To test the role of APOPT1-HA stabilization under oxidative stress, we measured the production of reactive oxygen species (ROS) using a dichlorofluorescein-based assay. While in basal conditions ROS levels were comparable between immortalized mutant S2 fibroblasts and control fibroblasts, after H2O2 incubation (100 μM or 1 mM for 3 hr) ROS levels in mutant S2 were higher than in control fibroblasts (Figure 4D). However, in S2 fibroblasts transduced with APOPT1-HA-expressing lentiviral vector, the amount of ROS was decreased with either treatment, being comparable to that found in control cells treated with the higher H2O2 concentration, suggesting a role for APOPT1 in mitochondrial response to ROS (Figure 4D).