The myeloperoxidase-derived oxidant HOSCN inhibits protein tyrosine phosphatases and modulates cell signalling via the mitogen-activated protein kinase (MAPK) pathway in macrophages

Amanda E. Lane, Joanne T.M. Tan, Clare L. Hawkins, Alison K. Heather, Michael J. Davies

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61 Citations (Scopus)


MPO (myeloperoxidase) catalyses the oxidation of chloride, bromide and thiocyanate by hydrogen peroxide to HOCl (hypochlorous acid), HOBr (hypobromous acid) and HOSCN (hypothiocyanous acid) respectively. Specificity constants indicate that SCN- is amajor substrate for MPO. HOSCN is also a major oxidant generated by other peroxidases including salivary, gastric and eosinophil peroxidases. While HOCl and HOBr are powerful oxidizing agents, HOSCN is a less reactive, but more specific, oxidant which targets thiols and especially low pKa species. In the present study we showthatHOSCNtargets cysteine residues present in PTPs (protein tyrosine phosphatases) with this resulting in a loss of PTP activity for the isolated enzyme, in cell lysates and intact J774A.1 macrophage-like cells. Inhibition also occurs with MPO-generated HOCl and HOBr, but ismoremarked with MPO-generated HOSCN, particularly at longer incubation times. This inhibition is reversed by dithiothreitol, particularly at early time points, consistent with the reversible oxidation of the active site cysteine residue to give either a cysteine-SCN adduct or a sulfenic acid. Inhibition of PTP activity is associated with increased phosphorylation of p38a and ERK2 (extracellular-signal-regulated kinase 2) as detected byWestern blot analysis and phosphoprotein arrays, and results in altered MAPK (mitogen-activated protein kinase) signalling. These data indicate that the highly selective targeting of some protein thiols by HOSCN can result in perturbation of cellular phosphorylation and altered cell signalling. These changes occur with (patho)physiological concentrations of SCN- ions, and implicate HOSCN as an important mediator of inflammation-induced oxidative damage, particularly in smokers who have elevated plasma levels of SCN-.

Original languageEnglish
Pages (from-to)161-169
Number of pages9
JournalBiochemical Journal
Issue number1
Publication statusPublished or Issued - 15 Aug 2010
Externally publishedYes


  • Cell signalling
  • Hypothiocyanous acid (HOSCN)
  • Mitogen-activated protein kinase (MAPK)
  • Myeloperoxidase
  • Protein tyrosine phosphatase
  • Thiol
  • p38

ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Cell Biology

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