RESUMEN
DNA double-strand breaks (DSBs) can arise from multiple sources, including exposure to ionizing radiation. The repair of DSBs involves both posttranslational modification of nucleosomes and concentration of DNA-repair proteins at the site of damage. Consequently, nucleosome packing and chromatin architecture surrounding the DSB may limit the ability of the DNA-damage response to access and repair the break. Here, we review early chromatin-based events that promote the formation of open, relaxed chromatin structures at DSBs and that allow the DNA-repair machinery to access the spatially confined region surrounding the DSB, thereby facilitating mammalian DSB repair.
Asunto(s)
Ensamble y Desensamble de Cromatina , Roturas del ADN de Doble Cadena , Reparación del ADN , Animales , Inestabilidad Genómica , Histonas/metabolismo , Humanos , Neoplasias/genéticaRESUMEN
Recent studies have implicated DNA polymerases θ (Pol θ) and ß (Pol ß) as mediators of alternative nonhomologous end-joining (Alt-NHEJ) events, including chromosomal translocations. Here we identify subunits of the replicative DNA polymerase δ (Pol δ) as promoters of Alt-NHEJ that results in more extensive intrachromosomal mutations at a single double-strand break (DSB) and more frequent translocations between two DSBs. Depletion of the Pol δ accessory subunit POLD2 destabilizes the complex, resulting in degradation of both POLD1 and POLD3 in human cells. POLD2 depletion markedly reduces the frequency of translocations with sequence modifications but does not affect the frequency of translocations with exact joins. Using separation-of-function mutants, we show that both the DNA synthesis and exonuclease activities of the POLD1 subunit contribute to translocations. As described in yeast and unlike Pol θ, Pol δ also promotes homology-directed repair. Codepletion of POLD2 with 53BP1 nearly eliminates translocations. POLD1 and POLD2 each colocalize with phosphorylated H2AX at ionizing radiation-induced DSBs but not with 53BP1. Codepletion of POLD2 with either ligase 3 (LIG3) or ligase 4 (LIG4) does not further reduce translocation frequency compared to POLD2 depletion alone. Together, these data support a model in which Pol δ promotes Alt-NHEJ in human cells at DSBs, including translocations.
Asunto(s)
Reparación del ADN por Unión de Extremidades , ADN Polimerasa III/metabolismo , Translocación Genética , Roturas del ADN de Doble Cadena , ADN Polimerasa III/genética , Técnicas de Silenciamiento del Gen , Células HEK293 , Células HeLa , Humanos , ARN Interferente Pequeño/metabolismoRESUMEN
Although stress-induced synthesis of mono(ADP-ribose) (mADPr) and poly(ADP-ribose) (pADPr) conjugates by pADPr polymerase (PARP) enzymes has been studied extensively, the removal and degradation of pADPr, as well as the fate of ADPr metabolites, have received less attention. The observations that stress-induced pADPr undergoes rapid turnover, and that deficiencies in ADPr degradation phenocopy loss of pADPr synthesis, suggest that ADPr degradation is fundamentally important to the cellular stress response. Recent work has identified several distinct families of pADPr hydrolases that can degrade pADPr to release pADPr or mADPr into the cytoplasm. Further, many stress-response proteins contain ADPr-binding domains that can interact with these metabolites. We discuss how pADPr metabolites generated during pADPr degradation can function as signaling intermediates in processes such as inflammation, apoptosis, and DNA damage responses. These studies highlight that the full cycle of ADPr metabolism, including both synthesis and degradation, is necessary for responses to genotoxic stress.
Asunto(s)
ADP-Ribosilación/genética , Poli Adenosina Difosfato Ribosa/genética , Proteínas/genética , Estrés Fisiológico/genética , Daño del ADN/genética , Dominios Proteicos/genética , Procesamiento Proteico-Postraduccional/genética , Transducción de Señal/genéticaRESUMEN
Fanconi anemia (FA) is a rare genetic disorder characterized by an increased susceptibility to squamous cell cancers. Fifteen FA genes are known, and the encoded proteins cooperate in a common DNA repair pathway. A critical step is the monoubiquitination of the FANCD2 protein, and cells from most FA patients are deficient in this step. How monoubiquitinated FANCD2 suppresses squamous cell cancers is unknown. Here we show that Fancd2-deficient mice are prone to Ras-oncogene-driven skin carcinogenesis, while Usp1-deficient mice, expressing elevated cellular levels of Fancd2-Ub, are resistant to skin tumors. Moreover, Fancd2-Ub activates the transcription of the tumor suppressor TAp63, thereby promoting cellular senescence and blocking skin tumorigenesis. For FA patients, the reduction of FANCD2-Ub and TAp63 protein levels may account for their susceptibility to squamous cell neoplasia. Taken together, Usp1 inhibition may be a useful strategy for upregulating TAp63 and preventing or treating squamous cell cancers in the general non-FA population.
Asunto(s)
Transformación Celular Neoplásica/genética , Proteína del Grupo de Complementación D2 de la Anemia de Fanconi/fisiología , Genes Supresores de Tumor , Fosfoproteínas/genética , Transactivadores/genética , Activación Transcripcional , Animales , Proteínas de Arabidopsis , Proliferación Celular , Células Cultivadas , Senescencia Celular , Daño del ADN , Resistencia a la Enfermedad/genética , Endopeptidasas/deficiencia , Endopeptidasas/genética , Anemia de Fanconi/genética , Femenino , Genes ras , Predisposición Genética a la Enfermedad , Humanos , Ratones , Ratones Endogámicos C57BL , Ratones Noqueados , Neoplasias de Células Escamosas/inducido químicamente , Neoplasias de Células Escamosas/genética , Neoplasias de Células Escamosas/patología , Fosfoproteínas/metabolismo , Regiones Promotoras Genéticas , Unión Proteica , Neoplasias Cutáneas/inducido químicamente , Neoplasias Cutáneas/genética , Neoplasias Cutáneas/patología , Transactivadores/metabolismo , Proteasas Ubiquitina-Específicas , UbiquitinaciónRESUMEN
Chromatin remodeling during DNA double-strand break (DSB) repair is required to facilitate access to and repair of DSBs. This remodeling requires increased acetylation of histones and a shift in nucleosome organization to create open, relaxed chromatin domains. However, the underlying mechanism driving changes in nucleosome structure at DSBs is poorly defined. Here, we demonstrate that histone H2A.Z is exchanged onto nucleosomes at DSBs by the p400 remodeling ATPase. H2A.Z exchange at DSBs shifts the chromatin to an open conformation and is required for acetylation and ubiquitination of histones and for loading of the brca1 complex. H2A.Z exchange also restricts single-stranded DNA production by nucleases and is required for loading of the Ku70/Ku80 DSB repair protein. H2A.Z exchange therefore promotes specific patterns of histone modification and reorganization of the chromatin architecture, leading to the assembly of a chromatin template that is an efficient substrate for the DSB repair machinery.
Asunto(s)
Ensamble y Desensamble de Cromatina , Roturas del ADN de Doble Cadena , Reparación del ADN , Histonas/metabolismo , Nucleosomas/metabolismo , Acetilación , Adenosina Trifosfatasas/metabolismo , Antígenos Nucleares/metabolismo , Sitios de Unión , Unión Competitiva , Proteínas Portadoras/metabolismo , Reparación del ADN por Unión de Extremidades , Proteínas de Unión al ADN/metabolismo , Relación Dosis-Respuesta en la Radiación , Endodesoxirribonucleasas , Células HEK293 , Células HeLa , Histonas/química , Histonas/genética , Humanos , Autoantígeno Ku , Proteínas Nucleares/metabolismo , Conformación de Ácido Nucleico , Nucleosomas/química , Nucleosomas/genética , Nucleosomas/efectos de la radiación , Interferencia de ARN , Factores de Tiempo , Transfección , UbiquitinaciónRESUMEN
CHD1 is a conserved chromatin remodeling enzyme required for development and linked to prostate cancer in adults, yet its role in human cells is poorly understood. Here, we show that targeted disruption of the CHD1 gene in human cells leads to a defect in early double-strand break (DSB) repair via homologous recombination (HR), resulting in hypersensitivity to ionizing radiation as well as PARP and PTEN inhibition. CHD1 knockout cells show reduced H2AX phosphorylation (γH2AX) and foci formation as well as impairments in CtIP recruitment to the damaged sites. Chromatin immunoprecipitation following a single DSB shows that the reduced levels of γH2AX accumulation at DSBs in CHD1-KO cells are due to both a global reduction in H2AX incorporation and poor retention of H2AX at the DSBs. We also identified a unique N-terminal region of CHD1 that inhibits the DNA binding, ATPase, and chromatin assembly and remodeling activities of CHD1. CHD1 lacking the N terminus was more active in rescuing the defects in γH2AX formation and CtIP recruitment in CHD1-KO cells than full-length CHD1, suggesting the N terminus is a negative regulator in cells. Our data point to a role for CHD1 in the DSB repair process and identify a novel regulatory region of the protein.
Asunto(s)
Daño del ADN , ADN Helicasas/metabolismo , Proteínas de Unión al ADN/metabolismo , Adenosina Trifosfatasas/química , Adenosina Trifosfatasas/genética , Adenosina Trifosfatasas/metabolismo , Sitios de Unión , Proteínas Portadoras/metabolismo , Línea Celular , Ensamble y Desensamble de Cromatina , Roturas del ADN de Doble Cadena , ADN Helicasas/química , ADN Helicasas/genética , Proteínas de Unión al ADN/química , Proteínas de Unión al ADN/genética , Endodesoxirribonucleasas , Técnicas de Inactivación de Genes , Histonas/metabolismo , Recombinación Homóloga , Humanos , Proteínas Nucleares/metabolismo , Fragmentos de Péptidos/química , Fragmentos de Péptidos/genética , Fragmentos de Péptidos/metabolismo , Fosforilación , Proteínas Recombinantes/química , Proteínas Recombinantes/genética , Proteínas Recombinantes/metabolismo , Transducción de SeñalRESUMEN
The repair of DNA double-strand breaks (DSBs) requires open, flexible chromatin domains. The NuA4-Tip60 complex creates these flexible chromatin structures by exchanging histone H2A.Z onto nucleosomes and promoting acetylation of histone H4. Here, we demonstrate that the accumulation of H2A.Z on nucleosomes at DSBs is transient, and that rapid eviction of H2A.Z is required for DSB repair. Anp32e, an H2A.Z chaperone that interacts with the C-terminal docking domain of H2A.Z, is rapidly recruited to DSBs. Anp32e functions to remove H2A.Z from nucleosomes, so that H2A.Z levels return to basal within 10 min of DNA damage. Further, H2A.Z removal by Anp32e disrupts inhibitory interactions between the histone H4 tail and the nucleosome surface, facilitating increased acetylation of histone H4 following DNA damage. When H2A.Z removal by Anp32e is blocked, nucleosomes at DSBs retain elevated levels of H2A.Z, and assume a more stable, hypoacetylated conformation. Further, loss of Anp32e leads to increased CtIP-dependent end resection, accumulation of single-stranded DNA, and an increase in repair by the alternative nonhomologous end joining pathway. Exchange of H2A.Z onto the chromatin and subsequent rapid removal by Anp32e are therefore critical for creating open, acetylated nucleosome structures and for controlling end resection by CtIP. Dynamic modulation of H2A.Z exchange and removal by Anp32e reveals the importance of the nucleosome surface and nucleosome dynamics in processing the damaged chromatin template during DSB repair.
Asunto(s)
Roturas del ADN de Doble Cadena , Reparación del ADN , Chaperonas de Histonas/metabolismo , Histonas/metabolismo , Proteínas Nucleares/metabolismo , Nucleosomas/metabolismo , Fosfoproteínas/metabolismo , Acetilación , Secuencia de Aminoácidos , Proteínas Portadoras/metabolismo , Línea Celular , Reparación del ADN por Unión de Extremidades , Endodesoxirribonucleasas , Células HEK293 , Células HeLa , Chaperonas de Histonas/química , Histonas/química , Histonas/genética , Humanos , Chaperonas Moleculares , Datos de Secuencia Molecular , Proteínas Nucleares/química , Fosfoproteínas/química , Dominios y Motivos de Interacción de ProteínasRESUMEN
Dynamic changes in histone modification are critical for regulating DNA double-strand break (DSB) repair. Activation of the Tip60 acetyltransferase by DSBs requires interaction of Tip60 with histone H3 methylated on lysine 9 (H3K9me3). However, how H3K9 methylation is regulated during DSB repair is not known. Here, we demonstrate that a complex containing kap-1, HP1, and the H3K9 methyltransferase suv39h1 is rapidly loaded onto the chromatin at DSBs. Suv39h1 methylates H3K9, facilitating loading of additional kap-1/HP1/suv39h1 through binding of HP1's chromodomain to the nascent H3K9me3. This process initiates cycles of kap-1/HP1/suv39h1 loading and H3K9 methylation that facilitate spreading of H3K9me3 and kap-1/HP1/suv39h1 complexes for tens of kilobases away from the DSB. These domains of H3K9me3 function to activate the Tip60 acetyltransferase, allowing Tip60 to acetylate both ataxia telangiectasia-mutated (ATM) kinase and histone H4. Consequently, cells lacking suv39h1 display defective activation of Tip60 and ATM, decreased DSB repair, and increased radiosensitivity. Importantly, activated ATM rapidly phosphorylates kap-1, leading to release of the repressive kap-1/HP1/suv39h1 complex from the chromatin. ATM activation therefore functions as a negative feedback loop to remove repressive suv39h1 complexes at DSBs, which may limit DSB repair. Recruitment of kap-1/HP1/suv39h1 to DSBs therefore provides a mechanism for transiently increasing the levels of H3K9me3 in open chromatin domains that lack H3K9me3 and thereby promoting efficient activation of Tip60 and ATM in these regions. Further, transient formation of repressive chromatin may be critical for stabilizing the damaged chromatin and for remodeling the chromatin to create an efficient template for the DNA repair machinery.
Asunto(s)
Ensamble y Desensamble de Cromatina , Cromatina/metabolismo , Roturas del ADN de Doble Cadena , Histonas/metabolismo , Proteínas de la Ataxia Telangiectasia Mutada/genética , Proteínas de la Ataxia Telangiectasia Mutada/metabolismo , Cromatina/genética , Células HEK293 , Células HeLa , Histona Acetiltransferasas/genética , Histona Acetiltransferasas/metabolismo , Histonas/genética , Humanos , Lisina/genética , Lisina/metabolismo , Lisina Acetiltransferasa 5 , Metilación , Metiltransferasas/genética , Metiltransferasas/metabolismo , Fosforilación , Estructura Terciaria de Proteína , Proteínas Represoras/genética , Proteínas Represoras/metabolismo , Proteína 28 que Contiene Motivos TripartitoRESUMEN
The major mammalian apurinic/apyrimidinic endonuclease Ape1 is a multifunctional protein operating in protection of cells from oxidative stress via its DNA repair, redox, and transcription regulatory activities. The importance of Ape1 has been marked by previous work demonstrating its requirement for viability in mammalian cells. However, beyond a requirement for Ape1-dependent DNA repair activity, deeper molecular mechanisms of the fundamental role of Ape1 in cell survival have not been defined. Here, we report that Ape1 is an essential factor stabilizing telomeric DNA, and its deficiency is associated with telomere dysfunction and segregation defects in immortalized cells maintaining telomeres by either the alternative lengthening of telomeres pathway (U2OS) or telomerase expression (BJ-hTERT), or in normal human fibroblasts (IMR90). Through the expression of Ape1 derivatives with site-specific changes, we found that the DNA repair and N-terminal acetylation domains are required for the Ape1 function at telomeres. Ape1 associates with telomere proteins in U2OS cells, and Ape1 depletion causes dissociation of TRF2 protein from telomeres. Consistent with this effect, we also observed that Ape1 depletion caused telomere shortening in both BJ-hTERT and in HeLa cells. Thus, our study describes a unique and unpredicted role for Ape1 in telomere protection, providing a direct link between base excision DNA repair activities and telomere metabolism.
Asunto(s)
Reparación del ADN/fisiología , ADN-(Sitio Apurínico o Apirimidínico) Liasa/metabolismo , Homeostasis del Telómero/genética , Western Blotting , Línea Celular Tumoral , Inmunoprecipitación de Cromatina , Cartilla de ADN/genética , ADN-(Sitio Apurínico o Apirimidínico) Liasa/genética , Técnica del Anticuerpo Fluorescente , Humanos , Inmunoprecipitación , Hibridación Fluorescente in Situ , Telomerasa/metabolismo , Homeostasis del Telómero/fisiologíaRESUMEN
HJURP is overexpressed in several cancer types and strongly correlates with patient survival. However, the mechanistic basis underlying the association of HJURP with cancer aggressiveness is not well understood. HJURP promotes the loading of the histone H3 variant, CENP-A, at the centromeric chromatin, epigenetically defining the centromeres and supporting proper chromosome segregation. In addition, HJURP is associated with DNA repair but its function in this process is still scarcely explored. Here, we demonstrate that HJURP is recruited to DSBs through a mechanism requiring chromatin PARylation and promotes epigenetic alterations that favor the execution of DNA repair. Incorporation of HJURP at DSBs promotes turnover of H3K9me3 and HP1, facilitating DNA damage signaling and DSB repair. Moreover, HJURP overexpression in glioma cell lines also affected global structure of heterochromatin independently of DNA damage induction, promoting genome-wide reorganization and assisting DNA damage response. HJURP overexpression therefore extensively alters DNA damage signaling and DSB repair, and also increases radioresistance of glioma cells. Importantly, HJURP expression levels in tumors are also associated with poor response of patients to radiation. Thus, our results enlarge the understanding of HJURP involvement in DNA repair and highlight it as a promising target for the development of adjuvant therapies that sensitize tumor cells to irradiation.
Asunto(s)
Cromatina , Glioma , Humanos , Centrómero/metabolismo , Proteína A Centromérica/genética , Proteína A Centromérica/metabolismo , Cromatina/genética , Proteínas Cromosómicas no Histona/genética , Proteínas Cromosómicas no Histona/metabolismo , Reparación del ADN/genética , Proteínas de Unión al ADN/genética , Proteínas de Unión al ADN/metabolismo , Glioma/genéticaRESUMEN
DNA damage leads to rapid synthesis of poly(ADP-ribose) (pADPr), which is important for damage signaling and repair. pADPr chains are removed by poly(ADP-ribose) glycohydrolase (PARG), releasing free mono(ADP-ribose) (mADPr). Here, we show that the NUDIX hydrolase NUDT5, which can hydrolyze mADPr to ribose-5-phosphate and either AMP or ATP, is recruited to damage sites through interaction with PARG. NUDT5 does not regulate PARP or PARG activity. Instead, loss of NUDT5 reduces basal cellular ATP levels and exacerbates the decrease in cellular ATP that occurs during DNA repair. Further, loss of NUDT5 activity impairs RAD51 recruitment, attenuates the phosphorylation of key DNA-repair proteins, and reduces both H2A.Z exchange at damage sites and repair by homologous recombination. The ability of NUDT5 to hydrolyze mADPr, and/or regulate cellular ATP, may therefore be important for efficient DNA repair. Targeting NUDT5 to disrupt PAR/mADPr and energy metabolism may be an effective anti-cancer strategy.
Asunto(s)
Adenosina Difosfato Ribosa , Reparación del ADN , Adenosina Difosfato Ribosa/metabolismo , Poli Adenosina Difosfato Ribosa/metabolismo , Glicósido Hidrolasas/metabolismo , Daño del ADN , Adenosina TrifosfatoRESUMEN
Resistance to adjuvant chemotherapy is a major clinical problem in the treatment of colorectal cancer (CRC). The aim of this study was to elucidate the role of an epithelial to mesenchymal transition (EMT)-inducing protein, ZEB2, in chemoresistance of CRC, and to uncover the underlying mechanism. We performed IHC for ZEB2 and association analyses with clinical outcomes on primary CRC and matched CRC liver metastases in compliance with observational biomarker study guidelines. ZEB2 expression in primary tumours was an independent prognostic marker of reduced overall survival and disease-free survival in patients who received adjuvant FOLFOX chemotherapy. ZEB2 expression was retained in 96% of liver metastases. The ZEB2-dependent EMT transcriptional programme activated nucleotide excision repair (NER) pathway largely via upregulation of the ERCC1 gene and other components in NER pathway, leading to enhanced viability of CRC cells upon oxaliplatin treatment. ERCC1-overexpressing CRC cells did not respond to oxaliplatin in vivo, as assessed using a murine orthotopic model in a randomised and blinded preclinical study. Our findings show that ZEB2 is a biomarker of tumour response to chemotherapy and risk of recurrence in CRC patients. We propose that the ZEB2-ERCC1 axis is a key determinant of chemoresistance in CRC.
Asunto(s)
Protocolos de Quimioterapia Combinada Antineoplásica/uso terapéutico , Neoplasias Colorrectales/genética , Reparación del ADN/genética , Proteínas de Unión al ADN/genética , Endonucleasas/genética , Transición Epitelial-Mesenquimal/genética , Transcripción Genética , Caja Homeótica 2 de Unión a E-Box con Dedos de Zinc/fisiología , Animales , Línea Celular Tumoral , Neoplasias Colorrectales/tratamiento farmacológico , Neoplasias Colorrectales/patología , Resistencia a Antineoplásicos , Fluorouracilo/uso terapéutico , Humanos , Leucovorina/uso terapéutico , Neoplasias Hepáticas/secundario , Ratones , Compuestos Organoplatinos/uso terapéutico , Ensayos Antitumor por Modelo de XenoinjertoRESUMEN
INTRODUCTION: Ionizing radiation (IR) is a widely used approach to cancer therapy, ranking second only to surgery in rate of utilization. Responses of cancer patients to radiotherapy depend in part on the intrinsic radiosensitivity of the tumor cells. Thus, promoting tumor cell sensitivity to IR could significantly enhance the treatment outcome and quality of life for patients. METHODS: Mammary tumor cells were treated by a 16-base phosphodiester-linked oligonucleotide homologous to the telomere G-rich sequence TTAGGG (T-oligo: GGTTAGGTGTAGGTTT) or a control-oligo (the partial complement, TAACCCTAACCCTAAC) followed by IR. The inhibition of tumor cell growth in vitro was assessed by cell counting and clonogenic cell survival assay. The tumorigenesis of tumor cells after various treatments was measured by tumor growth in mice. The mechanism underlying the radiosensitization by T-oligo was explored by immunouorescent determination of phosphorylated histone H2AX (γH2AX) foci, ß-galactosidase staining, comet and Terminal deoxynucleotidyl transferase dUTP Nick End Labeling (TUNEL) assays. The efficacy of the combined treatment was assessed in a spontaneous murine mammary tumor model. RESULTS: Pretreatment of tumor cells with T-oligo for 24 hours in vitro enhanced both senescence and apoptosis of irradiated tumor cells and reduced clonogenic potential. Radiosensitization by T-oligo was associated with increased formation and/or delayed resolution of γH2AX DNA damage foci and fragmented DNA. T-oligo also caused radiosensitization in two in vivo mammary tumor models. Indeed, combined T-oligo and IR-treatment in vivo led to a substantial reduction in tumor growth. Of further significance, treatment with T-oligo and IR led to synergistic inhibition of the growth of spontaneous mammary carcinomas. Despite these profound antitumor properties, T-oligo and IR caused no detectable side effects under our experimental conditions. CONCLUSIONS: Pretreatment with T-oligo sensitizes mammary tumor cells to radiation in both in vitro and in vivo settings with minimal or no normal tissue side effects.
Asunto(s)
Neoplasias Mamarias Animales/radioterapia , Oligonucleótidos/farmacología , Tolerancia a Radiación/efectos de los fármacos , Fármacos Sensibilizantes a Radiaciones/farmacología , Animales , Apoptosis/efectos de los fármacos , Apoptosis/efectos de la radiación , Línea Celular Tumoral , Proliferación Celular/efectos de los fármacos , Proliferación Celular/efectos de la radiación , Senescencia Celular/efectos de los fármacos , Senescencia Celular/efectos de la radiación , Terapia Combinada , Ensayo Cometa , Daño del ADN/efectos de los fármacos , Daño del ADN/efectos de la radiación , Femenino , Galactósidos/análisis , Histonas/metabolismo , Etiquetado Corte-Fin in Situ , Ratones , Ratones Endogámicos C57BL , Fosforilación/efectos de la radiación , Radiación Ionizante , Fármacos Sensibilizantes a Radiaciones/uso terapéutico , Telómero/genéticaRESUMEN
DNA repair requires reorganization of the local chromatin structure to facilitate access to and repair of the DNA. Studying DNA double-strand break (DSB) repair in specific chromatin domains has been aided by the use of sequence-specific endonucleases to generate targeted breaks. Here, we describe a new approach that combines KillerRed, a photosensitizer that generates reactive oxygen species (ROS) when exposed to light, and the genome-targeting properties of the CRISPR/Cas9 system. Fusing KillerRed to catalytically inactive Cas9 (dCas9) generates dCas9-KR, which can then be targeted to any desired genomic region with an appropriate guide RNA. Activation of dCas9-KR with green light generates a local increase in reactive oxygen species, resulting in "clustered" oxidative damage, including both DNA breaks and base damage. Activation of dCas9-KR rapidly (within minutes) increases both γH2AX and recruitment of the KU70/80 complex. Importantly, this damage is repaired within 10 minutes of termination of light exposure, indicating that the DNA damage generated by dCas9-KR is both rapid and transient. Further, repair is carried out exclusively through NHEJ, with no detectable contribution from HR-based mechanisms. Surprisingly, sequencing of repaired DNA damage regions did not reveal any increase in either mutations or INDELs in the targeted region, implying that NHEJ has high fidelity under the conditions of low level, limited damage. The dCas9-KR approach for creating targeted damage has significant advantages over the use of endonucleases, since the duration and intensity of DNA damage can be controlled in "real time" by controlling light exposure. In addition, unlike endonucleases that carry out multiple cut-repair cycles, dCas9-KR produces a single burst of damage, more closely resembling the type of damage experienced during acute exposure to reactive oxygen species or environmental toxins. dCas9-KR is a promising system to induce DNA damage and measure site-specific repair kinetics at clustered DNA lesions.
Asunto(s)
Sistemas CRISPR-Cas/genética , Repeticiones Palindrómicas Cortas Agrupadas y Regularmente Espaciadas/genética , Daño del ADN/genética , Reparación del ADN/genética , ADN/genética , Estrés Oxidativo/genética , Línea Celular , Cromatina/genética , Roturas del ADN de Doble Cadena , Endonucleasas/genética , Genoma/genética , Células HEK293 , Humanos , Luz , ARN Guía de Kinetoplastida/genéticaRESUMEN
The Holliday Junction-Recognition Protein (HJURP) was reported as overexpressed in several cancers and also strongly correlated with poor prognosis of patients, especially in glioblastoma (GBM), the most common and deadly type of primary brain tumor. HJURP is responsible for loading the histone H3 variant-the Centromeric Protein A (CENP-A)-at the centromeres in a cell cycle-regulated manner, being required for proper chromosome segregation. Here we investigated HJURP association with survival and radioresistance of different GBM cell lines. HJURP knockdown compromised the clonogenic capacity and severely impaired survival of five distinct GBM cells, while nontumor astrocytes were not affected. U251MG cells showed a robust cell cycle arrest in G2/M phases followed by a drastic increment in cell death after HJURP silencing, while U138MG and U343MG cell lines presented augmented senescence with a comparable increase in cell death. Importantly, we verified that the impact on cell cycle dynamics and clonogenic survival were associated with loss CENP-A at the centromeres. Moreover, radiation resistance was also impacted by HJURP modulation in several GBM cell lines. U87MG, T98G, U138MG, and U343MG cells were all sensitized to ionizing radiation after HJURP reduction. These data reinforce the requirement of HJURP for proliferative capacity and radioresistance of tumor cells, underlining its potential as a promising therapeutic target for GBM.
Asunto(s)
Neoplasias Encefálicas/radioterapia , Proteína A Centromérica/metabolismo , Proteínas de Unión al ADN/metabolismo , Glioblastoma/radioterapia , Células Madre Neoplásicas/efectos de la radiación , Neoplasias Encefálicas/patología , Puntos de Control del Ciclo Celular/genética , Puntos de Control del Ciclo Celular/efectos de la radiación , Línea Celular Tumoral , Proliferación Celular/genética , Proliferación Celular/efectos de la radiación , Supervivencia Celular/genética , Supervivencia Celular/efectos de la radiación , Centrómero/metabolismo , Centrómero/efectos de la radiación , Proteínas de Unión al ADN/genética , Técnicas de Silenciamiento del Gen , Glioblastoma/patología , Humanos , Células Madre Neoplásicas/patología , Tolerancia a Radiación/genética , Ensayo de Tumor de Célula MadreRESUMEN
With the increasing emergence of genome-wide analysis technologies (including comparative genomic hybridization (CGH), expression profiling on microarrays, differential display (DD), subtractive hybridization, and representational difference analysis (RDA)), there is frequently a need to amplify entire genomes or cDNAs by PCR to obtain enough material for comparisons among target and control samples. A major problem with PCR is that amplification occurs in a nonlinear manner and reproducibility is influenced by stray impurities. As a result, when two complex DNA populations are amplified separately, the quantitative relationship between two genes after amplification is generally not the same as their relation before amplification. Here we describe balanced PCR, a procedure that faithfully retains the difference among corresponding amplified genes by using a simple principle. Two distinct genomic DNA samples are tagged with oligonucleotides containing both a common and a unique DNA sequence. The genomic DNA samples are pooled and amplified in a single PCR tube using the common DNA tag. By mixing the two genomes, PCR loses the ability to discriminate among the different alleles and the influence of impurities is eliminated. The PCR-amplified pooled samples can be separated using the DNA tag unique to each individual genomic DNA sample. The principle of this method has been validated with synthetic DNA, genomic DNA, and cDNA applied on microarrays. By removing the bias of PCR, this method allows a balanced amplification of allelic fragments from two complex DNAs even after three sequential rounds of PCR. This balanced PCR approach should allow genetic analysis in minute laser-microdissected tissues, paraffin-embedded archived material, or single cells.
Asunto(s)
ADN Complementario/análisis , ADN Complementario/genética , Genoma Humano , Reacción en Cadena de la Polimerasa/métodos , Etiquetas de Secuencia Expresada , Humanos , Pulmón/química , Masculino , Próstata/química , Control de Calidad , Reproducibilidad de los Resultados , Sensibilidad y EspecificidadRESUMEN
Repairing DNA breaks within the complexity of the cell chromatin is challenging. In this issue, Gong et al. (2017. J. Cell Biol. https://doi.org/10.1083/jcb.201611135) identify the histone demethylase KDM5A as a critical editor of the cells' "histone code" that is required to recruit DNA repair complexes to DNA breaks.
Asunto(s)
Cromatina , Código de Histonas , Roturas del ADN , Reparación del ADN , Histonas/genéticaRESUMEN
The n-terminal tail of histone H4 recruits repair proteins, including 53BP1, to DNA double-strand breaks (DSB) and undergoes dynamic acetylation during DSB repair. However, how H4 acetylation (H4Ac) recruits repair proteins and reorganizes chromatin during DNA repair is unclear. Here, we show that the bromodomain protein BRD2 is recruited to DSBs. This recruitment requires binding of BRD2's tandem bromodomains to H4Ac, which is generated at DSBs by the Tip60/KAT5 acetyltransferase. Binding of BRD2 to H4Ac protects the underlying acetylated chromatin from attack by histone deacetylases and allows acetylation to spread along the flanking chromatin. However, BRD2 recruitment is spatially restricted to a chromatin domain extending only 2 kb either side of the DSB, and BRD2 does not spread into the chromatin domains flanking the break. Instead, BRD2 facilitates recruitment of a second bromodomain protein, ZMYND8, which spreads along the flanking chromatin, but is excluded from the DSB region. This creates a spatially restricted H4Ac/BRD2 domain which reorganizes chromatin at DSBs, limits binding of the L3MBTL1 repressor and promotes 53BP1 binding, while limiting end-resection of DSBs. BRD2 therefore creates a restricted chromatin environment surrounding DSBs which facilitates DSB repair and which is framed by extensive ZMYND8 domains on the flanking chromatin.
Asunto(s)
Roturas del ADN de Doble Cadena , Reparación del ADN , Histonas/metabolismo , Proteínas Serina-Treonina Quinasas/metabolismo , Acetilación , Línea Celular Tumoral , Proteínas Cromosómicas no Histona/metabolismo , Reparación del ADN por Unión de Extremidades , Humanos , Unión Proteica , Proteínas Represoras/metabolismo , Factores de Transcripción , Proteínas Supresoras de Tumor , Proteína 1 de Unión al Supresor Tumoral P53 , Proteína que Contiene Valosina/metabolismoRESUMEN
The ability of cells to detect and repair DNA double-strand breaks (DSBs) within the complex architecture of the genome requires co-ordination between the DNA repair machinery and chromatin remodelling complexes. This co-ordination is essential to process damaged chromatin and create open chromatin structures which are required for repair. Initially, there is a PARP-dependent recruitment of repressors, including HP1 and several H3K9 methyltransferases, and exchange of histone H2A.Z by the NuA4-Tip60 complex. This creates repressive chromatin at the DSB in which the tail of histone H4 is bound to the acidic patch on the nucleosome surface. These repressor complexes are then removed, allowing rapid acetylation of the H4 tail by Tip60. H4 acetylation blocks interaction between the H4 tail and the acidic patch on adjacent nucleosomes, decreasing inter-nucleosomal interactions and creating open chromatin. Further, the H4 tail is now free to recruit proteins such as 53BP1 to DSBs, a process modulated by H4 acetylation, and provides binding sites for bromodomain proteins, including ZMYND8 and BRD4, which are important for DSB repair. Here, we will discuss how the H4 tail functions as a dynamic hub that can be programmed through acetylation to alter chromatin packing and recruit repair proteins to the break site.This article is part of the themed issue 'Chromatin modifiers and remodellers in DNA repair and signalling'.
Asunto(s)
Cromatina/genética , Roturas del ADN de Doble Cadena , Reparación del ADN , Histonas/metabolismo , Acetilación , Animales , HumanosRESUMEN
Radiation therapy is widely used to treat human malignancies, but many tumor types, including gliomas, exhibit significant radioresistance. Radiation therapy creates DNA double-strand breaks (DSBs), and DSB repair is linked to rapid changes in epigenetic modifications, including increased histone methylation. This increased histone methylation recruits DNA repair proteins which can then alter the local chromatin structure and promote repair. Consequently, combining inhibitors of specific histone methyltransferases with radiation therapy may increase tumor radiosensitivity, particularly in tumors with significant therapeutic resistance. Here, we demonstrate that inhibitors of the H4K20 methyltransferase SETD8 (UNC-0379) and the H3K9 methyltransferase G9a (BIX-01294) are effective radiosensitizers of human glioma cells. UNC-0379 blocked H4K20 methylation and reduced recruitment of the 53BP1 protein to DSBs, although this loss of 53BP1 caused only limited changes in radiosensitivity. In contrast, loss of H3K9 methylation through G9a inhibition with BIX-01294 increased radiosensitivity of a panel of glioma cells (SER2Gy range: 1.5 - 2.9). Further, loss of H3K9 methylation reduced DSB signaling dependent on H3K9, including reduced activation of the Tip60 acetyltransferase, loss of ATM signaling and reduced phosphorylation of the KAP-1 repressor. In addition, BIX-0194 inhibited DSB repair through both the homologous recombination and nonhomologous end-joining pathways. Inhibition of G9a and loss of H3K9 methylation is therefore an effective approach for increasing radiosensitivity of glioma cells. These results suggest that combining inhibitors of histone methyltransferases which are critical for DSB repair with radiation therapy may provide a new therapeutic route for sensitizing gliomas and other tumors to radiation therapy.