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.

Down-Regulation of Glucose-Regulated Protein (GRP) 78 Potentiates Cytotoxic Effect of Celecoxib in Human Urothelial Carcinoma Cells

Abstract: Celecoxib is a selective cyclooxygenase-2 (COX-2) inhibitor that has been reported to elicit anti-proliferative response in various tumors. In this study, we aim to investigate the antitumor effect of celecoxib on urothelial carcinoma (UC) cells and the role endoplasmic reticulum (ER) stress plays in celecoxib-induced cytotoxicity. The cytotoxic effects were measured by MTT assay and flow cytometry. The cell cycle progression and ER stress-associated molecules were examined by Western blot and flow cytometry. Moreover, the cytotoxic effects of celecoxib combined with glucose-regulated protein (GRP) 78 knockdown (siRNA), (−)-epigallocatechin gallate (EGCG) or MG132 were assessed. We demonstrated that celecoxib markedly reduces the cell viability and causes apoptosis in human UC cells through cell cycle G1 arrest. Celecoxib possessed the ability to activate ER stress-related chaperones (IRE-1α and GRP78), caspase-4, and CCAAT/enhancer binding protein homologous protein (CHOP), which were involved in UC cell apoptosis. Down-regulation of GRP78 by siRNA, co-treatment with EGCG (a GRP78 inhibitor) or with MG132 (a proteasome inhibitor) could enhance celecoxib-induced apoptosis. We concluded that celecoxib induces cell cycle G1 arrest, ER stress, and eventually apoptosis in human UC cells. The down-regulation of ER chaperone GRP78 by siRNA, EGCG, or proteosome inhibitor potentiated the cytotoxicity of celecoxib in UC cells. These findings provide a new treatment strategy against UC.

Abstract P023: HDAC Inhibition Promotes Cardiogenesis and the Survival of Embryonic Stem Cells Through Proteasome-Dependent Pathway

Abstract: Objectives: Histone deacetylase (HDAC) inhibition plays a crucial role in mediating cardiogenesis and myocardial protection, whereas HDAC degradation has recently attracted attention in mediating the biological function of HDACs. However, it remains unknown whether HDAC inhibition modulates cardiogenesis and embryonic stem cell (ESC) survival through the proteasome pathway. Methods and Results: Using the well-established mouse CGR8 mouse ESC culture, we evaluated the impact of HDAC inhibition and proteasome pathway on the cell death, viability and apoptosis in ESCs in response to oxidant stress (100μ mol/L hydrogen peroxides). We demonstrated that HDAC inhibitors, both TSA (50 nmol/L) and sodium butyrate (200 μ mol/L) that causes the pronounced reduction of HDAC4 activity, decreased cell death and increased viability of ESCs. HDAC inhibition reduced the cleaved caspase 3, 6, 9, PARP and TUNE-positive ESCs, which were abrogated with MG132 (0.5 μ mol/L), a specific proteasome inhibitor. Furthermore, we employed in vitro “hanging drop” methods to carry out two weeks of embryoid bodies (EB) culture to assess the effect of HDAC inhibition and proteasome pathway on cardiogenesis. HDAC inhibition stimulates the growth of EB, which is associated with faster spontaneous rhythmic contraction. HDAC inhibition increased the up-regulation of GATA4, MEF2, NKX2.5, cardiac actin, and α-SMA mRNA and protein levels that were abrogated by MG132. Immunostaining analysis demonstrates that trichostatin A and sodium butyrate resulted in a significant increase in cardiac lineage commitments that were blocked by the proteasome inhibition. Notably, HDAC inhibitors led to noticeable HDAC4 degradation, which was effectively prevented by MG132. Luciferase assay demonstrates an activation of MEF2 cardiac transcriptional factor by HDAC inhibition, which was repressed by MG132, revealing that the degradation of HDAC4 allows the activation of MEF2. Conclusions: Taken together, our study is the first to demonstrate that HDAC inhibition through proteasome pathway forms a novel signaling to determine the cardiac lineage commitment and elicit the survival pathway, which is dependent on specific HDAC4 degradation and subsequent MEF2 activation of ESCs.

5-Androstenediol Promotes Survival of γ-Irradiated Human Hematopoietic Progenitors through Induction of Nuclear Factor-κB Activation and Granulocyte Colony-Stimulating Factor Expression

Abstract: 5-Androstenediol (5-AED) stimulates hematopoiesis and enhances survival in animals exposed to ionizing radiation (IR), suggesting that this steroid may act on hematopoietic progenitor cells. We used γ-irradiated primary human CD34+ hematopoietic progenitor cells to show that 5-AED protects hematopoietic cells from IR damage, as shown by enhanced cell survival, clonogenicity, proliferation, and differentiation. Unlike in tumor cells, IR did not induce nuclear factor-κB (NFκB) activation in primary progenitors. However, IR stimulated IκBβ release from NFκB/IκB complexes and caused NFκB1 (p50) degradation. 5-AED stabilized NFκB1 in irradiated cells and induced NFκB gene expression and NFκB activation (DNA binding). 5-AED stimulated interleukin-6 and granulocyte colony-stimulating factor (G-CSF) secretion. The survival-enhancing effects of 5-AED on clonogenic cells were abrogated by small interfering RNA inhibition of NFκB gene expression and by neutralization of G-CSF with antibody. The effects of 5-AED on survival and G-CSF secretion were blocked by the NFκB inhibitor N-benzoyloxycarbonyl (Z)-Leu-Leu-leucinal (MG132). 5-AED had no effect on accumulation of the proapoptotic factor p53 after IR, as determined by Western blot. The results indicate that NFκB1 degradation after IR may be responsible for the radiation sensitivity of CD34+ cells compared with tumor cells. 5-AED exerts survival-enhancing effects on irradiated human hematopoietic progenitor cells via induction, stabilization, and activation of NFκB, which results in increased secretion of hematopoietic growth factor G-CSF.