Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:3.4.25.1 (proteasome)
28,817 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Peroxisome proliferator-activated receptor gamma (PPARgamma) is a member of the nuclear hormonal receptor superfamily expressed in a large number of human cancers. Here, we demonstrate that PPARgamma is expressed and transcriptionally active in breast cancer cells independent of their p53, estrogen receptor, or human epidermal growth factor receptor 2 status. 2-Cyano-3,12-dioxooleana-1,9-dien-28-oic acid (CDDO), a novel synthetic triterpenoid, is a ligand for PPARgamma. We investigated the molecular mechanisms of CDDO on proliferation and apoptosis in breast cancer cells. In all breast cancer cell lines studied, CDDO transactivated PPARgamma, induced dose- and time-dependent cell growth inhibition, cell cycle arrest in G(1)-S and G(2)-M, and apoptosis. We then used differential cDNA array analysis to investigate the molecular changes induced by CDDO. After 16-h exposure of MCF-7 and MDA-MB-435 cells to CDDO, we found genes encoding the following proteins to be up-regulated in both cell lines: p21(Waf1/CIP1); GADD153; CAAT/enhancer binding protein transcription factor family members; and proteins involved in the ubiquitin-proteasome pathway. Among the down-regulated genes, we focused on the genes encoding cyclin D1, proliferating cell nuclear antigen, and the insulin receptor substrate 1. Using Western blot analysis and/or real-time PCR, we confirmed that CDDO regulated the expression of cyclin D1, p21(Waf1/CIP1), and Bcl-2. Cyclin D1 and p21(Waf1/CIP1) were additionally confirmed as important mediators of CDDO growth inhibition in genetically modified breast cancer cell lines. CDDO was able to significantly reduce the growth of MDA-MB-435 tumor cells in immunodeficient mice in vivo. The finding that CDDO can target genes critical for the regulation of cell cycle, apoptosis, and breast carcinogenesis suggests usage of CDDO as novel targeted therapy in breast cancer.
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PMID:Activation of peroxisome proliferator-activated receptor gamma by a novel synthetic triterpenoid 2-cyano-3,12-dioxooleana-1,9-dien-28-oic acid induces growth arrest and apoptosis in breast cancer cells. 1452 19

Antioxidants are important candidate agents for the prevention of disease. However, the possibility that different antioxidants may produce opposing effects in tissues has not been adequately explored. We have reported previously that (-)-epigallocatechin-3-gallate (EGCG), a green tea polyphenol antioxidant, stimulates expression of the keratinocyte differentiation marker, involucrin (hINV), via a Ras, MEKK1, MEK3, p38delta signaling cascade (Balasubramanian, S., Efimova, T., and Eckert, R. L. (2002) J. Biol. Chem. 277, 1828-1836). We now show that EGCG activation of this pathway results in increased CCAAT/enhancer-binding protein (C/EBPalpha and C/EBPbeta) factor level and increased complex formation at the hINV promoter C/EBP DNA binding site. This binding is associated with increased promoter activity. Mutation of the hINV promoter C/EBP binding site eliminates the regulation as does expression of GADD153, a dominant-negative C/EBP factor. In contrast, a second antioxidant, curcumin, inhibits the EGCG-dependent promoter activation. This is associated with inhibition of the EGCG-dependent increase in C/EBP factor level and C/EBP factor binding to the hINV promoter. Curcumin also inhibits the EGCG-dependent increase in endogenous hINV levels. The curcumin-dependent suppression of C/EBP factor level is inhibited by treatment with the proteasome inhibitor MG132, suggesting that the proteasome function is required for curcumin action. We conclude that curcumin and EGCG produce opposing effects on involucrin gene expression via regulation of C/EBP factor function. The observation that two antioxidants can produce opposite effects is an important consideration in the context of therapeutic antioxidant use.
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PMID:Green tea polyphenol and curcumin inversely regulate human involucrin promoter activity via opposing effects on CCAAT/enhancer-binding protein function. 1504 35

Protein ubiquitination and subsequent degradation by the proteasome are important mechanisms regulating cell cycle, growth and differentiation, and apoptosis. Recent studies in cancer therapy suggest that drugs that disrupt the ubiquitin/proteasome pathway induce apoptosis and sensitize malignant cells and tumors to conventional chemotherapy. In this study we addressed the role of phosphorylation of the alpha-subunit eukaryotic initiation factor-2 (eIF2), and its attendant regulation of gene expression, in the cellular stress response to proteasome inhibition. Phosphorylation of eIF2alpha in mouse embryo fibroblast (MEF) cells subjected to proteasome inhibition leads to a significant reduction in protein synthesis, concomitant with induced expression of the bZIP transcription regulator, ATF4, and its target gene CHOP/GADD153. The primary eIF2alpha kinase activated by exposure of these fibroblast cells to proteasome inhibition is GCN2 (EIF2AK4), which has a central role in the recognition of cytoplasmic stress signals. Endoplasmic reticulum (ER) stress is not effectively induced in MEF cells subjected to proteasome inhibition, with minimal activation of the ER stress sensory proteins, eIF2alpha kinase PEK (PERK/EIF2AK3), IRE1 protein kinase and the transcription regulator ATF6 following up to 6 h of proteasome inhibitor treatment. Loss of eIF2alpha phosphorylation thwarts caspase activation and delays apoptosis. Central to this pro-apoptotic function of eIF2alpha kinases during proteasome inhibition is the transcriptional regulator CHOP, as deletion of CHOP in MEF cells impedes apoptosis. We conclude that eIF2alpha kinases are integral to cellular stress pathways induced by proteasome inhibitors, and may be central to the efficacy of anticancer drugs that target the ubiquitin/proteasome pathway.
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PMID:Phosphorylation of the alpha-subunit of the eukaryotic initiation factor-2 (eIF2alpha) reduces protein synthesis and enhances apoptosis in response to proteasome inhibition. 1568 20

Metabolic labeling studies were conducted in freshly isolated mouse islets and a beta-cell line (MIN6) to examine the effects of proteasome inhibition on glucose-stimulated (pro)insulin synthesis and secretion. Glucose-stimulated (pro)insulin synthesis, as determined by the incorporation of [(3)H]tyrosine, decreased significantly by 90% in islets and 71% in MIN6 cells pretreated with the proteasome inhibitor lactacystin (10 microM) for 2 h. To follow the fate of newly synthesized (pro)insulin, islets were pulse-labeled with [(3)H]tyrosine (40 microCi) for 20 min and chased +/- lactacystin (10 microM) for up to 4 h. The release of newly synthesized (pro)insulin ([(3)H]tyrosine-labeled) was similar between lactacystin-treated and control islets despite a 51% decrease (p <0.05) in total immunoreactive (pro)insulin secretion by lactacystin-treated islets. The specific radioactivity of [(3)H]tyrosine-labeled (pro)insulin in the extracellular medium of lactacystin-treated islets (0.52 +/- 0.16 cpm/microunits) was 2-fold greater relative to control islets (0.25 +/- 0.06 cpm/microunits). Induction of the unfolded protein response by lactacystin, as evidenced by the up-regulation of endoplasmic reticulum (ER) chaperones (GRP78/BiP, GRP94, protein disulfide isomerase) and induction of the stress-inducible transcription factor C/EBP-homologous protein/GADD153 (CHOP/GADD153), likely contributed to the release of newly synthesized (pro)insulin to relieve ER stress. The present data indicate proteasome inhibition did not prevent, but increased (p <0.05), the intracellular degradation of [(3)H]tyrosine-labeled (pro-)insulin from 8 to 24% in islets. Collectively, these data indicate beta-cells may balance glucose-stimulated (pro)insulin synthesis and secretion with the activity of the proteasome to regulate protein concentrations in the ER.
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PMID:Proteasome inhibition alters glucose-stimulated (pro)insulin secretion and turnover in pancreatic {beta}-cells. 1570 91

The lipid and metabolic disturbances associated with human immunodeficiency virus (HIV) protease inhibitor therapy in AIDS have stimulated interest in developing new agents that minimize these side effects in the clinic. The underlying explanation of mechanism remains enigmatic, but a recently described link between endoplasmic reticulum (ER) stress and dysregulation of lipid metabolism suggests a provocative integration of existing and emerging data. We provide new evidence from in vitro models indicating that proteasome inhibition and differential glucose transport blockade by protease inhibitors are proximal events eliciting an ER stress transcriptional response that can regulate lipogenic pathways in hepatocytes or adipocytes. Proteasome activity was inhibited in vitro by several protease inhibitors at clinically relevant (micromolar) levels. In the intact cells, protease inhibitors rapidly elicited a pattern of gene expression diagnostic of intracellular proteasome inhibition and activation of an ER stress response. This included induction of transcription factors GADD153, ATF4, and ATF3; amino acid metabolic enzymes; proteasome components; and certain ER chaperones. In hepatocyte lines, the ER stress response was closely linked to moderate increases in lipogenic and cholesterogenic gene expression. However, in adipocytes where GLUT4 was directly inhibited by some protease inhibitors, time-dependent suppression of lipogenic genes and triglyceride synthesis was observed in coordination with the ER stress response. These results further link ER stress to dyslipidemia and contribute to a unifying mechanism for the pathophysiology of protease inhibitor-associated lipodystrophy, helping explain differences in clinical metabolic profiles among protease inhibitors.
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PMID:Endoplasmic reticulum stress links dyslipidemia to inhibition of proteasome activity and glucose transport by HIV protease inhibitors. 1575 8

Curcumin, a natural polyphenolic compound, has long been known as an anti-tumour and anti-inflammatory compound; although, the common mechanism through which it exhibits such properties are remains unclear. Recently, we reported that the curcumin-induced apoptosis is mediated through the impairment of ubiquitin proteasome system (UPS). Here, we show that curcumin disrupts UPS function by directly inhibiting the enzyme activity of the proteasome's 20S core catalytic component. Like other proteasome inhibitors, curcumin exposure induces neurite outgrowth and the stress response, as evident from the induction of various cytosolic and endoplasmic reticulum chaperones as well as induction of transcription factor CHOP/GADD153. The direct inhibition of proteasome activity also causes an increase in half-life of IkappaB-alpha that ultimately leads to the down-regulation of NF-kappaB activation. These results suggest that curcumin-induced proteasomal malfunction might be linked with both anti-proliferative and anti-inflammatory activities.
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PMID:Curcumin induces stress response, neurite outgrowth and prevent NF-kappaB activation by inhibiting the proteasome function. 1646 50

Multiple myeloma (MM) is an incurable plasma cell malignancy. The 26S proteasome inhibitor, bortezomib, selectively induces apoptosis in MM cells; however, the nature of its selectivity remains unknown. Here we demonstrate that 5 different MM cell lines display similar patterns of sensitivity to 3 proteasome inhibitors (PIs) but respond differently to specific NF-kappaB inhibition. We further show that PIs initiate the unfolded protein response (UPR), a signaling pathway activated by the accumulation of misfolded proteins within the endoplasmic reticulum (ER). Consistent with reports that prosurvival/physiologic UPR components are required for B-cell differentiation into antibody-secreting cells, we found that MM cells inherently expressed the ER chaperones GRP78/Bip and GRP94/gp96. However, bortezomib rapidly induced components of the proapoptotic/terminal UPR, including PERK, the ER stress-specific eIF-2alpha kinase; ATF4, an ER stress-induced transcription factor; and its proapoptotic target, CHOP/GADD153. Consistent with our hypothesis that PIs induce the accumulation of misfolded ER-processed proteins, we found that the amount of immunoglobulin subunits retained within MM cells correlated with their sensitivity to PIs. These findings suggest that MM cells have a lower threshold for PI-induced UPR induction and ER stress-induced apoptosis because they constitutively express ER stress survival factors to function as secretory cells.
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PMID:Proteasome inhibitors induce a terminal unfolded protein response in multiple myeloma cells. 1650 71

We examined whether the unfolded protein response is activated in cells expressing incorrectly folded cystic fibrosis transmembrane conductance regulator. Airway epithelial cells from three control and three CF patients homozygous for the deltaF508 mutation were tested. There were no differences in protein expression of the pro-apoptotic factor C/EBP homologous protein (CHOP) or the endoplasmic reticulum (ER) chaperone binding Ig protein. Nor were there differences in phosphorylation of protein kinase R-like ER kinase or eukaryotic initiation factor-2alpha, or the splicing of X-box binding protein (XBP)-1. However, CF cells showed increased mRNA expression of CHOP and XBP-1. A proteasome inhibitor increased CHOP expression in CF cells, suggesting that enhanced proteasome activation is responsible for the observed post-transcriptional regulation. Finally, CF cells were resistant to apoptosis, suggesting that post-transcriptional regulation of CHOP prevents apoptosis. While CHOP and XBP-1 mRNA expression is increased in CF cells, the classic UPR is not present.
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PMID:Absence of typical unfolded protein response in primary cultured cystic fibrosis airway epithelial cells. 1653 Jan 68

Endoplasmic reticulum (ER)-associated degradation (ERAD) is the major quality control pathway of the cell. The most common disease-causing protein folding mutation, DeltaF508-cystic fibrosis transmembrane regulator (CFTR), is destroyed by ERAD to cause cystic fibrosis (CF). p97/valosin-containing protein (VCP) physically interacts with gp78/autocrine motility factor receptor to couple ubiquitination, retrotranslocation, and proteasome degradation of misfolded proteins. We show here that p97/VCP and gp78 form complexes with CFTR during translocation from the ER for degradation by the cytosolic proteasome. Interference in the VCP-CFTR complex promoted accumulation of immature CFTR in the ER and partial rescue of functional chloride channels to the cell surface. Moreover, under these conditions, interleukin-8 (IL8), the expression of which is regulated by the proteasome, was reduced. Inhibition of the proteasome with bortezomib (PS-341/Velcade) also rescued CFTR, but with less efficiency, and suppressed NFkappaB-mediated IL8 activation. The inhibition of the major stress-inducible transcription factor CHOP (CCAAT/enhancer-binding protein homologous protein)/GADD153 together with bortezomib was most effective in repressing NFkappaB-mediated IL8 activation compared with interference of VCP, MLN-273 (proteasome inhibitor), or 4-phenylbutyrate (histone deacetylase inhibitor). Immunoprecipitation of DeltaF508-CFTR from primary CF bronchial epithelial cells confirmed the interaction with VCP and associated chaperones in CF. We conclude that VCP is an integral component of ERAD and cellular stress pathways induced by the unfolded protein response and may be central to the efficacy of CF drugs that target the ubiquitin-proteasome pathway.
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PMID:Selective inhibition of endoplasmic reticulum-associated degradation rescues DeltaF508-cystic fibrosis transmembrane regulator and suppresses interleukin-8 levels: therapeutic implications. 1662 97

The role of the proteasome in the regulation of cellular levels of the transcription factor CCAAT/enhancer-binding protein beta (C/EBPbeta) is poorly understood. We tested the hypothesis that C/EBPbeta levels in cultured myotubes are regulated, at least in part, by proteasome activity. Treatment of cultured L6 myotubes, a rat skeletal muscle cell line, with the specific proteasome inhibitor beta-lactone resulted in increased nuclear levels of C/EBPbeta as determined by Western blotting and immunofluorescent detection. This effect of beta-lactone reflected inhibited degradation of C/EBPbeta. Surprisingly, the increased C/EBPbeta levels in beta-lactone-treated myotubes did not result in increased DNA-binding activity. In additional experiments, treatment of the myotubes with beta-lactone resulted in increased nuclear levels of growth arrest DNA damage/C/EBP homologous protein (Gadd153/CHOP), a dominant-negative member of the C/EBP family that can form heterodimers with other members of the C/EBP family and block DNA binding. Coimmunoprecipitation and immunofluorescent detection provided evidence that C/EBPbeta and Gadd153/CHOP interacted and colocalized in the nuclei of the beta-lactone-treated myotubes. When Gadd153/CHOP expression was downregulated by transfection of myotubes with siRNA targeting Gadd153/CHOP, C/EBPbeta DNA-binding activity was restored in beta-lactone-treated myotubes. The results suggest that C/EBPbeta is degraded by a proteasome-dependent mechanism in skeletal muscle cells and that Gadd153/CHOP can interact with C/EBPbeta and block its DNA-binding activity. The observations are important because they increase the understanding of the complex regulation of the expression and activity of C/EBPbeta in skeletal muscle.
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PMID:Treatment of cultured myotubes with the proteasome inhibitor beta-lactone increases the expression of the transcription factor C/EBPbeta. 1698 92


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