Watabe M, Nagafuchi A, Tsukita S, Takeichi M
Department of Biophysics, Faculty of Science, Kyoto University, Japan.
J Cell Biol. 1994 Oct;127(1):247-56. doi: 10.1083/jcb.127.1.247.
PC9 lung carcinoma cells cannot tightly associate with one another, and therefore grow singly, despite their expression of E-cadherin, because of their lack of alpha-catenin, a cadherin-associated protein. However, when the E-cadherin is activated by transfection with alpha-catenin cDNA, they form spherical aggregates, each consisting of an enclosed monolayer cell sheet. In the present work, we examined whether the alpha-catenin-transfected cell layers expressed epithelial phenotypes, by determining the distribution of various cell adhesion molecules on their surfaces, including E-cadherin, ZO-1, desmoplakin, integrins, and laminin. In untransfected PC9 cells, all these molecules were randomly distributed on their cell surface. In the transfected cells, however, each of them was redistributed into a characteristic polarized pattern without a change in the amount of expression. Electron microscopic study demonstrated that the alpha-catenin-transfected cell layers acquired apical-basal polarity typical of simple epithelia; they formed microvilli only on the outer surface of the aggregates, and a junctional complex composed of tight junction adherens junction, and desmosome arranged in this order. These results indicate that the activation of E-cadherin triggered the formation of the junctional complex and the polarized distribution of cell surface proteins and structures. We also found that, in untransfected PC9 cells, ZO-1 formed condensed clusters and colocalized with E-cadherin, but that other adhesion molecules rarely showed such colocalization with E-cadherin, suggesting that there is some specific interaction between ZO-1 and E-cadherin even in the absence of cell-cell contacts. In addition, we found that the activation of E-cadherin caused a retardation of PC9 cell growth. Thus, we concluded that the E-cadherin-catenin adhesion system is essential not only for structural organization of epithelial cells but also for the control of their growth.
PC9肺癌细胞彼此之间无法紧密相连，因此尽管它们表达E-钙黏蛋白，但由于缺乏α-连环蛋白（一种与钙黏蛋白相关的蛋白质），所以单个生长。然而，当通过用α-连环蛋白cDNA转染激活E-钙黏蛋白时，它们会形成球形聚集体，每个聚集体由一个封闭的单层细胞片组成。在本研究中，我们通过确定包括E-钙黏蛋白、ZO-1、桥粒斑蛋白、整合素和层粘连蛋白在内的各种细胞黏附分子在其表面的分布，来检测α-连环蛋白转染的细胞层是否表达上皮表型。在未转染的PC9细胞中，所有这些分子随机分布在其细胞表面。然而，在转染的细胞中，它们各自重新分布成特征性的极化模式，而表达量没有变化。电子显微镜研究表明，α-连环蛋白转染的细胞层获得了典型的简单上皮细胞的顶端-基底极性；它们仅在聚集体的外表面形成微绒毛，并且形成了由紧密连接、黏着连接和桥粒按此顺序排列组成的连接复合体。这些结果表明，E-钙黏蛋白的激活触发了连接复合体的形成以及细胞表面蛋白质和结构的极化分布。我们还发现，在未转染的PC9细胞中，ZO-1形成浓缩簇并与E-钙黏蛋白共定位，但其他黏附分子很少与E-钙黏蛋白显示这种共定位，这表明即使在没有细胞间接触的情况下，ZO-1和E-钙黏蛋白之间也存在一些特异性相互作用。此外，我们发现E-钙黏蛋白的激活导致PC9细胞生长迟缓。因此，我们得出结论，E-钙黏蛋白-连环蛋白黏附系统不仅对于上皮细胞的结构组织至关重要，而且对于其生长控制也至关重要。
