GSE121370
Maintenance of mammary epithelial phenotype by AML1/RUNX1 through mitotic gene bookmarking
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. Overall design: Investigation of RUNX1 binding sites within asynchronous, mitotic, and G1 MCF10A breast epithelial cells