Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P62988 (Ubiquitin)
 4,326 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Atypical protein kinase C zeta (PKCzeta) is known to transduce signals that influence cell proliferation and survival. Here we show that recombinant human caspases can process PKCzeta at three sites in the hinge region between the regulatory and catalytic domains. Caspase-3, -6, -7, and -8 chiefly cleaved human PKCzeta at EETD downward arrowG, and caspase-3 and -7 also cleaved PKCzeta at DGMD downward arrowG and DSED downward arrowL, respectively. Processing of PKCzeta expressed in transfected cells occurred chiefly at EETD downward arrowG and DGMD downward arrowG and produced carboxyl-terminal polypeptides that contained the catalytic domain. Epitope-tagged PKCzeta that lacked the regulatory domain was catalytically active following expression in HeLa cells. Induction of apoptosis in HeLa cells by tumor necrosis factor alpha plus cycloheximide evoked the conversion of full-length epitope-tagged PKCzeta to two catalytic domain polypeptides and increased PKCzeta activity. A caspase inhibitor, zVAD-fmk, prevented epitope-tagged PKCzeta processing and activation following the induction of apoptosis. Induction of apoptosis in rat parotid C5 cells produced catalytic domain polypeptides of endogenous PKCzeta and increased PKCzeta activity. Caspase inhibitors prevented the increase in PKCzeta activity and production of the catalytic domain polypeptides. Treatment with lactacystin, a selective inhibitor of the proteasome, caused polyubiquitin-PKCzeta conjugates to accumulate in cells transfected with the catalytic domain or full-length PKCzeta, or with a PKCzeta mutant that was resistant to caspase processing. We conclude that caspases process PKCzeta to carboxyl-terminal fragments that are catalytically active and that are degraded by the ubiquitin-proteasome pathway.
J Biol Chem 2000 Dec 22
PMID:Activation of atypical protein kinase C zeta by caspase processing and degradation by the ubiquitin-proteasome system. 1101 47

The ubiquitin-dependent proteasome-mediated (Ub-Pr) degradation pathway has been shown to regulate a large variety of substrates, including nuclear, cytosolic, and membrane proteins. In mammalian systems, polyubiquitin modification has been identified in a number of cell surface receptors for more than a decade; however, its biological significance has remained unclear until recently. For growth factor receptors with intrinsic tyrosine kinase domains, polyubiquitination is believed to trigger the internalization and subsequent degradation via the lysosomal pathway. In this study we provide the first evidence that non-tyrosine kinase-type cytokine surface receptors, IL-9R alpha-chain, IL-2 receptor ss-chain, and erythropoietin receptor, can be polyubiquitinated and degraded by proteasomes. The Ub-Pr pathway regulates both the basal level turnover and the ligand-induced degradation of the receptors. A previously identified putative molecular chaperon, valosin-containing protein, undergoes tyrosine phosphorylation in a cytokine-dependent manner and associates with the receptor complexes following receptor engagement, suggesting that valosin-containing protein may target the ubiquitinated receptors to the proteasome for degradation.
J Immunol 2000 Dec 01
PMID:Involvement of the ubiquitin-proteasome pathway in the degradation of nontyrosine kinase-type cytokine receptors of IL-9, IL-2, and erythropoietin. 1108 75

The Drosophila Fat facets protein is a deubiquitinating enzyme required for patterning the developing compound eye. Ubiquitin, a 76-amino-acid polypeptide, serves as a tag to direct proteins to the proteasome, a protein degradation complex. Deubiquitinating enzymes are a large group of proteins that cleave ubiquitin-protein bonds. Fat facets belongs to a class of deubiquitinating enzymes called Ubps that share a conserved catalytic domain. Fat facets is unique among them in its large size and also because Fat facets is thought to deubiquitinate a specific substrate thereby preventing its proteolysis. Here we asked which portions of the Fat facets protein are essential for its function. P-element constructs that express partial Fat facets proteins were tested for function. In addition, the DNA sequences of 12 mutant fat facets alleles were determined. Finally, regions of amino acid sequence similarity in 18 Drosophila Ubps revealed by the Genome Project were identified. The results indicate functions for specific conserved amino acids in the catalytic region of Fat facets and also indicate that regions of the protein both N- and C-terminal to the catalytic region are required for Fat facets function.
Genetics 2000 Dec
PMID:In vivo Structure/Function analysis of the Drosophila fat facets deubiquitinating enzyme gene. 1110 77

Ubiquitin-specific proteases (UBPs) are a family of unique hydrolases that specifically remove polypeptides covalently linked via peptide or isopeptide bonds to the C-terminal glycine of ubiquitin. UBPs help regulate the ubiquitin/26S proteolytic pathway by generating free ubiquitin monomers from their initial translational products, recycling ubiquitins during the breakdown of ubiquitin-protein conjugates, and/or by removing ubiquitin from specific targets and thus presumably preventing target degradation. Here, we describe a family of 27 UBP genes from Arabidopsis that contain both the conserved cysteine (Cys) and histidine boxes essential for catalysis. They can be clustered into 14 subfamilies based on sequence similarity, genomic organization, and alignments with their closest relatives from other organisms, with seven subfamilies having two or more members. Recombinant AtUBP2 functions as a bona fide UBP: It can release polypeptides attached to ubiquitins via either alpha- or epsilon-amino linkages by an activity that requires the predicted active-site Cys within the Cys box. From the analysis of T-DNA insertion mutants, we demonstrate that the AtUBP1 and 2 subfamily helps confer resistance to the arginine analog canavanine. This phenotype suggests that the AtUBP1 and 2 enzymes are needed for abnormal protein turnover in Arabidopsis.
Plant Physiol 2000 Dec
PMID:The ubiquitin-specific protease family from Arabidopsis. AtUBP1 and 2 are required for the resistance to the amino acid analog canavanine. 1111 97

Ubiquitin-mediated proteolysis regulates the activity of diverse receptor systems. Here, we identify Smurf2, a C2-WW-HECT domain ubiquitin ligase and show that Smurf2 associates constitutively with Smad7. Smurf2 is nuclear, but binding to Smad7 induces export and recruitment to the activated TGF beta receptor, where it causes degradation of receptors and Smad7 via proteasomal and lysosomal pathways. IFN gamma, which stimulates expression of Smad7, induces Smad7-Smurf2 complex formation and increases TGF beta receptor turnover, which is stabilized by blocking Smad7 or Smurf2 expression. Furthermore, Smad7 mutants that interfere with recruitment of Smurf2 to the receptors are compromised in their inhibitory activity. These studies thus define Smad7 as an adaptor in an E3 ubiquitin-ligase complex that targets the TGF beta receptor for degradation.
Mol Cell 2000 Dec
PMID:Smad7 binds to Smurf2 to form an E3 ubiquitin ligase that targets the TGF beta receptor for degradation. 1116 10

Ubiquitin (UB), an intracellular protein that binds to other proteins to target them for proteolysis, is associated with Mallory hyalin (MH), which supports a biopsy diagnosis of nonalcoholic steatohepatitis (NASH). We analyzed 54 liver biopsy specimens from 49 patients with a clinical diagnosis of NASH for immunoreactive UB and multiple features of necroinflammation, fibrosis, and Prussian blue-positive iron to determine whether the presence of immunoreactive UB increases detection of MH or correlates with other features of cell injury or mutations of the HFE gene. MH and UB were graded. Analysis for HFE gene mutations was performed in 48 patients. Biopsy diagnoses were distributed as follows: NASH, 42; steatosis, 10; and nonspecific changes, 2. UB was present in 20 specimens and MH in 23. Of 31 specimens with 0 MH, 6 had UB; of 14 with 1 + (questionable) MH, 7 had 1+ or 2+ UB. UB correlated positively and significantly with the diagnosis and grade of NASH, presence of MH, cell swelling, lobular inflammation, and fibrosis. Immunostaining for UB may enhance detection of MH in questionable cases, support the diagnosis of NASH, and indicate which patients may be at risk for progression of disease.
Am J Clin Pathol 2000 Dec
PMID:Ubiquitin as a marker of cell injury in nonalcoholic steatohepatitis. 1133 74

Ubiquitin-B+1 (UBB+1) is a mutant ubiquitin that accumulates in the neurones of patients with Alzheimer's disease (AD). Here we report on the biochemical and functional differences between ubiquitin and UBB+1 and the effect of the mutant protein on neuronal cells. UBB+1 lacks the capacity to ubiquitinate, and although it is ubiquitinated itself, UBB+1 is not degraded by the ubiquitin-proteasomal system and is quite stable in neuronal cells. Overexpression of UBB+1 in neuroblastoma cells significantly induces nuclear fragmentation and cell death. Our results demonstrate that accumulation of UBB+1 in neurones is detrimental and may contribute to neuronal dysfunction in AD patients.
FASEB J 2001 Dec
PMID:Mutant ubiquitin expressed in Alzheimer's disease causes neuronal death. 1172 44

Ubiquitin-conjugated proteins in human colorectal cancer tissues were analyzed by the immunoprecipitation with the antibody FK2 against conjugated ubiquitin followed with SDS-PAGE. In these immunoprecipitable proteins, a 38-kDa protein was abundant in the tumor regions but almost absent in the adjacent normal regions in 17/26 patients, thus we attempted to purify it. Using immunoaffinity chromatography with the antibody FK2 followed by gel filtration and SDS-PAGE, approximately 10 pmol of this protein was separated from 34 g of the pooled cancerous tissue and transferred onto a PVDF membrane. The 38-kDa protein was further digested with Achromobacter protease I, resulting in several peptide fragments. Amino acid sequences of these peptides showed complete sequence identity to those derived from either ubiquitin or phosphoglycerate mutase-B, suggesting that the 38-kDa protein is monoubiquitinated phosphoglycerate mutase-B, whose calculated mass is 37,369 Da. Western blot using an antibody against phosphoglycerate mutase-B revealed the presence of the 38-kDa protein in the anti-ubiquitin immunoprecipitates derived from the tumor regions, but not from normal counterparts. In addition, part of non-ubiquitinated phosphoglycerate mutase-B (29 kDa) was also found in the anti-ubiquitin immunoprecipitates, whose levels were higher in the tumor regions than in the adjacent normal regions. These results suggest that monoubiquitination of phosphoglycerate mutase-B as well as formation of a noncovalent complex containing ubiquitin and phosphoglycerate mutase-B increases in colorectal cancer and novel modification of phosphoglycerate mutase-B might have a pathophysiological role.
Int J Cancer 2001 Dec 01
PMID:Purification and identification of monoubiquitin-phosphoglycerate mutase B complex from human colorectal cancer tissues. 1174 60

Ubiquitin-like proteins (ub-lps) are conjugated by a conserved enzymatic pathway, involving ATP-dependent activation at the C terminus by an activating enzyme (E1) and formation of a thiolester intermediate with a conjugating enzyme (E2) prior to ligation to the target. Ubc9, the E2 for SUMO, synthesizes polymeric chains in the presence of its E1 and MgATP. To better understand conjugation of ub-lps, we have performed mutational analysis of Saccharomyces cerevisiae Ubc9p, which conjugates the SUMO family member Smt3p. We have identified Ubc9p surfaces involved in thiolester bond and Smt3p-Smt3p chain formation. The residues involved in thiolester bond formation map to a surface we show is the E1 binding site, and E2s for other ub-lps are likely to bind to their E1s at a homologous site. We also find that this same surface binds Smt3p. A mutation that impairs binding to E1 but not Smt3p impairs thiolester bond formation, suggesting that it is the E1 interaction at this site that is crucial. Interestingly, other E2s and their relatives also use this same surface for binding to ubiquitin, E3s, and other proteins, revealing this to be a multipurpose binding site and suggesting that the entire E1-E2-E3 pathway has coevolved for a given ub-lp.
J Biol Chem 2002 Dec 06
PMID:Identification of a multifunctional binding site on Ubc9p required for Smt3p conjugation. 1235 63

It has been well documented that Mdm2 and its homologue MdmX not only are critical negative regulators of the tumor suppressor p53 but that both Mdm2 and MdmX interact to affect the function of the other. The mechanisms through which these effects are manifested, however, remain unclear. Although Mdm2 has been established as a RING finger ubiquitin ligase, MdmX has not been shown to possess this activity despite the extensive sequence homology between their respective RING finger domains. Here we demonstrate that MdmX acts as a ubiquitin ligase in vitro, being capable of autoubiquitination, as well as mediating the ubiquitination of p53. The addition of Mdm2 to in vitro ubiquitination assays containing MdmX results in a synergistic increase of ubiquitin conjugation. Analysis of the resulting ubiquitin conjugates reveals that this observed synergy reflects an increase in Mdm2 ubiquitination. This study also suggests that ubiquitination of Mdm2 and MdmX may not serve as a signal for degradation, as we show that each are capable of synthesizing non-lysine 48 polyubiquitin chains and, in fact, utilize multiple lysine linkages. Taken together, these findings suggest a more active role for MdmX in the Mdm2-MdmX-p53 regulatory network than has been proposed previously.
J Biol Chem 2002 Dec 20
PMID:MdmX is a RING finger ubiquitin ligase capable of synergistically enhancing Mdm2 ubiquitination. 1239 2


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