RESUMO
While cellular senescence is a critical mechanism to prevent malignant transformation of potentially mutated cells, persistence of senescent cells can also promote cancer and aging phenotypes. NonO/p54nrb and PSF are multifunctional hnRNPs typically found as a complex exclusively within the nuclei of all mammalian cells. We demonstrate here that either increase or reduction of expression of either factor results in cellular senescence. Coincident with this, we observe expulsion of NonO and PSF-containing nuclear paraspeckles and posttranslational modification at G2/M. That senescence is mediated most robustly by overexpression of a cytoplasmic C-truncated form of NonO further indicated that translocation of NonO and PSF from the nucleus is critical to senescence induction. Modulation of NonO and PSF expression just prior to or coincident with senescence induction disrupts the normally heterodimeric NonO-PSF nuclear complex resulting in a dramatic shift in stoichiometry to heterotetramers and monomer with highest accumulation within the cytoplasm. This is accompanied by prototypic cell cycle checkpoint activation and chromatin condensation. These observations identify yet another role for these multifunctional factors and provide a hitherto unprecedented mechanism for cellular senescence and nuclear-cytoplasmic trafficking.
Assuntos
Senescência Celular/fisiologia , Proteínas Associadas à Matriz Nuclear/metabolismo , Fatores de Transcrição de Octâmero/metabolismo , Fator de Processamento Associado a PTB/metabolismo , Proteínas de Ligação a RNA/metabolismo , Animais , Linhagem Celular , Citoplasma/fisiologia , Dano ao DNA , Proteínas de Ligação a DNA , Regulação da Expressão Gênica , Humanos , Mitose , Mutação , Proteínas Associadas à Matriz Nuclear/genética , Fatores de Transcrição de Octâmero/genética , Fator de Processamento Associado a PTB/genética , Plasmídeos , Processamento de Proteína Pós-Traducional , Proteínas de Ligação a RNA/genética , Encurtamento do Telômero , Transformação Genética , Regulação para CimaRESUMO
The correlation between epigenetic aberrations and disease underscores the importance of epigenetic mechanisms. Here, we review recent findings regarding chromatin modifications and their relevance to cancer.
Assuntos
Cromatina/metabolismo , Epigênese Genética , Neoplasias/genética , Trifosfato de Adenosina/metabolismo , Animais , Cromatina/química , Metilação de DNA , Regulação da Expressão Gênica , Histonas/metabolismo , Humanos , Camundongos , Nucleossomos/química , RNA não Traduzido/fisiologiaRESUMO
In the absence of ligands the corepressor N-CoR mediates transcriptional repression by some nuclear hormone receptors. Several protein-protein interactions of N-CoR are known, of which mainly complex formation with histone deacetylases (HDACs) leads to the repression of target genes. On the other hand, the role of posttranslational modifications in corepressor function is not well established. Here, we show that N-CoR is modified by Sumo-1. We found SUMO-E2-conjugating enzyme Ubc9 and SUMO-E3 ligase Pias1 as novel N-CoR interaction partners. The SANT1 domain of N-CoR was found to mediate this interaction. We show that K152, K1117, and K1330 of N-CoR can be conjugated to SUMO and that mutation of all sites is necessary to fully block SUMOylation in vitro. Because these lysine residues are located within repression domains I and III, respectively, we investigated a possible correlation between the functions of the repression domains and SUMOylation. Coexpression of Ubc9 protein resulted in enhanced N-CoR-dependent transcriptional repression. Studies using SUMOylation-deficient N-CoR RDI mutants suggest that SUMO modification contributes to repression by N-CoR. Mutation of K152 to R in RD1, for example, not only significantly reduced repression of a reporter gene, but also abolished the effect of Ubc9 on transcriptional repression.
