Regulation of macrophage inflammatory protein-1 alpha mRNA by oxidative stress

Accumulation of inflammatory cells within the lung has been implicated in oxidative injury, Recruitment of these cells to a tissue site is a complex process that depends in part upon the local expression of appropriate proinflammatory chemokines, Macrophage inflammatory protein-1 alpha (MIP-1 alpha), a member of the CC subfamily of chemokines, has been shown to contribute to monocyte/macrophage and neutrophil chemotaxis and activation, Our previous work demonstrated that MIP-1 alpha mRNA expression in macrophages is induced by bacterial endotoxin, The objective of this study was to test the hypothesis that an oxidative stress alone may trigger expression of MIP-1 alpha mRNA in macrophages and to determine the mechanism leading to increased expression, A rat alveolar macrophage cell line (NR8383) was exposed to H2O2 or menadione (2-methyl-1,4-naphthoquinone (MQ)), a quinone compound that undergoes redox cycling and generates reactive oxygen species continuously, Steady-state mRNA levels encoding MIP-1 alpha were markedly increased (3-fold) in these cells after 1 h of exposure to 0.5 mw H2O2, remained higher than control levels after 4 h, and decreased after 6 h, Similarly, MQ (25 or 50 mu M) caused a significant increase of MIP-1 alpha mRNA with a maximal induction after 4 h of exposure (5-fold), Both H2O2 and MQ-induced up-regulation of MIP-1 alpha mRNA was suppressed by co-treatment with N-acetylcysteine, a synthetic antioxidant. Co-treatment with actinomycin D reduced the MQ induction of MIP-1 alpha mRNA to a greater extent than the H2O2-induced increase, Transcription of the MIP-1 alpha gene was increased by exposure to both H2O2 and MQ. H2O2 treatment also induced a marked increase of the MIP-1 alpha mRNA half-life, indicating post-transcriptional stabilization, These observations indicate that an oxidative stress can regulate MIP-1 alpha mRNA expression by two distinct mechanisms: transcriptional activation of the MIP-1 alpha gene and post-transcriptional stabilization of MIP-1 alpha mRNA.