p120 binding can be uncoupled from control of cadherin endocytosis. Three consecutive sets of amino acids in the core p120-binding region, DEE 646–648, GGG 649–651, and EMD 652–654 (also see Fig. 1 C), were mutated to alanines in IL-2R–VE-cadherin (VE-cad) cytoplasmic tail chimeras and expressed in COS-7 cells. (A) Chimeras were isolated by immunoprecipitation of IL-2R, and coprecipitation of p120 and β-catenin (β) was determined by Western blotting. (B and C) Endocytosis of the chimeras was measured using a fluorescence-based internalization assay with a 10-min internalization period. Although each mutation prevented pull-down of p120, only the DEE mutation significantly inhibited endocytosis. Means ± SEM (n = 15 cells per group); **, P < 0.01; ***, P < 0.001 compared with IL-2R and DEE mutation. (D) Surface expression of the chimeras in COS-7 cells was quantified by antibody labeling of surface IL-2R and immunofluorescence microscopy. Thick line, median (n = 17–21 cells per group); box, interquartile range; whiskers, 90% range. intern., internalization; IP, immunoprecipitation; WT, wild type. Bar, 20 µm.