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Genome-wide chromatin occupancy of transcription factor TBX2 in luminal breast cancer cells

ABSTRACT: Here we demonstrate a previously unknown mechanism of TBX2-mediated gene repression in breast tumours, whereby TBX2 physically interacts with CoREST-associated proteins LSD1, HDAC1 and the ZNF217 oncogene. Through Chromatin Immunoprecipitation sequencing (ChIP-seq) we find that while over 80% of TBX2 binding sites are concentrated at promoters, these regions show remarkably no enrichment for the T-box element; rather TBX2-bound regions are biased toward a small number of non-T-box motifs, with the most abundant being Specificity Protein 1 (Sp1), EGR1 and Nuclear Transcription Factor Y (NF-Y). Furthermore, we uncover that Sp1 is crucial for recruitment of TBX2 to the NDRG1 promoter and subsequent repression of this gene. We also observe that ZNF217 cooccupies approximately 30% of TBX2-bound sites, a number of which contain RCOR1 and exhibit upregulation of the associated transcripts following disruption of TBX2/CoREST function. Overall these data highlight a novel potential therapeutic opportunity whereby poor-prognosis, TBX2 overexpressing breast tumours may be pharmacologically exploited by targeting the CoREST-dependent gene repression network, to recover normal growth control.

ORGANISM(S): Homo sapiens

PROVIDER: GSE180213 | GEO | 2022/05/23

REPOSITORIES: GEO

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Project description:The mouse auditory organ cochlea contains two types of sound receptors: inner hair cells (IHCs) and outer hair cells (OHCs). Tbx2 is expressed in IHCs but repressed in OHCs, and neonatal OHCs that misexpress Tbx2 transdifferentiate into IHC-like cells. However, the extent of this switch from OHCs to IHC-like cells and the underlying molecular mechanism remain poorly understood. Furthermore, whether Tbx2 can transform fully mature adult OHCs into IHC-like cells is unknown. Here, our single-cell transcriptomic analysis revealed that in neonatal OHCs misexpressing Tbx2, 85.6% of IHC genes, including Slc17a8, are upregulated, but only 38.6% of OHC genes, including Ikzf2 and Slc26a5, are downregulated. This suggests that Tbx2 cannot fully reprogram neonatal OHCs into IHCs. Moreover, Tbx2 also failed to completely reprogram cochlear progenitors into IHCs. Lastly, restoring Ikzf2 expression alleviated the abnormalities detected in Tbx2+ OHCs, which supports the notion that Ikzf2 repression by Tbx2 contributes to the transdifferentiation of OHCs into IHC-like cells. Our study evaluates the effects of ectopic Tbx2 expression on OHC lineage development at distinct stages of either male or female mice and provides molecular insights into how Tbx2 disrupts the gene-expression profile of OHCs. This research also lays the groundwork for future studies on OHC regeneration.Significance Statement Elucidation of the molecular and genetic mechanisms governing the determination and stability of cochlear inner hair cells (IHCs) and outer hair cells (OHCs) should provide valuable insights into the regeneration of damaged IHCs and OHCs. Here, we conditionally overexpress Tbx2 in vivo in cochlear sensory progenitors, neonatal OHCs, or adult OHCs. Our results show that Tbx2 overexpression alone can partially destabilize the OHC fate but cannot fully convert OHCs into IHCs. Specifically, we demonstrate that Ikzf2 repression due to Tbx2 overexpression is one of the key pathways disrupting the OHC fate.

Project description:Rationale: A critical step in heart development is the coordinated formation of nodal myocardium and cushion tissue from the atrioventricular canal (AVC). After its specification, the myocardium of the AVC aligns the chambers, forms the AV node, and induces the formation of the mesenchymal AV cushions, primordia of valves and septa, while it resists working myocardial differentiation. Objective: To assess what roles Tbx2 and Tbx3, two closely related T-box transcription factors expressed in the AVC, play in these processes. Methods and Results: We analyzed mice ectopically expressing Tbx3 in the atrial myocardium by genome-wide microarray and expression analysis. We found a prominent role for Tbx3 in defining the nodal phenotype by repressing working myocardial genes (sarcomeric, mitochondrial, fast conduction) and cell proliferation regulators, and in inducing node-associated genes. Moreover, there was a striking induction of genes associated with endocardial cushions and mesenchyme. Using gain-of-function models, we found that in the developing heart both Tbx2 and Tbx3 induce ectopic Bmp2 and Tgfb2 expression and endocardial cushion formation. Analysis of compound Tbx2/Tbx3 mutant embryos revealed that upon loss of more than two functional alleles, expansion of the AV myocardium does not occur and AV cushions fail to form. Conclusions: Tbx2 and Tbx3 locally stimulate development of the AVC myocardium, induce the AV nodal phenotype therein and trigger AV cushion formation from the overlying AV endocardium, providing a mechanism for the colocalization and coordination of these two important processes in heart development. Nppa-Cre4 (Cre4) mice were crossed with CT mice to obtain efficient activation of Tbx3 in atria of double transgenic Cre4-CT mice, as previously described (Hoogaars et al., 2007). To investigate the gene expression profile of atria of Cre4-CT mice, we performed whole genome microarray analysis using Sentrix Mouse-6 oligonucleotide beadchips. We compared the atrial gene expression profiles of six male double transgenic Cre4-CT mice and six male Cre4 control mice.

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Genome-wide chromatin occupancy of transcription factor TBX2 in luminal breast cancer cells

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