Transcriptional regulation of deoxynivalenol-induced IL-8 expression in human monocytes

The trichothecene mycotoxin deoxynivalenol (DON), commonly present in contaminated grains worldwide, induces expression of the chemokine interleukin (IL)-8 in human monocytes. The purpose of this study was to test the hypothesis that DON modulates transcriptional and posttranscriptional regulation of IL-8 expression in the U937 human monocyte model. When U937 cells were transfected with a wild-type IL-8 promoter luciferase construct (-162/+44 IL-8 LUC) and incubated with DON (1 mug/ml) or the positive control, lipopolysaccharide (LPS) (1 mug/ml), there was a significant increase in luciferase expression. Mutation of the nuclear factor-kappaB (NF-kappaB) binding site significantly impaired both DON- and LPS-induced luciferase expression. In contrast, mutating the activator protein-1 binding site resulted in significantly increased DON- and LPS-induced luciferase expression. CCAAT/enhancer-binding protein beta, octamer-1, or NF-kappaB repressing factor binding site mutations did not affect DON-induced luciferase activity. Consistent with reporter studies, the NF-kappaB inhibitor caffeic acid phenethyl ester completely ablated both DON-induced IL-8 mRNA and protein expression. When NF-kappaB subunit binding to a specific IL-8 promoter probe was evaluated by enzyme-linked immunosorbent assay (ELISA), DON was observed to increase p65 binding by 21-fold, have no effect on p50 binding and decrease p52 binding. DON was not found to stabilize IL-8 mRNA in U937 cells. Taken together, these data suggest that DON-induced IL-8 expression is likely to be mediated at the transcriptional level by NF-kappaB, specifically p65, but does not appear to involve mRNA stabilization.