1
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IRES-mediated Wnt2 translation in apoptotic neurons triggers astrocyte dedifferentiation. NPJ Regen Med 2022; 7:42. [PMID: 36056026 PMCID: PMC9440034 DOI: 10.1038/s41536-022-00248-1] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2021] [Accepted: 08/08/2022] [Indexed: 11/30/2022] Open
Abstract
Reactive astrogliosis usually bears some properties of neural progenitors. How injury triggers astrocyte dedifferentiation remains largely unclear. Here, we report that ischemia induces rapid up-regulation of Wnt2 protein in apoptotic neurons and activation of canonical Wnt signaling in reactive astrocytes in mice, primates and human. Local delivery of Wnt2 shRNA abolished the dedifferentiation of astrocytes while over-expressing Wnt2 promoted progenitor marker expression and neurogenesis. Both the activation of Wnt signaling and dedifferentiation of astrocytes was compromised in ischemic caspase-3−/− cortex. Over-expressing stabilized β-catenin not only facilitated neurogenesis but also promoted functional recovery in ischemic caspase-3−/− mice. Further analysis showed that apoptotic neurons up-regulated Wnt2 protein via internal ribosome entry site (IRES)-mediated translation. Knocking down death associated protein 5 (DAP5), a key protein in IRES-mediated protein translation, significantly diminished Wnt activation and astrocyte dedifferentiation. Our data demonstrated an apoptosis-initiated Wnt-activating mechanism which triggers astrocytic dedifferentiation and facilitates neuronal regeneration.
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2
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Dai S, Wang C, Zhang C, Feng L, Zhang W, Zhou X, He Y, Xia X, Chen B, Song W. PTB: Not just a polypyrimidine tract-binding protein. J Cell Physiol 2022; 237:2357-2373. [PMID: 35288937 DOI: 10.1002/jcp.30716] [Citation(s) in RCA: 17] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2021] [Revised: 02/19/2022] [Accepted: 02/22/2022] [Indexed: 01/21/2023]
Abstract
Polypyrimidine tract-binding protein (PTB), as a member of the heterogeneous nuclear ribonucleoprotein family, functions by rapidly shuttling between the nucleus and the cytoplasm. PTB is involved in the alternative splicing of pre-messenger RNA (mRNA) and almost all steps of mRNA metabolism. PTB regulation is organ-specific; brain- or muscle-specific microRNAs and long noncoding RNAs partially contribute to regulating PTB, thereby modulating many physiological and pathological processes, such as embryonic development, cell development, spermatogenesis, and neuron growth and differentiation. Previous studies have shown that PTB knockout can inhibit tumorigenesis and development. The knockout of PTB in glial cells can be reprogrammed into functional neurons, which shows great promise in the field of nerve regeneration but is controversial.
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Affiliation(s)
- Shirui Dai
- National Clinical Research Center for Geriatric Diseases, Xiangya Hospital of Central South University, Changsha, Hunan, P. R. China.,Eye Center of Xiangya Hospital, Central South University, Changsha, Hunan, P. R. China.,Hunan Key Laboratory of Ophthalmology, Changsha, Hunan, P. R. China.,Department of Ophthalmology, The Second Xiangya Hospital, Central South University, Changsha, Hunan, P. R. China.,Hunan Clinical Research Center of Ophthalmic Disease, Changsha, Hunan, P. R. China
| | - Chao Wang
- National Clinical Research Center for Geriatric Diseases, Xiangya Hospital of Central South University, Changsha, Hunan, P. R. China.,Eye Center of Xiangya Hospital, Central South University, Changsha, Hunan, P. R. China.,Hunan Key Laboratory of Ophthalmology, Changsha, Hunan, P. R. China
| | - Cheng Zhang
- National Clinical Research Center for Geriatric Diseases, Xiangya Hospital of Central South University, Changsha, Hunan, P. R. China.,Eye Center of Xiangya Hospital, Central South University, Changsha, Hunan, P. R. China.,Hunan Key Laboratory of Ophthalmology, Changsha, Hunan, P. R. China
| | - Lemeng Feng
- National Clinical Research Center for Geriatric Diseases, Xiangya Hospital of Central South University, Changsha, Hunan, P. R. China.,Eye Center of Xiangya Hospital, Central South University, Changsha, Hunan, P. R. China.,Hunan Key Laboratory of Ophthalmology, Changsha, Hunan, P. R. China
| | - Wulong Zhang
- National Clinical Research Center for Geriatric Diseases, Xiangya Hospital of Central South University, Changsha, Hunan, P. R. China.,Eye Center of Xiangya Hospital, Central South University, Changsha, Hunan, P. R. China.,Hunan Key Laboratory of Ophthalmology, Changsha, Hunan, P. R. China
| | - Xuezhi Zhou
- National Clinical Research Center for Geriatric Diseases, Xiangya Hospital of Central South University, Changsha, Hunan, P. R. China.,Eye Center of Xiangya Hospital, Central South University, Changsha, Hunan, P. R. China.,Hunan Key Laboratory of Ophthalmology, Changsha, Hunan, P. R. China
| | - Ye He
- National Clinical Research Center for Geriatric Diseases, Xiangya Hospital of Central South University, Changsha, Hunan, P. R. China.,Eye Center of Xiangya Hospital, Central South University, Changsha, Hunan, P. R. China.,Hunan Key Laboratory of Ophthalmology, Changsha, Hunan, P. R. China
| | - Xiaobo Xia
- National Clinical Research Center for Geriatric Diseases, Xiangya Hospital of Central South University, Changsha, Hunan, P. R. China.,Eye Center of Xiangya Hospital, Central South University, Changsha, Hunan, P. R. China.,Hunan Key Laboratory of Ophthalmology, Changsha, Hunan, P. R. China
| | - Baihua Chen
- Department of Ophthalmology, The Second Xiangya Hospital, Central South University, Changsha, Hunan, P. R. China.,Hunan Clinical Research Center of Ophthalmic Disease, Changsha, Hunan, P. R. China
| | - Weitao Song
- National Clinical Research Center for Geriatric Diseases, Xiangya Hospital of Central South University, Changsha, Hunan, P. R. China.,Eye Center of Xiangya Hospital, Central South University, Changsha, Hunan, P. R. China.,Hunan Key Laboratory of Ophthalmology, Changsha, Hunan, P. R. China
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3
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Therizols G, Bash-Imam Z, Panthu B, Machon C, Vincent A, Ripoll J, Nait-Slimane S, Chalabi-Dchar M, Gaucherot A, Garcia M, Laforêts F, Marcel V, Boubaker-Vitre J, Monet MA, Bouclier C, Vanbelle C, Souahlia G, Berthel E, Albaret MA, Mertani HC, Prudhomme M, Bertrand M, David A, Saurin JC, Bouvet P, Rivals E, Ohlmann T, Guitton J, Dalla Venezia N, Pannequin J, Catez F, Diaz JJ. Alteration of ribosome function upon 5-fluorouracil treatment favors cancer cell drug-tolerance. Nat Commun 2022; 13:173. [PMID: 35013311 PMCID: PMC8748862 DOI: 10.1038/s41467-021-27847-8] [Citation(s) in RCA: 18] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/25/2020] [Accepted: 12/10/2021] [Indexed: 02/06/2023] Open
Abstract
Mechanisms of drug-tolerance remain poorly understood and have been linked to genomic but also to non-genomic processes. 5-fluorouracil (5-FU), the most widely used chemotherapy in oncology is associated with resistance. While prescribed as an inhibitor of DNA replication, 5-FU alters all RNA pathways. Here, we show that 5-FU treatment leads to the production of fluorinated ribosomes exhibiting altered translational activities. 5-FU is incorporated into ribosomal RNAs of mature ribosomes in cancer cell lines, colorectal xenografts, and human tumors. Fluorinated ribosomes appear to be functional, yet, they display a selective translational activity towards mRNAs depending on the nature of their 5'-untranslated region. As a result, we find that sustained translation of IGF-1R mRNA, which encodes one of the most potent cell survival effectors, promotes the survival of 5-FU-treated colorectal cancer cells. Altogether, our results demonstrate that "man-made" fluorinated ribosomes favor the drug-tolerant cellular phenotype by promoting translation of survival genes.
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MESH Headings
- Antimetabolites, Antineoplastic/pharmacology
- Cell Line, Tumor
- Cell Survival/drug effects
- Colorectal Neoplasms/drug therapy
- Colorectal Neoplasms/genetics
- Colorectal Neoplasms/metabolism
- Colorectal Neoplasms/pathology
- DNA Replication
- DNA, Neoplasm/genetics
- DNA, Neoplasm/metabolism
- Drug Resistance, Neoplasm/genetics
- Drug Tolerance/genetics
- Fluorouracil/pharmacology
- HCT116 Cells
- Halogenation
- Humans
- Protein Biosynthesis/drug effects
- RNA, Messenger/genetics
- RNA, Messenger/metabolism
- RNA, Ribosomal/genetics
- RNA, Ribosomal/metabolism
- Receptor, IGF Type 1/agonists
- Receptor, IGF Type 1/genetics
- Receptor, IGF Type 1/metabolism
- Ribosomes/drug effects
- Ribosomes/genetics
- Ribosomes/metabolism
- Xenograft Model Antitumor Assays
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Affiliation(s)
- Gabriel Therizols
- Inserm U1052, CNRS UMR5286 Centre de Recherche en Cancérologie de Lyon, F-69000, Lyon, France
- Centre Léon Bérard, F-69008, Lyon, France
- Université de Lyon 1, F-69000, Lyon, France
| | - Zeina Bash-Imam
- Inserm U1052, CNRS UMR5286 Centre de Recherche en Cancérologie de Lyon, F-69000, Lyon, France
- Centre Léon Bérard, F-69008, Lyon, France
- Université de Lyon 1, F-69000, Lyon, France
| | - Baptiste Panthu
- CIRI-Inserm U1111, Ecole Normale Supérieure de Lyon, Lyon, F-693643, France
- Inserm U1060, CARMEN, F-69310, Pierre Bénite, France
| | - Christelle Machon
- Inserm U1052, CNRS UMR5286 Centre de Recherche en Cancérologie de Lyon, F-69000, Lyon, France
- Centre Léon Bérard, F-69008, Lyon, France
- Université de Lyon 1, F-69000, Lyon, France
- Laboratoire de chimie analytique, Faculté de pharmacie de Lyon, 8 avenue Rockefeller, F-69373, Lyon, France
- Laboratoire de biochimie et de pharmaco-toxicologie, Centre hospitalier Lyon-Sud - HCL, F-69495, Pierre Bénite, France
| | - Anne Vincent
- Inserm U1052, CNRS UMR5286 Centre de Recherche en Cancérologie de Lyon, F-69000, Lyon, France
- Centre Léon Bérard, F-69008, Lyon, France
- Université de Lyon 1, F-69000, Lyon, France
| | - Julie Ripoll
- LIRMM, UMR 5506, University of Montpellier, CNRS, Montpellier, France
| | - Sophie Nait-Slimane
- Inserm U1052, CNRS UMR5286 Centre de Recherche en Cancérologie de Lyon, F-69000, Lyon, France
- Centre Léon Bérard, F-69008, Lyon, France
- Université de Lyon 1, F-69000, Lyon, France
| | - Mounira Chalabi-Dchar
- Inserm U1052, CNRS UMR5286 Centre de Recherche en Cancérologie de Lyon, F-69000, Lyon, France
- Centre Léon Bérard, F-69008, Lyon, France
- Université de Lyon 1, F-69000, Lyon, France
| | - Angéline Gaucherot
- Inserm U1052, CNRS UMR5286 Centre de Recherche en Cancérologie de Lyon, F-69000, Lyon, France
- Centre Léon Bérard, F-69008, Lyon, France
- Université de Lyon 1, F-69000, Lyon, France
| | - Maxime Garcia
- Inserm U1052, CNRS UMR5286 Centre de Recherche en Cancérologie de Lyon, F-69000, Lyon, France
- Centre Léon Bérard, F-69008, Lyon, France
- Université de Lyon 1, F-69000, Lyon, France
| | - Florian Laforêts
- Inserm U1052, CNRS UMR5286 Centre de Recherche en Cancérologie de Lyon, F-69000, Lyon, France
- Centre Léon Bérard, F-69008, Lyon, France
- Université de Lyon 1, F-69000, Lyon, France
| | - Virginie Marcel
- Inserm U1052, CNRS UMR5286 Centre de Recherche en Cancérologie de Lyon, F-69000, Lyon, France
- Centre Léon Bérard, F-69008, Lyon, France
- Université de Lyon 1, F-69000, Lyon, France
| | | | - Marie-Ambre Monet
- Inserm U1052, CNRS UMR5286 Centre de Recherche en Cancérologie de Lyon, F-69000, Lyon, France
- Centre Léon Bérard, F-69008, Lyon, France
- Université de Lyon 1, F-69000, Lyon, France
| | | | - Christophe Vanbelle
- Inserm U1052, CNRS UMR5286 Centre de Recherche en Cancérologie de Lyon, F-69000, Lyon, France
- Centre Léon Bérard, F-69008, Lyon, France
- Université de Lyon 1, F-69000, Lyon, France
| | - Guillaume Souahlia
- Inserm U1052, CNRS UMR5286 Centre de Recherche en Cancérologie de Lyon, F-69000, Lyon, France
- Centre Léon Bérard, F-69008, Lyon, France
- Université de Lyon 1, F-69000, Lyon, France
| | - Elise Berthel
- Inserm U1052, CNRS UMR5286 Centre de Recherche en Cancérologie de Lyon, F-69000, Lyon, France
- Centre Léon Bérard, F-69008, Lyon, France
- Université de Lyon 1, F-69000, Lyon, France
| | - Marie Alexandra Albaret
- Inserm U1052, CNRS UMR5286 Centre de Recherche en Cancérologie de Lyon, F-69000, Lyon, France
- Centre Léon Bérard, F-69008, Lyon, France
- Université de Lyon 1, F-69000, Lyon, France
- Department of Translational Research and Innovation, Centre Léon Bérard, 69373, Lyon, France
| | - Hichem C Mertani
- Inserm U1052, CNRS UMR5286 Centre de Recherche en Cancérologie de Lyon, F-69000, Lyon, France
- Centre Léon Bérard, F-69008, Lyon, France
- Université de Lyon 1, F-69000, Lyon, France
| | - Michel Prudhomme
- Department of Digestive Surgery, CHU Nimes, Univ Montpellier, Nimes, France
| | - Martin Bertrand
- Department of Digestive Surgery, CHU Nimes, Univ Montpellier, Nimes, France
| | - Alexandre David
- IGF, Univ. Montpellier, CNRS, INSERM, Montpellier, France
- IRMB-PPC, Univ Montpellier, INSERM, CHU Montpellier, CNRS, Montpellier, France
| | - Jean-Christophe Saurin
- Inserm U1052, CNRS UMR5286 Centre de Recherche en Cancérologie de Lyon, F-69000, Lyon, France
- Centre Léon Bérard, F-69008, Lyon, France
- Université de Lyon 1, F-69000, Lyon, France
- Department of Endoscopy and Gastroenterology, Pavillon L, Edouard Herriot Hospital, Lyon, France
| | - Philippe Bouvet
- Inserm U1052, CNRS UMR5286 Centre de Recherche en Cancérologie de Lyon, F-69000, Lyon, France
- Centre Léon Bérard, F-69008, Lyon, France
- Université de Lyon 1, F-69000, Lyon, France
- Ecole Normale Supérieure de Lyon, Lyon, France
| | - Eric Rivals
- LIRMM, UMR 5506, University of Montpellier, CNRS, Montpellier, France
- Institut Français de Bioinformatique, CNRS UMS 3601, Évry, France
| | - Théophile Ohlmann
- CIRI-Inserm U1111, Ecole Normale Supérieure de Lyon, Lyon, F-693643, France
| | - Jérôme Guitton
- Inserm U1052, CNRS UMR5286 Centre de Recherche en Cancérologie de Lyon, F-69000, Lyon, France
- Centre Léon Bérard, F-69008, Lyon, France
- Université de Lyon 1, F-69000, Lyon, France
- Laboratoire de biochimie et de pharmaco-toxicologie, Centre hospitalier Lyon-Sud - HCL, F-69495, Pierre Bénite, France
- Laboratoire de toxicologie, Faculté de pharmacie de Lyon, Université de Lyon, 8 avenue Rockefeller, F-69373, Lyon, France
| | - Nicole Dalla Venezia
- Inserm U1052, CNRS UMR5286 Centre de Recherche en Cancérologie de Lyon, F-69000, Lyon, France
- Centre Léon Bérard, F-69008, Lyon, France
- Université de Lyon 1, F-69000, Lyon, France
| | | | - Frédéric Catez
- Inserm U1052, CNRS UMR5286 Centre de Recherche en Cancérologie de Lyon, F-69000, Lyon, France.
- Centre Léon Bérard, F-69008, Lyon, France.
- Université de Lyon 1, F-69000, Lyon, France.
- Institut Convergence PLAsCAN, F-69373, Lyon, France.
| | - Jean-Jacques Diaz
- Inserm U1052, CNRS UMR5286 Centre de Recherche en Cancérologie de Lyon, F-69000, Lyon, France.
- Centre Léon Bérard, F-69008, Lyon, France.
- Université de Lyon 1, F-69000, Lyon, France.
- Institut Convergence PLAsCAN, F-69373, Lyon, France.
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4
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Godet AC, Roussel E, David F, Hantelys F, Morfoisse F, Alves J, Pujol F, Ader I, Bertrand E, Burlet-Schiltz O, Froment C, Henras AK, Vitali P, Lacazette E, Tatin F, Garmy-Susini B, Prats AC. Long non-coding RNA Neat1 and paraspeckle components are translational regulators in hypoxia. eLife 2022; 11:69162. [PMID: 36546462 PMCID: PMC9799981 DOI: 10.7554/elife.69162] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2021] [Accepted: 12/18/2022] [Indexed: 12/24/2022] Open
Abstract
Internal ribosome entry sites (IRESs) drive translation initiation during stress. In response to hypoxia, (lymph)angiogenic factors responsible for tissue revascularization in ischemic diseases are induced by the IRES-dependent mechanism. Here, we searched for IRES trans-acting factors (ITAFs) active in early hypoxia in mouse cardiomyocytes. Using knock-down and proteomics approaches, we show a link between a stressed-induced nuclear body, the paraspeckle, and IRES-dependent translation. Furthermore, smiFISH experiments demonstrate the recruitment of IRES-containing mRNA into paraspeckle during hypoxia. Our data reveal that the long non-coding RNA Neat1, an essential paraspeckle component, is a key translational regulator, active on IRESs of (lymph)angiogenic and cardioprotective factor mRNAs. In addition, paraspeckle proteins p54nrb and PSPC1 as well as nucleolin and RPS2, two p54nrb-interacting proteins identified by mass spectrometry, are ITAFs for IRES subgroups. Paraspeckle thus appears as a platform to recruit IRES-containing mRNAs and possibly host IRESome assembly. Polysome PCR array shows that Neat1 isoforms regulate IRES-dependent translation and, more widely, translation of mRNAs involved in stress response.
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Affiliation(s)
| | - Emilie Roussel
- UMR 1297-I2MC, Inserm, Université de ToulouseToulouseFrance
| | - Florian David
- UMR 1297-I2MC, Inserm, Université de ToulouseToulouseFrance
| | | | | | - Joffrey Alves
- UMR 1297-I2MC, Inserm, Université de ToulouseToulouseFrance
| | | | - Isabelle Ader
- UMR 1301-RESTORE, Inserm, CNRS 5070, Etablissement Français du Sang-Occitanie (EFS), National Veterinary School of Toulouse (ENVT), Université de ToulouseToulouseFrance
| | | | - Odile Burlet-Schiltz
- Institut de Pharmacologie et Biologie Structurale (IPBS), Université de Toulouse, CNRSToulouseFrance
| | - Carine Froment
- Institut de Pharmacologie et Biologie Structurale (IPBS), Université de Toulouse, CNRSToulouseFrance
| | - Anthony K Henras
- Molecular, Cellular and Developmental Biology Unit (MCD), Centre de Biologie Intégrative (CBI), Université de ToulouseToulouseFrance
| | - Patrice Vitali
- Molecular, Cellular and Developmental Biology Unit (MCD), Centre de Biologie Intégrative (CBI), Université de ToulouseToulouseFrance
| | - Eric Lacazette
- UMR 1297-I2MC, Inserm, Université de ToulouseToulouseFrance
| | - Florence Tatin
- UMR 1297-I2MC, Inserm, Université de ToulouseToulouseFrance
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5
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Park M, Kim JY, Kim J, Lee JH, Kwon YG, Kim YM. Low-dose metronomic doxorubicin inhibits mobilization and differentiation of endothelial progenitor cells through REDD1-mediated VEGFR-2 downregulation. BMB Rep 2021. [PMID: 34488932 PMCID: PMC8505230 DOI: 10.5483/bmbrep.2021.54.9.096] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023] Open
Abstract
Low-dose metronomic chemotherapy has been introduced as a less toxic and effective strategy to inhibit tumor angiogenesis, but its anti-angiogenic mechanism on endothelial progenitor cells (EPCs) has not been fully elucidated. Here, we investigated the functional role of regulated in development and DNA damage response 1 (REDD1), an endogenous inhibitor of mTORC1, in low-dose doxorubicin (DOX)-mediated dysregulation of EPC functions. DOX treatment induced REDD1 expression in bone marrow mononuclear cells (BMMNCs) and subsequently reduced mTORC1-dependent translation of endothelial growth factor (VEGF) receptor (Vegfr)-2 mRNA, but not that of the mRNA transcripts for Vegfr-1, epidermal growth factor receptor, and insulin-like growth factor-1 receptor. This selective event was a risk factor for the inhibition of BMMNC differentiation into EPCs and their angiogenic responses to VEGF-A, but was not observed in Redd1-deficient BMMNCs. Low-dose metronomic DOX treatment reduced the mobilization of circulating EPCs in B16 melanoma-bearing wild-type but not Redd1-deficient mice. However, REDD1 overexpression inhibited the differentiation and mobilization of EPCs in both wild-type and Redd1-deficient mice. These data suggest that REDD1 is crucial for metronomic DOX-mediated EPC dysfunction through the translational repression of Vegfr-2 transcript, providing REDD1 as a potential therapeutic target for the inhibition of tumor angiogenesis and tumor progression.
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Affiliation(s)
- Minsik Park
- Department of Molecular and Cellular Biochemistry, Kangwon National University School of Medicine, Chuncheon 24341, Korea
| | - Ji Yoon Kim
- Department of Anaesthesiology and Pain Medicine, Hanyang University Hospital, Seoul 04763, Korea
| | - Joohwan Kim
- Department of Molecular and Cellular Biochemistry, Kangwon National University School of Medicine, Chuncheon 24341, Korea
| | - Jeong-Hyung Lee
- Department of Biochemistry, Kangwon National University, Chuncheon 24341, Korea
| | - Young-Guen Kwon
- Department of Biochemistry, College of Life Science and Biotechnology, Yonsei University, Seoul 03722, Korea
| | - Young-Myeong Kim
- Department of Molecular and Cellular Biochemistry, Kangwon National University School of Medicine, Chuncheon 24341, Korea
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6
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Park M, Kim JY, Kim J, Lee JH, Kwon YG, Kim YM. Low-dose metronomic doxorubicin inhibits mobilization and differentiation of endothelial progenitor cells through REDD1-mediated VEGFR-2 downregulation. BMB Rep 2021; 54:470-475. [PMID: 34488932 PMCID: PMC8505230] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2021] [Revised: 07/29/2021] [Accepted: 08/10/2021] [Indexed: 04/04/2024] Open
Abstract
Low-dose metronomic chemotherapy has been introduced as a less toxic and effective strategy to inhibit tumor angiogenesis, but its anti-angiogenic mechanism on endothelial progenitor cells (EPCs) has not been fully elucidated. Here, we investigated the functional role of regulated in development and DNA damage response 1 (REDD1), an endogenous inhibitor of mTORC1, in low-dose doxorubicin (DOX)-mediated dysregulation of EPC functions. DOX treatment induced REDD1 expression in bone marrow mononuclear cells (BMMNCs) and subsequently reduced mTORC1-dependent translation of endothelial growth factor (VEGF) receptor (Vegfr)-2 mRNA, but not that of the mRNA transcripts for Vegfr-1, epidermal growth factor receptor, and insulin-like growth factor-1 receptor. This selective event was a risk factor for the inhibition of BMMNC differentiation into EPCs and their angiogenic responses to VEGF-A, but was not observed in Redd1-deficient BMMNCs. Low-dose metronomic DOX treatment reduced the mobilization of circulating EPCs in B16 melanoma-bearing wild-type but not Redd1-deficient mice. However, REDD1 overexpression inhibited the differentiation and mobilization of EPCs in both wild-type and Redd1-deficient mice. These data suggest that REDD1 is crucial for metronomic DOX-mediated EPC dysfunction through the translational repression of Vegfr-2 transcript, providing REDD1 as a potential therapeutic target for the inhibition of tumor angiogenesis and tumor progression. [BMB Reports 2021; 54(9): 470-475].
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Affiliation(s)
- Minsik Park
- Department of Molecular and Cellular Biochemistry, Kangwon National University School of Medicine, Chuncheon 24341, Korea
| | - Ji Yoon Kim
- Department of Anaesthesiology and Pain Medicine, Hanyang University Hospital, Seoul 04763, Korea
| | - Joohwan Kim
- Department of Molecular and Cellular Biochemistry, Kangwon National University School of Medicine, Chuncheon 24341, Korea
| | - Jeong-Hyung Lee
- Department of Biochemistry, Kangwon National University, Chuncheon 24341, Korea
| | - Young-Guen Kwon
- Department of Biochemistry, College of Life Science and Biotechnology, Yonsei University, Seoul 03722, Korea
| | - Young-Myeong Kim
- Department of Molecular and Cellular Biochemistry, Kangwon National University School of Medicine, Chuncheon 24341, Korea
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7
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Péladeau C, Jasmin BJ. Targeting IRES-dependent translation as a novel approach for treating Duchenne muscular dystrophy. RNA Biol 2020; 18:1238-1251. [PMID: 33164678 DOI: 10.1080/15476286.2020.1847894] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
Internal-ribosomal entry sites (IRES) are translational elements that allow the initiation machinery to start protein synthesis via internal initiation. IRESs promote tissue-specific translation in stress conditions when conventional cap-dependent translation is inhibited. Since many IRES-containing mRNAs are relevant to diseases, this cellular mechanism is emerging as an attractive therapeutic target for pharmacological and genetic modulations. Indeed, there has been growing interest over the past years in determining the therapeutic potential of IRESs for several disease conditions such as cancer, neurodegeneration and neuromuscular diseases including Duchenne muscular dystrophy (DMD). IRESs relevant for DMD have been identified in several transcripts whose protein product results in functional improvements in dystrophic muscles. Together, these converging lines of evidence indicate that activation of IRES-mediated translation of relevant transcripts in DMD muscle represents a novel and appropriate therapeutic strategy for DMD that warrants further investigation, particularly to identify agents that can modulate their activity.
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Affiliation(s)
- Christine Péladeau
- Department of Cellular and Molecular Medicine, and the Eric Poulin Centre for Neuromuscular Disease, Faculty of Medicine, University of Ottawa, Ottawa, Ontario, Canada
| | - Bernard J Jasmin
- Department of Cellular and Molecular Medicine, and the Eric Poulin Centre for Neuromuscular Disease, Faculty of Medicine, University of Ottawa, Ottawa, Ontario, Canada
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8
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Translation Regulation by eIF2α Phosphorylation and mTORC1 Signaling Pathways in Non-Communicable Diseases (NCDs). Int J Mol Sci 2020; 21:ijms21155301. [PMID: 32722591 PMCID: PMC7432514 DOI: 10.3390/ijms21155301] [Citation(s) in RCA: 20] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2020] [Revised: 07/20/2020] [Accepted: 07/22/2020] [Indexed: 02/07/2023] Open
Abstract
Non-communicable diseases (NCDs) are medical conditions that, by definition, are non-infectious and non-transmissible among people. Much of current NCDs are generally due to genetic, behavioral, and metabolic risk factors that often include excessive alcohol consumption, smoking, obesity, and untreated elevated blood pressure, and share many common signal transduction pathways. Alterations in cell and physiological signaling and transcriptional control pathways have been well studied in several human NCDs, but these same pathways also regulate expression and function of the protein synthetic machinery and mRNA translation which have been less well investigated. Alterations in expression of specific translation factors, and disruption of canonical mRNA translational regulation, both contribute to the pathology of many NCDs. The two most common pathological alterations that contribute to NCDs discussed in this review will be the regulation of eukaryotic initiation factor 2 (eIF2) by the integrated stress response (ISR) and the mammalian target of rapamycin complex 1 (mTORC1) pathways. Both pathways integrally connect mRNA translation activity to external and internal physiological stimuli. Here, we review the role of ISR control of eIF2 activity and mTORC1 control of cap-mediated mRNA translation in some common NCDs, including Alzheimer’s disease, Parkinson’s disease, stroke, diabetes mellitus, liver cirrhosis, chronic obstructive pulmonary disease (COPD), and cardiac diseases. Our goal is to provide insights that further the understanding as to the important role of translational regulation in the pathogenesis of these diseases.
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Dierschke SK, Toro AL, Miller WP, Sunilkumar S, Dennis MD. Diabetes enhances translation of Cd40 mRNA in murine retinal Müller glia via a 4E-BP1/2-dependent mechanism. J Biol Chem 2020; 295:10831-10841. [PMID: 32475820 DOI: 10.1074/jbc.ra120.013711] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/02/2020] [Revised: 05/27/2020] [Indexed: 11/06/2022] Open
Abstract
Activation of the immune costimulatory molecule cluster of differentiation 40 (CD40) in Müller glia has been implicated in the initiation of diabetes-induced retinal inflammation. Results from previous studies support that CD40 protein expression is elevated in Müller glia of diabetic mice; however, the mechanisms responsible for this increase have not been explored. Here, we evaluated the hypothesis that diabetes augments translation of the Cd40 mRNA. Mice receiving thiamet G (TMG), an inhibitor of the O-GlcNAc hydrolase O-GlcNAcase, exhibited enhanced retinal protein O-GlcNAcylation and increased Cd40 mRNA translation. TMG administration also promoted Cd40 mRNA association with Müller cell-specific ribosomes isolated from the retina of RiboTag mice. Similar effects on O-GlcNAcylation and Cd40 mRNA translation were also observed in the retina of a mouse model of type 1 diabetes. In cultured cells, TMG promoted sequestration of the cap-binding protein eIF4E (eukaryotic translation in initiation factor 4E) by 4E-BP1 (eIF4E-binding protein 1) and enhanced cap-independent Cd40 mRNA translation as assessed by a bicistronic reporter that contained the 5'-UTR of the Cd40 mRNA. Ablation of 4E-BP1/2 prevented the increase in Cd40 mRNA translation in TMG-exposed cells, and expression of a 4E-BP1 variant that constitutively sequesters eIF4E promoted reporter activity. Extending on the cell culture results, we found that in contrast to WT mice, diabetic 4E-BP1/2-deficient mice did not exhibit enhanced retinal Cd40 mRNA translation and failed to up-regulate expression of the inflammatory marker nitric-oxide synthase 2. These findings support a model wherein diabetes-induced O-GlcNAcylation of 4E-BP1 promotes Cd40 mRNA translation in Müller glia.
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Affiliation(s)
- Sadie K Dierschke
- Department of Cellular and Molecular Physiology, Pennsylvania State College of Medicine, Hershey, Pennsylvania, USA
| | - Allyson L Toro
- Department of Cellular and Molecular Physiology, Pennsylvania State College of Medicine, Hershey, Pennsylvania, USA
| | - William P Miller
- Department of Cellular and Molecular Physiology, Pennsylvania State College of Medicine, Hershey, Pennsylvania, USA
| | - Siddharth Sunilkumar
- Department of Cellular and Molecular Physiology, Pennsylvania State College of Medicine, Hershey, Pennsylvania, USA
| | - Michael D Dennis
- Department of Cellular and Molecular Physiology, Pennsylvania State College of Medicine, Hershey, Pennsylvania, USA .,Department of Ophthalmology, Pennsylvania State College of Medicine, Hershey, Pennsylvania, USA
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Yoon SO, Shin S, Karreth FA, Buel GR, Jedrychowski MP, Plas DR, Dedhar S, Gygi SP, Roux PP, Dephoure N, Blenis J. Focal Adhesion- and IGF1R-Dependent Survival and Migratory Pathways Mediate Tumor Resistance to mTORC1/2 Inhibition. Mol Cell 2017; 67:512-527.e4. [PMID: 28757207 DOI: 10.1016/j.molcel.2017.06.033] [Citation(s) in RCA: 35] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2017] [Revised: 05/24/2017] [Accepted: 06/27/2017] [Indexed: 01/22/2023]
Abstract
Aberrant signaling by the mammalian target of rapamycin (mTOR) contributes to the devastating features of cancer cells. Thus, mTOR is a critical therapeutic target and catalytic inhibitors are being investigated as anti-cancer drugs. Although mTOR inhibitors initially block cell proliferation, cell viability and migration in some cancer cells are quickly restored. Despite sustained inhibition of mTORC1/2 signaling, Akt, a kinase regulating cell survival and migration, regains phosphorylation at its regulatory sites. Mechanistically, mTORC1/2 inhibition promotes reorganization of integrin/focal adhesion kinase-mediated adhesomes, induction of IGFR/IR-dependent PI3K activation, and Akt phosphorylation via an integrin/FAK/IGFR-dependent process. This resistance mechanism contributes to xenograft tumor cell growth, which is prevented with mTOR plus IGFR inhibitors, supporting this combination as a therapeutic approach for cancers.
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Affiliation(s)
- Sang-Oh Yoon
- Department of Pharmacology, Meyer Cancer Center, Weill Cornell Medical College, New York, NY 10065, USA.
| | - Sejeong Shin
- Department of Pharmacology, Meyer Cancer Center, Weill Cornell Medical College, New York, NY 10065, USA
| | - Florian A Karreth
- Department of Medicine, Meyer Cancer Center, Weill Cornell Medical College, New York, NY 10065, USA
| | - Gwen R Buel
- Department of Pharmacology, Meyer Cancer Center, Weill Cornell Medical College, New York, NY 10065, USA
| | | | - David R Plas
- Department of Cancer Biology, University of Cincinnati, Cincinnati, OH 45267, USA
| | - Shoukat Dedhar
- Department of Integrative Oncology, British Columbia Cancer Research Centre, Vancouver, BC V5Z 1L3, Canada
| | - Steven P Gygi
- Department of Cell Biology, Harvard Medical School, Boston, MA 02115, USA
| | - Philippe P Roux
- Institute for Research in Immunology and Cancer (IRIC), Université de Montréal, Montreal, QC H3T 1J4, Canada
| | - Noah Dephoure
- Department of Biochemistry, Weill Cornell Medical College, New York, NY 10065, USA
| | - John Blenis
- Department of Pharmacology, Meyer Cancer Center, Weill Cornell Medical College, New York, NY 10065, USA.
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Das F, Dey N, Bera A, Kasinath BS, Ghosh-Choudhury N, Choudhury GG. MicroRNA-214 Reduces Insulin-like Growth Factor-1 (IGF-1) Receptor Expression and Downstream mTORC1 Signaling in Renal Carcinoma Cells. J Biol Chem 2016; 291:14662-76. [PMID: 27226530 DOI: 10.1074/jbc.m115.694331] [Citation(s) in RCA: 32] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/23/2015] [Indexed: 01/21/2023] Open
Abstract
Elevated IGF-1/insulin-like growth factor-1 receptor (IGF-1R) autocrine/paracrine signaling in patients with renal cell carcinoma is associated with poor prognosis of the disease independent of their von Hippel-Lindau (VHL) status. Increased expression of IGF-1R in renal cancer cells correlates with their potency of tumor development and progression. The mechanism by which expression of IGF-1R is increased in renal carcinoma is not known. We report that VHL-deficient and VHL-positive renal cancer cells possess significantly decreased levels of mature, pre-, and pri-miR-214 than normal proximal tubular epithelial cells. We identified an miR-214 recognition element in the 3'UTR of IGF-1R mRNA and confirmed its responsiveness to miR-214. Overexpression of miR-214 decreased the IGF-1R protein levels, resulting in the inhibition of Akt kinase activity in both types of renal cancer cells. IGF-1 provoked phosphorylation and inactivation of PRAS40 in an Akt-dependent manner, leading to the activation of mTORC1 signal transduction to increase phosphorylation of S6 kinase and 4EBP-1. Phosphorylation-deficient mutants of PRAS40 and 4EBP-1 significantly inhibited IGF-1R-driven proliferation of renal cancer cells. Expression of miR-214 suppressed IGF-1R-induced phosphorylation of PRAS40, S6 kinase, and 4EBP-1, indicating inhibition of mTORC1 activity. Finally, miR-214 significantly blocked IGF-1R-forced renal cancer cell proliferation, which was reversed by expression of 3'UTR-less IGF-1R and constitutively active mTORC1. Together, our results identify a reciprocal regulation of IGF-1R levels and miR-214 expression in renal cancer cells independent of VHL status. Our data provide evidence for a novel mechanism for IGF-1R-driven renal cancer cell proliferation involving miR-214 and mTORC1.
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Affiliation(s)
| | | | | | | | - Nandini Ghosh-Choudhury
- From Veterans Affairs Research and Geriatric Research, Pathology, University of Texas Health Science Center at San Antonio, San Antonio, Texas 78229
| | - Goutam Ghosh Choudhury
- the Departments of Medicine and From Veterans Affairs Research and Geriatric Research, Education and Clinical Center, South Texas Veterans Health Care System, San Antonio, Texas 78229-3900 and
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Lahlali T, Plissonnier ML, Romero-López C, Michelet M, Ducarouge B, Berzal-Herranz A, Zoulim F, Mehlen P, Parent R. Netrin-1 Protects Hepatocytes Against Cell Death Through Sustained Translation During the Unfolded Protein Response. Cell Mol Gastroenterol Hepatol 2016; 2:281-301.e9. [PMID: 28174720 PMCID: PMC5042567 DOI: 10.1016/j.jcmgh.2015.12.011] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/26/2015] [Accepted: 12/21/2015] [Indexed: 02/08/2023]
Abstract
BACKGROUND & AIMS Netrin-1, a multifunctional secreted protein, is up-regulated in cancer and inflammation. Netrin-1 blocks apoptosis induced by the prototypical dependence receptors deleted in colorectal carcinoma and uncoordinated phenotype-5. Although the unfolded protein response (UPR) triggers apoptosis on exposure to stress, it first attempts to restore endoplasmic reticulum homeostasis to foster cell survival. Importantly, UPR is implicated in chronic liver conditions including hepatic oncogenesis. Netrin-1's implication in cell survival on UPR in this context is unknown. METHODS Isolation of translational complexes, determination of RNA secondary structures by selective 2'-hydroxyl acylation and primer extension/dimethyl sulfate, bicistronic constructs, as well as conventional cell biology and biochemistry approaches were used on in vitro-grown hepatocytic cells, wild-type, and netrin-1 transgenic mice. RESULTS HepaRG cells constitute a bona fide model for UPR studies in vitro through adequate activation of the 3 sensors of the UPR (protein kinase RNA-like endoplasmic reticulum kinase (PERK)), inositol requiring enzyme 1α (IRE1α), and activated transcription factor 6 (ATF6). The netrin-1 messenger RNA 5'-end was shown to fold into a complex double pseudoknot and bear E-loop motifs, both of which are representative hallmarks of related internal ribosome entry site regions. Cap-independent translation of netrin 5' untranslated region-driven luciferase was observed on UPR in vitro. Unlike several structurally related oncogenic transcripts (l-myc, c-myc, c-myb), netrin-1 messenger RNA was selected for translation during UPR both in human hepatocytes and in mice livers. Depletion of netrin-1 during UPR induces apoptosis, leading to cell death through an uncoordinated phenotype-5A/C-mediated involvement of protein phosphatase 2A and death-associated protein kinase 1 in vitro and in netrin transgenic mice. CONCLUSIONS UPR-resistant, internal ribosome entry site-driven netrin-1 translation leads to the inhibition of uncoordinated phenotype-5/death-associated protein kinase 1-mediated apoptosis in the hepatic context during UPR, a hallmark of chronic liver disease.
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Key Words
- ATF6, activated transcription factor 6
- CMV, cytomegalovirus
- DAPK, death-associated protein kinase
- DMS, dimethyl sulfate
- DR, dependence receptor
- DTT, dithiothreitol
- ER, endoplasmic reticulum
- FLuc, Firefly luciferase
- HBV, hepatitis B virus
- HCC, hepatocellular carcinoma
- HCV, hepatitis C virus
- Hepatocyte
- IRE1α, inositol requiring enzyme 1α
- IRES, internal ribosome entry site
- LSL, (Lox-Stop-Lox)
- NMIA, N-methyl-isatoic anhydride
- Netrin
- PBS, phosphate-buffered saline
- PERK, protein kinase RNA (PKR)-like endoplasmic reticulum kinase
- PP2A, protein phosphatase 2A
- PR65β, erine/threonine-protein phosphatase 2A 65 kDa regulatory subunit A beta isoform
- RLuc, Renilla lucerifase
- TUNEL, terminal deoxynucleotidyl transferase–mediated deoxyuridine triphosphate nick-end labeling
- Translation
- Tu, tunicamycin
- UNC5, uncoordinated phenotype-5
- UPR
- UPR, unfolded protein response
- UTR, untranslated region
- VR1, vanilloid receptor 1
- eIF2α, Eukaryotic translation initiation factor 2A
- mRNA, messenger RNA
- pBic, Bicistronic plasmid
- qRT-PCR, quantitative reverse-transcription polymerase chain reaction
- siRNA, small interfering RNA
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Affiliation(s)
- Thomas Lahlali
- Inserm U1052-UMR CNRS 5286, Centre Léon Berard, Centre de Recherche en Cancérologie, Lyon, France
| | - Marie-Laure Plissonnier
- Inserm U1052-UMR CNRS 5286, Centre Léon Berard, Centre de Recherche en Cancérologie, Lyon, France
| | - Cristina Romero-López
- Instituto de Parasitología y Biomedicina López-Neyra Consejo Superior de Investigaciones Científicas, Ciencia e Investigación (IPBLN-CSIC), Parque Tecnológico Ciencias de la Salud Granada, Armilla, Granada, Spain
| | - Maud Michelet
- Inserm U1052-UMR CNRS 5286, Centre Léon Berard, Centre de Recherche en Cancérologie, Lyon, France
| | - Benjamin Ducarouge
- Inserm U1052-UMR Centre National de la Recherche Scientifique 5286, Centre Léon Berard, Centre de Recherche en Cancérologie, Lyon, France
| | - Alfredo Berzal-Herranz
- Instituto de Parasitología y Biomedicina López-Neyra Consejo Superior de Investigaciones Científicas, Ciencia e Investigación (IPBLN-CSIC), Parque Tecnológico Ciencias de la Salud Granada, Armilla, Granada, Spain
| | - Fabien Zoulim
- Inserm U1052-UMR CNRS 5286, Centre Léon Berard, Centre de Recherche en Cancérologie, Lyon, France
| | - Patrick Mehlen
- Inserm U1052-UMR Centre National de la Recherche Scientifique 5286, Centre Léon Berard, Centre de Recherche en Cancérologie, Lyon, France
| | - Romain Parent
- Inserm U1052-UMR CNRS 5286, Centre Léon Berard, Centre de Recherche en Cancérologie, Lyon, France,Correspondence Address correspondence to: Romain Parent, PharmD, PhD, Inserm U1052, 151 Cours Albert Thomas, F-69424 Lyon Cedex 03, France. fax: (33) 4-72-68-19-71.Inserm U1052151 Cours Albert ThomasF-69424 Lyon Cedex 03France
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Souii A, Ben M'hadheb-Gharbi M, Gharbi J. Role of RNA structure motifs in IRES-dependent translation initiation of the coxsackievirus B3: new insights for developing live-attenuated strains for vaccines and gene therapy. Mol Biotechnol 2014; 55:179-202. [PMID: 23881360 DOI: 10.1007/s12033-013-9674-4] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Internal ribosome entry site (IRES) elements are highly structured RNA sequences that function to recruit ribosomes for the initiation of translation. In contrast to the canonical cap-binding, the mechanism of IRES-mediated translation initiation is still poorly understood. Translation initiation of the coxsackievirus B3 (CVB3), a causative agent of viral myocarditis, has been shown to be mediated by a highly ordered structure of the 5' untranslated region (5'UTR), which harbors an IRES. Taking into account that efficient initiation of mRNA translation depends on temporally and spatially orchestrated sequence of RNA-protein and RNA-RNA interactions, and that, at present, little is known about these interactions, we aimed to describe recent advances in our understanding of molecular structures and biochemical functions of the translation initiation process. Thus, this review will explore the IRES elements as important RNA structures and the significance of these structures in providing an alternative mechanism of translation initiation of the CVB3 RNA. Since translation initiation is the first intracellular step during the CVB3 infection cycle, the IRES region provides an ideal target for antiviral therapies. Interestingly, the 5' and 3'UTRs represent promising candidates for the study of CVB3 cardiovirulence and provide new insights for developing live-attenuated vaccines.
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Affiliation(s)
- Amira Souii
- Institut Supérieur de Biotechnologie de Monastir-Université de Monastir, Avenue Tahar Hadded, BP 74, 5000, Monastir, Tunisia
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New insights into functional roles of the polypyrimidine tract-binding protein. Int J Mol Sci 2013; 14:22906-32. [PMID: 24264039 PMCID: PMC3856098 DOI: 10.3390/ijms141122906] [Citation(s) in RCA: 87] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2013] [Revised: 11/13/2013] [Accepted: 11/13/2013] [Indexed: 12/20/2022] Open
Abstract
Polypyrimidine Tract Binding Protein (PTB) is an intensely studied RNA binding protein involved in several post-transcriptional regulatory events of gene expression. Initially described as a pre-mRNA splicing regulator, PTB is now widely accepted as a multifunctional protein shuttling between nucleus and cytoplasm. Accordingly, PTB can interact with selected RNA targets, structural elements and proteins. There is increasing evidence that PTB and its paralog PTBP2 play a major role as repressors of alternatively spliced exons, whose transcription is tissue-regulated. In addition to alternative splicing, PTB is involved in almost all steps of mRNA metabolism, including polyadenylation, mRNA stability and initiation of protein translation. Furthermore, it is well established that PTB recruitment in internal ribosome entry site (IRES) activates the translation of picornaviral and cellular proteins. Detailed studies of the structural properties of PTB have contributed to our understanding of the mechanism of RNA binding by RNA Recognition Motif (RRM) domains. In the present review, we will describe the structural properties of PTB, its paralogs and co-factors, the role in post-transcriptional regulation and actions in cell differentiation and pathogenesis. Defining the multifunctional roles of PTB will contribute to the understanding of key regulatory events in gene expression.
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15
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Adams GR, Bamman MM. Characterization and regulation of mechanical loading-induced compensatory muscle hypertrophy. Compr Physiol 2013; 2:2829-70. [PMID: 23720267 DOI: 10.1002/cphy.c110066] [Citation(s) in RCA: 67] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
In mammalian systems, skeletal muscle exists in a dynamic state that monitors and regulates the physiological investment in muscle size to meet the current level of functional demand. This review attempts to consolidate current knowledge concerning development of the compensatory hypertrophy that occurs in response to a sustained increase in the mechanical loading of skeletal muscle. Topics covered include: defining and measuring compensatory hypertrophy, experimental models, loading stimulus parameters, acute responses to increased loading, hyperplasia, myofiber-type adaptations, the involvement of satellite cells, mRNA translational control, mechanotransduction, and endocrinology. The authors conclude with their impressions of current knowledge gaps in the field that are ripe for future study.
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Affiliation(s)
- Gregory R Adams
- Department of Physiology and Biophysics, University of California Irvine, Irvine, California, USA.
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Panda AC, Grammatikakis I, Yoon JH, Abdelmohsen K. Posttranscriptional regulation of insulin family ligands and receptors. Int J Mol Sci 2013; 14:19202-29. [PMID: 24051403 PMCID: PMC3794829 DOI: 10.3390/ijms140919202] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/03/2013] [Revised: 08/17/2013] [Accepted: 09/06/2013] [Indexed: 01/02/2023] Open
Abstract
Insulin system including ligands (insulin and IGFs) and their shared receptors (IR and IGFR) are critical regulators of insulin signaling and glucose homeostasis. Altered insulin system is associated with major pathological conditions like diabetes and cancer. The mRNAs encoding for these ligands and their receptors are posttranscriptionally controlled by three major groups of regulators; (i) alternative splicing regulatory factors; (ii) turnover and translation regulator RNA-binding proteins (TTR-RBPs); and (iii) non-coding RNAs including miRNAs and long non-coding RNAs (lncRNAs). In this review, we discuss the influence of these regulators on alternative splicing, mRNA stability and translation. Due to the pathological impacts of insulin system, we also discussed the possibilities of discovering new potential regulators which will improve understanding of insulin system and associated diseases.
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Affiliation(s)
- Amaresh C Panda
- Laboratory of Genetics, National Institute on Aging-Intramural Research Program, National Institutes of Health, Baltimore, MD 21224, USA.
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Marcel V, Ghayad S, Belin S, Therizols G, Morel AP, Solano-Gonzàlez E, Vendrell J, Hacot S, Mertani H, Albaret M, Bourdon JC, Jordan L, Thompson A, Tafer Y, Cong R, Bouvet P, Saurin JC, Catez F, Prats AC, Puisieux A, Diaz JJ. p53 acts as a safeguard of translational control by regulating fibrillarin and rRNA methylation in cancer. Cancer Cell 2013; 24:318-30. [PMID: 24029231 PMCID: PMC7106277 DOI: 10.1016/j.ccr.2013.08.013] [Citation(s) in RCA: 206] [Impact Index Per Article: 18.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/20/2012] [Revised: 07/08/2013] [Accepted: 08/12/2013] [Indexed: 01/01/2023]
Abstract
Ribosomes are specialized entities that participate in regulation of gene expression through their rRNAs carrying ribozyme activity. Ribosome biogenesis is overactivated in p53-inactivated cancer cells, although involvement of p53 on ribosome quality is unknown. Here, we show that p53 represses expression of the rRNA methyl-transferase fibrillarin (FBL) by binding directly to FBL. High levels of FBL are accompanied by modifications of the rRNA methylation pattern, impairment of translational fidelity, and an increase of internal ribosome entry site (IRES)-dependent translation initiation of key cancer genes. FBL overexpression contributes to tumorigenesis and is associated with poor survival in patients with breast cancer. Thus, p53 acts as a safeguard of protein synthesis by regulating FBL and the subsequent quality and intrinsic activity of ribosomes.
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Affiliation(s)
- Virginie Marcel
- Centre de Recherche en Cancérologie de Lyon UMR Inserm 1052 CNRS 5286, Centre Léon Bérard, F-69373, Lyon, France
- Université de Lyon, Université Lyon 1, ISPB, Lyon F-69622, France
| | - Sandra E. Ghayad
- Centre de Recherche en Cancérologie de Lyon UMR Inserm 1052 CNRS 5286, Centre Léon Bérard, F-69373, Lyon, France
- Université de Lyon, Université Lyon 1, ISPB, Lyon F-69622, France
| | - Stéphane Belin
- Centre de Recherche en Cancérologie de Lyon UMR Inserm 1052 CNRS 5286, Centre Léon Bérard, F-69373, Lyon, France
- Université de Lyon, Université Lyon 1, ISPB, Lyon F-69622, France
| | - Gabriel Therizols
- Centre de Recherche en Cancérologie de Lyon UMR Inserm 1052 CNRS 5286, Centre Léon Bérard, F-69373, Lyon, France
- Université de Lyon, Université Lyon 1, ISPB, Lyon F-69622, France
| | - Anne-Pierre Morel
- Centre de Recherche en Cancérologie de Lyon UMR Inserm 1052 CNRS 5286, Centre Léon Bérard, F-69373, Lyon, France
- Université de Lyon, Université Lyon 1, ISPB, Lyon F-69622, France
| | - Eduardo Solano-Gonzàlez
- Université de Toulouse, UPS, TRADGENE, EA4554, Institut des Maladies Métaboliques et Cardiovasculaires, 1 Avenue Jean Poulhès, BP 84225, F-31432 Toulouse, France
| | - Julie A. Vendrell
- Centre de Recherche en Cancérologie de Lyon UMR Inserm 1052 CNRS 5286, Centre Léon Bérard, F-69373, Lyon, France
- Université de Lyon, Université Lyon 1, ISPB, Lyon F-69622, France
- ISPB, Faculté de Pharmacie, Université Lyon 1, Lyon, France
- Dundee Cancer Centre, Clinical Research Centre, University of Dundee, Dundee DD1 9SY, UK
| | - Sabine Hacot
- Centre de Recherche en Cancérologie de Lyon UMR Inserm 1052 CNRS 5286, Centre Léon Bérard, F-69373, Lyon, France
- Université de Lyon, Université Lyon 1, ISPB, Lyon F-69622, France
| | - Hichem C. Mertani
- Centre de Recherche en Cancérologie de Lyon UMR Inserm 1052 CNRS 5286, Centre Léon Bérard, F-69373, Lyon, France
- Université de Lyon, Université Lyon 1, ISPB, Lyon F-69622, France
| | - Marie Alexandra Albaret
- Centre de Recherche en Cancérologie de Lyon UMR Inserm 1052 CNRS 5286, Centre Léon Bérard, F-69373, Lyon, France
- Université de Lyon, Université Lyon 1, ISPB, Lyon F-69622, France
| | | | - Lee Jordan
- Department of Pathology, Ninewells Hospital and Medical School, Dundee DD1 9SY, UK
| | - Alastair Thompson
- Dundee Cancer Centre, Clinical Research Centre, University of Dundee, Dundee DD1 9SY, UK
| | - Yasmine Tafer
- Centre de Recherche en Cancérologie de Lyon UMR Inserm 1052 CNRS 5286, Centre Léon Bérard, F-69373, Lyon, France
- Université de Lyon, Université Lyon 1, ISPB, Lyon F-69622, France
| | - Rong Cong
- Laboratoire Joliot-Curie, Ecole Normale Supérieure de Lyon, Université de Lyon, CNRS USR 3010, SFR BioSciences UMS3444, Lyon 69364, France
| | - Philippe Bouvet
- Laboratoire Joliot-Curie, Ecole Normale Supérieure de Lyon, Université de Lyon, CNRS USR 3010, SFR BioSciences UMS3444, Lyon 69364, France
| | - Jean-Christophe Saurin
- Centre de Recherche en Cancérologie de Lyon UMR Inserm 1052 CNRS 5286, Centre Léon Bérard, F-69373, Lyon, France
- Université de Lyon, Université Lyon 1, ISPB, Lyon F-69622, France
- Gastroenterology Unit, Édouard Herriot Hospital, Hospices Civils de Lyon, 69002 Lyon, France
| | - Frédéric Catez
- Centre de Recherche en Cancérologie de Lyon UMR Inserm 1052 CNRS 5286, Centre Léon Bérard, F-69373, Lyon, France
- Université de Lyon, Université Lyon 1, ISPB, Lyon F-69622, France
| | - Anne-Catherine Prats
- Université de Toulouse, UPS, TRADGENE, EA4554, Institut des Maladies Métaboliques et Cardiovasculaires, 1 Avenue Jean Poulhès, BP 84225, F-31432 Toulouse, France
| | - Alain Puisieux
- Centre de Recherche en Cancérologie de Lyon UMR Inserm 1052 CNRS 5286, Centre Léon Bérard, F-69373, Lyon, France
- Université de Lyon, Université Lyon 1, ISPB, Lyon F-69622, France
| | - Jean-Jacques Diaz
- Centre de Recherche en Cancérologie de Lyon UMR Inserm 1052 CNRS 5286, Centre Léon Bérard, F-69373, Lyon, France
- Université de Lyon, Université Lyon 1, ISPB, Lyon F-69622, France
- Corresponding author
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Olson CM, Donovan MR, Spellberg MJ, Marr MT. The insulin receptor cellular IRES confers resistance to eIF4A inhibition. eLife 2013; 2:e00542. [PMID: 23878722 PMCID: PMC3713452 DOI: 10.7554/elife.00542] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2013] [Accepted: 06/11/2013] [Indexed: 11/17/2022] Open
Abstract
Under conditions of stress, such as limited growth factor signaling, translation is inhibited by the action of 4E-BP and PDCD4. These proteins, through inhibition of eIF4E and eIF4A, respectively, impair cap-dependent translation. Under stress conditions FOXO transcription factors activate 4E-BP expression amplifying the repression. Here we show that Drosophila FOXO binds the PDCD4 promoter and stimulates the transcription of PDCD4 in response to stress. We have shown previously that the 5′ UTR of the Drosophila insulin-like receptor (dINR) supports cap-independent translation that is resistant to 4E-BP. Using hippuristanol, an eIF4A inhibitor, we find that translation of dINR UTR containing transcripts are also resistant to eIF4A inhibition. In addition, the murine insulin receptor and insulin-like growth factor receptor 5′ UTRs support cap-independent translation and have a similar resistance to hippuristanol. This resistance to inhibition of eIF4E and eIF4A indicates a conserved strategy to allow translation of growth factor receptors under stress conditions. DOI:http://dx.doi.org/10.7554/eLife.00542.001 Protein synthesis in eukaryotes occurs in two stages: transcription of DNA into messenger RNA (mRNA) in the nucleus, and then translation of that mRNA into a protein by ribosomes in the cytoplasm. These processes are regulated by a complex network of signaling pathways that enables cells to tailor protein synthesis to match current conditions. This involves regulating the expression of the genes that code for these proteins. When cells experience stressful events, such as a shortage of oxygen or nutrients, they reduce the synthesis of most proteins. This response is regulated, in part, by a signaling pathway known as the insulin and insulin-like receptor pathway. In particular, stressful events inhibit a protein complex called eIF4F, which normally initiates the translation of mRNA molecules by binding to a structure on one end of the mRNA called the 5′ cap. Despite this general inhibition, the production of certain other proteins—including the insulin receptor itself—is actually increased in response to stress. Olson et al. have carried out a series of experiments to explore how inhibition of the eIF4F protein complex influences the translation of the mRNA for the insulin receptor. The eIF4F complex is made up of three proteins, including one that binds to the 5′ cap and a helicase that unwinds the RNA. Previous work in the fruit fly Drosophila showed that translation of this mRNA can continue even if formation of the eIF4F complex is inhibited by targeting the cap binding protein. Olsen et al. now show that translation of this mRNA is also independent of the helicase. Instead, translation is maintained under these conditions because the insulin receptor mRNA contains a sequence called an internal ribosome entry site, which allows ribosomes to bind to the mRNA without the influence of the 5′ cap. Olson et al. reveal the details of this regulatory pathway in Drosophila and show that similar mechanisms are at work in mammalian cells, suggesting this pathway represents a crucial regulatory process that has been conserved during evolution. A key question for future research is whether other genes within the insulin and insulin-receptor like signaling pathway use this same trick to evade translational inhibitors. DOI:http://dx.doi.org/10.7554/eLife.00542.002
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Affiliation(s)
- Calla M Olson
- Department of Biology and the Rosenstiel Basic Medical Sciences Research Center , Brandeis University , Waltham , United States
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Cen B, Mahajan S, Wang W, Kraft AS. Elevation of receptor tyrosine kinases by small molecule AKT inhibitors in prostate cancer is mediated by Pim-1. Cancer Res 2013; 73:3402-11. [PMID: 23585456 DOI: 10.1158/0008-5472.can-12-4619] [Citation(s) in RCA: 53] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
The PI3K/AKT pathway is hyperactivated in prostate cancer but its effective therapeutic targeting has proven difficult. In particular, the antitumor activity of AKT inhibitors is attenuated by upregulation of receptor tyrosine kinases (RTK) through an uncharacterized feedback mechanism. In this report, we show that RNA interference-mediated silencing or pharmacologic inhibition of Pim-1 activity curtails AKT inhibitor-induced upregulation of RTKs in prostate cancer cells. Although Pim kinases have been implicated in cap-dependent translational control, we find that in the context of AKT inhibition, the expression of RTKs is controlled by Pim-1 in a cap-independent manner by controlling internal ribosome entry. Combination of Pim and AKT inhibitors resulted in synergistic inhibition of prostate tumor growth in vitro and in vivo. Together, our results show that Pim-1 mediates resistance to AKT inhibition and suggest its targeting to improve the efficacy of AKT inhibitors in anticancer therapy.
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Affiliation(s)
- Bo Cen
- Department of Medicine, and The Hollings Cancer Center, Medical University of South Carolina, Charleston, SC29425, USA.
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20
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Li S, Hu GF. Emerging role of angiogenin in stress response and cell survival under adverse conditions. J Cell Physiol 2012; 227:2822-6. [PMID: 22021078 PMCID: PMC3271170 DOI: 10.1002/jcp.23051] [Citation(s) in RCA: 122] [Impact Index Per Article: 10.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Angiogenin (ANG), also known as ribonuclease (RNASE) 5, is a member of the vertebrate-specific, secreted RNASE superfamily. ANG was originally identified as a tumor angiogenic factor, but its biological activity has been extended from inducing angiogenesis to stimulating cell proliferation and more recently, to promoting cell survival. Under growth conditions, ANG is translocated to nucleus where it accumulates in nucleolus and stimulates ribosomal RNA (rRNA) transcription, thus facilitating cell growth and proliferation. Under stress conditions, ANG is accumulated in cytoplasmic compartments and modulates the production of tiRNA, a novel class of small RNA that is derived from tRNA and is induced by stress. tiRNA suppress global protein translation by inhibiting both cap-dependent and -independent translation including that mediated by weak IRESes. However, strong IRES-mediated translation, a mechanism often used by genes involved in pro-survival and anti-apoptosis, is not affected. Thus, ANG-mediated tiRNA reprogram protein translation, save anabolic energy, and promote cell survival. This recently uncovered function of ANG presents a novel mechanism of action in regulating cell growth and survival.
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Affiliation(s)
- Shuping Li
- Molecular Oncology Research Institute, Tufts Medical Center, Boston, MA, USA
- State Key Laboratory for Diagnosis and Treatment of Infectious Disease, The First Affiliated Hospital, Zhejiang University School of Medicine, Hangzhou, China
| | - Guo-Fu Hu
- Molecular Oncology Research Institute, Tufts Medical Center, Boston, MA, USA
- Graduate Program in Biochemistry, Sackler School of Graduate Biomedical Sciences, Tufts University, Boston, MA, USA
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21
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Abstract
The majority of mRNAs in eukaryotic cells are translated via a method that is dependent upon the recognition of, and binding to, the methylguanosine cap at the 5' end of the mRNA, by a set of protein factors termed eIFs (eukaryotic initiation factors). However, many of the eIFs involved in this process are modified and become less active under a number of pathophysiological stress conditions, including amino acid starvation, heat shock, hypoxia and apoptosis. During these conditions, the continued synthesis of proteins essential to recovery from stress or maintenance of a cellular programme is mediated via an alternative form of translation initiation termed IRES (internal ribosome entry site)-mediated translation. This relies on the mRNA containing a complex cis-acting structural element in its 5'-UTR (untranslated region) that is able to recruit the ribosome independently of the cap, and is often dependent upon additional factors termed ITAFs (IRES trans-acting factors). A limited number of ITAFs have been identified to date, particularly for cellular IRESs, and it is not yet fully understood how they exert their control and which cellular pathways are involved in their regulation.
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22
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Higashi Y, Holder K, Delafontaine P. Thiazolidinediones up-regulate insulin-like growth factor-1 receptor via a peroxisome proliferator-activated receptor gamma-independent pathway. J Biol Chem 2010; 285:36361-8. [PMID: 20843793 PMCID: PMC2978564 DOI: 10.1074/jbc.m110.137661] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2010] [Revised: 09/01/2010] [Indexed: 11/06/2022] Open
Abstract
There is increasing evidence that thiazolidinediones (TZDs), antidiabetic compounds that are synthetic ligands for the peroxisome proliferator-activated receptor γ (PPARγ), have cardiovascular effects through as yet poorly defined mechanisms. We tested the effect of two TZD class drugs, rosiglitazone and pioglitazone, on human aortic smooth muscle cell (SMC) expression of insulin-like growth factor-1 receptor (IGF-1R). Both TZDs dose dependently up-regulated IGF-1R protein levels (rosiglitazone, 10 μmol/liter, 67% increase, n = 4, p < 0.01; pioglitazone, 10 μmol/liter, 41% increase, n = 4, p < 0.01) and increased IGF-1R signaling activity (36% increase in Akt phosphorylation). However, the endogenous PPARγ ligand, 15-deoxy-Δ(12,14)-prostaglandin J(2), dose dependently reduced IGF-1R (10 μmol/liter, 80% decrease, n = 4, p < 0.01), and overexpression of PPARγ using an adenovirus likewise reduced IGF-1R (50% decrease versus SMC infected with control adenovirus), suggesting a PPARγ-independent action of TZDs. All three PPARγ ligands (rosiglitazone, pioglitazone, and 15-deoxy-Δ(12,14)-prostaglandin J(2)), however, did not change IGF-1R mRNA levels, indicating that their effects were posttranscriptional. Use of bicistronic constructs revealed that TZD induction of IGF-1R translation occurred via internal ribosomal entry. To examine the potential physiological relevance of TZD up-regulation of IGF-1R, we determined the effect of rosiglitazone on oxidized LDL (oxLDL)-induced apoptosis. 20 μmol/liter of rosiglitazone reduced oxidized LDL-induced apoptosis by 40% and neutralizing antibody to IGF-1R (αIR3) counteracted this rescue, suggesting the rosiglitazone survival effect was, at least in part, mediated by IGF-1R. In conclusion, TZDs markedly up-regulate SMC IGF-1R expression and signaling, likely via a PPARγ-independent mechanism. This novel action of TZDs may play an important role in their cardiovascular effects.
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MESH Headings
- Aorta/cytology
- Aorta/drug effects
- Aorta/metabolism
- Blotting, Western
- Cells, Cultured
- Humans
- Hypoglycemic Agents/pharmacology
- Lipoproteins, LDL/genetics
- Lipoproteins, LDL/metabolism
- Myocytes, Smooth Muscle/cytology
- Myocytes, Smooth Muscle/drug effects
- Myocytes, Smooth Muscle/metabolism
- PPAR gamma/genetics
- PPAR gamma/metabolism
- Phosphorylation
- RNA, Messenger/genetics
- Receptor, IGF Type 1/genetics
- Receptor, IGF Type 1/metabolism
- Receptor, Insulin/genetics
- Receptor, Insulin/metabolism
- Reverse Transcriptase Polymerase Chain Reaction
- Rosiglitazone
- Signal Transduction/drug effects
- Thiazolidinediones/pharmacology
- Up-Regulation
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Affiliation(s)
- Yusuke Higashi
- From the Tulane University Heart & Vascular Institute, Tulane University School of Medicine, New Orleans, Louisiana 70112
| | - Kevin Holder
- From the Tulane University Heart & Vascular Institute, Tulane University School of Medicine, New Orleans, Louisiana 70112
| | - Patrice Delafontaine
- From the Tulane University Heart & Vascular Institute, Tulane University School of Medicine, New Orleans, Louisiana 70112
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23
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Lee EK, Gorospe M. Minireview: posttranscriptional regulation of the insulin and insulin-like growth factor systems. Endocrinology 2010; 151:1403-8. [PMID: 20032049 PMCID: PMC2850238 DOI: 10.1210/en.2009-1123] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Insulin and IGFs share structural similarities and regulate metabolic processes including glucose homeostasis. Acute alterations in glucose levels trigger rapid changes in insulin concentration and insulin signaling. These processes are tightly regulated by posttranscriptional mechanisms that alter the stability and translation of mRNAs encoding insulin and the insulin receptor. Long-term glucose homeostasis is also modulated by IGFs and IGF receptors, whose expression is likewise subject to changes in the stability and translation of the encoding mRNAs. The control of mRNA half-life and translation is governed by RNA-binding proteins and microRNAs that interact with target transcripts at the 3' and 5' untranslated regions. In this review, we describe the RNA-binding proteins and microRNAs that target the mRNAs encoding insulin, IGFs, and their receptors. We discuss how these mRNA-binding factors help to elicit timely, versatile, and tissue-specific changes in insulin and IGF function, thereby effecting critical control of energy metabolism.
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Affiliation(s)
- Eun Kyung Lee
- National Institute on Aging-Intramural Research Program, National Institutes of Health, 251 Bayview Boulevard, Baltimore, Maryland 21224, USA
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24
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Dysregulation of ribosome biogenesis and translational capacity is associated with tumor progression of human breast cancer cells. PLoS One 2009; 4:e7147. [PMID: 19779612 PMCID: PMC2744998 DOI: 10.1371/journal.pone.0007147] [Citation(s) in RCA: 162] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2009] [Accepted: 08/05/2009] [Indexed: 12/21/2022] Open
Abstract
Protein synthesis is a fundamental cell process and ribosomes - particularly through the ribosomal RNA that display ribozyme activity - are the main effectors of this process. Ribosome biogenesis is a very complex process involving transcriptional as well as many post-transcriptional steps to produce functional ribosomes. It is now well demonstrated that ribosome production is enhanced in cancer cells and that ribosome biogenesis plays a crucial role in tumor progression. However, at present there is an important lack of data to determine whether the entire process of ribosome biogenesis and ribosome assembly is modified during tumor progression and what could be the potential impact on the dysregulation of translational control that is observed in cancer cells. In breast cancer cells displaying enhanced aggressivity, both in vitro and in vivo, we have analyzed the major steps of ribosome biogenesis and the translational capacity of the resulting ribosome. We show that increased tumorigenicity was associated with modifications of nucleolar morphology and profound quantitative and qualitative alterations in ribosomal biogenesis and function. Specifically cells with enhanced tumor aggressivity displayed increased synthesis of 45S pre-rRNA, with activation of an alternative preRNA synthetic pathway containing a 43S precursor and enhanced post-transcriptional methylation of specifc sites located in the 28S rRNA. While the global translational activity was not modified, IRES-initiated translation, notably that of p53 mRNA, was less efficient and the control of translational fidelity was importantly reduced in cells with increased aggressivity. These results suggest that acquisition of enhanced tumor aggressivity can be associated with profound qualitative alterations in ribosomal control, leading to reduced quality control of translation in cancer cells
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25
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Fox JT, Stover PJ. Mechanism of the internal ribosome entry site-mediated translation of serine hydroxymethyltransferase 1. J Biol Chem 2009; 284:31085-96. [PMID: 19734143 DOI: 10.1074/jbc.m109.035576] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023] Open
Abstract
The 5'-untranslated region (UTR) of serine hydroxymethyltransferase 1 (SHMT1) contains an internal ribosome entry site (IRES) that regulates SHMT1 expression, a rate-limiting enzyme in de novo thymidylate biosynthesis. In this study, we show that the SHMT1 IRES is the first example of a cellular IRES that is poly(A) tail-independent. Interactions between the 5'-UTR and 3'-UTR functionally replaced interactions between the poly(A) tail and the poly(A)-binding protein (PABP) to achieve maximal IRES-mediated translational efficiency. Depletion of the SHMT1 IRES-specific trans-acting factor (ITAF) CUG-binding protein 1 (CUGBP1) from in vitro translation extracts or deletion of the CUGBP1 binding site on the 3'-UTR of the SHMT1 transcript decreased the IRES activity of non-polyadenylylated biscistronic mRNAs relative to polyadenylylated biscistronic mRNAs and resulted in a requirement for PABP. We also identified a novel ITAF, heterogeneous nuclear ribonucleoprotein H2 (hnRNP H2), that stimulates SHMT1 IRES activity by binding to the 5'-UTR of the transcript and interacting with CUGBP1. Collectively, these data support a model for the IRES-mediated translation of SHMT1 whereby the circularization of the mRNA typically provided by the eukaryotic initiation factor (eIF) 4G/PABP/poly(A) tail interaction is achieved instead through the hnRNP H2/CUGBP1-mediated interaction of the 5'- and 3'-UTRs of the SHMT1 transcript. This circularization enhances the IRES activity of SHMT1 by facilitating the recruitment and/or recycling of ribosomal subunits, which bind to the transcript in the middle of the 5'-UTR and migrate to the initiation codon via eIF4A-mediated scanning.
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Affiliation(s)
- Jennifer T Fox
- Graduate Field of Biochemistry and Molecular and Cellular Biology, Cornell University, Ithaca, New York 14853, USA
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26
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Spriggs KA, Cobbold LC, Ridley SH, Coldwell M, Bottley A, Bushell M, Willis AE, Siddle K. The human insulin receptor mRNA contains a functional internal ribosome entry segment. Nucleic Acids Res 2009; 37:5881-93. [PMID: 19654240 PMCID: PMC2761284 DOI: 10.1093/nar/gkp623] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
Regulation of mRNA translation is an important mechanism determining the level of expression of proteins in eukaryotic cells. Translation is most commonly initiated by cap-dependent scanning, but many eukaryotic mRNAs contain internal ribosome entry segments (IRESs), providing an alternative means of initiation capable of independent regulation. Here, we show by using dicistronic luciferase reporter vectors that the 5′-UTR of the mRNA encoding human insulin receptor (hIR) contains a functional IRES. RNAi-mediated knockdown showed that the protein PTB was required for maximum IRES activity. Electrophoretic mobility shift assays confirmed that PTB1, PTB2 and nPTB, but not unr or PTB4, bound to hIR mRNA, and deletion mapping implicated a CCU motif 448 nt upstream of the initiator AUG in PTB binding. The IR-IRES was functional in a number of cell lines, and most active in cells of neuronal origin, as assessed by luciferase reporter assays. The IRES was more active in confluent than sub-confluent cells, but activity did not change during differentiation of 3T3-L1 fibroblasts to adipocytes. IRES activity was stimulated by insulin in sub-confluent cells. The IRES may function to maintain expression of IR protein in tissues such as the brain where mRNA translation by cap-dependent scanning is less effective.
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Affiliation(s)
- Keith A Spriggs
- University of Nottingham, School of Pharmacy, University Park, Nottingham NG7 2RD, UK
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27
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Fitzgerald KD, Semler BL. Bridging IRES elements in mRNAs to the eukaryotic translation apparatus. BIOCHIMICA ET BIOPHYSICA ACTA-GENE REGULATORY MECHANISMS 2009; 1789:518-28. [PMID: 19631772 DOI: 10.1016/j.bbagrm.2009.07.004] [Citation(s) in RCA: 131] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/11/2009] [Revised: 07/10/2009] [Accepted: 07/14/2009] [Indexed: 02/07/2023]
Abstract
IRES elements are highly structured RNA sequences that function to recruit ribosomes for the initiation of translation. In contrast to the canonical cap-binding, ribosome-scanning model, the mechanism of IRES-mediated translation initiation is not well understood. IRES elements, first discovered in viral RNA genomes, were subsequently found in a subset of cellular RNAs as well. Interestingly, these cellular IRES-containing mRNAs appear to play important roles during conditions of cellular stress, development, and disease (e.g., cancer). It has been shown for viral IRESes that some require specific IRES trans-acting factors (ITAFs), while others require few if any additional proteins and can bind ribosomes directly. Current studies are aimed at elucidating the mechanism of IRES-mediated translation initiation and features that may be common or differ greatly among cellular and viral IRESes. This review will explore IRES elements as important RNA structures that function in both cellular and viral RNA translation and the significance of these structures in providing an alternative mechanism of eukaryotic translation initiation.
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Affiliation(s)
- Kerry D Fitzgerald
- Department of Microbiology and Molecular Genetics, School of Medicine, University of California, Irvine, CA 92697, USA
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28
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Meng Z, Jackson NL, Choi H, King PH, Emanuel PD, Blume SW. Alterations in RNA-binding activities of IRES-regulatory proteins as a mechanism for physiological variability and pathological dysregulation of IGF-IR translational control in human breast tumor cells. J Cell Physiol 2008; 217:172-83. [PMID: 18452152 DOI: 10.1002/jcp.21486] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
The type I insulin-like growth factor receptor (IGF-IR) is integrally involved in the control of cellular proliferation and survival. An internal ribosomal entry site (IRES) within the 1,038 nucleotide 5'-untranslated region of the human IGF-IR mRNA helps to provide the tight control of IGF-IR expression necessary for maintenance of normal cellular and tissue homeostasis. The IRES maps to a discrete sequence of 85 nucleotides positioned just upstream of the IGF-IR initiation codon, allowing the ribosome to bypass the highly structured regions of the 5'-UTR as well as the upstream open reading frame. The authenticity of the IGF-IR IRES has been confirmed by its sensitivity to deletion of the promoter from a bicistronic reporter construct, and its resistance in a monocistronic reporter construct to co-expression of a viral 2A protease. We previously characterized HuR as a potent repressor of IGF-IR translation. Here we demonstrate that hnRNP C competes with HuR for binding the IGF-IR 5'-UTR and enhances IRES-mediated translation initiation in a concentration-dependent manner. We observed changes in binding of hnRNP C versus HuR to the IGF-IR 5'-UTR in response to physiological alterations in cellular environment or proliferative status. Furthermore, we have found distinct alterations in the pattern of protein binding to the IGF-IR 5'-UTR in human breast tumor cells in which IGF-IR IRES activity and relative translational efficiency are aberrantly increased. These results suggest that dysregulation of the IGF-IR IRES through changes in the activities of RNA-binding translation-regulatory proteins could be responsible for IGF-IR overexpression in a proportion of human breast tumors.
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Affiliation(s)
- Zheng Meng
- Department of Biochemistry and Molecular Genetics, University of Alabama at Birmingham, Birmingham, Alabama, USA
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29
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Abstract
c-MYC inhibits differentiation and regulates the process by which cells acquire biomass, cell growth. Down-regulation of c-MYC, reduced cell growth, and decreased activity of the PI3K/AKT/mTORC1 signal transduction pathway are features of the terminal differentiation of committed myeloid precursors to polymorphonuclear neutrophils. Since mTORC1 regulates growth, we hypothesized that pharmacological inhibition of mTORC1 by rapamycin may reverse the phenotypic effects of c-MYC. Here we show that granulocytes blocked in their ability to differentiate by enforced expression of c-MYC can be induced to differentiate by reducing exogenous c-MYC expression through rapamycin treatment. Rapamycin also reduced expression of endogenous c-MYC and resulted in enhanced retinoid-induced differentiation. Total cellular c-Myc mRNA and c-MYC protein stability were unchanged by rapamycin, however the amount of c-Myc mRNA associated with polysomes was reduced. Therefore rapamycin limited expression of c-MYC by inhibiting c-Myc mRNA translation. These findings suggest that mTORC1 could be targeted to promote terminal differentiation in myeloid malignancies characterized by dysregulated expression of c-MYC.
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30
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Scrable H, Medrano S, Ungewitter E. Running on empty: how p53 controls INS/IGF signaling and affects life span. Exp Gerontol 2008; 44:93-100. [PMID: 18598747 DOI: 10.1016/j.exger.2008.05.017] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2008] [Revised: 05/21/2008] [Accepted: 05/27/2008] [Indexed: 10/21/2022]
Abstract
In higher organisms dependent on the regenerative ability of tissue stem cells to maintain tissue integrity throughout adulthood, the failure of stem cells to replace worn out, dead, or damaged cells is seen as one mechanism that limits life span. In these organisms, tumor suppressors such as p53 are central participants in the control of longevity because they regulate stem cell proliferation. Several recent reports have identified p53 as a longevity gene in organisms such as Caenorhabditis elegans and Drosophila melanogaster, which lack proliferative stem cells in all but the germline and have relatively short life spans. This has forced us to reevaluate the role of p53 in the control of life span. We discuss how p53 might regulate longevity in both long- and short-lived species by controlling the activity of insulin-like molecules that operate in proliferating and non-proliferating compartments of adult somatic tissues. We also discuss the hierarchical structure of life span regulation where loss of p53 has life span extending effects. Finally, we suggest a molecular mechanism by which p53 might facilitate the response to severe nutrient deprivation that allows metabolically active cells to survive periods of starvation. Paradoxically, loss of p53 function in these cells would compromise life span.
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Affiliation(s)
- Heidi Scrable
- University of Virginia, Department of Neuroscience, Charlottesville, Virginia, USA.
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31
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Timmerman SL, Pfingsten JS, Kieft JS, Krushel LA. The 5' leader of the mRNA encoding the mouse neurotrophin receptor TrkB contains two internal ribosomal entry sites that are differentially regulated. PLoS One 2007; 3:e3242. [PMID: 18779873 PMCID: PMC2531235 DOI: 10.1371/journal.pone.0003242] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2008] [Accepted: 08/27/2008] [Indexed: 12/30/2022] Open
Abstract
A single internal ribosomal entry site (IRES) in conjunction with IRES transactivating factors (ITAFs) is sufficient to recruit the translational machinery to a eukaryotic mRNA independent of the cap structure. However, we demonstrate that the mouse TrkB mRNA contains two independent IRESes. The mouse TrkB mRNA consists of one of two 5′ leaders (1428 nt and 448 nt), both of which include the common 3′ exon (Ex2, 344 nt). Dicistronic RNA transfections and in vitro translation of monocistronic RNA demonstrated that both full-length 5′ leaders, as well as Ex2, exhibit IRES activity indicating the IRES is located within Ex2. Additional analysis of the upstream sequences demonstrated that the first 260 nt of exon 1 (Ex1a) also contains an IRES. Dicistronic RNA transfections into SH-SY5Y cells showed the Ex1a IRES is constitutively active. However, the Ex2 IRES is only active in response to retinoic acid induced neural differentiation, a state which correlates with the synthesis of the ITAF polypyrimidine tract binding protein (PTB1). Correspondingly, addition or knock-down of PTB1 altered Ex2, but not Ex1a IRES activity in vitro and ex vivo, respectively. These results demonstrate that the two functionally independent IRESes within the mouse TrkB 5′ leader are differentially regulated, in part by PTB1.
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Affiliation(s)
- Stephanie L. Timmerman
- Department of Biochemistry and Molecular Genetics, University of Colorado Denver School of Medicine, Aurora, Colorado, United States of America
| | - Jennifer S. Pfingsten
- Department of Biochemistry and Molecular Genetics, University of Colorado Denver School of Medicine, Aurora, Colorado, United States of America
| | - Jeffrey S. Kieft
- Department of Biochemistry and Molecular Genetics, University of Colorado Denver School of Medicine, Aurora, Colorado, United States of America
| | - Les A. Krushel
- Department of Biochemistry and Molecular Genetics, University of Colorado Denver School of Medicine, Aurora, Colorado, United States of America
- Department of Pharmacology, University of Colorado Denver School of Medicine, Aurora, Colorado, United States of America
- * E-mail:
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32
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De Jesus NH. Epidemics to eradication: the modern history of poliomyelitis. Virol J 2007; 4:70. [PMID: 17623069 PMCID: PMC1947962 DOI: 10.1186/1743-422x-4-70] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/27/2007] [Accepted: 07/10/2007] [Indexed: 11/13/2022] Open
Abstract
Poliomyelitis has afflicted humankind since antiquity, and for nearly a century now, we have known the causative agent, poliovirus. This pathogen is an enterovirus that in recent history has been the source of a great deal of human suffering. Although comparatively small, its genome is packed with sufficient information to make it a formidable pathogen. In the last 20 years the Global Polio Eradication Initiative has proven successful in greatly diminishing the number of cases worldwide but has encountered obstacles in its path which have made halting the transmission of wild polioviruses a practical impossibility. As we begin to realize that a change in strategy may be crucial in achieving success in this venture, it is imperative that we critically evaluate what is known about the molecular biology of this pathogen and the intricacies of its interaction with its host so that in future attempts we may better equipped to more effectively combat this important human pathogen.
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Affiliation(s)
- Nidia H De Jesus
- Department of Molecular Genetics & Microbiology, Stony Brook University School of Medicine, Stony Brook, New York, USA.
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33
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Baird SD, Lewis SM, Turcotte M, Holcik M. A search for structurally similar cellular internal ribosome entry sites. Nucleic Acids Res 2007; 35:4664-77. [PMID: 17591613 PMCID: PMC1950536 DOI: 10.1093/nar/gkm483] [Citation(s) in RCA: 67] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2007] [Revised: 05/31/2007] [Accepted: 06/04/2007] [Indexed: 01/01/2023] Open
Abstract
Internal ribosome entry sites (IRES) allow ribosomes to be recruited to mRNA in a cap-independent manner. Some viruses that impair cap-dependent translation initiation utilize IRES to ensure that the viral RNA will efficiently compete for the translation machinery. IRES are also employed for the translation of a subset of cellular messages during conditions that inhibit cap-dependent translation initiation. IRES from viruses like Hepatitis C and Classical Swine Fever virus share a similar structure/function without sharing primary sequence similarity. Of the cellular IRES structures derived so far, none were shown to share an overall structural similarity. Therefore, we undertook a genome-wide search of human 5'UTRs (untranslated regions) with an empirically derived structure of the IRES from the key inhibitor of apoptosis, X-linked inhibitor of apoptosis protein (XIAP), to identify novel IRES that share structure/function similarity. Three of the top matches identified by this search that exhibit IRES activity are the 5'UTRs of Aquaporin 4, ELG1 and NF-kappaB repressing factor (NRF). The structures of AQP4 and ELG1 IRES have limited similarity to the XIAP IRES; however, they share trans-acting factors that bind the XIAP IRES. We therefore propose that cellular IRES are not defined by overall structure, as viral IRES, but are instead dependent upon short motifs and trans-acting factors for their function.
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Affiliation(s)
- Stephen D. Baird
- Department of Biochemistry, Microbiology and Immunology, Department of Pediatrics and School of Information Technology and Engineering, University of Ottawa, ON, Canada and Apoptosis Research Centre, Children's Hospital of Eastern Ontario, Ottawa, ON, Canada, K1H 8L1
| | - Stephen M. Lewis
- Department of Biochemistry, Microbiology and Immunology, Department of Pediatrics and School of Information Technology and Engineering, University of Ottawa, ON, Canada and Apoptosis Research Centre, Children's Hospital of Eastern Ontario, Ottawa, ON, Canada, K1H 8L1
| | - Marcel Turcotte
- Department of Biochemistry, Microbiology and Immunology, Department of Pediatrics and School of Information Technology and Engineering, University of Ottawa, ON, Canada and Apoptosis Research Centre, Children's Hospital of Eastern Ontario, Ottawa, ON, Canada, K1H 8L1
| | - Martin Holcik
- Department of Biochemistry, Microbiology and Immunology, Department of Pediatrics and School of Information Technology and Engineering, University of Ottawa, ON, Canada and Apoptosis Research Centre, Children's Hospital of Eastern Ontario, Ottawa, ON, Canada, K1H 8L1
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34
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Rabadan-Diehl C, Martínez A, Volpi S, Subburaju S, Aguilera G. Inhibition of vasopressin V1b receptor translation by upstream open reading frames in the 5'-untranslated region. J Neuroendocrinol 2007; 19:309-19. [PMID: 17355321 DOI: 10.1111/j.1365-2826.2007.01533.x] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The 5'-UTR of the vasopressin V1b receptor (V1bR) mRNA contains small open reading frames (ORF) located upstream (u) of the main ORF encoding the V1bR. The ability of the three proximal uORFs to be translated into peptides and their influence on V1bR translation was examined using fusion constructs of uORFs and V5 epitope, or ATG/ATA uORF mutations in the V1bR cDNA. In vitro translation and western blot analysis after transfection of uORF1-V5 or uORF2-V5 into cells revealed that uORF1 can be translated. As predicted by computer analysis, in vitro translation using a rabbit reticulocyte/canine microsome system, immunohistochemistry and western blot in membranes of transfected cells with uORF1-V5 revealed translocation of the uORF1 peptide into membrane fractions. In vitro translation of V1bR cDNA with mutations of the two uORFs proximal to the initiating methionine, uORFs 1 and 2 (Mut 1-2), or uORF2 (Mut 2) showed significantly increased translation of a 46 kDa band corresponding to the V1bR, compared with wild-type (WT) V1bR, an effect that was attenuated by cotranslation of uORF1-V5. Consistently, VP-induced inositol phosphate formation was higher in Chinese hamster ovay cells transfected with Mut 1-2 than with WT V1bR. Immunohistochemical and western blot analysis, using an antibody against uORF1, revealed peptide immunoreactivity in rat pituitary but not in liver. Pituitary uORF immunoreactivity increased following glucocorticoid administration. The present study shows that uORFs in the 5'-UTR of the V1bR mRNA inhibit V1bR translation, and suggests that translation of a 38-amino acid membrane peptide encoded by uORF1 exerts tonic inhibition of V1bR translation.
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Affiliation(s)
- C Rabadan-Diehl
- Section on Endocrine Physiology, Developmental Endocrinology Branch, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892, USA
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35
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Lasko P, Sonenberg N. Coordinated transcriptional and translational control in metabolic homeostasis in flies. Genes Dev 2007; 21:235-7. [PMID: 17289913 DOI: 10.1101/gad.1524707] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Affiliation(s)
- Paul Lasko
- Department of Biology and Developmental Biology Research Initiative, McGill University, Montréal, Québec H3A 1B1, Canada
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36
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Abstract
The cell has many ways to regulate the production of proteins. One mechanism is through the changes to the machinery of translation initiation. These alterations favor the translation of one subset of mRNAs over another. It was first shown that internal ribosome entry sites (IRESes) within viral RNA genomes allowed the production of viral proteins more efficiently than most of the host proteins. The RNA secondary structure of viral IRESes has sometimes been conserved between viral species even though the primary sequences differ. These structures are important for IRES function, but no similar structure conservation has yet to be shown in cellular IRES. With the advances in mathematical modeling and computational approaches to complex biological problems, is there a way to predict an IRES in a data set of unknown sequences? This review examines what is known about cellular IRES structures, as well as the data sets and tools available to examine this question. We find that the lengths, number of upstream AUGs, and %GC content of 5'-UTRs of the human transcriptome have a similar distribution to those of published IRES-containing UTRs. Although the UTRs containing IRESes are on the average longer, almost half of all 5'-UTRs are long enough to contain an IRES. Examination of the available RNA structure prediction software and RNA motif searching programs indicates that while these programs are useful tools to fine tune the empirically determined RNA secondary structure, the accuracy of de novo secondary structure prediction of large RNA molecules and subsequent identification of new IRES elements by computational approaches, is still not possible.
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Affiliation(s)
- Stephen D Baird
- Department of Biochemistry, Microbiology and Immunology, University of Ottawa, Ontario K1H 8M5, Canada
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37
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Cheung HC, Corley LJ, Fuller GN, McCutcheon IE, Cote GJ. Polypyrimidine tract binding protein and Notch1 are independently re-expressed in glioma. Mod Pathol 2006; 19:1034-41. [PMID: 16729017 DOI: 10.1038/modpathol.3800635] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
Abstract
Polypyrimidine tract binding protein (PTB) is expressed in developing mammalian astrocytes, absent in mature adult astrocytes, and aberrantly elevated in gliomas. It is unclear whether PTB is a coincidental marker of tumor progression or a significant mediator of tumorigenesis. In developing Drosophila, the absence of the PTB homolog, hephaestus, results in increased Notch activity. Since Notch is a well-known inducer of glial cell fate, we determined whether overexpression of PTB in glial cell tumors provides a selective growth advantage by inhibiting activated Notch (Notch1IC)-mediated differentiation. To do this, we performed an immunohistochemical analysis for expression of PTB, activated Notch1 (Notch1IC), Hes1 (a Notch target), and GFAP on an extensive human tissue microarray that included 246 gliomas, 10 gliosarcomas, and 10 normal brains. Statistically significant PTB overexpression was seen in all glioma grades, with the highest increase in grade IV tumors. Notch1IC was also abnormally expressed in gliomas except in a subset of grade IV tumors in which it was absent. This decrease in Notch1IC was not associated with increased PTB expression. We conclude that PTB, and Notch1 serve as independent and functionally unlinked markers of glioma progression.
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Affiliation(s)
- Hannah C Cheung
- Department of Endocrine Neoplasia and Hormonal Disorders, The University of Texas MD Anderson Cancer Center, Houston, 77030, USA
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38
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Ma Y, Zhang L, Peng T, Cheng J, Taneja S, Zhang J, Delafontaine P, Du J. Angiotensin II stimulates transcription of insulin-like growth factor I receptor in vascular smooth muscle cells: role of nuclear factor-kappaB. Endocrinology 2006; 147:1256-63. [PMID: 16322063 PMCID: PMC3228638 DOI: 10.1210/en.2005-0888] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Increased expression of the IGF-I receptor (IGF-IR) is associated with proliferation and survival of vascular smooth muscle cells (VSMCs). In cultured VSMCs, we reported that angiotensin II (Ang II) increases transcription and expression of IGF-IR. Now, we show that mesenteric arteries of rats infused with Ang II develop thickening and increased IGF-IR expression. To determine how Ang II transcriptionally regulates IGF-IR expression in VSMCs, we generated 5'-end deletions of the IGF-IR promoter and measured Ang II-induced promoter-luciferase activity in VSMCs. Activities from these promoter sequences suggested that the Ang II-responsive region is located between -270 and -135 of the IGF-IR promoter. Using a DNase I foot printing analysis, we identified two putative nuclear factor-kappaB (NF-kappaB)-like sequences located in the same region of the IGF-IR promoter. When we mutated either of these NF-kappaB-like sites, Ang II-induced IGF-IR promoter activity decreased sharply. Electrophoretic mobility gel shift, anti-p50 of NF-kappaB supershift and chromatin immunoprecipitation assays demonstrated that both the p65 and p50 subunits of NF-kappaB will bind to this Ang II response element in the IGF-IR promoter. When we blocked the Ras/MAPK kinase 1 pathway or the inhibitory-kappaB kinase pathway, both Ang II-induced IGF-IR promoter activity and expression of IGF-IR protein significantly declined. Our results indicate that the mechanism by which Ang II stimulates IGF-IR expression in VSMCs involves NF-kappaB binding to NF-kappaB sites in the IGF-IR promoter, leading to expression of IGF-IR through both Ras/MAPK kinase 1-and inhibitory-kappaB kinase-dependent pathways. Because IGF-IR is a major factor associated with thickening of mesenteric vessels, our results provide potential therapeutic targets.
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MESH Headings
- Angiotensin II/metabolism
- Angiotensin II/physiology
- Animals
- Binding Sites
- Cells, Cultured
- Chromatin Immunoprecipitation
- Deoxyribonuclease I/metabolism
- Gene Deletion
- Genes, Reporter
- Immunohistochemistry
- Immunoprecipitation
- Luciferases/metabolism
- MAP Kinase Signaling System
- Male
- Muscle, Smooth, Vascular/cytology
- Muscle, Smooth, Vascular/metabolism
- Myocytes, Smooth Muscle/cytology
- NF-kappa B/metabolism
- NF-kappa B p50 Subunit/metabolism
- Promoter Regions, Genetic
- Protein Binding
- Rats
- Rats, Sprague-Dawley
- Receptor, IGF Type 1/metabolism
- Reverse Transcriptase Polymerase Chain Reaction
- Transcription Factor RelA/metabolism
- Transcription, Genetic
- Transfection
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Affiliation(s)
- Yewei Ma
- Department of Medicine, One Baylor Plaza, N520, Baylor College of Medicine, Houston, Texas 77030, USA
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39
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Spriggs KA, Bushell M, Mitchell SA, Willis AE. Internal ribosome entry segment-mediated translation during apoptosis: the role of IRES-trans-acting factors. Cell Death Differ 2005; 12:585-91. [PMID: 15900315 DOI: 10.1038/sj.cdd.4401642] [Citation(s) in RCA: 131] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023] Open
Abstract
During apoptosis, there is a reduction in translation initiation caused by caspase cleavage of several of the factors required for the cap-dependent scanning mechanism. Under these circumstances, many proteins that are required for apoptosis are instead translated by the alternative method of internal ribosome entry. This mechanism requires the formation of a complex RNA structural element and in the presence of internal ribosome entry segment (IRES)-trans-acting factors (ITAFs), the ribosome is recruited to the RNA. The interactions of several ITAFs with IRESs have been investigated in detail, and several mechanisms of action have been noted, including acting as chaperones, stabilising and remodelling the RNA structure. Structural remodelling by PTB in particular will be discussed, and how this protein is able to facilitate recruitment of the ribosome to several IRESs by causing previously occluded sites to become more accessible.
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Affiliation(s)
- K A Spriggs
- School of Pharmacy, University of Nottingham, University Park, Nottingham, UK
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40
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Miura P, Thompson J, Chakkalakal JV, Holcik M, Jasmin BJ. The utrophin A 5'-untranslated region confers internal ribosome entry site-mediated translational control during regeneration of skeletal muscle fibers. J Biol Chem 2005; 280:32997-3005. [PMID: 16061482 DOI: 10.1074/jbc.m503994200] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
Utrophin up-regulation in muscle fibers of Duchenne muscular dystrophy patients represents a potential therapeutic strategy. It is thus important to delineate the regulatory events presiding over utrophin in muscle in attempts to develop pharmacological interventions aimed at increasing utrophin expression. A number of studies have now shown that under several experimental conditions, the abundance of utrophin is increased without a corresponding elevation in its mRNA. Here, we examine whether utrophin expression is regulated at the translational level in regenerating muscle fibers. Treatment of mouse tibialis anterior muscles with cardiotoxin to induce muscle degeneration/regeneration led to a large (approximately 14-fold) increase in the levels of utrophin A with a modest change in expression of its transcript (40%). Isolation of the mouse utrophin A 5'-untranslated region (UTR) revealed that it is relatively long with a predicted high degree of secondary structure. In control muscles, the 5'-UTR of utrophin A caused an inhibition upon translation of a reporter protein. Strikingly, this inhibition was removed during regeneration, indicating that expression of utrophin A in regenerating muscles is translationally regulated via its 5'-UTR. Using bicistronic reporter vectors, we observed that this translational effect involves an internal ribosome entry site in the utrophin A 5'-UTR. Thus, internal ribosome entry site-mediated translation of utrophin A can, at least partially, account for the discordant expression of utrophin A protein and transcript in regenerating muscle. These findings provide a novel target for up-regulating levels of utrophin A in Duchenne muscular dystrophy muscle fibers via pharmacological interventions.
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MESH Headings
- 5' Untranslated Regions
- Animals
- Binding Sites
- Blotting, Northern
- Blotting, Western
- Cells, Cultured
- Cobra Cardiotoxin Proteins/metabolism
- Gene Expression Regulation
- Genes, Reporter
- Genetic Vectors
- Mice
- Mice, Inbred C57BL
- Microscopy, Fluorescence
- Models, Genetic
- Muscle Fibers, Skeletal/metabolism
- Muscle, Skeletal/metabolism
- Muscles/metabolism
- Plasmids/metabolism
- Protein Biosynthesis
- Protein Structure, Secondary
- RNA/metabolism
- RNA, Messenger/metabolism
- Regeneration
- Reverse Transcriptase Polymerase Chain Reaction
- Ribosomes/metabolism
- Up-Regulation
- Utrophin/chemistry
- Utrophin/genetics
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Affiliation(s)
- Pedro Miura
- Department of Cellular and Molecular Medicine and Centre for Neuromuscular Disease, Faculty of Medicine, University of Ottawa, Ottawa, Ontario K1H 8M5, Canada
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41
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Mitchell SA, Spriggs KA, Bushell M, Evans JR, Stoneley M, Le Quesne JPC, Spriggs RV, Willis AE. Identification of a motif that mediates polypyrimidine tract-binding protein-dependent internal ribosome entry. Genes Dev 2005; 19:1556-71. [PMID: 15998809 PMCID: PMC1172062 DOI: 10.1101/gad.339105] [Citation(s) in RCA: 99] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2005] [Accepted: 05/19/2005] [Indexed: 02/05/2023]
Abstract
We have identified a novel motif which consists of the sequence (CCU)(n) as part of a polypyrimidine-rich tract and permits internal ribosome entry. A number of constructs containing variations of this motif were generated and these were found to function as artificial internal ribosome entry segments (AIRESs) in vivo and in vitro in the presence of polypyrimidine tract-binding protein (PTB). The data show that for these sequences to function as IRESs the RNA must be present as a double-stranded stem and, in agreement with this, rather surprisingly, we show that PTB binds strongly to double-stranded RNA. All the cellular 5' untranslated regions (UTRs) tested that harbor this sequence were shown to contain internal ribosome entry segments that are dependent upon PTB for function in vivo and in vitro. This therefore raises the possibility that PTB or its interacting protein partners could provide a bridge between the IRES-RNA and the ribosome. Given the number of putative cellular IRESs that could be dependent on PTB for function, these data strongly suggest that PTB-1 is a universal IRES-trans-acting factor.
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Affiliation(s)
- Sally A Mitchell
- School of Pharmacy, University of Nottingham, University Park, Nottingham, NG7 2RD, UK
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42
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Meng Z, King PH, Nabors LB, Jackson NL, Chen CY, Emanuel PD, Blume SW. The ELAV RNA-stability factor HuR binds the 5'-untranslated region of the human IGF-IR transcript and differentially represses cap-dependent and IRES-mediated translation. Nucleic Acids Res 2005; 33:2962-79. [PMID: 15914670 PMCID: PMC1140080 DOI: 10.1093/nar/gki603] [Citation(s) in RCA: 93] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
The type I insulin-like growth factor receptor (IGF-IR) is an integral component in the control of cell proliferation, differentiation and apoptosis. The IGF-IR mRNA contains an extraordinarily long (1038 nt) 5'-untranslated region (5'-UTR), and we have characterized a diverse series of proteins interacting with this RNA sequence which may provide for intricate regulation of IGF-IR gene expression at the translational level. Here, we report the purification and identification of one of these IGF-IR 5'-UTR-binding proteins as HuR, using a novel RNA crosslinking/RNase elution strategy. Because HuR has been predominantly characterized as a 3'-UTR-binding protein, enhancing mRNA stability and generally increasing gene expression, we sought to determine whether HuR might serve a different function in the context of its binding the IGF-IR 5'-UTR. We found that HuR consistently repressed translation initiation through the IGF-IR 5'-UTR. The inhibition of translation by HuR was concentration dependent, and could be reversed in trans by addition of a fragment of the IGF-IR 5'-UTR containing the HuR binding sites as a specific competitor, or abrogated by deletion of the third RNA recognition motif of HuR. We determined that HuR repressed translation initiation through the IGF-IR 5'-UTR in cells as well, and that siRNA knockdown of HuR markedly increased IGF-IR protein levels. Interestingly, we also found that HuR potently inhibited IGF-IR translation mediated through internal ribosome entry. Kinetic assays were performed to investigate the mechanism of translation repression by HuR and the dynamic interplay between HuR and the translation apparatus. We found that HuR, occupying a cap-distal position, significantly delayed translation initiation mediated by cap-dependent scanning, but was eventually displaced from its binding site, directly or indirectly, as a consequence of ribosomal scanning. However, HuR perpetually blocked the activity of the IGF-IR IRES, apparently arresting the IRES-associated translation pre-initiation complex in an inactive state. This function of HuR as a 5'-UTR-binding protein and dual-purpose translation repressor may be critical for the precise regulation of IGF-IR expression essential to normal cellular homeostasis.
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Affiliation(s)
- Zheng Meng
- Department of Biochemistry and Molecular Genetics, University of Alabama at BirminghamBirmingham, AL, USA
| | - Peter H. King
- Department of Neurology, University of Alabama at BirminghamBirmingham, AL, USA
- Birmingham Veterans Affairs Medical CenterBirmingham, AL 35294, USA
| | - L. Burt Nabors
- Department of Neurology, University of Alabama at BirminghamBirmingham, AL, USA
| | - Nateka L. Jackson
- Department of Medicine, University of Alabama at BirminghamBirmingham, AL, USA
| | - Ching-Yi Chen
- Department of Biochemistry and Molecular Genetics, University of Alabama at BirminghamBirmingham, AL, USA
| | - Peter D. Emanuel
- Department of Biochemistry and Molecular Genetics, University of Alabama at BirminghamBirmingham, AL, USA
- Department of Medicine, University of Alabama at BirminghamBirmingham, AL, USA
- Comprehensive Cancer Center, University of Alabama at BirminghamBirmingham, AL, USA
| | - Scott W. Blume
- Department of Biochemistry and Molecular Genetics, University of Alabama at BirminghamBirmingham, AL, USA
- Department of Medicine, University of Alabama at BirminghamBirmingham, AL, USA
- Comprehensive Cancer Center, University of Alabama at BirminghamBirmingham, AL, USA
- To whom correspondence should be addressed at 1824 6th Avenue South, Wallace Tumor Institute, Room 508, University of Alabama at Birmingham, Birmingham, AL 35294, USA. Tel: +1 205 975 2409; Fax: +1 205 975 6911;
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43
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Kozak M. Alternative ways to think about mRNA sequences and proteins that appear to promote internal initiation of translation. Gene 2004; 318:1-23. [PMID: 14585494 DOI: 10.1016/s0378-1119(03)00774-1] [Citation(s) in RCA: 76] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Translation of some mRNAs is postulated to occur via an internal initiation mechanism which is said to be augmented by a variety of RNA-binding proteins. A pervasive problem is that the RNA sequences to which the proteins bind were not rigorously proven to function as internal ribosome entry sites (IRESs). Critical examination of the evidence reveals flaws that leave room for alternative interpretations, such as the possibility that IRES elements might function as cryptic promoters, splice sites, or sequences that modulate cleavage by RNases. The growing emphasis on IRES-binding proteins diverts attention from these fundamental unresolved issues. Many of the putative IRES-binding proteins are heterogeneous nuclear ribonucleoproteins that have recognized roles in RNA processing or stability and no recognized role in translation. Thus the mechanism whereby they promote internal initiation, if indeed they do, is not obvious. Some recent experiments were said to support the idea that IRES-binding proteins cause functionally important changes in folding of the RNA, but the evidence is not convincing when examined closely. The proteins that bind to some (not all) viral IRES elements include a subset of authentic initiation factors. This has not been demonstrated with any candidate IRES of cellular origin, however; and even with viral RNAs, the required chase experiment has not been done to prove that a pre-bound initiation factor actually mediates subsequent entry of ribosomes. In short, the focus on IRES-binding proteins has gotten us no closer to understanding the mechanism of internal initiation. Given the aforementioned uncertainty about whether other mechanisms (splicing, cryptic promoters) might underlie what-appears-to-be internal initiation, a temporary solution might be to redefine IRES to mean "internal regulatory expression sequence." This compromise would allow the sequences to be used for gene expression studies, for which they sometimes work, without asserting more than has been proven about the mechanism.
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Affiliation(s)
- Marilyn Kozak
- Department of Biochemistry, Robert Wood Johnson Medical School, University of Medicine and Dentistry of New Jersey, 675 Hoes Lane, Piscataway, NJ 08854, USA.
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44
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Meng Z, Snyder RC, Shrestha K, Miller DM, Emanuel PD, Blume SW. Evidence for differential ribonucleoprotein complex assembly in vitro on the 5'-untranslated region of the human IGF-IR transcript. Mol Cell Endocrinol 2003; 200:127-40. [PMID: 12644306 DOI: 10.1016/s0303-7207(02)00381-7] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The type I insulin-like growth factor receptor (IGF-IR) plays a key role in the control of cellular proliferation and survival. The human IGF-IR transcript is characterized by an unusually long 1038 nucleotide 5'-untranslated region (5'-UTR). We hypothesized that the contribution of this complex 5'-untranslated RNA sequence to the post-transcriptional regulation of IGF-IR expression would involve a dynamic interplay between RNA structure and specific RNA-binding proteins. Here we have detected and characterized a diverse series of regulatory proteins binding the IGF-IR 5'-UTR under disparate conditions. One pair of proteins ( approximately 42/38 kDa) binds readily to the intact 5'-UTR, which is predicted to adopt a highly base-paired, highly favorable (dG=-498 kcal/mol) three-domain structure. Another protein(s) (p20*) specifically induces formation of a novel RNA structure from within the initial 209 nucleotides of the nascent IGF-IR transcript, but fails to UV crosslink to this RNA sequence. A third group of proteins recognizes and binds the IGF-IR 5'-UTR under highly stringent conditions, but only after higher-ordered RNA structure has been disrupted. Our in vitro results indicate that the IGF-IR 5'-UTR may exist in at least three distinct states, and we propose that interconversion between these states might take place in vivo and differentially alter IGF-IR transcript utilization.
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Affiliation(s)
- Zheng Meng
- The Department of Biochemistry and Molecular Genetics, University of Alabama at Birmingham, 35294, USA
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45
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Larsen LK, Amri EZ, Mandrup S, Pacot C, Kristiansen K. Genomic organization of the mouse peroxisome proliferator-activated receptor beta/delta gene: alternative promoter usage and splicing yield transcripts exhibiting differential translational efficiency. Biochem J 2002; 366:767-75. [PMID: 12059785 PMCID: PMC1222822 DOI: 10.1042/bj20011821] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2001] [Revised: 05/07/2002] [Accepted: 06/12/2002] [Indexed: 11/17/2022]
Abstract
Peroxisome proliferator-activated receptor (PPAR) beta/delta is ubiquitously expressed, but the level of expression differs markedly between different cell types. In order to determine the molecular mechanisms governing PPARbeta/delta gene expression, we have isolated and characterized the mouse gene encoding PPARbeta/delta. The gene spans approx. 41 kb and comprises 11 exons of which the six exons located in the 3'-end of the gene are included in all transcripts. Primer-extension and 5'-rapid amplification of cDNA ends experiments revealed the presence of multiple transcription start points and splice variants, originating from the use of at least four different promoters. One of these transcription start points was found to be used predominantly in all tissues examined. Initiation from this major transcription start point gives rise to a transcript with a 548 nt 5'-untranslated leader containing eight upstream AUG codons. We show that the presence of the 548 nt leader resulted in a low translational efficiency of the corresponding PPARbeta/delta mRNA and propose, based on structural features of the 5'-untranslated region, that translational initiation may be mediated via an internal ribosome entry site-dependent mechanism.
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MESH Headings
- 3T3 Cells
- 5' Untranslated Regions
- Animals
- Blotting, Northern
- Blotting, Southern
- Blotting, Western
- Cloning, Molecular
- Codon
- DNA, Complementary/metabolism
- Exons
- Mice
- Models, Genetic
- Molecular Sequence Data
- Promoter Regions, Genetic
- RNA, Messenger/metabolism
- Receptors, Cytoplasmic and Nuclear/biosynthesis
- Receptors, Cytoplasmic and Nuclear/genetics
- Reverse Transcriptase Polymerase Chain Reaction
- Tissue Distribution
- Transcription Factors/biosynthesis
- Transcription Factors/genetics
- Transcription, Genetic
- Transfection
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Affiliation(s)
- Leif K Larsen
- Rheoscience A/S, Glerupvej 2, DK-2610 Rødovre, Denmark.
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46
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Back SH, Shin S, Jang SK. Polypyrimidine tract-binding proteins are cleaved by caspase-3 during apoptosis. J Biol Chem 2002; 277:27200-9. [PMID: 12004072 DOI: 10.1074/jbc.m203887200] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The polypyrimidine tract-binding protein (PTB), an RNA-binding protein, is required for efficient translation of some mRNAs containing internal ribosomal entry sites (IRESs). Here we provide evidence that the addition of apoptosis-inducing agents to cells results in the cleavage of PTB isoforms 1, 2, and 4 by caspase-3. This cleavage of PTB separated the N-terminal region, containing NLS-RRM1, from the C-terminal region, containing RRM2-3-4. Our data indicate that there are three noncanonical caspase-3 target sites in PTBs, namely Ile-Val-Pro-Asp(7)Ile, Leu-Tyr-Thr-Asp(139)Ser, and Ala-Ala-Val-Asp(172)Ala. The C-terminal PTB fragments localized to the cytoplasm, as opposed to the nucleus where most intact PTBs are found. Moreover, these C-terminal PTB fragments inhibited translation of polioviral mRNA, which contains an IRES element requiring PTB for its activation. This suggests that translation of some IRES-containing mRNAs is regulated by proteolytic cleavage of PTB during apoptosis.
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Affiliation(s)
- Sung Hoon Back
- National Research Laboratory, Department of Life Science, Division of Molecular and Life Sciences, Pohang University of Science and Technology, San31, Hyoja-Dong, Pohang, Kyungbuk 790-784, Korea
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47
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Feuer R, Mena I, Pagarigan R, Slifka MK, Whitton JL. Cell cycle status affects coxsackievirus replication, persistence, and reactivation in vitro. J Virol 2002; 76:4430-40. [PMID: 11932410 PMCID: PMC155066 DOI: 10.1128/jvi.76.9.4430-4440.2002] [Citation(s) in RCA: 140] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Enteroviral persistence has been implicated in the pathogenesis of several chronic human diseases, including dilated cardiomyopathy, insulin-dependent diabetes mellitus, and chronic inflammatory myopathy. However, these viruses are considered highly cytolytic, and it is unclear what mechanisms might permit their long-term survival. Here, we describe the generation of a recombinant coxsackievirus B3 (CVB3) expressing the enhanced green fluorescent protein (eGFP), which we used to mark and track infected cells in vitro. Following exposure of quiescent tissue culture cells to either wild-type CVB3 or eGFP-CVB3, virus production was very limited but increased dramatically after cells were permitted to divide. Studies with cell cycle inhibitors revealed that cells arrested at the G(1) or G(1)/S phase could express high levels of viral polyprotein and produced abundant infectious virus. In contrast, both protein expression and virus yield were markedly reduced in quiescent cells (i.e., cells in G(0)) and in cells blocked at the G(2)/M phase. Following infection with eGFP-CVB3, quiescent cells retained viral RNA for several days in the absence of infectious virus production. Furthermore, RNA extracted from nonproductive quiescent cells was infectious when transfected into dividing cells, indicating that CVB3 appears to be capable of establishing a latent infection in G(0) cells, at least in tissue culture. Finally, wounding of infected quiescent cells resulted in viral protein expression limited to cells in and adjacent to the lesion. We suggest that (i) cell cycle status determines the distribution of CVB3 during acute infection and (ii) the persistence of CVB3 in vivo may rely on infection of quiescent (G(0)) cells incapable of supporting viral replication; a subsequent change in the cell cycle status may lead to virus reactivation, triggering chronic viral and/or immune-mediated pathology in the host.
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Affiliation(s)
- Ralph Feuer
- Department of Neuropharmacology, The Scripps Research Institute, La Jolla, California 92037, USA
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Kamath RV, Leary DJ, Huang S. Nucleocytoplasmic shuttling of polypyrimidine tract-binding protein is uncoupled from RNA export. Mol Biol Cell 2001; 12:3808-20. [PMID: 11739782 PMCID: PMC60757 DOI: 10.1091/mbc.12.12.3808] [Citation(s) in RCA: 56] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2001] [Revised: 08/21/2001] [Accepted: 09/05/2001] [Indexed: 02/05/2023] Open
Abstract
Polypyrimidine tract binding protein, PTB/hnRNP I, is involved in pre-mRNA processing in the nucleus and RNA localization and translation in the cytoplasm. In this report, we demonstrate that PTB shuttles between the nucleus and cytoplasm in an energy-dependent manner. Deletion mutagenesis demonstrated that a minimum of the N terminus and RNA recognition motifs (RRMs) 1 and 2 are necessary for nucleocytoplasmic shuttling. Deletion of RRM3 and 4, domains that are primarily responsible for RNA binding, accelerated the nucleocytoplasmic shuttling of PTB. Inhibition of transcription directed by either RNA polymerase II alone or all RNA polymerases yielded similar results. In contrast, selective inhibition of RNA polymerase I did not influence the shuttling kinetics of PTB. Furthermore, the intranuclear mobility of GFP-PTB, as measured by fluorescence recovery after photobleaching analyses, increased significantly in transcriptionally inactive cells compared with transcriptionally active cells. These observations demonstrate that nuclear RNA transcription and export are not necessary for the shuttling of PTB. In addition, binding to nascent RNAs transcribed by RNA polymerase II and/or III retards both the nuclear export and nucleoplasmic movement of PTB. The uncoupling of PTB shuttling and RNA export suggests that the nucleocytoplasmic shuttling of PTB may also play a regulatory role for its functions in the nucleus and cytoplasm.
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Affiliation(s)
- R V Kamath
- Department of Cell and Molecular Biology, Northwestern University Medical School, Chicago, Illinois 60611, USA
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Affiliation(s)
- M Kozak
- Department of Biochemistry, Robert Wood Johnson Medical School, University of Medicine and Dentistry of New Jersey, Piscataway, New Jersey 08854, USA.
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