Garvan Institute for Medical Research, Sydney, New South Wales 2010, Australia.
J Biol Chem. 2011 Jun 3;286(22):19724-34. doi: 10.1074/jbc.M110.205781. Epub 2011 Apr 12.
Scapinin is an actin- and PP1-binding protein that is exclusively expressed in the brain; however, its function in neurons has not been investigated. Here we show that expression of scapinin in primary rat cortical neurons inhibits axon elongation without affecting axon branching, dendritic outgrowth, or polarity. This inhibitory effect was dependent on its ability to bind actin because a mutant form that does not bind actin had no effect on axon elongation. Immunofluorescence analysis showed that scapinin is predominantly located in the distal axon shaft, cell body, and nucleus of neurons and displays a reciprocal staining pattern to phalloidin, consistent with previous reports that it binds actin monomers to inhibit polymerization. We show that scapinin is phosphorylated at a highly conserved site in the central region of the protein (Ser-277) by Cdk5 in vitro. Expression of a scapinin phospho-mimetic mutant (S277D) restored normal axon elongation without affecting actin binding. Instead, phosphorylated scapinin was sequestered in the cytoplasm of neurons and away from the axon. Because its expression is highest in relatively plastic regions of the adult brain (cortex, hippocampus), scapinin is a new regulator of neurite outgrowth and neuroplasticity in the brain.
Scapinin 是一种肌动蛋白和 PP1 结合蛋白，仅在大脑中表达；然而，其在神经元中的功能尚未被研究过。在这里，我们发现 scapinin 在原代大鼠皮质神经元中的表达抑制轴突伸长，而不影响轴突分支、树突生长或极性。这种抑制作用依赖于其与肌动蛋白结合的能力，因为不与肌动蛋白结合的突变体形式对轴突伸长没有影响。免疫荧光分析表明，scapinin 主要位于神经元的远端轴突干、细胞体和核内，并与鬼笔环肽呈现相互染色模式，与先前报道的它结合肌动蛋白单体以抑制聚合一致。我们表明 Cdk5 在体外将 scapinin 蛋白的中心区域（Ser-277）的一个高度保守位点磷酸化。表达 scapinin 的磷酸模拟突变体（S277D）可恢复正常的轴突伸长，而不影响肌动蛋白结合。相反，磷酸化的 scapinin 被隔离在神经元的细胞质中，远离轴突。由于其在成年大脑（皮质、海马体）中相对可塑性较高的区域表达最高，scapinin 是大脑中神经突生长和神经可塑性的新调节剂。
