page 177, Zhang et al. show that the extracellular domain of the α3β1 integrin can hijack a glycolipid- anchored receptor and thus trigger movement of an epithelial cell by inhibiting E-cadherin–mediated cell contacts.
Integrins on epithelial cells are well known to tether the cells to matrix components—laminin-5 in the case of α3β1—but are not usually associated with cell–cell contacts. Zhang et al. show that α3β1 can inhibit cell–cell contacts when α3 binds to the urokinase receptor, uPAR, a known inducer of cell migration in response to certain cytokines. Expression of both uPAR and α3β1 mobilized cells by reducing E-cadherin and γ-catenin levels at cell junctions, thus dissociating the cells. Other uPAR-induced changes included expression of several genes that are associated with the epithelial–mesenchymal transition, such as the transcription factor SLUG.
The mesenchymal phenotype is a result of localized Src kinase activation induced by the uPAR–α3β1 complex. Disruption of Src signaling by overexpression of its protein interaction domains inhibited uPAR-induced cell motility. High uPAR levels are associated with tumor metastasis and a poor prognosis. Since mutations in the α3 extracellular domain that abolish uPAR binding also block motility, mice expressing these mutants may have a better prognosis. ▪