Cis-Dimerization Mediates Function of Junctional Adhesion Molecule A

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Abstract
Junctional adhesion molecule-A (JAM-A) is a transmembrane component of tight junctions that has been proposed to play a role in regulating epithelial cell adhesion and migration, yet mechanistic structure–function studies are lacking. Although biochemical and structural studies indicate that JAM-A forms cis-homodimers, the functional significance of dimerization is unclear. Here, we report the effects of cis-dimerization–defective JAM-A mutants on epithelial cell migration and adhesion. Overexpression of dimerization-defective JAM-A mutants in 293T cells inhibited cell spreading and migration across permeable filters. Similar inhibition was observed with using dimerization-blocking antibodies. Analyses of cells expressing the JAM-A dimerization-defective mutant proteins revealed diminished β1 integrin protein but not mRNA levels. Further analyses of β1 protein localization and expression after disruption of JAM-A dimerization suggested that internalization of β1 integrin precedes degradation. A functional link between JAM-A and β1 integrin was confirmed by restoration of cell migration to control levels after overexpression of β1 integrin in JAM-A dimerization-defective cells. Last, we show that the functional effects of JAM dimerization require its carboxy-terminal postsynaptic density 95/disc-large/zonula occludins-1 binding motif. These results suggest that dimerization of JAM-A regulates cell migration and adhesion through indirect mechanisms involving posttranscriptional control of β1 integrin levels.

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