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Genome-wide profiling of H3K56 acetylation and transcription factor binding sites in human adipocytes

ABSTRACT: We use ChIP-seq to discover the genome-wide sites of acetylation of lysine 56 of the histone H3 (H3K56), which is a target of three histone modifying enzymes with known roles in diabetes and insulin resistance, in human adipocytes derived from mesenchymal stem cells. Surprisingly, we find that a very large fraction of genes show some level of acetylation on H3K56, but the highest levels of acetylation are associated with genes previously reported to be involved in type 2 diabetes. Using computational methods, we propose that the transcription factor E2F4 may be involved in recruiting histone modifying enzymes to these sites. We confirm this prediction by measuring the binding of E2F4 using ChIP-seq. We also examine the binding of two other proteins using ChIP-Seq: HSF-1 and C/EBPα . HSF-1 is a master regulator of stress responses, and is a target of the same histone modifiers as H3K56. We find a high degree of overlap between HSF-1 binding and H3K56 acetylation even in cells that are not stressed. By contrast, C/EBPα , which is not known to be modified by these enzymes, shows much less overlap with the sites of H3K56 acetylation. Our results represent the first mapping of the regulatory code of human adipocytes.

ORGANISM(S): Homo sapiens

PROVIDER: GSE24326 | GEO | 2011/05/31

SECONDARY ACCESSION(S): PRJNA132733

REPOSITORIES: GEO

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Project description:DNA sequence and local chromatin landscape act jointly to determine transcription factor (TF) binding intensity profiles. To disentangle these influences, we developed an experimental approach, called protein/DNA binding and high-throughput sequencing (PB-seq), that allows the binding energy landscape to be characterized genome-wide in the absence of chromatin. We applied our methods to the Drosophila Heat Shock Factor (HSF), which inducibly binds a target DNA sequence element (HSE) following heat shock stress. PB-seq involves incubating sheared naked genomic DNA with recombinant HSF, partitioning the HSF-bound and HSF-free DNA, and then detecting HSF-bound DNA by high throughput sequencing. We compared PB-seq binding profiles with ones observed in vivo by ChIP-seq, and developed statistical models to predict the observed departures from idealized binding patterns based on covariates describing the local chromatin environment. We found that DNase I hypersensitivity and tetra-acetylation of H4 were the most influential covariates in predicting changes in HSF binding affinity. We also investigated the extent to which DNA accessibility, as measured by digital DNase I footprinting data, could be predicted from MNase-seq data and the ChIP-chip profiles for many histone modifications and TFs, and found GAGA element associated factor (GAF), tetra-acetylation of H4, and H4K16 acetylation to be the most predictive covariates. Lastly, we generated an unbiased model of HSF binding sequences, which revealed distinct biophysical properties of the HSF/HSE interaction and a previously unrecognized substructure within the HSE. These findings provide new insights into the interplay between the genomic sequence and the chromatin landscape in determining transcription factor binding intensity. We performed an in vitro binding experiment with purified HSF and naked, sheared genomic Drosophila S2 DNA (PB-seq), to derive an accurate set of potential HSF binding sites in the Drosophila genome. HSF-bound DNA was specifically eluted and detected by high throughput sequencing. Drosophila HSF was N-terminally tagged with glutathione s-transferase and a tobacco etch virus (TEV) protease cleavage site. The C-terminus of the recombinant HSF was fused to the 3xFLAG epitope. Recombinant HSF was purified from E. coli with glutathione resin as previously described (PMID: 20078429) , with the following modifications: HSF-3xFLAG elution was achieved by addition of 6xHistidine tagged TEV protease and TEV protease was cleared from the HSF preparation using a Nickel-NTA column. We incubated 600pM HSF and 2500ng genomic DNA (sonicated to 100-600bp fragment size as previously described in PMID: 20844575) in 1500μl final volume of 1xHSF binding buffer and let it come to equilibrium for an hour at room temperature. We added 20μl ANTI-FLAG M2 affinity gel for 10 minutes, washed 8 times with 1xHSF binding buffer to remove unbound DNA; 3xFLAG peptide was added to a final concentration of 200ng/μl to specifically elute HSF and HSF-bound DNA. The mock IP was done in the absence of recombinant HSF.

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Genome-wide profiling of H3K56 acetylation and transcription factor binding sites in human adipocytes

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