Colorectal cancer (CRC) is the third leading cause of cancer-related deaths among both men and women in the United States, with an estimated 53,200 deaths in 2020 (Siegel, Miller, & Jemal, 2020). Our lab identified Cystic Fibrosis Transmembrane Regulator (CFTR) as a CRC tumor suppressor gene in mice and humans. However, the mechanism by which CFTR acts as a tumor suppressor gene in CRC is unknown. To identify potential pathways, we compared gene expression in CFTR-low expressing CRC vs. CFTR high expressing tumors in several publicly available databases using gene set enrichment analysis. These analyses revealed that a common subset of genes is responsive in CFTR-low expressing tumors and in HIF1α-high tumors. HIF1α protein is induced by oxidative stress and is known to play a protective role in the oxidative stress pathway. To investigate the significance of this correlation, I hypothesized that downregulation of CFTR protects against oxidative stress. To test this hypothesis, I compared cell viability in human Caco-2 CRC cell lines: one in which CFTR has been knocked out by CRISPR-Cas9 modification (CFTR-KO) vs. matched parental controls (CFTR-WT). Each cell line was treated with menadione to induce oxidative stress. When cell viability was measured using an MTT assay, a trend was observed, where CFTR-KO cells were less affected by menadione than CFTR-WT. This suggests that CFTR deficiency may help colon cancer cells to survive better in an oxidative stress environment. To determine if CFTR deficiency promotes this survival of CRC cells by change in ROS levels, ROS detection assays were carried out to compare ROS levels between CFTR WT and CFTR KO cell lines. We observed a trend where CFTR-WT cells had higher ROS levels than CFTR-KO in this oxidative stress environment. This suggests that CFTR deficiency maybe promoting survival of CRC cells in an oxidative stress environment by reducing ROS levels. This work will help to better understand the role of CFTR as a tumor suppressor gene in CRC.
University of Minnesota M.S. thesis. May 2020. Major: Biology. Advisors: Patricia Scott, Robert Cormier. 1 computer file (PDF); vii, 78 pages.
Investigating The Role Of Cystic Fibrosis Transmembrane Conductance Regulator On Oxidative Stress In Colorectal Cancer.
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