Year: 2019
Type: dissertation
Abstract: Despite being one of the most genetically understood cancers, colorectal cancer is still one of the leading causes of death due to cancer. Here we focus on two mechanisms of chemoresistance in colorectal cancer; the increased antioxidant response of colorectal cancer-initiating cells (CC-ICs) and the aggregation of p53. Most CRCs contain a subset of self-renewing CC-ICs responsible for tumor initiation and maintenance that are chemoresistant compared to the bulk tumor cell population. The overexpression of Nrf2, the master regulator of the antioxidant response system, allows for the detoxification of chemotherapy and increased CC-IC survival. We show that CRC cells upregulate their antioxidant activity in response to chemotherapy and that CC-IC self-renewal is dependent on Nrf2 function where genetic knockdown of Nrf2 results in decreased CC-IC frequency in vitro. Since transcription factors like Nrf2 are difficult to target, we instead targeted mechanisms that regulate Nrf2 activity. Nrf2 is significantly correlated with the epigenetic regulator histone acetyl transferase (HAT1) and studies show that acetylation of Nrf2 promotes enhanced Nrf2 activity. Treating CC-IC enriched Nrf2 knockdown cells with chemotherapy results in HAT1 upregulation. Furthermore, treating CC-IC enriched HAT1 knockdown cells with chemotherapy caused increased cell death and a decrease in CC-IC frequency in vitro. Another mechanism of CRC chemoresistance is the aggregation of p53, causing the loss of its pro-apoptotic function. It has previously been established that CBP/p300 bromodomain inhibition decreases protein amyloid-like aggregation. CBP/p300 regulates p53 through its acetylation, ubiquination, and bromodomain activity, however it has never been shown that CBP/p300 bromodomain inhibition results in a decrease in p53 disaggregation. We show that treatment of mutant p53 CRC cells with 5FU increases p53 aggregation and acetylation of p53 lysine K382, a binding site for the CBP/p300 bromodomain. By treating cells with the CBP/p300 bromodomain inhibitor, SGC CBP30 (CBP30), we decreased 5FU-induced p53 aggregation and restored the pro-apoptotic function of p53. p53 mutant cells treated with CBP30 became more sensitive to 5FU, while CBP30 had no significant effect on CRC viability in p53 knockdown cell lines. Therapeutically targeting mechanisms that drive chemoresistance in CRC will improve chemotherapeutic response and decrease relapse in CRC patients.
Source: TSpace (University of Toronto)
Author: Lauren Alicia Agro
Language: English
Subfield: Molecular Biology
Domain: Life Sciences
Open Access status: green
OpenAlex ID: W2998020000