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Martín-Villanueva S, Gutiérrez G, Kressler D, de la Cruz J. Ubiquitin and Ubiquitin-Like Proteins and Domains in Ribosome Production and Function: Chance or Necessity? Int J Mol Sci 2021; 22:ijms22094359. [PMID: 33921964 PMCID: PMC8122580 DOI: 10.3390/ijms22094359] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2021] [Revised: 04/19/2021] [Accepted: 04/20/2021] [Indexed: 12/11/2022] Open
Abstract
Ubiquitin is a small protein that is highly conserved throughout eukaryotes. It operates as a reversible post-translational modifier through a process known as ubiquitination, which involves the addition of one or several ubiquitin moieties to a substrate protein. These modifications mark proteins for proteasome-dependent degradation or alter their localization or activity in a variety of cellular processes. In most eukaryotes, ubiquitin is generated by the proteolytic cleavage of precursor proteins in which it is fused either to itself, constituting a polyubiquitin precursor, or as a single N-terminal moiety to ribosomal proteins, which are practically invariably eL40 and eS31. Herein, we summarize the contribution of the ubiquitin moiety within precursors of ribosomal proteins to ribosome biogenesis and function and discuss the biological relevance of having maintained the explicit fusion to eL40 and eS31 during evolution. There are other ubiquitin-like proteins, which also work as post-translational modifiers, among them the small ubiquitin-like modifier (SUMO). Both ubiquitin and SUMO are able to modify ribosome assembly factors and ribosomal proteins to regulate ribosome biogenesis and function. Strikingly, ubiquitin-like domains are also found within two ribosome assembly factors; hence, the functional role of these proteins will also be highlighted.
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Affiliation(s)
- Sara Martín-Villanueva
- Instituto de Biomedicina de Sevilla, Hospital Universitario Virgen del Rocío/CSIC/Universidad de Sevilla, 41009 Seville, Spain;
- Departamento de Genética, Universidad de Sevilla, 41013 Seville, Spain;
| | - Gabriel Gutiérrez
- Departamento de Genética, Universidad de Sevilla, 41013 Seville, Spain;
| | - Dieter Kressler
- Unit of Biochemistry, Department of Biology, University of Fribourg, CH-1700 Fribourg, Switzerland
- Correspondence: (D.K.); (J.d.l.C.); Tel.: +41-26-300-86-45 (D.K.); +34-955-923-126 (J.d.l.C.)
| | - Jesús de la Cruz
- Instituto de Biomedicina de Sevilla, Hospital Universitario Virgen del Rocío/CSIC/Universidad de Sevilla, 41009 Seville, Spain;
- Departamento de Genética, Universidad de Sevilla, 41013 Seville, Spain;
- Correspondence: (D.K.); (J.d.l.C.); Tel.: +41-26-300-86-45 (D.K.); +34-955-923-126 (J.d.l.C.)
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Preparation and characterization of nanoliposomal bortezomib formulations and evaluation of their anti-cancer efficacy in mice bearing C26 colon carcinoma and B16F0 melanoma. NANOMEDICINE-NANOTECHNOLOGY BIOLOGY AND MEDICINE 2019; 20:102013. [DOI: 10.1016/j.nano.2019.04.016] [Citation(s) in RCA: 17] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/09/2019] [Revised: 04/13/2019] [Accepted: 04/24/2019] [Indexed: 12/20/2022]
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Liu ZY, Cao J, Zhang JT, Xu GL, Li XP, Wang FT, Ansari KH, Mohamed H, Fan YZ. Ring finger protein 125, as a potential highly aggressive and unfavorable prognostic biomarker, promotes the invasion and metastasis of human gallbladder cancers via activating the TGF- β1-SMAD3-ID1 signaling pathway. Oncotarget 2018; 8:49897-49914. [PMID: 28611292 PMCID: PMC5564816 DOI: 10.18632/oncotarget.18180] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2016] [Accepted: 04/19/2017] [Indexed: 01/06/2023] Open
Abstract
Human gallbladder cancer (GBC) is a lethal aggressive malignant neoplasm. Identification of potential molecular biomarkers and development of targeted therapeutics for GBC patients is very necessary. In this study, we firstly investigated the correlation between ring finger protein 125 (RNF125) expression and the metastasis and prognosis of GBC, and the underlying molecular mechanism. RNF125 expression in a cohort of GBC tissues was examined; its correlation with clinicopathological and prognostic factors of GBC patients was analyzed. Moreover, the metastasis-related difference expressed genes in highly and lowly aggressive GBC cell lines were identified; and the influence of RNF125 knockdown on the metastatic phenotypes and characteristic EMT markers in highly aggressive GBC NOZ cells was detected. Furthermore, the underlying molecular mechanism of RNF125 effect was explored. The results showed that RNF125 was highly expressed in GBC tissues and related with aggressive characteristics such as Nevin stage (P = 0.041) etc. and unfavorable prognosis of GBC patients (P = 0.023, log-rank test). And, RNF125 was proved to a positive metastasis-related gene in vitro. RNF125 knockdown inhibited the invasion and migration, enhanced the adhesion, upregulated E-cadherin and β-catenin expression, and downregulated vimentin and N-cadherin expression (all P < 0.001) of NOZ cells in vitro. RNF125 promoting effect on GBC tumor progression was identified to relate with the activation of TGF-β1-SMAD3-ID1 signaling pathway. These findings firstly confirm that high RNF125 expression is related with aggressive characteristics and unfavorable prognosis of GBC patients; RNF125 promotes the invasion and metastasis of human GBCs via activating the TGF-β1-SMAD3-ID1 signaling pathway.
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Affiliation(s)
- Zhong-Yan Liu
- Department of Surgery, Tongji Hospital, Tongji University School of Medicine, Tongji University, Shanghai 200065, P.R. China
| | - Jin Cao
- Department of Surgery, Tongji Hospital, Tongji University School of Medicine, Tongji University, Shanghai 200065, P.R. China
| | - Jing-Tao Zhang
- Department of Surgery, Tongji Hospital, Tongji University School of Medicine, Tongji University, Shanghai 200065, P.R. China
| | - Guo-Li Xu
- Department of Surgery, Tongji Hospital, Tongji University School of Medicine, Tongji University, Shanghai 200065, P.R. China
| | - Xin-Ping Li
- Department of Surgery, Tongji Hospital, Tongji University School of Medicine, Tongji University, Shanghai 200065, P.R. China
| | - Fang-Tao Wang
- Department of Surgery, Tongji Hospital, Tongji University School of Medicine, Tongji University, Shanghai 200065, P.R. China
| | - Kamar Hasan Ansari
- Department of Surgery, Tongji Hospital, Tongji University School of Medicine, Tongji University, Shanghai 200065, P.R. China
| | - Hassan Mohamed
- Department of Surgery, Tongji Hospital, Tongji University School of Medicine, Tongji University, Shanghai 200065, P.R. China
| | - Yue-Zu Fan
- Department of Surgery, Tongji Hospital, Tongji University School of Medicine, Tongji University, Shanghai 200065, P.R. China
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Suppression of 19S proteasome subunits marks emergence of an altered cell state in diverse cancers. Proc Natl Acad Sci U S A 2016; 114:382-387. [PMID: 28028240 DOI: 10.1073/pnas.1619067114] [Citation(s) in RCA: 40] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
The use of proteasome inhibitors to target cancer's dependence on altered protein homeostasis has been greatly limited by intrinsic and acquired resistance. Analyzing data from thousands of cancer lines and tumors, we find that those with suppressed expression of one or more 19S proteasome subunits show intrinsic proteasome inhibitor resistance. Moreover, such proteasome subunit suppression is associated with poor outcome in myeloma patients, where proteasome inhibitors are a mainstay of treatment. Beyond conferring resistance to proteasome inhibitors, proteasome subunit suppression also serves as a sentinel of a more global remodeling of the transcriptome. This remodeling produces a distinct gene signature and new vulnerabilities to the proapoptotic drug, ABT-263. This frequent, naturally arising imbalance in 19S regulatory complex composition is achieved through a variety of mechanisms, including DNA methylation, and marks the emergence of a heritably altered and therapeutically relevant state in diverse cancers.
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Tsvetkov P, Mendillo ML, Zhao J, Carette JE, Merrill PH, Cikes D, Varadarajan M, van Diemen FR, Penninger JM, Goldberg AL, Brummelkamp TR, Santagata S, Lindquist S. Compromising the 19S proteasome complex protects cells from reduced flux through the proteasome. eLife 2015; 4. [PMID: 26327695 PMCID: PMC4551903 DOI: 10.7554/elife.08467] [Citation(s) in RCA: 58] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2015] [Accepted: 07/29/2015] [Indexed: 12/11/2022] Open
Abstract
Proteasomes are central regulators of protein homeostasis in eukaryotes. Proteasome function is vulnerable to environmental insults, cellular protein imbalance and targeted pharmaceuticals. Yet, mechanisms that cells deploy to counteract inhibition of this central regulator are little understood. To find such mechanisms, we reduced flux through the proteasome to the point of toxicity with specific inhibitors and performed genome-wide screens for mutations that allowed cells to survive. Counter to expectation, reducing expression of individual subunits of the proteasome's 19S regulatory complex increased survival. Strong 19S reduction was cytotoxic but modest reduction protected cells from inhibitors. Protection was accompanied by an increased ratio of 20S to 26S proteasomes, preservation of protein degradation capacity and reduced proteotoxic stress. While compromise of 19S function can have a fitness cost under basal conditions, it provided a powerful survival advantage when proteasome function was impaired. This means of rebalancing proteostasis is conserved from yeast to humans.
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Affiliation(s)
- Peter Tsvetkov
- Whitehead Institute for Biomedical Research, Cambridge, United States
| | - Marc L Mendillo
- Department of Biology, Howard Hughes Medical Institute, Massachusetts Institute of Technology, Cambridge, United States
| | - Jinghui Zhao
- Department of Cell Biology, Harvard Medical School, Boston, United States
| | - Jan E Carette
- Department of Microbiology and Immunology, Stanford University School of Medicine, Stanford, United States
| | - Parker H Merrill
- Department of Pathology, Brigham and Women's Hospital, Harvard Medical School, Boston, United States
| | - Domagoj Cikes
- Institute of Molecular Biotechnology of the Austrian Academy of Sciences, Vienna, Austria
| | | | - Ferdy R van Diemen
- Department of Biochemistry, Netherlands Cancer Institute, Amsterdam, Netherlands
| | - Josef M Penninger
- Institute of Molecular Biotechnology of the Austrian Academy of Sciences, Vienna, Austria
| | - Alfred L Goldberg
- Department of Cell Biology, Harvard Medical School, Boston, United States
| | - Thijn R Brummelkamp
- Department of Biochemistry, Netherlands Cancer Institute, Amsterdam, Netherlands
| | - Sandro Santagata
- Whitehead Institute for Biomedical Research, Cambridge, United States
| | - Susan Lindquist
- Whitehead Institute for Biomedical Research, Cambridge, United States
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Yu T, Tao Y, Yang M, Chen P, Gao X, Zhang Y, Zhang T, Chen Z, Hou J, Zhang Y, Ruan K, Wang H, Hu R. Profiling human protein degradome delineates cellular responses to proteasomal inhibition and reveals a feedback mechanism in regulating proteasome homeostasis. Cell Res 2014; 24:1214-30. [PMID: 25223703 DOI: 10.1038/cr.2014.122] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2013] [Revised: 02/14/2014] [Accepted: 06/26/2014] [Indexed: 12/15/2022] Open
Abstract
Global change in protein turnover (protein degradome) constitutes a central part of cellular responses to intrinsic or extrinsic stimuli. However, profiling protein degradome remains technically challenging. Recently, inhibition of the proteasome, e.g., by using bortezomib (BTZ), has emerged as a major chemotherapeutic strategy for treating multiple myeloma and other human malignancies, but systematic understanding of the mechanisms for BTZ drug action and tumor drug resistance is yet to be achieved. Here we developed and applied a dual-fluorescence-based Protein Turnover Assay (ProTA) to quantitatively profile global changes in human protein degradome upon BTZ-induced proteasomal inhibition. ProTA and subsequent network analyses delineate potential molecular basis for BTZ action and tumor drug resistance in BTZ chemotherapy. Finally, combined use of BTZ with drugs targeting the ProTA-identified key genes or pathways in BTZ action reduced BTZ resistance in multiple myeloma cells. Remarkably, BTZ stabilizes proteasome subunit PSMC1 and proteasome assembly factor PSMD10, suggesting a previously under-appreciated mechanism for regulating proteasome homeostasis. Therefore, ProTA is a novel tool for profiling human protein degradome to elucidate potential mechanisms of drug action and resistance, which might facilitate therapeutic development targeting proteostasis to treat human disorders.
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Affiliation(s)
- Tao Yu
- 1] State Key Laboratory of Molecular Biology, Institute of Biochemistry and Cell Biology, University of Chinese Academy of Sciences, 320 Yueyang Road, Shanghai 200031, China [2] Graduate School, Institute of Biochemistry and Cell Biology, University of Chinese Academy of Sciences, 320 Yueyang Road, Shanghai 200031, China
| | - Yonghui Tao
- 1] State Key Laboratory of Molecular Biology, Institute of Biochemistry and Cell Biology, University of Chinese Academy of Sciences, 320 Yueyang Road, Shanghai 200031, China [2] Graduate School, Institute of Biochemistry and Cell Biology, University of Chinese Academy of Sciences, 320 Yueyang Road, Shanghai 200031, China
| | - Meiqiang Yang
- State Key Laboratory of Molecular Biology, Institute of Biochemistry and Cell Biology, University of Chinese Academy of Sciences, 320 Yueyang Road, Shanghai 200031, China
| | - Peng Chen
- 1] State Key Laboratory of Molecular Biology, Institute of Biochemistry and Cell Biology, University of Chinese Academy of Sciences, 320 Yueyang Road, Shanghai 200031, China [2] Graduate School, Institute of Biochemistry and Cell Biology, University of Chinese Academy of Sciences, 320 Yueyang Road, Shanghai 200031, China
| | - Xiaobo Gao
- 1] State Key Laboratory of Molecular Biology, Institute of Biochemistry and Cell Biology, University of Chinese Academy of Sciences, 320 Yueyang Road, Shanghai 200031, China [2] Graduate School, Institute of Biochemistry and Cell Biology, University of Chinese Academy of Sciences, 320 Yueyang Road, Shanghai 200031, China
| | - Yanbo Zhang
- 1] Graduate School, Institute of Biochemistry and Cell Biology, University of Chinese Academy of Sciences, 320 Yueyang Road, Shanghai 200031, China [2] State Key Laboratory of Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, 320 Yueyang Road, Shanghai 200031, China
| | - Tao Zhang
- Department of Laboratory Medicine, Hua-Shan Hospital, Fudan University, 12 Road Wulumuqi middle Road, Shanghai 200040, China
| | - Zi Chen
- Department of Hematology, Hua-Shan Hospital, Fudan University, 12 Road Wulumuqi middle Road, Shanghai 200040, China
| | - Jian Hou
- Department of Hematology, Changzheng Hospital, The Second Military Medical University, 415 Fengyang Road, Shanghai 200003, China
| | - Yan Zhang
- Key Laboratory of Nutrition and Metabolism, Institute for Nutritional Sciences, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, 320 Yueyang Road, Shanghai 200031, China
| | - Kangcheng Ruan
- State Key Laboratory of Molecular Biology, Institute of Biochemistry and Cell Biology, University of Chinese Academy of Sciences, 320 Yueyang Road, Shanghai 200031, China
| | - Hongyan Wang
- State Key Laboratory of Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, 320 Yueyang Road, Shanghai 200031, China
| | - Ronggui Hu
- 1] State Key Laboratory of Molecular Biology, Institute of Biochemistry and Cell Biology, University of Chinese Academy of Sciences, 320 Yueyang Road, Shanghai 200031, China [2] Cancer Research Center, SIBS-Xuhui Central Hospital, Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, 320 Yueyang Road, Shanghai 200031, China
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Shen J, Song G, An M, Li X, Wu N, Ruan K, Hu J, Hu R. The use of hollow mesoporous silica nanospheres to encapsulate bortezomib and improve efficacy for non-small cell lung cancer therapy. Biomaterials 2014; 35:316-26. [DOI: 10.1016/j.biomaterials.2013.09.098] [Citation(s) in RCA: 81] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/27/2013] [Accepted: 09/25/2013] [Indexed: 01/13/2023]
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van Wijk SJL, Fiškin E, Dikic I. Selective monitoring of ubiquitin signals with genetically encoded ubiquitin chain-specific sensors. Nat Protoc 2013; 8:1449-58. [PMID: 23807287 DOI: 10.1038/nprot.2013.089] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
Despite intensive research, there is a distinct lack of methodology for visualizing endogenous ubiquitination in living cells. In this protocol, we describe how unique properties of ubiquitin (Ub)-binding domains (UBDs) can be used to selectively detect, visualize and inhibit Ub-dependent processes in mammalian cells. The procedure deals with designing and validating the binding selectivity of GFP-tagged K63- and linear-linked sensors (TAB2 NZF and NEMO UBAN, respectively) in vitro. We describe how these moieties can be used to inhibit tumor necrosis factor (TNF)-mediated NF-κB signaling and to detect ubiquitinated cytosolic Salmonella in living cells, emphasizing a more flexible use compared with chain-specific antibodies. These chain-specific sensors can be used to detect Ub-like or autophagy-related modifiers and, in combination with mass spectrometry, to identify new Ub targets. These Ub (-like) sensors can be designed, constructed and tested in ~2-3 weeks.
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Affiliation(s)
- Sjoerd J L van Wijk
- Institute of Biochemistry II, School of Medicine, Goethe University, Frankfurt am Main, Germany
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Harty C, Römisch K. Analysis of Sec61p and Ssh1p interactions in the ER membrane using the split-ubiquitin system. BMC Cell Biol 2013; 14:14. [PMID: 23497013 PMCID: PMC3618304 DOI: 10.1186/1471-2121-14-14] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/31/2012] [Accepted: 02/28/2013] [Indexed: 01/12/2023] Open
Abstract
BACKGROUND The split-ubiquitin system monitors interactions of transmembrane proteins in yeast. It is based on the formation of a quasi-native ubiquitin structure upon interaction of two proteins to which the N- and C-terminal halves of ubiquitin have been fused. In the system we use here ubiquitin formation leads to proteolytic cleavage liberating a transcription factor (PLV) from the C-ubiquitin (C) fusion protein which can then activate reporter genes. Generation of fusion proteins is, however, rife with problems, and particularly in transmembrane proteins often disturbs topology, structure and function. RESULTS We show that both the Sec61 protein which forms the principal protein translocation channel in the endoplasmic reticulum (ER) membrane, and its non-essential homologue, Ssh1p, when fused C-terminally to CPLV are inactive. In a heterozygous diploid Sec61-CPLV is present in protein translocation channels in the ER membrane without disturbing their function and displays a limited set of protein-protein interactions similar to those found for the wildtype protein using biochemical methods. Although its expression level is similar, Ssh1-CPLV interactions are less strong, and, in contrast to Sec61p, Ssh1p does not distinguish between Sbh1p and Sbh2p. We show that interactions can be monitored by reporter gene activity or directly by PLV cleavage, which is more sensitive, but leads to quantitatively different results. CONCLUSIONS We conclude that the split-ubiquitin system we used here has high fidelity, but low sensitivity and is of limited use for detection of new, transient interactions with protein translocation channels in the ER membrane.
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Affiliation(s)
- Carol Harty
- Cambridge Institute for Medical Research, Hills Road, Cambridge, CB2 2XY, UK
- Current address: Sauder School of Business, Henry Angus Building, 2053 Main Mall, University of British Columbia, Vancouver, BC V6T 1Z2, Canada
| | - Karin Römisch
- Cambridge Institute for Medical Research, Hills Road, Cambridge, CB2 2XY, UK
- Department of Microbiology, Faculty of Biology, Saarland University, Campus A1.5, Saarbruecken, 66123, Germany
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Fernández-Sáiz V, Targosz BS, Lemeer S, Eichner R, Langer C, Bullinger L, Reiter C, Slotta-Huspenina J, Schroeder S, Knorn AM, Kurutz J, Peschel C, Pagano M, Kuster B, Bassermann F. SCFFbxo9 and CK2 direct the cellular response to growth factor withdrawal via Tel2/Tti1 degradation and promote survival in multiple myeloma. Nat Cell Biol 2013; 15:72-81. [PMID: 23263282 DOI: 10.1038/ncb2651] [Citation(s) in RCA: 63] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/03/2012] [Accepted: 11/09/2012] [Indexed: 12/17/2022]
Abstract
The Tel2 (also known as Telo2) and Tti1 proteins control the cellular abundance of mammalian PIKKs and are integral components of mTORC1 and mTORC2. Here we report that Tel2 and Tti1 are targeted for degradation within mTORC1 by the SCFFbxo9 ubiquitin ligase to adjust mTOR signalling to growth factor availability. This process is primed by CK2, which translocates to the cytoplasm to mediate mTORC1-specific phosphorylation of Tel2/Tti1, subsequent to growth factor deprivation. As a consequence, mTORC1 is inactivated to restrain cell growth and protein translation whereas relief of feedback inhibition activates the PI(3)K/TORC2/Akt pathway to sustain survival. Significantly, primary human multiple myelomas exhibit high levels of Fbxo9. In this setting, PI(3)K/TORC2/Akt signalling and survival of multiple myeloma cells is dependent on Fbxo9 expression. Thus, mTORC1-specific degradation of the Tel2 and Tti1 proteins represents a central mTOR regulatory mechanism with implications in multiple myeloma, both in promoting survival and in providing targets for the specific treatment of multiple myeloma with high levels of Fbxo9 expression.
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Affiliation(s)
- Vanesa Fernández-Sáiz
- Department of Medicine III, Klinikum rechts der Isar, Technische Universität München, Ismaninger Strasse 22, 81675 Munich, Germany
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Ee G, Lehming N. How the ubiquitin proteasome system regulates the regulators of transcription. Transcription 2012; 3:235-9. [PMID: 22885980 DOI: 10.4161/trns.21249] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023] Open
Abstract
The ubiquitin proteasome system plays an important role in transcription. Monoubiquitination of activators is believed to aid their function, while the 26S proteasomal degradation of repressors is believed to restrict their function. What remains controversial is the question of whether the degradation of activators aids or restricts their function.
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Affiliation(s)
- Gary Ee
- Department of Microbiology, Yong Loo Lin School of Medicine, National University of Singapore, Singapore
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