Genotoxic Polycyclic Aromatic Hydrocarbons Fail to Induce the P53-dependent DNA Damage Response, Apoptosis or Cell-cycle Arrest in Human Prostate Carcinoma LNCaP Cells

Exposure to polycyclic aromatic hydrocarbons (PAHs) has been positively associated with prostate cancer, but knowledge of the formation of PAH-DNA adducts and related genotoxic events in prostatic cells is limited. In the present study, benzo[a]pyrene (BaP), a potent mutagenic PAH, formed significant levels of DNA adducts in cell lines derived from human prostate carcinoma. When analyzing the effect of BaP on the induction of CYP1 enzymes participating in the metabolic activation of PAHs in LNCaP cells, we found that BaP induced expression of CYP1A1 and CYP1A2, but not CYP1B1 enzyme. Despite a significant amount of DNA adducts being formed by BaP and, to a lesser extent also by another strong genotoxin, dibenzo[a,l]pyrene, neither apoptosis nor cell-cycle arrest were induced in LNCaP cells. LNCaP cells were not sensitized to the induction of apoptosis by PAHs even through inhibition of the phosphoinositide-3-kinase/Akt pro-survival pathway. The lack of apoptosis was not due a disruption of expression of pro-apoptotic and pro-survival members of the Bcl-2 family of apoptosis regulators. In contrast to other genotoxic stimuli, genotoxic PAHs failed to induce DNA double-strand breaks, as illustrated by the lack of phosphorylation of histone H2AX or checkpoint kinase-2. BaP did not activate p53, as evidenced by the lack of p53 accumulation, phosphorylation at Ser15, or induction of p53 transcriptional targets. Taken together, although genotoxic PAHs produced significant levels of DNA adducts in a model of human prostate carcinoma cells, they did not activate the mechanisms leading to elimination of cells with significant damage to DNA, presumably due to their failure to activate the p53-dependent DNA damage response.