Inhibition of γ-secretase activity increases the cell surface presentation of APP and BACE1. (A) Top: 7W cells were treated with DAPT, and cell surface proteins were labeled with a non–cell permeable biotinylation reagent. Lysates from the biotinylated cells were pulled down with streptavidin. Whole lysates (left) and cell surface proteins (right) were probed for the indicated proteins. (B) CM from A were analyzed for APPs-α and total APPs by WB. (C) Surface levels of APP and BACE were quantitated from A and normalized to total APP or BACE levels in the lysate, respectively. A two-way ANOVA with a Sidak’s posttest was performed. ****, P < 0.0001. n = 8. (D) Total lysate levels of APP and BACE were quantitated from A and normalized to total protein concentration. A two-way ANOVA with a Sidak’s posttest was performed. ***, P < 0.001. n = 8. im, immature; m, mature.