Amazit Larbi, Alj Youssef, Tyagi Rakesh Kumar, Chauchereau Anne, Loosfelt Hugues, Pichon Christophe, Pantel Jacques, Foulon-Guinchard Emmanuelle, Leclerc Philippe, Milgrom Edwin, Guiochon-Mantel Anne
INSERM U135, Hormones, Gènes et Reproduction, IFR Bicêtre, Laboratoire d'Hormonologie et Biologie Moléculaire, AP-HP, Hôpital Bicêtre, 78 rue du Général Leclerc, 94275-Le Kremlin-Bicêtre cedex, France.
J Biol Chem. 2003 Aug 22;278(34):32195-203. doi: 10.1074/jbc.M300730200. Epub 2003 Jun 4.
Steroid hormone receptors are ligand-stimulated transcription factors that modulate gene transcription by recruiting coregulators to gene promoters. Subcellular localization and dynamic movements of transcription factors have been shown to be one of the major means of regulating their transcriptional activity. In the present report we describe the subcellular localization and the dynamics of intracellular trafficking of steroid receptor coactivator 1 (SRC-1). After its synthesis in the cytoplasm, SRC-1 is imported into the nucleus, where it activates transcription and is subsequently exported back to the cytoplasm. In both the nucleus and cytoplasm, SRC-1 is localized in speckles. The characterization of SRC-1 nuclear localization sequence reveals that it is a classic bipartite signal localized in the N-terminal region of the protein, between amino acids 18 and 36. This sequence is highly conserved within the other members of the p160 family. Additionally, SRC-1 nuclear export is inhibited by leptomycin B. The region involved in its nuclear export is localized between amino acids 990 and 1038. It is an unusually large domain differing from the classic leucine-rich NES sequences. Thus SRC-1 nuclear export involves either an alternate type of NES or is dependent on the interaction of SRC-1 with a protein, which is exported through the crm1/exportin pathway. Overall, the intracellular trafficking of SRC-1 might be a mechanism to regulate the termination of hormone action, the interaction with other signaling pathways in the cytoplasm and its degradation.
类固醇激素受体是配体刺激的转录因子，通过将共调节因子招募到基因启动子来调节基因转录。转录因子的亚细胞定位和动态移动已被证明是调节其转录活性的主要方式之一。在本报告中，我们描述了类固醇受体共激活因子1（SRC-1）的亚细胞定位和细胞内运输的动态变化。在细胞质中合成后，SRC-1被导入细胞核，在那里它激活转录，随后又被运回细胞质。在细胞核和细胞质中，SRC-1都定位在斑点中。对SRC-1核定位序列的表征显示，它是一个经典的双分型信号，位于蛋白质的N端区域，在氨基酸18和36之间。该序列在p160家族的其他成员中高度保守。此外，SRC-1的核输出受到雷帕霉素B的抑制。参与其核输出的区域位于氨基酸990和1038之间。它是一个异常大的结构域，不同于经典的富含亮氨酸的核输出信号序列。因此，SRC-1的核输出要么涉及一种另类的核输出信号，要么依赖于SRC-1与一种通过crm1/输出蛋白途径输出的蛋白质的相互作用。总体而言，SRC-1的细胞内运输可能是一种调节激素作用终止、与细胞质中其他信号通路相互作用及其降解的机制。
