ApoER2 increases cell surface APP levels but not total APP. Cell surface APP (A) and total cellular APP (B) were assessed by FACS analysis. LRP1-null CHO cells stably transfected with pcDNA3 vector, ApoER2, ApoER2ΔPro, ApoER2ΔPro-NPXA, or ApoER2-Tless were treated with or without saponin and then labeled with anti-APP antibody. Primary antibody was detected with PE-conjugated goat anti-mouse IgG. Values are the average of triplicate determinations. Error bars indicate S.E. C, lysates were prepared from CHO-pcDNA3 and ApoER2-expressing cells and equal amounts of protein were subjected to 10% SDS-PAGE. Blots were probed with anti-HA and anti-β-tubulin antibodies.