Poly(ADP-ribosyl)ation dependent changes in CTCF-chromatin binding and gene expression in breast cells
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ABSTRACT: CTCF is an evolutionary conserved and ubiquitously expressed architectural protein, which regulates a plethora of cellular functions using different molecular mechanisms. The main form of CTCF with an apparent molecular mass of 130 kDa (CTCF130) has been extensively studied, however the properties of CTCF180, highly modified by poly(ADP-ribosyl)ation (PARylation) are not well understood. In this study we performed ChIP-seq and RNA-seq analyses in breast cells 226LDM, proliferating (with CTCF130 as the most abundant CTCF form) and arrested in the cell cycle (with only CTCF180). A dramatic reorganization of CTCF binding was observed during this transition, whereby CTCF was evacuated from many sites ("lost" group), although some sites retained modified CTCF ("common") and others acquired CTCF180 ("gained"). The classic CTCF binding motifs were identified for the former two groups, whereas the latter had no CTCF binding motif. Changes in CTCF occupancies in lost/common (but not gained) sites were associated with increased chromatin densities and altered expression from the neighboring genes. We propose a model integrating CTCF130/180 transition with CTCF-DNA binding and gene expression patterns, and functional outcomes. This study issues an important cautionary note concerning design and interpretation of any experiments using cells and tissues where CTCF180 may be present.
Project description:Protein poly(ADP-ribosyl)ation (PARylation) primarily catalyzed by poly(ADP-ribose) polymerases (PARPs) plays a crucial role in controlling various cellular responses. However, PARylation targets and their functions remain largely elusive. In this study, we deployed an Arabidopsis protein microarray coupled with in vitro PARylation to globally identify PARylation targets in plants. In line with nuclear localization of Arabidopsis PARPs, 56% of PARylation targets are predicted to localize in nucleus. Consistent with the essential role of protein PARylation in plant innate immunity, forkhead-associated (FHA) domain protein DAWDLE (DDL), one of the PARylation targets, positively regulates plant defense to both adapted and non-adapted pathogens. Arabidopsis PARP2 interacts and PARylates DDL, which was enhanced upon treatment of microbe-associated molecular pattern. Mass spectrometry and mutagenesis analysis identified multiple PARylation sites of DDL by PARP2. Genetic complementation assays indicate that DDL PARylation is required for its function in plant immunity. In contrast, DDL PARylation appears to be dispensable for its previously reported function in plant development likely mediated by the regulation of microRNA biogenesis. Our study uncovers many previously unknown PARylation targets and points to the distinct functions of DDL in plant immunity and development mediated by protein PARylation and small RNA biogenesis respectively.
Project description:The three-dimensional genome organization is critical for gene regulation and can malfunction in diseases like cancer. As a key regulator of genome organization, CCCTC-binding factor (CTCF) has been characterized as a DNA-binding protein with important functions in maintaining the topological structure of chromatin and inducing DNA looping. Among the prolific binding sites in the genome, several events with altered CTCF occupancy have been reported as associated with effects in physiology or disease. However, hitherto there is no comprehensive survey of genome-wide CTCF binding patterns across different human cancers. To dissect functions of CTCF binding, we systematically analyze over 700 CTCF ChIP-seq profiles across human tissues and cancers and identify cancer-specific CTCF binding patterns in six cancer types. We show that cancer-specific lost and gained CTCF binding events are associated with altered chromatin interactions, partially with DNA methylation changes, and rarely with sequence mutations. While lost bindings primarily occur near gene promoters, most gained CTCF binding events exhibit enhancer activities and are induced by oncogenic transcription factors. We validate these findings in T-cell acute lymphoblastic leukemia cell lines and patient samples and show that oncogenic NOTCH1 induces specific CTCF binding and they cooperatively activate expression of target genes, indicating transcriptional condensation phenomena. Our results substantiate CTCF binding alteration as a functional epigenomic signature of cancer.
Project description:Poly(ADP-ribosyl)ation (PARylation) is a regulatory post-translational modification of proteins mediated by PARP family members, such as PARP-1. Although PARP-1 and PARylation have been widely studied, very few examples of definitive biological roles for site-specific PARylation of proteins exist in the literature. Here we show that C/EBPβ, a key pro-adipogenic transcription factor, is PARylated by PARP-1 at Glu135, as well as two adjacent amino acids (K133 and E139). PARylation at these sites inhibits C/EBPβ’s DNA binding and transcriptional activities, and attenuates adipogenesis in various cell-based models of adipogenesis. Interestingly, PARP-1 catalytic activity drops precipitously during the first 48 hours of hormone-induced differentiation, corresponding to a release of C/EBPβ from PARylation-mediated inhibition. This allows the binding of C/EBPβ to the promoters of pro-adipogenic target genes (e.g., Cebpa, Pparg2), their subsequent expression, and continued differentiation. In this regard, depletion of PARP-1 or chemical inhibition of its catalytic activity enhances early adipogenic events. Collectively, our results provide a clear example of how site-specific PARylation of a key transcription factor can affect its molecular and biochemical functions, as well as the biological outcomes that it controls.
Project description:Drosophila Insulator proteins mediate long-range chromosomal interactions. ChIP-seq revealed that binding of insulator proteins to some specific DNA sites was regulated by poly(ADP-ribosyl)ation in S2 cells. Three insulator sites regulated by poly(ADP-ribosyl)ation were used as baits to map their distant interacting sites using 4C assay in control S2 cells. Mapping the chromosomal interactions of three specific insulator binding sites with 4C assay in control S2 cells.
Project description:CCCTC-binding factor (CTCF) is an architectural protein involved in the three-dimensional organization of chromatin. In this study, we systematically assayed the 3D genomic contact profiles of hundreds of CTCF binding sites in multiple tissues with high-resolution 4C-seq. We find both developmentally stable and dynamic chromatin loops. As recently reported, our data also suggest that chromatin loops preferentially form between CTCF binding sites oriented in a convergent manner. To directly test this, we used CRISPR-Cas9 genome editing to delete core CTCF binding sites in three loci, including the CTCF site in the Sox2 super-enhancer. In all instances, CTCF and cohesin recruitment were lost, and chromatin loops with distal CTCF sites were disrupted or destabilized. Re-insertion of oppositely oriented CTCF recognition sequences restored CTCF and cohesin recruitment, but did not re-establish chromatin loops. We conclude that CTCF binding polarity plays a functional role in the formation of higher order chromatin structure. 4C-seq was performed on a large number of viewpoints in E14 embryonic stem cells, neural precursor cells and primary fetal liver cells
Project description:Drosophila Insulator proteins mediate long-range chromosomal interactions. ChIP-seq revealed that binding of insulator proteins to some specific DNA sites was regulated by poly(ADP-ribosyl)ation in S2 cells. Three insulator sites regulated by poly(ADP-ribosyl)ation were used as baits to map their distant interacting sites using 4C assay in control S2 cells.
Project description:Epstein Barr Virus (EBV) is a potentially oncogenic gammaherpesvirus that establishes a chronic, latent infection in memory B cells. The EBV genome persists in infected host cells as a chromatinized episome and is subject to chromatin-mediated regulation. Binding of the host insulator protein CTCF to the EBV genome has an established role in maintaining viral latency type. CTCF is post-translationally modified by the host enzyme PARP1. PARP1, or Poly(ADP-ribose) polymerase 1, catalyzes the transfer of a poly(ADP-ribose) (PAR) moiety from NAD+ onto acceptor proteins including itself, histone proteins, and CTCF. PARylation of CTCF by PARP1 can affect CTCF’s insulator activity, DNA binding capacity, and ability to form chromatin loops. Both PARP1 and CTCF have been implicated in the regulation of EBV latency and lytic reactivation. Thus, we predicted that pharmacological inhibition with PARP1 inhibitors would affect EBV latency type through a chromatin-specific mechanism. Here, we show that PARP1 and CTCF colocalize at specific sites throughout the EBV genome, and provide evidence to suggest that PARP1 acts to stabilize CTCF binding and maintain the open chromatin landscape at the active Cp promoter during type III latency. Further, PARP1 activity is important in maintaining latency type-specific viral gene expression. The data presented here provide a rationale for the use of PARP inhibitors in the treatment of EBV-associated cancers exhibiting type III latency, and could ultimately contribute to an EBV-specific treatment strategy for AIDS-related or post-transplant lymphomas.
Project description:To improve our understanding of transcriptional regulation by ESR1 in the liver, chromatin immunoprecipitation with an antibody against ESR1 followed by high-throughput sequencing (ESR1 ChIP-Seq) was conducted in human liver samples and in hepatocytes with or without 17beta-estradiol (E2) treatment. By comparing treated and untreated hepatocytes, we identified both ligand-dependent and ligand-independent binding sites throughout the genome. Ligand-dependent binding sites include ChIP-Seq peaks that either appeared (gained peaks) or disappeared (lost peaks) upon estrogen treatment. Gained peaks occurred at the Estrogen Response Element (ERE) whereas the sites for lost peaks were instead coenriched with a variety of transcription factors. In both cases, ESR1 binding primarily occurred in enhancer regions and was associated with general liver functions, such as lipid/energy metabolism. In contrast, we also observed a subset of ESR1 sites that were maintained regardless of estrogen treatment. These ligand-independent sites mostly occurred at promoter regions and were highly enriched with several cofactor motifs.
Project description:CCCTC-binding factor (CTCF) is an architectural protein involved in the three-dimensional organization of chromatin. In this study, we systematically assayed the 3D genomic contact profiles of hundreds of CTCF binding sites in multiple tissues with high-resolution 4C-seq. We find both developmentally stable and dynamic chromatin loops. As recently reported, our data also suggest that chromatin loops preferentially form between CTCF binding sites oriented in a convergent manner. To directly test this, we used CRISPR-Cas9 genome editing to delete core CTCF binding sites in three loci, including the CTCF site in the Sox2 super-enhancer. In all instances, CTCF and cohesin recruitment were lost, and chromatin loops with distal CTCF sites were disrupted or destabilized. Re-insertion of oppositely oriented CTCF recognition sequences restored CTCF and cohesin recruitment, but did not re-establish chromatin loops. We conclude that CTCF binding polarity plays a functional role in the formation of higher order chromatin structure.
Project description:This SuperSeries is composed of the SubSeries listed below. CTCF is a DNA-binding protein which plays critical roles in chromatin structure organization and transcriptional regulation; however, little is known about the functional determinants of different CTCF binding sites (CBS). Using a conditional mouse model, we have identified one set of CBSs that are lost upon CTCF depletion (lost CBSs) and another set that persists (retained CBSs). Retained CBSs are more similar to the consensus CTCF binding sequence and usually span tandem CTCF peaks. Lost CBSs are enriched at enhancers and promoters and associate with active chromatin marks and higher transcriptional activity. In contrast, retained CBSs are enriched at TAD and loop boundaries. Integration of ChIP-seq and RNA-seq data has revealed that retained CBSs are located at the boundaries between distinct chromatin states, acting as chromatin barriers. Our results provide evidence that transient, lost CBSs are involved in transcriptional regulation, whereas retained CBSs are critical for establishing higher-order chromatin architecture.