Tavalin Steven J, Colbran Roger J
Department of Pharmacology, University of Tennessee Health Science Center, Memphis, TN 38103, United States.
Department of Molecular Physiology & Biophysics, Brain Institute, and Kennedy Center for Research on Human Development, Vanderbilt University School of Medicine, Nashville, TN, 37232-0615, United States.
Mol Cell Neurosci. 2017 Mar;79:45-52. doi: 10.1016/j.mcn.2016.12.002. Epub 2016 Dec 18.
Some forms of long-term synaptic plasticity require docking of Ca/calmodulin-dependent protein kinase II α (CaMKIIα) to residues 1290-1309 within the intracellular C-terminal tail of the N-methyl-d-aspartate (NMDA) receptor GluN2B subunit. The phosphorylation of Ser1303 within this region destabilizes CaMKII binding. Interestingly, Ser1303 is a substrate for CaMKII itself, as well as PKC and DAPK1, but these kinases have been reported to have contradictory effects on the activity of GluN2B-containing NMDA receptors. Here, we re-assessed the effect of CaMKII on NMDA receptor desensitization in heterologous cells, as measured by the ratio of steady-state to peak currents induced during 3s agonist applications. CaMKIIα co-expression or infusion of constitutively active CaMKII limits the extent of desensitization and preserves current amplitude with repeated stimulation of recombinant GluN1A/GluN2B when examined using low intracellular chloride (Cl) levels, characteristic of neurons beyond the first postnatal week. In contrast, CaMKIIα enhances the acute rate and extent of desensitization when intracellular Cl concentrations are high. The apparent dependence of CaMKIIα effects on NMDA receptor desensitization on Cl concentrations is consistent with the presence of a Ca-activated Cl conductance endogenous to HEK 293 cells, which was confirmed by photolysis of caged-Ca. However, Ca-activated Cl conductances are unaffected by CaMKIIα expression, indicating that CaMKII affects agonist-induced whole cell currents via modulation of the NMDA receptor. In support of this idea, CaMKIIα modulation of GluN2B-NMDA receptors is abrogated by the phospho-null mutation of Ser1303 in GluN2B to alanine and occluded by phospho-mimetic mutation of Ser1303 to aspartate regardless of intracellular Cl concentration. Thus, CaMKII-mediated phosphorylation of GluN2B-containing NMDA receptors reduces desensitization at physiological (low) intracellular Cl, perhaps serving as a feed-forward mechanism to sustain NMDA-mediated Ca entry and continued CaMKII activation during learning and memory.
某些形式的长期突触可塑性需要钙/钙调蛋白依赖性蛋白激酶IIα（CaMKIIα）与N-甲基-D-天冬氨酸（NMDA）受体GluN2B亚基细胞内C末端尾巴中的1290 - 1309位残基对接。该区域内Ser1303的磷酸化会破坏CaMKII的结合。有趣的是，Ser1303是CaMKII自身以及蛋白激酶C（PKC）和死亡相关蛋白激酶1（DAPK1）的底物，但据报道这些激酶对含GluN2B的NMDA受体的活性有相互矛盾的影响。在这里，我们重新评估了CaMKII对异源细胞中NMDA受体脱敏的影响，这是通过在3秒激动剂应用期间诱导的稳态电流与峰值电流的比率来衡量的。当使用出生后第一周以后神经元特有的低细胞内氯化物（Cl）水平进行检测时，共表达CaMKIIα或注入组成型活性CaMKII会限制脱敏程度，并在重复刺激重组GluN1A/GluN2B时保持电流幅度。相反，当细胞内Cl浓度较高时，CaMKIIα会增强脱敏的急性速率和程度。CaMKIIα对NMDA受体脱敏的影响明显依赖于Cl浓度，这与HEK 293细胞内源性存在钙激活的Cl电导一致，这一点通过笼锁钙的光解得到证实。然而，钙激活的Cl电导不受CaMKIIα表达的影响，表明CaMKII通过调节NMDA受体来影响激动剂诱导的全细胞电流。支持这一观点的是，无论细胞内Cl浓度如何，将GluN2B中Ser1303突变为丙氨酸的磷酸化缺失突变会消除CaMKIIα对GluN2B - NMDA受体调制作用，而将Ser1303突变为天冬氨酸的磷酸化模拟突变会阻断这种调制作用。因此，CaMKII介导的含GluN2B的NMDA受体磷酸化在生理（低）细胞内Cl浓度下会减少脱敏，这可能作为一种前馈机制，在学习和记忆过程中维持NMDA介导的钙内流和持续的CaMKII激活。
