Genome-wide HIF-1 binding sites in HepG2 cells
Ontology highlight
ABSTRACT:
ORGANISM(S): Homo sapiens
PROVIDER: GSE16347 | GEO | 2009/06/02
SECONDARY ACCESSION(S): PRJNA116341
REPOSITORIES: GEO
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Project description:Many oncogenic transcription factors (TFs) are considered to be undruggable due to their reliance on large protein-protein and protein-DNA interfaces. TFs like hypoxia-inducible factors (HIFs) and X-box binding protein 1 (XBP1) are induced by hypoxia and other stressors in solid tumors and bind to UPRE/HRE motifs to control oncogenic gene programs. Here, we report a strategy to create synthetic transcriptional repressors (STRs) that mimic the bZIP domain of XBP1 and recognize the UPRE/HRE motif. A lead molecule, STR22, binds UPRE/HRE DNA sequences with high fidelity and competes with both TFs in cells. Under hypoxia, STR22 globally suppresses HIF1a binding to HRE-containing promoters/enhancers, inhibits hypoxia-induced gene expression and blocks pro-tumorigenic phenotypes in TNBC cells. In vivo, intratumoral and systemic STR22 treatment inhibited hypoxia-dependent gene expression, primary tumor growth and metastasis of TNBC tumors. These data validate a novel strategy to target the tumor hypoxia response through coordinated inhibition of TF-DNA binding.
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Project description:Transcription mediated by hypoxia inducible factor (HIF-1) contributes to tumor angiogenesis and metastasis but is also involved in the activation of cell-death pathways and normal physiological processes. Given the complexity of HIF-1 signaling it could be advantageous to target a subset of HIF-1 effectors rather than the entire pathway. We compared the genome-wide effects of three molecules that each interfere with the HIF-1-DNA interaction: a polyamide targeted to the hypoxia response element (HRE), siRNA targeted to HIF-1α, and echinomycin, a DNA binding natural product with a similar but less specific sequence preference to the polyamide. The polyamide affects a subset of hypoxia-induced genes that are consistent with the binding site preferences of the polyamide. For comparison, siRNA targeted to HIF-1α and echinomycin each affect the expression of nearly every gene induced by hypoxia. Remarkably, the total number of genes affected by either polyamide or HIF-1α siRNA over a range of thresholds is comparable. The data shows how polyamides can be used to affect a subset of a pathway regulated by a transcription factor. In addition, this study offers a unique comparison of three complementary approaches towards exogenous control of endogenous gene expression. Experiment Overall Design: Hypoxia-mimetic DFO (deferoxamine)-stimulated U251 cells that were treated with polyamide 1, HIF-1α siRNA, and echinomycin were compared to control cells that were also DFO-stimulated. Cells not stimulated with DFO were also compared to the DFO-stimulated controls. Three biological replicates were included for each treatment/condition.
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Project description:Hypoxia-Inducible Factor 1 (HIF-1) plays a key role in cellular adaptation to hypoxia. To better understand the determinants of HIF-1 binding and transactivation, we used ChIP-chip and gene expression profiling to define the relationship between the epigenetic landscape, sites of HIF-1 binding, and genes transactivated by hypoxia in two cell lines, HepG2 hepatoma cell line and U87 glioma cell line.
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Project description:Transcription factors (TFs) are classically attributed a modular construction, containing well-structured sequence specific DNA-binding domains (DBDs) paired with disordered activation domains (ADs) responsible for protein-protein interactions targeting cofactors or the core transcription initiation machinery. However, this simple division of labor model struggles to explain why TFs with identical DNA binding sequence specificity determined in vitro exhibit distinct binding profiles in vivo. The family of Hypoxia-Inducible Factors (HIFs) offer a stark example: aberrantly expressed in several cancer types, HIF-1α and HIF-2α subunit isoforms recognize the same DNA motif in vitro – the hypoxia response element (HRE) – but only share a subset of their target genes in vivo, while eliciting contrasting effects on cancer development and progression under certain circumstances. To probe the mechanisms mediating isoform-specific gene regulation, we used live cell single particle tracking (SPT) to investigate HIF nuclear dynamics and how they change upon genetic perturbation or drug treatment. We found that HIF-α subunits and their dimerization partner HIF-1β exhibit distinct diffusion and binding characteristics that are exquisitely sensitive to concentration and subunit stoichiometry. Using domain-swap variants, mutations, and a HIF-2α specific inhibitor, we found that although the DBD and dimerization domains are important, a major determinant of chromatin binding and diffusion behavior is dictated by the AD-containing intrinsically disordered regions (IDR). Using orthogonal genomic approaches such as Cut-and-Run and RNA-seq, we also confirmed IDR-dependent binding and activation for a specific subset of HIF-target genes. These findings reveal a previously unappreciated role of IDRs in regulating the TF search process that may play a role in selective functional target site binding on chromatin.
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Project description:Hypoxia inducible factor (HIF) is the major transcriptional regulator of cellular responses to hypoxia. The two principal HIF-a isoforms, HIF-1a and HIF-2a, are progressively stabilized in response to hypoxia and form heterodimers with HIF-1b to activate a broad range of transcriptional responses. Here we report on the pan-genomic distribution of isoform-specific HIF binding in response to hypoxia of varying severity and duration, and in response to genetic ablation of each HIF-a isoform. Our findings reveal that, despite an identical consensus recognition sequence in DNA, each HIF heterodimer loads progressively at a distinct repertoire of cell-type specific sites across the genome, with little evidence of redistribution under any of the conditions examined. Marked biases towards promoter proximal binding of HIF-1 and promoter distant binding of HIF-2 were observed under all conditions and were consistent in multiple cell type. The findings imply that each HIF isoform has an inherent property that determines its binding distribution across the genome, which might be exploited to therapeutically target the specific transcriptional output of each isoform independently.
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Project description:Transcription mediated by hypoxia inducible factor (HIF-1) contributes to tumor angiogenesis and metastasis but is also involved in the activation of cell-death pathways and normal physiological processes. Given the complexity of HIF-1 signaling it could be advantageous to target a subset of HIF-1 effectors rather than the entire pathway. We compared the genome-wide effects of three molecules that each interfere with the HIF-1-DNA interaction: a polyamide targeted to the hypoxia response element (HRE), siRNA targeted to HIF-1α, and echinomycin, a DNA binding natural product with a similar but less specific sequence preference to the polyamide. The polyamide affects a subset of hypoxia-induced genes that are consistent with the binding site preferences of the polyamide. For comparison, siRNA targeted to HIF-1α and echinomycin each affect the expression of nearly every gene induced by hypoxia. Remarkably, the total number of genes affected by either polyamide or HIF-1α siRNA over a range of thresholds is comparable. The data shows how polyamides can be used to affect a subset of a pathway regulated by a transcription factor. In addition, this study offers a unique comparison of three complementary approaches towards exogenous control of endogenous gene expression. Keywords: Gene expression changes in cultured U251 cells after DFO-stimulation and various treatment conditions
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