Increased endogenous Aβ secretion in LRP1-null, ApoER2-expressing CHO cells. LRP1-null CHO cells stably transfected with pcDNA3 vector, ApoER2, ApoER2ΔPro, ApoER2ΔPro-NPXA, or ApoER2-Tless encoding plasmids were incubated in low serum media. After 48 h, media was analyzed for Aβ levels by ELISA. (A) Aβ40 and (B) Aβ42 values were normalized to the amount of cellular protein in the corresponding cell extracts and expressed as fold increase over pcDNA3-expressing cells. Values are the mean average of triplicate determinations with S.E. indicated by error bars.