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Prion-like domains as epigenetic regulators, scaffolds for subcellular organization, and drivers of neurodegenerative disease.

ABSTRACT: Key challenges faced by all cells include how to spatiotemporally organize complex biochemistry and how to respond to environmental fluctuations. The budding yeast Saccharomyces cerevisiae harnesses alternative protein folding mediated by yeast prion domains (PrDs) for rapid evolution of new traits in response to environmental stress. Increasingly, it is appreciated that low complexity domains similar in amino acid composition to yeast PrDs (prion-like domains; PrLDs) found in metazoa have a prominent role in subcellular cytoplasmic organization, especially in relation to RNA homeostasis. In this review, we highlight recent advances in our understanding of the role of prions in enabling rapid adaptation to environmental stress in yeast. We also present the complete list of human proteins with PrLDs and discuss the prevalence of the PrLD in nucleic-acid binding proteins that are often connected to neurodegenerative disease, including: ataxin 1, ataxin 2, FUS, TDP-43, TAF15, EWSR1, hnRNPA1, and hnRNPA2. Recent paradigm-shifting advances establish that PrLDs undergo phase transitions to liquid states, which contribute to the structure and biophysics of diverse membraneless organelles. This structural functionality of PrLDs, however, simultaneously increases their propensity for deleterious protein-misfolding events that drive neurodegenerative disease. We suggest that even these PrLD-misfolding events are not irreversible and can be mitigated by natural or engineered protein disaggregases, which could have important therapeutic applications. This article is part of a Special Issue entitled SI:RNA Metabolism in Disease.

SUBMITTER: March ZM

PROVIDER: S-EPMC5003744 | biostudies-literature | 2016 Sep

REPOSITORIES: biostudies-literature

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Prion-like domains as epigenetic regulators, scaffolds for subcellular organization, and drivers of neurodegenerative disease.

March Zachary M ZM King Oliver D OD Shorter James J

Brain research 20160318

Key challenges faced by all cells include how to spatiotemporally organize complex biochemistry and how to respond to environmental fluctuations. The budding yeast Saccharomyces cerevisiae harnesses alternative protein folding mediated by yeast prion domains (PrDs) for rapid evolution of new traits in response to environmental stress. Increasingly, it is appreciated that low complexity domains similar in amino acid composition to yeast PrDs (prion-like domains; PrLDs) found in metazoa have a pro ...[more]

PMID: 26996412

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Project description:Prions are self-templating protein conformers that are naturally transmitted between individuals and promote phenotypic change. In yeast, prion-encoded phenotypes can be beneficial, neutral or deleterious depending upon genetic background and environmental conditions. A distinctive and portable 'prion domain' enriched in asparagine, glutamine, tyrosine and glycine residues unifies the majority of yeast prion proteins. Deletion of this domain precludes prionogenesis and appending this domain to reporter proteins can confer prionogenicity. An algorithm designed to detect prion domains has successfully identified 19 domains that can confer prion behavior. Scouring the human genome with this algorithm enriches a select group of RNA-binding proteins harboring a canonical RNA recognition motif (RRM) and a putative prion domain. Indeed, of 210 human RRM-bearing proteins, 29 have a putative prion domain, and 12 of these are in the top 60 prion candidates in the entire genome. Startlingly, these RNA-binding prion candidates are inexorably emerging, one by one, in the pathology and genetics of devastating neurodegenerative disorders, including: amyotrophic lateral sclerosis (ALS), frontotemporal lobar degeneration with ubiquitin-positive inclusions (FTLD-U), Alzheimer's disease and Huntington's disease. For example, FUS and TDP-43, which rank 1st and 10th among RRM-bearing prion candidates, form cytoplasmic inclusions in the degenerating motor neurons of ALS patients and mutations in TDP-43 and FUS cause familial ALS. Recently, perturbed RNA-binding proteostasis of TAF15, which is the 2nd ranked RRM-bearing prion candidate, has been connected with ALS and FTLD-U. We strongly suspect that we have now merely reached the tip of the iceberg. We predict that additional RNA-binding prion candidates identified by our algorithm will soon surface as genetic modifiers or causes of diverse neurodegenerative conditions. Indeed, simple prion-like transfer mechanisms involving the prion domains of RNA-binding proteins could underlie the classical non-cell-autonomous emanation of neurodegenerative pathology from originating epicenters to neighboring portions of the nervous system. This article is part of a Special Issue entitled RNA-Binding Proteins.

Project description:Analyses of cultured cells and transgenic mice expressing prion protein (PrP) deletion mutants have revealed that some properties of PrP -such as its ability to misfold, aggregate and trigger neurotoxicity- are controlled by discrete molecular determinants within its protein domains. Although the contributions of these determinants to PrP biosynthesis and turnover are relatively well characterized, it is still unclear how they modulate cellular functions of PrP. To address this question, we used two defined activities of PrP as functional readouts: 1) the recruitment of PrP to cell-cell contacts in Drosophila S2 and human MCF-7 epithelial cells, and 2) the induction of PrP embryonic loss- and gain-of-function phenotypes in zebrafish. Our results show that homologous mutations in mouse and zebrafish PrPs similarly affect their subcellular localization patterns as well as their in vitro and in vivo activities. Among PrP's essential features, the N-terminal leader peptide was sufficient to drive targeting of our constructs to cell contact sites, whereas lack of GPI-anchoring and N-glycosylation rendered them inactive by blocking their cell surface expression. Importantly, our data suggest that the ability of PrP to homophilically trans-interact and elicit intracellular signaling is primarily encoded in its globular domain, and modulated by its repetitive domain. Thus, while the latter induces the local accumulation of PrPs at discrete punctae along cell contacts, the former counteracts this effect by promoting the continuous distribution of PrP. In early zebrafish embryos, deletion of either domain significantly impaired PrP's ability to modulate E-cadherin cell adhesion. Altogether, these experiments relate structural features of PrP to its subcellular distribution and in vivo activity. Furthermore, they show that despite their large evolutionary history, the roles of PrP domains and posttranslational modifications are conserved between mouse and zebrafish.

Project description:Purpose: evaluation of the neuroprotective effects of VU846 compound, a positive allosteric modulator highly specific for the M1 muscarinic receptor, using the Next-generation sequencing (NGS) technology in a context of neurodegeneration induced by prion disease. Methods: Tg37 hemizygous mice at 3 to 4 weeks were inoculated with either the Rocky Mountain Laboratory (RML) scrapie prion brain homogenate, causative of the neurodegeneration, or normal brain homogenate for control purposes. Mice were also daily injected with either the M1 specific positive allosteric modulator VU836 or vehicle. The drug treatment started at 7week post brain homogenate inoculations (wpi) and 11wpi. The hippocampi from 3 mice of each group (control + vehicle, control + VU846, prion + vehicle and prion + VU846) were subject to tot RNA extraction. Raw reads were then converted into Fastq format, mapped to the “mouse-mm10” genome using HISAT2 (Galaxy Version 2.1.0) and processed with the StringTie (Galaxy Version 1.3.3.2) for assembling and quantification. Differential gene expression comparisons were performed with DESeq2 statistical tool (Galaxy Version 2.11.40.2) and data further analysed with two online software suites, Gene Ontology Panther (http://www.pantherdb.org/) and Pathway Studio (www.pathwaystudio.com). Results: we use the bioinformatic tool Pathway Studio (www.pathwaystudio.com) to quantitatively assesses the changes in the transcriptome with gene functions reported in the literature to assign an actication score. Strikingly, up and down regulation of genes changed by prion disease promote neuroinflammation and Alzheimer’s disease (AD) (positive activation scores), whereas the M1R specific positive allosteric modulator VU846 treatment modified the expression of genes to inhibit the neuroinflammatory and neurodegenerative processes directly associated with AD (negative activation score). Among these are genes associated with the complement system, microglia and astrocyte activation. Furthermore, consistent with the notion that neuroinflammatory pathways were activated in prion disease and diminished by VU846, the GO Pathway analysis revealed enrichment of genes in pathways such as the complement cascade and chemokine/cytokine signalling. Conversely, a group of genes that were down-regulated in prion disease were transcribed at significantly higher levels in the prion-effect of animals treated with VU846. These genes were strongly associated with synaptic plasticity, learning and memory, cognition and synaptic transmission by the GO Pathway analysis. Conclusions: These data point to the possibility that specific features of neuroinflammation and disease-adaptation may be directly regulated by M1-receptor activity strongly reinforcing the concept that pharmaceutically targeting M1 muscarinic receptor is neuroprotective and it might lead to the development of new treatments of Alzheimer’s like neurodegenerative diseases.

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Prion-like domains as epigenetic regulators, scaffolds for subcellular organization, and drivers of neurodegenerative disease.

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Prion-like domains as epigenetic regulators, scaffolds for subcellular organization, and drivers of neurodegenerative disease.

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