Reggies/Flotillins regulate E-cadherin-mediated cell contact formation by affecting EGFR trafficking

Abstract

The reggie/flotillin proteins were implicated in membrane trafficking and together with the cellular prion protein (PrP) in the recruitment of E-cadherin to cell contact sites. Here, we demonstrate that reggies as well as PrP downregulation in epithelial A431 cells caused overlapping processes and abnormal formation of adherens junctions (AJs). This defect in cell adhesion resulted from the reggie effects on Src tyrosine kinases and epidermal growth factor receptor (EGFR): loss of reggies reduced Src activation and EGFR phosphorylation at residues targeted by Src and c-cbl, and led to increased surface-exposure of EGFR by blocking its internalization. The prolonged EGFR signaling at the plasma membrane enhanced cell motility and macropinocytosis through which junction-associated E-cadherin is internalized and recycled back to AJs. Accordingly, blockage of EGFR signaling or macropinocytosis in reggie-deficient cells restored normal AJ formation. Thus, by promoting EGFR internalization, reggies restrict the EGFR signaling involved in E-cadherin macropinocytosis and recycling, regulate AJ formation and dynamics and thereby cell adhesion.