Xia H, Hornby Z D, Malenka R C
Nancy Pritzker Laboratory, Department of Psychiatry and Behavioral Sciences, School of Medicine, Stanford University, 1201 Welch Road, Room P105, 94304-Palo Alto, CA 5485, USA.
Neuropharmacology. 2001 Nov;41(6):714-23. doi: 10.1016/s0028-3908(01)00103-4.
The molecular mechanisms that control the surface expression of NMDA receptors (NMDARs) and AMPA receptors (AMPARs) are unknown. To determine the role of the intracellular C-terminal tails of glutamate receptor subunits in the synaptic targeting of AMPARs and NMDARs, we fused the tails of the AMPAR subunits, GluR1 and GluR2, and the NMDAR subunit, NR1, to the human T lymphocyte membrane protein CD8 and expressed these constructs in HEK293 cells and cultured hippocampal neurons. The GluR1 and GluR2 fusion proteins exhibited robust surface expression in the plasma membrane of neurons at synapses as did CD8 alone. In contrast, the NR1 fusion protein was retained intracellularly in both HEK293 cells and neurons because of the presence of an ER retention signal in the C1 cassette. This ER retention signal was overridden either by the addition of a PDZ domain-binding motif or by mimicking phosphorylation at a site adjacent to the retention signal. These results provide further evidence that the intracellular trafficking of AMPAR and NMDAR subunits are regulated independently at least in part because of differences in the protein-protein interactions of their intracellular C-terminal tails.
控制N-甲基-D-天冬氨酸受体（NMDARs）和α-氨基-3-羟基-5-甲基-4-异恶唑丙酸受体（AMPARs）表面表达的分子机制尚不清楚。为了确定谷氨酸受体亚基的细胞内C末端尾巴在AMPARs和NMDARs突触靶向中的作用，我们将AMPAR亚基GluR1和GluR2以及NMDAR亚基NR1的尾巴与人类T淋巴细胞膜蛋白CD8融合，并在HEK293细胞和培养的海马神经元中表达这些构建体。GluR1和GluR2融合蛋白在突触处神经元的质膜中表现出强大的表面表达，单独的CD8也是如此。相比之下，由于C1盒中存在内质网滞留信号，NR1融合蛋白在HEK293细胞和神经元中均保留在细胞内。通过添加PDZ结构域结合基序或模拟滞留信号相邻位点的磷酸化，可克服这种内质网滞留信号。这些结果提供了进一步的证据，表明AMPAR和NMDAR亚基的细胞内运输至少部分是独立调节的，这是由于它们细胞内C末端尾巴的蛋白质-蛋白质相互作用存在差异。
