REGULATION OF IL-8 PROMOTER ACTIVITY BY VERRUCARIN A IN HUMAN MONOCYTIC THP-1 CELLS

Macrocyclic trichothecenes have been frequently detected in fungi in water-damaged buildings and exhibited higher toxicity than the well-studied trichothecenes; however, the mechanism underlying their toxicity has been poorly understood. In this study, transcriptional regulation of the cytokine interleukin (IL)-8 by a macrocyclic trichothecene, verrucarin A (VA), in human monocytic THP-1 cells is reported. Consistent with previous findings, VA was 100-fold more cytotoxic than deoxynivalenol (DON), while ochratoxin A (OA) was not cytotoxic. In cells transduced with the wild-type IL-8 promoter luciferase construct, VA induced a biphasic dose response composed of an upregulation of luciferase expression at low concentrations of 0.01-1 ng/ml and a downregulation at high levels of 10 ng/ml and higher. In contrast, DON induced a sigmoid-shaped dose response with the EC50 of 11.6 ng/ml, while OA did not markedly affect the IL-8 expression. When cells were transduced with IL-8 promoter with a mutation of transcription factor nuclear factor-B (NF-B)-binding site, VA (1 ng/ml), DON (1000 ng/ml), and tumor necrosis factor (TNF) (20 ng/ml)-induced luciferase expression were impaired. In addition, the NF-B inhibitor caffeic acid phenethyl ester inhibited VA-, DON-, and TNF-induced luciferase expression. Mutation of the CCAAT/enhancer-binding protein (CEBP) binding site of the IL-8 promoter affected only DON-, but not VA- and TNF-induced luciferase expression. Taken together, these results suggested that VA activated IL-8 promoter via an NF-B-dependent, but not CEBP-dependent, pathway in human monocytes.