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Khan D, Fox PL. Host-like RNA Elements Regulate Virus Translation. Viruses 2024; 16:468. [PMID: 38543832 PMCID: PMC10976276 DOI: 10.3390/v16030468] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2024] [Revised: 03/14/2024] [Accepted: 03/17/2024] [Indexed: 04/01/2024] Open
Abstract
Viruses are obligate, intracellular parasites that co-opt host cell machineries for propagation. Critical among these machineries are those that translate RNA into protein and their mechanisms of control. Most regulatory mechanisms effectuate their activity by targeting sequence or structural features at the RNA termini, i.e., at the 5' or 3' ends, including the untranslated regions (UTRs). Translation of most eukaryotic mRNAs is initiated by 5' cap-dependent scanning. In contrast, many viruses initiate translation at internal RNA regions at internal ribosome entry sites (IRESs). Eukaryotic mRNAs often contain upstream open reading frames (uORFs) that permit condition-dependent control of downstream major ORFs. To offset genome compression and increase coding capacity, some viruses take advantage of out-of-frame overlapping uORFs (oORFs). Lacking the essential machinery of protein synthesis, for example, ribosomes and other translation factors, all viruses utilize the host apparatus to generate virus protein. In addition, some viruses exhibit RNA elements that bind host regulatory factors that are not essential components of the translation machinery. SARS-CoV-2 is a paradigm example of a virus taking advantage of multiple features of eukaryotic host translation control: the virus mimics the established human GAIT regulatory element and co-opts four host aminoacyl tRNA synthetases to form a stimulatory binding complex. Utilizing discontinuous transcription, the elements are present and identical in all SARS-CoV-2 subgenomic RNAs (and the genomic RNA). Thus, the virus exhibits a post-transcriptional regulon that improves upon analogous eukaryotic regulons, in which a family of functionally related mRNA targets contain elements that are structurally similar but lacking sequence identity. This "thrifty" virus strategy can be exploited against the virus since targeting the element can suppress the expression of all subgenomic RNAs as well as the genomic RNA. Other 3' end viral elements include 3'-cap-independent translation elements (3'-CITEs) and 3'-tRNA-like structures. Elucidation of virus translation control elements, their binding proteins, and their mechanisms can lead to novel therapeutic approaches to reduce virus replication and pathogenicity.
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Affiliation(s)
- Debjit Khan
- Department of Cardiovascular and Metabolic Sciences, Lerner Research Institute, Cleveland Clinic, Cleveland, OH 44195, USA
| | - Paul L. Fox
- Department of Cardiovascular and Metabolic Sciences, Lerner Research Institute, Cleveland Clinic, Cleveland, OH 44195, USA
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Dave P, Roth G, Griesbach E, Mateju D, Hochstoeger T, Chao JA. Single-molecule imaging reveals translation-dependent destabilization of mRNAs. Mol Cell 2023; 83:589-606.e6. [PMID: 36731471 PMCID: PMC9957601 DOI: 10.1016/j.molcel.2023.01.013] [Citation(s) in RCA: 18] [Impact Index Per Article: 18.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2021] [Revised: 11/07/2022] [Accepted: 01/06/2023] [Indexed: 02/04/2023]
Abstract
The relationship between mRNA translation and decay is incompletely understood, with conflicting reports suggesting that translation can either promote decay or stabilize mRNAs. The effect of translation on mRNA decay has mainly been studied using ensemble measurements and global transcription and translation inhibitors, which can have pleiotropic effects. We developed a single-molecule imaging approach to control the translation of a specific transcript that enabled simultaneous measurement of translation and mRNA decay. Our results demonstrate that mRNA translation reduces mRNA stability, and mathematical modeling suggests that this process is dependent on ribosome flux. Furthermore, our results indicate that miRNAs mediate efficient degradation of both translating and non-translating target mRNAs and reveal a predominant role for mRNA degradation in miRNA-mediated regulation. Simultaneous observation of translation and decay of single mRNAs provides a framework to directly study how these processes are interconnected in cells.
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Affiliation(s)
- Pratik Dave
- Friedrich Miescher Institute for Biomedical Research, 4058 Basel, Switzerland
| | - Gregory Roth
- Friedrich Miescher Institute for Biomedical Research, 4058 Basel, Switzerland
| | - Esther Griesbach
- Friedrich Miescher Institute for Biomedical Research, 4058 Basel, Switzerland
| | - Daniel Mateju
- Friedrich Miescher Institute for Biomedical Research, 4058 Basel, Switzerland
| | - Tobias Hochstoeger
- Friedrich Miescher Institute for Biomedical Research, 4058 Basel, Switzerland; University of Basel, 4003 Basel, Switzerland
| | - Jeffrey A Chao
- Friedrich Miescher Institute for Biomedical Research, 4058 Basel, Switzerland.
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Condé L, Allatif O, Ohlmann T, de Breyne S. Translation of SARS-CoV-2 gRNA Is Extremely Efficient and Competitive despite a High Degree of Secondary Structures and the Presence of an uORF. Viruses 2022; 14:1505. [PMID: 35891485 PMCID: PMC9322171 DOI: 10.3390/v14071505] [Citation(s) in RCA: 9] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2022] [Revised: 07/06/2022] [Accepted: 07/07/2022] [Indexed: 12/15/2022] Open
Abstract
The SARS-CoV-2 infection generates up to nine different sub-genomic mRNAs (sgRNAs), in addition to the genomic RNA (gRNA). The 5'UTR of each viral mRNA shares the first 75 nucleotides (nt.) at their 5'end, called the leader, but differentiates by a variable sequence (0 to 190 nt. long) that follows the leader. As a result, each viral mRNA has its own specific 5'UTR in term of length, RNA structure, uORF and Kozak context; each one of these characteristics could affect mRNA expression. In this study, we have measured and compared translational efficiency of each of the ten viral transcripts. Our data show that most of them are very efficiently translated in all translational systems tested. Surprisingly, the gRNA 5'UTR, which is the longest and the most structured, was also the most efficient to initiate translation. This property is conserved in the 5'UTR of SARS-CoV-1 but not in MERS-CoV strain, mainly due to the regulation imposed by the uORF. Interestingly, the translation initiation mechanism on the SARS-CoV-2 gRNA 5'UTR requires the cap structure and the components of the eIF4F complex but showed no dependence in the presence of the poly(A) tail in vitro. Our data strongly suggest that translation initiation on SARS-CoV-2 mRNAs occurs via an unusual cap-dependent mechanism.
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Affiliation(s)
| | | | - Théophile Ohlmann
- CIRI, Centre International de Recherche en Infectiologie, (Team Ohlmann), Univ Lyon, Inserm U1111, Université Claude Bernard Lyon 1, CNRS UMR5308, ENS de Lyon, F-69007 Lyon, France; (L.C.); (O.A.)
| | - Sylvain de Breyne
- CIRI, Centre International de Recherche en Infectiologie, (Team Ohlmann), Univ Lyon, Inserm U1111, Université Claude Bernard Lyon 1, CNRS UMR5308, ENS de Lyon, F-69007 Lyon, France; (L.C.); (O.A.)
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Rethinking IRPs/IRE system in neurodegenerative disorders: Looking beyond iron metabolism. Ageing Res Rev 2022; 73:101511. [PMID: 34767973 DOI: 10.1016/j.arr.2021.101511] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2021] [Revised: 10/21/2021] [Accepted: 11/04/2021] [Indexed: 12/11/2022]
Abstract
Iron regulatory proteins (IRPs) and iron regulatory element (IRE) systems are well known in the progression of neurodegenerative disorders by regulating iron related proteins. IRPs are also regulated by iron homeostasis. However, an increasing number of studies have suggested a close relationship between the IRPs/IRE system and non-iron-related neurodegenerative disorders. In this paper, we reviewed that the IRPs/IRE system is not only controlled by iron ions, but also regulated by such factors as post-translational modification, oxygen, nitric oxide (NO), heme, interleukin-1 (IL-1), and metal ions. In addition, by regulating the transcription of non-iron related proteins, the IRPs/IRE system functioned in oxidative metabolism, cell cycle regulation, abnormal proteins aggregation, and neuroinflammation. Finally, by emphasizing the multiple regulations of IRPs/IRE system and its potential relationship with non-iron metabolic neurodegenerative disorders, we provided new strategies for disease treatment targeting IRPs/IRE system.
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Sloan MA, Aghabi D, Harding CR. Orchestrating a heist: uptake and storage of metals by apicomplexan parasites. MICROBIOLOGY (READING, ENGLAND) 2021; 167. [PMID: 34898419 PMCID: PMC7612242 DOI: 10.1099/mic.0.001114] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Affiliation(s)
- Megan A Sloan
- Wellcome Centre for Integrative Parasitology, Institute for Infection, Immunity and Inflammation, University of Glasgow, UK
| | - Dana Aghabi
- Wellcome Centre for Integrative Parasitology, Institute for Infection, Immunity and Inflammation, University of Glasgow, UK
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Zhou CY, Zheng XD, Yang DQ. Knockout fth1b affects early mineralization of zebrafish pharyngeal teeth. HUA XI KOU QIANG YI XUE ZA ZHI = HUAXI KOUQIANG YIXUE ZAZHI = WEST CHINA JOURNAL OF STOMATOLOGY 2021; 39:32-37. [PMID: 33723934 DOI: 10.7518/hxkq.2021.01.005] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
OBJECTIVES A study was conducted to explore the expression pattern and function of ferritin heavy polypeptide gene (fth1b) in zebrafish pharyngeal teeth development and lay the foundation for subsequent research on teeth development and mineralization. METHODS The zebrafish embryos were harvested at 56, 72, 96, and 120 h after fertilization. The expression of fth1b in zebrafish pharyngeal teeth development was detected by whole embryo in situ hybridization and compared with the known pharyngeal teeth marker dlx2b. The specific knockout of fth1b gene was performed using clustered regularly interspaced short palindromic repeats (CRISPR)/Cas9 gene editing technology. The development of zebrafish pharyngeal teeth was detected in the fth1b-/- mutant. RESULTS The expression pattern of fth1b gene was very similar to that of the known zebrafish pharyngeal teeth marker dlx2b and was specifically expressed in the zebrafish pharyngeal teeth during development. After the specific knockout of the gene fth1b, the earliest gene that can be detect in zebrafish pharyngeal teeth-pitx2 was expressed normally during early development. The dlx2b expression was not significantly different from that of wild type zebrafish, but the mineralization of pharyngeal teeth in the mutant was weaker than that of wild type zebrafish. CONCLUSIONS The gene fth1b is specifically expressed in zebrafish pharyngeal teeth and acts on their early mineralization.
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Affiliation(s)
- Chun-Yan Zhou
- Dept. of Endodontics, Stomatological Hospital of Chongqing Medical University; Chongqing Key Laboratory of Oral Diseases and Biomedical Sciences; Chongqing Municipal Key Laboratory of Oral Biomedical Engineering of Higher Education, Chongqing 401147, China
| | - Xue-Dan Zheng
- Dept. of Endodontics, Stomatological Hospital of Chongqing Medical University; Chongqing Key Laboratory of Oral Diseases and Biomedical Sciences; Chongqing Municipal Key Laboratory of Oral Biomedical Engineering of Higher Education, Chongqing 401147, China
| | - De-Qin Yang
- Dept. of Endodontics, Stomatological Hospital of Chongqing Medical University; Chongqing Key Laboratory of Oral Diseases and Biomedical Sciences; Chongqing Municipal Key Laboratory of Oral Biomedical Engineering of Higher Education, Chongqing 401147, China
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Zuccotti P, Peroni D, Potrich V, Quattrone A, Dassi E. Hyperconserved Elements in Human 5'UTRs Shape Essential Post-transcriptional Regulatory Networks. Front Mol Biosci 2020; 7:220. [PMID: 33005630 PMCID: PMC7484617 DOI: 10.3389/fmolb.2020.00220] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/29/2020] [Accepted: 08/05/2020] [Indexed: 01/03/2023] Open
Abstract
Post-transcriptional regulation (PTR) of gene expression is a powerful determinant of cellular phenotypes. The 5′ and 3′ untranslated regions of the mRNA (UTRs) mediate this role through sequence and secondary structure elements bound by RNA-binding proteins (RBPs) and non-coding RNAs. While functional regions in the 3′UTRs have been extensively studied, the 5′UTRs are still relatively uncharacterized. To fill this gap, we used a computational approach exploiting phylogenetic conservation to identify hyperconserved elements in human 5′UTRs (5′HCEs). Our assumption was that 5′HCEs would represent evolutionarily stable and hence important PTR sites. We identified over 5000 5′HCEs occurring in 10% of human protein-coding genes. These sequence elements are rather short and mostly found in narrowly-spaced clusters. 5′HCEs-containing genes are enriched in essential cellular functions and include 20% of all homeotic genes. Homeotic genes are essential transcriptional regulators, driving body plan and neuromuscular development. However, the role of PTR in their expression is mostly unknown. By integrating computational and experimental approaches we identified RBMX as the initiator RBP of a post-transcriptional cascade regulating many homeotic genes. This work thus establishes 5′HCEs as mediators of essential post-transcriptional regulatory networks.
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Affiliation(s)
- Paola Zuccotti
- Department of Cellular, Computational and Integrative Biology, University of Trento, Trento, Italy
| | - Daniele Peroni
- Department of Cellular, Computational and Integrative Biology, University of Trento, Trento, Italy
| | - Valentina Potrich
- Department of Cellular, Computational and Integrative Biology, University of Trento, Trento, Italy
| | - Alessandro Quattrone
- Department of Cellular, Computational and Integrative Biology, University of Trento, Trento, Italy
| | - Erik Dassi
- Department of Cellular, Computational and Integrative Biology, University of Trento, Trento, Italy
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Zhang Y, Feng X, Zhang J, Chen X. Iron Regulatory Protein 2 Exerts its Oncogenic Activities by Suppressing TAp63 Expression. Mol Cancer Res 2020; 18:1039-1049. [PMID: 32276991 DOI: 10.1158/1541-7786.mcr-19-1104] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2019] [Revised: 02/19/2020] [Accepted: 04/07/2020] [Indexed: 12/15/2022]
Abstract
Iron regulatory protein 2 (IRP2) is a key regulator of iron homeostasis and is found to be altered in several types of human cancer. However, how IRP2 contributes to tumorigenesis remains to be elucidated. In this study, we sought to investigate the role of IRP2 in tumorigenesis and found that IRP2 promotes cell growth by repressing TAp63, a member of p53 tumor suppressor family. Specifically, we found that IRP2 overexpression decreased, whereas IRP2 deficiency increased, TAp63 expression. We also showed that the repression of TAp63 by IRP2 was independent of tumor suppressor p53. To uncover the molecular basis, we found that IRP2 stabilized TAp63 mRNA by binding to an iron response element in the 3'UTR of p63 mRNA. To determine the biological significance of this regulation, we showed that IRP2 facilitates cell proliferation, at least in part, via repressing TAp63 expression. Moreover, we found that IRP2 deficiency markedly alleviated cellular senescence in TAp63-deficient mouse embryo fibroblasts. Together, we have uncovered a novel regulation of TAp63 by IRP2 and our data suggest that IRP2 exerts its oncogenic activities at least in part by repressing TAp63 expression. IMPLICATIONS: We have revealed a novel regulation of TAp63 by IRP2 and our data suggest that IRP2 exerts its oncogenic activities, at least in part, by repressing TAp63 expression.
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Affiliation(s)
- Yanhong Zhang
- Comparative Oncology Laboratory, Schools of Veterinary Medicine and Medicine, University of California at Davis, Davis, California
| | - Xiuli Feng
- Comparative Oncology Laboratory, Schools of Veterinary Medicine and Medicine, University of California at Davis, Davis, California
- College of Veterinary Medicine, Nanjing Agricultural University, Nanjing, China
| | - Jin Zhang
- Comparative Oncology Laboratory, Schools of Veterinary Medicine and Medicine, University of California at Davis, Davis, California
| | - Xinbin Chen
- Comparative Oncology Laboratory, Schools of Veterinary Medicine and Medicine, University of California at Davis, Davis, California.
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9
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Nash B, Tarn K, Irollo E, Luchetta J, Festa L, Halcrow P, Datta G, Geiger JD, Meucci O. Morphine-Induced Modulation of Endolysosomal Iron Mediates Upregulation of Ferritin Heavy Chain in Cortical Neurons. eNeuro 2019; 6:ENEURO.0237-19.2019. [PMID: 31300544 PMCID: PMC6675873 DOI: 10.1523/eneuro.0237-19.2019] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2019] [Accepted: 07/01/2019] [Indexed: 01/01/2023] Open
Abstract
HIV-associated neurocognitive disorders (HAND) remain prevalent and are aggravated by µ-opioid use. We have previously shown that morphine and other µ-opioids may contribute to HAND by inhibiting the homeostatic and neuroprotective chemokine receptor CXCR4 in cortical neurons, and this novel mechanism depends on upregulation of the protein ferritin heavy chain (FHC). Here, we examined the cellular events and potential mechanisms involved in morphine-mediated FHC upregulation using rat cortical neurons of either sex in vitro and in vivo. Morphine dose dependently increased FHC protein levels in primary neurons through µ-opioid receptor (µOR) and Gαi-protein signaling. Cytoplasmic FHC levels were significantly elevated, but nuclear FHC levels and FHC gene expression were unchanged. Morphine-treated rats also displayed increased FHC levels in layer 2/3 neurons of the prefrontal cortex. Importantly, both in vitro and in vivo FHC upregulation was accompanied by loss of mature dendritic spines, which was also dependent on µOR and Gαi-protein signaling. Moreover, morphine upregulated ferritin light chain (FLC), a component of the ferritin iron storage complex, suggesting that morphine altered neuronal iron metabolism. Indeed, prior to FHC upregulation, morphine increased cytoplasmic labile iron levels as a function of decreased endolysosomal iron. In line with this, chelation of endolysosomal iron (but not extracellular iron) blocked morphine-induced FHC upregulation and dendritic spine reduction, whereas iron overloading mimicked the effect of morphine on FHC and dendritic spines. Overall, these data demonstrate that iron mediates morphine-induced FHC upregulation and consequent dendritic spine deficits and implicate endolysosomal iron efflux to the cytoplasm in these effects.
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Affiliation(s)
- Bradley Nash
- Department of Pharmacology and Physiology, Drexel University College of Medicine, Philadelphia, PA 19102
| | - Kevin Tarn
- Department of Pharmacology and Physiology, Drexel University College of Medicine, Philadelphia, PA 19102
| | - Elena Irollo
- Department of Pharmacology and Physiology, Drexel University College of Medicine, Philadelphia, PA 19102
| | - Jared Luchetta
- Department of Pharmacology and Physiology, Drexel University College of Medicine, Philadelphia, PA 19102
| | - Lindsay Festa
- Department of Pharmacology and Physiology, Drexel University College of Medicine, Philadelphia, PA 19102
| | - Peter Halcrow
- Department of Biomedical Sciences, University of North Dakota School of Medicine and Health Sciences, Grand Forks, ND 58203
| | - Gaurav Datta
- Department of Biomedical Sciences, University of North Dakota School of Medicine and Health Sciences, Grand Forks, ND 58203
| | - Jonathan D Geiger
- Department of Biomedical Sciences, University of North Dakota School of Medicine and Health Sciences, Grand Forks, ND 58203
| | - Olimpia Meucci
- Department of Pharmacology and Physiology, Drexel University College of Medicine, Philadelphia, PA 19102
- Department of Microbiology and Immunology, Drexel University College of Medicine, Philadelphia, PA 19102
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Saadane A, Petrov A, Mast N, El-Darzi N, Dao T, Alnemri A, Song Y, Dunaief JL, Pikuleva IA. Mechanisms that minimize retinal impact of apolipoprotein E absence. J Lipid Res 2018; 59:2368-2382. [PMID: 30333155 DOI: 10.1194/jlr.m090043] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/25/2018] [Revised: 10/17/2018] [Indexed: 01/28/2023] Open
Abstract
Apolipoprotein E (APOE) is a component of lipid-transporting particles and a recognition ligand for receptors, which bind these particles. The APOE isoform ε2 is a risk factor for age-related macular degeneration; nevertheless, APOE absence in humans and mice does not significantly affect the retina. We found that retinal cholesterol biosynthesis and the levels of retinal cholesterol were increased in Apoe-/- mice, whereas cholesterol elimination by metabolism was decreased. No focal cholesterol deposits were observed in the Apoe-/- retina. Retinal proteomics identified the most abundant cholesterol-related proteins in WT mice and revealed that, of these cholesterol-related proteins, only APOA4 had increased expression in the Apoe-/- retina. In addition, there were changes in retinal abundance of proteins involved in proinflammatory and antiinflammatory responses, cellular cytoskeleton maintenance, vesicular traffic, and retinal iron homeostasis. The data obtained indicate that when APOE is absent, particles containing APOA1, APOA4, and APOJ still transport cholesterol in the intraretinal space, but these particles are not taken up by retinal cells. Therefore, cholesterol biosynthesis inside retinal cells increase, whereas metabolism to oxysterols decreases to prevent cells from cholesterol depletion. These and other compensatory changes underlie only a minor retinal phenotype in Apoe-/- mice.
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Affiliation(s)
- Aicha Saadane
- Department of Ophthalmology and Visual Sciences, Case Western Reserve University, Cleveland, OH
| | - Alexey Petrov
- Department of Ophthalmology and Visual Sciences, Case Western Reserve University, Cleveland, OH
| | - Natalia Mast
- Department of Ophthalmology and Visual Sciences, Case Western Reserve University, Cleveland, OH
| | - Nicole El-Darzi
- Department of Ophthalmology and Visual Sciences, Case Western Reserve University, Cleveland, OH
| | - Tung Dao
- Department of Ophthalmology and Visual Sciences, Case Western Reserve University, Cleveland, OH
| | - Ahab Alnemri
- F. M. Kirby Center for Molecular Ophthalmology, Scheie Eye Institute, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA
| | - Ying Song
- F. M. Kirby Center for Molecular Ophthalmology, Scheie Eye Institute, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA
| | - Joshua L Dunaief
- F. M. Kirby Center for Molecular Ophthalmology, Scheie Eye Institute, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA
| | - Irina A Pikuleva
- Department of Ophthalmology and Visual Sciences, Case Western Reserve University, Cleveland, OH
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Rendleman J, Cheng Z, Maity S, Kastelic N, Munschauer M, Allgoewer K, Teo G, Zhang YBM, Lei A, Parker B, Landthaler M, Freeberg L, Kuersten S, Choi H, Vogel C. New insights into the cellular temporal response to proteostatic stress. eLife 2018; 7:39054. [PMID: 30272558 PMCID: PMC6185107 DOI: 10.7554/elife.39054] [Citation(s) in RCA: 38] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2018] [Accepted: 09/28/2018] [Indexed: 12/13/2022] Open
Abstract
Maintaining a healthy proteome involves all layers of gene expression regulation. By quantifying temporal changes of the transcriptome, translatome, proteome, and RNA-protein interactome in cervical cancer cells, we systematically characterize the molecular landscape in response to proteostatic challenges. We identify shared and specific responses to misfolded proteins and to oxidative stress, two conditions that are tightly linked. We reveal new aspects of the unfolded protein response, including many genes that escape global translation shutdown. A subset of these genes supports rerouting of energy production in the mitochondria. We also find that many genes change at multiple levels, in either the same or opposing directions, and at different time points. We highlight a variety of putative regulatory pathways, including the stress-dependent alternative splicing of aminoacyl-tRNA synthetases, and protein-RNA binding within the 3’ untranslated region of molecular chaperones. These results illustrate the potential of this information-rich resource.
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Affiliation(s)
- Justin Rendleman
- Center for Genomics and Systems Biology, Department of Biology, New York University, New York, United States
| | - Zhe Cheng
- Center for Genomics and Systems Biology, Department of Biology, New York University, New York, United States
| | - Shuvadeep Maity
- Center for Genomics and Systems Biology, Department of Biology, New York University, New York, United States
| | - Nicolai Kastelic
- Berlin Institute for Medical Systems Biology, Max Delbrück Center for Molecular Medicine, Berlin, Germany
| | - Mathias Munschauer
- Berlin Institute for Medical Systems Biology, Max Delbrück Center for Molecular Medicine, Berlin, Germany
| | - Kristina Allgoewer
- Center for Genomics and Systems Biology, Department of Biology, New York University, New York, United States
| | - Guoshou Teo
- Center for Genomics and Systems Biology, Department of Biology, New York University, New York, United States
| | - Yun Bin Matteo Zhang
- Center for Genomics and Systems Biology, Department of Biology, New York University, New York, United States
| | - Amy Lei
- Center for Genomics and Systems Biology, Department of Biology, New York University, New York, United States
| | - Brian Parker
- Center for Genomics and Systems Biology, Department of Biology, New York University, New York, United States
| | - Markus Landthaler
- Berlin Institute for Medical Systems Biology, Max Delbrück Center for Molecular Medicine, Berlin, Germany.,Integrative Research Institute for the Life Sciences, Institute of Biology, Humboldt University, Berlin, Germany
| | | | | | - Hyungwon Choi
- National University of Singapore, Singapore.,Institute of Molecular and Cell Biology, Agency for Science, Technology and Research, Singapore
| | - Christine Vogel
- Center for Genomics and Systems Biology, Department of Biology, New York University, New York, United States
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12
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Lemler DJ, Lynch ML, Tesfay L, Deng Z, Paul BT, Wang X, Hegde P, Manz DH, Torti SV, Torti FM. DCYTB is a predictor of outcome in breast cancer that functions via iron-independent mechanisms. Breast Cancer Res 2017; 19:25. [PMID: 28270217 PMCID: PMC5341190 DOI: 10.1186/s13058-017-0814-9] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2016] [Accepted: 02/09/2017] [Indexed: 02/08/2023] Open
Abstract
BACKGROUND Duodenal cytochrome b (DCYTB) is a ferrireductase that functions together with divalent metal transporter 1 (DMT1) to mediate dietary iron reduction and uptake in the duodenum. DCYTB is also a member of a 16-gene iron regulatory gene signature (IRGS) that predicts metastasis-free survival in breast cancer patients. To better understand the relationship between DCYTB and breast cancer, we explored in detail the prognostic significance and molecular function of DCYTB in breast cancer. METHODS The prognostic significance of DCYTB expression was evaluated using publicly available microarray data. Signaling Pathway Impact Analysis (SPIA) of microarray data was used to identify potential novel functions of DCYTB. The role of DCYTB was assessed using immunohistochemistry and measurements of iron uptake, iron metabolism, and FAK signaling. RESULTS High DCYTB expression was associated with prolonged survival in two large independent cohorts, together totaling 1610 patients (cohort #1, p = 1.6e-11, n = 741; cohort #2, p = 1.2e-05, n = 869; log-rank test) as well as in the Gene expression-based Outcome for Breast cancer Online (GOBO) cohort (p < 1.0e-05, n = 1379). High DCYTB expression was also associated with increased survival in homogeneously treated groups of patients who received either tamoxifen or chemotherapy. Immunohistochemistry revealed that DCYTB is localized on the plasma membrane of breast epithelial cells, and that expression is dramatically reduced in high-grade tumors. Surprisingly, neither overexpression nor knockdown of DCYTB affected levels of ferritin H, transferrin receptor, labile iron or total cellular iron in breast cancer cells. Because SPIA pathway analysis of patient microarray data revealed an association between DCYTB and the focal adhesion pathway, we examined the influence of DCYTB on FAK activation in breast cancer cells. These experiments reveal that DCYTB reduces adhesion and activation of focal adhesion kinase (FAK) and its adapter protein paxillin. CONCLUSIONS DCYTB is an important predictor of outcome and is associated with response to therapy in breast cancer patients. DCYTB does not affect intracellular iron in breast cancer cells. Instead, DCYTB may retard cancer progression by reducing activation of FAK, a kinase that plays a central role in tumor cell adhesion and metastasis.
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Affiliation(s)
- David J. Lemler
- Department of Molecular Biology and Biophysics, University of Connecticut Health Center, Farmington, CT 06030 USA
- Present address: Department of Molecular Biomedical Sciences, North Carolina State University, CVM Research Building 474, Raleigh, NC 27695 USA
| | - Miranda L. Lynch
- Center for Quantitative Medicine, University of Connecticut Health Center, Farmington, CT 06030 USA
- Present address: Statistical Sciences Group CCS-6, Los Alamos National Laboratory, Los Alamos, NM 87545 USA
| | - Lia Tesfay
- Department of Molecular Biology and Biophysics, University of Connecticut Health Center, Farmington, CT 06030 USA
| | - Zhiyong Deng
- Department of Molecular Biology and Biophysics, University of Connecticut Health Center, Farmington, CT 06030 USA
| | - Bibbin T. Paul
- Department of Molecular Biology and Biophysics, University of Connecticut Health Center, Farmington, CT 06030 USA
| | - Xiaohong Wang
- Department of Pathology, University of Connecticut Health Center, Farmington, CT 06030 USA
| | - Poornima Hegde
- Department of Pathology, University of Connecticut Health Center, Farmington, CT 06030 USA
| | - David H. Manz
- Department of Molecular Biology and Biophysics, University of Connecticut Health Center, Farmington, CT 06030 USA
- School of Dental Medicine, University of Connecticut Health Center, Farmington, CT 06030 USA
| | - Suzy V. Torti
- Department of Molecular Biology and Biophysics, University of Connecticut Health Center, Farmington, CT 06030 USA
| | - Frank M. Torti
- Department of Medicine, University of Connecticut Health Center, Farmington, CT 06030 USA
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13
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Bose M, Bhattacharyya SN. Target-dependent biogenesis of cognate microRNAs in human cells. Nat Commun 2016; 7:12200. [PMID: 27448149 PMCID: PMC4961841 DOI: 10.1038/ncomms12200] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2015] [Accepted: 06/10/2016] [Indexed: 12/22/2022] Open
Abstract
Extensive research has established how miRNAs regulate target mRNAs by translation repression and/or endonucleolytic degradation in metazoans. However, information related to the effect of target mRNA on biogenesis and stability of corresponding miRNAs in animals is limited. Here we report regulated biogenesis of cognate miRNAs by their target mRNAs. Enhanced pre-miRNA processing by AGO-associated DICER1 contributes to this increased miRNP formation. The processed miRNAs are loaded onto AGO2 to form functionally competent miRISCs both in vivo and also in a cell-free in vitro system. Thus, we identify an additional layer of posttranscriptional regulation that helps the cell to maintain requisite levels of mature forms of respective miRNAs by modulating their processing in a target-dependent manner, a process happening for miR-122 during stress reversal in human hepatic cells. MicroRNAs are a widespread regulatory mechanism and are themselves extensively regulated. Here the authors show regulated miRNA biogenesis by the target mRNA, a layer of regulation that modulates miRNA levels dependent on target availability.
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Affiliation(s)
- Mainak Bose
- RNA Biology Research Laboratory, Molecular Genetics Division, CSIR-Indian Institute of Chemical Biology, 4, Raja SC Mullick Road, Kolkata 700032, India
| | - Suvendra N Bhattacharyya
- RNA Biology Research Laboratory, Molecular Genetics Division, CSIR-Indian Institute of Chemical Biology, 4, Raja SC Mullick Road, Kolkata 700032, India
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14
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Iron overload inhibits osteogenic commitment and differentiation of mesenchymal stem cells via the induction of ferritin. Biochim Biophys Acta Mol Basis Dis 2016; 1862:1640-9. [PMID: 27287253 DOI: 10.1016/j.bbadis.2016.06.003] [Citation(s) in RCA: 89] [Impact Index Per Article: 11.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2016] [Revised: 06/02/2016] [Accepted: 06/05/2016] [Indexed: 01/01/2023]
Abstract
Osteogenic differentiation of multipotent mesenchymal stem cells (MSCs) plays a crucial role in bone remodeling. Numerous studies have described the deleterious effect of iron overload on bone density and microarchitecture. Excess iron decreases osteoblast activity, leading to impaired extracellular matrix (ECM) mineralization. Additionally, iron overload facilitates osteoclast differentiation and bone resorption. These processes contribute to iron overload-associated bone loss. In this study we investigated the effect of iron on osteogenic differentiation of human bone marrow MSCs (BMSCs), the third player in bone remodeling. We induced osteogenic differentiation of BMSCs in the presence or absence of iron (0-50μmol/L) and examined ECM mineralization, Ca content of the ECM, mRNA and protein expressions of the osteogenic transcription factor runt-related transcription factor 2 (Runx2), and its targets osteocalcin (OCN) and alkaline phosphatase (ALP). Iron dose-dependently attenuated ECM mineralization and decreased the expressions of Runx2 and OCN. Iron accomplished complete inhibition of osteogenic differentiation of BMSCs at 50μmol/L concentration. We demonstrated that in response to iron BMSCs upregulated the expression of ferritin. Administration of exogenous ferritin mimicked the anti-osteogenic effect of iron, and blocked the upregulation of Runx2, OCN and ALP. Iron overload in mice was associated with elevated ferritin and decreased Runx2 mRNA levels in compact bone osteoprogenitor cells. The inhibitory effect of iron is specific toward osteogenic differentiation of MSCs as neither chondrogenesis nor adipogenesis were influenced by excess iron. We concluded that iron and ferritin specifically inhibit osteogenic commitment and differentiation of BMSCs both in vitro and in vivo.
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15
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Chiang S, Kovacevic Z, Sahni S, Lane DJR, Merlot AM, Kalinowski DS, Huang MLH, Richardson DR. Frataxin and the molecular mechanism of mitochondrial iron-loading in Friedreich's ataxia. Clin Sci (Lond) 2016; 130:853-70. [PMID: 27129098 DOI: 10.1042/cs20160072] [Citation(s) in RCA: 39] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2015] [Accepted: 02/16/2016] [Indexed: 12/19/2022]
Abstract
The mitochondrion is a major site for the metabolism of the transition metal, iron, which is necessary for metabolic processes critical for cell vitality. The enigmatic mitochondrial protein, frataxin, is known to play a significant role in both cellular and mitochondrial iron metabolism due to its iron-binding properties and its involvement in iron-sulfur cluster (ISC) and heme synthesis. The inherited neuro- and cardio-degenerative disease, Friedreich's ataxia (FA), is caused by the deficient expression of frataxin that leads to deleterious alterations in iron metabolism. These changes lead to the accumulation of inorganic iron aggregates in the mitochondrial matrix that are presumed to play a key role in the oxidative damage and subsequent degenerative features of this disease. Furthermore, the concurrent dys-regulation of cellular antioxidant defense, which coincides with frataxin deficiency, exacerbates oxidative stress. Hence, the pathogenesis of FA underscores the importance of the integrated homeostasis of cellular iron metabolism and the cytoplasmic and mitochondrial redox environments. This review focuses on describing the pathogenesis of the disease, the molecular mechanisms involved in mitochondrial iron-loading and the dys-regulation of cellular antioxidant defense due to frataxin deficiency. In turn, current and emerging therapeutic strategies are also discussed.
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Affiliation(s)
- Shannon Chiang
- Molecular Pharmacology and Pathology Program, Department of Pathology, University of Sydney, Sydney, New South Wales 2006, Australia
| | - Zaklina Kovacevic
- Molecular Pharmacology and Pathology Program, Department of Pathology, University of Sydney, Sydney, New South Wales 2006, Australia
| | - Sumit Sahni
- Molecular Pharmacology and Pathology Program, Department of Pathology, University of Sydney, Sydney, New South Wales 2006, Australia
| | - Darius J R Lane
- Molecular Pharmacology and Pathology Program, Department of Pathology, University of Sydney, Sydney, New South Wales 2006, Australia
| | - Angelica M Merlot
- Molecular Pharmacology and Pathology Program, Department of Pathology, University of Sydney, Sydney, New South Wales 2006, Australia
| | - Danuta S Kalinowski
- Molecular Pharmacology and Pathology Program, Department of Pathology, University of Sydney, Sydney, New South Wales 2006, Australia
| | - Michael L-H Huang
- Molecular Pharmacology and Pathology Program, Department of Pathology, University of Sydney, Sydney, New South Wales 2006, Australia )
| | - Des R Richardson
- Molecular Pharmacology and Pathology Program, Department of Pathology, University of Sydney, Sydney, New South Wales 2006, Australia )
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16
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Abstract
Cellular iron homeostasis is regulated by post-transcriptional feedback mechanisms, which control the expression of proteins involved in iron uptake, release and storage. Two cytoplasmic proteins with mRNA-binding properties, iron regulatory proteins 1 and 2 (IRP1 and IRP2) play a central role in this regulation. Foremost, IRPs regulate ferritin H and ferritin L translation and thus iron storage, as well as transferrin receptor 1 (TfR1) mRNA stability, thereby adjusting receptor expression and iron uptake via receptor-mediated endocytosis of iron-loaded transferrin. In addition splice variants of iron transporters for import and export at the plasma-membrane, divalent metal transporter 1 (DMT1) and ferroportin are regulated by IRPs. These mechanisms have probably evolved to maintain the cytoplasmic labile iron pool (LIP) at an appropriate level. In certain tissues, the regulation exerted by IRPs influences iron homeostasis and utilization of the entire organism. In intestine, the control of ferritin expression limits intestinal iron absorption and, thus, whole body iron levels. In bone marrow, erythroid heme biosynthesis is coordinated with iron availability through IRP-mediated translational control of erythroid 5-aminolevulinate synthase mRNA. Moreover, the translational control of HIF2α mRNA in kidney by IRP1 coordinates erythropoietin synthesis with iron and oxygen supply. Besides IRPs, body iron absorption is negatively regulated by hepcidin. This peptide hormone, synthesized and secreted by the liver in response to high serum iron, downregulates ferroportin at the protein level and thereby limits iron absorption from the diet. Hepcidin will not be discussed in further detail here.
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Affiliation(s)
- Lukas C Kühn
- Ecole Polytechnique Fédérale de Lausanne (EPFL), ISREC - Swiss Institute for Experimental Cancer Research, EPFL_SV_ISREC, Room SV2516, Station 19, CH-1015 Lausanne, Switzerland.
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17
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Cheng HT, Yen CJ, Chang CC, Huang KT, Chen KH, Zhang RY, Lee PY, Miaw SC, Huang JW, Chiang CK, Wu KD, Hung KY. Ferritin heavy chain mediates the protective effect of heme oxygenase-1 against oxidative stress. Biochim Biophys Acta Gen Subj 2015; 1850:2506-17. [PMID: 26423448 DOI: 10.1016/j.bbagen.2015.09.018] [Citation(s) in RCA: 43] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2015] [Revised: 08/30/2015] [Accepted: 09/24/2015] [Indexed: 12/12/2022]
Abstract
The phenomenon that heme oxygenase-1 (HO-1) protects cell from injury yet its enzymatic product, iron, may facilitate generation of free radical has been long puzzling. Here we establish a functional connection between ferritin heavy chain (FHC) and HO-1. In human lupus nephritis HO-1 and FHC are colocalized within the glomeruli. In rodent anti-Thy1 (thymocyte antigen 1) induced glomerulonephritis, heme oxygenase blockade lowers the expression of FHC and accelerates mesangial cell death. Stimulation of heme oxygenase in cultured rat mesangial cell enhances its resistance to hydrogen peroxide, whereas FHC knockdown by RNA interference compromises this salutary effect. RNA interference of HO-1 makes the cell more susceptible to hydrogen peroxide, which can be rescued by forced expression of wild-type FHC but not mutants that lose the capacity of iron storage and ferroxidase activity. Phosphorylation of JunD was not sustained in these cells. Microarray analysis identifies four candidate transcriptional factors that may regulate the HO-1-induced transcription of FHC. Our results support the role of FHC in neutralizing the iron toxicity as well as mediating the protective effect of HO-1 in response to oxidative stress.
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Affiliation(s)
- Hui-Teng Cheng
- Department of Internal Medicine, National Taiwan University Hospital Hsin-Chu Branch, Hsin Chu City 30059, Taiwan; Research Center for Developmental Biology and Regenerative Medicine, National Taiwan University, Taipei, Taiwan.
| | - Chung-Jen Yen
- Department of Internal Medicine, National Taiwan University Hospital, College of Medicine, National Taiwan University, Taipei 10002, Taiwan; Department of Geriatrics and Gerontology, National Taiwan University Hospital, College of Medicine, National Taiwan University, Taipei 10002, Taiwan
| | - Chen-Chih Chang
- Department of Internal Medicine, National Taiwan University Hospital, College of Medicine, National Taiwan University, Taipei 10002, Taiwan
| | - Kuo-Tong Huang
- Department of Internal Medicine, National Taiwan University Hospital, College of Medicine, National Taiwan University, Taipei 10002, Taiwan; Institute of Toxicology, College of Medicine, National Taiwan University, Taipei 10002, Taiwan
| | - Kuo-Hsuan Chen
- Department of Internal Medicine, National Taiwan University Hospital, College of Medicine, National Taiwan University, Taipei 10002, Taiwan
| | - Rui-Yang Zhang
- Department of Internal Medicine, National Taiwan University Hospital Hsin-Chu Branch, Hsin Chu City 30059, Taiwan
| | - Ping-Yi Lee
- Department of Internal Medicine, National Taiwan University Hospital, College of Medicine, National Taiwan University, Taipei 10002, Taiwan
| | - Shi-Chuen Miaw
- Graduate Institute of Immunology, College of Medicine, National Taiwan University, Taipei 10002, Taiwan
| | - Jenq-Wen Huang
- Department of Internal Medicine, National Taiwan University Hospital, College of Medicine, National Taiwan University, Taipei 10002, Taiwan.
| | - Chih-Kang Chiang
- Department of Internal Medicine, National Taiwan University Hospital, College of Medicine, National Taiwan University, Taipei 10002, Taiwan; Institute of Toxicology, College of Medicine, National Taiwan University, Taipei 10002, Taiwan; Department of Integrated Diagnostics and Therapeutics, National Taiwan University Hospital, College of Medicine, National Taiwan University, Taipei 10002, Taiwan.
| | - Kwan-Dun Wu
- Department of Internal Medicine, National Taiwan University Hospital, College of Medicine, National Taiwan University, Taipei 10002, Taiwan
| | - Kuan-Yu Hung
- Department of Internal Medicine, National Taiwan University Hospital, College of Medicine, National Taiwan University, Taipei 10002, Taiwan
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18
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White spot syndrome virus protein kinase 1 defeats the host cell's iron-withholding defense mechanism by interacting with host ferritin. J Virol 2014; 89:1083-93. [PMID: 25378496 DOI: 10.1128/jvi.02318-14] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
UNLABELLED Iron is an essential nutrient for nearly all living organisms, including both hosts and invaders. Proteins such as ferritin regulate the iron levels in a cell, and in the event of a pathogenic invasion, the host can use an iron-withholding mechanism to restrict the availability of this essential nutrient to the invading pathogens. However, pathogens use various strategies to overcome this host defense. In this study, we demonstrated that white spot syndrome virus (WSSV) protein kinase 1 (PK1) interacted with shrimp ferritin in the yeast two-hybrid system. A pulldown assay and 27-MHz quartz crystal microbalance (QCM) analysis confirmed the interaction between PK1 and both ferritin and apoferritin. PK1 did not promote the release of iron ions from ferritin, but it prevented apoferritin from binding ferrous ions. When PK1 was overexpressed in Sf9 cells, the cellular labile iron pool (LIP) levels were elevated significantly. Immunoprecipitation and atomic absorption spectrophotometry (AAS) further showed that the number of iron ions bound by ferritin decreased significantly at 24 h post-WSSV infection. Taken together, these results suggest that PK1 prevents apoferritin from iron loading, and thus stabilizes the cellular LIP levels, and that WSSV uses this novel mechanism to counteract the host cell's iron-withholding defense mechanism. IMPORTANCE We show here that white spot syndrome virus (WSSV) ensures the availability of iron by using a previously unreported mechanism to defeat the host cell's iron-withholding defense mechanism. This defense is often implemented by ferritin, which can bind up to 4,500 iron atoms and acts to sequester free iron within the cell. WSSV's novel counterstrategy is mediated by a direct protein-protein interaction between viral protein kinase 1 (PK1) and host ferritin. PK1 interacts with both ferritin and apoferritin, suppresses apoferritin's ability to sequester free iron ions, and maintains the intracellular labile iron pool (LIP), and thus the availability of free iron is increased within cells.
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19
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mRNA destabilization is the dominant effect of mammalian microRNAs by the time substantial repression ensues. Mol Cell 2014; 56:104-15. [PMID: 25263593 DOI: 10.1016/j.molcel.2014.08.028] [Citation(s) in RCA: 358] [Impact Index Per Article: 35.8] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2014] [Revised: 08/21/2014] [Accepted: 08/22/2014] [Indexed: 01/01/2023]
Abstract
MicroRNAs (miRNAs) regulate target mRNAs through a combination of translational repression and mRNA destabilization, with mRNA destabilization dominating at steady state in the few contexts examined globally. Here, we extend the global steady-state measurements to additional mammalian contexts and find that regardless of the miRNA, cell type, growth condition, or translational state, mRNA destabilization explains most (66%->90%) miRNA-mediated repression. We also determine the relative dynamics of translational repression and mRNA destabilization for endogenous mRNAs as a miRNA is induced. Although translational repression occurs rapidly, its effect is relatively weak, such that by the time consequential repression ensues, the effect of mRNA destabilization dominates. These results imply that consequential miRNA-mediated repression is largely irreversible and provide other insights into the nature of miRNA-mediated regulation. They also simplify future studies, dramatically extending the known contexts and time points for which monitoring mRNA changes captures most of the direct miRNA effects.
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20
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Theil EC. IRE mRNA riboregulators use metabolic iron (Fe(2+)) to control mRNA activity and iron chemistry in animals. Metallomics 2014; 7:15-24. [PMID: 25209685 DOI: 10.1039/c4mt00136b] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
Abstract
A family of noncoding RNAs bind Fe(2+) to increase protein synthesis. The structures occur in messenger RNAs encoding animal proteins for iron metabolism. Each mRNA regulatory sequence, ∼30 ribonucleotides long, is called an IRE (Iron Responsive Element), and folds into a bent, A-RNA helix with a terminal loop. Riboregulatory RNAs, like t-RNAs, r-RNAs micro-RNAs, etc. contrast with DNA, since single-stranded RNA can fold into a variety of complex, three-dimensional structures. IRE-RNAs bind two types of proteins: (1) IRPs which are protein repressors, sequence-related to mitochondrial aconitases. (2) eIF-4F, which bind ribosomes and enhances general protein biosynthesis. The competition between IRP and eIF-4F binding to IRE-RNA is controlled by Fe(2+)-induced changes in the IRE-RNA conformation. Mn(2+), which also binds to IRE-RNA in solution, is a convenient experimental proxy for air-sensitive Fe(2+) studies of in vitro protein biosynthesis and protein binding. However, only Fe(2+) has physiological effects on protein biosynthesis directed by IRE-mRNAs. The structures of the IRE-RNA riboregulators is known indirectly from effects of base substitutions on function, from solution NMR of the free RNA, and of X-ray crystallography of the IRE-RNA-IRP repressor complex. However, the inability to date, to crystallize the free IRE-RNA, and the dissociation of the IRE-RNA-IRP complex when metal binds, have hampered direct identification and characterization of the RNA-metal binding sites. The high conservation of the primary sequence in IRE-mRNA control elements has facilitated their identification and analysis of metal-assisted riboregulator function. Expansion of RNA search analyses beyond primary will likely reveal other, metal-dependent families of mRNA riboregulators.
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Affiliation(s)
- Elizabeth C Theil
- The Children's Hospital Oakland Research Institute, Oakland, CA 94609, USA.
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21
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Espinoza A, Morales S, Arredondo M. Effects of acute dietary iron overload in pigs (Sus scrofa) with induced type 2 diabetes mellitus. Biol Trace Elem Res 2014; 158:342-52. [PMID: 24699828 DOI: 10.1007/s12011-014-9944-4] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/19/2014] [Accepted: 03/12/2014] [Indexed: 01/29/2023]
Abstract
Epidemiological studies have reported an association between high iron (Fe) levels and elevated risk of developing type 2 diabetes mellitus (T2D). It is believed that the formation of Fe-catalyzed hydroxyl radicals may contribute to the development of diabetes. Our goal was to determine the effect of a diet with a high Fe content on type 2 diabetic pigs. Four groups of piglets were studied: (1) control group, basal diet; (2) Fe group, basal diet with 3,000 ppm ferrous sulfate; (3) diabetic group (streptozotocin-induced type 2 diabetes) with basal diet; (4) diabetic/Fe group, diabetic animals/3,000 ppm ferrous sulfate. For 2 months, biochemical and hematological parameters were evaluated. Tissue samples of liver and duodenum were obtained to determine mRNA relative abundance of DMT1, ferroportin (Fpn), ferritin (Fn), hepcidin (Hpc), and transferrin receptor by qRT-PCR. Fe group presented increased levels of hematological (erythrocytes, hematocrit, and hemoglobin) and iron parameters. Diabetic/Fe group showed similar behavior as Fe group but in lesser extent. The relative abundance of different genes in the four study groups yielded a different expression pattern. DMT1 showed a lower expression in the two iron groups compared with control and diabetic animals, and Hpc showed an increased on its expression in Fe and diabetic/Fe groups. Diabetic/Fe group presents greater expression of Fn and Fpn. These results suggest that there is an interaction between Fe nutrition, inflammation, and oxidative stress in the diabetes development.
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MESH Headings
- Analysis of Variance
- Animals
- Blood Glucose/metabolism
- C-Reactive Protein/metabolism
- Cation Transport Proteins/genetics
- Cholesterol/blood
- Cholesterol, LDL/blood
- Diabetes Mellitus, Experimental/blood
- Diabetes Mellitus, Experimental/genetics
- Diabetes Mellitus, Experimental/metabolism
- Diabetes Mellitus, Type 2/blood
- Diabetes Mellitus, Type 2/genetics
- Diabetes Mellitus, Type 2/metabolism
- Diet
- Duodenum/drug effects
- Duodenum/metabolism
- Ferritins/genetics
- Ferrous Compounds/administration & dosage
- Ferrous Compounds/metabolism
- Gene Expression/drug effects
- Hepcidins/genetics
- Iron Overload/metabolism
- Iron Overload/physiopathology
- Iron, Dietary/administration & dosage
- Iron, Dietary/metabolism
- Liver/drug effects
- Liver/metabolism
- Male
- Receptors, Transferrin/genetics
- Reverse Transcriptase Polymerase Chain Reaction
- Sus scrofa
- Time Factors
- Triglycerides/blood
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Affiliation(s)
- A Espinoza
- Micronutrient laboratory, Nutrition Institute and Food Technology (INTA), University of Chile, El Líbano 5524, Macul, Santiago, Chile
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23
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Carmona U, Zhang L, Li L, Münchgesang W, Pippel E, Knez M. Tuning, inhibiting and restoring the enzyme mimetic activities of Pt–apoferritin. Chem Commun (Camb) 2014; 50:701-3. [DOI: 10.1039/c3cc48000c] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Selective inhibition of the enzyme mimetic activity of nanoparticles and a novel way to recover the inhibited activity.
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Affiliation(s)
| | | | - Le Li
- CIC nanoGUNE
- 20018 Donostia-San Sebastian, Spain
| | | | - Eckhard Pippel
- Max Planck Institute of Microstructure Physics
- 06120 Halle, Germany
| | - Mato Knez
- CIC nanoGUNE
- 20018 Donostia-San Sebastian, Spain
- IKERBASQUE
- Basque Foundation for Science
- 48011 Bilbao, Spain
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24
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Klass DM, Scheibe M, Butter F, Hogan GJ, Mann M, Brown PO. Quantitative proteomic analysis reveals concurrent RNA-protein interactions and identifies new RNA-binding proteins in Saccharomyces cerevisiae. Genome Res 2013; 23:1028-38. [PMID: 23636942 PMCID: PMC3668357 DOI: 10.1101/gr.153031.112] [Citation(s) in RCA: 48] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
A growing body of evidence supports the existence of an extensive network of RNA-binding proteins (RBPs) whose combinatorial binding affects the post-transcriptional fate of every mRNA in the cell—yet we still do not have a complete understanding of which proteins bind to mRNA, which of these bind concurrently, and when and where in the cell they bind. We describe here a method to identify the proteins that bind to RNA concurrently with an RBP of interest, using quantitative mass spectrometry combined with RNase treatment of affinity-purified RNA–protein complexes. We applied this method to the known RBPs Pab1, Nab2, and Puf3. Our method significantly enriched for known RBPs and is a clear improvement upon previous approaches in yeast. Our data reveal that some reported protein–protein interactions may instead reflect simultaneous binding to shared RNA targets. We also discovered more than 100 candidate RBPs, and we independently confirmed that 77% (23/30) bind directly to RNA. The previously recognized functions of the confirmed novel RBPs were remarkably diverse, and we mapped the RNA-binding region of one of these proteins, the transcriptional coactivator Mbf1, to a region distinct from its DNA-binding domain. Our results also provided new insights into the roles of Nab2 and Puf3 in post-transcriptional regulation by identifying other RBPs that bind simultaneously to the same mRNAs. While existing methods can identify sets of RBPs that interact with common RNA targets, our approach can determine which of those interactions are concurrent—a crucial distinction for understanding post-transcriptional regulation.
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Affiliation(s)
- Daniel M Klass
- Department of Biochemistry, Stanford University School of Medicine, Stanford, California 94305, USA
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25
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Hou J, Yamada S, Kajikawa T, Ozaki N, Awata T, Yamaba S, Murakami S. Role of ferritin in the cytodifferentiation of periodontal ligament cells. Biochem Biophys Res Commun 2012; 426:643-8. [DOI: 10.1016/j.bbrc.2012.09.008] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2012] [Accepted: 09/02/2012] [Indexed: 10/27/2022]
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Beisang D, Bohjanen PR. Perspectives on the ARE as it turns 25 years old. WILEY INTERDISCIPLINARY REVIEWS-RNA 2012; 3:719-31. [PMID: 22733578 DOI: 10.1002/wrna.1125] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
The AU-rich element (ARE) was discovered in 1986 as a conserved mRNA sequence found in the 3' untranslated region of the TNF-α transcript and other transcripts encoding cytokines and inflammatory mediators. Shortly thereafter, the ARE was shown to function as a regulator of mRNA degradation, and AREs were later shown to regulate other posttranscriptional mechanisms such as translation and mRNA localization. AREs coordinately regulate networks of chemokine, cytokine, and growth regulatory transcripts involved in cellular activation, proliferation, and inflammation. ARE-mediated regulation is carried out by a host of ARE-binding proteins, whose activity is regulated in a cell type and activation-dependent manner. The last 25 years of ARE research has offered insight into the mechanisms and regulation of ARE-mediated mRNA decay, and has provided a road map for the discovery of additional mRNA regulatory motifs. The future of ARE research will transition from a discovery phase to a phase focused on translating basic biological findings into novel therapeutic targets. Our understanding of ARE-mediated gene regulation and posttranscriptional control has implications for many fields of study including developmental biology, neuroscience, immunobiology, and cancer biology.
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Affiliation(s)
- Daniel Beisang
- Department of Microbiology, Center for Infectious Diseases and Microbiology Translational Research, University of Minnesota, Minneapolis, MN, USA
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27
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Siddique A, Kowdley KV. Review article: the iron overload syndromes. Aliment Pharmacol Ther 2012; 35:876-93. [PMID: 22385471 DOI: 10.1111/j.1365-2036.2012.05051.x] [Citation(s) in RCA: 84] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/08/2011] [Revised: 06/26/2011] [Accepted: 02/08/2012] [Indexed: 12/12/2022]
Abstract
BACKGROUND Iron overload syndromes encompass a wide range of hereditary and acquired conditions. Major developments in the field of genetics and the discovery of hepcidin as a central regulator of iron homeostasis have greatly increased our understanding of the pathophysiology of iron overload syndromes. AIM To review advances in iron regulation and iron overload syndrome with special emphasis on hereditary haemochromatosis, the prototype iron overload syndrome. METHODS A PubMed search using words such as 'iron overload', 'hemochromatosis', 'HFE', 'Non-HFE', 'secondary iron overload' was undertaken. RESULTS Iron overload is associated with significant morbidity and mortality. Sensitive diagnostic tests and effective therapy are widely available and can prevent complications associated with iron accumulation in end- organs. Therapeutic phlebotomy remains the cornerstone of therapy for removal of excess body iron, but novel therapeutic agents including oral iron chelators have been developed for iron overload associated with anaemia. CONCLUSIONS Iron overload disorders are common. Inexpensive screening tests as well as confirmatory diagnostic tests are widely available. Increased awareness of the causes and importance of early diagnosis and knowledge of the appropriate use of genetic testing are encouraged. The availability of novel treatments should increase therapeutic options for patients with iron overload disorders.
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Affiliation(s)
- A Siddique
- Department of Hepatology, Virginia Mason Medical Center, Seattle, WA, USA.
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28
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Effects of novel neuroprotective and neurorestorative multifunctional drugs on iron chelation and glucose metabolism. J Neural Transm (Vienna) 2012; 120:37-48. [DOI: 10.1007/s00702-012-0795-x] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2012] [Accepted: 03/06/2012] [Indexed: 12/27/2022]
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29
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Huang MLH, Lane DJR, Richardson DR. Mitochondrial mayhem: the mitochondrion as a modulator of iron metabolism and its role in disease. Antioxid Redox Signal 2011; 15:3003-19. [PMID: 21545274 DOI: 10.1089/ars.2011.3921] [Citation(s) in RCA: 75] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
The mitochondrion plays vital roles in various aspects of cellular metabolism, ranging from energy transduction and apoptosis to the synthesis of important molecules such as heme. Mitochondria are also centrally involved in iron metabolism, as exemplified by disruptions in mitochondrial proteins that lead to perturbations in whole-cell iron processing. Recent investigations have identified a host of mitochondrial proteins (e.g., mitochondrial ferritin; mitoferrins 1 and 2; ABCBs 6, 7, and 10; and frataxin) that may play roles in the homeostasis of mitochondrial iron. These mitochondrial proteins appear to participate in one or more processes of iron storage, iron uptake, and heme and iron-sulfur cluster synthesis. In this review, we present and critically discuss the evidence suggesting that the mitochondrion may contribute to the regulation of whole-cell iron metabolism. Further, human diseases that arise from a dysregulation of these mitochondrial molecules reveal the ability of the mitochondrion to communicate with cytosolic iron metabolism to coordinate whole-cell iron processing and to fulfill the high demands of this organelle for iron. This review highlights new advances in understanding iron metabolism in terms of novel molecular players and diseases associated with its dysregulation.
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Affiliation(s)
- Michael Li-Hsuan Huang
- Iron Metabolism and Chelation Program, Department of Pathology and Bosch Institute, University of Sydney, Sydney, New South Wales, Australia
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Bourseau-Guilmain E, Griveau A, Benoit JP, Garcion E. The importance of the stem cell marker prominin-1/CD133 in the uptake of transferrin and in iron metabolism in human colon cancer Caco-2 cells. PLoS One 2011; 6:e25515. [PMID: 21966538 PMCID: PMC3180456 DOI: 10.1371/journal.pone.0025515] [Citation(s) in RCA: 55] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2011] [Accepted: 09/07/2011] [Indexed: 12/22/2022] Open
Abstract
As the pentaspan stem cell marker CD133 was shown to bind cholesterol and to localize in plasma membrane protrusions, we investigated a possible function for CD133 in endocytosis. Using the CD133 siRNA knockdown strategy and non-differentiated human colon cancer Caco-2 cells that constitutively over-expressed CD133, we provide for the first time direct evidence for a role of CD133 in the intracellular accumulation of fluorescently labeled extracellular compounds. Assessed using AC133 monoclonal antibody, CD133 knockdown was shown to improve Alexa488-transferrin (Tf) uptake in Caco-2 cells but had no impact on FITC-dextran or FITC-cholera-toxin. Absence of effect of the CD133 knockdown on Tf recycling established a role for CD133 in inhibiting Tf endocytosis rather than in stimulating Tf exocytosis. Use of previously identified inhibitors of known endocytic pathways and the positive impact of CD133 knockdown on cellular uptake of clathrin-endocytosed synthetic lipid nanocapsules supported that CD133 impact on endocytosis was primarily ascribed to the clathrin pathway. Also, cholesterol extraction with methyl-β-cyclodextrine up regulated Tf uptake at greater intensity in the CD133high situation than in the CD133low situation, thus suggesting a role for cholesterol in the inhibitory effect of CD133 on endocytosis. Interestingly, cell treatment with the AC133 antibody down regulated Tf uptake, thus demonstrating that direct extracellular binding to CD133 could affect endocytosis. Moreover, flow cytometry and confocal microscopy established that down regulation of CD133 improved the accessibility to the TfR from the extracellular space, providing a mechanism by which CD133 inhibited Tf uptake. As Tf is involved in supplying iron to the cell, effects of iron supplementation and deprivation on CD133/AC133 expression were investigated. Both demonstrated a dose-dependent down regulation here discussed to the light of transcriptional and post-transciptional effects. Taken together, these data extend our knowledge of the function of CD133 and underline the interest of further exploring the CD133-Tf-iron network.
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Affiliation(s)
- Erika Bourseau-Guilmain
- Laboratoire d'Ingénierie de la Vectorisation Particulaire, Inserm, UMR-S 646, Université d'Angers, Angers, France
| | - Audrey Griveau
- Laboratoire d'Ingénierie de la Vectorisation Particulaire, Inserm, UMR-S 646, Université d'Angers, Angers, France
| | - Jean-Pierre Benoit
- Laboratoire d'Ingénierie de la Vectorisation Particulaire, Inserm, UMR-S 646, Université d'Angers, Angers, France
| | - Emmanuel Garcion
- Laboratoire d'Ingénierie de la Vectorisation Particulaire, Inserm, UMR-S 646, Université d'Angers, Angers, France
- * E-mail:
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Speeckaert MM, Speeckaert R, Delanghe JR. Biological and clinical aspects of soluble transferrin receptor. Crit Rev Clin Lab Sci 2011; 47:213-28. [DOI: 10.3109/10408363.2010.550461] [Citation(s) in RCA: 74] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
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Takami T, Sakaida I. Iron regulation by hepatocytes and free radicals. J Clin Biochem Nutr 2011; 48:103-6. [PMID: 21373260 PMCID: PMC3045680 DOI: 10.3164/jcbn.10-76] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2010] [Accepted: 07/13/2010] [Indexed: 12/21/2022] Open
Abstract
Iron is an essential metallic microelement for life. However, iron overload is toxic. The liver serves an important role as a storehouse for iron in the body. About 20–25 mg of iron is required each day for hemoglobin synthesis. To maintain iron homeostasis, transferrin and transferrin receptors are primarily involved in the uptake of iron into hepatocytes, ferritin in its storage, and ferroportin in its export. Moreover, hepcidin controls ferroportin and plays a central role in the iron metabolism. Excess “free” reactive iron produces damaging free radicals via Fenton or Harber-Weiss reactions. Produced free radicals attack cellular proteins, lipids and nucleic acid. Several detoxification system and anti-oxidant defense mechanisms exist to prevent cellular damage by free radicals. Excessive free radicals can lead to hepatocellular damage, liver fibrosis, and hepatocarcinogenesis.
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Affiliation(s)
- Taro Takami
- Division of Laboratory, Yamaguchi University Hospital, 1-1-1 Minami-kogushi, Ube, Yamaguchi 755-8505, Japan
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Martin FM, Xu X, von Löhneysen K, Gilmartin TJ, Friedman JS. SOD2 deficient erythroid cells up-regulate transferrin receptor and down-regulate mitochondrial biogenesis and metabolism. PLoS One 2011; 6:e16894. [PMID: 21326867 PMCID: PMC3033911 DOI: 10.1371/journal.pone.0016894] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2010] [Accepted: 01/05/2011] [Indexed: 01/19/2023] Open
Abstract
Background Mice irradiated and reconstituted with hematopoietic cells lacking manganese superoxide dismutase (SOD2) show a persistent hemolytic anemia similar to human sideroblastic anemia (SA), including characteristic intra-mitochondrial iron deposition. SA is primarily an acquired, clonal marrow disorder occurring in individuals over 60 years of age with uncertain etiology. Methodology/Principal Findings To define early events in the pathogenesis of this murine model of SA, we compared erythroid differentiation of Sod2-/- and normal bone marrow cells using flow cytometry and gene expression profiling of erythroblasts. The predominant transcriptional differences observed include widespread down-regulation of mitochondrial metabolic pathways and mitochondrial biogenesis. Multiple nuclear encoded subunits of complexes I-IV of the electron transport chain, ATP synthase (complex V), TCA cycle and mitochondrial ribosomal proteins were coordinately down-regulated in Sod2-/- erythroblasts. Despite iron accumulation within mitochondria, we found increased expression of transferrin receptor, Tfrc, at both the transcript and protein level in SOD2 deficient cells, suggesting deregulation of iron delivery. Interestingly, there was decreased expression of ABCb7, the gene responsible for X-linked hereditary SA with ataxia, a component required for iron-sulfur cluster biogenesis. Conclusions/Significance These results indicate that in erythroblasts, mitochondrial oxidative stress reduces expression of multiple nuclear genes encoding components of the respiratory chain, TCA cycle and mitochondrial protein synthesis. An additional target of particular relevance for SA is iron:sulfur cluster biosynthesis. By decreasing transcription of components of cluster synthesis machinery, both iron utilization and regulation of iron uptake are impacted, contributing to the sideroblastic phenotype.
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Affiliation(s)
- Florent M. Martin
- Department of Molecular and Experimental Medicine, The Scripps Research Institute, La Jolla, California, United States of America
| | - Xiuling Xu
- Department of Molecular and Experimental Medicine, The Scripps Research Institute, La Jolla, California, United States of America
| | - Katharina von Löhneysen
- Department of Molecular and Experimental Medicine, The Scripps Research Institute, La Jolla, California, United States of America
| | - Timothy J. Gilmartin
- DNA Array Core Facility, The Scripps Research Institute, La Jolla, California, United States of America
| | - Jeffrey S. Friedman
- Department of Molecular and Experimental Medicine, The Scripps Research Institute, La Jolla, California, United States of America
- * E-mail:
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Millonig G, Muckenthaler MU, Mueller S. Hyperferritinaemia-cataract syndrome: worldwide mutations and phenotype of an increasingly diagnosed genetic disorder. Hum Genomics 2010; 4:250-62. [PMID: 20511138 PMCID: PMC3525215 DOI: 10.1186/1479-7364-4-4-250] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
The hereditary hyperferritinaemia-cataract syndrome (HHCS) is characterised by an autosomal dominant cataract and high levels of serum ferritin without iron overload. The cataract develops due to L-ferritin deposits in the lens and its pulverulent aspect is pathognomonic. The syndrome is caused by mutations within the iron-responsive element of L-ferritin. These mutations prevent efficient binding of iron regulatory proteins 1 and 2 to the IRE in L-ferritin mRNA, resulting in an unleashed ferritin translation. This paper reviews all 31 mutations (27 single nucleotide transitions and four deletions) that have been described since 1995. Laboratory test showing hyperferritinaemia, normal serum iron and normal transferrin saturation are indicative for HHCS after exclusion of other causes of increased ferritin levels (inflammation, malignancy, alcoholic liver disease) and should prompt an ophthalmological consultation for diagnostic confirmation. Invasive diagnostics such as liver biopsy are not indicated. HHCS is an important differential diagnosis of hyperferritinaemia. Haematologists, gastroenterologists and ophthalmologists should be aware of this syndrome to spare patients from further invasive diagnosis (liver biopsy), and also from a false diagnosis of hereditary haemochromatosis followed by venesections. Patients diagnosed with HHCS should be counselled regarding the relative harmlessness of this genetic disease, with early cataract surgery as the only clinical consequence.
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Affiliation(s)
- Gunda Millonig
- Center for Alcohol Research and Salem Medical Center, University of Heidelberg, Heidelberg, Germany.
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Campillos M, Cases I, Hentze MW, Sanchez M. SIREs: searching for iron-responsive elements. Nucleic Acids Res 2010; 38:W360-7. [PMID: 20460462 PMCID: PMC2896125 DOI: 10.1093/nar/gkq371] [Citation(s) in RCA: 59] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023] Open
Abstract
The iron regulatory protein/iron-responsive element regulatory system plays a crucial role in the post-transcriptional regulation of gene expression and its disruption results in human disease. IREs are cis-acting regulatory motifs present in mRNAs that encode proteins involved in iron metabolism. They function as binding sites for two related trans-acting factors, namely the IRP-1 and -2. Among cis-acting RNA regulatory elements, the IRE is one of the best characterized. It is defined by a combination of RNA sequence and structure. However, currently available programs to predict IREs do not show a satisfactory level of sensitivity and fail to detect some of the functional IREs. Here, we report an improved software for the prediction of IREs implemented as a user-friendly web server tool. The SIREs web server uses a simple data input interface and provides structure analysis, predicted RNA folds, folding energy data and an overall quality flag based on properties of well characterized IREs. Results are reported in a tabular format and as a schematic visual representation that highlights important features of the IRE. The SIREs (Search for iron-responsive elements) web server is freely available on the web at http://ccbg.imppc.org/sires/index.html
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Affiliation(s)
- Monica Campillos
- European Molecular Biology Laboratory, Meyerhofstrasse 1, 69117 Heidelberg, Germany
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Abstract
Hemochromatosis is a known cause of osteoporosis, and iron overload has deleterious effects on bone. Although iron overload and its association with osteoporosis has long been recognized, the pathogenesis and exact role of iron have been undefined. Bone is an active tissue with constant remodeling capacity. Osteoblast (OB) development and maturation are under the influence of core binding factor alpha-1 (CBF-alpha1), which induces expression of OB-specific genes, including alkaline phosphatase, an important enzyme in early osteogenesis, and osteocalcin, a noncollagenous protein deposited within the osteoid. This study investigates the mechanism by which iron inhibits human OB activity, which in vivo may lead to decreased mineralization, osteopenia, and osteoporosis. We demonstrate that iron-provoked inhibition of OB activity is mediated by ferritin and its ferroxidase activity. We confirm this notion by using purified ferritin H-chain and ceruloplasmin, both known to possess ferroxidase activity that inhibited calcification, whereas a site-directed mutant of ferritin H-chain lacking ferroxidase activity failed to provide any inhibition. Furthermore, we are reporting that such suppression is not restricted to inhibition of calcification, but OB-specific genes such as alkaline phosphatase, osteocalcin, and CBF-alpha1 are all downregulated by ferritin in a dose-responsive manner. This study corroborates that iron decreases mineralization and demonstrates that this suppression is provided by iron-induced upregulation of ferritin. In addition, we conclude that inhibition of OB activity, mineralization, and specific gene expression is attributed to the ferroxidase activity of ferritin.
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Theil EC, Goss DJ. Living with iron (and oxygen): questions and answers about iron homeostasis. Chem Rev 2009; 109:4568-79. [PMID: 19824701 PMCID: PMC2919049 DOI: 10.1021/cr900052g] [Citation(s) in RCA: 172] [Impact Index Per Article: 11.5] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Affiliation(s)
- Elizabeth C Theil
- CHORI (Children's Hospital Oakland Research Institute), Oakland, California 94609, USA.
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Ovariectomy and estrogen treatment modulate iron metabolism in rat adipose tissue. Biochem Pharmacol 2009; 78:1001-7. [PMID: 19501056 DOI: 10.1016/j.bcp.2009.05.034] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2009] [Revised: 05/26/2009] [Accepted: 05/26/2009] [Indexed: 11/21/2022]
Abstract
Iron is essential for many biological processes and its deficiency or excess is involved in pathological conditions. At cellular level, the maintenance of iron homeostasis is largely accomplished by the transferrin receptor (TfR-1) and by ferritin, whose expression is mainly regulated post-transcriptionally by iron regulatory proteins (IRPs). This study examines the hypothesis that modification of serum estrogen levels by ovariectomy and 17beta-estradiol (E(2)) treatment in rats modulate serum iron-status parameters and iron metabolism in adipose tissue. In particular, we evaluated the RNA binding of IRP1 by electrophoretic mobility-shift assay and IRP1, ferritin, and TfR-1 expression in adipose tissue by Western blot analysis. Ovariectomy, besides a lowered serum iron and transferrin iron binding capacity, remarkably decreased the binding activity of IRP1 in peritoneal and subcutaneous adipose tissues, and these effects were reversed by E(2) treatment. Moreover, ovariectomy determined a decrease of IRP1 expression, which was significant in subcutaneous adipose tissue. Consistent with IRP1 regulation, an increase of ferritin and a decrease of TfR-1 expression were observed in peritoneal adipose tissue from ovariectomized animals, while the treatment with E(2) reconstituted TfR-1 level. A similar expression profile of TfR-1 was observed in subcutaneous adipose tissue, where ferritin level did not change in ovariectomized animals, and was increased after E(2) treatment. Our results indicate that estrogen level changes can regulate the binding activity of the IRP1, and consequently ferritin and TfR-1 expression in adipose tissue, suggesting a relationship among serum and tissue iron parameters, estrogen status and adiposity.
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Maffettone C, De Martino L, Irace C, Santamaria R, Pagnini U, Iovane G, Colonna A. Expression of iron-related proteins during infection by bovine herpes virus type-1. J Cell Biochem 2008; 104:213-23. [PMID: 17990282 DOI: 10.1002/jcb.21618] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
Abstract
Bovine herpesvirus 1 (BHV-1), a dsDNA animal virus, is an economically important pathogen of cattle and the aetiological agent of many types of disease. The efficient replication of a DNA virus is strictly dependent on iron since this metal plays a crucial role in the catalytic center of viral ribonucleotide reductase. Consequently, iron metabolism is an important area for virus/host interaction and a large body of evidence suggests that viral infection is potentially influenced by the iron status of the host. The aim of the present study was to address the effects of BHV-1 on iron metabolism in Madin-Darby bovine kidney (MDBK) cells at different times of post-infection. For this purpose, cell viability, iron regulatory proteins (IRPs) activity and levels, transferrin receptor 1 (TfR-1), ferritin expression and LIP were evaluated. Our data demonstrate that a productive BHV-1 infection in MDBK cells determines an overall decrease of IRPs RNA-binding activity without affecting their expression. As consequence of this modulation, an increased ferritin mRNA translation and a decreased TfR-1 mRNA translation were also observed. Moreover, the LIP level was decreased following viral infection. These results are consistent with the hypothesis that by reducing the iron up-take and by enhancing the sequestration of free iron, animal cells will limit the iron availability for virus proliferation. Therefore, the results presented herein support the view that iron metabolism could be critical for the interaction between DNA viruses, such as BHV-1, and mammalian cells. Delineation of the interplay among pathogen and host may provide new antimicrobial agents.
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Affiliation(s)
- Carmen Maffettone
- Dipartimento di Farmacologia Sperimentale, Università di Napoli Federico II, via D. Montesano 49, I-80131 Napoli, Italy
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Wang W, Di X, D'Agostino RB, Torti SV, Torti FM. Excess capacity of the iron regulatory protein system. J Biol Chem 2007; 282:24650-9. [PMID: 17604281 DOI: 10.1074/jbc.m703167200] [Citation(s) in RCA: 58] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Iron regulatory proteins (IRP1 and IRP2) are master regulators of cellular iron metabolism. IRPs bind to iron-responsive elements (IREs) present in the untranslated regions of mRNAs encoding proteins of iron storage, uptake, transport, and export. Because simultaneous knockout of IRP1 and IRP2 is embryonically lethal, it has not been possible to use dual knockouts to explore the consequences of loss of both IRP1 and IRP2 in mammalian cells. In this report, we describe the use of small interfering RNA to assess the relative contributions of IRP1 and IRP2 in epithelial cells. Stable cell lines were created in which either IRP1, IRP2, or both were knocked down. Knockdown of IRP1 decreased IRE binding activity but did not affect ferritin H and transferrin receptor 1 (TfR1) expression, whereas knockdown of IRP2 marginally affected IRE binding activity but caused an increase in ferritin H and a decrease in TfR1. Knockdown of both IRPs resulted in a greater reduction of IRE binding activity and more severe perturbation of ferritin H and TfR1 expression compared with single IRP knockdown. Even though the knockdown of IRP-1, IRP-2, or both was efficient, resulting in nondetectable protein and under 5% of wild type levels of mRNA, all stable knockdowns retained an ability to modulate ferritin H and TfR1 appropriately in response to iron challenge. However, further knockdown of IRPs accomplished by transient transfection of small interfering RNA in stable knockdown cells completely abolished the response of ferritin H and TfR1 to iron challenge, demonstrating an extensive excess capacity of the IRP system.
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Affiliation(s)
- Wei Wang
- Department of Cancer Biology, Public Health Sciences, Wake Forest University Health Sciences, Winston-Salem, North Carolina 27157, USA
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42
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Berg JM. Metal-Binding Domains in Nucleic Acid-Binding and Gene-Regulatory Proteins. PROGRESS IN INORGANIC CHEMISTRY 2007. [DOI: 10.1002/9780470166383.ch3] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
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Theil EC. The ferritin family of iron storage proteins. ADVANCES IN ENZYMOLOGY AND RELATED AREAS OF MOLECULAR BIOLOGY 2006; 63:421-49. [PMID: 2407067 DOI: 10.1002/9780470123096.ch7] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
The ferritins are a family of proteins produced in a variety of amounts and types depending on the state of development of an animal, or the state of differentiation of a particular cell type, or the environment. Iron storage is the main function of the ferritins when iron is needed for intracellular use (housekeeping) for iron proteins such as ribonucleotide reductase, cytochromes, oxidases, nitrogenases, or photosynthetic reaction centers or for extracellular use by other cells (specialized). Under abnormal conditions, such as the breach of transferrin-receptor-controlled incorporation of iron, ferritin can also serve to detoxify excess intracellular iron. The structure of ferritin is very complex, consisting of a protein coat of 24 polypeptide subunits, approximately 20 kDa, which surrounds an inorganic phase of hydrous ferric oxide. The polypeptide subunits, bundles of four alpha helices, display remarkable conservation of sequence among plants and animals, which is probably related to the necessity of forming the hollow sphere pierced by 14 channels through which iron may pass. In spite of the conserved regions of sequence, there are multiple genes for ferritin polypeptide subunits within an organism; at the moment three distinct subunit types, H H'(or M), and L, have been identified which are expressed in a cell-specific fashion. How many different subunit types exist, the influence on function, and the number of genes required to encode them are currently being actively investigated. Not only does the protein coat of ferritin display variations, the inorganic phase of ferritin can vary as well. For instance, differences can occur in the number of Fe atoms (up to 4500), as well as in the phosphorus content and in the degree of hydration and order. Such observations have depended on the use of a variety of physical techniques such as X-ray diffraction, EXAFS, and Mössbauer spectroscopy. The same approaches, as well as EPR spectroscopy, have been used to monitor the path taken by Fe as it passes from mononuclear Fe(II) outside the protein coat to polynuclear Fe(III) inside the protein coat. Both mononuclear Fe(II) and Fe(III) have been observed, as well as dimeric Fe(II)-O-Fe(III), and Fe(III)-oxo bridged clusters attached to the protein. A possible protein site for the Fe(III) cluster is a groove on the inner surface of the dimeric interface, suggested by the structure and from the affect of natural cross-links between subunit pairs.(ABSTRACT TRUNCATED AT 400 WORDS)
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Affiliation(s)
- E C Theil
- North Carolina State University, Raleigh 27695
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Schranzhofer M, Schifrer M, Cabrera JA, Kopp S, Chiba P, Beug H, Müllner EW. Remodeling the regulation of iron metabolism during erythroid differentiation to ensure efficient heme biosynthesis. Blood 2006; 107:4159-67. [PMID: 16424395 DOI: 10.1182/blood-2005-05-1809] [Citation(s) in RCA: 69] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Terminal erythropoiesis is accompanied by extreme demand for iron to ensure proper hemoglobinization. Thus, erythroblasts must modify the "standard" post-transcriptional feedback regulation, balancing expression of ferritin (Fer; iron storage) versus transferrin receptor (TfR1; iron uptake) via specific mRNA binding of iron regulatory proteins (IRPs). Although erythroid differentiation involves high levels of incoming iron, TfR1 mRNA stability must be sustained and Fer mRNA translation must not be activated because iron storage would counteract hemoglobinization. Furthermore, translation of the erythroid-specific form of aminolevulinic acid synthase (ALAS-E) mRNA, catalyzing the first step of heme biosynthesis and regulated similarly as Fer mRNA by IRPs, must be ensured. We addressed these questions using mass cultures of primary murine erythroid progenitors from fetal liver, either undergoing sustained proliferation or highly synchronous differentiation. We indeed observed strong inhibition of Fer mRNA translation and efficient ALAS-E mRNA translation in differentiating erythroblasts. Moreover, in contrast to self-renewing cells, TfR1 stability and IRP mRNA binding were no longer modulated by iron supply. These and additional data stemming from inhibition of heme synthesis with succinylacetone or from iron overload suggest that highly efficient utilization of iron in mitochondrial heme synthesis during normal erythropoiesis alters the regulation of iron metabolism via the IRE/IRP system.
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Affiliation(s)
- Matthias Schranzhofer
- Department of Medical Biochemistry, Division of Molecular Biology, Max F. Perutz Laboratories, University Departments at the Vienna Biocenter, Medical University of Vienna, Dr Bohr-Gasse 9, A-1030 Vienna, Austria
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45
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You SA, Wang Q. Ferritin in atherosclerosis. Clin Chim Acta 2005; 357:1-16. [PMID: 15963791 DOI: 10.1016/j.cccn.2005.02.001] [Citation(s) in RCA: 88] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2004] [Revised: 01/25/2005] [Accepted: 02/01/2005] [Indexed: 11/20/2022]
Abstract
Iron, an essential element for many important cellular functions in all living organisms, can catalyze the formation of potentially toxic free radicals. Excessive iron is sequestered by ferritin in a nontoxic and readily available form in a cell. Ferritin is composed of 24 subunits of different proportions of two functionally distinct subunits: ferritin H and L. The former is involved in ferroxidase activity necessary for iron uptake and oxidation of ferrous iron, while the latter is involved in nucleation of the iron core. The expression of ferritin is under delicate control and is regulated at both the transcriptional and posttranscriptional levels by iron, cytokines and oxidative stress. Elevated ferritin levels are associated with an increased risk of atherosclerotic coronary artery disease (CAD), the leading cause of death and illness in developed countries. Serum ferritin levels are a good indicator of iron stores in the body. In fact, epidemiological studies have suggested that elevated serum ferritin levels are associated with an increased risk of CAD and myocardial infarction (MI), though inconsistent results were obtained in some other studies. Moreover, recent proteomics and molecular biology studies have shown that ferritin levels in arteries are increased in diseased tissues, which further supports the link of ferritin to CAD/MI. Future studies will determine whether increased ferritin levels can serve as a distinct biomarker for the incidence of CAD/MI and distinguish whether increased ferritin levels are a cause of CAD or a consequence of the disease process.
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Affiliation(s)
- Sun-Ah You
- Center for Molecular Genetics, Department of Molecular Cardiology, ND4-38, Lerner Research Institute, and Center for Cardiovascular Genetics, The Cleveland Clinic Foundation, 9500 Euclid Ave., Cleveland, OH 44195, USA
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Cadet E, Gadenne M, Capron D, Rochette J. [Advances in iron metabolism: a transition state]. Rev Med Interne 2004; 26:315-24. [PMID: 15820567 DOI: 10.1016/j.revmed.2004.09.024] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/06/2004] [Accepted: 09/19/2004] [Indexed: 11/16/2022]
Abstract
PURPOSE Advances towards the understanding of gene regulation and protein function recently discovered through iron metabolism disorders are the subject of this review. CURRENT KNOWLEDGE AND KEY POINTS Within a few years the discovery of genes that determine heritable defects of cellular iron uptake or regulation in mice as in humans have provided new insights for investigation into iron metabolism pathways. FUTURE PROSPECTS AND PROJECTS It is still unclear how connections are made between new proteins in iron uptake, trafficking and regulation of iron homeostasis. Gene expression studies using microarrays technology in different iron conditions should help to explore iron homeostasis further.
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Affiliation(s)
- E Cadet
- Service de génétique moléculaire médicale et UPRES EA 2629, CHU d'Amiens, université de Picardie-Jules-Verne, 3, rue des Louvels, 80036 Amiens cedex, France.
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Wiemann S, Arlt D, Huber W, Wellenreuther R, Schleeger S, Mehrle A, Bechtel S, Sauermann M, Korf U, Pepperkok R, Sültmann H, Poustka A. From ORFeome to biology: a functional genomics pipeline. Genome Res 2004; 14:2136-44. [PMID: 15489336 PMCID: PMC528930 DOI: 10.1101/gr.2576704] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
As several model genomes have been sequenced, the elucidation of protein function is the next challenge toward the understanding of biological processes in health and disease. We have generated a human ORFeome resource and established a functional genomics and proteomics analysis pipeline to address the major topics in the post-genome-sequencing era: the identification of human genes and splice forms, and the determination of protein localization, activity, and interaction. Combined with the understanding of when and where gene products are expressed in normal and diseased conditions, we create information that is essential for understanding the interplay of genes and proteins in the complex biological network. We have implemented bioinformatics tools and databases that are suitable to store, analyze, and integrate the different types of data from high-throughput experiments and to include further annotation that is based on external information. All information is presented in a Web database (http://www.dkfz.de/LIFEdb). It is exploited for the identification of disease-relevant genes and proteins for diagnosis and therapy.
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Affiliation(s)
- Stefan Wiemann
- Molecular Genome Analysis, German Cancer Research Center, 69120 Heidelberg, Germany.
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48
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Widera A, Norouziyan F, Shen WC. Mechanisms of TfR-mediated transcytosis and sorting in epithelial cells and applications toward drug delivery. Adv Drug Deliv Rev 2003; 55:1439-66. [PMID: 14597140 DOI: 10.1016/j.addr.2003.07.004] [Citation(s) in RCA: 120] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Transferrin receptor has been an important protein for many of the advances made in understanding the intricacies of the intramolecular sorting pathways of endocytosed molecules. The unique internalization and recycling functions of transferrin receptor have also made it an attractive choice for drug targeting and delivery of large protein-based therapeutics and toxins. Recent advances in elucidating the role of the intracellular controllers of transferrin recycling and sorting, such as Rab proteins and their effectors, have led to enhancement of transferrin receptor as a drug delivery vehicle. This review focuses on the use of transferrin receptor as an agent for facilitating drug delivery and targeting, and the role that mechanisms of transferrin receptor sorting and transcytosis play in these events.
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Affiliation(s)
- A Widera
- Department of Pharmaceutical Sciences, School of Pharmacy, University of Southern California, PSC 404B, 1985 Zonal Avenue, Los Angeles, CA 90033, USA
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49
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Abstract
Reactive oxygen species (ROS) have been shown to be associated with a wide variety of pathological phenomena such as carcinogenesis, inflammation, radiation and reperfusion injury. Iron, the most abundant transition metal ion in our body, may work as a catalyst for the generation of ROS in pathological conditions. In the past few years, there have been great advances in the understanding of iron metabolism. These include the discoveries of iron transporters and the gene responsible for hereditary hemochromatosis. Iron overload has been shown to be associated with carcinogenesis. We recently identified the major target genes (p16(INK4A) and p15(INK4B) tumor suppressor genes, which encode cyclin-dependent kinase inhibitors) in a ferric nitrilotriacetate-induced rat renal carcinogenesis model, in which the Fenton reaction is induced in the renal proximal tubules. Allelic loss of the p16 gene occurs early in carcinogenesis and specifically at the p16 loci as compared with other tumor suppressor genes. This led to the novel concept of 'genomic sites vulnerable to the Fenton reaction'. Here, recent new findings on iron metabolism are reviewed and the concept of the vulnerable sites explored. More effort to link iron metabolism with human carcinogenesis is anticipated.
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Affiliation(s)
- Shinya Toyokuni
- Department of Pathology and Biology of Diseases, Graduate School of Medicine, Kyoto University, Kyoto, Japan.
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Nichol H, Winzerling J. Structured RNA upstream of insect cap distal iron responsive elements enhances iron regulatory protein-mediated control of translation. INSECT BIOCHEMISTRY AND MOLECULAR BIOLOGY 2002; 32:1699-1710. [PMID: 12429122 DOI: 10.1016/s0965-1748(02)00110-8] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
Iron regulatory protein (IRP) blocks ribosomal assembly by binding to an iron responsive element (IRE) located proximal (<60 nts) to the mRNA cap, thereby repressing translation. Constructs with IREs located 60-100 nts from the cap permit ribosomal assembly but the ribosomes pause at IRE/IRP complexes resulting in partial repression of translation. However, insect ferritin mRNAs have cap-distal IREs located 90-156 nts from the cap. Because iron can be toxic, it seems unlikely that insects would be unable to fully regulate ferritin synthesis at the level of translation. Calpodes ferritin consists of two subunits, S and G. In vitro translation of Calpodes ferritin and IRP1 from fat body mRNA yields only G subunits suggesting that IRP1 more efficiently represses translation of the S subunit than the G. When repression is removed by the addition of IRE competitor RNA, the synthesis of both subunits is greatly increased. S and G ferritin mRNAs have identical IREs in similar far cap-distal positions. While both ferritin mRNAs are predicted to have stem-loops between the IRE and the RNA cap, in general insect S mRNAs have more cap-proximal RNA structure than G mRNAs. Therefore, we examined the effect of upstream secondary structure on ribosomal assembly onto S ferritin mRNA constructs using sucrose gradient analysis of translation initiation complexes. We found no evidence for ribosomal assembly on wild type Calpodes S ferritin mRNA in the presence of IRP1 while constructs lacking the wild type secondary structure showed ribosomal pausing. Constructs with wild type secondary structure preceded by an unstructured upstream leader assemble ribosomes in the presence or absence of IRP1. Sequence and RNA folding analyses of other insect ferritins with cap-distal IREs failed to identify any common sequences or IRE-like structures that might bind to IRP1 with lower affinity or to another RNA binding protein. We propose that stem-loops upstream from the IRE act like pleats that shorten the effective distance between the IRE and cap and allow full translational repression by IRP1. In this way some cap-distal IREs may function like cap-proximal ones.
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Affiliation(s)
- Helen Nichol
- Department of Nutritional Sciences, University of Arizona, Tucson 85721, USA.
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