The core p120-binding region is the primary endocytic signal in VE-cadherin. Fluorescence-based internalization assays with a 10-min internalization period were used to measure endocytosis of various IL-2R–cadherin chimeras expressed in COS-7 cells. (A and B) Internalization (intern.) of chimeras containing the core p120-binding regions of human VE-cadherin (VE-cad), E-cadherin, and N-cadherin and Drosophila DE-cadherin joined to IL-2R by a linker peptide. Means ± SEM (n = 12–25 cells per group); ***, P < 0.001 compared with IL-2R; ^◊, P < 0.05; ^◊◊◊, P < 0.001 compared with the linker. (C and D) Internalization of chimeras containing the VE-cadherin cytoplasmic tail, wild type (WT), or with a Y685A mutation joined to IL-2R. Means ± SEM (n = 15 cells per group); ***, P < 0.001 compared with IL-2R. (E and F) Internalization of chimeras containing the E-cadherin cytoplasmic tail, wild type, or with DEE 758–760 (corresponding to the VE-cadherin DEE mutation), EED 664–666 (corresponding the VE-cadherin EMD mutation), or LL 743–744 mutated to alanines joined to IL-2R. Means ± SEM (n = 12 cells per group); *, P < 0.05; ***, P < 0.001 compared with IL-2R and LL mutation. Bars, 20 µm.