MG132, a proteasome inhibitor-induced calf pulmonary arterial endothelial cell growth and death, are changed by MAPK inhibitors

MG132, as a proteasome inhibitor, has been shown to induce apoptotic cell death through the formation of reactive oxygen species (ROS). In this study, we investigated the effects of MAPK inhibitors on MG132-treated calf pulmonary artery endothelial cells (CPAECs) in relation to cell death, ROS, and glutathione (GSH). MG132 inhibited the growth of CPAEC and also induced apoptosis, which was accompanied by the loss of mitochondrial membrane potential (MMP; Delta psi(m)). MG132 increased ROS levels and GSH-depleted cell numbers in CPAEC. Treatment with MAPK (MEK, JNK, and p38) inhibitors showed a slight enhancement of cell-growth inhibition by MG132. All the MAPK inhibitors decreased cell death by MG132. Especially, the JNK inhibitor showed a strong effect. They all did not affect ROS levels and GSH depletion in MG132-treated CPAEC, but increased ROS and GSH levels in MG132-untreated CPAEC. In conclusion, MG132 induced apoptosis in CPAEC, which was accompanied by ROS increase and GSH depletion. The changes of MG132-induced CPAEC growth inhibition and death by MAPK inhibitors were not tightly correlated to ROS and GSH levels.