Investigating the Tumor Suppressor Role of RUNX1 in Human Breast Cancer

Breast cancer (BrCa) remains the leading cause of cancer-related deaths in women worldwide. Current research suggests that the transcription factor RUNX1 functions as a regulator and potentially as a tumor suppressor in breast cancer progression. RUNX1 is the most dominant RUNX family member expressed in normal mammary epithelial cells and it has been demonstrated that RUNX1 activity decreases as breast cancer aggression increases. Yet, the mechanism of this regulation remains unclear. The significance of this project is to further the in-depth investigation of the relationship between RUNX1 and differentially expressed genes that influence human breast cancer progression. This study addresses the hypothesis that RUNX1 controls a myriad of genes that play roles in the suppression of the breast cancer stem cell (BCSC) population, a subpopulation of cancer cells that are capable of self-renewal and demonstrate an ability to resist common chemotherapies and treatments. BCSCs are therefore the most dangerous and most essential to eradicate if the cancer is to be cured. To test this hypothesis, RUNX1 was downregulated in the MCF10A breast cancer cell line using both the inducible CRISPRi and the shRNA-mediated gene knockdown approaches. Fluorescence-activated cell sorting (FACS) and quantitative polymerase chain reaction (qPCR) confirmed successful knockdown of RUNX1 and further genetic and proteomic expression analyses of known breast cancer driver genes was performed to determine how RUNX1 depletion exerts control over the progression of BrCa. It was found that RUNX1 may aid in maintaining the epithelial phenotype in BrCa while also suppressing the expression of key BrCa driver genes such as phosphatidylinositol-3-kinases (PI3K) PIK3CA and PIK3R1. Investigating the role of RUNX1 as a suppressor of the BCSC population adds a new level of knowledge to the field of breast cancer research, and may allow development of a safer, more targeted, and more effective plan of action to eradicate one of the deadliest diseases that exists today