1
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Moir RD, Merheb E, Chitu V, Richard Stanley E, Willis IM. Molecular basis of neurodegeneration in a mouse model of Polr3-related disease. bioRxiv 2023:2023.12.12.571310. [PMID: 38168294 PMCID: PMC10760057 DOI: 10.1101/2023.12.12.571310] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 01/05/2024]
Abstract
Pathogenic variants in subunits of RNA polymerase (Pol) III cause a spectrum of neurodegenerative diseases including 4H leukodystrophy. Disease onset occurs from infancy to early adulthood and is associated with a variable range and severity of neurological and non-neurological features. The molecular basis of disease pathogenesis is unknown. We developed a postnatal whole-body mouse model expressing pathogenic Polr3a mutations to examine the molecular mechanisms by which reduced Pol III transcription results primarily in central nervous system phenotypes. Polr3a mutant mice exhibit behavioral deficits, cerebral pathology and exocrine pancreatic atrophy. Transcriptome and immunohistochemistry analyses of cerebra during disease progression show a reduction in most Pol III transcripts, induction of innate immune and integrated stress responses and cell type-specific gene expression changes reflecting neuron and oligodendrocyte loss and microglial activation. Earlier in the disease when integrated stress and innate immune responses are minimally induced, mature tRNA sequencing revealed a global reduction in tRNA levels and an altered tRNA profile but no changes in other Pol III transcripts. Thus, changes in the size and/or composition of the tRNA pool have a causal role in disease initiation. Our findings reveal different tissue- and brain region-specific sensitivities to a defect in Pol III transcription.
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Affiliation(s)
- Robyn D. Moir
- Department of Biochemistry, Albert Einstein College of Medicine, 1300 Morris Park Ave, Bronx NY 10461, USA
| | - Emilio Merheb
- Department of Biochemistry, Albert Einstein College of Medicine, 1300 Morris Park Ave, Bronx NY 10461, USA
| | - Violeta Chitu
- Department of Developmental and Molecular Biology, Albert Einstein College of Medicine, 1300 Morris Park Ave, Bronx NY 10461, USA
| | - E. Richard Stanley
- Department of Developmental and Molecular Biology, Albert Einstein College of Medicine, 1300 Morris Park Ave, Bronx NY 10461, USA
| | - Ian M. Willis
- Department of Biochemistry, Albert Einstein College of Medicine, 1300 Morris Park Ave, Bronx NY 10461, USA
- Department of Systems and Computational Biology, Albert Einstein College of Medicine, 1300 Morris Park Ave, Bronx NY 10461, USA
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2
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Moir RD, Lavados C, Lee J, Willis IM. Functional characterization of Polr3a hypomyelinating leukodystrophy mutations in the S. cerevisiae homolog, RPC160. Gene 2020; 768:145259. [PMID: 33148458 DOI: 10.1016/j.gene.2020.145259] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2020] [Revised: 09/23/2020] [Accepted: 10/20/2020] [Indexed: 12/12/2022]
Abstract
Mutations in RNA polymerase III (Pol III) cause hypomeylinating leukodystrophy (HLD) and neurodegeneration in humans. POLR3A and POLR3B, the two largest Pol III subunits, together form the catalytic center and carry the majority of disease alleles. Disease-causing mutations include invariant and highly conserved residues that are predicted to negatively affect Pol III activity and decrease transcriptional output. A subset of HLD missense mutations in POLR3A cluster in the pore region that provides nucleotide access to the Pol III active site. These mutations were engineered at the corresponding positions in the Saccharomyces cerevisiae homolog, Rpc160, to evaluate their functional deficits. None of the mutations caused a growth or transcription phenotype in yeast. Each mutation was combined with a frequently occurring pore mutation, POLR3A G672E, which was also wild-type for growth and transcription. The double mutants showed a spectrum of phenotypes from wild-type to lethal, with only the least fit combinations showing an effect on Pol III transcription. In one slow-growing temperature-sensitive mutant the steady-state level of tRNAs was unaffected, however global tRNA synthesis was compromised, as was the synthesis of RPR1 and SNR52 RNAs. Affinity-purified mutant Pol III was broadly defective in both factor-independent and factor-dependent transcription in vitro across genes that represent the yeast Pol III transcriptome. Thus, the robustness of yeast Rpc160 to single Pol III leukodystrophy mutations in the pore domain can be overcome by a second mutation in the domain.
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Affiliation(s)
- Robyn D Moir
- Department of Biochemistry, Albert Einstein College of Medicine, Bronx, NY 10461, USA.
| | - Christian Lavados
- Graduate Program in Biomedical Science, Albert Einstein College of Medicine, Bronx, NY 10461, USA
| | - JaeHoon Lee
- Department of Medicine (Cardiology), Albert Einstein College of Medicine, Bronx, NY 10461, USA
| | - Ian M Willis
- Departments of Biochemistry and Systems and Computational Biology, Albert Einstein College of Medicine, Bronx, NY 10461, USA
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3
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Vorländer MK, Baudin F, Moir RD, Wetzel R, Hagen WJH, Willis IM, Müller CW. Structural basis for RNA polymerase III transcription repression by Maf1. Nat Struct Mol Biol 2020; 27:229-232. [PMID: 32066962 PMCID: PMC7104376 DOI: 10.1038/s41594-020-0383-y] [Citation(s) in RCA: 28] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2019] [Accepted: 01/16/2020] [Indexed: 01/10/2023]
Abstract
Maf1 is a conserved inhibitor of RNA polymerase III (Pol III) that influences phenotypes from metabolic efficiency to lifespan. Here, we present a 3.3 Å cryo-EM structure of yeast Maf1 bound to Pol III, establishing that Maf1 sequesters Pol III elements involved in transcription initiation and binds the mobile C34 WH2 domain, sealing off the active site. The Maf1 binding site overlaps with that of TFIIIB in the pre-initiation complex.
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Affiliation(s)
- Matthias K Vorländer
- Structural and Computational Biology Unit, European Molecular Biology Laboratory (EMBL), Heidelberg, Germany.,Collaboration for Joint PhD Degree between EMBL and Heidelberg University Faculty of Biosciences, Heidelberg University, Heidelberg, Germany
| | - Florence Baudin
- Structural and Computational Biology Unit, European Molecular Biology Laboratory (EMBL), Heidelberg, Germany
| | - Robyn D Moir
- Department of Biochemistry, Albert Einstein College of Medicine, Bronx, NY, USA
| | - René Wetzel
- Structural and Computational Biology Unit, European Molecular Biology Laboratory (EMBL), Heidelberg, Germany
| | - Wim J H Hagen
- Structural and Computational Biology Unit, European Molecular Biology Laboratory (EMBL), Heidelberg, Germany
| | - Ian M Willis
- Department of Biochemistry, Albert Einstein College of Medicine, Bronx, NY, USA.,Department of Systems and Computational Biology, Albert Einstein College of Medicine, Bronx, NY, USA
| | - Christoph W Müller
- Structural and Computational Biology Unit, European Molecular Biology Laboratory (EMBL), Heidelberg, Germany.
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Choquet K, Pinard M, Yang S, Moir RD, Poitras C, Dicaire MJ, Sgarioto N, Larivière R, Kleinman CL, Willis IM, Gauthier MS, Coulombe B, Brais B. The leukodystrophy mutation Polr3b R103H causes homozygote mouse embryonic lethality and impairs RNA polymerase III biogenesis. Mol Brain 2019; 12:59. [PMID: 31221184 PMCID: PMC6587292 DOI: 10.1186/s13041-019-0479-7] [Citation(s) in RCA: 20] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2019] [Accepted: 06/11/2019] [Indexed: 01/16/2023] Open
Abstract
Recessive mutations in the ubiquitously expressed POLR3A and POLR3B genes are the most common cause of POLR3-related hypomyelinating leukodystrophy (POLR3-HLD), a rare childhood-onset disorder characterized by deficient cerebral myelin formation and cerebellar atrophy. POLR3A and POLR3B encode the two catalytic subunits of RNA Polymerase III (Pol III), which synthesizes numerous small non-coding RNAs. We recently reported that mice homozygous for the Polr3a mutation c.2015G > A (p.Gly672Glu) have no neurological abnormalities and thus do not recapitulate the human POLR3-HLD phenotype. To determine if other POLR3-HLD mutations can cause a leukodystrophy phenotype in mouse, we characterized mice carrying the Polr3b mutation c.308G > A (p.Arg103His). Surprisingly, homozygosity for this mutation was embryonically lethal with only wild-type and heterozygous animals detected at embryonic day 9.5. Using proteomics in a human cell line, we found that the POLR3B R103H mutation severely impairs assembly of the Pol III complex. We next generated Polr3aG672E/G672E/Polr3b+/R103Hdouble mutant mice but observed that this additional mutation was insufficient to elicit a neurological or transcriptional phenotype. Taken together with our previous study on Polr3a G672E mice, our results indicate that missense mutations in Polr3a and Polr3b can variably impair mouse development and Pol III function. Developing a proper model of POLR3-HLD is crucial to gain insights into the pathophysiological mechanisms involved in this devastating neurodegenerative disease.
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Affiliation(s)
- Karine Choquet
- Montreal Neurological Institute, McGill University, 3801 University Street, room 622, Montréal, Québec, H3A 2B4, Canada.,Department of Human Genetics, McGill University, Québec, Montréal, Canada.,Lady Davis Institute for Medical Research, Jewish General Hospital, Québec, Montréal, Canada
| | - Maxime Pinard
- Translational Proteomics Laboratory, Institut de recherches cliniques de Montréal (IRCM), Québec, Montréal, Canada
| | - Sharon Yang
- Montreal Neurological Institute, McGill University, 3801 University Street, room 622, Montréal, Québec, H3A 2B4, Canada
| | - Robyn D Moir
- Department of Biochemistry, Albert Einstein College of Medicine, New York, Bronx, USA
| | - Christian Poitras
- Translational Proteomics Laboratory, Institut de recherches cliniques de Montréal (IRCM), Québec, Montréal, Canada
| | - Marie-Josée Dicaire
- Montreal Neurological Institute, McGill University, 3801 University Street, room 622, Montréal, Québec, H3A 2B4, Canada
| | - Nicolas Sgarioto
- Montreal Neurological Institute, McGill University, 3801 University Street, room 622, Montréal, Québec, H3A 2B4, Canada
| | - Roxanne Larivière
- Montreal Neurological Institute, McGill University, 3801 University Street, room 622, Montréal, Québec, H3A 2B4, Canada
| | - Claudia L Kleinman
- Department of Human Genetics, McGill University, Québec, Montréal, Canada.,Lady Davis Institute for Medical Research, Jewish General Hospital, Québec, Montréal, Canada
| | - Ian M Willis
- Department of Biochemistry, Albert Einstein College of Medicine, New York, Bronx, USA
| | - Marie-Soleil Gauthier
- Translational Proteomics Laboratory, Institut de recherches cliniques de Montréal (IRCM), Québec, Montréal, Canada
| | - Benoit Coulombe
- Translational Proteomics Laboratory, Institut de recherches cliniques de Montréal (IRCM), Québec, Montréal, Canada.,Département de biochimie et médecine moléculaire, Université de Montréal, Québec, Montréal, Canada
| | - Bernard Brais
- Montreal Neurological Institute, McGill University, 3801 University Street, room 622, Montréal, Québec, H3A 2B4, Canada. .,Department of Human Genetics, McGill University, Québec, Montréal, Canada.
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Abstract
As a master negative regulator of RNA polymerase (Pol) III, Maf1 modulates transcription in response to nutrients and stress to balance the production of highly abundant tRNAs, 5S rRNA, and other small noncoding RNAs with cell growth and maintenance. This regulation of Pol III transcription is important for energetic economy as mice lacking Maf1 are lean and resist weight gain on normal and high fat diets. The lean phenotype of Maf1 knockout (KO) mice is attributed in part to metabolic inefficiencies which increase the demand for cellular energy and elevate catabolic processes, including autophagy/lipophagy and lipolysis. A futile RNA cycle involving increased synthesis and turnover of Pol III transcripts has been proposed as an important driver of these changes. Here, using targeted metabolomics, we find changes in the liver of fed and fasted Maf1 KO mice consistent with the function of mammalian Maf1 as a chronic Pol III repressor. Differences in long-chain acylcarnitine levels suggest that energy demand is higher in the fed state of Maf1 KO mice versus the fasted state. Quantitative metabolite profiling supports increased activity in the TCA cycle, the pentose phosphate pathway, and the urea cycle and reveals changes in nucleotide levels and the creatine system. Metabolite profiling also confirms key predictions of the futile RNA cycle hypothesis by identifying changes in many metabolites involved in nucleotide synthesis and turnover. Thus, constitutively high levels of Pol III transcription in Maf1 KO mice reprogram central metabolic pathways and waste metabolic energy through a futile RNA cycle.
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Affiliation(s)
- Ian M Willis
- Department of Biochemistry, Albert Einstein College of Medicine, Bronx, NY 10461;
- Department of Systems and Computational Biology, Albert Einstein College of Medicine, Bronx, NY 10461
| | - Robyn D Moir
- Department of Biochemistry, Albert Einstein College of Medicine, Bronx, NY 10461
| | - Nouria Hernandez
- Center for Integrative Genomics, Faculty of Biology and Medicine, University of Lausanne, 1015 Lausanne, Switzerland
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6
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Qiu Y, Moir RD, Willis IM, Seethapathy S, Biniakewitz RC, Kurland IJ. Enhanced Isotopic Ratio Outlier Analysis (IROA) Peak Detection and Identification with Ultra-High Resolution GC-Orbitrap/MS: Potential Application for Investigation of Model Organism Metabolomes. Metabolites 2018; 8:metabo8010009. [PMID: 29346327 PMCID: PMC5875999 DOI: 10.3390/metabo8010009] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2017] [Revised: 01/10/2018] [Accepted: 01/10/2018] [Indexed: 02/06/2023] Open
Abstract
Identifying non-annotated peaks may have a significant impact on the understanding of biological systems. In silico methodologies have focused on ESI LC/MS/MS for identifying non-annotated MS peaks. In this study, we employed in silico methodology to develop an Isotopic Ratio Outlier Analysis (IROA) workflow using enhanced mass spectrometric data acquired with the ultra-high resolution GC-Orbitrap/MS to determine the identity of non-annotated metabolites. The higher resolution of the GC-Orbitrap/MS, together with its wide dynamic range, resulted in more IROA peak pairs detected, and increased reliability of chemical formulae generation (CFG). IROA uses two different 13C-enriched carbon sources (randomized 95% 12C and 95% 13C) to produce mirror image isotopologue pairs, whose mass difference reveals the carbon chain length (n), which aids in the identification of endogenous metabolites. Accurate m/z, n, and derivatization information are obtained from our GC/MS workflow for unknown metabolite identification, and aids in silico methodologies for identifying isomeric and non-annotated metabolites. We were able to mine more mass spectral information using the same Saccharomyces cerevisiae growth protocol (Qiu et al. Anal. Chem 2016) with the ultra-high resolution GC-Orbitrap/MS, using 10% ammonia in methane as the CI reagent gas. We identified 244 IROA peaks pairs, which significantly increased IROA detection capability compared with our previous report (126 IROA peak pairs using a GC-TOF/MS machine). For 55 selected metabolites identified from matched IROA CI and EI spectra, using the GC-Orbitrap/MS vs. GC-TOF/MS, the average mass deviation for GC-Orbitrap/MS was 1.48 ppm, however, the average mass deviation was 32.2 ppm for the GC-TOF/MS machine. In summary, the higher resolution and wider dynamic range of the GC-Orbitrap/MS enabled more accurate CFG, and the coupling of accurate mass GC/MS IROA methodology with in silico fragmentation has great potential in unknown metabolite identification, with applications for characterizing model organism networks.
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Affiliation(s)
- Yunping Qiu
- Stable Isotope and Metabolomics Core Facility, Diabetes Center, Department of Medicine, Albert Einstein College of Medicine, Bronx, NY 10461, USA.
| | - Robyn D Moir
- Department of Biochemistry, Albert Einstein College of Medicine, Bronx, NY 10461, USA.
| | - Ian M Willis
- Department of Biochemistry, Albert Einstein College of Medicine, Bronx, NY 10461, USA.
| | | | | | - Irwin J Kurland
- Stable Isotope and Metabolomics Core Facility, Diabetes Center, Department of Medicine, Albert Einstein College of Medicine, Bronx, NY 10461, USA.
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7
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Abstract
RNA polymerase (Pol) III has a specialized role in transcribing the most abundant RNAs in eukaryotic cells, transfer RNAs (tRNAs), along with other ubiquitous small noncoding RNAs, many of which have functions related to the ribosome and protein synthesis. The high energetic cost of producing these RNAs and their central role in protein synthesis underlie the robust regulation of Pol III transcription in response to nutrients and stress by growth regulatory pathways. Downstream of Pol III, signaling impacts posttranscriptional processes affecting tRNA function in translation and tRNA cleavage into smaller fragments that are increasingly attributed with novel cellular activities. In this review, we consider how nutrients and stress control Pol III transcription via its factors and its negative regulator, Maf1. We highlight recent work showing that the composition of the tRNA population and the function of individual tRNAs is dynamically controlled and that unrestrained Pol III transcription can reprogram central metabolic pathways.
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Affiliation(s)
- Ian M Willis
- Department of Biochemistry, Albert Einstein College of Medicine, Bronx, New York 10461, USA; , .,Department of Systems and Computational Biology, Albert Einstein College of Medicine, Bronx, New York 10461, USA
| | - Robyn D Moir
- Department of Biochemistry, Albert Einstein College of Medicine, Bronx, New York 10461, USA; ,
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8
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Choquet K, Yang S, Moir RD, Forget D, Larivière R, Bouchard A, Poitras C, Sgarioto N, Dicaire MJ, Noohi F, Kennedy TE, Rochford J, Bernard G, Teichmann M, Coulombe B, Willis IM, Kleinman CL, Brais B. Absence of neurological abnormalities in mice homozygous for the Polr3a G672E hypomyelinating leukodystrophy mutation. Mol Brain 2017; 10:13. [PMID: 28407788 PMCID: PMC5391615 DOI: 10.1186/s13041-017-0294-y] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/03/2017] [Accepted: 04/04/2017] [Indexed: 01/08/2023] Open
Abstract
Recessive mutations in the ubiquitously expressed POLR3A gene cause one of the most frequent forms of childhood-onset hypomyelinating leukodystrophy (HLD): POLR3-HLD. POLR3A encodes the largest subunit of RNA Polymerase III (Pol III), which is responsible for the transcription of transfer RNAs (tRNAs) and a large array of other small non-coding RNAs. In order to study the central nervous system pathophysiology of the disease, we introduced the French Canadian founder Polr3a mutation c.2015G > A (p.G672E) in mice, generating homozygous knock-in (KI/KI) as well as compound heterozygous mice for one Polr3a KI and one null allele (KI/KO). Both KI/KI and KI/KO mice are viable and are able to reproduce. To establish if they manifest a motor phenotype, WT, KI/KI and KI/KO mice were submitted to a battery of behavioral tests over one year. The KI/KI and KI/KO mice have overall normal balance, muscle strength and general locomotion. Cerebral and cerebellar Luxol Fast Blue staining and measurement of levels of myelin proteins showed no significant differences between the three groups, suggesting that myelination is not overtly impaired in Polr3a KI/KI and KI/KO mice. Finally, expression levels of several Pol III transcripts in the brain showed no statistically significant differences. We conclude that the first transgenic mice with a leukodystrophy-causing Polr3a mutation do not recapitulate the childhood-onset HLD observed in the majority of human patients with POLR3A mutations, and provide essential information to guide selection of Polr3a mutations for developing future mouse models of the disease.
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Affiliation(s)
- Karine Choquet
- Montreal Neurological Institute, McGill University, 3801 University Street, room 622, Montréal, Québec, H3A 2B4, Canada.,Department of Human Genetics, McGill University, Montréal, Québec, Canada.,Lady Davis Institute for Medical Research, Jewish General Hospital, Montréal, Québec, Canada
| | - Sharon Yang
- Montreal Neurological Institute, McGill University, 3801 University Street, room 622, Montréal, Québec, H3A 2B4, Canada
| | - Robyn D Moir
- Department of Biochemistry, Albert Einstein College of Medicine, Bronx, New York, USA
| | - Diane Forget
- Translational Proteomics Laboratory, Institut de recherches cliniques de Montréal (IRCM), Montréal, Québec, Canada
| | - Roxanne Larivière
- Montreal Neurological Institute, McGill University, 3801 University Street, room 622, Montréal, Québec, H3A 2B4, Canada
| | - Annie Bouchard
- Translational Proteomics Laboratory, Institut de recherches cliniques de Montréal (IRCM), Montréal, Québec, Canada
| | - Christian Poitras
- Translational Proteomics Laboratory, Institut de recherches cliniques de Montréal (IRCM), Montréal, Québec, Canada
| | - Nicolas Sgarioto
- Montreal Neurological Institute, McGill University, 3801 University Street, room 622, Montréal, Québec, H3A 2B4, Canada
| | - Marie-Josée Dicaire
- Montreal Neurological Institute, McGill University, 3801 University Street, room 622, Montréal, Québec, H3A 2B4, Canada
| | - Forough Noohi
- Montreal Neurological Institute, McGill University, 3801 University Street, room 622, Montréal, Québec, H3A 2B4, Canada.,Department of Human Genetics, McGill University, Montréal, Québec, Canada
| | - Timothy E Kennedy
- Montreal Neurological Institute, McGill University, 3801 University Street, room 622, Montréal, Québec, H3A 2B4, Canada
| | | | - Geneviève Bernard
- Departments of Neurology and Neurosurgery, and Pediatrics, McGill University, Montreal, Canada.,Department of Medical Genetics, Montreal Children's Hospital, McGill University Health Center, Montreal, Canada.,Child Health and Human Development Program, Research Institute of the McGill University Health Center, Montreal, Canada
| | - Martin Teichmann
- INSERM U1212 - CNRS UMR5320, Université de Bordeaux, Bordeaux, France
| | - Benoit Coulombe
- Translational Proteomics Laboratory, Institut de recherches cliniques de Montréal (IRCM), Montréal, Québec, Canada.,Département de biochimie et médecine moléculaire, Université de Montréal, Montréal, Québec, Canada
| | - Ian M Willis
- Department of Biochemistry, Albert Einstein College of Medicine, Bronx, New York, USA
| | - Claudia L Kleinman
- Department of Human Genetics, McGill University, Montréal, Québec, Canada.,Lady Davis Institute for Medical Research, Jewish General Hospital, Montréal, Québec, Canada
| | - Bernard Brais
- Montreal Neurological Institute, McGill University, 3801 University Street, room 622, Montréal, Québec, H3A 2B4, Canada. .,Department of Human Genetics, McGill University, Montréal, Québec, Canada.
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9
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Dasgupta S, Yang C, Castro LM, Tashima AK, Ferro ES, Moir RD, Willis IM, Fricker LD. Analysis of the Yeast Peptidome and Comparison with the Human Peptidome. PLoS One 2016; 11:e0163312. [PMID: 27685651 PMCID: PMC5042401 DOI: 10.1371/journal.pone.0163312] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2016] [Accepted: 09/07/2016] [Indexed: 12/22/2022] Open
Abstract
Peptides function as signaling molecules in species as diverse as humans and yeast. Mass spectrometry-based peptidomics techniques provide a relatively unbiased method to assess the peptidome of biological samples. In the present study, we used a quantitative peptidomic technique to characterize the peptidome of the yeast Saccharomyces cerevisiae and compare it to the peptidomes of mammalian cell lines and tissues. Altogether, 297 yeast peptides derived from 75 proteins were identified. The yeast peptides are similar to those of the human peptidome in average size and amino acid composition. Inhibition of proteasome activity with either bortezomib or epoxomicin led to decreased levels of some yeast peptides, suggesting that these peptides are generated by the proteasome. Approximately 30% of the yeast peptides correspond to the N- or C-terminus of the protein; the human peptidome is also highly represented in N- or C-terminal protein fragments. Most yeast and humans peptides are derived from a subset of abundant proteins, many with functions involving cellular metabolism or protein synthesis and folding. Of the 75 yeast proteins that give rise to peptides, 24 have orthologs that give rise to human and/or mouse peptides and for some, the same region of the proteins are found in the human, mouse, and yeast peptidomes. Taken together, these results support the hypothesis that intracellular peptides may have specific and conserved biological functions.
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Affiliation(s)
- Sayani Dasgupta
- Department of Molecular Pharmacology, Albert Einstein College of Medicine, Bronx, New York, 10461, United States of America
| | - Ciyu Yang
- Department of Pathology, Memorial Sloan Kettering Cancer Center, New York, New York, 10065, United States of America
| | - Leandro M. Castro
- Biomedical Science Institute, Campus on the São Paulo Coast, São Paulo State University, São Vicente, 11330–900, SP, Brazil
| | - Alexandre K. Tashima
- Department of Biochemistry, Escola Paulista de Medicina, Federal University of Sao Paulo, Sao Paulo, SP, 04023–901, SP, Brazil
| | - Emer S. Ferro
- Department of Pharmacology, Biomedical Science Institute, University of São Paulo, São Paulo, 05508–000, SP, Brazil
| | - Robyn D. Moir
- Department of Biochemistry, Albert Einstein College of Medicine, Bronx, New York, 10461, United States of America
| | - Ian M. Willis
- Department of Biochemistry, Albert Einstein College of Medicine, Bronx, New York, 10461, United States of America
- Department of Systems & Computational Biology, Albert Einstein College of Medicine, Bronx, New York, 10461, United States of America
| | - Lloyd D. Fricker
- Department of Molecular Pharmacology, Albert Einstein College of Medicine, Bronx, New York, 10461, United States of America
- Department of Neuroscience, Albert Einstein College of Medicine, Bronx, New York, 10461, United States of America
- * E-mail:
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10
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Bonhoure N, Byrnes A, Moir RD, Hodroj W, Preitner F, Praz V, Marcelin G, Chua SC, Martinez-Lopez N, Singh R, Moullan N, Auwerx J, Willemin G, Shah H, Hartil K, Vaitheesvaran B, Kurland I, Hernandez N, Willis IM. Loss of the RNA polymerase III repressor MAF1 confers obesity resistance. Genes Dev 2015; 29:934-47. [PMID: 25934505 PMCID: PMC4421982 DOI: 10.1101/gad.258350.115] [Citation(s) in RCA: 81] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
MAF1 is a global repressor of RNA polymerase III transcription that regulates the expression of highly abundant noncoding RNAs in response to nutrient availability and cellular stress. Thus, MAF1 function is thought to be important for metabolic economy. Here we show that a whole-body knockout of Maf1 in mice confers resistance to diet-induced obesity and nonalcoholic fatty liver disease by reducing food intake and increasing metabolic inefficiency. Energy expenditure in Maf1(-/-) mice is increased by several mechanisms. Precursor tRNA synthesis was increased in multiple tissues without significant effects on mature tRNA levels, implying increased turnover in a futile tRNA cycle. Elevated futile cycling of hepatic lipids was also observed. Metabolite profiling of the liver and skeletal muscle revealed elevated levels of many amino acids and spermidine, which links the induction of autophagy in Maf1(-/-) mice with their extended life span. The increase in spermidine was accompanied by reduced levels of nicotinamide N-methyltransferase, which promotes polyamine synthesis, enables nicotinamide salvage to regenerate NAD(+), and is associated with obesity resistance. Consistent with this, NAD(+) levels were increased in muscle. The importance of MAF1 for metabolic economy reveals the potential for MAF1 modulators to protect against obesity and its harmful consequences.
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Affiliation(s)
- Nicolas Bonhoure
- Center for Integrative Genomics, Faculty of Biology and Medicine, University of Lausanne, 1015 Lausanne, Switzerland
| | - Ashlee Byrnes
- Department of Biochemistry, Albert Einstein College of Medicine, Bronx, New York 10461, USA
| | - Robyn D Moir
- Department of Biochemistry, Albert Einstein College of Medicine, Bronx, New York 10461, USA
| | - Wassim Hodroj
- Center for Integrative Genomics, Faculty of Biology and Medicine, University of Lausanne, 1015 Lausanne, Switzerland
| | - Frédéric Preitner
- Mouse Metabolic Evaluation Facility, Center for Integrative Genomics, University of Lausanne, 1015 Lausanne, Switzerland
| | - Viviane Praz
- Center for Integrative Genomics, Faculty of Biology and Medicine, University of Lausanne, 1015 Lausanne, Switzerland; Swiss Institute of Bioinformatics, 1015 Lausanne, Switzerland
| | - Genevieve Marcelin
- Division of Endocrinology, Department of Medicine, Albert Einstein College of Medicine, Bronx, New York 10461, USA
| | - Streamson C Chua
- Division of Endocrinology, Department of Medicine, Albert Einstein College of Medicine, Bronx, New York 10461, USA; Diabetes Research Center, Albert Einstein College of Medicine, Bronx, New York 10461, USA
| | - Nuria Martinez-Lopez
- Division of Endocrinology, Department of Medicine, Albert Einstein College of Medicine, Bronx, New York 10461, USA
| | - Rajat Singh
- Division of Endocrinology, Department of Medicine, Albert Einstein College of Medicine, Bronx, New York 10461, USA; Diabetes Research Center, Albert Einstein College of Medicine, Bronx, New York 10461, USA
| | - Norman Moullan
- Laboratory for Integrative and Systems Physiology, Ecole Polytechnique Fédérale de Lausanne (EPFL), 1015 Lausanne, Switzerland
| | - Johan Auwerx
- Laboratory for Integrative and Systems Physiology, Ecole Polytechnique Fédérale de Lausanne (EPFL), 1015 Lausanne, Switzerland
| | - Gilles Willemin
- Center for Integrative Genomics, Faculty of Biology and Medicine, University of Lausanne, 1015 Lausanne, Switzerland; Mouse Metabolic Evaluation Facility, Center for Integrative Genomics, University of Lausanne, 1015 Lausanne, Switzerland
| | - Hardik Shah
- Division of Endocrinology, Department of Medicine, Albert Einstein College of Medicine, Bronx, New York 10461, USA
| | - Kirsten Hartil
- Division of Endocrinology, Department of Medicine, Albert Einstein College of Medicine, Bronx, New York 10461, USA
| | - Bhavapriya Vaitheesvaran
- Division of Endocrinology, Department of Medicine, Albert Einstein College of Medicine, Bronx, New York 10461, USA
| | - Irwin Kurland
- Division of Endocrinology, Department of Medicine, Albert Einstein College of Medicine, Bronx, New York 10461, USA; Diabetes Research Center, Albert Einstein College of Medicine, Bronx, New York 10461, USA
| | - Nouria Hernandez
- Center for Integrative Genomics, Faculty of Biology and Medicine, University of Lausanne, 1015 Lausanne, Switzerland;
| | - Ian M Willis
- Department of Biochemistry, Albert Einstein College of Medicine, Bronx, New York 10461, USA; Diabetes Research Center, Albert Einstein College of Medicine, Bronx, New York 10461, USA;
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Lee J, Moir RD, Willis IM. Differential Phosphorylation of RNA Polymerase III and the Initiation Factor TFIIIB in Saccharomyces cerevisiae. PLoS One 2015; 10:e0127225. [PMID: 25970584 PMCID: PMC4430316 DOI: 10.1371/journal.pone.0127225] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2014] [Accepted: 04/13/2015] [Indexed: 11/19/2022] Open
Abstract
The production of ribosomes and tRNAs for protein synthesis has a high energetic cost and is under tight transcriptional control to ensure that the level of RNA synthesis is balanced with nutrient availability and the prevailing environmental conditions. In the RNA polymerase (pol) III system in yeast, nutrients and stress affect transcription through a bifurcated signaling pathway in which protein kinase A (PKA) and TORC1 activity directly or indirectly, through downstream kinases, alter the phosphorylation state and function of the Maf1 repressor and Rpc53, a TFIIF-like subunit of the polymerase. However, numerous lines of evidence suggest greater complexity in the regulatory network including the phosphoregulation of other pol III components. To address this issue, we systematically examined all 17 subunits of pol III along with the three subunits of the initiation factor TFIIIB for evidence of differential phosphorylation in response to inhibition of TORC1. A relatively high stoichiometry of phosphorylation was observed for several of these proteins and the Rpc82 subunit of the polymerase and the Bdp1 subunit of TFIIIB were found to be differentially phosphorylated. Bdp1 is phosphorylated on four major sites during exponential growth and the protein is variably dephosphorylated under conditions that inhibit tRNA gene transcription. PKA, the TORC1-regulated kinase Sch9 and protein kinase CK2 are all implicated in the phosphorylation of Bdp1. Alanine substitutions at the four phosphosites cause hyper-repression of transcription indicating that phosphorylation of Bdp1 opposes Maf1-mediated repression. The new findings suggest an integrated regulatory model for signaling events controlling pol III transcription.
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Affiliation(s)
- Jaehoon Lee
- Department of Biochemistry, Albert Einstein College of Medicine, Bronx, New York, United States of America
| | - Robyn D. Moir
- Department of Biochemistry, Albert Einstein College of Medicine, Bronx, New York, United States of America
- * E-mail: (RDM); (IMW)
| | - Ian M. Willis
- Department of Biochemistry, Albert Einstein College of Medicine, Bronx, New York, United States of America
- Department of Systems and Computational Biology, Albert Einstein College of Medicine, Bronx, New York, United States of America
- * E-mail: (RDM); (IMW)
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Frame IJ, Deniskin R, Rinderspacher A, Katz F, Deng SX, Moir RD, Adjalley SH, Coburn-Flynn O, Fidock DA, Willis IM, Landry DW, Akabas MH. Yeast-based high-throughput screen identifies Plasmodium falciparum equilibrative nucleoside transporter 1 inhibitors that kill malaria parasites. ACS Chem Biol 2015; 10:775-83. [PMID: 25602169 DOI: 10.1021/cb500981y] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Equilibrative transporters are potential drug targets; however, most functional assays involve radioactive substrate uptake that is unsuitable for high-throughput screens (HTS). We developed a robust yeast-based growth assay that is potentially applicable to many equilibrative transporters. As proof of principle, we applied our approach to Equilibrative Nucleoside Transporter 1 of the malarial parasite Plasmodium falciparum (PfENT1). PfENT1 inhibitors might serve as novel antimalarial drugs since PfENT1-mediated purine import is essential for parasite proliferation. To identify PfENT1 inhibitors, we screened 64 560 compounds and identified 171 by their ability to rescue the growth of PfENT1-expressing fui1Δ yeast in the presence of a cytotoxic PfENT1 substrate, 5-fluorouridine (5-FUrd). In secondary assays, nine of the highest activity compounds inhibited PfENT1-dependent growth of a purine auxotrophic yeast strain with adenosine as the sole purine source (IC50 0.2-2 μM). These nine compounds completely blocked [(3)H]adenosine uptake into PfENT1-expressing yeast and erythrocyte-free trophozoite-stage parasites (IC50 5-50 nM), and inhibited chloroquine-sensitive and -resistant parasite proliferation (IC50 5-50 μM). Wild-type (WT) parasite IC50 values were up to 4-fold lower compared to PfENT1-knockout (pfent1Δ) parasites. pfent1Δ parasite killing showed a delayed-death phenotype not observed with WT. We infer that, in parasites, the compounds inhibit both PfENT1 and a secondary target with similar efficacy. The secondary target identity is unknown, but its existence may reduce the likelihood of parasites developing resistance to PfENT1 inhibitors. Our data support the hypothesis that blocking purine transport through PfENT1 may be a novel and compelling approach for antimalarial drug development.
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Affiliation(s)
- I. J. Frame
- Department of Physiology & Biophysics, ‡Department of Biochemistry, §Department of Neuroscience, and ∥Department of Medicine, Albert Einstein College of Medicine, 1300 Morris Park Avenue, Bronx, New York 10461, United States
- Department of Medicine and #Department of Microbiology & Immunology, Columbia University Medical Center, 630 and 701 West 168th Street, New York, New York 10032, United States
| | - Roman Deniskin
- Department of Physiology & Biophysics, ‡Department of Biochemistry, §Department of Neuroscience, and ∥Department of Medicine, Albert Einstein College of Medicine, 1300 Morris Park Avenue, Bronx, New York 10461, United States
- Department of Medicine and #Department of Microbiology & Immunology, Columbia University Medical Center, 630 and 701 West 168th Street, New York, New York 10032, United States
| | - Alison Rinderspacher
- Department of Physiology & Biophysics, ‡Department of Biochemistry, §Department of Neuroscience, and ∥Department of Medicine, Albert Einstein College of Medicine, 1300 Morris Park Avenue, Bronx, New York 10461, United States
- Department of Medicine and #Department of Microbiology & Immunology, Columbia University Medical Center, 630 and 701 West 168th Street, New York, New York 10032, United States
| | - Francine Katz
- Department of Physiology & Biophysics, ‡Department of Biochemistry, §Department of Neuroscience, and ∥Department of Medicine, Albert Einstein College of Medicine, 1300 Morris Park Avenue, Bronx, New York 10461, United States
- Department of Medicine and #Department of Microbiology & Immunology, Columbia University Medical Center, 630 and 701 West 168th Street, New York, New York 10032, United States
| | - Shi-Xian Deng
- Department of Physiology & Biophysics, ‡Department of Biochemistry, §Department of Neuroscience, and ∥Department of Medicine, Albert Einstein College of Medicine, 1300 Morris Park Avenue, Bronx, New York 10461, United States
- Department of Medicine and #Department of Microbiology & Immunology, Columbia University Medical Center, 630 and 701 West 168th Street, New York, New York 10032, United States
| | - Robyn D. Moir
- Department of Physiology & Biophysics, ‡Department of Biochemistry, §Department of Neuroscience, and ∥Department of Medicine, Albert Einstein College of Medicine, 1300 Morris Park Avenue, Bronx, New York 10461, United States
- Department of Medicine and #Department of Microbiology & Immunology, Columbia University Medical Center, 630 and 701 West 168th Street, New York, New York 10032, United States
| | - Sophie H. Adjalley
- Department of Physiology & Biophysics, ‡Department of Biochemistry, §Department of Neuroscience, and ∥Department of Medicine, Albert Einstein College of Medicine, 1300 Morris Park Avenue, Bronx, New York 10461, United States
- Department of Medicine and #Department of Microbiology & Immunology, Columbia University Medical Center, 630 and 701 West 168th Street, New York, New York 10032, United States
| | - Olivia Coburn-Flynn
- Department of Physiology & Biophysics, ‡Department of Biochemistry, §Department of Neuroscience, and ∥Department of Medicine, Albert Einstein College of Medicine, 1300 Morris Park Avenue, Bronx, New York 10461, United States
- Department of Medicine and #Department of Microbiology & Immunology, Columbia University Medical Center, 630 and 701 West 168th Street, New York, New York 10032, United States
| | - David A. Fidock
- Department of Physiology & Biophysics, ‡Department of Biochemistry, §Department of Neuroscience, and ∥Department of Medicine, Albert Einstein College of Medicine, 1300 Morris Park Avenue, Bronx, New York 10461, United States
- Department of Medicine and #Department of Microbiology & Immunology, Columbia University Medical Center, 630 and 701 West 168th Street, New York, New York 10032, United States
| | - Ian M. Willis
- Department of Physiology & Biophysics, ‡Department of Biochemistry, §Department of Neuroscience, and ∥Department of Medicine, Albert Einstein College of Medicine, 1300 Morris Park Avenue, Bronx, New York 10461, United States
- Department of Medicine and #Department of Microbiology & Immunology, Columbia University Medical Center, 630 and 701 West 168th Street, New York, New York 10032, United States
| | - Donald W. Landry
- Department of Physiology & Biophysics, ‡Department of Biochemistry, §Department of Neuroscience, and ∥Department of Medicine, Albert Einstein College of Medicine, 1300 Morris Park Avenue, Bronx, New York 10461, United States
- Department of Medicine and #Department of Microbiology & Immunology, Columbia University Medical Center, 630 and 701 West 168th Street, New York, New York 10032, United States
| | - Myles H. Akabas
- Department of Physiology & Biophysics, ‡Department of Biochemistry, §Department of Neuroscience, and ∥Department of Medicine, Albert Einstein College of Medicine, 1300 Morris Park Avenue, Bronx, New York 10461, United States
- Department of Medicine and #Department of Microbiology & Immunology, Columbia University Medical Center, 630 and 701 West 168th Street, New York, New York 10032, United States
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Sanchez-Casalongue ME, Lee J, Diamond A, Shuldiner S, Moir RD, Willis IM. Differential phosphorylation of a regulatory subunit of protein kinase CK2 by target of rapamycin complex 1 signaling and the Cdc-like kinase Kns1. J Biol Chem 2015; 290:7221-33. [PMID: 25631054 DOI: 10.1074/jbc.m114.626523] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
Transcriptional regulation of ribosome and tRNA synthesis plays a central role in determining protein synthetic capacity and is tightly controlled in response to nutrient availability and cellular stress. In Saccharomyces cerevisiae, the regulation of ribosome and tRNA synthesis was recently shown to involve the Cdc-like kinase Kns1 and the GSK-3 kinase Mck1. In this study, we explored additional roles for these conserved kinases in processes connected to the target of rapamycin complex 1 (TORC1). We conducted a synthetic chemical-genetic screen in a kns1Δ mck1Δ strain and identified many novel rapamycin-hypersensitive genes. Gene ontology analysis showed enrichment for TORC1-regulated processes (vesicle-mediated transport, autophagy, and regulation of cell size) and identified new connections to protein complexes including the protein kinase CK2. CK2 is considered to be a constitutively active kinase and in budding yeast, the holoenzyme comprises two regulatory subunits, Ckb1 and Ckb2, and two catalytic subunits, Cka1 and Cka2. We show that Ckb1 is differentially phosphorylated in vivo and that Kns1 mediates this phosphorylation when nutrients are limiting and under all tested stress conditions. We determined that the phosphorylation of Ckb1 does not detectably affect the stability of the CK2 holoenzyme but correlates with the reduced occupancy of Ckb1 on tRNA genes after rapamycin treatment. Thus, the differential occupancy of tRNA genes by CK2 is likely to modulate its activation of RNA polymerase III transcription. Our data suggest that TORC1, via its effector kinase Kns1, may regulate the association of CK2 with some of its substrates by phosphorylating Ckb1.
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Affiliation(s)
| | | | | | | | | | - Ian M Willis
- From the Departments of Biochemistry and Systems and Computational Biology, Albert Einstein College of Medicine, Bronx, New York 10461
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14
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Affiliation(s)
- Robyn D. Moir
- Department of Biochemistry, Albert Einstein College of Medicine, Bronx, New York, New York, United States of America
- * E-mail: (RDM); (IMW)
| | - Ian M. Willis
- Department of Biochemistry, Albert Einstein College of Medicine, Bronx, New York, New York, United States of America
- Department of Systems and Computational Biology, Albert Einstein College of Medicine, Bronx, New York, New York, United States of America
- * E-mail: (RDM); (IMW)
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Moir RD, Willis IM. Regulation of pol III transcription by nutrient and stress signaling pathways. Biochim Biophys Acta 2012; 1829:361-75. [PMID: 23165150 DOI: 10.1016/j.bbagrm.2012.11.001] [Citation(s) in RCA: 103] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/12/2012] [Revised: 11/06/2012] [Accepted: 11/08/2012] [Indexed: 12/29/2022]
Abstract
Transcription by RNA polymerase III (pol III) is responsible for ~15% of total cellular transcription through the generation of small structured RNAs such as tRNA and 5S RNA. The coordinate synthesis of these molecules with ribosomal protein mRNAs and rRNA couples the production of ribosomes and their tRNA substrates and balances protein synthetic capacity with the growth requirements of the cell. Ribosome biogenesis in general and pol III transcription in particular is known to be regulated by nutrient availability, cell stress and cell cycle stage and is perturbed in pathological states. High throughput proteomic studies have catalogued modifications to pol III subunits, assembly, initiation and accessory factors but most of these modifications have yet to be linked to functional consequences. Here we review our current understanding of the major points of regulation in the pol III transcription apparatus, the targets of regulation and the signaling pathways known to regulate their function. This article is part of a Special Issue entitled: Transcription by Odd Pols.
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Affiliation(s)
- Robyn D Moir
- Departments of Biochemistry, Albert Einstein College of Medicine, Bronx, NY 10461, USA
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16
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Moir RD, Gross DA, Silver DL, Willis IM. SCS3 and YFT2 link transcription of phospholipid biosynthetic genes to ER stress and the UPR. PLoS Genet 2012; 8:e1002890. [PMID: 22927826 PMCID: PMC3426550 DOI: 10.1371/journal.pgen.1002890] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2012] [Accepted: 06/19/2012] [Indexed: 11/21/2022] Open
Abstract
The ability to store nutrients in lipid droplets (LDs) is an ancient function that provides the primary source of metabolic energy during periods of nutrient insufficiency and between meals. The Fat storage-Inducing Transmembrane (FIT) proteins are conserved ER–resident proteins that facilitate fat storage by partitioning energy-rich triglycerides into LDs. FIT2, the ancient ortholog of the FIT gene family first identified in mammals has two homologs in Saccharomyces cerevisiae (SCS3 and YFT2) and other fungi of the Saccharomycotina lineage. Despite the coevolution of these genes for more than 170 million years and their divergence from higher eukaryotes, SCS3, YFT2, and the human FIT2 gene retain some common functions: expression of the yeast genes in a human embryonic kidney cell line promotes LD formation, and expression of human FIT2 in yeast rescues the inositol auxotrophy and chemical and genetic phenotypes of strains lacking SCS3. To better understand the function of SCS3 and YFT2, we investigated the chemical sensitivities of strains deleted for either or both genes and identified synthetic genetic interactions against the viable yeast gene-deletion collection. We show that SCS3 and YFT2 have shared and unique functions that connect major biosynthetic processes critical for cell growth. These include lipid metabolism, vesicular trafficking, transcription of phospholipid biosynthetic genes, and protein synthesis. The genetic data indicate that optimal strain fitness requires a balance between phospholipid synthesis and protein synthesis and that deletion of SCS3 and YFT2 impacts a regulatory mechanism that coordinates these processes. Part of this mechanism involves a role for SCS3 in communicating changes in the ER (e.g. due to low inositol) to Opi1-regulated transcription of phospholipid biosynthetic genes. We conclude that SCS3 and YFT2 are required for normal ER membrane biosynthesis in response to perturbations in lipid metabolism and ER stress. The ability to form lipid droplets is a conserved property of eukaryotic cells that allows the storage of excess metabolic energy in a form that can be readily accessed. In adipose tissue, the storage of excess calories in lipid droplets normally protects other tissues from lipotoxicity and insulin resistance, but this protection is lost with chronic over-nutrition. The FAT storage-inducing transmembrane (FIT) proteins were recently identified as a conserved family of proteins that reside in the lipid bilayer of the endoplasmic reticulum and are implicated in lipid droplet formation. In this work we show that specific functions of the FIT proteins are conserved between yeast and humans and that SCS3 and YFT2, the yeast homologs of mammalian FIT2, are part of a large genetic interaction network connecting lipid metabolism, vesicle trafficking, transcription, and protein synthesis. From these interactions we determined that yeast strains lacking SCS3 and YFT2 are defective in their response to chronic ER stress and cannot induce the unfolded protein response pathway or transcription of phospholipid biosynthetic genes in low inositol. Our findings suggest that the mammalian FIT genes may play an important role in ER stress pathways, which are linked to obesity and type 2 diabetes.
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Affiliation(s)
- Robyn D. Moir
- Department of Biochemistry, Albert Einstein College of Medicine, Bronx, New York, United States of America
| | - David A. Gross
- Department of Biochemistry, Albert Einstein College of Medicine, Bronx, New York, United States of America
- Signature Research Program in Cardiovascular and Metabolic Disorders, Duke–NUS Graduate Medical School Singapore, Singapore, Singapore
| | - David L. Silver
- Department of Biochemistry, Albert Einstein College of Medicine, Bronx, New York, United States of America
- Signature Research Program in Cardiovascular and Metabolic Disorders, Duke–NUS Graduate Medical School Singapore, Singapore, Singapore
- * E-mail: (IMW); (DLS)
| | - Ian M. Willis
- Department of Biochemistry, Albert Einstein College of Medicine, Bronx, New York, United States of America
- Department of Systems and Computational Biology, Albert Einstein College of Medicine, Bronx, New York, United States of America
- * E-mail: (IMW); (DLS)
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17
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Moir RD, Lee J, Willis IM. Recovery of RNA polymerase III transcription from the glycerol-repressed state: revisiting the role of protein kinase CK2 in Maf1 phosphoregulation. J Biol Chem 2012; 287:30833-41. [PMID: 22810236 DOI: 10.1074/jbc.m112.378828] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Maf1 is a conserved regulator of RNA polymerase (pol) III transcription and is required for transcriptional repression under diverse stress conditions. In yeast, Maf1 function is negatively regulated at seven phosphosites by the overlapping action of protein kinase A (PKA) and the TORC1-regulated kinase Sch9. Under stress conditions, Maf1 is dephosphorylated at these sites leading to its nuclear accumulation, increased association with pol III genes and direct physical interactions with the polymerase which ultimately inhibit transcription. These changes are reversed upon return to optimal growth conditions. Transcription in this system is also regulated by protein kinase CK2. CK2 stimulates pol III transcription in yeast and human cells via phosphorylation of the initiation factor TFIIIB. Recently it was proposed that CK2 phosphorylation of Maf1 is required for reactivation of pol III transcription following growth on glycerol. We have examined this hypothesis using two Maf1 mutants (Maf1-id S388A and Maf1-ck2(0)) which lack all of the CK2 phosphosites implicated in the response. Both mutant proteins are phosphoregulated, function normally during repression and transcription is fully restored to the wild-type level upon transfer from glycerol to glucose. Additionally, phos-tag gel analysis of Maf1 7SA, a functional mutant that cannot be phosphorylated by PKA/Sch9, did not reveal any evidence for differential phosphorylation of Maf1 during carbon source switching. Together, these data do not support the proposed requirement for CK2 phosphorylation of Maf1 during derepression of pol III transcription.
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Affiliation(s)
- Robyn D Moir
- Departments of Biochemistry, Albert Einstein College of Medicine, Bronx, NY 10461, USA
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18
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Lee J, Moir RD, McIntosh KB, Willis IM. TOR signaling regulates ribosome and tRNA synthesis via LAMMER/Clk and GSK-3 family kinases. Mol Cell 2012; 45:836-43. [PMID: 22364741 DOI: 10.1016/j.molcel.2012.01.018] [Citation(s) in RCA: 64] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2011] [Revised: 08/23/2011] [Accepted: 01/09/2012] [Indexed: 01/13/2023]
Abstract
Target of rapamycin (TOR)-dependent signaling and the control of cell growth is deregulated in many cancers. However, the signaling molecules downstream of TOR that coordinately regulate the synthesis of ribosomes and tRNAs are not well defined. Here, we show in yeast that conserved kinases of the LAMMER/Cdc-like and GSK-3 families function downstream of TOR complex 1 to repress ribosome and tRNA synthesis in response to nutrient limitation and other types of cellular stress. As a part of this response, we found that the LAMMER kinase Kns1 is differentially expressed and hyperphosphorylated and accumulates in the nucleus after rapamycin treatment, whereupon it primes the phosphorylation of the RNA polymerase III subunit Rpc53 by a specific GSK-3 family member, Mck1. In cooperation with another polymerase subunit, Rpc11, this phosphorylation of Rpc53 modifies the function of the enzyme and together with dephosphorylation of the Maf1 repressor inhibits the growth-promoting activity of RNA polymerase III transcription.
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Affiliation(s)
- Jaehoon Lee
- Department of Biochemistry, Albert Einstein College of Medicine, Bronx, NY 10461, USA
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Abstract
The endoplasmic reticulum (ER) unfolded protein response (UPR) is correlated with changes in unfolded secretory levels. A novel fluorescence biosensor now reports changes in the unfolded protein burden. This reporter reveals a form of ER stress—inositol withdrawal—that stimulates the UPR without changes in unfolded protein levels. Accumulation of misfolded secretory proteins in the endoplasmic reticulum (ER) activates the unfolded protein response (UPR) stress pathway. To enhance secretory protein folding and promote adaptation to stress, the UPR upregulates ER chaperone levels, including BiP. Here we describe chromosomal tagging of KAR2, the yeast homologue of BiP, with superfolder green fluorescent protein (sfGFP) to create a multifunctional endogenous reporter of the ER folding environment. Changes in Kar2p-sfGFP fluorescence levels directly correlate with UPR activity and represent a robust reporter for high-throughput analysis. A novel second feature of this reporter is that photobleaching microscopy (fluorescence recovery after photobleaching) of Kar2p-sfGFP mobility reports on the levels of unfolded secretory proteins in individual cells, independent of UPR status. Kar2p-sfGFP mobility decreases upon treatment with tunicamycin or dithiothreitol, consistent with increased levels of unfolded proteins and the incorporation of Kar2p-sfGFP into slower-diffusing complexes. During adaptation, we observe a significant lag between down-regulation of the UPR and resolution of the unfolded protein burden. Finally, we find that Kar2p-sfGFP mobility significantly increases upon inositol withdrawal, which also activates the UPR, apparently independent of unfolded protein levels. Thus Kar2p mobility represents a powerful new tool capable of distinguishing between the different mechanisms leading to UPR activation in living cells.
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Affiliation(s)
- Patrick Lajoie
- Department of Anatomy and Structural Biology, Albert Einstein College of Medicine of Yeshiva University, Bronx, NY 10461, USA
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Lee J, Moir RD, Willis IM. Regulation of RNA polymerase III transcription involves SCH9-dependent and SCH9-independent branches of the target of rapamycin (TOR) pathway. J Biol Chem 2009; 284:12604-8. [PMID: 19299514 PMCID: PMC2675989 DOI: 10.1074/jbc.c900020200] [Citation(s) in RCA: 90] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/09/2009] [Revised: 03/12/2009] [Indexed: 11/06/2022] Open
Abstract
Maf1 is a conserved repressor of transcription that functions at the downstream end of multiple nutrient and stress signaling pathways. How these different signaling pathways converge on Maf1 is not known. Previous work in yeast indicates that protein kinase A (PKA) regulates RNA polymerase (pol) III transcription, in part, by phosphorylating multiple sites in Maf1. Here we present additional evidence for this view and show that a parallel nutrient and stress-sensing pathway involving Sch9, an homologous kinase to metazoan S6 kinase, targets Maf1 at a subset of PKA sites. Using ATP analog-sensitive alleles of PKA and Sch9, we find that these two kinases account for the bulk of the phosphorylation on consensus PKA sites in Maf1. Deletion of Sch9 reduces RNA pol III transcription in a Maf1-dependent manner, yet the cells remain susceptible to further repression by rapamycin and other treatments. Because the rapamycin-sensitive kinase activity of the TORC1 complex is necessary for Sch9 function in vivo and in vitro, our results show that transcriptional regulation of RNA pol III and the coordinate control of ribosomal protein genes can be achieved by Sch9-dependent and -independent branches of the target of rapamycin (TOR) signaling pathway.
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Affiliation(s)
- Jaehoon Lee
- Department of Biochemistry, Albert Einstein College of Medicine, Bronx, NY 10461, USA
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21
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Willis IM, Chua G, Tong AH, Brost RL, Hughes TR, Boone C, Moir RD. Genetic interactions of MAF1 identify a role for Med20 in transcriptional repression of ribosomal protein genes. PLoS Genet 2008; 4:e1000112. [PMID: 18604275 PMCID: PMC2435279 DOI: 10.1371/journal.pgen.1000112] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2008] [Accepted: 05/28/2008] [Indexed: 11/19/2022] Open
Abstract
Transcriptional repression of ribosomal components and tRNAs is coordinately regulated in response to a wide variety of environmental stresses. Part of this response involves the convergence of different nutritional and stress signaling pathways on Maf1, a protein that is essential for repressing transcription by RNA polymerase (pol) III in Saccharomyces cerevisiae. Here we identify the functions buffering yeast cells that are unable to down-regulate transcription by RNA pol III. MAF1 genetic interactions identified in screens of non-essential gene-deletions and conditionally expressed essential genes reveal a highly interconnected network of 64 genes involved in ribosome biogenesis, RNA pol II transcription, tRNA modification, ubiquitin-dependent proteolysis and other processes. A survey of non-essential MAF1 synthetic sick/lethal (SSL) genes identified six gene-deletions that are defective in transcriptional repression of ribosomal protein (RP) genes following rapamycin treatment. This subset of MAF1 SSL genes included MED20 which encodes a head module subunit of the RNA pol II Mediator complex. Genetic interactions between MAF1 and subunits in each structural module of Mediator were investigated to examine the functional relationship between these transcriptional regulators. Gene expression profiling identified a prominent and highly selective role for Med20 in the repression of RP gene transcription under multiple conditions. In addition, attenuated repression of RP genes by rapamycin was observed in a strain deleted for the Mediator tail module subunit Med16. The data suggest that Mediator and Maf1 function in parallel pathways to negatively regulate RP mRNA and tRNA synthesis. The Maf1 protein is an essential negative regulator of transcription by RNA polymerase III in S. cerevisiae and functions to integrate responses from diverse nutritional and stress signaling pathways that coordinately regulate ribosome and tRNA synthesis. These signaling pathways are not well-defined, and efforts to understand the role of Maf1 in this process have been complicated by a lack of known functional motifs in the protein and by a paucity of direct physical interactions with Maf1. To understand the biological importance of down-regulating RNA polymerase III transcription and to identify functional relationships with Maf1, we employed synthetic genetic array (SGA) analysis. We show that the genetic neighborhood around Maf1 is highly interconnected and enriched for a small number of functional categories, most of which are logically linked to the function of Maf1 as the regulator of RNA polymerase III transcription. We found that deletions in a subset of MAF1 SSL genes, including subunits of the RNA polymerase II Mediator complex, lead to defects in transcriptional repression of ribosomal protein (RP) genes. Since Mediator subunits are not efficiently cross-linked to RP genes in chromatin, our results suggest that Mediator interactions with these highly expressed genes are fundamentally different from many other genes.
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Affiliation(s)
- Ian M Willis
- Department of Biochemistry, Albert Einstein College of Medicine, Bronx, New York, United States of America.
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Willis IM, Moir RD. Integration of nutritional and stress signaling pathways by Maf1. Trends Biochem Sci 2006; 32:51-3. [PMID: 17174096 DOI: 10.1016/j.tibs.2006.12.001] [Citation(s) in RCA: 67] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2006] [Revised: 10/26/2006] [Accepted: 12/07/2006] [Indexed: 11/30/2022]
Abstract
Repression of RNA polymerase III transcription under many conditions requires Maf1, a yeast protein with close sequence homologs in all eukaryotes. Three recent studies have identified key aspects of Maf1 regulation, which suggest that Maf1 integrates the responses from convergent nutritional and stress signaling pathways. These new findings indicate that the opposing actions of protein kinase A and protein phosphatase 2A alter the phosphorylation state of Maf1 and thereby regulate its localization and repressing activity.
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Affiliation(s)
- Ian M Willis
- Department of Biochemistry, Albert Einstein College of Medicine, 1300 Morris Park Avenue, Bronx, NY 10461, USA.
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23
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Moir RD, Lee J, Haeusler RA, Desai N, Engelke DR, Willis IM. Protein kinase A regulates RNA polymerase III transcription through the nuclear localization of Maf1. Proc Natl Acad Sci U S A 2006; 103:15044-9. [PMID: 17005718 PMCID: PMC1622776 DOI: 10.1073/pnas.0607129103] [Citation(s) in RCA: 111] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Maf1 is an essential and specific mediator of transcriptional repression in the RNA polymerase (pol) III system. Maf1-dependent repression occurs in response to a wide range of conditions, suggesting that the protein itself is targeted by the major nutritional and stress-signaling pathways. We show that Maf1 is a substrate for cAMP-dependent PKA in vitro and is differentially phosphorylated on PKA sites in vivo under normal versus repressing conditions. PKA activity negatively regulates Maf1 function because strains with unregulated high PKA activity block repression of pol III transcription in vivo, and strains lacking all PKA activity are hyperrepressible. Nuclear accumulation of Maf1 is required for transcriptional repression and is regulated by two nuclear localization sequences in the protein. An analysis of PKA phosphosite mutants shows that the localization of Maf1 is affected via the N-terminal nuclear localization sequence. In particular, mutations that prevent phosphorylation at PKA consensus sites promote nuclear accumulation of Maf1 without inducing repression. These results indicate that negative regulation of Maf1 by PKA is achieved by inhibiting its nuclear import and suggest that a PKA-independent activation step is required for nuclear Maf1 to function in the repression of pol III transcription. Finally, we report a previously undescribed phenotype for Maf1 in tRNA gene-mediated silencing of nearby RNA pol II transcription.
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Affiliation(s)
- Robyn D. Moir
- *Department of Biochemistry, Albert Einstein College of Medicine, 1300 Morris Park Avenue, Bronx, NY 10461; and
| | - JaeHoon Lee
- *Department of Biochemistry, Albert Einstein College of Medicine, 1300 Morris Park Avenue, Bronx, NY 10461; and
| | - Rebecca A. Haeusler
- Department of Biological Chemistry, University of Michigan Medical School, 3200 MSRB III, Ann Arbor, MI 48109-0606
| | - Neelam Desai
- *Department of Biochemistry, Albert Einstein College of Medicine, 1300 Morris Park Avenue, Bronx, NY 10461; and
| | - David R. Engelke
- Department of Biological Chemistry, University of Michigan Medical School, 3200 MSRB III, Ann Arbor, MI 48109-0606
| | - Ian M. Willis
- *Department of Biochemistry, Albert Einstein College of Medicine, 1300 Morris Park Avenue, Bronx, NY 10461; and
- To whom correspondence should be addressed. E-mail:
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24
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Liao Y, Moir RD, Willis IM. Interactions of Brf1 peptides with the tetratricopeptide repeat-containing subunit of TFIIIC inhibit and promote preinitiation complex assembly. Mol Cell Biol 2006; 26:5946-56. [PMID: 16880507 PMCID: PMC1592789 DOI: 10.1128/mcb.00689-06] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
The binding of Brf1 to the tetratricopeptide repeat (TPR)-containing transcription factor IIIC (TFIIIC) subunit (Tfc4) represents a rate-limiting step in the ordered assembly of the RNA polymerase III initiation factor TFIIIB. Tfc4 contains multiple binding sites for Brf1 within its amino terminus and adjacent TPR arrays, but the access of Brf1 to these sites is limited by autoinhibition. Moreover, the Brf1 binding sites in Tfc4 overlap with sites important for the subsequent recruitment of another TFIIIB subunit, Bdp1, implying that repositioning of Brf1 is required after its initial interaction with Tfc4. As a starting point for dissecting the steps in TFIIIC-directed assembly of TFIIIB, we conducted yeast two-hybrid screens of Brf1 peptide libraries against different TPR-containing Tfc4 fragments. Short, biochemically active peptides were identified in three distinct regions of Brf1. Two peptides defined conserved but distal regions of Brf1 that participate in stable binding of Brf1 to TFIIIC-DNA. Remarkably, a third peptide that binds specifically to TPR6-9 of Tfc4 was found to promote the formation of both TFIIIC-DNA and Brf1-TFIIIC-DNA complexes and to reduce the mobility of these complexes in native gels. The data are consistent with this peptide causing a conformational change in TFIIIC that overcomes Tfc4 autoinhibition of Brf1 binding and suggest a structural model for the Brf1-Tfc4 interaction.
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Affiliation(s)
- Yanling Liao
- Department of Biochemistry, Albert Einstein College of Medicine, 1300 Morris Park Ave., Bronx, NY 10461, USA
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25
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Sauve AA, Moir RD, Schramm VL, Willis IM. Chemical Activation of Sir2-Dependent Silencing by Relief of Nicotinamide Inhibition. Mol Cell 2005; 17:595-601. [PMID: 15721262 DOI: 10.1016/j.molcel.2004.12.032] [Citation(s) in RCA: 126] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2004] [Revised: 11/16/2004] [Accepted: 12/14/2004] [Indexed: 11/25/2022]
Abstract
Sir2 is a nicotinamide adenine dinucleotide (NAD+)-dependent protein deacetylase involved in gene silencing and longevity. Cellular stresses affect Sir2 activity, but the mechanisms of Sir2 regulation are debated. Nicotinamide has been proposed as a physiological regulator that inhibits Sir2 deacetylase activity by chemical reversal of a covalent reaction intermediate. We demonstrate a chemical strategy to activate Sir2-dependent transcriptional silencing and present evidence that the endogenous level of nicotinamide limits Sir2 activity in wild-type (wt) yeast cells. Nicotinamide inhibition of Sir2 is antagonized in vitro by isonicotinamide, which causes an increase in Sir2 deacetylation activity. Isonicotinamide also substantially increases transcriptional silencing at Sir2-regulated loci in wt strains and in strains lacking key NAD+ salvage pathway enzymes (PNC1 and NPT1). Thus, a nicotinamide antagonist is a Sir2 agonist in vitro and in vivo.
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Affiliation(s)
- Anthony A Sauve
- Department of Biochemistry, Albert Einstein College of Medicine, 1300 Morris Park Avenue, Bronx, NY 10461, USA
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26
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Abstract
In Saccharomyces cerevisiae, Maf1 is essential for mediating the repression of transcription by RNA polymerase (pol) III in response to diverse cellular conditions. These conditions activate distinct signaling pathways that converge at or above Maf1. Thus, Maf1-dependent repression is thought to involve a common set of downstream inhibitory effects on the pol III machinery. Here we provide support for this view and define two steps in Maf1-dependent transcriptional repression. We show that chlorpromazine (CPZ)-induced repression of pol III transcription is achieved by inhibiting de novo assembly of transcription factor (TF) IIIB onto DNA as well as the recruitment of pol III to preassembled TFIIIB.DNA complexes. Additionally Brf1 was identified as a target of repression in extracts of CPZ-treated cells. Maf1-Brf1 and Maf1-pol III interactions were implicated in the inhibition of TFIIIB.DNA complex assembly and polymerase recruitment by recombinant Maf1. Co-immunoprecipitation experiments confirmed these interactions in yeast extracts and demonstrated that Maf1 does not differentially sequester Brf1 or pol III under repressing conditions. The results suggest that Maf1 functions by a non-stoichiometric mechanism to repress pol III transcription.
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Affiliation(s)
- Neelam Desai
- Department of Biochemistry, Albert Einstein College of Medicine, Bronx, New York 10461, USA
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27
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Abstract
The amyloid hypothesis of Alzheimer's disease (AD) maintains that the accumulation of the amyloid beta protein (Abeta) is a critical event in disease pathogenesis. A great deal of both academic and commercial research has focused on the mechanisms by which Abeta is generated. However, investigations into the mechanisms underlying Abeta clearance have blossomed over the last several years. This minireview will summarize pathways involved in the removal of cerebral Abeta, including enzymatic degradation and receptor-mediated efflux out of the brain.
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Affiliation(s)
- R E Tanzi
- Genetics and Aging Research Unit, MassGeneral Institute for Neurodegenerative Disease, Department of Neurology, Massachusetts General Hospital, Charlestown 02129, USA.
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28
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Affiliation(s)
- Robyn D Moir
- Department of Biochemistry, Albert Einstein College of Medicine, Bronx, New York 10461, USA
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29
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Liao Y, Willis IM, Moir RD. The Brf1 and Bdp1 subunits of transcription factor TFIIIB bind to overlapping sites in the tetratricopeptide repeats of Tfc4. J Biol Chem 2003; 278:44467-74. [PMID: 12930823 DOI: 10.1074/jbc.m308354200] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023] Open
Abstract
The RNA polymerase III initiation factor TFIIIB is assembled onto DNA through interactions involving the Tfc4 subunit of the assembly factor TFIIIC and two subunits of TFIIIB, Brf1 and Bdp1. Tfc4 contains two arrays of tetratricopeptide repeats (TPRs), each of which provides a binding site for Brf1. Dominant mutations in the ligand binding channel of the first TPR array, TPRs1-5, and on the back side of this array, increase Brf1 binding by Tfc4. Here we examine the biological importance of the second TPR array, TPRs6 -9. Radical mutations at phylogenetically conserved residues in the ligand binding channel of TPRs6 -9 impair pol III reporter gene transcription. Biochemical studies on one such mutation, L469K in TPR7, revealed a defect in the recruitment of Brf1 into TFIIIB-TFIIIC-DNA complexes and diminished the direct interaction between Tfc4 and Brf1. Multicopy suppression analysis implicates TPR9 in Brf1 binding and TPRs7 and 8 in binding to more than one ligand. Indeed, the L469K mutation also decreased the binding affinity for Bdp1 incorporation into TFIIIB-TFIIIC-DNA complexes and inhibited binary interactions between Bdp1 and Tfc4. The Bdp1 binding domain in Tfc4 was mapped to TPRs1-9, a domain that contains both TPR arrays and thus overlaps two of the known binding sites for Brf1. The properties of the L469K mutation identify both Brf1 and Bdp1 as ligands for the second TPR array.
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Affiliation(s)
- Yanling Liao
- Department of Biochemistry, Albert Einstein College of Medicine, Bronx, New York 10461, USA
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30
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Abstract
The interaction between the tetratricopeptide repeat (TPR)-containing subunit of TFIIIC, TFIIIC131, and the TFIIB-related factor Brf1 represents a limiting step in the assembly of the RNA polymerase III (pol III) initiation factor TFIIIB. This assembly reaction is facilitated by dominant mutations that map in and around TPR2. Structural modeling of TPR1 to TPR3 from TFIIIC131 shows that one such mutation, PCF1-2, alters a residue in the ligand-binding groove of the TPR superhelix whereas another mutation, PCF1-1, changes a surface-accessible residue on the back side of the TPR superhelix. In this work, we show that the PCF1-1 mutation (H190Y) increases the binding affinity for Brf1, but does not affect the binding affinity for Bdp1, in the TFIIIC-dependent assembly of TFIIIB. Interestingly, binding studies with TFIIIC131 fragments indicate that Brf1 does not interact directly at the site of the PCF1-1 mutation. Rather, the data suggest that the mutation overcomes the previously documented autoinhibition of Brf1 binding. These findings together with the results from site-directed mutagenesis support the hypothesis that gain-of-function mutations at amino acid 190 in TPR2 stabilize an alternative conformation of TFIIIC131 that promotes its interaction with Brf1.
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MESH Headings
- Amino Acid Substitution
- DNA, Fungal/metabolism
- Genes, Dominant
- Ligands
- Macromolecular Substances
- Models, Molecular
- Mutation, Missense
- Protein Binding
- Protein Conformation
- Protein Structure, Tertiary
- RNA Polymerase III/metabolism
- Repetitive Sequences, Amino Acid/genetics
- Repetitive Sequences, Amino Acid/physiology
- Saccharomyces cerevisiae/genetics
- Saccharomyces cerevisiae/metabolism
- Saccharomyces cerevisiae Proteins/chemistry
- Saccharomyces cerevisiae Proteins/genetics
- Saccharomyces cerevisiae Proteins/metabolism
- Structure-Activity Relationship
- Transcription Factor TFIIIB
- Transcription Factors/metabolism
- Transcription Factors, TFIII/chemistry
- Transcription Factors, TFIII/genetics
- Transcription Factors, TFIII/metabolism
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Affiliation(s)
- Robyn D Moir
- Department of Biochemistry, Albert Einstein College of Medicine, Bronx, New York 10461, USA
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31
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Abstract
An important step in the assembly of RNA polymerase (pol) III transcription complexes on tRNA and 5 S genes is the interaction between the tetratricopeptide repeat (TPR)-containing subunit of TFIIIC (TFIIIC131) and the TFIIB-related subunit of TFIIIB (TFIIIB70/Brf1). A fragment of TFIIIC131 that contains the hydrophilic amino terminus and two TPR arrays, with five and four repeats, respectively (Nt-TPR9), is sufficient to support an interaction with TFIIIB70. Here we evaluate the contribution of each TPR array to TFIIIB70 binding. Both TPR arrays bind independently to TFIIIB70 with TPR6-9 having a 4-fold higher apparent affinity than TPR1-5. However, the TPR arrays are not sufficient for a high affinity interaction with TFIIIB70. The addition of amino-terminal sequences increases the affinity of TPR1-5 18-fold to create a high affinity TFIIIB70 binding site (Nt-TPR5, 44 +/- 6 nm). Although the Nt-TPR5 and TPR6-9 fragments are contained entirely within the Nt-TPR9 fragment, the affinity of the latter is significantly lower than either of these smaller fragments. The results demonstrate that the TFIIIB70 binding sites in TFIIIC131 are subject to autoinhibition. We propose that the binding of TFIIIB70 to these sites within the TFIIIC complex may proceed in an ordered fashion.
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Affiliation(s)
- Robyn D Moir
- Department of Biochemistry, Albert Einstein College of Medicine, Bronx, New York 10461, USA
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32
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de Noronha CM, Sherman MP, Lin HW, Cavrois MV, Moir RD, Goldman RD, Greene WC. Dynamic disruptions in nuclear envelope architecture and integrity induced by HIV-1 Vpr. Science 2001; 294:1105-8. [PMID: 11691994 DOI: 10.1126/science.1063957] [Citation(s) in RCA: 209] [Impact Index Per Article: 9.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
Human immunodeficiency virus-1 (HIV-1) Vpr expression halts the proliferation of human cells at or near the G2 cell-cycle checkpoint. The transition from G2 to mitosis is normally controlled by changes in the state of phosphorylation and subcellular compartmentalization of key cell-cycle regulatory proteins. In studies of the intracellular trafficking of these regulators, we unexpectedly found that wild-type Vpr, but not Vpr mutants impaired for G2 arrest, induced transient, localized herniations in the nuclear envelope (NE). These herniations were associated with defects in the nuclear lamina. Intermittently, these herniations ruptured, resulting in the mixing of nuclear and cytoplasmic components. These Vpr-induced NE changes probably contribute to the observed cell-cycle arrest.
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Affiliation(s)
- C M de Noronha
- Gladstone Institute of Virology and Immunology, Department of Medicine, University of California, San Francisco, CA 94103, USA
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33
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Abstract
The nuclear lamins polymerize to form the nuclear lamina, a fibrous structure found on the inner face of the nuclear membrane. The lamins also appear to form structures within the nucleoplasm. These various lamin structures help to establish and maintain the shape and strength of the interphase nucleus, but recent work also suggests that the lamins have a role in nuclear processes such as DNA replication. Furthermore, mutations in the human lamin A/C gene have recently been linked to several diseases, including Emery-Dreifuss muscular dystrophy. This review discusses the nature of these mutations and the possible effects of lamin mutations on nuclear function.
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Affiliation(s)
- R D Moir
- Department of Cell and Molecular Biology, Northwestern University Medical School, Chicago, Illinois 60611, USA.
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34
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Kruppa M, Moir RD, Kolodrubetz D, Willis IM. Erratum. Mol Cell 2001. [DOI: 10.1016/s1097-2765(01)00351-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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35
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Lopez-Soler RI, Moir RD, Spann TP, Stick R, Goldman RD. A role for nuclear lamins in nuclear envelope assembly. J Cell Biol 2001; 154:61-70. [PMID: 11448990 PMCID: PMC2196852 DOI: 10.1083/jcb.200101025] [Citation(s) in RCA: 65] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2001] [Revised: 05/15/2001] [Accepted: 06/05/2001] [Indexed: 11/30/2022] Open
Abstract
The molecular interactions responsible for nuclear envelope assembly after mitosis are not well understood. In this study, we demonstrate that a peptide consisting of the COOH-terminal domain of Xenopus lamin B3 (LB3T) prevents nuclear envelope assembly in Xenopus interphase extracts. Specifically, LB3T inhibits chromatin decondensation and blocks the formation of both the nuclear lamina-pore complex and nuclear membranes. Under these conditions, some vesicles bind to the peripheral regions of the chromatin. These "nonfusogenic" vesicles lack lamin B3 (LB3) and do not bind LB3T; however, "fusogenic" vesicles containing LB3 can bind LB3T, which blocks their association with chromatin and, subsequently, nuclear membrane assembly. LB3T also binds to chromatin in the absence of interphase extract, but only in the presence of purified LB3. Additionally, we show that LB3T inhibits normal lamin polymerization in vitro. These findings suggest that lamin polymerization is required for both chromatin decondensation and the binding of nuclear membrane precursors during the early stages of normal nuclear envelope assembly.
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Affiliation(s)
- R I Lopez-Soler
- Department of Cell and Molecular Biology, Northwestern University Medical School, 303 East Chicago Avenue, Chicago, IL 60611, USA
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36
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Cherny RA, Atwood CS, Xilinas ME, Gray DN, Jones WD, McLean CA, Barnham KJ, Volitakis I, Fraser FW, Kim Y, Huang X, Goldstein LE, Moir RD, Lim JT, Beyreuther K, Zheng H, Tanzi RE, Masters CL, Bush AI. Treatment with a copper-zinc chelator markedly and rapidly inhibits beta-amyloid accumulation in Alzheimer's disease transgenic mice. Neuron 2001; 30:665-76. [PMID: 11430801 DOI: 10.1016/s0896-6273(01)00317-8] [Citation(s) in RCA: 1059] [Impact Index Per Article: 46.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
Inhibition of neocortical beta-amyloid (Abeta) accumulation may be essential in an effective therapeutic intervention for Alzheimer's disease (AD). Cu and Zn are enriched in Abeta deposits in AD, which are solubilized by Cu/Zn-selective chelators in vitro. Here we report a 49% decrease in brain Abeta deposition (-375 microg/g wet weight, p = 0.0001) in a blinded study of APP2576 transgenic mice treated orally for 9 weeks with clioquinol, an antibiotic and bioavailable Cu/Zn chelator. This was accompanied by a modest increase in soluble Abeta (1.45% of total cerebral Abeta); APP, synaptophysin, and GFAP levels were unaffected. General health and body weight parameters were significantly more stable in the treated animals. These results support targeting the interactions of Cu and Zn with Abeta as a novel therapy for the prevention and treatment of AD.
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Affiliation(s)
- R A Cherny
- Department of Pathology, The University of Melbourne and, The Mental Health Research Institute of Victoria, Australia
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37
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Rebeck GW, Moir RD, Mui S, Strickland DK, Tanzi RE, Hyman BT. Association of membrane-bound amyloid precursor protein APP with the apolipoprotein E receptor LRP. Brain Res Mol Brain Res 2001; 87:238-45. [PMID: 11245926 DOI: 10.1016/s0169-328x(01)00006-7] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
In order to identify cell surface proteins that interact with the amyloid precursor protein (APP), we biotinylated H4 human neuroglioma cells in culture with a water soluble biotinylating agent, immunoprecipitated APP with an antibody specific to the intracellular domain, and probed the precipitated proteins with anti-biotin. In human neuroglioma cells overexpressing APP751, we found a high molecular weight protein that immunoprecipitated with APP. This band was identified as the low density lipoprotein receptor-related protein (LRP) by three criteria: first, the band immunolabeled with anti-LRP antibodies; second, the band bound the LRP receptor associated protein, RAP; and third, this band was present in LRP-expressing fibroblasts, but not LRP-deficient fibroblasts. In complementary experiments, we found that APP co-precipitated with LRP, with a preference for an isoform of APP containing the Kunitz protease inhibitor domain. Interaction of APP and LRP on the surface of living cells was demonstrated by crosslinking APP and LRP with the water-soluble cross-linking agent BS(3). APP and LRP were shown by confocal microscopy to colocalize in perinuclear structures, but to primarily remain separate in vesicles and on the cell surface. We propose that full-length APP can transiently interact with the receptor LRP on the cell surface, affecting the processing and intracellular transport of APP.
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Affiliation(s)
- G W Rebeck
- Alzheimer Research Unit, 149 13th Street, Massachusetts General Hospital, Charlestown, MA 02129, USA.
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38
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Abstract
Nhp6A and Nhp6B are HMG1-like proteins required for the growth of S. cerevisiae at elevated temperatures. We show that the conditional lethality of an nhp6 strain results from defective transcription of SNR6 (U6 snRNA) by RNA polymerase III. Overexpression of U6 snRNA or Brf1, a limiting component of TFIIIB, and an activating mutation (PCF1-1) in TFIIIC were each found to suppress the nhp6 growth defect. Additionally, U6 snRNA levels, which are reduced over 10-fold in nhp6 cells at 37 degrees C, were restored by Brf1 overexpression and by PCF1-1. Nhp6A protein specifically enhanced TFIIIC-dependent, but not TATA box-dependent, SNR6 transcription in vitro by facilitating TFIIIC binding to the SNR6 promoter. Thus, Nhp6 has a direct role in transcription complex assembly at SNR6.
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MESH Headings
- DNA, Fungal/genetics
- DNA, Fungal/metabolism
- DNA-Binding Proteins/genetics
- DNA-Binding Proteins/metabolism
- Fungal Proteins/genetics
- Fungal Proteins/metabolism
- Gene Expression Regulation, Fungal
- Genes, Fungal/genetics
- Genes, Lethal/genetics
- HMGN Proteins
- High Mobility Group Proteins/metabolism
- Nuclear Proteins/genetics
- Nuclear Proteins/metabolism
- Phenotype
- Promoter Regions, Genetic/genetics
- Protein Binding
- RNA Polymerase III/chemistry
- RNA Polymerase III/metabolism
- RNA, Fungal/biosynthesis
- RNA, Fungal/genetics
- RNA, Ribosomal, 5S/biosynthesis
- RNA, Ribosomal, 5S/genetics
- RNA, Small Nuclear/genetics
- RNA, Small Nuclear/metabolism
- RNA, Transfer/biosynthesis
- RNA, Transfer/genetics
- Saccharomyces cerevisiae/enzymology
- Saccharomyces cerevisiae/genetics
- Saccharomyces cerevisiae/growth & development
- Saccharomyces cerevisiae/metabolism
- Saccharomyces cerevisiae Proteins
- Suppression, Genetic/genetics
- Temperature
- Transcription Factor TFIIIB
- Transcription Factors/genetics
- Transcription Factors/metabolism
- Transcription Factors, TFIII/genetics
- Transcription Factors, TFIII/metabolism
- Transcription, Genetic/genetics
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Affiliation(s)
- M Kruppa
- Department of Microbiology, University of Texas Health Science Center, San Antonio, TX 78229, USA
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39
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Liu Y, Jones M, Hingtgen CM, Bu G, Laribee N, Tanzi RE, Moir RD, Nath A, He JJ. Uptake of HIV-1 tat protein mediated by low-density lipoprotein receptor-related protein disrupts the neuronal metabolic balance of the receptor ligands. Nat Med 2000; 6:1380-7. [PMID: 11100124 DOI: 10.1038/82199] [Citation(s) in RCA: 307] [Impact Index Per Article: 12.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Neurological disorders develop in most people infected with human immunodeficiency virus type 1 (HIV-1). However, the underlying mechanisms remain largely unknown. Here we report that binding of HIV-1 transactivator (Tat) protein to low-density lipoprotein receptor-related protein (LRP) promoted efficient uptake of Tat into neurons. LRP-mediated uptake of Tat was followed by translocation to the neuronal nucleus. Furthermore, the binding of Tat to LRP resulted in substantial inhibition of neuronal binding, uptake and degradation of physiological ligands for LRP, including alpha2-macroglobulin, apolipoprotein E4, amyloid precursor protein and amyloid beta-protein. In a model of macaques infected with a chimeric strain of simian-human immunodeficiency virus, increased staining of amyloid precursor protein was associated with Tat expression in the brains of simian-human immunodeficiency virus-infected macaques with encephalitis. These results indicate that HIV-1 Tat may mediate HIV-1-induced neuropathology through a pathway involving disruption of the metabolic balance of LRP ligands and direct activation of neuronal genes.
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Affiliation(s)
- Y Liu
- Department of Microbiology and Immunology, Indiana University School of Medicine, Indianapolis, Indiana 46202, USA
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40
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Atwood CS, Scarpa RC, Huang X, Moir RD, Jones WD, Fairlie DP, Tanzi RE, Bush AI. Characterization of copper interactions with alzheimer amyloid beta peptides: identification of an attomolar-affinity copper binding site on amyloid beta1-42. J Neurochem 2000; 75:1219-33. [PMID: 10936205 DOI: 10.1046/j.1471-4159.2000.0751219.x] [Citation(s) in RCA: 465] [Impact Index Per Article: 19.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Cu and Zn have been shown to accumulate in the brains of Alzheimer's disease patients. We have previously reported that Cu(2+) and Zn(2+) bind amyloid beta (Abeta), explaining their enrichment in plaque pathology. Here we detail the stoichiometries and binding affinities of multiple cooperative Cu(2+)-binding sites on synthetic Abeta1-40 and Abeta1-42. We have developed a ligand displacement technique (competitive metal capture analysis) that uses metal-chelator complexes to evaluate metal ion binding to Abeta, a notoriously self-aggregating peptide. This analysis indicated that there is a very-high-affinity Cu(2+)-binding site on Abeta1-42 (log K(app) = 17.2) that mediates peptide precipitation and that the tendency of this peptide to self-aggregate in aqueous solutions is due to the presence of trace Cu(2+) contamination (customarily approximately 0.1 microM). In contrast, Abeta1-40 has much lower affinity for Cu(2+) at this site (estimated log K(app) = 10.3), explaining why this peptide is less self-aggregating. The greater Cu(2+)-binding affinity of Abeta1-42 compared with Abeta1-40 is associated with significantly diminished negative cooperativity. The role of trace metal contamination in inducing Abeta precipitation was confirmed by the demonstration that Abeta peptide (10 microM) remained soluble for 5 days only in the presence of high-affinity Cu(2+)-selective chelators.
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Affiliation(s)
- C S Atwood
- Laboratory for Oxidation Biology, Massachusetts General Hospital and Harvard Medical School, Boston 02129-9142, USA
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41
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Moir RD, Puglia KV, Willis IM. Interactions between the tetratricopeptide repeat-containing transcription factor TFIIIC131 and its ligand, TFIIIB70. Evidence for a conformational change in the complex. J Biol Chem 2000; 275:26591-8. [PMID: 10859316 DOI: 10.1074/jbc.m003991200] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
In the transcription of tRNA and 5 S genes by RNA polymerase III, recruitment of the transcription factor (TF)IIIB is mediated by the promoter-bound assembly factor TFIIIC. A critical limiting step in this process is the interaction between the tetratricopeptide repeat (TPR)-containing subunit of TFIIIC (TFIIIC131) and the TFIIB-related factor Brf1p/TFIIIB70. To facilitate biochemical studies of this interaction, we expressed a fragment of TFIIIC131, TFIIIC131-(1-580), that includes the minimal TFIIIB70 interaction domain defined by two-hybrid studies together with adjacent sequences, up to the end of TPR9, implicated in the assembly reaction. TFIIIC131-(1-580) interacts with TFIIIB70 in solution and inhibits the formation of TFIIIB70.TFIIIC.DNA complexes. In a coupled equilibrium binding assay, the formation of TFIIIC131-(1-580).TFIIIB70 complexes was adequately described by a single-site binding model and yielded an apparent equilibrium dissociation constant of 334 +/- 23 nm. CD spectroscopy and limited proteolysis experiments defined a well structured and largely protease-resistant core in TFIIIC131-(1-580) comprising part of the hydrophilic amino terminus, TPR1-5, the intervening non-TPR region, and TPR6-8. CD spectra showed that trifluoroethanol induced significant alpha-helical structure in TFIIIC131-(1-580). A more modest monovalent ion-dependent CD difference was observed in mixtures of TFIIIC131-(1-580) and TFIIIB70, suggesting that formation of the binary complex may proceed with the acquisition of alpha-helicity.
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Affiliation(s)
- R D Moir
- Department of Biochemistry, Albert Einstein College of Medicine, Bronx, New York 10461, USA
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42
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Atwood CS, Huang X, Khatri A, Scarpa RC, Kim YS, Moir RD, Tanzi RE, Roher AE, Bush AI. Copper catalyzed oxidation of Alzheimer Abeta. Cell Mol Biol (Noisy-le-grand) 2000; 46:777-83. [PMID: 10875439] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/16/2023]
Abstract
Abeta derived from amyloid plaques of Alzheimer's disease-affected brain contain several oxidative posttranslational modifications. In this study we have characterized the amino acid content of human amyloid-derived Abeta and compared it with that of human synthetic Abeta subjected to metal-catalyzed oxidation. Human amyloid derived Abeta has an increased content of arginine (46%) and glutamate/glutamine residues (28%), but a decreased content of histidine residues (-32%) as compared to the expected amino acid content. Incubation of synthetic human Abeta with Cu(II), but not Fe(III), in the presence of H2O2 similarly induced a decrease in histidine residues (-79%), but also a decrease in tyrosine residues (-28%). Our results suggest that histidine and tyrosine are most vulnerable to metal mediated oxidative attack, consistent with our earlier findings that Cu coordinated via histidine residues is redox competent. Our results suggest that the loss of histidine residues in human amyloid-derived Abeta may be a result of Cu oxidation, and that unidentified post-translational mechanisms operate to modify other amino acids of Abeta in vivo.
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Affiliation(s)
- C S Atwood
- Massachusetts General Hospital East, Charlestown, MA 02129-9142, USA
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43
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Li Y, Moir RD, Sethy-Coraci IK, Warner JR, Willis IM. Repression of ribosome and tRNA synthesis in secretion-defective cells is signaled by a novel branch of the cell integrity pathway. Mol Cell Biol 2000; 20:3843-51. [PMID: 10805727 PMCID: PMC85713 DOI: 10.1128/mcb.20.11.3843-3851.2000] [Citation(s) in RCA: 108] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The transcription of ribosomal DNA, ribosomal protein (RP) genes, and 5S and tRNA genes by RNA polymerases (Pols) I, II, and III, respectively, is rapidly and coordinately repressed upon interruption of the secretory pathway in Saccharomyces cerevisiae. We find that repression of ribosome and tRNA synthesis in secretion-defective cells involves activation of the cell integrity pathway. Transcriptional repression requires the upstream components of this pathway, including the Wsc family of putative plasma membrane sensors and protein kinase C (PKC), but not the downstream Bck1-Mkk1/2-Slt2 mitogen-activated protein kinase cascade. These findings reveal a novel PKC effector pathway that controls more than 85% of nuclear transcription. It is proposed that the coordination of ribosome and tRNA synthesis with cell growth may be achieved, in part, by monitoring the turgor pressure of the cell.
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Affiliation(s)
- Y Li
- Departments of Biochemistry, Albert Einstein College of Medicine, Bronx, New York 10461, USA
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44
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Pack-Chung E, Meyers MB, Pettingell WP, Moir RD, Brownawell AM, Cheng I, Tanzi RE, Kim TW. Presenilin 2 interacts with sorcin, a modulator of the ryanodine receptor. J Biol Chem 2000; 275:14440-5. [PMID: 10748169 DOI: 10.1074/jbc.m909882199] [Citation(s) in RCA: 90] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Perturbed Ca(2+) homeostasis is a common molecular consequence of familial Alzheimer's disease-linked presenilin mutations. We report here the molecular interaction of the large hydrophilic loop region of presenilin 2 (PS2) with sorcin, a penta-EF-hand Ca(2+)-binding protein that serves as a modulator of the ryanodine receptor intracellular Ca(2+) channel. The association of endogenous sorcin and PS2 was demonstrated in cultured cells and human brain tissues. Membrane-associated sorcin and a subset of the functional PS2 complexes were co-localized to a novel subcellular fraction that is distinctively positive for calcineurin B. Sorcin was found to interact with PS2 endoproteolytic fragments but not full-length PS2, and the sorcin/PS2 interaction was greatly enhanced by treatment with the Ca(2+) ionophore A23187. Our findings reveal a molecular link between PS2 and intracellular Ca(2+) channels (i.e. ryanodine receptor) and substantiate normal and/or pathological roles of PS2 in intracellular Ca(2+) homeostasis.
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Affiliation(s)
- E Pack-Chung
- Genetics and Aging Research Unit, Department of Neurology, Massachusetts General Hospital, Harvard Medical School, Charlestown, Massachusetts 02129, USA
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45
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Abstract
Alzheimer's disease (AD) is characterized by amyloid deposits within the neocortical parenchyma and the cerebrovasculature. The main component of these predominantly extracellular collections, Abeta, which is normally a soluble component of all biological fluids, is cleaved out of a ubiquitously expressed parent protein, the amyloid protein precursor (APP), one of the type 1 integral membrane glycoproteins. Considerable evidence has indicated that there is zinc dyshomeostasis and abnormal cellular zinc mobilization in AD. We have characterized both APP and Abeta as copper/zinc metalloproteins. Zinc, copper and iron have recently been reported to be concentrated to 0.5 to 1 mmol/L in amyloid plaque. In vitro, rapid Abeta aggregation is mediated by Zn(II), promoted by the alpha-helical structure of Abeta, and is reversible with chelation. In addition, Abeta produces hydrogen peroxide in a Cu(II)/Fe(III)-dependent manner, and the hydrogen peroxide formation is quenched by Zn(II). Moreover, zinc preserves the nontoxic properties of Abeta. Although the zinc-binding proteins apolipoprotein E epsilon4 allele and alpha(2)-macroglobulin have been characterized as two genetic risk factors for AD, zinc exposure as a risk factor for AD has not been rigorously studied. Based on our findings, we envisage that zinc may serve twin roles by both initiating amyloid deposition and then being involved in mechanisms attempting to quench oxidative stress and neurotoxicity derived from the amyloid mass. Hence, it remains debatable whether zinc supplementation is beneficial or deleterious for AD until additional studies clarify the issue.
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Affiliation(s)
- X Huang
- Laboratory for Oxidation Biology, Genetics and Aging Unit, Department of Psychiatry, Harvard Medical School, Massachusetts General Hospital, Charleston, MA 02129, USA
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46
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Moir RD, Spann TP, Lopez-Soler RI, Yoon M, Goldman AE, Khuon S, Goldman RD. Review: the dynamics of the nuclear lamins during the cell cycle-- relationship between structure and function. J Struct Biol 2000; 129:324-34. [PMID: 10806083 DOI: 10.1006/jsbi.2000.4251] [Citation(s) in RCA: 95] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
The nuclear lamins are members of the intermediate filament (IF) family of proteins. The lamins have an essential role in maintaining nuclear integrity, as do the other IF family members in the cytoplasm. Also like cytoplasmic IFs, the organization of lamins is dynamic. The lamins are found not only at the nuclear periphery but also in the interior of the nucleus, as distinct nucleoplasmic foci and possibly as a network throughout the nucleus. Nuclear processes such as DNA replication may be organized around these structures. In this review, we discuss changes in the structure and organization of the nuclear lamins during the cell cycle and during cell differentiation. These changes are correlated with changes in nuclear structure and function. For example, the interactions of lamins with chromatin and nuclear envelope components occur very early during nuclear assembly following mitosis. During S-phase, the lamins colocalize with markers of DNA replication, and proper lamin organization must be maintained for replication to proceed. When cells differentiate, the expression pattern of lamin isotypes changes. In addition, changes in lamin organization and expression patterns accompany the nuclear alterations observed in transformed cells. These lamin structures may modulate nuclear function in each of these processes.
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Affiliation(s)
- R D Moir
- Department of Cell and Molecular Biology, Northwestern University Medical School, 303 East Chicago Avenue, Chicago, Illinois, 60611, USA
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47
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Huang X, Cuajungco MP, Atwood CS, Hartshorn MA, Tyndall JD, Hanson GR, Stokes KC, Leopold M, Multhaup G, Goldstein LE, Scarpa RC, Saunders AJ, Lim J, Moir RD, Glabe C, Bowden EF, Masters CL, Fairlie DP, Tanzi RE, Bush AI. Cu(II) potentiation of alzheimer abeta neurotoxicity. Correlation with cell-free hydrogen peroxide production and metal reduction. J Biol Chem 1999; 274:37111-6. [PMID: 10601271 DOI: 10.1074/jbc.274.52.37111] [Citation(s) in RCA: 568] [Impact Index Per Article: 22.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
Oxidative stress markers as well as high concentrations of copper are found in the vicinity of Abeta amyloid deposits in Alzheimer's disease. The neurotoxicity of Abeta in cell culture has been linked to H(2)O(2) generation by an unknown mechanism. We now report that Cu(II) markedly potentiates the neurotoxicity exhibited by Abeta in cell culture. The potentiation of toxicity is greatest for Abeta1-42 > Abeta1-40 >> mouse/rat Abeta1-40, corresponding to their relative capacities to reduce Cu(II) to Cu(I), form H(2)O(2) in cell-free assays and to exhibit amyloid pathology. The copper complex of Abeta1-42 has a highly positive formal reduction potential ( approximately +500-550 mV versus Ag/AgCl) characteristic of strongly reducing cuproproteins. These findings suggest that certain redox active metal ions may be important in exacerbating and perhaps facilitating Abeta-mediated oxidative damage in Alzheimer's disease.
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Affiliation(s)
- X Huang
- Laboratory for Oxidation Biology, Genetics and Aging Unit, and Department of Psychiatry, Harvard Medical School, Massachusetts General Hospital, Charlestown, Massachusetts 02129, USA
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48
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Affiliation(s)
- R D Moir
- Massachusetts General Hospital East, Charlestown, MA 02129, USA
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49
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Huang X, Atwood CS, Hartshorn MA, Multhaup G, Goldstein LE, Scarpa RC, Cuajungco MP, Gray DN, Lim J, Moir RD, Tanzi RE, Bush AI. The A beta peptide of Alzheimer's disease directly produces hydrogen peroxide through metal ion reduction. Biochemistry 1999; 38:7609-16. [PMID: 10386999 DOI: 10.1021/bi990438f] [Citation(s) in RCA: 803] [Impact Index Per Article: 32.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
Oxidative stress markers characterize the neuropathology both of Alzheimer's disease and of amyloid-bearing transgenic mice. The neurotoxicity of amyloid A beta peptides has been linked to peroxide generation in cell cultures by an unknown mechanism. We now show that human A beta directly produces hydrogen peroxide (H2O2) by a mechanism that involves the reduction of metal ions, Fe(III) or Cu(II), setting up conditions for Fenton-type chemistry. Spectrophotometric experiments establish that the A beta peptide reduces Fe(III) and Cu(II) to Fe(II) and Cu(I), respectively. Spectrochemical techniques are used to show that molecular oxygen is then trapped by A beta and reduced to H2O2 in a reaction that is driven by substoichiometric amounts of Fe(II) or Cu(I). In the presence of Cu(II) or Fe(III), A beta produces a positive thiobarbituric-reactive substance (TBARS) assay, compatible with the generation of the hydroxyl radical (OH.). The amounts of both reduced metal and TBARS reactivity are greatest when generated by A beta 1-42 >> A beta 1-40 > rat A beta 1-40, a chemical relationship that correlates with the participation of the native peptides in amyloid pathology. These findings indicate that the accumulation of A beta could be a direct source of oxidative stress in Alzheimer's disease.
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Affiliation(s)
- X Huang
- Laboratory for Oxidation Biology, Genetics and Aging Unit, Massachusetts General Hospital, Charlestown 02129, USA
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50
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Moir RD, Atwood CS, Romano DM, Laurans MH, Huang X, Bush AI, Smith JD, Tanzi RE. Differential effects of apolipoprotein E isoforms on metal-induced aggregation of A beta using physiological concentrations. Biochemistry 1999; 38:4595-603. [PMID: 10194381 DOI: 10.1021/bi982437d] [Citation(s) in RCA: 77] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The epsilon 4 allele of apolipoprotein E (APOE) has been found to be a risk factor for late-onset Alzheimer's disease (AD). While the pathogenic mechanism of APOE in AD is not yet clear, APOE isoforms appear to differentially influence the aggregation of A beta, the principal component of Alzheimer-associated beta-amyloid deposits. To date, no data are available for the propensity of A beta to aggregate in the presence of APOE under conditions where these components are at physiological concentrations (in cerebrospinal fluid, APOE and A beta are approximately 100 nM and approximately 5 nM, respectively). We employed a novel in vitro filtration assay for detecting zinc(II)- and copper(II)-induced aggregation of A beta in solutions containing concentrations of the peptide that are similar to those reported for human cerebrospinal fluid. The potential for resolubilization with EDTA and the relative densities of zinc- and copper-induced A beta aggregates were also compared. Zinc-induced A beta aggregates were found to be denser and less easily resolubilized than copper-induced precipitates. Metal-induced aggregation of A beta was studied in the presence of purified apolipoprotein E2, apolipoprotein E3, and apolipoprotein E4 under conditions that approximate the physiological concentrations and ratios of these proteins. In the presence of all three APOE isoforms, zinc-induced aggregation of A beta was attenuated, while precipitation with copper was enhanced. Consistent with the increased risk for AD associated with the epsilon 4 allele of APOE, metal-induced aggregation of A beta was highest for both zinc and copper in the presence of apolipoprotein E4. Our data are consistent with a role for APOE as an in vivo molecular chaperone for A beta.
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Affiliation(s)
- R D Moir
- Genetics and Aging Unit, Department of Neurology, Massachusetts General Hospital, Charlestown, Massachusetts 02129-2060, USA
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