OBJECTIVETo explore the mechanism and significance of cytochrome c oxidase subunit IV (COX IV) downregulation during apoptosis of NB4 cells induced by sodium selenite.

METHODSNB4 cells were treated with 20 micromol/L sodium selenite at different time points. COX IV protein and mRNA were detected by Western blot and RT-PCR, respectively. NB4 cells were pretreated with reactive oxygen species (ROS) scavenger before selenite exposure, and then COX IV protein expression and caspase-3 activation were detected by Western blot. NB4 cells were pretreated with caspase-3 inhibitor before selenite exposure, and then COX IV protein expression was detected by Western blot. NB4 cells were transiently transfected with vectors to interfere with the expression of COX IV, and then the apoptosis induced by selenite was analyzed by flow cytometry.

RESULTSSodium selenite induced evident downregulation of COX IV protein in NB4 cells, while its mRNA level was almost unchanged. ROS scavenger completely reversed selenite-induced COX IV downregulation and caspase-3 activation. Caspase-3 inhibitor partially reversed selenite-induced COX IV downregulation. Interference with COX IV expression dramatically enhanced selenite-induced apoptosis of NB4 cells.

CONCLUSIONSCOX IV is remarkably downregulated during selenite-induced apoptosis of NB4 cells. ROS mediates COX IV downregulation and caspase-3 activation, while caspase-3 is partially involved in COX IV downregulation. COX IV interference markedly increases the sensitivity of NB4 cells to selenite-induced apoptosis.