Regulation of Metabotropic Glutamate Receptor Signaling

I组mGluR(mGluR1和mGluR5)主要是突触后mGluR，与磷脂酶C偶联，释放细胞内钙离子，激活多种细胞内信号分子。已知mGluR5的PKC磷酸化影响钙信号转导和受体脱敏已有一段时间，但对mGluR5的直接磷酸化还没有进行严格的研究。因此，我们正在研究mGluR5的磷酸化，并发现了几个被蛋白激酶C磷酸化的特定残基。这些PKC位点位于mGluR5 C末端结构域近三分之一的位置。一个名为Ser839的磷酸化位点决定了mGluR5激活后细胞内钙振荡的调节。我们已经确定的第二个磷酸化位点Ser901抑制了蛋白钙调蛋白与mGluR5的结合，并降低了mGluR5的表面表达。在对突触前受体mGluR7的平行研究中，我们发现Ser862的PKC磷酸化抑制了钙调蛋白的结合，并增加了受体表面的表达。因此，我们发现了一个共同的机制来快速修改mGluR表面表达，以响应钙离子、PKC活性和钙调蛋白结合的变化；然而，表面表达的变化取决于受体亚型和可能被钙调素结合破坏的额外的受体亚型特异结合蛋白。这些研究准确地定义了PKC对mGluRs的磷酸化，将使我们能够研究谷氨酸受体磷酸化的功能后果以及细胞内信号和受体运输的调节。

The group I mGluRs (mGluR1 and mGluR5) are predominantly postsynaptic mGluRs that are coupled to phospholipase C, release of intracellular Ca2+, and activation of a variety of intracellular signaling molecules. PKC phosphorylation of mGluR5 has been known to affect Ca2+ signaling and receptor desensitization for some time, but rigorous studies on the direct phosphorylation of mGluR5 havent been conducted. Therefore, we are investigating the phosphorylation of mGluR5 and have identified several specific residues that are phosphorylated by protein kinase C. These PKC sites are located within the proximal one-third of the mGluR5 C-terminal domain. One phosphorylation site, Ser839, determines the regulation of intracellular calcium oscillations in response to mGluR5 activation. A second phosphorylation site that we have identified, Ser901, inhibits the binding of the protein calmodulin to mGluR5 and decreases mGluR5 surface expression. In parallel studies on the presynaptic receptor, mGluR7, we find that PKC phosphorylation of Ser862 inhibits calmodulin binding, and increases receptor surface expression. Therefore, we find a common mechanism to rapidly modify mGluR surface expression in response to increases in Ca2+, PKC activity, and changes in calmodulin binding; however, the changes in surface expression depend on receptor subtype and likely additional receptor subtype-specific binding proteins that are disrupted by calmodulin binding. These studies precisely defining the phosphorylation of mGluRs by PKC will allow us to study the functional consequences of glutamate receptor phosphorylation and the regulation of intracellular signaling and receptor trafficking.