<p>Primary hyperparathyroidism (pHPT) due to parathyroid tumours with hypersecretion of parathyroid hormone and hypercalcaemia is a common disease with incompletely understood etiology affecting more than 1 % of the population, primarily postmenopausal women. In secondary hyperparathyroidism (sHPT), parathyroid tumours develop in response to calcium and vitamin D deficiency generally in patients with uraemia. HPT is usually treated by surgical removal of enlarged parathyroid glands.</p><p>The aim of this thesis was to examine the Wnt/β-catenin signalling pathway in parathyroid tumours.</p><p>Aberrantly accumulated β-catenin was found in all analysed pHPT and sHPT tumours, with a stabilising homozygous mutation (Ser37Ala) in 7.3% of the pHPT tumours. Truncation of the APC protein was not found. MYC, a β-catenin target gene was overexpressed in a substantial fraction of pHPT and sHPT parathyroid tumours. </p><p>A parathyroid tumour cell line (sHPT-1) was established from a hyperplastic gland removed at operation of a patient with sHPT. The cells produced parathyroid hormone and grew with a doubling time of approximately 72 hours. Stabilised nonphosphorylated transcriptionally active β-catenin was expressed. Efficient transfection of siRNA against β-catenin decreased expression of cyclin D1 and MYC, and inhibited cell growth with ensuring cell death. </p><p>The Wnt coreceptor LRP5 was found expressed with an internal deletion of 142 amino acids (LRP5Δ) in 86% and 100% of pHPT and sHPT tumours, respectively. Stabilising mutation of β-catenin and expression of LRP5Δ was mutually exclusive. Expression of LRP5Δ was required to maintain the nonphosphorylated transcriptionally active ß-catenin level, MYC expression, parathyroid cell growth in vitro, and tumour growth in transplanted SCID mice. Wnt3 ligand and LRP5Δ strongly activated transcription, and LRP5Δ was insensitive to inhibition by DKK1.</p><p>Aberrant accumulation of β-catenin by stabilising mutation or expression of LRP5Δ appears as a common pathogenic pathway for hyperparathyroid disease. LRP5Δ in particular presents a potential target for therapeutic intervention.</p>

Angiogenesis can be defined as the formation of new blood vessels from pre-existing ones. Angiogenesis is required for development and maintenance of our vascular system and thus of fundamental importance to our existence. The endothelial cells that line the inside of the vessels de-differentiate, migrate, proliferate and re-differentiate during angiogenesis. Angiogenesis is tightly regulated, controlled by several angiogenic factors of various classes that promote angiogenesis but also by anti-angiogenic factors that counteract the effect of the pro-angiogenic factors. We have examined three factors involved in angiogenesis regulation, Vascular endotelial growth factor (VEGFR) -3, the matrix protein laminin-1 and the collagen XVIII derived fragment endostatin. Five tyrosine phosphorylation sites in the cytoplasmic tail of VEGFR-3 were identified by phosphopeptide mapping (PPM). The data was confirmed by PPM using point-mutated receptors generated by site-directed mutagenesis. Laminin-1 was found to promote angiogenesis in the chicken chorioallantoic membrane assay and in a synergistic fashion together with suboptimal levels of fibroblast growth factor 2 (FGF-2) in embryoid bodies. Laminin-1 also promoted endothelial tubular morphogenesis in vitro, and upregulated the expression of the endothelial differentiation marker Jagged-1. Endostatin was shown to affect endothelial FGF-2-induced cell survival and morphogenesis. This was a result of direct binding to endothelial cells and induction of tyrosine phosphorylation of many proteins including the adaptor protein Shb. The apoptotic and morphogenic responses induced by endostatin was shown to be dependent on Shb. Further, endostatin inhibited endothelial migration and affected molecules implicated in migration. In particular, FGF-2 induced actin reorganization, and β-catenin regulation was modulated by endostatin.

Primary hyperparathyroidism (pHPT) due to parathyroid tumours with hypersecretion of parathyroid hormone and hypercalcaemia is a common disease with incompletely understood etiology affecting more than 1 % of the population, primarily postmenopausal women. In secondary hyperparathyroidism (sHPT), parathyroid tumours develop in response to calcium and vitamin D deficiency generally in patients with uraemia. HPT is usually treated by surgical removal of enlarged parathyroid glands. The aim of this thesis was to examine the Wnt/β-catenin signalling pathway in parathyroid tumours. Aberrantly accumulated β-catenin was found in all analysed pHPT and sHPT tumours, with a stabilising homozygous mutation (Ser37Ala) in 7.3% of the pHPT tumours. Truncation of the APC protein was not found. MYC, a β-catenin target gene was overexpressed in a substantial fraction of pHPT and sHPT parathyroid tumours. A parathyroid tumour cell line (sHPT-1) was established from a hyperplastic gland removed at operation of a patient with sHPT. The cells produced parathyroid hormone and grew with a doubling time of approximately 72 hours. Stabilised nonphosphorylated transcriptionally active β-catenin was expressed. Efficient transfection of siRNA against β-catenin decreased expression of cyclin D1 and MYC, and inhibited cell growth with ensuring cell death. The Wnt coreceptor LRP5 was found expressed with an internal deletion of 142 amino acids (LRP5Δ) in 86% and 100% of pHPT and sHPT tumours, respectively. Stabilising mutation of β-catenin and expression of LRP5Δ was mutually exclusive. Expression of LRP5Δ was required to maintain the nonphosphorylated transcriptionally active ß-catenin level, MYC expression, parathyroid cell growth in vitro, and tumour growth in transplanted SCID mice. Wnt3 ligand and LRP5Δ strongly activated transcription, and LRP5Δ was insensitive to inhibition by DKK1. Aberrant accumulation of β-catenin by stabilising mutation or expression of LRP5Δ appears as a common pathogenic pathway for hyperparathyroid disease. LRP5Δ in particular presents a potential target for therapeutic intervention.

Squamous cell carcinoma of the head and neck (SCCHN), the 6th most common cancer worldwide, has a low 5-year survival. Disease as well as treatment often causes patients severe functional and aesthetic problems. In order to improve treatment and diagnosis at earlier stages of tumour development it is important to learn more about the molecular mechanisms behind the disease. p63, an important regulator of epithelial formation, has been suggested to play a role in the development of SCCHN. Six different isoforms of p63 have been found and shown to have various functions. The aim of the studies in this thesis was to learn more about the role of p63 and proteins connected to p63 in SCCHN. Expression of p63, Cox-2, EGFR, beta-catenin, PP2A and p53 isoforms was mapped in tumours and normal tumour adjacent tissue from patients with SCCHN using western blot or RT-PCR. Results showed no significant difference between tumours and normal tumour adjacent tissue concerning expression of EGFR and beta-catenin. Cox-2 and PP2A showed significantly higher expression in tumours while p63 was more expressed in normal tumour adjacent tissue. However, expression of all these proteins in normal tumour adjacent tissue differed from tissue from disease-free non-smoking individuals. Smoking in itself did not affect expression of these proteins. The p53 isoforms p53, p53beta, p53gamma, ∆133p53, ∆133p53beta and ∆133p53gamma were expressed at RNA level in samples both from tumours and normal tumour adjacent tissue, though most of them at fairly low levels. The functional properties of the different p63 isoforms have not been fully mapped. By establishing stable cell lines over-expressing the different p63 isoforms we investigated their specific effect on tumour cells from SCCHN. Only the ∆Np63 isoforms could be stably over-expressed, whereas no clones over-expressing TAp63 could be established. Using microarray technique, cell lines stably expressing the ∆Np63 isoforms were studied and CD44, Keratins 4, 6, 14, 19 and Cox-2 were found to be regulated by p63. In conclusion, the present project adds new data to the field of p63 and SCCHN. For example, we have shown that clinically normal tumour adjacent tissue is altered compared to normal oral mucosa in non tumour patients, and that smoking does not change expression of p63, Cox-2, EGFR, beta-catenin or PP2A in oral mucosa. Novel p53 isoforms are expressed in SCCHN, and even though levels are very low they should not be overlooked. Furthermore, CD44, keratins 4, 6, 14, 19 and Cox-2 were identified as p63 targets in SCCHN.

Acute myeloid leukemia (AML) is a genetic disease whereby sequential genetic aberrations alter essential white blood cell development leading to differentiation arrest and hyperproliferation. Pertinent animal models serve as essential intermediaries between in vitro molecular studies and the use of new agents in clinical trials. We previously generated a transgenic zebrafish model expressing human NUP98-HOXA9 (NHA9), a fusion oncogene found in high-risk AML. This expression yields a pre-leukemic state in both embryos and adults. Using this model, we have identified the overexpression of dnmt1 and the Wnt/β-catenin pathway as downstream contributors to the myeloproliferative phenotype. Targeted dnmt1 morpholino knockdown and pharmacological inhibition with methyltransferase inhibitors rescues NHA9 embryos. Similarly, inhibition of β-catenin with COX inhibitors partially restores normal hematopoiesis. Interestingly, concurrent treatment with a histone deacetylase inhibitor and either a methyltransferase inhibitor or a COX inhibitor, synergistically inhibits the effects of NHA9 on embryonic hematopoiesis. Thus, we have identified potential pharmacological targets in NHA9-induced myeloid disease that may offer a highly efficient therapy with limited toxicity – addressing a major long-term goal of AML research.

La transició epiteli-mesènquima (TEM) és un procés en què cèl lules epitelials, immòbils i amb polaritat apico-basal transiten cap un fenotip mesenquimal o fibroblàstic. L'expressió del factor de transcripció snail1 és suficient per induir TEM en cèl lules en cultiu i és necessari per la majoria de les TEM fisiològiques descrites. Snail1 és un membre de la família de proteïnes amb dits de Zinc que reprimeix gens epitelials (com l'E-cadherina) a través de la unió directa a seqüències especifiques dels promotors anomenades caixes E i posterior reclutament de corepressors. La TEM també es caracteritza per l'activació de gens mesenquimals, però el mecanisme pel qual snail1 indueix l'expressió d'aquests és poc conegut. En aquest treball demostrem que snail1 actua a nivell transcripcional per incrementar els nivells dels marcadors mesenquimals FN1 (fibronectina) i LEF1 (de l'anglès, lymphoid enhancer-binding factor 1) a través d'un mecanisme nou per aquesta proteïna de dits de Zn que no requereix ni caixes E ni unió directa a l'ADN. A més a més, mostrem que, per a dur a terme l'activació, snail1 coopera amb dos factors de transcripció ja descrits en relació a la TEM: beta-catenina i NF-kappa-B. Els nostres resultats també proven que l'expressió forçada de la E-cadherina evita aquesta cooperació i conseqüent activació gènica. A banda d'aquest mecanisme, també hem descrit que el factor de transcripció TFCP2c, que no havia estat prèviament relacionat amb TEM, és necessari per l'activació del gen FN1 induïda per snail1. / Epithelial-mesenchymal transition (EMT) is a cellular process by which no motile epithelial, apico-basal-polarized cells transit towards a motile mesenchymal front-backpolarized phenotype. Expression of the transcription factor snail1 is sufficient to induce EMT in cultured cells and it is required for most of the physiological EMTs described. Snail1 is a member of the Zn finger protein family that represses epithelial genes (such as E-cadherin) by directly binding to specific promoter sequences called E-boxes and subsequent recruitment of corepressors. EMT is also accompanied by activation of mesenchymal genes, however, little is known of how snail1 induces their expression.In this work we provide evidence that snail1 acts at the transcriptional level to increase the levels of the mesenchymal FN1 (fibronectin) and LEF1 (lymphoid enhancer-binding factor 1) genes through a novel mechanism for this Zn finger protein that does not require neither E-boxes nor direct binding to DNA. Furthermore, we describe a cooperative action in such mechanism between snail1 and two transcription factors previously related to EMT: beta-catenin and NF-kappaB. Our results also show that restoration of E-cadherin levels prevents such cooperation and subsequent activation. In addition, we also demonstrate that TFCP2c, which had not been previously linked to EMT, is also required for snail1-induced transcriptional activation of the FN1 gene.

WW domain-containing oxidoreductase (WWOX) is a novel tumor suppressor gene discovered few years ago. Many researches indicate that expression of WWOX is reduced in a variety of cancers including heptocellular carcinoma (HCC). A recent report suggests that WWOX is implicated in Wnt/£]-catenin pathway which is frequently affected in HCC. In this study, we used immunohistochemical (IHC) staining to analyze the expression of WWOX and Wnt/£]-catenin pathway components in HCC and adjacent non-tumor tissues. Our result showed that WWOX was significantly downregulated in poor differentiated HCC. In addition, downregulation of WWOX was significantly correlated with cytoplasmic £]-catenin expression. We also found that TCF4 was strongly expressed in HCC tissues and the expression was associated with tumor grade and stage. Consequently, our result implied that downregulation of WWOX in HCC might lead to accumulation of £]-catenin in the cytoplasm and the subsequent activation of Wnt/£]-catenin signaling pathway.

The ability to spatially restrict specific activities across the cell cortex functionally defines individual cells and tissues. This is achieved, in part, via the assembly of protein complexes that link the plasma membrane to the underlying cortical actin cytoskeleton. The neurofibromatosis type 2 (NF2) tumor suppressor Merlin and closely related ERM proteins (Ezrin, Radixin and Moesin) are a special class of such membrane:cytoskeleton associated proteins that function to organize specialized cortical domains. In addition to their high degree of similarity, mounting evidence suggests that Merlin/ERMs share a functional relationship, which is largely unexplored. Unlike Merlin, the ERMs are not known to inhibit cell proliferation; in fact, Ezrin is thought to promote tumor metastasis. Defining the relationship between Merlin and the ERMs is essential to appreciating their respective roles in cancer development. Here I demonstrate a novel role for Merlin and the ERMs in generating cortical asymmetry in the absence of external cues. Our data reveal that Merlin functions to restrict the cortical distribution of Ezrin, which in turn positions the interphase centrosome in single epithelial cells and 3D organotypic cultures. In the absence of Merlin, ectopic cortical Ezrin yields mispositioned centrosomes, misoriented spindles and aberrant epithelial architecture. Furthermore, in tumor cells with centrosome amplification, the failure to restrict cortical Ezrin abolishes centrosome clustering, yielding multipolar mitoses. Consistent with a functional relationship, I observe a strong genetic interaction between Nf2 and Ezrin in the mouse intestine in vivo. Finally, I begin to address the basis of their functional interaction by testing whether they are coordinately regulated by the Ste-20 like kinase SLK. Altogether, these data uncover fundamental roles for Merlin/ERM proteins in spatiotemporally organizing the cell cortex in vitro and in vivo and suggest that Merlin’s role in promoting cortical heterogeneity may contribute to tumorigenesis by disrupting cell polarity, spindle orientation and potentially genome stability.

Both Notch and the Wnt pathways are key regulators in maintaining the homeostasis in the intestine. Defects on the key tumor suppressor adenomatous polyposis coli, APC a gene in the Wnt pathway is most frequently mutated in colorectal cancer. Previous studies have indicated that there is a crosstalk between these two pathways. We investigate if there is correlation by first using bioinformatics to find Lef1/Tcf sites in several of the Notch pathway gene promoters. Bioinformatically we found that a lot of the genes contained theses sites controlled by the APC's destruction target β-catenin. By using semi quantitative PCR and western blot we found that Hes 1, Hes 7, JAG 2, MAML 1, Notch 2, NUMB, NUMBL, RFNG and LFNG was downregulated in HT29 colon cancer cells carrying a vector containing wild type APC. All but JAG 2 contains at least one Lef1/Tcf site in their promoter region. The results were verified in HT29 cells transfected with siRNA against β-catenin. We also investigated what would happen to the Lef1/Tcf target gene program of the Wnt pathway, if the Notch pathway was inhibited with the gamma-secretase inhibitor DAPT. Results showed no downregulution of β-catenin or its target gene Cyclin D1.Taken together, these results demonstrate that the Wnt pathway can be placed upstream of the Notch pathway and regulates the latter through β-catenin and the Lef1/Tcf target gene program. However, preliminary results indicate that there is no regulation of APC/β-catenin by the Notch pathway.

The RET receptor tyrosine kinase has essential roles in cell survival, differentiation, and proliferation. Oncogenic activation of RET causes the cancer syndrome multiple endocrine neoplasia type 2 (MEN 2), and is a frequent event in sporadic thyroid carcinomas. Multiple endocrine neoplasia 2B (MEN 2B), a subtype of MEN 2, is caused primarily by a methionine to threonine substitution of residue 918 in the kinase domain of the RET receptor (2B-RET), however the molecular mechanisms that lead to the disease phenotype are unclear. In this study, we show that the M918T mutation causes a 10 fold increase in ATP binding affinity, and leads to a more stable receptor-ATP complex, relative to the wildtype receptor. We also show that 2B-RET can dimerize and become autophosphorylated in the absence of ligand. Our data suggest that multiple distinct but complementary molecular mechanisms underlie the MEN 2B phenotype and provide potential targets for effective therapeutics for this disease. In the second part of the study, we identified a novel β-catenin-RET kinase signaling pathway which is a critical contributor to the development and metastasis of human thyroid carcinoma. We show that RET binds to, and tyrosine phosphorylates, β-catenin and demonstrate that the interaction between RET and β-catenin can be direct and independent of cytoplasmic kinases, such as SRC. As a result of RET-mediated tyrosine phosphorylation, β-catenin escapes cytosolic downregulation by the APC/Axin/GSK3 complex and accumulates in the nucleus, where it can stimulate β-catenin-specific transcriptional programs in a RET-dependent fashion. We show that downregulation of β-catenin activity decreases RET-mediated cell proliferation, colony formation, and tumour growth in nude mice. Finally, we used a structure guided approach to identify and characterize a novel, non-ATP competitive, RET inhibitor; SW-01. We show that SW-01 provides significant RET inhibition in an in vitro kinase assay using purified RET. Moreover, RET phosphorylation is blocked, or dramatically reduced, in vivo in cells overexpressing active RET. We observe a significant decrease in cell proliferation and colony formation in RET-expressing cells in the presence of SW-01. Together, our data suggest that SW-01 has potential as a novel RET kinase inhibitor with clinical utility. / Thesis (Ph.D, Pathology & Molecular Medicine) -- Queen's University, 2008-09-15 16:20:59.976