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Maintenance of mammary epithelial phenotype by AML1/RUNX1 through mitotic gene bookmarking

ABSTRACT: Genetic and epigenetic changes in mammary epithelial cells facilitate epithelial-to-mesenchymal transition (EMT) which leads to invasion and metastasis. RUNX1 is a phenotypic transcription factor pivotal for maintenance of mammary epithelial phenotype, whose loss leads to EMT. However, the mechanisms by which RUNX1 maintains mammary epithelial phenotype are not known. Here, we report RUNX1-mediated mitotic gene bookmarking as a key epigenetic mechanism through which RUNX1 stabilizes mammary epithelial phenotype by conveying regulatory information for cell proliferation, growth, and identity through successive cell divisions. Immunofluorescence microscopy and chromatin immunoprecipitation with high throughput sequencing of asynchronous, mitotic, and G1 MCF10A breast epithelial cells revealed RUNX1 association with target genes through interphase and mitosis. RUNX1 mitotically bookmarked both RNA Pol and II transcribed genes involved in proliferation, growth, and mammary epithelial phenotype maintenance. Inhibition of RUNX1 DNA binding by a specific small molecule inhibitor led to phenotypic changes, apoptosis, and differential expression of ribosomal RNA as well as protein coding genes (e.g. HES1 and H2AFX) and long non-coding RNA (e.g. NEAT1 and MALAT1) genes involved in cellular phenotype. Together these findings reveal a novel epigenetic regulatory role of RUNX1 in normal-like breast epithelial cells and demonstrate mitotic bookmarking target genes by RUNX1 is necessary to maintain breast epithelial phenotype. Disruption of RUNX1 bookmarking by a pharmacological inhibitor results in initiation of epithelial to mesenchymal transition, an essential first step in the onset of breast cancer.

ORGANISM(S): Homo sapiens

PROVIDER: GSE121370 | GEO | 2020/07/14

REPOSITORIES: GEO

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Project description:Purpose: to characterize epigenetic changes following Twist1 mediated Epithelial-Mesenchymal Transition in human Methods: we characterized the epigenetic and transcriptome landscapes using whole genome transcriptome analysis by RNA-seq, DNA methylation by digital restriction enzyme analysis of methylation (DREAM) and histone modifications by CHIP-seq of H3K4me3 and H3K27me3 in immortalized human mammary epithelial cells relative to cells induced to undergo EMT by Twist1. Results: EMT is accompanied by focal hypermethylation and widespread global DNA hypomethylation, predominantly within transcriptionally repressed gene bodies. At the chromatin level, the number of gene promoters marked by H3K4me3 increases by more than one fifth; H3K27me3 undergoes dynamic genomic redistribution characterized by loss at half of gene promoters and overall reduction of peak size by almost one-half. This is paralleled by increased phosphorylation of EZH2 at serine 21. Among genes with highly altered mRNA expression, 23.1% switch between H3K4me3 and H3K27me3 marks, and those point to the master EMT targets and regulators CDH1, PDGFRA and ESRP1. Strikingly, Twist1 increases the number of bivalent genes by more than two fold. Inhibition of the H3K27 methyltransferases EZH2 and EZH1, which form part of the PRC2 complex, results in blocking EMT and stemness properties. Conclusion: Our findings demonstrate that the EMT program requires epigenetic remodeling by the Polycomb/Trithorax complexes leading to increased cellular plasticity which suggests that its inhibition will prevent EMT, and the associated breast cancer metastasis. DREAM profiles of human mammary epithelial cells before (HMLE_parental) and after Twist1 transfection (HMLE_Twist) were generated in monolayer (HMLE_Twist2D) and sphere culture by deep sequencing using Illumina GAIIx or Illumina hiseq2000. Furthermore, DREAM profile was also obtained in parental human mammary epithelial cells transfected with GFP

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Maintenance of mammary epithelial phenotype by AML1/RUNX1 through mitotic gene bookmarking

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