Differential effects of polycyclic aromatic hydrocarbons on transactivation of AP-1 and NF-κB in mouse epidermal Cl41 cells

Polycyclic aromatic hydrocarbons (PAHs) and their derivatives, such as benzo[a]pyrene (B[a]P), (±)-antibenzo[a]pyrene-7,8-diol-9,10-epoxide (B[a]PDE), and 5-methylchrysene-1,2-diol-3,4-epoxide (5-MCDE), are complete carcinogens. However, the tumor promotion effects of PAHs remain unclear. We therefore investigated the possible activation of activator protein-1 (AP-1) and nuclear factor-κB (NFκB) in mouse epidermal Cl41 cells after different PAHs treatments, including B[a]P, B[a]PDE, chrysene-1,2-diol-3,4-epoxid (CDE), and 5-MCDE. The results showed that B[a]PDE and 5-MCDE were able to activate AP-1 and NF-κB, whereas B[a]P showed only marginal effect on AP-1 activation, and B[a]P and CDE had no effect on NF-κB activation. Treatment with either B[a]PDE or 5-MCDE also resulted in mitogen-activated protein kinases (MAPKs) activation as well as inhibitory subunit kappa-B (IκBα) phosphorylation and degradation, whereas B[a]P and CDE had no effect. Pretreatment with PD98059, a specific inhibitor for extracellular signal-regulated protein kinases (ERKs) upstream kinase MEK1/2, or SB202190, a p38 kinase inhibitor, resulted in a dramatic inhibition of B[a]PDE-induced AP-1 transactivation. In addition, B[a]PDE-induced AP-1 activation was also inhibited by overexpressing a dominant negative mutant of JNK1 in the cells. All these suggest ERKs, c-jun N-terminal kinases (JNKs), and p38 kinase signal transduction pathways are required for AP-1 induction by B[a]PDE. Taken together, B[a]PDE and 5-MCDE are the active compounds of PAHs to initiate signaling pathways. Considering the important roles of AP-1 and NF-κB in tumor promotion, we speculated the activation of AP-1 and NF-κB by B[a]PDE and 5-MCDE may involve in their or their parent compounds' tumor promotion effects. This study may help in better understanding the tumor promotion effects of PAHs.