AH-RECEPTOR-DEPENDENT MODULATION OF GENE-EXPRESSION BY AGED AND DILUTED SIDESTREAM CIGARETTE-SMOKE

Cigarette smoke is known to induce cytochrome P4501A1 expression and a ctivity in a variety of species. Although the elevation of this isozym e is assumed to be associated with the activation of the CYP1A1 gene t hrough a ligand-mediated mechanism involving the Ah-receptor (AhR), th is has not been determined. In this study we have examined the mechani sm by which an ambient level of aged and diluted sidestream cigarette smoke (ADSS) induces cytochrome P4501A1. Effects of ADSS on C57BL/6N a nd DBA/2N mice were examined, Induction of P4501A1-associated ethoxyre sorufin-O-dealkylase (EROD) activity was observed in the lungs of C57B L/6N mice, while there was no induction in DBA/2N mice, ADSS also indu ced EROD in wild-type mouse hepatoma (Hepa1c1c7) cells (hepa1), but no t in variant hepa1 cells defective in the AhR nuclear translocator (AR NT) protein, ADSS exposure of recombinant hepa1 cells, stably transfec ted with a reporter plasmid containing the luciferase gene under contr ol of several dioxin responsive enhancers (DREs), resulted in a time- and exposure-dependent induction of luciferase activity. ADSS-mediated induction of luciferase activity was inhibited by alpha-naphthoflavon e (alpha NF), an Ah-receptor antagonist, Gel retardation analysis demo nstrated that exposure to ADSS induced transformation and DNA binding of the AhR complex. In summary, our results not only indicate a role f or the AhR in mediating the induction of P4501A1 by ADSS, but also dem onstrate that environmentally relevant levels of ADSS must contain AhR ligands at sufficient concentrations to activate gene expression in a n AhR-dependent manner. (C) 1996 Academic Press, Inc.