title: Activation of ERK1/2 pathway mediates oxidant-induced decreases in mitochondrial function in renal cells.
abstract: Previously, we showed that oxidant exposure in renal proximal tubular cells (RPTC) induces mitochondrial dysfunction mediated by PKC-epsilon. This study examined the role of ERK1/2 in mitochondrial dysfunction induced by oxidant injury and whether PKC-epsilon mediates its effects on mitochondrial function through the Raf-MEK1/2-ERK1/2 pathway. Sublethal injury produced by tert-butylhydroperoxide (TBHP) resulted in three- to fivefold increase in phosphorylation of ERK1/2 and p38 but not JNK. This was followed by decreases in basal and uncoupled respirations (41%), state 3 respiration and ATP production coupled to complex I (46%), and complex I activity (42%). Oxidant exposure decreased aconitase activity 30% but not pyruvate, alpha-ketoglutarate, and malate dehydrogenase activities. Inhibition of ERK1/2 restored basal and state 3 respirations, DeltaPsi(m), ATP production, and complex I activity but not aconitase activity. In contrast, activation of ERK1/2 by expression of constitutively active MEK1 suppressed basal, uncoupled, and state 3 respirations in noninjured RPTC to the levels observed in TBHP-injured RPTC. MEK1/2 inhibition did not change Akt or p38 phosphorylation, demonstrating that the protective effect of MEK1/2 inhibitor was not due to activation of Akt or inhibition of p38 pathway. Inhibition of PKC-epsilon did not block TBHP-induced ERK1/2 phosphorylation in whole RPTC or in mitochondria. We conclude that 1) oxidant-induced activation of ERK1/2 but not p38 or JNK reduces mitochondrial respiration and ATP production by decreasing complex I activity and substrate oxidation through complex I, 2) citric acid cycle dehydrogenases are not under control of the ERK1/2 pathway in oxidant-injured RPTC, 3) the protective effects of ERK1/2 inhibition are not due to activation of Akt, and 4) ERK1/2 and PKC-epsilon mediate oxidant-induced mitochondrial dysfunction through independent pathways.
authors.affiliation: Department of Pharmaceutical Sciences, College of Pharmacy, University of Arkansas for Medical Sciences, 4301 West Markham St., Little Rock, AR 72205, USA. gnowak@uams.edu
authors.forename: Grazyna
authors.initials: G
authors.lastname: Nowak
authors.forename: Ginger L
authors.initials: GL
authors.lastname: Clifton
authors.forename: Malinda L
authors.initials: ML
authors.lastname: Godwin
authors.forename: Diana
authors.initials: D
authors.lastname: Bakajsova
mesh_terms: D000154:Aconitate Hydratase / Q000378:metabolism; D000818:Animals; D002478:Cells, Cultured; D004789:Enzyme Activation; D005260:Female; D007687:Kidney Tubules, Proximal / Q000166:cytology* / Q000502:physiology*; D008564:Membrane Potentials; D008928:Mitochondria / Q000187:drug effects / Q000502:physiology*; D051336:Mitochondrial Membranes / Q000502:physiology*; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism*; D016877:Oxidants / Q000494:pharmacology*; D010101:Oxygen Consumption; D051744:Protein Kinase C-epsilon / Q000378:metabolism; D011768:Pyruvate Dehydrogenase Complex / Q000378:metabolism; D011817:Rabbits
chemical_list: D016877:Oxidants; D011768:Pyruvate Dehydrogenase Complex; D051744:Protein Kinase C-epsilon; D019950:Mitogen-Activated Protein Kinase 1; D000154:Aconitate Hydratase