Mitochondrial KATP channel openers activate the ERK kinase by an oxidant-dependent mechanism

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Abstract
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. Because mitochondria are a major source of ROS, we investigated whether mitochondria-derived ROS play a role in ERK activation. Diazoxide, a potent mitochondrial ATP-sensitive K+ (KATP) 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 mitochondrial KATP channels would increase production of ROS and, thereby, regulate the activity of the ERK kinase. We found that opening mitochondrial KATP channels by diazoxide induced production of ROS as determined by an increased rate of dihydroethidium and dichlorofluorescein fluorescence. This increased production of ROS was associated with increased phosphorylation of ERK kinase in a time-dependent fashion. The MEK inhibitors PD-98059 and U-0126 blocked ERK activation mediated by diazoxide. N -acetylcysteine, but not diphenyleneiodonium, attenuated ERK activation mediated by diazoxide. Adenovirus-mediated overexpression of manganese superoxide dismutase, which is expressed in mitochondria, decreased the rate of dihydroethidium oxidation as well as ERK activation. We conclude that mitochondrial KATP channel openers trigger ERK activation via mitochondria-derived ROS.