Project description:The effects of diverse stresses on promoter selectivity and transcription regulation by the tumor suppressor p53 are poorly understood. We have taken a comprehensive approach to characterizing the human p53 network that includes p53 levels, binding, expression and chromatin changes under diverse stresses. Human osteosarcoma U2OS cells treated with anti-cancer drugs Doxorubicin or Nutlin-3 led to strikingly different p53 gene binding patterns based on ChIP-seq experiments. While two contiguous RRRCWWGYYY decamers is the consensus binding motif, p53 can bind a single decamer and function in vivo. Although the number of sites bound by p53 was 6-times greater for Nutlin-3 than Doxorubicin, expression changes induced by Nutlin-3 were much less dramatic compared to Doxorubicin. Unexpectedly, the solvent DMSO alone induced p53 binding to many sites common to Doxorubicin; however, this binding had no effect on target gene expression. Together, these data imply a two-stage mechanism for p53 transactivation where p53 binding only constitutes the first stage. Furthermore, both p53 binding and transactivation were associated with increased active histone modification H3K4me3. We discovered 149 putative new p53 target genes including several that are relevant to tumor suppression, revealing potential new targets for cancer therapy and expanding our understanding of the p53 regulatory network. Gene expression analysis (using Affymetrix Human Genome U133 Plus 2.0 GeneChip® arrays) of the p53 response in U2OS cells treated with either Doxorubicin or Nutlin-3, relative to their controls No Treatment and DMSO, respectively.
Project description:The effects of diverse stresses on promoter selectivity and transcription regulation by the tumor suppressor p53 are poorly understood. We have taken a comprehensive approach to characterizing the human p53 network that includes p53 levels, binding, expression and chromatin changes under diverse stresses. Human osteosarcoma U2OS cells treated with anti-cancer drugs Doxorubicin or Nutlin-3 led to strikingly different p53 gene binding patterns based on ChIP-seq experiments. While two contiguous RRRCWWGYYY decamers is the consensus binding motif, p53 can bind a single decamer and function in vivo. Although the number of sites bound by p53 was 6-times greater for Nutlin-3 than Doxorubicin, expression changes induced by Nutlin-3 were much less dramatic compared to Doxorubicin. Unexpectedly, the solvent DMSO alone induced p53 binding to many sites common to Doxorubicin; however, this binding had no effect on target gene expression. Together, these data imply a two-stage mechanism for p53 transactivation where p53 binding only constitutes the first stage. Furthermore, both p53 binding and transactivation were associated with increased active histone modification H3K4me3. We discovered 149 putative new p53 target genes including several that are relevant to tumor suppression, revealing potential new targets for cancer therapy and expanding our understanding of the p53 regulatory network.
Project description:The effects of diverse stresses on promoter selectivity and transcription regulation by the tumor suppressor p53 are poorly understood. We have taken a comprehensive approach to characterizing the human p53 network that includes p53 levels, binding, expression and chromatin changes under diverse stresses. Human osteosarcoma U2OS cells treated with anti-cancer drugs Doxorubicin or Nutlin-3 led to strikingly different p53 gene binding patterns based on ChIP-seq experiments. While two contiguous RRRCWWGYYY decamers is the consensus binding motif, p53 can bind a single decamer and function in vivo. Although the number of sites bound by p53 was 6-times greater for Nutlin-3 than Doxorubicin, expression changes induced by Nutlin-3 were much less dramatic compared to Doxorubicin. Unexpectedly, the solvent DMSO alone induced p53 binding to many sites common to Doxorubicin; however, this binding had no effect on target gene expression. Together, these data imply a two-stage mechanism for p53 transactivation where p53 binding only constitutes the first stage. Furthermore, both p53 binding and transactivation were associated with increased active histone modification H3K4me3. We discovered 149 putative new p53 target genes including several that are relevant to tumor suppression, revealing potential new targets for cancer therapy and expanding our understanding of the p53 regulatory network.
Project description:To determine if induced p53 binding is associated with gene expression in genome-wide. We examined mRNA levels with the Affymetrix Human Exon 1.0 ST platform in human lymphoblastoid GM12878 cells treated with doxorubicin to activate p53. In response to various cellular stresses, the tumor suppressor gene p53 induces activation or repression of more than a thousand human genes. Selective binding and transactivation of a large potential pool of p53 response elements (REs) is believed to regulate the variation in stress response across stress types and between cell types. To elucidate how the human genome is targeted by p53 at the chromatin level, we mapped the genome-wide localization of p53 and H3K4me3 from Doxo-treated human lymphoblastoid cells, and examined the relationships among p53 occupancy, gene expression, H3K4me3, chromatin accessibility (DNase 1 Hypersensitivity, DHS), ENCODE chromatin states, RE sequence specificity and evolutionary conservation.
Project description:As HBx has been reported to interact with p53 and alter the recruitment of p53 to its binding sites, we obtained a comprehensive genome-wide profile of deregulated p53 transcription complex-DNA binding by the HBx protein using massively parallel deep sequencing coupled to p53 chromatin immunoprecipitation (ChIP-Seq) on HBx-expressing and control HepG2 liver cell culture model system.
Project description:We report here genome-wide analysis of the tumor suppressor p53 binding sites in normal human cells. 743 high-confidence ChIP-seq peaks representing putative genomic binding sites were identified in normal IMR90 fibroblasts using a reference chromatin sample. More than 40 % were located within 2 kb of a transcription start site (TSS), a distribution similar to that documented for individually studied functional p53 binding sites and to date not observed by previous genome-wide studies. Nearly half of the high-confidence binding sites in the IMR90 cells reside in CpG islands, in marked contrast to sites reported in cancer-derived cells. The distinct genomic features of the IMR90 binding sites do not reflect a distinct preference for specific sequences, since the de novo developed p53 motif based on our study is similar to those reported by genome-wide studies of cancer cells. More likely the different chromatin landscape in normal compared to cancer-derived cells influences p53 binding via modulating availability of the sites. We compared the IMR90 ChIP-seq peaks to the recently published IMR90 methylome1, and demonstrated that they are enriched at hypomethylated DNA. Our study represents the first genome-wide, de novo mapping of p53 binding sites in normal human cells and reveals that p53 binding sites reside in distinct genomic landscapes in normal and cancer-derived human cells. Identification of genomic p53 binding sites in normal human cells by ChIP-seq.
Project description:To determine if induced p53 binding is associated with gene expression in genome-wide. We examined mRNA levels with the Affymetrix Human Exon 1.0 ST platform in human lymphoblastoid GM12878 cells treated with doxorubicin to activate p53. In response to various cellular stresses, the tumor suppressor gene p53 induces activation or repression of more than a thousand human genes. Selective binding and transactivation of a large potential pool of p53 response elements (REs) is believed to regulate the variation in stress response across stress types and between cell types. To elucidate how the human genome is targeted by p53 at the chromatin level, we mapped the genome-wide localization of p53 and H3K4me3 from Doxo-treated human lymphoblastoid cells, and examined the relationships among p53 occupancy, gene expression, H3K4me3, chromatin accessibility (DNase 1 Hypersensitivity, DHS), ENCODE chromatin states, RE sequence specificity and evolutionary conservation. Human lymphoblastoid (GM 12878) cells at a density of 900,000 cells/ml were prepared in triplicate for each time point and treated with 0.5 µM doxorubicin (Calbiochem) for 4, 18 hr or no treatment (at 0 time). Total RNA will be extracted from each culture (9 RNA samples) using the Qiagen RNeasy kit with DNase digestion. RNA was quantified using RiboGreen (Invitrogen), check for quality by OD and Bioanalyzer and stored at -80°C. Expression analysis was conducted at at NIEHS Microarray Core using Affymetrix Human Exon 1.0 ST arrays following the Affymetrix hybridization protocols. Exon expression data were analyzed through Affymetrix Expression Console using gene-level RMA summarization and sketch-quantile normalization methods.