ABSTRACT: Tumor suppressor p53 regulates various role in the cell including cell cycle arrest, DNA repair and apoptosis. Current research achieved to investigate p53 target genes in human osteosarcoma cell line-SaOS2 cell. Examination of p53 binding protein by transfecting flag-tagged wild type p53 into SaOS2 cells.
Project description:Missense mutations in the TP53 gene are frequent genetic alterations in human tumor tissue and cell lines. In contrast to wild-type p53, the mutant p53 (mutp53) protein has lost the transcriptional activity towards pro-apoptotic and growth arrest genes, but retained the property to interact with DNA in a structure-specific fashion. Expression of mutp53 is advantageous for tumor cells, however the molecular mechanism of mutp53 action is still not known. We used the glioblastoma-derived U-251 MG human cell line to analyze DNA binding of mutant p53 (R273H mutation) on a Nimblegen custom 135k tiling array and to correlate mutp53 binding regions with the epigenetic state and occupation by other transcription factors (ETS1 and SP1). We found that mutp53-binding regions are G/C-rich and are located around transcriptional start sites (TSS) of many protein-coding genes, which in most cases are active, but are not always regulated upon transient mutp53 depletion. We propose a model which does not only rely on interactions of mutp53 with diverse transcriptional regulators at active promoters, but primarily is based on a DNA binding activity of mutp53. We designed a Nimblegen custom 135k tiling array that covers a large set of putative and known p53 (wild-type and mutant) target genes in the human genome. For analysis of the epigenetic state of genes covered by the tiling array in control and mutant p53-depleted U251 cells we focused on changes in active histone marks, H3K4me3 and H3K9Ac, and RNA polymerase II recruitment and processivity. H3K4me3 and H3K9Ac marks are enriched in active promoter regions and the phosphorylation of serine 5 (S5-P) and serine 2 (S2-P) in the CTD of RNA polymerase II have been described to define initiated and elongating complexes, respectively. We performed the ChIP-chip experiments for H3K4me3, H3K9Ac, RNA polymerase II (S5-P) and RNA polymerase II (S2-P) from U251 cells transfected with p53-specific siRNA or control siRNA (2 biological replicates each). To analyze binding of mutant p53 to the genes covered by the tiling array we performed mutant p53 ChIP-chip experiments in 4 biological replicates of. In addition, we analyzed the distribution of SP1 and ETS1 binding sites in 3 biological replicates.
Project description:The p53-regulated long non-coding RNA, lincRNA-p21, has been proposed to promote apoptosis and to repress in trans the expression of genes in the p53 transcriptional network. Here, we report the generation of a conditional knockout mouse model developed to further examine lincRNA-p21 function. Using this genetic approach, we find that the primary function of lincRNA-p21 is to activate in cis the expression of its neighboring gene, the cyclin-dependent kinase inhibitor p21. Mechanistically, we show that lincRNA-p21 acts in concert with hnRNP-K as a co-activator for p53-dependent transcription of p21. Additional phenotypes of lincRNA-p21 deficiency, including deregulated expression and altered chromatin state of a set of Polycomb target genes, defective G1/S checkpoint, increased proliferation rates, and enhanced reprogramming efficiency could be attributed to diminished p21 levels. This study reveals a novel paradigm, whereby the long non-coding RNA lincRNA-p21 affects global gene expression and influences events in the p53 tumor suppressor pathway by acting in cis as a locus-restricted transcriptional co-activator for p53-mediated expression of p21. Examination of 2 different histone modifications (H3K4me3 and H3K27me3) in 2 cell types (WT and lincRNA-p21 KO) in the presence and absence of Doxorubicin.
Project description:ChIP-chip study using Saos-2 cell line infected with adenoviruses encoding GFP (Mock) or GFP together with the p53 H1 helix mutants EL or RE. DNA-protein-complexes were precipitated with monoclonal p53-antibody (clone DO-1). Mock-chromatin was immunoprecipitated in the absence of antibody.<br>Three completely independent biological replicates were performed for each antibody, obtaining the corresponding input as total genomic DNA reference. Hybridizations were performed using Affymetrix GeneChip Human Tiling 2.0R Array set (7 arrays set).<br><br> Affymetrix .BAR files and an additional processed data file containing the coordinates of the identified binding sites can be found in the FTP directory for this experiment. <A HREF="ftp://ftp.ebi.ac.uk/pub/databases/microarray/data/experiment/MEXP/E-MEXP-1748">FTP directory</A>
Project description:Chromatin Immunoprecipitation of Centromeric Proteins, CenpA, CenpC or CenpH from human cell lines containing a neocentromere in band 13q32<br><br>Processed data files with additional statistics are available for download from <a href="ftp://ftp.ebi.ac.uk/pub/databases/microarray/data/experiment/TABM/E-TABM-238/">ftp://ftp.ebi.ac.uk/pub/databases/microarray/data/experiment/TABM/E-TABM-238</a>
Project description:Heterochromatin protein 1 (HP1) proteins are important regulators of heterochromatin mediated gene silencing and chromosome structure and it is well known as the reader of the heterochromatin mark methylation of histone H3 lysine 9 (H3K9me). In Drosophila three different histone lysine methyl transferases (HKMTs) are associated with the methylation of H3K9; Su(var)3-9, Setdb1 and G9a. To gain insights on the dependence of HP1a on the three different HKMTs, the division of labor between these methyl transferases and the dependence of HP1a on H3K9me we have studied HP1a binding in relation to H3K9me in mutants of these HKMTs. We show that Su(var)3-9 is responsible for the HP1a H3K9me-dependent binding in pericentromeric regions while Setdb1 controls the HP1a H3K9me-dependent binding to cytological region 2L:31 and together with POF chromosome 4. HP1a binds to the promoters and within gene bodies of active genes in these three regions. More importantly, HP1a bound at promoters of active genes are independent of H3K9me and POF and is associated to heterochromatin protein 2 (HP2) and open chromatin. Our results supports a model where HP1a nucleates with high affinity independent of H3K9me in promoters of active genes and then spreads via H3K9 methylation and transient looping contacts with those H3K9me target sites. In total 44 samples; 2 replicates for each genotype and for each ChIP (HP1a, H3K9me2 and H3K9me3)
Project description:Cellular metabolism and chromatin landscape both contribute to cell fate determination. However, their interplay remains poorly understood. Here we show that Prohibitin (PHB), an evolutionarily conserved protein, involves in a histone variant H3.3 chaperon HIRA complex-dependent epigenetic and metabolic circuitry to maintain the identity of human embryonic stem cells (hESCs). We found that silencing of PHB triggers hESC differentiation with concomitant enhancements of histone 3 (H3) lysine (K) methyl modifications as a result of the reduced production of α-ketoglutarate (α-KG), a metabolite required for activities of many dioxygenase and in turn chromatin structure1,2. Mechanistically, PHB acts as a functional member of the HIRA complex3,4. Resembling PHB deficiency, loss of HIRA in hESCs leads to massive differentiation and aberrant histone modifications, although it was previously found not to disrupt the self-renewal in mouse ESCs (mESCs)5. Genome-wide H3.3 ChIP- sequence analyses indicate that reduction of H3.3 deposition caused by PHB knock down is extremely similar to that induced by HIRA knock down. Specifically, silencing either HIRA or PHB leads to repressive chromatin characters at promoters of pluripotency genes and isocitrate dehydrogenases (IDHs), the enzyme responsible for α-KG production, but active chromatin features at promoters of developmental genes, paralleling to transcript levels of these genes. Our results identify PHB as an essential factor not only for hESC self-renewal but also for the proper function of the HIRA complex, linking the HIRA complex-dependent H3.3 deposition to the production of a critical metabolite required for shaping chromatin structure, and demonstrating the importance of the interplay between epigenetic state and metabolic regulation in cell fate determination. Examination of H3.3 deposition in NT, PHB, and HIRA siRNA treated hESCs respectively.
Project description:In Drosophila melanogaster, two chromosome-specific targeting and regulatory systems have been described. The male-specific lethal (MSL) complex supports dosage compensation by stimulating gene expression from the male X-chromosome and the protein Painting of fourth (POF) specifically targets and stimulates expression from the heterochromatic 4th chromosome. The targeting sites of both systems are well characterized, but the principles underlying the targeting mechanisms have remained elusive. Here we present an original observation, namely that POF specifically targets two loci on the X-chromosome, PoX1 and PoX2 (POF-on-X). PoX1 and PoX2 are located close to the roX1 and roX2 genes, which encode ncRNAs important for the correct targeting and spreading of the MSL-complex. We also found that the targeting of POF to PoX1 and PoX2 is largely dependent on roX expression and identified a high-affinity target region which ectopically recruits POF. The results presented support a model linking the MSL-complex to POF and dosage compensation to regulation of heterochromatin. POF salivary glands ChIP
Project description:We recently developed a high-resolution genome wide assay for mapping DNA excision repair named eXcision Repair-sequencing (XR-seq) (GEO accession: GSE67941) We have now used this assay to assay the effect of chromatin state on DNA repair. Here we report the results of a time-course of the repair of the UV induced damages cyclobutane pyrimidine dimers (CPDs) and (6-4) pyrimidine-pyrimidone photoproducts [(6-4)PPs] in normal human skin fibroblasts. Comparison of this data to histone modification and DNA-seq maps (ENCODE) revealed initial repair of both damages is enriched in open and active chromatin states, whereas repair in heterochromatic and repressed chromatin states is relatively low and persists to later time points. We performed XR-seq for two types of UV induced damages (CPD and (6-4)PP) at multiple time points after UV irradiation, in normal NHF1, and CS-B (CS1ANps3g2, GM16095) fibroblast cell lines. Two biological replicates were performed for each experiment in which independent independent cell populations were UV treated and subjected to XR-seq. For assaying CPD repair, cells were irradiated with 10J/m2 and for assaying (6-4)PP cells were irradiated with 20J/m2. Raw data for the 1h time points of (6-4)PP repair are the same as in GEO accession GSE67941).
Project description:SPOC1 is a chromatin affiliated protein with a functional role in stem cell differentiation, cell division, DNA damage response and higher order chromatin organization. To gain insight into SPOC1’s ability to modulate these processes, we elucidated the mechanisms targeting SPOC1 to chromatin and its genome wide localization. Our results demonstrate that SPOC1 binds chromatin in a multivalent fashion via its PHD domain and a centrally located domain, which interact with H3K4me2/3 and DNA, respectively. Consistently, the 3-dimensial structure of SPOC1’s PHD domain in complex with an H3K4me3 peptide could be solved. ChIP sequencing of SPOC1 in murine ES cells revealed an extensive co-occurrence with H3K4me2/3, DNAse hypersensitivity sites and Polycomb at key metabolic, cell cycle and developmental targets. Furthermore RNA sequencing demonstrated that a substantial fraction of these targets were either up or down regulated after SPOC1 depletion. Together these data identify SPOC1 as a bona fide H3K4me2/3 molecular reader and transcriptional regulator of diverse chromatin functions.