Proteasome inhibitor MG-132 induces C6 glioma cell apoptosis via oxidative stress

Abstract

Aim: Proteasome inhibitors have been found to suppress glioma cell proliferation and induce apoptosis, but the mechanisms are not fully elucidated. In this study we investigated the mechanisms underlying the apoptosis induced by the proteasome inhibitor MG-132 in glioma cells. Methods: C6 glioma cells were used. MTT assay was used to analyze cell proliferation. Proteasome activity was assayed using Succinyl-LLVY-AMC, and intracellular ROS level was evaluated with the redox-sensitive dye DCFH-DA. Apoptosis was detected using fluorescence and transmission electron microscopy as well as flow cytometry. The expression of apoptosis-related proteins was investigated using Western blot analysis. Results: MG-132 inhibited C6 glioma cell proliferation in a time-and dose-dependent manner (the IC 50 value at 24 h was 18.5 μmol/L). MG-132 (18.5 μmol/L) suppressed the proteasome activity by about 70% at 3 h. It induced apoptosis via down-regulation of antiapoptotic proteins Bcl-2 and XIAP, up-regulation of pro-apoptotic protein Bax and caspase-3, and production of cleaved C-terminal 85 kDa PARP). It also caused a more than 5-fold increase of reactive oxygen species. Tiron (1 mmol/L) effectively blocked oxidative stress induced by MG-132 (18.5 μmol/L), attenuated proliferation inhibition and apoptosis in C6 glioma cells, and reversed the expression pattern of apoptosis-related proteins. Conclusion: MG-132 induced apoptosis of C6 glioma cells via the oxidative stress.

ROS inhibitor N-acetyl-L-cysteine antagonizes the activity of proteasome inhibitors

“…Taken together, we conclude that PL inhibits proteasome activity, which may lead to the accumulation of ROS as a secondary effect, as was demonstrated previously for other proteasome inhibitors [23,24]. Since proteasome inhibitors may elevate intracellular ROS by inducing ER stress [25] and by inhibiting FOXM1 [16], which has been shown to induce the expression of ROS scavengers [26], their essential proteasome inhibitory activity may be overlooked.…”

Thiostrepton is an inducer of oxidative and proteotoxic stress that impairs viability of human melanoma cells but not primary melanocytes

“…Early induction of oxidative stress that precedes proteasome inhibition is a specific feature of thiostrepton-induced cytotoxicity not shared by other proteasome inhibitors such as MG132 and bortezomib known to produce oxidative stress downstream of proteasomal and mitochondrial impairment [57,58]. However, the specific molecular mechanism underlying thiostrepton-induced dysregulation of cellular redox homeostasis observed by us is in cultured melanoma and myeloma cells remains to be elucidated, and numerous factors may contribute to thiostrepton-associated oxidative stress.…”

Steviol Reduces MDCK Cyst Formation and Growth by Inhibiting CFTR Channel Activity and Promoting Proteasome-Mediated CFTR Degradation

“…However, it should be mentioned that MG-132 not only inhibits proteasomal activity, but also produces reactive oxygen species (ROS). Previous studies showed that prolonged treatment (24 h) of MG-132 at dose of 1–30 µM induces apoptosis via formation of ROS in several cancer cell types [42], [43]. It was also reported that incubation with 25 µM of MG-132 for 4 h prevented misfolded CFTR degradation in CHO cells expressing GFP tagged F508del-CFTR [44].…”