Department of Pharmacology, University of Iowa, Iowa City, IA 52242, USA.
Neuron. 2013 May 8;78(3):483-97. doi: 10.1016/j.neuron.2013.02.032.
Regulation of neuronal excitability and cardiac excitation-contraction coupling requires the proper localization of L-type Ca²⁺ channels. We show that the actin-binding protein α-actinin binds to the C-terminal surface targeting motif of α11.2, the central pore-forming Ca(V)1.2 subunit, in order to foster its surface expression. Disruption of α-actinin function by dominant-negative or small hairpin RNA constructs reduces Ca(V)1.2 surface localization in human embryonic kidney 293 and neuronal cultures and dendritic spine localization in neurons. We demonstrate that calmodulin displaces α-actinin from their shared binding site on α11.2 upon Ca²⁺ influx through L-type channels, but not through NMDAR, thereby triggering loss of Ca(V)1.2 from spines. Coexpression of a Ca²⁺-binding-deficient calmodulin mutant does not affect basal Ca(V)1.2 surface expression but inhibits its internalization upon Ca²⁺ influx. We conclude that α-actinin stabilizes Ca(V)1.2 at the plasma membrane and that its displacement by Ca²⁺-calmodulin triggers Ca²⁺-induced endocytosis of Ca(V)1.2, thus providing an important negative feedback mechanism for Ca²⁺ influx.
神经元兴奋性和心脏兴奋-收缩偶联的调节需要 L 型 Ca²⁺ 通道的正确定位。我们表明，肌动蛋白结合蛋白 α-辅肌动蛋白与α11.2 的 C 端表面靶向基序结合，α11.2 是中央孔形成 Ca(V)1.2 亚基，以促进其表面表达。通过显性负性或短发夹 RNA 构建体破坏 α-辅肌动蛋白的功能会减少人胚肾 293 和神经元培养物中的 Ca(V)1.2 表面定位和神经元中的树突棘定位。我们证明，钙调蛋白在 Ca²⁺ 通过 L 型通道而不是通过 NMDA 受体流入时，从其在α11.2 上的共享结合位点取代α-辅肌动蛋白，从而导致 Ca(V)1.2 从棘突中丢失。共表达钙结合缺陷型钙调蛋白突变体不会影响基础 Ca(V)1.2 表面表达，但会抑制其在 Ca²⁺ 流入时内化。我们得出结论，α-辅肌动蛋白稳定 Ca(V)1.2 在质膜上，并且其被 Ca²⁺-钙调蛋白取代会触发 Ca²⁺ 诱导的 Ca(V)1.2 内吞作用，从而为 Ca²⁺ 流入提供重要的负反馈机制。
