Expression of amyloid beta peptide in human platelets: Pivotal role of the phospholipase Cγ2-protein kinase C pathway in platelet activation

Abstract Prostaglandin E2 (PGE2) is produced by activated platelets and by several other cells, including capillary endothelial cells. PGE2 exerts a dual effect on platelet aggregation: inhibitory, at high, supraphysiologic concentrations, and potentiating, at low concentrations. No information exists on the biochemical mechanisms through which PGE2 exerts its proaggregatory effect on human platelets. We have evaluated the activity of PGE2 on human platelets and have analyzed the second messenger pathways involved. PGE2 (5 to 500 nmol/L) significantly enhanced aggregation induced by subthreshold concentrations of U46619, thrombin, adenosine diphosphate (ADP), and phorbol 12-myristate 13-acetate (PMA) without simultaneously increasing calcium transients. At a high concentration (50 mumol/L), PGE2 inhibited both aggregation and calcium movements. PGE2 (5 to 500 nmol/L) significantly enhanced secretion of beta-thromboglobulin (beta TG) and adenosine triphosphate from U46619- and ADP-stimulated platelets, but it did not affect platelet shape change. PGE2 also increased the binding of radiolabeled fibrinogen to the platelet surface and increased the phosphorylation of the 47-kD protein in 32P- labeled platelets stimulated with subthreshold doses of U46619. Finally, the amplification of U46619-induced aggregation by PGE2 (500 nmol/L) was abolished by four different protein kinase C (PKC) inhibitors (calphostin C, staurosporine, H7, and TMB8). Our results suggest that PGE2 exerts its facilitating activity on agonist-induced platelet activation by priming PKC to activation by other agonists. PGE2 potentiates platelet activation at concentrations produced by activated platelets and may thus be of pathophysiologic relevance.

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Arsenic trioxide-mediated antiplatelet activity: pivotal role of the phospholipase Cγ2-protein kinase C-p38 MAPK cascade

Translational Research ◽

10.1016/j.trsl.2009.08.005 ◽

2010 ◽

Vol 155 (2) ◽

pp. 97-108 ◽

Cited By ~ 4

Author(s):

Kuan H. Lin ◽

Yi F. Chang ◽

Chiao Y. Fan ◽

Thanasekaran Jayakumar ◽

Jie J. Lee ◽

...

Keyword(s):

Protein Kinase C ◽

Protein Kinase ◽

Arsenic Trioxide ◽

P38 Mapk ◽

Mapk Cascade ◽

Pivotal Role ◽

Antiplatelet Activity ◽

Kinase C

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Use of d-erythro-sphingosine as a pharmacological inhibitor of protein kinase C in human platelets

Biochemical Journal ◽

10.1042/bj2780387 ◽

1991 ◽

Vol 278 (2) ◽

pp. 387-392 ◽

Cited By ~ 19

Author(s):

W A Khan ◽

S W Mascarella ◽

A H Lewin ◽

C D Wyrick ◽

F I Carroll ◽

...

Keyword(s):

Protein Kinase C ◽

Protein Kinase ◽

Platelet Activation ◽

Biological Activities ◽

Dose Dependence ◽

Human Platelets ◽

Kinase C ◽

Similar Dose ◽

Induced Aggregation

Sphingosine is a naturally occurring long-chain amino diol with potent inhibitory activity against protein kinase C in vitro and in cell systems. The use of sphingosine as a pharmacological tool to probe the activity of protein kinase C has been hampered by its amphiphilicity, possible contamination of its commercial preparations, and the existence of other targets for its action. To address these problems, high-purity D-erythro-sphingosine was prepared and employed to develop an approach for the use of sphingosine as a pharmacological agent. The addition of synthetic D-erythro-sphingosine to intact human platelets resulted in quick uptake and preferential partitioning into the particulate fraction. It was rapidly metabolized by intact platelets, 60% being degraded within 1 min after addition. Sphingosine was found to be a potent inhibitor of gamma-thrombin-induced aggregation and secretion of washed human platelets. Multiple criteria indicated that this effect is probably mediated through the inhibition of protein kinase C: (1) sphingosine inhibited protein kinase C activity in intact platelets with a similar dose/response to its inhibition of platelet aggregation and secretion; (2) sphingosine inhibited phorbol binding to intact platelets under identical conditions and with a similar dose-dependence; (3) exogenous dioctanoylglycerol overcame sphingosine's inhibition of platelet activation. The effectiveness of sphingosine in inhibiting platelet activation was primarily determined by the ratio of sphingosine to total number of platelets. These data are discussed in relation to a general approach for the use of sphingosine and other parameters for determining biological activities of protein kinase C.

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Modification of Na+/H+ Exchanger in Human Platelets by 1,2-Dioctanoylglycerol, a Protein Kinase C Activator

Thrombosis and Haemostasis ◽

10.1055/s-0038-1647275 ◽

1990 ◽

Vol 64 (01) ◽

pp. 165-171 ◽

Cited By ~ 14

Author(s):

Yukio Ozaki ◽

Yuki Mastsumoto ◽

Yutaka Yatomi ◽

Masaaki Higashihara

Keyword(s):

Protein Kinase C ◽

Protein Kinase ◽

Rate Constant ◽

Human Platelets ◽

Kinase C ◽

Km Value ◽

The Difference ◽

The One ◽

Protein Kinase C Activation

SummaryProtein kinase C activation in human platelets has a modulatory role in maintaining intracellular pH (pHi), by adjusting pHi at a particular value (7.22). Changes in pHi induced by protein kinase C appeared to be dependent upon the difference between H+ efflux catalyzed by the Na+/H+ exchanger and H+ production. The pHi recovery after acid loading was significantly facilitated by protein kinase C activation. Analysis of the rate constant for pHi recovery suggested that the turnover rate or the apparent affinity of the Na+/H+ exchanger for H+ was increased. Protein kinase C also decreased the Km value of the Na+/H+ exchanger for extracellular Na+. Thus, it is suggested that the role of protein kinase C in platelet pHi regulation is dual, adjusting the pHi value at a certain setpoint on the one hand, and increasing the rate constant of the Na+/H+ exchanger on the other.

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Role of protein kinase C in platelet activation

The Japanese Journal of Pharmacology ◽

10.1016/s0021-5198(19)62716-2 ◽

1984 ◽

Vol 36 ◽

pp. 255

Author(s):

Michiko Naka ◽

Hiroyoshi Hidaka

Keyword(s):

Protein Kinase C ◽

Protein Kinase ◽

Platelet Activation ◽

Kinase C

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PROTEIN KINASE C CONTROLS CA2+ MOBILIZATION IN HUMAN PLATELETS

10.1055/s-0038-1644509 ◽

1987 ◽

Cited By ~ 1

Author(s):

W Siffert ◽

P Scheid ◽

JW N Akkerman

Keyword(s):

Protein Kinase C ◽

Protein Kinase ◽

Human Platelets ◽

Cytosolic Ph ◽

Fluorescent Indicators ◽

Kinase C ◽

Deutsche Forschungsgemeinschaft ◽

Ionophore Monensin ◽

Stimulation Of

Platelet stimulation has been shown to result in a rise of cytosolic pH (pHi) as a result of an activation of a Na+/H+ antiport. We have investigated the role of pH in Ca2+ mobilization in human platelets. pHi and free Ca2+, {Ca2+)i, were measured in platelets loaded with the fluorescent indicators BCECF and quin2, respectively. Stimulation of platelets by either thrombin or OAG, an activator of protein kinase C (Pk-C), increased pHi. Pretreatment of platelets with inhibitors of Pk-C, trifluoperazine (TFP) or sphingosine (SPH), blocked the stimulus-induced rise in pHi, suggesting a role of Pk-C in the activation of Na+/H+ exchange. Blocking Na+/H+ exchange by an amiloride analogue or by TFP similarly suppressed the thrombin-induced increase in {Ca2*}i. This effect could be prevented by increasing pHi with the Na+/H+ ionophore monensin or with NH4Cl. The thrombin-induced (0.05 U/ml) rise in {Ca2+}i was more than 3-fold enhanced when the pH was raised from 6.8 to 7.4.Our results demonstrate that pHi controls Ca2+ mobilization in human platelets and suggest that Pk-C contributes to this control by activating the Na+/H+ exchanger.Supported by the Deutsche Forschungsgemeinschaft. No Sche 46/5-2.

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