Benzo[a]pyrene Induces Apoptosis in RL95-2 Human Endometrial Cancer Cells by Cytochrome P450 1A1 Activation

Abstract

Benzo[a]pyrene (B[a]P) has been shown to be an inducer of apoptosis in some cell types. To date, due to the lack of an appropriate model system, studies of the cellular and biochemical mechanism(s) by which B[a]P induces apoptosis have been focused on Hepa1c1c7 cells. Moreover, the precise relationship between the bioactivation of B[a]P by CYP1A1 or CYP1B1 and the occurrence of cytotoxicity-mediated apoptosis requires further elucidation. In the present study, we showed that B[a]P-induced apoptosis in RL95-2 cells is accompanied by the activation of caspases. In addition, the mitochondrial changes, including the decrease of mitochondrial potential and the release of mitochondrial cytochrome c and second mitochondria-derived activator of caspases/direct inhibitor of apoptosis protein binding protein with low PI (Smac/DIABLO) into the cytosol, support the suggestion that the mitochondrial pathway is robustly associated with B[a]P-evoked apoptosis. This study showed the involvement of the nuclear translocation of mitochondrial apoptosis-inducing factor in B[a]P-induced apoptosis of RL95-2 cells. Exposure to B[a]P up-regulates aryl hydrocarbon receptor, heat-shock protein 90, cytochrome P450 1A1 (CYP1A1), cytochrome P450 1B1 (CYP1B1), and epoxide hydrolase significantly, which might be prerequisites for the conversion of B[a]P to B[a]P-7,8-dihydroxy-9,10-epoxide. Although both CYP1A1 and CYP1B1 proteins were up-regulated significantly by B[a]P, only CYP1A1 exhibited activity. Thus, CYP1A1 is believed to be a central oxidative enzyme that is ultimately required for formation of B[a]P-7,8-dihydroxy-9,10-epoxide from B[a]P in RL95-2 cells. Altogether, our data showed that RL95-2 cells are susceptible to apoptosis by exposure to B[a]P and that B[a]P-evoked apoptosis is mediated predominantly by the activation of CYP1A1. Here we suggest that RL95-2 cells are an excellent model for the investigation of xenobiotic mechanisms associated with CYP1A1 as well as CYP1B1.