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)

Ubiquitin-proteasome-mediated destruction of rate-limiting proteins is required for timely progression through the main cell cycle transitions. The anaphase-promoting complex (APC), periodically activated by the Cdh1 subunit, represents one of the major cellular ubiquitin ligases which, in Saccharomyces cerevisiae and Drosophila spp., triggers exit from mitosis and during G(1) prevents unscheduled DNA replication. In this study we investigated the importance of periodic oscillation of the APC-Cdh1 activity for the cell cycle progression in human cells. We show that conditional interference with the APC-Cdh1 dissociation at the G(1)/S transition resulted in an inability to accumulate a surprisingly broad range of critical mitotic regulators including cyclin B1, cyclin A, Plk1, Pds1, mitosin (CENP-F), Aim1, and Cdc20. Unexpectedly, although constitutively assembled APC-Cdh1 also delayed G(1)/S transition and lowered the rate of DNA synthesis during S phase, some of the activities essential for DNA replication became markedly amplified, mainly due to a progressive increase of E2F-dependent cyclin E transcription and a rapid turnover of the p27(Kip1) cyclin-dependent kinase inhibitor. Consequently, failure to inactivate APC-Cdh1 beyond the G(1)/S transition not only inhibited productive cell division but also supported slow but uninterrupted DNA replication, precluding S-phase exit and causing massive overreplication of the genome. Our data suggest that timely oscillation of the APC-Cdh1 ubiquitin ligase activity represents an essential step in coordinating DNA replication with cell division and that failure of mechanisms regulating association of APC with the Cdh1 activating subunit can undermine genomic stability in mammalian cells.
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PMID:Nonperiodic activity of the human anaphase-promoting complex-Cdh1 ubiquitin ligase results in continuous DNA synthesis uncoupled from mitosis. 1100 57

Treating HepG2 cells with MG132 for 4 h to inhibit proteasomal activity increased androgen receptor immunoreactivity in two major bands with molecular weights of 102 and 110 kDa by 77% each (P < 0. 05). MG132 treatment also increased the overall level of polyubiquitinated proteins between 66 and 220 kDa by 140% (P < 0.05). Antiubiquitin immunoreactivity comigrating with the androgen receptor bands was also increased by MG132 treatment. Two other proteasome inhibitors, lactacystin and epoxomycin, caused similar increases in the androgen receptor in HepG2 cells. Proteosome-inhibition studies conducted in LNCaP cells also showed that the two major androgen receptor bands with molecular weights of 102 and 110 kDa were increased by 85 and 115%, respectively (P < 0. 05 for both) by MG132 treatment. Overall levels of polyubiquitinated proteins with molecular weights between 66 and 220 kDa increased 365%. Ubiquitin immunoreactivity comigrating with the androgen receptor bands was also significantly increased. Thus inhibiting proteasomes in two human androgen-responsive cell lines increases endogenous androgen receptor levels as well as androgen receptor-associated ubiquitin-modified immunoreactivity. The regulation of steady-state levels of endogenous androgen receptor by proteasomal degradation could be involved in its rapid turnover in the absence of ligand and would provide a mechanism for limiting androgen responses. A PEST sequence similar to one in the vitamin D receptor is present in the hinge region of all known mammalian androgen receptors, suggesting that it may function in proteasome-mediated androgen receptor turnover.
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PMID:Inhibiting proteasomes in human HepG2 and LNCaP cells increases endogenous androgen receptor levels. 1100 97

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.
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PMID:Activation of atypical protein kinase C zeta by caspase processing and degradation by the ubiquitin-proteasome system. 1101 47

Alzheimer's disease (AD) is characterized by the presence of neurofibrillary tangles (NFT), senile plaques, and cerebrovascular deposits of amyloid-beta. Ubiquitin has also been shown to be present in some of the inclusions characteristic of this disease. To obtain further insight into the role played by the ubiquitin pathway in AD, we investigated the capacity of postmortem samples of cerebral cortex from normal and AD patients to form high-molecular-weight ubiquitin-protein conjugates. Activity of the ubiquitin-activating enzyme (E1) and ubiquitin-conjugating enzymes (E2) involved in the ubiquitin pathway was also determined. In normal samples, the amount of high-molecular-weight ubiquitin-protein conjugates (HMW-UbPC) in cytosol increased with incubation time, whereas, in samples of AD cases, these were almost undetectable. The addition of an adult rat fraction, enriched in ubiquitinating enzymes, restored the capacity of AD brain cytosolic fraction to form conjugates. The trypsin-like proteolytic activity of the 26S proteasome was found to be decreased in AD cytosol brain. Assay of the activity of E1 and E2 by thiol-ester formation revealed a significant decrease in AD samples. Moreover, Western blotting using a specific antibody against E1 showed a dramatic drop of this enzyme in the cytosolic fraction, whereas normal levels were found in the particulate fraction, suggesting a possible delocalization of the enzyme. Our results suggest that a failure in the ubiquitination enzymatic system in brain cytosol may contribute to fibrillar pathology in AD.
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PMID:Defective ubiquitination of cerebral proteins in Alzheimer's disease. 1102 Feb 23

Ubiquitin-dependent proteolysis is catalyzed by the 26S proteasome, a dynamic complex of 32 different proteins whose mode of assembly and mechanism of action are poorly understood, in part due to the difficulties encountered in purifying the intact complex. Here we describe a one-step affinity method for purifying intact 26S proteasomes, 19S regulatory caps, and 20S core particles from budding yeast cells. Affinity-purified 26S proteasomes hydrolyze both model peptides and the ubiquitinated Cdk inhibitor Sic1. Affinity purifications performed in the absence of ATP or presence of the poorly hydrolyzable analog ATP-gamma-S unexpectedly revealed that a large number of proteins, including subunits of the skp1-cullin-F-box protein ligase (SCF) and anaphase-promoting complex (APC) ubiquitin ligases, copurify with the 19S cap. To identify these proteasome-interacting proteins, we used a recently developed method that enables the direct analysis of the composition of large protein complexes (DALPC) by mass spectrometry. Using DALPC, we identified more than 24 putative proteasome-interacting proteins, including Ylr421c (Daq1), which we demonstrate to be a new subunit of the budding yeast 19S cap, and Ygr232w (Nas6), which is homologous to a subunit of the mammalian 19S cap (PA700 complex). Additional PIPs include the heat shock proteins Hsp70 and Hsp82, the deubiquitinating enzyme Ubp6, and proteins involved in transcriptional control, mitosis, tubulin assembly, RNA metabolism, and signal transduction. Our data demonstrate that nucleotide hydrolysis modulates the association of many proteins with the 26S proteasome, and validate DALPC as a powerful tool for rapidly identifying stoichiometric and substoichiometric components of large protein assemblies.
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PMID:Proteasomal proteomics: identification of nucleotide-sensitive proteasome-interacting proteins by mass spectrometric analysis of affinity-purified proteasomes. 1102 46

TRAF6 is a signal transducer in the NF-kappaB pathway that activates IkappaB kinase (IKK) in response to proinflammatory cytokines. We have purified a heterodimeric protein complex that links TRAF6 to IKK activation. Peptide mass fingerprinting analysis reveals that this complex is composed of the ubiquitin conjugating enzyme Ubc13 and the Ubc-like protein Uev1A. We find that TRAF6, a RING domain protein, functions together with Ubc13/Uev1A to catalyze the synthesis of unique polyubiquitin chains linked through lysine-63 (K63) of ubiquitin. Blockade of this polyubiquitin chain synthesis, but not inhibition of the proteasome, prevents the activation of IKK by TRAF6. These results unveil a new regulatory function for ubiquitin, in which IKK is activated through the assembly of K63-linked polyubiquitin chains.
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PMID:Activation of the IkappaB kinase complex by TRAF6 requires a dimeric ubiquitin-conjugating enzyme complex and a unique polyubiquitin chain. 2941 May 30

Presenilin is an essential gene for development that when disrupted leads to a neurogenic phenotype that closely resembles Notch loss of function in Drosophila. In humans, many naturally occurring mutations in Presenilin 1 or 2 cause early onset Alzheimer's disease. Both loss of expression and overexpression of Presenilin suggested a role for this protein in the localization of Armadillo/beta-catenin. In blastoderm stage Presenilin mutants, Arm is aberrantly distributed, often in Ubiquitin-immunoreactive cytoplasmic inclusions predominantly located basally in the cell. These inclusions were not observed in loss of function Notch mutants, suggesting that failure to process Notch is not the only consequence of the loss of Presenilin function. Human presenilin 1 expressed in Drosophila produces embryonic phenotypes resembling those associated with mutations in Armadillo and exhibited reduced Armadillo at the plasma membrane that is likely due to retention of Armadillo in a complex with Presenilin. The interaction between Armadillo/beta-catenin and Presenilin 1 requires a third protein which may be delta-catenin. Our results suggest that Presenilin may regulate the delivery of a multiprotein complex that regulates Armadillo trafficking between the adherens junction and the proteasome.
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PMID:Presenilin affects arm/beta-catenin localization and function in Drosophila. 1107 66

The ubiquitin-proteasome system fulfills an essential function in eukaryotes by controlling the levels of crucial intracellular regulatory proteins. In this system, a specific type of polyubiquitin chain acts as the proximal signal for targeting substrates to 26S proteasomes for degradation. Recent results have revealed important determinants of polyubiquitin-chain recognition by proteasomes, helping to explain the biological rationale behind this novel signaling mechanism.
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PMID:Ubiquitin in chains. 1108 66

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.
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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.
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PMID:In vivo Structure/Function analysis of the Drosophila fat facets deubiquitinating enzyme gene. 1110 77


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