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

钙调素依赖的蛋白激酶II(CaM Kinase II)中第286位苏氨酸(Thr-286)的自动磷酸化使其从依赖于钙的形式转变为非依赖于钙的形式(结构性活性形式)，这导致了一种假说，即该酶的非依赖形式的形成可以编码突触使用的频率，并作为“记忆”的分子开关。事实上，海马片CA1区长时程增强(LTP)的诱导与钙非依赖性和总的CaM激酶IL活性的长期增加以及自磷酸化的增加有关。我们用一种识别Thr-286自身磷酸化的特异性抗体进一步证实，在LTP诱导后，对CA1传入神经元施加高频刺激而不是低频刺激导致CA1神经元胞体和树突的免疫荧光强度增加。与抗Ph…的强免疫反应性更多的磷酸化特异性抗体与抗NMDA受体的免疫反应共同定位在CA1区。由于钙非依赖性的活性可以被蛋白磷酸酶逆转，我们接下来研究了LTP诱导过程中蛋白磷酸酶活性的调节。LTP诱导后，以自磷酸化的CaM激酶II为底物，CA1区可溶组分中的蛋白磷酸酶2A活性显著降低，而蛋白磷酸酶2C的活性无明显变化。体外和体内研究表明，在LTP诱导过程中，蛋白磷酸酶2A的调节亚基B‘α亚基被CaM激酶II磷酸化是抑制蛋白磷酸酶活性的基础。这些结果表明，CaM kiriase II降低蛋白磷酸酶2A的活性可能通过促进固有活性的CaM激酶II的产生和调节特定突触蛋白的磷酸化而协同作用于LTP的表达。较少

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