Inhibition of NF-κB activation and its target genes by heparin-binding epidermal growth factor-like growth factor

Many cells upon injury mount extensive, compensatory responses that increase cell survival; however, the intracellular signals that regulate these responses are not completely understood. Heparin-binding epidermal growth factor-like growth factor (HB-EGF) has been implicated as a cytoprotective agent. We have previously demonstrated that pretreatment of human intestinal epithelial cells with HB-EGF, significantly decreased cytokine-induced activation of inducible NO synthase mRNA expression and NO production and protected the cells from apoptosis and necrosis. However, the mechanisms by which HB-EGF exerts these effects are not known. Here we show that cytokine exposure (IL-1beta and IFN-gamma) induced NF-kappaB activation and IL-8 and NO production in DLD-1 cells. Transient expression of a dominant negative form of IkappaBalpha decreased NO production, suggesting that the cytokines stimulated NO production in part through activation of NF-kappaB. HB-EGF dramatically suppressed NF-kappaB activity and IL-8 release and decreased NO production in cells pretreated with HB-EGF. HB-EGF blocked NF-kappaB activation by inhibiting IkappaB kinase activation and IkappaB phosphorylation and degradation, thus interfering with NF-kappaB nuclear translocation, DNA-binding activity, and NF-kappaB-dependent transcriptional activity. The data demonstrate that HB-EGF decreases inflammatory cytokine and NO production by interfering with the NF-kappaB signaling pathway. Inhibition of NF-kappaB may represent one of the mechanisms by which HB-EGF exerts its potent anti-inflammatory and cytoprotective effects.