AbstractColorectal cancer (CRC) is the second most common cause of cancer-related death in the UK and Western world. More than 90% of sporadic CRCs harbour mutations in the multi-functional tumour suppressor gene Adenomatous polyposis coli (Apc). The most commonly studied function of APC is its role as a scaffold for the β-catenin destruction complex involved in Wnt signalling. However, APC binds many other proteins. For example, it directly binds to and stabilises microtubules and actin. These non-Wnt related functions of APC are poorly understood.
My PhD examines non-Wnt functions of APC. To this end, I created degron-tagged APC in DT40 cells that allowed for the rapid, conditional degradation of endogenous APC. The aim was to identify the immediate effects on cellular processes. Then, to identify the contribution of different APC domains by measuring the ability to rescue any defects when reintroducing fragments of APC. However, creation of these degron-tagged Apc knock-in cell lines resulted in hypomorphic phenotypes and auxin-associated off-target effects. Nonetheless, I compared the response of APChigh, APClow, and APCminimal cells to DNA damaging agents and Taxol® but found no significant differences.
Subsequently, I focused on the relationship between APC and apoptosis. Previous observations suggested that deficiency in Apc rendered cells less sensitive to low doses of Taxol®. However, Apc deficient cells were more readily killed when Taxol® was combined with the Bcl-2 inhibitor, ABT-737. One possible explanation is the increase in Bcl-2 protein upon Apc depletion. However, I found that ABT-737, Taxol® and Apc depletion each cause activation of the unfolded protein response. This suggests that these treatments elicit a stress response that can stimulate apoptosis. Moreover, the same treatments also cause changes in mitochondria. Importantly, all of these effects do not require an increase in the β-catenin protein. Together, my data reveal novel links between APC and apoptosis that could be exploited clinically.
|Date of Award||2016|
|Supervisor||Kevin Hiom (Supervisor) & Inke Nathke (Supervisor)|
- Colorectal cancer
- Unfolded protein response