Synapse-Associated Protein 97 Selectively Associates with a Subset of AMPA Receptors Early in their Biosynthetic Pathway

Abstract

The regulation of AMPA receptors at the postsynaptic membrane is a fundamental component of synaptic plasticity. In the hippocampus, the induction of long-term potentiation increases the delivery of GluR1, a major AMPA receptor subunit in hippocampal pyramidal neurons, to the synaptic plasma membrane through a mechanism that requires the PDZ binding domain of GluR1. Synapse-associated protein 97 (SAP97), a member of the membrane-associated guanylate kinase family, is believed to associate with AMPA receptors (AMPARs) containing the GluR1 subunit, but the functional significance of these interactions is unclear. We investigated the interaction of GluR1 with SAP97, the only PDZ protein known to interact with GluR1. We find that interactions involving SAP97 and GluR1 occur early in the secretory pathway, while the receptors are in the endoplasmic reticulum or cis-Golgi. In contrast, few synaptic receptors associate with SAP97, suggesting that SAP97 dissociates from the receptor complex at the plasma membrane. We also show that internalization of GluR1, as triggered by NMDAR activation, does not require SAP97. These results implicate GluR1-SAP97 interactions in mechanisms underlying AMPA receptor targeting.

Selective reduction of a PDZ protein, SAP‐97, in the prefrontal cortex of patients with chronic schizophrenia

“…As discussed above, the PDZ protein, SAP97, is implicated in the expression of AMPA receptor subunits as well as in the stabilization of the AMPA receptor complexes (Jourdi et al 2001;Sans et al 2001). In agreement, our preliminary study revealed that other AMPA receptor subunits, GluR2/3, were also decreased in the same prefrontal samples (58% reduction, U 25,14 ¼ 249, Z ¼ 2.16, p ¼ 0.03).…”

“…For example, Pick 1 and GRIP1, which both interact with the C-terminal terminal of the AMPA receptor subunits, GluR2/3, are involved in their internalization and synaptic stabilization (Dong et al 1999;Dev et al 1999;Chung et al 2000;Daw et al 2000;El-Husseini et al 2000;Osten et al 2000). SAP97 interacts with the AMPA receptor subunit GluR1 and stabilizes receptor protein expression at postsynaptic sites (Leonard et al 1998;Jourdi et al 2001;Sans et al 2001). Among the various PDZ proteins, levels of the PDZ protein SAP97 were specifically decreased in the prefrontal cortex of schizophrenics (59%, p < 0.05) compared to those in controls in the present experiment.…”

“…Similarly, a group of PDZ molecules interacting with a-amino-3-hydroxy-5-methyl-4-isoxzolepropionic acid (AMPA)-type glutamate receptors has been identified. SAP97 associates with the C-terminal motif of glutamate receptor 1 (GluR1) (Leonard et al 1998;Sans et al 2001) and GRIP, AMPA receptorbinding protein (ABP), stargazin and Pick1 bind to the C-terminal motif of GluR2/3 (Dong et al 1997;Srivastava et al 1998;Dong et al 1999;Xia et al 1999;Chen et al 2000). The PDZ domain of PSD-95 and other proteins also interacts with a variety of other signaling molecules at synapses (O'Brien et al 1998;Nagano et al 1998;Fanning and Anderson 1999).…”

Ontogeny of postsynaptic density proteins at glutamatergic synapses

“…Three antibodies to mGluR5 were obtained from Chemicon International (Temecula, CA, USA); another from Chemicon was made to the last 13 amino acids and recognizes both mGluR5 and mGluR1alpha. Antibodies to AMPA receptors, NR1, NR2A/B, PSD-95, PSD-93, SAP97 and SAP102 were characterized in general and for immunogold labeling in hippocampus by our lab (Petralia and Wenthold, 1992;Petralia et al, 1994aPetralia et al, ,b, 1999Sans et al, 2000Sans et al, , 2001. Some new labeling studies were carried out for NR1 (amino acids 909-938; affinity-purified; recognizes the intracellular domain), SAP97 (amino acids 1-105; previous published studies used both this antiserum and an identical affinity-purified antibody), and SAP102 (amino acids 1-119; antiserum; previous published studies used an identical affinity-purified antibody).…”

“…After chemiluminescence detection, films were scanned using a Molecular Dynamics densitometer. Subcellular fractionation of P2 rat brains was performed as described in Sans et al (2001). The synaptosome fraction, isolated by discontinuous sucrose gradient centrifugation, was solubilized in cold 0.5% Triton X-100 and centrifuged to obtain the PSD I pellet.…”