Myeloperoxidase deficiency induces MIP-2 production via ERK activation in zymosan-stimulated mouse neutrophils

Abstract

Myeloperoxidase (MPO), a major constituent of neutrophils, catalyzes the production of hypochlorous acid (HOCl) from hydrogen peroxide (H₂O₂) and chloride anion. We have previously reported that MPO-deficient (MPO^?/?) neutrophils produce greater amount of macrophage inflammatory protein-2 (MIP-2) in vitro than do wild type when stimulated with zymosan. In this study, we investigated the molecular mechanisms governing the up-regulation of MIP-2 production in the mutant neutrophils. Interestingly, we found that zymosan-induced production of MIP-2 was blocked by pre-treatment with U0126, an inhibitor of mitogen-activated protein kinase/extracellular-signal-regulated kinase (ERK), and with BAY11-7082, an inhibitor of nuclear factor (NF)-κB. Western blot analysis indicated that U0126 also inhibited the phosphorylation of p65 subunit of NF-κB (p65), indicating that MIP-2 was produced via the ERK/NF-κB pathway. Intriguingly, we found that ERK1/2, p65, and alpha subunit of inhibitor of κB (IκBα) in the MPO^?/? neutrophils were phosphorylated more strongly than in the wild type when stimulated with zymosan. Exogenous H₂O₂ treatment in addition to zymosan stimulation enhanced the phosphorylation of ERK1/2 without affecting the zymosan-induced MIP-2 production. In contrast, exogenous HOCl inhibited the production of MIP-2 as well as IκBα phosphorylation without affecting ERK activity. The zymosan-induced production of MIP-2 in the wild-type neutrophils was enhanced by pre-treatment of the MPO inhibitor 4-aminobenzoic acid hydrazide. Collectively, these results strongly suggest that both lack of HOCl and accumulation of H₂O₂ due to MPO deficiency contribute to the up-regulation of MIP-2 production in mouse neutrophils stimulated with zymosan.