title: MKK6 phosphorylation regulates production of superoxide by enhancing Rac GTPase activity.
abstract: Rac-dependent NADPH oxidases generate reactive oxygen species used in cell signaling and microbial killing or both. Whereas the mechanisms leading to NADPH oxidase activation are fairly well studied, the mechanisms that control downregulation of this enzyme complex remain unclear. We hypothesized that reactive oxygen species produced by NADPH oxidase may autoregulate the complex by inhibiting Rac activity. To this end, we searched for binding partners of Rac1 and identified a tyrosine-phosphorylated fragment of MKK6 that bound to Rac1 under redox-stress conditions. Constitutively active MKK6 interacted directly with Rac1 in vitro, and this interaction was enhanced when MKK6 was phosphorylated on tyrosine 219. Both Rac1 and Rac2 immunoprecipitated an MKK6 fragment under conditions that elevate cellular peroxide levels in 293 and RAW cells, respectively. Constitutively active and wild-type MKK6 enhanced Rac-GTPase activity in vitro, and their overexpression inhibited PMA-induced NADPH oxidase activation in RAW cells. In contrast, a Y219F mutant of MKK6 only partially enhanced Rac1 GTPase activity, and its overexpression did not alter PMA-induced NADPH oxidase activation in RAW cells. Last, MKK6 deficiency led to an increase in Rac1-GTP levels in brain tissue. Our findings suggest that MKK6 downregulates NADPH oxidase activity by enhancing Rac-GTPase activity.
authors.affiliation: Department of Anatomy & Cell Biology, The University of Iowa, Iowa City, Iowa 52242, USA.
authors.forename: Maged M
authors.initials: MM
authors.lastname: Harraz
authors.forename: Andrea
authors.initials: A
authors.lastname: Park
authors.forename: Duane
authors.initials: D
authors.lastname: Abbott
authors.forename: Weihong
authors.initials: W
authors.lastname: Zhou
authors.forename: Yulong
authors.initials: Y
authors.lastname: Zhang
authors.forename: John F
authors.initials: JF
authors.lastname: Engelhardt
mesh_terms: D000256:Adenoviridae / Q000235:genetics; D000818:Animals; D002460:Cell Line; D002478:Cells, Cultured; D004926:Escherichia coli / Q000235:genetics; D015971:Gene Expression Regulation, Enzymologic; D005982:Glutathione Transferase / Q000378:metabolism; D006861:Hydrogen Peroxide / Q000494:pharmacology; D048669:MAP Kinase Kinase 6 / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008264:Macrophages / Q000187:drug effects / Q000378:metabolism; D051379:Mice; D008822:Mice, Transgenic; D009154:Mutation; D016877:Oxidants / Q000494:pharmacology; D010766:Phosphorylation; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000378:metabolism; D013481:Superoxides / Q000378:metabolism*; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D014443:Tyrosine / Q000378:metabolism; D020744:rac GTP-Binding Proteins / Q000032:analysis / Q000378:metabolism*
chemical_list: D016877:Oxidants; D011993:Recombinant Fusion Proteins; D013481:Superoxides; D014443:Tyrosine; D006861:Hydrogen Peroxide; D005982:Glutathione Transferase; D048669:MAP Kinase Kinase 6; C482567:Map2k6 protein, mouse; D020744:rac GTP-Binding Proteins; D013755:Tetradecanoylphorbol Acetate