Balsamo J, Arregui C, Leung T, Lilien J
Department of Biological Sciences, Wayne State University, Detroit, Michigan 48202, USA.
J Cell Biol. 1998 Oct 19;143(2):523-32. doi: 10.1083/jcb.143.2.523.
Cadherin-mediated adhesion depends on the association of its cytoplasmic domain with the actin-containing cytoskeleton. This interaction is mediated by a group of cytoplasmic proteins: alpha-and beta- or gamma- catenin. Phosphorylation of beta-catenin on tyrosine residues plays a role in controlling this association and, therefore, cadherin function. Previous work from our laboratory suggested that a nonreceptor protein tyrosine phosphatase, bound to the cytoplasmic domain of N-cadherin, is responsible for removing tyrosine-bound phosphate residues from beta-catenin, thus maintaining the cadherin-actin connection (). Here we report the molecular cloning of the cadherin-associated tyrosine phosphatase and identify it as PTP1B. To definitively establish a causal relationship between the function of cadherin-bound PTP1B and cadherin-mediated adhesion, we tested the effect of expressing a catalytically inactive form of PTP1B in L cells constitutively expressing N-cadherin. We find that expression of the catalytically inactive PTP1B results in reduced cadherin-mediated adhesion. Furthermore, cadherin is uncoupled from its association with actin, and beta-catenin shows increased phosphorylation on tyrosine residues when compared with parental cells or cells transfected with the wild-type PTP1B. Both the transfected wild-type and the mutant PTP1B are found associated with N-cadherin, and recombinant mutant PTP1B binds to N-cadherin in vitro, indicating that the catalytically inactive form acts as a dominant negative, displacing endogenous PTP1B, and rendering cadherin nonfunctional. Our results demonstrate a role for PTP1B in regulating cadherin-mediated cell adhesion.
钙黏蛋白介导的黏附作用依赖于其胞质结构域与含肌动蛋白的细胞骨架的结合。这种相互作用由一组胞质蛋白介导：α-连环蛋白和β-或γ-连环蛋白。β-连环蛋白酪氨酸残基的磷酸化在控制这种结合以及钙黏蛋白功能方面发挥作用。我们实验室之前的研究表明，一种与N-钙黏蛋白胞质结构域结合的非受体蛋白酪氨酸磷酸酶负责从β-连环蛋白上去除酪氨酸结合的磷酸残基，从而维持钙黏蛋白与肌动蛋白的连接（）。在此我们报道了与钙黏蛋白相关的酪氨酸磷酸酶的分子克隆，并将其鉴定为蛋白酪氨酸磷酸酶1B（PTP1B）。为了明确建立与钙黏蛋白结合的PTP1B的功能和钙黏蛋白介导的黏附之间的因果关系，我们测试了在组成性表达N-钙黏蛋白的L细胞中表达催化失活形式的PTP1B的效果。我们发现催化失活的PTP1B的表达导致钙黏蛋白介导的黏附作用降低。此外，与亲代细胞或转染野生型PTP1B的细胞相比，钙黏蛋白与其与肌动蛋白的结合解偶联，并且β-连环蛋白在酪氨酸残基上的磷酸化增加。转染的野生型和突变型PTP1B均被发现与N-钙黏蛋白相关，并且重组突变型PTP1B在体外与N-钙黏蛋白结合，表明催化失活形式作为显性负性物发挥作用，取代内源性PTP1B，并使钙黏蛋白失去功能。我们的结果证明了PTP1B在调节钙黏蛋白介导的细胞黏附中的作用。
