RESUMEN
Out of the several hundred copies of rRNA genes arranged in the nucleolar organizing regions (NOR) of the five human acrocentric chromosomes, ~50% remain transcriptionally inactive. NOR-associated sequences and epigenetic modifications contribute to the differential expression of rRNAs. However, the mechanism(s) controlling the dosage of active versus inactive rRNA genes within each NOR in mammals is yet to be determined. We have discovered a family of ncRNAs, SNULs (Single NUcleolus Localized RNA), which form constrained sub-nucleolar territories on individual NORs and influence rRNA expression. Individual members of the SNULs monoallelically associate with specific NOR-containing chromosomes. SNULs share sequence similarity to pre-rRNA and localize in the sub-nucleolar compartment with pre-rRNA. Finally, SNULs control rRNA expression by influencing pre-rRNA sorting to the DFC compartment and pre-rRNA processing. Our study discovered a novel class of ncRNAs influencing rRNA expression by forming constrained nucleolar territories on individual NORs.
Asunto(s)
Región Organizadora del Nucléolo , Precursores del ARN , Humanos , Animales , Región Organizadora del Nucléolo/genética , Región Organizadora del Nucléolo/metabolismo , Precursores del ARN/genética , Precursores del ARN/metabolismo , Nucléolo Celular/genética , Nucléolo Celular/metabolismo , ARN Ribosómico/genética , ARN Ribosómico/metabolismo , Cromosomas Humanos/metabolismo , ARN no Traducido/genética , ARN no Traducido/metabolismo , Mamíferos/genéticaRESUMEN
Basal p53 levels are tightly suppressed under normal conditions. Disrupting this regulation results in elevated p53 levels to induce cell cycle arrest, apoptosis, and tumor suppression. Here, we report the suppression of basal p53 levels by a nuclear, p53-regulated long noncoding RNA that we termed PURPL (p53 upregulated regulator of p53 levels). Targeted depletion of PURPL in colorectal cancer cells results in elevated basal p53 levels and induces growth defects in cell culture and in mouse xenografts. PURPL associates with MYBBP1A, a protein that binds to and stabilizes p53, and inhibits the formation of the p53-MYBBP1A complex. In the absence of PURPL, MYBBP1A interacts with and stabilizes p53. Silencing MYBBP1A significantly rescues basal p53 levels and proliferation in PURPL-deficient cells, suggesting that MYBBP1A mediates the effect of PURPL in regulating p53. These results reveal a p53-PURPL auto-regulatory feedback loop and demonstrate a role for PURPL in maintaining basal p53 levels.
Asunto(s)
Neoplasias Colorrectales/genética , ARN Largo no Codificante/genética , Proteína p53 Supresora de Tumor/genética , Apoptosis/genética , Apoptosis/fisiología , Ciclo Celular/genética , Ciclo Celular/fisiología , Puntos de Control del Ciclo Celular/genética , Puntos de Control del Ciclo Celular/fisiología , Línea Celular , Línea Celular Tumoral , Proliferación Celular/genética , Proliferación Celular/fisiología , Neoplasias Colorrectales/metabolismo , Proteínas de Unión al ADN , Proteína 1 Similar a ELAV/genética , Proteína 1 Similar a ELAV/metabolismo , Células HCT116 , Humanos , Proteínas Nucleares/genética , Proteínas Nucleares/metabolismo , Proteínas de Transporte Nucleocitoplasmático/genética , Proteínas de Transporte Nucleocitoplasmático/metabolismo , ARN Largo no Codificante/fisiología , Proteínas de Unión al ARN , Factores de Transcripción , Proteína p53 Supresora de Tumor/metabolismoRESUMEN
Thousands of long noncoding RNAs (lncRNAs) have been discovered, yet the function of the vast majority remains unclear. Here, we show that a p53-regulated lncRNA which we named PINCR (p53-induced noncoding RNA), is induced ~100-fold after DNA damage and exerts a prosurvival function in human colorectal cancer cells (CRC) in vitro and tumor growth in vivo. Targeted deletion of PINCR in CRC cells significantly impaired G1 arrest and induced hypersensitivity to chemotherapeutic drugs. PINCR regulates the induction of a subset of p53 targets involved in G1 arrest and apoptosis, including BTG2, RRM2B and GPX1. Using a novel RNA pulldown approach that utilized endogenous S1-tagged PINCR, we show that PINCR associates with the enhancer region of these genes by binding to RNA-binding protein Matrin 3 that, in turn, associates with p53. Our findings uncover a critical prosurvival function of a p53/PINCR/Matrin 3 axis in response to DNA damage in CRC cells.