Variable overoxidation of peroxiredoxins in human lung cells in severe oxidative stress

Peroxiredoxins (Prxs) are a group of thiol containing proteins that participate both in signal transduction and in the breakdown of hydrogen peroxide (H₂O₂) during oxidative stress. Six distinct Prxs have been characterized in human cells (Prxs I-VI). Prxs I-IV form dimers held together by disulfide bonds, Prx V forms intramolecular bond, but the mechanism of Prx VI, so-called 1-Cys Prx, is still unclear. Here we describe the regulation of all six Prxs in cultured human lung A549 and BEAS-2B cells. The cells were exposed to variable concentrations of H₂O₂, menadione, tumor necrosis factor-α or transforming growth factor-β. To evoke glutathione depletion, the cells were furthermore treated with buthionine sulfoximine. Only high concentrations (300 μM) of H ₂O₂ caused a minor increase (<28%, 4 h) in the expression of Prxs I, IV, and VI. Severe oxidant stress (250-500 μM H ₂O₂) caused a significant increase in the proportion of the monomeric forms of Prxs I-IV; this was reversible at lower H ₂O₂ concentrations (≤250 μM). This recovery of Prx overoxidation differed among the various Prxs; Prx I was recovered within 24 h, but recovery required 48 h for Prx III. Overall, Prxs are not significantly modulated by mild oxidant stress or cytokines, but there is variable, though reversible, overoxidation in these nroteins durine severe oxidant exposure.