Aromatic hydrocarbon receptor (AhR)center dot AhR nuclear translocator- and p53-mediated induction of the murine multidrug resistance mdr1 gene by 3-methylcholanthrene and benzo(a)pyrene in hepatoma cells

The mouse multidrug resistance gene family consists of three genes (mdr1, m dr2, and mdr3) encoding P-glycoprotein, We show that the expression of mdr1 is increased at the transcriptional level upon treatment of the hepatoma c ell line Hepa-1c1c7 with the polycyclic aromatic hydrocarbon 3-methylcholan threne (3-MC). This increase is not observed in the aromatic hydrocarbon re ceptor (AhR)-defective TAOc1BP(r)c1 and the AhR nuclear translocator (Arnt) -defective BP(r)c1 variants, demonstrating that the induction of mdr1 by 3- MC requires AhR.Arnt. We show that the mdr1 promoter (-1165 to +84) is able to activate the expression of a reporter gene in response to 3-MC in Hepa- 1c1c7 but not in BP(r)c1 cells. Deletion analysis indicated that the region from -245 to -141 contains cis-acting sequences mediating the induction, i ncluding a potential p53 binding sequence, 3-MC treatment of the cells incr eased the levels of p53 and induced p53 binding to the mdr1 promoter in an AhR.Arnt-dependent manner. Mutations in the p53 binding site abrogated indu ction of mdr1 by 3-MC, indicating that p53 binding to the mdr1 promoter is essential for the induction. Benzo(a)pyrene, a polycyclic aromatic hydrocar bon and AhR ligand, which, like 3-MC, is oxidized by metabolizing enzymes r egulated by AhR.Arnt, also activated p53 and induced mdr1 transcription. 2, 3,7,8-Tetrachlorodibenzo-p-dioxin, an AhR ligand resistant to metabolic bre akdown, had no effect. These results indicate that the transcriptional indu ction of mdr1 by 3-MC and benzo(a)pyrene is directly mediated by p53 but th at the metabolic activation of these compounds into reactive species is nec essary to trigger p53 activation. The ability of the anticancer drug and po tent genotoxic agent daunorubicin to induce mdr1 independently of AhR.Arnt further supports the proposition that mdr1 is transcriptionally up-regulate d by p53 in response to DNA damage.