scholarly journals Protein kinase C- and calcium-regulated pathways independently synergize with Gi pathways in agonist-induced fibrinogen receptor activation

2002 ◽  
Vol 368 (2) ◽  
pp. 535-543 ◽  
Author(s):  
Todd M. QUINTON ◽  
Soochong KIM ◽  
Carol DANGELMAIER ◽  
Robert T. DORSAM ◽  
Jianguo JIN ◽  
...  
Keyword(s):  
Protein Kinase C ◽  
Protein Kinase ◽  
Intracellular Calcium ◽  
Phospholipase C ◽  
Calcium Release ◽  
Receptor Activation ◽  
Dense Granule ◽  
Fibrinogen Receptor ◽  
Kinase C ◽  
Induced Aggregation

Platelet fibrinogen receptor activation is a critical step in platelet plug formation. The fibrinogen receptor (integrin αIIbβ3) is activated by agonist-mediated Gq stimulation and resultant phospholipase C activation. We investigated the role of downstream signalling events from phospholipase C, namely the activation of protein kinase C (PKC) and rise in intracellular calcium, in agonist-induced fibrinogen receptor activation using Ro 31-8220 (a PKC inhibitor) or dimethyl BAPTA [5,5′-dimethyl-bis-(o-aminophenoxy)ethane-N,N,N′,N′-tetra-acetic acid], a high-affinity calcium chelator. All the experiments were performed with human platelets treated with aspirin, to avoid positive feedback from thromboxane A2. In the presence of Ro 31-8220, platelet aggregation caused by U46619 was completely inhibited while no effect or partial inhibition was seen with ADP and the thrombin-receptor-activating peptide SFLLRN, respectively. In the presence of intracellular dimethyl BAPTA, ADP- and U46619-induced aggregation and anti-αIIbβ3 antibody PAC-1 binding were completely abolished. However, similar to the effects of Ro 31-8220, dimethyl BAPTA only partially inhibited SFLLRN-induced aggregation, and was accompanied by diminished dense-granule secretion. When either PKC activation or intracellular calcium release was abrogated, aggregation and fibrinogen receptor activation with U46619 or SFLLRN was partially restored by additional selective activation of the Gi signalling pathway. In contrast, when both PKC activity and intracellular calcium increase were simultaneously inhibited, the complete inhibition of aggregation that occurred in response to either U46619 or SFLLRN could not be restored with concomitant Gi signalling. We conclude that, while the PKC- and calcium-regulated signalling pathways are capable of inducing activating fibrinogen receptor independently and that each can synergize with Gi signalling to cause irreversible fibrinogen receptor activation, both pathways act synergistically to effect irreversible fibrinogen receptor activation.

Impaired Activation of Platelets Lacking Protein Kinase C Theta (PKCΘ) Isoform.

Blood ◽  
2008 ◽  
Vol 112 (11) ◽  
pp. 1845-1845
Author(s):  
Bela Nagy ◽  
Kamala Bhavaraju ◽  
Todd Getz ◽  
Yamini Saraswathy Bynagari ◽  
Soochong Kim ◽  
...  
Keyword(s):  
Protein Kinase C ◽  
Protein Kinase ◽  
Thrombus Formation ◽  
Arterial Occlusion ◽  
Receptor Activation ◽  
Functional Responses ◽  
Glycoprotein Vi ◽  
Fibrinogen Receptor ◽  
Kinase C ◽  
Induced Aggregation

Abstract Protein kinase C (PKC) has been implicated in platelet functional responses, but the contribution of individual isoforms has not been directly evaluated. PKCΘ is activated by glycoprotein VI (GPVI) and protease-activated receptor (PAR) agonists, but not by ADP. In human platelets, PKCΘ-selective receptor for activated C kinase (RACK) antagonistic peptide inhibited agonist-induced aggregation and secretion. Consistently, in murine platelets lacking PKCΘ, GPVI- or PAR-mediated aggregation and secretion were also impaired. Previously, fibrinogen receptor has been shown to be activated independently by calcium and PKC pathways. In the presence of dimethyl BAPTA, AYPGKF-induced platelet aggregation was inhibited by PKCΘ antagonistic RACK peptides, suggesting a role for this isoform in PKC-dependent fibrinogen receptor activation. In addition, the levels of thromboxane A2 (TXA2) release measured in GPVI and PAR-mediated activation of PKCΘ −/− murine platelets, were significantly lower compared to WT platelets. Moreover, agonist-induced extracellular-signal regulated kinase (ERK) phosphorylation was also significantly decreased in PKCΘ −/− murine platelets, which could be contributing to decreased TXA2 levels. PKCΘ −/− mice displayed unstable thrombus formation and prolonged arterial occlusion in the FeCl3 in vivo thrombosis model versus WT mice. In conclusion, PKCΘ isoform plays a significant role in platelet functional responses downstream of GPVI and PARs.

scholarly journals Thapsigargin potentiates histamine-stimulated HCl secretion in gastric parietal cells but does not mimic cholinergic responses.

1991 ◽  
Vol 2 (1) ◽  
pp. 27-39 ◽  
Author(s):  
C S Chew ◽  
A C Petropoulos
Keyword(s):  
Protein Kinase C ◽  
Protein Kinase ◽  
Intracellular Calcium ◽  
Parietal Cell ◽  
Calcium Release ◽  
Parietal Cells ◽  
Kinase C ◽  
Hcl Secretion ◽  
Protein Kinase C Activation ◽  
Cholinergic Response

The role of calcium in control of HCl secretion by the gastric parietal cell was examined using a recently available intracellular calcium-releasing agent, thapsigargin, which has been shown, in some cell types, to induce sustained elevation of intracellular calcium ([Ca2+]i), an action that appears to be independent of inositol lipid breakdown and protein kinase C activation and to be mediated, at least partially, by selective inhibition of endoplasmic reticulum Ca2(+)-ATPase. Using the calcium-sensitive fluorescent probe, fura-2, in combination with digitized video image analysis of single cells as well as standard fluorimetric techniques, we found that thapsigargin induced sustained elevation of [Ca2+]i in single parietal cells and in parietal cells populations. Chelation of medium calcium led to a transient rise and fall in [Ca2+]i, indicating that the sustained elevation in [Ca2+]i in response to thapsigargin was due to both intracellular calcium release and influx. Although thapsigargin appeared to affect the same calcium pool(s) regulated by the cholinergic agonist, carbachol, and the pattern of thapsigargin-induced increases in [Ca2+]i were similar to the plateau phase of the cholinergic response, thapsigargin did not induce acid secretory responses of the same magnitude as those initiated by carbachol (28 vs 600% of basal). The protein kinase C activator, 12-O-tetradecanoyl phorbol-13-acetate (TPA) potentiated the secretory response to thapsigargin but this combined response also did not attain the same magnitude as the maximal cholinergic response. In the presence but not the absence of medium calcium, thapsigargin potentiated acid secretory responses to histamine, which elevate both cyclic AMP (cAMP) and [Ca2+]i in parietal cells, as well as forskolin and cAMP analogues but had no effect on submaximal and an inhibitory effect on maximal cholinergic stimulation. Furthermore, thapsigargin did not fully mimic potentiating interactions between histamine and carbachol, either in magnitude or in the pattern of temporal response. Assuming that the action of thapsigargin is specific for intracellular calcium release mechanisms, these data suggest that 1) sustained influx of calcium is necessary but not sufficient for cholinergic activation of parietal cell HCl secretion and for potentiating interactions between cAMP-dependent agonists and carbachol; 2) mechanisms in addition to elevated [Ca2+]i and protein kinase C activation may be involved in cholinergic regulation; and 3) increases in [Ca2+]i in response to histamine are not directly involved in the mechanism of histamine-stimulated secretion.

Glycoprotein VI–mediated platelet fibrinogen receptor activation occurs through calcium-sensitive and PKC-sensitive pathways without a requirement for secreted ADP

Blood ◽  
2002 ◽  
Vol 99 (9) ◽  
pp. 3228-3234 ◽  
Author(s):  
Todd M. Quinton ◽  
Fatih Ozdener ◽  
Carol Dangelmaier ◽  
James L. Daniel ◽  
Satya P. Kunapuli
Keyword(s):  
Protein Kinase C ◽  
Platelet Aggregation ◽  
Protein Kinase ◽  
Response Curve ◽  
Receptor Activation ◽  
Glycoprotein Vi ◽  
Fibrinogen Receptor ◽  
Kinase C ◽  
The Right ◽  
Concentration Response Curve

Abstract Collagen activates platelets by transducing signals through glycoprotein VI (GPVI). It is not clear whether collagen can directly activate fibrinogen receptors on the adherent platelets without a role for positive feedback agonists. We investigated the contribution of secondary G protein signaling to the mechanism of GPVI-stimulated platelet aggregation using the GPVI-selective agonists, convulxin and collagen-related peptide (CRP) as well as collagen. Adenosine diphosphate (ADP) scavengers or ADP receptor antagonists shifted the concentration-response curve slightly to the right at low concentrations of convulxin, whereas platelet aggregation at higher concentrations of convulxin was unaffected by these agents. ADP receptor antagonists shifted the concentration-response curve of collagen- or CRP-induced platelet aggregation to the right at all the concentrations. Protein kinase C inhibitor, Ro 31-8220, or a calcium chelator 5,5′-dimethyl-BAPTA shifted the concentration-response curve of convulxin-induced platelet aggregation to the right. In addition, pretreatment with both Ro 31-8220 and dimethyl-BAPTA resulted in total inhibition of convulxin-mediated aggregation. Blockade of either the calcium- or protein kinase C–regulated pathway leads to inhibition of fibrinogen receptor activation on platelets adherent to collagen, but inhibition of both pathways leads to abolished fibrinogen receptor activation. We conclude that collagen-induced activation of fibrinogen receptor on adherent platelets through GPVI signaling occurs without any significant role for secreted ADP or thromboxane A2. Furthermore, protein kinase C– and calcium-regulated pathways independently contribute to GPVI-mediated platelet aggregation.

scholarly journals Modulation of platelet-activating-factor-induced calcium influx and intracellular calcium release in platelets by phorbol esters

1987 ◽  
Vol 247 (3) ◽  
pp. 669-674 ◽  
Author(s):  
F H Valone ◽  
B Johnson
Keyword(s):  
Protein Kinase C ◽  
Protein Kinase ◽  
Intracellular Calcium ◽  
Calcium Release ◽  
Phorbol Esters ◽  
Calcium Influx ◽  
Platelet Activating Factor ◽  
Kinase C ◽  
Kinetics Of ◽  
Activate Protein Kinase

The mechanisms by which platelet-activating factor (PAF) and thrombin increase intracellular calcium were examined. Platelets were loaded with the calcium-sensitive fluorescent probe Quin 2 and then were suspended in buffer containing 0.5 mM-Mn2+ in order to quantify simultaneously calcium release from intracellular stores and divalent cation influx. Pretreating platelets with agents which activate protein kinase C [the phorbol ester phorbol myristate acetate (PMA) or the diacylglycerol 1-oleoyl-2-acetylglycerol (OAG)] inhibited increased intracellular calcium by PAF and thrombin in a dose-related manner. That protein kinase C regulates intracellular calcium by phosphorylating proteins in two distinct pathways was suggested by two observations. PAF-induced calcium release was more sensitive to inhibition by PMA and OAG than was manganese influx and the kinetics of recovery from inhibition were different for the two pathways. Both PMA and OAG aggregated Quin 2-loaded platelets without eliciting measurable increases in intracellular calcium. In contrast, prostacyclin, which increases intracellular cyclic AMP, inhibited calcium release and influx in parallel, suggesting that this agent acts at a step common to both pathways.

Protein Kinase Cδ Differentially Regulates Platelet Functional Responses.

Blood ◽  
2008 ◽  
Vol 112 (11) ◽  
pp. 1841-1841
Author(s):  
Ramya Chari ◽  
Todd Getz ◽  
Bela Nagy ◽  
Kamala Bhavaraju ◽  
Yingying Mao ◽  
...  
Keyword(s):  
Protein Kinase ◽  
Receptor Activation ◽  
Dense Granule ◽  
Small Contribution ◽  
Functional Responses ◽  
Fibrinogen Receptor ◽  
Granule Secretion ◽  
Induced Aggregation ◽  
Protein Kinase Cδ

Abstract Protein Kinase Cδ (PKCδ), a novel PKC isoform is expressed and activated in platelets downstream of PARs and GPVI receptors. In the current study, the role of PKCδ in regulating platelet functional responses was investigated using a pharmacological inhibitor, (δV1-1)TAT (a PKCδ inhibitor) in human platelets. These studies were further confirmed by a knockout approach using PKCδ+/+ and PKCδ−/− mice. In both human and murine platelets, PAR4-mediated dense granule secretions were inhibited, whereas GPVI-mediated dense granule secretions were potentiated. Furthermore, α-granule secretions and thromboxane A2 (TXA2) generation were differentially regulated in murine platelets.. These data suggest a differential role for this isoform in regulating dense granule secretion, α-granule secretion and TXA2 generation. Previous studies have shown that PAR-mediated fibrinogen receptor activation is regulated by a Calcium-dependent and a PKC-dependent pathway. The contribution of PKCδ to PAR-mediated fibrinogen receptor activation was studied by pretreating human and murine platelets with BAPTA. Our results showed a inhibition of AYPGKF-induced aggregation in human and murine platelets in the presence of BAPTA and fibrinogen. These results suggest a small contribution of PKCδ to PAR-4- mediated platelet aggregation and aIIbb3 activation. The in vivo significance of PKCδ was tested using a FeCl3 injury model. While the wildtype mice occluded in 7 minutes, PKCδ −/− mice occluded after 4 minutes of injury with 10 % FeCl3. Therefore, we conclude that PKCδ regulates platelet functional responses such as dense, α-granule secretions, TXA2 generation downstream of both PARs and GPVI receptors, contributes to PAR-4-mediated fibrinogen receptor activation ex vivo and plays a critical role in the thrombus formation in vivo. This study is supported by predoctoral fellowships to Ramya Chari and Swaminathan Murugappan from American Heart Association, Great Rivers affiliate.

Sign in / Sign up

Export Citation Format

Share Document