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

Peptide N-glycanase (PNGase) is involved in the cleavage of oligosaccharide chains from misfolded glycoproteins that are destined for degradation by the proteasome. Earlier, a number of potential binding partners of mouse PNGase (mPNGase) were detected by using the yeast two-hybrid system. In the current study, an in vitro system was set up to investigate direct interactions between mPNGase and these candidate proteins. Although the yeast two-hybrid system suggested an interaction of six different proteins with mPNGase, only mHR23B and the proteasome subunit mS4 were found to interact with mPNGase. In fact, mS4 competes with mHR23B for binding to mPNGase. These results suggested two possible pathways for the interaction between mPNGase and the proteasome. In one pathway, mHR23B mediates the interaction between mPNGase and the proteasome. In an alternative pathway, mPNGase directly binds to the proteasome subunit, mS4. In either case, it is clear that PNGase is located in close proximity to the proteasome and is available for deglycosylation of glycoproteins destined for degradation. Surprisingly, mPNGase also was found to mediate binding of the cytoplasmic protein, p97, to the proteasome through the formation of a ternary complex made up of mHR23B, mPNGase, and p97. Because p97 is known to bind to the endoplasmic reticulum membrane protein AMFR (gp78), an E3 ligase, we propose a model in which p97, mPNGase, and mHR23B mediate interaction of the endoplasmic reticulum with the proteasome.
...
PMID:Multiple modes of interaction of the deglycosylation enzyme, mouse peptide N-glycanase, with the proteasome. 1624 33

Quality control mechanisms in the endoplasmic reticulum prevent deployment of aberrant or unwanted proteins to distal destinations and target them to degradation by a process known as endoplasmic reticulum-associated degradation, or ERAD. Attempts to characterize ERAD by identifying a specific component have revealed that the most general characteristic of ERAD is that the protein substrates are initially translocated to the ER and eventually eliminated in the cytosol by the ubiquitin-proteasome pathway. Hence, dislocation from the ER back to the cytosol is a hallmark in ERAD and p97/Cdc48p, a cytosolic AAA-ATPase that is essential for ERAD, appears to provide the driving force for this process. Moreover, unlike many ERAD components that participate in degradation of either lumenal or membrane substrates, p97/Cdc48p has a more general role in that it is required for ERAD of both types of substrates. Although p97/Cdc48p is not dedicated exclusively to ERAD, its ability to physically associate with ERAD substrates, with VIMP and with the E3 gp78 suggest that the p97/Cdc48Ufdl/Npl4 complex acts as a coordinator that maintains coupling between the different steps in ERAD.
...
PMID:The role of p97/Cdc48p in endoplasmic reticulum-associated degradation: from the immune system to yeast. 1657 38

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.
...
PMID:Selective inhibition of endoplasmic reticulum-associated degradation rescues DeltaF508-cystic fibrosis transmembrane regulator and suppresses interleukin-8 levels: therapeutic implications. 1662 97

In eukaryotic cells, many short-lived proteins are conjugated with Lys 48-linked ubiquitin chains and degraded by the proteasome. Ubiquitination requires an activating enzyme (E1), a conjugating enzyme (E2) and a ligase (E3). Most ubiquitin ligases use either a HECT (homologous to E6-associated protein C terminus) or a RING (really interesting new gene) domain to catalyse polyubiquitination, but the mechanism of E3 catalysis is poorly defined. Here we dissect this process using mouse Ube2g2 (E2; identical at the amino acid level to human Ube2g2) and human gp78 (E3), an endoplasmic reticulum (ER)-associated conjugating system essential for the degradation of misfolded ER proteins. We demonstrate by expressing recombinant proteins in Escherichia coli that Ube2g2/gp78-mediated polyubiquitination involves preassembly of Lys 48-linked ubiquitin chains at the catalytic cysteine of Ube2g2. The growth of Ube2g2-anchored ubiquitin chains seems to be mediated by an aminolysis-based transfer reaction between two Ube2g2 molecules that each carries a ubiquitin moiety in its active site. Intriguingly, polyubiquitination of a substrate can be achieved by transferring preassembled ubiquitin chains from Ube2g2 to a lysine residue in a substrate.
...
PMID:A ubiquitin ligase transfers preformed polyubiquitin chains from a conjugating enzyme to a substrate. 1731 Jan 45

The membrane-anchored ubiquitin ligase gp78 promotes degradation of misfolded endoplasmic reticulum (ER) proteins and sterol-regulated degradation of HMG-CoA reductase. It was known previously that Ufd1 plays a critical role in ER-associated degradation (ERAD) together with Npl4 and VCP. The VCP-Ufd1-Npl4 complex recognizes polyubiquitin chains and transfers the ubiquitinated proteins to the proteasome. Here we show that Ufd1 directly interacts with gp78 and functions as a cofactor. Ufd1 enhances the E3 activity of gp78, accelerates the ubiquitination and degradation of reductase, and eventually promotes receptor-mediated uptake of low-density lipoprotein. Furthermore, we demonstrate that the monoubiquitin-binding site in Ufd1 is required for the enhancement of gp78 activity and that the polyubiquitin-binding site in Ufd1 is critical for a postubiquitination step in ERAD. In summary, our study identifies Ufd1 as a cofactor of gp78, reveals an unappreciated function of Ufd1 in the ubiquitination reaction during ERAD, and illustrates that Ufd1 plays a critical role in cholesterol metabolism.
...
PMID:Ufd1 is a cofactor of gp78 and plays a key role in cholesterol metabolism by regulating the stability of HMG-CoA reductase. 1768 Nov 47

Misfolded proteins in the endoplasmic reticulum (ER) are eliminated by a process known as ER-associated degradation (ERAD), which starts with misfolded protein recognition, followed by ubiquitination, retrotranslocation to the cytosol, deglycosylation, and targeting to the proteasome for degradation. Actions of multisubunit protein machineries in the ER membrane integrate these steps. We hypothesized that regulation of the multisubunit machinery assembly is a mechanism by which ERAD activity is regulated. To test this hypothesis, we investigated the potential regulatory role of the small p97/VCP-interacting protein (SVIP) on the formation of the ERAD machinery that includes ubiquitin ligase gp78, AAA ATPase p97/VCP, and the putative channel Derlin1. We found that SVIP is anchored to microsomal membrane via myristoylation and co-fractionated with gp78, Derlin1, p97/VCP, and calnexin to the ER. Like gp78, SVIP also physically interacts with p97/VCP and Derlin1. Overexpression of SVIP blocks unassembled CD3delta from association with gp78 and p97/VCP, which is accompanied by decreases in CD3delta ubiquitination and degradation. Silencing SVIP expression markedly enhances the formation of gp78-p97/VCP-Derlin1 complex, which correlates with increased degradation of CD3delta and misfolded Z variant of alpha-1-antitrypsin, established substrates of gp78. These results suggest that SVIP is an endogenous inhibitor of ERAD that acts through regulating the assembly of the gp78-p97/VCP-Derlin1 complex.
...
PMID:Identification of SVIP as an endogenous inhibitor of endoplasmic reticulum-associated degradation. 1787 46

Misfolded or improperly assembled proteins in the endoplasmic reticulum (ER) are exported into the cytosol and degraded via the ubiquitin-proteasome pathway, a process termed ER-associated degradation (ERAD). Saccharomyces cerevisiae Hrd1p/Der3p is an ER membrane-spanning ubiquitin ligase that participates in ERAD of the cystic fibrosis transmembrane conductance regulator (CFTR) when CFTR is exogenously expressed in yeast cells. Two mammalian orthologues of yeast Hrd1p/Der3p, gp78 and HRD1, have been reported. Here, we demonstrate that gp78, but not HRD1, participates in ERAD of the CFTR mutant CFTRDeltaF508, by specifically promoting ubiquitylation of CFTRDeltaF508. Domain swapping experiments and deletion analysis revealed that gp78 binds to CFTRDeltaF508 through its ubiquitin binding region, the so-called coupling of ubiquitin to ER degradation (CUE) domain. Gp78 polyubiquitylated in vitro an N-terminal ubiquitin-glutathione-S-transferase (GST)-fusion protein, but not GST alone. This suggests that gp78 recognizes the ubiquitin that is already conjugated to CFTRDeltaF508 and catalyzes further polyubiquitylation of CFTRDeltaF508 in a manner similar to that of a multiubiquitin chain assembly factor (E4). Furthermore, we revealed by small interfering RNA methods that the ubiquitin ligase RMA1 functioned as an E3 enzyme upstream of gp78. Our data demonstrates that gp78 cooperates with RMA1 with E4-like activity in the ERAD of CFTRDeltaF508.
...
PMID:Gp78 cooperates with RMA1 in endoplasmic reticulum-associated degradation of CFTRDeltaF508. 1821 83

In eukaryotic cells, the endoplasmic reticulum-associated degradation (ERAD) pathway is essential for the disposal of misfolded proteins. Recently, we demonstrated the existence of a higher order complex consisting of the ER bound E3 ligase gp78, p97, PNGase, and HR23B in mammals. This complex may serve to facilitate the routing of misfolded glycoproteins out of the ER to the cytosol where they are degraded by the proteasome. In this complex, p97 functions as an organizer to mediate the interactions with gp78 and the deglycosylating enzyme PNGase. A novel protein-binding motif of mouse p97 was identified that consists of its last 10 amino acid residues; this motif is sufficient to mediate the interaction of p97 with PNGase and Ufd3. Phosphorylation of p97's highly conserved penultimate tyrosine residue, completely blocks binding of both PNGase and Ufd3 to mp97. We have found that c-Src kinase directly and selectively phosphorylated the penultimate tyrosine of p97 in vitro, and that overexpression of c-Src significantly increased the phosphorylation level of p97 in cells and caused accumulation of the ERAD substrate TCRalpha-GFP, as well as ubiquitin-conjugated substrates. These results suggest a role for p97 phosphorylation in the degradation of misfolded glycoproteins.
...
PMID:Tyrosine phosphorylation of ATPase p97 regulates its activity during ERAD. 1870 91

Lys-48-linked polyubiquitination regulates a variety of cellular processes by targeting ubiquitinated proteins to the proteasome for degradation. Although polyubiquitination had been presumed to occur by transferring ubiquitin molecules, one at a time, from an E2 active site to a substrate, we recently showed that the endoplasmic reticulum-associated RING finger ubiquitin ligase gp78 can mediate the preassembly of Lys-48-linked polyubiquitin chains on the catalytic cysteine of its cognate E2 Ube2g2 and subsequent transfer to a substrate. Active site-linked polyubiquitin chains are detected in cells on Ube2g2 and its yeast homolog Ubc7p, but how these chains are assembled is unclear. Here, we show that gp78 forms an oligomer via 2 oligomerization sites, one of which is a hydrophobic segment located in the gp78 cytosolic domain. We further demonstrate that a gp78 oligomer can simultaneously associate with multiple Ube2g2 molecules. This interaction is mediated by a novel Ube2g2 surface distinct from the predicted RING binding site. Our data suggest that a large gp78-Ube2g2 heterooligomer brings multiple Ube2g2 molecules into close proximity, allowing ubiquitin moieties to be transferred between neighboring Ube2g2s to form active site-linked polyubiquitin chains.
...
PMID:Mechanistic insights into active site-associated polyubiquitination by the ubiquitin-conjugating enzyme Ube2g2. 1922 79

Sterol-accelerated degradation of the enzyme 3-hydroxy-3-methylglutaryl-coenzyme A reductase is one of several mechanisms through which cholesterol synthesis is controlled in mammalian cells. This degradation results from sterol-induced binding of the membrane domain of reductase to endoplasmic reticulum membrane proteins called Insig-1 and Insig-2, which are carriers of a ubiquitin ligase called gp78. The ensuing gp78-mediated ubiquitination of reductase is a prerequisite for its rapid, 26 S proteasome-mediated degradation from endoplasmic reticulum membranes, a reaction that slows a rate-limiting step in cholesterol synthesis. Here, we report that the membrane domain of hamster reductase is subject to sterol-accelerated degradation in Drosophila S2 cells, but only when mammalian Insig-1 or Insig-2 are co-expressed. This degradation mimics the reaction that occurs in mammalian cells with regard to its absolute requirement for the action of Insigs, sensitivity to proteasome inhibition, augmentation by nonsterol isoprenoids, and sterol specificity. RNA interference studies reveal that this degradation requires the Drosophila Hrd1 ubiquitin ligase and several other proteins, including a putative substrate selector, which associate with the enzyme in yeast and mammalian systems. These studies define Insigs as the minimal requirement for sterol-accelerated degradation of the membrane domain of reductase in Drosophila S2 cells.
...
PMID:Insig-mediated, sterol-accelerated degradation of the membrane domain of hamster 3-hydroxy-3-methylglutaryl-coenzyme A reductase in insect cells. 1963 38


1 2 3 Next >>

---