RT Journal Article SR Electronic T1 PDZ Protein Interactions Underlying NMDA Receptor-Mediated Excitotoxicity and Neuroprotection by PSD-95 Inhibitors JF The Journal of Neuroscience JO J. Neurosci. FD Society for Neuroscience SP 9901 OP 9915 DO 10.1523/JNEUROSCI.1464-07.2007 VO 27 IS 37 A1 Hong Cui A1 Amy Hayashi A1 Hong-Shuo Sun A1 Michael P. Belmares A1 Carolyn Cobey A1 Thuymy Phan A1 Johannes Schweizer A1 Michael W. Salter A1 Yu Tian Wang A1 R. Andrew Tasker A1 David Garman A1 Joshua Rabinowitz A1 Peter S. Lu A1 Michael Tymianski YR 2007 UL http://www.jneurosci.org/content/27/37/9901.abstract AB 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, ∼1 μm), and fusing the NR2B C terminus to Tat enhanced its affinity for PSD-95 PDZ2 by >100-fold (EC50, ∼7 nm). IC50 values for Tat-NR2B9c inhibiting NR2A–NR2C/PSD-95 interactions (∼1–10 μm) 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.