Abstract

Glomerular mesangial cells express matrix metalloproteinase-9 (MMP-9) in response to the proinflammatory cytokine interleukin-1 beta (IL-1 beta). To elucidate the signal transduction systems involved, we focused on the role of nuclear factor-kappa B (NF-kappa B) and activator protein-1 (AP-1), since the 5'-flanking region of MMP-9 gene contains binding sequences for these transacting molecules. In rat mesangial cells treated with an inhibitor of NF-kappa B, pyrrolidine dithiocarbamate, induction of MMP-9 by IL-1 beta was suppressed at both mRNA and protein levels. Mesangial cells stably transfected with a transdominant negative mutant of NF-kappa B also showed blunted induction of MMP-9. Transient transfection study with a kappa B reporter plasmid revealed that IL-1 beta indeed activated the kappa B site and that pyrrolidine dithiocarbamate abolished this activation. These results suggest that IL-1 beta induced MMP-9 via the stimulation of NF-kappa B pathway. to examine whether tyrosine kinase is involved in this pathway, mesangial cells were stimulated by IL-1 beta in the presence of a tyrosine kinase inhibitor genistein. This inhibitor dose dependently suppressed the expression of MMP-9, as well as the activation of the kappa B site by IL-1 beta, indicating the involvement of tyrosine kinase in the stimulation of NF-kappa B. Because mesangial cells stimulated by IL-1 beta transiently expressed c-fos and c-jun nRNAs prior to the expression of MMP-9, the role of these genes in mediating the IL-1 beta response was further examined. Transfection of mesangial cells with a c-jun antisense cDNA and treatment with a pharmacological inhibitor of c-Jun/ AP-1, curcumin, revealed that the induction of c-Jun/AP-1 is essential for the expression of MMP-9 by IL-1 beta. Although protein kinase C (PKC) is regarded as a potential inducer of AP-1, stimulation of mesangial cells with phorbol 12-myristate 13-acetate failed to induce MMP-9. Similarly, depletion of intracellular PKC did not obviously affect the induction of MMP-9 by IL-1 beta. These findings demonstrate that dual operation of tyrosine kinase-mediated NF-kappa B stimulation and c-Jun/AP-1 activation is essential to the induction of MMP-9 by IL-1 beta in cultured mesangial cells.