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Title: Nicastrin as a novel therapeutic target in breast cancer
Author: Filipovic, Aleksandra
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2011
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Nicastrin is an essential component of the gamma-secretase (GS) enzyme complex, required for its synthesis and recognition of substrates for proteolytic cleavage. The purpose of this study was to investigate whether nicastrin has a prognostic value or the potential as a therapeutic target in breast cancer. Tissue microarrays (TMAs) (n = 1050), and breast cancer cell line analyses confirmed that nicastrin expression was upregulated in breast cancer compared to normal breast cells. In TMA patient samples, high nicastrin expression was observed in 47.5% of cases and correlated with worse breast cancer specific survival in the ERα negative cohort. Transient and stable gene silencing of nicastrin in vitro, resulted in the disruption of the GS complex activity and a decrease in Notch1 cleavage. Nicastrin silencing in invasive MDA-MB-231 and HCC1806 cells resulted in the loss of vimentin expression and a reduction in cell invasion, which was concomitant with the formation of cell-cell junctions, as well as cellular repolarisation. In a population of breast cancer cells harbouring the cancer stem cell phenotype (CD44+/CD24-), nicastrin depletion abrogated expression of the epithelial to mesenchymal (EMT) markers, vimentin, SIP1 and Snail. Furthermore, nicastrin overexpression in the non-malignant MCF10A breast cells increased expression of other GS components, Notch activation, vimentin expression and invasive capacity. These data indicate that nicastrin can function to maintain the EMT transition during breast cancer progression. We have developed anti-nicastrin polyclonal and monoclonal antibodies and have shown that they are able to decrease the invasive and proliferative capacity of MDA-MB-231 breast cancer cells in vitro. In order to dissect the role of nicastrin within the GS complex from its presumed GS-independent signaling role in breast cancer cells, we have performed gene array analyses and identified a subset of genes that are nicastrin-dependent and are not affected by silencing of the Notch receptors. The data presented in this thesis therefore support our hypothesis that an antagonising monoclonal antibody could be suitable to inhibit nicastrin as a potential therapeutic target in invasive breast cancer.
Supervisor: Coombes, Charles ; Yague, Ernesto Sponsor: Cancer Research UK
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available