Snyder Gretchen L, Galdi Stacey, Fienberg Allen A, Allen Patrick, Nairn Angus C, Greengard Paul
Laboratory of Molecular and Cellular Neuroscience, The Rockefeller University, 1230 York Avenue, New York, NY 10021, USA.
Neuropharmacology. 2003 Nov;45(6):703-13. doi: 10.1016/s0028-3908(03)00319-8.
Phosphorylation of the alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) receptor subunit GluR1 at Ser(845) enhances AMPA channel activity. This study demonstrates that Ser(845) is rapidly dephosphorylated upon AMPA receptor activation in nucleus accumbens slices. AMPA-induced dephosphorylation at Ser(845) was blocked by CNQX, an AMPA receptor antagonist, by nifedipine, an L-type Ca(2+) channel antagonist, or by cyclosporin A, a calcineurin inhibitor. N-methyl-D-aspartate (NMDA) treatment also decreased phosphorylation of Ser(845), an effect that was blocked by MK-801, an NMDA receptor antagonist, but not by nifedipine. Accumbens neurons are enriched for dopamine- and cyclic AMP (cAMP)-regulated phosphoprotein, Mr 32,000 (DARPP-32), a potent inhibitor of protein phosphatase 1 (PP1) when phosphorylated by PKA (at Thr(34)). We tested the hypothesis that the AMPA/KA or NMDA-stimulated dephosphorylation of DARPP-32 via calcineurin, leading to increased PP1 activity and dephosphorylation of GluR1. AMPA or NMDA treatment decreased phospho-Thr(34)-DARPP-32 levels, effects that were blocked by receptor antagonists, or cyclosporin A. However, dephosphorylation of Ser(845) mediated by AMPA or NMDA receptors was unaffected in DARPP-32/inhibitor-1 knockout mice. These data suggest that AMPA- or NMDA-induced dephosphorylation of GluR1 at Ser(845) occurs by a mechanism that is independent of DARPP-32 and PP1, but involves activation of calcineurin. Thus, Ca(2+)-dependent dephosphorylation of GluR1 may serve as a negative feedback mechanism for the regulation of AMPA receptor activity in neurons.
α-氨基-3-羟基-5-甲基异恶唑-4-丙酸（AMPA）受体亚基GluR1在丝氨酸845位点（Ser(845)）的磷酸化增强了AMPA通道活性。本研究表明，在伏隔核切片中，AMPA受体激活后，Ser(845)会迅速去磷酸化。AMPA受体拮抗剂CNQX、L型钙通道拮抗剂硝苯地平或钙调神经磷酸酶抑制剂环孢素A可阻断AMPA诱导的Ser(845)去磷酸化。N-甲基-D-天冬氨酸（NMDA）处理也会降低Ser(845)的磷酸化水平，NMDA受体拮抗剂MK-801可阻断该效应，但硝苯地平无此作用。伏隔核神经元富含多巴胺和环磷酸腺苷（cAMP）调节的磷蛋白，分子量为32,000（DARPP-32），当被蛋白激酶A（PKA）磷酸化（苏氨酸34位点（Thr(34)））时，它是蛋白磷酸酶1（PP1）的有效抑制剂。我们检验了以下假设：AMPA/KA或NMDA通过钙调神经磷酸酶刺激DARPP-32去磷酸化，导致PP1活性增加以及GluR1去磷酸化。AMPA或NMDA处理降低了磷酸化苏氨酸34-DARPP-32（phospho-Thr(34)-DARPP-32）水平，受体拮抗剂或环孢素A可阻断该效应。然而，在DARPP-32/抑制剂-1基因敲除小鼠中，AMPA或NMDA受体介导的Ser(845)去磷酸化未受影响。这些数据表明，AMPA或NMDA诱导的GluR1在Ser(845)位点的去磷酸化通过一种独立于DARPP-32和PP1的机制发生，但涉及钙调神经磷酸酶的激活。因此，GluR1的钙依赖性去磷酸化可能作为一种负反馈机制，用于调节神经元中AMPA受体的活性。
