Regulation of beta-catenin levels and localization by overexpression of plakoglobin and inhibition of the ubiquitin-proteasome system
Regulation of beta-catenin levels and localization by overexpression of plakoglobin and inhibition of the ubiquitin-proteasome system
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DOI：
10.1083/jcb.139.5.1325
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发表时间：
1997-12-01
影响因子：
7.8
通讯作者：
BenZeev, A
中科院分区：
文献类型：
--
作者：
Salomon, D;Sacco, PA;BenZeev, A
-连环蛋白和血小板红蛋白（-连环蛋白）是犰狳蛋白家族中密切相关的分子。它们定位于细胞-细胞粘附连接的膜下斑块，在那里它们与经典的钙粘蛋白和α -连环蛋白形成独立的复合物，建立与肌动蛋白细胞骨架的联系。血小板红蛋白也存在于桥粒钙粘蛋白复合物中，参与将中间丝锚定在桥粒斑块上。除了在连接组装中发挥作用外，β -连环蛋白已被证明在Wnt通路的信号转导中发挥重要作用，导致其易位到细胞核中。为了研究血小板红蛋白表达与β -连环蛋白水平之间的关系，以及这些蛋白在同一细胞中的定位，我们采用了两种不同的肿瘤细胞系，它们分别表达n -钙粘蛋白、α -和α -连环蛋白，但不表达血小板红蛋白或桥粒体成分。通过稳定转染，建立了表达不同水平血小板红蛋白的个体克隆。在每个克隆中，血小板蛋白过表达导致β -连环蛋白水平呈剂量依赖性下降。诱导血小板红蛋白表达增加了β -连环蛋白的周转率，但不影响RNA水平，提示β -连环蛋白存在翻译后调控。在血小板红蛋白过表达的细胞中，β -连环蛋白和血小板红蛋白都定位于细胞-细胞连接处。稳定转染突变型血小板红蛋白分子表明，n -钙粘蛋白结合域的缺失，而α -连环蛋白结合域的缺失，消除了β -连环蛋白的下调。在血小板红蛋白过表达的细胞中，抑制泛素-蛋白酶体通路阻断了β -连环蛋白水平的下降，并导致β -连环蛋白和血小板红蛋白在细胞核内的积累。这些结果表明：(a)血小板红蛋白与β -连环蛋白在粘附体连接中有效地替代了与n -钙粘蛋白的结合，(b)连接外的β -连环蛋白被蛋白酶体-泛素系统迅速降解，但(c)过量的β -连环蛋白和血小板红蛋白转运到细胞核中。
beta-Catenin and plakoglobin (gamma-catenin) are closely related molecules of the armadillo family of proteins. They are localized at the submembrane plaques of cell-cell adherens junctions where they form independent complexes with classical cadherins and alpha-catenin to establish the link with the actin cytoskeleton. Plakoglobin is also found in a complex with desmosomal cadherins and is involved in anchoring intermediate filaments to desmosomal plaques. In addition to their role in junctional assembly, beta-catenin has been shown to play an essential role in signal transduction by the Wnt pathway that results in its translocation into the nucleus. To study the relationship between plakoglobin expression and the level of beta-catenin, and the localization of these proteins in the same cell, we employed two different tumor cell lines that express N-cadherin, and alpha- and alpha-catenin, but no plakoglobin or desmosomal components. Individual clones expressing various levels of plakoglobin were established by stable transfection. Plakoglobin overexpression resulted in a dose-dependent decrease in the level of beta-catenin in each clone. Induction of plakoglobin expression increased the turnover of beta-catenin without affecting RNA levels, suggesting posttranslational regulation of beta-catenin. In plakoglobin overexpressing cells, both beta-catenin and plakoglobin were localized at cell-cell junctions. Stable transfection of mutant plakoglobin molecules showed that deletion of the N-cadherin binding domain, but not the alpha-catenin binding domain, abolished beta-catenin downregulation. Inhibition of the ubiquitin-proteasome pathway in plakoglobin overexpressing cells blocked the decrease in beta-catenin levels and resulted in accumulation of both beta-catenin and plakoglobin in the nucleus. These results suggest that (a) plakoglobin substitutes effectively with beta-catenin for association with N-cadherin in adherens junctions, (b) extrajunctional beta-catenin is rapidly degraded by the proteasome-ubiquitin system but, (c) excess beta-catenin and plakoglobin translocate into the nucleus.