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)

We purified by fractionation on 10-40% glycerol gradients, 26S proteasomes from normal human spermatozoa. These proteasomes, which participate in the ATP-dependent degradation of ubiquitinated proteins, share a similar sedimentation coefficient to those purified from other human tissues. Fluorogenic peptide assays reveal they have chymotrypsin, trypsin and peptidyl-glutamyl-like peptide hydrolysing activities; the chymotrypsin activity is ablated by the specific 26S proteasome inhibitor MG132. Confirmation that these large proteases are 26S proteasomes is provided by detection of the 20S proteasome subunits HC2, XAPC7, RN3 and Z and regulatory ATPases MSS1, TBP1, SUG1 and SUG2 by Western analyses with monoclonal antisera. These antigens are found only in the gradient fractions enriched in proteolytic activities. We have also shown that, although mature spermatozoa from mice have considerably reduced amounts of a ubiquitin-conjugating enzyme (E2) and ubiquitin-protein conjugates in comparison with less mature germ cells, they retain relatively high values of 26S proteasome activity. This suggests that proteasomes may have further roles to play in normal sperm physiology.
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PMID:Purification and characterization of 26S proteasomes from human and mouse spermatozoa. 946 50

Activating transcription factor 2 (ATF2) is regulated by phosphorylation via the Jun N-terminal kinase, and its binding activity is markedly induced at late stages of T and B lymphocyte activation (Feuerstein, N., Firestein, R., Aiyer, N., Xiao, H., Murasko, D., and Cristofalo, V. (1996) J. Immunol. 156, 4582-4593). To identify proteins that interact specifically with ATF2 in lymphocytes, the yeast two-hybrid interaction system was employed using ATF2 cDNA as a "bait." In two separate screenings, a clone was identified that revealed a novel sequence with homology to several members of the ubiquitin-conjugating enzyme family. An identical sequence was recently reported as the human homolog of the yeast UBC9, hUBC9. Northern blot analysis revealed a 1.3-kilobase RNA transcript, which showed differential levels of expression in various human tissues and a moderate induction after a 48-h stimulation of peripheral blood T lymphocytes. An antibody that was generated against the bacterially expressed glutathione S-transferase-hUBC9 detected a approximately 19-kDa protein, which localizes predominantly in the nuclei of T cells. Further quantitative assays using the yeast two-hybrid system confirmed a high and specific level of interaction of hUBC9 with ATF2 and lack of interaction with lamin or control vectors. Two other cyclic AMP-responsive element-binding transcription factors, CREB and ATF1, also showed significant levels of interaction with hUBC9. However, this interaction was severalfold lower as compared with ATF2. Far Western blot analysis confirmed the specific binding of ATF2 and hUBC9 also in vitro. Evidence is presented that indicates a physiological significance for the interaction of hUBC9 with ATF2. (a) We show that ATF2 is ubiquitinated in vivo and in vitro, and (b) ATF2 ubiquitination in vitro is facilitated by addition of purified hUBC9. (c) ATF2 is shown to undergo a proteolytic process, which is rapidly regulated upon T cell activation concomitant with induction of ATF2 phosphorylation. (d) A proteasome inhibitor delays the down-regulation of ATF2 phophorylation after T cell activation. Taken collectively, these results implicate a role for hUBC9 and the ubiquitin/proteasome pathway in regulation of ATF2 in T cells.
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PMID:Association of activating transcription factor 2 (ATF2) with the ubiquitin-conjugating enzyme hUBC9. Implication of the ubiquitin/proteasome pathway in regulation of ATF2 in T cells. 948 27

MyoD is a basic helix-loop-helix transcription factor involved in the activation of genes encoding skeletal muscle-specific proteins. Independent of its ability to transactivate muscle-specific genes, MyoD can also act as a cell cycle inhibitor. MyoD activity is regulated by transcriptional and posttranscriptional mechanisms. While MyoD can be found phosphorylated, the functional significance of this posttranslation modification has not been established. MyoD contains several consensus cyclin-dependent kinase (CDK) phosphorylation sites. In these studies, we examined whether a link could be established between MyoD activity and phosphorylation at putative CDK sites. Site-directed mutagenesis of potential CDK phosphorylation sites in MyoD revealed that S200 is required for MyoD hyperphosphorylation as well as the normally short half-life of the MyoD protein. Additionally, we determined that turnover of the MyoD protein requires the proteasome and Cdc34 ubiquitin-conjugating enzyme activity. Results of these studies demonstrate that hyperphosphorylated MyoD is targeted for rapid degradation by the ubiquitin pathway. The targeted degradation of MyoD following CDK phosphorylation identifies a mechanism through which MyoD activity can be regulated coordinately with the cell cycle machinery (CDK2 and CDK4) and/or coordinately with the cellular transcriptional machinery (CDK7, CDK8, and CDK9).
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PMID:Phosphorylation of nuclear MyoD is required for its rapid degradation. 971 May 83

Previous studies provided evidence that sepsis is associated with increased ubiquitin-proteasome-dependent protein breakdown in skeletal muscle. The 14-kDa ubiquitin-conjugating enzyme (E214k) has been proposed to be a key regulator of the ubiquitin proteolytic pathway. We tested the hypothesis that E214k message and protein levels are increased in skeletal muscle during sepsis. Sepsis was induced in rats by cecal ligation and puncture (CLP). Control rats were sham operated. E214k mRNA and protein levels were quantitated after Northern and Western blot analysis, respectively, 16 h after CLP or sham operation. Sepsis resulted in a 70% increase in the 1. 2-kb E214k transcript in the fast-twitch extensor digitorum longus muscle, whereas no changes were seen in the slow-twitch soleus muscle. E214k protein levels were not influenced by sepsis in any of the muscles studied. Although the changes in the expression of the E214k 1.2-kb transcript paralleled the differential effect of sepsis on protein breakdown in fast- and slow-twitch muscle, the potential role of E214k in the regulation of sepsis-induced muscle proteolysis needs to be interpreted with caution, because the results demonstrated that increased message levels were not associated with increased E214k protein levels.
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PMID:Sepsis is associated with increased ubiquitinconjugating enzyme E214k mRNA in skeletal muscle. 995 Sep 26

Posttranslational modification of a protein by ubiquitin usually results in rapid degradation of the ubiquitinated protein by the proteasome. The transfer of ubiquitin to substrate is a multistep process. Cdc4p is a component of a ubiquitin ligase that tethers the ubiquitin-conjugating enzyme Cdc34p to its substrates. Among the domains of Cdc4p that are crucial for function are the F-box, which links Cdc4p to Cdc53p through Skp1p, and the WD-40 repeats, which are required for binding the substrate for Cdc34p. In addition to Cdc4p, other F-box proteins, including Grr1p and Met30p, may similarly act together with Cdc53p and Skp1p to function as ubiquitin ligase complexes. Because the relative abundance of these complexes, known collectively as SCFs, is important for cell viability, we have sought evidence of mechanisms that modulate F-box protein regulation. Here we demonstrate that the abundance of Cdc4p is subject to control by a peptide segment that we term the R-motif (for "reduced abundance"). Furthermore, we show that binding of Skp1p to the F-box of Cdc4p inhibits R-motif-dependent degradation of Cdc4p. These results suggest a general model for control of SCF activities.
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PMID:The abundance of cell cycle regulatory protein Cdc4p is controlled by interactions between its F box and Skp1p. 1002 63

Proteins modified by multiubiquitin chains are the preferred substrates of the proteasome. Ubiquitination involves a ubiquitin-activating enzyme, E1, a ubiquitin-conjugating enzyme, E2, and often a substrate-specific ubiquitin-protein ligase, E3. Here we show that efficient multiubiquitination needed for proteasomal targeting of a model substrate requires an additional conjugation factor, named E4. This protein, previously known as UFD2 in yeast, binds to the ubiquitin moieties of preformed conjugates and catalyzes ubiquitin chain assembly in conjunction with E1, E2, and E3. Intriguingly, E4 defines a novel protein family that includes two human members and the regulatory protein NOSA from Dictyostelium required for fruiting body development. In yeast, E4 activity is linked to cell survival under stress conditions, indicating that eukaryotes utilize E4-dependent proteolysis pathways for multiple cellular functions.
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PMID:A novel ubiquitination factor, E4, is involved in multiubiquitin chain assembly. 1008 79

The ubiquitin-proteasome proteolytic system is stimulated in conditions causing muscle atrophy. Signals initiating this response in these conditions are unknown, although glucocorticoids are required but insufficient to stimulate muscle proteolysis in starvation, acidosis, and sepsis. To identify signals that activate this system, we studied acutely diabetic rats that had metabolic acidosis and increased corticosterone production. Protein degradation was increased 52% (P < 0.05), and mRNA levels encoding ubiquitin-proteasome system components, including the ubiquitin-conjugating enzyme E214k, were higher (transcription of the ubiquitin and proteasome subunit C3 genes in muscle was increased by nuclear run-off assay). In diabetic rats, prevention of acidemia by oral NaHCO3 did not eliminate muscle proteolysis. Adrenalectomy blocked accelerated proteolysis and the rise in pathway mRNAs; both responses were restored by administration of a physiological dose of glucocorticoids to adrenalectomized, diabetic rats. Finally, treating diabetic rats with insulin for >/=24 h reversed muscle proteolysis and returned pathway mRNAs to control levels. Thus acidification is not necessary for these responses, but glucocorticoids and a low insulin level in tandem activate the ubiquitin-proteasome proteolytic system.
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PMID:Evaluation of signals activating ubiquitin-proteasome proteolysis in a model of muscle wasting. 1032 62

The destruction of the cyclin B protein is necessary for the cell to exit from mitosis. The destruction of cyclin B occurs via the ubiquitin/proteasome system and involves a specific ubiquitin-conjugating enzyme (Ubc) that donates ubiquitin to cyclin B. Here we present the crystal structure of the cyclin-specific Ubc from clam, E2-C, determined at 2.0 A resolution. The E2-C enzyme contains an N-terminal extension in addition to the Ubc core domain. The N-terminal extension is disordered, perhaps reflecting a need for flexibility as it interacts with various partners in the ubiquitination system. The overall structure of the E2-C core domain is quite similar to those in previously determined Ubc proteins. The interaction between particular pairs of E2-C proteins in the crystal has some of the hallmarks of a functional dimer, though solution studies suggest that the E2-C protein exists as a monomer. Comparison of the E2-C structure with that of the other available Ubc structures indicates conserved surface residues that may interact with common components of the ubiquitination system. Such comparison also reveals a remarkable spine of conserved hydrophobic residues in the center of the protein that may drive the protein to fold and stabilize the protein once folded. Comparison of residues conserved only among E2-C and its homologues indicates surface areas that may be involved in mitotic-specific ubiquitination.
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PMID:Crystal structure of the cyclin-specific ubiquitin-conjugating enzyme from clam, E2-C, at 2.0 A resolution. 1035 Apr 65

Several lines of evidence suggest that the ubiquitin-proteasome pathway is involved in sepsis-induced muscle catabolism. The gene expression of ubiquitin and several of the proteasome subunits was increased in muscle from both septic rats and patients. In other studies, the activity of isolated 20S proteasomes was stimulated in septic muscles. Sepsis-induced increase in muscle total and myofibrillar protein breakdown was inhibited with specific proteasome blockers. Although the ubiquitin-proteasome pathway is upregulated in septic muscle, it is still unclear how the myofibrillar proteins actin and myosin are ubiquitinated and become substrates for the 26S proteasome. Recent studies suggest that a calcium-dependent, calpain-mediated process releases myofilaments from the Z-disks during sepsis. It is possible that this process exposes destabilizing N-terminal residues on actin and myosin, making them suitable substrates for the N-end rule pathway involving the 14 kD ubiquitin-conjugating enzyme E214k and the ubiquitin-protein ligase E3alpha.
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PMID:Role of the ubiquitin-proteasome pathway in sepsis-induced muscle catabolism. 1036 50

Hypothemycin was originally isolated as an antifungal metabolite of Hypomyces trichothecoides. Here we report that treatment on v-K-ras-transformed NIH3T3 cells (DT cells) with hypothemycin caused drastic decrease in amount of cyclin D1 protein with concomitant prolongation of G1 phase in their cell cycle. Analysis using hypothemycin-resistant mutant of Schizosaccharomyces pombe (S. pombe) was carried out to show that S. pombe rhp6+ (homologue of Saccharomyces cerevisiae RAD6) and mammalian ubiquitin-conjugating enzyme 2 (ubc2) are the targets of hypothemycin or its downstream molecules in ubiquitin-conjugation process. Furthermore, in the presence of lactacystin, a specific inhibitor for proteasome, hypothemycin greatly enhanced the accumulation of multi-ubiquitinated form of cyclin D1 in DT cells. Therefore, it is indicated that hypothemycin facilitates ubiquitinating process of cyclin D1. In terms of malignant phenotype, hypothemycin inhibited anchorage-independent growth and reverted the morphology of DT cells. On the contrary, their morphology still remained transformed in the additional presence of lactacystin. Our results suggest that cyclin D1 is a key molecule working downstream in ras-signaling and that the transformation can be inhibited by the compound which can activate ubiquitin-proteasome pathway including degradation of cyclin D1.
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PMID:Suppression of oncogenic transformation by hypothemycin associated with accelerated cyclin D1 degradation through ubiquitin-proteasome pathway. 1042 24


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