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.

RNF4 and VHL regulate the proteasomal degradation of SUMO-conjugated Hypoxia-Inducible Factor-2α

Abstract: Hypoxia-inducible factors (HIFs) are critical transcription factors that mediate cell survival during reduced oxygen conditions (hypoxia) At regular oxygen conditions (normoxia), HIF-1alpha and HIF-2alpha are continuously synthesized in cells and degraded via the ubiquitin-proteasome pathway During hypoxia, these proteins are stabilized and translocate to the nucleus to activate transcription of target genes that enable cell survival at reduced oxygen levels HIF proteins are tightly regulated via post-translational modifications including phosphorylation, acetylation, prolyl-hydroxylation and ubiquitination Here we show for the first time that exogenous and endogenous HIF-2alpha are also regulated via the ubiquitin-like modifier small ubiquitin-like modifiers (SUMO) Using mutational analysis, we found that K394, which is situated in the sumoylation consensus site LKEE, is the major SUMO acceptor site in HIF-2alpha Functionally, sumoylation reduced the transcriptional activity of HIF-2alpha Similar to HIF-1alpha, HIF-2alpha is regulated by the SUMO protease SENP1 The proteasome inhibitor MG132 strongly stabilized SUMO-2-conjugated HIF-2alpha during hypoxia but did not affect the total level of HIF-2alpha The ubiquitin E3 ligases von Hippel-Lindau and RNF4 control the levels of sumoylated HIF-2alpha, indicating that sumoylated HIF-2alpha is degraded via SUMO-targeted ubiquitin ligases

Inhibition of p53-murine double minute 2 interaction by nutlin-3A stabilizes p53 and induces cell cycle arrest and apoptosis in Hodgkin lymphoma.

Abstract: Purpose: p53 is frequently expressed but rarely mutated in Hodgkin and Reed-Sternberg (HRS) cells of Hodgkin9s lymphoma (HL). p53 protein levels are regulated by murine double minute 2 (MDM2) through a well-established autoregulatory feedback loop. In this study, we investigated the effects of nutlin-3A, a recently developed small molecule that antagonizes MDM2 and disrupts the p53-MDM2 interaction, on p53-dependent cell cycle arrest and apoptosis in cultured HRS cells. Experimental Design: HL cell lines carrying wild-type (wt) or mutated p53 gene were treated with the potent MDM2 inhibitor nutlin-3A or a 150-fold less active enantiomer, nutlin-3B. Results: We show that nutlin-3A, but not nutlin-3B, stabilizes p53 in cultured HRS cells carrying wt p53 gene resulting in p53-dependent cell cycle arrest and apoptosis. Cell cycle arrest was associated with up-regulation of the cyclin-dependent kinase inhibitor p21. Nutlin-3A–induced apoptotic cell death was accompanied by Bax and Puma up-regulation and caspase-3 cleavage and was abrogated, in part, by inhibition of caspase-9 and caspase-3 activity. By contrast, no effects on cell cycle or apoptosis were found in HL cell lines harboring mutated p53 gene. Furthermore, combined treatment with nutlin-3A and doxorubicin revealed enhanced cytotoxicity in HRS cells with wt p53 gene. Blocking of nuclear export by leptomycin B, or inhibition of proteasome by MG132, stabilized p53 at a level comparable with that of nutlin-3A treatment in HRS cells with wt p53. Conclusions: These data suggest that nutlin-3A stabilized p53 by preventing MDM2-mediated p53 degradation in HRS cells. wt p53 stabilization and activation by nutlin-3A may be a novel therapeutic approach for patients with HL.

Ubiquitin protein ligase 3 mediates the proteasomal degradation of GLABROUS 3 and ENHANCER OF GLABROUS 3, regulators of trichome development and flavonoid biosynthesis in Arabidopsis.

Abstract: Summary Ubiquitin/26S proteasome (UPS)-dependent proteolysis of a variety of cellular proteins plays an essential role in many basic cellular processes. UPS impacts transcriptional regulation by controlling the stability, and thus the activity, of numerous transcription factors (TFs). In Arabidopsis, trichome development and flavonoid metabolism are intimately connected, and several TFs have been identified that simultaneously control both processes. Here we show that UPS-dependent proteolysis of two of these TFs, GLABROUS 3 (GL3) and ENHANCER OF GL3 (EGL3), is mediated by ubiquitin protein ligase 3 (UPL3). Cell-free degradation and in planta stabilization assays in the presence of MG132, an inhibitor of proteasome activity, demonstrated that the degradation of GL3 and EGL3 proteins is 26S UPS-dependent. Yeast- or protoplast-based two-hybrid and bimolecular fluorescent complementation assays showed that GL3 and EGL3 interact via their C-terminal domains with the N-terminal portion of UPL3. Moreover, both TFs are stabilized and show increased activities in a upl3 mutant background. Gene expression analyses revealed that UPL3 expression is negatively affected by mutation in the gl3 locus, but is moderately upregulated by the overexpression of GL3, suggesting the presence of a regulatory loop involving GL3 and UPL3. Our findings underscore the importance of post-translational controls in epidermal cell differentiation and flavonoid metabolism.

Curcumin inhibits HIV-1 by promoting Tat protein degradation.

Abstract: HIV-1 Tat is an intrinsically unfolded protein playing a pivotal role in viral replication by associating with TAR region of viral LTR. Unfolded proteins are degraded by 20S proteasome in an ubiquitin independent manner. Curcumin is known to activate 20S proteasome and promotes the degradation of intrinsically unfolded p53 tumor suppressor protein. Since HIV-1 Tat protein is largerly unfolded, we hypothesized that Tat may also be targeted through this pathway. Curcumin treated Tat transfected HEK-293T cells showed a dose and time dependent degradation of Tat protein. Contrary to this HIV-1 Gag which is a properly folded protein, remained unaffected with curcumin. Semi-quantitative RT-PCR analysis showed that curcumin treatment did not affect Tat gene transcription. Curcumin increased the rate of Tat protein degradation as shown by cycloheximide (CHX) chase assay. Degradation of the Tat protein is accomplished through proteasomal pathway as proteasomal inhibitor MG132 blocked Tat degradation. Curcumin also decreased Tat mediated LTR promoter transactivation and inhibited virus production from HIV-1 infected cells. Taken together our study reveals a novel observation that curcumin causes potent degradation of Tat which may be one of the major mechanisms behind its anti HIV activity.

A coordinated action of Bax, PUMA, and p53 promotes MG132-induced mitochondria activation and apoptosis in colon cancer cells

Abstract: Targeting the ubiquitin-proteasome degradation pathway has become a promising approach for cancer therapy Previous studies have shown that proteasome inhibition leads to apoptosis in various cancer cells The mechanism by which apoptosis occurs are not fully understood and can be cell type and/or inhibitor specific In this study, we investigated the mechanism of mitochondrial activation by proteasome inhibitors in colon cancer cells We found that Bax activation and mitochondria translocation were required for apoptosis induced by multiple proteasome inhibitors In contrast, reactive oxygen species did not seem to be induced by MG132 or bortezomib and antioxidants had no effects on MG132-induced apoptosis In contrast, treatment with MG132 or bortezomib induced a significant accumulation of p53 and PUMA Genetic deletion of either p53 or PUMA led to a marked suppression of apoptosis induced by these inhibitors, accompanied with reduced Bax activation and cytochrome c release Consistently, inhibition of translation by cycloheximide could also effectively abolish the accumulation of p53 and PUMA and suppress MG132-induced Bax activation and apoptosis These findings thus strongly indicate the critical involvement of p53-, PUMA-, and Bax-mediated mitochondrial activation in proteasome inhibitor-induced apoptosis in colon cancer cells