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.

High Glucose-induced repression of RAR/RXR in cardiomyocytes is mediated through oxidative stress/JNK signaling

Abstract: The biological actions of retinoids are mediated by nuclear retinoic acid receptors (RARs) and retinoid X receptors (RXRs). We have recently reported that decreased expression of RARα and RXRα has an important role in high glucose (HG)-induced cardiomyocyte apoptosis. However, the regulatory mechanisms of HG effects on RARα and RXRα remain unclear. Using neonatal cardiomyocytes, we found that ligand-induced promoter activity of RAR and RXR was significantly suppressed by HG. HG promoted protein destabilization and serine-phosphorylation of RARα and RXRα. Proteasome inhibitor MG132 blocked the inhibitory effect of HG on RARα and RXRα. Inhibition of intracellular reactive oxidative species (ROS) abolished the HG effect. In contrast, H(2)O(2) stimulation suppressed the expression and ligand-induced promoter activity of RARα and RXRα. HG promoted phosphorylation of ERK1/2, JNK and p38 MAP kinases, which was abrogated by an ROS inhibitor. Inhibition of JNK, but not ERK and p38 activity, reversed HG effects on RARα and RXRα. Activation of JNK by over expressing MKK7 and MEKK1, resulted in significant downregulation of RARα and RXRα. Ligand-induced promoter activity of RARα and RXRα was also suppressed by overexpression of MEKK1. HG-induced cardiomyocyte apoptosis was potentiated by activation of JNK, and prevented by all-trans retinoic acid and inhibition of JNK. Silencing the expression of RARα and RXRα activated the JNK pathway. In conclusion, HG-induced oxidative stress and activation of the JNK pathway negatively regulated expression/activation of RAR and RXR. The impaired RAR/RXR signaling and oxidative stress/JNK pathway forms a vicious circle, which significantly contributes to hyperglycemia induced cardiomyocyte apoptosis.

Protease inhibitors restore radiation-induced apoptosis to Bcl-2-expressing lymphoma cells.

Abstract: The proteasome pathway is important for the turnover of many regulatory proteins. This pathway has recently become a target for antitumor agents and several research groups have demonstrated that inhibitors with specificities for the proteasome are potent apoptosis-inducing agents. Many mechanisms by which proteasome inhibitors exert their effects have been suggested, including inhibition of NF-κB activity and stabilization of the p53 tumor suppressor protein. We investigated the ability of inhibitors with specificities for the proteasome and for another protein degradation enzyme, calpain, to sensitize a murine B-cell lymphoma with constitutive NF-κB1 homodimer activity and high expression of Bcl-2 protein to radiation-induced apoptosis. Protease inhibitors tested were calpain inhibitor I, calpain inhibitor II, calpeptin, MG132, and Lactacystin. All five inhibitors induced apoptosis and sensitized cells to radiation despite the maintenance of Bcl-2 protein levels throughout the course of treatment. An electrophoretic migration shift assay for NF-κB1 activity provided evidence that reversal of NF-κB activity was not required for induction of cell death; however, p53 levels were elevated for all inhibitors tested. HL-60 cells, devoid of p53, could not be sensitized to radiation by MG132 treatment, suggesting that p53 was important for cell death induced by combined treatment with protease inhibitors and radiation. We concluded that protease inhibitors are capable of overcoming the protective effects of Bcl-2 to induce apoptosis and suggest that protease inhibitor treatment, when combined with ionizing radiation, leads to p53-mediated apoptosis. © 2001 Wiley-Liss, Inc.

Celastrol can inhibit proteasome activity and upregulate the expression of heat shock protein genes, hsp30 and hsp70, in Xenopus laevis A6 cells.

Abstract: In eukaryotes, the ubiquitin–proteasome system (UPS) is responsible for the degradation of most proteins. Proteasome inhibition, which has been associated with various diseases, can cause alterations in various intracellular processes including the expression of heat shock protein ( hsp ) genes. In this study, we show that celastrol, a quinone methide triterpene and anti-inflammatory agent, inhibited proteasome activity and enhanced HSP accumulation in Xenopus laevis A6 kidney epithelial cells. Treatment of cells with celastrol induced the accumulation of ubiquitinated protein and inhibited chymotrypsin-like activity. This was accompanied by a dose- and time-dependent accumulation of HSP30 and HSP70. Celastrol-induced HSP accumulation was mediated by HSF1–DNA binding activity since this response was inhibited by the HSF1 activation inhibitor, KNK437. Simultaneous exposure of cells with celastrol plus either mild heat shock or the proteasome inhibitor, MG132, produced an enhanced accumulation of HSP30 that was greater than the sum of the individual stressors alone. Immunocytochemical analysis revealed that celastrol-induced HSP30 accumulation occurred in the cytoplasm in a granular pattern supplemented with larger circular HSP30 staining structures. HSP30 was also noted in the nucleus with less staining in the nucleolus. In some cells, celastrol induced the collapse of the actin cytoskeleton and conversion to a rounder morphology. In conclusion, this study has shown that celastrol inhibited proteasome activity and induced HSF1-mediated expression of hsp genes in amphibian cells.

Proteolytic Mechanisms Underlying Mitochondrial Degradation in the Ocular Lens

Abstract: PURPOSE. To remove light-scattering structures from the visual axis, all intracellular organelles are eliminated from cells in the center of the developing ocular lens. Organelle degradation is accompanied by an increase in VEIDase (caspase-6-like) activity, but data from caspase-null mice suggest that the lens VEIDase is not caspase-6. The goal of the present work was to identify the lens VEIDase and determine whether it plays a role in organelle breakdown. METHODS. The approximate molecular mass of the lens VEIDase was determined by size-exclusion chromatography. Three proteasome inhibitors (NLVS, MG132, and clasto-lactacystin betalactone) were tested for their ability to inhibit lens VEIDase activity. Lens lysates were immunodepleted of proteasomes using an antibody against the 20S proteasome. To inhibit the ubiquitin–proteasome pathway (UPP) in vivo, lactacystin was injected into the vitreous humor of the developing chicken eye. The effect of lactacystin on mitochondrial degradation was assessed by examining the disappearance of succinate– ubiquinone oxidoreductase, an integral protein of the inner mitochondrial membrane. RESULTS. The lens VEIDase eluted at approximately 700 kDa from a size-exclusion column and was inhibited by the proteasome inhibitors NLVS, MG132, and clasto-lactacystin beta-lactone. In vivo, the trypsin-like activity of the proteasome was reduced by 60% to 70% after lactacystin injection. Proteasome inhibition was associated with the accumulation of ubiquitinated proteins and reversible opacification of the lens cortex. In lactacystin-injected eyes, the programmed degradation of succinate– ubiquinone oxidoreductase was inhibited in the central lens fiber cells. CONCLUSIONS. These data suggest that lens VEIDase activity is attributable to the proteasome and that the UPP may function in the removal of organelle components during lens fiber cell differentiation. (Invest Ophthalmol Vis Sci. 2007;48:293–302) DOI:10.1167/iovs.06-0656