The αvβ6 integrin plays an integral role in promoting metastatic phenotypes in colorectal cancer

Globally, colorectal cancer (CRC) afflicts millions of men and women each year. The progression of an abnormal epithelial cell to a benign tumour and then a malignant cancer exploits several mutated genes and perturbed signalling and biochemical pathways. The expression of proteins such as the β6 integrin subunit, uPAR and TGFβ have been extensively associated with CRC progression. The primary aim of this thesis was to contribute new knowledge regarding the role of integrin αvβ6 in CRC by investigating the proposed uPAR•αvβ6•TGFβ metastasome. This was achieved by employing five CRC cell lines as model cellular systems, in which β6 had been artificially overexpressed, suppressed or truncated (SW480Mock, SW480β6OE, SW480β6DEL, HT29Mock, HT29β6AS). The consequences of β6 expression following latent TGFβ or plasminogen treatment was assessed using a variety of phenotypic, cellsignalling (i.e., AlphaScreen® SureFire® Assay) and state-of-the-art proteomic technologies. β6-expressing cells were significantly more proliferative and invasive with increased ERK1/2 activity, which was further promoted following ligand (latent TGFβand/or plasminogen) treatment. Integrin β6 expression was found to translate subphysiological levels of these zymogens into significantly enhanced metastatic behaviours, through a mechanism that could be disrupted either by antagonising TGFβ receptor signalling, plasmin activity or the uPAR•αvβ6 interaction. β6 overexpression and suppression induced extensive proteomic changes, altering pivotal biomolecular pathways that can be associated with CRC and provided insights into the role and central function of β6 within the uPAR•αvβ6•TGFβ metastasome. Furthermore, an Olink Proseek multiplexed study, interrogated Dukes’ stage A-D CRC patient plasma samples and identified CEA, IL-8 and prolactin as differential markers of early stage Dukes’ A/ B and later (malignant) stage Dukes’ C/D plasmas from those obtained from unaffected healthy controls. This thesis demonstrates the power of modern proteomic and multiplexing technologies to elucidate β6-promoted CRC pathenogenesis at the molecular level whilst identifying potential avenues for future biomarker exploration.