Investigating the role of WSB-1 in breast cancer

Breast cancer is the second most represented cancer type worldwide and will affect 1 in 8 women in the UK. Overall patient survival can reach 90% when the disease is diagnosed early but rapidly drops as the tumour progresses and metastasises. The steps required for tumour formation are known but numerous factors are involved and the specific mechanisms controlling this phenomenon are still poorly understood. WSB-1 is a hypoxia-responsive E3 ubiquitin ligase which was found to be upregulated in metastatic tissues, compared to normal or non invasive tissues. In addition, studies demonstrated that WSB-1 was involved in pancreatic cancer, neuroblastoma, and osteosarcoma progression. However, its role in breast cancer has not been particularly studied. The objective of this thesis is to study the role of WSB-1 in breast cancer. Initially, level of WSB1 in patients' tumour cDNA samples was evaluated according to known clinical and biological variables. Impact of high WSB1 levels on patients' distant metastasis-free survival, relapse-free survival and overall survival was also investigated. Then, the effect of WSB-1 knockdown on protein levels of epithelial to mesenchymal transition markers, as well as several matrix metalloproteinases (MMP) transcript and protein levels, and activity was examined. Consequence of these modifications on cell motility (migration, invasion) was studied, using single cells, cellular monolayers and spheroids. Finally, affinity purification followed by mass spectrometry was used to identify novel WSB-1 partners. Overall, in MDA-MB-231 cells, WSB-1 appeared to drive metastasis formation by upregulating MMPs expression and activity, promoting EMT and inducing invasiveness. WSB-1 had a more conflicting effect in MCF7 cells. In fact, WSB-1 effect appeared to be depending on the ER- and ER+ status. Together, these results validated WSB-1 as an important player in breast cancer development, particularly in metastasis formation.