<p>Abstract</p><p>The trefoil factor family of secreted proteins contains three members; trefoil factor 1 or TFF1, trefoil factor 2 or TFF2, and trefoil factor 3 or TFF3. These three proteins share a conserved 42-43 amino acid domain containing 6 cysteine residues resulting in three disulfide bonds that holds the protein in a characteristic three-loop or "trefoil structure" known as the P domain. TFF1 is primarily localized to the stomach and secreted by the gastric mucosa while TFF2 and TFF3 are primarily localized to the colon and duodenum and secreted by the goblet cells. All three of these proteins play a protective role in the gastrointestinal tract where they are normally localized and have been identified as possible tumor suppressors, however, these proteins are also upregulated in cancer within tissues where they are not normally expressed including the breast, pancreas, prostate, and liver. The mechanisms by which two of these factors, TFF1 and TFF3, promote tumorigenesis remain largely undefined. In this dissertation we will attempt to elucidate these mechanisms as well as the regulation of these two proteins in both pancreatic and prostate cancer. Many of the underlying genetic and molecular mechanisms involved in the development of both pancreatic and prostate cancer remain largely unknown and as a result, therapeutic and diagnostic tools for treating these diseases are not as effective as they could be. By deciphering the role of TFF1 and TFF3 in these cancers, they could potentially serve as new therapeutic targets or biomarkers for treating both diseases.</p><p>Chapter 2 of this dissertation will examine the functional role of TFF1 promoting tumorigenesis in pancreatic and prostate cancer. We will show that TFF1 expression is critical for the viability of both pancreatic and prostate cancer cells and that reduction of TFF1 expression in these cells results in decreased tumorigenicity when implanted in immunocompromised mice. It will also be demonstrated that TFF1's function in promoting tumorigenicity is its ability to assist tumor cells overcome the tumor suppressive barrier of senescence. Thirdly, we show that the form of senescence that TFF1 assists in allowing the cells overcome is oncogene-induced senescence (OIS). Lastly, a cell cycle array identifies the potential downstream target p21CIP, a cyclin-dependent kinase inhibitor and OIS marker, whose expression is induced by loss of TFF1 expression.</p><p>In Chapter 3 of this work, we examine the role of another trefoil factor family member, TFF3, and its role in promoting prostate tumorigenesis. Just as with TFF1, it appears that TFF3 3 expression is critical for prostate cancer cell viability and tumorigenicity using the same experimental techniques used in Chapter 2. Using a genetically defined model of prostate cancer, a PI3-kinase-dependent regulatory mechanism of TFF3 emerges in this prostate cancer context. Using this system we begin to see a divergence in both regulation and function of TFF1 and TFF3 in prostate cancer. Finally, a mouse model expressing TFF3 was developed to monitor the histopthological changes associated with expression of this protein. Initial characterization of this model suggests a hyperplastic phenotype coinciding with TFF3 expression in the prostate.</p><p>The two studies in this dissertation establish a role of TFF1 and TFF3 in both prostate and pancreatic tumorigenesis and demonstrate that ablation of expression of both proteins is a potent inhibitor of tumorigenesis. With this knowledge, it is possible that TFF1 and TFF3 may become a potential therapeutic target or diagnostic marker for better treatment of prostate and pancreatic cancer.</p> / Dissertation

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La décision du traitement adjuvant du cancer du sein est souvent difficile. Actuellement, il est nécessaire de développer de nouveaux outils pronostiques et prédictifs de sensibilité aux traitements. TFF1 (Trefoil Factor 1) et TFF3 (Trefoil Factor 3) sont deux petites protéines sécrétées dont l'expression est induite par l'estradiol dans les cellules épithéliales de cancer du sein. Étudiés séparément, leur intérêt pronostique est controversé et des résultats contradictoires ont été reportés. L'objectif de notre étude était d'évaluer l'intérêt pronostique du dosage combiné de TFF1 et de TFF3 dans une série prospective de tumeurs du sein. En accord avec la littérature, nous avons trouvé que l'expression de TFF1 et/ou de TFF3 était spécifique des tumeurs exprimant le récepteur aux estrogènes ("luminal-like"). Contrairement aux résultats d'études précédentes,TFF1 et TFF3 étaient exprimés indépendamment l'un de l'autre dans certaines tumeurs. De manière intéressante, la présence conjointe de TFF1 et de TFF3 dans les tumeurs a été associée à des éléments de pronostic péjoratif, discriminant un sous-groupe de plus haut risque au sein des cancers du sein luminaux. Par conséquent, les tumeurs TFF1 +/TFF3+ pourraient être candidates à une thérapie adjuvante. TFF1 et TFF3 sont sécrétés sous différentes formes moléculaires, comme monomères, homodimères ou hétérodimères. Ces différentes formes moléculaires sont supposées avoir différentes fonctions. En utilisant la PLA (Proximity Ligation Assay), nous avons montré la présence de l'hétérodimère TFF1/TFF3 dans des échantillons de cancer du sein double-positifs.Ces données suggèrent que l'hétérodimère TFF1/TFF3 pourrait participer au phénotype plus agressif des tumeurs doubles positives. / The breast cancer adjuvant treatment decision is often difficult. Currently, it is necessary to develop new prognostic and predictive markers in oncology. Trefoil factor 1 (TFF1) and trefoil factor 3 (TFF3) are two related small secreted proteins induced by estradiol in mammary epithelial cancer cells. Studied in isolation, their value as prognostic markers was controversial and contradictory results were reported. The aim of our study was to evaluate the prognostic value of combined TFF1 and TFF3 dosages in a prospective breast cancer series. ln agreement with the literature, we found that TFF1 and/or TFF3 expressions were specific to estrogen-receptor positive tumours ("luminal-like"). ln contrast with previous reports, TFFi and TFF3 were expressed independently from each other in some tumors. Of interest, the presence of bath TFF1 and TFF3 was associated with poor prognosis elements, distinguishing a high-risk subtype within luminal breast cancers.Therefore, TFF1 +/TFF3+ breast cancers should be considered for adjuvant therapy. TFF1 andTFF3 are secreted under distinct molecular forms, monomers, homodimers and heterodimers.These distinct molecular forms are supposed to have different functions. By using proximity ligation assay (PLA), we found TFF1/TFF3 heterodimers in double-positives cancer samples. These data suggest that TFF1/TFF3 heterodimer may contribute to the aggressive phenotype observed in double positive tumors.

Peripheral blood biomarkers can inform clinical care and drug development. Establishing causality between biomarker and disease is often critical for such applications, but epidemiological studies are limited due to biases from confounding and reverse causation. Mendelian randomization analysis leverages random inheritance of genetic variants at conception to mimic properties of randomized studies and estimate unconfounded effects between biomarker and disease, or vice-versa. This thesis demonstrates the utility of Mendelian randomization as a complementary tool to elucidate observational studies, predict drug safety and repurposing opportunities, and improve diagnostic biomarkers for cardiometabolic diseases. First, we characterized the hypothesized relationship between lipoprotein(a) and atrial fibrillation. We demonstrated both observed and genetically predicted lipoprotein(a) levels were associated with higher risk of atrial fibrillation across multiple independent cohorts. Importantly, risk was partly mediated independent of atherosclerotic cardiovascular disease, a known consequence of elevated lipoprotein(a) and itself a risk factor for atrial fibrillation. Next, we explored the lifelong effects of endogenous testosterone across a comprehensive set of 461 health outcomes in 161,268 males from the UK Biobank cohort. Using Mendelian randomization analysis, we found higher testosterone had beneficial effects on body composition and bone mineral density but adverse effects on prostate cancer, androgenic alopecia, spinal stenosis, and hypertension. Finally, we applied Mendelian randomization with the intention of discovering biomarkers caused by disease, which are expected to represent markers of early disease. As a proof-of-concept, we applied this framework to identify biomarkers associated with genetic predisposition to kidney function among 238 biomarkers measured in the ORIGIN trial. We discovered reduced kidney function caused increased trefoil factor 3 and showed its addition to models with known risk factors improved discrimination of incident early-stage chronic kidney disease. Taken together, Mendelian randomization identified biomarkers that warrant further study, with promising implications for screening, prevention, and treatment of different cardiometabolic diseases. / Thesis / Doctor of Philosophy (PhD) / Biological markers associated with disease can inform novel therapeutics or diagnostics but distinguishing causation from correlation is challenging. Mendelian randomization – a technique that leverages random inheritance of genetic variation to infer causality – was used to examine the role of biomarkers in cardiometabolic diseases. First, we implicated lipoprotein(a) as a risk factor for atrial fibrillation that acts independent of atherosclerotic cardiovascular disease. Second, we comprehensively characterized the lifelong effects of testosterone on health outcomes in males, where we found evidence of both beneficial and adverse effects on disease. Finally, we discovered trefoil factor 3 as a diagnostic marker for early-stage chronic kidney disease. Altogether, this thesis demonstrated different applications of Mendelian randomization that showcase its utility as a complementary tool to reveal causal biomarkers, and served to identify biomarkers for cardiometabolic diseases that merit further studies to evaluate their potential benefit on patient care.