Tomas Alejandra, Moss Stephen E
Division of Cell Biology, Institute of Ophthalmology, 11-43 Bath Street, London EC1V 9EL, United Kingdom.
J Biol Chem. 2003 May 30;278(22):20210-6. doi: 10.1074/jbc.M212669200. Epub 2003 Feb 24.
Annexin 11 is a widely expressed calcium- and phospholipid-binding protein that resides in the nucleoplasm in many cultured cell lines. This is in contrast to its most extensively characterized in vitro ligand, the small calcium-binding protein S100A6 (calcyclin), which is concentrated in the nuclear envelope. Here we have examined the significance of the association of annexin 11 and S100A6 by asking whether circumstances exist in which the two proteins occupy the same subcellular localization. First, we show that in both A431 and vascular smooth muscle cells, elevation of intracellular Ca2+ leads to translocation of annexin 11 from the nucleus to the nuclear envelope where it co-localizes with S100A6. We also demonstrate, using fusions of annexin 11 with green fluorescent protein, that whereas the C-terminal core domain of annexin 11 is essential for Ca2+ sensitivity, the N-terminal domain is required for targeting to the nuclear envelope. Second, we show that annexin 11 relocalizes to the nuclear envelope as A431 cells transit from early to mid-prophase. In late prophase, at the time of nuclear envelope breakdown, annexin 11 and S100A6 become intensely localized with lamina-associated polypeptide 2 to folds in the nuclear envelope. From metaphase to telophase S100A6 is degraded, but in late telophase annexin 11 associates with the reforming nuclear envelope before resuming a nucleoplasmic location in interphase. These results show that co-localization of annexin 11 and S100A6 at the nuclear envelope may be regulated either by elevation of intracellular Ca2+ or by cell cycle progression and provide the first evidence that these proteins may associate in vivo.
膜联蛋白11是一种广泛表达的钙结合和磷脂结合蛋白，在许多培养细胞系中位于核质中。这与其在体外最具特征的配体——小钙结合蛋白S100A6（钙周期蛋白）形成对比，后者集中在核膜中。在这里，我们通过询问是否存在两种蛋白质占据相同亚细胞定位的情况，研究了膜联蛋白11和S100A6关联的意义。首先，我们表明在A431细胞和血管平滑肌细胞中，细胞内Ca2+浓度升高会导致膜联蛋白11从细胞核转移到核膜，在那里它与S100A6共定位。我们还利用膜联蛋白11与绿色荧光蛋白的融合体证明，虽然膜联蛋白11的C末端核心结构域对Ca2+敏感性至关重要，但N末端结构域是靶向核膜所必需的。其次，我们表明当A431细胞从早期向中期前期转变时，膜联蛋白11重新定位于核膜。在前期后期，在核膜破裂时，膜联蛋白11和S100A6与核纤层相关多肽2一起强烈定位于核膜的褶皱处。从中期到末期，S100A6被降解，但在末期后期，膜联蛋白11在间期恢复核质定位之前与重新形成的核膜结合。这些结果表明，膜联蛋白11和S100A6在核膜处的共定位可能受细胞内Ca2+浓度升高或细胞周期进程的调节，并提供了这些蛋白质可能在体内相互作用的首个证据。
