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Ortega Z, Lucas JJ. Ubiquitin-proteasome system involvement in Huntington's disease. Front Mol Neurosci 2014; 7:77. [PMID: 25324717 PMCID: PMC4179678 DOI: 10.3389/fnmol.2014.00077] [Citation(s) in RCA: 75] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2014] [Accepted: 09/10/2014] [Indexed: 11/13/2022] Open
Abstract
Huntington’s disease (HD) is a genetic autosomal dominant neurodegenerative disease caused by the expansion of a CAG repeat in the huntingtin (htt) gene. This triplet expansion encodes a polyglutamine stretch (polyQ) in the N-terminus of the high molecular weight (348-kDa) and ubiquitously expressed protein htt. Normal individuals have between 6 and 35 CAG triplets, while expansions longer than 40 repeats lead to HD. The onset and severity of the disease depend on the length of the polyQ tract: the longer the polyglutamine stretch (polyQ) is, the earlier the disease begins and the more severe the symptoms are. One of the main histopathological hallmarks of HD is the presence of intraneuronal proteinaceous inclusion bodies, whose prominent and invariant feature is the presence of ubiquitin (Ub); therefore, they can be detected with anti-ubiquitin and anti-proteasome antibodies. This, together with the observation that mutations in components of the ubiquitin–proteasome system (UPS) give rise to some neurodegenerative diseases, suggests that UPS impairment may be causative of HD. Even though the link between disrupted Ub homeostasis and protein aggregation to HD is undisputed, the functional significance of these correlations and their mechanistic implications remains unresolved. Moreover, there is no consistent evidence documenting an accompanying decrease in levels of free Ub or disruption of Ub pool dynamics in neurodegenerative disease or models thus suggesting that the Ub-conjugate accumulation may be benign and just underlie lesion in 26S function. In this chapter we will elaborate on the different studies that have been performed using different experimental approaches, in order to shed light to this matter.
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Affiliation(s)
- Zaira Ortega
- Department of Molecular Biology, Centro de Biología Molecular "Severo Ochoa," Consejo Superior de Investigaciones Científicas (CSIC), Universidad Autónoma de Madrid (UAM), Centro Investigación Biomédica en Red Enfermedades Neurodegenerativa (CIBERNED), Madrid, Spain
| | - Jose J Lucas
- Department of Molecular Biology, Centro de Biología Molecular "Severo Ochoa," Consejo Superior de Investigaciones Científicas (CSIC), Universidad Autónoma de Madrid (UAM), Centro Investigación Biomédica en Red Enfermedades Neurodegenerativa (CIBERNED), Madrid, Spain
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Li XJ, Li S. Proteasomal dysfunction in aging and Huntington disease. Neurobiol Dis 2010; 43:4-8. [PMID: 21145396 DOI: 10.1016/j.nbd.2010.11.018] [Citation(s) in RCA: 77] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2010] [Revised: 11/23/2010] [Accepted: 11/30/2010] [Indexed: 12/13/2022] Open
Abstract
Protein degradation plays a central role in many cellular functions. Misfolded and damaged proteins are removed from the cells to avoid toxicity. Eukaryotic cells have two main routes for clearing misfolded or toxic proteins: the ubiquitin-proteasome and autophagy-lysosome pathways. The ubiquitin-proteasome system (UPS) is ubiquitously present in the cytoplasm, nucleus, and various subcellular regions whereas autophagy predominantly functions in the cytoplasm. The activity of the UPS often remains at a high level, whereas basal autophagy constitutively occurs at low levels in cells for the performance of homeostatic functions. Because of the presence of the UPS in the nucleus, the UPS function may be more important for clearing misfolded proteins in the nucleus. Polyglutamine diseases, including Huntington disease (HD), show the age-dependent neurological symptoms and the accumulation of misfolded proteins that are often found in the nucleus. The selective neuropathology in HD is also found to associate with the preferential accumulation of the disease protein huntingtin in neuronal cells. Although it is clear that the UPS is important for clearing mutant huntingtin, it remains unclear whether aging or HD affects the capacity of neuronal UPS to remove toxic and misfolded proteins. In this review, we focus on the relationship between the UPS function and aging as well as Huntington disease. We also discuss findings that suggest that aging is a more important factor that can negatively impact the function of the UPS. This article is part of a Special Issue entitled "Autophagy and protein degradation in neurological diseases."
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Affiliation(s)
- Xiao-Jiang Li
- Department of Human Genetics, Emory University School of Medicine, Atlanta, GA 30322, USA.
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Day IN, Thompson RJ. UCHL1 (PGP 9.5): Neuronal biomarker and ubiquitin system protein. Prog Neurobiol 2010; 90:327-62. [DOI: 10.1016/j.pneurobio.2009.10.020] [Citation(s) in RCA: 141] [Impact Index Per Article: 10.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2009] [Revised: 10/18/2009] [Accepted: 10/21/2009] [Indexed: 12/16/2022]
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Membrane-associated farnesylated UCH-L1 promotes alpha-synuclein neurotoxicity and is a therapeutic target for Parkinson's disease. Proc Natl Acad Sci U S A 2009; 106:4635-40. [PMID: 19261853 DOI: 10.1073/pnas.0806474106] [Citation(s) in RCA: 108] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Ubiquitin C-terminal hydrolase-L1 (UCH-L1) is linked to Parkinson's disease (PD) and memory and is selectively expressed in neurons at high levels. Its expression pattern suggests a function distinct from that of its widely expressed homolog UCH-L3. We report here that, in contrast to UCH-L3, UCH-L1 exists in a membrane-associated form (UCH-L1(M)) in addition to the commonly studied soluble form. C-terminal farnesylation promotes the association of UCH-L1 with cellular membranes, including the endoplasmic reticulum. The amount of UCH-L1(M) in transfected cells is shown to correlate with the intracellular level of alpha-synuclein, a protein whose accumulation is associated with neurotoxicity and the development of PD. Reduction of UCH-L1(M) in cell culture models of alpha-synuclein toxicity by treatment with a farnesyltransferase inhibitor (FTI-277) reduces alpha-synuclein levels and increases cell viability. Proteasome function is not affected by UCH-L1(M), suggesting that it may negatively regulate the lysosomal degradation of alpha-synuclein. Therefore, inhibition of UCH-L1 farnesylation may be a therapeutic strategy for slowing the progression of PD and related synucleinopathies.
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Intracellular degradation of misfolded proteins in polyglutamine neurodegenerative diseases. ACTA ACUST UNITED AC 2008; 59:245-52. [PMID: 18773920 DOI: 10.1016/j.brainresrev.2008.08.003] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2008] [Revised: 08/15/2008] [Accepted: 08/17/2008] [Indexed: 01/15/2023]
Abstract
A number of neurodegenerative diseases, including Alzheimer's, Parkinson's, and polyglutamine diseases, are characterized by the age-dependent formation of intracellular protein aggregates and neurodegeneration. Although there is some debate surrounding the role of these aggregates in neurotoxicity, the formation of aggregates is known to reflect the accumulation of misfolded and toxic proteins. The degradation of misfolded proteins occurs mainly via the ubiquitin-proteasome and autophagy pathways. In neuronal cells, polyglutamine protein inclusions are present predominantly in the nucleus, which is not accessible to autophagy. It remains unclear how the ubiquitin-proteasomal and autophagy pathways remove misfolded proteins in the different subcellular regions of neurons, where disease proteins become misfolded and aggregated in an age-dependent manner. Here we discuss the key findings to date about the roles of the ubiquitin-proteasome system and autophagy in polyglutamine diseases. Understanding how these two pathways function to clear mutant polyglutamine proteins will further the development of effective treatments for polyglutamine and other neurodegenerative diseases.
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Vitte AL, Jalinot P. Intracellular delivery of peptides via association with ubiquitin or SUMO-1 coupled to protein transduction domains. BMC Biotechnol 2008; 8:24. [PMID: 18312666 PMCID: PMC2287181 DOI: 10.1186/1472-6750-8-24] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2007] [Accepted: 02/29/2008] [Indexed: 01/18/2023] Open
Abstract
Background We previously developed small hybrid proteins consisting of SUMO-1 linked to an heptapeptide fused to the Tat protein transduction domain (PTD). The heptapeptide motif was selected from a library of random sequences to specifically bind HIV-1 regulatory proteins Tat or Rev. These constructs, named SHP, are able to enter primary lymphocytes and some of them inhibit HIV-1 replication. Considering these positive results and other data from the literature, we further tested the ability of ubiquitin or SUMO-1 linked to various PTD at their N-terminus to deliver within cells proteins or peptides fused downstream of their diglycine motif. In this system it is expected that the intracellular ubiquitin or SUMO-1 hydrolases cleave the PTD-Ub or PTD-SUMO-1 modules from the cargo polypeptide, thereby allowing its delivery under an unmodified form. Results Several bacterial expression vectors have been constructed to produce modular proteins containing from the N- to the C-terminus: the FLAG epitope, a cleavage site for a protease, a PTD, human ubiquitin or SUMO-1, and either GFP or the HA epitope. Nine different PTDs were tested, including the Tat basic domain, wild type or with various mutations, and stretches of arginine or lysine. It was observed that some of these PTDs, mainly the Tat PTD and seven or nine residues long polyarginine motifs, caused association of the hybrid proteins with cells, but none of these constructs were delivered to the cytosol. This conclusion was derived from biochemical and immunofluorescence studies, and also from the fact that free cargo protein resulting from cleavage by proteases after ubiquitin or SUMO-1 was never observed. However, in agreement with our previous observations, mutation of the diglycine motif into alanine-arginine, as in the SHP constructs, allows cytosol entry demonstrated by immunofluorescence observations on living cells and by cell fractionation analyses. This process results from a non-endocytic pathway. Conclusion Our observations indicate that fusion of SUMO-1 to a peptide-PTD module allows generation of a stable hybrid protein that is easily produced in bacteria and which efficiently enters into cells but this property necessitates mutation of the diglycine motif at the end of SUMO-1, thereby impairing delivery of the peptide alone.
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Affiliation(s)
- Anne-Laure Vitte
- LBMC, UMR5239 CNRS - ENS de Lyon, IFR 128 Biosciences Lyon Gerland 46 Allée d'Italie, 69364 Lyon cedex 07, France.
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Arnold JJ, Bernal A, Uche U, Sterner DE, Butt TR, Cameron CE, Mattern MR. Small ubiquitin-like modifying protein isopeptidase assay based on poliovirus RNA polymerase activity. Anal Biochem 2005; 350:214-21. [PMID: 16356462 PMCID: PMC2094218 DOI: 10.1016/j.ab.2005.11.001] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2005] [Revised: 10/26/2005] [Accepted: 11/01/2005] [Indexed: 11/23/2022]
Abstract
The ubiquitin-proteasome pathway is the major nonlysosomal proteolytic system in eukaryotic cells responsible for regulating the level of many key regulatory molecules within the cells. Modification of cellular proteins by ubiquitin and ubiquitin-like proteins, such as small ubiquitin-like modifying protein (SUMO), plays an essential role in a number of biological schemes, and ubiquitin pathway enzymes have become important therapeutic targets. Ubiquitination is a dynamic reversible process; a multitude of ubiquitin ligases and deubiquitinases (DUBs) are responsible for the wide-ranging influence of this pathway as well as its selectivity. The DUB enzymes serve to maintain adequate pools of free ubiquitin and regulate the ubiquitination status of cellular proteins. Using SUMO fusions, a novel assay system, based on poliovirus RNA-dependent RNA polymerase activity, is described here. The method simplifies the isopeptidase assay and facilitates high-throughput analysis of these enzymes. The principle of the assay is the dependence of the viral polymerase on a free N terminus for activity; accordingly, the polymerase is inactive when fused at its N terminus to SUMO or any other ubiquitin-like protein. The assay is sensitive, reproducible, and adaptable to a high-throughput format for use in screens for inhibitors/activators of clinically relevant SUMO proteases and deubiquitinases.
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Affiliation(s)
- Jamie J. Arnold
- 201 Althouse Laboratory, Pennsylvania State University, University Park, PA 16802, USA
| | | | - Uzo Uche
- 201 Althouse Laboratory, Pennsylvania State University, University Park, PA 16802, USA
| | - David E. Sterner
- 201 Althouse Laboratory, Pennsylvania State University, University Park, PA 16802, USA
| | | | - Craig E. Cameron
- 201 Althouse Laboratory, Pennsylvania State University, University Park, PA 16802, USA
| | - Michael R. Mattern
- Progenra Inc., Malvern, PA 19355, USA
- * Corresponding author. Fax: +1 610 644 8616., E-mail address: (M.R. Mattern)
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Bingol B, Schuman EM. Synaptic protein degradation by the ubiquitin proteasome system. Curr Opin Neurobiol 2005; 15:536-41. [PMID: 16150592 DOI: 10.1016/j.conb.2005.08.016] [Citation(s) in RCA: 99] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2005] [Accepted: 08/25/2005] [Indexed: 11/15/2022]
Abstract
Synaptic plasticity -- the modulation of synaptic strength between a presynaptic terminal and a postsynaptic dendrite -- is thought to be a mechanism that underlies learning and memory. It has become increasingly clear that regulated protein synthesis is an important mechanism used to regulate the protein content of synapses that results in changes in synaptic strength. Recent experiments have highlighted a role for the opposing process, that is, regulated protein degradation via the ubiquitin-proteasome system, in synaptic plasticity. These recent findings raise exciting questions as to how proteasomal activity can regulate synapses over different temporal and spatial scales.
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Affiliation(s)
- Baris Bingol
- Division of Biology 114-96, California Institute of Technology, Howard Hughes Medical Institute Pasadena, CA 91125, USA
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Tian QB, Okano A, Nakayama K, Miyazawa S, Endo S, Suzuki T. A novel ubiquitin-specific protease, synUSP, is localized at the post-synaptic density and post-synaptic lipid raft. J Neurochem 2003; 87:665-75. [PMID: 14535949 DOI: 10.1046/j.1471-4159.2003.02024.x] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Recent reports suggest an important role for protein ubiquitination in synaptic plasticity. We cloned, from the rat brain, a novel gene that encoded an ubiquitin-specific protease (USP), and termed this protein synaptic ubiquitin-specific protease (synUSP, GenBankTM Accession no. AB073880). The homologous human gene was mapped to a locus on chromosome 1p36.12. The deduced synUSP protein consisted of 1036 amino acids, and possessed an ubiquitin-like domain at the C-terminus, Cys- and His-boxes, leucine zipper motifs, and six amino acid-repeats of L/ILCPHG. The protein possessed de-ubiquitinating activity toward a model substrate, as expected from its sequence. The protein of 125 kDa was present in the rat brain; in particular, it was enriched in the post-synaptic density and the dendritic lipid raft fractions. The immunostaining of cortical neurons confirmed the post-synaptic localization. The mRNA for synUSP was localized to dendrites, as well as somas, of neuronal cells. Thus, both the mRNA and the protein were localized in the post-synaptic compartments. These results suggest a regulatory mechanism for the ubiquitin-related system at the post-synaptic sites.
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Affiliation(s)
- Qing Bao Tian
- Department of Neuroplasty, Research Institute on Aging and Adaptation, Shinshu University Graduate School of Medicine, Matsumoto, Japan
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Deubiquitinating enzymes--the importance of driving in reverse along the ubiquitin-proteasome pathway. Int J Biochem Cell Biol 2003; 35:590-605. [PMID: 12672452 DOI: 10.1016/s1357-2725(02)00392-8] [Citation(s) in RCA: 130] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
Ubiquitination of proteins is now recognized to target proteins for degradation by the proteasome and for internalization into the lysosomal system, as well as to modify functions of some target proteins. Although much progress has been made in characterizing enzymes that link ubiquitin to proteins, our understanding of deubiquitinating enzymes is less developed. These enzymes are involved in processing the products of ubiquitin genes which all encode fusion proteins, in negatively regulating the functions of ubiquitination (editing), in regenerating free ubiquitin after proteins have been targeted to the proteasome or lysosome (recycling) and in salvaging ubiquitin from possible adducts formed with small molecule nucleophiles in the cell. A large number of genes encode deubiquitinating enzymes suggesting that many have highly specific and regulated functions. Indeed, recent findings provide strong support for the concept that ubiquitination is regulated by both specific pathways of ubiquitination and deubiquitination. Interestingly, many of these enzymes are localized to subcellular structures or to molecular complexes. These localizations play important roles in determining specificity of function and can have major influences on their catalytic activities. Future studies, particularly aimed at characterizing the interacting partners and potential substrates in these complexes as well as at determining the effects of loss of function of specific deubiquitinating enzymes will rapidly advance our understanding of the important roles of these enzymes as biological regulators.
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Kieffer AE, Goumon Y, Ruh O, Chasserot-Golaz S, Nullans G, Gasnier C, Aunis D, Metz-Boutigue MH. The N- and C-terminal fragments of ubiquitin are important for the antimicrobial activities. FASEB J 2003; 17:776-8. [PMID: 12594174 DOI: 10.1096/fj.02-0699fje] [Citation(s) in RCA: 78] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Secretory granules of chromaffin cells contain catecholamines and several antimicrobial peptides derived from chromogranins and proenkephalin-A. These peptides are secreted in the extracellular medium following exocytosis. Here, we show that ubiquitin is stored in secretory chromaffin granules and released into the circulation upon stimulation of chromaffin cells. We also show that the C-terminal fragment (residues 65-76) of ubiquitin displays, at the micromolar range, a lytic antifungal activity. Using confocal laser scan microscopy and rhodamine-labeled synthetic peptides, we could demonstrate that the C-terminal peptide (residues 65-76) is able to cross the cell wall and the plasma membrane of fungi and to accumulate in fungi, whereas the N-terminal peptide (residues 1-34) is stopped at the fungal wall level. Furthermore, these two peptides act synergistically to kill filamentous fungi. Because of the interaction of the C-terminal sequence of ubiquitin with calmodulin, the synthetic peptide (residues 65-76) was tested in vitro against calmodulin-dependent calcineurin, an enzyme crucial for fungal growth. This peptide was found to inhibit the phosphatase activity of calcineurin. Our data show a new property of ubiquitin C-terminal-derived peptide (65-76) that could be used with N-terminal peptide (1-34) as a new potent antifungal agent.
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Affiliation(s)
- Anne-Estelle Kieffer
- INSERM Unité 575, IFR 37, Physiopathologie du Système Nerveux, Strasbourg, France
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Malakhov MP, Malakhova OA, Kim KI, Ritchie KJ, Zhang DE. UBP43 (USP18) specifically removes ISG15 from conjugated proteins. J Biol Chem 2002; 277:9976-81. [PMID: 11788588 DOI: 10.1074/jbc.m109078200] [Citation(s) in RCA: 376] [Impact Index Per Article: 17.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023] Open
Abstract
UBP43 shows significant homology to well characterized ubiquitin-specific proteases and previously was shown to hydrolyze ubiquitin-beta-galactosidase fusions in Escherichia coli. In our assays, the activity of UBP43 toward Ub fusions was undetectable in vitro directing us to investigate the possibility of Ub-like proteins such as SUMO, Nedd8, and ISG15 as probable substrates. We consequently demonstrate that UBP43 can efficiently cleave only ISG15 fusions including native ISG15 conjugates linked via isopeptide bonds. In addition to commonly used methods we introduce a new experimental design featuring ISG15-UBP43 fusion self-processing. Deletion of the UBP43 gene in mouse leads to a massive increase of ISG15 conjugates in tissues indicating that UBP43 is a major ISG15-specific protease. UBP43 is the first bona fide ISG15-specific protease reported. Both ISG15 and UBP43 genes are known to be strongly induced by interferon, genotoxic stress, and viral infection. We postulate that UBP43 is necessary to maintain a critical cellular balance of ISG15-conjugated proteins in both healthy and stressed organisms.
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Affiliation(s)
- Michael P Malakhov
- Department of Molecular and Experimental Medicine, The Scripps Research Institute, La Jolla, California 92037, USA
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Bauer SH, Wiechers MF, Bruns K, Przybylski M, Stuermer CA. Isolation and identification of the plasma membrane-associated intracellular protein reggie-2 from goldfish brain by chromatography and Fourier-transform ion cyclotron resonance mass spectrometry. Anal Biochem 2001; 298:25-31. [PMID: 11673891 DOI: 10.1006/abio.2001.5330] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The neuronal protein reggie-2 is localized at the cytoplasmic face of the plasma membrane and participates, together with reggie-1, in the formation of plasma membrane microdomains. Reggie-2 exhibits several potential phosphorylation sites but whether the relevant sites are modified accordingly is not yet known. In order to obtain a detailed, molecular characterization of the primary structure of the native protein, an effective procedure for the isolation of the different reggie proteins from animal tissue is required. The specific properties of the proteins, particularly their membrane association and low abundance, make approaches for isolation such as affinity chromatography and 2D gel electrophoresis unfeasible. This study describes a rapid and efficient procedure for the isolation of reggie-2 by use of two consecutive HPLC steps and subsequent SDS-PAGE. The protein fractions were characterized by SDS-PAGE and Western blot analysis as well as by mass spectrometry. In the primary structure analysis by matrix-assisted laser desorption-ionization mass spectrometry (MALDI-MS), the efficiency of high-resolution Fourier-transform ion cyclotron resonance-MALDI-MS was demonstrated, enabling the direct, unequivocal, and sensitive characterization of posttranslationally and/or chemically modified proteins.
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Affiliation(s)
- S H Bauer
- Department of Biology, University of Konstanz, Konstanz, 78457, Germany
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Lee J, Jee C, Lee JI, Lee MH, Lee MH, Koo HS, Chung CH, Ahnn J. A deubiquitinating enzyme, UCH/CeUBP130, has an essential role in the formation of a functional microtubule-organizing centre (MTOC) during early cleavage in C. elegans. Genes Cells 2001; 6:899-911. [PMID: 11683918 DOI: 10.1046/j.1365-2443.2001.00471.x] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
BACKGROUND Deubiquitinating enzymes generate monomeric ubiquitin in protein degradation pathways and are known to be important for the early development in many organisms. RESULTS RNA interference experiments targeted for a UBP homologue, UCH/CeUBP130, in C. elegans resulted in cell division defective embryos. Immunostaining localized UCH/CeUBP130 in the sperm and at the microtubule-organizing centre (MTOC) during early cleavage. Furthermore, the embryonic lethal phenotype was rescued by mating with wild-type males. CONCLUSIONS Since it is known that the MTOC in the fertilized embryo is contributed by sperm asters in C. elegans, we suggest that UCH/CeUBP130 and ubiquitin protein degradation pathways may be involved in microtubule-based sperm aster formation. Therefore UCH/CeUBP130 is necessary for the formation of a functional MTOC in the fertilized embryo of C. elegans.
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Affiliation(s)
- J Lee
- Department of Life Science, Kwangju Institute of Science and Technology, Kwangju 500-712, Korea
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Abstract
A growing number of important regulatory proteins within cells are modified by conjugation of ubiquitin, a well-conserved 76-amino-acid polypeptide. The ubiquitinated proteins are targeted to proteasome for degradation or alternative metabolic fates, such as triggering of plasma membrane endocytosis and trafficking to vacuoles or lysosomes. Deubiquitination, reversal of this modification, is being recognized as an important regulatory step. Deubiquitinating enzymes are cysteine proteases that specifically cleave off ubiquitin from ubiquitin-conjugated protein substrates as well as from its precursor proteins. Genome sequencing projects have identified more than 90 deubiquitinating enzymes, making them the largest family of enzymes in the ubiquitin system. This review will concentrate on recent important findings as well as new insights into the diversity and emerging roles of deubiquitinating enzymes in the ubiquitin-dependent pathway.
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Affiliation(s)
- C H Chung
- Department of Molecular Biology, College of Natural Sciences, Seoul National University, Seoul, 151-742, Korea.
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