Figure 7.

Degradation of APP by UPR activation. a, Degradation of overexpressed APP protein by ATF6 and XBP1. HEK293 cells were transiently transfected with APP-FLAG and an empty vector (mock), HA-ATF6, or HA-XBP1 for the indicated periods. The total cell lysates were analyzed by Western blotting using FLAG, KDEL and HRD1 (Otsuka) antibodies. b, c, Aβ levels were measured by sandwich ELISA using the culture medium of a at 36 h. Data (pg/ml Aβ peptide) are normalized to the amount of APP mRNA quantified by real-time PCR. Results are expressed as a fold increase compared with normal cells (mean ± SEM; n = 4). Statistical analysis was performed with ANOVA followed by Bonferroni correction (control vs mock, ATF6, and XBP1; **p < 0.01). d, Degradation of endogenous APP protein by XBP1 under ER stress conditions. XBP1 were induced using a tetracycline-inducible expression system (Tet-on) in HEK293 cells. The cells were treated with 1 μm Tg and 5 μg/ml Tm for 12 h. Total cell lysates were analyzed by Western blotting using APP (C-terminal) and HRD1 (Sigma) antibodies.