PDZ Protein Interactions Underlying NMDA Receptor-Mediated Excitotoxicity and Neuroprotection by PSD-95 Inhibitors

• Published in: The Journal of neuroscience Vol. 27; no. 37; pp. 9901 - 9915
• Main Authors: Cui, Hong, Hayashi, Amy, Sun, Hong-Shuo, Belmares, Michael P, Cobey, Carolyn, Phan, Thuymy, Schweizer, Johannes, Salter, Michael W, Wang, Yu Tian, Tasker, R. Andrew, Garman, David, Rabinowitz, Joshua, Lu, Peter S, Tymianski, Michael
• Format: Journal Article
• Language: English
• Published: United States Soc Neuroscience 12.09.2007; Society for Neuroscience
• Subjects: Databases, Protein; Disks Large Homolog 4 Protein; Excitatory Amino Acid Agents - metabolism; Excitatory Amino Acid Agents - pharmacology; Humans; Intracellular Signaling Peptides and Proteins - antagonists & inhibitors; Intracellular Signaling Peptides and Proteins - metabolism; Membrane Proteins - antagonists & inhibitors; Membrane Proteins - metabolism; Nerve Tissue Proteins - antagonists & inhibitors; Nerve Tissue Proteins - metabolism; Neuroprotective Agents - metabolism; Neuroprotective Agents - pharmacology; Protein Interaction Mapping; Receptors, N-Methyl-D-Aspartate - agonists; Receptors, N-Methyl-D-Aspartate - metabolism
• ISSN: 0270-6474; 1529-2401
• DOI: 10.1523/JNEUROSCI.1464-07.2007

In neuronal synapses, PDZ domains [postsynaptic density-95 (PSD-95)/Discs large/zona occludens-1] of PSD-95 proteins interact with C termini of NMDA receptor [NMDAR (NR)] subunits, linking them to downstream neurotoxic signaling molecules. Perturbing NMDAR/PSD-95 interactions with a Tat peptide comprising the nine C-terminal residues of the NR2B subunit (Tat-NR2B9c) reduces neurons' vulnerability to excitotoxicity and ischemia. However, NR subunit C termini may bind many of >240 cellular PDZs, any of which could mediate neurotoxic signaling independently of PSD-95. Here, we performed a proteomic and biochemical analysis of the interactions of all known human PDZs with synaptic signaling proteins including NR1, NR2A-NR2D, and neuronal nitric oxide synthase (nNOS). Tat-NR2B9c, whose interactions define PDZs involved in neurotoxic signaling, was also used. NR2A-NR2D subunits and Tat-NR2B9c had similar, highly specific, PDZ protein interactions, of which the strongest were with the PSD-95 family members (PSD-95, PSD-93, SAP97, and SAP102) and Tax interaction protein 1 (TIP1). The PSD-95 PDZ2 domain bound NR2A-NR2C subunits most strongly (EC50, approximately 1 microM), and fusing the NR2B C terminus to Tat enhanced its affinity for PSD-95 PDZ2 by >100-fold (EC50, approximately 7 nM). IC50 values for Tat-NR2B9c inhibiting NR2A-NR2C/PSD-95 interactions (approximately 1-10 microM) and nNOS/PSD-95 interactions (200 nM) confirmed the feasibility of such inhibition. To determine which of the PDZ interactions of Tat-NR2B9c mediate neuroprotection, one of PSD-95, PSD-93, SAP97, SAP102, TIP1, or nNOS expression was inhibited in cortical neurons exposed to NMDA toxicity. Only neurons lacking PSD-95 or nNOS but not PSD-93, SAP97, SAP102, or TIP1 exhibited reduced excitotoxic vulnerability. Thus, despite the ubiquitousness of PDZ domain-containing proteins, PSD-95 and nNOS above any other PDZ proteins are keys in effecting NMDAR-dependent excitotoxicity. Consequently, PSD-95 inhibition may constitute a highly specific strategy for treating excitotoxic disorders.