PT  - JOURNAL ARTICLE
AU  - Hong Cui
AU  - Amy Hayashi
AU  - Hong-Shuo Sun
AU  - Michael P. Belmares
AU  - Carolyn Cobey
AU  - Thuymy Phan
AU  - Johannes Schweizer
AU  - Michael W. Salter
AU  - Yu Tian Wang
AU  - R. Andrew Tasker
AU  - David Garman
AU  - Joshua Rabinowitz
AU  - Peter S. Lu
AU  - Michael Tymianski
TI  - PDZ Protein Interactions Underlying NMDA Receptor-Mediated Excitotoxicity and Neuroprotection by PSD-95 Inhibitors
AID  - 10.1523/JNEUROSCI.1464-07.2007
DP  - 2007 Sep 12
TA  - The Journal of Neuroscience
PG  - 9901--9915
VI  - 27
IP  - 37
4099  - http://www.jneurosci.org/content/27/37/9901.short
4100  - http://www.jneurosci.org/content/27/37/9901.full
SO  - J. Neurosci.2007 Sep 12; 27
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.