RESUMEN
AMPA-type glutamate receptors (AMPARs) mediate fast excitatory neurotransmission in the mammalian central nervous system. Preferential AMPAR subunit assembly favors heteromeric GluA1/GluA2 complexes. The presence of the GluA2 subunit generates Ca2+-impermeable (CI) AMPARs that have linear current-voltage (I-V) relationships. However, diverse forms of synaptic plasticity and pathophysiological conditions are associated with shifts from CI to inwardly rectifying, GluA2-lacking, Ca2+-permeable (CP) AMPARs on time scales ranging from minutes to days. These shifts have been linked to GluA1 phosphorylation at Ser-845, a protein kinase A (PKA)-targeted site within its intracellular C-terminal tail, often in conjunction with protein kinase A anchoring protein 79 (AKAP79; AKAP150 in rodents), which targets PKA to GluA1. However, AKAP79 may impact GluA1 phosphorylation at other sites by interacting with other signaling enzymes. Here, we evaluated the ability of AKAP79, its signaling components, and GluA1 phosphorylation sites to induce CP-AMPARs under conditions in which CI-AMPARs normally predominate. We found that GluA1 phosphorylation at Ser-831 is sufficient for the appearance of CP-AMPARs and that AKAP79-anchored protein kinase C (PKC) primarily drives the appearance of these receptors via this site. In contrast, other AKAP79-signaling components and C-terminal tail GluA1 phosphorylation sites exhibited a permissive role, limiting the extent to which AKAP79 promotes CP-AMPARs. This may reflect the need for these sites to undergo active phosphorylation/dephosphorylation cycles that control their residency within distinct subcellular compartments. These findings suggest that AKAP79, by orchestrating phosphorylation, represents a key to a GluA1 phosphorylation passcode, which allows the GluA1 subunit to escape GluA2 dominance and promote the appearance of CP-AMPARs.
Asunto(s)
Proteínas de Anclaje a la Quinasa A/metabolismo , Proteína Quinasa C/metabolismo , Receptores AMPA/metabolismo , Transducción de Señal , Proteínas de Anclaje a la Quinasa A/genética , Células HEK293 , Humanos , Fosforilación , Proteína Quinasa C/genética , Receptores AMPA/genéticaRESUMEN
Some forms of long-term synaptic plasticity require docking of Ca2+/calmodulin-dependent protein kinase II α (CaMKIIα) to residues 1290-1309 within the intracellular C-terminal tail of the N-methyl-d-aspartate (NMDA) receptor GluN2B subunit. The phosphorylation of Ser1303 within this region destabilizes CaMKII binding. Interestingly, Ser1303 is a substrate for CaMKII itself, as well as PKC and DAPK1, but these kinases have been reported to have contradictory effects on the activity of GluN2B-containing NMDA receptors. Here, we re-assessed the effect of CaMKII on NMDA receptor desensitization in heterologous cells, as measured by the ratio of steady-state to peak currents induced during 3s agonist applications. CaMKIIα co-expression or infusion of constitutively active CaMKII limits the extent of desensitization and preserves current amplitude with repeated stimulation of recombinant GluN1A/GluN2B when examined using low intracellular chloride (Cl-) levels, characteristic of neurons beyond the first postnatal week. In contrast, CaMKIIα enhances the acute rate and extent of desensitization when intracellular Cl- concentrations are high. The apparent dependence of CaMKIIα effects on NMDA receptor desensitization on Cl- concentrations is consistent with the presence of a Ca2+-activated Cl- conductance endogenous to HEK 293 cells, which was confirmed by photolysis of caged-Ca2+. However, Ca2+-activated Cl- conductances are unaffected by CaMKIIα expression, indicating that CaMKII affects agonist-induced whole cell currents via modulation of the NMDA receptor. In support of this idea, CaMKIIα modulation of GluN2B-NMDA receptors is abrogated by the phospho-null mutation of Ser1303 in GluN2B to alanine and occluded by phospho-mimetic mutation of Ser1303 to aspartate regardless of intracellular Cl- concentration. Thus, CaMKII-mediated phosphorylation of GluN2B-containing NMDA receptors reduces desensitization at physiological (low) intracellular Cl-, perhaps serving as a feed-forward mechanism to sustain NMDA-mediated Ca2+ entry and continued CaMKII activation during learning and memory.
Asunto(s)
Potenciales de Acción , Proteína Quinasa Tipo 2 Dependiente de Calcio Calmodulina/metabolismo , Procesamiento Proteico-Postraduccional , Receptores de N-Metil-D-Aspartato/metabolismo , Señalización del Calcio , Cloruros/metabolismo , Células HEK293 , Humanos , Fosforilación , Unión ProteicaRESUMEN
PKMζ is generated via an alternative transcriptional start site in the atypical protein kinase C (PKC)ζ isoform, which removes N-terminal regulatory elements, including the inhibitory pseudosubstrate domain, consequently rendering the kinase constitutively active. Persistent PKMζ activity has been proposed as a molecular mechanism for the long-term maintenance of synaptic plasticity underlying some forms of memory. Many studies supporting a role for PKMζ in synaptic plasticity and memory have relied on the PKCζ pseudosubstrate-derived ζ-inhibitory peptide (ZIP). However, recent studies have demonstrated that ZIP-induced impairments to synaptic plasticity and memory occur even in the absence of PKCζ, suggesting that ZIP exerts its actions via additional cellular targets. In this study, we demonstrated that ZIP interacts with conventional and novel PKC, in addition to atypical PKC isoforms. Moreover, when brain abundance of each PKC isoform and affinity for ZIP are taken into account, the signaling capacity of ZIP-responsive pools of conventional and novel PKCs may match or exceed that for atypical PKCs. Pseudosubstrate-derived peptides, like ZIP, are thought to exert their cellular action primarily by inhibiting PKC catalytic activity; however, the ZIP-sensitive catalytic core of PKC is known to participate in the enzyme's subcellular targeting, suggesting an additional mode of ZIP action. Indeed, we have demonstrated that ZIP potently disrupts PKCα interaction with the PKC-targeting protein A-kinase anchoring protein (AKAP) 79 and interferes with ionomycin-induced translocation of conventional PKC to the plasma membrane. Thus, ZIP exhibits broad-spectrum action toward the PKC family of enzymes, and this action may contribute to its unique ability to impair memory.
Asunto(s)
Encéfalo/metabolismo , Proteínas Gestacionales/metabolismo , Proteína Quinasa C/antagonistas & inhibidores , Proteína Quinasa C/metabolismo , Inhibidores de Proteínas Quinasas/metabolismo , Animales , Encéfalo/efectos de los fármacos , Relación Dosis-Respuesta a Droga , Células HEK293 , Humanos , Isoenzimas/antagonistas & inhibidores , Isoenzimas/metabolismo , Proteínas Gestacionales/farmacología , Unión Proteica/efectos de los fármacos , Unión Proteica/fisiología , Inhibidores de Proteínas Quinasas/farmacología , Ratas , Ratas Sprague-Dawley , Especificidad por Sustrato/efectos de los fármacos , Especificidad por Sustrato/fisiologíaRESUMEN
Selective control of receptor trafficking provides a mechanism for remodeling the receptor composition of excitatory synapses, and thus supports synaptic transmission, plasticity, and development. GluN3A (formerly NR3A) is a nonconventional member of the NMDA receptor (NMDAR) subunit family, which endows NMDAR channels with low calcium permeability and reduced magnesium sensitivity compared with NMDARs comprising only GluN1 and GluN2 subunits. Because of these special properties, GluN3A subunits act as a molecular brake to limit the plasticity and maturation of excitatory synapses, pointing toward GluN3A removal as a critical step in the development of neuronal circuitry. However, the molecular signals mediating GluN3A endocytic removal remain unclear. Here we define a novel endocytic motif (YWL), which is located within the cytoplasmic C-terminal tail of GluN3A and mediates its binding to the clathrin adaptor AP2. Alanine mutations within the GluN3A endocytic motif inhibited clathrin-dependent internalization and led to accumulation of GluN3A-containing NMDARs at the cell surface, whereas mimicking phosphorylation of the tyrosine residue promoted internalization and reduced cell-surface expression as shown by immunocytochemical and electrophysiological approaches in recombinant systems and rat neurons in primary culture. We further demonstrate that the tyrosine residue is phosphorylated by Src family kinases, and that Src-activation limits surface GluN3A expression in neurons. Together, our results identify a new molecular signal for GluN3A internalization that couples the functional surface expression of GluN3A-containing receptors to the phosphorylation state of GluN3A subunits, and provides a molecular framework for the regulation of NMDAR subunit composition with implications for synaptic plasticity and neurodevelopment.
Asunto(s)
Endocitosis/fisiología , Potenciales Postsinápticos Excitadores/fisiología , Neuronas/metabolismo , Receptores de N-Metil-D-Aspartato/química , Receptores de N-Metil-D-Aspartato/metabolismo , Tirosina/metabolismo , Adenosina Trifosfato/farmacocinética , Secuencias de Aminoácidos/efectos de los fármacos , Secuencias de Aminoácidos/genética , Análisis de Varianza , Animales , Biofisica , Biotinilación , Células Cultivadas , Corteza Cerebral/citología , Chlorocebus aethiops , Clatrina/farmacología , Proteínas de Unión al ADN/genética , Proteínas de Unión al ADN/metabolismo , Estimulación Eléctrica , Embrión de Mamíferos , Endocitosis/efectos de los fármacos , Potenciales Postsinápticos Excitadores/efectos de los fármacos , Regulación de la Expresión Génica/efectos de los fármacos , Regulación de la Expresión Génica/genética , Ácido Glutámico/farmacología , Proteínas Fluorescentes Verdes/genética , Proteínas Fluorescentes Verdes/metabolismo , Hipocampo/citología , Humanos , Inmunoprecipitación , Mutagénesis/fisiología , Mutación/fisiología , Neuronas/efectos de los fármacos , Neurotransmisores/farmacología , Técnicas de Placa-Clamp , Isótopos de Fósforo/farmacocinética , Fosforilación/efectos de los fármacos , Polipéptido Hipofisario Activador de la Adenilato-Ciclasa/farmacología , Unión Proteica/efectos de los fármacos , Unión Proteica/genética , Conformación Proteica , Transporte de Proteínas/efectos de los fármacos , Transporte de Proteínas/genética , ARN Interferente Pequeño/genética , ARN Interferente Pequeño/metabolismo , Ratas , Receptores de N-Metil-D-Aspartato/genética , Transfección , Transferrina/metabolismoRESUMEN
GluA1 (formerly GluR1) AMPA receptor subunit phosphorylation at Ser-831 is an early biochemical marker for long-term potentiation and learning. This site is a substrate for Ca(2+)/calmodulin (CaM)-dependent protein kinase II (CaMKII) and protein kinase C (PKC). By directing PKC to GluA1, A-kinase anchoring protein 79 (AKAP79) facilitates Ser-831 phosphorylation and makes PKC a more potent regulator of GluA1 than CaMKII. PKC and CaM bind to residues 31-52 of AKAP79 in a competitive manner. Here, we demonstrate that common CaMKII inhibitors alter PKC and CaM interactions with AKAP79(31-52). Most notably, the classical CaMKII inhibitors KN-93 and KN-62 potently enhanced the association of CaM to AKAP79(31-52) in the absence (apoCaM) but not the presence of Ca(2+). In contrast, apoCaM association to AKAP79(31-52) was unaffected by the control compound KN-92 or a mechanistically distinct CaMKII inhibitor (CaMKIINtide). In vitro studies demonstrated that KN-62 and KN-93, but not the other compounds, led to apoCaM-dependent displacement of PKC from AKAP79(31-52). In the absence of CaMKII activation, complementary cellular studies revealed that KN-62 and KN-93, but not KN-92 or CaMKIINtide, inhibited PKC-mediated phosphorylation of GluA1 in hippocampal neurons as well as AKAP79-dependent PKC-mediated augmentation of recombinant GluA1 currents. Buffering cellular CaM attenuated the ability of KN-62 and KN-93 to inhibit AKAP79-anchored PKC regulation of GluA1. Therefore, by favoring apoCaM binding to AKAP79, KN-62 and KN-93 derail the ability of AKAP79 to efficiently recruit PKC for regulation of GluA1. Thus, AKAP79 endows PKC with a pharmacological profile that overlaps with CaMKII.
Asunto(s)
Proteínas de Anclaje a la Quinasa A/metabolismo , Proteína Quinasa Tipo 2 Dependiente de Calcio Calmodulina/metabolismo , Proteína Quinasa C/metabolismo , Inhibidores de Proteínas Quinasas/farmacología , Receptores AMPA/metabolismo , Transducción de Señal/efectos de los fármacos , Proteínas de Anclaje a la Quinasa A/genética , Proteína Quinasa Tipo 2 Dependiente de Calcio Calmodulina/genética , Activación Enzimática/efectos de los fármacos , Células HEK293 , Hipocampo/metabolismo , Humanos , Neuronas/metabolismo , Fosforilación/efectos de los fármacos , Proteína Quinasa C/antagonistas & inhibidores , Proteína Quinasa C/genética , Receptores AMPA/genéticaRESUMEN
The ubiquitously expressed and highly promiscuous protein phosphatase 1 (PP1) regulates many cellular processes. Targeting PP1 to specific locations within the cell allows for the regulation of PP1 by conferring substrate specificity. In the present study, we identified AKAP79 as a novel PP1 regulatory subunit. Immunoprecipitaiton of the AKAP from rat brain extract found that the PP1 catalytic subunit copurified with the anchoring protein. This is a direct interaction, demonstrated by pulldown experiments using purified proteins. Interestingly, the addition of AKAP79 to purified PP1 catalytic subunit decreased phosphatase activity with an IC(50) of 811 ± 0.56 nM of the anchoring protein. Analysis of AKAP79 identified a PP1 binding site that conformed to a consensus PP1 binding motif (FxxR/KxR/K) in the first 44 amino acids of the anchoring protein. This was confirmed when a peptide mimicking this region of AKAP79 was able to bind PP1 by both pulldown assay and surface plasmon resonance. However, PP1 was still able to bind to AKAP79 upon deletion of this region, suggesting additional sites of contact between the anchoring protein and the phosphatase. Importantly, this consensus PP1 binding motif was found not to be responsible for PP1 inhibition, but rather enhanced phosphatase activity, as deletion of this domain resulted in an increased inhibition of PP1 activity. Instead, a second interaction domain localized to residues 150-250 of AKAP79 was required for the inhibition of PP1. However, the inhibitory actions of AKAP79 on PP1 are substrate dependent, as the anchoring protein did not inhibit PP1 dephosphorylation of phospho-PSD-95, a substrate found in AKAP79 complexes in the brain. These combined observations suggest that AKAP79 acts as a PP1 regulatory subunit that can direct PP1 activity toward specific targets in the AKAP79 complex.
Asunto(s)
Proteínas de Anclaje a la Quinasa A/química , Proteína Fosfatasa 1/química , Proteínas de Anclaje a la Quinasa A/metabolismo , Secuencia de Aminoácidos , Animales , Sitios de Unión , Catálisis , Células Cultivadas , Datos de Secuencia Molecular , Proteína Fosfatasa 1/metabolismo , Estructura Terciaria de Proteína , Ratas , Resonancia por Plasmón de SuperficieRESUMEN
Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) promotes trafficking and activation of the GluR1 subunit of alpha-amino- 3-hydroxy-5-methyl-4-isoxazolepropionic acid-type glutamate receptors (AMPARs) during synaptic plasticity. GluR1 is also modulated in parallel by multiprotein complexes coordinated by synapse-associated protein 97 (SAP97) that contain A-kinase anchoring protein 79/150 (AKAP79/150), protein kinase A, and protein phosphatase 2B. Here we show that SAP97 is present in CaMKII immune complexes isolated from rodent brain as well as from HEK293 cells co-expressing CaMKIIalpha and SAP97. CaMKIIalpha phosphorylated recombinant SAP97 within immune complexes in vitro and in intact cells. Four alternative mRNA splice variants of SAP97 expressing combinations of four inserts (I2, I3, I4, I5) in the U5 region between Src homology 3 (SH3) and guanylyl kinase-like (GK) domains were identified in rat brain at postnatal day 21. CaMKIIalpha preferentially phosphorylated a full-length SAP97 and a glutathione S-transferase (GST) fusion protein containing the I3 and I5 inserts (SAP97-I3I5 and GST-SH3-I3I5-GK, respectively) and also specifically interacted with GST-SH3-I3I5-GK compared with GST proteins containing other naturally occurring insert combinations. AKAP79/150 also directly and specifically bound only to GST-SH3-I3I5-GK, but CaMKII phosphorylation of GST-SH3-I3I5-GK prevented this interaction. AKAP79-dependent down-regulation of GluR1 AMPAR currents was ablated by overexpression of SAP97-I2I5 (which does not bind AKAP79) or by infusion of active CaMKIIalpha. Collectively, the data suggest that CaMKIIalpha targets a specific SAP97 splice variant to disengage AKAP79/150 from regulating GluR1 AMPARs, providing new insight into protein-protein interactions and phosphorylation events that are required for normal regulation of glutamatergic synaptic transmission, learning, and memory.
Asunto(s)
Proteínas de Anclaje a la Quinasa A/metabolismo , Proteínas Adaptadoras Transductoras de Señales/metabolismo , Proteína Quinasa Tipo 2 Dependiente de Calcio Calmodulina/metabolismo , Proteínas de la Membrana/metabolismo , Receptores AMPA/metabolismo , Sinapsis/metabolismo , Transmisión Sináptica/fisiología , Proteínas de Anclaje a la Quinasa A/genética , Proteínas Adaptadoras Transductoras de Señales/genética , Animales , Encéfalo/metabolismo , Calcineurina/genética , Calcineurina/metabolismo , Proteína Quinasa Tipo 2 Dependiente de Calcio Calmodulina/genética , Línea Celular , Homólogo 1 de la Proteína Discs Large , Guanilato-Quinasas , Humanos , Aprendizaje/fisiología , Proteínas de la Membrana/genética , Ratones , Complejos Multiproteicos/genética , Complejos Multiproteicos/metabolismo , Fosforilación/fisiología , Unión Proteica/fisiología , Estructura Terciaria de Proteína/fisiología , Ratas , Receptores AMPA/genética , Sinapsis/genéticaRESUMEN
De novo protein synthesis is required for synapse modifications underlying stable memory encoding. Yet neurons are highly compartmentalized cells and how protein synthesis can be regulated at the synapse level is unknown. Here, we characterize neuronal signaling complexes formed by the postsynaptic scaffold GIT1, the mechanistic target of rapamycin (mTOR) kinase, and Raptor that couple synaptic stimuli to mTOR-dependent protein synthesis; and identify NMDA receptors containing GluN3A subunits as key negative regulators of GIT1 binding to mTOR. Disruption of GIT1/mTOR complexes by enhancing GluN3A expression or silencing GIT1 inhibits synaptic mTOR activation and restricts the mTOR-dependent translation of specific activity-regulated mRNAs. Conversely, GluN3A removal enables complex formation, potentiates mTOR-dependent protein synthesis, and facilitates the consolidation of associative and spatial memories in mice. The memory enhancement becomes evident with light or spaced training, can be achieved by selectively deleting GluN3A from excitatory neurons during adulthood, and does not compromise other aspects of cognition such as memory flexibility or extinction. Our findings provide mechanistic insight into synaptic translational control and reveal a potentially selective target for cognitive enhancement.
Asunto(s)
Memoria/fisiología , Biosíntesis de Proteínas/fisiología , Receptores de N-Metil-D-Aspartato/metabolismo , Serina-Treonina Quinasas TOR/metabolismo , Animales , Femenino , Masculino , Diana Mecanicista del Complejo 1 de la Rapamicina , Ratones Endogámicos C57BL , Ratones Transgénicos , Transducción de SeñalRESUMEN
A key step in glutamatergic synapse maturation is the replacement of developmentally expressed N-methyl-D-aspartate receptors (NMDARs) with mature forms that differ in subunit composition, electrophysiological properties and propensity to elicit synaptic plasticity. However, the mechanisms underlying the removal and replacement of synaptic NMDARs are poorly understood. Here we demonstrate that NMDARs containing the developmentally regulated NR3A subunit undergo rapid endocytosis from the dendritic plasma membrane in cultured rat hippocampal neurons. This endocytic removal is regulated by PACSIN1/syndapin1, which directly and selectively binds the carboxy-terminal domain of NR3A through its NPF motifs and assembles a complex of proteins including dynamin and clathrin. Endocytosis of NR3A by PACSIN1 is activity dependent, and disruption of PACSIN1 function causes NR3A accumulation at synaptic sites. Our results reveal a new activity-dependent mechanism involved in the regulation of NMDAR expression at synapses during development, and identify a brain-specific endocytic adaptor that confers spatiotemporal and subunit specificity to NMDAR endocytosis.
Asunto(s)
Endocitosis/fisiología , Glicoproteínas de Membrana/fisiología , Neuronas/citología , Proteoglicanos/fisiología , Receptores de N-Metil-D-Aspartato/metabolismo , Sinapsis/metabolismo , Animales , Western Blotting/métodos , Células Cultivadas , Clonación Molecular/métodos , Electrofisiología/métodos , Embrión de Mamíferos , Endocitosis/efectos de los fármacos , Técnica del Anticuerpo Fluorescente/métodos , Proteínas Fluorescentes Verdes/metabolismo , Hipocampo/citología , Humanos , Hibridación in Situ/métodos , Glicoproteínas de Membrana/genética , Microscopía Inmunoelectrónica/métodos , Mutación/fisiología , N-Metilaspartato/farmacología , Neuronas/efectos de los fármacos , Proteoglicanos/genética , Ratas , Receptores de N-Metil-D-Aspartato/genética , Sinapsis/efectos de los fármacos , Sinapsis/ultraestructura , Sindecanos , Transfección/métodos , Técnicas del Sistema de Dos HíbridosRESUMEN
Preservation of a balance between synaptic excitation and inhibition is critical for normal brain function. A number of homeostatic cellular mechanisms have been suggested to play a role in maintaining this balance, including long-term plasticity of GABAergic inhibitory synapses. Many previous studies have demonstrated a coupling of postsynaptic spiking with modification of perisomatic inhibition. Here, we demonstrate that activation of NMDA-type glutamate receptors leads to input-specific long-term potentiation of dendritic inhibition mediated by somatostatin-expressing interneurons. This form of plasticity is expressed postsynaptically and requires both CaMKIIα and the ß2 subunit of the GABA-A receptor. Importantly, this process may function to preserve dendritic inhibition, as genetic deletion of NMDAR signaling results in a selective weakening of dendritic inhibition. Overall, our results reveal a new mechanism for linking excitatory and inhibitory input in neuronal dendrites and provide novel insight into the homeostatic regulation of synaptic transmission in cortical circuits.
Asunto(s)
Dendritas/fisiología , Potenciación a Largo Plazo/fisiología , Proteínas del Tejido Nervioso/fisiología , Inhibición Neural/fisiología , Receptores de N-Metil-D-Aspartato/fisiología , Ácido gamma-Aminobutírico/fisiología , Animales , Señalización del Calcio/fisiología , Proteína Quinasa Tipo 2 Dependiente de Calcio Calmodulina/fisiología , Femenino , Masculino , Ratones , Ratones Endogámicos C57BL , Ratones Transgénicos , Células Piramidales/fisiología , Receptores de GABA-A/fisiologíaRESUMEN
Second messengers regulate synaptic plasticity by influencing the balance between kinase and phosphatase activity. One target of this balance is the phosphorylation state of the AMPA receptor glutamate receptor 1 (GluR1) subunit. Hippocampal long-term depression (LTD) is a calcium-dependent downregulation of synaptic AMPA receptor currents associated with dephosphorylation of Ser845, a cAMP-dependent protein kinase (PKA) site on GluR1. Recruitment of kinases and phosphatases to the AMPA receptor might enable modulation of AMPA receptor function. The neuronal A-kinase anchoring protein AKAP79/150 interacts with PKA and the calcium-dependent protein phosphatase PP2B and is linked to the AMPA receptor GluR1 subunit by synapse-associated protein 97 (SAP97), a membrane-associated guanylate kinase family protein. Here we demonstrate that AKAP79 not only promotes basal phosphorylation of Ser845 but also confers a calcium- and PP2B-mediated downregulation to GluR1 receptor currents. This AKAP79-dependent downregulation is contingent on the local presence of PKA, Ser845 of GluR1, and a PDZ (postsynaptic density 95/Discs large/zona occludens 1)-domain interaction between GluR1 and SAP97, all of which support basal phosphorylation of the receptor. These findings suggest that the AKAP79 signaling complex is sufficient to couple intracellular calcium levels to the PKA phosphorylation state of GluR1. Thus, the integration of intracellular signals relevant for LTD may be transduced to GluR1 by the AKAP79 signaling complex.
Asunto(s)
Proteínas Adaptadoras Transductoras de Señales , Proteínas Portadoras/metabolismo , Inhibición Neural/fisiología , Receptores AMPA/metabolismo , Transducción de Señal/fisiología , Proteínas de Anclaje a la Quinasa A , Animales , Sitios de Unión/fisiología , Calcineurina/metabolismo , Calcio/metabolismo , Células Cultivadas , Proteínas Quinasas Dependientes de AMP Cíclico/metabolismo , Ácido Glutámico/farmacología , Riñón/citología , Riñón/metabolismo , Sustancias Macromoleculares , Proteínas de la Membrana , Proteínas del Tejido Nervioso/metabolismo , Plasticidad Neuronal/fisiología , Neuronas/citología , Neuronas/metabolismo , Técnicas de Placa-Clamp , Fosforilación , Pruebas de Precipitina , Unión Proteica , Ratas , Ratas Sprague-Dawley , Sistemas de Mensajero Secundario/fisiología , TiempoRESUMEN
Enhancement of AMPA receptor activity in response to synaptic plasticity inducing stimuli may arise, in part, through phosphorylation of the GluR1 AMPA receptor subunit at Ser-831. This site is a substrate for both Ca(2+)-calmodulin-dependent protein kinase II (CaMKII) and protein kinase C (PKC). However, neuronal protein levels of CaMKII may exceed those of PKC by an order of magnitude. Thus, it is unclear how PKC could effectively regulate this common target site. The multivalent neuronal scaffold A-kinase-anchoring protein 79 (AKAP79) is known to bind PKC and is linked to GluR1 by synapse-associated protein 97 (SAP97). Here, biochemical studies demonstrate that AKAP79 localizes PKC activity near the receptor, thus accelerating Ser-831 phosphorylation. Complementary electrophysiological studies indicate that AKAP79 selectively shifts the dose-dependence for PKC modulation of GluR1 receptor currents approximately 20-fold, such that low concentrations of PKC are as effective as much higher CaMKII concentrations. By boosting PKC activity near a target substrate, AKAP79 provides a mechanism to overcome limitations in kinase abundance thereby ensuring faithful signal propagation and efficient modification of AMPA receptor-mediated responses.
Asunto(s)
Proteínas de Anclaje a la Quinasa A/fisiología , Proteína Quinasa Tipo 2 Dependiente de Calcio Calmodulina/metabolismo , Calcio/metabolismo , Regulación de la Expresión Génica , Proteína Quinasa C/metabolismo , Proteína Quinasa C/fisiología , Receptores AMPA/metabolismo , Proteínas de Anclaje a la Quinasa A/metabolismo , Línea Celular , Electrofisiología/métodos , Hipocampo/metabolismo , Humanos , Modelos Biológicos , Neuronas/metabolismo , Fosforilación , Factores de TiempoRESUMEN
L-type calcium channels (Ca(v)1.1-Ca(v)1.4) link Ca(2+) influx to membrane depolarization and serve a critical role in regulating membrane excitability, muscle contraction, hormone secretion, and gene transcription. In many tissues, L-type calcium channel activity (Ca(v)1.1 and Ca(v)1.2) is enhanced by transmitters and hormones that activate the cAMP-dependent protein kinase (PKA), which is largely thought to be mediated via phosphorylation of the pore forming alpha subunit. However, the ability of PKA to regulate Ca(v)1.3 and the sites contributing to effective modulation of channel activity remains to be established. Using HEK 293 cells, we demonstrate that currents carried by the long C-terminal splice variant of Ca(v)1.3 (Ca(v)1.3L) are selectively enhanced compared to the short C-terminal splice variant (Ca(v)1.3S) when the catalytic subunit of PKA is introduced into the cell via the whole-cell recording electrode. However, the persistence of this regulation is dependent on the identity of the auxiliary beta subunit, such that PKA produces only a transient increase in the presence of beta(3) while a persistent increase is observed in the presence of the beta(2a) subunit. Site-directed mutagenesis of consensus PKA phosphorylation sites revealed that Ser1964 and Ser1743 in Ca(v)1.3L were the predominant sites controlling PKA modulation in the presence of the beta(3) and beta(2a) auxiliary subunits, respectively. Therefore, beta subunits determine the contribution of distinct sites within Ca(v)1.3 towards PKA-mediated enhancement of channel activity. These data suggest that auxiliary beta subunits govern the access of signaling enzymes to L-type calcium channels.
Asunto(s)
Canales de Calcio Tipo L/metabolismo , Proteínas Quinasas Dependientes de AMP Cíclico/metabolismo , Subunidades de Proteína/metabolismo , Animales , Encéfalo/metabolismo , Canales de Calcio Tipo L/genética , Línea Celular , ADN Complementario/genética , Electrofisiología , Proteínas Fluorescentes Verdes/metabolismo , Atrios Cardíacos/química , Ventrículos Cardíacos/química , Humanos , Riñón/citología , Miocardio/metabolismo , Técnicas de Placa-Clamp , Fosforilación , Plásmidos , Isoformas de Proteínas/genética , Isoformas de Proteínas/metabolismo , Estructura Terciaria de Proteína , Subunidades de Proteína/genética , Ratas , TransfecciónRESUMEN
Resensitization of G protein-coupled receptors (GPCR) following prolonged agonist exposure is critical for restoring the responsiveness of the receptor to subsequent challenges by agonist. The 3'-5' cyclic AMP-dependent protein kinase (PKA) and serine 312 in the third intracellular loop of the human beta(1)-adrenergic receptor (beta(1)-AR) were both necessary for efficient recycling and resensitization of the agonist-internalized beta(1)-AR (Gardner, L. A., Delos Santos, N. M., Matta, S. G., Whitt, M. A., and Bahouth, S. W. (2004) J. Biol. Chem. 279, 21135-21143). Because PKA is compartmentalized near target substrates by interacting with protein kinase A anchoring proteins (AKAPs), the present study was undertaken to identify the AKAP involved in PKA-mediated phosphorylation of the beta(1)-AR and in its recycling and resensitization. Here, we report that Ht-31 peptide-mediated disruption of PKA/AKAP interactions prevented the recycling and functional resensitization of heterologously expressed beta(1)-AR in HEK-293 cells and endogenously expressed beta(1)-AR in SK-N-MC cells and neonatal rat cortical neurons. Whereas several endogenous AKAPs were identified in HEK-293 cells, small interfering RNA-mediated down-regulation of AKAP79 prevented the recycling of the beta(1)-AR in this cell line. Co-immunoprecipitations and fluorescence resonance energy transfer (FRET) microscopy experiments in HEK-293 cells revealed that the beta(1)-AR, AKAP79, and PKA form a ternary complex at the carboxyl terminus of the beta(1)-AR. This complex was involved in PKA-mediated phosphorylation of the third intracellular loop of the beta(1)-AR because disruption of PKA/AKAP interactions or small interfering RNA-mediated down-regulation of AKAP79 both inhibited this response. Thus, AKAP79 provides PKA to phosphorylate the beta(1)-AR and thereby dictate the recycling and resensitization itineraries of the beta(1)-AR.
Asunto(s)
Proteínas Adaptadoras Transductoras de Señales/metabolismo , Proteínas Quinasas Dependientes de AMP Cíclico/metabolismo , Receptores Adrenérgicos beta 1/metabolismo , Proteínas de Anclaje a la Quinasa A , Proteínas Adaptadoras Transductoras de Señales/genética , Agonistas de Receptores Adrenérgicos beta 1 , Línea Celular , Proteínas Quinasas Dependientes de AMP Cíclico/genética , Humanos , Microscopía Fluorescente , Fosforilación , Unión Proteica , Subunidades de Proteína/genética , Subunidades de Proteína/metabolismo , ARN Interferente Pequeño , Receptores Adrenérgicos beta 1/genéticaRESUMEN
Compartmentalization of protein kinases and phosphatases with substrates is a means to increase the efficacy of signal transduction events. The A-kinase anchoring protein, AKAP79, is a multivalent anchoring protein that maintains the cAMP-dependent protein kinase, protein kinase C, and protein phosphatase-2B (PP2B/calcineurin) at the postsynaptic membrane of excitatory synapses where it is recruited into complexes with N-methyl-d-aspartic acid or alpha-amino-3-hydroxy-5-methyl-isoxazole-4-propionic acid (AMPA)-subtype glutamate receptors. We have used cellular targeting of AKAP79 truncation and deletion mutants as an assay to map the PP2B-binding site on AKAP79. We demonstrate that residues 315-360 are necessary and sufficient for AKAP79-PP2B anchoring in cells. Multiple determinants contained within this region bind directly to the A subunit of PP2B and inhibit phosphatase activity. Peptides spanning the 315-360 region of AKAP79 can antagonize PP2B anchoring in vitro and targeting in transfected cells. Electrophysiological experiments further emphasize this point by demonstrating that a peptide encompassing residues 330-357 of AKAP79 attenuates PP2B-dependent down-regulation of GluR1 receptor currents when perfused into HEK293 cells. We propose that the structural features of this AKAP79-PP2B-binding domain may share similarities with other proteins that serve to coordinate PP2B localization and activity.
Asunto(s)
Calcineurina/metabolismo , Proteínas Portadoras/metabolismo , Animales , Sitios de Unión , Células COS , Inhibidores de la Calcineurina , Proteínas Portadoras/química , Membrana Celular/enzimología , RatonesRESUMEN
The influx of calcium (Ca(2+)) ions through L-type channels underlies many cellular processes, ranging from initiation of gene transcription to activation of Ca(2+)-activated potassium channels. L-type channels possess a diagnostic pharmacology, being enhanced by the dihydropyridine BAY K 8644 and benzoylpyrrole FPL 64176. It is assumed that the action of these compounds is independent of the ion conducted through the channel. In contrast to this assumption, modulation of L-type channel activity in acutely dissociated rat CA1 hippocampal neurons depended on the divalent ion identity. BAY K 8644 and FPL 64176 substantially increased single-channel open time only when barium (Ba(2+)) was the permeant ion. BAY K 8644 increased single-channel conductance when either Ba(2+) or Ca(2+) ions were the charge carrier, an effect not observed with FPL 64176. BAY K 8644 enhanced the whole cell L-type channel Ca(2+)- or Ba(2+)-carried current without a change in deactivation tail kinetics. In contrast, enhancement by FPL 64176 was associated with a dramatic slowing of deactivation kinetics only when Ba(2+) and not Ca(2+) was the charge carrier. Current activation was slowed by FPL 64176 with either charge carrier, an effect arising from a clustering of agonist-modified long-duration openings toward the end of the voltage step. These data indicate that agonists enhanced L-type current by distinct mechanisms dependent on the permeant ion, indicating that care must be considered when used as diagnostic tools.