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)

Some disease-associated truncations within the 100-residue domain C-terminal of the second nucleotide-binding domain destabilize the mature protein (Haardt, M., Benharouga, M., Lechardeur, D., Kartner, N., and Lukacs, G. L. (1999) J. Biol. Chem. 274, 21873-21877). We now have identified three short oligopeptide regions in the C-terminal domain which impact cystic fibrosis transmembrane conductance regulator (CFTR) maturation and stability in different ways. A highly conserved hydrophobic patch (region I) formed by residues 1413-1416 (FLVI) was found to be crucial for the stability of the mature protein. Nascent chain stability was severely decreased by shortening the protein by 81 amino acids (1400X). This accelerated degradation was sensitive to proteasome inhibitors but not influenced by brefeldin A, indicating that it occurred at the endoplasmic reticulum. The five residues at positions 1400 to 1404 (region II) normally maintain nascent CFTR stability in a positional rather than a sequence-specific manner. A third modulating region (III) constituted by residues 1390 to 1394 destabilizes the protein. Hence the nascent form regains stability on further truncation back to residues 1390 or 1380, permitting some degree of maturation and a low level of cyclic AMP-stimulated chloride channel activity at the cell surface. Thus while not absolutely essential, the C-terminal domain strongly modulates the biogenesis and maturation of CFTR.
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PMID:Localization of sequences within the C-terminal domain of the cystic fibrosis transmembrane conductance regulator which impact maturation and stability. 1102 33

Cystic fibrosis (CF) is a lethal monogenetic disease characterised by impaired water and ion transport over epithelia. The lung pathology is fatal and causes death in 95% of CF patients. The genetic basis of the disease is a mutation in the cystic fibrosis transmembrane conductance regulator (CFTR), a cAMP-regulated chloride channel. The most common mutation, DeltaF508, results in a protein that cannot properly be folded in the endoplasmic reticulum, is destroyed and hence does not reach the apical cell membrane. This paper will discuss those pharmacological approaches that are directed at correcting the defect in ion transport. At present, no clinically effective drug is available, although research has defined areas in which progress might be made. These are the following: (1) the drug 4-phenylbutyrate (4PBA) increases the expression of DeltaF508-CFTR in the cell membrane, probably by breaking the association between DeltaF508-CFTR and a chaperone; (2) a number of xanthines, in particular 8-cyclopentyl-1, 3-dipropylxanthine (CPX), are effective in activating CFTR, presumably by direct binding and also possibly by correcting the trafficking defect; (3) the isoflavone genistein can activate both wild-type and mutant CFTR, probably through direct binding to the channel; (4) purinergic agonists (ATP and UTP) can stimulate chloride secretion via a Ca(2+)-dependent chloride channel and in this way compensate for the defect in CFTR, but stable analogues will be required before this type of treatment has clinical significance; (5) treatment with inhaled amiloride may correct the excessive absorption of Na(+) ions and water by airway epithelial cells that appears connected to the defect in CFTR; although clinical tests have not been very successful so far, amiloride analogues with a longer half-life may give better results. The role of CFTR in bicarbonate secretion has not yet been established with certainty, but correction of the defect in bicarbonate secretion may be important in clinical treatment of the disease. Currently, major efforts are directed at developing a pharmacological treatment of the ion transport defect in CF, but much basic research remains to be done, in particular, with regard to the mechanism by which defective CFTR is removed in the endoplasmic reticulum by the ubiquitin-proteasome pathway, which is a central pathway in protein production and of significance for several other diseases apart from CF.
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PMID:Pharmacological treatment of the ion transport defect in cystic fibrosis. 1111 77

Membrane and secretory proteins fold in the endoplasmic reticulum (ER), and misfolded proteins may be retained and targeted for ER-associated protein degradation (ERAD). To elucidate the mechanism by which an integral membrane protein in the ER is degraded, we studied the fate of the cystic fibrosis transmembrane conductance regulator (CFTR) in the yeast Saccharomyces cerevisiae. Our data indicate that CFTR resides in the ER and is stabilized in strains defective for proteasome activity or deleted for the ubiquitin-conjugating enzymes Ubc6p and Ubc7p, thus demonstrating that CFTR is a bona fide ERAD substrate in yeast. We also found that heat shock protein 70 (Hsp70), although not required for the degradation of soluble lumenal ERAD substrates, is required to facilitate CFTR turnover. Conversely, calnexin and binding protein (BiP), which are required for the proteolysis of ER lumenal proteins in both yeast and mammals, are dispensable for the degradation of CFTR, suggesting unique mechanisms for the disposal of at least some soluble and integral membrane ERAD substrates in yeast.
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PMID:Hsp70 molecular chaperone facilitates endoplasmic reticulum-associated protein degradation of cystic fibrosis transmembrane conductance regulator in yeast. 1135 23

Endogenous S-nitrosoglutathione (GSNO) is known to increase the expression of certain proteins at concentrations present in the normal human airway. We hypothesized that GSNO would increase expression and maturation of the cystic fibrosis transmembrane conductance regulator (CFTR). Cells expressing DeltaF508 and wild type CFTR were exposed to GSNO and analyzed for expression and maturation by Western blot analysis. Physiologically relevant concentrations of GSNO resulted in dose- and time-dependent increases in expression. The GSNO-induced increases were eliminated by cycloheximide, suggesting a posttranscriptional effect. Unlike proteasome inhibitors, GSNO resulted in an increase CFTR maturation. The GSNO effect could be reversed by dithiothreitol and inhibited by acivicin, a gamma glutamyl transpeptidase inhibitor. These observations suggest that GSNO leads to maturation of mutated DeltaF508 CFTR, a process associated with restoration of CFTR function. Because endogenous levels of GSNO are low in the cystic fibrosis (CF) airway, these results raise the possibility that GSNO replacement therapy could be an effective treatment for CF.
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PMID:S-nitrosoglutathione increases cystic fibrosis transmembrane regulator maturation. 1137 71

Intracellular deposition of aggregated and ubiquitylated proteins is a prominent cytopathological feature of most neurodegenerative disorders. Whether protein aggregates themselves are pathogenic or are the consequence of an underlying molecular lesion is unclear. Here, we report that protein aggregation directly impaired the function of the ubiquitin-proteasome system. Transient expression of two unrelated aggregation-prone proteins, a huntingtin fragment containing a pathogenic polyglutamine repeat and a folding mutant of cystic fibrosis transmembrane conductance regulator, caused nearly complete inhibition of the ubiquitin-proteasome system. Because of the central role of ubiquitin-dependent proteolysis in regulating fundamental cellular events such as cell division and apoptosis, our data suggest a potential mechanism linking protein aggregation to cellular disregulation and cell death.
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PMID:Impairment of the ubiquitin-proteasome system by protein aggregation. 1137 12

Degradation of proteins that, because of improper or suboptimal processing, are retained in the endoplasmic reticulum (ER) involves retrotranslocation to reach the cytosolic ubiquitin-proteasome machinery. We found that substrates of this pathway, the precursor of human asialoglycoprotein receptor H2a and free heavy chains of murine class I major histocompatibility complex (MHC), accumulate in a novel preGolgi compartment that is adjacent to but not overlapping with the centrosome, the Golgi complex, and the ER-to-Golgi intermediate compartment (ERGIC). On its way to degradation, H2a associated increasingly after synthesis with the ER translocon Sec61. Nevertheless, it remained in the secretory pathway upon proteasomal inhibition, suggesting that its retrotranslocation must be tightly coupled to the degradation process. In the presence of proteasomal inhibitors, the ER chaperones calreticulin and calnexin, but not BiP, PDI, or glycoprotein glucosyltransferase, concentrate in the subcellular region of the novel compartment. The "quality control" compartment is possibly a subcompartment of the ER. It depends on microtubules but is insensitive to brefeldin A. We discuss the possibility that it is also the site for concentration and retrotranslocation of proteins that, like the mutant cystic fibrosis transmembrane conductance regulator, are transported to the cytosol, where they form large aggregates, the "aggresomes."
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PMID:A novel quality control compartment derived from the endoplasmic reticulum. 1140 79

Misfolded proteins in the endoplasmic reticulum (ER) are degraded by N-terminal threonine proteases within the 26S proteasome. Each protease is formed by an activated beta subunit, beta5/X, beta1/Y, or beta2/Z, that exhibits chymotrypsin-like, peptidylglutamyl-peptide hydrolyzing, or trypsin-like activity, respectively. Little is known about the relative contribution of specific beta subunits in the degradation of endogenous protein substrates. Using active site proteasome inhibitors and a reconstituted degradation system, we now show that all three active beta subunits can independently contribute to ER-associated degradation of the cystic fibrosis transmembrane conductance regulator (CFTR). Complete inactivation (>99.5%) of the beta5/X subunit decreased the rate of ATP-dependent conversion of CFTR to trichloroacetic acid soluble fragments by only 40%. Similarly, proteasomes containing only active beta1/Y or beta2/Z subunits degraded CFTR at approximately 50% of the rate observed for fully functional proteasomes. Simultaneous inhibition (>93%) of all three beta subunits blocked CFTR degradation by approximately 90%, and inhibition of both protease and ATPase activities was required to completely prevent generation of small peptide fragments. Our results demonstrate both a conserved hierarchy (ChT-L > PGPH > or = T-L) as well as a redundancy of beta subunit function and provide insight into the mechanism by which active site proteasome inhibitors influence degradation of endogenous protein substrates at the ER membrane.
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PMID:Redundancy of mammalian proteasome beta subunit function during endoplasmic reticulum associated degradation. 1168 50

Endoplasmic reticulum-associated degradation of misfolded cystic fibrosis transmembrane conductance regulator (CFTR) protein is known to involve the ubiquitin-proteasome system. In addition, an ATP-independent proteolytic system has been suggested to operate in parallel with this pathway and become up-regulated when proteasomes are inhibited (Jensen, T. J., Loo, M. A., Pind, S., Williams, D. B., Goldberg, A. L., and Riordan, J. R. (1995) Cell 83, 129-135). In this study, we use two independent techniques, pulse-chase labeling and a noninvasive fluorescence cell-based assay, to investigate the proteolytic pathways underlying the degradation of misfolded CFTR. Here we report that only inhibitors of the proteasome have a significant effect on preventing the degradation of CFTR, whereas cell-permeable inhibitors of lysosomal degradation, autophagy, and several classes of protease had no measurable effect on CFTR degradation, when used either alone or in combination with the specific proteasome inhibitor carbobenzoxy-l-leucyl-leucyl-l-leucinal (MG132). Our results suggest that ubiquitin-proteasome-mediated degradation is the dominant pathway for disposal of misfolded CFTR in mammalian cells and provide new mechanistic insight into endoplasmic reticulum-associated degradation.
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PMID:A principal role for the proteasome in endoplasmic reticulum-associated degradation of misfolded intracellular cystic fibrosis transmembrane conductance regulator. 1181 94

We investigated putative mechanisms by which nitric oxide modulates cystic fibrosis transmembrane conductance regulator (CFTR) expression and function in epithelial cells. Immunoprecipitation followed by Western blotting, as well as immunocytochemical and cell surface biotinylation measurements, showed that incubation of both stably transduced (HeLa) and endogenous CFTR expressing (16HBE14o-, Calu-3, and mouse tracheal epithelial) cells with 100 microm diethylenetriamine NONOate (DETA NONOate) for 24-96 h decreased both intracellular and apical CFTR levels. Calu-3 and mouse tracheal epithelial cells, incubated with DETA NONOate but not with 100 microm 8-bromo-cGMP for 96 h, exhibited reduced cAMP-activated short circuit currents when mounted in Ussing chambers. Exposure of Calu-3 cells to nitric oxide donors resulted in the nitration of a number of proteins including CFTR. Nitration was augmented by proteasome inhibition, suggesting a role for the proteasome in the degradation of nitrated proteins. Our studies demonstrate that levels of nitric oxide that are likely to be encountered in the vicinity of airway cells during inflammation may nitrate CFTR resulting in enhanced degradation and decreased function. Decreased levels and function of normal CFTR may account for some of the cystic fibrosis-like symptoms that occur in chronic inflammatory lung diseases associated with increased NO production.
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PMID:Reactive oxygen nitrogen species decrease cystic fibrosis transmembrane conductance regulator expression and cAMP-mediated Cl- secretion in airway epithelia. 1219 70

Proteins comprising the first nucleotide-binding- and R-domains of wild-type and Delta F508 cystic fibrosis transmembrane conductance regulator (CFTR) have been synthesised by in vitro transcription/translation. The kinetics and extent of degradation of wild-type and Delta F508 cytoplasmic domain proteins in rabbit reticulocyte lysates, in which proteasome activity was inhibited, were similar, with a half-life of approximately 4h. The results show for the first time, that the benzo(c)quinolizinium compounds, MPB-07 and MPB-91, selectively inhibit degradation of the Delta F508 cytoplasmic domain protein. Studies using protease inhibitors demonstrated that both Delta F508 and wild-type proteins are substrates for cysteine proteases. The studies provide evidence that benzo(c)quinolizinium compounds protect a proteolytic cleavage site by direct binding to the first cytoplasmic domain of Delta F508-CFTR and this is a likely mechanism for increasing Delta F508-CFTR trafficking in intact cells.
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PMID:Benzo(c)quinolizinium drugs inhibit degradation of Delta F508-CFTR cytoplasmic domain. 1250 15


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