Tingley W G, Roche K W, Thompson A K, Huganir R L
Department of Neuroscience, Howard Hughes Medical Institute, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205.
Nature. 1993 Jul 1;364(6432):70-3. doi: 10.1038/364070a0.
The NMDA (N-methyl D-aspartate) receptors in the brain play a critical role in synaptic plasticity, synaptogenesis and excitotoxicity. Molecular cloning has demonstrated that NMDA receptors consist of several homologous subunits (NMDAR1, 2A-2D). A variety of studies have suggested that protein phosphorylation of NMDA receptors may regulate their function and play a role in many forms of synaptic plasticity such as long-term potentiation. We have examined the phosphorylation of the NMDA receptor subunit NMDAR1 (NR1) by protein kinase C (PKC) in cells transiently expressing recombinant NR1 and in primary cultures of cortical neurons. PKC phosphorylation occurs on several distinct sites on the NR1 subunit. Most of these sites are contained within a single alternatively spliced exon in the C-terminal domain, which has previously been proposed to be on the extracellular side of the membrane. These results demonstrate that alternative splicing of the NR1 messenger RNA regulates its phosphorylation by PKC, and that mRNA splicing is a novel mechanism for regulating the sensitivity of glutamate receptors to protein phosphorylation. These results also provide evidence that the C-terminal domain of the NR1 protein is located intracellularly, suggesting that the proposed transmembrane topology model for glutamate receptors may be incorrect.
大脑中的NMDA（N-甲基-D-天冬氨酸）受体在突触可塑性、突触形成和兴奋性毒性中起关键作用。分子克隆表明，NMDA受体由几个同源亚基（NMDAR1、2A - 2D）组成。各种研究表明，NMDA受体的蛋白质磷酸化可能调节其功能，并在多种形式的突触可塑性（如长时程增强）中发挥作用。我们已经在瞬时表达重组NR1的细胞和皮质神经元原代培养物中研究了蛋白激酶C（PKC）对NMDA受体亚基NMDAR1（NR1）的磷酸化作用。PKC磷酸化发生在NR1亚基的几个不同位点上。这些位点大多数包含在C末端结构域的一个单一可变剪接外显子中，该外显子先前被认为位于膜的细胞外侧。这些结果表明，NR1信使RNA的可变剪接调节其被PKC的磷酸化作用，并且mRNA剪接是调节谷氨酸受体对蛋白质磷酸化敏感性的一种新机制。这些结果还提供了证据，表明NR1蛋白的C末端结构域位于细胞内，这表明所提出的谷氨酸受体跨膜拓扑模型可能是不正确的。
