Modulation of transcription factor AP-1 activity in murine EL-4 thymoma cells by vomitoxin (deoxynivalenol)

Trichothecene mycotoxins have been reported to suppress or superinduce cyto kine mRNA expression by leukocytes both in vitro and in vivo. Modulation of transcription factor activities may be critical for these observations. He re, the effect of trichothecene vomitoxin (VT, deoxynivalenol) on activator protein-1 (AP-1) activity was determined in the murine EL-4 thymoma. Elect rophoretic mobility shift assay (EMSA) revealed that VT modulated AP-1 bind ing activity in a concentration- and time-dependent manner when using a syn chronous model in which VT was added concurrently with phorbol 12-myristate 13-acetate (PMA) and ionomycin (ION) to EL-4 cells. Induction of AP-1 bind ing activity by PMA/ION was suppressed in the presence of VT for a short pe riod (1 to 12 h), but was enhanced upon prolonged VT exposure (48 to 72 h). VT also enhanced AP-1 binding activity when added to the cell culture 12 h after PMA/ION activation (delayed synchronous model). Using specific antib odies against AP-1 complex proteins, it was demonstrated by gel supershift assay that VT preferentially affected phosphorylated c-Jun, Jun B, c-Fos, a nd Fra-2 binding activities, whereas it did not alter Jun D and Fra-1 bindi ng. A transient transfection assay demonstrated that these increased bindin g activities are associated with enhanced AP-1 transactivation potential. E levation of AP-1 activity may contribute to cytokine dysregulation and immu notoxic effects associated with exposure to trichothecene mycotoxins such a s VT. (C) 2000 Academic Press.