RESUMEN

A GGGGCC (G4C2) hexanucleotide repeat expansion in C9ORF72 causes amyotrophic lateral sclerosis and frontotemporal dementia (C9ALS/FTD), while a CGG trinucleotide repeat expansion in FMR1 leads to the neurodegenerative disorder Fragile X-associated tremor/ataxia syndrome (FXTAS). These GC-rich repeats form RNA secondary structures that support repeat-associated non-AUG (RAN) translation of toxic proteins that contribute to disease pathogenesis. Here we assessed whether these same repeats might trigger stalling and interfere with translational elongation. We find that depletion of ribosome-associated quality control (RQC) factors NEMF, LTN1 and ANKZF1 markedly boost RAN translation product accumulation from both G4C2 and CGG repeats while overexpression of these factors reduces RAN production in both reporter assays and C9ALS/FTD patient iPSC-derived neurons. We also detected partially made products from both G4C2 and CGG repeats whose abundance increased with RQC factor depletion. Repeat RNA sequence, rather than amino acid content, is central to the impact of RQC factor depletion on RAN translation-suggesting a role for RNA secondary structure in these processes. Together, these findings suggest that ribosomal stalling and RQC pathway activation during RAN translation inhibits the generation of toxic RAN products. We propose augmenting RQC activity as a therapeutic strategy in GC-rich repeat expansion disorders.

Asunto(s)

Esclerosis Amiotrófica Lateral , Proteína C9orf72 , Demencia Frontotemporal , Biosíntesis de Proteínas , Proteínas Ribosómicas , Expansión de Repetición de Trinucleótido , Humanos , Esclerosis Amiotrófica Lateral/genética , Esclerosis Amiotrófica Lateral/metabolismo , Ataxia , Proteína C9orf72/genética , Proteína C9orf72/metabolismo , Expansión de las Repeticiones de ADN/genética , Proteína de la Discapacidad Intelectual del Síndrome del Cromosoma X Frágil/genética , Proteína de la Discapacidad Intelectual del Síndrome del Cromosoma X Frágil/metabolismo , Síndrome del Cromosoma X Frágil/genética , Síndrome del Cromosoma X Frágil/metabolismo , Demencia Frontotemporal/genética , Demencia Frontotemporal/metabolismo , Secuencia Rica en GC , Células HEK293 , Células Madre Pluripotentes Inducidas/metabolismo , Neuronas/metabolismo , Ribosomas/metabolismo , Ribosomas/genética , Temblor , Expansión de Repetición de Trinucleótido/genética , Proteínas Ribosómicas/metabolismo

RESUMEN

Thiolutin is a natural product transcription inhibitor with an unresolved mode of action. Thiolutin and the related dithiolopyrrolone holomycin chelate Zn2+ and previous studies have concluded that RNA Polymerase II (Pol II) inhibition in vivo is indirect. Here, we present chemicogenetic and biochemical approaches to investigate thiolutin's mode of action in Saccharomyces cerevisiae. We identify mutants that alter sensitivity to thiolutin. We provide genetic evidence that thiolutin causes oxidation of thioredoxins in vivo and that thiolutin both induces oxidative stress and interacts functionally with multiple metals including Mn2+ and Cu2+, and not just Zn2+. Finally, we show direct inhibition of RNA polymerase II (Pol II) transcription initiation by thiolutin in vitro in support of classical studies that thiolutin can directly inhibit transcription in vitro. Inhibition requires both Mn2+ and appropriate reduction of thiolutin as excess DTT abrogates its effects. Pause prone, defective elongation can be observed in vitro if inhibition is bypassed. Thiolutin effects on Pol II occupancy in vivo are widespread but major effects are consistent with prior observations for Tor pathway inhibition and stress induction, suggesting that thiolutin use in vivo should be restricted to studies on its modes of action and not as an experimental tool.

Asunto(s)

Pirrolidinonas , ARN Polimerasa II , Proteínas de Saccharomyces cerevisiae , Pirrolidinonas/farmacología , ARN Polimerasa II/antagonistas & inhibidores , Saccharomyces cerevisiae/efectos de los fármacos , Saccharomyces cerevisiae/enzimología , Proteínas de Saccharomyces cerevisiae/genética , Transcripción Genética , Zinc

RESUMEN

This commentary discusses a comprehensive history of the first-ever use of pertinent words directly related to DNA, such as desoxyribose, deoxyribose, desoxyribonucleic acid, and deoxyribonucleic acid. With almost 100 years of the identification and nomenclature of desoxyribose sugar and desoxyribonucleic acid, the term "desoxy" continues to see limited use. We hope that whenever young researchers come across the sporadic occurrence of "desoxy" in any published text, they will not consider it a mistake.

Asunto(s)

ADN , Terminología como Asunto

RESUMEN

Neurodegeneration in Fragile X-associated tremor/ataxia syndrome (FXTAS) is caused by a CGG trinucleotide repeat expansion in the 5' UTR of FMR1. Expanded CGG repeat RNAs form stable secondary structures, which in turn support repeat-associated non-AUG (RAN) translation to produce toxic peptides. The parameters that impact RAN translation initiation efficiency are not well understood. Here we used a Drosophila melanogaster model of FXTAS to evaluate the role of the eIF4G family of eukaryotic translation initiation factors (EIF4G1, EIF4GII and EIF4G2/DAP5) in modulating RAN translation and CGG repeat-associated toxicity. DAP5 knockdown robustly suppressed CGG repeat-associated toxicity and inhibited RAN translation. Furthermore, knockdown of initiation factors that preferentially associate with DAP5 (such as EIF2ß, EIF3F and EIF3G) also selectively suppressed CGG repeat-induced eye degeneration. In mammalian cellular reporter assays, DAP5 knockdown exhibited modest and cell-type specific effects on RAN translation. Taken together, these data support a role for DAP5 in CGG repeat associated toxicity possibly through modulation of RAN translation.

Asunto(s)

Proteínas de Drosophila , Síndrome del Cromosoma X Frágil , Animales , Drosophila/metabolismo , Temblor/genética , Drosophila melanogaster/metabolismo , Factor 4G Eucariótico de Iniciación/genética , Proteína de la Discapacidad Intelectual del Síndrome del Cromosoma X Frágil/genética , Proteína de la Discapacidad Intelectual del Síndrome del Cromosoma X Frágil/metabolismo , Síndrome del Cromosoma X Frágil/genética , Expansión de Repetición de Trinucleótido , Ataxia/genética , Mamíferos/metabolismo , Proteínas de Drosophila/genética , Proteínas de Drosophila/metabolismo

RESUMEN

A GGGGCC (G4C2) hexanucleotide repeat expansion in C9ORF72 causes amyotrophic lateral sclerosis and frontotemporal dementia (C9ALS/FTD), while a CGG trinucleotide repeat expansion in FMR1 leads to the neurodegenerative disorder Fragile X-associated tremor/ataxia syndrome (FXTAS). These GC-rich repeats form RNA secondary structures that support repeat-associated non-AUG (RAN) translation of toxic proteins that contribute to disease pathogenesis. Here we assessed whether these same repeats might trigger stalling and interfere with translational elongation. We find that depletion of ribosome-associated quality control (RQC) factors NEMF, LTN1, and ANKZF1 markedly boost RAN translation product accumulation from both G4C2 and CGG repeats while overexpression of these factors reduces RAN production in both reporter cell lines and C9ALS/FTD patient iPSC-derived neurons. We also detected partially made products from both G4C2 and CGG repeats whose abundance increased with RQC factor depletion. Repeat RNA sequence, rather than amino acid content, is central to the impact of RQC factor depletion on RAN translation - suggesting a role for RNA secondary structure in these processes. Together, these findings suggest that ribosomal stalling and RQC pathway activation during RAN translation elongation inhibits the generation of toxic RAN products. We propose augmenting RQC activity as a therapeutic strategy in GC-rich repeat expansion disorders.

RESUMEN

Fragile X­associated tremor/ataxia syndrome (FXTAS) is a debilitating late-onset neurodegenerative disease in premutation carriers of the expanded CGG repeat in FMR1 that presents with a spectrum of neurological manifestations, such as gait ataxia, intention tremor, and parkinsonism [P. J. Hagerman, R. J. Hagerman, Ann. N. Y. Acad. Sci. 1338, 58­70 (2015); S. Jacquemont et al., JAMA 291, 460­469 (2004)]. Here, we performed whole-genome sequencing (WGS) on male premutation carriers (CGG55­200) and prioritized candidate variants to screen for candidate genetic modifiers using a Drosophila model of FXTAS. We found 18 genes that genetically modulate CGG-associated neurotoxicity in Drosophila, such as Prosbeta5 (PSMB5), pAbp (PABPC1L), e(y)1 (TAF9), and CG14231 (OSGEPL1). Among them, knockdown of Prosbeta5 (PSMB5) suppressed CGG-associated neurodegeneration in the fly as well as in N2A cells. Interestingly, an expression quantitative trait locus variant in PSMB5, PSMB5rs11543947-A, was found to be associated with decreased expression of PSMB5 and delayed onset of FXTAS in human FMR1 premutation carriers. Finally, we demonstrate evidence that PSMB5 knockdown results in suppression of CGG neurotoxicity via both the RAN translation and RNA-mediated toxicity mechanisms, thereby presenting a therapeutic strategy for FXTAS.

Asunto(s)

Ataxia , Síndrome del Cromosoma X Frágil , Complejo de la Endopetidasa Proteasomal , Temblor , Animales , Ataxia/genética , Modelos Animales de Enfermedad , Drosophila melanogaster , Proteína de la Discapacidad Intelectual del Síndrome del Cromosoma X Frágil/genética , Síndrome del Cromosoma X Frágil/genética , Humanos , Masculino , Complejo de la Endopetidasa Proteasomal/genética , Temblor/genética

RESUMEN

Repeat-associated non-AUG (RAN) translation of expanded repeat-mutation mRNA produces toxic peptides in neurons of patients suffering from neurodegenerative diseases. Recent findings indicate that RAN translation in diverse model systems is not inhibited by cellular stressors that impair global translation through phosphorylation of the alpha subunit of eIF2, the essential eukaryotic translation initiation factor that brings the initiator tRNA to the 40S ribosome. Using in vitro, cell-based and Drosophila models, we examined the role of alternative ternary complex factors that may function in place of eIF2, including eIF2A, eIF2D, DENR and MCTS1. Among these factors, DENR knockdown had the greatest inhibitory effect on RAN translation of expanded GGGGCC and CGG repeat reporters and its reduction improved the survival of Drosophila expressing expanded GGGGCC repeats. Taken together, these data support a role for alternative initiation factors in RAN translation and suggest these may serve as novel therapeutic targets in neurodegenerative disease.

Asunto(s)

Proteínas de Drosophila , Enfermedades Neurodegenerativas , Animales , Drosophila/genética , Drosophila/metabolismo , Proteínas de Drosophila/genética , Proteínas de Drosophila/metabolismo , Factor 2 Eucariótico de Iniciación/genética , Factor 2 Eucariótico de Iniciación/metabolismo , Factores Eucarióticos de Iniciación/genética , Factores Eucarióticos de Iniciación/metabolismo , Enfermedades Neurodegenerativas/genética , Enfermedades Neurodegenerativas/metabolismo , Biosíntesis de Proteínas/genética , ARN Mensajero/genética , Ribosomas/genética , Ribosomas/metabolismo

RESUMEN

Transcribed CGG repeat expansions cause neurodegeneration in Fragile X-associated tremor/ataxia syndrome (FXTAS). CGG repeat RNAs sequester RNA-binding proteins (RBPs) into nuclear foci and undergo repeat-associated non-AUG (RAN) translation into toxic peptides. To identify proteins involved in these processes, we employed a CGG repeat RNA-tagging system to capture repeat-associated RBPs by mass spectrometry in mammalian cells. We identified several SR (serine/arginine-rich) proteins that interact selectively with CGG repeats basally and under cellular stress. These proteins modify toxicity in a Drosophila model of FXTAS. Pharmacologic inhibition of serine/arginine protein kinases (SRPKs), which alter SRSF protein phosphorylation, localization, and activity, directly inhibits RAN translation of CGG and GGGGCC repeats (associated with C9orf72 ALS/FTD) and triggers repeat RNA retention in the nucleus. Lowering SRPK expression suppressed toxicity in both FXTAS and C9orf72 ALS/FTD model flies, and SRPK inhibitors suppressed CGG repeat toxicity in rodent neurons. Together, these findings demonstrate roles for CGG repeat RNA binding proteins in RAN translation and repeat toxicity and support further evaluation of SRPK inhibitors in modulating RAN translation associated with repeat expansion disorders.

Asunto(s)

Esclerosis Amiotrófica Lateral , Proteínas de Drosophila , Síndrome del Cromosoma X Frágil , Demencia Frontotemporal , Proteínas Serina-Treonina Quinasas , Esclerosis Amiotrófica Lateral/genética , Animales , Proteína C9orf72/genética , Proteína C9orf72/metabolismo , Proteínas de Drosophila/genética , Proteínas de Drosophila/metabolismo , Drosophila melanogaster/genética , Proteína de la Discapacidad Intelectual del Síndrome del Cromosoma X Frágil/genética , Proteína de la Discapacidad Intelectual del Síndrome del Cromosoma X Frágil/metabolismo , Síndrome del Cromosoma X Frágil/genética , Proteínas Serina-Treonina Quinasas/genética , Proteínas Serina-Treonina Quinasas/metabolismo , Expansión de Repetición de Trinucleótido

RESUMEN

The human genome contains over one million short tandem repeats. Expansion of a subset of these repeat tracts underlies over fifty human disorders, including common genetic causes of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (C9orf72), polyglutamine-associated ataxias and Huntington disease, myotonic dystrophy, and intellectual disability disorders such as Fragile X syndrome. In this Review, we discuss the four major mechanisms by which expansion of short tandem repeats causes disease: loss of function through transcription repression, RNA-mediated gain of function through gelation and sequestration of RNA-binding proteins, gain of function of canonically translated repeat-harbouring proteins, and repeat-associated non-AUG translation of toxic repeat peptides. Somatic repeat instability amplifies these mechanisms and influences both disease age of onset and tissue specificity of pathogenic features. We focus on the crosstalk between these disease mechanisms, and argue that they often synergize to drive pathogenesis. We also discuss the emerging native functions of repeat elements and how their dynamics might contribute to disease at a larger scale than currently appreciated. Lastly, we propose that lynchpins tying these disease mechanisms and native functions together offer promising therapeutic targets with potential shared applications across this class of human disorders.

Asunto(s)

Expansión de las Repeticiones de ADN/genética , Enfermedades Neurodegenerativas/genética , Animales , Silenciador del Gen , Inestabilidad Genómica , Humanos , Mutación , Enfermedades Neurodegenerativas/patología , Enfermedades Neurodegenerativas/fisiopatología , Especificidad de Órganos , Biosíntesis de Proteínas , Estructuras R-Loop , ARN/química , ARN/metabolismo , Proteínas de Unión al ARN/metabolismo

RESUMEN

BACKGROUND: The majority of eukaryotic promoters utilize multiple transcription start sites (TSSs). How multiple TSSs are specified at individual promoters across eukaryotes is not understood for most species. In Saccharomyces cerevisiae, a pre-initiation complex (PIC) comprised of Pol II and conserved general transcription factors (GTFs) assembles and opens DNA upstream of TSSs. Evidence from model promoters indicates that the PIC scans from upstream to downstream to identify TSSs. Prior results suggest that TSS distributions at promoters where scanning occurs shift in a polar fashion upon alteration in Pol II catalytic activity or GTF function. RESULTS: To determine the extent of promoter scanning across promoter classes in S. cerevisiae, we perturb Pol II catalytic activity and GTF function and analyze their effects on TSS usage genome-wide. We find that alterations to Pol II, TFIIB, or TFIIF function widely alter the initiation landscape consistent with promoter scanning operating at all yeast promoters, regardless of promoter class. Promoter architecture, however, can determine the extent of promoter sensitivity to altered Pol II activity in ways that are predicted by a scanning model. CONCLUSIONS: Our observations coupled with previous data validate key predictions of the scanning model for Pol II initiation in yeast, which we term the shooting gallery. In this model, Pol II catalytic activity and the rate and processivity of Pol II scanning together with promoter sequence determine the distribution of TSSs and their usage.

Asunto(s)

ADN Polimerasa II/metabolismo , Saccharomyces cerevisiae/enzimología , Factores Generales de Transcripción/metabolismo , Sitio de Iniciación de la Transcripción , Iniciación de la Transcripción Genética , Modelos Genéticos , Regiones Promotoras Genéticas , Saccharomyces cerevisiae/genética

RESUMEN

RNA polymerase II (RNAPII) transcription is crucial for gene expression. RNAPII density peaks at gene boundaries, associating these key regions for gene expression control with limited RNAPII movement. The connections between RNAPII transcription speed and gene regulation in multicellular organisms are poorly understood. Here, we directly modulate RNAPII transcription speed by point mutations in the second largest subunit of RNAPII in Arabidopsis thaliana. A RNAPII mutation predicted to decelerate transcription is inviable, while accelerating RNAPII transcription confers phenotypes resembling auto-immunity. Nascent transcription profiling revealed that RNAPII complexes with accelerated transcription clear stalling sites at both gene ends, resulting in read-through transcription. The accelerated transcription mutant NRPB2-Y732F exhibits increased association with 5' splice site (5'SS) intermediates and enhanced splicing efficiency. Our findings highlight potential advantages of RNAPII stalling through local reduction in transcription speed to optimize gene expression for the development of multicellular organisms.

Asunto(s)

Proteínas de Arabidopsis , Arabidopsis , ARN Polimerasa II , Arabidopsis/genética , Arabidopsis/metabolismo , Proteínas de Arabidopsis/genética , Proteínas de Arabidopsis/metabolismo , Regulación de la Expresión Génica , Mutación Puntual , ARN Polimerasa II/genética , ARN Polimerasa II/metabolismo

RESUMEN

Here we employ a set of RNA Polymerase II (Pol II) activity mutants to determine the consequences of increased or decreased Pol II catalysis on gene expression in Saccharomyces cerevisiae. We find that alteration of Pol II catalytic rate, either fast or slow, leads to decreased Pol II occupancy and apparent reduction in elongation rate in vivo. However, we also find that determination of elongation rate in vivo by chromatin immunoprecipitation can be confounded by the kinetics and conditions of transcriptional shutoff in the assay. We identify promoter and template-specific effects on severity of gene expression defects for both fast and slow Pol II mutants. We show that mRNA half-lives for a reporter gene are increased in both fast and slow Pol II mutant strains and the magnitude of half-life changes correlate both with mutants' growth and reporter expression defects. Finally, we tested a model that altered Pol II activity sensitizes cells to nucleotide depletion. In contrast to model predictions, mutated Pol II retains normal sensitivity to altered nucleotide levels. Our experiments establish a framework for understanding the diversity of transcription defects derived from altered Pol II activity mutants, essential for their use as probes of transcription mechanisms.

Asunto(s)

ARN Polimerasa II/genética , ARN Mensajero/genética , Saccharomyces cerevisiae/genética , Biocatálisis , Inmunoprecipitación de Cromatina , Regulación Fúngica de la Expresión Génica , Semivida , Mutación , Nucleótidos/deficiencia , Regiones Promotoras Genéticas , ARN Polimerasa II/metabolismo , Estabilidad del ARN , ARN Mensajero/metabolismo , Saccharomyces cerevisiae/enzimología , Elongación de la Transcripción Genética , Sitio de Iniciación de la Transcripción

RESUMEN

Notwithstanding numerous published structures of RNA Polymerase II (Pol II), structural details of Pol II engaging a complete nucleic acid scaffold have been lacking. Here, we report the structures of TFIIF-stabilized transcribing Pol II complexes, revealing the upstream duplex and full transcription bubble. The upstream duplex lies over a wedge-shaped loop from Rpb2 that engages its minor groove, providing part of the structural framework for DNA tracking during elongation. At the upstream transcription bubble fork, rudder and fork loop 1 residues spatially coordinate strand annealing and the nascent RNA transcript. At the downstream fork, a network of Pol II interactions with the non-template strand forms a rigid domain with the trigger loop (TL), allowing visualization of its open state. Overall, our observations suggest that "open/closed" conformational transitions of the TL may be linked to interactions with the non-template strand, possibly in a synchronized ratcheting manner conducive to polymerase translocation.

Asunto(s)

ARN Polimerasa II/química , Proteínas de Saccharomyces cerevisiae/química , Secuencia de Bases , Cristalografía por Rayos X , ADN de Hongos/química , ADN de Hongos/genética , ADN de Hongos/metabolismo , ARN Polimerasas Dirigidas por ADN/química , ARN Polimerasas Dirigidas por ADN/metabolismo , Modelos Moleculares , Conformación de Ácido Nucleico , Dominios y Motivos de Interacción de Proteínas , Estructura Cuaternaria de Proteína , Subunidades de Proteína , ARN Polimerasa II/metabolismo , ARN de Hongos/química , ARN de Hongos/genética , ARN de Hongos/metabolismo , Saccharomyces cerevisiae/genética , Saccharomyces cerevisiae/metabolismo , Proteínas de Saccharomyces cerevisiae/metabolismo , Electricidad Estática , Transcripción Genética

RESUMEN

Screening chemical libraries to identify compounds that affect overall cell proliferation is common. However, in most cases, it is not known whether the compounds tested alter the timing of particular cell cycle transitions. Here, we evaluated an FDA-approved drug library to identify pharmaceuticals that alter cell cycle progression in yeast, using DNA content measurements by flow cytometry. This approach revealed strong cell cycle effects of several commonly used pharmaceuticals. We show that the antilipemic gemfibrozil delays initiation of DNA replication, while cells treated with the antidepressant fluoxetine severely delay progression through mitosis. Based on their effects on cell cycle progression, we also examined cell proliferation in the presence of both compounds. We discovered a strong suppressive interaction between gemfibrozil and fluoxetine. Combinations of interest among diverse pharmaceuticals are difficult to identify, due to the daunting number of possible combinations that must be evaluated. The novel interaction between gemfibrozil and fluoxetine suggests that identifying and combining drugs that show cell cycle effects might streamline identification of drug combinations with a pronounced impact on cell proliferation.

Asunto(s)

Ciclo Celular/efectos de los fármacos , Fluoxetina/farmacología , Gemfibrozilo/farmacología , Proliferación Celular/efectos de los fármacos , Interacciones Farmacológicas , Citometría de Flujo , Mitosis/efectos de los fármacos

RESUMEN

A multicomponent reaction of 3-aminopyrazol-5-ones with substituted salicylic aldehydes and acetylacetic ester leading to the formation of novel 2,3-dihydrochromeno[4,3-d]pyrazolo[3,4-b]pyridine-1,6-diones was discovered. The elucidation of the reaction scope revealed that 5-aminopyrazoles, 3-amino-1,2,4-triazoles and 6-aminouracil could be used as the heterocyclic amine component. Selected heterocyclic products were found to possess notable antibacterial activities.

RESUMEN

A novel reaction of indole with aryldiazonium salts leading to the formation of 2-aryl-3-(arylazo)indoles was discovered. The products were found to possess potent anti-MRSA and anti-LLVRE activities. The SAR studies indicate that the potentially metabolically labile azo functionality can be replaced with ether oxygen and thioether sulfur atoms without any loss of activity.

Asunto(s)

Antibacterianos/síntesis química , Antibacterianos/farmacología , Antifúngicos/farmacología , Bacterias/efectos de los fármacos , Compuestos de Diazonio/química , Hongos/efectos de los fármacos , Indoles/farmacología , Antibacterianos/química , Antifúngicos/síntesis química , Antifúngicos/química , Indoles/síntesis química , Indoles/química , Pruebas de Sensibilidad Microbiana , Estructura Molecular , Sales (Química)/química , Estereoisomerismo , Relación Estructura-Actividad

RESUMEN

Privileged medicinal scaffolds based on the structures of tetra- and pentasubstituted 2-aminopyrroles were prepared via one-pot multicomponent reactions of structurally diverse aldehydes and N-(aryl-, hetaryl-, alkylsulfonamido)acetophenones with activated methylene compounds. This methodology was used in a four-step synthesis of alkaloids rigidins A, B, C, and D in overall yields of 61%, 58%, 60%, and 53%, respectively. Of these, rigidins B, C, and D were synthesized for the first time.

Asunto(s)

Acetofenonas/síntesis química , Productos Biológicos/síntesis química , Pirimidinas/síntesis química , Pirroles/síntesis química , Acetofenonas/química , Alcaloides , Productos Biológicos/química , Técnicas Químicas Combinatorias , Biología Marina , Estructura Molecular , Pirimidinas/química , Pirroles/química