Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:2.7.11.1 (protein kinase)
 81,284 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

An eosinophilic substrain of HL-60 cells (HL-60#7) predominantly synthesized cysteinyl leukotrienes after stimulation with the calcium ionophore A23187. Activation of protein kinase C (PKC) by phorbol 12-myristate 13-acetate (PMA) specifically attenuated cysteinyl leukotriene production without affecting the biosynthesis of non-cysteinyl leukotrienes. The inhibition of cysteinyl leukotriene biosynthesis was prevented only by specific PKC inhibitors (staurosporine and bisindolylmaleimide) but not by inhibitors of tyrosine kinases (genistein, tyrphostin 47, and herbimycin A), protein kinase A (KT5720), or the oxidative burst (apocynin). Similar results were obtained when LTC4 synthase enzymatic activity was measured directly in the presence of saturating concentrations of exogenously added substrates. Therefore, the inhibitory effects of PKC activation on cysteinyl leukotriene formation in intact cells was attributable to effects on the LTC4 synthase enzyme. The mechanism of inhibition of LTC4 synthase by PKC activation was determined by kinetic analysis to be noncompetitive in both eosinophil-like HL-60#7 cells and monocytic THP-1 cells. Contrary to the effect of PKC activation on cysteinyl leukotriene biosynthesis, the formation of prostaglandin E2 and thromboxane B2 was elevated twofold to threefold after PMA treatment, which was prevented by the PKC inhibitor, staurosporine. We propose a regulatory model in which PKC activation shifts the profile of eicosanoid mediators produced by eosinophils from cysteinyl leukotrienes to prostanoids.
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PMID:Activation of protein kinase C down-regulates leukotriene C4 synthase activity and attenuates cysteinyl leukotriene production in an eosinophilic substrain of HL-60 cells. 802 12

In response to calcium ionophore (A23187) stimulation, human granulocyte/macrophage colony-stimulating factor-primed, dimethylsulfoxide-differentiated HL-60 cells (which resemble mature granulocytes) synthesized leukotrienes (LTs) LTA4, LTB4, LTC4, and LTD4. The synthesis of the sulfidopeptide LTs, LTC4 and LTD4, was specifically inhibited in cells incubated in the presence of both A23187 and phorbol-12-myristate-13-acetate (PMA), an activator of protein kinase C (PKC). In contrast, neither the synthesis of LTB4, a product of the nonpeptide branch of the LT pathway, nor the formation of LTA4, the precursor for both branches of the LT biosynthetic pathway, was significantly affected by the presence of PMA during A23187 stimulation. The inhibition by PMA of LTC4 production in A23187-stimulated HL-60 cells was dose dependent, with an IC50 value of approximately 3.5 nM. The PKC inhibitor staurosporine completely reversed the inhibition by PMA of LTC4 production in A23187-stimulated cells, in a dose-dependent fashion, with an IC50 value of approximately 30 nM. Bisindolylmaleimide, another PKC inhibitor, was also able to prevent PMA-mediated inhibition of LTC4 formation, whereas inhibitors of protein kinase A, tyrosine kinases, or the respiratory-burst oxidase were not. Measurement of LTC4 synthase enzymatic activity in cells challenged with A23187 and PMA in the presence or absence of staurosporine demonstrated that the activity of the LTC4 synthase enzyme was inhibited in cells costimulated with A23187 and PMA and that inhibition could also be completely prevented by the presence of staurosporine. Because PMA is known to activate PKC, and staurosporine and bisindolylmaleimide are inhibitors of PKC, these results suggest that LTC4 synthase in HL-60 cells may be phosphoregulated.
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PMID:Protein kinase C-dependent regulation of sulfidopeptide leukotriene biosynthesis and leukotriene C4 synthase in neutrophilic HL-60 cells. 819 95

Human platelets possess a specific membrane-bound leukotriene (LT) C4 synthase, which catalyzes the conversion of LTA4 to LTC4. Stimulation of the receptors for thrombin, collagen or thromboxane A2 provoked inhibition of this enzyme, as judged by suppressed transformation of exogenous LTA4 to LTC4. Similarly, direct activation of protein kinase (PK) C with nanomolar concentrations of 4 beta-phorbol 12-myristate 13-acetate (PMA) inhibited the production of LTC4. Kinetic studies demonstrated that the inhibition induced by thrombin and PMA was non-competitive. Elevation of intracellular cAMP levels with carbacyclin did not affect basal LTC4 formation, but abolished the attenuation of platelet LTC4 synthase activity induced by the thromboxane receptor agonist U-46619. The unselective protein kinase inhibitor staurosporine prevented both receptor-mediated and PMA-induced suppression of LTC4 formation. In contrast, two selective PKC inhibitors, Ro 31-8220 and GF 109203X, reversed the inhibitory effect provoked by PMA, but failed to prevent thrombin-induced inhibition. Furthermore, the protein tyrosine phosphatase inhibitor, sodium orthovanadate, induced dose-dependent inhibition of LTC4 production in platelet sonicates. In conclusion, receptor-mediated activation of human platelets leads to decreased LTC4 synthase activity via phosphoregulation. Although the present results demonstrate that platelet LTC4 synthase can be regulated via PKC-dependent events, alternative mechanisms appears to be involved in the physiological regulation of this enzyme. The findings suggest the possible importance of protein tyrosine phosphorylations in this process.
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PMID:Receptor-mediated regulation of leukotriene C4 synthase activity in human platelets. 853 97