Potential Role of Mitochondrial ROS in Sestrin2 Degradation

Sestrin2 (SESN2) is a stress-inducible antioxidant protein that controls redox-homeostasis via its oxidoreductase activity. Although the induction mechanism of SESN2 has been reported, the mechanism for regulation of SESN2 protein stability has not yet been elucidated. In the present study, we investigated the role of mitochondrial reactive oxygen species (ROS) in the degradation of SESN2 and the related mechanism. First, we found that rotenone, an inhibitor of mitochondrial complex I, significantly lowered the SESN2 protein level in hepatocytes. In addition, antimycin A (an inhibitor of mitochondrial complex III) and Mn-TBAP (a superoxide dismutase mimetic) were also shown to reduce SESN2. Rotenone decreased mitochondrial ROS; this result implied that mitochondrial ROS production was involved in SESN2 regulation. However, the level of SESN2 mRNA was unchanged by rotenone treatment. Next, SESN2 protein stability was observed after treatment with cycloheximide and rotenone. Decreased SESN2 protein stability was detected in the presence of cycloheximide, and rotenone accelerated this SESN2 decay. MG132 (a proteasome inhibitor) treatment causes significant accumulation of SESN2 protein, but rotenone still reduced SESN2 levels in the presence of MG132. However, chloroquine, a lysosomal inhibitor, restored rotenone-reduced SESN2 levels. These results suggest that mitochondrial ROS prevent SESN2 protein degradation, and this is dependent on lysosomal activity.