The cells subjected to the indicated treatments were lysed by the Laemmli sample buffer as previously described (16 (link),19 (link)). The protein of lysate was then separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and western blot analysis was performed as previously described (19 (link)). Briefly, following SDS-PAGE, the separated proteins were transferred onto PVDF membranes and probed with rabbit anti-UCP2 antibody and mouse anti-ubiquitin (sc-166553) (both from Santa Cruz Biotechnology, Inc.). Specific reactions were detected using goat anti-rabbit IgG or goat anti-mouse IgG conjugated with horseradish peroxidase (Sigma, St. Louis, MO, USA) and revealed by a chemiluminescence substrate (Bio-Rad Laboratories, Hercules, CA, USA). The membranes were also blotted with tubulin antibody (sc-33749; Santa Cruz Biotechnology, Inc.) to normalize protein loading. The chemiluminescence signal was recorded using the ChemiDoc MP imaging system (Bio-Rad Laboratories). The luminescence signal was captured and analyzed using the Image Lab Program (version 6.1).