Differential Modulation of Cadherin-mediated Cell–Cell Adhesion by Platelet Endothelial Cell Adhesion Molecule-1 Isoforms through Activation of Extracellular Regulated Kinases

摘要

The role of platelet endothelial cell adhesion molecule-1 (PECAM-1) in endothelial cell–cell interactions and its contribution to cadherin-mediated cell adhesion are poorly understood. Such studies have been difficult because all known endothelial cells express PECAM-1. We have used Madin-Darby canine kidney (MDCK) cells as a model system in which to evaluate the role of PECAM-1 isoforms that differ in their cytoplasmic domains in cell–cell interactions. MDCK cells lack endogenous PECAM-1 but form cell–cell junctions similar to those of endothelial cells, in which PECAM-1 is concentrated. MDCK cells were transfected with two isoforms of murine PECAM-1, Δ15 and Δ14&15, the predominant isoforms expressed in vivo. Expression of the Δ15 isoform resulted in apparent dedifferentiation of MDCK cells concomitant with the loss of adherens junctions, down-regulation of E-cadherin, α- and β-catenin expression, and sustained activation of extracellular regulated kinases. The Δ15 isoform was not concentrated at cell–cell contacts. In contrast, the Δ14&15 isoform localized to sites of cell–cell contact and had no effect on MDCK cell morphology, cadherin/catenin expression, or extracellular regulated kinase activity. Thus, the presence of exon 14 in the cytoplasmic domain of PECAM-1 has dramatic effects on the ability of cells to maintain adherens junctions and an epithelial phenotype. Therefore, changes in the expression of exon 14 containing PECAM-1 isoforms, which we have observed during development, may have profound functional consequences.