Wang Ping, Wu Yalan, Ge Xin, Ma Lan, Pei Gang
Laboratory of Molecular Cell Biology, Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200031, People's Republic of China.
J Biol Chem. 2003 Mar 28;278(13):11648-53. doi: 10.1074/jbc.M208109200. Epub 2003 Jan 21.
beta-Arrestin1 and beta-arrestin2 play a key role in the regulation of G protein-coupled receptor-mediated signaling, whereas the subcellular distribution of beta-arrestin1 and beta-arrestin2 has been shown to be quite different. In this study, we found that although both beta-arrestin1 and beta-arrestin2 are able to interact with ubiquitin-protein isopeptide ligase (E3) Mdm2, only expression of beta-arrestin2 leads to the relocalization of Mdm2 from the nucleus to the cytoplasm. Further study reveals that beta-arrestin2 but not beta-arrestin1 shuttles between the cytoplasm and nucleus in a leptomycin B-sensitive manner. A hydrophobic amino acid-rich region (VXXXFXXLXL) at the C terminus of beta-arrestin2 was further demonstrated to serve as a nuclear export signal responsible for the extranuclear localization of beta-arrestin2. In the corresponding region of beta-arrestin1, there is a single amino acid difference (Glu instead of Leu in beta-arrestin2), and mutation of Glu to Leu conferred to beta-arrestin1 similar subcellular distribution to that of beta-arrestin2. Moreover, data from a series of deletion mutations demonstrated that the N domain (residues 1-185) was indispensable for the nuclear localization of both beta-arrestins, and the results from a Val to Asp point mutation in the N domain also supported this notion. In addition, our data showed that nucleocytoplasmic shuttling of beta-arrestin2 was required, via protein/protein interaction, for the cytoplasmic relocalization of Mdm2 and JNK3, another well known beta-arrestin2-binding protein. Our study thus suggests that both the nuclear export signal motif and the N domain of beta-arrestins are critical for the regulation of their subcellular localization and that beta-arrestin2 may modulate the function of its binding partners such as Mdm2 and JNK3 by alteration of their subcellular distribution.
β-抑制蛋白1和β-抑制蛋白2在G蛋白偶联受体介导的信号传导调节中起关键作用，然而，β-抑制蛋白1和β-抑制蛋白2的亚细胞分布已显示出相当大的差异。在本研究中，我们发现，虽然β-抑制蛋白1和β-抑制蛋白2都能够与泛素-蛋白异肽连接酶（E3）Mdm2相互作用，但只有β-抑制蛋白2的表达会导致Mdm2从细胞核重新定位到细胞质。进一步的研究表明，β-抑制蛋白2而非β-抑制蛋白1以对 leptomycin B敏感的方式在细胞质和细胞核之间穿梭。β-抑制蛋白2 C末端富含疏水氨基酸的区域（VXXXFXXLXL）进一步被证明作为核输出信号负责β-抑制蛋白2的核外定位。在β-抑制蛋白1的相应区域，存在单个氨基酸差异（β-抑制蛋白2中的Leu被Glu取代），将Glu突变为Leu使β-抑制蛋白1具有与β-抑制蛋白2相似的亚细胞分布。此外，一系列缺失突变的数据表明，N结构域（第1 - 185位氨基酸残基）对于两种β-抑制蛋白的核定位都是必不可少的，并且N结构域中Val到Asp的点突变结果也支持了这一观点。此外，我们的数据表明，β-抑制蛋白2的核质穿梭通过蛋白质/蛋白质相互作用，对于Mdm2和JNK3（另一种众所周知的β-抑制蛋白2结合蛋白）的细胞质重新定位是必需的。因此，我们的研究表明，β-抑制蛋白的核输出信号基序和N结构域对于其亚细胞定位的调节至关重要，并且β-抑制蛋白2可能通过改变其结合伴侣如Mdm2和JNK3的亚细胞分布来调节它们的功能。
