Chen Xinyu, Bonne Stefan, Hatzfeld Mechthild, van Roy Frans, Green Kathleen J
Department of Pathology, Northwestern University Medical School, Chicago, Illinois 60611, USA.
J Biol Chem. 2002 Mar 22;277(12):10512-22. doi: 10.1074/jbc.M108765200. Epub 2002 Jan 14.
Plakophilins are a subfamily of p120-related arm-repeat proteins that can be found in both desmosomes and the nucleus. Among the three known plakophilin members, plakophilin 1 has been linked to a genetic skin disorder and shown to play important roles in desmosome assembly and organization. However, little is known about the binding partners and functions of the most widely expressed member, plakophilin 2. To better understand the cellular functions of plakophilin 2, we have examined its protein interactions with other junctional molecules using co-immunoprecipitation and yeast two-hybrid assays. Here we show that plakophilin 2 can interact directly with several desmosomal components, including desmoplakin, plakoglobin, desmoglein 1 and 2, and desmocollin 1a and 2a. The head domain of plakophilin 2 is critical for most of these interactions and is sufficient to direct plakophilin 2 to cell borders. In addition, plakophilin 2 is less efficient than plakophilin 1 in localizing to the nucleus and enhancing the recruitment of excess desmoplakin to cell borders in transiently transfected COS cells. Furthermore, plakophilin 2 is able to associate with beta-catenin through its head domain, and the expression of plakophilin 2 in SW480 cells up-regulates the endogenous beta-catenin/T cell factor-signaling activity. This up-regulation by plakophilin 2 is abolished by ectopic expression of E-cadherin, suggesting that these proteins compete for the same pool of signaling active beta-catenin. Our results demonstrate that plakophilin 2 interacts with a broader repertoire of desmosomal components than plakophilin 1 and provide new insight into the possible roles of plakophilin 2 in regulating the signaling activity of beta-catenin.
桥粒斑菲素蛋白是与p120相关的臂重复蛋白亚家族，存在于桥粒和细胞核中。在已知的三种桥粒斑菲素蛋白成员中，桥粒斑菲素蛋白1与一种遗传性皮肤病有关，并在桥粒组装和组织中发挥重要作用。然而，对于表达最广泛的成员桥粒斑菲素蛋白2的结合伙伴和功能却知之甚少。为了更好地理解桥粒斑菲素蛋白2的细胞功能，我们使用免疫共沉淀和酵母双杂交试验检测了它与其他连接分子的蛋白质相互作用。我们在此表明，桥粒斑菲素蛋白2可直接与几种桥粒成分相互作用，包括桥粒斑珠蛋白、桥粒芯蛋白、桥粒芯糖蛋白1和2，以及桥粒胶蛋白1a和2a。桥粒斑菲素蛋白2的头部结构域对大多数这些相互作用至关重要，并且足以将桥粒斑菲素蛋白2导向细胞边界。此外，在瞬时转染的COS细胞中，桥粒斑菲素蛋白2在定位到细胞核以及增强过量桥粒斑珠蛋白向细胞边界募集方面比桥粒斑菲素蛋白1效率更低。此外，桥粒斑菲素蛋白2能够通过其头部结构域与β-连环蛋白结合，并且在SW480细胞中桥粒斑菲素蛋白2的表达上调内源性β-连环蛋白/T细胞因子信号活性。E-钙黏蛋白的异位表达消除了桥粒斑菲素蛋白2的这种上调作用，表明这些蛋白质竞争相同的信号活性β-连环蛋白池。我们的结果表明，桥粒斑菲素蛋白2比桥粒斑菲素蛋白1与更广泛的桥粒成分相互作用，并为桥粒斑菲素蛋白2在调节β-连环蛋白信号活性中的可能作用提供了新的见解。
