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)

Several studies have suggested that the function of glutamate receptor channels can be regulated by protein phosphorylation. Furthermore, a basal level of phosphorylation may be necessary to maintain receptor function. Little is known, however, about the phosphorylation state of glutamate receptor channels in neurons and how it is regulated by synaptic activity. In this study, we have investigated the phosphorylation of the AMPA-preferring glutamate receptor subunit GluR1 in cortical neurons in primary culture. These neurons elaborate extensive processes, form functional synapses, and exhibit spontaneous 4-8 sec bursts of synaptic activity every 15-20 sec. In cultures in which this synaptic activity was suppressed by tetrodotoxin and MK-801, the GluR1 protein was phosphorylated on serine residues within a single tryptic phosphopeptide, as determined by phosphoamino acid analysis and phosphopeptide mapping. This same peptide was basally phosphorylated in recombinant GluR1 receptors transiently expressed in human embryonal kidney 293 cells. Treatment of these synaptically inactive cortical neurons with the adenylyl cyclase activator forskolin resulted in a robust increase in phosphorylation on serine residues on a phosphopeptide distinct from the basally phosphorylated peptide. Again, this same phosphopeptide was observed in recombinant GluR1 receptors isolated from 293 cells coexpressing the catalytic subunit of cAMP-dependent protein kinase. Spontaneous synaptic activity in cultures of cortical neurons resulted in a consistent, rapid (within 10-30 sec) increase in phosphorylation on serine and threonine residues. Interestingly, these phosphopeptides were also phosphorylated when neurons from inactive cultures were stimulated with phorbol esters, which activate protein kinase C. These results indicate that AMPA receptors containing the GluR1 subunit may be regulated by extracellular signals working through the cAMP second messenger system as well as by synaptic activity, possibly acting through protein kinase C. Such regulation by protein phosphorylation may be involved in short-term changes in synaptic efficacy thought to involve the functional modulation of AMPA receptors.
 ...
PMID:Cyclic AMP and synaptic activity-dependent phosphorylation of AMPA-preferring glutamate receptors. 752 45

Glutamate receptors are the major excitatory neurotransmitter receptors in the central nervous system. A variety of data has recently suggested that protein phosphorylation of glutamate receptors regulates their function. To examine at a molecular level the role of protein phosphorylation in the modification of glutamate receptors, we have transiently expressed the non-NMDA glutamate receptor subunit GluR1 (flop) in human embryonic kidney 293 cells. Using a polyclonal antipeptide antiserum directed specifically against GluR1, we have immunoprecipitated a 106 kDa phosphoprotein corresponding to the GluR1 subunit. Phosphoamino acid analysis and thermolytic peptide mapping demonstrate that this basal phosphorylation occurs exclusively on serine residues in two phosphopeptides. Application of activators of endogenous cAMP-dependent protein kinase or protein kinase C revealed no consistent changes in the phosphorylation of GluR1. However, co-expression of the GluR1 subunit with the well characterized protein tyrosine kinase v-src results in phosphorylation of GluR1 on tyrosine residues, in a single thermolytic phosphopeptide. These results suggest that GluR1 may be a substrate for protein serine/threonine kinases as well as protein tyrosine kinases in the central nervous system.
 ...
PMID:Phosphorylation of recombinant non-NMDA glutamate receptors on serine and tyrosine residues. 768 38

We have characterized the phosphorylation of the glutamate receptor subunit GluR1, using biochemical and electrophysiological techniques. GluR1 is phosphorylated on multiple sites that are all located on the C-terminus of the protein. Cyclic AMP-dependent protein kinase specifically phosphorylates SER-845 of GluR1 in transfected HEK cells and in neurons in culture. Phosphorylation of this residue results in a 40% potentiation of the peak current through GluR1 homomeric channels. In addition, protein kinase C specifically phosphorylates Ser-831 of GluR1 in HEK-293 cells and in cultured neurons. These results are consistent with the recently proposed transmembrane topology models of glutamate receptors, in which the C-terminus is intracellular. In addition, the modulation of GluR1 by PKA phosphorylation of Ser-845 suggests that phosphorylation of this residue may underlie the PKA-induced potentiation of AMPA receptors in neurons.
 ...
PMID:Characterization of multiple phosphorylation sites on the AMPA receptor GluR1 subunit. 866 94

The PICK1 protein interacts in neurons with the AMPA-type glutamate receptor subunit 2 (GluR2) and with several other membrane receptors via its single PDZ domain. We show that PICK1 also binds in neurons and in heterologous cells to protein kinase Calpha (PKCalpha) and that the interaction is highly dependent on the activation of the kinase. The formation of PICK1-PKCalpha complexes is strongly induced by TPA, and PICK1-PKCalpha complexes are cotargeted with PICK1-GluR2 complexes to spines, where GluR2 is found to be phosphorylated by PKC on serine 880. PICK1 also reduces the plasma membrane levels of the GluR2 subunit, consistent with a targeting function of PICK1 and a PKC-facilitated release of GluR2 from the synaptic anchoring proteins ABP and GRIP. This work indicates that PICK1 functions as a targeting and transport protein that directs the activated form of PKCalpha to GluR2 in spines, leading to the activity-dependent release of GluR2 from synaptic anchor proteins and the PICK1-dependent transport of GluR2 from the synaptic membrane.
 ...
PMID:PICK1 targets activated protein kinase Calpha to AMPA receptor clusters in spines of hippocampal neurons and reduces surface levels of the AMPA-type glutamate receptor subunit 2. 1146 13

Sodium-dependent transporters clear extracellular glutamate in the mammalian CNS. Activation of protein kinase C (PKC) rapidly increases the activity of the neuronal glutamate transporter EAAC1 (excitatory amino acid carrier-1). This effect is associated with redistribution of EAAC1 to the cell membrane and appears to be dependent on a particular PKC subtype, PKCalpha. In the present study, we sought to determine whether this specificity for regulation of EAAC1 is associated with the formation of EAAC1-PKCalpha complexes. In C6 glioma cells, activation of PKC with phorbol 12-myristate 13-acetate (PMA) induced formation of EAAC1-PKCalpha complexes but did not induce formation of complexes with PKCdelta, a PKC not thought to regulate EAAC1. Formation of these complexes was blocked by inhibitors of PKC. Confocal microscopy revealed that PMA caused EAAC1 and PKCalpha to colocalize in clusters at or near the cell surface. The EAAC1-PKCalpha complexes were also observed in rat brain synaptosomes, demonstrating that this interaction is not restricted to C6 cells. These data demonstrate that EAAC1 and PKCalpha interact in a PKC-dependent manner that is associated with EAAC1 redistribution. Although PKC activation has been implicated in the regulation of many different neurotransmitter transporters, this study provides the first example of an interaction between a neurotransmitter transporter and PKC. PKCalpha also forms complexes with GluR2 (glutamate receptor subunit 2) and causes a reduction in the levels of GluR2-containing AMPA receptors at the plasma membrane. Together, these data suggest that PKCalpha may simultaneously trigger the redistribution of EAAC1 and glutamate receptors.
 ...
PMID:Phorbol myristate acetate-dependent interaction of protein kinase Calpha and the neuronal glutamate transporter EAAC1. 1284 60

The retinal rod bipolar cell type is involved in the sign-inverting depolarizing ON-type response to light. This response is mediated by the metabotropic glutamate receptor type 6 (mGluR6) expressed on the rod bipolar dendrites. In a previous immunocytochemical study, an unexpected colocalization was reported [W. Kamphuis et al. (2003) J. Comp. Neurol., 455, 172-186] of mGluR6 with the ionotropic AMPA-type glutamate receptor subunit GluR2 in rod bipolar cells of rat retina. The aim of the present study was to investigate whether expression of both genes could be found at the single-cell level. Two approaches were followed. (i). Retinal cells were isolated by enzymatic and mechanical treatment. Single cells with a bipolar morphology were harvested, subjected to multiplex PCR with protein kinase C (PKC)-, mGluR6- and GluR1-4-specific primers, followed by a real-time quantitative PCR assay. Of 23 studied cells, 74% expressed PKC and 87% expressed mGluR6. Using the presence of both transcripts as the criterion for a rod bipolar cell signature (n = 15), 73% of these cells expressed GluR2, with a minor contribution of GluR1 (20%), GluR3 (7%), and GluR4 (20%). Quantification of the transcript levels demonstrated that mGluR6 and GluR2 genes are expressed at similar levels in rod ON-type bipolar cells. (ii). Rod bipolar cells were identified in retinal sections by immunolabelling with a protein kinase C antibody and isolated using laser pressure catapulting (LPC). Quantitative PCR was employed to assess gene expression levels of reference genes, PKCalpha, mGluR6 and the GluR subunits. However, in samples from PKCalpha-immunopositive somata no significant enrichment of PKCalpha transcript levels was observed when compared with control samples from immunonegative somata. We conclude that this approach lacks sufficient spatial specificity. In conclusion, the results show coexpression of mGluR6 and GluR2 in rod bipolar cells; this is in good agreement with the results of previous immunocytochemical studies. The functional implications of AMPA-type glutamate receptors for ON-type rod bipolar-mediated signal transduction remains to be elucidated.
 ...
PMID:Gene expression of AMPA-type glutamate receptor subunits in rod-type ON bipolar cells of rat retina. 1295 8

Phorbol esters, such as tetradecanoylphorbol 13-acetate (TPA), have been used extensively in studies of cerebellar long-term depression (LTD), based on the hypothesis that activated protein kinase C (PKC) directly mediates alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor phosphorylation. Here, we show that TPA-induced depression of synaptic transmission between granule cells and Purkinje cells in culture is mediated through activation of the MEK1/2-ERK1/2 pathway. Phosphorylation of ERK1/2 induced by TPA and co-application of high potassium and glutamate was greatly attenuated by preincubating Purkinje cells with the MEK1/2 (MAPK ERK kinase 1/2) inhibitor PD98059. TPA-induced depression of synaptic transmission between granule cells and Purkinje cells was attenuated by PD98059. The MEK1/2 inhibitor also suppressed declustering of the ionotropic glutamate receptor subunit 2/3 (GluR2/3) induced by TPA and co-application of high potassium and glutamate, even though phosphorylation of Ser880 of GluR2/3 was not inhibited significantly in the presence of PD98059. These results suggest that ERK1/2 plays an essential role in TPA-induced depression via regulation of GluR2/3 declustering at the synapse.
 ...
PMID:ERKs regulate PKC-dependent synaptic depression and declustering of glutamate receptors in cerebellar Purkinje cells. 1452 24

The cytoplasmic C termini of AMPA receptor subunits contain PDZ (postsynaptic density 95/Discs large/zona occludens 1) ligand domains that can control their synaptic trafficking during plasticity. The glutamate receptor subunit 2 (GluR2) PDZ ligand domain can be phosphorylated at serine 880 (S880), and this disrupts interactions with GRIP/ABP (glutamate receptor-interacting protein/AMPA-binding protein) but not with PICK1 (PKC-interacting protein 1). Here, the impact of GluR2 S880 phosphorylation on synaptic transmission and plasticity was explored by expressing, in hippocampal slice cultures, GluR2 subunits containing point mutations that mimic or prevent phosphorylation at this residue. Our results indicate that mimicking GluR2 S880 phosphorylation excludes these receptors from synapses, depresses transmission, and partially occludes long-term depression (LTD). Conversely, mutations that prevent phosphorylation reduce LTD. Disruption of the interaction between GluR2 and GRIP/ABP by S880 phosphorylation may thus facilitate removal of synaptic AMPA receptors and mediate some forms of activity-dependent synaptic depression.
 ...
PMID:Glutamate receptor subunit 2 Serine 880 phosphorylation modulates synaptic transmission and mediates plasticity in CA1 pyramidal cells. 1453 56

The induction of long-term depression (LTD) can be divided into two main forms, one dependent upon activation of postsynaptic NMDAR, and another independent of postsynaptic NMDAR. Non-postsynaptic NMDAR-LTD (non-NMDAR-LTD) occurs in many regions of the brain, and encompasses a wide variety of induction and expression mechanisms. In this article, the induction and expression mechanisms of such LTD in over 10 brain regions are described, with a number of common mechanisms compared across a large range of types of LTD. The article describes the involvement of different presynaptic or postsynaptic receptors in the induction of non-NMDAR-LTD, especially metabotropic glutamate receptors, cannabinoid receptors and dopamine receptors. An increase in presynaptic or postsynaptic intracellular Ca concentration is a key event in induction, commonly followed by activation of certain kinases, especially PKC, p38 MAPK and ERK. Expression mechanisms are either presynaptic via a reduction in release probability, or postsynaptic involving a decrease in AMPAR via phosphorylation of a glutamate receptor subunit, especially GluR2, followed by clathrin-mediated endocytosis. Retrograde signalling from postsynaptic to presynaptic occurs when induction is postsynaptic and expression is presynaptic.
 ...
PMID:Induction and expression mechanisms of postsynaptic NMDA receptor-independent homosynaptic long-term depression. 1642 42

Regulated AMPA receptor (AMPAR) trafficking at excitatory synapses is a mechanism critical to activity-dependent alterations in synaptic efficacy. The role of regulated AMPAR trafficking in insult-induced synaptic remodeling and/or cell death is, however, as yet unclear. Here we show that brief oxygen-glucose deprivation (OGD), an in vitro model of brain ischemia, promotes redistribution of AMPARs at synapses of hippocampal neurons, leading to a switch in AMPAR subunit composition. Ischemic insults promote internalization of glutamate receptor subunit 2 (GluR2)-containing AMPARs from synaptic sites via clathrin-dependent endocytosis and facilitate delivery of GluR2-lacking AMPARs to synaptic sites via soluble N-ethylmaleimide-sensitive factor attachment protein receptor-dependent exocytosis, evident at early times after insult. The OGD-induced switch in receptor subunit composition requires PKC activation, dissociation of GluR2 from AMPA receptor-binding protein, and association with protein interacting with C kinase-1. We further show that AMPARs at synapses of insulted neurons exhibit functional properties of GluR2-lacking AMPARs. AMPAR-mediated miniature EPSCs exhibit increased amplitudes and enhanced sensitivity to subunit-specific blockers of GluR2-lacking AMPARs, evident at 24 h after ischemia. The OGD-induced alterations in synaptic AMPA currents require clathrin-mediated receptor endocytosis and PKC activation. Thus, ischemic insults promote targeting of GluR2-lacking AMPARs to synapses of hippocampal neurons, mechanisms that may be relevant to ischemia-induced synaptic remodeling and/or neuronal death.
 ...
PMID:Ischemic insults direct glutamate receptor subunit 2-lacking AMPA receptors to synaptic sites. 1670 83


1 2 Next >>