Nicholas T Seyfried

Emory University, Atlanta, Georgia, United States

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Publications (74)362.51 Total impact

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    ABSTRACT: The ataxia telangiectasia-mutated and Rad3-related (ATR) kinase checkpoint pathway maintains genome integrity; however, the role of the sirtuin 2 (SIRT2) acetylome in regulating this pathway is not clear. We found that deacetylation of ATR-interacting protein (ATRIP), a regulatory partner of ATR, by SIRT2 potentiates the ATR checkpoint. SIRT2 interacts with and deacetylates ATRIP at lysine 32 (K32) in response to replication stress. SIRT2 deacetylation of ATRIP at K32 drives ATR autophosphorylation and signaling and facilitates DNA replication fork progression and recovery of stalled replication forks. K32 deacetylation by SIRT2 further promotes ATRIP accumulation to DNA damage sites and binding to replication protein A-coated single-stranded DNA (RPA-ssDNA). Collectively, these results support a model in which ATRIP deacetylation by SIRT2 promotes ATR-ATRIP binding to RPA-ssDNA to drive ATR activation and thus facilitate recovery from replication stress, outlining a mechanism by which the ATR checkpoint is regulated by SIRT2 through deacetylation.
    No preview · Article · Feb 2016 · Cell Reports
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    ABSTRACT: Pseudomonas aeruginosa is a Gram-negative opportunistic pathogen that trimethylates elongation factor-Tu (EF-Tu) on lysine 5. Lysine 5 methylation occurs in a temperature-dependent manner and is generally only seen when P. aeruginosa is grown at temperatures close to ambient (25°C), but not at higher temperatures (37°C). We have previously identified the gene, eftM (for EF-Tu modifying enzyme), responsible for this modification and shown its activity to be associated with increase adhesion to and invasion of respiratory epithelial cells. Bioinformatic analyses predicted EftM to be a Class I S-adenosyl-L-methionine (SAM)-dependent methyltransferase. An in vitro methyltransferase assay was employed to show that, in the presence of SAM, EftM directly trimethylates EF-Tu. A natural variant of EftM, with a glycine to arginine substitution at position 50, in the predicted SAM-binding domain lacks both SAM binding and enzyme activity. Mass spectrometry analysis of the in vitro methyltransferase reaction products revealed that EftM exclusively methylates at lysine 5 of EF-Tu in a distributive manner. Consistent with the in vivo temperature dependence of methylation of EF-Tu, pre-incubation of EftM at 37°C abolished methyltransferase activity, while this activity was retained when EftM was pre-incubated at 25°C. Irreversible protein unfolding at 37°C was observed and we propose is the molecular basis for the temperature dependence of EftM activity. Collectively, our results show that EftM is a thermolabile, SAM-dependent methyltransferase that directly trimethylates lysine 5 of EF-Tu in P. aeruginosa.
    Full-text · Article · Dec 2015 · Journal of Biological Chemistry
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    ABSTRACT: Protein O-glycosylation has key roles in many biological processes, but the repertoire of O-glycans synthesized by cells is difficult to determine. Here we describe an approach termed Cellular O-Glycome Reporter/Amplification (CORA), a sensitive method used to amplify and profile mucin-type O-glycans synthesized by living cells. Cells convert added peracetylated benzyl-α-N-acetylgalactosamine to a large variety of modified O-glycan derivatives that are secreted from cells, allowing for easy purification for analysis by HPLC and mass spectrometry (MS). Relative to conventional O-glycan analyses, CORA resulted in an ∼100-1,000-fold increase in sensitivity and identified a more complex repertoire of O-glycans in more than a dozen cell types from Homo sapiens and Mus musculus. Furthermore, when coupled with computational modeling, CORA can be used for predictions about the diversity of the human O-glycome and offers new opportunities to identify novel glycan biomarkers for human diseases.
    No preview · Article · Nov 2015 · Nature Methods
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    ABSTRACT: The age-dependent deposition of amyloid-b peptides, derived from amyloid precursor protein (APP), is a neuropathological hallmark of Alzheimer's disease (AD). Despite age being the greatest risk factor for AD, the molecular mechanisms linking ageing to APP processing are unknown. Here we show that asparagine endopeptidase (AEP), a pH-controlled cysteine proteinase, is activated during ageing and mediates APP proteolytic processing. AEP cleaves APP at N373 and N585 residues, selectively influencing the amyloidogenic fragmentation of APP. AEP is activated in normal mice in an age-dependent manner, and is strongly activated in 5XFAD transgenic mouse model and human AD brains. Deletion of AEP from 5XFAD or APP/PS1 mice decreases senile plaque formation, ameliorates synapse loss, elevates long-term potentiation and protects memory. Blockade of APP cleavage by AEP in mice alleviates pathological and behavioural deficits. Thus, AEP acts as a d-secretase, contributing to the age-dependent pathogenic mechanisms in AD.
    Full-text · Article · Nov 2015 · Nature Communications

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  • No preview · Article · Jul 2015
  • Nicholas Seyfried · Eric Dammer · Rujing Ren · Marla Gearing · Duc Duong · James Lah · Allan Levey

    No preview · Article · Apr 2015 · The FASEB Journal
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    Eric B Dammer · Martin Göttle · Duc M Duong · John Hanfelt · Nicholas T Seyfried · H.A. Jinnah

    Full-text · Dataset · Mar 2015
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    Eric B Dammer · Martin Göttle · Duc M Duong · John Hanfelt · Nicholas T Seyfried · H.A. Jinnah
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    ABSTRACT: The importance of specific pathways of purine metabolism for normal brain function is highlighted by several inherited disorders, such as Lesch-Nyhan disease (LND). In this disorder, deficiency of the purine recycling enzyme, hypoxanthine-guanine phosphoribosyltransferase (HGprt), causes severe neurological and behavioral abnormalities. Despite many years of research, the mechanisms linking the defect in purine recycling to the neurobehavioral abnormalities remain unclear. In the current studies, an unbiased approach to the identification of potential mechanisms was undertaken by examining changes in protein expression in a model of HGprt deficiency based on the dopaminergic rat PC6-3 line, before and after differentiation with nerve growth factor (NGF). Protein expression profiles of 5 mutant sublines carrying different mutations affecting HGprt enzyme activity were compared to the HGprt-competent parent line using the method of stable isotopic labeling by amino acids in cell culture (SILAC) followed by denaturing gel electrophoresis with liquid chromatography and tandem mass spectrometry (LC-MS/MS) of tryptic digests, and subsequent identification of affected biochemical pathways using the Database for Annotation, Visualization and Integrated Discovery (DAVID) functional annotation chart analysis. The results demonstrate that HGprt deficiency causes broad changes in protein expression that depend on whether the cells are differentiated or not. Several of the pathways identified reflect predictable consequences of defective purine recycling. Other pathways were not anticipated, disclosing previously unknown connections with purine metabolism and novel insights into the pathogenesis of LND. Copyright © 2015 Elsevier Inc. All rights reserved.
    Full-text · Article · Mar 2015 · Molecular Genetics and Metabolism
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    ABSTRACT: MicroRNAs (miRNAs) regulate the translational potential of their mRNA targets and control many cellular processes. The key step in canonical miRNA biogenesis is the cleavage of the primary transcripts by the nuclear RNase III enzyme Drosha. Emerging evidence suggests that the miRNA biogenic cascade is tightly controlled. However, little is known whether Drosha is regulated. Here, we show that Drosha is targeted by stress. Under stress, p38 MAPK directly phosphorylates Drosha at its N terminus. This reduces its interaction with DiGeorge syndrome critical region gene 8 and promotes its nuclear export and degradation by calpain. This regulatory mechanism mediates stress-induced inhibition of Drosha function. Reduction of Drosha sensitizes cells to stress and increases death. In contrast, increase in Drosha attenuates stress-induced death. These findings reveal a critical regulatory mechanism by which stress engages p38 MAPK pathway to destabilize Drosha and inhibit Drosha-mediated cellular survival. Copyright © 2015 Elsevier Inc. All rights reserved.
    Full-text · Article · Feb 2015 · Molecular Cell
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    ABSTRACT: How mitochondrial glutaminolysis contributes to redox homeostasis in cancer cells remains unclear. Here we report that the mitochondrial enzyme glutamate dehydrogenase 1 (GDH1) is commonly upregulated in human cancers. GDH1 is important for redox homeostasis in cancer cells by controlling the intracellular levels of its product alpha-ketoglutarate and subsequent metabolite fumarate. Mechanistically, fumarate binds to and activates a reactive oxygen species scavenging enzyme glutathione peroxidase 1. Targeting GDH1 by shRNA or a small molecule inhibitor R162 resulted in imbalanced redox homeostasis, leading to attenuated cancer cell proliferation and tumor growth. Copyright © 2015 Elsevier Inc. All rights reserved.
    Full-text · Article · Feb 2015 · Cancer Cell
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    ABSTRACT: Abnormal phosphorylation contributes to the formation of neurofibrillary tangles in Alzheimer's Disease (AD), but may play other signaling roles during AD pathogenesis. In this study, we employed immobilized metal affinity chromatography (IMAC) followed by liquid chromatography-tandem mass spectrometry to identify phosphopeptides from 8 individual AD and 8 age-matched control postmortem human brain tissues. Using this approach, we identified 5569 phosphopeptides in frontal cortex across all 16 cases in which phosphopeptides represented 80 percent of all peptide spectral counts collected following IMAC enrichment. Marker selection identified 253 significantly altered phosphopeptides by precursor intensity, changed by at least 1.75 fold relative to controls, with an empirical false discovery rate below 7 percent. Approximately 21 percent of all significantly altered phosphopeptides in AD tissue were derived from tau. Of the other 142 proteins hyperphosphorylated in AD, membrane, synapse, cell junction, and alternatively spliced proteins were overrepresented. Of these, we validated differential phosphorylation of heat shock protein 27 (HSPB1) and crystallin-alpha-B (CRYAB) as hyperphosphorylated by western blotting. We further identified a network of phosphorylated kinases, which co-enriched with phosphorylated small heat shock proteins. This supports a hypothesis that a number of kinases are regulating and/or regulated by the small heat shock protein folding network.This article is protected by copyright. All rights reserved
    No preview · Article · Jan 2015 · Proteomics
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    ABSTRACT: Recent evidence indicates that U1-70K and other U1 small nuclear ribonucleoproteins (snRNPs) are sarkosyl-insoluble and associate with tau neurofibrillary tangles selectively in Alzheimer disease (AD). Currently, the mechanisms underlying the conversion of soluble nuclear U1 snRNPs into insoluble cytoplasmic aggregates remain elusive. Based on the biochemical and subcellular distribution properties of U1-70K in AD we hypothesized that aggregated U1-70K itself or other biopolymers (e.g. proteins or nucleic acids) interact with and sequester natively folded soluble U1-70K into insoluble aggregates. Here we demonstrate that total homogenates from AD brain induce soluble U1-70K from control brain or recombinant U1-70K to become sarkosyl-insoluble. This effect was not dependent on RNA, and did not correlate with detergent-insoluble tau levels as AD homogenates with reduced levels of these components were still capable of inducing U1-70K aggregation. In contrast, proteinase K-treated AD homogenates and sarkosyl-soluble AD fractions were unable to induce U1-70K aggregation, indicating that aggregated proteins in AD brain are responsible for inducing soluble U1-70K aggregation. It was determined that the C-terminus of U1-70K, that harbors two disordered low-complexity (LC) domains, is necessary for U1-70K aggregation. Moreover, both LC1 and LC2 domains were sufficient for aggregation. Finally, protein cross-linking and mass spectrometry studies demonstrated that a U1-70K fragment harboring the LC1 domain directly interacts with aggregated U1-70K in AD brain. Our results support a hypothesis that aberrant forms of U1-70K in AD can directly sequester soluble forms of U1-70K into insoluble aggregates.
    Full-text · Article · Oct 2014 · Journal of Biological Chemistry
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    ABSTRACT: Neurofibrillary tangles (NFTs), composed of truncated and hyperphosphorylated tau, are a common feature of numerous aging-related neurodegenerative diseases, including Alzheimer's disease (AD). However, the molecular mechanisms mediating tau truncation and aggregation during aging remain elusive. Here we show that asparagine endopeptidase (AEP), a lysosomal cysteine proteinase, is activated during aging and proteolytically degrades tau, abolishes its microtubule assembly function, induces tau aggregation and triggers neurodegeneration. AEP is upregulated and active during aging and is activated in human AD brain and tau P301S-transgenic mice with synaptic pathology and behavioral impairments, leading to tau truncation in NFTs. Tau P301S-transgenic mice with deletion of the gene encoding AEP show substantially reduced tau hyperphosphorylation, less synapse loss and rescue of impaired hippocampal synaptic function and cognitive deficits. Mice infected with adeno-associated virus encoding an uncleavable tau mutant showed attenuated pathological and behavioral defects compared to mice injected with adeno-associated virus encoding tau P301S. Together, these observations indicate that AEP acts as a crucial mediator of tau-related clinical and neuropathological changes. Inhibition of AEP may be therapeutically useful for treating tau-mediated neurodegenerative diseases.
    Full-text · Article · Oct 2014 · Nature Medicine
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    Ru-Jing Ren · Eric B Dammer · Gang Wang · Nicholas T Seyfried · Allan I Levey
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    ABSTRACT: Mass spectrometry (MS)-based proteomics has developed into a battery of approaches that is exceedingly adept at identifying with high mass accuracy and precision any of the following: oxidative damage to proteins (redox proteomics), phosphorylation (phosphoproteomics), ubiquitination (diglycine remnant proteomics), protein fragmentation (degradomics), and other posttranslational modifications (PTMs). Many studies have linked these PTMs to pathogenic mechanisms of neurodegeneration. To date, identifying PTMs on specific pathology-associated proteins has proven to be a valuable step in the evaluation of functional alteration of proteins and also elucidates biochemical and structural explanations for possible pathophysiological mechanisms of neurodegenerative diseases. This review provides an overview of methods applicable to the identification and quantification of PTMs on proteins and enumerates historic, recent, and potential future research endeavours in the field of proteomics furthering the understanding of PTM roles in the pathogenesis of neurodegeneration.
    Full-text · Article · Oct 2014 · Translational Neurodegeneration
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    ABSTRACT: Yeast prions are self-propagating amyloid-like aggregates of Q/N-rich protein that confer heritable traits and provide a model of mammalian amyloidoses. [PSI+] is a prion isoform of the translation termination factor Sup35. Propagation of [PSI+] during cell division under normal conditions and during the recovery from damaging environmental stress depends on cellular chaperones and is influenced by ubiquitin proteolysis and the actin cytoskeleton. The paralogous yeast proteins Lsb1 and Lsb2 bind the actin assembly protein Las17 (a yeast homolog of human Wiskott-Aldrich syndrome protein) and participate in the endocytic pathway. Lsb2 was shown to modulate maintenance of [PSI+] during and after heat shock. Here, we demonstrate that Lsb1 also regulates maintenance of the Sup35 prion during and after heat shock. These data point to the involvement of Lsb proteins in the partitioning of protein aggregates in stressed cells. Lsb1 abundance and cycling between actin patches, endoplasmic reticulum, and cytosol is regulated by the Guided Entry of Tail-anchored proteins pathway and Rsp5-dependent ubiquitination. Heat shock-induced proteolytic processing of Lsb1 is crucial for prion maintenance during stress. Our findings identify Lsb1 as another component of a tightly regulated pathway controlling protein aggregation in changing environments.
    Full-text · Article · Aug 2014 · Journal of Biological Chemistry
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    ABSTRACT: Abnormal cytoplasmic accumulation of Fused in Sarcoma (FUS) in neurons defines subtypes of amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration (FTLD). FUS is a member of the FET protein family that includes Ewing's sarcoma (EWS) and TATA-binding protein-associated factor 2N (TAF15). FET proteins are predominantly localized to the nucleus, where they bind RNA and DNA to modulate transcription, mRNA splicing, and DNA repair. In ALS cases with FUS inclusions (ALS-FUS), mutations in the FUS gene cause disease, whereas FTLD cases with FUS inclusions (FTLD-FUS) do not harbor FUS mutations. Notably, in FTLD-FUS, all FET proteins accumulate with their nuclear import receptor Transportin 1 (TRN1), in contrast ALS-FUS inclusions are exclusively positive for FUS. In the present study, we show that induction of DNA damage replicates several pathologic hallmarks of FTLD-FUS in immortalized human cells and primary human neurons and astrocytes. Treatment with the antibiotic calicheamicin γ1, which causes DNA double-strand breaks, leads to the cytoplasmic accumulation of FUS, TAF15, EWS, and TRN1. Moreover, cytoplasmic translocation of FUS is mediated by phosphorylation of its N terminus by the DNA-dependent protein kinase. Finally, we observed elevated levels of phospho-H2AX in FTLD-FUS brains, indicating that DNA damage occurs in patients. Together, our data reveal a novel regulatory mechanism for FUS localization in cells and suggest that DNA damage may contribute to the accumulation of FET proteins observed in human FTLD-FUS cases, but not in ALS-FUS.
    Full-text · Article · Jun 2014 · The Journal of Neuroscience : The Official Journal of the Society for Neuroscience
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    ABSTRACT: We recently identified U1 small nuclear ribonucleoprotein (snRNP) tangle-like aggregates and RNA splicing abnormalities in sporadic Alzheimer's disease (AD). However little is known about snRNP biology in early onset AD due to autosomal dominant genetic mutations or trisomy 21 in Down syndrome. Therefore we investigated snRNP biochemical and pathologic features in these disorders. We performed quantitative proteomics and immunohistochemistry in postmortem brain from genetic AD cases. Electron microscopy was used to characterize ultrastructural features of pathologic aggregates. U1-70k and other snRNPs were biochemically enriched in the insoluble fraction of human brain from subjects with presenilin 1 (PS1) mutations. Aggregates of U1 snRNP-immunoreactivity formed cytoplasmic tangle-like structures in cortex of AD subjects with PS1 and amyloid precursor protein (APP) mutations as well as trisomy 21. Ultrastructural analysis with electron microscopy in an APP mutation case demonstrated snRNP immunogold labeling of paired helical filaments (PHF). These studies identify U1 snRNP pathologic changes in brain of early onset genetic forms of AD. Since dominant genetic mutations and trisomy 21 result in dysfunctional amyloid processing, the findings suggest that aberrant beta-amyloid processing may influence U1 snRNP aggregate formation.
    Full-text · Article · Apr 2014 · Molecular Neurodegeneration
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    James Atwood · Eric Dammer · Duc Duong · Chelsea Dunn · Nicholas Seyfried
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    ABSTRACT: Formalin fixation is the universal standard for preserving tissue samples. However, due to the nature of the formalin fixation process, protein extraction and recovery is typically compromised when compared to proteomic analysis of fresh tissues. Herein, we performed a comparative proteomic analysis between matched fresh and formalin fixed brain tissue samples in order to evaluate the degree of proteome degradation and to establish and optimized protocol for protein extraction from formalin fixed samples. Method: Fresh and free floating formalin fixed brain tissues were homogenized under non-denaturing and denaturing conditions. Protein recoveries were quantified and the protein mixture was enzymatically digested. Resulting peptides were analyzed by quantitative LC-MS/MS to compare total proteome coverage between tissue types and preparation methods. Results: While total protein recovery was comparable across both tissue types the homogenization buffer affected yields dramatically. Proteomic analysis revealed a significant decrease in total proteome coverage in the formalin fixed tissues with proteins of known high abundance being most affected.
    Full-text · Conference Paper · Apr 2014

Publication Stats

1k Citations
362.51 Total Impact Points

Institutions

  • 2008-2015
    • Emory University
      • • Department of Biochemistry
      • • Department of Human Genetics
      Atlanta, Georgia, United States
  • 2011
    • Center for Human Genetics, Inc.
      Cambridge, Massachusetts, United States
  • 2007-2008
    • University of Georgia
      • Complex Carbohydrate Research Center
      Атина, Georgia, United States
  • 2005
    • University of Oxford
      • Department of Biochemistry
      Oxford, England, United Kingdom