1
|
Khatlani T, Pradhan S, Langlois K, Subramanyam D, Rumbaut RE, Vijayan KV. Opposing Roles for the α Isoform of the Catalytic Subunit of Protein Phosphatase 1 in Inside-Out and Outside-In Integrin Signaling in Murine Platelets. Cells 2023; 12:2424. [PMID: 37887268 PMCID: PMC10605409 DOI: 10.3390/cells12202424] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2023] [Revised: 10/04/2023] [Accepted: 10/06/2023] [Indexed: 10/28/2023] Open
Abstract
Platelet activation during hemostasis and thrombosis is facilitated by agonist-induced inside-out and integrin αIIbβ3-initiated outside-in signaling via protein kinases and phosphatases. Pharmacological inhibitor studies suggest that the serine/threonine protein phosphatase 1 (PP1) promotes platelet activation. However, since phosphatase inhibitors block all the isoforms of the catalytic subunit of PP1 (PP1c), the role of specific PP1c isoform in platelet signaling remains unclear. Here, we employed a platelet-specific PP1cα-/- mice to explore the contribution of a major PP1 isoform in platelet functions. Loss of PP1cα moderately decreased activation of integrin αIIbβ3, binding of soluble fibrinogen, and aggregation to low-dose thrombin, ADP, and collagen. In contrast, PP1cα-/- platelets displayed increased adhesion to immobilized fibrinogen, fibrin clot retraction, and thrombus formation on immobilized collagen. Mechanistically, post-fibrinogen engagement potentiated p38 mitogen-activated protein kinase (MAPK) activation in PP1cα-/- platelets and the p38 inhibitor blocked the increased integrin-mediated outside-in signaling function. Tail bleeding time and light-dye injury-induced microvascular thrombosis in the cremaster venules and arterioles were not altered in PP1cα-/- mice. Thus, PP1cα displays pleiotropic signaling in platelets as it amplifies agonist-induced signaling and attenuates integrin-mediated signaling with no impact on hemostasis and thrombosis.
Collapse
Affiliation(s)
- Tanvir Khatlani
- Cardiovascular Research Section, Department of Medicine, Baylor College of Medicine, Houston, TX 77030, USA
- Center for Translational Research on Inflammatory Diseases (CTRID), Michael E. DeBakey Veterans Affairs Medical Center (MEDVAMC), Houston, TX 77030, USA
| | - Subhashree Pradhan
- Cardiovascular Research Section, Department of Medicine, Baylor College of Medicine, Houston, TX 77030, USA
- Center for Translational Research on Inflammatory Diseases (CTRID), Michael E. DeBakey Veterans Affairs Medical Center (MEDVAMC), Houston, TX 77030, USA
| | - Kimberly Langlois
- Center for Translational Research on Inflammatory Diseases (CTRID), Michael E. DeBakey Veterans Affairs Medical Center (MEDVAMC), Houston, TX 77030, USA
- Pulmonary Section, Department of Medicine, Baylor College of Medicine, Houston, TX 77030, USA
| | - Deepika Subramanyam
- Cardiovascular Research Section, Department of Medicine, Baylor College of Medicine, Houston, TX 77030, USA
- Center for Translational Research on Inflammatory Diseases (CTRID), Michael E. DeBakey Veterans Affairs Medical Center (MEDVAMC), Houston, TX 77030, USA
| | - Rolando E. Rumbaut
- Center for Translational Research on Inflammatory Diseases (CTRID), Michael E. DeBakey Veterans Affairs Medical Center (MEDVAMC), Houston, TX 77030, USA
- Pulmonary Section, Department of Medicine, Baylor College of Medicine, Houston, TX 77030, USA
| | - K. Vinod Vijayan
- Cardiovascular Research Section, Department of Medicine, Baylor College of Medicine, Houston, TX 77030, USA
- Center for Translational Research on Inflammatory Diseases (CTRID), Michael E. DeBakey Veterans Affairs Medical Center (MEDVAMC), Houston, TX 77030, USA
| |
Collapse
|
2
|
Khatlani T, Pradhan S, Da Q, Shaw T, Buchman VL, Cruz MA, Vijayan KV. A Novel Interaction of the Catalytic Subunit of Protein Phosphatase 2A with the Adaptor Protein CIN85 Suppresses Phosphatase Activity and Facilitates Platelet Outside-in αIIbβ3 Integrin Signaling. J Biol Chem 2016; 291:17360-8. [PMID: 27334924 DOI: 10.1074/jbc.m115.704296] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2015] [Indexed: 11/06/2022] Open
Abstract
The transduction of signals generated by protein kinases and phosphatases are critical for the ability of integrin αIIbβ3 to support stable platelet adhesion and thrombus formation. Unlike kinases, it remains unclear how serine/threonine phosphatases engage the signaling networks that are initiated following integrin ligation. Because protein-protein interactions form the backbone of signal transduction, we searched for proteins that interact with the catalytic subunit of protein phosphatase 2A (PP2Ac). In a yeast two-hybrid study, we identified a novel interaction between PP2Ac and an adaptor protein CIN85 (Cbl-interacting protein of 85 kDa). Truncation and alanine mutagenesis studies revealed that PP2Ac binds to the P3 block ((396)PAIPPKKPRP(405)) of the proline-rich region in CIN85. The interaction of purified PP2Ac with CIN85 suppressed phosphatase activity. Human embryonal kidney 293 αIIbβ3 cells overexpressing a CIN85 P3 mutant, which cannot support PP2Ac binding, displayed decreased adhesion to immobilized fibrinogen. Platelets contain the ∼85 kDa CIN85 protein along with the PP2Ac-CIN85 complex. A myristylated cell-permeable peptide derived from residues 395-407 of CIN85 protein (P3 peptide) disrupted the platelet PP2Ac-CIN85 complex and decreased αIIbβ3 signaling dependent functions such as platelet spreading on fibrinogen and thrombin-mediated fibrin clot retraction. In a phospho-profiling study P3 peptide treated platelets also displayed decreased phosphorylation of several signaling proteins including Src and GSK3β. Taken together, these data support a role for the novel PP2Ac-CIN85 complex in supporting integrin-dependent platelet function by dampening the phosphatase activity.
Collapse
Affiliation(s)
| | | | - Qi Da
- From the Departments of Medicine
| | | | - Vladimir L Buchman
- the School of Biosciences, Cardiff University, Wales CF10 3AX, United Kingdom
| | - Miguel A Cruz
- From the Departments of Medicine, Pediatrics, and Molecular Physiology and Biophysics, Baylor College of Medicine and Center for Translational Research on Inflammatory Diseases (CTRID), Michael E. DeBakey Veterans Affairs Medical Center (MEDVAMC), Houston, Texas 77030 and
| | - K Vinod Vijayan
- From the Departments of Medicine, Pediatrics, and Molecular Physiology and Biophysics, Baylor College of Medicine and Center for Translational Research on Inflammatory Diseases (CTRID), Michael E. DeBakey Veterans Affairs Medical Center (MEDVAMC), Houston, Texas 77030 and
| |
Collapse
|
3
|
Ma P, Foote DC, Sinnamon AJ, Brass LF. Dissociation of SHP-1 from spinophilin during platelet activation exposes an inhibitory binding site for protein phosphatase-1 (PP1). PLoS One 2015; 10:e0119496. [PMID: 25785436 PMCID: PMC4364895 DOI: 10.1371/journal.pone.0119496] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2014] [Accepted: 01/27/2015] [Indexed: 02/05/2023] Open
Abstract
We have recently shown that a critical regulatory node in the platelet signaling network lies immediately downstream of platelet receptors for thrombin and TxA2. This node is comprised of a scaffold protein (spinophilin, SPL), a protein tyrosine phosphatase (SHP-1), and either of the two members of the Regulators of G protein Signaling family predominantly expressed in platelets (RGS10 or RGS18). The SPL/RGS/SHP-1 complex is present in resting platelets, dissociating when thrombin or TxA2, but not ADP or collagen, activate SHP-1 and release RGS10 and RGS18 to dampen signaling. Here we demonstrate an additional regulatory role for spinophilin, showing that dissociation of SHP-1 from spinophilin is followed by an increase in the binding of spinophilin to PP1, a serine/threonine phosphatase whose binding site maps to a region close to the SHP-1 binding site. The increase in PP1 binding to spinophilin is limited to platelet agonists that cause dissociation of the complex and is selective for the α and γ isoforms of PP1. Studies in cell culture show that SHP-1 and PP1 can compete for binding to spinophilin and that binding inhibits PP1 activity since over-expression of wild type spinophilin, but not spinophilin with a disabled PP1 binding site, causes an increase in the phosphorylation of myosin light chain, a well-characterized PP1 substrate. Collectively, these results indicate that in addition to regulating RGS protein availability in resting platelets, spinophilin can serve as a time-dependent, agonist- and isoform-selective regulator of PP1, inhibiting its activity when decay of the SPL/RGS/SHP-1 complex releases SHP-1 from spinophilin, exposing a binding site for PP1.
Collapse
Affiliation(s)
- Peisong Ma
- Department of Medicine and Pharmacology, University of Pennsylvania, Philadelphia, Pennsylvania, United States of America
- * E-mail: (PM); (LFB)
| | - Darci C. Foote
- Department of Medicine and Pharmacology, University of Pennsylvania, Philadelphia, Pennsylvania, United States of America
| | - Andrew J. Sinnamon
- Department of Medicine and Pharmacology, University of Pennsylvania, Philadelphia, Pennsylvania, United States of America
| | - Lawrence F. Brass
- Department of Medicine and Pharmacology, University of Pennsylvania, Philadelphia, Pennsylvania, United States of America
- * E-mail: (PM); (LFB)
| |
Collapse
|
4
|
Pradhan S, Vijayan KV. Lipid rafts contribute to agonist-induced serine/threonine phosphatase activation and platelet aggregation. J Thromb Haemost 2013; 11:1612-5. [PMID: 23789860 PMCID: PMC3749069 DOI: 10.1111/jth.12329] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2013] [Accepted: 06/13/2013] [Indexed: 01/15/2023]
|
5
|
Alrehani N, Pradhan S, Khatlani T, Kailasam L, Vijayan KV. Distinct roles for the α , β and γ1 isoforms of protein phosphatase 1 in the outside-in αIIbβ3 integrin signalling-dependent functions. Thromb Haemost 2012. [PMID: 23197154 DOI: 10.1160/th12-04-0237] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
Abstract
Although protein kinases and phosphatases participate in integrin αIIbβ3 signalling, whether integrin functions are regulated by the catalytic subunit of protein phosphatase 1(PP1c)isoforms are unclear. We show that siRNA mediated knockdown of all PP1c isoforms(α, β and γ1)in 293 αIIbβ3 cells decreased adhesion to immobilised fibrinogen and fibrin clot retraction. Selective knockdown of only PP1cγ1 did not alter adhesion or clot retraction, while depletion of PP1cβ decreased both functions. Unexpectedly, knockdown of PP1cα enhanced αIIbβ3 adhesion to fibrinogen and clot retraction. Protein interaction studies revealed that all PP1c isoforms can interact with the integrin αIIb subunit. Phospho-profiling studies revealed an enhanced activation of mitogen-activated protein kinase (MAPK) p38 in the PP1cα depleted cells. Enhanced adhesive phenotype displayed by the PP1cα-depleted 293 αIIbβ3 cells was blocked by pharmacological inhibition of p38. Conversely, the decreased adhesion of PP1cα overexpressing cells was rescued by the expression of constitutively active p38α or p38γ. Thus, PP1c isoforms have distinct contribution to the outside-in αIIbβ3 signalling-dependent functions in 293 αIIbβ3 cells. Moreover, PP1cα negatively regulates integrin function by suppressing the p38 pathway.
Collapse
Affiliation(s)
- Nawaf Alrehani
- Department of Medicine, Baylor College of Medicine, Houston, Texas, USA
| | | | | | | | | |
Collapse
|
6
|
Thomas SG, Calaminus SDJ, Machesky LM, Alberts AS, Watson SP. G-protein coupled and ITAM receptor regulation of the formin FHOD1 through Rho kinase in platelets. J Thromb Haemost 2011; 9:1648-51. [PMID: 21605332 DOI: 10.1111/j.1538-7836.2011.04357.x] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
|
7
|
Simon Z, Kiss A, Erdödi F, Setiadi H, Beke Debreceni I, Nagy B, Kappelmayer J. Protein phosphatase inhibitor calyculin – A modulates activation markers in TRAP-stimulated human platelets. Platelets 2010; 21:555-62. [DOI: 10.3109/09537104.2010.499156] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
|
8
|
Gushiken FC, Hyojeong H, Pradhan S, Langlois KW, Alrehani N, Cruz MA, Rumbaut RE, Vijayan KV. The catalytic subunit of protein phosphatase 1 gamma regulates thrombin-induced murine platelet alpha(IIb)beta(3) function. PLoS One 2009; 4:e8304. [PMID: 20016849 PMCID: PMC2788699 DOI: 10.1371/journal.pone.0008304] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/10/2009] [Accepted: 11/19/2009] [Indexed: 11/19/2022] Open
Abstract
Background Hemostasis and thrombosis are regulated by agonist-induced activation of platelet integrin αIIbβ3. Integrin activation, in turn is mediated by cellular signaling via protein kinases and protein phosphatases. Although the catalytic subunit of protein phosphatase 1 (PP1c) interacts with αIIbβ3, the role of PP1c in platelet reactivity is unclear. Methodology/Principal Findings Using γ isoform of PP1c deficient mice (PP1cγ−/−), we show that the platelets have moderately decreased soluble fibrinogen binding and aggregation to low concentrations of thrombin or protease-activated receptor 4 (PAR4)-activating peptide but not to adenosine diphosphate (ADP), collagen or collagen-related peptide (CRP). Thrombin-stimulated PP1cγ−/− platelets showed decreased αIIbβ3 activation despite comparable levels of αIIbβ3, PAR3, PAR4 expression and normal granule secretion. Functions regulated by outside-in integrin αIIbβ3 signaling like adhesion to immobilized fibrinogen and clot retraction were not altered in PP1cγ−/− platelets. Thrombus formation induced by a light/dye injury in the cremaster muscle venules was significantly delayed in PP1cγ−/− mice. Phosphorylation of glycogen synthase kinase (GSK3)β-serine 9 that promotes platelet function, was reduced in thrombin-stimulated PP1cγ−/− platelets by an AKT independent mechanism. Inhibition of GSK3β partially abolished the difference in fibrinogen binding between thrombin-stimulated wild type and PP1cγ−/− platelets. Conclusions/Significance These studies illustrate a role for PP1cγ in maintaining GSK3β-serine9 phosphorylation downstream of thrombin signaling and promoting thrombus formation via fibrinogen binding and platelet aggregation.
Collapse
Affiliation(s)
- Francisca C. Gushiken
- Department of Medicine, Baylor College of Medicine, Houston, Texas, United States of America
| | - Han Hyojeong
- Department of Medicine, Baylor College of Medicine, Houston, Texas, United States of America
| | - Subhashree Pradhan
- Department of Medicine, Baylor College of Medicine, Houston, Texas, United States of America
| | - Kimberly W. Langlois
- Department of Pediatrics, Baylor College of Medicine, Houston, Texas, United States of America
| | - Nawaf Alrehani
- Department of Medicine, Baylor College of Medicine, Houston, Texas, United States of America
| | - Miguel A. Cruz
- Department of Medicine, Baylor College of Medicine, Houston, Texas, United States of America
| | - Rolando E. Rumbaut
- Department of Medicine, Baylor College of Medicine, Houston, Texas, United States of America
- Department of Pediatrics, Baylor College of Medicine, Houston, Texas, United States of America
- Medical Care Line, Michael E DeBakey VA Medical Center, Houston, Texas, United States of America
| | - K. Vinod Vijayan
- Department of Medicine, Baylor College of Medicine, Houston, Texas, United States of America
- * E-mail:
| |
Collapse
|
9
|
Gushiken FC, Patel V, Liu Y, Pradhan S, Bergeron AL, Peng Y, Vijayan KV. Protein phosphatase 2A negatively regulates integrin alpha(IIb)beta(3) signaling. J Biol Chem 2008; 283:12862-9. [PMID: 18334487 DOI: 10.1074/jbc.m708804200] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
Integrin alpha(IIb)beta(3) activation is critical for platelet physiology and is controlled by signal transduction through kinases and phosphatases. Compared with kinases, a role for phosphatases in platelet integrin alpha(IIb)beta(3) signaling is less understood. We report that the catalytic subunit of protein phosphatase 2A (PP2Ac) associates constitutively with the integrin alpha(IIb)beta(3) in resting platelets and in human embryonal kidney 293 cells expressing alpha(IIb)beta(3). The membrane proximal KVGFFKR sequence within the cytoplasmic domain of integrin alpha(IIb) is sufficient to support a direct interaction with PP2Ac. Fibrinogen binding to alpha(IIb)beta(3) during platelet adhesion decreased integrin-associated PP2A activity and increased the phosphorylation of a PP2A substrate, vasodilator associated phosphoprotein. Overexpression of PP2Ac(alpha) in 293 cells decreased alpha(IIb)beta(3)-mediated adhesion to immobilized fibrinogen. Conversely, small interference RNA mediated knockdown of endogenous PP2Ac(alpha) expression in 293 cells, enhanced extracellular signal-regulated kinase (ERK1/2) and p38 activation, and accelerated alpha(IIb)beta(3) adhesion to fibrinogen and von Willebrand factor. Inhibition of ERK1/2, but not p38 activation, abolished the increased adhesiveness of PP2Ac (alpha)-depleted 293 cells to fibrinogen. Furthermore, knockdown of PP2A(calpha) expression in bone marrow-derived murine megakaryocytes increased soluble fibrinogen binding induced by protease-activated receptor 4-activating peptide. These studies demonstrate that PP2Ac (alpha) can negatively regulate integrin alpha(IIb)beta(3) signaling by suppressing the ERK1/2 signaling pathway.
Collapse
|
10
|
Lerea KM, Venjara AY, Olson SC, Kelly MR. Threonine phosphorylation of integrin beta3 in calyculin A-treated platelets is selectively sensitive to 5'-iodotubercidin. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2006; 1773:185-91. [PMID: 17052767 DOI: 10.1016/j.bbamcr.2006.08.053] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/02/2006] [Revised: 08/23/2006] [Accepted: 08/30/2006] [Indexed: 10/24/2022]
Abstract
Exposure of platelets to toxins (calyculin A or okadaic acid) that inhibit protein serine/threonine phosphatases types 1 and 2A, at concentrations that block aggregatory and secretory responses, results in the phosphorylation of several platelet proteins including integrin beta(3). Since protein phosphorylation represents a balance between kinase and phosphatase activities, this increase in phosphorylation reflects either the removal of phosphatases that oppose constitutively active kinases known to reside in the platelet (e.g., casein kinase 2) or the activation of endogenous kinases. In this study, we demonstrate that the addition of calyculin A promotes the activation of several endogenous platelet protein kinases, including p42/44(mapk), p38(mapk), Akt/PKB, and LKB1. Using a pharmacologic approach, we assessed whether inhibition of these and other enzymes block phosphorylation of beta(3). Inhibitors of p38(mapk), casein kinase, AMP kinase, protein kinase C, and calcium-calmodulin-dependent kinases did not block phosphorylation of beta(3) on thr(753). In contrast, 5'-iodotubercidin, at 50 muM, blocks beta(3) phosphorylation without affecting the efficacy of calyculin A to inhibit platelet aggregation and spreading. These data dissociate threonine phosphorylation of beta(3) molecules and inhibition of platelet responses by protein phosphatase inhibitors.
Collapse
Affiliation(s)
- Kenneth M Lerea
- Department of Cell Biology and Anatomy, New York Medical College, Valhalla, NY 10595, USA.
| | | | | | | |
Collapse
|
11
|
Bennett JS, Zigmond S, Vilaire G, Cunningham ME, Bednar B. The platelet cytoskeleton regulates the affinity of the integrin alpha(IIb)beta(3) for fibrinogen. J Biol Chem 1999; 274:25301-7. [PMID: 10464255 DOI: 10.1074/jbc.274.36.25301] [Citation(s) in RCA: 67] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Agonist-generated inside-out signals enable the platelet integrin alpha(IIb)beta(3) to bind soluble ligands such as fibrinogen. We found that inhibiting actin polymerization in unstimulated platelets with cytochalasin D or latrunculin A mimics the effects of platelet agonists by inducing fibrinogen binding to alpha(IIb)beta(3). By contrast, stabilizing actin filaments with jasplakinolide prevented cytochalasin D-, latrunculin A-, and ADP-induced fibrinogen binding. Cytochalasin D- and latrunculin A-induced fibrinogen was inhibited by ADP scavengers, suggesting that subthreshold concentrations of ADP provided the stimulus for the actin filament turnover required to see cytochalasin D and latrunculin A effects. Gelsolin, which severs actin filaments, is activated by calcium, whereas the actin disassembly factor cofilin is inhibited by serine phosphorylation. Consistent with a role for these factors in regulating alpha(IIb)beta(3) function, cytochalasin D- and latrunculin A-induced fibrinogen binding was inhibited by the intracellular calcium chelators 1,2-bis(2-aminophenoxy)ethane-N,N,N', N'-tetraacetic acid acetoxymethyl ester and EGTA acetoxymethyl ester and the Ser/Thr phosphatase inhibitors okadaic acid and calyculin A. Our results suggest that the actin cytoskeleton in unstimulated platelets constrains alpha(IIb)beta(3) in a low affinity state. We propose that agonist-stimulated increases in platelet cytosolic calcium initiate actin filament turnover. Increased actin filament turnover then relieves cytoskeletal constraints on alpha(IIb)beta(3), allowing it to assume the high affinity conformation required for soluble ligand binding.
Collapse
Affiliation(s)
- J S Bennett
- Department of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA.
| | | | | | | | | |
Collapse
|
12
|
Lerea KM, Cordero KP, Sakariassen KS, Kirk RI, Fried VA. Phosphorylation sites in the integrin beta3 cytoplasmic domain in intact platelets. J Biol Chem 1999; 274:1914-9. [PMID: 9890945 DOI: 10.1074/jbc.274.4.1914] [Citation(s) in RCA: 41] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Protein seryl/threonyl phosphatase inhibitors such as calyculin A block inside-out and outside-in platelet signaling. Our studies demonstrate that the addition of calyculin A blocks platelet adhesion and spreading on fibrinogen, responses that depend on integrin alphaIIb beta3 signaling. We hypothesized that this reflects a change in alphaIIb beta3 structure caused by a specific state of phosphorylation. We show that addition of calyculin A leads to increased phosphorylation of the beta3 subunit, and phosphoamino acid analysis reveals that only threonine residues become phosphorylated; sequence analysis by Edman degradation established that threonine 753 became stoichiometrically phosphorylated during inhibition of platelet phosphatases by calyculin A. This region of beta3 is linked to outside-in signaling such as platelet spreading responses. The effect of calyculin A on platelet adhesion and spreading and on the phosphorylation of T-753 in beta3 is reversed by the calcium ionophore A23187, demonstrating that these effects of calyculin A are not generally toxic ones. We propose that phosphorylation of beta3 on threonine 753, a region of beta3 linked to outside-in signaling, may be a mechanism by which integrin alphaIIb beta3 function is regulated.
Collapse
Affiliation(s)
- K M Lerea
- Department of Cell Biology and Anatomy, New York Medical College, Valhalla, New York 10595, USA.
| | | | | | | | | |
Collapse
|
13
|
Serebruany VL, Gurbel PA. Effect of thrombolytic therapy on platelet expression and plasma concentration of PECAM-1 (CD31) in patients with acute myocardial infarction. Arterioscler Thromb Vasc Biol 1999; 19:153-8. [PMID: 9888878 DOI: 10.1161/01.atv.19.1.153] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Animal studies have shown that the administration of antibodies against platelet/endothelial cell adhesion molecule-1 (PECAM-1) before reperfusion can reduce infarct size. The purpose of the present study was to define the effects of thrombolytic therapy in acute myocardial infarction (AMI) patients on the platelet expression and plasma concentrations of PECAM-1 at prespecified time points after attempted reperfusion. The plasma concentration and platelet expression of PECAM-1 were determined in 23 AMI patients enrolled in the Global Use of Strategies to Open Occluded Coronary Arteries (GUSTO-III) trial before thrombolysis and at 3, 6, 12, and 24 hours thereafter and compared with 22 healthy controls. At baseline, PECAM-1 was expressed significantly more on the platelet surface in the AMI patients than in controls (P=0.027) while soluble PECAM-1 plasma levels were almost identical between groups. There were no significant diurnal variations in both plasma and platelet PECAM-1 levels in controls. A significant decrease in platelet PECAM-1 expression was observed 3 hours after thrombolysis (P=0.03) compared with baseline, followed by a significant increase (P=0.004) in fluorescence intensity later at 24 hours after thrombolysis. Conversely, a significant increase in soluble PECAM-1 was observed 3 hours after thrombolysis (P=0.02), followed by a significant decrease later at 24 hours after attempted reperfusion (P=0.03). The expression of platelet-bound PECAM-1 is increased in AMI patients. Discordantly directed changes in soluble and platelet PECAM-1 after the first 24 hours after thrombolytic therapy may represent redistribution of the whole PECAM-1 pool. Further investigation of the possible role of PECAM-1 and the relationship between its soluble and platelet fractions in AMI are warranted.
Collapse
Affiliation(s)
- V L Serebruany
- Center for Thrombosis Research, Sinai Hospital of Baltimore, Baltimore, Md, USA.
| | | |
Collapse
|
14
|
Murányi A, Erdodi F, Ito M, Gergely P, Hartshorne DJ. Identification and localization of myosin phosphatase in human platelets. Biochem J 1998; 330 ( Pt 1):225-31. [PMID: 9461514 PMCID: PMC1219131 DOI: 10.1042/bj3300225] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Type 1 (PP1) and type 2A (PP2A) phosphatase activity was measured in three subcellular fractions of human platelets. About 80% of the activity was in the high-speed supernatant. Western blots showed that the catalytic subunit of PP1 (PP1c), including alpha- and delta-isoforms, was present in each fraction, but the level of the catalytic subunit of PP2A was very low in the low-speed pellet (cytoskeletal fraction). Various antibodies detected a subunit similar to the 130 kDa subunit (M130) of myosin phosphatase (MP) of smooth muscle in the low- and the high-speed pellets of human platelets. PP1c and associated proteins were isolated by microcystin-Sepharose. Many proteins were separated from each fraction, including myosin, actin and PP1c. M130 was separated only from the low-speed and the high-speed pellets. Kinase activities were detected in the unbound fractions, and fractions from the low- and high-speed pellets phosphorylated M130 and myosin respectively. Treatment of platelets with calyculin A increased the phosphorylation level of many proteins, including myosin heavy- and light-chains, and caused association of cytoskeletal proteins with the low-speed pellet. No marked change in the distribution of PP1c and M130 was detected. These results suggest that the MP in human platelets is composed of PP1c plus a subunit similar to M130 of the smooth muscle phosphatase.
Collapse
Affiliation(s)
- A Murányi
- Department of Medical Chemistry, University Medical School of Debrecen, H-4026 Debrecen, Bem tér 18/B, Hungary
| | | | | | | | | |
Collapse
|
15
|
Wu XW, Lian EC. Binding properties and inhibition of platelet aggregation by a monoclonal antibody to CD31 (PECAM-1). Arterioscler Thromb Vasc Biol 1997; 17:3154-8. [PMID: 9409305 DOI: 10.1161/01.atv.17.11.3154] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
CD31/platelet endothelial cell adhesion molecule 1 (PECAM-1) is expressed on platelets, endothelial cells, myeloid cells, monocytes, and certain lymphocyte subsets. It has been shown that CD31 is involved in the homophilic and heterophilic cellular adhesion and leukocyte transendothelial migration, but little is known about the role of CD31 in platelet functions. Previously we have shown that monoclonal antibody (MAb) AAP2 produced in our laboratory bound to a 110-kD platelet antigen and gave an enhanced binding to activated platelet membrane. In this study we demonstrated that platelet lysate depleted of the antigen through adsorption by an AAP2-solidified affinity column was bound by MAbs against CD62 and CD42 but not by MAb 5.6E against CD31 or AAP2 on the immunoblot. Rabbit antibodies against CD31 completely inhibited the binding of AAP2 to platelets in the flow cytometry analysis. This indicates that AAP2 is specifically against CD31. 125I-labeled AAP2 bound to resting platelets with 5587 +/- 1765 sites/platelet and a Kd of 1 nmol/L and to thrombin-activated platelets with 17,625 +/- 4865 sites/platelet and a Kd of 0.24 nmol/L. Addition of 10 micrograms/mL AAP2 inhibited the aggregation induced by 4 mumol/L ADP by 78.6%, 6 mumol/L epinephrine by 79.4%, 1 microgram/mL collagen by 78.7%, and 0.25 U/mL thrombin by 29%. The platelet aggregation was completely restored when higher concentration of agonists were used. MAb 5.6E did not have any effect on platelet aggregation. These results suggest that AAP2 binds to a special epitope of CD31 on platelets and that CD31 is involved in platelet aggregation.
Collapse
Affiliation(s)
- X W Wu
- Hemophilia and Thrombosis Center/Sylvester Cancer Center, University of Miami, Fla., USA
| | | |
Collapse
|
16
|
Mauco G, Artçanuthurry V, Pidard D, Grelac F, Maclouf J, Lévy-Tolédano S. Total inhibition of phospholipase C and phosphatidylinositol 3-kinase by okadaic acid in thrombin-stimulated platelets. Cell Signal 1997; 9:117-24. [PMID: 9067640 DOI: 10.1016/s0898-6568(96)00119-2] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
The strong inhibition of thrombin-induced platelet functions induced by okadaic acid is not correlated with the partial modification of pleckstrin phosphorylation, which remains still phosphorylated two min after stimulation, indicating that protein kinase C is not affected by okadaic acid. We then investigated the effect of okadaic acid on platelet lipid metabolism. Our data indicate that inhibition indeed strongly affects phosphatidic acid as well as phosphatidylinositol 3,4-bisphosphate synthesis at low concentrations of okadaic acid, and phosphatidylinositol 4,5-bisphosphate at higher concentrations. Since thrombin-induced tyrosine phosphorylations were completely inhibited in the presence of okadaic acid, as a consequence, phosphatidylinositol 3-kinase was no longer detected in antiphosphotyrosine immunoprecipitates, thus explaining the absence of phosphatidylinositol, 3,4-bisphosphate synthesis. Finally, okadaic acid inhibited thrombin-induced fibrinogen binding, indicating that serine/threonine phosphatases may affect the inside-out signalling which regulates the alpha 11bb3 integrin, downstream protein kinase C activation.
Collapse
Affiliation(s)
- G Mauco
- INSERM Unité 326, Hôpital Purpan, Toulouse, France
| | | | | | | | | | | |
Collapse
|
17
|
Iorio P, Gresele P, Stasi M, Nucciarelli F, Vezza R, Nenci GG, Goracci G. Protein kinase C inhibitors enhance G-protein induced phospholipase A2 activation in intact human platelets. FEBS Lett 1996; 381:244-8. [PMID: 8601464 DOI: 10.1016/0014-5793(96)00117-2] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Washed intact human platelets were prelabelled with [3H]arachidonic acid ([3H]AA) and stimulated with thrombin or with AlF4-, a known unspecific activator of G-proteins. Both stimuli induced the liberation of [3H]AA, the release of beta-thromboglobulin (beta-TG) and platelet aggregation. PMA did not induce liberation of [3H]AA although it induced beta-TG release and aggregation; preincubation with PMA did not modify significantly the amounts of [3H]AA and beta-TG released by thrombin or AlF4-. Different inhibitors of PKC (staurosporine, H-7 and calphostin C) increased the release of [3H]AA and inhibited beta-TG release and aggregation induced by AlF4- but they had no effect when platelets were stimulated with thrombin (0.5 U/ml). Calphostin C was able to release [3H]AA by itself without inducing aggregation of beta-TG release. Okadaic acid (a serine/threonine phosphoprotein phosphatase inhibitor) greatly inhibited the release of [3H]AA, beta-TG and aggregation in AlF4--stimulated platelets. These results indicate the presence of a G-protein mediated mechanism for the activation of a platelet phospholipase A2 which is negatively affected by a protein kinase, sensible to putative inhibitors of protein kinase C, and it is activated by a protein phosphatase, sensible to okadaic acid.
Collapse
Affiliation(s)
- P Iorio
- Institute of Medical Biochemistry, University of Perugia, Italy
| | | | | | | | | | | | | |
Collapse
|