Protein-protein coupling/uncoupling enables dopamine D2 receptor regulation of AMPA receptor-mediated excitotoxicity

There is considerable evidence that dopamine D-2 receptors can modulate AMPA receptor-mediated neurotoxicity. However, the molecular mechanism underlying this process remains essentially unclear. Here we report that D-2 receptors inhibit AMPA-mediated neurotoxicity through two pathways: the activation of phosphoinositide-3 kinase (PI-3K) and downregulation of AMPA receptor plasma membrane expression, both involving a series of protein - protein coupling/ uncoupling events. Agonist stimulation of D-2 receptors promotes the formation of the direct protein - protein interaction between the third intracellular loop of the D-2 receptor and the ATPase N-ethylmaleimide-sensitive factor (NSF) while uncoupling the NSF interaction with the carboxyl tail (CT) of the glutamate receptor GluR2 subunit of AMPA receptors. Previous studies have shown that full-length NSF directly couples to the GluR2(CT) and facilitates AMPA receptor plasma membrane expression. Furthermore, the CT region of GluR2 subunit is also responsible for several other intracellular protein couplings, including p85 subunit of PI-3K. Therefore, the direct coupling of D-2 - NSF and concomitant decrease in the NSF - GluR2 interaction results in a decrease of AMPA receptor membrane expression and an increase in the interaction between GluR2 and the p85 and subsequent activation of PI-3K. Disruption of the D-2 - NSF interaction abolished the ability of D-2 receptor to attenuate AMPA-mediated neurotoxicity by blocking the D-2 activation-induced changes in PI-3K activity and AMPA receptor plasma membrane expression. Furthermore, the D-2 - NSF - GluR2 - p85 interactions are also responsible for the D-2 inhibition of ischemia-induced cell death. These data may provide a new avenue to identify specific targets for therapeutics to modulate glutamate receptor-governed diseases, such as stroke.