Importance of CYP1A1 and CYP1B1 in bioactivation of benzo[a]pyrene in human lung cell lines

Abstract

Polycyclic aromatic hydrocarbons are ubiquitous environmental pollutants classified as carcinogens in humans and rodents. The cytochromes P4501A1 and 1B1 have both shown capacity to carry out bioactivation of the prototype PAH, benzo[a]pyrene (B[a]P) to its ultimate carcinogenic B[a]P-diol-epoxide-I-1 form. The part played by each enzyme in human lung cells, however, has not been clarified. To get further insight into their individual role in the metabolic activation of B[a]P, RNA-interference was used to down-regulate CYP1A1 and/or CYP1B1 gene expression in the human lung cell lines BEP2D and NCIH2009. Fluorescence-HPLC analysis revealed that formation of B[a]P-tetrol-I-1 (hydrolyzed form of the corresponding diol-epoxide) was dependent primarily on CYP1A1. In cells without down-regulation of CYP1A1, the B[a]P-tetrol-I-1 was the major tested isomer formed. In contrast, the B[a]P-cis- and trans-7,8-dihydrodiol isomers were readily formed in cells expressing high levels of either CYP-gene. Simultaneous down-regulation of CYP1A1 and CYP1B1 mRNA resulted in low levels of metabolites overall. Residual unmetabolized B[a]P levels followed the expression of CYP1A1 in an inverse manner. In conclusion, these results indicate a major role of CYP1A1 in the bioactivation of B[a]P to carcinogenic B[a]P-diol-epoxides and in overall metabolism of B[a]P in human lung cell lines. In contrast, both CYP1A1 and CYP1B1 contribute significantly to the formation of the B[a]P-cis- and trans-7,8-dihydrodiol isomers.

DNA methylation of the CYP1A1 enhancer is associated with smoking‐induced genetic alterations in human lung

“…6,15 We are showing here that DNA methylation of CYP1A1 enhancer inversely correlate with (i) the mRNA levels of CYP1A1 and (ii) levels of smoking-induced DNA adducts in histologically normal human lung tissues. Thus, in addition to the important role played by smoking-induced activation of the AHR/ARNT complex, inter-individual differences in CYP1A1 mRNA levels and in smoking-induced DNA damage may be due to inter-individual differences in DNA methylation of CYP1A1 enhancer.…”

“…3,4 CYP1A1 (cytochrome P4501A1) converts PAH into reactive metabolites, which may participate in the initiation of carcinogenesis via the formation of bulky PAH-DNA adducts. 5,6 In human lung, CYP1A1 is induced by PAH, and high expression has been associated with increased lung cancer risk. 7 Large inter-individual differences in CYP1A1 induction and in levels of DNA adducts in lung have been observed.…”

“…13 Thus, CYP1A1 gene expression and activity might be relevant factors for formation of major genetic alterations in lung cancer. 6,7,14,15 In addition to genomic base pair differences, gene expression can be altered by epigenetic changes such as DNA methylation and covalent modifications of histones. 16 The enhancer of CYP1A1 gene contains a transcriptional control region located several hundred base pairs upstream of the transcription start site.…”

Influence of DNA Lesions on Polymerase-Mediated DNA Replication at Single-Molecule Resolution

“…Various isomers of bioactivated B[a]P can be created leading to structural variation in the DNA adducts that can form. 103,104 Each of these adduct conformers have different mutagenic outcomes during replication. 105,106 A report by Liyanage and colleagues has investigated the mechanism of bypass at (+)-cis-B[a]P-N 2 -dG (Figure 1), by the model Y-family polymerase Dpo4 at single-molecule resolution.…”

Molecular cloning and cDNA characterization of Camelus dromedarius putative cytochrome P450s 1A1, 2C, and 3A

“…Many other CYPs are inducible enzymes, and their expression levels increase markedly when exposed to various chemicals, such as ethanol and polychlorinated dibenzo-ρ-dioxins (Uppstad et al, 2010). P450 proteins are conveniently arranged into families and subfamilies, based on the percentage of amino acid sequence identity.…”