SK2-associated protein kinase CK2: molecular basis and physiological roles

描述(由申请人提供)：小电导钙激活的钾通道(SK通道)由钙离子通过结构性相关的钙调蛋白(CaM)直接门控。在许多中枢神经元中，如CA1海马神经元，SK通道活动是动作电位后超极化(MAHP)的中间成分，影响动作电位的数目和动作电位爆发时的峰间间期，从而调节神经元的兴奋性。此外，CA1神经元中的SK通道调节突触可塑性和改变记忆编码。阻断SK通道降低了在Schaffer侧支突触诱导NMDA受体依赖的长时程增强所需的刺激强度，并减少了海马体依赖学习所需的训练试验次数。因此，SK通道的调节剂将对神经元的综合功能产生深远的影响。我们发现，第三种蛋白质，丝氨酸/苏氨酸蛋白激酶CK2，形成了SK2通道复合体的稳定和不可或缺的组成部分。SK2相关的CK2使CaM的T80磷酸化，并诱导SK2通道门控的钙敏感性发生改变。更多的数据表明，SK2通道的N-末端和C-末端结构域与CaM结合域在空间上接近，并且这三个结构域都与CK2相互作用。此外，N-末端结构域是CK2的强激活剂，而C-末端结构域包含大量的磷酸化位点。这一应用的驱动假设是SK2通道的N-末端和C-末端结构域调节相关的CK2活性以响应动态代谢信号，并且SK2相关的CK2活性影响神经元的兴奋性和突触可塑性的诱导。为了验证这一假设，我们将确定SK2和CK2之间相互作用的准确位置，并确定N-末端和C-末端结构域对CK2活性的贡献。我们将确定SK2-CaM-CK2络合物的高分辨结构。我们将把非CK2依赖的SK2通道引入SK2基因缺失小鼠的CA1区，并确定其对兴奋性和突触可塑性的影响。这些研究将使用一系列新的试剂和技术，以产生对多蛋白SK2通道复合体的完整理解，以及它们在神经元兴奋性和突触可塑性的基本方面的作用。此外，降低SK2相关CK2活性从而降低神经元兴奋性的药物可能是治疗精神分裂症和癫痫等过度兴奋性障碍的治疗途径。

DESCRIPTION (provided by applicant): Small conductance Ca2+-activated K+ channels (SK channels) are gated directly by Ca2+ ions, via constitutively associated calmodulin (CaM). In many central neurons such as CA1 hippocampal neurons, SK channel activity underlies a medium component of the after hyperpolarization (mAHP) that follows an action potential, influencing the number of action potentials and the interspike interval during a burst of action potentials, thereby regulating neuronal excitability. In addition, SK channels in CA1 neurons modulate synaptic plasticity and alter memory encoding. Blocking SK channels reduces the stimulus intensity that is required to induce NMDA receptor-dependent long-term potentiation at Schaffer collateral synapses, and reduces the number of training trials required for hippocampal dependent learning. Therefore, modulators of SK channels will exert profound effects on integrated neuronal functions. We have found that a third protein, the serine/threonine protein kinase CK2, forms a stable and integral component of the SK2 channel complex. SK2-associated CK2 phosphorylates T80 of CaM and induces a shift in the Ca2+ sensitivity of SK2 channel gating. Additional data suggest that the N- and C-terminal domains of SK2 channels are in spatial proximity to the CaM binding domain, and all three domains interact with CK2. Further, the N-terminal domain is a strong activator of CK2, while the C-terminal domain contains numerous phosphorylation sites. The driving hypothesis for this application is that the N- and C-terminal domains of the SK2 channel regulate associated CK2 activity in response to dynamic metabolic signals and that SK2-associated CK2 activity influences neuronal excitability and the induction of synaptic plasticity. To test this hypothesis, we will identify the precise sites of interaction between SK2 and CK2 and determine the contributions of the N- and C-terminal domains to CK2 activity. We will determine high resolution structures of SK2-CaM-CK2 complexes. We will introduce CK2-independent SK2 channels into the CA1 area of SK2-null mice and determine the consequences for excitability and synaptic plasticity. These studies will employ a novel repertoire of reagents and techniques to engender an integrated understanding of multi-protein SK2 channel complexes, and their roles in fundamental aspects of neuronal excitability as well as synaptic plasticity. In addition, drugs that decrease SK2-associated CK2 activity and thereby decrease neuronal excitability may be therapeutic avenues for treatments of hyperexcitability disorders such as schizophrenia and epilepsy.