Involvement of LMO7 in the association of two cell-cell adhesion molecules, nectin and E-cadherin, through afadin and α-actinin in epithelial cells
Involvement of LMO7 in the association of two cell-cell adhesion molecules, nectin and E-cadherin, through afadin and α-actinin in epithelial cells
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DOI：
10.1074/jbc.m401957200
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发表时间：
2004-07-23
影响因子：
4.8
通讯作者：
Takai, Y
中科院分区：
文献类型：
--
作者：
Ooshio, T;Irie, K;Takai, Y
果胶凝集素是一种钙离子非依赖性免疫球蛋白样细胞间黏附分子，参与钙粘附素黏附连接(AJ)的形成。以Nectin为基础的细胞间黏附诱导CDc42和Rac小G蛋白的激活，最终通过肌动蛋白细胞骨架的重组促进AJs的形成。虽然已有越来越多的证据表明，果胶凝集素通过其细胞质相关蛋白afadin和catenins将钙粘附素募集到基于粘附素的细胞-细胞黏附部位，但目前还不完全清楚果胶凝集素与钙粘附素之间的物理联系。在这里，我们确定了人类LIM结构域仅7(LMO7)的一个大鼠对应体，是一种afadin和α-actinin结合蛋白。大鼠LMO7有两个剪接变异体LMO7a和LMO7b，分别由1,729和1,395个氨基酸组成。LMO7具有钙蛋白同源、PDZ和LIM结构域。Western blotting显示，LMO7在大鼠各组织中普遍表达。免疫荧光和免疫电子显微镜显示LMO7定位于细胞间AJs，afadin定位于大鼠胆囊腺上皮细胞。此外，在同一上皮细胞中，LMO7定位于顶膜的细胞质表面。我们进一步揭示了LMO7结合了α-肌动蛋白，这是一种肌动蛋白细丝捆绑蛋白，它与α-连环蛋白结合。免疫沉淀分析表明，LMO7与Nectin-afadin和E-cadherin-catenin系统有关。Nectin-afadin和E-cadherin-catenin系统组装完成后，LMO7在细胞-细胞黏附部位组装。这些结果表明，LMO7是一种afadin和α-actinin结合蛋白，通过α-actinin连接Nectin-afadin和E-cadherin-catenin系统。
Nectins are Ca2+-independent immunoglobulin-like cell-cell adhesion molecules that are involved in formation of cadherin-based adherens junctions (AJs). The nectin-based cell-cell adhesion induces activation of Cdc42 and Rac small G proteins, which eventually enhances the formation of AJs through reorganization of the actin cytoskeleton. Although evidence has accumulated that nectins recruit cadherins to the nectin-based cell-cell adhesion sites through their cytoplasm-associated proteins, afadin and catenins, it is not fully understood how nectins are physically associated with cadherins. Here we identified a rat counterpart of the human LIM domain only 7 (LMO7) as an afadin- and alpha-actinin-binding protein. Rat LMO7 has two splice variants, LMO7a and LMO7b, consisting of 1,729 and 1,395 amino acids, respectively. LMO7 has calponin homology, PDZ, and LIM domains. Western blotting revealed that LMO7 was expressed ubiquitously in various rat tissues. Immunofluorescence and immunoelectron microscopy revealed that LMO7 localized at cell-cell AJs, where afadin localized, in epithelial cells of rat gallbladder. In addition, LMO7 localized at the cytoplasmic faces of apical membranes in the same epithelial cells. We furthermore revealed that LMO7 bound alpha-actinin, an actin filament-bundling protein, which bound to alpha-catenin. Immunoprecipitation analysis revealed that LMO7 was associated with both the nectin-afadin and E-cadherin-catenin systems. LMO7 was assembled at the cell-cell adhesion sites after both the nectin-afadin and E-cadherin-catenin systems had been assembled. These results indicate that LMO7 is an afadin- and alpha-actinin-binding protein that connects the nectin-afadin and E-cadherin-catenin systems through alpha-actinin.