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)

Programmed cell death (PCD) is a fundamental component of development in virtually all animals. Despite the ubiquity of this phenomenon, little is known about what tells a cell to die, and less still about the physiological and molecular mechanisms that bring about death. One system that has proven to be very amenable for the study of PCD is the intersegmental muscle (ISM) of the tobacco hawkmoth Manduca sexta. These giant muscle cells are used during the eclosion (emergence) behavior of the adult moth, and then die during the subsequent 30 h. This review uses the ISMs as a model system to address questions that are basic to any cell death system, including the following: (1) how do cells know when to die; (2) what physiological changes accompany death; (3) what are the molecular mechanisms that mediate death; and (4) do all cells die by the same process? For the ISMs, the trigger for PCD is a decline in the circulating titer of the insect molting hormone, 20-hydroxyecdysone (20-HE). During cell death there are rapid decreases in both the myofibrillar sensitivity to intracellular calcium and the resulting force of fiber contraction. The ability of the ISMs to undergo PCD requires the repression and activation of specific genes. Two of the repressed genes encode actin and myosin. One of the upregulated presumptive cell-death genes encodes polyubiquitin, which appears to play a critical role in the rapid proteolysis that accompanies ISM death.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Insect muscle as a model for programmed cell death. 146 90

In plants Ca2+ plays a crucial role as second messenger. Thus calmodulin is one of the most important signal transducing molecules for metabolic regulation in plants. Previously we showed that bovine testis calmodulin can be covalently coupled at one site to ubiquitin in a Ca2(+)-dependent manner in the presence of ATP/Mg2+ by ubiquityl-calmodulin synthetase. Since calmodulin from spinach has 13 amino acid sequence differences to bovine calmodulin - two of them in Ca2(+)-binding loops - it was unclear, whether a conjugation of ubiquitin to this molecule would be possible. In this paper it is shown that calmodulin from spinach and a similar calmodulin from the mold Neurospora crassa can be covalently conjugated to ubiquitin in a Ca2(+)-dependent manner. It is shown that higher molecular mass conjugates containing up to three ubiquitin molecules per calmodulin are obtained. Experiments with methylated ubiquitin demonstrate that, as with vertebrate calmodulins, only one lysine residue is linked to ubiquitin and that the incorporation of additional ubiquitin molecules leads to a polyubiquitin chain.
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PMID:Plant and fungus calmodulins are polyubiquitinated at a single site in a Ca2(+)-dependent manner. 217 31

Ubiquitin is a protein of 76 amino acids found in every eukaryotic cell. Although ubiquitin is implicated in ATP-dependent nonlysosomal protein degradation and is also conjugated to specific cellular proteins, the role played by ubiquitin in cellular events has not been defined. We report that purified ubiquitin has intrinsic proteolytic activity and demonstrate that this activity is comparable to that of other well-characterized proteases. Monoclonal antibodies specific to ubiquitin inhibit proteolysis. Ubiquitin has protease activity over a broad pH range with an optimum at pH 8.0. It is stimulated by Ca2+ and is inhibited by high concentrations of phenylmethylsulfonyl fluoride and diisopropyl fluorophosphate. Ubiquitin will cleave proteins at a limited number of sites. We propose that the ubiquitination of a protein can convert that protein into an ad hoc specific protease and models are presented as to how this can play a role in regulating a variety of cellular events.
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PMID:Ubiquitin has intrinsic proteolytic activity: implications for cellular regulation. 303 47

We tested the role of different intracellular proteolytic pathways in sepsis-induced muscle proteolysis. Sepsis was induced in rats by cecal ligation and puncture; controls were sham operated. Total and myofibrillar proteolysis was determined in incubated extensor digitorum longus muscles as release of tyrosine and 3-methylhistidine, respectively. Lysosomal proteolysis was assessed by using the lysosomotropic agents NH4Cl, chloroquine, leupeptin, and methylamine. Ca(2+)-dependent proteolysis was determined in the absence or presence of Ca2+ or by blocking the Ca(2+)-dependent proteases calpain I and II. Energy-dependent proteolysis was determined in muscles depleted of ATP by 2-deoxyglucose and 2.4-dinitrophenol. Muscle ubiquitin mRNA and the concentrations of free and conjugated ubiquitin were determined by Northern and Western blots, respectively, to assess the role of the ATP-ubiquitin-dependent proteolytic pathway. Total and myofibrillar protein breakdown was increased during sepsis by 50 and 440%, respectively. Lysosomal and Ca(2+)-dependent proteolysis was similar in control and septic rats. In contrast, energy-dependent total and myofibrillar protein breakdown was increased by 172% and more than fourfold, respectively, in septic muscle. Ubiquitin mRNA was increased severalfold in septic muscle. The results suggest that the increase in muscle proteolysis during sepsis is due to an increase in nonlysosomal energy-dependent protein breakdown, which may involve the ubiquitin system.
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PMID:Sepsis stimulates nonlysosomal, energy-dependent proteolysis and increases ubiquitin mRNA levels in rat skeletal muscle. 798 81

Metabolic acidosis often leads to loss of body protein due mainly to accelerated protein breakdown in muscle. To identify which proteolytic pathway is activated, we measured protein degradation in incubated epitrochlearis muscles from acidotic (NH4Cl-treated) and pair-fed rats under conditions that block different proteolytic systems. Inhibiting lysosomal and calcium-activated proteases did not reduce the acidosis-induced increase in muscle proteolysis. However, when ATP production was also blocked, proteolysis fell to the same low level in muscles of acidotic and control rats. Acidosis, therefore, stimulates selectively an ATP-dependent, nonlysosomal, proteolytic process. We also examined whether the activated pathway involves ubiquitin and proteasomes (multicatalytic proteinases). Acidosis was associated with a 2.5- to 4-fold increase in ubiquitin mRNA in muscle. There was no increase in muscle heat shock protein 70 mRNA or in kidney ubiquitin mRNA, suggesting specificity of the response. Ubiquitin mRNA in muscle returned to control levels within 24 h after cessation of acidosis. mRNA for subunits of the proteasome (C2 and C3) in muscle were also increased 4-fold and 2.5-fold, respectively, with acidosis; mRNA for cathepsin B did not change. These results are consistent with, but do not prove that acidosis stimulates muscle proteolysis by activating the ATP-ubiquitin-proteasome-dependent, proteolytic pathway.
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PMID:Metabolic acidosis stimulates muscle protein degradation by activating the adenosine triphosphate-dependent pathway involving ubiquitin and proteasomes. 818 44

Ubiquitin-dependent proteolysis is required for cell cycle progression. Here, we demonstrate that the proteasome is activated during in vivo Xenopus egg activation, induced by treatment with the calcium ionophore A23187. It was found that activation is due to the calcium-induced assembly of the 26 S proteasome from the 20 S proteasome. We propose that proteasome activation is regulated by cell cycle calcium transients, which are controlled upstream by an endogenous cell cycle oscillator that is independent of the cyclin-dependent kinase cycle.
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PMID:Activation of the proteasome during Xenopus egg activation implies a link between proteasome activation and intracellular calcium release. 857 36

The promoter activity of an Acanthamoeba polyubiquitin gene was analyzed in its homologous system. A modified calcium phosphate transfection method using a neomycin marker vector was developed to achieve highly efficient transfection of the Acanthamoeba polyubiquitin gene into Acanthamoeba cells. In this transfection procedure, the calcium phosphate-DNA complex was formed gradually in the medium during incubation with cells and precipitated on the cells. The crucial factors for obtaining efficient transfection were the pH (6.95) of the transfection buffer used for the calcium phosphate precipitation and the amount (25 micrograms/96-well tissue culture plate) and form (circular) of transfecting DNA. Under these conditions, Acanthamoeba isolate 1B6 was transfected at an efficiency of about 40% with the constructed vector pOPSBU, a pOP13CAT-based polyubiquitin gene incorporated neomycin resistance vector. Acanthamoeba polyphaga was transfected at an efficiency of about 10% with this vector. Transfection of both Acanthamoeba strains appeared to result in low copy plasmid integration (about two copies per cell are suggested). The chloramphenicol acetyltransferase (CAT) assays showed that the promoter of the Acanthamoeba polyubiquitin gene in the constructed vector was especially strong in A. polyphaga, thus the pOPSBU-Acanthamoeba system may be useful for the construction of cDNA expression libraries, as well as for the expression of cloned genes.
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PMID:Stable transfection of Acanthamoeba. 909 Jan 13

Proteolytic digestion of ryanodine receptor (RyR) purified from skeletal muscle generated 25 short peptides. The amino acid sequences of two, 'KC5' and 'KC7', were absent from the RyR primary structure deduced by cDNA cloning. The sequence of KC7 corresponded to the N-terminus of the 12 kDa FK506-binding protein, which associates with the RyR and modulates its Ca2+ release channel (CRC) function. The sequence of KC5 was not similar to any proteins in the databases searched at that time. In the present study, the sequence of KC5 was compared to proteins in the current Swissprot database release and corresponds most closely to S5a, a proteasome subunit. Since S5a targets the 26S proteasome to polyubiquitinated proteins, and inositol 1,4,5-trisphosphate receptors, a related class of CRC, are down-regulated by a polyubiquitin-dependent mechanism in hormone stimulated cells, the abundance of RyRs may be controlled by association with this regulatory subunit.
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PMID:Possible regulation of the skeletal muscle ryanodine receptor by a polyubiquitin binding subunit of the 26S proteasome. 957 Nov 68

The human epidermoid carcinoma-derived cell line MA1, established by introduction of the adenovirus E1A 12 S cDNA linked to the hormone-inducible promoter, elicits apoptosis after induction of E1A12 S in response to dexamethasone. E1A expression caused accumulation of wild type p53 more than 10-fold within 24 h after dexamethasone treatment. The cell lines that express E1A mutants containing a deletion either in the amino terminus or the conserved region 1 were unable to accumulate p53. p53 accumulated was degraded efficiently in vitro in the S10-0 extract (S10-0) prepared from MA1 cells in an ATP and ubiquitin-dependent manner, but not in S10-24 prepared after treatment with dexamethasone for 24 h. The p53 polyubiquitination activity in S100-0 was calcium-dependent and reduced greatly in S100-24. Ubiquitin affinity chromatography revealed that p53 ubiquitination activity in eluates thought to contain ubiquitin-conjugating enzymes decreased greatly in S100-24 as compared with S100-0. The accumulation of p53 was accompanied by the increase in the level of Mdm2, which has been shown to degrade p53 through binding to it. The high p53 level, however, was maintained until the late stage of the apoptotic process. These results indicate that the stabilization of p53 by E1A occurs through modification of a ubiquitin-specific enzyme(s) in the ubiquitin-proteasome pathway.
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PMID:Stabilization of p53 by adenovirus E1A occurs through its amino-terminal region by modification of the ubiquitin-proteasome pathway. 968 42

Ubiquitin is often implicated as a specific tag for protein degradation via the ubiquitin system although only a limited number of physiological proteins have been shown to be degraded in their native tissues via this pathway in vivo. Ubiquitin may also, however, have other functions of a regulatory nature (non-catabolic ubiquitylation). The ubiquitylation of calmodulin appears to fall into this category. Ubiquitin is linked to free calmodulin in the presence of the second messenger Ca2+ by the enzyme ubiquitin-calmodulin ligase (uCaM synthetase: EC 6.3.2.21) and there is no evidence that this step is followed by degradation of calmodulin via the ATP-dependent 26-S protease. Due to a lack of natural substrates and sufficient tissue material, only a few components of the ubiquitin system have been obtained in truly homogeneous form from reticulocytes. We therefore decided to attempt this for the calmodulin ligase. The enzymic components of the uCaM synthetase system copurified over several steps and could be highly enriched by a novel sample displacement technique on an ion-exchange resin. A fractionation of the synthetase components by affinity chromatography on ubiquitin-Sepharose and calmodulin-Sepharose yielded two essentially inactive components: a ubiquitin-Sepharose binding fraction (uCaM Syn-F1) and a calmodulin-Sepharose binding fraction (uCaM Syn-F2). The full activity of uCaM synthetase can be reconstituted when these two fractions are reunited. uCaM Syn-F1 could then be separated from all other enzymes of ubiquitin metabolism and, employing the second component with the natural substrate calmodulin, could be purified over 3500-fold to homogeneity. The ability to catalyze its own thiol labile ubiquitylation identified it as a member of the ubiquitin-activating enzyme family (E1). The homogeneous preparation contained a single protein of molecular mass 213 +/- 21 kDa (mean +/- SEM) as determined by gel filtration. The molecular mass of the monomer was determined by electrospray ion mass spectrometry to 112,140 +/- 47 Da (mean +/- SD). N-terminal sequence analysis (20 amino acids) led to a single N-terminal peptide beginning at residue 57 of the known rabbit cDNA sequence. No ragged N-terminus was detected, as would be expected by the action of an aminopeptidase or other peptidases of low specificity. The monomer molecular mass calculated from the cDNA sequence (Arg57-Arg1058) is 111,975 Da, characterizing this enzyme from reticulocytes as a homodimer of 224 kDa.
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PMID:The ubiquityl-calmodulin synthetase system from rabbit reticulocytes: isolation of the ubiquitin-binding first component, a ubiquitin-activating enzyme. 971 91


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