1
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Simonenko SY, Bogdanova DA, Kuldyushev NA. Emerging Roles of Vitamin B 12 in Aging and Inflammation. Int J Mol Sci 2024; 25:5044. [PMID: 38732262 PMCID: PMC11084641 DOI: 10.3390/ijms25095044] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/09/2024] [Revised: 04/28/2024] [Accepted: 04/29/2024] [Indexed: 05/13/2024] Open
Abstract
Vitamin B12 (cobalamin) is an essential nutrient for humans and animals. Metabolically active forms of B12-methylcobalamin and 5-deoxyadenosylcobalamin are cofactors for the enzymes methionine synthase and mitochondrial methylmalonyl-CoA mutase. Malfunction of these enzymes due to a scarcity of vitamin B12 leads to disturbance of one-carbon metabolism and impaired mitochondrial function. A significant fraction of the population (up to 20%) is deficient in vitamin B12, with a higher rate of deficiency among elderly people. B12 deficiency is associated with numerous hallmarks of aging at the cellular and organismal levels. Cellular senescence is characterized by high levels of DNA damage by metabolic abnormalities, increased mitochondrial dysfunction, and disturbance of epigenetic regulation. B12 deficiency could be responsible for or play a crucial part in these disorders. In this review, we focus on a comprehensive analysis of molecular mechanisms through which vitamin B12 influences aging. We review new data about how deficiency in vitamin B12 may accelerate cellular aging. Despite indications that vitamin B12 has an important role in health and healthy aging, knowledge of the influence of vitamin B12 on aging is still limited and requires further research.
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Affiliation(s)
- Sergey Yu. Simonenko
- Research Center for Translational Medicine, Sirius University of Science and Technology, 354340 Sochi, Russia;
| | - Daria A. Bogdanova
- Division of Immunobiology and Biomedicine, Center for Genetics and Life Sciences, Sirius University of Science and Technology, 354340 Sochi, Russia
| | - Nikita A. Kuldyushev
- Research Center for Translational Medicine, Sirius University of Science and Technology, 354340 Sochi, Russia;
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2
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Guéant JL, Guéant-Rodriguez RM, Kosgei VJ, Coelho D. Causes and consequences of impaired methionine synthase activity in acquired and inherited disorders of vitamin B 12 metabolism. Crit Rev Biochem Mol Biol 2021; 57:133-155. [PMID: 34608838 DOI: 10.1080/10409238.2021.1979459] [Citation(s) in RCA: 20] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
Methyl-Cobalamin (Cbl) derives from dietary vitamin B12 and acts as a cofactor of methionine synthase (MS) in mammals. MS encoded by MTR catalyzes the remethylation of homocysteine to generate methionine and tetrahydrofolate, which fuel methionine and cytoplasmic folate cycles, respectively. Methionine is the precursor of S-adenosyl methionine (SAM), the universal methyl donor of transmethylation reactions. Impaired MS activity results from inadequate dietary intake or malabsorption of B12 and inborn errors of Cbl metabolism (IECM). The mechanisms at the origin of the high variability of clinical presentation of impaired MS activity are classically considered as the consequence of the disruption of the folate cycle and related synthesis of purines and pyrimidines and the decreased synthesis of endogenous methionine and SAM. For one decade, data on cellular and animal models of B12 deficiency and IECM have highlighted other key pathomechanisms, including altered interactome of MS with methionine synthase reductase, MMACHC, and MMADHC, endoplasmic reticulum stress, altered cell signaling, and genomic/epigenomic dysregulations. Decreased MS activity increases catalytic protein phosphatase 2A (PP2A) and produces imbalanced phosphorylation/methylation of nucleocytoplasmic RNA binding proteins, including ELAVL1/HuR protein, with subsequent nuclear sequestration of mRNAs and dramatic alteration of gene expression, including SIRT1. Decreased SAM and SIRT1 activity induce ER stress through impaired SIRT1-deacetylation of HSF1 and hypomethylation/hyperacetylation of peroxisome proliferator-activated receptor-γ coactivator-1α (PGC1α), which deactivate nuclear receptors and lead to impaired energy metabolism and neuroplasticity. The reversibility of these pathomechanisms by SIRT1 agonists opens promising perspectives in the treatment of IECM outcomes resistant to conventional supplementation therapies.
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Affiliation(s)
- Jean-Louis Guéant
- UMR Inserm 1256 N-GERE (Nutrition, Génetique et Exposition aux Risques Environmentaux), Université de Lorraine, Vandoeuvre-lès-Nancy, France.,Departments of Digestive Diseases and Molecular Medicine and National Center of Inborn Errors of Metabolism, University Hospital Center, Université de Lorraine, Vandoeuvre-lès-Nancy, France
| | - Rosa-Maria Guéant-Rodriguez
- UMR Inserm 1256 N-GERE (Nutrition, Génetique et Exposition aux Risques Environmentaux), Université de Lorraine, Vandoeuvre-lès-Nancy, France.,Departments of Digestive Diseases and Molecular Medicine and National Center of Inborn Errors of Metabolism, University Hospital Center, Université de Lorraine, Vandoeuvre-lès-Nancy, France
| | - Viola J Kosgei
- UMR Inserm 1256 N-GERE (Nutrition, Génetique et Exposition aux Risques Environmentaux), Université de Lorraine, Vandoeuvre-lès-Nancy, France
| | - David Coelho
- UMR Inserm 1256 N-GERE (Nutrition, Génetique et Exposition aux Risques Environmentaux), Université de Lorraine, Vandoeuvre-lès-Nancy, France
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3
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Abstract
The recently delineated structure- and reactivity-based concept of antivitamins B12 has begun to bear fruit by the generation, and study, of a range of such B12 -dummies, either vitamin B12 -derived, or transition metal analogues that also represent potential antivitamins B12 or specific B12 -antimetabolites. As reviewed here, this has opened up new research avenues in organometallic B12 -chemistry and bioinorganic coordination chemistry. Exploratory studies with antivitamins B12 have, furthermore, revealed some of their potential, as pharmacologically interesting compounds, for inducing B12 -deficiency in a range of organisms, from hospital resistant bacteria to laboratory mice. The derived capacity of antivitamins B12 to induce functional B12 -deficiency in mammalian cells and organs also suggest their valuable potential as growth inhibitors of cancerous human and animal cells.
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Affiliation(s)
- Bernhard Kräutler
- Institute of Organic Chemistry and Center for Molecular Biosciences (CMBI)University of Innsbruck6020InnsbruckAustria
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4
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Bito T, Bito M, Hirooka T, Okamoto N, Harada N, Yamaji R, Nakano Y, Inui H, Watanabe F. Biological Activity of Pseudovitamin B 12 on Cobalamin-Dependent Methylmalonyl-CoA Mutase and Methionine Synthase in Mammalian Cultured COS-7 Cells. Molecules 2020; 25:molecules25143268. [PMID: 32709013 PMCID: PMC7396987 DOI: 10.3390/molecules25143268] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2020] [Revised: 07/15/2020] [Accepted: 07/15/2020] [Indexed: 11/23/2022] Open
Abstract
Adenyl cobamide (commonly known as pseudovitamin B12) is synthesized by intestinal bacteria or ingested from edible cyanobacteria. The effect of pseudovitamin B12 on the activities of cobalamin-dependent enzymes in mammalian cells has not been studied well. This study was conducted to investigate the effects of pseudovitamin B12 on the activities of the mammalian vitamin B12-dependent enzymes methionine synthase and methylmalonyl-CoA mutase in cultured mammalian COS-7 cells to determine whether pseudovitamin B12 functions as an inhibitor or a cofactor of these enzymes. Although the hydoroxo form of pseudovitamin B12 functions as a coenzyme for methionine synthase in cultured cells, pseudovitamin B12 does not activate the translation of methionine synthase, unlike the hydroxo form of vitamin B12 does. In the second enzymatic reaction, the adenosyl form of pseudovitamin B12 did not function as a coenzyme or an inhibitor of methylmalonyl-CoA mutase. Experiments on the cellular uptake were conducted with human transcobalamin II and suggested that treatment with a substantial amount of pseudovitamin B12 might inhibit transcobalamin II-mediated absorption of a physiological trace concentration of vitamin B12 present in the medium.
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Affiliation(s)
- Tomohiro Bito
- Department of Agricultural, Life and Environmental Sciences, Faculty of Agriculture, Tottori University, Tottori 680-8553, Japan;
- Correspondence: ; Tel.: +81-857-31-5443
| | - Mariko Bito
- Division of Applied Life Sciences, Graduate School of Life and Environmental Sciences, Osaka Prefecture University, Sakai, Osaka 599-8531, Japan; (M.B.); (T.H.); (N.H.); (R.Y.); (Y.N.)
| | - Tomomi Hirooka
- Division of Applied Life Sciences, Graduate School of Life and Environmental Sciences, Osaka Prefecture University, Sakai, Osaka 599-8531, Japan; (M.B.); (T.H.); (N.H.); (R.Y.); (Y.N.)
| | - Naho Okamoto
- The United Graduate School of Agricultural Sciences, Tottori University, Tottori 680-8553, Japan;
| | - Naoki Harada
- Division of Applied Life Sciences, Graduate School of Life and Environmental Sciences, Osaka Prefecture University, Sakai, Osaka 599-8531, Japan; (M.B.); (T.H.); (N.H.); (R.Y.); (Y.N.)
| | - Ryoichi Yamaji
- Division of Applied Life Sciences, Graduate School of Life and Environmental Sciences, Osaka Prefecture University, Sakai, Osaka 599-8531, Japan; (M.B.); (T.H.); (N.H.); (R.Y.); (Y.N.)
| | - Yoshihisa Nakano
- Division of Applied Life Sciences, Graduate School of Life and Environmental Sciences, Osaka Prefecture University, Sakai, Osaka 599-8531, Japan; (M.B.); (T.H.); (N.H.); (R.Y.); (Y.N.)
| | - Hiroshi Inui
- Department of Nutrition, College of Health and Human Sciences, Osaka Prefecture University, Habikino, Osaka 583-8555, Japan;
| | - Fumio Watanabe
- Department of Agricultural, Life and Environmental Sciences, Faculty of Agriculture, Tottori University, Tottori 680-8553, Japan;
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5
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Froese DS, Fowler B, Baumgartner MR. Vitamin B 12 , folate, and the methionine remethylation cycle-biochemistry, pathways, and regulation. J Inherit Metab Dis 2019; 42:673-685. [PMID: 30693532 DOI: 10.1002/jimd.12009] [Citation(s) in RCA: 192] [Impact Index Per Article: 38.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/21/2018] [Revised: 09/27/2018] [Accepted: 10/19/2018] [Indexed: 12/16/2022]
Abstract
Vitamin B12 (cobalamin, Cbl) is a nutrient essential to human health. Due to its complex structure and dual cofactor forms, Cbl undergoes a complicated series of absorptive and processing steps before serving as cofactor for the enzymes methylmalonyl-CoA mutase and methionine synthase. Methylmalonyl-CoA mutase is required for the catabolism of certain (branched-chain) amino acids into an anaplerotic substrate in the mitochondrion, and dysfunction of the enzyme itself or in production of its cofactor adenosyl-Cbl result in an inability to successfully undergo protein catabolism with concomitant mitochondrial energy disruption. Methionine synthase catalyzes the methyl-Cbl dependent (re)methylation of homocysteine to methionine within the methionine cycle; a reaction required to produce this essential amino acid and generate S-adenosylmethionine, the most important cellular methyl-donor. Disruption of methionine synthase has wide-ranging implications for all methylation-dependent reactions, including epigenetic modification, but also for the intracellular folate pathway, since methionine synthase uses 5-methyltetrahydrofolate as a one-carbon donor. Folate-bound one-carbon units are also required for deoxythymidine monophosphate and de novo purine synthesis; therefore, the flow of single carbon units to each of these pathways must be regulated based on cellular needs. This review provides an overview on Cbl metabolism with a brief description of absorption and intracellular metabolic pathways. It also provides a description of folate-mediated one-carbon metabolism and its intersection with Cbl at the methionine cycle. Finally, a summary of recent advances in understanding of how both pathways are regulated is presented.
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Affiliation(s)
- D Sean Froese
- Division of Metabolism and Children's Research Center, University Children's Hospital, Zurich, Switzerland
| | - Brian Fowler
- Division of Metabolism and Children's Research Center, University Children's Hospital, Zurich, Switzerland
| | - Matthias R Baumgartner
- Division of Metabolism and Children's Research Center, University Children's Hospital, Zurich, Switzerland
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6
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Campanello GC, Ruetz M, Dodge GJ, Gouda H, Gupta A, Twahir UT, Killian MM, Watkins D, Rosenblatt DS, Brunold TC, Warncke K, Smith JL, Banerjee R. Sacrificial Cobalt-Carbon Bond Homolysis in Coenzyme B 12 as a Cofactor Conservation Strategy. J Am Chem Soc 2018; 140:13205-13208. [PMID: 30282455 DOI: 10.1021/jacs.8b08659] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
A sophisticated intracellular trafficking pathway in humans is used to tailor vitamin B12 into its active cofactor forms, and to deliver it to two known B12-dependent enzymes. Herein, we report an unexpected strategy for cellular retention of B12, an essential and reactive cofactor. If methylmalonyl-CoA mutase is unavailable to accept the coenzyme B12 product of adenosyltransferase, the latter catalyzes homolytic scission of the cobalt-carbon bond in an unconventional reversal of the nucleophilic displacement reaction that was used to make it. The resulting homolysis product binds more tightly to adenosyltransferase than does coenzyme B12, facilitating cofactor retention. We have trapped, and characterized spectroscopically, an intermediate in which the cobalt-carbon bond is weakened prior to being broken. The physiological relevance of this sacrificial catalytic activity for cofactor retention is supported by the significantly lower coenzyme B12 concentration in patients with dysfunctional methylmalonyl-CoA mutase but normal adenosyltransferase activity.
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Affiliation(s)
- Gregory C Campanello
- Department of Biological Chemistry , University of Michigan , Ann Arbor , Michigan 48109-0600 , United States
| | - Markus Ruetz
- Department of Biological Chemistry , University of Michigan , Ann Arbor , Michigan 48109-0600 , United States
| | - Greg J Dodge
- Department of Biological Chemistry , University of Michigan , Ann Arbor , Michigan 48109-0600 , United States.,Life Sciences Institute, University of Michigan , Ann Arbor , Michigan 48109-0600 , United States
| | - Harsha Gouda
- Department of Biological Chemistry , University of Michigan , Ann Arbor , Michigan 48109-0600 , United States.,Indian Institute of Science Education and Research , Pune 411008 , India
| | - Aditi Gupta
- Department of Biological Chemistry , University of Michigan , Ann Arbor , Michigan 48109-0600 , United States
| | - Umar T Twahir
- Department of Physics , Emory University , Atlanta , Georgia 30322-2430 , United States
| | - Michelle M Killian
- Department of Chemistry , University of Wisconsin-Madison , Madison , Wisconsin 53706 , United States
| | - David Watkins
- Department of Human Genetics , McGill University , Montreal , Quebec H3A 1B1 , Canada
| | - David S Rosenblatt
- Department of Human Genetics , McGill University , Montreal , Quebec H3A 1B1 , Canada
| | - Thomas C Brunold
- Department of Chemistry , University of Wisconsin-Madison , Madison , Wisconsin 53706 , United States
| | - Kurt Warncke
- Department of Physics , Emory University , Atlanta , Georgia 30322-2430 , United States
| | - Janet L Smith
- Department of Biological Chemistry , University of Michigan , Ann Arbor , Michigan 48109-0600 , United States.,Life Sciences Institute, University of Michigan , Ann Arbor , Michigan 48109-0600 , United States
| | - Ruma Banerjee
- Department of Biological Chemistry , University of Michigan , Ann Arbor , Michigan 48109-0600 , United States
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7
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An Amoebal Grazer of Cyanobacteria Requires Cobalamin Produced by Heterotrophic Bacteria. Appl Environ Microbiol 2017; 83:AEM.00035-17. [PMID: 28283521 DOI: 10.1128/aem.00035-17] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2017] [Accepted: 03/03/2017] [Indexed: 01/22/2023] Open
Abstract
Amoebae are unicellular eukaryotes that consume microbial prey through phagocytosis, playing a role in shaping microbial food webs. Many amoebal species can be cultivated axenically in rich media or monoxenically with a single bacterial prey species. Here, we characterize heterolobosean amoeba LPG3, a recent natural isolate, which is unable to grow on unicellular cyanobacteria, its primary food source, in the absence of a heterotrophic bacterium, a Pseudomonas species coisolate. To investigate the molecular basis of this requirement for heterotrophic bacteria, we performed a screen using the defined nonredundant transposon library of Vibrio cholerae, which implicated genes in corrinoid uptake and biosynthesis. Furthermore, cobalamin synthase deletion mutations in V. cholerae and the Pseudomonas species coisolate do not support the growth of amoeba LPG3 on cyanobacteria. While cyanobacteria are robust producers of a corrinoid variant called pseudocobalamin, this variant does not support the growth of amoeba LPG3. Instead, we show that it requires cobalamin that is produced by the Pseudomonas species coisolate. The diversity of eukaryotes utilizing corrinoids is poorly understood, and this amoebal corrinoid auxotroph serves as a model for examining predator-prey interactions and micronutrient transfer in bacterivores underpinning microbial food webs.IMPORTANCE Cyanobacteria are important primary producers in aquatic environments, where they are grazed upon by a variety of phagotrophic protists and, hence, have an impact on nutrient flux at the base of microbial food webs. Here, we characterize amoebal isolate LPG3, which consumes cyanobacteria as its primary food source but also requires heterotrophic bacteria as a source of corrinoid vitamins. Amoeba LPG3 specifically requires the corrinoid variant produced by heterotrophic bacteria and cannot grow on cyanobacteria alone, as they produce a different corrinoid variant. This same corrinoid specificity is also exhibited by other eukaryotes, including humans and algae. This amoebal model system allows us to dissect predator-prey interactions to uncover factors that may shape microbial food webs while also providing insight into corrinoid specificity in eukaryotes.
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8
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Yamada Y, Koori D, Oshikawa Y, Koikawa M. Stereospecific interaction of optically active sulfur-bridged dinuclear Co(III)–Pt(II) complex with pseudo-enantiomeric Co(III)–M(II) (M: Pd or Pt) complex involving unequivalent π electronic system. Inorganica Chim Acta 2016. [DOI: 10.1016/j.ica.2016.06.002] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
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9
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Abstract
B12 -antimetabolites are compounds that counteract the physiological effects of vitamin B12 and related natural cobalamins. Presented here is a structure- and reactivity-based concept of the specific 'antivitamins B12 ': it refers to analogues of vitamin B12 that display high structural similarity to the vitamin and are 'locked chemically' to prevent their metabolic conversion into the crucial organometallic B12 -cofactors. Application of antivitamins B12 to healthy laboratory animals is, thus, expected to induce symptoms of B12 -deficiency. Antivitamins B12 may, hence, be helpful in elucidating still largely puzzling pathophysiological phenomena associated with B12 -deficiency, and also in recognizing physiological roles of B12 that probably still remain to be discovered.
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Affiliation(s)
- Bernhard Kräutler
- Institute of Organic Chemistry & Center for Molecular Biosciences (CMBI), University of Innsbruck, Innrain 80/82, 6020 Innsbruck (Austria).
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10
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Yamada Y, Nagasaki T. Stereospecific π–π stacking interactions between pseudo-enantiomeric sulfur-bridged dinuclear Co(III)–Pd(II) and Co(III)–Pt(II) complexes of optically active penicillaminates. Polyhedron 2015. [DOI: 10.1016/j.poly.2015.01.013] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
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11
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Reversible induction of translational isoforms of p53 in glucose deprivation. Cell Death Differ 2015; 22:1203-18. [PMID: 25721046 DOI: 10.1038/cdd.2014.220] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2014] [Revised: 11/13/2014] [Accepted: 11/14/2014] [Indexed: 02/01/2023] Open
Abstract
Tumor suppressor protein p53 is a master transcription regulator, indispensable for controlling several cellular pathways. Earlier work in our laboratory led to the identification of dual internal ribosome entry site (IRES) structure of p53 mRNA that regulates translation of full-length p53 and Δ40p53. IRES-mediated translation of both isoforms is enhanced under different stress conditions that induce DNA damage, ionizing radiation and endoplasmic reticulum stress, oncogene-induced senescence and cancer. In this study, we addressed nutrient-mediated translational regulation of p53 mRNA using glucose depletion. In cell lines, this nutrient-depletion stress relatively induced p53 IRES activities from bicistronic reporter constructs with concomitant increase in levels of p53 isoforms. Surprisingly, we found scaffold/matrix attachment region-binding protein 1 (SMAR1), a predominantly nuclear protein is abundant in the cytoplasm under glucose deprivation. Importantly under these conditions polypyrimidine-tract-binding protein, an established p53 ITAF did not show nuclear-cytoplasmic relocalization highlighting the novelty of SMAR1-mediated control in stress. In vivo studies in mice revealed starvation-induced increase in SMAR1, p53 and Δ40p53 levels that was reversible on dietary replenishment. SMAR1 associated with p53 IRES sequences ex vivo, with an increase in interaction on glucose starvation. RNAi-mediated-transient SMAR1 knockdown decreased p53 IRES activities in normal conditions and under glucose deprivation, this being reflected in changes in mRNAs in the p53 and Δ40p53 target genes involved in cell-cycle arrest, metabolism and apoptosis such as p21, TIGAR and Bax. This study provides a new physiological insight into the regulation of this critical tumor suppressor in nutrient starvation, also suggesting important functions of the p53 isoforms in these conditions as evident from the downstream transcriptional target activation.
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12
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Gherasim C, Hannibal L, Rajagopalan D, Jacobsen DW, Banerjee R. The C-terminal domain of CblD interacts with CblC and influences intracellular cobalamin partitioning. Biochimie 2013; 95:1023-32. [PMID: 23415655 DOI: 10.1016/j.biochi.2013.02.003] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/03/2012] [Accepted: 02/01/2013] [Indexed: 11/15/2022]
Abstract
Mutations in cobalamin or B12 trafficking genes needed for cofactor assimilation and targeting lead to inborn errors of cobalamin metabolism. The gene corresponding to one of these loci, cblD, affects both the mitochondrial and cytoplasmic pathways for B12 processing. We have demonstrated that fibroblast cell lines from patients with mutations in CblD, can dealkylate exogenously supplied methylcobalamin (MeCbl), an activity catalyzed by the CblC protein, but show imbalanced intracellular partitioning of the cofactor into the MeCbl and 5'-deoxyadenosylcobalamin (AdoCbl) pools. These results confirm that CblD functions downstream of CblC in the cofactor assimilation pathway and that it plays an important role in controlling the traffic of the cofactor between the competing cytoplasmic and mitochondrial routes for MeCbl and AdoCbl synthesis, respectively. In this study, we report the interaction of CblC with four CblD protein variants with variable N-terminal start sites. We demonstrate that a complex between CblC and CblD can be isolated particularly under conditions that permit dealkylation of alkylcobalamin by CblC or in the presence of the corresponding dealkylated and oxidized product, hydroxocobalamin (HOCbl). A weak CblC·CblD complex is also seen in the presence of cyanocobalamin. Formation of the CblC·CblD complex is observed with all four CblD variants tested suggesting that the N-terminal 115 residues missing in the shortest variant are not essential for this interaction. Furthermore, limited proteolysis of the CblD variants indicates the presence of a stable C-terminal domain spanning residues ∼116-296. Our results are consistent with an adapter function for CblD, which in complex with CblC·HOCbl, or possibly the less oxidized CblC·cob(II)alamin, partitions the cofactor between AdoCbl and MeCbl assimilation pathways.
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Affiliation(s)
- Carmen Gherasim
- Department of Biological Chemistry, University of Michigan Medical Center, Ann Arbor, MI 48109-0600, USA
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13
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Ruetz M, Gherasim C, Gruber K, Fedosov S, Banerjee R, Kräutler B. Access to organometallic arylcobaltcorrins through radical synthesis: 4-ethylphenylcobalamin, a potential "antivitamin B(12)". Angew Chem Int Ed Engl 2013; 52:2606-10. [PMID: 23404623 DOI: 10.1002/anie.201209651] [Citation(s) in RCA: 54] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2012] [Indexed: 11/11/2022]
Abstract
Locked B(12): 4-Ethylphenylcobalamin, a novel organometallic arylcobalamin, has been synthesized in a radical reaction. This vitamin B(12) antimetabolite features a strong Co-C bond, and represents a "locked" form of vitamin B(12) . It may be used in animal studies to induce functional vitamin B(12) deficiency artificially to help clarify still controversial issues related to the pathophysiology of vitamin B(12) deficiency.
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Affiliation(s)
- Markus Ruetz
- Institute of Organic Chemistry and Centre of Molecular Biosciences, University of Innsbruck, Innrain 80/82, 6020 Innsbruck, Austria
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14
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Ruetz M, Gherasim C, Gruber K, Fedosov S, Banerjee R, Kräutler B. Zugang zu metallorganischen Arylcobaltcorrinen durch radikalische Synthese: 4-Ethylphenylcobalamin, ein potenzielles “Antivitamin B12”. Angew Chem Int Ed Engl 2013. [DOI: 10.1002/ange.201209651] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
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15
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Preynat A, Lapierre H, Thivierge M, Palin M, Cardinault N, Matte J, Desrochers A, Girard C. Effects of supplementary folic acid and vitamin B12 on hepatic metabolism of dairy cows according to methionine supply. J Dairy Sci 2010; 93:2130-42. [DOI: 10.3168/jds.2009-2796] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2009] [Accepted: 01/06/2010] [Indexed: 01/03/2023]
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16
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Abstract
There is a growing awareness that natural vitamins (with the only exception of pantothenic acid) positively or negatively modulate the synthesis of some cytokines and growth factors in the CNS, and various mammalian cells and organs. As natural vitamins are micronutrients in the human diet, studying their effects can be considered a part of nutritional genomics or nutrigenomics. A given vitamin selectively modifies the synthesis of only a few cytokines and/or growth factors, although the same cytokine and/or growth factor may be regulated by more than one vitamin. These effects seem to be independent of the effects of vitamins as coenzymes and/or reducing agents, and seem to occur mainly at genomic and/or epigenetic level, and/or by modulating NF-kappaB activity. Although most of the studies reviewed here have been based on cultured cell lines, but their findings have been confirmed by some key in vivo studies. The CNS seems to be particularly involved and is severely affected by most avitaminoses, especially in the case of vitamin B(12). However, the vitamin-induced changes in cytokine and growth factor synthesis may initiate a cascade of events that can affect the function, differentiation, and morphology of the cells and/or structures not only in the CNS, but also elsewhere because most natural vitamins, cytokines, and growth factors cross the blood-brain barrier. As cytokines are essential to CNS-immune and CNS-hormone system communications, natural vitamins also interact with these circuits. Further studies of such vitamin-mediated effects could lead to vitamins being used for the treatment of diseases which, although not true avitaminoses, involve an imbalance in cytokine and/or growth factor synthesis.
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Affiliation(s)
- Giuseppe Scalabrino
- Laboratory of Neuropathology, 'Città Studi' Department, Faculty of Medicine and Surgery, University of Milan, Milan, Italy.
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17
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Anchoring secreted proteins in endoplasmic reticulum by plant oleosin: the example of vitamin B12 cellular sequestration by transcobalamin. PLoS One 2009; 4:e6325. [PMID: 19623264 PMCID: PMC2710007 DOI: 10.1371/journal.pone.0006325] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2009] [Accepted: 06/08/2009] [Indexed: 12/03/2022] Open
Abstract
Background Oleosin is a plant protein localized to lipid droplets and endoplasmic reticulum of plant cells. Our idea was to use it to target functional secretory proteins of interest to the cytosolic side of the endoplasmic reticulum of mammalian cells, through expressing oleosin-containing chimeras. We have designed this approach to create cellular models deficient in vitamin B12 (cobalamin) because of the known problematics associated to the obtainment of effective vitamin B12 deficient cell models. This was achieved by the overexpression of transcobalamin inside cells through anchoring to oleosin. Methodology chimera gene constructs including transcobalamin-oleosin (TC-O), green fluorescent protein-transcobalamin-oleosin (GFP-TC-O) and oleosin-transcobalamin (O-TC) were inserted into pAcSG2 and pCDNA3 vectors for expression in sf9 insect cells, Caco2 (colon carcinoma), NIE-115 (mouse neuroblastoma), HEK (human embryonic kidney), COS-7 (Green Monkey SV40-transfected kidney fibroblasts) and CHO (Chinese hamster ovary cells). The subcellular localization, the changes in vitamin B12 binding activity and the metabolic consequences were investigated in both Caco2 and NIE-115 cells. Principal findings vitamin B12 binding was dramatically higher in TC-O than that in O-TC and wild type (WT). The expression of GFP-TC-O was observed in all cell lines and found to be co-localized with an ER-targeted red fluorescent protein and calreticulin of the endoplasmic reticulum in Caco2 and COS-7 cells. The overexpression of TC-O led to B12 deficiency, evidenced by impaired conversion of cyano-cobalamin to ado-cobalamin and methyl-cobalamin, decreased methionine synthase activity and reduced S-adenosyl methionine to S-adenosyl homocysteine ratio, as well as increases in homocysteine and methylmalonic acid concentration. Conclusions/Significance the heterologous expression of TC-O in mammalian cells can be used as an effective strategy for investigating the cellular consequences of vitamin B12 deficiency. More generally, expression of oleosin-anchored proteins could be an interesting tool in cell engineering for studying proteins of pharmacological interest.
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Birch CS, Brasch NE, McCaddon A, Williams JHH. A novel role for vitamin B(12): Cobalamins are intracellular antioxidants in vitro. Free Radic Biol Med 2009; 47:184-8. [PMID: 19409980 DOI: 10.1016/j.freeradbiomed.2009.04.023] [Citation(s) in RCA: 124] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/22/2008] [Revised: 04/14/2009] [Accepted: 04/22/2009] [Indexed: 01/29/2023]
Abstract
Oxidative stress is a feature of many chronic inflammatory diseases. Such diseases are associated with up-regulation of a vitamin B(12) (cobalamin) blood transport protein and its membrane receptor, suggesting a link between cobalamin and the cellular response to inflammation. The ability of cobalamin to regulate inflammatory cytokines suggests that it may have antioxidative properties. Here we show that cobalamins, including the novel thiolatocobalamins N-acetyl-l-cysteinylcobalamin and glutathionylcobalamin, are remarkably effective antioxidants in vitro. We also show that thiolatocobalamins have superior efficacy compared with other cobalamin forms, other cobalamins in combination with N-acetyl-l-cysteine (NAC) or glutathione (GSH), and NAC or GSH alone. Pretreatment of Sk-Hep-1 cells with thiolatocobalamins afforded robust protection (>90% cell survival) against exposure to 30 microM concentrations of the pro-oxidants homocysteine and hydrogen peroxide. The compounds inhibited intracellular peroxide production, maintained intracellular glutathione levels, and prevented apoptotic and necrotic cell death. Moreover, thiolatocobalamins are remarkably nontoxic in vitro at supraphysiological concentrations (>2 mM). Our results demonstrate that thiolatocobalamins act as powerful but benign antioxidants at pharmacological concentrations. Because inflammatory oxidative stress is a component of many conditions, including atherosclerosis, dementia, and trauma, their utility in treating such disorders merits further investigation.
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Affiliation(s)
- Catherine S Birch
- Chester Centre for Stress Research, University of Chester, Parkgate Road, Chester CH1 4BJ, UK
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Scalabrino G. The multi-faceted basis of vitamin B12 (cobalamin) neurotrophism in adult central nervous system: Lessons learned from its deficiency. Prog Neurobiol 2009; 88:203-20. [DOI: 10.1016/j.pneurobio.2009.04.004] [Citation(s) in RCA: 96] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/31/2008] [Revised: 03/03/2009] [Accepted: 04/16/2009] [Indexed: 10/20/2022]
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Scalabrino G, Veber D, Mutti E. Experimental and clinical evidence of the role of cytokines and growth factors in the pathogenesis of acquired cobalamin-deficient leukoneuropathy. ACTA ACUST UNITED AC 2008; 59:42-54. [DOI: 10.1016/j.brainresrev.2008.05.001] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2008] [Revised: 04/30/2008] [Accepted: 05/01/2008] [Indexed: 01/08/2023]
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Cobalamin deficiency results in an abnormal increase inl-methylmalonyl-co-enzyme-A mutase expression in rat liver and COS-7 cells. Br J Nutr 2008; 101:492-8. [PMID: 18710602 DOI: 10.1017/s0007114508023398] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
The aim of the present study was to examine the effects of cobalamin (Cbl) on the activity and expression ofl-methylmalonyl-CoA mutase (MCM) in rat liver and cultured COS-7 cells. The MCM holoenzyme activity was less than 5 % of the total (holoenzyme+apoenzyme) activity in the liver although rats were fed a diet containing sufficient Cbl. When weanling rats were maintained on a Cbl-deficient diet, the holo-MCM activity became almost undetectable at the age of 10 weeks. In contrast, a marked increase in the total-MCM activity occurred under the Cbl-deficient conditions, and at the age of 20 weeks it was about 3-fold higher in the deficient rats than in the controls (108 (sd14·5)v.35 (sd8·5) nmol/mg protein per min (n5);P < 0·05). Western blot analysis confirmed that the MCM protein level increased significantly in the Cbl-deficient rats. However, the MCM mRNA level, determined by real-time PCR, was rather decreased. When COS-7 cells were cultured in a medium in which 10 % fetal bovine serum was the sole source of Cbl, holo-MCM activity was barely detected. The supplementation of Cbl resulted in a large increase in the holo-MCM activity in the cells, but the activity did not exceed 30 % of the total-MCM activity even in the presence of Cbl at 10 μmol/l. In contrast, the total-MCM activity was significantly decreased by the Cbl supplementation, indicating that Cbl deficiency results in an increase in the MCM protein level in COS-7 cells as well as in rat liver.
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Kozak M. Faulty old ideas about translational regulation paved the way for current confusion about how microRNAs function. Gene 2008; 423:108-15. [PMID: 18692553 DOI: 10.1016/j.gene.2008.07.013] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2008] [Revised: 07/07/2008] [Accepted: 07/15/2008] [Indexed: 12/14/2022]
Abstract
Despite a recent surge of reports about how microRNAs might regulate translation, the question has not been answered. The proposed mechanisms contradict one another, and none is supported by strong evidence. This review explains some deficiencies in the experiments with microRNAs. Some of the problems are traceable to bad habits carried over from older studies of translational regulation, here illustrated by discussing two models involving mRNA binding proteins. One widely-accepted model, called into doubt by recent findings, is the maskin hypothesis for translational repression of cyclin B1 in Xenopus oocytes. The second dubious model postulates repression of translation of ceruloplasmin by mRNA binding proteins. A big fault in the latter case is reconstructing the imagined mechanism before looking carefully at the real thing--a criticism that applies also to studies with microRNAs. Experiments with microRNAs often employ internal ribosome entry sequences (IRESs) as tools, necessitating brief discussion of that topic. A sensitive new assay reveals that many putative IRESs promote expression of downstream cistrons via splicing rather than internal initiation of translation. Recent claims about the biological importance of IRES-binding proteins--including suggestions that these proteins might serve as targets for cancer therapy--are not supported by any meaningful evidence. The bottom line is that older studies of mRNA binding proteins and putative IRESs have created a confusing picture of translational regulation which is not helpful when trying to understand how microRNAs might work. The obvious biological importance of microRNAs makes it essential to understand how they do what they do. Fresh ways of thinking and looking are needed.
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Affiliation(s)
- Marilyn Kozak
- Department of Biochemistry, Robert Wood Johnson Medical School, 675 Hoes Lane, Piscataway, NJ 08854, USA.
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Pérez-Marín MC, Padmanabhan S, Polanco MC, Murillo FJ, Elías-Arnanz M. Vitamin B12 partners the CarH repressor to downregulate a photoinducible promoter in Myxococcus xanthus. Mol Microbiol 2008; 67:804-19. [PMID: 18315685 DOI: 10.1111/j.1365-2958.2007.06086.x] [Citation(s) in RCA: 57] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
A light-inducible promoter, P(B), drives expression of the carB operon in Myxococcus xanthus. Repressed by CarA in the dark, P(B) is activated when CarS, produced in the light, sequesters CarA to prevent operator-CarA binding. The MerR-type, N-terminal domain of CarA, which mediates interactions with both operator and CarS, is linked to a C-terminal oligomerization module with a predicted cobalamin-binding motif. Here, we show that although CarA does bind vitamin B12, mutating the motif involved has no effect on its ability to repress P(B). Intriguingly, P(B) could be repressed in the dark even with no CarA, so long as B12 and an intact CarA operator were present. We have discovered that this effect of B12 depends on the gene immediately downstream of carA. Its product, CarH, also consists of a MerR-type, N-terminal domain that specifically recognizes the CarA operator and CarS, linked to a predicted B12-binding C-terminal oligomerization module. The B12-mediated repression of P(B) in the dark is relieved by deleting carH, by mutating the DNA- or B12-binding residues of CarH, or by illumination. Our findings unveil parallel regulatory circuits that control a light-inducible promoter using a transcriptional factor repertoire that includes a paralogous gene pair and vitamin B12.
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Affiliation(s)
- Mari Cruz Pérez-Marín
- Departamento de Genética y Microbiología, Area de Genética (Unidad Asociada al IQFR-CSIC), Facultad de Biología, Universidad de Murcia, Murcia 30100, Spain
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Giancaspero TA, Wait R, Boles E, Barile M. Succinate dehydrogenase flavoprotein subunit expression in Saccharomyces cerevisiae--involvement of the mitochondrial FAD transporter, Flx1p. FEBS J 2008; 275:1103-17. [PMID: 18279395 DOI: 10.1111/j.1742-4658.2008.06270.x] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
The mitochondrial FAD transporter, Flx1p, is a member of the mitochondrial carrier family responsible for FAD transport in Saccharomyces cerevisiae. It has also been suggested that it has a role in maintaining the normal activity of mitochondrial FAD-binding enzymes, including lipoamide dehydrogenase and succinate dehydrogenase flavoprotein subunit Sdh1p. A decrease in the amount of Sdh1p in the flx1Delta mutant strain has been determined here to be due to a post-transcriptional control that involves regulatory sequences located upstream of the SDH1 coding sequence. The SDH1 coding sequence and the regulatory sequences located downstream of the SDH1 coding region, as well as protein import and cofactor attachment, seem to be not involved in the decrease in the amount of protein.
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Affiliation(s)
- Teresa A Giancaspero
- Dipartimento di Biochimica e Biologia Molecolare E. Quagliariello, Università degli Studi di Bari, Via Orabona 4, Bari, Italy
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Abstract
Tetrahydrofolate (THF) polyglutamates are a family of cofactors that carry and chemically activate one-carbon units for biosynthesis. THF-mediated one-carbon metabolism is a metabolic network of interdependent biosynthetic pathways that is compartmentalized in the cytoplasm, mitochondria, and nucleus. One-carbon metabolism in the cytoplasm is required for the synthesis of purines and thymidylate and the remethylation of homocysteine to methionine. One-carbon metabolism in the mitochondria is required for the synthesis of formylated methionyl-tRNA; the catabolism of choline, purines, and histidine; and the interconversion of serine and glycine. Mitochondria are also the primary source of one-carbon units for cytoplasmic metabolism. Increasing evidence indicates that folate-dependent de novo thymidylate biosynthesis occurs in the nucleus of certain cell types. Disruption of folate-mediated one-carbon metabolism is associated with many pathologies and developmental anomalies, yet the biochemical mechanisms and causal metabolic pathways responsible for the initiation and/or progression of folate-associated pathologies have yet to be established. This chapter focuses on our current understanding of mammalian folate-mediated one-carbon metabolism, its cellular compartmentation, and knowledge gaps that limit our understanding of one-carbon metabolism and its regulation.
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Affiliation(s)
- Jennifer T Fox
- Graduate Field of Biochemistry, Molecular and Cellular Biology, Cornell University, Ithaca, New York 14853, USA
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Leclerc D, Rozen R. Endoplasmic reticulum stress increases the expression of methylenetetrahydrofolate reductase through the IRE1 transducer. J Biol Chem 2007; 283:3151-3160. [PMID: 18065414 DOI: 10.1074/jbc.m708598200] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Methylenetetrahydrofolate reductase (MTHFR), an enzyme in folate and homocysteine metabolism, influences many cellular processes including methionine and nucleotide synthesis, methylation reactions, and maintenance of homocysteine at nontoxic levels. Mild deficiency of MTHFR is common in many populations and modifies risk for several complex traits including vascular disease, birth defects, and cancer. We recently demonstrated that MTHFR can be up-regulated by NF-kappaB, an important mediator of cell survival that is activated by endoplasmic reticulum (ER) stress. This observation, coupled with the reports that homocysteine can induce ER stress, prompted us to examine the possible regulation of MTHFR by ER stress. We found that several well characterized stress inducers (tunicamycin, thapsigargin, and A23187) as well as homocysteine could increase Mthfr mRNA and protein in Neuro-2a cells. The induction of MTHFR was also observed after overexpression of inositol-requiring enzyme-1 (IRE1) and was inhibited by a dominant-negative mutant of IRE1. Because IRE1 triggers c-Jun signaling, we examined the possible involvement of c-Jun in up-regulation of MTHFR. Transfection of c-Jun and two activators of c-Jun (LiCl and sodium valproate) increased MTHFR expression, whereas a reported inhibitor of c-Jun (SP600125) and a dominant-negative derivative of c-Jun N-terminal kinase-1 reduced MTHFR activation. We conclude that ER stress increases MTHFR expression and that IRE1 and c-Jun mediate this activation. These findings provide a novel mechanism by which the ER can regulate homeostasis and allude to an important role for MTHFR in cell survival.
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Affiliation(s)
- Daniel Leclerc
- Departments of Human Genetics and Pediatrics, McGill University Health Center-Montreal Children's Hospital, Montreal H3Z 2Z3, Canada
| | - Rima Rozen
- Departments of Human Genetics and Pediatrics, McGill University Health Center-Montreal Children's Hospital, Montreal H3Z 2Z3, Canada.
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In vitamin B12 deficiency, higher serum folate is associated with increased total homocysteine and methylmalonic acid concentrations. Proc Natl Acad Sci U S A 2007; 104:19995-20000. [PMID: 18056804 DOI: 10.1073/pnas.0709487104] [Citation(s) in RCA: 158] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
In a recent study of older participants (age >/=60 years) in the 1999-2002 National Health and Nutrition Examination Survey (NHANES), we showed that a combination of high serum folate and low vitamin B(12) status was associated with higher prevalence of cognitive impairment and anemia than other combinations of vitamin B(12) and folate status. In the present study, we sought to determine the joint influence of serum folate and vitamin B(12) concentrations on two functional indicators of vitamin B(12) status, total homocysteine (tHcy) and methylmalonic acid (MMA), among adult participants in phase 2 of the NHANES III (1991-1994) and the NHANES 1999-2002. Exclusion of subjects who were <20 years old, were pregnant, had evidence of kidney or liver dysfunction, or reported a history of alcohol abuse or recent anemia therapy left 4,940 NHANES III participants and 5,473 NHANES 1999-2002 participants for the study. Multivariate analyses controlled for demographic factors, smoking, alcohol use, body mass index, self-reported diabetes diagnosis, and serum concentrations of creatinine and alanine aminotransferase revealed significant interactions between serum folate and serum vitamin B(12) in relation to circulating concentrations of both metabolites. In subjects with serum vitamin B(12) >148 pmol/liter (L), concentrations of both metabolites decreased significantly as serum folate increased. In subjects with lower serum vitamin B(12), however, metabolite concentrations increased as serum folate increased starting at approximately 20 nmol/L. These results suggest a worsening of vitamin B(12)'s enzymatic functions as folate status increases in people who are vitamin B(12)-deficient.
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Woeller CF, Fox JT, Perry C, Stover PJ. A ferritin-responsive internal ribosome entry site regulates folate metabolism. J Biol Chem 2007; 282:29927-35. [PMID: 17702748 DOI: 10.1074/jbc.m706264200] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
Cytoplasmic serine hydroxymethyltransferase (cSHMT) enzyme levels are elevated by the expression of the heavy chain ferritin (H ferritin) cDNA in cultured cells without corresponding changes in mRNA levels, resulting in enhanced folate-dependent de novo thymidylate biosynthesis and impaired homocysteine remethylation. In this study, the mechanism whereby H ferritin regulates cSHMT expression was determined. cSHMT translation is shown to be regulated by an H ferritin-responsive internal ribosome entry site (IRES) located within the cSHMT mRNA 5'-untranslated region (5'-UTR). The cSHMT 5'-UTR exhibited IRES activity during in vitro translation of bicistronic mRNA templates, and in MCF-7 and HeLa cells transfected with bicistronic mRNAs. IRES activity was depressed in H ferritin-deficient mouse embryonic fibroblasts and elevated in cells expressing the H ferritin cDNA. H ferritin was shown to interact with the mRNA-binding protein CUGBP1, a protein known to interact with the alpha and beta subunits of eukaryotic initiation factor eIF2. Small interference RNA-mediated depletion of CUGBP1 decreased IRES activity from bicistronic templates that included the cSHMT 3'-UTR in the bicistronic construct. The identification of this H ferritin-responsive IRES represents a mechanism that accounts for previous observations that H ferritin regulates folate metabolism.
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Affiliation(s)
- Collynn F Woeller
- Graduate Field of Biochemistry, Molecular and Cellular Biology, Cornell University, Ithaca, New York 14853, USA
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29
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Col B, Oltean S, Banerjee R. Translational regulation of human methionine synthase by upstream open reading frames. ACTA ACUST UNITED AC 2007; 1769:532-40. [PMID: 17683808 PMCID: PMC2682437 DOI: 10.1016/j.bbaexp.2007.06.003] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2007] [Revised: 06/11/2007] [Accepted: 06/27/2007] [Indexed: 01/17/2023]
Abstract
Methionine synthase is a key enzyme poised at the intersection of folate and sulfur metabolism and functions to reclaim homocysteine to the methionine cycle. The 5' leader sequence in human MS is 394 nucleotides long and harbors two open reading frames (uORFs). In this study, regulation of the main open reading frame by the uORFs has been elucidated. Both uORFs downregulate translation as demonstrated by mutation of the upstream AUG codons (uAUG) either singly or simultaneously. The uAUGs are capable of recruiting the 40S ribosomal complex as revealed by their ability to drive reporter expression in constructs in which the luciferase is fused to the uORFs. uORF2, which is predicted to encode a 30 amino acid long polypeptide, has a clustering of rare codons encoding arginine and proline. Mutation of a tandemly repeated rare codon for arginine at positions 3 and 4 in uORF2 to either common codons for the same amino acid or common codons for alanine results in complete alleviation of translation inhibition. This suggests a mechanism for ribosome stalling and demonstrates that the cis-effects on translation by uORF2 is dependent on the nucleotide sequence but is apparently independent of the sequence of the encoded peptide. This study reveals complex regulation of the essential housekeeping gene, methionine synthase, by the uORFs in its leader sequence.
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Affiliation(s)
| | | | - Ruma Banerjee
- Address Correspondence to: Ruma Banerjee, Biochemistry, Redox Biology Center, Biochemistry Department, University of Nebraska, Lincoln, NE 68588-0664, Tel. (402)-472-2941,
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Solomon LR. Disorders of cobalamin (Vitamin B12) metabolism: Emerging concepts in pathophysiology, diagnosis and treatment. Blood Rev 2007; 21:113-30. [DOI: 10.1016/j.blre.2006.05.001] [Citation(s) in RCA: 83] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
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Abstract
The cell has many ways to regulate the production of proteins. One mechanism is through the changes to the machinery of translation initiation. These alterations favor the translation of one subset of mRNAs over another. It was first shown that internal ribosome entry sites (IRESes) within viral RNA genomes allowed the production of viral proteins more efficiently than most of the host proteins. The RNA secondary structure of viral IRESes has sometimes been conserved between viral species even though the primary sequences differ. These structures are important for IRES function, but no similar structure conservation has yet to be shown in cellular IRES. With the advances in mathematical modeling and computational approaches to complex biological problems, is there a way to predict an IRES in a data set of unknown sequences? This review examines what is known about cellular IRES structures, as well as the data sets and tools available to examine this question. We find that the lengths, number of upstream AUGs, and %GC content of 5'-UTRs of the human transcriptome have a similar distribution to those of published IRES-containing UTRs. Although the UTRs containing IRESes are on the average longer, almost half of all 5'-UTRs are long enough to contain an IRES. Examination of the available RNA structure prediction software and RNA motif searching programs indicates that while these programs are useful tools to fine tune the empirically determined RNA secondary structure, the accuracy of de novo secondary structure prediction of large RNA molecules and subsequent identification of new IRES elements by computational approaches, is still not possible.
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Affiliation(s)
- Stephen D Baird
- Department of Biochemistry, Microbiology and Immunology, University of Ottawa, Ontario K1H 8M5, Canada
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Vitvitsky V, Thomas M, Ghorpade A, Gendelman HE, Banerjee R. A functional transsulfuration pathway in the brain links to glutathione homeostasis. J Biol Chem 2006; 281:35785-93. [PMID: 17005561 DOI: 10.1074/jbc.m602799200] [Citation(s) in RCA: 173] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Oxidative stress and diminished glutathione pools play critical roles in the pathogenesis of neurodegenerative diseases, including Alzheimer and Parkinson disease. Synthesis of glutathione, the most abundant mammalian antioxidant, is regulated at the substrate level by cysteine, which is synthesized from homocysteine via the transsulfuration pathway. Elevated homocysteine and diminished glutathione levels, seen in Alzheimer and Parkinson disease patients suggest impairments in the transsulfuration pathway that connects these metabolites. However, the very existence of this metabolic pathway in the brain is a subject of controversy. The product of the first of two enzymes in this pathway, cystathionine, is present at higher levels in brain as compared with other organs. This, together with the reported absence of the second enzyme, gamma-cystathionase, has led to the suggestion that the transsulfuration pathway is incomplete in the brain. In this study, we incubated mouse and human neurons and astrocytes and murine brain slices in medium with [35S]methionine and detected radiolabel incorporation into glutathione. This label transfer was sensitive to inhibition of gamma-cystathionase. In adult brain slices, approximately 40% of the glutathione was depleted within 10 h following gamma-cystathionase inhibition. In cultured human astrocytes, flux through the transsulfuration pathway increased under oxidative stress conditions, and blockade of this pathway led to reduced cell viability under oxidizing conditions. This study establishes the presence of an intact transsulfuration pathway and demonstrates its contribution to glutathione-dependent redox-buffering capacity under ex vivo conditions in brain cells and slices.
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Affiliation(s)
- Victor Vitvitsky
- Redox Biology Center, University of Nebraska-Lincoln, Lincoln, Nebraska 68588, USA
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Aguado C, Pérez B, Ugarte M, Desviat LR. Analysis of the effect of tetrahydrobiopterin on PAH gene expression in hepatoma cells. FEBS Lett 2006; 580:1697-701. [PMID: 16504182 DOI: 10.1016/j.febslet.2006.02.005] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2006] [Revised: 02/03/2006] [Accepted: 02/07/2006] [Indexed: 11/29/2022]
Abstract
Tetrahydrobiopterin (BH4)-responsive phenylalanine hydroxylase (PAH) deficiency is a recently recognized variant of phenylketonuria, with a probable multifactorial molecular basis. In this study we have investigated the effect of BH4 on PAH gene expression in human hepatoma. Our results show that increased BH4 levels result in an enhancement of PAH activity and PAH protein, due to longer turnover rates, while PAH mRNA levels remain unchanged. This was confirmed for mutant PAH proteins (A309V, V388M and Y414C) associated to in vivo BH4 responsiveness, validating previous studies. We can conclude that there is no effect of the cofactor on PAH gene transcription, probably being the chemical chaperone effect of BH4 stabilizing mutant PAH proteins the major underlying mechanism of the response.
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Affiliation(s)
- Cristina Aguado
- Centro de Biología Molecular Severo Ochoa, CSIC-UAM, Universidad Autónoma de Madrid, Cantoblanco, 28049 Madrid, Spain
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Kozak M. A second look at cellular mRNA sequences said to function as internal ribosome entry sites. Nucleic Acids Res 2005; 33:6593-602. [PMID: 16314320 PMCID: PMC1298923 DOI: 10.1093/nar/gki958] [Citation(s) in RCA: 129] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2005] [Accepted: 10/26/2005] [Indexed: 01/27/2023] Open
Abstract
This review takes a second look at a set of mRNAs that purportedly employ an alternative mechanism of initiation when cap-dependent translation is reduced during mitosis or stress conditions. A closer look is necessary because evidence cited in support of the internal initiation hypothesis is often flawed. When putative internal ribosome entry sequences (IRESs) are examined more carefully, they often turn out to harbor cryptic promoters or splice sites. This undermines the dicistronic assay, wherein IRES activity is measured by the ability to support translation of the 3' cistron. Most putative IRESs still have not been checked carefully to determine whether the dicistronic vector produces only the intended dicistronic mRNA. The widespread use of the pRF vector is a major problem because this vector, which has Renilla luciferase as the 5' cistron and firefly luciferase as the 3' cistron, has been found to generate spliced transcripts. RNA transfection assays could theoretically circumvent these problems, but most candidate IRESs score very weakly in that test. The practice of calling even very weak results 'positive' is one of the problems discussed herein. The extremely low efficiency of putative IRESs is inconsistent with their postulated biological roles.'
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Affiliation(s)
- Marilyn Kozak
- Department of Biochemistry, Robert Wood Johnson Medical School, 675 Hoes Lane, Piscataway, NJ 08854, USA.
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