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

The multiplicity of opioid receptors (mu, delta, kappa) and the limited knowledge of their coupling mechanisms explain why cellular and biochemical changes underlying opioid tolerance/dependence remain poorly understood. Following chronic exposure to opioids, both down- and up-regulation of opioid receptors can occur, depending on the receptor type and/or the central region examined. As these changes generally appear after the tolerance is installed, they are very likely not responsible for it. Instead, opioid tolerance seems to be associated with some uncoupling (probably functional rather than physical) of the opioid receptors from G proteins normally associated with them, therefore resulting in a loss of the capacity of these proteins to exchange GDP for GTP. However, considerable variations might exist in the mechanisms underlying tolerance from one opioid receptor type to another. With regard to dependence, an increase in adenylate cyclase activity, and therefore of cyclic AMP levels and certain protein kinase activities, have been claimed to be responsible for this phenomenon in some cell types. As highly selective opioid agonists and antagonists are now available, experiments with such compounds are expected to yield more informative data on the consequences of the chronic stimulation of a given receptor type. This should contribute to a better understanding of the biochemical and cellular events really responsible for the development of morphine tolerance and dependence.
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PMID:Neurobiological mechanisms of opioid tolerance and dependence. 166 19

The effects of phosphorylation of a mu-opioid receptor on signal transduction to G-protein were studied. The mu-opioid receptor purified from rat whole brains was reconstituted with purified Gi1 in phosphatidylcholine vesicles. DAGO, a mu-opioid agonist at 1 microM-1 mM increased GTPase activity by 10-110% of control, in a concentration-dependent manner. When the mu-opioid receptor was phosphorylated by cyclic AMP-dependent protein kinase prior to reconstitution with Gi1, the DAGO-stimulation was markedly reduced (20% increase at 1 mM DAGO).
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PMID:Phosphorylated mu-opioid receptor purified from rat brains lacks functional coupling with Gi1, a GTP-binding protein in reconstituted lipid vesicles. 216 75

The effects of agonists at mu and delta opioid receptors were compared by measuring membrane currents under voltage clamp from neurons of the rat nucleus locus coeruleus and guinea pig submucous plexus. In each tissue, the appropriate selective agonist (Tyr-D-Ala-Gly-MePhe-Gly-ol for mu receptors in locus coeruleus or Tyr-D-Pen-Gly-Phe-D-Pen for delta receptors in submucous plexus) increased the conductance of an inwardly rectifying potassium conductance and strongly hyperpolarized the membrane. The properties of the potassium conductance affected by the two opioids could not be distinguished. Experiments with intracellular application of guanosine 5'-[gamma-thio]triphosphate indicated that a guanine nucleotide-binding regulatory protein was involved in the coupling between opioid receptor and potassium channel, but there was no evidence for activation of either cAMP-dependent protein kinase or protein kinase C. It is noted that a number of vertebrate neurotransmitter receptors are coupled to potassium channels. The potassium conductance associated with these channels has properties similar to the conductance activated by mu and delta opioids; this family includes the following receptors: acetylcholine M2, norepinephrine alpha 2, dopamine D2, 5-hydroxytryptamine 5-HT1, adenosine A1, gamma-aminobutyric acid GABAB, and somatostatin. It is suggested that this conductance is a conserved neuronal effector coupled to one of the receptor types that mediates the effects of each of several major transmitters. The mu and delta opioid receptors appear to be unusual in that both utilize this same effector mechanism.
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PMID:Mu and delta receptors belong to a family of receptors that are coupled to potassium channels. 244 52

Morphine and [D-Ala2,D-Leu5]enkephalinamide enhance the phosphorylation of a 58 kDa protein in mouse brain synaptosomal membranes. The enhancement of phosphorylation was inhibited by naloxone, an antagonist of morphine. The phosphorylated 58 kDa protein was retained on wheat-germ-agglutinin-agarose and morphinone-Affi-Gel 401 columns and biospecifically eluted out from the columns with N-acetyl-D-glucosamine and naloxone respectively. These results suggest a strong possibility that the opiate-binding protein undergoes phosphorylation by endogenous protein kinase. Since the molecular mass of a mu-type opioid receptor in mouse brain is suggested to be 58 kDa, coincident with those of rat brain and neuroblastoma x glioma hybrid cells, it is conceivable that the phosphorylated 58 kDa protein is a mu-type receptor.
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PMID:Morphine enhances the phosphorylation of a 58 kDa protein in mouse brain membranes. 253 22

The mu-opioid receptor agonist stimulation of low-Km GTPase in rat striatal membranes was abolished by islet-activating protein (IAP) treatment, and recovered by Gi reconstitution. When the IAP-treated membranes were phosphorylated with a cAMP-dependent protein kinase, there was no such recovery by Gi. The agonist binding was not affected with respect to Kd, Bmax and sensitivity to guanine nucleotides in the phosphorylated membranes. These findings suggest that phosphorylation of mu-opioid receptors dissociates the agonist change in G-protein activity from the guanine nucleotide-sensitive agonist binding.
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PMID:Phosphorylation of mu-opioid receptors--a putative mechanism of selective uncoupling of receptor--Gi interaction, measured with low-Km GTPase and nucleotide-sensitive agonist binding. 254 27

The molecular basis of opioid receptor mechanisms was studied in reconstitution experiments using purified or membrane-bound opioid receptors and purified GTP-binding proteins (G-proteins). mu-Opioid receptor exclusively purified from rat brains was reconstituted with G-proteins in lipid vesicles. The mu-agonist stimulated the G-protein activity in both G1 or Go-reconstituted vesicles. The stoichiometry revealed that one molecule of mu-receptor is functionally coupled to plural numbers of Gi or Go molecules and that mu-receptor exists in at least two different subtypes, mu i and mu o, separately coupled to Gi and Go, respectively. In addition, when the mu-receptor was phosphorylated by cAMP-dependent protein kinase, the mu-agonist-stimulation of G-protein activity disappeared, while the guanine nucleotide-sensitivity of agonist binding was unchanged. These findings suggest that there are independent domains in the receptor which are related to functional coupling to G-protein and to the agonist-binding modulation by G-protein. kappa-Opioid receptor agonist inhibited the G-protein activity in guinea pig cerebellar membranes. Further experiments revealed that the kappa-opioid receptor is functionally coupled to an inhibition of phospholipase C activity via an inhibition of Gi-activity. Such a receptor-mediated inhibition of G-protein activity may be the first demonstration of a signal transduction mechanism. The delta-opioid receptor agonist showed no effect on G-protein activity in guinea pig striatal and rat cortical membranes, while it stimulated it in NG108-15 cells. In all these membranes, the delta-agonist binding was markedly reduced by GTP gamma S in the presence of MgCl2. These findings suggest that delta-receptors in the brain might be coupled to G-protein without signal transduction.
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PMID:[Molecular pharmacology of opioid receptor mechanisms]. 255 62

The duration of the calcium component of the action potential (APD) of dorsal root ganglion (DRG) neurons in mouse spinal cord-ganglion explants has been shown to be dually modulated via excitatory and inhibitory opioid receptors. In order to determine if opioid-induced APD prolongation is modulated by receptors that are positively coupled to the adenylate cyclase (AC)/cyclic AMP second messenger system, whole-cell recordings were made from mouse DRG neurons grown in dissociated cell cultures. Tests for opioid responsivity were carried out after intracellular dialysis of an inhibitor of cAMP-dependent protein kinase (PKI). In control recordings, both DADLE-induced APD prolongation as well as shortening were prevented by co-perfusion with the opioid antagonist, diprenorphine (10 nM). Intracellular dialysis of PKI in these neurons completely blocked opioid-induced APD prolongation but did not attenuate APD shortening generally elicited by higher opioid concentrations. Bath perfusion of 10 nM DADLE elicited APD prolongation in 59% of the DRG neurons (n = 34) tested with control solution in the recording pipette, whereas none showed APD prolongation when the pipette contained PKI (n = 18). In control tests with 1 microM DADLE, the APD was prolonged in 37% of the cells and shortened in 26% (n = 19); in contrast, a matched group of PKI-treated cells showed no APD prolongation, whereas 42% showed APD shortening (n = 26). The results support the hypothesis that opioid-induced APD prolongation in DRG neurons is mediated by opioid receptor subtypes that are positively coupled via Gs to AC/cAMP-dependent voltage-sensitive ionic conductances.
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PMID:Inhibitor of cyclic AMP-dependent protein kinase blocks opioid-induced prolongation of the action potential of mouse sensory ganglion neurons in dissociated cell cultures. 284 53

In freshly isolated spinal dorsal horn (DH) neurons (laminae I-IV) of the young rat, the effects of dynorphin A1-17, U-50,488H and U-69,593 on inward currents induced by alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) and kainate (KA) were studied under whole-cell voltage-clamp conditions. When the cells were clamped to a holding potential of -60 mV, co-application of dynorphin A1-17 (10(-6) M) and AMPA (2 x 10(-5) M) reversibly decreased the peak amplitude of the initial transient component of the AMPA-induced current in 72% of the examined cells. In addition, dynorphin (10 microM) in perforated patch-recordings consistently produced a decrease in the steady-state component of the AMPA response. The depressant effect was concentration-dependent (IC50 = 86 nM) and reversible. The dynorphin A1-17-induced depression of the AMPA response was associated with slowing of the response kinetics, including both a 10-90% rise-time and time constant of decay. The AMPA-induced currents were modulated by dynorphin not only during the co-administration but also after the removal of the peptide. Dynorphin increased the initial peak AMPA current in 42% of the examined cells. Similar as with dynorphin A1-17, the peak amplitude of the AMPA-induced current was reversibly suppressed in the presence of 1 microM U-50,488H and U-69,593 in 75% and 86% of the examined cells, respectively. Naloxone and the kappa 1-selective antagonist norbinaltorphimine (nor-BNI) blocked the initial depressant but not late excitatory effects of dynorphin A1-17 and U-50,488H. This antagonistic effect of naloxone and norbinaltorphimine suggests that the depressant effect of dynorphin A1-17 on the AMPA-activated conductance is a true opioid, probably kappa 1-opioid receptor-mediated event. In contrast, the dynorphin-induced late potentiation of AMPA/KA responses appears to be a non-opioid effect since it was not inhibited by nor-BNI, CTAP and naltrindole, the selective kappa-, mu- and delta-opioid receptor blocking agents, respectively. Pretreatment of DH neurons with pertussis toxin blocked the depressant action of dynorphin A1-17, indicating that a Gi- or Go-type G protein was required for this effect on AMPA-activated currents. Intracellular dialysis with a highly specific peptide inhibitor (peptide 6-22) of the cAMP-activated protein kinase (PKA), and with Rp-cAMPS, prevented the depressant effect of dynorphin A1-17. In addition, staurosporine, a nonselective kinase inhibitor, blocked the dynorphin depression of the AMPA response.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:The opioid peptide dynorphin modulates AMPA and kainate responses in acutely isolated neurons from the dorsal horn. 753 29

A specific protein kinase C inhibitor, calphostin C, which injected alone had no effect on the antinociception induced by intrathecal (i.t.) administration of a selective mu-opioid receptor agonist, [D-Ala2,NMePhe4,Gly(ol)5]enkephalin (DAMGO), dose-dependently attenuated the development of acute tolerance to the i.t. DAMGO-induced antinociception in male ICR mice. On the other hand, a selective protein kinase A inhibitor, KT5720, did not have any effect on the development of acute tolerance to DAMGO antinociception. These findings suggest that protein kinase C, but not protein kinase A, plays an important role in the development of acute tolerance to the mu-opioid receptor agonist-induced antinociception.
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PMID:Inhibition of protein kinase C, but not of protein kinase A, blocks the development of acute antinociceptive tolerance to an intrathecally administered mu-opioid receptor agonist in the mouse. 758 70

Continuous elevation of intracellular cyclic AMP (cAMP) by culturing neuroblastoma x glioma NG108-15 hybrid cells in the presence of forskolin and isobutylmethylxanthine (IBMX) in a chemically defined medium resulted in differentiation of the hybrid cells, as indicated by extension of neurite-like structures and induction of a subclass of G-protein, Go, as monitored by Western analysis. This cellular differentiation also resulted in an initial 25 to 30% increase in [3H]diprenorphine binding 3 hr after forskolin and IBMX treatment, followed by a decrease in opioid receptor density to the maximal level of 35% of control 4 days later. However, the potencies and maximal inhibitory levels of various opioid agonists to inhibit adenylate cyclase activity was not altered during differentiation. When the differentiated hybrid cells were treated with DADLE chronically, an apparent decrease in the ability of the agonist to desensitize and to down-regulate the delta-opioid receptor was observed. It is unlikely that this observed attenuation was due to activation of cAMP-dependent protein kinase A, because (1) attenuation of DADLE desensitization was time-dependent, reaching maximal effects 48 hr after the initiation of treatment; and (2) pretreatment of NG108-15 cells with forskolin and IBMX resulted in attenuation of forskolin's ability to stimulate adenylate cyclase activity and parallel decrease in the ability of forskolin to activate the cAMP-dependent protein kinases in these cells was also observed. Thus, it is unlikely that the activation of protein kinase A by forskolin and IBMX is the cause for the attenuation of DADLE-induced delta-opioid receptor desensitization in differentiated NG108-15 cells.
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PMID:Effect of forskolin and isobutylmethylxanthine on delta-opioid receptor activity in neuroblastoma x glioma NG108-15 cells. 768 Jul 18


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