REGULATION OF MACROPHAGE INFLAMMATORY PROTEIN-1-ALPHA MESSENGER-RNA 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 app ropriate 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 chemota xis and activation, Our previous work demonstrated that MIP-1 alpha mR NA expression in macrophages is induced by bacterial endotoxin, The ob jective of this study was to test the hypothesis that an oxidative str ess alone may trigger expression of MIP-1 alpha mRNA in macrophages an d to determine the mechanism leading to increased expression, A rat al veolar 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, Stea dy-state mRNA levels encoding MIP-1 alpha were markedly increased (3-f old) in these cells after 1 h of exposure to 0.5 mw H2O2, remained hig her 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-tre atment with N-acetylcysteine, a synthetic antioxidant. Co-treatment wi th actinomycin D reduced the MQ induction of MIP-1 alpha mRNA to a gre ater extent than the H2O2-induced increase, Transcription of the MIP-1 alpha gene was increased by exposure to both H2O2 and MQ. H2O2 treatm ent also induced a marked increase of the MIP-1 alpha mRNA half-life, indicating post-transcriptional stabilization, These observations indi cate that an oxidative stress can regulate MIP-1 alpha mRNA expression by two distinct mechanisms: transcriptional activation of the MIP-1 a lpha gene and post-transcriptional stabilization of MIP-1 alpha mRNA.