Signaling from E-cadherins to the MAPK pathway by the recruitment and activation of epidermal growth factor receptors upon cell-cell contact formation.
E-cadherins are well characterized cell surface molecules expressed in epithelial cells, which play a major role in cell adhesion through the establishment of calcium-dependent homophilic interactions at sites of cell-cell contacts. They are also integral components of morphogenetic programs controlling the maintenance of the structural and functional integrity of epithelia. Accumulated evidence indicates that the E-cadherin-mediated cell adhesion system is highly regulated from inside the cells by a number of intracellular signaling pathways. Recently available information suggests that E-cadherins may also play a role in the transduction of signals from the outside of the cell to the cytoplasm. However, the nature of the biochemical routes regulated by E-cadherins is still largely unknown. In this study, we set out to explore the possibility that E-cadherins may regulate the activity of MAPK, a key signaling pathway involved in cell fate decisions, upon the formation of cell-cell contacts among neighboring cells. By using an immortalized non-tumorigenic keratinocyte cell line, HaCat, as a model system, we provide evidence that the assembly of calcium-dependent adherens junctions leads to a rapid and remarkable increase in the state of activation of MAPK and that this event is mediated by E-cadherins. Furthermore, we found that E-cadherins stimulate the MAPK pathway through the ligand-independent activation of epidermal growth factor receptors and the consequent activation of a biochemical route leading to the stimulation of MAPKs. These findings suggest that E-cadherins can initiate outside-in signal transducing pathways through the engagement of tyrosine kinase receptors for epidermal growth factor, thus providing a novel molecular mechanism whereby these cell adhesion molecules may ultimately control the fate of normal and transformed epithelial cells.
Pece
S
S
Oral and Pharyngeal Cancer Branch, NIDCR, National Institutes of Health, Bethesda, Maryland 20892-4330, USA.
Gutkind
J S
JS
D015820:Cadherins / Q000502:physiology; D002448:Cell Adhesion; D002450:Cell Communication; D002478:Cells, Cultured; D004789:Enzyme Activation; D066246:ErbB Receptors / Q000502:physiology*; D006801:Humans; D020928:Mitogen-Activated Protein Kinases / Q000502:physiology*; D010766:Phosphorylation; D014443:Tyrosine / Q000378:metabolism
D015820:Cadherins; D014443:Tyrosine; D066246:ErbB Receptors; D020928:Mitogen-Activated Protein Kinases