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

---

Query: EC:6.3.2.19 (ubiquitin-protein ligase)
799 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The maltose transporter in Saccharomyces cerevisiae is degraded in the vacuole after internalization by endocytosis when protein synthesis is impaired and a fermentable substrate is present. The possible implication of the ubiquitin pathway in this inactivation, known as catabolite inactivation, has been investigated. Using mutants deficient in npi1/rsp5 ubiquitin-protein ligase and npi2/doa4 ubiquitin-protein hydrolase, we have shown that these two enzymes are required for normal endocytosis and degradation of the transporter. These facts indicate that the ubiquitin pathway is involved in catabolite inactivation of the maltose transporter. The results also revealed that both enzymes act in the internalization step of endocytosis.
...
PMID:Catabolite inactivation of the yeast maltose transporter requires ubiquitin-ligase npi1/rsp5 and ubiquitin-hydrolase npi2/doa4. 911 4

Glucose triggers transcriptional and post-transcriptional mechanisms that increase the level and activity of Saccharomyces cerevisiae plasma membrane H+-ATPase. We have studied the post-transcriptional activation of the enzyme by glucose and have found that Rsp5, a ubiquitin-protein ligase enzyme, Ubc4, a ubiquitin-conjugating enzyme, and the 26S proteasome complex are implicated in this activation. These results suggest that ATPase activation by glucose requires the ubiquitin-proteasome proteolytic pathway. This is supported by the fact that over-expression of the ubiquitin-specific protease Ubp2, which cleaves ubiquitin from its branched conjugates, inhibits this activation. We propose that glucose triggers degradation of an inhibitory protein resulting in enzyme activation.
...
PMID:Glucose activation of the yeast plasma membrane H+-ATPase requires the ubiquitin-proteasome proteolytic pathway. 927 Dec 26

The hypoxia-inducible factor 1 transcriptional activator complex (HIF-1) is involved in the activation of the erythropoietin and several other hypoxia-responsive genes. The HIF-1 complex is composed of two protein subunits: HIF-1beta/ARNT (aryl hydrocarbon receptor nuclear translocator), which is constitutively expressed, and HIF-1alpha, which is not present in normal cells but induced under hypoxic conditions. The HIF-1alpha subunit is continuously synthesized and degraded under normoxic conditions, while it accumulates rapidly following exposure to low oxygen tensions. The involvement of the ubiquitin-proteasome system in the proteolytic destruction of HIF-1 in normoxia was studied by the use of specific inhibitors of the proteasome system. Lactacystin and MG-132 were found to protect the degradation of the HIF-1 complex in cells transferred from hypoxia to normoxia. The same inhibitors were able to induce HIF-1 complex formation when added to normoxic cells. Final confirmation of the involvement of the ubiquitin-proteasome system in the regulated degradation of HIF-1alpha was obtained by the use of ts20TGR cells, which contain a temperature-sensitive mutant of E1, the ubiquitin-activating enzyme. Exposure of ts20 cells, under normoxic conditions, to the non-permissive temperature induced a rapid and progressive accumulation of HIF-1. The effect of proteasome inhibitors on the normoxic induction of HIF-1 binding activity was mimicked by the thiol reducing agent N-(2-mercaptopropionyl)-glycine and by the oxygen radical scavenger 2-acetamidoacrylic acid. Furthermore, N-(2-mercaptopropionyl)-glycine induced gene expression as measured by the stimulation of a HIF-1-luciferase expression vector and by the induction of erythropoietin mRNA in normoxic Hep 3B cells. These last findings strongly suggest that the hypoxia induced changes in HIF-1alpha stability and subsequent gene activation are mediated by redox-induced changes.
...
PMID:Hypoxia-inducible factor 1alpha (HIF-1alpha) protein is rapidly degraded by the ubiquitin-proteasome system under normoxic conditions. Its stabilization by hypoxia depends on redox-induced changes. 927 21

Glucocorticoids signal enhanced proteolysis in various instances of muscle atrophy and increased gene expression of components of the lysosomal, Ca(2+)-dependent, and/or ubiquitin-proteasome proteolytic pathways in both rat skeletal muscle and myotubes. Cushing's syndrome is characterized by chronic excessive glucocorticoid production, which results in muscle wasting. We report here no change in messenger RNA levels for cathepsin D (a lysosomal proteinase), m-calpain (a Ca(2+)-activated proteinase), ubiquitin, 14-kDa ubiquitin-activating enzyme E2, and 20S proteasome subunits (i.e. critical components of the ubiquitin-proteasome proteolytic process) in skeletal muscle from such patients. Thus, in striking contrast with animal studies, glucocorticoids did not regulate the expression of muscle proteolytic genes in Cushing's syndrome. In humans, messenger RNA levels, for at least ubiquitin and proteasome subunits, are elevated in acute situations of muscle wasting, such as head trauma or sepsis. Because Cushing's syndrome is a chronic catabolic condition, we suggest that the lack of regulation of proteolytic genes in such patients may represent an adaptive regulatory mechanisms, preventing sustained increased protein breakdown and avoiding rapid muscle wasting.
...
PMID:Glucocorticoids do not regulate the expression of proteolytic genes in skeletal muscle from Cushing's syndrome patients. 928 62

Relations between the ubiquitin pathway and cellular stress have been noted, but data regarding responses of the ubiquitin pathway to oxidative stress are scanty. This paper documents the response of this pathway to oxidative stress in lens cells. A brief exposure of lens epithelial cells to physiologically relevant levels of H2O2 induces a transient increase in activity of the ubiquitin-dependent pathway. Ubiquitin conjugation activity was maximal and increased 3. 5-9.2-fold over the activity noted in untreated cells by 4 h after removal of H2O2. By 24 h after removal of H2O2, ubiquitin conjugation activity returned to the level noted in untreated cells. In parallel to the changes in ubiquitin conjugation activity, the activity of ubiquitin-activating enzyme (E1), as determined by thiol ester formation, increased 2-6.7-fold during recovery from oxidation. Addition of exogenous E1 resulted in an increase in ubiquitin conjugation activity and in the levels of ubiquitin carrier protein (E2)-ubiquitin thiol esters in both the untreated cells and the H2O2-treated cells. These data suggest that E1 is the rate-limiting enzyme in the ubiquitin conjugation process and that the increases in ubiquitin conjugation activity which are induced upon recovery from oxidation are primarily due to increased E1 activity. The oxidation- and recovery-induced up-regulation of E1 activity is primarily due to post-synthetic events. Substrate availability and up-regulation of E2 activities also appear to be related to the enhancement in ubiquitinylation upon recovery from oxidative stress. The oxidation-induced increases in ubiquitin conjugation activity were associated with an increase in intracellular proteolysis, suggesting that the transient increase in ubiquitinylation noted upon recovery from oxidative stress may play a role in removal of damaged proteins from the cells.
...
PMID:Activity of ubiquitin-dependent pathway in response to oxidative stress. Ubiquitin-activating enzyme is transiently up-regulated. 928 9

Some receptor tyrosine kinases such as the receptors for epidermal-growth factor (EGF) and platelet-derived growth factor undergo polyubiquitination as a consequence of ligand binding. The EGF receptor is also ubiquitinated by treatment with herbimycin A, an ansamycin antibiotic widely used as a tyrosine kinase inhibitor. To investigate the mechanism of the receptor ubiquitination, we have established an assay system in which herbimycin-A-induced ubiquitination processes can be analyzed in vitro. We now show that herbimycin A treatment of the purified EGF receptor induces polyubiquitination of the receptor in rabbit-reticulocyte lysate. Both DEAE unadsorbed material (fraction I) and high salt eluate (fraction II) of the reticulocyte lysate are involved cooperatively in the ubiquitination process, where the ubiquitin-conjugating enzyme UBC4 can functionally substitute for fraction I. A ubiquitin-protein ligase-like activity, partially purified from fraction II by DEAE anion-exchange chromatography, also functions in concert with UBC4. The precise mechanism of herbimycin A-induced ubiquitination of the EGF receptor is not fully understood, however, our present findings suggest that direct interaction with herbimycin A results in some modification of the receptor which is recognized by the ubiquitin-conjugating system in rabbit-reticulocyte lysate.
...
PMID:Identification of an ubiquitin-ligation system for the epidermal-growth-factor receptor--herbimycin A induces in vitro ubiquitination in rabbit-reticulocyte lysate. 928 47

Topoisomerase I (TOP1) relaxes superhelical DNA through a breakage/rejoining reaction in which the active site tyrosine links covalently to a 3' phosphate at the break site as a transient intermediate. The antitumor drug camptothecin (CPT) and its analogs inhibit the rejoining step of the breakage/rejoining reaction, which traps the enzyme in covalent linkage with DNA (the cleavable complex). Little is known about the fate of cellular TOP1 trapped in the cleavable complex. We have analyzed TOP1 in mammalian cell lines treated with CPT. When CPT-treated cells were lysed with either SDS or alkali and analyzed by Western blotting, greater than 90% of the TOP1 was linked to DNA. Nuclease treatment of the cell lysate to remove the covalently linked DNA from TOP1 revealed a distinct ladder of higher molecular weight bands having properties indicative of multi-ubiquitin (Ub) conjugates of TOP1. Approximately 5-10% of TOP1 was present as these conjugates within minutes of CPT treatment. Consistent with ubiquitination, TOP1 was not modified in ts85 cells at the restrictive temperature for its thermolabile ubiquitin-activating enzyme (E1). Because conjugation with ubiquitin can mark proteins for destruction by the 26S proteasome, we analyzed TOP1 protein levels during prolonged CPT treatment. TOP1 protein levels were reduced to about 25% during CPT treatments of 2-4 h resulting from increased destruction, with the half-life dropping from 10-16 h down to 1-2 h. The destruction of TOP1, like the formation of Ub-TOP1 conjugates, was not observed in ts85 cells at the restrictive temperature. The destruction of TOP1 was also prevented in cells treated with MG-132 and lactacystin, specific inhibitors of the 26S proteasome. Finally, the multi-Ub conjugates of TOP1 were observed whether or not aphidicolin was included in cotreatment with CPT, indicating that replication fork activity was not involved in making TOP1 a substrate for ubiquitination. These results demonstrate that independent of DNA replication, the TOP1 cleavable complex is ubiquitinated and destroyed in cells treated with antitumor drugs that block the religation step of the TOP1 reaction.
...
PMID:Ubiquitin-dependent destruction of topoisomerase I is stimulated by the antitumor drug camptothecin. 930 65

We have recently reported that the yeast plasma membrane uracil permease undergoes cell-surface ubiquitination, which is dependent on the Npi1/Rsp5 ubiquitin-protein ligase. Ubiquitination of this permease, like that of some other transporters and receptors, signals endocytosis of the protein, leading to its subsequent vacuolar degradation. This process does not involve the proteasome, which binds and degrades ubiquitin-protein conjugates carrying Lys48-linked ubiquitin chains. The data presented here show that ubiquitination and endocytosis of uracil permease are impaired in yeast cells lacking the Doa4p ubiquitin-isopeptidase. Both processes were rescued by overexpression of wild-type ubiquitin. Mutant ubiquitins carrying Lys-->Arg mutations at Lys29 and Lys48 restored normal permease ubiquitination. In contrast, a ubiquitin mutated at Lys63 did not restore permease polyubiquitination. Ubiquitin-permease conjugates are therefore extended through the Lys63 of ubiquitin. When polyubiquitination through Lys63 is blocked, the permease still undergoes endocytosis, but at a reduced rate. We have thus identified a natural target of Lys63-linked ubiquitin chains. We have also shown that monoubiquitination is sufficient to induce permease endocytosis, but that Lys63-linked ubiquitin chains appear to stimulate this process.
...
PMID:Ubiquitin lys63 is involved in ubiquitination of a yeast plasma membrane protein. 931 43

Upon oxidative stress cells show an increase in the oxidized glutathione (GSSG) to reduced glutathione (GSH) ratio with a concomitant decrease in activity of the ubiquitinylation pathway. Because most of the enzymes involved in the attachment of ubiquitin to substrate proteins contain active site sulfhydryls that might be covalently modified (thiolated) upon enhancement of GSSG levels (glutathiolation), it appeared plausible that glutathiolation might alter ubiquitinylation rates upon cellular oxidative stress. This hypothesis was explored using intact retina and retinal pigment epithelial (RPE) cell models. Exposure of intact bovine retina and RPE cells to H2O2 (0.1-1.7 micromol/mg) resulted in a dose-dependent increase in the GSSG:GSH ratio and coincident dose-dependent reductions in the levels of endogenous ubiquitin-activating enzyme (E1)-ubiquitin thiol esters and endogenous protein-ubiquitin conjugates and in the ability to form de novo retinal protein-125I-labeled ubiquitin conjugates. Oxidant-induced decrements in ubiquitin conjugates were associated with 60-80% reductions in E1 and ubiquitin-conjugating enzyme (E2) activities as measured by formation of ubiquitin thiol esters. When GSH levels in RPE cells recovered to preoxidation levels following H2O2 removal, endogenous E1 activity and protein-ubiquitin conjugates were restored. Evidence that S thiolation of E1 and E2 enzymes is the biochemical link between cellular redox state and E1/E2 activities includes: (i) 5-fold increases in levels of immunoprecipitable, dithiothreitol-labile 35S-E1 adducts in metabolically labeled, H2O2-treated, RPE cells; (ii) diminished formation of E1- and E2-125I-labeled ubiquitin thiol esters, oligomerization of E225K, and coincident reductions in protein-125I-labeled ubiquitin conjugates in supernatants from nonstressed retinas upon addition of levels of GSSG equivalent to levels measured in oxidatively stressed retinas; and (iii) partial restoration of E1 and E2 activities and levels of protein-125I-labeled ubiquitin conjugates in supernatants from H2O2-treated retinas when GSSG:GSH ratios were restored to preoxidation levels by the addition of physiological levels of GSH. These data suggest that the cellular redox status modulates protein ubiquitinylation via reversible S thiolation of E1 and E2 enzymes, presumably by glutathione.
...
PMID:Regulation of ubiquitin-conjugating enzymes by glutathione following oxidative stress. 935 72

The covalent attachment of the polypeptide ubiquitin to proteins marks them for degradation by the ubiquitin/26S proteasome-dependent degradation pathway. This pathway functions in regulating many fundamental processes required for cell viability. Phylogenetic analysis of ubiquitin sequences reveals greater variability among lower eukaryotes and defines essential residues, many of which are conserved among the three ubiquitin-like proteins known to undergo parallel ligation pathways. The hierarchical design of the ubiquitin conjugation mechanism provides great flexibility for the divergent evolution of new functions mediated by this posttranslational modification. Within this hierarchy, a single ubiquitin-activating enzyme provides charged intermediates to multiple targeting pathways defined by cognate ubiquitin carrier protein (E2)/ligase (E3) pairs. Sequence analysis of E2 isozymes shows that the E2 superfamily is composed of distinct function-specific families. The apparent lack of E2/E3 specificity suggested in the literature results from the presence of multiple isozymes within many E2 families and erroneous family assignments based on incomplete data sets. Other apparent inconsistencies are explained by interfamily sequence relationships among some E2 isoforms.
...
PMID:Pathways of ubiquitin conjugation. 940 44


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

---