Working mechanism of Ca^<2+>/calmodulin-dependent protein kinase II in synaptic plasticity

观察到Ca^<2+>/钙调素依赖蛋白激酶II （CaM kinase II）中286位苏氨酸（Thr-286）的自磷酸化将其从Ca^<2+>依赖形式转化为Ca^<2+>独立形式（组成活性形式），这导致了Ca^<2+>独立形式的酶的形成可以编码突触使用频率并作为“记忆”的分子开关。事实上，海马CA1区长期增强（LTP）的诱导与Ca^<2+>-不依赖和总CaM激酶IL活性的持续增加以及自磷酸化的增加有关。我们进一步用一种特异性抗体确认了Thr-286的自磷酸化，在LTP诱导后，高而非低频率的CA1传入刺激导致CA1神经元细胞体和树突的免疫荧光强度增加。在CA1区，更多的ospho特异性抗体与NMDA受体的免疫反应共定位。由于Ca^<2+>-不依赖的活性可以被蛋白磷酸酶逆转，我们接下来研究了蛋白磷酸酶在LTP诱导过程中的活性调节。在LTP诱导后，CA1区可溶性部分的蛋白磷酸酶2A活性显著降低，而自磷酸化CaM激酶II作为底物的蛋白磷酸酶2C活性没有变化。体外和体内研究表明，在LTP诱导过程中，CaM激酶II对蛋白磷酸酶2A的调节亚基B' α亚基的磷酸化是抑制蛋白磷酸酶活性的基础。这些结果表明，CaM基化酶II降低了蛋白磷酸酶2A的活性，通过促进组成活性CaM激酶II的产生和调节特定突触蛋白的磷酸化，协同促进LTP的表达。少

The observation that autophosphorylation of threonine at position 286 (Thr-286) in Ca^<2+>/calmodulin-dependent protein kinase II (CaM kinase II) converts it from the Ca^<2+>-dependent form to the Ca^<2+>-independent form (constitutively active form) have led to hypothesis that the formation of Ca^<2+>-independent form of the enzyme could encode the frequency of synaptic usage and serve as a molecular switch of "memory". Indeed, induction of long-term potentiation (LTP) in CA1 region of hippocampal slices was associated with long-lasting increases in Ca^<2+>-independent and total activities of CaM kinase IL as well as an increase in the autophosphorylation. We further confirmed with a specific antibody recognized the autophosphorylation of Thr-286 that high, but not low frequency stimulation applied to CA1 afferents resulted in increases in immunofluorescent intensity in the cell bodies and dendrites in the CA1 neurons after LTP induction. The strong immunoreactivities with the anti-ph … More ospho-specific antibody were co-localized with immunoreactivities against NMDA receptor in the CA1 regions. Since the Ca^<2+>-independent activity can be reversed by protein phosphatases, we next investigated regulation of protein phosphatase activity during LTP induction. A significant decrease in protein phosphatase 2A activity in the soluble fractions was observed in the CA1 regions following LTP induction without change in protein phosphatase 2C activity using autophosphorylated CaM kinase II as substrate. In vitro and in vivo studies revealed that phosphorylation of B'alpha subunit, a regulatory subunit of protein phosphatase 2A, by CaM kinase II is underlying the inhibition of the protein phosphatase activity during LTP induction. These results suggest that the decreased protein phosphatase 2A activity by CaM kiriase II can synergistically contribute to the expression of LTP by favoring generation of the constitutively active CaM kinase II and by regulating the phosphorylation of specific synaptic proteins. Less