MG132

About: MG132 is a research topic. Over the lifetime, 1499 publications have been published within this topic receiving 56589 citations. The topic is also known as: MG132 & Z-Leu-leu-leu-al.

Proteasome inhibitors cause induction of heat shock proteins and trehalose, which together confer thermotolerance in saccharomyces cerevisiae

Abstract: An accumulation in cells of unfolded proteins is believed to be the common signal triggering the induction of heat shock proteins (hsps). Accordingly, in Saccharomyces cerevisiae, inhibition of protein breakdown at 30°C with the proteasome inhibitor MG132 caused a coordinate induction of many heat shock proteins within 1 to 2 h. Concomitantly, MG132, at concentrations that had little or no effect on growth rate, caused a dramatic increase in the cells’ resistance to very high temperature. The magnitude of this effect depended on the extent and duration of the inhibition of proteolysis. A similar induction of hsps and thermotolerance was seen with another proteasome inhibitor, clasto-lactacystin β-lactone, but not with an inhibitor of vacuolar proteases. Surprisingly, when the reversible inhibitor MG132 was removed, thermotolerance decreased rapidly, while synthesis of hsps continued to increase. In addition, exposure to MG132 and 37°C together had synergistic effects in promoting thermotolerance but did not increase hsp expression beyond that seen with either stimulus alone. Although thermotolerance did not correlate with hsp content, another thermoprotectant trehalose accumulated upon exposure of cells to MG132, and the cellular content of this disaccharide, unlike that of hsps, quickly decreased upon removal of MG132. Also, MG132 and 37°C had additive effects in causing trehalose accumulation. Thus, the resistance to heat induced by proteasome inhibitors is not just due to induction of hsps but also requires a short-lived metabolite, probably trehalose, which accumulates when proteolysis is reduced.

Differential regulation of endothelial cell adhesion molecule expression by nitric oxide donors and antioxidants

Abstract: Although nitric oxide (NO) and antioxidants inhibit adhesion molecule expression, their inhibitory effects on nuclear factor kappaB (NF-kappaB) activation may differ. The NO donors, but not 8-bromo-cGMP, decreased tumor necrosis factor alpha (TNF-alpha)-induced VCAM-1, ICAM-1, and E-selectin expression by 11-70%. In contrast, NAC completely abolished VCAM-1 and E-selectin expression and decreased ICAM-1 expression by 56%. Gel shift assays demonstrate that NF-kappaB activation was inhibited by both NO and antioxidants. The activation of NF-kappaB involves the phosphorylation and degradation of its cytoplasmic inhibitor IkappaB-alpha by 26S proteasomes. The 26S proteasome inhibitor MG132 prevented the degradation of phosphorylated IkappaB-alpha. NAC inhibited IkappaB kinase (IKK) activity and prevented IkappaB-alpha phosphorylation and degradation. In contrast, NO did not inhibit IKK activity, IkappaB-alpha phosphorylation, or IkappaB-alpha degradation. However, NO, but not antioxidants, induced IkappaB-alpha promoter activity. The inhibitory effects of NO on adhesion molecule expression, therefore, differs from that of antioxidants in terms of the mechanism by which NF-kappaB is inactivated.

Potential role of nuclear translocation of glyceraldehyde-3-phosphate dehydrogenase in apoptosis and oxidative stress.

Abstract: Recent studies indicating a role of glyceraldehyde-3-phosphate dehydrogenase (GAPDH) in apoptosis or oxidative stress has been reported. Using confocal laser-scanning microscopy, we have investigated the cellular distribution of GAPDH in central nervous system (CNS)-derived cells (neuroblastoma mNB41A3), in non-CNS derived cells (R6 fibroblast) and in an apoptosis-resistant Bcl2 overexpressing cell line (R6-Bcl2). Induction of apoptosis by staurosporine or MG132 and oxidative stress by H(2)O(2) or FeCN enhanced the nuclear translocation of endogenous GAPDH in all cell types, as detected by immunocytochemistry. In apoptotic cells, GAPDH expression is three times higher than in non-apoptotic cells. Consistent with a role for GAPDH in apoptosis, overexpression of a GAPDH-green fluorescent protein (GAPDH-GFP) hybrid increased nuclear import of GAPDH-GFP into transfected cells and the number of apoptotic cells, and made them more sensitive to agents that induce apoptosis. Bcl2 overexpression prevents nuclear translocation of GAPDH and apoptosis in untransfected cells, but not in transfected cells that overexpress GAPDH-GFP. Our observations indicate that nuclear translocation of GAPDH may play a role in apoptosis and oxidative stress, probably related to the activity of GAPDH as a DNA repair enzyme or as a nuclear carrier for pro-apoptotic molecules.

Induction of murine NAD(P)H:quinone oxidoreductase by 2,3,7,8-tetrachlorodibenzo-p-dioxin requires the CNC (cap 'n' collar) basic leucine zipper transcription factor Nrf2 (nuclear factor erythroid 2-related factor 2): cross-interaction between AhR (aryl hydrocarbon receptor) and Nrf2 signal transduction

Abstract: TCDD (2,3,7,8-tetrachlorodibenzo- p -dixoin) induces phase II drug-metabolizing enzyme NQO1 [NAD(P)H:quinone oxidoreductase; EC 1.6.99.2; DT-diaphorase] in a wide range of mammalian tissues and cells. Here, we analysed the molecular pathway mediating NQO1 induction by TCDD in mouse hepatoma cells. Inhibition of protein synthesis with CHX (cycloheximide) completely blocks induction of NQO1 by TCDD as well as the basal expression and induction by phenolic antioxidant tBHQ (2-t-butylbenzene-1,4-diol), implicating a labile factor in NQO1 mRNA expression. The inhibition is both time- and concentration-dependent, requires inhibition of protein synthesis, and occurs at a transcriptional level. Inhibition of NQO1 transcription by CHX correlates with a rapid reduction of the CNC bZip (cap 'n' collar basic leucine zipper) transcription factor Nrf2 (nuclear factor erythroid 2-related factor 2) through the 26 S proteasome pathway. Moreover, blocking Nrf2 degradation with proteasome inhibitor MG132 increases the amount of Nrf2 and superinduces NQO1 in the presence of TCDD or tBHQ. Finally, genetic experiments using AhR (aryl hydrocarbon receptor)-, Arnt (aryl hydrocarbon receptor nuclear translocator)- or Nrf2-deficient cells reveal that, while induction of NQO1 by TCDD depends on the presence of AhR and Arnt, the basal and inducible expression of NQO1 by either TCDD or tBHQ requires functional Nrf2. The findings demonstrate a novel role of Nrf2 in the induction of NQO1 by TCDD and provide new insights into the mechanism by which Nrf2 regulates the induction of phase II enzymes by both phenolic antioxidants and AhR ligands.

Proteasome function is required for DNA damage response and fanconi anemia pathway activation.

Abstract: Proteasome inhibitors sensitize tumor cells to DNA-damaging agents, including ionizing radiation (IR), and DNA cross-linking agents (melphalan and cisplatin) through unknown mechanisms. The Fanconi anemia pathway is a DNA damage-activated signaling pathway, which regulates cellular resistance to DNA cross-linking agents. Monoubiquitination and nuclear foci formation of FANCD2 are critical steps of the Fanconi anemia pathway. Here, we show that proteasome function is required for the activation of the Fanconi anemia pathway and for DNA damage signaling. Proteasome inhibitors (bortezomib and MG132) and depletion of 19S and 20S proteasome subunits (PSMD4, PSMD14, and PSMB3) inhibited monoubiquitination and/or nuclear foci formation of FANCD2, whereas depletion of DSS1/SHFM1, a subunit of the 19S proteasome that also directly binds to BRCA2, did not inhibit FANCD2 monoubiquitination or foci formation. On the other hand, DNA damage-signaling processes, such as IR-induced foci formation of phosphorylated ATM (phospho-ATM), 53BP1, NBS1, BRCA1, FANCD2, and RAD51, were delayed in the presence of proteasome inhibitors, whereas ATM autophosphorylation and nuclear foci formation of gammaH2AX, MDC1, and RPA were not inhibited. Furthermore, persistence of DNA damage and abrogation of the IR-induced G(1)-S checkpoint resulted from proteasome inhibition. In summary, we showed that the proteasome function is required for monoubiquitination of FANCD2, foci formation of 53BP1, phospho-ATM, NBS1, BRCA1, FANCD2, and RAD51. The dependence of specific DNA damage-signaling steps on the proteasome may explain the sensitization of tumor cells to DNA-damaging chemotherapeutic agents by proteasome inhibitors.