Benzene (BZ) is a class I carcinoge

Benzene (BZ) is a class I carcinogen and its oxidation to reactive intermediates is a prerequisite of hematoxicity and myelotoxicity. The generated metabolites include hydroquinone, which is further oxidized to the highly reactive 1,4-benzoquinone(BQ) in bone marrow. Therefore, we explored the mechanisms underlying BQ-induced HL-60 cell proliferation by studyingthe role of BQ-induced reactive oxygen species (ROS) in the activation of the ERK–MAPK signaling pathway. BQ treatment(0.01–30
M) showed that doses below 10
M did not significantly reduce viability. ROS production after 3
M BQ treatmentincreased threefold; however, catalase addition reduced ROS generation to basal levels. FACS analysis showed that BQ induced afivefold increase in the proportion of cells in S-phase. We also observed a high proportion of Bromodeoxyuridine (BrdU) stainedcells, indicating a higher DNA synthesis rate. BQ also produced rapid and prolonged phosphorylation of ERK1/2 proteins.Simultaneous treatment with catalase or PD98059, a potent MEK protein inhibitor, reduced cell recruitment into the S-phaseand also abolished the ERK1/2 protein phosphorylation induced by BQ, suggesting that MEK/ERK is an important pathwayinvolved in BQ-induced ROS mediated proliferation. The prolonged activation of ERK1/2 contributes to explain the increasedS-phase cell recruitment and to understand the leukemogenic processes associated with exposure to benzene metabolites. Thus,the possible mechanism by which BQ induce HL-60 cells to enter the cell cycle and proliferate is linked to ROS production andits growth promoting effects by specific activation of regulating genes known to be activated by redox mechanisms.© 2005 Elsevier Ireland Ltd. All rights reserved.