RESUMEN
DNA methylation is implicated in neuronal biology via the protein MeCP2, the mutation of which causes Rett syndrome. MeCP2 recruits the NCOR1/2 co-repressor complexes to methylated cytosine in the CG dinucleotide, but also to sites of non-CG methylation, which are abundant in neurons. To test the biological significance of the dual-binding specificity of MeCP2, we replaced its DNA binding domain with an orthologous domain from MBD2, which can only bind mCG motifs. Knockin mice expressing the domain-swap protein displayed severe Rett-syndrome-like phenotypes, indicating that normal brain function requires the interaction of MeCP2 with sites of non-CG methylation, specifically mCAC. The results support the notion that the delayed onset of Rett syndrome is due to the simultaneous post-natal accumulation of mCAC and its reader MeCP2. Intriguingly, genes dysregulated in both Mecp2 null and domain-swap mice are implicated in other neurological disorders, potentially highlighting targets of relevance to the Rett syndrome phenotype.
Asunto(s)
Metilación de ADN , Proteína 2 de Unión a Metil-CpG/metabolismo , Neuronas/metabolismo , Animales , Islas de CpG , Técnicas de Sustitución del Gen , Células HeLa , Humanos , Masculino , Proteína 2 de Unión a Metil-CpG/genética , Ratones , Ratones Transgénicos , Mutación , Células 3T3 NIH , Neuronas/patología , Dominios Proteicos , Síndrome de Rett/genética , Síndrome de Rett/metabolismo , Síndrome de Rett/patologíaRESUMEN
Mammalian genomes contain long domains with distinct average compositions of A/T versus G/C base pairs. In a screen for proteins that might interpret base composition by binding to AT-rich motifs, we identified the stem cell factor SALL4, which contains multiple zinc fingers. Mutation of the domain responsible for AT binding drastically reduced SALL4 genome occupancy and prematurely upregulated genes in proportion to their AT content. Inactivation of this single AT-binding zinc-finger cluster mimicked defects seen in Sall4 null cells, including precocious differentiation of embryonic stem cells (ESCs) and embryonic lethality in mice. In contrast, deletion of two other zinc-finger clusters was phenotypically neutral. Our data indicate that loss of pluripotency is triggered by downregulation of SALL4, leading to de-repression of a set of AT-rich genes that promotes neuronal differentiation. We conclude that base composition is not merely a passive byproduct of genome evolution and constitutes a signal that aids control of cell fate.
Asunto(s)
Composición de Base , Diferenciación Celular , Proteínas de Unión al ADN/metabolismo , Células Madre Embrionarias de Ratones/metabolismo , Neuronas/metabolismo , Factores de Transcripción/metabolismo , Animales , Línea Celular , Proteínas de Unión al ADN/genética , Regulación hacia Abajo , Ratones , Ratones Mutantes , Células Madre Embrionarias de Ratones/citología , Mutación , Neuronas/citología , Factores de Transcripción/genética , Regulación hacia Arriba , Dedos de ZincRESUMEN
'Epigenome' refers to the panoply of chemical modifications borne by DNA and its associated proteins that locally affect genome function. Epigenomic patterns are thought to be determined by external constraints resulting from development, disease and the environment, but DNA sequence is also a potential influence. We propose that domains of relatively uniform DNA base composition may modulate the epigenome through cell type-specific proteins that recognize short, frequent sequence motifs. Differential recruitment of epigenomic modifiers may adjust gene expression in multigene blocks as an alternative to tuning the activity of each gene separately, thus simplifying gene expression programming.
Asunto(s)
Epigenómica , Regulación de la Expresión Génica/genética , Motivos de Nucleótidos/genética , Animales , Secuencia de Bases , Islas de CpG/genética , HumanosRESUMEN
R-loops are three-stranded nucleic acid structures that form during transcription, especially over unmethylated CpG-rich promoters of active genes. In mouse embryonic stem cells (mESCs), CpG-rich developmental regulator genes are repressed by the Polycomb complexes PRC1 and PRC2. Here, we show that R-loops form at a subset of Polycomb target genes, and we investigate their contribution to Polycomb repression. At R-loop-positive genes, R-loop removal leads to decreased PRC1 and PRC2 recruitment and Pol II activation into a productive elongation state, accompanied by gene derepression at nascent and processed transcript levels. Stable removal of PRC2 derepresses R-loop-negative genes, as expected, but does not affect R-loops, PRC1 recruitment, or transcriptional repression of R-loop-positive genes. Our results highlight that Polycomb repression does not occur via one mechanism but consists of different layers of repression, some of which are gene specific. We uncover that one such mechanism is mediated by an interplay between R-loops and RING1B recruitment.
Asunto(s)
Islas de CpG , Regulación del Desarrollo de la Expresión Génica , Células Madre Embrionarias de Ratones/fisiología , Complejo Represivo Polycomb 1/metabolismo , Regiones Promotoras Genéticas , Transcripción Genética , Ubiquitina-Proteína Ligasas/metabolismo , Animales , Sitios de Unión , Línea Celular , Regulación hacia Abajo , Proteína Potenciadora del Homólogo Zeste 2/genética , Proteína Potenciadora del Homólogo Zeste 2/metabolismo , Ratones , Células Madre Embrionarias de Ratones/metabolismo , Conformación de Ácido Nucleico , Complejo Represivo Polycomb 1/genética , Unión Proteica , ARN Polimerasa II/genética , ARN Polimerasa II/metabolismo , Relación Estructura-Actividad , Ubiquitina-Proteína Ligasas/genéticaRESUMEN
Duplication of the X-linked MECP2 gene causes a severe neurological syndrome whose molecular basis is poorly understood. To determine the contribution of known functional domains to overexpression toxicity, we engineered a mouse model that expresses wild-type or mutated MeCP2 from the Mapt (Tau) locus in addition to the endogenous protein. Animals that expressed approximately four times the wild-type level of MeCP2 failed to survive to weaning. Strikingly, a single amino acid substitution that prevents MeCP2 from binding to the TBL1X(R1) subunit of nuclear receptor corepressor 1/2 (NCoR1/2) complexes, when expressed at equivalent high levels, was phenotypically indistinguishable from wild type, suggesting that excessive corepressor recruitment underlies toxicity. In contrast, mutations affecting the DNA-binding domain were toxic when overexpressed. As the NCoR1/2 corepressors are thought to act through histone deacetylation by histone deacetylase 3 (HDAC3), we asked whether mutations in NCoR1 and NCoR2 that drastically reduced their ability to activate this enzyme would relieve the MeCP2 overexpression phenotype. Surprisingly, severity was unaffected, indicating that the catalytic activity of HDAC3 is not the mediator of toxicity. Our findings shed light on the molecular mechanisms underlying MECP2 duplication syndrome and call for a re-evaluation of the precise biological role played by corepressor recruitment.
Asunto(s)
Expresión Génica , Histona Desacetilasas/metabolismo , Proteína 2 de Unión a Metil-CpG/genética , Proteína 2 de Unión a Metil-CpG/toxicidad , Animales , Proteínas Co-Represoras/metabolismo , Modelos Animales de Enfermedad , Activación Enzimática/genética , Técnicas de Inactivación de Genes , Histona Desacetilasas/genética , Masculino , Discapacidad Intelectual Ligada al Cromosoma X/genética , Discapacidad Intelectual Ligada al Cromosoma X/fisiopatología , Ratones , Mutación , Enfermedades del Sistema Nervioso/genética , Neuroglía/metabolismo , Neuronas/metabolismo , Co-Represor 1 de Receptor Nuclear/metabolismo , Co-Represor 2 de Receptor Nuclear/metabolismo , Dominios Proteicos , Proteínas tau/metabolismoRESUMEN
Methyl-CpG binding protein 2 (MeCP2) was first identified in 1992 as a protein that binds specifically to methylated DNA. Mutations in the MECP2 gene were later found to be the cause of an autism spectrum disorder, Rett syndrome. Despite almost 20 years of research into the molecular mechanisms of MeCP2 function, many questions are yet to be answered conclusively. This review considers several key questions and attempts to evaluate the current state of evidence. For example, is MeCP2 just a methyl-CpG binding protein? Is it a multifunctional protein or primarily a transcriptional repressor? We also consider whether MeCP2, as a chromosome-binding protein, acts at specific sites within the genome or more globally, and in which cell types it is functionally important. Finally, we consider two alternative views of MeCP2 in the brain: as a regulator of brain development or as a factor that helps maintain neuronal/glial function.
Asunto(s)
Encéfalo/metabolismo , Proteína 2 de Unión a Metil-CpG/metabolismo , Animales , Encéfalo/anatomía & histología , Encéfalo/crecimiento & desarrollo , Islas de CpG , Metilación de ADN , Humanos , Proteína 2 de Unión a Metil-CpG/química , Proteína 2 de Unión a Metil-CpG/genética , Neuroglía/metabolismo , Neuronas/metabolismo , Unión Proteica , Estructura Terciaria de Proteína , Proteínas Represoras/genética , Proteínas Represoras/metabolismoRESUMEN
Selfish genes were once controversial, but it is now accepted that the genome contains parasitic elements in addition to a complement of conventional genes. This opinion article argues that 'law-abiding' genes also indulge in game playing to ensure their propagation, so that initially nonessential processes secure a genetic heritage. A gene-centered view of this kind can help to explain otherwise puzzling aspects of biology, including the complexity and stability of living systems.
Asunto(s)
Evolución Biológica , Evolución Molecular , Genoma/genética , Secuencias Repetitivas de Ácidos Nucleicos/genética , Genómica/tendencias , HumanosAsunto(s)
ADN/genética , Genes , Animales , ADN Intergénico/genética , Epigénesis Genética , Genoma , Humanos , ARN Largo no CodificanteRESUMEN
Heterozygous mutations in the X-linked MECP2 gene cause the neurological disorder Rett syndrome. The methyl-CpG-binding protein 2 (MeCP2) protein is an epigenetic reader whose binding to chromatin primarily depends on 5-methylcytosine. Functionally, MeCP2 has been implicated in several cellular processes on the basis of its reported interaction with more than 40 binding partners, including transcriptional co-repressors (for example, the NCoR/SMRT complex), transcriptional activators, RNA, chromatin remodellers, microRNA-processing proteins and splicing factors. Accordingly, MeCP2 has been cast as a multi-functional hub that integrates diverse processes that are essential in mature neurons. At odds with the concept of broad functionality, missense mutations that cause Rett syndrome are concentrated in two discrete clusters coinciding with interaction sites for partner macromolecules: the methyl-CpG binding domain and the NCoR/SMRT interaction domain. Here we test the hypothesis that the single dominant function of MeCP2 is to physically connect DNA with the NCoR/SMRT complex, by removing almost all amino-acid sequences except the methyl-CpG binding and NCoR/SMRT interaction domains. We find that mice expressing truncated MeCP2 lacking both the N- and C-terminal regions (approximately half of the native protein) are phenotypically near-normal; and those expressing a minimal MeCP2 additionally lacking a central domain survive for over one year with only mild symptoms. This minimal protein is able to prevent or reverse neurological symptoms when introduced into MeCP2-deficient mice by genetic activation or virus-mediated delivery to the brain. Thus, despite evolutionary conservation of the entire MeCP2 protein sequence, the DNA and co-repressor binding domains alone are sufficient to avoid Rett syndrome-like defects and may therefore have therapeutic utility.
Asunto(s)
Prueba de Complementación Genética , Terapia Genética/métodos , Proteína 2 de Unión a Metil-CpG/genética , Proteína 2 de Unión a Metil-CpG/metabolismo , Síndrome de Rett/genética , Síndrome de Rett/terapia , Eliminación de Secuencia , Células 3T3 , Animales , Encéfalo/metabolismo , ADN/metabolismo , Células HeLa , Humanos , Masculino , Proteína 2 de Unión a Metil-CpG/química , Proteína 2 de Unión a Metil-CpG/deficiencia , Ratones , Mutación Missense , Fenotipo , Dominios Proteicos/genética , Estabilidad Proteica , Síndrome de Rett/patología , Síndrome de Rett/fisiopatología , Transducción GenéticaRESUMEN
MeCP2 is an abundant protein in mature nerve cells, where it binds to DNA sequences containing methylated cytosine. Mutations in the MECP2 gene cause the severe neurological disorder Rett syndrome (RTT), provoking intensive study of the underlying molecular mechanisms. Multiple functions have been proposed, one of which involves a regulatory role in splicing. Here we leverage the recent availability of high-quality transcriptomic data sets to probe quantitatively the potential influence of MeCP2 on alternative splicing. Using a variety of machine learning approaches that can capture both linear and non-linear associations, we show that widely different levels of MeCP2 have a minimal effect on alternative splicing in three different systems. Alternative splicing was also apparently indifferent to developmental changes in DNA methylation levels. Our results suggest that regulation of splicing is not a major function of MeCP2. They also highlight the importance of multi-variate quantitative analyses in the formulation of biological hypotheses.
Asunto(s)
Empalme Alternativo/genética , Proteína 2 de Unión a Metil-CpG/genética , Síndrome de Rett/genética , Transcriptoma/genética , Animales , Encéfalo/metabolismo , Citosina/metabolismo , ADN (Citosina-5-)-Metiltransferasa 1/genética , ADN (Citosina-5-)-Metiltransferasas/genética , Metilación de ADN/genética , ADN Metiltransferasa 3A , Modelos Animales de Enfermedad , Humanos , Metilación , Ratones , Ratones Noqueados , Mutación/genética , Neuronas/metabolismo , Neuronas/patología , Unión Proteica/genética , Síndrome de Rett/metabolismo , Síndrome de Rett/patología , ADN Metiltransferasa 3BRESUMEN
In recent years, it has become increasingly apparent that many neurological disorders are underpinned by a genetic aetiology. This has resulted in considerable efforts to develop therapeutic strategies which can treat the disease-causing mutation, either by supplying a functional copy of the mutated gene or editing the genomic sequence. In this review, we will discuss the main genetic strategies which are currently being explored for the treatment of monogenic neurological disorders, as well as some of the challenges they face. In addition, we will address some of the ethical difficulties which may arise.
Asunto(s)
Edición Génica , Enfermedades del Sistema Nervioso , Edición Génica/métodos , Terapia Genética/métodos , Humanos , Enfermedades del Sistema Nervioso/genética , Enfermedades del Sistema Nervioso/terapiaRESUMEN
MeCP2 is a nuclear protein that binds to sites of cytosine methylation in the genome. While most evidence confirms this epigenetic mark as the primary determinant of DNA binding, MeCP2 is also reported to have an affinity for non-methylated DNA sequences. Here we investigated the molecular basis and in vivo significance of its reported affinity for non-methylated GT-rich sequences. We confirmed this interaction with isolated domains of MeCP2 in vitro and defined a minimal target DNA sequence. Binding depends on pyrimidine 5' methyl groups provided by thymine and requires adjacent guanines and a correctly orientated A/T-rich flanking sequence. Unexpectedly, full-length MeCP2 protein failed to bind GT-rich sequences in vitro. To test for MeCP2 binding to these motifs in vivo, we analysed human neuronal cells using ChIP-seq and ATAC-seq technologies. While both methods robustly detected DNA methylation-dependent binding of MeCP2 to mCG and mCAC, neither showed evidence of MeCP2 binding to GT-rich motifs. The data suggest that GT binding is an in vitro phenomenon without in vivo relevance. Our findings argue that MeCP2 does not read unadorned DNA sequence and therefore support the notion that its primary role is to interpret epigenetic modifications of DNA.
Asunto(s)
ADN/química , ADN/metabolismo , Proteína 2 de Unión a Metil-CpG/metabolismo , Sitios de Unión , Línea Celular , Citosina/metabolismo , Guanina/química , Humanos , Motivos de Nucleótidos , Unión Proteica , Timina/químicaRESUMEN
Patterns of gene expression are primarily determined by proteins that locally enhance or repress transcription. While many transcription factors target a restricted number of genes, others appear to modulate transcription levels globally. An example is MeCP2, an abundant methylated-DNA binding protein that is mutated in the neurological disorder Rett syndrome. Despite much research, the molecular mechanism by which MeCP2 regulates gene expression is not fully resolved. Here, we integrate quantitative, multidimensional experimental analysis and mathematical modeling to indicate that MeCP2 is a global transcriptional regulator whose binding to DNA creates "slow sites" in gene bodies. We hypothesize that waves of slowed-down RNA polymerase II formed behind these sites travel backward and indirectly affect initiation, reminiscent of defect-induced shockwaves in nonequilibrium physics transport models. This mechanism differs from conventional gene-regulation mechanisms, which often involve direct modulation of transcription initiation. Our findings point to a genome-wide function of DNA methylation that may account for the reversibility of Rett syndrome in mice. Moreover, our combined theoretical and experimental approach provides a general method for understanding how global gene-expression patterns are choreographed.
Asunto(s)
Metilación de ADN , Modelos Teóricos , ARN Polimerasa II/metabolismo , Animales , Línea Celular , Proteína 2 de Unión a Metil-CpG/genética , Proteína 2 de Unión a Metil-CpG/metabolismo , Ratones , Unión Proteica , Elongación de la Transcripción Genética , Iniciación de la Transcripción Genética , Activación TranscripcionalRESUMEN
Rett syndrome (RTT) is a severe neurological disorder caused by mutations in the X-linked gene MECP2 (methyl-CpG-binding protein 2). Two decades of research have fostered the view that MeCP2 is a multifunctional chromatin protein that integrates diverse aspects of neuronal biology. More recently, studies have focused on specific RTT-associated mutations within the protein. This work has yielded molecular insights into the critical functions of MeCP2 that promise to simplify our understanding of RTT pathology.
Asunto(s)
Síndrome de Rett/genética , Animales , Encéfalo/patología , Encéfalo/fisiopatología , ADN/química , ADN/metabolismo , Modelos Animales de Enfermedad , Regulación de la Expresión Génica , Humanos , Proteína 2 de Unión a Metil-CpG/genética , Proteína 2 de Unión a Metil-CpG/fisiología , Ratones , Ratones Noqueados , Modelos Neurológicos , Mutación , Neuronas/patología , Neuronas/fisiología , Unión Proteica , Síndrome de Rett/patología , Síndrome de Rett/fisiopatología , Transactivadores/genética , Transactivadores/fisiologíaRESUMEN
Most missense mutations causing Rett syndrome (RTT) affect domains of MeCP2 that have been shown to either bind methylated DNA or interact with a transcriptional co-repressor complex. Several mutations, however, including the C-terminal truncations that account for â¼10% of cases, fall outside these characterized domains. We studied the molecular consequences of four of these 'non-canonical' mutations in cultured neurons and mice to see if they reveal additional essential domains without affecting known properties of MeCP2. The results show that the mutations partially or strongly deplete the protein and also in some cases interfere with co-repressor recruitment. These mutations therefore impact the activity of known functional domains and do not invoke new molecular causes of RTT. The finding that a stable C-terminal truncation does not compromise MeCP2 function raises the possibility that small molecules which stabilize these mutant proteins may be of therapeutic value.
Asunto(s)
Proteína 2 de Unión a Metil-CpG/genética , Proteínas Represoras/genética , Síndrome de Rett/genética , Animales , Proteínas Cromosómicas no Histona/genética , Metilación de ADN/genética , Modelos Animales de Enfermedad , Femenino , Humanos , Ratones , Mutación Missense/genética , Neuronas/patología , Síndrome de Rett/patologíaRESUMEN
Rett syndrome (RTT) is an X-linked neurological disorder caused by mutations in the methyl-CpG-binding protein 2 (MeCP2) gene. The majority of RTT missense mutations disrupt the interaction of the MeCP2 with DNA or the nuclear receptor corepressor (NCoR)/silencing mediator of retinoic acid and thyroid receptors (SMRT) corepressor complex. Here, we show that the "NCoR/SMRT interaction domain" (NID) of MeCP2 directly contacts transducin beta-like 1 (TBL1) and TBL1 related (TBLR1), two paralogs that are core components of NCoR/SMRT. We determine the cocrystal structure of the MeCP2 NID in complex with the WD40 domain of TBLR1 and confirm by in vitro and ex vivo assays that mutation of interacting residues of TBLR1 and TBL1 disrupts binding to MeCP2. Strikingly, the four MeCP2-NID residues mutated in RTT are those residues that make the most extensive contacts with TBLR1. Moreover, missense mutations in the gene for TBLR1 that are associated with intellectual disability also prevent MeCP2 binding. Our study therefore reveals the molecular basis of an interaction that is crucial for optimal brain function.
Asunto(s)
Proteína 2 de Unión a Metil-CpG/química , Mutación Missense , Proteínas Nucleares/química , Receptores Citoplasmáticos y Nucleares/química , Proteínas Represoras/química , Síndrome de Rett/genética , Cristalografía por Rayos X , Células HeLa , Humanos , Proteína 2 de Unión a Metil-CpG/genética , Proteína 2 de Unión a Metil-CpG/metabolismo , Proteínas Nucleares/genética , Proteínas Nucleares/metabolismo , Co-Represor 1 de Receptor Nuclear/química , Co-Represor 1 de Receptor Nuclear/genética , Co-Represor 1 de Receptor Nuclear/metabolismo , Conformación Proteica , Receptores Citoplasmáticos y Nucleares/genética , Receptores Citoplasmáticos y Nucleares/metabolismo , Proteínas Represoras/genética , Proteínas Represoras/metabolismo , Síndrome de Rett/patología , Transducina/química , Transducina/genética , Transducina/metabolismoRESUMEN
Mutations in the gene encoding the methyl-CG binding protein MeCP2 cause several neurological disorders including Rett syndrome. The di-nucleotide methyl-CG (mCG) is the classical MeCP2 DNA recognition sequence, but additional methylated sequence targets have been reported. Here we show by in vitro and in vivo analyses that MeCP2 binding to non-CG methylated sites in brain is largely confined to the tri-nucleotide sequence mCAC. MeCP2 binding to chromosomal DNA in mouse brain is proportional to mCAC + mCG density and unexpectedly defines large genomic domains within which transcription is sensitive to MeCP2 occupancy. Our results suggest that MeCP2 integrates patterns of mCAC and mCG in the brain to restrain transcription of genes critical for neuronal function.
Asunto(s)
Encéfalo/metabolismo , Metilación de ADN , Repeticiones de Dinucleótido , Proteína 2 de Unión a Metil-CpG/metabolismo , Repeticiones de Trinucleótidos , Animales , Islas de CpG , Citosina/metabolismo , Epigénesis Genética , Masculino , Proteína 2 de Unión a Metil-CpG/genética , Ratones , Ratones Endogámicos C57BL , Unión Proteica , Síndrome de Rett/genéticaRESUMEN
Trimethylation of histone H3 Lys 4 (H3K4me3) is a mark of active and poised promoters. The Set1 complex is responsible for most somatic H3K4me3 and contains the conserved subunit CxxC finger protein 1 (Cfp1), which binds to unmethylated CpGs and links H3K4me3 with CpG islands (CGIs). Here we report that Cfp1 plays unanticipated roles in organizing genome-wide H3K4me3 in embryonic stem cells. Cfp1 deficiency caused two contrasting phenotypes: drastic loss of H3K4me3 at expressed CGI-associated genes, with minimal consequences for transcription, and creation of "ectopic" H3K4me3 peaks at numerous regulatory regions. DNA binding by Cfp1 was dispensable for targeting H3K4me3 to active genes but was required to prevent ectopic H3K4me3 peaks. The presence of ectopic peaks at enhancers often coincided with increased expression of nearby genes. This suggests that CpG targeting prevents "leakage" of H3K4me3 to inappropriate chromatin compartments. Our results demonstrate that Cfp1 is a specificity factor that integrates multiple signals, including promoter CpG content and gene activity, to regulate genome-wide patterns of H3K4me3.
Asunto(s)
Islas de CpG/fisiología , Células Madre Embrionarias/metabolismo , Histonas/metabolismo , Transactivadores/metabolismo , Animales , Línea Celular , Metilación de ADN , Lisina/metabolismo , Ratones , Regiones Promotoras Genéticas , Transducción de Señal , Transcripción Genética/genéticaRESUMEN
Epigenetic regulation plays a key role in the link between inflammation and cancer. Here we examine Mbd2, which mediates epigenetic transcriptional silencing by binding to methylated DNA. In separate studies the Mbd2-/- mouse has been shown (1) to be resistant to intestinal tumourigenesis and (2) to have an enhanced inflammatory/immune response, observations that are inconsistent with the links between inflammation and cancer. To clarify its role in tumourigenesis and inflammation, we used constitutive and conditional models of Mbd2 deletion to explore its epithelial and non-epithelial roles in the intestine. Using a conditional model, we found that suppression of intestinal tumourigenesis is due primarily to the absence of Mbd2 within the epithelia. Next, we demonstrated, using the DSS colitis model, that non-epithelial roles of Mbd2 are key in preventing the transition from acute to tumour-promoting chronic inflammation. Combining models revealed that prior to inflammation the altered Mbd2-/- immune response plays a role in intestinal tumour suppression. However, following inflammation the intestine converts from tumour suppressive to tumour promoting. To summarise, in the intestine the normal function of Mbd2 is exploited by cancer cells to enable tumourigenesis, while in the immune system it plays a key role in preventing tumour-enabling inflammation. Which role is dominant depends on the inflammation status of the intestine. As environmental interactions within the intestine can alter DNA methylation patterns, we propose that Mbd2 plays a key role in determining whether these interactions are anti- or pro-tumourigenic and this makes it a useful new epigenetic model for inflammation-associated carcinogenesis. © 2018 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of Pathological Society of Great Britain and Ireland.
Asunto(s)
Transformación Celular Neoplásica/metabolismo , Colitis/metabolismo , Proteínas de Unión al ADN/metabolismo , Mucosa Intestinal/metabolismo , Neoplasias Intestinales/metabolismo , Animales , Transformación Celular Neoplásica/inducido químicamente , Transformación Celular Neoplásica/genética , Transformación Celular Neoplásica/patología , Colitis/inducido químicamente , Colitis/genética , Colitis/patología , Metilación de ADN , Proteínas de Unión al ADN/deficiencia , Proteínas de Unión al ADN/genética , Sulfato de Dextran , Modelos Animales de Enfermedad , Epigénesis Genética , Regulación Neoplásica de la Expresión Génica , Genes APC , Mucosa Intestinal/patología , Neoplasias Intestinales/inducido químicamente , Neoplasias Intestinales/genética , Neoplasias Intestinales/patología , Ratones Noqueados , Células Madre Neoplásicas/metabolismo , Células Madre Neoplásicas/patología , Transducción de Señal , Células TH1/metabolismo , Células TH1/patología , Células Th2/metabolismo , Células Th2/patologíaRESUMEN
Rett syndrome (RTT) is an X-linked human neurodevelopmental disorder with features of autism and severe neurological dysfunction in females. RTT is caused by mutations in methyl-CpG-binding protein 2 (MeCP2), a nuclear protein that, in neurons, regulates transcription, is expressed at high levels similar to that of histones, and binds to methylated cytosines broadly across the genome. By phosphotryptic mapping, we identify three sites (S86, S274 and T308) of activity-dependent MeCP2 phosphorylation. Phosphorylation of these sites is differentially induced by neuronal activity, brain-derived neurotrophic factor, or agents that elevate the intracellular level of 3',5'-cyclic AMP (cAMP), indicating that MeCP2 may function as an epigenetic regulator of gene expression that integrates diverse signals from the environment. Here we show that the phosphorylation of T308 blocks the interaction of the repressor domain of MeCP2 with the nuclear receptor co-repressor (NCoR) complex and suppresses the ability of MeCP2 to repress transcription. In knock-in mice bearing the common human RTT missense mutation R306C, neuronal activity fails to induce MeCP2 T308 phosphorylation, suggesting that the loss of T308 phosphorylation might contribute to RTT. Consistent with this possibility, the mutation of MeCP2 T308A in mice leads to a decrease in the induction of a subset of activity-regulated genes and to RTT-like symptoms. These findings indicate that the activity-dependent phosphorylation of MeCP2 at T308 regulates the interaction of MeCP2 with the NCoR complex, and that RTT in humans may be due, in part, to the loss of activity-dependent MeCP2 T308 phosphorylation and a disruption of the phosphorylation-regulated interaction of MeCP2 with the NCoR complex.