Phosphatidylinositol-4,5-bisphosphate regulates NMDA receptor activity through α-actinin

Phosphatidylinositol-4,5-bisphosphate (PIP₂) has been shown to regulate many ion channels, transporters, and other signaling proteins, but it is not known whether it also regulates neurotransmitter-gated channels. The NMDA receptors (NMDARs) are gated by glutamate and serve as a critical control point in synaptic function. Here we demonstrate that PIP2 supports NMDAR activity. In Xenopus oocytes, overexpression of phospholipase Cγ(PLCγ) or preincubation with 10 μM wortmannin markedly reduced NMDA currents. Stimulation of the epidermal growth factor receptor (EGFR) promoted the formation of an immunocomplex between PLCγ and NMDAR subunits. Stimulation of EGFR or the PLCβ-coupled M₁ acetylcholine receptor produced a robust transient inhibition of NMDA currents. Wortmannin application blocked the recovery of NMDA currents from the inhibition. Using mutagenesis, weidentified the structural elements on NMDAR intracellular tails that transduce the receptor-mediated inhibition, which pinpoint to the binding site for the cytoskeletal protein α-actinin. Mutation of the PIP₂-binding residues of α-actinin dramatically reduced NMDA currents and occluded the effect of EGF. Interestingly, EGF or wortmannin affected the interaction between NMDAR subunits and α-actinin, suggesting that this protein mediates the effect of PIP₂ on NMDARs. In mature hippocampal neurons, expression of the mutant α-actinin reduced NMDA currents and accelerated inactivation. We propose a model in which α-actinin supports NMDAR activity via tethering their intracellular tails to plasma membrane PIP ₂. Thus, our results extend the influence of PIP₂ to the NMDA ionotropic glutamate receptors and introduce a novel mechanism of "indirect" regulation of transmembrane protein activity by PIP ₂.