, Royal College of Surgeons in Ireland, Dublin 2, Ireland.
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Robinson A, O'Neill S, Kiernan A, O'Donoghue N, Moran N. Bacitracin reveals a role for multiple thiol isomerases in platelet function. Br J Haematol 2006; 132:339-48. [PMID: 16409299 DOI: 10.1111/j.1365-2141.2005.05878.x] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The platelet-specific integrin alphaIIb beta3 has endogenous thiol isomerase activity associated with the CXXC motifs within the beta subunit. Using a highly purified form of bacitracin, a thiol isomerase inhibitor, we now provide further evidence of the functional significance of this enzymatic activity in integrin activation. In addition, we demonstrate a role for multiple thiol isomerases in platelet function. This bacitracin prevented platelet aggregation to thrombin and collagen, and directly inhibited alphaIIb beta3 activation, as detected by PAC-1 binding. In parallel, bacitracin inhibited the endogenous thiol isomerase activity of purified alphaIIb beta3 with a 50% inhibitory concentration of 15.5 micromol/l. In order to determine whether the effects of bacitracin are solely mediated by inhibition of integrin enzymatic activity, we examined integrin-independent indices of platelet activation. We found bacitracin inhibited both platelet secretion (CD62P and CD63) and thromboxane (TxA2) production, with complete inhibition at different concentrations. Thus, we demonstrated a role for multiple thiol isomerases in platelet function. Taken together, these studies support a role for the endogenous integrin thiol isomerase activity in activation of alphaIIb beta3 and highlight the novel regulation of platelet function by other, as yet undefined thiol isomerases.
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Affiliation(s)
- Aisling Robinson
- Department of Clinical Pharmacology, Royal College of Surgeons in Ireland, Dublin 2, Ireland
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34
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Ahrens IG, Moran N, Aylward K, Meade G, Moser M, Assefa D, Fitzgerald DJ, Bode C, Peter K. Evidence for a differential functional regulation of the two beta(3)-integrins alpha(V)beta(3) and alpha(IIb)beta(3). Exp Cell Res 2006; 312:925-37. [PMID: 16434034 DOI: 10.1016/j.yexcr.2005.11.036] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/25/2004] [Revised: 11/28/2005] [Accepted: 11/30/2005] [Indexed: 11/22/2022]
Abstract
The functional regulation of integrins is a major determinant of cell adhesion, migration and tissue maintenance. The binding of cytoskeletal proteins to various sites of integrin cytoplasmic domains is a key mechanism of this functional regulation. Expression of recombinant integrin alpha(IIb)beta(3) and alpha(M)beta(2) lacking the GFFKR-region in CHO cells results in constitutively activated integrins. In contrast, CHO cells stably expressing either a GFFKR-deleted alpha(V(del))beta(3) or a FF to AA-substituted alpha(V(AA))beta(3) do not reveal a constitutively activated integrin. Adhesion to immobilized fibrinogen is strongly impaired in alpha(V(del))beta(3) or alpha(V(AA))beta(3)-expressing cells, whereas it is not impaired in alpha(IIb)beta(3) and alpha(M)beta(2), both lacking the GFFKR-region. In a parallel plate flow chamber assay, alpha(V)beta(3)-expressing cells adhere firmly to fibrinogen and spread even at shear rates of 15 to 20 dyn/cm(2), whereas alpha(V(del))beta(3) or alpha(V(AA))beta(3) cells are detached at 15 dyn/cm(2). Actin stress fiber formation and focal adhesion plaques containing alpha(V)beta(3) are observed in alpha(V)beta(3) cells but not in alpha(V(del))beta(3) or alpha(V(AA))beta(3)-expressing cells. As an additional manifestation of impaired outside-in signaling, phosphorylation of pp125(FAK) was reduced in these cells. In summary, we report that the GFFKR-region of the alpha(V)-cytoplasmic domain and in particular two phenylalanines are essential for integrin alpha(V)beta(3) function, especially for outside-in signaling. Our results suggest that the two beta(3)-integrins alpha(IIb)beta(3) and alpha(V)beta(3) are differentially regulated via their GFFKR-region.
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Affiliation(s)
- I G Ahrens
- Department of Cardiology and Angiology, Internal Medicine III, University of Freiburg, Hugstetter Str. 55, 79106 Freiburg, Germany.
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35
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Lueking A, Cahill DJ, Müllner S. Protein biochips: A new and versatile platform technology for molecular medicine. Drug Discov Today 2005; 10:789-94. [PMID: 15922937 DOI: 10.1016/s1359-6446(05)03449-5] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
Abstract
The human genome has been sequenced and the challenges of understanding the function of the newly discovered genes have been addressed. High-throughput technologies such as DNA microarrays have been developed for the profiling of gene expression patterns in whole organisms or tissues. Protein arrays are emerging to follow DNA chips as possible screening tools. Here, we review the generation and application of microarray technology to obtain more information on the regulation of proteins, their biochemical functions and their potential interaction partners. Already, a large variety of assays based on antibody-antigen interactions exists. In addition, the medical relevance of protein arrays will be discussed.
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Affiliation(s)
- Angelika Lueking
- Ruhr-University Bochum, Medical Proteome Center, Universitätsstrasse 150, D-44780 Bochum, Germany
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36
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Liu J, Jackson CW, Gruppo RA, Jennings LK, Gartner TK. The beta3 subunit of the integrin alphaIIbbeta3 regulates alphaIIb-mediated outside-in signaling. Blood 2005; 105:4345-52. [PMID: 15701721 PMCID: PMC1895035 DOI: 10.1182/blood-2004-07-2718] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Bidirectional signaling is an essential feature of alphaIIbbeta3 function. The alphaIIb cytoplasmic domain negatively regulates beta3-mediated inside-out signaling, but little is known about the regulation of alphaIIb-mediated outside-in signaling. We show that alphaIIb-mediated outside-in signaling is enhanced in platelets of a patient lacking the terminal 39 residues of the beta3 cytoplasmic tail. This enhanced signaling was detected as thromboxane A(2) (TxA(2)) production and granule secretion, and required ligand cross-linking of alphaIIbbeta3 and platelet aggregation. This outside-in signaling was specifically inhibited by a palmitoylated version of a beta3 peptide corresponding to cytoplasmic domain residues R724-R734. Unlike the palmitoylated peptide, the nonpalmitoylated beta3 peptide could not cross the platelet membrane and did not inhibit this outside-in signaling. The physiologic relevance of this beta3-mediated negative regulation of alphaIIb outside-in signaling was demonstrated in normal platelets treated with the palmitoylated peptide and a physiologic agonist. Binding of alphaIIbbeta3 complexes to immobilized peptides demonstrated that a peptide corresponding to beta3 residues R724-R734 appears to bind to an alphaIIb cytoplasmic domain peptide containing residues K989-D1002, but not to control peptides. These results demonstrate that alphaIIb-mediated outside-in signaling resulting in TxA(2) production and granule secretion is negatively regulated by a sequence of residues in the membrane distal beta3 cytoplasmic domain sequence RKEFAKFEEER.
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Affiliation(s)
- Junling Liu
- Department of Microbiology and Molecular Cell Sciences, University of Memphis, Memphis, TN 38152, USA
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37
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Maguire PB, Moran N, Cagney G, Fitzgerald DJ. Application of proteomics to the study of platelet regulatory mechanisms. Trends Cardiovasc Med 2005; 14:207-20. [PMID: 15451512 DOI: 10.1016/j.tcm.2004.06.001] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
Newly developed proteomic technologies now permit the routine identification of hundreds or even thousands of proteins in a single experiment. However, the global study of any proteome has unique challenges that set it apart from comprehensive studies of genes and transcripts. The detection of low-abundance, biologically relevant proteins poses a particular challenge, especially given that the dynamic range of proteins in cells is estimated to be > or =10(6). Nevertheless, the incorporation of proteomics into functional biochemical and biologic investigation has proved to be a powerful tool when applied to platelet biology. This review highlights recent proteomic approaches to the characterization of the proteins released from activated platelets and to the identification of integrin-associated regulators of platelet function. Also described are efforts to link platelet-proteomic and platelet-transcriptional data.
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Affiliation(s)
- Patricia B Maguire
- Department of Clinical Pharmacology, Royal College of Surgeon's in Ireland, Dublin, Ireland.
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38
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Abstract
The ability of cells to regulate dynamically their adhesion to one another and to the extracellular matrix (ECM) that surrounds them is essential in multicellular organisms. The integrin family of transmembrane adhesion receptors mediates both cell-cell and cell-ECM adhesion. One important, rapid and reversible mechanism for regulating adhesion is by increasing the affinity of integrin receptors for their extracellular ligands (integrin activation). This is controlled by intracellular signals that, through their action on integrin cytoplasmic domains, induce conformational changes in integrin extracellular domains that result in increased affinity for ligand. Recent studies have shed light on the final intracellular steps in this process and have revealed a vital role for the cytoskeletal protein talin.
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Affiliation(s)
- David A Calderwood
- Department of Pharmacology, Yale University School of Medicine, Sterling Hall of Medicine, New Haven, CT 06520, USA.
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39
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Abstract
Platelets play a central role in the hemostatic process and consequently are similarly involved in the pathological counterpart, thrombosis. They adhere to various subendothelial proteins, exposed either by injury or disease, and subsequently become activated by the thrombogenic surface or locally produced agonists. These activated platelets aggregate to form a platelet plug, release agonists which recruit more platelets to the growing thrombus, and provide a catalytic surface for thrombin generation and fibrin formation. These platelet-rich thrombi are responsible for the acute occlusion of stenotic vessels and ischemic injury to heart and brain. A range of anti-platelet drugs are currently used, both prophylactically and therapeutically, in regimens to manage thrombo-embolic disorders. These include inhibitors of the generation, or effects, of locally produced agonists; several large clinical trials have supported roles for cyclooxygenase inhibitors, which prevent thromboxane generation, and thienopyridine derivatives, which antagonize ADP receptors. Similarly intravenous alpha IIb beta 3 antagonists have been shown to be effective anti-thrombotics, albeit in highly selective situations; in contrast, to date studies with their oral counterparts have been disappointing. Recent advances in understanding of platelet physiology have suggested several novel, if yet untested, targets for anti-platelet therapy. These include the thrombin receptor, the serotonin handling system, and the leptin receptor.
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Affiliation(s)
- Archibald McNicol
- Department of Oral Biology, University of Manitoba, Winnipeg, Canada.
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40
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Yamanouchi J, Hato T, Tamura T, Fujita S. Suppression of integrin activation by the membrane-distal sequence of the integrin alphaIIb cytoplasmic tail. Biochem J 2004; 379:317-23. [PMID: 14723599 PMCID: PMC1224082 DOI: 10.1042/bj20031753] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/17/2003] [Revised: 01/05/2004] [Accepted: 01/15/2004] [Indexed: 01/14/2023]
Abstract
Integrin cytoplasmic tails regulate integrin activation including an increase in integrin affinity for ligands. Although there is ample evidence that the membrane-proximal regions of the alpha and beta tails interact with each other to maintain integrins in a low-affinity state, little is known about the role of the membrane-distal region of the alpha tail in regulation of integrin activation. We report a critical sequence for regulation of integrin activation in the membrane-distal region of the alphaIIb tail. Alanine substitution of the RPP residues in the alphaIIb tail rendered alphaIIbbeta3 constitutively active in a metabolic energy-dependent manner. Although an alphaIIb/alpha6Abeta3 chimaeric integrin, in which the alphaIIb tail was replaced by the alpha6A tail, was in an energy-dependent active state to bind soluble ligands, introduction of the RPP sequence into the alpha6A tail inhibited binding of an activation-dependent antibody PAC1. In alphaIIb/alpha6Abeta3, deleting the TSDA sequence from the alpha6A tail or single amino acid substitutions of the TSDA residues inhibited alphaIIb/alpha6Abeta3 activation and replacing the membrane-distal region of the alphaIIb tail with TSDA rendered alphaIIbbeta3 active, suggesting a stimulatory role of TSDA in energy-dependent integrin activation. However, adding TSDA to the alphaIIb tail containing the RPP sequence of the membrane-distal region failed to activate alphaIIbbeta3. These results suggest that the RPP sequence after the GFFKR motif of the alphaIIb tail suppresses energy-dependent alphaIIbbeta3 activation. These findings provide a molecular basis for the regulation of energy-dependent integrin activation by alpha subunit tails.
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Affiliation(s)
- Jun Yamanouchi
- Department of Internal Medicine 1, Ehime University School of Medicine, Shigenobu, Ehime 791-0295, Japan
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41
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Vijayan KV, Liu Y, Li TT, Bray PF. Protein phosphatase 1 associates with the integrin alphaIIb subunit and regulates signaling. J Biol Chem 2004; 279:33039-42. [PMID: 15205468 DOI: 10.1074/jbc.c400239200] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023] Open
Abstract
Regulation of integrin activation occurs by specific interactions among cytoplasmic proteins and integrin alpha and beta cytoplasmic tails. We report that the catalytic subunit of protein phosphatase 1 (PP1c) constitutively associates with the prototypic integrin alphaIIbbeta3 in platelets and in cell lines overexpressing the integrin. PP1c binds directly to the cytoplasmic domain of integrin alphaIIb subunit containing a conserved PP1c binding motif 989KVGF992. Anchored PP1c is inactive, while thrombin-induced platelet aggregation or fibrinogen-alphaIIbbeta3 engagement caused PP1c dissociation and concomitant activation as revealed by dephosphorylation of PP1c substrate, myosin light chain. Inhibition of ligand binding to activated alphaIIbbeta3 blocks PP1c dissociation and represses PP1c activation. These studies reveal a previously unrecognized role for integrins whereby the alpha subunit cytoplasmic tail localizes the machinery for initiating and temporally maintaining the regulatory signaling activity of a phosphatase.
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Affiliation(s)
- K Vinod Vijayan
- Department of Medicine, Baylor College of Medicine, Houston, Texas 77030, USA.
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42
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Larkin D, Murphy D, Reilly DF, Cahill M, Sattler E, Harriott P, Cahill DJ, Moran N. ICln, a Novel Integrin αIIbβ3-Associated Protein, Functionally Regulates Platelet Activation. J Biol Chem 2004; 279:27286-93. [PMID: 15075326 DOI: 10.1074/jbc.m402159200] [Citation(s) in RCA: 54] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
A critical role for the conserved alpha-integrin cytoplasmic motif, KVGFFKR, is recognized in the regulation of activation of the platelet integrin alpha(IIb)beta(3). To understand the molecular mechanisms of this regulation, we sought to determine the nature of the protein interactions with this cytoplasmic motif. We used a tagged synthetic peptide, biotin-KVGFFKR, to probe a high density protein expression array (37,200 recombinant human proteins) for high affinity interactions. A number of potential integrin-binding proteins were identified. One such protein, a chloride channel regulatory protein, ICln, was characterized further because its affinity for the integrin peptide was highest as was its expression in platelets. We verified the presence of ICln in human platelets by PCR, Western blots, immunohistochemistry, and its co-association with alpha(IIb)beta(3) by surface plasmon resonance. The affinity of this interaction was 82.2 +/- 24.4 nm in a cell free assay. ICln co-immunoprecipitates with alpha(IIb)beta(3) in platelet lysates demonstrating that this interaction is physiologically relevant. Furthermore, immobilized KVGFFKR peptides, but not control KAAAAAR peptides, specifically extract ICln from platelet lysates. Acyclovir (100 microm to 5 mm), a pharmacological inhibitor of the ICln chloride channel, specifically inhibits integrin activation (PAC-1 expression) and platelet aggregation without affecting CD62 P expression confirming a specific role for ICln in integrin activation. In parallel, a cell-permeable peptide corresponding to the potential integrin-recognition domain on ICln (AKFEEE, 10-100 microm) also inhibits platelet function. Thus, we have identified, verified, and characterized a novel functional interaction between the platelet integrin and ICln, in the platelet membrane.
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Affiliation(s)
- Deirdre Larkin
- Department of Clinical Pharmacology, Royal College of Surgeons in Ireland, Dublin
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Martin K, Meade G, Moran N, Shields DC, Kenny D. A palmitylated peptide derived from the glycoprotein Ib beta cytoplasmic tail inhibits platelet activation. J Thromb Haemost 2003; 1:2643-52. [PMID: 14675101 DOI: 10.1046/j.1538-7836.2003.00478.x] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The platelet receptor GPIb/IX/V mediates a crucial role in hemostasis, yet the signaling mechanisms involved are incompletely understood. The complex consists of four polypeptides GPIb alpha, GPIb beta, GPIX and GPV. We identified an amino acid sequence in the cytoplasmic tail of the GPIb beta subunit between residues R151 and A161 that is highly conserved across species and hypothesized that it has functional importance. To target this motif, we synthesized a corresponding cell-permeable palmitylated peptide (Pal-RRLRARARARA) and investigated its effect on platelet function. Pal-RRLRARARARA completely inhibited low dose thrombin- and ristocetin-induced aggregation in washed platelets but only partially inhibited collagen- and U46619-induced aggregation. Thromboxane production in platelets stimulated with thrombin was significantly reduced by Pal-RRLRARARARA compared with collagen. Activation of the integrin alpha IIb beta 3 in response to thrombin was significantly reduced when platelets were preincubated with Pal-RRLRARARARA. The adhesion of washed platelets to von Willebrand factor (VWF) under static conditions was significantly reduced by Pal-RRLRARARARA. Under conditions of high shear, the velocity of platelets rolling on VWF was significantly increased when platelets are preincubated with Pal-RRLRARARARA. This study defines a novel function for the RRLRARARARA motif of GPIb beta in platelet activation.
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Affiliation(s)
- K Martin
- Department of Clinical Pharmacology, Royal College of Surgeons in Ireland, Dublin, Ireland
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44
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Wang Z, Leisner TM, Parise LV. Platelet alpha2beta1 integrin activation: contribution of ligand internalization and the alpha2-cytoplasmic domain. Blood 2003; 102:1307-15. [PMID: 12738679 DOI: 10.1182/blood-2002-09-2753] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The alpha2beta1 integrin is a major collagen receptor on platelets. Although it has been proposed that alpha2beta1, like alphaIIbbeta3, undergoes agonist-induced activation, neither the potential contributions of alpha2beta1 receptor/ligand internalization to the increase in ligand binding nor the roles of the alpha2 and beta1 cytoplasmic domains in activation of this integrin have been previously explored. Activation of alpha2beta1 was assessed with fluorescein isothiocyanate-labeled soluble type I collagen binding to platelets by flow cytometry. Although collagen internalization in response to agonist activation of platelets was significant, agonist-induced collagen binding still occurred under conditions that block internalization, with minimal changes in cell surface alpha2beta1 expression. Introduction of cell-permeable peptides containing the alpha2 cytoplasmic tail, and especially the membrane proximal KLGFFKR domain, induced alpha2beta1 activation in resting platelets, whereas a cell-permeable peptide containing the beta1 cytoplasmic tail was without effect. Thus, collagen binding to stimulated platelets is increased due to alpha2beta1 activation, in addition to internalization, and the GFFKR motif appears to play an important role in the activation process.
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Affiliation(s)
- Zhengyan Wang
- Department of Pharmacology, Center for Thrombosis and Hemostasis, Lineberger Comprehensive Cancer Center, University of North Carolina at Chapel Hill, 27599, USA
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45
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Abstract
AlphaIIbbeta3, the major membrane protein on the surface of platelets, is a member of the integrin family of heterodimeric adhesion receptors. The alphaIIb and beta3 subunits are each composed of a short cytoplasmic tail, a single transmembrane domain, and a large, extracellular region that consists of a series of linked domains. Recent structural analyses have provided insights into the organization of this and other integrins and how a signal is initiated at its cytoplasmic tail to transform the extracellular domain of alphaIIbbeta3 into a functional receptor for fibrinogen or von Willebrand factor to support platelet aggregation and thrombus formation. These functions of alphaIIbbeta3 have been targeted for antithrombotic therapy, and intravenous alphaIIbbeta3 antagonists have been remarkably effective in the setting of percutaneous coronary interventions, showing both short-term and long-term mortality benefits. However, the development of oral antagonists has been abandoned on the basis of excess of mortality in clinical trials, and the extension of therapy with existing alphaIIbbeta3 antagonists to broadly treat acute coronary syndromes has not fully met expectations. An in-depth understanding of how antagonists engage and influence the function of alphaIIbbeta3 and platelets in the context of the new structural insights may explain its salutary and potential deleterious effects.
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Affiliation(s)
- Martin J Quinn
- Joseph J. Jacobs Center for Thrombosis and Vascular Biology, Department of Molecular Cardiology/NB50, Cleveland Clinic Foundation, 9500 Euclid Ave, Cleveland, Ohio 44195, USA
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46
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Maguire PB, Wynne KJ, Harney DF, O'Donoghue NM, Stephens G, Fitzgerald DJ. Identification of the phosphotyrosine proteome from thrombin activated platelets. Proteomics 2002; 2:642-8. [PMID: 12112843 DOI: 10.1002/1615-9861(200206)2:6<642::aid-prot642>3.0.co;2-i] [Citation(s) in RCA: 145] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
Signalling cascades are regulated both positively and negatively by tyrosine phosphorylation. Integrin mediated platelet adhesion triggers signal transduction cascades involving translocation of proteins and tyrosine phosphorylation events, ultimately causing large signalling complexes to be assembled. In resting platelets, a small number of phosphorylated proteins are evident with molecular mass of 50-62 kDa and 120-130 kDa. In thrombin activated human platelets, however, there is a large increase in the number of tyrosine phosphorylated signalling proteins detected. These proteins include pCas (130 kDa), FAK (125 kDa), PI(3)k (85 kDa) and src (85 kDa). However, it is unlikely that this list of proteins represents all the dynamic changes that occur after platelet activation and it is understood that more proteins remain unidentified. In this study, we propose a method for the isolation of the phosphotyrosine proteome from both resting and thrombin activated human platelets. All the dynamic phosphotyrosine events that occur in the platelet after thrombin activation were isolated by immunoprecipitation, using the monoclonal antibody 4G10, allowing us to obtain higher concentrations of relatively low abundant proteins. The resulting phosphotyrosine proteomes were separated by two-dimensional gel electrophoresis. Sixty-seven proteins were reproducibly found to be unique in the thrombin activated platelet proteome when compared to resting platelets. We have positively identified ten of these proteins by Western blotting and matrix-assisted laser desorption/ionisation-time of flight mass spectrometry and these include FAK, Syk, ALK-4, P2X6 and MAPK kinase kinase. This proteomics approach to understanding the signalling events following platelet activation may elucidate potential drug targets for the treatment of coronary thrombosis.
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Affiliation(s)
- Patricia B Maguire
- Department of Clinical Pharmacology, Royal College of Surgeon's in Ireland, Dublin, Ireland
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47
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Weljie AM, Hwang PM, Vogel HJ. Solution structures of the cytoplasmic tail complex from platelet integrin alpha IIb- and beta 3-subunits. Proc Natl Acad Sci U S A 2002; 99:5878-83. [PMID: 11983888 PMCID: PMC122870 DOI: 10.1073/pnas.092515799] [Citation(s) in RCA: 82] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2001] [Indexed: 11/18/2022] Open
Abstract
Integrin adhesion receptors constitute a cell-signaling system whereby interactions in the small cytoplasmic domains of the heterodimeric alpha- and beta-subunits provoke major functional alterations in the large extracellular domains. With two-dimensional NMR spectroscopy, we examined two synthetic peptides [alphaIIb((987)MWKVGFFKRNR) and beta3((716)KLLITIHDRKEFAKFEEERARAKWD)] encompassing the membrane-proximal regions of the cytoplasmic domain motifs from the platelet integrin complex alphaIotaIotabbeta3. These membrane-proximal regions contain two conserved motifs, represented by (989)KVGFFKR in the alphaIIb-subunit, and (716)KLLITIHDR in the beta3-subunit. The dimer interaction consists of two adjacent helices with residues V990 and F993 of the alphaIotaIotab-subunit heavily implicated in the dimer interfacial region, as is I719 of beta3. These residues are situated within the conserved motifs of their respective proteins. Further structural analysis of this unique peptide heterodimer suggests that two distinct conformers are present. The major structural difference between the two conformers is a bend in the beta3-peptide between D723 and A728, whereas the helical character in the other regions remains intact. Earlier mutational analysis has shown that a salt bridge between the side chains of alphaIotaIotab(R955) and beta3(D723) is formed. When this ion pair was modeled into both conformers, increased nuclear Overhauser effect violations suggested that the more bent structure was less able to accommodate this interaction. These results provide a molecular level rationalization for previously reported biochemical studies, as well as a basis for an atomic level understanding of the intermolecular interactions that regulate integrin activity.
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Affiliation(s)
- Aalim M Weljie
- Department of Biological Sciences, University of Calgary, 2500 University Drive NW, Calgary, AB, Canada
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48
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Covic L, Gresser AL, Talavera J, Swift S, Kuliopulos A. Activation and inhibition of G protein-coupled receptors by cell-penetrating membrane-tethered peptides. Proc Natl Acad Sci U S A 2002; 99:643-8. [PMID: 11805322 PMCID: PMC117359 DOI: 10.1073/pnas.022460899] [Citation(s) in RCA: 261] [Impact Index Per Article: 11.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2001] [Indexed: 11/18/2022] Open
Abstract
Classical ligands bind to the extracellular surface of their cognate receptors and activate signaling pathways without crossing the plasma membrane barrier. We selectively targeted the intracellular receptor-G protein interface by using cell-penetrating membrane-tethered peptides. Attachment of a palmitate group to peptides derived from the third intracellular loop of protease-activated receptors-1 and -2 and melanocortin-4 receptors yields agonists and/or antagonists of receptor-G protein signaling. These lipidated peptides--which we have termed pepducins--require the presence of their cognate receptor for activity and are highly selective for receptor type. Mutational analysis of both intact receptor and pepducins demonstrates that the cell-penetrating agonists do not activate G proteins by the same mechanism as the intact receptor third intracellular loop but instead require the C-tail of the receptor. Construction of such peptide-lipid conjugates constitutes a new molecular strategy for the development of therapeutics targeted to the receptor-effector interface.
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MESH Headings
- Amino Acid Sequence
- Blood Platelets/drug effects
- Blood Platelets/metabolism
- GTP-Binding Proteins/metabolism
- Humans
- In Vitro Techniques
- Molecular Sequence Data
- Mutagenesis, Site-Directed
- Peptides/chemistry
- Peptides/pharmacology
- Receptor, PAR-1
- Receptors, Cell Surface/antagonists & inhibitors
- Receptors, Cell Surface/drug effects
- Receptors, Cell Surface/genetics
- Receptors, Cell Surface/metabolism
- Receptors, Thrombin/antagonists & inhibitors
- Receptors, Thrombin/drug effects
- Receptors, Thrombin/genetics
- Receptors, Thrombin/metabolism
- Signal Transduction
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Affiliation(s)
- Lidija Covic
- Molecular Cardiology Research Institute, Division of Hematology/Oncology, New England Medical Center, 750 Washington Street, Boston, MA 02111, USA
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49
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Abstract
alpha(IIb)beta(3), a platelet-specific integrin, plays a critical role in platelet aggregation. The affinity of alpha(IIb)beta(3) for its ligands such as fibrinogen and von Willebrand factor is tightly regulated in an uncharacterized intracellular process termed inside-out signaling. Calcium integrin-binding protein (CIB) has been identified as a protein interacting with the cytoplasmic tail of the alpha(IIb) subunit of alpha(IIb)beta(3), but its physiological role has not been defined. In the present study, I demonstrate that CIB activates alpha(IIb)beta(3) both in vitro and in vivo. CIB interacts directly with the alpha(IIb) cytoplasmic tail, thereby increasing the affinity of alpha(IIb)beta(3) for fibrinogen in an in vitro fibrinogen-binding assay. The interaction of CIB with the alpha(IIb) cytoplasmic tail is enhanced in a Ca(2+)-dependent manner. A physiological agonist, ADP, stimulates platelets, activating alpha(IIb)beta(3). When the interaction of CIB with the alpha(IIb) cytoplasmic tail is blocked in native platelets by a permeable competing peptide, alpha(IIb)beta(3) activation is not detected even in the presence of ADP. This result indicates that direct interaction of CIB with the alpha(IIb) cytoplasmic tail converts alpha(IIb)beta(3) from a resting to an active conformation. This suggests that CIB plays an important role in one of the pathways that modulate the affinity of alpha(IIb)beta(3) for its ligand.
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Affiliation(s)
- Shigeru Tsuboi
- Glycobiology Program, Cancer Research Center, The Burnham Institute, La Jolla, California 92037, USA.
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Ginsberg MH, Yaspan B, Forsyth J, Ulmer TS, Campbell ID, Slepak M. A membrane-distal segment of the integrin alpha IIb cytoplasmic domain regulates integrin activation. J Biol Chem 2001; 276:22514-21. [PMID: 11304543 DOI: 10.1074/jbc.m101915200] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Previous evidence suggests that interactions between integrin cytoplasmic domains regulate integrin activation. We have constructed and validated recombinant structural mimics of the heterodimeric alpha(IIb)beta(3) cytoplasmic domain. The mimics elicited polyclonal antibodies that recognize a combinatorial epitope(s) formed in mixtures of the alpha(IIb) and beta(3) cytoplasmic domains but not present in either isolated tail. This epitope(s) is present within intact alpha(IIb)beta(3), indicating that interaction between the tails can occur in the native integrin. Furthermore, the combinatorial epitope(s) is also formed by introducing the activation-blocking beta(3)(Y747A) mutation into the beta(3) tail. A membrane-distal heptapeptide sequence in the alpha(IIb) tail ((997)RPPLEED) is responsible for this effect on beta(3). Membrane-permeant palmitoylated peptides, containing this alpha(IIb) sequence, specifically blocked alpha(IIb)beta(3) activation in platelets. Thus, this region of the alpha(IIb) tail causes the beta(3) tail to resemble that of beta(3)(Y747A) and suppresses activation of the integrin.
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Affiliation(s)
- M H Ginsberg
- Department of Vascular Biology, The Scripps Research Institute, La Jolla, California 92037, USA.
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