RESUMEN
Epigenetic gene silencing plays a critical role in regulating gene expression and contributes to organismal development and cell fate acquisition in eukaryotes. In fission yeast, Schizosaccharomyces pombe, heterochromatin-associated gene silencing is known to be mediated by RNA processing pathways including RNA interference (RNAi) and a 3'-5' exoribonuclease complex, the exosome. Here, we report a new RNA-processing pathway that contributes to epigenetic gene silencing and assembly of heterochromatin mediated by 5'-3' exoribonuclease Dhp1/Rat1/Xrn2. Dhp1 mutation causes defective gene silencing both at peri-centromeric regions and at the silent mating type locus. Intriguingly, mutation in either of the two well-characterized Dhp1-interacting proteins, the Din1 pyrophosphohydrolase or the Rhn1 transcription termination factor, does not result in silencing defects at the main heterochromatic regions. We demonstrate that Dhp1 interacts with heterochromatic factors and is essential in the sequential steps of establishing silencing in a manner independent of both RNAi and the exosome. Genomic and genetic analyses suggest that Dhp1 is involved in post-transcriptional silencing of repetitive regions through its RNA processing activity. The results describe the unexpected role of Dhp1/Rat1/Xrn2 in chromatin-based silencing and elucidate how various RNA-processing pathways, acting together or independently, contribute to epigenetic regulation of the eukaryotic genome.
Asunto(s)
Secuencia Conservada , Epigénesis Genética , Exorribonucleasas/metabolismo , Silenciador del Gen , Proteínas de Schizosaccharomyces pombe/genética , Schizosaccharomyces/genética , Secuencia de Aminoácidos , Biocatálisis , Centrómero/metabolismo , Segregación Cromosómica/genética , ARN Polimerasas Dirigidas por ADN/metabolismo , Exosomas/metabolismo , Genes del Tipo Sexual de los Hongos , Sitios Genéticos , Heterocromatina/metabolismo , Histonas/metabolismo , Lisina/metabolismo , Metilación , Datos de Secuencia Molecular , Mutación/genética , Unión Proteica , ARN Mensajero/genética , ARN Mensajero/metabolismo , Proteínas de Schizosaccharomyces pombe/metabolismo , Regiones Terminadoras GenéticasRESUMEN
Chromatin organization is essential for defining transcription units and maintaining genomic integrity in eukaryotes. In this study, we found that deletion of the Schizosaccharomyces pombe Chd1 chromatin remodelers, hrp1 and hrp3, causes strong, genome-wide accumulation of antisense transcripts. Nucleosome mapping revealed a specific role for Chd1 remodelers in the positioning of nucleosomes in gene coding regions. Other mutations associated with enhanced cryptic transcription activity, such as set2Δ, alp13Δ and FACT complex subunit pob3Δ, did not, or only mildly, affect nucleosome positioning. These data indicate several mechanisms in the repression of cryptic promoter activity in eukaryotic cells.
Asunto(s)
Adenosina Trifosfatasas/metabolismo , Ensamble y Desensamble de Cromatina , ADN Helicasas/metabolismo , Proteínas de Unión al ADN/metabolismo , Nucleosomas/química , Proteínas de Schizosaccharomyces pombe/metabolismo , Transcripción Genética , Adenosina Trifosfatasas/genética , Proteínas Portadoras/genética , Proteínas Portadoras/metabolismo , Proteínas de Ciclo Celular/genética , ADN Helicasas/genética , Proteínas de Unión al ADN/genética , Eliminación de Gen , Genoma Fúngico , N-Metiltransferasa de Histona-Lisina/genética , Nucleosomas/metabolismo , ARN sin Sentido/biosíntesis , Schizosaccharomyces/genética , Schizosaccharomyces/metabolismo , Proteínas de Schizosaccharomyces pombe/genética , Factores de Transcripción/genética , Factores de Transcripción/metabolismoRESUMEN
Energetic stress compels cells to evolve adaptive mechanisms to adjust their metabolism. Inhibition of mTOR kinase complex 1 (mTORC1) is essential for cell survival during glucose starvation. How mTORC1 controls cell viability during glucose starvation is not well understood. Here we show that the mTORC1 effectors eukaryotic initiation factor 4E binding proteins 1/2 (4EBP1/2) confer protection to mammalian cells and budding yeast under glucose starvation. Mechanistically, 4EBP1/2 promote NADPH homeostasis by preventing NADPH-consuming fatty acid synthesis via translational repression of Acetyl-CoA Carboxylase 1 (ACC1), thereby mitigating oxidative stress. This has important relevance for cancer, as oncogene-transformed cells and glioma cells exploit the 4EBP1/2 regulation of ACC1 expression and redox balance to combat energetic stress, thereby supporting transformation and tumorigenicity in vitro and in vivo. Clinically, high EIF4EBP1 expression is associated with poor outcomes in several cancer types. Our data reveal that the mTORC1-4EBP1/2 axis provokes a metabolic switch essential for survival during glucose starvation which is exploited by transformed and tumor cells.
Asunto(s)
Acetil-CoA Carboxilasa , Proteínas Adaptadoras Transductoras de Señales , Proteínas de Ciclo Celular , Supervivencia Celular , Ácidos Grasos , Glucosa , Diana Mecanicista del Complejo 1 de la Rapamicina , Animales , Humanos , Ratones , Acetil-CoA Carboxilasa/metabolismo , Acetil-CoA Carboxilasa/genética , Proteínas Adaptadoras Transductoras de Señales/metabolismo , Proteínas Adaptadoras Transductoras de Señales/genética , Proteínas de Ciclo Celular/metabolismo , Proteínas de Ciclo Celular/genética , Línea Celular Tumoral , Factores Eucarióticos de Iniciación/metabolismo , Factores Eucarióticos de Iniciación/genética , Ácidos Grasos/metabolismo , Glucosa/metabolismo , Diana Mecanicista del Complejo 1 de la Rapamicina/metabolismo , Diana Mecanicista del Complejo 1 de la Rapamicina/genética , NADP/metabolismo , Estrés Oxidativo , Fosfoproteínas/metabolismo , Fosfoproteínas/genética , Biosíntesis de ProteínasRESUMEN
Cryptic unstable transcripts (CUTs) are rapidly degraded by the nuclear exosome. However, the mechanism by which they are recognized and targeted to the exosome is not fully understood. Here we report that the MTREC complex, which has recently been shown to promote degradation of meiotic mRNAs and regulatory ncRNAs, is also the major nuclear exosome targeting complex for CUTs and unspliced pre-mRNAs in Schizosaccharomyces pombe. The MTREC complex specifically binds to CUTs, meiotic mRNAs and unspliced pre-mRNA transcripts and targets these RNAs for degradation by the nuclear exosome, while the TRAMP complex has only a minor role in this process. The MTREC complex physically interacts with the nuclear exosome and with various RNA-binding and RNA-processing complexes, coupling RNA processing to the RNA degradation machinery. Our study reveals the central role of the evolutionarily conserved MTREC complex in RNA quality control, and in the recognition and elimination of CUTs.