RESUMO
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.
Assuntos
Hipocampo/metabolismo , Plasticidade Neuronal/fisiologia , Células Piramidais/metabolismo , Receptores de AMPA/metabolismo , Transmissão Sináptica/fisiologia , Proteínas Adaptadoras de Transdução de Sinal , Animais , Proteínas de Transporte/metabolismo , Células Cultivadas , Proteínas do Citoesqueleto , Hipocampo/citologia , Técnicas In Vitro , Peptídeos e Proteínas de Sinalização Intracelular , Depressão Sináptica de Longo Prazo/fisiologia , Mimetismo Molecular/genética , Mimetismo Molecular/fisiologia , Mutagênese Sítio-Dirigida , Proteínas do Tecido Nervoso/metabolismo , Proteínas Nucleares/metabolismo , Técnicas de Patch-Clamp , Fosforilação , Estrutura Terciária de Proteína/fisiologia , Subunidades Proteicas/genética , Subunidades Proteicas/metabolismo , Ratos , Receptores de AMPA/genética , Serina/metabolismo , Sinapses/metabolismoRESUMO
Synaptic trafficking of AMPA-Rs, controlled by small GTPase Ras signaling, plays a key role in synaptic plasticity. However, how Ras signals synaptic AMPA-R trafficking is unknown. Here we show that low levels of Ras activity stimulate extracellular signal-regulated kinase kinase (MEK)-p42/44 MAPK (extracellular signal-regulated kinase [ERK]) signaling, whereas high levels of Ras activity stimulate additional Pi3 kinase (Pi3K)-protein kinase B (PKB) signaling, each accounting for approximately 50% of the potentiation during long-term potentiation (LTP). Spontaneous neural activity stimulates the Ras-MEK-ERK pathway that drives GluR2L into synapses. In the presence of neuromodulator agonists, neural activity also stimulates the Ras-Pi3K-PKB pathway that drives GluR1 into synapses. Neuromodulator release increases with increases of vigilance. Correspondingly, Ras-MEK-ERK activity in sleeping animals is sufficient to deliver GluR2L into synapses, while additional increased Ras-Pi3K-PKB activity in awake animals delivers GluR1 into synapses. Thus, state-dependent Ras signaling, which specifies downstream MEK-ERK and Pi3K-PKB pathways, differentially control GluR2L- and GluR1-dependent synaptic plasticity.