The biotransformation and detoxification of many carcinogens, including 2,3,7,8-tetrachlorodibenzodioxin, benzo [a] pyrene and 3-methylchloranthrene is dependent upon the activity of phase I and II enzymes, particularly CYP1A1 and NQO1. The transcriptional activation of these enzymes is regulated by the aryl hydrocarbon receptor (AhR) and Nuclear Factor-Erythroid 2-Related Factor. These transcription factors reside in the cytoplasm and when activated, shed their respective chaperones and translocate into the nucleus where they interact with nuclear proteins involved with transcription of genes possessing xenobiotic (XRE) and antioxidant (ARE) response elements. We have previously observed that the phytochemical benzyl isothiocyanate (BITC) induces nuclear translocation of the AhR independently of traditional ligands in Hepa1c1c7 cells and also induces AhR heterodimerization with ARNT. These observations suggest that BITC might bind the AhR and affect activity of these enzymes as well as the transcriptional regulation of XRE-responsive genes. In the current study we investigated whether BITC causes degradation of the AhR. This is important because it provides insight into potential mechanisms by which BITC affects AhR transcriptional regulation and the activity of phase I and II enzymes. Hepa1c1c7 cells were treated for 4 hours with DMSO alone, 10 μM BITC, 10 μM BNF or a combination of both 10 μM BITC and 10 μM BNF. Whole cell lysates were prepared and AhR immunoprecipitated and analyzed by western blot. Results showed that AhR was rapidly degraded in cells treated with BITC alone compared to controls. Furthermore, BITC enhanced degradation of the receptor in cells treated with a combination of both BITC and BNF compared to cells treated with BNF alone. In other experiments, Hepa1 cells were treated for 16 hours with BNF alone or a combination of 1, 2, 5, 10 and 20 μM BITC. Isolated proteins analyzed by western blot indicated that BITC enhanced degradation of the AhR in a dose dependent manner in cells treated with both BITC and BNF compared to BNF-only treated cells. Cumulatively, these data show that BITC degrades the AhR, which might decrease its function in transcription of XRE responsive genes. The results also suggest that increased degradation of the AhR might affect the activity of CYP1A1 and NQO1 thus affecting biotransformation and detoxification of carcinogens. They also provide preliminary evidence into one of the potential mechanisms by which BITC is chemopreventive. (Support: NIH MBRS/GM028248; RCMI RR033032).

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 4066.