Coexpression of postsynaptic density-95 protein with NMDA receptors results in enhanced receptor expression together with a decreased sensitivity to L-glutamate

Abstract

Coexpression in human embryonic kidney (HEK) 293 cells of the postsynaptic density-95 protein (PSD-95) with NMDA receptor NR2A or NR2B single subunits or NR1-1a/NR2A and NR1-1a/NR2B subunit combinations induced an approximately threefold increase in NR2A and NR2B subunit expression. Deletion of the NR2 C-terminal ESDV motifs resulted in the loss of this increase following coexpression of NR1-1a/NR2A(Trunc) and NR1-1a/NR2B(Trunc) with PSD-95. Characterisation of the radioligand binding properties of [3H]MK-801 to NR1-1a/NR2A receptors with or without PSD-95 showed that PSD-95 induced a threefold increase in B(max) values and an apparent approximately fivefold decrease in affinity in the presence of 10 μM L-glutamate. In the presence of 1 mM L-glutamate, the K(i) for MK-801 binding to NR1-1a/NR2A with PSD-95 was not significantly different from that for NR1-1a/NR2A without PSD-95. The EC(50) value for the enhancement of [3H]MK-801 binding by L-glutamate to NR1-1a/NR2A was 1.8 ± 0.4 (n = 4) and 8.9 (mean of n = 2) μM in the absence and presence of PSD-95, respectively. Thus, coexpression of PSD-95 with NR1-1a/NR2A results in a decreased sensitivity to L-glutamate and an enhanced expression of NR2A and NR2B subunits. Deletion studies show that this effect is mediated via interaction of the C-terminal ESDV motif of the NR2 subunit with PSD-95.