ApoER2 expression specifically decreases APP695HA endocytosis. Dose-response effect of ApoER2 expression on APP695HA (A) and diferric transferrin (B) endocytosis. CHO-LRP null cells transiently transfected with APP695HA alone (solid square) or along with 5 μg (solid inverted triangle), 10 μg (open triangle) or 20 μg (open inverted triangle) of an ApoER2 coding plasmid were incubated with 1 nM 125I-labeled-anti-HA IgG or 5 nM 125I-labeled-diFeTf for 1 h at 4°C and then shifted to 37°C for the indicated times. The percent of ligand internalized at each time point is equal to the amount of ligand internalized divided by the total cell-associated ligand (see "Materials and Methods") Values are the mean average of triplicate determinations with S.E. indicated by error bars. (C) Lysates were prepared from similarly transfected cells and equal amounts of protein were subjected to 10% SDS-PAGE. Blots were probed with anti-HA, anti-ApoER2, anti-actin or anti-transferrin receptor (TfR) antibodies. ApoER2 expression decreases APP695 but not transferrin receptor endocytosis rate.