Li Dongjun, Wang Fushun, Lai Meizan, Chen Yuan, Zhang Ji-fang
Department of Physiology, Jefferson Medical College, Philadelphia, Pennsylvania 19107, USA.
J Neurosci. 2005 Feb 23;25(8):1914-23. doi: 10.1523/JNEUROSCI.4790-04.2005.
Phosphorylation and dephosphorylation are primary means for rapid regulation of a variety of neuronal functions, such as membrane excitability, neurotransmitter release, and gene expression. Voltage-gated Ca2+ channels are targets for phosphorylation by a variety of second messengers through activation of different types of protein kinases (PKs). Protein phosphatases (PPs), like PKs, are equally important in regulating Ca2+ channels in neurons. However, much less is understood about whether and how a particular type of PP contributes to regulating neuronal Ca2+ channel activities. This is primarily because of the lack of specific inhibitors/activators for different types of PPs, particularly the PP2c family. The functional roles of PP2c and its substrates in the brain remain virtually unknown. During our yeast two-hybrid screening, PP2calpha was pulled out by both N- and P/Q-type Ca2+ channel C termini. This raised the possibility that PP2calpha might be associated with voltage-gated Ca2+ channels for regulation of the Ca(2+) channel activity. Biochemical studies show that PP2calpha binds directly to neuronal Ca2+ channels forming a functional protein complex in vivo. PP2calpha, unlike PP1, PP2a and PP2b, is more effective in dephosphorylation of neuronal Ca2+ channels after their phosphorylation by PKC. In hippocampal neurons, disruption of the PP2calpha-Ca2+ channel interaction significantly enhances the response of Ca2+ channels to modulation by PKC. Thus, the PP2calpha-Ca2+ channel complex is responsible for rapid dephosphorylation of Ca2+ channels and may contribute to regulation of synaptic transmission in neurons.
磷酸化和去磷酸化是快速调节多种神经元功能的主要方式，如膜兴奋性、神经递质释放和基因表达。电压门控Ca2+通道是多种第二信使通过激活不同类型的蛋白激酶（PK）进行磷酸化的靶点。与PK一样，蛋白磷酸酶（PP）在调节神经元中的Ca2+通道方面同样重要。然而，对于特定类型的PP是否以及如何参与调节神经元Ca2+通道活性，人们了解得要少得多。这主要是因为缺乏针对不同类型PP的特异性抑制剂/激活剂，尤其是PP2c家族。PP2c及其底物在大脑中的功能作用实际上仍然未知。在我们的酵母双杂交筛选过程中，N型和P/Q型Ca2+通道的C末端均筛选出了PP2calpha。这增加了PP2calpha可能与电压门控Ca2+通道相关联以调节Ca(2+)通道活性的可能性。生化研究表明，PP2calpha在体内直接与神经元Ca2+通道结合形成功能性蛋白复合物。与PP1、PP2a和PP2b不同，PP2calpha在神经元Ca2+通道被PKC磷酸化后，对其去磷酸化更有效。在海马神经元中，PP2calpha-Ca2+通道相互作用的破坏显著增强了Ca2+通道对PKC调节的反应。因此，PP2calpha-Ca2+通道复合物负责Ca2+通道的快速去磷酸化，并可能有助于调节神经元中的突触传递。
