MG132 as a proteasome inhibitor induces cell growth inhibition and cell death in A549 lung cancer cells via influencing reactive oxygen species and GSH level

Carbobenzoxy-Leu-Leu-leucinal (MG132) as a proteasome inhibitor has been shown to induce apoptotic cell death through formation of reactive oxygen species (ROS). In the present study, we evaluated the effects of MG132 on the growth of A549 lung cancer cells in relation to cell growth, ROS and glutathione (GSH) levels. Treatment with MG132 inhibited the growth of A549 cells with an IC₅₀ of approximately 20 μM at 24 hours. DNA flow cytometric analysis indicated that 0.5 ∼ 30 μM MG132 induced a G1 phase arrest of the cell cycle in A549 cells. Treatment with 10 or 30 μM MG132 also induced apoptosis, as evidenced by sub-G1 cells and annexin V staining cells. This was accompanied by the loss of mitochondrial membrane potential (MMP; ΔΨm). The intracellular ROS levels including O₂ ^•- were strongly increased in 10 or 30 μM MG132-treated A549 cells but were down-regulated in 0.1, 0.5 or 1 μM MG132-treated cells. Furthermore, 10 or 30 μM MG132 increased mitochondrial O₂ ^•- level but 0.1, 0.5 or 1 μM MG132 decreased that. In addition, 10 or 30 μM MG132 induced GSH depletion in A549 cells. In conclusion, MG132 inhibited the growth of human A549 cells via inducing the cell cycle arrest as well as triggering apoptosis, which was in part correlated with the changes of ROS and GSH levels. Our present data provide important information on the anti-growth mechanisms of MG132 in A549 lung cancer cells in relation to ROS and GSH.