Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.4.25.1 (proteasome)
 28,817 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Telomerase, a stable complex of telomerase reverse transcriptase (TERT) and template RNA (TERC), is responsible for telomere maintenance. During purification trials of recombinant human telomerase of the two components reconstituted in insect cells, we identified two complexes of human telomerase of molecular masses 680 and 380 kDa, both of which retain telomerase activity in vitro. We show here that the former complex does not include Hsp90 (heat shock protein 90) and its telomerase activity is resistant to Hsp90 inhibitors, whereas the latter contains Hsp90 and its telomerase activity is sensitive to Hsp90 inhibitors. N-terminal of FLAG-hTERT in the former is exposed, as this complex was efficiently purified with anti-FLAG M2 affinity resin. We also identified two different telomerase complexes in HeLa cells, in addition to ectopically expressed hTERT. Most of endogenous hTERT and FLAG-hTERT was detected around 680 kDa. These two complexes in HeLa cells have the same properties as their respective reconstituted telomerases. The unstable property of the telomerase complex with Hsp90, especially in the presence of Hsp90 inhibitors, was due to proteasome-mediated degradation of hTERT, since proteasome inhibitors prevented hTERT degradation in vivo. To our knowledge, this is the first demonstration of two distinct active complexes of human telomerase ectopically expressed in insect and mammalian cells.
 ...
PMID:Human telomerase exists in two distinct active complexes in vivo. 1738 81

Spinal and bulbar muscular atrophy (SBMA) is an inherited motor neuron disease caused by the expansion of a polyglutamine tract within the androgen receptor (AR). The pathologic features of SBMA are motor neuron loss in the spinal cord and brainstem and diffuse nuclear accumulation and nuclear inclusions of the mutant AR in the residual motor neurons and certain visceral organs. Many components of the ubiquitin-proteasome and molecular chaperones are also sequestered in the inclusions, suggesting that they may be actively engaged in an attempt to degrade or refold the mutant AR. C terminus of Hsc70 (heat shock cognate protein 70)-interacting protein (CHIP), a U-box type E3 ubiquitin ligase, has been shown to interact with heat shock protein 90 (Hsp90) or Hsp70 and ubiquitylates unfolded proteins trapped by molecular chaperones and degrades them. Here, we demonstrate that transient overexpression of CHIP in a neuronal cell model reduces the monomeric mutant AR more effectively than it does the wild type, suggesting that the mutant AR is more sensitive to CHIP than is the wild type. High expression of CHIP in an SBMA transgenic mouse model also ameliorated motor symptoms and inhibited neuronal nuclear accumulation of the mutant AR. When CHIP was overexpressed in transgenic SBMA mice, mutant AR was also preferentially degraded over wild-type AR. These findings suggest that CHIP overexpression ameliorates SBMA phenotypes in mice by reducing nuclear-localized mutant AR via enhanced mutant AR degradation. Thus, CHIP overexpression would provide a potential therapeutic avenue for SBMA.
 ...
PMID:CHIP overexpression reduces mutant androgen receptor protein and ameliorates phenotypes of the spinal and bulbar muscular atrophy transgenic mouse model. 1749 97

The molecular chaperone heat shock protein 90 (Hsp90) is involved in multiple cellular processes including protein maturation, complex assembly and disassembly, and intracellular transport. We have recently shown that a disruption of Hsp90 activity in cultured Drosophila melanogaster cells suppresses Flock House virus (FHV) replication and the accumulation of protein A, the FHV RNA-dependent RNA polymerase. In the present study, we investigated whether the defect in FHV RNA polymerase accumulation induced by Hsp90 suppression was secondary to an effect on protein A synthesis, degradation, or intracellular membrane association. Treatment with the Hsp90-specific inhibitor geldanamycin selectively reduced FHV RNA polymerase synthesis by 80% in Drosophila S2 cells stably transfected with an inducible protein A expression plasmid. The suppressive effect of geldanamycin on protein A synthesis was not attenuated by proteasome inhibition, nor was it sensitive to changes in either the mRNA untranslated regions or protein A intracellular membrane localization. Furthermore, geldanamycin did not promote premature protein A degradation, nor did it alter the extremely rapid kinetics of protein A membrane association. These results identify a novel role for Hsp90 in facilitating viral RNA polymerase synthesis in Drosophila cells and suggest that FHV subverts normal cellular pathways to assemble functional replication complexes.
 ...
PMID:A functional heat shock protein 90 chaperone is essential for efficient flock house virus RNA polymerase synthesis in Drosophila cells. 1752 96

Plasma cells producing high levels of paraprotein are dependent on the unfolded protein response (UPR) and chaperone proteins to ensure correct protein folding and cell survival. We hypothesized that disrupting client-chaperone interactions using heat shock protein 90 (Hsp90) inhibitors would result in an inability to handle immunoglobulin production with the induction of the UPR and myeloma cell death. To study this, myeloma cells were treated with Hsp90 inhibitors as well as known endoplasmic reticulum stress inducers and proteasome inhibitors. Treatment with thapsigargin and tunicamycin led to the activation of all 3 branches of the UPR, with early splicing of XBP1 indicative of IRE1 activation, upregulation of CHOP consistent with ER resident kinase (PERK) activation, and activating transcription factor 6 (ATF6) splicing. 17-AAG and radicicol also induced splicing of XBP1, with the induction of CHOP and activation of ATF6, whereas bortezomib resulted in the induction of CHOP and activation of ATF6 with minimal effects on XBP1. After treatment with all drugs, expression levels of the molecular chaperones BiP and GRP94 were increased. All drugs inhibited proliferation and induced cell death with activation of JNK and caspase cleavage. In conclusion, Hsp90 inhibitors induce myeloma cell death at least in part via endoplasmic reticulum stress and the UPR death pathway.
 ...
PMID:Heat shock protein inhibition is associated with activation of the unfolded protein response pathway in myeloma plasma cells. 1752 89

Ansamycins exert their effects by binding heat shock protein 90 (Hsp90) and targeting important signalling molecules for degradation via the proteasome pathway. We wanted to study the effect of geldanamycin (GA) and its derivative 17-allylamino-17-demethoxygeldanamycin (17-AAG) on glioblastoma cell lines. We show that these cells are growth inhibited by ansamycins by being arrested in G(2)/M and, subsequently, cells undergo apoptosis. The protein levels of cell division cycle 2 (cdc2) kinase and cell division cycle 25c (cdc25c) were downregulated upon GA and 17-AAG treatment and cdc2 kinase activity was inhibited. However, other proteins involved in the G(2)/M checkpoint were not affected. The cdc2 and cdc25c mRNA levels did not show significant differences upon ansamycin treatment, but the stability of cdc2 protein was reduced. The association of cdc2 and cdc25c with p50(cdc37), an Hsp90 co-chaperone, decreased, but the interaction of cdc2 and cdc25c with the Hsp70 co-chaperone increased after ansamycin treatment. Proteasome inhibitors were able to rescue the cdc2 downregulation, but not the cdc25c reduction. However, calpain inhibitors were able to rescue the cdc25c downregulation, suggesting that cdc25c is proteolysed by calpains in the presence of ansamycins, and not by the proteasome. We conclude that ansamycins downregulate cdc2 and cdc25c by two different mechanisms.
 ...
PMID:Inhibition of Hsp90 function by ansamycins causes downregulation of cdc2 and cdc25c and G(2)/M arrest in glioblastoma cell lines. 1752 41

The molecular chaperone heat shock protein 90 (Hsp90) affects the function of many oncogenic signaling proteins including nucleophosmin-anaplastic lymphoma kinase (NPM-ALK) expressed in anaplastic large cell lymphoma (ALCL). While ALK-positive ALCL cells are sensitive to the Hsp90 inhibitor and the geldanamycin (GA) analog, 17-allylamino-17-demethoxygeldanamycin (17-AAG), the proteomic effects of these drugs on ALK-positive ALCL cells are unpublished. In this study, we investigated the cellular, biologic, and proteomic changes occurring in ALK-positive ALCL cells in response to GA treatment. GA induced G2/M cell cycle arrest and caspase-3-mediated apoptosis. Furthermore, quantitative proteomic changes analyzed by cleavable isotope-coded affinity tag-LC-MS/MS (cICAT-LC-MS/MS) identified 176 differentially expressed proteins. Out of these, 49 were upregulated 1.5-fold or greater and 70 were downregulated 1.5-fold or greater in GA-treated cells. Analysis of biological functions of differentially expressed proteins revealed diverse changes, including induction of proteins involved in the 26S proteasome as well as downregulation of proteins involved in signal transduction and protein and nucleic acid metabolism. Pathway analysis revealed changes in MAPK, WNT, NF-kappaB, TGFbeta, PPAR, and integrin signaling components. Our studies reveal some of the molecular and proteomic consequences of Hsp90 inhibition in ALK-positive ALCL cells and provide novel insights into the mechanisms of its diverse cellular effects.
 ...
PMID:Proteome-wide changes induced by the Hsp90 inhibitor, geldanamycin in anaplastic large cell lymphoma cells. 1761 Feb 8

The objective of this study was to investigate the role of heat shock protein 90 (hsp90) and the proteasome in regulating aryl hydrocarbon receptor (AhR) activation and cytochrome P450 1A (Cyp1A) protein expression in rainbow trout (Oncorhynchus mykiss). We exposed trout hepatocytes in primary culture to the AhR agonist beta-napthoflavone (betaNF; 10(-6) M) and examined AhR and Cyp1A expression. betaNF-induced a significant temporal accumulation of AhR and Cyp1A1 mRNA abundance in trout hepatocytes. This transcript response was followed by a significantly higher AhR and Cyp1A protein expression. Exposure to geldanamycin (GA; 1000 ng mL(-1)), a benzoquinone ansamycin antibiotic used to inhibit hsp90 function, significantly reduced ( approximately 70%) betaNF-induced Cyp1A protein expression. Also, exposure to the proteasomal inhibitor MG-132 (50 microM) completely abolished betaNF-induced Cyp1A protein expression in trout hepatocytes. In addition, MG-132 treatment further enhanced the GA-mediated suppression of the Cyp1A response. The effect of MG-132 on Cyp1A response corresponded with a significant inhibition of BNF-mediated AhR mRNA abundance, but not protein content. Altogether our results suggest a betaNF-mediated autoregulation of AhR content in trout hepatocytes. We propose a key role for hsp90 and the proteasome in this ligand-mediated AhR regulation and Cyp1A response.
 ...
PMID:Aryl hydrocarbon receptor signaling in rainbow trout hepatocytes: role of hsp90 and the proteasome. 1762 97

Within the last decade, several novel classes of anti-myeloma therapeutics have become available. The clinical successes achieved by thalidomide, lenalidomide, and the proteasome inhibitor bortezomib, and in particular the ability of these agents to lead to major clinical responses in patients resistant to conventional or high-dose chemotherapy, have highlighted the importance of expanding further the spectrum of classes of agents utilized for the treatment of myeloma. Herein, we review the current status for the development of novel anti-myeloma agents, with emphasis on classes of therapeutics which have already translated into clinical trials or those in advanced stages of preclinical development. These include second-generation proteasome inhibitors (NPI-0052 and PR-171), heat shock protein 90 (hsp90) inhibitors, 2-methoxyestradiol, histone deacetylase (HDAC) inhibitors (e.g. SAHA and LBH589), fibroblast growth factor receptor 3 (FGF-R3) inhibitors, insulin-like growth factor 1 receptor (IGF-1R) inhibitors, mTOR inhibitors, monoclonal antibodies, and agents specifically targeting the tumor microenvironment, such as defibrotide.
 ...
PMID:From the bench to the bedside: emerging new treatments in multiple myeloma. 1807 Jul 20

This study explored the effect of MS-275, a novel histone deacetylase inhibitor (HDACI), against a variety of human leukemia cells with defined genetic alterations. MS-275 profoundly induced growth arrest of acute myelogenous leukemia (AML) MOLM13 and biphenotypic leukemia MV4-11 cells, which possess internal tandem duplication mutation in the fms-like tyrosine kinase 3 (FLT3) gene (FLT3-ITD), with IC50s less than 1 microM, as measured by 3-(4,5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide assay on day two of culture. Exposure of these cells to MS-275 decreased levels of total, as well as, phosphorylated forms of FLT3, resulting in inactivation of its downstream signal pathways, including Akt, ERK, and STAT5. Further studies found that MS-275 induced acetylation of heat shock protein 90 (HSP90) in conjunction with ubiquitination of FLT3, leading to degradation of FLT3 proteins in these cells. This was blunted by treatment with the proteasome inhibitor bortezomib, confirming that FLT was degraded via ubiquitin/proteasome pathway. Moreover, we found that further inhibition of MEK/ERK signaling potentiated the action of MS-275 in leukemia cells. Taken together, MS-275 may be useful for treatment of individuals with leukemia possessing activating mutation of FLT3 gene.
 ...
PMID:MS-275, a novel histone deacetylase inhibitor with selectivity against HDAC1, induces degradation of FLT3 via inhibition of chaperone function of heat shock protein 90 in AML cells. 1839 2

Tubocapsenolide A (TA), a novel withanolide-type steroid, exhibits potent cytotoxicity against several human cancer cell lines. In the present study, we observed that treatment of human breast cancer MDA-MB-231 cells with TA led to cell cycle arrest at G(1) phase and apoptosis. The actions of TA were correlated with proteasome-dependent degradation of Cdk4, cyclin D1, Raf-1, Akt, and mutant p53, which are heat shock protein 90 (Hsp90) client proteins. TA treatment induced a transient increase in reactive oxygen species and a decrease in the intracellular glutathione contents. Nonreducing SDS-PAGE revealed that TA rapidly and selectively induced thiol oxidation and aggregation of Hsp90 and Hsp70, both in intact cells and in cell-free systems using purified recombinant proteins. Furthermore, TA inhibited the chaperone activity of Hsp90-Hsp70 complex in the luciferase refolding assay. N-Acetylcysteine, a thiol antioxidant, prevented all of the TA-induced effects, including oxidation of heat shock proteins, degradation of Hsp90 client proteins, and apoptosis. In contrast, non-thiol antioxidants (trolox and vitamin C) were ineffective to prevent Hsp90 inhibition and cell death. Taken together, our results demonstrate that the TA inhibits the activity of Hsp90-Hsp70 chaperone complex, at least in part, by a direct thiol oxidation, which in turn leads to the destabilization and depletion of Hsp90 client proteins and thus causes cell cycle arrest and apoptosis in MDA-MB-231 cells. Therefore, TA can be considered as a new type of inhibitor of Hsp90-Hsp70 chaperone complex, which has the potential to be developed as a novel strategy for cancer treatment.
 ...
PMID:Tubocapsenolide A, a novel withanolide, inhibits proliferation and induces apoptosis in MDA-MB-231 cells by thiol oxidation of heat shock proteins. 1844 81


<< Previous 1 2 3 4 5 6 7 8 9 10 Next >>