Benzo[a]pyrene carcinogenicity is lost in mice lacking the aryl hydrocarbon receptor

摘要

The contribution of the aryl hydrocarbon receptor (AhR) in induc- tion of a battery of xenobiotic-metabolizing enzymes has been studied extensively. However, no direct proof has been obtained that it plays a role in modulating carcinogenesis. To address the question of whether AhR is required for tumor induction, we have investigated the response of AhR-deficient mice to benzo[a]pyrene (Bla]P), a widely distributed environmental carcinogen. B[a]P treat- ment induced expression of the cytochrome P450 gene CyP1af in the skin and liver of AhR-positive mice bearing +/+ and +/- genotypes and did not induce expression of the cytochrome P450 gene CyP1a1 in AhR-null mice in either skin or liver. In contrast, CyP1a2 gene expression was positive in liver irrespective of the presence or absence of the AhR gene, or B[a]P treatment, although its inducibility was lost in the AhR(-/-) mouse. All AhR-positive male mice of both +/+ and +/- genotypes that received subcu- taneous injection of B[a]P (2 mg) on the first and the eighth days had developed subcutaneous tumors at the site of injection at the end of the 18-week experiment. In contrast, no tumors were apparent in any of the AhR-deficient mice. Likewise, topical appli- cation of B[alP (200 pg) at weekly intervals to the skin of female mice for 25 weeks produced skin tumors only in the AhR-positive mice. Thus the carcinogenic action of BlalP may be determined primarily by AhR, a transcriptional regulator of the gene for CYP1A1. The results of the present study provide direct evidence that AhR is involved in carcinogenesis.