Phosphorylation of the AMPA receptor subunit GluR2 differentially regulates its interaction with PDZ domain-containing proteins

PSD-95, DLG, ZO-1 (PDZ) domain-mediated protein interactions have been show n to play important roles in the regulation of glutamate receptor function at excitatory synapses. Recent studies demonstrating the rapid regulation o f AMPA receptor function during synaptic plasticity have suggested that AMP A receptor interaction with PDZ domain-containing proteins may be dynamical ly modulated. Here we show that PKC phosphorylation of the AMPA receptor Gl uR2 subunit differentially modulates its interaction with the PDZ domain-co ntaining proteins GRIP1 and PICK1. The serine residue [serine-880 (Ser880)] in the GluR2 C-terminal sequence (IESVKI) critical for PDZ domain binding is a substrate of PKC and is phosphorylated in vivo. In vitro binding and c oimmunoprecipitation studies show that phosphorylation of serine-880 within the GluR2 PDZ ligand significantly decreases GluR2 binding to GRIP1 but no t to PICK1. Immunostaining of cultured hippocampal neurons demonstrates tha t the Ser880-phosphorylated GluR2 subunits are enriched and colocalized wit h PICK1 in the dendrites, with very little staining observed at excitatory synapses. Interestingly, PKC activation in neurons increases the Ser880 pho sphorylation of GluR2 subunits and recruits PICK1 to excitatory synapses. M oreover, PKC stimulation in neurons results in rapid internalization of sur face GluR2 subunits. These results suggest that GluR2 phosphorylation of se rine-880 may be important in the regulation of the AMPA receptor internaliz ation during synaptic plasticity.