Online

Moskovitz, Eliana

Pharmacology

2020

M.S.

Disruption of normal mammary epithelial cell homeostasis through acquisition of deleterious somatic and/or germline mutations leads to breast cancer development. Breast cancer is the most commonly diagnosed cancer among women worldwide, and is associated with the second highest amount of cancer-related deaths. Breast cancer mortality rates are decreasing, likely through increased methods of detection and development of targeted therapies. However, due to the complexity and heterogeneity of the disease, the incidence rate remains high and the molecular events that lead to breast cancer initiation and progression are poorly understood. The epithelial-to-mesenchymal transition (EMT) is an essential molecular process involved in the initiation and progression of epithelial-based tumors. Loss of cell-cell connections, altered extracellular matrix interactions, and dramatic cytoskeletal changes promote cell individuality and development of a migratory and often invasive phenotype. Under normal physiological conditions, EMT is involved in processes such as embryonic development and wound healing. EMT is tightly regulated by a combination of signaling pathways and epigenetic factors. However, the molecular mechanisms that suppress EMT within the normal epithelium to prevent tumorigenesis remain understudied. Mitotic gene bookmarking -- retention of cell lineage-specific transcription factors with target genes, together with histone modifications, specific DNA methylation patterns, and components of transcriptional machinery on mitotic chromosomes -- is an epigenetic mechanism that maintains cellular identity throughout successive cell divisions. Mitotic occupancy and post-mitotic transcription regulation of target genes involved in proliferation, growth, and cellular identity by transcription factors, reestablishes epithelial-specific transcriptional programs in newly formed progeny cells. The RUNX1-CBF[Beta] heterodimeric transcription factor complex is essential for normal mammary gland development. Mutations in both subunits have been identified in breast cancers. Studies by our group have shown that RUNX proteins act as mitotic bookmarks in a variety of tissue types and depletion of RUNX1 in normal mammary epithelial cells leads to EMT. Findings reported in this study show that inhibition of the RUNX1-CBF[Beta] interaction disrupts the normal mammary epithelial phenotype, alters cell cycle regulation, and initiates EMT. Furthermore, results demonstrate RUNX1 is maintained on mitotic chromosomes during all topologically identifiable stages of mitosis in live MCF10A cells. Conditions and methods have been optimized to study the specific function of the RUNX1-CBF[Beta] transcription factor complex as a mitotic bookmark, essential for mitotic and post-mitotic transcriptional regulation of genes involved in proliferation, cell growth, and epithelial cell identity throughout successive cell divisions. Further studies utilizing these conditions and methods are required to address the functional role of the RUNX1-CBF[Beta] transcription factor complex as an essential mitotic bookmark involved in phenotypic maintenance in the normal mammary epithelium.