Brusatol-mediated inhibition of c-Myc expression increases HIF-1α degradation by inhibiting hypoxia-induced mitochondrial ROS production. (A and B) RKO (A) and HCT116 (B) cells were incubated with or without 100 nM brusatol. After a 1-h incubation, cells were exposed to 20% or 0.5% O2 for 8 h and then harvested at the indicated time. Whole-cell lysates were analyzed by immunoblotting for the indicated proteins. (C and D) RKO (C) and HCT116 (D) cells were transfected with pc-Myc or pCont (empty vector) for 48 h, and then incubated with or without 100 nM brusatol. After a 1-h incubation, cells were exposed to 20% or 0.5% O2 for 4 h and harvested. Whole-cell lysates were analyzed by immunoblotting for the indicated proteins. (E and F) RKO (E) and HCT116 (F) cells were treated with MitoTracker and MitoSOX for 1 h, washed three times with pre-warmed PBS, and exposed to 0.5% O2 for 4 h. Fluorescence was detected with a Nikon confocal laser-scanning microscope. (G and H) Effect of c-Myc expression on intracellular ferrous iron concentrations in RKO (G) and HCT116 (H) cells incubated with or without 100 nM brusatol under hypoxia. Data are presented as means ± SD (**P < 0.01, ***P < 0.001, ****P < 0.0001; ANOVA).