Regulated Binding of a PTP1B-like Phosphatase to N-Cadherin: Control of Cadherin-mediated Adhesion by Dephosphorylation of -Catenin

Cadherins are a family of cell-cell adhesion molecules which play a central role in controlling morphogenetic movements during development. Cadherin function is regulated by its association with the actin containing cytoskeleton, an association mediated by a complex of cytoplasmic proteins, the catenins: e~, [3, and ~/. Phosphorylated tyrosine residues on 13-catenin are correlated with loss of cadherin function. Consistent with this, we find that only nontyrosine phosphorylated 13-catenin is associated with N-cadherin in El0 chick retina tissue. Moreover, we demonstrate that a PTP1Blike tyrosine phosphatase associates with N-cadherin and may function as a regulatory switch controlling cadherin function by dephosphorylating 13-catenin, thereby maintaining cells in an adhesion-competent state, The PTP1B-Iike phosphatase is itself tyrosine phosphorylated. Moreover, both direct binding experiments performed with phosphorylated and dephosphorylated molecules, and treatment of cells with tyrosine kinase inhibitors indicate that the interaction of the PTPIBlike phosphatase with N-cadherin depends on its tyrosine phosphorylation. Concomitant with the tyrosine kinase inhibitor-induced loss of the PTP1B-Iike phosphatase from its association with N-cadherin, phosphorylated tyrosine residues are retained on 13-catenin, the association of N-cadherin with the actin containing cytoskeleton is lost and N-cadherin-mediated cell adhesion is prevented. Tyrosine phosphatase inhibitors also result in the accumulation of phosphorylated tyrosine residues on ~-catenin, loss of the association of N-cadherin with the actin-containing cytoskeleton, and prevent N-cadherin mediated adhesion, presumably by directly blocking the function of the PTP1B-Iike phosphatase. We previously showed that the binding of two ligands to the cell surface N-acetylgalactosaminylphosphotransferase (GalNAcPTase), the monoclonal antibody 1Bll and a proteoglycan with a 250-kD core protein, results in the accumulation of phosphorylated tyrosine residues on 13-catenin, uncoupling of N-cadherin from its association with the actin containing cytoskeleton, and loss of N-cadherin function. We now report that binding of these ligands to the GalNAcPTase resuits in the absence of the PTP1B-Iike phosphatase from its association with N-cadherin as well as the loss of the tyrosine kinase and tyrosine phosphatase activities that otherwise co-precipitate with N-cadherin. Control antibodies and proteoglycans have no such effect. This effect is similar to that observed with tyrosine kinase inhibitors, suggesting that the GalNAcPTase/proteoglycan interaction inhibits a tyrosine kinase, thereby preventing the phosphorylation of the PTP1B-like phosphatase, and its association with N-cadherin. Taken together these data indicate that a PTP1B-like tyrosine phosphatase can regulate N-cadherin function through its ability to dephosphorylate 13-catenin and that the association of the phosphatase with N-cadherin is regulated via the interaction of the GalNAcPTase with its proteoglycan ligand. In this manner the GalNAcPTase-proteoglycan interaction may play a major role in morphogenetic cell and tissue interactions during development. T HE cadherin family of calcium-dependent adhesion molecules mediate homophilic cell-cell adhesion (reviewed in Grunwald, 1993). During normal deAddress all correspondence to J. Lilien, Department of Biological Sciences, Wayne State University, Detroit, MI 48202. Tel.: (313) 577-2876. Fax: 313 577-6891. velopment they are suggested to play an important causal role in the onset and cessation of cell migration (Akitaya and Bronner-Fraser, 1992; reviewed in Vallrs et al., 1991) and in the separation of tissues (reviewed in Takeichi, 1991). Three lines of evidence have been marshaled in support of this critical role for cadherins in development: © The Rockefeller University Press, 0021-9525196/081801113 $2.00 The Journal of Cell Biology, Volume 134, Number 3, August 1996 801-813 801 on A ril 1, 2017 D ow nladed fom Published August 1, 1996