MG132, a proteasome inhibitor, induces human pulmonary fibroblast cell death via increasing ROS levels and GSH depletion

MG132 as a proteasome inhibitor can induce apoptotic cell death in lungcancer cells. However, little is known about the toxicological cellular effectsof MG132 on normal primary lung cells. Here, we investigated the effects of N-acetylcysteine (NAC) and vitamin C (well known antioxidants) or L-buthionine sulfoximine(BSO; an inhibitor of GSH synthesis) on MG132-treated human pulmonary fibroblast(HPF) cells in relation to cell death, reactive oxygen species (ROS) and glutathione(GSH). MG132 induced growth inhibition and death in HPF cells, accompanied bythe loss of mitochondrial membrane potential (MMP; ∆ψm). MG132 increased ROS levelsand GSH-depleted cell numbers in HPF cells. Both antioxidants, NAC and vitaminC, prevented growth inhibition, death and MMP (∆ψm) loss in MG132-treated HPFcells and also attenuated ROS levels in these cells. BSO showed a strong increasein ROS levels in MG132-treated HPF cells and slightly enhanced the growth inhibition,cell death, MMP (∆ψm) loss and GSH depletion. In addition, NAC decreased anonymousubiquitinated protein levels in MG132-treated HPF cells. Furthermore, superoxidedismutase (SOD) 2, catalase (CTX) and GSH peroxidase (GPX) siRNAs enhanced HPFcell death by MG132, which was not correlated with ROS and GSH level changes.In conclusion, MG132 induced the growth inhibition and death of HPF cells, whichwere accompanied by increasing ROS levels and GSH depletion. Both NAC and vitaminC attenuated HPF cell death by MG132, whereas BSO slightly enhanced the death.