Scott Mark G H, Le Rouzic Erwann, Périanin Axel, Pierotti Vincenzo, Enslen Hervé, Benichou Serge, Marullo Stefano, Benmerah Alexandre
Department of Cell Biology, Institut Cochin, Pavillon Gustave Roussy, 75679 Paris CEDEX 14, France.
J Biol Chem. 2002 Oct 4;277(40):37693-701. doi: 10.1074/jbc.M207552200. Epub 2002 Aug 6.
beta-arrestins (betaarrs) are two highly homologous proteins that uncouple G protein-coupled receptors from their cognate G proteins, serve as adaptor molecules linking G protein-coupled receptors to clathrin-coat components (AP-2 complex and clathrin), and act as scaffolding proteins for ERK1/2 and JNK3 cascades. A striking difference between the two betaarrs (betaarr1 and betaarr2) is that betaarr1 is evenly distributed throughout the cell, whereas betaarr2 shows an apparent cytoplasmic localization at steady state. Here, we investigate the molecular determinants underlying this differential distribution. betaarr2 is constitutively excluded from the nucleus by a leptomycin B-sensitive pathway because of the presence of a classical leucine-rich nuclear export signal in its C terminus (L395/L397) that is absent in betaarr1. In addition, using a nuclear import assay in yeast we showed that betaarr2 is actively imported into the nucleus, suggesting that betaarr2 undergoes constitutive nucleocytoplasmic shuttling. In cells expressing betaarr2, JNK3 is mostly cytosolic. A point mutation of the nuclear export signal (L395A) in betaarr2, which was sufficient to redistribute betaarr2 from the cytosol to the nucleus, also caused the nuclear relocalization of JNK3. These data indicate that the nucleocytoplasmic shuttling of betaarr2 controls the subcellular distribution of JNK3.
β-抑制蛋白（βarrs）是两种高度同源的蛋白质，它们使G蛋白偶联受体与其同源G蛋白解偶联，作为衔接分子将G蛋白偶联受体与网格蛋白包被成分（AP-2复合物和网格蛋白）相连，并作为ERK1/2和JNK3级联反应的支架蛋白。两种βarrs（βarr1和βarr2）之间的一个显著差异是，βarr1均匀分布于整个细胞，而βarr2在稳态时表现出明显的细胞质定位。在此，我们研究了这种差异分布背后的分子决定因素。由于βarr2的C末端存在一个典型的富含亮氨酸的核输出信号（L395/L397），而βarr1中不存在该信号，βarr2通过一种对放线菌素B敏感的途径被组成性地排除在细胞核之外。此外，通过在酵母中进行核输入测定，我们发现βarr2被主动转运到细胞核中，这表明βarr2经历了组成性的核质穿梭。在表达βarr2的细胞中，JNK3主要位于细胞质中。βarr2中核输出信号的点突变（L395A）足以将βarr2从细胞质重新分布到细胞核，同时也导致了JNK3的核重新定位。这些数据表明，βarr2的核质穿梭控制着JNK3的亚细胞分布。
