p120 occupies the DEE sequence to prevent cadherin endocytosis. (A and B) Close views of the predicted molecular interface between VE-cadherin and p120. Selected residues of VE-cadherin and p120 are labeled in magenta and black, respectively. Three negatively charged side chains of the DEE sequence are enveloped by positively charged binding pockets (blue) of p120. Hydrogen bonds are indicated by yellow dashes. (C and D) Wild-type (WT) or GGG mutant IL-2R–VE-cadherin cytoplasmic tail chimeras were expressed in COS-7 cells along with wild-type or K444M mutant fluorescently tagged p120. Untransfected cells adjacent to cells transfected with the wild-type p120 construct were used as negative controls (ctrl). Endocytosis of the chimeras was measured using a fluorescence-based internalization (intern.) assay with a 10-min internalization period. Mutation of p120 K444, which is predicted to interact with the last residue of the DEE endocytic signal (A), disrupts p120-mediated inhibition of IL-2R–VE-cadherin chimera internalization, as does mutation of VE-cadherin (VE-cad) GGG 649–651. Means ± SEM (n = 12–15 cells per group); ***, P < 0.001 compared with no exogenous p120 expression and GGG mutant chimera; ^◊, P < 0.05 compared with p120 K444M. Bar, 20 µm.