Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:3.1.3.16 (calcineurin)
17,112 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Phosphorylation of various AMPA receptor subunits can alter synaptic transmission and plasticity at excitatory glutamatergic synapses in the central nervous system. Here, we identified threonine-840 (T840) on the GluR1 subunit of AMPA receptors as a novel phosphorylation site. T840 is phosphorylated by protein kinase C (PKC) in vitro and is a highly turned-over phosphorylation site in the hippocampus. Interestingly, the high basal phosphorylation of T840 in the hippocampus is maintained by a persistent activity of a protein kinase, which is counter-balanced by a basal protein phosphatase activity. To study the function of T840, we generated a line of mutant mice lacking this phosphorylation site using a gene knock-in technique. The mice generated lack T840, in addition to two previously identified phosphorylation sites S831 and S845. Using this mouse, we demonstrate that T840 may regulate synaptic plasticity in an age-dependent manner.
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PMID:Identification and characterization of a novel phosphorylation site on the GluR1 subunit of AMPA receptors. 1768 77

Phosphorylation-dependent changes in AMPA receptor function have a crucial role in activity-dependent forms of synaptic plasticity such as long-term potentiation (LTP) and long-term depression (LTD). Although three previously identified phosphorylation sites in AMPA receptor glutamate receptor 1 (GluR1) subunits (S818, S831, and S845) appear to have important roles in LTP and LTD, little is known about the role of other putative phosphorylation sites in GluR1. Here, we describe the characterization of a recently identified phosphorylation site in GluR1 at threonine 840. The results of in vivo and in vitro phosphorylation assays suggest that T840 is not a substrate for protein kinases known to phosphorylate GluR1 at previously identified phosphorylation sites, such as protein kinase A, protein kinase C, and calcium/calmodulin-dependent kinase II. Instead, in vitro phosphorylation assays suggest that T840 is a substrate for p70S6 kinase. Although LTP-inducing patterns of synaptic stimulation had no effect on GluR1 phosphorylation at T840 in the hippocampal CA1 region, bath application of NMDA induced a strong, protein phosphatase 1- and/or 2A-mediated decrease in T840 phosphorylation. Moreover, GluR1 phosphorylation at T840 was transiently decreased by a chemical LTD induction protocol that induced a short-term depression of synaptic strength and persistently decreased by a chemical LTD induction protocol that induced a lasting depression of synaptic transmission. Together, our results show that GluR1 phosphorylation at T840 is regulated by NMDA receptor activation and suggest that decreases in GluR1 phosphorylation at T840 may have a role in LTD.
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PMID:NMDA receptor activation dephosphorylates AMPA receptor glutamate receptor 1 subunits at threonine 840. 1804 15

Neurabin is a scaffolding protein that interacts with actin and protein phosphatase-1. Highly enriched in the dendritic spine, neurabin is important for spine morphogenesis and synaptic formation. However, less is known about the role of neurabin in hippocampal plasticity and its possible effect on behavioral functions. Using neurabin knockout (KO) mice, here we studied the function of neurabin in hippocampal synaptic transmission, plasticity and behavioral memory. We demonstrated that neurabin KO mice showed a deficit in contextual fear memory but not auditory fear memory. Whole-cell patch clamp recordings in the hippocampal CA1 neurons showed that long-term potentiation (LTP) was significantly reduced, whereas long-term depression (LTD) was unaltered in neurabin KO mice. Moreover, increased AMPA receptor but not NMDA receptor-mediated synaptic transmission was found in neurabin KO mice, and is accompanied by decreased phosphorylation of GluR1 at the PKA site (Ser845) but no change at the CaMKII/PKC site (Ser831). Pre-conditioning with LTD induction rescued the following LTP in neurabin KO mice, suggesting the loss of LTP may be due to the saturated synaptic transmission. Our results indicate that neurabin regulates contextual fear memory and LTP in hippocampal CA1 pyramidal neurons.
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PMID:Neurabin contributes to hippocampal long-term potentiation and contextual fear memory. 1818 88

Phosphorylation of S880 within the GluR2 C-terminus has been reported to promote endocytosis of AMPA receptors (AMPARs) by preventing GluR2 interaction with the putative synaptic anchoring proteins GRIP and ABP. It is not yet established however, whether S880 phosphorylation induces removal of AMPARs from synaptic sites, and the trafficking of phosphorylated GluR2 subunits with surface and endocytosed GluR2 has not been directly compared within the same intact neurons. Here we show that phosphorylation of GluR2 subunits by PKC activated with phorbol esters is compartmentally restricted to receptors located at the cell surface. Endogenous AMPARs containing S880-phosphorylated GluR2 remained highly synaptic and colocalized with postsynaptic markers to the same extent as AMPARs which did not contain S880-phosphorylated GluR2. Moreover, following S880 phosphorylation, exogenous GluR2 homomers were found specifically at the cell surface and did not co-traffic with the internalized endosomal GluR2 population. We also show that GluR2 is endogenously phosphorylated by a constitutively active kinase pharmacologically related to PKC, and this phosphorylation is opposed by the protein phosphatase PP1. Our results demonstrate a population of hippocampal AMPARs which do not require interaction with GRIP/ABP for synaptic anchorage.
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PMID:Stable synaptic retention of serine-880-phosphorylated GluR2 in hippocampal neurons. 1841 60

GABAergic interneurons in prefrontal cortex (PFC) play a critical role in cortical circuits by providing feedforward and feedback inhibition and synchronizing neuronal activity. Impairments in GABAergic inhibition to PFC pyramidal neurons have been implicated in the abnormal neural synchrony and working memory disturbances in schizophrenia. The dopamine D(4) receptor, which is strongly linked to neuropsychiatric disorders, such as attention deficit-hyperactivity disorder (ADHD) and schizophrenia, is highly expressed in PFC GABAergic interneurons, while the physiological role of D(4) in these interneurons is largely unknown. In this study, we found that D(4) activation caused a persistent suppression of AMPAR-mediated synaptic transmission in PFC interneurons. This effect of D(4) receptors on AMPAR-EPSC was via a mechanism dependent on actin/myosin V motor-based transport of AMPA receptors, which was regulated by cofilin, a major actin depolymerizing factor. Moreover, we demonstrated that the major cofilin-specific phosphatase Slingshot, which was activated by calcineurin downstream of D(4) signaling, was required for the D(4) regulation of glutamatergic transmission. Thus, D(4) receptors, by using the unique calcineurin/Slingshot/cofilin signaling mechanism, regulate actin dynamics and AMPAR trafficking in PFC GABAergic interneurons. It provides a potential mechanism for D(4) receptors to control the excitatory synaptic strength in local-circuit neurons and GABAergic inhibition in the PFC network, which may underlie the role of D(4) receptors in normal cognitive processes and mental disorders.
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PMID:Dopamine D4 receptors regulate AMPA receptor trafficking and glutamatergic transmission in GABAergic interneurons of prefrontal cortex. 1914 55

The endocytosis of AMPA receptors (AMPARs) underlies several forms of synaptic plasticity, including NMDA receptor (NMDAR)-dependent long-term depression (LTD), but the molecular mechanisms responsible for this trafficking remain unknown. We found that PSD-95, a major postsynaptic density protein, is important for NMDAR-triggered endocytosis of synaptic AMPARs in rat neuron cultures because of its binding to A kinase-anchoring protein 150 (AKAP150), a scaffold for specific protein kinases and phosphatases. Knockdown of PSD-95 with shRNA blocked NMDAR-triggered, but not constitutive or mGluR-triggered, endocytosis of AMPARs. Deletion of PSD-95's Src homology 3 and guanylate kinase-like domains, as well as a point mutation (L460P), both of which inhibit binding of PSD-95 to AKAP150, also blocked NMDAR-triggered AMPAR endocytosis. Furthermore, expression of a mutant AKAP150 that does not bind calcineurin inhibited this NMDAR-triggered trafficking event. Our results suggest that PSD-95's interaction with AKAP150 is critical for NMDAR-triggered AMPAR endocytosis and LTD, possibly because these scaffolds position calcineurin in the appropriate subsynaptic domain.
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PMID:A critical role for PSD-95/AKAP interactions in endocytosis of synaptic AMPA receptors. 1916 50

A-kinase anchoring protein (AKAP) 79/150 is a scaffold protein found in dendritic spines that recruits the cAMP-dependent protein kinase (PKA) and protein phosphatase 2B-calcineurin (CaN) to membrane-associated guanylate kinase (MAGUK)-linked AMPA receptors (AMPARs) to control receptor phosphorylation and synaptic plasticity. However, AKAP79/150 may also coordinate regulation of AMPAR activity with spine structure directly through MAGUK binding and membrane-cytoskeletal interactions of its N-terminal targeting domain. In cultured hippocampal neurons, we observed that rat AKAP150 expression was low early in development but then increased coincident with spine formation and maturation. Overexpression of human AKAP79 in immature or mature neurons increased the number of dendritic filopodia and spines and enlarged spine area. However, RNA interference knockdown of AKAP150 decreased dendritic spine area only in mature neurons. Importantly, AKAP79 overexpression in immature neurons increased AMPAR postsynaptic localization and activity. Neither the AKAP79 PKA nor CaN anchoring domain was required for increasing dendritic protrusion numbers, spine area, or AMPAR synaptic localization; however, an internal region identified as the MAGUK binding domain was found to be essential as shown by expression of a MAGUK binding mutant that formed mainly filopodia and decreased AMPAR synaptic localization and activity. Expression of the AKAP79 N-terminal targeting domain alone also increased filopodia numbers but not spine area. Overall, these results demonstrate a novel structural role for AKAP79/150 in which the N-terminal targeting domain induces dendritic filopodia and binding to MAGUKs promotes spine enlargement and AMPAR recruitment.
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PMID:Regulation of postsynaptic structure and function by an A-kinase anchoring protein-membrane-associated guanylate kinase scaffolding complex. 1953 4

Dopamine-releasing neurons of the substantia nigra pars compacta produce an extraordinarily dense and expansive plexus of innervation in the striatum converging with glutamatergic corticostriatal and thalamostriatal axon terminals at dendritic spines of medium spiny neurons. Here, we investigated whether glutamatergic signaling promotes arborization and growth of dopaminergic axons. In postnatal ventral midbrain cultures, dopaminergic axons rapidly responded to glutamate stimulation with accelerated growth and growth cone splitting when NMDA and AMPA/kainate receptors were activated. In contrast, when AMPA/kainate receptors were selectively activated, axon growth rate was decreased. To address whether this switch in axonal growth response was mediated by distinct calcium signals, we used calcium imaging. Combined NMDA and AMPA/kainate receptor activation elicited calcium signals in axonal growth cones that were mediated by calcium influx through L-type voltage-gated calcium channels and ryanodine receptor-induced calcium release from intracellular stores. AMPA/kainate receptor activation alone elicited calcium signals that were solely attributable to calcium influx through L-type calcium channels. We found that inhibitors of calcium/calmodulin-dependent protein kinases prevented the NMDA receptor-dependent axonal growth acceleration, whereas AMPA/kainate-induced axonal growth decrease was blocked by inhibitors of calcineurin and by increased cAMP levels. Our data suggest that the balance between NMDA and AMPA/kainate receptor activation regulates the axonal arborization pattern of dopamine axons through the activation of competing calcium-dependent signaling pathways. Understanding the mechanisms of dopaminergic axonal arborization is essential to the development of treatments that aim to restore dopaminergic innervation in Parkinson's disease.
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PMID:Glutamate controls growth rate and branching of dopaminergic axons. 1977 83

The contribution of the NMDA receptors (NMDARs) to synaptic plasticity declines during aging, and the decline is thought to contribute to memory deficits. Here, we demonstrate that an age-related shift in intracellular redox state contributes to the decline in NMDAR responses through Ca(2+)/calmodulin-dependent protein kinase II (CaMKII). The oxidizing agent xanthine/xanthine oxidase (X/XO) decreased the NMDAR-mediated synaptic responses at hippocampal CA3-CA1 synapses in slices from young (3-8 months) but not aged (20-25 months) rats. Conversely, the reducing agent dithiothreitol (DTT) selectively enhanced NMDAR response to a greater extent in aged hippocampal slices. The enhancement of NMDAR responses facilitated induction of long-term potentiation in aged but not young animals. The DTT-mediated growth in the NMDAR response was not observed for the AMPA receptor-mediated synaptic responses. A similar increase was observed by intracellular application of the membrane-impermeable reducing agent, L-glutathione (L-GSH), through the intracellular recording pipette, indicating that the increased NMDAR response was dependent on intracellular redox state. DTT enhancement of the NMDAR response was dependent on CaMKII activity and was blocked by the CaMKII inhibitor--myristoylated autocamtide-2-related inhibitory peptide (myr-AIP)--but not by inhibition of the activity of protein phosphatases--PP1 and calcineurin (CaN/PP2B) or protein kinase C. CaMKII activity assays established that DTT increased CaMKII activity in CA1 cytosolic extracts in aged but not in young animals. These findings indicate a link between oxidation of CaMKII during aging, a decline in NMDAR responses, and altered synaptic plasticity.
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PMID:Intracellular redox state alters NMDA receptor response during aging through Ca2+/calmodulin-dependent protein kinase II. 2013 Feb

The initial reports regarding a cytotoxic role of calcium ions were published over 30 years ago. In neurons, calcium ions can gain entry into the cell through several mechanisms. These include the over-activation of glutamate receptors (NMDA, AMPA, KA) or of a range of channels and transporters (TRPM2, TRPM7, NCX, ASICs, CaV1.2, and hemichannels). Potentially toxic cytoplasmic calcium concentrations can also occur due to release from internal stores, either through physical damage to mitochondria and the endoplasmic reticulum, or a malfunction of receptors and channels present in their membranes. Such increases of cytoplasmic calcium concentrations can trigger a range of downstream neurotoxic cascades, including the uncoupling mitochondrial electron transfer from ATP synthesis, and the activation and overstimulation of enzymes such as calpains and other proteases, protein kinases, nitric oxide synthase (NOS), calcineurin and endonucleases. Despite the toxic role of calcium, drugs designed to block its entry into neurons have all failed to have any beneficial effects in clinical trials. We suggest that blocking certain receptors and ion channels is unlikely to be a useful therapeutic strategy due to potential deleterious side effects. However, identifying those that are most responsible for cell death and their downstream signalling pathways may lead to improved strategies for treating ischemic and excitotoxic disorders.
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PMID:Calcium, ischemia and excitotoxicity. 2016 68


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