NR promotes BACE1 degradation through an increase in the BACE1 ubiquitination
Because protein ubiquitination is an essential step for most proteins degraded by UPS, we further explored whether NR treatment increased the BACE1 ubiquitination. HEK293 cells stably transfected with BACE1 vector with Myc-tag (Myc-BACE1) were treated with NR, and infected with adenoviral PGC-1α, and adenoviral PGC-1α shRNA. The protein extracts were probed by Western blot with anti-ubiquitin antibody. We found that the ubiquitinated BACE1 protein levels markedly increased in NR-treated and PGC-1α overexpressing HEK293 cells relative to control cells, suggesting that PGC-1α promotes BACE1 degradation in UPS through BACE1 ubiquitination (Fig. 6, upper panel). Consistent with the increase in ubiquitinated BACE1 levels, the levels of monoubiquitin levels were decreased in the cells with NR treatment or PGC-1α expression (Fig. 6, lower panel).