scholarly journals Phosphorylation of CLEC-2 is dependent on lipid rafts, actin polymerization, secondary mediators, and Rac

Blood ◽  
2010 ◽  
Vol 115 (14) ◽  
pp. 2938-2946 ◽  
Author(s):  
Alice Y. Pollitt ◽  
Beata Grygielska ◽  
Bertrand Leblond ◽  
Laurent Désiré ◽  
Johannes A. Eble ◽  
...  
Keyword(s):  
Platelet Aggregation ◽  
Tyrosine Phosphorylation ◽  
Lipid Rafts ◽  
Tyrosine Kinases ◽  
Actin Polymerization ◽  
Sucrose Gradient ◽  
Thromboxane A2 ◽  
Sucrose Gradient Ultracentrifugation ◽  
Activation Motif

Abstract The C-type lectin-like receptor 2 (CLEC-2) activates platelets through Src and Syk tyrosine kinases via a single cytoplasmic YxxL motif known as a hem immunoreceptor tyrosine-based activation motif (hemITAM). Here, we demonstrate using sucrose gradient ultracentrifugation and methyl-β-cyclodextrin treatment that CLEC-2 translocates to lipid rafts upon ligand engagement and that translocation is essential for hemITAM phosphorylation and signal initiation. HemITAM phosphorylation, but not translocation, is also critically dependent on actin polymerization, Rac1 activation, and release of ADP and thromboxane A2 (TxA2). The role of ADP and TxA2 in mediating phosphorylation is dependent on ligand engagement and rac activation but is independent of platelet aggregation. In contrast, tyrosine phosphorylation of the GPVI-FcRγ-chain ITAM, which has 2 YxxL motifs, is independent of actin polymerization and secondary mediators. These results reveal a unique series of proximal events in CLEC-2 phosphorylation involving actin polymerization, secondary mediators, and Rac activation.

scholarly journals Adhesive ligand binding to integrin alpha IIb beta 3 stimulates tyrosine phosphorylation of novel protein substrates before phosphorylation of pp125FAK

1993 ◽  
Vol 122 (2) ◽  
pp. 473-483 ◽  
Author(s):  
MM Huang ◽  
L Lipfert ◽  
M Cunningham ◽  
JS Brugge ◽  
MH Ginsberg ◽  
...  
Keyword(s):  
Platelet Aggregation ◽  
Tyrosine Phosphorylation ◽  
Tyrosine Kinases ◽  
Actin Polymerization ◽  
Protein Tyrosine Kinase ◽  
Free Calcium ◽  
Dependent Manner ◽  
Integrin Receptors ◽  
Fibrinogen Binding ◽  
Granule Secretion

Tyrosine phosphorylation of multiple platelet proteins is stimulated by thrombin and other agonists that cause platelet aggregation and secretion. The phosphorylation of a subset of these proteins, including a protein tyrosine kinase, pp125FAK, is dependent on the platelet aggregation that follows fibrinogen binding to integrin alpha IIb beta 3. In this report, we examined whether fibrinogen binding, per se, triggers a process of tyrosine phosphorylation in the absence of exogenous agonists. Binding of soluble fibrinogen was induced with Fab fragments of an anti-beta 3 antibody (anti-LIBS6) that directly exposes the fibrinogen binding site in alpha IIb beta3. Proteins of 50-68 KD and 140 kD became phosphorylated on tyrosine residues in a fibrinogen-dependent manner. This response did not require prostaglandin synthesis, an increase in cytosolic free calcium, platelet aggregation or granule secretion, nor was it associated with tyrosine phosphorylation of pp125FAK. Tyrosine phosphorylation of the 50-68-kD and 140-kD proteins was also observed when (a) fibrinogen binding was stimulated by agonists such as epinephrine, ADP, or thrombin instead of by anti-LIBS6; (b) fragment X, a dimeric plasmin-derived fragment of fibrinogen was used instead of fibrinogen; or (c) alpha IIb beta 3 complexes were cross-linked by antibodies, even in the absence of fibrinogen. In contrast, no tyrosine phosphorylation was observed when the ligand consisted of monomeric cell recognition peptides derived from fibrinogen (RGDS or gamma 400-411). Fibrinogen-dependent tyrosine phosphorylation was inhibited by cytochalasin D. These studies demonstrate that fibrinogen binding to alpha IIb beta 3 initiates a process of tyrosine phosphorylation that precedes platelet aggregation and the phosphorylation of pp125FAK. This reaction may depend on the oligomerization of integrin receptors and on the state of actin polymerization, organizational processes that may juxtapose tyrosine kinases with their substrates.

scholarly journals Effect of OKY-046, a thromboxane A2 synthetase inhibitor, on arachidonate-induced platelet aggregation : Possible role of "prostaglandin H2 steal" mechanism.

1986 ◽  
Vol 50 (11) ◽  
pp. 1071-1078 ◽  
Author(s):  
Tsunehiko KUZUYA ◽  
Masaharu OHMORI ◽  
Shiro HOSHIDA ◽  
Masakazu YAMAGISHI ◽  
Michitoshi INOUE ◽  
...  
Keyword(s):  
Platelet Aggregation ◽  
Thromboxane A2 ◽  
Synthetase Inhibitor ◽  
Thromboxane A2 Synthetase Inhibitor

Abstract 488: Sinoatrial Nodal Pacemaker Cells (SANC) Exhibit High Basal CA Activated Adenylyl Cyclase (AC) Activity and Express Multiple Distinctly Localized AC Types

Circulation ◽  
2007 ◽  
Vol 116 (suppl_16) ◽  
Author(s):  
David R Graham ◽  
Antoine Younes ◽  
Alexey Lyashkov ◽  
Anna Sheydina ◽  
Maria Volkova ◽  
...  
Keyword(s):  
Lipid Rafts ◽  
Sucrose Gradient ◽  
Soluble Fraction ◽  
Membrane Microdomains ◽  
Membrane Domains ◽  
Lipid Domains ◽  
Rt Pcr ◽  
Pacemaker Cells ◽  
Pacemaker Function ◽  
Sucrose Gradient Ultracentrifugation

In SANC constituitive AC generates high basal cAMP, inducing PKA-dependent phosphorylation that regulates Ca2+ cycling, that is essential for normal pacemaker function. Our goals were to identify, in rabbit SANC, the types of AC expressed, and their Ca2+ sensitivity and location. Radioimmunoassay (with total phosphodiasterase inhibition) showed a high Ca2+ activated basal AC activity. AC activity increased 5-fold from Ca2+ free (EGTA) to 1 uM free Ca2+. RT PCR (using specifically designed rabbit primers) showed that AC types II and V, and Ca2+ activated types, I and VIII, are expressed in SANC. The organization of these distinct AC types within calveolar or non-calveolar membrane microdomains was determined in pooled SANC isolated from 5 hearts, using triton x100, and sucrose gradient ultracentrifugation. Lipid domains segregated into caveolin containing and non-caveolin containing membrane microdomains, where AC activity was concentrated (fig , AC activity). Immunoblots demonstrated localization of different AC types between these two membrane domains, with AC I, II, V/VI localizing to caveolin containing lipid rafts, and AC VIII present in both caveolin and GM1 lipid domains, and also in the soluble fraction (fig ). In summary, multiple ACs, both Ca2+ activated and non-CA2+ activated types, are expressed in SANC, and these reside in distinct calveolar and non-calveolar lipid domains. We conclude that constituitive basal AC activity is, generated, in part, at least, by a Ca2+ activated AC. type.

Diabetic Retinopathy And Thromboxane Like Substance

1981 ◽  
Author(s):  
M A Lazzari ◽  
M Gimeno ◽  
N M Sutton ◽  
J R Lopez
Keyword(s):  
Diabetes Mellitus ◽  
Arachidonic Acid ◽  
Diabetic Retinopathy ◽  
Risk Factor ◽  
Platelet Aggregation ◽  
Platelet Rich Plasma ◽  
Thromboxane A2 ◽  
Initial Step ◽  
Platelet Activity

Diabetes Mellitus (DM) is a risk factor in the development of vasculopathies and its complications. It produces also its own microangiopathy. Evidence was reported of increased platelet activity in DM in different assays. Platelets aggregation and the arachidonic cycle could play a key role in the increased tendency to thrombosis. A disorder of ratio TXA2/PGI2, two opposing prostaglandin derivatives, could be the initial step. We intended to evaluate a thromboxane like substance (TLS) produced from platelet rich plasma (PRP) and to compare between normals and diabetic retinopathy (DR) patients. TLS was measured in 16 controls and 16 patients. Assay was done with the aggregating activity developed in PRP (considered TLS) after addition of arachidonic acid (f.c. 2 mM). The supernatant of the PRP (100 μl) was taken 40 sec. after the aggregation started and were added to a normal PRP treated with aspirin (f.c. 40 μl/ml) adjusted to 250.000 - 300.000 pl/μl and the degree of platelet aggregation measured in a Chrono Log Aggregometer. TLS was inactivated after its incubation during 2 min. at 37°C. This finding suggests this activity is due to TXA2.The results obtained (expressed in % of platelet aggregation) were: controls x 16.37% ± 6.28 and DR x 36.00% ± 9.72.The increase detected in the DR group supports previous experimental reports suggesting the role of the thromboxane A2 in vaso occlusive complication of diabetes mellitus.

Role of phosphoinositide 3-kinase β in platelet aggregation and thromboxane A2 generation mediated by Gi signalling pathways

2010 ◽  
Vol 429 (2) ◽  
pp. 369-377 ◽  
Author(s):  
Analia Garcia ◽  
Soochong Kim ◽  
Kamala Bhavaraju ◽  
Simone M. Schoenwaelder ◽  
Satya P. Kunapuli
Keyword(s):  
Platelet Aggregation ◽  
Critical Role ◽  
Thromboxane A2 ◽  
Inhibitory Effect ◽  
Human Platelets ◽  
P2y12 Receptor ◽  
Functional Responses ◽  
Induce Platelet Aggregation ◽  
Erk Phosphorylation

PI3Ks (phosphoinositide 3-kinases) play a critical role in platelet functional responses. PI3Ks are activated upon P2Y12 receptor stimulation and generate pro-aggregatory signals. P2Y12 receptor has been shown to play a key role in the platelet aggregation and thromboxane A2 generation caused by co-stimulation with Gq or Gz, or super-stimulation of Gi pathways. In the present study, we evaluated the role of specific PI3K isoforms α, β, γ and δ in platelet aggregation, thromboxane A2 generation and ERK (extracellular-signal-regulated kinase) activation. Our results show that loss of the PI3K signal impaired the ability of ADP to induce platelet aggregation, ERK phosphorylation and thromboxane A2 generation. We also show that Gq plus Gi- or Gi plus Gz-mediated platelet aggregation, ERK phosphorylation and thromboxane A2 generation in human platelets was inhibited by TGX-221, a PI3Kβ-selective inhibitor, but not by PIK75 (a PI3Kα inhibitor), AS252424 (a PI3Kγ inhibitor) or IC87114 (a PI3Kδ inhibitor). TGX-221 also showed a similar inhibitory effect on the Gi plus Gz-mediated platelet responses in platelets from P2Y1−/− mice. Finally, 2MeSADP (2-methyl-thio-ADP)-induced Akt phosphorylation was significantly inhibited in the presence of TGX-221, suggesting a critical role for PI3Kβ in Gi-mediated signalling. Taken together, our results demonstrate that PI3Kβ plays an important role in ADP-induced platelet aggregation. Moreover, PI3Kβ mediates ADP-induced thromboxane A2 generation by regulating ERK phosphorylation.

scholarly journals Na+/H+ exchange activity during phagocytosis in human neutrophils: role of Fcgamma receptors and tyrosine kinases.

1996 ◽  
Vol 132 (6) ◽  
pp. 1037-1052 ◽  
Author(s):  
T Fukushima ◽  
T K Waddell ◽  
S Grinstein ◽  
G G Goss ◽  
J Orlowski ◽  
...  
Keyword(s):  
Tyrosine Phosphorylation ◽  
Tyrosine Kinases ◽  
Plasma Membranes ◽  
Kinase Inhibitors ◽  
Human Neutrophils ◽  
Cross Linking ◽  
Fcgamma Receptors ◽  
Beta2 Integrins ◽  
Cytosolic Acidification

In neutrophils, binding and phagocytosis facilitate subsequent intracellular killing of microorganisms. Activity of Na+/H+ exchangers (NHEs) participates in these events, especially in regulation of intracellular pH (pHi) by compensating for the H+ load generated by the respiratory burst. Despite the importance of these functions, comparatively little is known regarding the nature and regulation of NHE(s) in neutrophils. The purpose of this study was to identify which NHE(s) are expressed in neutrophils and to elucidate the mechanisms regulating their activity during phagocytosis. Exposure of cells to the phagocytic stimulus opsonized zymosan (OpZ) induced a transient cytosolic acidification followed by a prolonged alkalinization. The latter was inhibited in Na+-free medium and by amiloride analogues and therefore was due to activation of Na+/H+ exchange. Reverse transcriptase PCR and cDNA sequencing demonstrated that mRNA for the NHE-1 but not for NHE-2, 3, or 4 isoforms of the exchanger was expressed. Immunoblotting of purified plasma membranes with isoform-specific antibodies confirmed the presence of NHE-1 protein in neutrophils. Since phagocytosis involves Fcgamma (FcgammaR) and complement receptors such as CR3 (a beta2 integrin) which are linked to pathways involving alterations in intracellular [Ca2+]i and tyrosine phosphorylation, we studied these pathways in relation to activation of NHE-1. Cross-linking of surface bound antibodies (mAb) directed against FcgammaRs (FcgammaRII > FcgammaRIII) but not beta2 integrins induced an amiloride-sensitive cytosolic alkalinization. However, anti-beta2 integrin mAb diminished OpZ-induced alkalinization suggesting that NHE-1 activation involved cooperation between integrins and FcgammaRs. The tyrosine kinase inhibitors genistein and herbimycin blocked cytosolic alkalinization after OpZ or FcgammaR cross-linking suggesting that tyrosine phosphorylation was involved in NHE-I activation. An increase in [Ca2+]i was not required for NHE-1 activation because neither removal of extracellular Ca2+ nor buffering of changes in [Ca2+]i inhibited alkalinization after OpZ or Fc-gammaR cross-linking. In summary, Fc-gammaRs and beta2 integrins cooperate in activation of NHE-1 in neutrophils during phagocytosis by a signaling pathway involving tyrosine phosphorylation.

Fyn and Lyn phosphorylate the Fc receptor γ chain downstream of glycoprotein VI in murine platelets, and Lyn regulates a novel feedback pathway

Blood ◽  
2000 ◽  
Vol 96 (13) ◽  
pp. 4246-4253 ◽  
Author(s):  
Lynn S. Quek ◽  
Jean-Max Pasquet ◽  
Ingeborg Hers ◽  
Richard Cornall ◽  
Graham Knight ◽  
...  
Keyword(s):  
Tyrosine Phosphorylation ◽  
Fc Receptor ◽  
Inhibitory Pathway ◽  
Functional Responses ◽  
Glycoprotein Vi ◽  
Granule Secretion ◽  
Activation Motif ◽  
Additional Role ◽  
Feedback Pathway

Abstract Activation of platelets by collagen is mediated by the complex glycoprotein VI (GPVI)/Fc receptor γ (FcRγ chain). In the current study, the role of 2 Src family kinases, Fyn and Lyn, in GPVI signaling has been examined using murine platelets deficient in one or both kinases. In the fyn−/−platelets, tyrosine phosphorylation of FcRγ chain, phopholipase C (PLC) activity, aggregation, and secretion are reduced, though the time of onset of response is unchanged. In the lyn−/−platelets, there is a delay of up to 30 seconds in the onset of tyrosine phosphorylation and functional responses, followed by recovery of phosphorylation and potentiation of aggregation and α-granule secretion. Tyrosine phosphorylation and aggregation in response to stimulation by collagen-related peptide is further attenuated and delayed in fyn−/−lyn−/−double-mutant platelets, and potentiation is not seen. This study provides the first genetic evidence that Fyn and Lyn mediate FcR immune receptor tyrosine-based activation motif phosphorylation and PLCγ2 activation after the ligation of GPVI. Lyn plays an additional role in inhibiting platelet activation through an uncharacterized inhibitory pathway.

ADRENALINE (ADR) INTERACTIONS WITH THROMBIN AND COLLAGEN -EFFECTS ON PLATELET ARACHIDONATE RELEASE AND 5HT SECRETION AND ROLE OF ENDOGENOUSLY FORMED THROMBOXANE A2 (TxA2)

1987 ◽  
Author(s):  
Y Patel ◽  
S Krishnamurthi ◽  
V V Kakkar
Keyword(s):  
Arachidonic Acid ◽  
Platelet Aggregation ◽  
Adenylate Cyclase ◽  
Synergistic Effects ◽  
Thromboxane A2 ◽  
Human Platelets ◽  
Presence And Absence ◽  
Pre Treatment ◽  
Arachidonate Release

We have examined the effect of combinations of ADR + thrombin (T) and ADR + collagen (C) on platelet arachidonate release and 5HT secretion, and assessed the role of endogenously formed TxA2 on these responses using indomethacin (I). Washed, human platelets prelabelled with [3H]-arachidonic acid (AA) or [14C]-5HT were used, ADR was added 10 sec before T or C and the reaction was terminated 3 min later. In the range 1-100μM, ADR induced no detectable aggregation or 5HT secretion but potentiated platelet aggregation when added with sub-threshold concentrations of T or C, which on their own induced no aggregation. At 2-4 fold higher concentrations of T and C (threshold for 5HT secretion), 5HT secretion and AA/TXB2 release were also potentiated by ADR (1-10μM) by 30-50%. Pre-treatment of platelets with I (10μM) abolished threshold T and C-induced 5HT secretion, as well as its potentiation by ADR. However, approximately 2-fold and 5-fold higher concentrations of T and C respectively were able to induce 'I-insensitive'secretion, which was further potentiated by ADR. In I-treated platelets, C-induced AA release and its potentiation by ADR were also abolished suggesting a role for endogenously formed TxA2 This was confirmed by addition of the TxA2 mimetic, U46619 (0.3μM), which potentiated C-induced AA release in the presence and absence of ADR, even though it induced no AA release on its own or, in combination with ADR alone in the absence of collagen. The latter suggests agonist specificity regarding the ability of TxA2 to synergistically stimulate AA release. Finally, unstirred platelets in PRP pre-incubated with ADR (10μM) for 120 min lost their responsiveness to ADR, when eventually stirred; however, these 'ADR-desensitised' platelets when washed and resuspended, were able to demonstrate synergistic effects on secretion when stimulated with ADR+T or ADR+C. This is analogous to the previously demonstrated ability of ADR to inhibit adenylate cyclase even in 'ADR-desensitised' platelets and re-inforces the separation regarding the mechanisms underlying the various effects of ADR on platelets.

A Dual Role for the α-Subunit KVGFFKR Motif of αIIbβ3: Integrin Activation and Intracellular Signaling.

Blood ◽  
2004 ◽  
Vol 104 (11) ◽  
pp. 1545-1545
Author(s):  
Kelly Aylward ◽  
Marc Devocelle ◽  
Niamh Moran
Keyword(s):  
Platelet Aggregation ◽  
Ligand Binding ◽  
Tyrosine Phosphorylation ◽  
Cho Cells ◽  
Intracellular Signaling ◽  
Dual Role ◽  
Cytoskeletal Reorganization ◽  
Integrin Activation ◽  
Α Subunit

Abstract The platelet-specific integrin αIIbβ3 plays a critical role in platelet aggregation and pathological thrombosis. Integrin affinity and ligand binding are regulated by the highly conserved αIIb membrane-proximal motif 989KVGFFKR995. We have recently shown that this motif is dependent on the presence of two phenylalanines (FF) for its activity. In order to investigate the role of KVGFFKR on integrin transmembrane signaling we used two parallel systems: (1) stable Chinese Hamster Ovary (CHO) cells expressing mutant αIIbβ3 integrins and (2) platelets treated with synthetic palmitylated (pal) peptides corresponding to the seven amino acid motif. In CHO cells, we chose cytoskeletal reorganization as a means to explore outside-in signaling. Alanine substitutions were introduced to the α-subunit KVGFFKR domain and co-expressed with wildtype β3. Cells were stably transfected with wildtype αIIb(992FF993)/β3, αIIb(992AA993)/β3 and αIIb (992AF993)/β3 to produce the FF, AA and AF cells respectively. Their ability to reorganize their cytoskeleton upon adhesion to fibrinogen was then determined. Even though double alanine substitution produced a constitutively activated integrin, the AA cells were unable to give rise to cytoskeletal reassembly as seen in the FF and AF cells. Using phalloidin as a marker, the AA cells displayed polymerized F-actin but failed to show the elaborate elongated stress fibers formed in the FF and AF cells. To further investigate the role of the KVGFFKR motif on downstream signaling events, we focused on using pal-peptides in platelets. We have shown that in addition to stimulating platelet aggregation presumably by facilitating the spatial separation of the integrin cytoplasmic tails, pal-KVGFFKR (pal-FF) induced tyrosine phosphorylation even in the absence of ligand (EDTA:5mM) or (ReoPro:10μg/ml). The tyrosine phosphoproteome associated with alanine-substituted peptides pal-KVGAFKR (pal-AF) and pal-KVGFAKR (pal-FA) was similar to that of pal-FF. However there is a remarkable absence of a specific 100kDa band (probably α-actinin) in the phosphoprotein profile in response to pal-KVGAAKR (pal-AA) both with peptide treatment alone and in the presence of TRAP. A closer look at ppFAK125 revealed that its tyrosine phosphorylation is also inhibited by pal-AA. Since α-actinin and ppFAK125 phosphorylation are closely linked events it supports α-actinin as the 100kDa missing phosphoprotein. However, pal-AA did not inhibit ppSyk72or ppSrc60 activation. Moreover pal-AA was identified as a potent antagonist, inhibiting platelet aggregation, PAC-1 binding and tyrosine phosphorylation. In summary, a double alanine substitution of the α-subunit membrane proximal domain disturbs cytoskeletal reorganization downstream, even though this substitution produces a constitutively activated integrin. This suggests a signaling role for the conserved α-integrin motif in addition to regulating integrin affinity. Furthermore in platelets, pal-FF peptide, by mimicking the endogenous αIIb KVGFFKR sequence can both activate the integrin and contribute to an intracellular signaling response even when ligand binding is absent. Taken together, both the stable cell system and pal-peptides in platelets support a role for the KVGFFKR domain in outside-in signaling. Also since pal-AA is an antagonist of integrin function it highlights the complexity of the proximal regulation of αIIbβ3 activation and suggests a dual role for this motif in integrin activation and intracellular signaling.

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