Although benzo[g,h,i]
perylene (BghiP) has been found to promote the
carcinogenesis of
benzo[a]pyrene (BaP) in animal models, not much is known about this cocarcinogenic mechanism. In this study, human
hepatoma HepG2 cells cotreated with BaP and BghiP were used as a model to investigate the cocarcinogenic mechanism of BghiP in BaP-induced
carcinogenesis.
DNA adduct formation is thought to initiate
carcinogenesis, so the effect of BghiP on
BaP-DNA adduct formation was evaluated using a (32)P-postlabeling assay. The
BaP-DNA adduct levels increased following the addition of BghiP, in a dose-dependent manner. However, no adducts were formed with BghiP alone. Our previous report showed that
cytochrome P450 1A1 (
CYP1A1) is responsible for the metabolic activation of BaP and the formation of B[a]P adduct in HepG2 cells. Western blot and Northern blot analyses were used to evaluate whether BaP-induced
CYP1A1 protein and
mRNA levels increased following the addition of BghiP. Our data showed that BghiP enhanced BaP-induced
CYP1A1 protein and its
mRNA levels. To understand whether BghiP enhances BaP-induced
CYP1A1 gene expression through the
aryl hydrocarbon receptor (AhR) signaling pathway, a gel retardation assay was performed to elucidate the synergistic mechanism of BghiP in BaP-induced
CYP1A1 gene expression. The results showed that BghiP causes an increase in the nuclear accumulation of AhR in cells and/or activation of AhR to
a DNA-binding form. There was a concordant increase in the transcription activation of
CYP1A1 gene and the induction of AhR signal pathway. Our findings demonstrated that BghiP enhances BaP-induced
CYP1A1 transcription by AhR activation and suggested that the induction mechanism of
CYP1A1 contributes to the cocarcinogenic potential of BghiP in BaP-induced
carcinogenesis.