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Moreno-Gutierrez DS, Zepeda-Cervantes J, Vaca L, Hernandez-Garcia A. An artificial virus-like triblock protein shows low in vivo humoral immune response and high stability. MATERIALS SCIENCE & ENGINEERING. C, MATERIALS FOR BIOLOGICAL APPLICATIONS 2021; 129:112348. [PMID: 34579876 DOI: 10.1016/j.msec.2021.112348] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/22/2021] [Revised: 07/13/2021] [Accepted: 07/24/2021] [Indexed: 10/20/2022]
Abstract
The use of viral vectors for in vivo gene therapy can be severely limited by their immunogenicity. Non-viral vectors may represent an alternative, however, reports analyzing their immunogenicity are still lacking. Here, we studied the humoral immune response in a murine model triggered by artificial virus-like particles (AVLPs) carrying plasmid or antisense DNA. The AVLPs were assembled using a family of modular proteins based on bioinspired collagen-like and silk-like sequences that produce virus-like particles. We compared our AVLPs against an Adeno Associated Virus 1 (AAV), a widely used viral vector for in vivo gene delivery that has been approved by the FDA and EMA for gene therapy. We found that a 1000-fold higher mass of AVLPs than AAV are necessary to obtain similar specific antibody titters. Furthermore, we studied the stability of AVLPs against relevant biological reagents such as heparin and fetal bovine serum to ensure nucleic acid protection in biological media. Our study demonstrates that the AVLPs are stable in physiological conditions and can overcome safety limitations such as immunogenicity. The scarce humoral immunogenicity and high stability found with AVLPs suggest that they have potential to be used as stealth non-viral gene delivery systems for in vivo studies or gene therapy.
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Affiliation(s)
- David Silverio Moreno-Gutierrez
- Laboratory of Biomolecular Engineering and Bionanotechnology, Department of Chemistry of Biomacromolecules, Institute of Chemistry, UNAM, 04510 Mexico City, Mexico
| | - Jesús Zepeda-Cervantes
- Department of Cellular and Developmental Biology, Institute of Cellular Physiology, UNAM, Mexico; Department of Microbiology and Immunology, Faculty of Veterinary Medicine and Zootechnics, UNAM, Mexico
| | - Luis Vaca
- Department of Cellular and Developmental Biology, Institute of Cellular Physiology, UNAM, Mexico; Department of Physiology and Biophysics, University of Washington School of Medicine, Seattle, WA, United States
| | - Armando Hernandez-Garcia
- Laboratory of Biomolecular Engineering and Bionanotechnology, Department of Chemistry of Biomacromolecules, Institute of Chemistry, UNAM, 04510 Mexico City, Mexico.
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Shen CR, Chen YS, Hwang YS, Chen HJ, Liu CL. Differential bicistronic gene translation mediated by the internal ribosome entry site element of encephalomyocarditis virus. Biomed J 2020; 44:S54-S62. [PMID: 35747995 PMCID: PMC9038940 DOI: 10.1016/j.bj.2020.06.006] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2019] [Revised: 05/29/2020] [Accepted: 06/16/2020] [Indexed: 12/31/2022] Open
Abstract
Background Internal ribosome entry sites (IRESs) allow the translation of a transcript independent of its cap structure. They are distributed in some viruses and cellular RNA. The element is applied in dual gene expression in a single vector. Although it appears the lower efficiency of IRES-mediated translation than that of cap-dependent translation, it is with the crucial needs to know the precise differences in translational efficacy between upstream cistrons (cap-dependent) and downstream cistrons (IRES-mediate, cap-independent) before applying the bicistronic vector in biomedical applications. Methods This study aimed to provide real examples and showed the precise differences for translational efficiency dependent upon target gene locations. We generated various bicistronic constructs with quantifiable reporter genes as upstream and downstream cistrons of the encephalomyocarditis virus (EMCV) IRES to precisely evaluate the efficacy of IRES-mediated translation in mammalian cells. Results There was no significant difference in protein production when the reporter gene was cloned as an upstream cistron. However, lower levels of protein production were obtained when the reporter gene was located downstream of the IRES. Moreover, in the presence of an upstream cistron, a markedly reduced level of protein production was observed. Conclusion Our findings demonstrate the version of the EMCV IRES that is provided in many commercial vectors is relatively less efficient than cap-dependent translation and provide valuable information regarding the utilization of IRES to facilitate the expression of more than one protein from a transcript.
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Affiliation(s)
- Chia-Rui Shen
- Department of Medical Biotechnology and Laboratory Science, College of Medicine, Chang Gung University, Taoyuan, Taiwan; Graduate Institute of Biomedical Sciences, College of Medicine, Chang Gung University, Taoyuan, Taiwan; Department of Ophthalmology, Chang Gung Memorial Hospital at Linkou, Taoyuan, Taiwan.
| | - Ya-Shan Chen
- Department of Medical Biotechnology and Laboratory Science, College of Medicine, Chang Gung University, Taoyuan, Taiwan; Graduate Institute of Biomedical Sciences, College of Medicine, Chang Gung University, Taoyuan, Taiwan
| | - Yih-Shiou Hwang
- Department of Ophthalmology, Chang Gung Memorial Hospital at Linkou, Taoyuan, Taiwan; Department of Medicine, College of Medicine, Chang Gung University, Taoyuan, Taiwan
| | - Hsi-Jien Chen
- Department of Safety, Health and Environmental Engineering, Ming Chi University of Technology, New Taipei City, Taiwan
| | - Chao-Lin Liu
- Department of Chemical Engineering, Ming Chi University of Technology, New Taipei City, Taiwan; Department of Chemical and Materials Engineering, College of Engineering, Chang Gung University, Taoyuan, Taiwan.
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Renaud-Gabardos E, Tatin F, Hantelys F, Lebas B, Calise D, Kunduzova O, Masri B, Pujol F, Sicard P, Valet P, Roncalli J, Chaufour X, Garmy-Susini B, Parini A, Prats AC. Therapeutic Benefit and Gene Network Regulation by Combined Gene Transfer of Apelin, FGF2, and SERCA2a into Ischemic Heart. Mol Ther 2017; 26:902-916. [PMID: 29249393 DOI: 10.1016/j.ymthe.2017.11.007] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2017] [Revised: 11/06/2017] [Accepted: 11/10/2017] [Indexed: 01/16/2023] Open
Abstract
Despite considerable advances in cardiovascular disease treatment, heart failure remains a public health challenge. In this context, gene therapy appears as an attractive approach, but clinical trials using single therapeutic molecules result in moderate benefit. With the objective of improving ischemic heart failure therapy, we designed a combined treatment, aimed to simultaneously stimulate angiogenesis, prevent cardiac remodeling, and restore contractile function. We have previously validated IRES-based vectors as powerful tools to co-express genes of interest. Mono- and multicistronic lentivectors expressing fibroblast growth factor 2 (angiogenesis), apelin (cardioprotection), and/or SERCA2a (contractile function) were produced and administrated by intramyocardial injection into a mouse model of myocardial infarction. Data reveal that combined treatment simultaneously improves vessel number, heart function parameters, and fibrosis prevention, due to FGF2, SERCA2a, and apelin, respectively. Furthermore, addition of SERCA2a in the combination decreases cardiomyocyte hypertrophy. Large-scale transcriptome analysis reveals that the triple treatment is the most efficient in restoring angiogenic balance as well as expression of genes involved in cardiac function and remodeling. Our study validates the concept of combined treatment of ischemic heart disease with apelin, FGF2, and SERCA2a and shows that such therapeutic benefit is mediated by a more effective recovery of gene network regulation.
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Affiliation(s)
| | - Florence Tatin
- UMR 1048-I2MC, Université de Toulouse, INSERM, FHU IMPACT, 31432 Toulouse, France
| | - Fransky Hantelys
- UMR 1048-I2MC, Université de Toulouse, INSERM, FHU IMPACT, 31432 Toulouse, France
| | - Benoît Lebas
- UMR 1048-I2MC, Université de Toulouse, INSERM, FHU IMPACT, 31432 Toulouse, France; Centre Hospitalier Universitaire de Toulouse, 31059 Toulouse, France
| | - Denis Calise
- UMS 006, Université de Toulouse, INSERM, 31432 Toulouse, France
| | - Oksana Kunduzova
- UMR 1048-I2MC, Université de Toulouse, INSERM, FHU IMPACT, 31432 Toulouse, France
| | - Bernard Masri
- UMR 1048-I2MC, Université de Toulouse, INSERM, FHU IMPACT, 31432 Toulouse, France
| | - Françoise Pujol
- UMR 1048-I2MC, Université de Toulouse, INSERM, FHU IMPACT, 31432 Toulouse, France
| | - Pierre Sicard
- UMR 1048-I2MC, Université de Toulouse, INSERM, FHU IMPACT, 31432 Toulouse, France
| | - Philippe Valet
- UMR 1048-I2MC, Université de Toulouse, INSERM, FHU IMPACT, 31432 Toulouse, France
| | - Jérôme Roncalli
- UMR 1048-I2MC, Université de Toulouse, INSERM, FHU IMPACT, 31432 Toulouse, France; Centre Hospitalier Universitaire de Toulouse, 31059 Toulouse, France
| | - Xavier Chaufour
- UMR 1048-I2MC, Université de Toulouse, INSERM, FHU IMPACT, 31432 Toulouse, France; Centre Hospitalier Universitaire de Toulouse, 31059 Toulouse, France
| | - Barbara Garmy-Susini
- UMR 1048-I2MC, Université de Toulouse, INSERM, FHU IMPACT, 31432 Toulouse, France
| | - Angelo Parini
- UMR 1048-I2MC, Université de Toulouse, INSERM, FHU IMPACT, 31432 Toulouse, France
| | - Anne-Catherine Prats
- UMR 1048-I2MC, Université de Toulouse, INSERM, FHU IMPACT, 31432 Toulouse, France.
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Lebas B, Galley J, Renaud-Gabardos E, Pujol F, Lenfant F, Garmy-Susini B, Chaufour X, Prats AC. Therapeutic Benefits and Adverse Effects of Combined Proangiogenic Gene Therapy in Mouse Critical Leg Ischemia. Ann Vasc Surg 2017; 40:252-261. [DOI: 10.1016/j.avsg.2016.08.027] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2016] [Revised: 08/08/2016] [Accepted: 08/10/2016] [Indexed: 01/07/2023]
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Renaud-Gabardos E, Hantelys F, Morfoisse F, Chaufour X, Garmy-Susini B, Prats AC. Internal ribosome entry site-based vectors for combined gene therapy. World J Exp Med 2015; 5:11-20. [PMID: 25699230 PMCID: PMC4308528 DOI: 10.5493/wjem.v5.i1.11] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/18/2014] [Revised: 11/25/2014] [Accepted: 12/19/2014] [Indexed: 02/06/2023] Open
Abstract
Gene therapy appears as a promising strategy to treat incurable diseases. In particular, combined gene therapy has shown improved therapeutic efficiency. Internal ribosome entry sites (IRESs), RNA elements naturally present in the 5’ untranslated regions of a few mRNAs, constitute a powerful tool to co-express several genes of interest. IRESs are translational enhancers allowing the translational machinery to start protein synthesis by internal initiation. This feature allowed the design of multi-cistronic vectors expressing several genes from a single mRNA. IRESs exhibit tissue specificity, and drive translation in stress conditions when the global cell translation is blocked, which renders them useful for gene transfer in hypoxic conditions occurring in ischemic diseases and cancer. IRES-based viral and non viral vectors have been used successfully in preclinical and clinical assays of combined gene therapy and resulted in therapeutic benefits for various pathologies including cancers, cardiovascular diseases and degenerative diseases.
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Prats AC, Van den Berghe L, Rayssac A, Ainaoui N, Morfoisse F, Pujol F, Legonidec S, Bikfalvi A, Prats H, Pyronnet S, Garmy-Susini B. CXCL4L1-fibstatin cooperation inhibits tumor angiogenesis, lymphangiogenesis and metastasis. Microvasc Res 2013; 89:25-33. [PMID: 23747987 DOI: 10.1016/j.mvr.2013.05.005] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2013] [Revised: 04/28/2013] [Accepted: 05/20/2013] [Indexed: 01/12/2023]
Abstract
Anti-angiogenic and anti-lymphangiogenic drugs slow tumor progression and dissemination. However, an important difficulty is that a tumor reacts and compensates to obtain the blood supply needed for tumor growth and lymphatic vessels to escape to distant loci. Therefore, there is a growing consensus on the requirement of multiple anti-(lymph)angiogenic molecules to stop cell invasion efficiently. Here we studied the cooperation between endogenous anti-angiogenic molecules, endostatin and fibstatin, and a chemokine, the Platelet Factor-4 variant 1, CXCL4L1. Anti-angiogenic factors were co-expressed by IRES-based bicistronic vectors and their cooperation was analyzed either by local delivery following transduction of pancreatic adenocarcinoma cells with lentivectors, or by distant delivery resulting from intramuscular administration in vivo of adeno-associated virus derived vectors followed by tumor subcutaneous injection. In this study, fibstatin and CXCL4L1 cooperate to inhibit endothelial cell proliferation, migration and tubulogenesis in vitro. No synergistic effect was found for fibstatin-endostatin combination. Importantly, we demonstrated for the first time that fibstatin and CXCL4L1 not only inhibit in vivo angiogenesis, but also lymphangiogenesis and tumor spread to the lymph nodes, whereas no beneficial effect was found on tumor growth inhibition using molecule combinations compared to molecules alone. These data reveal the synergy of CXCL4L1 and fibstatin in inhibition of tumor angiogenesis, lymphangiogenesis and metastasis and highlight the potential of IRES-based vectors to develop anti-metastasis combined gene therapies.
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Affiliation(s)
- A C Prats
- Université de Toulouse, UPS, TRADGENE, EA4554, F-31432 Toulouse, France
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Liang Y, Walczak P, Bulte JWM. Comparison of red-shifted firefly luciferase Ppy RE9 and conventional Luc2 as bioluminescence imaging reporter genes for in vivo imaging of stem cells. JOURNAL OF BIOMEDICAL OPTICS 2012; 17:016004. [PMID: 22352654 PMCID: PMC3380811 DOI: 10.1117/1.jbo.17.1.016004] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/10/2023]
Abstract
One critical issue for noninvasive imaging of transplanted bioluminescent cells is the large amount of light absorption in tissue when emission wavelengths below 600 nm are used. Luciferase with a red-shifted spectrum can potentially bypass this limitation. We assessed and compared a mutant of firefly luciferase (Ppy RE9, PRE9) against the yellow luciferase luc2 gene for use in cell transplantation studies. C17.2 neural stem cells expressing PRE9-Venus and luc2-Venus were sorted by flow cytometry and assessed for bioluminescence in vitro in culture and in vivo after transplantation into the brain of immunodeficient Rag2-/- mice. We found that the luminescence from PRE9 was stable, with a peak emission at 620 nm, shifted to the red compared to that of luc2. The emission peak for PRE9 was pH-independent, in contrast to luc2, and much less affected by tissue absorbance compared to that of luc2. However, the total emitted light radiance from PRE9 was substantially lower than that of luc2, both in vitro and in vivo. We conclude that PRE9 has favorable properties as compared to luc2 in terms of pH independence, red-shifted spectrum, tissue light penetration, and signal quantification, justifying further optimization of protein expression and enzymatic activity.
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Affiliation(s)
- Yajie Liang
- Johns Hopkins University School of Medicine, Division of MR Research, Russell H. Morgan Department of Radiology and Radiological Science, and Cellular Imaging Section and Vascular Biology Program, Institute for Cell Engineering, Baltimore, Maryland 21205
| | - Piotr Walczak
- Johns Hopkins University School of Medicine, Division of MR Research, Russell H. Morgan Department of Radiology and Radiological Science, and Cellular Imaging Section and Vascular Biology Program, Institute for Cell Engineering, Baltimore, Maryland 21205
| | - Jeff W. M. Bulte
- Johns Hopkins University School of Medicine, Division of MR Research, Russell H. Morgan Department of Radiology and Radiological Science, and Cellular Imaging Section and Vascular Biology Program, Institute for Cell Engineering, Baltimore, Maryland 21205
- Address all correspondence to: Jeff W. M. Bulte, Johns Hopkins University School of Medicine, 217 Traylor Building 720 Rutland Avenue, Baltimore, Maryland 21205-2195. Tel: +443 287 0996; Fax: +443 287 7945; E-mail:
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In vitro and in vivo comparison of viral and cellular internal ribosome entry sites for bicistronic vector expression. Gene Ther 2011; 18:631-6. [PMID: 21368899 DOI: 10.1038/gt.2011.11] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Bicistronic vectors are essential to achieve efficient expression of multiple genes in gene therapy protocols and biomedical applications. Internal ribosome entry site (IRES) elements have been utilized to initiate expression of an additional protein from a bicistronic vector. The IRES element commonly used in current bicistronic vectors originates from the encephalomyocarditis virus (EMCV). As IRES-mediated translation is dependent on availability of IRES trans-acting factors, which vary between cell types and species, adequate gene expression from the EMCV IRES element is not always achieved. To identify a novel IRES element that mediates gene expression consistently with a higher efficiency than the EMCV IRES, we tested 13 bicistronic reporter constructs containing different viral and cellular IRES elements. The in vitro screening in human and mouse fibroblast and hepatocarcinoma cells revealed that the vascular endothelial growth factor and type 1 collagen-inducible protein (VCIP) IRES was the only IRES element that directed translation more efficiently than the EMCV IRES in all cell lines. Furthermore, the VCIP IRES initiated greater reporter expression levels than the EMCV IRES in transfected mouse livers. These results suggest that VCIP-IRES containing vectors improve gene expression compared with those harboring an EMCV-IRES. This could increase the potential benefits of bicistronic vectors for experimental and therapeutic purposes.
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A Novel Unstructured Scaffold Based on 4EBP1 Enables the Functional Display of a Wide Range of Bioactive Peptides. J Mol Biol 2010; 404:819-31. [DOI: 10.1016/j.jmb.2010.09.063] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2010] [Revised: 09/22/2010] [Accepted: 09/29/2010] [Indexed: 01/11/2023]
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Rayssac A, Neveu C, Pucelle M, Van den Berghe L, Prado-Lourenco L, Arnal JF, Chaufour X, Prats AC. IRES-based vector coexpressing FGF2 and Cyr61 provides synergistic and safe therapeutics of lower limb ischemia. Mol Ther 2009; 17:2010-9. [PMID: 19738600 PMCID: PMC2814383 DOI: 10.1038/mt.2009.211] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2009] [Accepted: 08/13/2009] [Indexed: 01/12/2023] Open
Abstract
Due to the lack of an adequate conventional therapy against lower limb ischemia, gene transfer for therapeutic angiogenesis is seen as an attractive alternative. However, the possibility of side effects, due to the expression of large amounts of angiogenic factors, justifies the design of devices that express synergistic molecules in low controlled doses. We have developed an internal ribosome entry site (IRES)-based bicistronic vector expressing two angiogenic molecules, fibroblast growth factor 2 (FGF2), and Cyr61. Through electrotransfer into the ApoE(-/-) mice hindlimb ischemic muscle model, we show that the IRES-based vector gives more stable expression than either monocistronic plasmid. Furthermore, laser Doppler analysis, arteriography, and immunochemistry clearly show that the bicistronic vector promotes a more abundant and functional revascularization than the monocistronic vectors, despite the fact that the bicistronic system produces 5-10 times less of each angiogenic molecule. Furthermore, although the monocistronic Cyr61 vector accelerates B16 melanoma growth in mice, the bicistronic vector is devoid of such side effects. Our results show an active cooperation of FGF2 and Cyr61 in therapeutic angiogenesis of hindlimb ischemia, and validate the use of IRES-based bicistronic vectors for the coexpression of controlled low doses of therapeutic molecules, providing perspectives for a safer gene therapy of lower limb ischemia.
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Conte C, Ainaoui N, Delluc-Clavières A, Khoury MP, Azar R, Pujol F, Martineau Y, Pyronnet S, Prats AC. Fibroblast growth factor 1 induced during myogenesis by a transcription-translation coupling mechanism. Nucleic Acids Res 2009; 37:5267-78. [PMID: 19561198 PMCID: PMC2760804 DOI: 10.1093/nar/gkp550] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023] Open
Abstract
Fibroblast growth factor 1 (FGF1) is involved in muscle development and regeneration. The FGF1 gene contains four tissue-specific promoters allowing synthesis of four transcripts with distinct leader regions. Two of these transcripts contain internal ribosome entry sites (IRESs), which are RNA elements allowing mRNA translation to occur in conditions of blockade of the classical cap-dependent mechanism. Here, we investigated the function and the regulation of FGF1 during muscle differentiation and regeneration. Our data show that FGF1 protein expression is induced in differentiating myoblasts and regenerating mouse muscle, whereas siRNA knock-down demonstrated FGF1 requirement for myoblast differentiation. FGF1 induction occurred at both transcriptional and translational levels, involving specific activation of both promoter A and IRES A, whereas global cap-dependent translation was inhibited. Furthermore, we identified, in the FGF1 promoter A distal region, a cis-acting element able to activate the IRES A-driven translation. These data revealed a mechanism of molecular coupling of mRNA transcription and translation, involving a unique process of IRES activation by a promoter element. The crucial role of FGF1 in myoblast differentiation provides physiological relevance to this novel mechanism. This finding also provides a new insight into the molecular mechanisms linking different levels of gene expression regulation.
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Affiliation(s)
- Caroline Conte
- Inserm, U858 and Institut de Médecine Moléculaire de Rangueil, Université de Toulouse, UPS, IFR150, F-31432 Toulouse, France
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FGF2 translationally induced by hypoxia is involved in negative and positive feedback loops with HIF-1alpha. PLoS One 2008; 3:e3078. [PMID: 18728783 PMCID: PMC2518102 DOI: 10.1371/journal.pone.0003078] [Citation(s) in RCA: 57] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2008] [Accepted: 08/06/2008] [Indexed: 12/25/2022] Open
Abstract
Background Fibroblast growth factor 2 (FGF2) is a major angiogenic factor involved in angiogenesis and arteriogenesis, however the regulation of its expression during these processes is poorly documented. FGF2 mRNA contains an internal ribosome entry site (IRES), a translational regulator expected to allow mRNA expression during cellular stress. Methodology/Principal Findings In the present study, we have developed a skin ischemia model in transgenic mice expressing a reporter transgene under the control of the FGF2 IRES. The results reveal that FGF2 is induced at the protein level during ischemia, concomitant with HIF-1α induction and a decrease in FGF2 mRNA. In addition, the FGF2 IRES is strongly activated under these ischemic conditions associated with hypoxia, whereas cap-dependent translation is repressed by 4E-BP hypophosphorylation. We also show that up-regulation of FGF2 protein expression in response to hypoxia correlates with the increase of FGF2 IRES activity in vitro, in human retinoblasts 911. The use of siRNAs targeting HIF or FGF2 indicates that FGF2 and HIF-1α reciprocally regulate their expression/accumulation, by a negative feedback loop in early hypoxia, followed by a positive feedback loop in late hypoxia. Conclusion/Significance FGF2 expression is up-regulated in vivo and in vitro in response to hypoxia. Strikingly, this up-regulation is not transcriptional. It seems to occur by an IRES-dependent mechanism, revealing new mechanistic aspects of the hypoxic response. In addition, our data show that FGF2 interacts with HIF-1α in a unique crosstalk, with distinct stages in early and late hypoxia. These data reveal the physiological importance of IRES-dependent translation during hypoxic stress and underline the complexity of the cellular response to hypoxia, suggesting a novel role of FGF2 in the regulation of HIF-1α during the induction of angiogenesis.
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