A trans-dominant negative AhR ablates CYP1A1 induction in MonoMac1 cells. (A) Ectopic overexpression of a truncated AhR (AhR515) in MonoMac1 cells. A Western blot analysis is shown. At the left, the position of molecular weight standards is indicated. (B) AhR515 acts as in a trans-dominant negative fashion by blocking the induction of CYP1A1 expression by VAF347. vector indicates cells infected with the parental retroviral vector.