Abundant expression of CYP1A1 is positively, while CYP1B1 and NQ01 are negatively, associated with benzo(a)pyrene (BP)-DNA adduct formation in normal human mammary epithelial cells (NHMECs).
Polycyclic aromatic hydrocarbons (PAHs), including BP, are activated to DNA binding species by Phase I enzymes and detoxified by Phase II enzymes, Identifying the enzymes involved in BP-DNA adduct formation may be useful for cancer prevention strategies, Our previous studies in NHMECs indicated that BP up-regulates CYP1A1, CYP1B1 and NQO1, To understand how expression levels of these genes affect BP-DNA adduct formation, 16 NHMEC strains were exposed for 12 hr to BP (4 microM), and BP-DNA adducts were measured by chemiluminescence immunoassay, The BP-DNA adduct levels ranged from 0.2-15.8 adducts/10(8) nucleotides, Gene expression levels (transcripts/ng RNA or tpn) of CYP1A1, CYP1B1 and NQO1, measured by quantitative RT-PCR, showed large variations in unexposed and BP-exposed cells. In the 16 cell strains, basal tpn ranged from 56-836 for CYP1A1, 336-5587 for CYP1B1 and 5943-40112 for NQO1, BP-induced tpn values were 251-13234 for CYP1A1, 4133-61627 for CYP181 and 445655887 for NQO1. BP-induced CYP1A1 was positively associated with BP-DNA adduct levels (r=0.737, p=0.0003). CYP181 and NQO1 tpn levels in unexposed cells were negatively associated with BP-DNA adduct levels (r=-0.495, p=0.03; and r=-0.423. p=0.07, respectively). These associations were further confirmed in 3 NHMEC strains by Western-blot for all the three proteins, ethoxyresorufin deethylase assay for CYP1A1/1B1, and dicumerol-sensitive NQO1 activity. These data indicate that, in NHMECs, BP-induced CYP1A1 is necessary for BP-DNA adduct formation, and high basal levels of CYP1B1 and NQO1 appear to protect against BP-DNA adduct formation.