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

Four naturally occurring flavones (baicalein, quercetin, quercetagetin and myricetin) and two novel catechins [(-)-epicatechin gallate and (-)-epigallocatechin gallate, from the tea plant Camellia sinensis], which are known inhibitors of reverse transcriptase, were shown to induce mammalian topoisomerase II-dependent DNA-cleavage in vitro. The flavones differed from the catechins in causing unwinding of duplex DNA, but both classes of compound induced enzymic DNA breakage at the same sites on DNA. Moreover, the cleavage specificity was the same as that for the known intercalator 4'-(acridin-9-ylamino)methanesulphon-m-anisidide, suggesting that these agents trap the same cleavable complex. Analysis of some 30 flavonoid compounds allowed elucidation of the structure-function relationships for topoisomerase II-mediated DNA cleavage. For flavonoid inhibitors an unsaturated double bond between positions 2 and 3 of the pyrone ring and hydroxy groups at the 5, 7, 3' and 4' positions favoured efficient cleavage. Hydroxy substitutions could be tolerated at the 3, 6 and 5' positions. Indeed, the absence of substituents at the 3', 4' and 5' positions could be compensated by a hydroxy group at position 6 (baicalein). Similar requirements have been reported for flavonoid inhibitors of protein kinase C that act competitively with ATP, suggesting interaction with a conserved protein feature. Formation of the cleavable complex is a cytotoxic lesion that may contribute to the growth-inhibitory properties of flavones observed for three human tumour cell lines. These results are discussed in regard to the selectivity of antiviral agents.
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PMID:Site-specific DNA cleavage by mammalian DNA topoisomerase II induced by novel flavone and catechin derivatives. 131 32

Fructose-1,6-diphosphate (FDP) is a physiological product which exhibits pharmacological properties. This study shows that FDP (1-3 mM) inhibits platelet aggregation induced by the agonists thrombin, vasopressin, platelet activating factor, ADP, adrenaline, arachidonate and the stable thromboxane analogue U 44069. Thrombin-promoted ATP secretion and cytosolic Ca2+ rise are also drastically inhibited by FDP, which decreases, although to a lesser extent, the protein kinase C-dependent phosphorylation of the 47 kDa protein. The inhibition on thrombin-induced aggregation is shared, albeit less efficiently, by glucose-1,6-diphosphate and fructose-2,6-diphosphate but not by other phosphorylated monosaccharides (fructose-1:2 cyclic,6-diphosphate, glucose-1- and glucose-6-phosphate, fructose-1- and fructose-6-phosphate, mannose-6-phosphate and 5-phosphoryl ribose-1-pyrophosphate). FDP does not affect platelet activation induced by the protein kinase C activators dioctanoylglycerol or phorbol 12-myristate 13-acetate. No increase of cAMP concentration is observed in FDP-treated platelets. Altogether, these results indicate that FDP inhibits platelet activation at a level preceding phospholipase C. The data are consistent with a general inhibitory action of FDP on signal transmission.
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PMID:Fructose-1,6-diphosphate inhibits platelet activation. 131 5

Na+/H+ exchange activity was investigated in cultured rat thyroid follicular FRTL-5 cells using the pH sensitive dye 2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein (BCECF). Basal intracellular pH (pHi) was 7.13 +/- 0.10 in cells incubated in Hepes-buffered saline solution. The intracellular buffering capacity beta i was determined using the NH4Cl-pulse method, yielding a beta i value of 85 +/- 12 mM/pH unit. The relationship between extracellular Na+ and the initial rate of alkalinization of acid-loaded cells showed simple saturation kinetics, with an apparent Km value of 44 +/- 26 mM, and an Vmax value of 0.3 +/- 0.01 pH unit/min. The agonist-induced activation of Na+/H+ exchange was investigated in cells acidified with nigericin. Addition of 12-O-tetradecanoylphorbol 13-acetate (TPA) or ATP induced rapid cytosolic alkalinization in acid-loaded cells. The action of both TPA and ATP was abolished by preincubating the cells with 100 microM amiloride, by substituting extracellular Na+ with equimolar concentrations of choline+, and by pretreating the cells with TPA for 24 h. Chelating extracellular Ca2+, or depleating intracellular Ca2+ pools did not affect the ATP-induced alkalinization. The results indicate, that FRTL-5 cells have a functional Na+/H+ exchange mechanism. Furthermore, stimulation of protein kinase C activity is of importance in activating the antiport.
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PMID:Characterization of Na+/H+ exchange in FRTL-5 thyroid cells. Evidence for dependence on activation of protein kinase C. 131 62

1. Using internal perfusion and concentration-clamp procedures applied to Helix neurons, the effects of cAMP, Ca2+, and phorbol esters on ouabain-induced depression of acetylcholine Cl-dependent responses were determined. 2. Intracellular cAMP (10(-4) M) depressed those acetylcholine responses which were blocked by ouabain but had no effect on ouabain-insensitive acetylcholine responses. In the presence of elevated intracellular cAMP, ouabain had no further depressant effect on these acetylcholine responses. Both elevated cAMP and ouabain reduced the acetylcholine response without altering the current-voltage curves. 3. An increase in intracellular Ca2+ concentration depressed the amplitude of current induced by application of acetylcholine in neurons with ouabain-sensitive responses and shifted the dose-response relationship to the right. However, elevated Ca2+ did not reduce the maximal response induced by acetylcholine, nor did it prevent the reduction of that response by ouabain. 4. 12-O-Tetradecanoylphorbol-13-acetate (TPA), a potent stimulator of protein kinase C activity, caused depression of both the ouabain-sensitive and the ouabain-insensitive acetylcholine responses. The inhibitory effect of TPA was markedly enhanced after addition of ATP to the intracellular medium and was greatly reduced by cooling to 5 degrees C. The blocking effect of ouabain, however, reexamined in the presence of TPA. 5. These observations are consistent with the hypothesis that the depression of acetylcholine induced Cl--responses in Helix neurons is a result of an increase in intracellular cAMP concentration but is unrelated to activation of protein kinase C or increases in intracellular Ca2+.
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PMID:The effects of cAMP, Ca2+, and phorbol esters on ouabain-induced depression of acetylcholine responses in Helix neurons. 131 66

The effects of protein kinase C (PKC) activators on gamma-aminobutyric acidA (GABAA) receptor function were studied by two-electrode voltage-clamp in Xenopus oocytes expressing brain mRNA or subunit cDNAs and in isolated mouse brain cerebellar membrane vesicles (microsacs), using 36Cl- uptake. Both oocytes and microsacs showed transient (desensitizing) and sustained (nondesensitizing) GABAA receptor responses. In oocytes expressing brain mRNA, the PKC activator phorbol myristoyl acetate (PMA), but not the inactive analog phorbol 12-monomyristate, inhibited both transient and sustained GABA-gated chloride currents. The inhibition by PMA was concentration dependent, with an EC50 of approximately 5 nM, and resulted in a decrease in the efficacy, but not the potency, of GABA. Additionally, PMA inhibited GABA-gated chloride currents in oocytes expressing alpha 1 beta 1 gamma 2L subunit cDNAs. The effect of PMA on recombinant receptors was significantly antagonized by PKC inhibitory peptide (PKCI). In the microsac preparation, the PKC activators (-)-7-octylindolactam V and PMA inhibited the sustained phase of 36Cl- flux without altering the transient phase. The action of PMA was blocked by kinase inhibitors and by depletion of Mg-ATP and was mimicked by protein phosphatase inhibitors. These results demonstrate that activation of PKC inhibits GABAA receptor function, and the results from the microsac experiments suggest that PKC-dependent phosphorylation preferentially inactivates a nondesensitized form or state of the receptor.
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PMID:Activation of protein kinase C selectively inhibits the gamma-aminobutyric acidA receptor: role of desensitization. 131 47

The cellular transduction pathways used by alpha 1-adrenergic and cholinergic agonists were compared in isolated acini from rat exorbital lacrimal glands. Peroxidase secretion was the index of protein secretion. Inositol phosphates were measured by anion exchange chromatography, intracellular free Ca2+ concentration ([Ca2+]i) by fluorescence methods using fura-2, cellular adenosine 3',5'-cyclic monophosphate (cAMP) levels by protein binding radioassay, and protein kinase C (PKC) activity by [32P]ATP incorporation into exogenous substrate. Protein secretion stimulated by simultaneous addition of the alpha 1-adrenergic agonist phenylephrine and the cholinergic agonist carbachol was additive. Carbachol (10(-3) M) significantly increased the ratios of inositol phosphates to inositol during a 1- or 20-min incubation in contrast to phenylephrine (10(-5) to 10(-2) M), which did not. Phenylephrine (10(-3) M) significantly increased the [Ca2+]i by a maximum of 15 +/- 3 nM compared with carbachol (10(-4) M), which increased [Ca2+]i to a maximum of 90 +/- 14 nM. Phenylephrine (10(-4) M) did not increase cAMP levels. Phenylephrine (10(-5) to 10(-3) M) decreased cytosolic PKC activity in a concentration-dependent manner. Carbachol (10(-3) M) transiently caused a slight decrease in cytosolic PKC activity. Our results indicate that alpha 1-adrenergic and cholinergic agonists use separate and different pathways to stimulate the lacrimal gland.
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PMID:Alpha 1-adrenergic and cholinergic agonists use separate signal transduction pathways in lacrimal gland. 131 86

Protein ubiquitination has been implicated in ATP-dependent protein turnover and in a number of biological processes in eukaryotic cells. The ubiquitination activating enzyme, E1, and ubiquitin carrier protein, E2, are two essential enzymes in the protein ubiquitination machinery. Using purified E1 and E2 from rabbit reticulocytes and various protein kinases, which include cAMP-dependent protein kinase, protein kinase C, and protein tyrosine kinase, we demonstrated that E1 is phosphorylated by protein kinase C, with a stoichiometry of 0.65 mol of phosphate/mol of E1, and one of the E2 isoforms, E2(32kDa), is phosphorylated by protein tyrosine kinase to 2 eq of phosphate/mol of protein. Phosphorylation of E1 causes a 2-fold enhancement of its activity as monitored by ubiquitin-dependent ATP in equilibrium PPi exchange. When 1 eq of phosphate was incorporated into E2(32kDa), a 2.4-fold activation was also observed for its activity to catalyze the ubiquitination of histone H2A. The regulatory significance of this finding is discussed.
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PMID:Protein ubiquitination is regulated by phosphorylation. An in vitro study. 132 Nov 38

Microtubule-associated protein 2 (MAP2) kinase has been isolated and characterized from rat brain. The enzyme has an apparent M(r) of approximately 42,000 and its pI is 4.9. MAP2 was the preferred substrate, but it also phosphorylated myelin basic protein (MBP), histone V-S, tubulin and the PC12 protein substrate pp250. The enzyme is distinct from protein kinase C, cAMP-dependent kinase and the calcium/calmodulin-dependent kinases, as specific inhibitors of these kinases did not affect MAP2 phosphorylation. The addition of the relatively non-specific protein kinase inhibitor H7 (20 microM) had a modest inhibitory effect. The enzyme was active in both 5 mM Mn2+ and Mg2+, and displayed Kms for MAP2, MBP, and ATP of 56 nM, 254 nM, and 4 microM, respectively. This enzyme, which represents a low abundance protein in whole brain, is analogous to the MAP2 kinase observed in growth factor-stimulated cell lines.
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PMID:Isolation and characterization of microtubule-associated protein 2 (MAP2) kinase from rat brain. 132 16

The specific activity of Na(+)-K(+)-ATPase in the renal medulla and cortex of 50-day-old streptozotocin (STZ)-induced diabetic mice was increased 58% and 50%, respectively, as compared to controls. Km values of Na+ and K+ for this enzyme were unaltered, while that of ATP was decreased in diabetic mice. The Na(+)-K(+)-ATPase in control medulla and cortex was activated by both cholera and pertussis toxins, while this effect was abolished in diabetics. Since dibutyryl cAMP stimulates cortical Na(+)-K(+)-ATPase activity in control mice, the activation effect of cholera toxin on this enzyme might be due to its interaction with a Gs-protein and the persistent stimulation of adenylate cyclase activity, while the effect of pertussis toxin might be due to its masking of the inhibitory action of a Gi-protein on adenylate cyclase activity. However, the protein kinase C (PKC)-associated Na(+)-K(+)-ATPase might also be quiescent in diabetes, because the stimulating effect of phorbol 12,13-dibutyrate (PDBu) and phorbol 12-myristate 13-acetate (PMA) on this enzyme was abolished in diabetic cortex. In addition, nicardipine and ouabain were found to have differential effects on this enzyme derived from control and diabetic mice.
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PMID:Differentiation of renal Na(+)-K(+)-ATPase in control and streptozotocin-induced diabetic mice by G-protein acting toxins and phorbol esters. 132 74

Bovine brain 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase was purified to homogeneity and characterized. This bifunctional enzyme is a homodimer with a subunit molecular weight of 120,000, which is twice that of all other known bifunctional enzyme isozymes. The kinase/bisphosphatase activity ratio was 3.0. The Km values for fructose 6-phosphate and ATP of the 6-phosphofructo-2-kinase were 27 and 55 microM, respectively. The Km for fructose 2,6-bisphosphate and the Ki for fructose 6-phosphate for the bisphosphatase were 70 and 20 microM, respectively. Physiologic concentrations of citrate had reciprocal effects on the enzyme's activities, i.e. inhibiting the kinase (Ki of 35 microM) and activating the bisphosphatase (Ka of 16 microM). Phosphorylation of the brain enzyme was catalyzed by the cyclic AMP-dependent protein kinase with a stoichiometry of 0.9 mol of phosphate/mol of subunit and at a rate similar to that seen with the liver isozyme. In contrast to the liver isozyme, the kinetic properties of the brain enzyme were unaffected by cyclic AMP-dependent protein kinase phosphorylation, and also was not a substrate for protein kinase C. The brain isozyme formed a labeled phosphoenzyme intermediate and cross-reacted with antibodies raised against the liver isozyme. However, the NH2-terminal amino acid sequence of a peptide generated by cyanogen bromide cleavage of the enzyme had no identity with any known bifunctional enzyme sequences. These results indicate that a novel isozyme, which is related to other 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase isozymes, is expressed specifically in neural tissues.
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PMID:Bovine brain 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase. Evidence for a neural-specific isozyme. 132 53


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