Date of Award


Document Type


Degree Name

Master of Science (MS)



First Advisor

Jonathan A. Gordon


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-CBFβ 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-CBFβ 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-CBFβ 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-CBFβ transcription factor complex as an essential mitotic

bookmark involved in phenotypic maintenance in the normal mammary epithelium.



Number of Pages

123 p.