Exposing cells to B[a]P provokes a complex intracellular response. Exposing cells to B[a]P provokes a complex intracellular response. In Ahr expressing cells (+Ahr) B[a]P is metabolized, causing side effects due to its active metabolite BPDE. Since this metabolism is dependent on P450 enzymes that are activated by Ahr, side effects caused by B[a]P metabolism should only be detectable in +Ahr, while effects of direct exposure to BPDE should be independent of Ahr (A). Primary responders to Ahr are activated by B[a]P exposure only in +Ahr (B); these include other TFs. These TFs can in turn activate their target genes with a time lag compared to the primary Ahr response (C).