Different Roles of C-terminal Cassettes in the Trafficking of Full-length NR1 Subunits to the Cell Surface
Different Roles of C-terminal Cassettes in the Trafficking of Full-length NR1 Subunits to the Cell Surface
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DOI：
10.1074/jbc.m807050200
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发表时间：
2009-04-10
影响因子：
4.8
通讯作者：
Wenthold, Robert J.
中科院分区：
文献类型：
--
作者：
Horak, Martin;Wenthold, Robert J.
N-甲基-D-天冬氨酸（NMDA）受体是由NR 1和NR 2亚基组成的谷氨酸门控离子通道。当单独表达时，最普遍的NR 1剪接变体和所有NR 2亚基保留在内质网（ER）中，而其他NR 1剪接变体以不同程度到达细胞表面。由于类似的运输模式已被视为单跨膜结构域嵌合蛋白与附加的C末端的NMDA受体亚基，这些嵌合蛋白已被用作模型，用于研究潜在的机制的ER保留和表面贩运的NMDA受体。使用这种方法，在C1盒的RRR基序已被确定为一个主要的ER保留信号存在于NR 1亚基，和其他NR 1剪接变体的表面定位已被解释的C1盒的情况下，或通过存在的PDZ/外被体蛋白复合物II-结合域中的C2'盒。然而，当我们使用全长NR 1构建体测试这些结论时，出现了C-末端盒在NR 1亚基运输中的更复杂的作用。我们的实验表明，两个独立的ER保留基序在C1盒，KKK和RRR，是信号介导的全长NR 1亚基的ER保留和C2盒有一个额外的抑制作用的NR 1亚基的前向运输。另一方面，C 0和C2'盒对NR 1亚基向细胞表面的运输具有增强作用。我们的观察确定了C-末端盒在全长NR 1亚基的运输中的独特作用。
N-Methyl-D-aspartate (NMDA) receptors are glutamategated ion channels composed of NR1 and NR2 subunits. When expressed alone, the most prevalent NR1 splice variant and all NR2 subunits are retained in the endoplasmic reticulum (ER), whereas other NR1 splice variants reach the cell surface to varying degrees. Because similar trafficking patterns have been seen for single transmembrane domain chimeric proteins with appended C termini of NMDA receptor subunits, these chimeric proteins have been used as a model for studying the mechanisms underlying the ER retention and surface trafficking of NMDA receptors. Using this approach, an RRR motif in the C1 cassette has been identified as a major ER retention signal present in NR1 subunits, and the surface localization of other NR1 splice variants has been explained by the absence of the C1 cassette or by the presence of a PDZ/coatomer protein complex II-binding domain in the C2' cassette. However, when we tested these conclusions using full-length NR1 constructs, a more complex role of the C-terminal cassettes in the trafficking of NR1 subunits emerged. Our experiments showed that two independent ER retention motifs in the C1 cassette, KKK and RRR, are the signals mediating ER retention of the full-length NR1 subunits and that the C2 cassette has an additional inhibitory effect on the forward trafficking of NR1 subunits. On the other hand, C0 and C2' cassettes had an enhancing effect on the trafficking of NR1 subunits to the cell surface. Our observations identify the unique roles of C-terminal cassettes in the trafficking of full-length NR1 subunits.