Abstract
Acenaphthenequinone (AcQ) is a polycyclic aromatic hydrocarbon, present in diesel exhausts. In this report, mechanism(s) of cytotoxicity of AcQ in human lung epithelial cells (A549) and human peripheral blood mononuclear cells (PBMC) have been investigated. Treatment with AcQ resulted in the disruption of the microtubule network in A549 cells in time and concentration-dependent manners and caused cell cycle arrest in the G2/M phase and apoptosis, with an IC50 value of ∼35 and ∼14 μM for 24 h and 48 h respectively. AcQ induced apoptosis in PBMC cells (IC50 ≈ 15 μM, 24 h). We found up-regulation of cyclin B1 and down-regulation of cyclin D1 caused G2/M arrest in treated cells. Up-regulation of pro-apoptotic proteins like p53 and Bax, and down-regulation of anti-apoptotic protein Bcl-2 were observed in treated A549 cells. Loss of mitochondrial membrane potential and activation of caspase-3 as well as release of mitochondrial cytochrome c was also obtained. AcQ also inhibited the tubulin polymerization in cell free system (IC50 ≈ 10 μM). The stoichiometry of AcQ binding to purified tubulin was nearly 1 : 1 with a dissociation constant of 11.0 ± 0.8 μM at 25 °C. Interaction of AcQ with tubulin resulted in conformational changes, monitored by quenching of tryptophan fluorescence, tubulin–colchicine and tubulin–ANS binding and CD experiments.
The cytotoxicity of the environmental pollutant AcQ is due to disruption of the tubulin–microtubule dynamic equilibrium in cells.
