MKK6 phosphorylation regulates production of superoxide by enhancing Rac GTPase activity

Maged M. Harraz, Andrea Park, Duane Abbott, Weihong Zhou, Yulong Zhang, John F. Engelhardt

Research output: Contribution to journalArticlepeer-review

10 Scopus citations


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.

Original languageEnglish (US)
Pages (from-to)1803-1813
Number of pages11
JournalAntioxidants and Redox Signaling
Issue number11
StatePublished - Oct 1 2007
Externally publishedYes

ASJC Scopus subject areas

  • Biochemistry
  • Physiology
  • Molecular Biology
  • Clinical Biochemistry
  • Cell Biology


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