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)

Previous studies have found that ethanol (EtOH) will consistently potentiate gamma-aminobutyric acid (GABA) receptor function in the cerebellum during beta adrenergic receptor activation. One consequence of beta adrenergic receptor stimulation is to increase cAMP levels, which, in turn, activate protein kinase A (PKA)-mediated phosphorylation of intracellular protein sites. In the present study, we investigated three cAMP analogues, two activators and one inhibitor of PKA to determine whether this cAMP-mediated second-messenger system may be one mechanism involved in the previously observed beta adrenergic interaction of EtOH with the GABA(A) receptor. Furthermore, because the phosphorylation state of the GABA(A) receptor may be an important determinant of function, we investigated the effect of the block of phosphatase activity on EtOH/GABA receptor interactions. We found that similar to the beta adrenergic agonist isoproterenol, local applications of the membrane-permeable cAMP analogues 8-bromo-cAMP and Sp-cAMP could modulate responses to iontophoretically applied GABA and that these modulated GABA responses were sensitized to the potentiative effects of EtOH. EtOH did not facilitate unmodulated GABA effects or GABA responses that were maximally modulated by 8-bromo-cAMP, suggesting that the cAMP mechanism mediates the observed EtOH interaction with GABA mechanisms. Furthermore, the PKA inhibitor Rp-cAMP reversed the EtOH-induced potentiation of the isoproterenol-modulated GABA responses. Finally, microcystin-LR and okadaic acid, which are type I and IIa phosphatase inhibitors, could also modulate and sensitize GABA responses to EtOH. These data suggest that beta adrenergic sensitization of GABA(A) receptors to EtOH involves the intracellular cAMP/PKA second-messenger cascade.
 ...
PMID:Beta adrenergic sensitization of gamma-aminobutyric acid receptors to ethanol involves a cyclic AMP/protein kinase A second-messenger mechanism. 906 3

Cholinergic interneurons have been implicated in striatally mediated associative learning. In classical conditioning paradigms, conditioned stimuli trigger a transient suppression of neuronal activity that is dependent upon an intact dopaminergic innervation. Our hypothesis was that this suppression reflected dopaminergic enhancement of sensory-linked GABAergic input. As a test, the impact of dopamine on interneuronal GABA(A) receptor function was studied by combined patch-clamp recording and single-cell reverse transcription PCR. Activation of D5 dopamine receptors reversibly enhanced a Zn2+-sensitive component of GABA(A) currents. Although dependent upon protein kinase A (PKA) activation, the modulation was blocked by protein phosphatase 1 (PP1) inhibition, suggesting it was dependent upon dephosphorylation. These results establish a novel mechanism by which intrastriatally released dopamine mediates changes in GABAergic signaling that could underlie the initial stages of associative learning.
 ...
PMID:D5 dopamine receptors enhance Zn2+-sensitive GABA(A) currents in striatal cholinergic interneurons through a PKA/PP1 cascade. 939 May 24

All mammalian GABA(A) receptor beta subunits contain a conserved consensus site for phosphorylation by a number of serine/threonine protein kinases. This site corresponds to Serine 410 of the beta2 subunit and Serine 409 of the beta3 subunit, each of which lies within the conserved sequence R-R-R-X-S-L-Q-K, where X = A (beta1, beta2 and beta4) or S (beta3). We have analysed the phosphorylation of the beta2 and beta3 subunits of the murine GABA(A) receptor by expressing the large intracellular domains of these subunits as soluble fusion proteins in E. coli. The intracellular domain of the beta2 subunit was phosphorylated to high stoichiometry by both cAMP- and cGMP-dependent protein kinases, protein kinase C and Ca2+/calmodulin type II-dependent protein kinase in vitro. Site-directed mutagenesis identified Serine 410 as the single site within the beta2 subunit phosphorylated by these four protein kinases. Using similar methodologies, Serine 409 of the beta3 subunit was shown to be a substrate for phosphorylation by these protein kinases. Serine 408 was also seen to be phosphorylated by protein kinase C and Serine 383 was phosphorylated by Ca2+/calmodulin type II-dependent protein kinase. Since beta subunits are believed to be essential for robust GABA(A) receptor expression, these results suggest a critical role for conserved phosphorylated amino acids within the beta subunits in coordinating cellular regulation of GABA(A) receptors via multiple protein kinases.
 ...
PMID:Conserved phosphorylation of the intracellular domains of GABA(A) receptor beta2 and beta3 subunits by cAMP-dependent protein kinase, cGMP-dependent protein kinase protein kinase C and Ca2+/calmodulin type II-dependent protein kinase. 942 25

The effect of calcium-phospholipid-dependent protein kinase (PKC) activation on neurosteroid modulation of the GABA(A) receptor was examined in Xenopus oocytes expressing human recombinant alpha1beta2gamma2L GABA(A) receptors. GABA-gated chloride currents were measured using the two-electrode voltage-clamp technique. The peak amplitude of GABA-gated chloride currents was reduced by the PKC activator phorbol 12-myristate 13-acetate (PMA), but not by the inactive analog phorbol 12-mono-myristate (PMM). This effect of PMA was inhibited by the protein kinase inhibitor staurosporine. To investigate whether the activation of PKC could alter neurosteroid modulation of the GABA(A) receptor, the effect of PMA was studied on the positive allosteric modulatory steroid 3alpha,21-dihydroxy-5alpha-pregnan-20-one (THDOC) and the negative modulatory neurosteroid pregnenolone sulfate (PS). THDOC potentiation of GABA-gated chloride currents was found to be increased by approximately 120% following PMA treatment, while PS inhibition was not affected. The increase in THDOC potentiation by PMA was blocked by staurosporine. No change in THDOC potentiation was observed following PMM treatment. The enhancement of THDOC potentiation following PMA treatment was not due to a shift in the GABA EC50. In addition to inhibiting the peak amplitude of the GABA response, PMA treatment resulted in non-desensitizing GABA responses. Similarly, GABA responses of receptors which had been desensitized with prolonged GABA application also showed a reduction in peak amplitude and reduced desensitization. THDOC potentiation of desensitized receptors was enhanced approximately 70% with respect to non-desensitized receptors. The present results demonstrate that protein phosphorylation and receptor desensitization alter modulation of the GABA(A) receptor complex by some neurosteroids.
 ...
PMID:Effects of PKC activation and receptor desensitization on neurosteroid modulation of GABA(A) receptors. 949 38

The role of protein kinase A (PKA) and protein kinase C (PKC) in the function and modulation by mercury chloride of the GABA(A) receptor-chloride channel complex was studied with rat dorsal root ganglion cells using the whole-cell patch clamp technique. When added to the internal pipette solutions, both KT 5720, a selective PKA inhibitor, and calphostin C, a selective PKC inhibitor, increased the maximal current and shifted the EC50 for GABA in the direction of higher GABA concentrations. GABA-activated currents were decreased by the addition of 5 mM cAMP to the internal pipette solution, and by external perfusion of 100 nM phorbol 13-myristate 13-acetate. Mercury chloride potentiation of GABA-activated currents was blocked by internal application of 5 mM cAMP. PKA in the recording pipette abolished the mercury chloride potentiation of GABA-activated currents. In contrast, 0.56 microM KT 5720, but not calphostin C, in the internal pipette solution enhanced the effect of mercury chloride. In conclusion, both PKA and PKC negatively regulate the activity of the GABA(A) receptor-channel complex probably through phosphorylation of the receptor, and the PKA system underlies the mechanism of mercury chloride potentiation of GABA-activated currents.
 ...
PMID:The role of phosphorylation in the activity and mercury modulation of GABA-induced currents in rat neurons. 951 34

The studies discussed in this review demonstrate that phosphorylation is an important mechanism for the regulation of ligand-gated ion channels. Structurally, ligand-gated ion channels are heteromeric proteins comprised of homologous subunits. For both the AChR and the GABA(A) receptor, each subunit has a large extracellular N-terminal domain, four transmembrane domains, a large intracellular loop between transmembrane domains M3 and M4, and an extracellular C-terminal domain (Fig. 1B). All the phosphorylation sites on these receptors have been mapped to the major intracellular loop between M3 and M4 (Table 1). In contrast, glutamate receptors appear to have a very large extracellular N-terminal domain, one membrane hairpin loop, three transmembrane domains, a large extracellular loop between transmembrane domains M3 and M4, and an intracellular C-terminal domain (Fig. 1C). Most phosphorylation sites on glutamate receptors have been shown to be on the intracellular C-terminal domain, although some have been suggested to be on the putative extracellular loop between M3 and M4 (Table 1). A variety of extracellular factors and intracellular signal transduction cascades are involved in regulating phosphorylation of these ligand-gated ion channels (Fig. 2). Once again, the AChR at the neuromuscular junction is the most fully understood system. Phosphorylation of the AChR by PKA is stimulated synaptically by the neuropeptide CGRP and in an autocrine fashion by adenosine released from the muscle in response to acetylcholine. In addition, acetylcholine, via calcium influx through the AChR, appears to activate calcium-dependent kinases including PKC to stimulate serine phosphorylation of the receptor. Presently, agrin is the only extracellular factor known to stimulate phosphorylation of the AChR on tyrosine residues. For glutamate receptors, non-NMDA receptor phosphorylation by PKA is stimulated by dopamine, while NMDA receptor phosphorylation by PKA and PKC can be induced via the activation of beta-adrenergic receptors, and metabotropic glutamate or opioid receptors, respectively. In addition, Ca2+ influx through the NMDA receptor has been shown to activate PKC. CaMKII, and calcineurin, resulting in phosphorylation of AMPA receptors (by CaMKII) and inactivation of NMDA receptors (at least in part through calcineurin). In contrast to the AChR and glutamate receptors, no information is presently available regarding the identities of the extracellular factors and intracellular signal transduction cascades that regulate phosphorylation of the GABA(A) receptor. Surely, future studies will be aimed at further clarifying the molecular mechanisms by which the central receptors are regulated. The presently understood functional effects of ligand-gated ion channel phosphorylation are diverse. At the neuromuscular junction, a regulation of the AChR desensitization rate by both serine and tyrosine phosphorylation has been demonstrated. In addition, tyrosine phosphorylation of the AChR or other synaptic components appears to play a role in AChR clustering during synaptogenesis. For the GABA(A) receptor, the data are complex. Both activation and inhibition of GABA(A) receptor currents as a result of PKA and PKC phosphorylation have been reported, while phosphorylation by PTK enhances function. The predominant effect of glutamate receptor phosphorylation by a variety of kinases is a potentiation of the peak current response. However, PKC also modulates clustering of NMDA receptors. This complexity in the regulation of ligand-gated ion channels by phosphorylation provides diverse mechanisms for mediating synaptic plasticity. In fact, accumulating evidence supports the involvement of protein phosphorylation and dephosphorylation of AMPA receptors in LTP and LTD respectively. There has been a dramatic increase in our understanding of the nature by which phosphorylation regulates ligand-gated ion channels. However, many questions remain unanswered. (AB
 ...
PMID:Regulation of ligand-gated ion channels by protein phosphorylation. 1021 14

Tuning of gamma-aminobutyric acid type A (GABA(A)) receptor function via phosphorylation of the receptor potentially allows neurons to modulate their inhibitory input. Several kinases, both of the serine-threonine kinase and the tyrosine kinase families, have been proposed as candidates for such a modulatory role in vivo. However, no GABA(A) receptor-phosphorylating kinase physically associated with the receptor has been identified so far on a molecular level. In this study, we demonstrate a GABA(A) receptor-associated protein serine kinase phosphorylating specifically beta3-subunits of native GABA(A) receptors. The characteristics of this novel kinase clearly distinguish it from enzymatic activities that have been shown so far to phosphorylate the GABA(A) receptor. We putatively identify this protein kinase as the previously described GTAP34 (GABA(A) receptor-tubulin complex-associated protein of molecular mass 34 kDa). Using expressed recombinant fusion proteins, we identify serine 408 as a major target of the phosphorylation reaction, whereas serine 407 is not phosphorylated. This demonstrates the high specificity of the kinase. Phosphorylation of serine 408 is known to result in a decreased receptor function. The direct association of this kinase with the receptor indicates an important physiological role.
 ...
PMID:A novel serine kinase with specificity for beta3-subunits is tightly associated with GABA(A) receptors. 1040 83

The effect of Waglerin-1, a 22-amino acid peptide purified from the venom of Wagler's pit viper on the whole cell current response (I(GABA)) to gamma-aminobutyric acid (GABA) was examined for neurons freshly isolated from the nucleus accumbens of 3- to 7-day-old rats. Waglerin-1 depressed I(GABA) induced by subsaturating concentrations of GABA; the IC(50) for I(GABA) induced by 10 microM GABA was 2.5 microM Waglerin-1. This concentration of Waglerin-1 shifted the GABA concentration-response curve to the right in a parallel manner, increasing the GABA EC(50) from 12+/-3 to 27+/-5 microM. The depressant effect of Waglerin-1 was greater at negative holding potentials. Zn(2+) also inhibited I(GABA) with an IC(50) of 0.3 microM. Phosphorylation state appeared to modulate GABA(A) receptor sensitivity to the inhibitory effect of Waglerin-1 since dialysis of neurons with N-[2-((p-bromocinnamyl)amino)ethyl]-5-isoquinolinesulfonamide HCl (H-89), an inhibitor of protein kinase A, prevented inhibition. The data are discussed in terms of developmental influences on the subunit composition of GABA(A) receptors in neurons of the nucleus accumbens.
 ...
PMID:Waglerin-1 inhibits GABA(A) current of neurons in the nucleus accumbens of neonatal rats. 1043 85

Interaction between GABAA and GABA(B) receptors was studied in rat cerebellar granule cells in culture, by the whole-cell patch-clamp approach. Our data show that the GABA(B) agonist (-)baclofen is not able, per se, to significantly change the muscimol-activated chloride current. However, (-)baclofen dose-dependently prevents the reduction of GABA(A) receptor function by forskolin, an activator of adenylate cyclase. The effect of baclofen is mediated by a pertussis toxin-sensitive G protein. In fact, in cells treated with pertussis toxin, baclofen and forskolin, the toxin is able to block baclofen action, allowing forskolin to act fully. The protective effect by GABA(B) receptor activation under these circumstances is most probably related to the prevention of cyclic AMP increases after forskolin treatment. In fact, in these neurons cyclic AMP and protein kinase A activation result in a down-regulation of GABA(A) receptor function. On the whole, the data indicate the presence of complex modulation of GABA(A) receptors by GABA(B) receptor types in cerebellum granule cells.
 ...
PMID:GABA(B) receptor activation protects GABA(A) receptor from cyclic AMP-dependent down-regulation in rat cerebellar granule cells. 1047 72

The GABA(A) receptor and the non-NMDA subtype of the ionotropic glutamate receptor were co-expressed in Xenopus oocytes by injection of quail brain mRNA. The oocytes were treated with various protein kinase (PK) and protein phosphatase (PP) activators and inhibitors and the effects on receptor functioning were monitored. Two phorbol esters, 4-beta-phorbol 12-myristate-13-acetate (PMA) and 4-beta-phorbol 12,13-dibutyrate (PDBu); the cGMP-dependent PK activators sodium nitroprusside (SNP) and S-nitrosoglutathione (SNOG); and the PP inhibitor okadaic acid (OA) reduced the amplitude of the GABA-induced currents, whilst the PK inhibitor staurosporine potentiated it. In addition, PMA, PDBu, SNP, and OA reduced the desensitization of the GABA-induced response. Identical treatments generally had similar but less pronounced effects on responses generated by kainate (KA) but the desensitization characteristic of the non-NMDA receptor was not affected. None of the treatments had any effect on the reversal potentials of the induced currents. Immunoblots revealed that the oocytes express endogenous PKG and guanylate cyclase. The results are discussed in terms of the molecular structures of GABA(A) and non-NMDA receptors and the potential functional consequences of phosphorylation/dephosphorylation.
 ...
PMID:Protein kinase and phosphatase modulation of quail brain GABA(A) and non-NMDA receptors co-expressed in Xenopus oocytes. 1067 79


1 2 3 4 5 6 7 8 Next >>