Amplification of IL-1β-induced matrix metalloproteinase-9 expression by superoxide in rat glomerular mesangial cells is mediated by increased activities of NF-κB and activating protein-1 and involves activation of the mitogen-activated protein kinase pathways

The modulation of cell signaling by free radicals is important for the pathogenesis of inflammatory diseases. Recently, we have shown that NO reduces IL-1 beta -induced matrix metalloproteinase (MMP-9) expression in glomerular mesangial cells (MC). Here we report that exogenously administrated superoxide, generated by the hypoxanthine/xanthine oxidase system (HXXO) or by the redox cycler 2,3-dimethoxy-1,4-naphtoquinone, caused a marked amplification of IL-1 beta -primed, steady state, MMP-9 mRNA level and an increase in gelatinolytic activity in the conditioned medium. Superoxide generators alone were ineffective. Cytokine-induced steady state mRNA levels of TIMP-1, an endogenous inhibitor of MMP-9, were affected similarly by HXXO. Transient transfection of rat mesangial cells with 0.6 kb of the 5'-flanking region of the rat MMP-9 gene proved a transcriptional regulation of MMP-9 expression by superoxide, HXXO augmented the IL-1 beta -triggered nuclear translocation of p65 and c-Jun and, in parallel, increased DNA binding activities of NF-kappaB and AP-1. Mutation of either response element completely prevented MMP-9 promoter activation by IL-1 beta. Moreover, specific inhibitors of the classical extracellular signal-regulated kinase (ERK) pathway and p38 mitogen-activated protein kinase (MAPK) cascade, partially reversed the HXXO-mediated effects on MMP-9 mRNA levels, thus demonstrating involvement of ERKs and p38 MAPKs in MMP-9 expression. Furthermore, IL-1 beta -triggered phosphorylation of all three MAPKs, including p38-MAPK, c-Jun N-terminal kinase, and ERK, was substantially enhanced by superoxide. Our data identify superoxide as a costimulatory factor amplifying cytokine-imduced MMP-9 expression by interfering with the signaling cascades leading to the activation of AP-1 and NF-kappaB.