Doyle J P, Stempak J G, Cowin P, Colman D R, D'Urso D
Brookdale Center for Molecular Biology, Mount Sinai School of Medicine, New York 10029, USA.
J Cell Biol. 1995 Oct;131(2):465-82. doi: 10.1083/jcb.131.2.465.
Protein zero (P(o)) is the immunoglobulin gene superfamily glycoprotein that mediates the self-adhesion of the Schwann cell plasma membrane that yields compact myelin. HeLa is a poorly differentiated carcinoma cell line that has lost characteristic morphological features of the cervical epithelium from which it originated. Normally, HeLa cells are not self-adherent. However, when P(o) is artificially expressed in this line, cells rapidly aggregate, and P(o) concentrates specifically at cell-cell contact sites. Rows of desmosomes are generated at these interfaces, the plasma membrane localization of cingulin and ZO-1, proteins that have been shown to be associated with tight junctions, is substantially increased, and cytokeratins coalesce into a cohesive intracellular network. Immunofluorescence patterns for the adherens junction proteins N-cadherin, alpha-catenin, and vinculin, and the desmosomal polypeptides desmoplakin, desmocollin, and desmoglein, are also markedly enhanced at the cell surface. Our data demonstrate that obligatory cell-cell adhesion, which in this case is initially brought about by the homophilic association of P(o) molecules across the intercellular cleft, triggers pronounced augmentation of the normally sluggish or sub-basal cell adhesion program in HeLa cells, culminating in suppression of the transformed state and reversion of the monolayer to an epithelioid phenotype. Furthermore, this response is apparently accompanied by an increase in mRNA and protein levels for desmoplakin and N-cadherin which are normally associated with epithelial junctions. Our conclusions are supported by analyses of ten proteins we examined immunochemically (P(o), cingulin, ZO-1, desmoplakin, desmoglein, desmocollin, N-cadherin, alpha-catenin, vinculin, and cytokeratin-18), and by quantitative polymerase chain reactions to measure relative amounts of desmoplakin and N-cadherin mRNAs. P(o) has no known signaling properties; the dramatic phenotypic changes we observed are highly likely to have developed in direct response to P(o)-induced cell adhesion. More generally, the ability of this "foreign" membrane adhesion protein to stimulate desmosome and adherens junction formation by augmenting well-studied cadherin-based adhesion mechanisms raises the possibility that perhaps any bona fide cell adhesion molecule, when functionally expressed, can engage common intracellular pathways and trigger reversion of a carcinoma to an epithelial-like phenotype.
零蛋白（P(o)）是免疫球蛋白基因超家族糖蛋白，介导雪旺细胞质膜的自身黏附，从而形成紧密髓鞘。海拉细胞系是一种低分化癌细胞系，已丧失其起源的宫颈上皮细胞的特征性形态特征。正常情况下，海拉细胞不会自我黏附。然而，当该细胞系中人工表达P(o)时，细胞会迅速聚集，且P(o)特异性地集中在细胞 - 细胞接触部位。在这些界面处会形成一排排桥粒，cingulin和ZO - 1（已证明与紧密连接相关的蛋白质）的质膜定位显著增加，并伴有细胞角蛋白聚集成一个有凝聚力的细胞内网络。黏附连接蛋白N - 钙黏蛋白、α - 连环蛋白和纽蛋白，以及桥粒多肽桥粒斑蛋白、桥粒芯蛋白和桥粒芯胶粘蛋白的免疫荧光模式在细胞表面也明显增强。我们的数据表明，这种情况下由P(o)分子跨细胞间隙的同嗜性结合最初引发的细胞 - 细胞间的强制性黏附，触发了海拉细胞中通常迟缓或处于基础水平以下的细胞黏附程序的显著增强，最终导致转化状态的抑制以及单层细胞向上皮样表型的逆转。此外，这种反应显然伴随着通常与上皮连接相关的桥粒斑蛋白和N - 钙黏蛋白的mRNA和蛋白质水平的增加。我们对通过免疫化学方法检测的十种蛋白质（P(o)、cingulin、ZO - 1、桥粒斑蛋白、桥粒芯胶粘蛋白、桥粒芯蛋白、N - 钙黏蛋白、α - 连环蛋白、纽蛋白和细胞角蛋白 - 18）的分析，以及通过定量聚合酶链反应测量桥粒斑蛋白和N - 钙黏蛋白mRNA的相对量，均支持了我们的结论。P(o)没有已知的信号传导特性；我们观察到的显著表型变化极有可能是对P(o)诱导的细胞黏附的直接反应。更普遍地说，这种“外来”膜黏附蛋白通过增强基于钙黏蛋白的、已被充分研究的黏附机制来刺激桥粒和黏附连接形成的能力，增加了一种可能性，即也许任何真正的细胞黏附分子在功能表达时，都能参与共同的细胞内途径并触发癌细胞向上皮样表型的逆转。
