RESUMEN
The nuclear pore complexes (NPCs), one of the hallmarks of eukaryotic nuclei, allow selective transport of macromolecules between the cytoplasm and the nucleus. Besides this canonical function, an increasing number of additional roles have been attributed to the NPCs and their constituents, the nucleoporins. Here we review recent insights into the mechanisms by which NPCs and nucleoporins affect transcription and DNA repair in metazoans. In the first part, we discuss how gene expression can be affected by the localization of genome-nucleoporin interactions at pores or "off-pores", by the role of nucleoporins in chromatin organization at different scales, or by the physical properties of nucleoporins. In the second part, we review the contribution of NPCs to genome stability, including transport-dependent and -independent functions and the role of positioning at NPCs in the repair of heterochromatic breaks and the regulation of replication stress.
Asunto(s)
Proteínas de Complejo Poro Nuclear , Poro Nuclear , Animales , Proteínas de Complejo Poro Nuclear/genética , Regulación de la Expresión Génica , Citoplasma , Inestabilidad GenómicaRESUMEN
Cornelia de Lange syndrome is a multisystem developmental disorder typically caused by mutations in the gene encoding the cohesin loader NIPBL. The associated phenotype is generally assumed to be the consequence of aberrant transcriptional regulation. Recently, we identified a missense mutation in BRD4 associated with a Cornelia de Lange-like syndrome that reduces BRD4 binding to acetylated histones. Here we show that, although this mutation reduces BRD4-occupancy at enhancers it does not affect transcription of the pluripotency network in mouse embryonic stem cells. Rather, it delays the cell cycle, increases DNA damage signalling, and perturbs regulation of DNA repair in mutant cells. This uncovers a role for BRD4 in DNA repair pathway choice. Furthermore, we find evidence of a similar increase in DNA damage signalling in cells derived from NIPBL-deficient individuals, suggesting that defective DNA damage signalling and repair is also a feature of typical Cornelia de Lange syndrome.
Asunto(s)
Daño del ADN , Reparación del ADN , Síndrome de Cornelia de Lange/genética , Mutación , Animales , Proteínas de Ciclo Celular/genética , Línea Celular , Línea Celular Tumoral , Células Cultivadas , Predisposición Genética a la Enfermedad/genética , Humanos , Ratones , RNA-Seq/métodos , Transducción de Señal/genética , Factores de Transcripción/genéticaRESUMEN
During oncogene-induced senescence (OIS), heterochromatin is lost from the nuclear periphery and forms internal senescence-associated heterochromatin foci (SAHFs). We show that an increased nuclear pore density during OIS is responsible for SAHF formation. In particular, the nucleoporin TPR is necessary for both formation and maintenance of SAHFs. Loss of SAHFs does not affect cell cycle arrest but abrogates the senescence-associated secretory phenotype-a program of inflammatory cytokine gene activation. Our results uncover a previously unknown role of nuclear pores in heterochromatin reorganization in mammalian nuclei and demonstrate the importance of heterochromatin organization for a specific gene activation program.
Asunto(s)
Senescencia Celular/fisiología , Heterocromatina/metabolismo , Proteínas de Complejo Poro Nuclear/metabolismo , Poro Nuclear/metabolismo , Proteínas Proto-Oncogénicas/metabolismo , Línea Celular , Núcleo Celular/metabolismo , Técnicas de Silenciamiento del Gen , Heterocromatina/genética , Humanos , Modelos Moleculares , Poro Nuclear/genética , Proteínas de Complejo Poro Nuclear/genética , Proteínas Proto-Oncogénicas/genética , ARN Interferente Pequeño/metabolismo , Activación Transcripcional/genéticaRESUMEN
Mammalian cells contain three closely related heterochromatin protein 1 (HP1) isoforms, HP1alpha, beta and gamma, which, by analogy to their unique counterpart in Schizosaccharomyces pombe, have been implicated in gene silencing, genome stability and chromosome segregation. However, the individual importance of each isoform during normal cell cycle and disease has remained an unresolved issue. Here, we reveal that HP1alpha shows a proliferation-dependent regulation, which neither HP1beta nor gamma display. During transient cell cycle exit, the HP1alpha mRNA and protein levels diminish. Transient depletion of HP1alpha, but not HP1beta or gamma, in tumoural and primary human cells leads to defects in chromosome segregation. Notably, analysis of an annotated collection of samples derived from carcinomas reveals an overexpression of HP1alpha mRNA and protein, which correlates with clinical data and disease outcome. Our results unveil a specific expression pattern for the HP1alpha isoform, suggesting a unique function related to cell division and tumour growth. The overexpression of HP1alpha constitutes a new example of a potential epigenetic contribution to tumourigenesis that is of clinical interest for cancer prognosis.