Sulfasalazine is a potent and specific inhibitor of IKB-kinases IKKa and IKKb

Abstract

Background & Aims: NF-KBlRel has been implicated in the pathogenesis of inflammatory bowel disease (IBD). Various drugs known to be effective for the treatment of IBD such as glucocorticoids and salicylates have been shown to interfere with NF-KBlRel signaling. The aim of this study was to define the molecular mechanism by which sulfasalazine inhibits NF-KB activation. Methods: The effects of sulfasalazine and its moieties on NF-KB signaling were evaluated using electromobility shift-, transfectionand immune complex kinase-assays. The direct effect of sulfasalazine on IKB kinase (IKK) activity was investigated using purified recombinant IKKaand IKKl3proteins. Results: NF-kBlRel activity induced by the overexpression of NF-KBinducing kinase (NIK), IKKa, IKKI3, or consitutively active IKKaand IKKl3mutants was inhibited in a dose dependent manner by sulfasalazine. Sulfasalazine inhibited TNFa, PMA and IL-I induced activation of endogenous IKKs in colonic epithelial and Jurkat T cells. Sulfasalazine did not affect other cell1ular kinases such as MAP-kinases JNK and p38. Sulfasalazine diminished the catalytic activity of purified IKKaand IKKl3in vitro. In contrast, the metabolic moieties of sulfasalazine, 5-aminosalicylic acid and sulfapyridine were not effective. The decrease in substrate phosphorylation by IKKaandl3is associated with a decrease of autophosphorylation of IKKs and can be antagonized by excess ATP. Conclusions: These data suggest that sulfasalazine is a competitive antagonist of ATP binding of IKKaand IKKI3. This suppression of NF-kB activation by inhibition of IKK activity may contribute to the well-known anti-inflammatory and immunosuppressive effects of sulfasalazine.