RESUMO
Understanding the packaging of DNA into chromatin has become a crucial aspect in the study of gene regulatory mechanisms. Heterochromatin establishment and maintenance dynamics have emerged as some of the main features involved in genome stability, cellular development, and diseases. The most extensively studied heterochromatin protein is HP1a. This protein has two main domains, namely the chromoshadow and the chromodomain, separated by a hinge region. Over the years, several works have taken on the task of identifying HP1a partners using different strategies. In this review, we focus on describing these interactions and the possible complexes and subcomplexes associated with this critical protein. Characterization of these complexes will help us to clearly understand the implications of the interactions of HP1a in heterochromatin maintenance, heterochromatin dynamics, and heterochromatin's direct relationship to gene regulation and chromatin organization.
Assuntos
Proteínas Cromossômicas não Histona/metabolismo , Eucromatina/metabolismo , Heterocromatina/metabolismo , Animais , Homólogo 5 da Proteína Cromobox , Proteínas Cromossômicas não Histona/química , Proteínas Cromossômicas não Histona/genética , Proteínas de Drosophila/química , Proteínas de Drosophila/genética , Proteínas de Drosophila/metabolismo , Drosophila melanogaster/genética , Drosophila melanogaster/metabolismo , Regulação da Expressão Gênica , Instabilidade Genômica , Humanos , Elementos Isolantes , Filogenia , Ligação Proteica , Conformação Proteica em Folha beta , Domínios e Motivos de Interação entre ProteínasRESUMO
Fibrillarin is a highly conserved nucleolar methyltransferase responsible for ribosomal RNA methylation across evolution from Archaea to humans. It has been reported that fibrillarin is involved in the methylation of histone H2A in nucleoli and other processes, including viral progression, cellular stress, nuclear shape, and cell cycle progression. We show that fibrillarin has an additional activity as a ribonuclease. The activity is affected by phosphoinositides and phosphatidic acid and insensitive to ribonuclease inhibitors. Furthermore, the presence of phosphatidic acid releases the fibrillarin-U3 snoRNA complex. We show that the ribonuclease activity localizes to the GAR (glycine/arginine-rich) domain conserved in a small group of RNA interacting proteins. The introduction of the GAR domain occurred in evolution in the transition from archaea to eukaryotic cells. The interaction of this domain with phospholipids may allow a phase separation of this protein in nucleoli.
Assuntos
Proteínas Cromossômicas não Histona/química , Proteínas Cromossômicas não Histona/metabolismo , Fosfolipídeos/metabolismo , Ribonucleases/química , Ribonucleases/metabolismo , Proteínas Cromossômicas não Histona/genética , Células HeLa , Humanos , Mutação/genética , Domínios Proteicos , RNA Nucleolar Pequeno/metabolismo , Proteínas Recombinantes/metabolismo , Ribonucleases/genética , Ribonucleoproteínas/metabolismo , Relação Estrutura-AtividadeRESUMO
Breast and cervical cancer are the first and fourth cancer types with the highest prevalence in women, respectively. The developmental profiles of cancer in women can vary by genetic markers and cellular events. In turn, age and lifestyle influence in the cellular response and also on the cancer progression and relapse. The human DEK protein, a histone chaperone, belongs to a specific subclass of chromatin topology modulators, being involved in the regulation of DNA-dependent processes. These epigenetic mechanisms have dynamic and reversible nature, have been proposed as targets for different treatment approaches, especially in tumor therapy. The expression patterns of DEK vary between healthy and cancer cells. High expression of DEK is associated with poor prognosis in many cancer types, suggesting that DEK takes part in oncogenic activities via different molecular pathways, including inhibition of senescence and apoptosis. The focus of this review was to highlight the role of the DEK protein in these two female cancers.
Assuntos
Biomarcadores Tumorais/metabolismo , Neoplasias da Mama/metabolismo , Proteínas Cromossômicas não Histona/metabolismo , Proteínas Oncogênicas/metabolismo , Proteínas de Ligação a Poli-ADP-Ribose/metabolismo , Neoplasias do Colo do Útero/metabolismo , Saúde da Mulher , Animais , Biomarcadores Tumorais/química , Biomarcadores Tumorais/genética , Neoplasias da Mama/genética , Neoplasias da Mama/patologia , Neoplasias da Mama/terapia , Proteínas Cromossômicas não Histona/química , Proteínas Cromossômicas não Histona/genética , Epigênese Genética , Feminino , Regulação Neoplásica da Expressão Gênica , Humanos , Proteínas Oncogênicas/química , Proteínas Oncogênicas/genética , Proteínas de Ligação a Poli-ADP-Ribose/química , Proteínas de Ligação a Poli-ADP-Ribose/genética , Prognóstico , Conformação Proteica , Relação Estrutura-Atividade , Neoplasias do Colo do Útero/genética , Neoplasias do Colo do Útero/patologia , Neoplasias do Colo do Útero/terapiaRESUMO
How the co-ordinated events of gene activation and silencing during cellular differentiation are influenced by spatial organization of the cell nucleus is still poorly understood. Little is known about the molecular mechanisms controlling subnuclear distribution of transcription factors, and their interplay with nuclear proteins that shape chromatin structure. Here we show that C/EBPß not only associates with pericentromeric heterochromatin but also interacts with the nucleoskeleton upon induction of adipocyte differentiation of 3T3-L1 cells. Different C/EBPß dimers localize in different nuclear domains. Using BiFC in living cells, we show that LAP (Liver Activating Protein) homodimers localize in euchromatin and heterochromatin. In contrast, LIP (Liver Inhibitory Protein) homodimers localize exclusively in heterochromatin. Importantly, their differential subnuclear distribution mirrors the site for interaction with HP1α. HP1α inhibits LAP transcriptional capacity and occupies the promoter of the C/EBPß-dependent gene c/ebpα in 3T3-L1 preadipocytes. When adipogenesis is induced, HP1α binding decreases from c/ebpα promoter, allowing transcription. Thus, the equilibrium among different pools of C/EBPß associated with chromatin or nucleoskeleton, and dynamic changes in their interaction with HP1α, play key roles in the regulation of C/EBP target genes during adipogenesis.
Assuntos
Proteína beta Intensificadora de Ligação a CCAAT/metabolismo , Núcleo Celular/metabolismo , Proteínas Cromossômicas não Histona/metabolismo , Proteínas Nucleares/metabolismo , Células 3T3 , Adipócitos/citologia , Adipócitos/metabolismo , Animais , Proteína beta Intensificadora de Ligação a CCAAT/química , Proteína beta Intensificadora de Ligação a CCAAT/genética , Diferenciação Celular , Núcleo Celular/química , Homólogo 5 da Proteína Cromobox , Proteínas Cromossômicas não Histona/química , Dimerização , Regulação da Expressão Gênica , Humanos , Camundongos , Microscopia de Fluorescência , Proteínas Nucleares/químicaRESUMO
Despite the significant improvements in anti HIV-1 treatment, AIDS remains a lifelong disease due to the impossibility to eradicate the viral reservoir established upon integration of the viral genome. Controlling the epigenetic block imposed by the host cell machinery to the viral transcription may represent a therapeutic alternative to purge the viral reservoir, offering a way to eradicate the infection. Heterochromatin protein 1 (HP1) has been reported to actively participate in the silencing of HIV-1 integrated genome by binding to histone 3 (H3) tail. This interaction is mediated by the Chromodomain of HP1. Nevertheless, the structural features that determine its binding to H3 tail upon post-transductional modifications, such as methylation and phosphorylation as well as isoform-specific effects have not yet been described. We have undertaken the systematic simulation of the Chromodomains of the isoforms beta and gamma of HP1 in complex with the H3 tail methylated at Lys9 in presence/absence of phosphorylation at Ser10. Our results pinpoint isoform-specific electrostatic interactions as important determinants for the stability of the complexes. Characterization of intermolecular contacts between HP1 variants and H3 furnishes new insights on isoform-specific recognition and the effect of phosphorylation.
Assuntos
Proteínas Cromossômicas não Histona/metabolismo , Histonas/metabolismo , Isoformas de Proteínas/metabolismo , Sequência de Aminoácidos , Homólogo 5 da Proteína Cromobox , Proteínas Cromossômicas não Histona/química , Humanos , Metilação , Modelos Moleculares , Dados de Sequência Molecular , Ressonância Magnética Nuclear Biomolecular , Fosforilação , Ligação Proteica , Isoformas de Proteínas/química , Homologia de Sequência de AminoácidosRESUMO
Changes in local chromatin structure accompany transcriptional activation of eukaryotic genes. In vivo these changes in chromatin organization can be catalyzed by ATP-dependent chromatin-remodeling complexes, such as SWI/SNF. These complexes alter the tight wrapping of DNA in the nucleosomes and can facilitate the mobilization of the histone octamer to adjacent DNA segments, leaving promoter regulatory elements exposed for transcription factor binding. To gain understanding of how the activity of SWI/SNF complexes may be modulated by the different DNA sequences within a natural promoter, we have reconstituted nucleosomes containing promoter segments of the transcriptionally active cell type-specific osteocalcin (OC) gene and determined how they affect the directional movements of the nucleosomes. Our results indicate that SWI/SNF complexes induce octamer sliding to preferential positions in the OC promoter, leading to a nucleosomal organization that resembles that described in intact cells expressing the OC gene. Our studies demonstrate that the position of the histone octamer is primarily determined by sequences within the OC promoter that include or exclude nucleosomes. We propose that these sequences are critical components of the regulatory mechanisms that mediate expression of this tissue-specific gene.