SAP102 Mediates Synaptic Clearance of NMDA Receptors

Abstract

Summary Membrane-associated guanylate kinases (MAGUKs) are the major family of scaffolding proteins at the postsynaptic density. The PSD-MAGUK subfamily, which includes PSD-95, PSD-93, SAP97 and SAP102, is well accepted to be primarily involved in the synaptic anchoring of numerous proteins, including N-methyl-D-aspartate receptors (NMDARs). Notably, the synaptic targeting of NMDARs depends on the binding of the PDZ ligand on the GluN2B subunit to MAGUK PDZ domains as disruption of this interaction dramatically decreases NMDAR surface and synaptic expression. We recently reported a secondary interaction between SAP102 and GluN2B, in addition to the PDZ interaction. Here, we identify two critical residues on GluN2B responsible for the non-PDZ binding to SAP102. Strikingly, either mutation of these critical residues or knock-down of endogenous SAP102 can rescue the defective surface expression and synaptic localization of PDZ binding-deficient GluN2B. These data reveal an unexpected, non-scaffolding role for SAP102 in the synaptic clearance of GluN2B-containing NMDARs.

Subunit-specific Regulation of N-Methyl-d-aspartate (NMDA) Receptor Trafficking by SAP102 Protein Splice Variants

“…Cultured cortical neurons were infected with lentivirus expressing a previously characterized SAP102 I1 shRNA that selectively knocked down expression of I1 region-containing SAP102 (16). In previous studies we have shown that I1 regioncontaining SAP102 mediates synaptic removal of GluN2B-containing NMDARs (15). Consistently, we found that surface expression of GluN2B was substantially increased upon knocking down the I1 region-containing SAP102, whereas surface expression of GluN2A was not changed (Fig.…”

“…The different mechanisms by which PSD-95 and SAP102 are targeted to synapses suggest that they play distinct roles in receptor stabilization and/or trafficking at synapses. Indeed, SAP102 is highly mobile in dendritic spines compared with PSD-95 and has recently been shown to mediate synaptic removal of GluN2B-containing NMDARs (15). We have now identified an alternatively spliced region I2 between the SH3 and GK domains that is important for SAP102 synaptic targeting, indicating that synaptic localization of SAP102 is regulated by splicing events.…”

“…The I1 region is located in the N terminus of SAP102, whereas the I2 region is located within a hinge region between the SH3 and GK domains. In previous studies we characterized the I1 region of SAP102 and revealed its function in NMDAR trafficking and spine morphology (15,16). Here we investigated the role of the I2 region of SAP102.…”

Selective synaptic targeting of the excitatory and inhibitory presynaptic organizers, FGF22 and FGF7

“…We thus focused on scaffolding proteins at excitatory and inhibitory synapses -PSD95, SAP102 (also known as DLG3) and gephyrin, which in fact act as adaptor proteins for glutamate receptors (PSD95 and SAP102), GABA A and glycine receptors (gephyrin) (Chen et al, 2012;Dumoulin et al, 2009;Lau and Zukin, 2007;Maas et al, 2006;Zheng et al, 2011). To examine whether these scaffolding proteins act as adaptor proteins for FGF22 and FGF7, we performed live-imaging experiments with fluorescent-protein-tagged FGFs and scaffolding proteins.…”

Identification of Novel 14-3-3 Residues That Are Critical for Isoform-specific Interaction with GluN2C to Regulate N-Methyl-d-aspartate (NMDA) Receptor Trafficking

“…Primary Culture of Hippocampal Neurons and Transfection-Primary hippocampal cultures were prepared from embryonic day 18 (E18) Sprague-Dawley rats as previously described (28). Briefly, hippocampal tissue was dissociated with trypsin and plated on poly-D-lysine-coated coverslips at a density of 2 ϫ 10 6 cells/ml.…”