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Chen Y, Kokic G, Dienemann C, Dybkov O, Urlaub H, Cramer P. Structure of the transcribing RNA polymerase II-Elongin complex. Nat Struct Mol Biol 2023; 30:1925-1935. [PMID: 37932450 PMCID: PMC10716050 DOI: 10.1038/s41594-023-01138-w] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2023] [Accepted: 09/26/2023] [Indexed: 11/08/2023]
Abstract
Elongin is a heterotrimeric elongation factor for RNA polymerase (Pol) II transcription that is conserved among metazoa. Here, we report three cryo-EM structures of human Elongin bound to transcribing Pol II. The structures show that Elongin subunit ELOA binds the RPB2 side of Pol II and anchors the ELOB-ELOC subunit heterodimer. ELOA contains a 'latch' that binds between the end of the Pol II bridge helix and funnel helices, thereby inducing a conformational change near the polymerase active center. The latch is required for the elongation-stimulatory activity of Elongin, but not for Pol II binding, indicating that Elongin functions by allosterically regulating the conformational mobility of the polymerase active center. Elongin binding to Pol II is incompatible with association of the super elongation complex, PAF1 complex and RTF1, which also contain an elongation-stimulatory latch element.
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Affiliation(s)
- Ying Chen
- Department of Molecular Biology, Max Planck Institute for Multidisciplinary Sciences, Göttingen, Germany
- Department of Clinical Laboratory, Qilu Hospital of Shandong University, Jinan, China
| | - Goran Kokic
- Department of Molecular Biology, Max Planck Institute for Multidisciplinary Sciences, Göttingen, Germany
| | - Christian Dienemann
- Department of Molecular Biology, Max Planck Institute for Multidisciplinary Sciences, Göttingen, Germany
| | - Olexandr Dybkov
- Bioanalytical Mass Spectrometry, Max Planck Institute for Multidisciplinary Sciences, Göttingen, Germany
| | - Henning Urlaub
- Bioanalytical Mass Spectrometry, Max Planck Institute for Multidisciplinary Sciences, Göttingen, Germany
- University Medical Center Göttingen, Institute of Clinical Chemistry, Bioanalytics Group, Göttingen, Germany
- Cluster of Excellence 'Multiscale Bioimaging: from Molecular Machines to Networks of Excitable Cells' (MBExC), University of Göttingen, Göttingen, Germany
| | - Patrick Cramer
- Department of Molecular Biology, Max Planck Institute for Multidisciplinary Sciences, Göttingen, Germany.
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2
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Zhang Z, Huang Q, Wang Z, Zou J, Yu Z, Strauss Iii JF, Zhang Z. Elongin B is a binding partner of the male germ cell nuclear speckle protein sperm-associated antigen 16S (SPAG16S) and is regulated post-transcriptionally in the testis. Reprod Fertil Dev 2020; 31:962-971. [PMID: 30811962 DOI: 10.1071/rd18303] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2018] [Accepted: 12/21/2018] [Indexed: 12/12/2022] Open
Abstract
In this study we identified Elongin B, a regulatory subunit of the trimeric elongation factor Elongin ABC, which increases the overall rate of elongation by RNA polymerase II, as a major binding partner of sperm-associated antigen 16S (SPAG16S), a component of nuclear speckles. Nuclear speckles are nuclear subcompartments involved in RNA maturation. Previously, we showed that SPAG16S is essential for spermatogenesis. In the present study, a specific antibody against mouse Elongin B was generated and reacted with a protein with the predicted size of Elongin B in the testis; immunofluorescence staining revealed that the Elongin B was located in the nuclei and residual bodies. In round spermatids, Elongin B was colocalised with splicing factor SC35 (SC35), a marker of nuclear speckles. During the first wave of spermatogenesis, Elongin B transcripts were initially detected at Postnatal Day (PND) 8, and levels were greatly increased afterwards. However, Elongin B protein was only found from PND30, when germ cells progressed through spermiogenesis. Polysomal gradient analysis of Elongin B transcripts isolated from adult mouse testes revealed that most of the Elongin B mRNA was associated with translationally inactive, non-polysomal ribonucleoproteins. An RNA electrophoretic mobility shift assay demonstrated that the 3' untranslated region of the Elongin B transcript was bound by proteins present in testis but not liver extracts. These findings suggest that post-transcriptional regulation of Elongin B occurs in the testis, which is a common phenomenon during male germ cell development. As a major binding partner of SPAG16S, Elongin B may play an important role in spermatogenesis by modulating RNA maturation.
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Affiliation(s)
- Zhengang Zhang
- Department of Gastroenterology, Tongji Hospital, Huazhong University of Science and Technology, 1095 Jiefang da dao, Wuhan, Hubei 430030, China; and Department of Obstetrics and Gynecology, Virginia Commonwealth University, 1101 E. Marshall Street, Richmond, VA 23298, USA
| | - Qian Huang
- Department of Physiology, Wayne State University, 275E Hancock Street, Detroit, MI 48201, USA; and Department of Occupational and Environmental Health, Hubei Province Key Laboratory of Occupational Hazard Identification and Control, School of Public Health, Wuhan University of Science and Technology, 2 Huangjiahu xi lu, Wuhan, Hubei 430060, China
| | - Zhenyu Wang
- Department of Physiology, Wayne State University, 275E Hancock Street, Detroit, MI 48201, USA; and Department of Biochemistry, School of Medicine, Wuhan University of Science and Technology, 2 Huangjiahu xi lu, Wuhan, Hubei 430065, China
| | - Jie Zou
- Wuhan Institute of Skin Disease Prevention and Control, 64 Wusheng lu, Wuhan, Hubei 430030, China
| | - Zuoren Yu
- Research Center for Translational Medicine, Tongji University School of Medicine, Shanghai East Hospital, 150 Jimo lu, Shanghai, China
| | - Jerome F Strauss Iii
- Department of Obstetrics and Gynecology, Virginia Commonwealth University, 1101 E. Marshall Street, Richmond, VA 23298, USA
| | - Zhibing Zhang
- Department of Physiology, Wayne State University, 275E Hancock Street, Detroit, MI 48201, USA; and Department of Obstetrics and Gynecology, Wayne State University, 275E Hancock Street, Detroit, MI 48201, USA; and Corresponding author.
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3
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Knapp B, Roedig J, Boldt K, Krzysko J, Horn N, Ueffing M, Wolfrum U. Affinity proteomics identifies novel functional modules related to adhesion GPCRs. Ann N Y Acad Sci 2019; 1456:144-167. [PMID: 31441075 DOI: 10.1111/nyas.14220] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2019] [Revised: 07/08/2019] [Accepted: 07/25/2019] [Indexed: 01/04/2023]
Abstract
Adhesion G protein-coupled receptors (ADGRs) have recently become a target of intense research. Their unique protein structure, which consists of a G protein-coupled receptor combined with long adhesive extracellular domains, suggests a dual role in cell signaling and adhesion. Despite considerable progress in the understanding of ADGR signaling over the past years, the knowledge about ADGR protein networks is still limited. For most receptors, only a few interaction partners are known thus far. We aimed to identify novel ADGR-interacting partners to shed light on cellular protein networks that rely on ADGR function. For this, we applied affinity proteomics, utilizing tandem affinity purifications combined with mass spectrometry. Analysis of the acquired proteomics data provides evidence that ADGRs not only have functional roles at synapses but also at intracellular membranes, namely at the endoplasmic reticulum, the Golgi apparatus, mitochondria, and mitochondria-associated membranes (MAMs). Specifically, we found an association of ADGRs with several scaffold proteins of the membrane-associated guanylate kinases family, elementary units of the γ-secretase complex, the outer/inner mitochondrial membrane, MAMs, and regulators of the Wnt signaling pathways. Furthermore, the nuclear localization of ADGR domains together with their physical interaction with nuclear proteins and several transcription factors suggests a role of ADGRs in gene regulation.
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Affiliation(s)
- Barbara Knapp
- Institute of Molecular Physiology, Molecular Cell Biology, Johannes Gutenberg University of Mainz, Mainz, Germany
| | - Jens Roedig
- Institute of Molecular Physiology, Molecular Cell Biology, Johannes Gutenberg University of Mainz, Mainz, Germany
| | - Karsten Boldt
- Institute for Ophthalmic Research and Medical Bioanalytics, Centre for Ophthalmology, Eberhard-Karls University Tübingen, Tübingen, Germany
| | - Jacek Krzysko
- Institute of Molecular Physiology, Molecular Cell Biology, Johannes Gutenberg University of Mainz, Mainz, Germany
| | - Nicola Horn
- Institute for Ophthalmic Research and Medical Bioanalytics, Centre for Ophthalmology, Eberhard-Karls University Tübingen, Tübingen, Germany
| | - Marius Ueffing
- Institute for Ophthalmic Research and Medical Bioanalytics, Centre for Ophthalmology, Eberhard-Karls University Tübingen, Tübingen, Germany
| | - Uwe Wolfrum
- Institute of Molecular Physiology, Molecular Cell Biology, Johannes Gutenberg University of Mainz, Mainz, Germany
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4
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Weems JC, Slaughter BD, Unruh JR, Boeing S, Hall SM, McLaird MB, Yasukawa T, Aso T, Svejstrup JQ, Conaway JW, Conaway RC. Cockayne syndrome B protein regulates recruitment of the Elongin A ubiquitin ligase to sites of DNA damage. J Biol Chem 2017; 292:6431-6437. [PMID: 28292928 PMCID: PMC5399097 DOI: 10.1074/jbc.c117.777946] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2017] [Revised: 02/27/2017] [Indexed: 01/05/2023] Open
Abstract
Elongin A performs dual functions as the transcriptionally active subunit of RNA polymerase II (Pol II) elongation factor Elongin and as the substrate recognition subunit of a Cullin-RING E3 ubiquitin ligase that ubiquitylates Pol II in response to DNA damage. Assembly of the Elongin A ubiquitin ligase and its recruitment to sites of DNA damage is a tightly regulated process induced by DNA-damaging agents and α-amanitin, a drug that induces Pol II stalling. In this study, we demonstrate (i) that Elongin A and the ubiquitin ligase subunit CUL5 associate in cells with the Cockayne syndrome B (CSB) protein and (ii) that this interaction is also induced by DNA-damaging agents and α-amanitin. In addition, we present evidence that the CSB protein promotes stable recruitment of the Elongin A ubiquitin ligase to sites of DNA damage. Our findings are consistent with the model that the Elongin A ubiquitin ligase and the CSB protein function together in a common pathway in response to Pol II stalling and DNA damage.
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Affiliation(s)
- Juston C Weems
- From the Stowers Institute for Medical Research, Kansas City, Missouri 64110
| | - Brian D Slaughter
- From the Stowers Institute for Medical Research, Kansas City, Missouri 64110
| | - Jay R Unruh
- From the Stowers Institute for Medical Research, Kansas City, Missouri 64110
| | - Stefan Boeing
- the Mechanisms of Transcription Laboratory, The Francis Crick Institute, Clare Hall Laboratories, South Mimms EN6 3LD, United Kingdom
| | - Shawn M Hall
- From the Stowers Institute for Medical Research, Kansas City, Missouri 64110
| | - Merry B McLaird
- From the Stowers Institute for Medical Research, Kansas City, Missouri 64110
| | - Takashi Yasukawa
- the Department of Functional Genomics, Kochi Medical School, Kohasu, Oko-cho, Nankoku, Kochi 783-8505, Japan
| | - Teijiro Aso
- the Department of Functional Genomics, Kochi Medical School, Kohasu, Oko-cho, Nankoku, Kochi 783-8505, Japan
| | - Jesper Q Svejstrup
- the Mechanisms of Transcription Laboratory, The Francis Crick Institute, Clare Hall Laboratories, South Mimms EN6 3LD, United Kingdom
| | - Joan W Conaway
- From the Stowers Institute for Medical Research, Kansas City, Missouri 64110,
- the Department of Biochemistry and Molecular Biology, University of Kansas Medical Center, Kansas City, Kansas 66160, and
| | - Ronald C Conaway
- From the Stowers Institute for Medical Research, Kansas City, Missouri 64110,
- the Department of Biochemistry and Molecular Biology, University of Kansas Medical Center, Kansas City, Kansas 66160, and
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5
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Cai W, Yang H. The structure and regulation of Cullin 2 based E3 ubiquitin ligases and their biological functions. Cell Div 2016; 11:7. [PMID: 27222660 PMCID: PMC4878042 DOI: 10.1186/s13008-016-0020-7] [Citation(s) in RCA: 54] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2016] [Accepted: 05/11/2016] [Indexed: 11/23/2022] Open
Abstract
Background Cullin-RING E3 ubiquitin ligase complexes play a central role in targeting cellular proteins for ubiquitination-dependent protein turnover through 26S proteasome. Cullin-2 is a member of the Cullin family, and it serves as a scaffold protein for Elongin B and C, Rbx1 and various substrate recognition receptors to form E3 ubiquitin ligases. Main body of the abstract First, the composition, structure and the regulation of Cullin-2 based E3 ubiquitin ligases were introduced. Then the targets, the biological functions of complexes that use VHL, Lrr-1, Fem1b, Prame, Zyg-11, BAF250, Rack1 as substrate targeting subunits were described, and their involvement in diseases was discussed. A small molecule inhibitor of Cullins as a potential anti-cancer drug was introduced. Furthermore, proteins with VHL box that might bind to Cullin-2 were described. Finally, how different viral proteins form E3 ubiquitin ligase complexes with Cullin-2 to counter host viral defense were explained. Conclusions Cullin-2 based E3 ubiquitin ligases, using many different substrate recognition receptors, recognize a number of substrates and regulate their protein stability. These complexes play critical roles in biological processes and diseases such as cancer, germline differentiation and viral defense. Through the better understanding of their biology, we can devise and develop new therapeutic strategies to treat cancers, inherited diseases and viral infections.
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Affiliation(s)
- Weijia Cai
- Department of Pathology and Cell Biology, Thomas Jefferson University, Philadelphia, PA 19107 USA
| | - Haifeng Yang
- Department of Pathology and Cell Biology, Thomas Jefferson University, Philadelphia, PA 19107 USA
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6
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DENG ZHUO, ZHOU JIANCHENG, HAN XI, LI XU. TCEB2 confers resistance to VEGF-targeted therapy in ovarian cancer. Oncol Rep 2015; 35:359-65. [DOI: 10.3892/or.2015.4388] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2015] [Accepted: 08/26/2015] [Indexed: 11/05/2022] Open
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7
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Weems JC, Slaughter BD, Unruh JR, Hall SM, McLaird MB, Gilmore JM, Washburn MP, Florens L, Yasukawa T, Aso T, Conaway JW, Conaway RC. Assembly of the Elongin A Ubiquitin Ligase Is Regulated by Genotoxic and Other Stresses. J Biol Chem 2015; 290:15030-41. [PMID: 25878247 DOI: 10.1074/jbc.m114.632794] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2014] [Indexed: 11/06/2022] Open
Abstract
Elongin A performs dual functions in cells as a component of RNA polymerase II (Pol II) transcription elongation factor Elongin and as the substrate recognition subunit of a Cullin-RING E3 ubiquitin ligase that has been shown to target Pol II stalled at sites of DNA damage. Here we investigate the mechanism(s) governing conversion of the Elongin complex from its elongation factor to its ubiquitin ligase form. We report the discovery that assembly of the Elongin A ubiquitin ligase is a tightly regulated process. In unstressed cells, Elongin A is predominately present as part of Pol II elongation factor Elongin. Assembly of Elongin A into the ubiquitin ligase is strongly induced by genotoxic stress; by transcriptional stresses that lead to accumulation of stalled Pol II; and by other stimuli, including endoplasmic reticulum and nutrient stress and retinoic acid signaling, that activate Elongin A-dependent transcription. Taken together, our findings shed new light on mechanisms that control the Elongin A ubiquitin ligase and suggest that it may play a role in Elongin A-dependent transcription.
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Affiliation(s)
- Juston C Weems
- From the Stowers Institute for Medical Research, Kansas City, Missouri 64110
| | - Brian D Slaughter
- From the Stowers Institute for Medical Research, Kansas City, Missouri 64110
| | - Jay R Unruh
- From the Stowers Institute for Medical Research, Kansas City, Missouri 64110
| | - Shawn M Hall
- From the Stowers Institute for Medical Research, Kansas City, Missouri 64110
| | - Merry B McLaird
- From the Stowers Institute for Medical Research, Kansas City, Missouri 64110
| | - Joshua M Gilmore
- From the Stowers Institute for Medical Research, Kansas City, Missouri 64110
| | - Michael P Washburn
- From the Stowers Institute for Medical Research, Kansas City, Missouri 64110, the Departments of Pathology and Laboratory Medicine and
| | - Laurence Florens
- From the Stowers Institute for Medical Research, Kansas City, Missouri 64110
| | - Takashi Yasukawa
- the Department of Functional Genomics, Kochi Medical School, Kohasu, Oko-cho, Nankoku, Kochi 783-8505, Japan
| | - Teijiro Aso
- the Department of Functional Genomics, Kochi Medical School, Kohasu, Oko-cho, Nankoku, Kochi 783-8505, Japan
| | - Joan W Conaway
- From the Stowers Institute for Medical Research, Kansas City, Missouri 64110, Biochemistry and Molecular Biology, University of Kansas Medical Center, Kansas City, Kansas 66160, and
| | - Ronald C Conaway
- From the Stowers Institute for Medical Research, Kansas City, Missouri 64110, Biochemistry and Molecular Biology, University of Kansas Medical Center, Kansas City, Kansas 66160, and
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8
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Wilson MD, Harreman M, Taschner M, Reid J, Walker J, Erdjument-Bromage H, Tempst P, Svejstrup JQ. Proteasome-mediated processing of Def1, a critical step in the cellular response to transcription stress. Cell 2013; 154:983-995. [PMID: 23993092 PMCID: PMC3778974 DOI: 10.1016/j.cell.2013.07.028] [Citation(s) in RCA: 57] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/11/2012] [Revised: 05/30/2013] [Accepted: 07/19/2013] [Indexed: 11/25/2022]
Abstract
DNA damage triggers polyubiquitylation and degradation of the largest subunit of RNA polymerase II (RNAPII), a "mechanism of last resort" employed during transcription stress. In yeast, this process is dependent on Def1 through a previously unresolved mechanism. Here, we report that Def1 becomes activated through ubiquitylation- and proteasome-dependent processing. Def1 processing results in the removal of a domain promoting cytoplasmic localization, resulting in nuclear accumulation of the clipped protein. Nuclear Def1 then binds RNAPII, utilizing a ubiquitin-binding domain to recruit the Elongin-Cullin E3 ligase complex via a ubiquitin-homology domain in the Ela1 protein. This facilitates polyubiquitylation of Rpb1, triggering its proteasome-mediated degradation. Together, these results outline the multistep mechanism of Rpb1 polyubiquitylation triggered by transcription stress and uncover the key role played by Def1 as a facilitator of Elongin-Cullin ubiquitin ligase function.
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Affiliation(s)
- Marcus D Wilson
- Mechanisms of Transcription Laboratory, Clare Hall Laboratories, Cancer Research UK London Research Institute, South Mimms EN6 3LD, UK
| | - Michelle Harreman
- Mechanisms of Transcription Laboratory, Clare Hall Laboratories, Cancer Research UK London Research Institute, South Mimms EN6 3LD, UK
| | - Michael Taschner
- Mechanisms of Transcription Laboratory, Clare Hall Laboratories, Cancer Research UK London Research Institute, South Mimms EN6 3LD, UK
| | - James Reid
- Mechanisms of Transcription Laboratory, Clare Hall Laboratories, Cancer Research UK London Research Institute, South Mimms EN6 3LD, UK
| | - Jane Walker
- Mechanisms of Transcription Laboratory, Clare Hall Laboratories, Cancer Research UK London Research Institute, South Mimms EN6 3LD, UK
| | - Hediye Erdjument-Bromage
- Molecular Biology Programme, Memorial Sloan-Kettering Cancer Center, York Avenue 1275, New York, NY 10021, USA
| | - Paul Tempst
- Molecular Biology Programme, Memorial Sloan-Kettering Cancer Center, York Avenue 1275, New York, NY 10021, USA
| | - Jesper Q Svejstrup
- Mechanisms of Transcription Laboratory, Clare Hall Laboratories, Cancer Research UK London Research Institute, South Mimms EN6 3LD, UK.
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Wang X, Wang X, Zhang H, Lv M, Zuo T, Wu H, Wang J, Liu D, Wang C, Zhang J, Li X, Wu J, Yu B, Kong W, Yu X. Interactions between HIV-1 Vif and human ElonginB-ElonginC are important for CBF-β binding to Vif. Retrovirology 2013; 10:94. [PMID: 23988114 PMCID: PMC3765967 DOI: 10.1186/1742-4690-10-94] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2013] [Accepted: 08/26/2013] [Indexed: 01/18/2023] Open
Abstract
Background The HIV-1 accessory factor Vif is necessary for efficient viral infection in non-permissive cells. Vif antagonizes the antiviral activity of human cytidine deaminase APOBEC3 proteins that confer the non-permissive phenotype by tethering them (APOBEC3DE/3F/3G) to the Vif-CBF-β-ElonginB-ElonginC-Cullin5-Rbx (Vif-CBF-β-EloB-EloC-Cul5-Rbx) E3 complex to induce their proteasomal degradation. EloB and EloC were initially reported as positive regulatory subunits of the Elongin (SIII) complex. Thereafter, EloB and EloC were found to be components of Cul-E3 complexes, contributing to proteasomal degradation of specific substrates. CBF-β is a newly identified key regulator of Vif function, and more information is needed to further clarify its regulatory mechanism. Here, we comprehensively investigated the functions of EloB (together with EloC) in the Vif-CBF-β-Cul5 E3 ligase complex. Results The results revealed that: (1) EloB (and EloC) positively affected the recruitment of CBF-β to Vif. Both knockdown of endogenous EloB and over-expression of its mutant with a 34-residue deletion in the COOH-terminal tail (EloBΔC34/EBΔC34) impaired the Vif-CBF-β interaction. (2) Introduction of both the Vif SLQ → AAA mutant (VifΔSLQ, which dramatically impairs Vif-EloB-EloC binding) and the Vif PPL → AAA mutant (VifΔPPL, which is thought to reduce Vif-EloB binding) could reduce CBF-β binding. (3) EloB-EloC but not CBF-β could greatly enhance the folding of full-length Vif in Escherichia coli. (4) The over-expression of EloB or the N-terminal ubiquitin-like (UbL) domain of EloB could significantly improve the stability of Vif/VifΔSLQ/VifΔPPL through the region between residues 9 and 14. Conclusion Our results indicate that the Vif interaction with EloB-EloC may contribute to recruitment of CBF-β to Vif, demonstrating that the EloB C-teminus may play a role in improving Vif function and that the over-expression of EloB results in Vif stabilization.
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Affiliation(s)
- Xiaodan Wang
- National Engineering Laboratory for AIDS Vaccine, College of Life Science, Jilin University, Changchun, Jilin Province, People's Republic of China.
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10
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Integrated molecular analysis of clear-cell renal cell carcinoma. Nat Genet 2013; 45:860-7. [DOI: 10.1038/ng.2699] [Citation(s) in RCA: 785] [Impact Index Per Article: 71.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2013] [Accepted: 06/18/2013] [Indexed: 12/11/2022]
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11
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Culig Z, Puhr M. Interleukin-6: a multifunctional targetable cytokine in human prostate cancer. Mol Cell Endocrinol 2012; 360:52-8. [PMID: 21664423 PMCID: PMC3409376 DOI: 10.1016/j.mce.2011.05.033] [Citation(s) in RCA: 122] [Impact Index Per Article: 10.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/08/2011] [Revised: 05/19/2011] [Accepted: 05/23/2011] [Indexed: 12/19/2022]
Abstract
Several cytokines are involved in regulation of cellular events in prostate cancer. Interleukin-6 (IL-6) was frequently investigated in prostate cancer models because of its increased expression in cancer tissue at early stages of the disease. In patients with metastatic prostate cancer, it is well-known that IL-6 levels increase in serum. High levels of IL-6 were measured in the supernatants of cells which do not respond to androgenic stimulation. IL-6 expression in prostate cancer increases due to enhanced expression of transforming growth factor-beta, and members of the activating protein-1 complex, and loss of the retinoblastoma tumour suppressor. IL-6 activation of androgen receptor (AR) may contribute to progression of a subgroup of prostate cancers. Results obtained with two prostate cancer cell lines, LNCaP and MDA PCa 2b, indicate that IL-6 activation of AR may cause either stimulatory or inhibitory responses on proliferation. Interestingly, prolonged treatment with IL-6 led to establishment of an IL-6 autocrine loop, suppressed signal transducer and activator of transcription (STAT)3 activation, and increased mitogen-activated protein kinase phosphorylation. In several cell lines IL-6 acts as a survival molecule through activation of the signalling pathway of phosphotidylinositol 3-kinase. Expression of suppressors of cytokine signalling (SOCS) has been studied in prostate cancer. SOCS-3 prevents phosphorylation of STAT3 and is an important anti-apoptotic factor in AR-negative prostate cancer cells. Experimental therapy against IL-6 in prostate cancer is based on the use of the monoclonal antibody siltuximab which may be used for personalised therapy coming in the future.
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Affiliation(s)
- Zoran Culig
- Department of Urology, Experimental Urology, Innsbruck Medical University, Anichstrasse 35, A-6020 Innsbruck, Austria.
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12
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Yang ZM, Chen WW, Wang YF. Gene expression profiling in gastric mucosa from Helicobacter pylori-infected and uninfected patients undergoing chronic superficial gastritis. PLoS One 2012; 7:e33030. [PMID: 22438889 PMCID: PMC3306372 DOI: 10.1371/journal.pone.0033030] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2011] [Accepted: 02/09/2012] [Indexed: 12/13/2022] Open
Abstract
Helicobacter pylori infection reprograms host gene expression and influences various cellular processes, which have been investigated by cDNA microarray using in vitro culture cells and in vivo gastric biopsies from patients of the Chronic Abdominal Complaint. To further explore the effects of H. pylori infection on host gene expression, we have collected the gastric antral mucosa samples from 6 untreated patients with gastroscopic and pathologic confirmation of chronic superficial gastritis. Among them three patients were infected by H. pylori and the other three patients were not. These samples were analyzed by a microarray chip which contains 14,112 cloned cDNAs, and microarray data were analyzed via BRB ArrayTools software and Ingenuity Pathways Analysis (IPA) website. The results showed 34 genes of 38 differentially expressed genes regulated by H. pylori infection had been annotated. The annotated genes were involved in protein metabolism, inflammatory and immunological reaction, signal transduction, gene transcription, trace element metabolism, and so on. The 82% of these genes (28/34) were categorized in three molecular interaction networks involved in gene expression, cancer progress, antigen presentation and inflammatory response. The expression data of the array hybridization was confirmed by quantitative real-time PCR assays. Taken together, these data indicated that H. pylori infection could alter cellular gene expression processes, escape host defense mechanism, increase inflammatory and immune responses, activate NF-κB and Wnt/β-catenin signaling pathway, disturb metal ion homeostasis, and induce carcinogenesis. All of these might help to explain H. pylori pathogenic mechanism and the gastroduodenal pathogenesis induced by H. pylori infection.
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Affiliation(s)
- Ze-Min Yang
- Pi-Wei Institute, Guangzhou University of Chinese Medicine, Guangzhou, Guangdong, China
- School of Basic Courses, Guangdong Pharmaceutical University, Guangzhou, Guangdong, China
| | - Wei-Wen Chen
- Pi-Wei Institute, Guangzhou University of Chinese Medicine, Guangzhou, Guangdong, China
- E-Institute of Traditional Chinese Medicine Internal Medicine, Shanghai Municipal Education Committee, Shanghai, China
- * E-mail:
| | - Ying-Fang Wang
- School of Chinese Materia Medica, Guangdong Pharmaceutical University, Guangzhou, Guangdong, China
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Okumura F, Matsuzaki M, Nakatsukasa K, Kamura T. The Role of Elongin BC-Containing Ubiquitin Ligases. Front Oncol 2012; 2:10. [PMID: 22649776 PMCID: PMC3355856 DOI: 10.3389/fonc.2012.00010] [Citation(s) in RCA: 55] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2011] [Accepted: 01/17/2012] [Indexed: 02/06/2023] Open
Abstract
The Elongin complex was originally identified as a positive regulator of RNA polymerase II and is composed of a transcriptionally active subunit (A) and two regulatory subunits (B and C). The Elongin BC complex enhances the transcriptional activity of Elongin A. “Classical” SOCS box-containing proteins interact with the Elongin BC complex and have ubiquitin ligase activity. They also interact with the scaffold protein Cullin (Cul) and the RING domain protein Rbx and thereby are members of the Cullin RING ligase (CRL) superfamily. The Elongin BC complex acts as an adaptor connecting Cul and SOCS box proteins. Recently, it was demonstrated that classical SOCS box proteins can be further divided into two groups, Cul2- and Cul5-type proteins. The classical SOCS box-containing protein pVHL is now classified as a Cul2-type protein. The Elongin BC complex containing CRL family is now considered two distinct protein assemblies, which play an important role in regulating a variety of cellular processes such as tumorigenesis, signal transduction, cell motility, and differentiation.
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Affiliation(s)
- Fumihiko Okumura
- Division of Biological Science, Graduate School of Science, Nagoya University Nagoya, Aichi, Japan
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Mammalian Elongin A complex mediates DNA-damage-induced ubiquitylation and degradation of Rpb1. EMBO J 2008; 27:3256-66. [PMID: 19037258 DOI: 10.1038/emboj.2008.249] [Citation(s) in RCA: 80] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2008] [Accepted: 11/05/2008] [Indexed: 01/21/2023] Open
Abstract
The Elongin complex stimulates the rate of transcription elongation by RNA polymerase II (pol II) by suppressing transient pausing of the pol II at many sites along the DNA. Elongin is composed of a transcriptionally active A subunit and two small regulatory B and C subunits, which can form an isolable Elongin BC subcomplex. Here, we have shown that both the ubiquitylation and proteasomal degradation of the largest subunit of pol II (Rpb1) following UV-irradiation are significantly suppressed in Elongin A-deficient cells; however, in both cases suppression is rescued by transfection of wild-type Elongin A. Moreover, we have demonstrated that the Elongin A-Elongin BC complex is capable of assembling with the Cul5/Rbx2 module, and that this hetero-pentamer complex efficiently ubiquitylates Rpb1 in vitro. Mechanistic studies indicate that colocalization of Elongin A and Cul5 in cells and the interaction of Elongin A with the Ser5-phosphorylated form of Rpb1 are strongly enhanced following UV-irradiation. Taken together, our results suggest that mammalian Elongin A is directly involved in ubiquitylation and degradation of Rpb1 following DNA damage.
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Pattanakitsakul SN, Rungrojcharoenkit K, Kanlaya R, Sinchaikul S, Noisakran S, Chen ST, Malasit P, Thongboonkerd V. Proteomic analysis of host responses in HepG2 cells during dengue virus infection. J Proteome Res 2007; 6:4592-600. [PMID: 17979228 DOI: 10.1021/pr070366b] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Dengue virus infection remains a public health problem worldwide. However, its pathogenic mechanisms and pathophysiology are still poorly understood. We performed proteomic analysis to evaluate early host responses (as indicated by altered proteins) in human target cells during dengue virus infection. HepG2 cells were infected with dengue virus serotype 2 (DEN-2) at multiplicity of infection (MOI) of 0.1, 0.5, and 1.0. Quantitative analyses of DEN-2 infection and cell death at 12, 24, and 48 h postinfection showed that the MOI of 1.0 with 24 h postinfection duration was the optimal condition to evaluate early host responses, as this condition provided the high %Infection ( approximately 80%), while %Cell death ( approximately 20%) was comparable to that of the mock-control cells. Proteins derived from the mock-control and DEN-2-infected cells were resolved by 2-D PAGE ( n = 5 gels for each group) and visualized by SYPRO Ruby stain. Quantitative intensity analysis revealed 17 differentially expressed proteins, which were successfully identified by peptide mass fingerprinting. Most of these altered proteins were the key factors involved in transcription and translation processes. Further functional study on these altered proteins may lead to better understanding of the pathogenic mechanisms and host responses to dengue virus infection, and also to the identification of new therapeutic targets for dengue virus infection.
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Affiliation(s)
- Sa-Nga Pattanakitsakul
- Medical Molecular Biology Unit, Office for Research and Development, Faculty of Medicine Siriraj Hospital, Mahidol University, Bangkok, Thailand
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Miyata K, Yasukawa T, Fukuda M, Takeuchi T, Yamazaki K, Sakumi K, Tamamori-Adachi M, Ohnishi Y, Ohtsuki Y, Nakabeppu Y, Kitajima S, Onishi S, Aso T. Induction of apoptosis and cellular senescence in mice lacking transcription elongation factor, Elongin A. Cell Death Differ 2006; 14:716-26. [PMID: 17170753 DOI: 10.1038/sj.cdd.4402067] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
Elongin A is a transcription elongation factor that increases the overall rate of mRNA chain elongation by RNA polymerase II. To gain more insight into the physiological functions of Elongin A, we generated Elongin A-deficient mice. Elongin A homozygous mutant (Elongin A(-/-)) embryos demonstrated a severely retarded development and died at between days 10.5 and 12.5 of gestation, most likely due to extensive apoptosis. Moreover, mouse embryonic fibroblasts (MEFs) derived from Elongin A(-/-) embryos exhibited not only increased apoptosis but also senescence-like growth defects accompanied by the activation of p38 MAPK and p53. Knockdown of Elongin A in MEFs by RNA interference also dramatically induced the senescent phenotype. A study using inhibitors of p38 MAPK and p53 and the generation of Elongin A-deficient mice with p53-null background suggests that both the p38 MAPK and p53 pathways are responsible for the induction of senescence-like phenotypes, whereas additional signaling pathways appear to be involved in the mediation of apoptosis in Elongin A(-/-) cells. Taken together, our results suggest that Elongin A is required for the transcription of genes essential for early embryonic development and downregulation of its activity is tightly associated with cellular senescence.
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Affiliation(s)
- K Miyata
- Department of Functional Genomics, Kochi Medical School, Kohasu, Oko-cho, Nankoku, Kochi, Japan
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17
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Yasukawa T, Sugimura K, Fukuda M, Yamazaki K, Kitajima S, Okumura K, Aso T. Functional characterization of a mammalian transcription factor, Elongin A. Biochem Biophys Res Commun 2006; 352:237-43. [PMID: 17112477 DOI: 10.1016/j.bbrc.2006.11.012] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2006] [Accepted: 11/06/2006] [Indexed: 11/17/2022]
Abstract
Elongin A is the transcriptionally active subunit of the Elongin complex that strongly stimulates the rate of elongation by RNA polymerase II (pol II) by suppressing the transient pausing of the polymerase at many sites along the DNA template. We have recently shown that Elongin A-deficient mice are embryonic lethal, and mouse embryonic fibroblasts (MEFs) derived from Elongin A(-/-) embryos display not only increased apoptosis but also senescence-like phenotypes accompanied by the activation of p53. To further understand the function of Elongin A in vivo, we have carried out the structure-function analysis of Elongin A and identified sequences critical to its nuclear localization and direct interaction with pol II. Moreover, we have analyzed the replication fork movement in wild-type and Elongin A(-/-) MEFs, and shown the possibility that the genomic instability observed in Elongin A(-/-) MEFs might be caused by the replication fork collapse due to Elongin A deficiency.
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Affiliation(s)
- Takashi Yasukawa
- Department of Functional Genomics, Kochi Medical School, Kohasu, Oko-cho, Nankoku, Kochi 783-8505, Japan
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18
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Kamura T, Maenaka K, Kotoshiba S, Matsumoto M, Kohda D, Conaway RC, Conaway JW, Nakayama KI. VHL-box and SOCS-box domains determine binding specificity for Cul2-Rbx1 and Cul5-Rbx2 modules of ubiquitin ligases. Genes Dev 2005; 18:3055-65. [PMID: 15601820 PMCID: PMC535916 DOI: 10.1101/gad.1252404] [Citation(s) in RCA: 371] [Impact Index Per Article: 19.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
The ECS (Elongin B/C-Cul2/Cul5-SOCS-box protein) complex is a member of a family of ubiquitin ligases that share a Cullin-Rbx module. SOCS-box proteins recruit substrates to the ECS complex and are linked to Cullin-Rbx via Elongin B/C. VHL has been implicated as a SOCS-box protein, but lacks a C-terminal sequence (downstream of the BC box) of the SOCS box. We now show that VHL specifically interacts with endogenous Cul2-Rbx1 in mammalian cells, whereas SOCS-box proteins associate with Cul5-Rbx2. We also identify LRR-1 and FEM1B as proteins that share a region of homology with VHL (the VHL box, including the BC box and downstream residues) and associate with Cul2-Rbx1. ECS complexes can thus be classified into two distinct protein assemblies, that is, those that contain a subunit with a VHL box (composed of the BC box and a downstream Cul2 box) that interacts with Cul2-Rbx1, and those that contain a subunit with a SOCS box (BC box and downstream Cul5 box) that interacts with Cul5-Rbx2. Domain-swapping analyses showed that the specificity of interaction of VHL-box and SOCS-box proteins with Cullin-Rbx modules is determined by the Cul2 and Cul5 boxes, respectively. Finally, RNAi-mediated knockdown of the Cul2-Rbx1 inhibited the VHL-mediated degradation of HIF-2alpha, whereas knockdown of Cul5-Rbx2 did not affect it. These data suggest that the functions of the Cul2-Rbx1 and Cul5-Rbx2 modules are distinct.
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Affiliation(s)
- Takumi Kamura
- Department of Molecular and Cellular Biology, Medical Institute of Bioregulation, Kyushu University, Higashi-ku, Fukuoka, Fukuoka 812-8582, Japan
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Sims RJ, Belotserkovskaya R, Reinberg D. Elongation by RNA polymerase II: the short and long of it. Genes Dev 2004; 18:2437-68. [PMID: 15489290 DOI: 10.1101/gad.1235904] [Citation(s) in RCA: 533] [Impact Index Per Article: 26.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
Appreciable advances into the process of transcript elongation by RNA polymerase II (RNAP II) have identified this stage as a dynamic and highly regulated step of the transcription cycle. Here, we discuss the many factors that regulate the elongation stage of transcription. Our discussion includes the classical elongation factors that modulate the activity of RNAP II, and the more recently identified factors that facilitate elongation on chromatin templates. Additionally, we discuss the factors that associate with RNAP II, but do not modulate its catalytic activity. Elongation is highlighted as a central process that coordinates multiple stages in mRNA biogenesis and maturation.
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Affiliation(s)
- Robert J Sims
- Howard Hughes Medical Institute, Robert Wood Johnson Medical School, Piscataway, New Jersey 08854, USA
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20
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Gerber M, Eissenberg JC, Kong S, Tenney K, Conaway JW, Conaway RC, Shilatifard A. In vivo requirement of the RNA polymerase II elongation factor elongin A for proper gene expression and development. Mol Cell Biol 2004; 24:9911-9. [PMID: 15509793 PMCID: PMC525478 DOI: 10.1128/mcb.24.22.9911-9919.2004] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
A number of transcription factors that increase the catalytic rate of mRNA synthesis by RNA polymerase II (Pol II) have been purified from higher eukaryotes. Among these are the ELL family, DSIF, and the heterotrimeric elongin complex. Elongin A, the largest subunit of the elongin complex, is the transcriptionally active subunit, while the smaller elongin B and C subunits appear to act as regulatory subunits. While much is known about the in vitro properties of elongin A and other members of this class of elongation factors, the physiological role(s) of these proteins remain largely unclear. To elucidate in vivo functions of elongin A, we have characterized its Drosophila homologue (dEloA). dEloA associates with transcriptionally active puff sites within Drosophila polytene chromosomes and exhibits many of the expected biochemical and cytological properties consistent with a Pol II-associated elongation factor. RNA interference-mediated depletion of dEloA demonstrated that elongin A is an essential factor that is required for proper metamorphosis. Consistent with this observation, dEloA expression peaks during the larval stages of development, suggesting that this factor may be important for proper regulation of developmental events during these stages. The discovery of the role of elongin A in an in vivo model system defines the novel contribution played by RNA polymerase II elongation machinery in regulation of gene expression that is required for proper development.
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Affiliation(s)
- Mark Gerber
- Edward A. Doisy Department of Biochemistry and Molecular Biology, St. Louis University Health Sciences Center, 1402 South Grand Blvd., St. Louis, MO 63104, USA
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21
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Li Z, Metze D, Nashan D, Müller-Tidow C, Serve HL, Poremba C, Luger TA, Böhm M. Expression of SOCS-1, suppressor of cytokine signalling-1, in human melanoma. J Invest Dermatol 2004; 123:737-45. [PMID: 15373779 DOI: 10.1111/j.0022-202x.2004.23408.x] [Citation(s) in RCA: 62] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Cytokine resistance is a well-established feature of melanoma cell progression and represents also a major obstacle in immunotherapy of patients with metastatic melanoma. To check whether suppressors of cytokine signalling (SOCS) play a role in cytokine resistance and tumor progression of melanoma, we investigated the expression and regulation of SOCS-1, an established negative regulator of interleukin-6 (IL-6) and interferon (IFN) signalling. In vitro SOCS-1 transcripts were detectable by RT-PCR in 8 out of 8 human melanoma cell lines derived from different tumor stages. Normal human melanocytes also expressed SOCS-1 mRNA in the presence or absence of artificial growth factors. Both IL-6 and alpha-IFN induced rapid and transient SOCS-1 mRNA expression in WM35 and WM9 melanoma cells. At the protein level, SOCS-1 was undetectable in normal human melanocytes whereas uniformly expressed in all tested melanoma cell lines. The aberrant SOCS-1 protein expression in melanoma cells was recapitalized in situ as shown by immunohistochemical analysis. SOCS-1 immunoreactivity was closely related to tumor invasion (Clark level), tumor thickness according to Breslow, and stage of the disease. In contrast, melanocytes in normal skin or melanocytic nevi lacked SOCS-1 protein expression. Our findings show that melanoma cells express a member of the SOCS family, SOCS-1, in vitro and in situ. SOCS-1 is a progression marker of human melanoma and may downregulate biological responses by endogenous and/or therapeutically administered cytokines.
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Affiliation(s)
- Zhuo Li
- Department of Dermatology and Ludwig Boltzmann Institute for Cell Biology and Immunobiology of the Skin, University of Münster, Münster, Germany
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22
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Yan Q, Kamura T, Cai Y, Jin J, Ivan M, Mushegian A, Conaway RC, Conaway JW. Identification of Elongin C and Skp1 sequences that determine Cullin selection. J Biol Chem 2004; 279:43019-26. [PMID: 15280393 DOI: 10.1074/jbc.m408018200] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
The multiprotein von Hippel-Lindau (VHL) tumor suppressor and Skp1-Cul1-F-box protein (SCF) complexes belong to families of structurally related E3 ubiquitin ligases. In the VHL ubiquitin ligase, the VHL protein serves as the substrate recognition subunit, which is linked by the adaptor protein Elongin C to a heterodimeric Cul2/Rbx1 module that activates ubiquitylation of target proteins by the E2 ubiquitin-conjugating enzyme Ubc5. In SCF ubiquitin ligases, F-box proteins serve as substrate recognition subunits, which are linked by the Elongin C-like adaptor protein Skp1 to a Cul1/Rbx1 module that activates ubiquitylation of target proteins, in most cases by the E2 Cdc34. In this report, we investigate the functions of the Elongin C and Skp1 proteins in reconstitution of VHL and SCF ubiquitin ligases. We identify Elongin C and Skp1 structural elements responsible for selective interaction with their cognate Cullin/Rbx1 modules. In addition, using altered specificity Elongin C and F-box protein mutants, we investigate models for the mechanism underlying E2 selection by VHL and SCF ubiquitin ligases. Our findings provide evidence that E2 selection by VHL and SCF ubiquitin ligases is determined not solely by the Cullin/Rbx1 module, the target protein, or the integrity of the substrate recognition subunit but by yet to be elucidated features of these macromolecular complexes.
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Affiliation(s)
- Qin Yan
- Stowers Institute for Medical Research, Kansas City, Missouri 64110, USA
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Schneider A, Fischer A, Krüger C, Aronowski J. Identification of regulated genes during transient cortical ischemia in mice by restriction-mediated differential display (RMDD). ACTA ACUST UNITED AC 2004; 124:20-8. [PMID: 15093682 DOI: 10.1016/j.molbrainres.2004.02.002] [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] [Accepted: 02/05/2004] [Indexed: 01/07/2023]
Abstract
Cerebral ischemia induces transcriptional changes in a number of pathophysiologically important genes. Here we have systematically studied gene expression changes in the cortex after 150 min of focal cortical ischemia and 2 and 6 h reperfusion in the mouse by a fragment display technique (restriction-mediated differential display, RMDD). We identified 57 transcriptionally altered genes, of which 46 were known genes, and 11 unknown sequences. Of note, 14% of the regulated genes detected at 2 h reperfusion time were co-regulated in the contralateral cortex. Four genes were verified to be upregulated by quantitative PCR. These were Metallothionein-II (mt2), Receptor (calcitonin)-activity modifying protein 2 (ramp2), Mitochondrial phosphoprotein 65 (MIPP65), and the transcription elongation factor B2/elongin B (tceb). We could identify several genes that are known to be induced by cerebral ischemia, such as the metallothioneins and c-fos. Many of the genes identified provide hints to potential new mechanisms in ischemic pathophysiology. We discuss the identity of the regulated genes in view of their possible usefulness for pharmacological intervention in cerebral ischemia.
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Affiliation(s)
- Armin Schneider
- Department of Molecular Neurology and Technology, Axaron Bioscience AG, Im Neuenheimer Feld 515, 69120 Heidelberg, Germany.
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24
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Shilatifard A. Transcriptional elongation control by RNA polymerase II: a new frontier. ACTA ACUST UNITED AC 2004; 1677:79-86. [PMID: 15020049 DOI: 10.1016/j.bbaexp.2003.11.013] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2003] [Revised: 11/18/2003] [Accepted: 11/18/2003] [Indexed: 01/22/2023]
Abstract
The transcription elongation complex, once thought to be composed of merely the DNA template, RNA polymerase II and the nascent RNA transcript, is now burgeoning as a unit as multifaceted and complicated as the transcription initiation complex. Studies concentrated in defining the elongation stage of transcription during the past recent years have resulted in the discovery of a diverse collection of transcription elongation factors that are either directly involved in the regulation of the rate of the elongating RNA polymerase II or can modulate messenger RNA (mRNA) processing and transport. Such studies have demonstrated that the elongation stage of transcription is highly regulated and has opened a new era of studies defining the molecular role of such transcription elongation factors in cellular development, differentiation and disease progression. Recent studies on the role of RNA polymerase II elongation factors in regulating of the overall rate of transcription both in vitro and in vivo, histone modification by methylation and organismal development will be reviewed here.
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Affiliation(s)
- Ali Shilatifard
- Department of Biochemistry and the Cancer Center, Saint Louis University School of Medicine, 1402 South Grand Blvd, St. Louis, MO 63104, USA.
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25
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Abstract
Synthesis of eukaryotic mRNA by RNA polymerase II is an elaborate biochemical process that requires the concerted action of a large set of transcription factors. RNA polymerase II transcription proceeds through multiple stages designated preinitiation, initiation, and elongation. Historically, studies of the elongation stage of eukaryotic mRNA synthesis have lagged behind studies of the preinitiation and initiation stages; however, in recent years, efforts to elucidate the mechanisms governing elongation have led to the discovery of a diverse collection of transcription factors that directly regulate the activity of elongating RNA polymerase II. Moreover, these studies have revealed unanticipated roles for the RNA polymerase II elongation complex in such processes as DNA repair and recombination and the proper processing and nucleocytoplasmic transport of mRNA. Below we describe these recent advances, which highlight the important role of the RNA polymerase II elongation complex in regulation of eukaryotic gene expression.
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Affiliation(s)
- Ali Shilatifard
- Edward A. Doisey Department of Biochemistry, St. Louis University School of Medicine, St. Louis, Missouri 63104, USA.
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Tamura K, Miyata K, Sugahara K, Onishi S, Shuin T, Aso T. Identification of EloA-BP1, a novel Elongin A binding protein with an exonuclease homology domain. Biochem Biophys Res Commun 2003; 309:189-95. [PMID: 12943681 DOI: 10.1016/s0006-291x(03)01556-0] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The Elongin complex stimulates the rate of transcription elongation by RNA polymerase II by suppressing the transient pausing of the polymerase at many sites along the DNA template. Elongin is composed of a transcriptionally active A subunit, and two positive regulatory B and C subunits. Although the NH(2)-terminal approximately 120 amino acid region of Elongin A is dispensable for its transcriptional activity in vitro, it shares significant sequence similarity with the NH(2)-terminus of other class of transcription factors SII and CRSP70, suggesting that the NH(2)-terminus mediates interactions important for the regulation of transcription in vivo. To identify proteins that can bind to these conserved sequences, a human B cell cDNA library was screened using the NH(2)-terminus of Elongin A as bait in a yeast two-hybrid system. Here, we report on the cloning and characterization of a novel human exonuclease domain-containing protein, Elongin A-binding protein 1 (EloA-BP1). EloA-BP1 is composed of 1221 amino acids and its mRNA is ubiquitously expressed. Double immunofluorescence labeling in COS7 cells suggested that EloA-BP1 and Elongin A are colocalized to the cell nucleus. By using an in vitro binding assay, we show that EloA-BP1 is capable of binding not only the NH(2)-terminal approximately 120 amino acid region of Elongin A, but also that of SII. Although the purified EloA-BP1 had no detectable effect on the rate of transcription elongation in vitro, it may play some role in the regulation of elongation in vivo.
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Affiliation(s)
- Kenji Tamura
- Department of Functional Genomics, Faculty of Medicine, Kochi Medical School, Kohasu, Oko-cho, Nankoku, Kochi, Japan
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27
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Yamazaki K, Aso T, Ohnishi Y, Ohno M, Tamura K, Shuin T, Kitajima S, Nakabeppu Y. Mammalian elongin A is not essential for cell viability but is required for proper cell cycle progression with limited alteration of gene expression. J Biol Chem 2003; 278:13585-9. [PMID: 12604609 DOI: 10.1074/jbc.c300047200] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Elongin A is a transcription elongation factor that increases the overall rate of mRNA chain elongation by RNA polymerase II. To investigate the function of Elongin A in vivo, the two alleles of the Elongin A gene have been disrupted by homologous recombination in murine embryonic stem (ES) cells. The Elongin A-deficient ES cells are viable, but show a slow growth phenotype because they undergo a delayed mitosis. The cDNA microarray and RNase protection assay using the wild-type and Elongin A-deficient ES cells indicate that the expression of only a small subset of genes is affected in the mutant cells. Taken together, our results suggest that Elongin A regulates transcription of a subset but not all of genes and reveal a linkage between Elongin A function and cell cycle progression.
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Affiliation(s)
- Katsuhisa Yamazaki
- Medical Institute of Bioregulation, Kyushu University, and CREST, Japan Science and Technology Corporation, 3-1-1, Maidashi, Higashi-ku, Fukuoka 812-8582, Japan
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28
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Abstract
The mechanism of positive regulation of cytokine signalling pathways has been well investigated, whereas our knowledge of negative regulation is relatively sparse. Here we review recent literature on important negative regulators: the family of suppressors of cytokine signalling, SOCS, consisting of eight members (SOCS-1 to SOCS-7 and CIS) all sharing a central SH2 domain and a C-terminal SOCS box. Expression of CIS, SOCS-1, SOCS-2 and SOCS-3 is induced by various cytokines, and overexpression studies in various cell lines have demonstrated their inhibitory roles. These family members have been implicated in the negative regulation of several pathways, particularly the JAK/STAT pathway, and since this signalling pathway is responsible for their induction, they form part of a classical negative feedback circuit. To date, at least three different modulating mechanisms have been demonstrated: through the SH2 domain they bind to phosphotyrosines on the target protein, leading to inhibition of signal transduction by N-terminal inactivation of JAK, by blocking access of STAT to the receptor sites, or by SOCS box-targeting bound proteins to proteasomal degradation. In gene modification studies in mice, it has been demonstrated that SOCS-1 plays an important role in IFNgamma-regulation and T-cell differentiation, while SOCS-2 seems necessary for normal growth regulation. SOCS-3(-/-) mice die during embryogenesis for a reason still not fully understood, but insufficient control of fetal erythropoiesis or defects in placental development may be involved. The physiological role for the other family members, as well as their molecular regulation mechanisms, remain to be revealed.
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Affiliation(s)
- Lykke Larsen
- Department of Medical Anatomy, University of Copenhagen, Panum Institute, Copenhagen, Denmark
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Harada JN, Shevchenko A, Shevchenko A, Pallas DC, Berk AJ. Analysis of the adenovirus E1B-55K-anchored proteome reveals its link to ubiquitination machinery. J Virol 2002; 76:9194-206. [PMID: 12186903 PMCID: PMC136464 DOI: 10.1128/jvi.76.18.9194-9206.2002] [Citation(s) in RCA: 182] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/17/2002] [Accepted: 06/12/2002] [Indexed: 12/26/2022] Open
Abstract
During the early phase of infection, the E1B-55K protein of adenovirus type 5 (Ad5) counters the E1A-induced stabilization of p53, whereas in the late phase, E1B-55K modulates the preferential nucleocytoplasmic transport and translation of the late viral mRNAs. The mechanism(s) by which E1B-55K performs these functions has not yet been clearly elucidated. In this study, we have taken a proteomics-based approach to identify and characterize novel E1B-55K-associated proteins. A multiprotein E1B-55K-containing complex was immunopurified from Ad5-infected HeLa cells and found to contain E4-orf6, as well as several cellular factors previously implicated in the ubiquitin-proteasome-mediated destruction of proteins, including Cullin-5, Rbx1/ROC1/Hrt1, and Elongins B and C. We further demonstrate that a complex containing these as well as other proteins is capable of directing the polyubiquitination of p53 in vitro. These ubiquitin ligase components were found in a high-molecular-mass complex of 800 to 900 kDa. We propose that these newly identified binding partners (Cullin-5, Elongins B and C, and Rbx1) complex with E1B-55K and E4-orf6 during Ad infection to form part of an E3 ubiquitin ligase that targets specific protein substrates for degradation. We further suggest that E1B-55K functions as the principal substrate recognition component of this SCF-type ubiquitin ligase, whereas E4-orf6 may serve to nucleate the assembly of the complex. Lastly, we describe the identification and characterization of two novel E1B-55K interacting factors, importin-alpha 1 and pp32, that may also participate in the functions previously ascribed to E1B-55K and E4-orf6.
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Affiliation(s)
- Josephine N Harada
- Molecular Biology Institute, University of California, Los Angeles, Los Angeles, California 90095-1570, USA
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30
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Kamura T, Brower CS, Conaway RC, Conaway JW. A molecular basis for stabilization of the von Hippel-Lindau (VHL) tumor suppressor protein by components of the VHL ubiquitin ligase. J Biol Chem 2002; 277:30388-93. [PMID: 12048197 DOI: 10.1074/jbc.m203344200] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The multiprotein von Hippel-Lindau (VHL) tumor suppressor (CBC(VHL), Cul2-Elongin BC-VHL) and SCF (Skp1-Cul1/Cdc53-F-box protein) complexes are members of structurally related families of E3 ubiquitin ligases that use a heterodimeric module composed of a member of the Cullin protein family and the RING finger protein Rbx1 (ROC1/Hrt1) to activate ubiquitylation of target proteins by the E2 ubiquitin-conjugating enzymes Ubc5 and Cdc34. VHL and F-box proteins function as the substrate recruitment subunits of CBC(VHL) and SCF complexes, respectively. In cells, many F-box proteins are short lived and are proposed to be ubiquitylated by an autocatalytic mechanism and destroyed by the proteasome following assembly into SCF complexes. In contrast, the VHL protein is stabilized by interaction with the Elongin B and C subunits of CBC(VHL) in cells. In this report, we have presented direct biochemical evidence that unlike the F-box protein Cdc4, which is ubiquitylated in vitro by Cdc34 in the context of the SCF, the VHL protein is protected from Ubc5-catalyzed ubiquitylation following assembly into the CBC(VHL) complex. CBC(VHL) is continuously required for negative regulation of hypoxia-inducible transcription factors in normoxic cells and of SCF complexes, many of which function only transiently during the cell cycle or in response to cellular signals. Our findings provide a molecular basis for the different modes of cellular regulation of VHL and F-box proteins and are consistent with the known roles of CBC(VHL).
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Affiliation(s)
- Takumi Kamura
- Department of Molecular and Cellular Biology, Medical Institute of Bioregulation, Kyushu University, Fukuoka 812-8582, Japan
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31
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Brower CS, Sato S, Tomomori-Sato C, Kamura T, Pause A, Stearman R, Klausner RD, Malik S, Lane WS, Sorokina I, Roeder RG, Conaway JW, Conaway RC. Mammalian mediator subunit mMED8 is an Elongin BC-interacting protein that can assemble with Cul2 and Rbx1 to reconstitute a ubiquitin ligase. Proc Natl Acad Sci U S A 2002; 99:10353-8. [PMID: 12149480 PMCID: PMC124918 DOI: 10.1073/pnas.162424199] [Citation(s) in RCA: 71] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2001] [Indexed: 11/18/2022] Open
Abstract
The heterodimeric Elongin BC complex has been shown to interact in vitro and in cells with a conserved BC-box motif found in an increasing number of proteins including RNA polymerase II elongation factor Elongin A, suppressor of cytokine signaling (SOCS)-box proteins, and the von Hippel-Lindau tumor suppressor protein. Recently, the Elongin BC complex was found to function as an adaptor that links these BC-box proteins to a module composed of Cullin family members Cul2 or Cul5 and RING-H2 finger protein Rbx1 to reconstitute a family of E3 ubiquitin ligases that activate ubiquitylation by the E2 ubiquitin-conjugating enzyme Ubc5. As part of our effort to understand the functions of Elongin BC-based ubiquitin ligases, we exploited a modified yeast two-hybrid screen to identify a mammalian BC-box protein similar in sequence to Saccharomyces cerevisiae Mediator subunit Med8p. In this report we demonstrate (i) that mammalian MED8 is a subunit of the mammalian Mediator complex and (ii) that MED8 can assemble with Elongins B and C, Cul2, and Rbx1 to reconstitute a ubiquitin ligase. Taken together, our findings are consistent with the model that MED8 could function to recruit ubiquitin ligase activity directly to the RNA polymerase II transcriptional machinery.
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32
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Yamazaki K, Guo L, Sugahara K, Zhang C, Enzan H, Nakabeppu Y, Kitajima S, Aso T. Identification and biochemical characterization of a novel transcription elongation factor, Elongin A3. J Biol Chem 2002; 277:26444-51. [PMID: 11994304 DOI: 10.1074/jbc.m202859200] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The Elongin complex stimulates the rate of transcription elongation by RNA polymerase II by suppressing the transient pausing of the polymerase at many sites along the DNA template. Elongin is composed of a transcriptionally active A subunit and two small regulatory B and C subunits, the latter binding stably to each other to form a binary complex that interacts with Elongin A and strongly induces its transcriptional activity. To further understand the role of Elongin A in transcriptional regulation by RNA polymerase II, we are attempting to identify Elongin A-related proteins. Here, we report on the molecular cloning, expression, and biochemical characterization of human Elongin A3, a novel transcription elongation factor that exhibits 49 and 81% identity to Elongin A and the recently identified Elongin A2, respectively. The mRNA of Elongin A3 is ubiquitously expressed, and the protein is localized to the nucleus of cells. Mechanistic studies have demonstrated that Elongin A3 possesses similar biochemical features to Elongin A2. Both stimulate the rate of transcription elongation by RNA polymerase II and are capable of forming a stable complex with Elongin BC. In contrast to Elongin A, however, their transcriptional activities are not activated by Elongin BC. Structure-function analyses using fusion proteins composed of Elongin A3 and Elongin A revealed that the COOH-terminal region of Elongin A is important for the activation by Elongin BC.
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Affiliation(s)
- Katsuhisa Yamazaki
- Department of Biochemical Genetics, Medical Research Institute, Tokyo Medical and Dental University, 1-5-45, Yushima, Bunkyo-ku, Tokyo 113-8510, Japan
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33
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Khattak S, Im H, Park T, Ahnn J, Spoerel NA. dELL, a drosophila homologue of transcription elongation factor ELL (Eleven-nineteen Lysine rich Leukemia), is required for early development. Cell Biochem Funct 2002; 20:119-27. [PMID: 11979508 DOI: 10.1002/cbf.960] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
ELL (Eleven-nineteen Lysine rich Leukemia) is known to be an elongation factor resembling elongin for RNA polymerase II transcription. A homologue of human ELL (hELL) was identified in Drosophila melanogaster (dELL) and several cDNA clones were isolated from the embryonic cDNA library. We showed that dELL is expressed mainly in the ovaries and early embryonic stages by developmental Northern blot. dELL encodes a protein of 912 amino acids which is substantially longer than the hELL (612 aa). Immunostaining revealed that dELL was localized to nuclei in early embryos and to nuclei of nurse cells and follicle cells in the ovary suggesting its important role in early development of drosophila. To elucidate the function of this gene in drosophila, P-element mobilization was performed by utilizing a P-element inserted upstream of dELL. Southern analysis showed that isolated mutants are internal P-element deletions. These P-element deletions can now be used to isolate dELL mutations by EMS mutagenesis.
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Affiliation(s)
- Shahryar Khattak
- Department of Life Science, Kwangju Institute of Science and Technology, Kwangju 500-712, Korea
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34
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Botuyan MV, Mer G, Yi GS, Koth CM, Case DA, Edwards AM, Chazin WJ, Arrowsmith CH. Solution structure and dynamics of yeast elongin C in complex with a von Hippel-Lindau peptide. J Mol Biol 2001; 312:177-86. [PMID: 11545595 DOI: 10.1006/jmbi.2001.4938] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Elongin is a transcription elongation factor that stimulates the rate of elongation by suppressing transient pausing by RNA polymerase II at many sites along the DNA. It is heterotrimeric in mammals, consisting of elongins A, B and C subunits, and bears overall similarity to a class of E3 ubiquitin ligases known as SCF (Skp1-Cdc53 (cullin)-F-box) complexes. A subcomplex of elongins B and C is a target for negative regulation by the von Hippel-Lindau (VHL) tumor-suppressor protein. Elongin C from Saccharomyces cerevisiae, Elc1, exhibits high sequence similarity to mammalian elongin C. Using NMR spectroscopy we have determined the three-dimensional structure of Elc1 in complex with a human VHL peptide, VHL(157-171), representing the major Elc1 binding site. The bound VHL peptide is entirely helical. Elc1 utilizes two C-terminal helices and an intervening loop to form a binding groove that fits VHL(157-171). Chemical shift perturbation and dynamics analyses reveal that a global conformational change accompanies Elc1/VHL(157-171) complex formation. Moreover, the disappearance of conformational exchange phenomena on the microsecond to millisecond time scale within Elc1 upon VHL peptide binding suggests a role for slow internal motions in ligand recognition.
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Affiliation(s)
- M V Botuyan
- Division of Molecular and Structural Biology, Ontario Cancer Institute and Department of Medical Biophysics, University of Toronto, Toronto, ON M5G 2M9, Canada
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35
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Schoenfeld AR, Davidowitz EJ, Burk RD. Endoplasmic reticulum/cytosolic localization of von Hippel-Lindau gene products is mediated by a 64-amino acid region. Int J Cancer 2001; 91:457-67. [PMID: 11251966 DOI: 10.1002/1097-0215(20010215)91:4<457::aid-ijc1072>3.0.co;2-p] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
Inactivation of the von Hippel-Lindau (VHL) tumor-suppressor gene causes both the familial cancer syndrome VHL disease and corresponding sporadic tumor types, including renal-cell carcinoma. Subcellular localization of VHL gene products was determined by indirect immunofluorescence. Both native and exogenously expressed VHL proteins displayed a cytoplasmic peri-nuclear immunostaining pattern, which co-localized with markers for the endoplasmic reticulum (ER). In addition, subcellular fractionation indicated that both native and exogenously expressed VHL products are found predominantly in the cytosolic compartment. Deletion analyses demonstrated that a 64-amino acid region of VHL (residues 114-177) is responsible for cytosolic as well as ER subcellular localization. Taken together, the immunostaining and biochemical fractionation studies suggest that VHL localizes to the cytosolic face of the ER. The relationship between VHL subcellular localization and VHL-associated ubiquitination was examined. Chimeric VHL-green fluorescent protein (GFP) products, which localized to the peri-nuclear region, were shown to undergo ubiquitination. VHL amino acids 114-177 were necessary and sufficient for this modification. Consistent with a role of VHL in ubiquitination, expression of VHL led to enhanced ubiquitination of cellular proteins, and amino acids 114-177 were also critical for this effect. Therefore, amino acids 114-177 were required for accurate VHL subcellular localization, ubiquitination of VHL-GFP products and VHL-dependent increases in cellular ubiquitination. Since mutations in this region of VHL are frequently detected in renal-cell carcinomas, these results suggest that proper VHL subcellular localization and associated ubiquitination functions may be necessary for VHL-mediated tumor suppression.
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Affiliation(s)
- A R Schoenfeld
- Department of Microbiology and Immunology, Marion Bessin Liver Research Center and Albert Einstein Comprehensive Cancer Center, Albert Einstein College of Medicine, Bronx, NY 10461, USA
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36
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Kamura T, Sato S, Iwai K, Czyzyk-Krzeska M, Conaway RC, Conaway JW. Activation of HIF1alpha ubiquitination by a reconstituted von Hippel-Lindau (VHL) tumor suppressor complex. Proc Natl Acad Sci U S A 2000; 97:10430-5. [PMID: 10973499 PMCID: PMC27041 DOI: 10.1073/pnas.190332597] [Citation(s) in RCA: 487] [Impact Index Per Article: 20.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2000] [Accepted: 07/17/2000] [Indexed: 12/31/2022] Open
Abstract
Mutations in the VHL tumor suppressor gene result in constitutive expression of many hypoxia-inducible genes, at least in part because of increases in the cellular level of hypoxia-inducible transcription factor HIF1alpha, which in normal cells is rapidly ubiquitinated and degraded by the proteasome under normoxic conditions. The recent observation that the VHL protein is a subunit of an Skp1-Cul1/Cdc53-F-box (SCF)-like E3 ubiquitin ligase raised the possibility that VHL may be directly responsible for regulating cellular levels of HIF1alpha by targeting it for ubiquitination and proteolysis. In this report, we test this hypothesis directly. We report development of methods for production of the purified recombinant VHL complex and present direct biochemical evidence that it can function with an E1 ubiquitin-activating enzyme and E2 ubiquitin-conjugating enzyme to activate HIF1alpha ubiquitination in vitro. Our findings provide new insight into the function of the VHL tumor suppressor protein, and they provide a foundation for future investigations of the mechanisms underlying VHL regulation of oxygen-dependent gene expression.
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Affiliation(s)
- T Kamura
- Program in Molecular and Cell Biology, Oklahoma Medical Research Foundation, 825 Northeast 13th Street, Oklahoma City, OK 73104, USA
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37
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Abstract
Eukaryotic mRNA synthesis is catalyzed by multisubunit RNA polymerase II and proceeds through multiple stages referred to as preinitiation, initiation, elongation, and termination. Over the past 20 years, biochemical studies of eukaryotic mRNA synthesis have largely focused on the preinitiation and initiation stages of transcription. These studies led to the discovery of the class of general initiation factors (TFIIB, TFIID, TFIIE, TFIIF, and TFIIH), which function in intimate association with RNA polymerase II and are required for selective binding of polymerase to its promoters, formation of the open complex, and synthesis of the first few phosphodiester bonds of nascent transcripts. Recently, biochemical studies of the elongation stage of eukaryotic mRNA synthesis have led to the discovery of several cellular proteins that have properties expected of general elongation factors and that have been found to play unanticipated roles in human disease. Among these candidate general elongation factors are the positive transcription elongation factor b (P-TEFb), eleven-nineteen lysine-rich in leukemia (ELL), Cockayne syndrome complementation group B (CSB), and elongin proteins, which all function in vitro to expedite elongation by RNA polymerase II by suppressing transient pausing or premature arrest by polymerase through direct interactions with the elongation complex. Despite their similar activities in elongation, the P-TEFb, ELL, CSB, and elongin proteins appear to play roles in a diverse collection of human diseases, including human immunodeficiency virus-1 infection, acute myeloid leukemia, Cockayne syndrome, and the familial cancer predisposition syndrome von Hippel-Lindau disease. here we review our current understanding of the P-TEFb, ELL, CSB, and elongin proteins, their mechanisms of action, and their roles in human disease.
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Affiliation(s)
- J W Conaway
- Howard Hughes Medical Institute, Oklahoma Medical Research Foundation, Oklahoma City 73104, USA
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38
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Koth CM, Botuyan MV, Moreland RJ, Jansma DB, Conaway JW, Conaway RC, Chazin WJ, Friesen JD, Arrowsmith CH, Edwards AM. Elongin from Saccharomyces cerevisiae. J Biol Chem 2000; 275:11174-80. [PMID: 10753924 DOI: 10.1074/jbc.275.15.11174] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Elongin is a transcription elongation factor that was first identified in mammalian systems and is composed of the three subunits, elongin A, B, and C. Sequence homologues of elongin A and elongin C, but not elongin B, were identified in the yeast genome. Neither yeast elongin A nor C sequence homologues was required for cell viability. The two gene products could be purified from yeast as a complex. A recombinant form of the complex, which could only be produced in bacteria if the gene products were co-expressed, was purified over several chromatographic steps. The complex did not stimulate transcription elongation by yeast RNA polymerase II. Using limited proteolysis, the N-terminal 144 residues of yeast elongin A were shown to be sufficient for interaction with yeast elongin C. The purified complex of yeast elongin C/elongin A(1-143) was analyzed using circular dichroism and nuclear magnetic spectroscopy. These studies revealed that yeast elongin A is unfolded but undergoes a dramatic modification of its structure in the presence of elongin C, and that elongin C forms a stable dimer in the absence of elongin A.
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Affiliation(s)
- C M Koth
- Department of Medical Genetics and Microbiology, University of Toronto, Toronto, Ontario M5S 1A8
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39
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Aso T, Yamazaki K, Amimoto K, Kuroiwa A, Higashi H, Matsuda Y, Kitajima S, Hatakeyama M. Identification and characterization of Elongin A2, a new member of the Elongin family of transcription elongation factors, specifically expressed in the testis. J Biol Chem 2000; 275:6546-52. [PMID: 10692460 DOI: 10.1074/jbc.275.9.6546] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The Elongin complex stimulates the rate of transcription elongation by RNA polymerase II by suppressing the transient pausing of the polymerase at many sites along the DNA template. Elongin is composed of a transcriptionally active A subunit and two small regulatory B and C subunits, the latter of which bind stably to each other to form a binary complex that interacts with Elongin A and strongly induces its transcriptional activity. To further understand the roles of Elongin in transcriptional regulation, we attempted to identify Elongin-related proteins. Here, we report on the cloning, expression, and characterization of human Elongin A2, a novel transcription elongation factor that exhibited 47% identity and 61% similarity to Elongin A. Biochemical studies have shown that Elongin A2 stimulates the rate of transcription elongation by RNA polymerase II and is capable of forming a stable complex with Elongin BC. However, in contrast to Elongin A, its transcriptional activity is not activated by Elongin BC. Northern blot analysis revealed that Elongin A2 mRNA was specifically expressed in the testis, suggesting that Elongin A2 may regulate the transcription of testis-specific genes.
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Affiliation(s)
- T Aso
- Department of Viral Oncology, Cancer Institute, Japanese Foundation for Cancer Research, Tokyo 170-8455, Japan.
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40
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Wada H, Yeh ET, Kamitani T. The von Hippel-Lindau tumor suppressor gene product promotes, but is not essential for, NEDD8 conjugation to cullin-2. J Biol Chem 1999; 274:36025-9. [PMID: 10585493 DOI: 10.1074/jbc.274.50.36025] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
We have previously shown that human cullin-2 (Cul-2) is covalently modified at Lys-689 by NEDD8 (Wada, H., Yeh, E. T. H., and Kamitani, T. (1999) Biochem. Biophys. Res. Commun. 257, 100-105). Cul-2 has also been reported to form a multiprotein complex, Cul-2.VBC, with the von Hippel-Lindau tumor suppressor gene product (pVHL) and elongins B and C. In this study, using an in vivo coexpression system in COS cells, we show that NEDD8 conjugation to Cul-2 is promoted by coexpression with wild-type pVHL and elongins B and C. Interestingly, tumorigenic mutants and deletion mutants of pVHL, which are unable to form a Cul-2.VBC complex, do not have the activity to promote NEDD8 conjugation to Cul-2. These results suggest that the complex formation is required for NEDD8 conjugation to Cul-2. Furthermore, we used a pVHL-deficient cell line, 786-0, to show that Cul-2 is poorly but clearly conjugated by NEDD8, indicating that pVHL is not the only molecule that promotes NEDD8 conjugation to Cul-2. Taken together, the VBC complex appears to have ligase activity in the conjugation of NEDD8 to Cul-2.
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Affiliation(s)
- H Wada
- Division of Molecular Medicine, Department of Internal Medicine, Institute of Molecular Medicine, University of Texas Health Science Center, Houston, Texas 77030, USA
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41
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Ohh M, Takagi Y, Aso T, Stebbins CE, Pavletich NP, Zbar B, Conaway RC, Conaway JW, Kaelin WG. Synthetic peptides define critical contacts between elongin C, elongin B, and the von Hippel-Lindau protein. J Clin Invest 1999; 104:1583-91. [PMID: 10587522 PMCID: PMC481054 DOI: 10.1172/jci8161] [Citation(s) in RCA: 80] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
Abstract
The von Hippel-Lindau tumor suppressor protein (pVHL) negatively regulates hypoxia-inducible mRNAs such as the mRNA encoding vascular endothelial growth factor (VEGF). This activity has been linked to its ability to form multimeric complexes that contain elongin C, elongin B, and Cul2. To understand this process in greater detail, we performed a series of in vitro binding assays using pVHL, elongin B, and elongin C variants as well as synthetic peptide competitors derived from pVHL or elongin C. A subdomain of elongin C (residues 17-50) was necessary and sufficient for detectable binding to elongin B. In contrast, elongin B residues required for binding to elongin C were not confined to a discrete colinear domain. We found that the pVHL (residues 157-171) is necessary and sufficient for binding to elongin C in vitro and is frequently mutated in families with VHL disease. These mutations preferentially involve residues that directly bind to elongin C and/or alter the conformation of pVHL such that binding to elongin C is at least partially diminished. These results are consistent with the view that diminished binding of pVHL to the elongins plays a causal role in VHL disease.
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Affiliation(s)
- M Ohh
- Department of Adult Oncology, Dana-Farber Cancer Institute and Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts 02115, USA
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42
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Botuyan MV, Koth CM, Mer G, Chakrabartty A, Conaway JW, Conaway RC, Edwards AM, Arrowsmith CH, Chazin WJ. Binding of elongin A or a von Hippel-Lindau peptide stabilizes the structure of yeast elongin C. Proc Natl Acad Sci U S A 1999; 96:9033-8. [PMID: 10430890 PMCID: PMC17727 DOI: 10.1073/pnas.96.16.9033] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Elongin is a heterotrimeric transcription elongation factor composed of subunits A, B, and C in mammals. Elongin A and C are F-box-containing and SKP1 homologue proteins, respectively, and are therefore of interest for their potential roles in cell cycle-dependent proteolysis. Mammalian elongin C interacts with both elongin A and elongin B, as well as with the von Hippel-Lindau tumor suppressor protein VHL. To investigate the corresponding interactions in yeast, we have utilized NMR spectroscopy combined with ultracentrifugal sedimentation experiments to examine complexes of yeast elongin C (Elc1) with yeast elongin A (Ela1) and two peptides from homologous regions of Ela1 and human VHL. Elc1 alone is a homotetramer composed of subunits with a structured N-terminal region and a dynamically unstable C-terminal region. Binding of a peptide fragment of the Elc1-interaction domain of Ela1 or with a homologous peptide from VHL promotes folding of the C-terminal region of Elc1 into two regular helical structures and dissociates Elc1 into homodimers. Moreover, analysis of the complex of Elc1 with the full Elc1-interaction domain of Ela1 reveals that the Elc1 homodimer is dissociated to preferentially form an Ela1/Elc1 heterodimer. Thus, elongin C is found to oligomerize in solution and to undergo significant structural rearrangements upon binding of two different partner proteins. These results suggest a structural basis for the interaction of an F-box-containing protein with a SKP1 homologue and the modulation of this interaction by the tumor suppressor VHL.
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Affiliation(s)
- M V Botuyan
- Division of Molecular and Structural Biology, Ontario Cancer Institute and Department of Medical Biophysics, University of Toronto, 610 University Avenue, Toronto, ON, Canada M5G 2M9
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43
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Lisztwan J, Imbert G, Wirbelauer C, Gstaiger M, Krek W. The von Hippel-Lindau tumor suppressor protein is a component of an E3 ubiquitin-protein ligase activity. Genes Dev 1999; 13:1822-33. [PMID: 10421634 PMCID: PMC316884 DOI: 10.1101/gad.13.14.1822] [Citation(s) in RCA: 301] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
pVHL, the product of the VHL tumor suppressor gene, plays an important role in the regulation of cell growth and differentiation of human kidney cells, and inactivation of the VHL gene is the most frequent genetic event in human kidney cancer. The biochemical function of pVHL is unknown. Here we report that pVHL exists in vivo in a complex that displays ubiquitination-promoting activity in conjunction with the universally required components E1, E2, and ubiquitin. pVHL-associated ubiquitination activity requires, at a minimum, pVHL to bind elongin C and Cul-2, relatives of core components of SCF (Skp1-Cdc53/Cul-1-F-box protein) E3 ligase complexes. Notably, certain tumor-derived mutants of pVHL demonstrate loss of associated ubiquitination promoting activity. These results identify pVHL as a component of a potential SCF-like E3 ubiquitin-protein ligase complex and suggest a direct link between pVHL tumor suppressor and the process of ubiquitination.
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Affiliation(s)
- J Lisztwan
- Friedrich Miescher Institut, CH-4058 Basel, Switzerland
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44
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Wyndham AM, Baker RT, Chelvanayagam G. The Ubp6 family of deubiquitinating enzymes contains a ubiquitin-like domain: SUb. Protein Sci 1999; 8:1268-75. [PMID: 10386876 PMCID: PMC2144364 DOI: 10.1110/ps.8.6.1268] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
A sequence motif that is Similar to Ubiquitin (SUb) has been identified in the Saccharomyces cerevisiae ubiquitin-specific protease Ubp6. SUb is conserved in all known Ubp6 homologues from a spectrum of eukaryotic species and is also present in a group of hypothetical proteins of unknown function (Unk1-3) present in sequence databases. An N-terminal deletion mutant of Ubp6 that lacks SUb is still capable of cleaving alpha-linked ubiquitin fusions, suggesting that SUb forms a separate domain to the catalytic core of Ubp6 and demonstrating that it is not required for in vitro cleavage activity. A homology model of the 78 N-terminal amino acids of human Ubp6, based on the known fold of ubiquitin, is presented. In human Ubp6, SUb shares only 20% sequence identity with ubiquitin. Even weaker similarity occurs between S. cerevisiae SUb and ubiquitin. The homology model supports a ubiquitin-like fold for SUb and suggests that two conserved Lys residues, corresponding to Lys48 and Lys63 of ubiquitin, are functionally important.
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Affiliation(s)
- A M Wyndham
- Molecular Genetics Group, John Curtin School of Medical Research, Australian National University, Canberra ACT
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45
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Russell SJ, Reed SH, Huang W, Friedberg EC, Johnston SA. The 19S regulatory complex of the proteasome functions independently of proteolysis in nucleotide excision repair. Mol Cell 1999; 3:687-95. [PMID: 10394357 DOI: 10.1016/s1097-2765(01)80001-0] [Citation(s) in RCA: 164] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/17/2022]
Abstract
The 26S proteasome degrades proteins targeted by the ubiquitin pathway, a function thought to explain its role in cellular processes. The proteasome interacts with the ubiquitin-like N terminus of Rad23, a nucleotide excision repair (NER) protein, in Saccharomyces cerevisiae. Deletion of the ubiquitin-like domain causes UV radiation sensitivity. Here, we show that the ubiquitin-like domain of Rad23 is required for optimal activity of an in vitro NER system. Inhibition of proteasomal ATPases diminishes NER activity in vitro and increases UV sensitivity in vivo. Surprisingly, blockage of protein degradation by the proteasome has no effect on the efficiency of NER. This establishes that the regulatory complex of the proteasome has a function independent of protein degradation.
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Affiliation(s)
- S J Russell
- Department of Medicine and Biochemistry, University of Texas Southwestern Medical Center, Dallas 75235, USA
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46
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Brower CS, Shilatifard A, Mather T, Kamura T, Takagi Y, Haque D, Treharne A, Foundling SI, Conaway JW, Conaway RC. The elongin B ubiquitin homology domain. Identification of Elongin B sequences important for interaction with Elongin C. J Biol Chem 1999; 274:13629-36. [PMID: 10224134 DOI: 10.1074/jbc.274.19.13629] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
Mammalian Elongin B is a 118-amino acid protein composed of an 84-amino acid amino-terminal ubiquitin-like domain and a 34-amino acid carboxyl-terminal tail. Elongin B is found in cells as a subunit of the heterodimeric Elongin BC complex, which was originally identified as a positive regulator of RNA polymerase II elongation factor Elongin A and subsequently as a component of the multiprotein von Hippel-Lindau tumor suppressor and suppressor of cytokine signaling complexes. As part of our effort to understand how the Elongin BC complex regulates the activity of Elongin A, we are characterizing Elongin B functional domains. In this report, we show that the Elongin B ubiquitin-like domain is necessary and sufficient for interaction with Elongin C and for positive regulation of Elongin A transcriptional activity. In addition, by site-directed mutagenesis of the Elongin B ubiquitin-like domain, we identify a short Elongin B region that is important for its interaction with Elongin C. Finally, we observe that both the ubiquitin-like domain and carboxyl-terminal tail are conserved in Drosophila melanogaster and Caenorhabditis elegans Elongin B homologs that efficiently substitute for mammalian Elongin B in reconstitution of the transcriptionally active Elongin ABC complex, suggesting that the carboxyl-terminal tail performs an additional function not detected in our assays.
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Affiliation(s)
- C S Brower
- Program in Molecular and Cell Biology, Oklahoma Medical Research Foundation, Oklahoma City, Oklahoma 73104, USA
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47
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Stebbins CE, Kaelin WG, Pavletich NP. Structure of the VHL-ElonginC-ElonginB complex: implications for VHL tumor suppressor function. Science 1999; 284:455-61. [PMID: 10205047 DOI: 10.1126/science.284.5413.455] [Citation(s) in RCA: 616] [Impact Index Per Article: 24.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
Mutation of the VHL tumor suppressor is associated with the inherited von Hippel-Lindau (VHL) cancer syndrome and the majority of kidney cancers. VHL binds the ElonginC-ElonginB complex and regulates levels of hypoxia-inducible proteins. The structure of the ternary complex at 2.7 angstrom resolution shows two interfaces, one between VHL and ElonginC and another between ElonginC and ElonginB. Tumorigenic mutations frequently occur in a 35-residue domain of VHL responsible for ElonginC binding. A mutational patch on a separate domain of VHL indicates a second macromolecular binding site. The structure extends the similarities to the SCF (Skp1-Cul1-F-box protein) complex that targets proteins for degradation, supporting the hypothesis that VHL may function in an analogous pathway.
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Affiliation(s)
- C E Stebbins
- Department of Biochemistry and Structural Biology, Joan and Sanford I. Weill Graduate School of Medical Sciences, Cornell University, New York, NY 10021, USA
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48
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Liu YC, Pan J, Zhang C, Fan W, Collinge M, Bender JR, Weissman SM. A MHC-encoded ubiquitin-like protein (FAT10) binds noncovalently to the spindle assembly checkpoint protein MAD2. Proc Natl Acad Sci U S A 1999; 96:4313-8. [PMID: 10200259 PMCID: PMC16329 DOI: 10.1073/pnas.96.8.4313] [Citation(s) in RCA: 142] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
Recently a number of nonclass I genes were discovered in the human MHC class I region. One of these, FAT10, encodes a protein consisting of two domains with homology to ubiquitin. FAT10 mRNA is expressed constitutively in some lymphoblastoid lines and dendritic cells and in certain other cells after gamma-interferon induction. FAT10 protein expression is controlled at several levels including transcription, translation, and protein stability. Yeast two-hybrid screening of a human lymphocyte library and immunoprecipitation studies revealed that FAT10 noncovalently associated with MAD2, a protein implicated in a cell-cycle checkpoint for spindle assembly during anaphase. Thus, FAT10 may modulate cell growth during B cell or dendritic cell development and activation.
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Affiliation(s)
- Y C Liu
- Department of Genetics, Internal Medicine, Boyer Center for Molecular Medicine, Yale University School of Medicine, New Haven, CT 06511, USA
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49
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Liou ML, Liou HC. The ubiquitin-homology protein, DAP-1, associates with tumor necrosis factor receptor (p60) death domain and induces apoptosis. J Biol Chem 1999; 274:10145-53. [PMID: 10187798 DOI: 10.1074/jbc.274.15.10145] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The tumor necrosis factor receptor, p60 (TNF-R1), transduces death signals via the association of its cytoplasmic domain with several intracellular proteins. By screening a mammalian cDNA library using the yeast two-hybrid cloning technique, we isolated a ubiquitin-homology protein, DAP-1, which specifically interacts with the cytoplasmic death domain of TNF-R1. Sequence analysis reveals that DAP-1 shares striking sequence homology with the yeast SMT3 protein that is essential for the maintenance of chromosome integrity during mitosis (Meluh, P. B., and Koshland, D. (1995) Mol. Biol. Cell 6, 793-807). DAP-1 is nearly identical to PIC1, a protein that interacts with the PML tumor suppressor implicated in acute promyelocytic leukemia (Boddy, M. N., Howe, K., Etkin, L. D., Solomon, E., and Freemont, P. S. (1996) Oncogene 13, 971-982), and the sentrin protein, which associates with the Fas death receptor (Okura, T., Gong, L., Kamitani, T., Wada, T., Okura, I., Wei, C. F., Chang, H. M., and Yeh, E. T. (1996) J. Immunol. 157, 4277-4281). The in vivo interaction between DAP-1 and TNF-R1 was further confirmed in mammalian cells. In transient transfection assays, overexpression of DAP-1 suppresses NF-kappaB/Rel activity in 293T cells, a human kidney embryonic carcinoma cell line. Overexpression of either DAP-1 or sentrin causes apoptosis of TNF-sensitive L929 fibroblast cell line, as well as TNF-resistant osteosarcoma cell line, U2OS. Furthermore, the dominant negative Fas-associated death domain protein (FADD) protein blocks the cell death induced by either DAP-1 or FADD. Collectively, these observations highly suggest a role for DAP-1 in mediating TNF-induced cell death signaling pathways, presumably through the recruitment of FADD death effector.
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Affiliation(s)
- M L Liou
- Division of Immunology, Department of Medicine, Cornell University Medical College, New York, New York 10021, USA.
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50
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Zhang JG, Farley A, Nicholson SE, Willson TA, Zugaro LM, Simpson RJ, Moritz RL, Cary D, Richardson R, Hausmann G, Kile BT, Kile BJ, Kent SB, Alexander WS, Metcalf D, Hilton DJ, Nicola NA, Baca M. The conserved SOCS box motif in suppressors of cytokine signaling binds to elongins B and C and may couple bound proteins to proteasomal degradation. Proc Natl Acad Sci U S A 1999; 96:2071-6. [PMID: 10051596 PMCID: PMC26738 DOI: 10.1073/pnas.96.5.2071] [Citation(s) in RCA: 522] [Impact Index Per Article: 20.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The suppressors of cytokine signaling (SOCS) family of proteins act as intracellular inhibitors of several cytokine signal transduction pathways. Their expression is induced by cytokine activation of the Janus kinase/signal transducer and activator of transcription (JAK/STAT) pathway and they act as a negative feedback loop by subsequently inhibiting the JAK/STAT pathway either by direct interaction with activated JAKs or with the receptors. These interactions are mediated at least in part by the SH2 domain of SOCS proteins but these proteins also contain a highly conserved C-terminal homology domain termed the SOCS box. Here we show that the SOCS box mediates interactions with elongins B and C, which in turn may couple SOCS proteins and their substrates to the proteasomal protein degradation pathway. Analogous to the family of F-box-containing proteins, it appears that the SOCS proteins may act as adaptor molecules that target activated cell signaling proteins to the protein degradation pathway.
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Affiliation(s)
- J G Zhang
- Walter and Eliza Hall Institute of Medical Research and the Cooperative Research Centre for Cellular Growth Factors, P.O. Royal Melbourne Hospital, Victoria 3050, Australia
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