Hydrogen peroxide is widely viewed as the main second messenger in redox signaling, and it has been proposed that deactivation of the antioxidant peroxiredoxin (Prdx) enzymes allows free peroxide to accumulate and directly oxidize target proteins (the floodgate model). We assessed the role of cytosolic Prdxs 1 and 2 in peroxide-induced activation of the apoptosis signaling kinase 1 (ASK1)/p38 signaling pathway, in which oxidation of ASK1 is required for phosphorylation of p38. In response to peroxide, Prdx1 catalyzed oxidation of ASK1 to a disulfide-linked multimer, and this occurred via transient formation of a Prdx1-ASK1 mixed disulfide intermediate. Oxidation of ASK1 and phosphorylation of p38 were inhibited by knockdown of Prdx1, but also by overexpression of Prdx2. This suggests that these two cytosolic Prdxs have distinct roles in the cellular peroxide response and compete for available peroxide substrate. These data imply that Prdx1 can function as a peroxide receptor in response to extracellular H(2)O(2), receiving the peroxide signal and transducing it into a disulfide bond that is subsequently transmitted to the substrate, ASK1, resulting in p38 phosphorylation. Interestingly, in response to peroxide, Prdx1 and Prdx3 transiently formed reducible higher molecular weight complexes, suggesting that multiple proteins are targets for Prdx-mediated oxidation via a disulfide-exchange mechanism. This model of active peroxide signal distribution via disulfide exchange is consistent with Prdx function in yeast and explains how peroxides may trigger specific disulfide bond formation in mammalian cells.
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