RESUMO
Glucocorticoids and their synthetic analogs exert potent antiinflammatory actions that, in most cases, are due to an inhibition of the expression of inflammatory genes. In this study, we elucidated the mechanisms of dexamethasone-mediated suppression of matrix metalloproteinase-9 (MMP-9) expression triggered by IL-1beta in rat mesangial cells. Treatment of mesangial cells with dexamethasone markedly reduced the gelatinolytic content of conditioned media due to a decrease in MMP-9 expression. Cloning of a 1.3-kb fragment of the rat MMP-9 gene promoter and subsequent site- directed mutagenesis revealed that a nuclear factor kappaB (NF-kappaB) site at -561 to -550 and a region from -511 to -497 bearing a distal activator protein 1 site adjacent to an Ets-binding site are essentially involved in the IL-1beta-mediated transactivation of MMP-9. Inhibition of MMP-9 expression by dexamethasone resides in a promoter region downstream of -597. The IL-1beta-caused increase in DNA binding of both NF-kappaB and Ets-1 immunopositive complexes was substantially suppressed by dexamethasone as shown by EMSA. This was paralleled with a reduced abundance of p65 and Ets-1 proteins in cell nuclei concomitantly with a reduced inhibitor of kappaB (IkappaB) degradation. In addition to NF-kappaB, we suggest a pivotal role for the Ets binding site, in concert with a distal activator protein-1 element, in the transcriptional suppression of cytokine-induced MMP-9 expression by glucocorticoids.
