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You S, Xu J, Guo Y, Guo X, Zhang Y, Zhang N, Sun G, Sun Y. E3 ubiquitin ligase WWP2 as a promising therapeutic target for diverse human diseases. Mol Aspects Med 2024; 96:101257. [PMID: 38430667 DOI: 10.1016/j.mam.2024.101257] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2023] [Revised: 02/05/2024] [Accepted: 02/13/2024] [Indexed: 03/05/2024]
Abstract
Mammalian E3 ubiquitin ligases have emerged in recent years as critical regulators of cellular homeostasis due to their roles in targeting substrate proteins for ubiquitination and triggering subsequent downstream signals. In this review, we describe the multiple roles of WWP2, an E3 ubiquitin ligase with unique and important functions in regulating a wide range of biological processes, including DNA repair, gene expression, signal transduction, and cell-fate decisions. As such, WWP2 has evolved to play a key role in normal physiology and diseases, such as tumorigenesis, skeletal development and diseases, immune regulation, cardiovascular disease, and others. We attempt to provide an overview of the biochemical, physiological, and pathophysiological roles of WWP2, as well as open questions for future research, particularly in the context of putative therapeutic opportunities.
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Affiliation(s)
- Shilong You
- Department of Cardiology, First Hospital of China Medical University, Shenyang, Liaoning, China
| | - Jiaqi Xu
- Department of Cardiology, First Hospital of China Medical University, Shenyang, Liaoning, China
| | - Yushan Guo
- Department of Cardiology, First Hospital of China Medical University, Shenyang, Liaoning, China
| | - Xiaofan Guo
- Department of Cardiology, First Hospital of China Medical University, Shenyang, Liaoning, China
| | - Ying Zhang
- Department of Cardiology, First Hospital of China Medical University, Shenyang, Liaoning, China; Institute of Health Sciences, China Medical University, Shenyang, Liaoning, China.
| | - Naijin Zhang
- Department of Cardiology, First Hospital of China Medical University, Shenyang, Liaoning, China; Institute of Health Sciences, China Medical University, Shenyang, Liaoning, China; NHC Key Laboratory of Advanced Reproductive Medicine and Fertility, National Health Commission, China Medical University, Shenyang, Liaoning, China.
| | - Guozhe Sun
- Department of Cardiology, First Hospital of China Medical University, Shenyang, Liaoning, China.
| | - Yingxian Sun
- Department of Cardiology, First Hospital of China Medical University, Shenyang, Liaoning, China; Institute of Health Sciences, China Medical University, Shenyang, Liaoning, China.
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Suen TC, DeBruyne JP. Lysine-independent ubiquitination and degradation of REV-ERBα involves a bi-functional degradation control sequence at its N-terminus. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.05.01.538963. [PMID: 37205588 PMCID: PMC10187254 DOI: 10.1101/2023.05.01.538963] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/21/2023]
Abstract
REV-ERBα and REV-ERBβ proteins play crucial roles in linking the circadian system to overt daily rhythms in mammalian physiology and behavior. In most tissues, REV-ERBα protein robustly cycles such that it is detected only within a tight interval of 4-6 hours each day, suggesting both its synthesis and degradation are tightly controlled. Several ubiquitin ligases are known to drive REV-ERBα degradation, but how they interact with REV-ERBα and which lysine residues they ubiquitinate to promote degradation are unknown. In this study, we attempted to identify both ubiquitin-ligase-binding and ubiquitination sites within REV-ERBα required for its degradation. Surprisingly, mutating all lysine residues, the common sites for ubiquitin conjugation, in REV-ERBα to arginines (K20R), did very little to impair its degradation in cells. K20R were degraded much faster by co-expression of two E3 ligases, SIAH2 or SPSB4, suggesting possible N-terminal ubiquitination. To explore this, we examined if small deletions at the N-terminus of REV-ERBα would alter its degradation. Interestingly, deletion of amino acid (AA) residues 2 to 9 (delAA2-9) clearly resulted in a less stable REV-ERBα. We found that it was the length (i.e. 8 AA), and not the specific sequence, that confers stability in this region. Simultaneously, we also mapped the interaction site of the E3 ligase SPSB4 to this same region, specifically requiring AA4-9 of REV-ERBα. Thus, the first 9 AA of REV-ERBα has two opposing roles in regulating REV-ERBα turnover. Further, deleting eight additional AAs (delAA2-17) from the N-terminus strongly prevents REV-ERBα degradation. Combined, these results suggest that complex interactions within the first 25AAs potentially act as an endogenous 'switch' that allows REV-ERBα to exist in a stabilized conformation in order to accumulate at one time of day, but then rapidly shifts to a destabilized form, to enhance its removal at the end of its daily cycle.
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Oswald J, Constantine M, Adegbuyi A, Omorogbe E, Dellomo AJ, Ehrlich ES. E3 Ubiquitin Ligases in Gammaherpesviruses and HIV: A Review of Virus Adaptation and Exploitation. Viruses 2023; 15:1935. [PMID: 37766341 PMCID: PMC10535929 DOI: 10.3390/v15091935] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2023] [Revised: 09/10/2023] [Accepted: 09/12/2023] [Indexed: 09/29/2023] Open
Abstract
For productive infection and replication to occur, viruses must control cellular machinery and counteract restriction factors and antiviral proteins. Viruses can accomplish this, in part, via the regulation of cellular gene expression and post-transcriptional and post-translational control. Many viruses co-opt and counteract cellular processes via modulation of the host post-translational modification machinery and encoding or hijacking kinases, SUMO ligases, deubiquitinases, and ubiquitin ligases, in addition to other modifiers. In this review, we focus on three oncoviruses, Epstein-Barr virus (EBV), Kaposi's sarcoma herpesvirus (KSHV), and human immunodeficiency virus (HIV) and their interactions with the ubiquitin-proteasome system via viral-encoded or cellular E3 ubiquitin ligase activity.
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Affiliation(s)
| | | | | | | | | | - Elana S. Ehrlich
- Department of Biological Sciences, Towson University, Towson, MD 21252, USA
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Functional diversity: update of the posttranslational modification of Epstein-Barr virus coding proteins. Cell Mol Life Sci 2022; 79:590. [PMID: 36376593 DOI: 10.1007/s00018-022-04561-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2022] [Revised: 08/26/2022] [Accepted: 09/14/2022] [Indexed: 11/16/2022]
Abstract
Epstein-Barr virus (EBV), a human oncogenic herpesvirus with a typical life cycle consisting of latent phase and lytic phase, is associated with many human diseases. EBV can express a variety of proteins that enable the virus to affect host cell processes and evade host immunity. Additionally, these proteins provide a basis for the maintenance of viral infection, contribute to the formation of tumors, and influence the occurrence and development of related diseases. Posttranslational modifications (PTMs) are chemical modifications of proteins after translation and are very important to guarantee the proper biological functions of these proteins. Studies in the past have intensely investigated PTMs of EBV-encoded proteins. EBV regulates the progression of the latent phase and lytic phase by affecting the PTMs of its encoded proteins, which are critical for the development of EBV-associated human diseases. In this review, we summarize the PTMs of EBV-encoded proteins that have been discovered and studied thus far with focus on their effects on the viral life cycle.
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The Central Role of the Ubiquitin-Proteasome System in EBV-Mediated Oncogenesis. Cancers (Basel) 2022; 14:cancers14030611. [PMID: 35158879 PMCID: PMC8833352 DOI: 10.3390/cancers14030611] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2021] [Revised: 01/19/2022] [Accepted: 01/24/2022] [Indexed: 12/30/2022] Open
Abstract
Simple Summary Epstein–Barr virus (EBV) is the first discovered human tumor virus, which contributes to the oncogenesis of many human cancers. The ubiquitin–proteasome system is a key player during EBV-mediated oncogenesis and has been developed as a crucial therapeutic target for treatment. In this review, we briefly describe how EBV antigens can modulate the ubiquitin–proteasome system for targeted protein degradation and how they are regulated in the EBV life cycle to mediate oncogenesis. Additionally, the developed proteasome inhibitors are discussed for the treatment of EBV-associated cancers. Abstract Deregulation of the ubiquitin–proteasome system (UPS) plays a critical role in the development of numerous human cancers. Epstein–Barr virus (EBV), the first known human tumor virus, has evolved distinct molecular mechanisms to manipulate the ubiquitin–proteasome system, facilitate its successful infection, and drive opportunistic cancers. The interactions of EBV antigens with the ubiquitin–proteasome system can lead to oncogenesis through the targeting of cellular factors involved in proliferation. Recent studies highlight the central role of the ubiquitin–proteasome system in EBV infection. This review will summarize the versatile strategies in EBV-mediated oncogenesis that contribute to the development of specific therapeutic approaches to treat EBV-associated malignancies.
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Proulx J, Borgmann K, Park IW. Post-translational modifications inducing proteasomal degradation to counter HIV-1 infection. Virus Res 2020; 289:198142. [PMID: 32882242 DOI: 10.1016/j.virusres.2020.198142] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2020] [Revised: 08/20/2020] [Accepted: 08/21/2020] [Indexed: 12/14/2022]
Abstract
Post-translational modifications (PTMs) are integral to regulating a wide variety of cellular processes in eukaryotic cells, such as regulation of protein stability, alteration of celluar location, protein activity modulation, and regulation of protein interactions. HIV-1, like other eukaryotic viruses, and its infected host exploit the proteasomal degradation system for their respective proliferation and survival, using various PTMs, including but not limited to ubiquitination, SUMOylation, NEDDylation, interferon-stimulated gene (ISG)ylation. Essentially all viral proteins within the virions -- and in the HIV-1-infected cells -- interact with their cellular counterparts for this degradation, utilizing ubiquitin (Ub), and the Ub-like (Ubl) modifiers less frequently, to eliminate the involved proteins throughout the virus life cycle, from the entry step to release of the assembled virus particles. Such interplay is pivotal for, on the one hand, the cell to restrict proliferation of the infecting virus, and on the other, for molecular counteraction by the virus to overcome this cellular protein-imposed restriction. Recent reports indicate that not only viral/cellular proteins but also viral/viral protein interactions play vital roles in regulating viral protein stability. We hence give an overview of the molecular processes of PTMs involved in proteasomal degradation of the viral and cellular proteins, and the viral/viral and viral/cellular protein interplay in restriction and competition for HIV-1 vs. host cell survival. Insights in this realm could open new avenues for developing therapeutics against HIV-1 via targeting specific steps of the proteasome degradation pathway during the HIV-1 life cycle.
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Affiliation(s)
- Jessica Proulx
- Department of Pharmacology and Neuroscience, University of North Texas Health Science Center, Fort Worth, TX, 76107, United States
| | - Kathleen Borgmann
- Department of Pharmacology and Neuroscience, University of North Texas Health Science Center, Fort Worth, TX, 76107, United States
| | - In-Woo Park
- Microbiology, Immunology, and Genetics, University of North Texas Health Science Center, Fort Worth, TX, 76107, United States.
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Wang B, Zeng L, Merillat SA, Fischer S, Ochaba J, Thompson LM, Barmada SJ, Scaglione KM, Paulson HL. The ubiquitin conjugating enzyme Ube2W regulates solubility of the Huntington's disease protein, huntingtin. Neurobiol Dis 2017; 109:127-136. [PMID: 28986324 DOI: 10.1016/j.nbd.2017.10.002] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2017] [Revised: 08/29/2017] [Accepted: 10/01/2017] [Indexed: 12/20/2022] Open
Abstract
Huntington's disease (HD) is caused by a CAG repeat expansion that encodes a polyglutamine (polyQ) expansion in the HD disease protein, huntingtin (HTT). PolyQ expansion promotes misfolding and aggregation of mutant HTT (mHTT) within neurons. The cellular pathways, including ubiquitin-dependent processes, by which mHTT is regulated remain incompletely understood. Ube2W is the only ubiquitin conjugating enzyme (E2) known to ubiquitinate substrates at their amino (N)-termini, likely favoring substrates with disordered N-termini. By virtue of its N-terminal polyQ domain, HTT has an intrinsically disordered amino terminus. In studies employing immortalized cells, primary neurons and a knock-in (KI) mouse model of HD, we tested the effect of Ube2W deficiency on mHTT levels, aggregation and neurotoxicity. In cultured cells, deficiency of Ube2W activity markedly decreases mHTT aggregate formation and increases the level of soluble monomers, while reducing mHTT-induced cytotoxicity. Consistent with this result, the absence of Ube2W in HdhQ200 KI mice significantly increases levels of soluble monomeric mHTT while reducing insoluble oligomeric species. This study sheds light on the potential function of the non-canonical ubiquitin-conjugating enzyme, Ube2W, in this polyQ neurodegenerative disease.
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Affiliation(s)
- Bo Wang
- Department of Neurology, University of Michigan, Ann Arbor, MI 48109, USA; Neuroscience Program, University of Michigan, Ann Arbor, MI 48109, USA; Department of Dermatology, Ruijin Hospital, School of Medicine, Shanghai Jiaotong University, Shanghai, China
| | - Li Zeng
- Department of Neurology, University of Michigan, Ann Arbor, MI 48109, USA; Department of Neurology, Sichuan Provincial Academy of Medical Sciences and Sichuan Provincial People's Hospital, Chengdu, China
| | - Sean A Merillat
- Department of Neurology, University of Michigan, Ann Arbor, MI 48109, USA
| | - Svetlana Fischer
- Department of Neurology, University of Michigan, Ann Arbor, MI 48109, USA
| | - Joseph Ochaba
- Department of Neurobiology and Behavior, Institute of Memory Impairment and Neurological Disorders, University of California, Irvine, CA 92697, USA; Department of Psychiatry and Human Behavior, Institute of Memory Impairment and Neurological Disorders, University of California, Irvine, CA 92697, USA
| | - Leslie M Thompson
- Department of Neurobiology and Behavior, Institute of Memory Impairment and Neurological Disorders, University of California, Irvine, CA 92697, USA; Department of Psychiatry and Human Behavior, Institute of Memory Impairment and Neurological Disorders, University of California, Irvine, CA 92697, USA
| | - Sami J Barmada
- Department of Neurology, University of Michigan, Ann Arbor, MI 48109, USA
| | - Kenneth M Scaglione
- Neuroscience Research Center and Department of Biochemistry, Medical College of Wisconsin, Milwaukee, WI 53226, USA
| | - Henry L Paulson
- Department of Neurology, University of Michigan, Ann Arbor, MI 48109, USA; Neuroscience Program, University of Michigan, Ann Arbor, MI 48109, USA.
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Expression, Polyubiquitination, and Therapeutic Potential of Recombinant E6E7 from HPV16 Antigens Fused to Ubiquitin. Mol Biotechnol 2017; 59:46-56. [PMID: 28025776 DOI: 10.1007/s12033-016-9990-6] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Abstract
Ubiquitin-proteasome system plays an essential role in the immune response due to its involvement in the antigen generation and presentation to CD8+ T cells. Hereby, ubiquitin fused to antigens has been explored as an immunotherapeutic strategy that requires the activation of cytotoxic T lymphocytes. Here we propose to apply this ubiquitin fusion approach to a recombinant vaccine against human papillomavirus 16-infected cells. E6E7 multi-epitope antigen was fused genetically at its N- or C-terminal end to ubiquitin and expressed in Escherichia coli as inclusion bodies. The antigens were solubilized using urea and purified by nickel affinity chromatography in denatured condition. Fusion of ubiquitin to E6E7 resulted in marked polyubiquitination in vitro mainly when fused to the E6E7 N-terminal. When tested in a therapeutic scenario, the fusion of ubiquitin to E6E7 reinforced the anti-tumor protection and increased the E6/E7-specific cellular immune responses. Present results encourage the investigation of the adjuvant potential of the ubiquitin fusion to recombinant vaccines requiring CD8+ T cells.
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McDowell G, Philpott A. New Insights Into the Role of Ubiquitylation of Proteins. INTERNATIONAL REVIEW OF CELL AND MOLECULAR BIOLOGY 2016; 325:35-88. [DOI: 10.1016/bs.ircmb.2016.02.002] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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10
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Wang B, Merillat SA, Vincent M, Huber AK, Basrur V, Mangelberger D, Zeng L, Elenitoba-Johnson K, Miller RA, Irani DN, Dlugosz AA, Schnell S, Scaglione KM, Paulson HL. Loss of the Ubiquitin-conjugating Enzyme UBE2W Results in Susceptibility to Early Postnatal Lethality and Defects in Skin, Immune, and Male Reproductive Systems. J Biol Chem 2015; 291:3030-42. [PMID: 26601958 DOI: 10.1074/jbc.m115.676601] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2015] [Indexed: 12/21/2022] Open
Abstract
UBE2W ubiquitinates N termini of proteins rather than internal lysine residues, showing a preference for substrates with intrinsically disordered N termini. The in vivo functions of this intriguing E2, however, remain unknown. We generated Ube2w germ line KO mice that proved to be susceptible to early postnatal lethality without obvious developmental abnormalities. Although the basis of early death is uncertain, several organ systems manifest changes in Ube2w KO mice. Newborn Ube2w KO mice often show altered epidermal maturation with reduced expression of differentiation markers. Mirroring higher UBE2W expression levels in testis and thymus, Ube2w KO mice showed a disproportionate decrease in weight of these two organs (~50%), suggesting a functional role for UBE2W in the immune and male reproductive systems. Indeed, Ube2w KO mice displayed sustained neutrophilia accompanied by increased G-CSF signaling and testicular vacuolation associated with decreased fertility. Proteomic analysis of a vulnerable organ, presymptomatic testis, showed a preferential accumulation of disordered proteins in the absence of UBE2W, consistent with the view that UBE2W preferentially targets disordered polypeptides. These mice further allowed us to establish that UBE2W is ubiquitously expressed as a single isoform localized to the cytoplasm and that the absence of UBE2W does not alter cell viability in response to various stressors. Our results establish that UBE2W is an important, albeit not essential, protein for early postnatal survival and normal functioning of multiple organ systems.
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Affiliation(s)
- Bo Wang
- From the Departments of Neurology, Neuroscience Graduate Program, and
| | | | - Michael Vincent
- Molecular and Integrative Physiology and Computational Medicine and Bioinformatics
| | | | | | | | - Li Zeng
- From the Departments of Neurology
| | | | - Richard A Miller
- Pathology and Geriatrics Center, University of Michigan, Ann Arbor, Michigan 48109 and
| | | | | | - Santiago Schnell
- Molecular and Integrative Physiology and Computational Medicine and Bioinformatics
| | - Kenneth Matthew Scaglione
- Department of Biochemistry and Neuroscience Research Center, Medical College of Wisconsin, Milwaukee, Wisconsin 53226
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Varland S, Osberg C, Arnesen T. N-terminal modifications of cellular proteins: The enzymes involved, their substrate specificities and biological effects. Proteomics 2015; 15:2385-401. [PMID: 25914051 PMCID: PMC4692089 DOI: 10.1002/pmic.201400619] [Citation(s) in RCA: 127] [Impact Index Per Article: 14.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2014] [Revised: 03/04/2015] [Accepted: 04/21/2015] [Indexed: 01/18/2023]
Abstract
The vast majority of eukaryotic proteins are N-terminally modified by one or more processing enzymes. Enzymes acting on the very first amino acid of a polypeptide include different peptidases, transferases, and ligases. Methionine aminopeptidases excise the initiator methionine leaving the nascent polypeptide with a newly exposed amino acid that may be further modified. N-terminal acetyl-, methyl-, myristoyl-, and palmitoyltransferases may attach an acetyl, methyl, myristoyl, or palmitoyl group, respectively, to the α-amino group of the target protein N-terminus. With the action of ubiquitin ligases, one or several ubiquitin molecules are transferred, and hence, constitute the N-terminal modification. Modifications at protein N-termini represent an important contribution to proteomic diversity and complexity, and are essential for protein regulation and cellular signaling. Consequently, dysregulation of the N-terminal modifying enzymes is implicated in human diseases. We here review the different protein N-terminal modifications occurring co- or post-translationally with emphasis on the responsible enzymes and their substrate specificities.
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Affiliation(s)
- Sylvia Varland
- Department of Molecular Biology, University of Bergen, Bergen, Norway
| | - Camilla Osberg
- Department of Molecular Biology, University of Bergen, Bergen, Norway.,Department of Surgery, Haukeland University Hospital, Bergen, Norway
| | - Thomas Arnesen
- Department of Molecular Biology, University of Bergen, Bergen, Norway.,Department of Surgery, Haukeland University Hospital, Bergen, Norway
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Abstract
LMP2A is an EBV-encoded protein with three domains: (a) an N-terminal cytoplasmic domain, which has PY motifs that bind to WW domain-containing E3 ubiquitin ligases and an ITAM that binds to SH2 domain-containing proteins, (b) a transmembrane domain with 12 transmembrane segments that localizes LMP2A in cellular membranes, and (c) a 27-amino acid C-terminal domain which mediates homodimerization and heterodimerization of LMP2 protein isoforms. The most prominent two isoforms of the protein are LMP2A and LMP2B. The LMP2B isoform lacks the 19-amino acid N-terminal domain found in LMP2A, which modulates cellular signaling resulting in a baseline activation of B cells and degradation of cellular kinases leading to the downregulation of normal B cell signaling pathways. These two seemingly contradictory processes allow EBV to establish and maintain latency. LMP2 is expressed in many EBV-associated malignancies. While its antigenic properties may be useful in developing LMP2-specific immunity, the LMP2A N-terminal motifs also provide a basis to target LMP2A-modulated cellular kinases for the development of treatment strategies.
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Tooley JG, Schaner Tooley CE. New roles for old modifications: emerging roles of N-terminal post-translational modifications in development and disease. Protein Sci 2014; 23:1641-9. [PMID: 25209108 DOI: 10.1002/pro.2547] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2014] [Accepted: 09/08/2014] [Indexed: 01/07/2023]
Abstract
The importance of internal post-translational modification (PTM) in protein signaling and function has long been known and appreciated. However, the significance of the same PTMs on the alpha amino group of N-terminal amino acids has been comparatively understudied. Historically considered static regulators of protein stability, additional functional roles for N-terminal PTMs are now beginning to be elucidated. New findings show that N-terminal methylation, along with N-terminal acetylation, is an important regulatory modification with significant roles in development and disease progression. There are also emerging studies on the enzymology and functional roles of N-terminal ubiquitylation and N-terminal propionylation. Here, will discuss the recent advances in the functional studies of N-terminal PTMs, recount the new N-terminal PTMs being identified, and briefly examine the possibility of dynamic N-terminal PTM exchange.
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Affiliation(s)
- John G Tooley
- Department of Biochemistry and Molecular Biology, James Graham Brown Cancer Center, University of Louisville School of Medicine, Louisville, Kentucky
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Epstein-Barr virus latent membrane protein 2 effects on epithelial acinus development reveal distinct requirements for the PY and YEEA motifs. J Virol 2013; 87:13803-15. [PMID: 24109232 DOI: 10.1128/jvi.02203-13] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Epstein-Barr virus (EBV) is a gammaherpesvirus associated with numerous cancers, including the epithelial cancers nasopharyngeal carcinoma (NPC) and gastric carcinoma. The latent membrane protein 2 (LMP2) encoded by EBV is consistently detected in NPC tumors and promotes a malignant phenotype when expressed in epithelial cells by inducing transformation and migration and inhibiting differentiation. Grown in three dimensions (3D) on Matrigel, the nontumorigenic mammary epithelial cell line MCF10A forms hollow, spherical acinar structures that maintain normal glandular features. Expression of oncogenes in these cells allows for the study of multiple aspects of tumor development in a 3D culture system. This study sought to examine the effects of LMP2 on the generation of MCF10A acini. LMP2 expression induced abnormal acini that were large, misshapen, and filled, indicating that LMP2 induced proliferation, impaired cellular polarization, and induced resistance to cell death, leading to luminal filling. Induction of cell death resistance required the PY, immunoreceptor tyrosine activation motif (ITAM), and YEEA signaling domains of LMP2 and activation of the Src and Akt signaling pathways. The PY domain was required for the inhibition of anoikis and also the delayed proliferative arrest of the LMP2-expressing cells. In addition to directly altering acinus formation, expression of LMP2 also induced morphological and protein expression changes consistent with epithelial-mesenchymal transition (EMT) in a manner that required only the YEEA signaling motif of LMP2. These findings indicate that LMP2 has considerable transforming properties that are not evident in standard tissue culture and requires the ability of LMP2A to bind ubiquitin ligases and Src family kinases.
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Ciechanover A, Stanhill A. The complexity of recognition of ubiquitinated substrates by the 26S proteasome. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2013; 1843:86-96. [PMID: 23872423 DOI: 10.1016/j.bbamcr.2013.07.007] [Citation(s) in RCA: 117] [Impact Index Per Article: 10.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/30/2013] [Revised: 07/02/2013] [Accepted: 07/08/2013] [Indexed: 02/03/2023]
Abstract
The Ubiquitin Proteasome System (UPS) was discovered in two steps. Initially, APF-1 (ATP-dependent proteolytic Factor 1) later identified as ubiquitin (Ub), a hitherto known protein of unknown function, was found to covalently modify proteins. This modification led to degradation of the tagged protein by - at that time - an unknown protease. This was followed later by the identification of the 26S proteasome complex which is composed of a previously identified Multi Catalytic Protease (MCP) and an additional regulatory complex, as the protease that degrades Ub-tagged proteins. While Ub conjugation and proteasomal degradation are viewed as a continued process responsible for most of the regulated proteolysis in the cell, the two processes have also independent roles. In parallel and in the years that followed, the hallmark signal that links the substrate to the proteasome was identified as an internal Lys48-based polyUb chain. However, since these initial findings were described, our understanding of both ends of the process (i.e. Ub-conjugation to proteins, and their recognition and degradation), have advanced significantly. This enabled us to start bridging the ends of this continuous process which suffered until lately from limited structural data regarding the 26S proteasomal architecture and the structure and diversity of the Ub chains. These missing pieces are of great importance because the link between ubiquitination and proteasomal processing is subject to numerous regulatory steps and are found to function improperly in several pathologies. Recently, the molecular architecture of the 26S proteasome was resolved in great detail, enabling us to address mechanistic questions regarding the various molecular events that polyubiquitinated (polyUb) substrates undergo during binding and processing by the 26S proteasome. In addition, advancement in analytical and synthetic methods enables us to better understand the structure and diversity of the degradation signal. The review summarizes these recent findings and addresses the extrapolated meanings in light of previous reports. Finally, it addresses some of the still remaining questions to be solved in order to obtain a continuous mechanistic view of the events that a substrate undergoes from its initial ubiquitination to proteasomal degradation. This article is part of a Special Issue entitled: Ubiquitin-Proteasome System. Guest Editors: Thomas Sommer and Dieter H. Wolf.
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Affiliation(s)
- Aaron Ciechanover
- The David and Janet Polak Cancer and Vascular Biology Research Center, The Rappaport Faculty of Medicine and Research Institute, Technion-Israel Institute of Technology, Haifa 31096, Israel
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McDowell GS, Philpott A. Non-canonical ubiquitylation: mechanisms and consequences. Int J Biochem Cell Biol 2013; 45:1833-42. [PMID: 23732108 DOI: 10.1016/j.biocel.2013.05.026] [Citation(s) in RCA: 113] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2013] [Revised: 05/10/2013] [Accepted: 05/22/2013] [Indexed: 01/04/2023]
Abstract
Post-translational protein modifications initiate, regulate, propagate and terminate a wide variety of processes in cells, and in particular, ubiquitylation targets substrate proteins for degradation, subcellular translocation, cell signaling and multiple other cellular events. Modification of substrate proteins is widely observed to occur via covalent linkages of ubiquitin to the amine groups of lysine side-chains. However, in recent years several new modes of ubiquitin chain attachment have emerged. For instance, covalent modification of non-lysine sites in substrate proteins is theoretically possible according to basic chemical principles underlying the ubiquitylation process, and evidence is building that sites such as the N-terminal amine group of a protein, the hydroxyl group of serine and threonine residues and even the thiol groups of cysteine residues are all employed as sites of ubiquitylation. However, the potential importance of this "non-canonical ubiquitylation" of substrate proteins on sites other than lysine residues has been largely overlooked. This review aims to highlight the unusual features of the process of non-canonical ubiquitylation and the consequences of these events on the activity and fate of a protein.
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Affiliation(s)
- Gary S McDowell
- Department of Oncology, University of Cambridge, Hutchison/Medical Research Council (MRC) Research Centre, Cambridge, UK
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17
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Scaglione KM, Basrur V, Ashraf NS, Konen JR, Elenitoba-Johnson KSJ, Todi SV, Paulson HL. The ubiquitin-conjugating enzyme (E2) Ube2w ubiquitinates the N terminus of substrates. J Biol Chem 2013; 288:18784-8. [PMID: 23696636 DOI: 10.1074/jbc.c113.477596] [Citation(s) in RCA: 74] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023] Open
Abstract
Attachment of ubiquitin to substrate is typically thought to occur via formation of an isopeptide bond between the C-terminal glycine residue of ubiquitin and a lysine residue in the substrate. In vitro, Ube2w is nonreactive with free lysine yet readily ubiquitinates substrate. Ube2w also contains novel residues within its active site that are important for its ability to ubiquitinate substrate. To identify the site of modification, we analyzed ubiquitinated substrates by mass spectrometry and found the N-terminal -NH2 group as the site of conjugation. To confirm N-terminal ubiquitination, we generated lysine-less and N-terminally blocked versions of one substrate, the polyglutamine disease protein ataxin-3, and showed that Ube2w can ubiquitinate a lysine-less, but not N-terminally blocked, ataxin-3. This was confirmed with a second substrate, the neurodegenerative disease protein Tau. Finally, we directly sequenced the N terminus of unmodified and ubiquitinated ataxin-3, demonstrating that Ube2w attaches ubiquitin to the N terminus of its substrates. Together these data demonstrate that Ube2w has novel enzymatic properties that direct ubiquitination of the N terminus of substrates.
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18
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Kravtsova-Ivantsiv Y, Sommer T, Ciechanover A. The lysine48-based polyubiquitin chain proteasomal signal: not a single child anymore. Angew Chem Int Ed Engl 2012; 52:192-8. [PMID: 23124625 DOI: 10.1002/anie.201205656] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2012] [Indexed: 11/07/2022]
Abstract
The conjugation of ubiquitin (Ub) to proteins is involved in the regulation of many processes. The modification serves as a recognition element in trans, in which downstream effectors bind to the modified protein and determine its fate and/or function. A polyUb chain that is linked through internal lysine (Lys)-48 of Ub and anchored to an internal Lys residue of the substrate has become the accepted "canonical" signal for proteasomal targeting and degradation. However, recent studies show that the signal is far more diverse and that chains based on other internal linkages, as well as linear or heterologous chains made of Ub and Ub-like proteins and even monoUb, are recognized by the proteasome. In addition, chains linked to residues other than internal Lys were described, all challenging the current paradigm.
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Affiliation(s)
- Yelena Kravtsova-Ivantsiv
- Cancer and Vascular Biology Research Center, Faculty of Medicine, Technion-Israel Institute of Technology, Haifa, Israel.
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19
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Wang YE, Pernet O, Lee B. Regulation of the nucleocytoplasmic trafficking of viral and cellular proteins by ubiquitin and small ubiquitin-related modifiers. Biol Cell 2011; 104:121-38. [PMID: 22188262 PMCID: PMC3625690 DOI: 10.1111/boc.201100105] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/25/2011] [Accepted: 11/22/2011] [Indexed: 12/29/2022]
Abstract
Nucleocytoplasmic trafficking of many cellular proteins is regulated by nuclear import/export signals as well as post-translational modifications such as covalent conjugation of ubiquitin and small ubiquitin-related modifiers (SUMOs). Ubiquitination and SUMOylation are rapid and reversible ways to modulate the intracellular localisation and function of substrate proteins. These pathways have been co-opted by some viruses, which depend on the host cell machinery to transport their proteins in and out of the nucleus. In this review, we will summarise our current knowledge on the ubiquitin/SUMO-regulated nuclear/subnuclear trafficking of cellular proteins and describe examples of viral exploitation of these pathways.
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Affiliation(s)
- Yao E Wang
- Department of Microbiology, Immunology, and Molecular Genetics, UCLA, Los Angeles, CA 90095, USA
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20
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Lin A, Hou Q, Jarzylo L, Amato S, Gilbert J, Shang F, Man HY. Nedd4-mediated AMPA receptor ubiquitination regulates receptor turnover and trafficking. J Neurochem 2011; 119:27-39. [PMID: 21338354 DOI: 10.1111/j.1471-4159.2011.07221.x] [Citation(s) in RCA: 134] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
α-Amino-3-hydroxy-5-methyl-isoxazole-4-propionic acid receptors (AMPARs) are the primary mediators of excitatory synaptic transmission in the brain. Alterations in AMPAR localization and turnover have been considered critical mechanisms underpinning synaptic plasticity and higher brain functions, but the molecular processes that control AMPAR trafficking and stability are still not fully understood. Here, we report that mammalian AMPARs are subject to ubiquitination in neurons and in transfected heterologous cells. Ubiquitination facilitates AMPAR endocytosis, leading to a reduction in AMPAR cell-surface localization and total receptor abundance. Mutation of lysine residues to arginine residues at the glutamate receptor subunit 1 (GluA1) C-terminus dramatically reduces GluA1 ubiquitination and abolishes ubiquitin-dependent GluA1 internalization and degradation, indicating that the lysine residues, particularly K868, are sites of ubiquitination. We also find that the E3 ligase neural precursor cell expressed, developmentally down-regulated 4 (Nedd4) is enriched in synaptosomes and co-localizes and associates with AMPARs in neurons. Nedd4 expression leads to AMPAR ubiquitination, leading to reduced AMPAR surface expression and suppressed excitatory synaptic transmission. Conversely, knockdown of Nedd4 by specific siRNAs abolishes AMPAR ubiquitination. These data indicate that Nedd4 is the E3 ubiquitin ligase responsible for AMPAR ubiquitination, a modification that regulates multiple aspects of AMPAR molecular biology including trafficking, localization and stability.
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Affiliation(s)
- Amy Lin
- Department of Biology, Boston University, Boston, Massachusetts, USA
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21
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Cen O, Longnecker R. Rapamycin reverses splenomegaly and inhibits tumor development in a transgenic model of Epstein-Barr virus-related Burkitt's lymphoma. Mol Cancer Ther 2011; 10:679-86. [PMID: 21282357 DOI: 10.1158/1535-7163.mct-10-0833] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Epstein-Barr virus (EBV) infection and latency has been associated with malignancies, including nasopharyngeal carcinoma and Burkitt's lymphoma. EBV encoded latent membrane protein 2A (LMP2A) is expressed in most EBV-associated malignancies and as such provides a therapeutic target. Burkitt's lymphoma is a hematopoietic cancer associated with the translocation of c-MYC to one of the immunoglobulin gene promoters leading to abnormally high expression of MYC and development of lymphoma. Our laboratory has developed a murine model of EBV-associated Burkitt's lymphoma by crossing LMP2A transgenic mice with MYC transgenic mice. Since LMP2A has been shown to activate the PI3K/Akt/mTOR pathway, we tested the therapeutic efficacy of mTOR inhibitor rapamycin on the tumors and splenomegaly in these double transgenic mice (Tg6/λ-MYC). We found that rapamycin reversed splenomegaly in Tg6/λ-MYC mice prior to tumor formation by targeting B cells. In a tumor transfer model, we also found that rapamycin significantly decreased tumor growth, splenomegaly, and metastasis of tumor cells in the bone marrow of tumor recipients. Our data show that rapamycin may be a valuable candidate for the development of a treatment modality for EBV-positive lymphomas, such as Burkitt's lymphoma, and more importantly, provides a basis to develop inhibitors that specifically target viral gene function in tumor cells that depend on LMP2A signaling for survival and/or growth.
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Affiliation(s)
- Osman Cen
- Department of Microbiology and Immunology, Feinberg School of Medicine, Northwestern University, 303 E. Chicago Avenue, Ward 6-241, Chicago, IL 60611, USA
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22
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Ushijima Y, Luo C, Kamakura M, Goshima F, Kimura H, Nishiyama Y. Herpes simplex virus UL56 interacts with and regulates the Nedd4-family ubiquitin ligase Itch. Virol J 2010; 7:179. [PMID: 20682038 PMCID: PMC2922189 DOI: 10.1186/1743-422x-7-179] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2010] [Accepted: 08/03/2010] [Indexed: 12/04/2022] Open
Abstract
Background Herpes simplex virus type 2 (HSV-2) is one of many viruses that exploits and modifies the cellular ubiquitin system. HSV-2 expresses the tegument protein UL56 that has been implicated in cytoplasmic transport and/or release of virions, and is a putative regulatory protein of Nedd4 ubiquitin ligase. In order to elucidate the biological function of UL56, this study examined the interaction of UL56 with the Nedd4-family ubiquitin ligase Itch and its role in the regulation of Itch. Additionally, we assessed the similarity between UL56 and regulatory proteins of Itch and Nedd4, Nedd4-family-interactins proteins (Ndfip). Results UL56 interacted with Itch, independent of additional viral proteins, and mediated more striking degradation of Itch, compared to Nedd4. Moreover, it was suggested that the lysosome pathway as well as the proteasome pathway was involved in the degradation of Itch. Other HSV-2 proteins with PY motifs, such as VP5 and VP16, did not mediate the degradation of endogenous Itch. Ndfip1 and Ndfip2 were similar in subcellular distribution patterns to UL56 and colocalized with UL56 in co-transfected cells. Conclusions We believe that this is the first report demonstrating the interaction of a HSV-specific protein and Itch. Thus, UL56 could function as a regulatory protein of Itch. The mechanism, function and significance of regulating Itch in HSV-2 infection remain unclear and warrant further investigation.
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Affiliation(s)
- Yoko Ushijima
- Department of Virology, Nagoya University Graduate School of Medicine, Showa-ku, Nagoya, Japan
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23
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Lysine-independent turnover of cyclin G1 can be stabilized by B'alpha subunits of protein phosphatase 2A. Mol Cell Biol 2008; 29:919-28. [PMID: 18981217 DOI: 10.1128/mcb.00907-08] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023] Open
Abstract
Although the cyclin G1 gene is known to be regulated at the transcriptional level by p53, less is understood about the turnover of its protein product. We found that ectopically and endogenously expressed cyclin G1 protein is highly unstable and is degraded by a proteasome-mediated pathway. The N-terminal 137 amino acids of cyclin G1 (cyclin G(1-137)) are necessary and sufficient for both cyclin G1 ubiquitination and turnover. Interestingly, a mutant cyclin G1 (8KR) in which all lysine residues in this region have been replaced with arginine can be both ubiquitinated in cells and stabilized by a proteasome inhibitor to a similar extent as wild-type cyclin G(1-137). Furthermore, the presence of a six-Myc tag at the N terminus of cyclin G(1-137) significantly inhibits the protein's turnover, suggesting a role for the extreme N terminus of the protein in ubiquitin-mediated proteolysis. Although we and others previously showed that cyclin G1 protein can bind to MDM2, which functions as an E3 ubiquitin ligase to p53 and itself, cyclin G1 protein can be degraded in cells without MDM2 and p53. Interestingly, the B'alpha1 subunit of the serine/threonine protein phosphatase 2A, which binds to cyclin G1, can stabilize cyclin G1 under unstressed conditions and upon DNA damage, as well as inhibit the ability of cyclin G1 to be ubiquitinated. Our results thus indicate that proteasomal turnover of cyclin G1 is regulated by noncanonical processes.
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The N-terminal domain of MyoD is necessary and sufficient for its nuclear localization-dependent degradation by the ubiquitin system. Proc Natl Acad Sci U S A 2008; 105:15690-5. [PMID: 18836078 DOI: 10.1073/pnas.0808373105] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023] Open
Abstract
A growing number of proteins, including the myogenic transcription factor MyoD, are targeted for proteasomal degradation after N-terminal ubiquitination (NTU) where the first ubiquitin moiety is conjugated to the N-terminal residue rather than to an internal lysine. NTU might be essential in targeting both lysine-containing and naturally occurring lysine-less proteins such as p16(INK4a) and p14(ARF); however, the mechanisms that underlie this process are largely unknown. Specifically, the recognition motif(s) in the target substrates and the ubiquitin ligase(s) that catalyze NTU are still obscure. Here we show that the N-terminal domain of MyoD is critical for its degradation and that its destabilizing effect depends on nuclear localization of the protein. Deletion of the first 15 aa of MyoD blocked completely its lysine-independent degradation. Importantly, transfer of the first 30 N-terminal residues of MyoD to GFP destabilized this otherwise stable protein, and, here too, targeting for degradation depended on localization of the protein to the nucleus. Deletion of the N-terminal domain of lysine-less MyoD did not abolish completely ubiquitination of the protein, suggesting that this domain may be required for targeting the protein also in a postubiquitination step. Interestingly, NTU is evolutionarily conserved: in the yeast Saccharomyces cerevisiae lysine-less (LL) MyoD is degraded in a ubiquitin-, N-terminal domain-, and nuclear localization-dependent manner. Taken together, our data suggest that a short N-terminal segment of MyoD is necessary and sufficient to render MyoD susceptible for ubiquitin- and nuclear-dependent degradation.
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25
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Li RF, Shang Y, Liu D, Ren ZS, Chang Z, Sui SF. Differential Ubiquitination of Smad1 Mediated by CHIP: Implications in the Regulation of the Bone Morphogenetic Protein Signaling Pathway. J Mol Biol 2007; 374:777-90. [DOI: 10.1016/j.jmb.2007.09.082] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/25/2007] [Revised: 09/26/2007] [Accepted: 09/27/2007] [Indexed: 01/29/2023]
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26
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Tomaszewski-Flick MJ, Rowe DT. Minimal protein domain requirements for the intracellular localization and self-aggregation of Epstein-Barr Virus Latent Membrane Protein 2. Virus Genes 2007; 35:225-34. [PMID: 17564822 DOI: 10.1007/s11262-007-0118-8] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2007] [Accepted: 05/14/2007] [Indexed: 12/11/2022]
Abstract
The EBV Latent Membrane Protein 2 (LMP2) may have a role in the establishment and maintenance of in vivo latency. The gene is transcribed into two mRNAs that produce two LMP2 protein isoforms. The LMP2a protein isoform has 12 transmembrane segments (TMs) and an amino terminal cytoplasmic signaling domain (CSD) while the LMP2b isoform is identical but lacks the CSD. There has not been a consensus on the cellular membrane localization being sometimes ascribed to either a plasma membrane or an intracellular location [M. Rovedo, R. Longnecker, J. Virol. 81:89-94, 2007; D. Lynch, J. Zimmerman, D.T. Rowe, J. Gen. Virol. 83:1025-1035, 2002; C. Dawson, J. George, S. Blake, R. Longnecker, L.S. Young, Virology 289:192-207, 2001]. Fluorescent marker and epitope tagged LMP2b truncation mutants progressively removing TMs from the N and C termini were used to assess the localization and aggregation properties of LMP2b. wtLMP2b had an exclusively intracellular perinuclear localization, while all truncations of the protein resulted in localization to the cell surface. By epitope loop-tagging, all the truncated LMP2b proteins were verified to be in the predicted membrane orientation. In co-transfection experiments, the C-terminal region was implicated in the self-aggregation properties of LMP2b. Thus, an intact 12 TM domain was required for intracellular localization and protein-protein interaction while a C-terminal region was responsible for auto-aggregative properties.
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Affiliation(s)
- Monica Jo Tomaszewski-Flick
- Department of Infectious Diseases and Microbiology, Graduate School of Public Health, University of Pittsburgh, 130 DeSoto St, Pittsburgh, PA 15213, USA
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27
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Matskova LV, Helmstetter C, Ingham RJ, Gish G, Lindholm CK, Ernberg I, Pawson T, Winberg G. The Shb signalling scaffold binds to and regulates constitutive signals from the Epstein–Barr virus LMP2A membrane protein. Oncogene 2007; 26:4908-17. [PMID: 17311000 DOI: 10.1038/sj.onc.1210298] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
The Epstein-Barr virus latency-associated membrane protein LMP2A has been shown to activate the survival kinase Akt in epithelial and B cells in a phosphoinositide 3-kinase-dependent fashion. In this study, we demonstrate that the signalling scaffold Shb associates through SH2 and PTB domain interactions with phosphorylated tyrosine motifs in the LMP2A N-terminal tail. Additionally, we show that mutation of tyrosines in these motifs as well as shRNA-mediated downregulation of Shb leads to a loss of constitutive Akt-activation in LMP2A-expressing cells. Furthermore, utilization by Shb of the LMP2A ITAM motif regulates stability of the Syk tyrosine kinase in LMP2A-expressing cells. Our data set the precedent for viral utilization of the Shb signalling scaffold and implicate Shb as a regulator of LMP2A-dependent Akt activation.
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Affiliation(s)
- L V Matskova
- Microbiology and Tumor Biology Center, Karolinska Institutet, Stockholm, Sweden.
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28
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Ikeda M, Longnecker R. Cholesterol is critical for Epstein-Barr virus latent membrane protein 2A trafficking and protein stability. Virology 2006; 360:461-8. [PMID: 17150237 PMCID: PMC1868700 DOI: 10.1016/j.virol.2006.10.046] [Citation(s) in RCA: 57] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2006] [Revised: 10/17/2006] [Accepted: 10/27/2006] [Indexed: 12/12/2022]
Abstract
Latent membrane protein 2A (LMP2A) of Epstein-Barr virus (EBV) plays a key role in regulating viral latency and EBV pathogenesis by functionally mimicking signals induced by the B cell receptor (BCR) altering normal B cell development. LMP2A specifically associates with Nedd4 family ubiquitin-protein ligases which downmodulate LMP2A activity by ubiquitinating LMP2A and LMP2A-associated protein tyrosine kinases (PTKs). Since specific ubiquitin tags provide an endocytic sorting signal for plasma membrane proteins which traffic to membrane vesicles, we examined LMP2A localization and trafficking. We found that LMP2A is secreted through exosomes, small endocytic membrane vesicles, as previously demonstrated for LMP1. Interestingly, the treatment of cells with methyl-beta-cyclodextrin (MCD), which depletes cholesterol from plasma membrane, dramatically increased LMP2A abundance and LMP2A exosome secretion. Cholesterol depletion also blocked LMP2A endocytosis resulting in the accumulation of LMP2A on plasma membrane. LMP2A phosphorylation and ubiquitination were blocked by cholesterol depletion. LMP2A in the exosomal fraction was ubiquitinated but not phosphorylated. These results indicate that cholesterol-dependent LMP2A trafficking determines the fate of LMP2A degradation.
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Affiliation(s)
| | - Richard Longnecker
- *Corresponding author, Phone: +1-312-503-0467, Fax: +1-312-503-1339, E-mail:
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29
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Kirisako T, Kamei K, Murata S, Kato M, Fukumoto H, Kanie M, Sano S, Tokunaga F, Tanaka K, Iwai K. A ubiquitin ligase complex assembles linear polyubiquitin chains. EMBO J 2006; 25:4877-87. [PMID: 17006537 PMCID: PMC1618115 DOI: 10.1038/sj.emboj.7601360] [Citation(s) in RCA: 600] [Impact Index Per Article: 33.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2006] [Accepted: 08/29/2006] [Indexed: 11/08/2022] Open
Abstract
The ubiquitin system plays important roles in the regulation of numerous cellular processes by conjugating ubiquitin to target proteins. In most cases, conjugation of polyubiquitin to target proteins regulates their function. In the polyubiquitin chains reported to date, ubiquitin monomers are linked via isopeptide bonds between an internal Lys and a C-terminal Gly. Here, we report that a protein complex consisting of two RING finger proteins, HOIL-1L and HOIP, exhibits ubiquitin polymerization activity by recognizing ubiquitin moieties of proteins. The polyubiquitin chain generated by the complex is not formed by Lys linkages, but by linkages between the C- and N-termini of ubiquitin, indicating that the ligase complex possesses a unique feature to assemble a novel head-to-tail linear polyubiquitin chain. Moreover, the complex regulates the stability of Ub-GFP (a GFP fusion protein with an N-terminal ubiquitin). The linear polyubiquitin chain generated post-translationally may function as a new modulator of proteins.
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Affiliation(s)
- Takayoshi Kirisako
- Department of Molecular Cell Biology, Graduate School of Medicine, Osaka City University, Osaka, Japan
- Core Research for Evolutional Science and Technology (CREST), Japan Science and Technology Corporation, Kawaguchi, Saitama, Japan
| | - Kiyoko Kamei
- Department of Molecular Cell Biology, Graduate School of Medicine, Osaka City University, Osaka, Japan
| | - Shigeo Murata
- Laboratory of Frontier Science, Tokyo Metropolitan Institute of Medical Science, Tokyo, Japan
- Precursory Research for Embryonic Science and Technology (PRESTO), Japan Science and Technology Corporation, Kawaguchi, Saitama, Japan
| | - Michiko Kato
- Department of Molecular Cell Biology, Graduate School of Medicine, Osaka City University, Osaka, Japan
- Core Research for Evolutional Science and Technology (CREST), Japan Science and Technology Corporation, Kawaguchi, Saitama, Japan
| | - Hiromi Fukumoto
- Department of Molecular Cell Biology, Graduate School of Medicine, Osaka City University, Osaka, Japan
| | - Masato Kanie
- Department of Molecular Cell Biology, Graduate School of Medicine, Osaka City University, Osaka, Japan
| | - Soichi Sano
- Department of Molecular Cell Biology, Graduate School of Medicine, Osaka City University, Osaka, Japan
| | - Fuminori Tokunaga
- Department of Molecular Cell Biology, Graduate School of Medicine, Osaka City University, Osaka, Japan
- Core Research for Evolutional Science and Technology (CREST), Japan Science and Technology Corporation, Kawaguchi, Saitama, Japan
| | - Keiji Tanaka
- Laboratory of Frontier Science, Tokyo Metropolitan Institute of Medical Science, Tokyo, Japan
| | - Kazuhiro Iwai
- Department of Molecular Cell Biology, Graduate School of Medicine, Osaka City University, Osaka, Japan
- Core Research for Evolutional Science and Technology (CREST), Japan Science and Technology Corporation, Kawaguchi, Saitama, Japan
- Department of Molecular Cell Biology, Graduate School of Medicine, Osaka City University, 1-4-3 Asahi-Machi, Abeno-Ku, Osaka 545-8585, Japan. Tel.: +81 6 6645 3905; Fax: +81 6 6645 3907; E-mail:
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30
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Brinkmann MM, Schulz TF. Regulation of intracellular signalling by the terminal membrane proteins of members of the Gammaherpesvirinae. J Gen Virol 2006; 87:1047-1074. [PMID: 16603506 DOI: 10.1099/vir.0.81598-0] [Citation(s) in RCA: 83] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
The human gamma(1)-herpesvirus Epstein-Barr virus (EBV) and the gamma(2)-herpesviruses Kaposi's sarcoma-associated herpesvirus (KSHV), rhesus rhadinovirus (RRV), herpesvirus saimiri (HVS) and herpesvirus ateles (HVA) all contain genes located adjacent to the terminal-repeat region of their genomes, encoding membrane proteins involved in signal transduction. Designated 'terminal membrane proteins' (TMPs) because of their localization in the viral genome, they interact with a variety of cellular signalling molecules, such as non-receptor protein tyrosine kinases, tumour-necrosis factor receptor-associated factors, Ras and Janus kinase (JAK), thereby initiating further downstream signalling cascades, such as the MAPK, PI3K/Akt, NF-kappaB and JAK/STAT pathways. In the case of TMPs expressed during latent persistence of EBV and HVS (LMP1, LMP2A, Stp and Tip), their modulation of intracellular signalling pathways has been linked to the provision of survival signals to latently infected cells and, hence, a contribution to occasional cellular transformation. In contrast, activation of similar pathways by TMPs of KSHV (K1 and K15) and RRV (R1), expressed during lytic replication, may extend the lifespan of virus-producing cells, alter their migration and/or modulate antiviral immune responses. Whether R1 and K1 contribute to the oncogenic properties of KSHV and RRV has not been established satisfactorily, despite their transforming qualities in experimental settings.
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Affiliation(s)
- Melanie M Brinkmann
- Institut für Virologie, Medizinische Hochschule Hannover, Carl-Neuberg Str. 1, D-30625 Hannover, Germany
| | - Thomas F Schulz
- Institut für Virologie, Medizinische Hochschule Hannover, Carl-Neuberg Str. 1, D-30625 Hannover, Germany
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31
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Pendleton AR, Machamer CE. Differential localization and turnover of infectious bronchitis virus 3b protein in mammalian versus avian cells. Virology 2005; 345:337-45. [PMID: 16298409 PMCID: PMC7111863 DOI: 10.1016/j.virol.2005.09.069] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2005] [Revised: 09/15/2005] [Accepted: 09/22/2005] [Indexed: 12/24/2022]
Abstract
Infectious bronchitis virus (IBV) 3b protein is highly conserved among group 3 coronaviruses, suggesting that it is important for infection. A previous report (Virology 2003, 311:16-27) indicated that transfected IBV 3b localized to the nucleus in mammalian cells using a vaccinia-virus expression system. Although we confirmed these findings, we observed cytoplasmic localization of IBV 3b with apparent exclusion from the nucleus in avian cells (IBV normally infects chickens). IBV 3b was virtually undetectable by microscopy in mammalian cells transfected without vaccinia virus and in IBV-infected mammalian cells because of a greatly reduced half-life in these cells. A proteasome inhibitor stabilized IBV 3b in mammalian cells, but had little effect on IBV 3b in avian cells, suggesting that rapid turnover of IBV 3b in mammalian cells is proteasome-dependent while turnover in avian cells may be proteasome-independent. Our results highlight the importance of using cells derived from the natural host when studying coronavirus non-structural proteins.
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Affiliation(s)
- Amanda R Pendleton
- Department of Cell Biology, Johns Hopkins University School of Medicine, 725 N. Wolfe St., Baltimore, MD 21205, USA
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32
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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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33
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Chen C, Sun X, Guo P, Dong XY, Sethi P, Cheng X, Zhou J, Ling J, Simons JW, Lingrel JB, Dong JT. Human Kruppel-like factor 5 is a target of the E3 ubiquitin ligase WWP1 for proteolysis in epithelial cells. J Biol Chem 2005; 280:41553-61. [PMID: 16223724 DOI: 10.1074/jbc.m506183200] [Citation(s) in RCA: 117] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
The transcription factor KLF5 plays an important role in human carcinogenesis. In epithelial cells, the KLF5 protein is tightly regulated by the ubiquitin-proteasome pathway. To better understand the mechanisms for the regulation of KLF5 protein, we identified and characterized an E3 ubiquitin ligase for KLF5, i.e. WWP1. We found that WWP1 formed a protein complex with KLF5 in vivo and in vitro. Furthermore, WWP1 mediated the ubiquitination and degradation of KLF5, and the catalytic cysteine residue of WWP1 is essential for its function. A PY motif in a transactivation domain of KLF5 is necessary for its interaction with WWP1. Finally, WWP1 was amplified and overexpressed in some cancer cell lines from the prostate and breast, which negatively regulated the function of KLF5 in gene regulation. These findings not only established WWP1 as an E3 ubiquitin ligase for KLF5, they also further implicated the KLF5 pathway in human carcinogenesis.
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Affiliation(s)
- Ceshi Chen
- Winship Cancer Institute and Department of Hematology and Oncology, Emory University School of Medicine, Atlanta, Georgia 30322, USA
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34
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Ingham RJ, Raaijmakers J, Lim CSH, Mbamalu G, Gish G, Chen F, Matskova L, Ernberg I, Winberg G, Pawson T. The Epstein-Barr virus protein, latent membrane protein 2A, co-opts tyrosine kinases used by the T cell receptor. J Biol Chem 2005; 280:34133-42. [PMID: 16087662 DOI: 10.1074/jbc.m507831200] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
Epstein-Barr virus (EBV) is the causative agent of infectious mononucleosis and is associated with several human malignancies. The EBV protein latent membrane protein 2A (LMP2A) promotes viral latency in memory B cells by interfering with B cell receptor signaling and provides a survival signal for mature B cells that have lost expression of surface immunoglobulin. The latter function has suggested that LMP2A may enhance the survival of EBV-positive tumors. EBV is associated with several T cell malignancies and, since LMP2A has been detected in several of these disorders, we examined the ability of LMP2A to transmit signals and interfere with T cell receptor signaling in T cells. We show that LMP2A is tyrosine-phosphorylated in Jurkat TAg T cells, which requires expression of the Src family tyrosine kinases, Lck and Fyn. Lck and Fyn are recruited to the tyrosine-phosphorylated Tyr112 site in LMP2A, whereas phosphorylation of an ITAM motif in LMP2A creates a binding site for the ZAP-70/Syk tyrosine kinases. LMP2A also associates through its two PPPPY motifs with AIP4, a NEDD4 family E3 ubiquitin ligase; this interaction results in ubiquitylation of LMP2A and serves to regulate the stability of LMP2A and LMP2A-kinase complexes. Furthermore, stable expression of LMP2A in Jurkat T cells down-regulated T cell receptor levels and attenuated T cell receptor signaling. Thus, through recruiting tyrosine kinases involved in T cell receptor activation, LMP2A may provide a survival signal for EBV-positive T cell tumors, whereas LMP2A-associated NEDD4 E3 ligases probably titer the strength of this signal.
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Affiliation(s)
- Robert J Ingham
- Samuel Lunenfeld Research Institute, Mount Sinai Hospital, Toronto, Ontario M5G 1X5, Canada
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35
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Lallemand F, Seo SR, Ferrand N, Pessah M, L'Hoste S, Rawadi G, Roman-Roman S, Camonis J, Atfi A. AIP4 Restricts Transforming Growth Factor-β Signaling through a Ubiquitination-independent Mechanism. J Biol Chem 2005; 280:27645-53. [PMID: 15946939 DOI: 10.1074/jbc.m500188200] [Citation(s) in RCA: 54] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Smad7 functions as an intracellular antagonist in transforming growth factor-beta (TGF-beta) signaling. In addition to interacting stably with the activated TGF-beta type I receptor (TbetaRI) to prevent phosphorylation of the receptor-regulated Smads (Smad2 and Smad3), Smad7 also induces degradation of the activated TbetaRI through association with different E3 ubiquitin ligases. Using the two-hybrid screen, we identified atrophin 1-interacting protein 4 (AIP4) as an E3 ubiquitin ligase that specifically targets Smad7 for ubiquitin-dependent degradation without affecting the turnover of the activated TbetaRI. Surprisingly, we found that despite the ability to degrade Smad7, AIP4 can inhibit TGF-beta signaling, presumably by enhancing the association of Smad7 with the activated TbetaRI. Consistent with this notion, expression of a catalytic mutant of AIP4, which is unable to induce ubiquitination and degradation of Smad7, also stabilizes the TbetaRI.Smad7 complex, resulting in inhibition of TGF-beta signaling. The ability of AIP4 to enhance the inhibitory function of Smad7 independent of its ubiquitin ligase activity reveals a new mechanism by which E3 ubiquitin ligases may function to turn off TGF-beta signaling.
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Affiliation(s)
- François Lallemand
- INSERM U482, Hôpital Saint-Antoine, 184 Rue du Faubourg Saint-Antoine, 75571 Paris Cedex 12, France
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36
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Aoshi T, Suzuki M, Uchijima M, Nagata T, Koide Y. Expression mapping using a retroviral vector for CD8+ T cell epitopes: definition of a Mycobacterium tuberculosis peptide presented by H2-Dd. J Immunol Methods 2005; 298:21-34. [PMID: 15847794 DOI: 10.1016/j.jim.2004.12.015] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2004] [Revised: 11/29/2004] [Accepted: 12/17/2004] [Indexed: 11/22/2022]
Abstract
Identification of CD8+ T cell epitopes is important because detection of specific CD8+ T cells after infection or immunization requires prior knowledge of epitope specificity. Furthermore, identification of CD8+ T cell epitopes permits the development of specific preventive and therapeutic approaches to both infections and tumors. Thus far, CD8+ T cell epitopes have been identified either using an overlapping peptide library covering an entire protein, or using algorithms designed to identify likely peptides that bind to major histocompatibility complex (MHC) class I molecules. The synthesis of overlapping peptides can be prohibitively expensive, and the algorithm programs used to predict CD8+ T cell epitopes are not always accurate. Here we describe a retroviral expression system that specifically allows longer polypeptides and shorter peptides to be expressed in the cytoplasm, and thereby to be processed onto class I MHC molecules. T cells from mice that were immunized with a DNA vaccine encoding MPT-51 were probed against MHC-compatible cell lines retrovirally transduced with overlapping gene fragments encoding 120-140 amino acids of the MPT-51 molecule. After further testing of shorter peptide sequences, we identified a CD8+ T cell epitope using cell lines expressing a relatively small number of algorithm-predicted candidate epitopes. We found that one of the requirements for cell surface display of the 20-mer peptide was the need for cotranslational ubiquitination. The restriction molecule was identified as Dd following transduction with MHC class I genes followed by transduction with the oligonucleotide encoding the epitope. The retroviral expression system described here is cost-effective, particularly if the target molecule is large, and could be adapted to identifying T cell epitopes recognized in infectious disease and against tumor cell antigens.
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Affiliation(s)
- Taiki Aoshi
- Department of Microbiology and Immunology, Hamamatsu University School of Medicine, 1-20-1 Handa-yama, Hamamatsu 431-3192, Japan
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37
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Lévy F, Muehlethaler K, Salvi S, Peitrequin AL, Lindholm CK, Cerottini JC, Rimoldi D. Ubiquitylation of a melanosomal protein by HECT-E3 ligases serves as sorting signal for lysosomal degradation. Mol Biol Cell 2005; 16:1777-87. [PMID: 15703212 PMCID: PMC1073660 DOI: 10.1091/mbc.e04-09-0803] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023] Open
Abstract
The production of pigment by melanocytic cells of the skin involves a series of enzymatic reactions that take place in specialized organelles called melanosomes. Melan-A/MART-1 is a melanocytic transmembrane protein with no enzymatic activity that accumulates in vesicles at the trans side of the Golgi and in melanosomes. We show here that, in melanoma cells, Melan-A associates with two homologous to E6-AP C-terminus (HECT)-E3 ubiquitin ligases, NEDD4 and Itch, and is ubiquitylated. Both NEDD4 and Itch participate in the degradation of Melan-A. A mutant Melan-A lacking ubiquitin-acceptor residues displays increased half-life and, in pigmented cells, accumulates in melanosomes. These results suggest that ubiquitylation regulates the lysosomal sorting and degradation of Melan-A/MART-1 from melanosomes in melanocytic cells.
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Affiliation(s)
- Frédéric Lévy
- Ludwig Institute for Cancer Research, University of Lausanne, Epalinges, Switzerland.
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38
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Abstract
Ubiquitin-mediated proteolysis is a major pathway of protein degradation that regulates numerous cellular processes. An understanding of the circumstances that contribute to the ubiquitylation of a specific protein can yield vast insight into its regulation. This article examines multiple procedures that explain whether a protein is ubiquitylated and suggests methods to investigate the factors that specifically target the substrate for ubiquitylation, as well as the site of ubiquitin conjugation.
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Affiliation(s)
- Joanna Bloom
- Department of Pathology, New York University School of Medicine and NYU Cancer Institute, New York, USA
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39
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Petroski MD, Deshaies RJ. In vitro reconstitution of SCF substrate ubiquitination with purified proteins. Methods Enzymol 2005; 398:143-58. [PMID: 16275326 DOI: 10.1016/s0076-6879(05)98013-0] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
The development of in vitro systems to monitor ubiquitin ligase activity with highly purified proteins has allowed for new insights into the mechanisms of protein ubiquitination to be uncovered. This chapter describes the methodologies employed to reconstitute ubiquitination of the budding yeast cyclin-dependent kinase inhibitor Sic1 by the evolutionarily conserved ubiquitin ligase SCF(Cdc4) and its ubiquitin-conjugating enzyme Cdc34. Based on our experience in reconstituting Sic1 ubiquitination, we suggest some parameters to consider that should be generally applicable to the study of different SCF complexes and other ubiquitin ligases.
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Affiliation(s)
- Matthew D Petroski
- Howard Hughes Medical Institute, Division of Biology, California Institute of Technology, Pasadena, CA 91125, USA
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40
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Katzman RB, Longnecker R. LMP2A does not require palmitoylation to localize to buoyant complexes or for function. J Virol 2004; 78:10878-87. [PMID: 15452208 PMCID: PMC521828 DOI: 10.1128/jvi.78.20.10878-10887.2004] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Epstein-Barr virus (EBV) latent membrane protein 2A (LMP2A) is expressed constitutively in lipid rafts in latently infected B lymphocytes. Lipid rafts are membrane microdomains enriched in cholesterol and sphingolipids selective for specific protein association. Lipid rafts have been shown to be necessary for B-cell receptor (BCR) signal transduction. LMP2A prevents BCR recruitment to lipid rafts, thereby abrogating BCR function. As LMP2A is palmitoylated, whether this fatty acid modification is necessary for LMP2A to localize to lipid rafts and for protein function was investigated. LMP2A palmitoylation was confirmed in latently infected B cells. LMP2A was found to be palmitoylated on multiple cysteines only by S acylation. An LMP2A mutant that was not palmitoylated was identified and functioned similar to wild-type LMP2A; unmodified LMP2A localized to lipid rafts, was tyrosine phosphorylated, was associated with LMP2A-associated proteins, was ubiquitinated, and was able to block calcium mobilization following BCR cross-linking. Therefore, palmitoylation of LMP2A is not required for LMP2A targeting to buoyant complexes or for function.
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Affiliation(s)
- Rebecca B Katzman
- Department of Microbiology-Immunology, Northwestern University Medical School, Chicago, IL 60611, USA
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41
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Portis T, Ikeda M, Longnecker R. Epstein–Barr virus LMP2A: regulating cellular ubiquitination processes for maintenance of viral latency? Trends Immunol 2004; 25:422-6. [PMID: 15275641 DOI: 10.1016/j.it.2004.05.009] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Affiliation(s)
- Toni Portis
- Department of Microbiology and Immunology, Feinberg School of Medicine, Northwestern University, Chicago, IL 60611, USA
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42
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Ben-Saadon R, Fajerman I, Ziv T, Hellman U, Schwartz AL, Ciechanover A. The tumor suppressor protein p16(INK4a) and the human papillomavirus oncoprotein-58 E7 are naturally occurring lysine-less proteins that are degraded by the ubiquitin system. Direct evidence for ubiquitination at the N-terminal residue. J Biol Chem 2004; 279:41414-21. [PMID: 15254040 DOI: 10.1074/jbc.m407201200] [Citation(s) in RCA: 91] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Conjugation of ubiquitin to an internal lysine is the initial step in the degradation of the majority of the substrates of the ubiquitin system. For several substrates, it has been shown that the first ubiquitin moiety is conjugated to the N-terminal residue. In all these substrates, however, the internal lysines also played a role in modulating their stability. To better understand the physiological significance of this novel mode of modification, it was important to identify proteins in which degradation is completely dependent on N-terminal ubiquitination. Also, although the experimental evidence for N-terminal ubiquitination is rather strong, nevertheless, it has remained indirect. Here we demonstrate that an important group of proteins that are targeted via N-terminal ubiquitination are the naturally occurring lysine-less proteins such as the human papillomavirus (HPV)-58 E7 oncoprotein and the cell cycle inhibitor and tumor suppressor p16(INK4a). For these proteins, the only residue that can be targeted is the N-terminal residue. Interestingly, p16(INK4a) is degraded in a cell density-dependent manner. Importantly, we provide for the first time direct evidence for N-terminal ubiquitination. Analysis of tryptic digest of the ubiquitin conjugate of HPV-58 E7 revealed a fusion peptide that is composed of the C-terminal domain of ubiquitin and the N-terminal domain of E7. With the abundance of native lysine-less proteins, among which are important viral and cell regulators, this novel mode of protein targeting has implications for both physiological and pathophysiological processes.
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Affiliation(s)
- Ronen Ben-Saadon
- Cancer and Vascular Biology Research Center, The Rappaport Family Institute for Research in the Medical Sciences, Technion-Israel Institute of Technology, Efron Street, Bat Galim, P. O. Box 9649, Haifa 31096, Israel
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43
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Ingham RJ, Gish G, Pawson T. The Nedd4 family of E3 ubiquitin ligases: functional diversity within a common modular architecture. Oncogene 2004; 23:1972-84. [PMID: 15021885 DOI: 10.1038/sj.onc.1207436] [Citation(s) in RCA: 390] [Impact Index Per Article: 19.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Neuronal precursor cell-expressed developmentally downregulated 4 (Nedd4) is the prototypical protein in a family of E3 ubiquitin ligases that have a common domain architecture. They are comprised of a catalytic C-terminal HECT domain and N-terminal C2 domain and WW domains responsible for cellular localization and substrate recognition. These proteins are found throughout eukaryotes and regulate diverse biological processes through the targeted degradation of proteins that generally have a PPxY motif for WW domain recognition, and are found in the nucleus and at the plasma membrane. Whereas the yeast Saccharomyces cerevisiae uses a single protein, Rsp5p, to carry out these functions, evolution has provided higher eukaryotes with several related Nedd4 proteins that appear to have specialized roles. In this review we discuss how knowledge of individual domain function has provided insight into the physiological roles of the Nedd4 proteins and describe recent results that suggest discrete functions for individual family members.
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Affiliation(s)
- Robert J Ingham
- Samuel Lunenfeld Research Institute, Mt. Sinai Hospital, Toronto, Ontario, Canada M5G 1X5.
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44
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Abstract
Epstein-Barr virus (EBV), a human herpesvirus associated with lymphoid and epithelial cell tumors, encodes several proteins that exploit the ubiquitin-proteasome system to regulate latency and allow the persistence of infected cells in immunocompetent hosts. Further modifications of ubiquitin-dependent proteolysis by activated cellular oncogenes contribute to malignant transformation. A detailed understanding of these processes may lead to the development of new therapeutic strategies for EBV-associated cancers.
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Affiliation(s)
- Maria G Masucci
- Microbiology and Tumor Biology Center, Karolinska Institutet, Box 280, S-171 77 Stockholm, Sweden.
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45
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Fajerman I, Schwartz AL, Ciechanover A. Degradation of the Id2 developmental regulator: targeting via N-terminal ubiquitination. Biochem Biophys Res Commun 2004; 314:505-12. [PMID: 14733935 DOI: 10.1016/j.bbrc.2003.12.116] [Citation(s) in RCA: 56] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
Degradation of cellular proteins via the ubiquitin-proteasome system (UPS) involves: (i) generation of a substrate-anchored polyubiquitin degradation signal and (ii) destruction of the tagged protein by the 26S proteasome with release of free and reusable ubiquitin. For most substrates, it is believed that the first ubiquitin moiety is conjugated to a epsilon-NH(2) group of an internal Lys residue. Recent findings indicate that for several proteins, the first ubiquitin moiety is fused, in a linear manner, to the free alpha-NH(2) group of the protein. Here, we demonstrate that the inhibitor of differentiation (or inhibitor of DNA binding) 2, Id2, that downregulates gene expression in undifferentiated and self-renewing cells, is degraded by the UPS following ubiquitination at its N-terminal residue. Lysine-less (LL) Id2 is degraded efficiently by the proteasome following ubiquitination. Fusion of a Myc tag to the N-terminal but not to the C-terminal residue of Id2 stabilizes the protein. Furthermore, deletion of the first 15 N-terminal residues of Id2 stabilizes the protein, suggesting that this domain serves as a recognition element, possibly for the ubiquitin ligase, E3. The mechanisms and structural motives that govern Id2 stability may have important implications to the regulation of the protein during normal differentiation and malignant transformation.
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Affiliation(s)
- Ifat Fajerman
- Department of Biochemistry and the Rappaport Family Institute for Research in the Medical Sciences, the Bruce Rappaport Faculty of Medicine, Technion-Israel Institute of Technology, 31096 Haifa, Israel
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46
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Ikeda A, Caldwell RG, Longnecker R, Ikeda M. Itchy, a Nedd4 ubiquitin ligase, downregulates latent membrane protein 2A activity in B-cell signaling. J Virol 2003; 77:5529-34. [PMID: 12692257 PMCID: PMC153961 DOI: 10.1128/jvi.77.9.5529-5534.2003] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Nedd4 family ubiquitin protein ligases (E3s) specifically associate with latent membrane protein 2A (LMP2A) of Epstein-Barr virus. Our previous studies analyzing LMP2A function in vitro have suggested that Nedd4 family E3s regulate LMP2A function. To determine the role of Nedd4 family E3s in LMP2A B-cell signaling, LMP2A transgenic (LMP2A(+)) mice were crossed with mice with the Itch-deficient (Itch(-/-)) background. Itchy, a mouse homologue of human AIP4, is a Nedd4 family E3 and is also the most abundant Nedd4 family E3 found in LMP2A affinity precipitates from B cells. There were significantly fewer B-cell receptor-positive B cells in spleen and bone marrow B cells in LMP2A(+) Itch(-/-) mice than in LMP2A(+) mice. In addition, LMP2A(+) Itch(-/-) bone marrow B cells formed larger colonies in cultures treated with interleukin-7 (IL-7) than control bone marrow B cells did. Finally, there was a dramatic increase in tyrosine phosphorylation of LMP2A and Syk in IL-7-cultured LMP2A(+) Itch(-/-) B cells. These results indicate that Nedd4 family E3s, in particular Itchy, downmodulate LMP2A activity in B-cell signaling.
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Affiliation(s)
- Akiko Ikeda
- Department of Microbiology-Immunology, Northwestern University Medical School, Chicago, Illinois 60611, USA
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