Antioxidant PDTC induces stromelysin expression in mesangial cells via a tyrosine kinase-AP-1 pathway

We found that pyrrolidine dithiocarbamate (PDTC) induces the matrix metalloproteinase stromelysin in cultured glomerular mesangial cells. Although PDTC is a well-known inhibitor of nuclear factor-kappa B (NF-kappa B), this effect was independent of the NF-kappa B activity, since overexpression of a dominant negative mutant of p50 NF-kappa B subunit repressed activity of the kappa B site, whereas it failed to induce stromelysin. To elucidate the intracellular mechanisms involved, we focused on the role of activator protein 1 (AP-1), since its binding site, the 12-O-tetradecanoylphorbol 13-acetate (TPA) response element (TRE), is located in the 5'-flanking region of the stromelysin gene. Northern blot analysis revealed that PDTC upregulated expression of c-jun and c-fos before the expression of stromelysin. Transient transfection studies using a TRE-LacZ reporter plasmid elucidated that activity of AP-1 was significantly increased by PDTC. Stable transfection with a c-jun antisense cDNA or pretreatment with curcumin, a pharmacological inhibitor of c-Jun/AP-1, revealed that inactivation of AP-1 diminished the induction of stromelysin by PDTC. To identify the machinery involved upstream of AP-1 activation, the role of tyrosine kinases was investigated. Western blot analysis showed that PDTC induced phosphorylation of tyrosine kinases. Treatment of mesangial cells with tyrosine kinase inhibitors suppressed activation of AP-1 as well as induction of stromelysin by PDTC. These findings demonstrate that the antioxidant PDTC induces stromelysin expression via stimulation of the tyrosine kinase-AP-1 pathway independent of its suppressive action on NF-kappa B.