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)

Sensitization of purinergic P2X receptors is one of the mechanisms responsible for exaggerated pain responses to inflammatory injuries. Prostaglandin E2 (PGE2), produced by inflamed tissues, is known to contribute to abnormal pain states. In a previous study, we showed that PGE2 increases fast inactivating ATP currents that are mediated by homomeric P2X3 receptors in dorsal root ganglion (DRG) neurons isolated from normal rats. Protein kinase A (PKA) is the signalling pathway used by PGE2. Little is known about the action of PGE2 on ATP currents after inflammation, although the information is crucial for understanding the mechanisms underlying inflammation-induced sensitization of P2X receptors. We therefore studied the effects of PGE2 on P2X3 receptor-mediated ATP currents in DRG neurons dissociated from complete Freund's adjuvant (CFA)-induced inflamed rats. We found that PGE2 produces a large increase in ATP currents. PKCepsilon, in addition to PKA, becomes involved in the modulatory action of PGE2. Thus, PGE2 signalling switches from a solely PKA-dependent pathway under normal conditions to both PKA- and PKC-dependent pathways after inflammation. Studying the mechanisms underlying the switch, we demonstrated that cAMP-responsive guanine nucleotide exchange factor 1 (Epac1) is up-regulated after inflammation. The Epac agonist CPT-OMe mimics the potentiating effect of PGE2 and occludes the PKC-mediated PGE2 action on ATP currents. These results suggest that Epac plays a critical role in P2X3 sensitization by activation of de novo PKC-dependent signalling of PGE2 after inflammation and would be a useful therapeutic target for pain therapies.
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PMID:A critical role of the cAMP sensor Epac in switching protein kinase signalling in prostaglandin E2-induced potentiation of P2X3 receptor currents in inflamed rats. 1770 20

Glutamate clearance by astrocytes is critical for controlling excitatory neurotransmission and ATP is an important mediator for neuron-astrocyte interaction. However, the effect of ATP on glutamate clearance has never been examined. Here we report that treatment of RBA-2 cells, a type-2-like astrocyte cell line, with ATP and the P2X(7) receptor selective agonist 3'-O-(4-benzoylbenzoyl) adenosine 5'-triphosphate (BzATP) decreased the Na+-dependent [3H]glutamate uptake within minutes. Mechanistic studies revealed that the decreases were augmented by removal of extracellular Mg2+ or Ca2+, and was restored by P2X7 selective antagonist , periodate-oxidized 2',3'-dialdehyde ATP (oATP), indicating that the decreases were mediated through P2X(7) receptors. Furthermore, stimulation of P2X7 receptors for 2 h inhibited both activity and protein expression of glutamine synthetase (GS), and oATP abolished the inhibition. In addition, removal of extracellular Ca(2+) and inhibition of protein kinase C (PKC) restored the ATP-decreased GS expression but failed to restore the P2X(7)-decreased [3H]glutamate uptake. Therefore, P2X7-mediated intracellular signals play a role in the down-regulation of GS activity/expression. Activation of P2X7 receptors stimulated increases in intracellular Na+ concentration ([Na+](i)) suggesting that the P2X(7)-induced increases in [Na+](i) may affect the local Na+ gradient and decrease the Na+-dependent [3H]glutamate uptake. These findings demonstrate that the P2X7-mediated decreases in glutamate uptake and glutamine synthesis were mediated through distinct mechanisms in these cells.
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PMID:Activation of P2X(7) receptors decreases glutamate uptake and glutamine synthetase activity in RBA-2 astrocytes via distinct mechanisms. 1806 49

A physiological concentration of extracellular ATP stimulated biphasic Ca(2+) signal, and the Ca(2+) transient was decreased and the Ca(2+) sustain was eliminated immediately after removal of ATP and Ca(2+) in RBA-2 astrocytes. Reintroduction of Ca(2+) induced Ca(2+) sustain. Stimulation of P2Y(1) receptors with 2-methylthioadenosine 5'-diphosphate (2MeSADP) also induced a biphasic Ca(2+) signaling and the Ca(2+) sustains were eliminated using Ca(2+)-free buffer. The 2MeSADP-mediated biphasic Ca(2+) signals were inhibited by phospholipase C (PLC) inhibitor U73122, and completely blocked by P2Y(1) selective antagonist MRS2179 and protein kinase C (PKC) activator phorbol 12-myristate 13-acetate (PMA) whereas enhanced by PKC inhibitors GF109203X and Go6979. Inhibition of capacitative Ca(2+) entry (CCE) decreased the Ca(2+)-induced Ca(2+) entry; nevertheless, ATP further enhanced the Ca(2+)-induced Ca(2+) entry in the intracellular Ca(2+) store-emptied and CCE-inhibited cells indicating that ATP stimulated Ca(2+) entry via CCE and ionotropic P2X receptors. Furthermore, the 2MeSADP-induced Ca(2+) sustain was eliminated by apyrase but potentiated by P2X(4) allosteric effector ivermectin (IVM). The agonist ADPbetaS stimulated a lesser P2Y(1)-mediated Ca(2+) signal and caused a two-fold increase in ATP release but that were not affected by IVM whereas inhibited by PMA, PLC inhibitor ET-18-OCH(3) and phospholipase D (PLD) inhibitor D609, and enhanced by removal of intra- or extracellular Ca(2+). Taken together, the P2Y(1)-mediated Ca(2+) sustain was at least in part via P2X receptors activated by the P2Y(1)-induced ATP release, and PKC played a pivotal role in desensitization of P2Y(1) receptors in RBA-2 astrocytes.
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PMID:Functional characterization of P2Y1 versus P2X receptors in RBA-2 astrocytes: elucidate the roles of ATP release and protein kinase C. 1807 86

P2X(3) and P2X(2+3) receptors are present on sensory neurons, where they contribute not only to transient nociceptive responses, but also to hypersensitivity underlying pathological pain states elicited by nerve injuries. Increased signalling through P2X(3) and P2X(2+3) receptors may arise from an increased routing to the plasma membrane and/or gain of function of pre-existing receptors. An obvious effector mechanism for functional modulation is protein kinase C (PKC)-mediated phosphorylation, since all P2X family members share a conserved consensus sequence for PKC, TXR/K, within the intracellularly located N-terminal domain. Contradictory reports have been published regarding the exact role of this motif. In the present study, we confirm that site-directed elimination of the potential phosphor-acceptor threonine or the basic residue in the P+2 position of the TXR/K sequence accelerates desensitization of P2X(2) receptors and abolishes P2X(3) receptor function. Moreover, the PKC activator phorbol 12-myristate 13-acetate increased P2X(3) (but not P2X(2)) receptor-mediated currents. Biochemically, however, we were unable to demonstrate by various experimental approaches a direct phosphorylation of wild-type P2X(2) and P2X(3) receptors expressed in both Xenopus laevis oocytes and HEK293 cells. In conclusion, our data support the view that the TXR/K motif plays an important role in P2X function and that phorbol 12-myristate 13-acetate is capable of modulating some P2X receptor subtypes. The underlying mechanism, however, is unlikely to involve direct PKC-mediated P2X receptor phosphorylation.
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PMID:Lack of evidence for direct phosphorylation of recombinantly expressed P2X(2) and P2X (3) receptors by protein kinase C. 1840 51

ATP in the 100 muM-1 mM concentration range provoked a calcium-independent increase of the oxidation of dichlorodihydrofluorescein (DCFH) to dichlorofluorescein (DCF) by mouse submandibular cells. 3'-O-(4-benzoyl)benzoyl adenosine 5'-triphosphate (BzATP), a P2X(7) agonist, but not a muscarinic or an adrenergic agonist, reproduced the effect of ATP. The inhibition of phospholipase C by U73122 or the potentiation of P2X(4) receptor activation with ivermectin did not modify the response to ATP. ATP did not increase the oxidation of DCFH in cells isolated from submandibular glands of P2X(7) knockout mice or in cells pretreated with a P2X(7) antagonist. The inhibition of protein kinase C or of mitogen-activated protein kinase (MAP kinase) or of reduced nicotinamide adenine dinucleotide phosphate (NADPH) oxidase blocked the oxidation of DCFH without affecting the increase of the intracellular concentration of calcium or the uptake of ethidium bromide in response to extracellular ATP. From these results it is concluded that the activation of the P2X(7) receptors from submandibular glands triggers an intracellular signalling cascade involving protein kinase C and MAP kinase leading to the stimulation of NADPH oxidase and the subsequent generation of reactive oxygen species.
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PMID:Pharmacological evidence for the stimulation of NADPH oxidase by P2X(7) receptors in mouse submandibular glands. 1858 Dec 62

Arginine vasopressin (AVP) neurons of the hypothalamo-neurohypophseal system (HNS) are innervated by numerous afferent pathways carrying information about two physiologically important parameters: blood volume/pressure and osmolality. These pathways use a variety of neurotransmitters/neuropeptides. In order to understand normal and pathological regulation of VP secretion, the mechanisms underlying integration of these complex afferent signals by the AVP neurons must be understood. The importance of neurotransmitter interactions in determining hormone release is highlighted by the finding that simultaneous exposure to adenosine triphosphate (ATP, a neurotransmitter acting on purinergic receptors) and phenylephrine (PE; to mimic norepinephrine activation of alpha1-adrenergic receptors) results in potentiation of AVP release that is characterized by an increase in the peak response and conversion of a transient response to a response that is sustained for hours. Evaluation of the mechanisms responsible for this response indicated that (1) activation of P2X purinergic receptors (P2X-R) is required, (2) protein kinase C (PKC) activation is required, (3) the sustained component requires new gene transcription, (4) the synergism does not involve presynaptic mechanisms nor does it occur directly in the neural lobe and (5) live-cell Ca(++) imaging techniques demonstrated a sustained increase in [Ca(++)](i) and that ATP activates P2Y-Rs as well as P2X-Rs in supraoptic neurons. Since the subtypes of P2X-Rs differ in their rate of desensitization, identification of the subtype of P2X-Rs participating in the initial and sustained responses to ATP+PE may elucidate mechanisms underlying the abrupt and transient responses to orthostatic hypotension versus sustained responses to chronic hypovolemia or vasodilation.
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PMID:Regulation of vasopressin release by co-released neurotransmitters: mechanisms of purinergic and adrenergic synergism. 1865 75

Adenosine triphosphate (ATP) is coreleased with catecholamines from adrenal medullary chromaffin cells in response to sympathetic nervous system stimulation and may regulate these cells in an autocrine or paracrine manner. Increases in extracellular signal-regulated kinase (ERK) 1/2 phosphorylation were observed in response to ATP stimulation of bovine chromaffin cells. The signaling pathway involved in ATP-mediated ERK1/2 phosphorylation was investigated via Western blot analysis. ATP and uridine 5'-triphosphate (UTP) increased ERK1/2 phosphorylation potently, peaking between 5 and 15 min. The mitogen-activated protein kinase (MAPK/ERK)-activating kinase (MEK) inhibitor PD98059 blocked this response. UTP, which is selective for G-protein-coupled P2Y receptors, was the most potent agonist among several nucleotides tested. Adenosine 5'-O-(3-thio) triphosphate (ATPgammaS) and ATP were also potent agonists, characteristic of the P2Y(2) or P2Y(4) receptor subtypes, whereas agonists selective for P2X receptors or other P2Y receptor subtypes were weakly effective. The receptor involved was further characterized by the nonspecific P2 antagonists suramin and reactive blue 2, which each partially inhibited ATP-mediated ERK1/2 phosphorylation. Inhibitors of protein kinase C (PKC), protein kinase A (PKA), Ca(2+)/calmodulin-dependent protein kinase II (CaMKII), and phosphoinositide-3 kinase (PI3K) had no effect on ATP-mediated ERK1/2 phosphorylation. The Src inhibitor PP2, epidermal growth factor receptor (EGFR) inhibitor AG1478, and metalloproteinase inhibitor GM6001 decreased ATP-mediated ERK1/2 phosphorylation. These results suggest nucleotide-mediated ERK1/2 phosphorylation is mediated by a P2Y(2) or P2Y(4) receptor, which stimulates metalloproteinase-dependent transactivation of the EGFR.
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PMID:UTP and ATP increase extracellular signal-regulated kinase 1/2 phosphorylation in bovine chromaffin cells through epidermal growth factor receptor transactivation. 1877 8

The potentiation of P2X(1) receptor currents by phorbol ester (PMA) treatment and stimulation of mGluR1alpha receptors was sensitive to inhibition of novel forms of protein kinase C. Potentiation was also reduced by co-expression of an amino terminal P2X(1) receptor minigene. Cysteine point mutants of residues Tyr(16)-Gly(30) were expressed in Xenopus oocytes. Peak current amplitudes to ATP for Y16C, T18C and R20C mutants were reduced, however this did not result from a decrease in surface expression of the channels. The majority of the mutants showed changes in the time-course of desensitization of ATP evoked currents indicating the important role of this region in regulation of channel properties. PMA and mGluR1alpha potentiation was abolished for the mutants Y16C, T18C, R20C, K27C and G30C. Minigenes incorporating either Y16C, K27C, V29C or G30C still inhibited PMA responses. However D17C, T18C or R20C mutant minigenes were no longer effective suggesting that these residues are important for interaction with regulatory factors. These results demonstrate that the conserved YXTXK/R sequence and a region with a conserved glycine residue close to the first transmembrane segment contribute to PMA and GPCR regulation of P2X(1) receptors.
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PMID:Regions of the amino terminus of the P2X receptor required for modification by phorbol ester and mGluR1alpha receptors. 1904 21

In this study we report the coupling of nucleotide receptors to GSK-3 signalling, a relevant survival pathway in cerebellar granule neurons. P2X(7) agonist BzATP induced a 3-4-fold increase in GSK-3 phosphorylation, which is reported to be associated with the catalytic activity inhibition. This effect was dependent on extracellular calcium and PKC, and independent of PI3-K (phosphatidyl-inositol-3-kinase)/Akt, the main survival route of neurotrophins. BzATP also prevented the apoptosis of granule neurons induced by the pharmacological inhibition of the PI3-K signalling. Both effects, BzATP-mediated GSK-3 phosphorylation and neuroprotection, were abolished by P2X(7) receptor antagonists, BBG, PPADS and A-438079. We found that BzATP prevented the progressive GSK-3 dephosphorylation and caspase-3 activation occurring under conditions of sustained PI3-K inhibition. These results reveal that P2X(7) receptor activation could provide a relevant survival route alternative to classical neurotrophic factors.
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PMID:P2X7 nucleotide receptor is coupled to GSK-3 inhibition and neuroprotection in cerebellar granule neurons. 1938 92

Purinoreceptors of the P2 family contribute strongly to signaling in the cochlea, but little is known about the effects of purinergic neurotransmission in the central auditory system. Here we examine P2 receptor-mediated signaling in the large spherical bushy cells (SBCs) of Mongolian gerbils around the onset of acoustically evoked signal processing (P9-P14). Brief adenosine 5'-O-(3-thiotriphosphate) (ATPgammaS) application evoked inward current, membrane depolarization, and somatic Ca2+ signals. Moreover, ATPgammaS changed the SBCs firing pattern from phasic to tonic, when the application was synchronized with depolarizing current injection. This bursting discharge activity was dependent on [Ca2+]i and Ca2+-dependent protein kinase (PKC) activity and is presumably caused by modulation of low-threshold K+ conductance. Activation of P2Y1 receptors could not evoke these changes per se, thus it was concluded that the involvement of P2X receptors seems to be necessary. Ca2+ imaging data showed that both P2X and P2Y1 receptors mediate Ca2+ signals in SBCs where P2Y1 receptors most likely activate the PLC-IP3 (inositol trisphosphate) pathway and release Ca2+ from internal stores. Immunohistochemical staining confirmed the expression of P2X2 and P2Y1 receptor proteins in SBCs, providing additional evidence for the involvement of both receptors in signal transduction in these neurons. Purinergic signaling might modulate excitability of SBCs and thereby contribute to regulation of synaptic strength. Functionally, the increase in firing rate mediated by P2 receptors could reduce temporal precision of the postsynaptic firing, e.g., phase locking, which has an immediate effect on signal processing related to sound localization. This might provide a mechanism for adaptation to the ambient acoustic environment.
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PMID:P2 receptor-mediated signaling in spherical bushy cells of the mammalian cochlear nucleus. 1957 Dec


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