Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:2.7.11.13 (protein kinase C)
 49,245 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The human erythroleukemia (K562) cell line is induced to differentiate into megakaryocytic cells by treatment with the tumor promoter phorbol myristate acetate (PMA). PMA-induced differentiation is characterized by (1) almost complete cessation of cellular proliferation, (2) expression of the megakaryocytic cell surface marker glycoprotein IIb/IIIa (gpIIIa), (3) increased secretion of granulocyte/macrophage-colony stimulating factor (GM-CSF) and (4) increased secretion of interleukin-6 (IL-6). PMA-induced differentiation is dose-dependent with maximal activity seen at 10 nM PMA. In contrast, bryostatin (bryo), a structurally distinct protein kinase C (PKC) activator, fails to induce megakaryocytic differentiation or growth arrest at the concentrations tested (0.01-100 nM). Rather, bryo inhibits PMA-induced growth arrest and megakaryocytic differentiation in a dose-dependent fashion (full inhibition at 100 nM). The divergent biological effects of PMA and bryo correspond to the differential activation and translocation of PKC isotypes in K562 cells. PKC isotype analysis demonstrates that undifferentiated cells express both alpha and beta II PKC but no detectable beta I, gamma or epsilon PKC. Treatment of cells with either PMA or bryo leads to rapid translocation of both alpha and beta II PKC from the cytosol to the non-nuclear particulate fraction. However, bryo also induces selective translocation of beta II PKC to the nuclear membrane.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Protein kinase C isotypes in human erythroleukemia cell proliferation and differentiation. 152 49

smg p21A and -B (smg p21s) are ras p21-like small GTP-binding proteins (G proteins) with the same putative effector domain as ras p21s. Both smg p21A mRNA and smg p21B mRNA were detected in CMK, a human megakaryocytic leukemia cell line, and their levels were markedly elevated by treatment with 12-O-tetradecanoyl-phorbol-13-acetate (TPA), which caused the differentiation of this cell line into more mature megakaryocytes. The smg p21 protein molecules also increased during the TPA-induced differentiation of CMK cells. The mRNA level of glycoprotein IIb (GPIIb), a typical marker of the megakaryocytes, was increased by this treatment, but the time course of the increase in the smg p21 mRNA levels as more rapid than that of the increase in the GPIIb mRNA level. Ha-ras p21 mRNA was undetectable, but both Ki- and N-ras p21 mRNAs were detected in CMK cells and their levels were also increased during TPA-induced differentiation of CMK cells, although to a lesser extent than those of smg p21 mRNAs. Protein kinase C inhibitors inhibited the basal and TPA-induced smg p21A mRNA level, but cyclic AMP-elevating prostaglandin E1 or Ca(2+)-mobilizing ionomycin did not inhibit them. Cycloheximide enhanced the basal and TPA-induced smg p21A mRNA levels. Actinomycin D blocked the TPA-induced smg p21A mRNA levels, but showed no detectable effect on the elevated smg p21A mRNA level which was induced by pretreatment with TPA. A dramatic increase in the smg p21 mRNA levels was also observed in other leukemia cell lines during TPA-induced differentiation. These results suggest that TPA stimulated expression of the smg p21A gene, presumably through the action of protein kinase C at the transcriptional level rather than at the post-transcriptional level, in hematopoietic leukemia cells.
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PMID:Induction of smg p21/rap1A p21/krev-1 p21 gene expression during phorbol ester-induced differentiation of a human megakaryocytic leukemia cell line. 154 53

Platelets adhere to artificial surfaces in the initial stage of thrombus formation, but the subsequent steps in signal transduction that lead to platelet activation by artificial surfaces are not understood. When 0.325-micron diameter beads composed of a hydrophobic polymer, polymethylmethacrylate (PMMA), were added to gel-filtered aequorin-loaded platelets suspended in media containing Ca2+, the platelets aggregated; addition of fibrinogen was not required. Platelet aggregation was preceded by an increase in cytoplasmic Ca2+ and was accompanied by phosphorylation of the 47-Kd substrate of protein kinase C (PKC), 5-hydroxytryptamine (5-HT) release, and accumulation of phosphatidic acid. All these effects were partially inhibited by apyrase and aspirin. Monoclonal antibodies (MoAbs) 7E3 and M148 and the synthetic peptides RGDS and fibrinogen gamma chain fragment 400-411, all of which bind to the platelet fibrinogen receptor glycoprotein IIb-IIIa (GPIIb-IIIa) and inhibit fibrinogen binding, prevented PMMA-induced aggregation but did not inhibit the Ca2+ increase. Chymotrypsin-treated platelets aggregated after addition of fibrinogen, but not PMMA. We conclude that platelets interact initially with PMMA at membrane sites other than those required for fibrinogen binding, leading to activation of membrane phospholipases and PKC, an increase in cytoplasmic Ca2+, release of 5-HT, ADP, and fibrinogen from storage granules, and to platelet aggregation.
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PMID:Platelet activation by a synthetic hydrophobic polymer, polymethylmethacrylate. 191 61

The glycoprotein IIb-IIIa complex (GP IIb-IIIa) is a multifunctional transmembrane protein on platelets. Its most completely described function is as a fibrinogen receptor that mediates platelet aggregation, but it is also involved in clot retraction, signal transduction, calcium transport, and other events. However, the mechanisms that regulate the functions of GP IIb-IIIa during platelet activation are largely unknown. One possible mechanism is phosphorylation, since several other receptors are regulated by this process. We found that GP IIIa, but not GP IIb, was phosphorylated in 32P-labeled platelets, predominantly on threonine residues. Furthermore, GP IIIa phosphorylation increased four-fold in platelets activated with thrombin or phorbol 12-myristate 13-acetate, but not at all in platelets treated with prostacyclin, an inhibitor of platelet activation. The thrombin-induced increase in phosphorylation was inhibited by pretreating platelets with prostacyclin or with staurosporin, a specific protein kinase C inhibitor. Thus, there is an increase in the level or turnover of phosphate on GP IIIa during platelet activation, most likely involving protein kinase C. This phosphorylation may regulate some aspect(s) of GP IIb-IIIa function.
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PMID:Glycoprotein IIIa is phosphorylated in intact human platelets. 211 11

Monoclonal antibody P256, which is specific for glycoprotein IIb-IIIa complex, was found to induce aggregation of normal platelets in plasma. The mechanism of platelet activation induced by this monoclonal antibody was thoroughly studied. The divalent binding to the IIb-IIIa molecule was necessary for triggering aggregation since Fab' fragments did not induce aggregation as did IgG and F(ab')2 fragments; however, F(ab')2 did not induce the release as did the whole IgG. P256-induced aggregation was accompanied by release of all three granule constituents, namely dense granules, alpha-granules and lysosomes, with parallel kinetics showing half-maximum release 50 s after addition of P256. Thromboxane synthesis was initiated at the same time. Using 32P-prelabeled platelets, no variation in level of [32P]phosphatidylinositol 4,5-bisphosphate could be detected in the first minute after P256 addition, indicating no activation of the calcium-independent phospholipase C specific for polyphosphoinositol phospholipid. P256 induced a calcium mobilization as measured by Indo-1 fluorescence of about the third of that measured in the presence of a thrombin concentration giving the same intensity of aggregation. P256 induced phosphorylation of the myosin light chain p20 and of the main substrate of protein kinase C, p43. Addition of aspirin inhibited almost totally calcium mobilization and partially aggregation, release and protein phosphorylations. By contrast, in the absence of external calcium, although no aggregation could occur, the release reaction was only partially reduced. In this activation, the glycoprotein IIb-IIIa complex thus appears to play a role in modulating platelet response, not only via calcium fluxes but also in activating protein kinase C responsible for p43 phosphorylation.
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PMID:Activation of platelets induced by mAb P256 specific for glycoprotein IIb-IIIa. Possible evidence for a role for IIb-IIIa in membrane signal transduction. 236 45

The major platelet integrin, glycoprotein IIb-IIIa, binds soluble fibrinogen only after platelet activation. To investigate the mechanism by which platelets convert glycoprotein IIb-IIIa into a functional fibrinogen receptor, we characterized the opening and closing of fibrinogen-binding sites in isolated platelet membranes and compared the regulatory properties of membrane-bound glycoprotein IIb-IIIa with those of the detergent-solubilized receptor. Basal fibrinogen binding to the membranes possessed many of the properties of fibrinogen binding to activated platelets; however, less than 10% of glycoprotein IIb-IIIa in the membranes was capable of binding fibrinogen. Preincubating the membranes with either an activating glycoprotein IIb-IIIa antibody or alpha-chymotrypsin increased fibrinogen binding. In contrast, agents that require intracellular mediators, such as platelet agonists, guanine-nucleotide-binding-protein activators and purified protein kinase C, did not stimulate fibrinogen binding to the membranes, suggesting that cytosolic factor(s) may be required for activation of the receptor in platelets. Occupancy of glycoprotein IIb-IIIa in the membranes with RGD (Arg-Gly-Asp)-containing peptides reversibly exposed neoantigenic epitopes and fibrinogen-binding sites in the receptor. These conformational changes required membrane fixation to be maintained following peptide removal. Similar results were obtained with purified glycoprotein IIb-IIIa incorporated into phospholipid vesicles, indicating that the resting state of the receptor is favoured in these environments. In contrast, when the conformation of detergent-solubilized glycoprotein IIb-IIIa was altered by exposure to RGD-containing peptides, the receptor remained active even after incorporation into phospholipid vesicles. These results demonstrate that platelet membranes are a useful model in which to study the regulation of glycoprotein IIb-IIIa and suggest that the environment surrounding the receptor may have a profound influence on this process.
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PMID:Regulation of ligand binding to glycoprotein IIb-IIIa (integrin alpha IIb beta 3) in isolated platelet membranes. 768 66

The peptide YFLLRNP antagonizes the aggregation of human platelets when induced by low concentrations of alpha-thrombin or the thrombin receptor agonist peptide (SFLLRNP), demonstrating that it interacts specifically with the thrombin receptor. Platelets exposed to YFLLRNP show immediate shape change (pseudopod formation) and potentiation of the ADP and platelet-activating factor response, but no Ca2+ mobilization, P47 (pleckstrin) phosphorylation, secretion, or aggregation. Thus, YFLLRNP induces a state of partial activation of the platelets. Furthermore, with platelets prestimulated with adrenalin (10 microM), YFLLRNP induces aggregation, but no secretion, and only in the presence of added fibrinogen. We also found that prostacyclin inhibits the YFLLRNP-induced shape change; but EDTA, aspirin, and apyrase (ADP scavenger) do not. Thus, the thrombin receptor in platelets may communicate, independently of Ca2+ mobilization and P47 phosphorylation (protein kinase C activation), with intracellular signaling mechanisms that 1) modulate the cytoskeleton structure, 2) potentiate other platelet responses, and 3) stimulate coupling between the thrombin receptor and fibrinogen binding (the glycoprotein IIb-IIIa complex). YFLLRNP may be useful for differentiating between several possible activation states of the platelet thrombin receptor.
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PMID:A peptide ligand of the human thrombin receptor antagonizes alpha-thrombin and partially activates platelets. 839 Sep 90

Previous studies demonstrated that Zn2+ at a concentration of 50 microM increases the number of fibrinogen receptors exposed on ADP-stimulated platelets and that higher concentrations of Zn2+ induce platelet aggregation that appears to be mediated by receptors associated with the glycoprotein IIb/IIIa complex. The purpose of this study was to identify the mechanism by which Zn2+ modulates exposure of fibrinogen receptors on the surface of human washed platelets. We determined that Zn2+ (300-800 microM)-induced platelet aggregation that was not accompanied by the release of [14C]serotonin was not blocked by ADP scavenging enzymes and 5'-p-fluorosulfonylbenzoyl-adenosine, an affinity label for ADP binding sites, but it was inhibited by disintegrins, staurosporine, and EDTA. Zn2+ (50-200 microM) showed a synergistic effect on platelet aggregation and platelet release caused by ADP and N,N,N',N'-tetrakis(2-pyridylmethyl)ethylenediamine, a Zn2+ chelator, and inhibited ADP-induced platelet aggregation that was reversed by Zn2+ (50 microM). Zn2+ (200 microM) increased the number of fibrinogen binding sites and the affinity of albolabrin (a disintegrin isolated from Trimeresurus albolabris snake venom that has been shown to bind to the fibrinogen receptor) on ADP-activated platelets. On the other hand, Zn2+ (100-800 microM) did not increase fibrinogen binding to the purified receptor. Incubation of platelets with Zn2+ (200 microM) resulted in the phosphorylation of a 47-kDa protein that was blocked by staurosporine, an inhibitor of protein kinase C. In conclusion, Zn2+ ions activate protein kinase C and enhance fibrinogen receptor exposure on the surface of platelets stimulated by ADP.
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PMID:Exposure of platelet fibrinogen receptors by zinc ions: role of protein kinase C. 847 31

In static condition, 6F1, an anti-glycoprotein Ia/IIa monoclonal antibody, almost completely prevented initial platelet adhesion to fibrillar collagen, but markedly lost its action with prolonged incubation. The platelet adhesion and spreading at the later stage were prevented by adding the peptide GRGDS, aspirin, and apyrase, suggesting that after initial recognition of platelet glycoprotein Ia/IIa with collagen the activation of glycoprotein IIb/IIIa and the release of thromboxane A2/ADP would promote platelet spreading, thus strengthening the stability of adhesion. Both initial platelet adhesion and platelet spreading were prevented by cytochalasin B, an inhibitor of actin polymerization. In contrast, BAPTA (an intracellular Ca2+ chelator) only inhibited platelet spreading. Inhibition of protein kinase C or protein tyrosine kinase by staurosporine or genistein, respectively, had only little effect on platelet adhesion. These data suggest that actin polymerization and intracellular Ca2+ mobilization are involved in the regulation of platelet spreading after initial platelet contact with collagen.
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PMID:Mechanisms-regulated platelet spreading after initial platelet contact with collagen. 864 15

Theonezolide-A (TZ-A), a novel polyketide macrolide, isolated from the Okinawan marine sponge Theonella sp., caused a marked platelet shape change at low concentrations (0.2-0.6 microM). Increasing concentrations of TZ-A to 6 microM or more caused shape change followed by a small but sustained aggregation. In a Ca(2+)-free solution, TZ-A-induced aggregation was markedly inhibited, although the marked shape change was still observed. Aggregation stimulated by TZ-A increased in a linear fashion with increasing Ca2+ concentrations from 0.1 to 3.0 mM. Furthermore TZ-A markedly enhanced 45Ca2+ uptake into platelets. Aggregation induced by TZ-A was inhibited by Arg-Gly-Asp-Ser, an inhibitor of fibrinogen binding to glycoprotein IIb-IIIa, H-7 and staurosporine, protein kinase C inhibitors, or genistein and tyrphostin A23, protein tyrosine kinase inhibitors, whereas shape change was blocked by genistein and tyrphostin A23. H-7 or staurosporine did not affect the TZ-A-induced shape change. These results suggest that TZ-A-induced platelet shape change is not dependent on external Ca2+, whereas TZ-A-induced aggregation is caused by an increase in Ca2+ permeability of the plasma membrane. It is also suggested that both aggregation and shape change induced by TZ-A are associated with protein phosphorylation by protein kinase C and tyrosine kinase.
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PMID:The mode of rabbit platelet shape change and aggregation induced by theonezolide-A, a novel polyketide macrolide, isolated from the Okinawan marine sponge Theonella sp. 872 32


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