FINAL ACCEPTED VERSION Mitochondrial KATP Channel Openers Activate the ERK Kinase by an Oxidant- Dependent Mechanism

Extracellular signal regulated kinases (ERKs) are key regulatory proteins that mediate cell survival, proliferation and differentiation. Reactive oxygen species (ROS) may play a role in activation of the ERK pathway. Since mitochondria are a major source of ROS, we investigated whether mitochondrial-derived ROS play a role in ERK activation. Diazoxide, a potent mitochondrial ATP-sensitive K + channel opener, is known to depolarize the mitochondrial membrane potential and cause a reversible oxidation of respiratory chain flavoproteins, thus increasing mitochondrial ROS production. Using THP-1 cells as a model, we postulated that opening of mitochondrial ATP-sensitive K + channels would increase production of ROS and thereby regulate the activity of the ERK kinase. We found that opening mitochondrial ATP sensitive K + channels by diazoxide induced production of ROS as determined by an increased rate of dihydroethidium (DHE) and dichlorofluorescein (DCF) fluorescence. This increased production of ROS was associated with increased phosphorylation of ERK kinase in a time-dependent fashion. The MEK-inhibitors, PD98059 and U0126, blocked ERK activation mediated by diazoxide. N-acetylcysteine (NAC), but not diphenyleneiodonium (DPI), attenuated ERK activation mediated by diazoxide. Adenoviral mediated overexpression of manganese superoxide dismutase (MnSOD), which is expressed in mitochondria, decreased the rate of DHE oxidation as well as ERK activation. We conclude that mitochondrial K ATP channel openers trigger ERK activation via mitochondrial-derived ROS.