Mutations in the tumour suppressor gene Adenomatous polyposis coli (APC) are found in 80 % of sporadic colorectal cancer (CRC) tumours and are also responsible for the inherited form of CRC, Familial adenomatous polyposis (FAP). In order to identify novel therapeutic targets for the treatment of APC mutated CRC, we have generated an in vitro model of APC mutant CRC using CRISPR-cas9 gene editing. Using the APC wildtype colorectal carcinoma cell line RKO, we targeted the cells with guide RNA (gRNA) targeting exon 2 or exon 15 (encodes 80 % of APC) of the APC gene. We generated isogenic cell lines which differed in the expression of APC, the controls were APC wildtype and the APC mutant (APC Lys736fs) cell lines expressed a truncated ~80 kDa APC protein. We used these cell lines to perform an siRNA screen against 720 kinases and kinase-related genes. We selected seven genes to investigate further, unfortunately none of the potential hits validated. Additionally, we performed an FDA-approved compound screen targeting over 1000 compounds. From this, we identified a group of HMG-CoA reductase (HMGCR) inhibitors known as statins, which selectively cause a greater loss in cell viability in the APC mutated cell lines, compared to the APC wildtype cells. Mechanistically, our data suggests this synthetic lethal relationship is due to a greater decrease in the anti-apoptotic protein survivin. We propose this is due to statins altering the localisation of Rac1, reducing Pak1 activation and reducing the level of Wnt signalling. This results in the reduction of the Wnt target gene survivin. We have successfully identified an FDA-approved family of compounds, which show synthetic lethality with the APC mutation in our in vitro model.

The type II tumour suppressor ING3 has been shown to modulate transcription, cell cycle control, and apoptosis. To investigate the putative role of ING3 in melanoma development, we examined the expression of ING3 in 58 dysplastic nevi, 114 primary melanomas, and 50 metastatic melanomas with tissue microarray and immunohistochemistry. Overall ING3 was reduced in metastatic melanomas compared with dyslastic nevi and primary melanomas. Reduced nuclear ING3 staining also correlated with melanoma progression, increased cytoplasmic ING3 level, tumour location at sun-exposed sites, and a poorer disease-specific 5-year survival of patients with primary melanoma. Multivariate analysis revealed that nuclear ING3 staining can independently predict patient outcome in primary melanomas. In melanoma cells, ING3 expression was rapidly induced by UV irradiation. Using stable clones of melanoma cells overexpressing ING3, we showed that ING3 significantly promoted UV-induced apoptosis. Unlike its homologues ING1b and ING2, ING3-enhanced apoptosis upon UV irradiation was independent of functional p53. Furthermore, ING3 did not affect the expression of mitochondrial proteins but increased the cleavage of Bid and caspases. Moreover, ING3 upregulated Fas expression and ING3-mediated apoptosis was blocked by inhibiting caspase-8 or Fas activation. Knockdown of ING3 expression decreased UV-induced apoptosis remarkably, suggesting that ING3 plays a crucial role in cellular response to UV radiation. To explore how ING3 is deregulated in advanced melanomas, we examined ING3 expression in metastatic melanoma cells and found that ING3 was downregulated due to a rapid protein turnover in these cells. Further studies demonstrated that ING3 undergoes degradation via the ubiquitin-proteasome pathway. We also demonstrate that ING3 interacts with the SCF (Skp1/Cul1/Roc1/Skp2) E3 ligase complex. Knockdown of Cul1 or Skp2 significantly stabilized ING3 in melanoma cells. In addition, lysine residue 96 is essential for ING3 ubiquitination as its mutation to arginine completely abrogated ING3 turnover and enhanced ING3-stimulatd apoptosis upon UV irradiation. Taken together, ING3 is deregulated in melanomas as a result of both nucleus-to-cytoplasm shift and rapid degradation. The level of ING3 in the nucleus may be an important marker for human melanoma progression and prognosis. Restoration of ING3 expression significantly sensitizes melanoma cells to UV radiation through the activation of Fas/caspase-8 pathway.

The type II tumour suppressor ING3 has been shown to modulate transcription, cell cycle control, and apoptosis. To investigate the putative role of ING3 in melanoma development, we examined the expression of ING3 in 58 dysplastic nevi, 114 primary melanomas, and 50 metastatic melanomas with tissue microarray and immunohistochemistry. Overall ING3 was reduced in metastatic melanomas compared with dyslastic nevi and primary melanomas. Reduced nuclear ING3 staining also correlated with melanoma progression, increased cytoplasmic ING3 level, tumour location at sun-exposed sites, and a poorer disease-specific 5-year survival of patients with primary melanoma. Multivariate analysis revealed that nuclear ING3 staining can independently predict patient outcome in primary melanomas. In melanoma cells, ING3 expression was rapidly induced by UV irradiation. Using stable clones of melanoma cells overexpressing ING3, we showed that ING3 significantly promoted UV-induced apoptosis. Unlike its homologues ING1b and ING2, ING3-enhanced apoptosis upon UV irradiation was independent of functional p53. Furthermore, ING3 did not affect the expression of mitochondrial proteins but increased the cleavage of Bid and caspases. Moreover, ING3 upregulated Fas expression and ING3-mediated apoptosis was blocked by inhibiting caspase-8 or Fas activation. Knockdown of ING3 expression decreased UV-induced apoptosis remarkably, suggesting that ING3 plays a crucial role in cellular response to UV radiation. To explore how ING3 is deregulated in advanced melanomas, we examined ING3 expression in metastatic melanoma cells and found that ING3 was downregulated due to a rapid protein turnover in these cells. Further studies demonstrated that ING3 undergoes degradation via the ubiquitin-proteasome pathway. We also demonstrate that ING3 interacts with the SCF (Skp1/Cul1/Roc1/Skp2) E3 ligase complex. Knockdown of Cul1 or Skp2 significantly stabilized ING3 in melanoma cells. In addition, lysine residue 96 is essential for ING3 ubiquitination as its mutation to arginine completely abrogated ING3 turnover and enhanced ING3-stimulatd apoptosis upon UV irradiation. Taken together, ING3 is deregulated in melanomas as a result of both nucleus-to-cytoplasm shift and rapid degradation. The level of ING3 in the nucleus may be an important marker for human melanoma progression and prognosis. Restoration of ING3 expression significantly sensitizes melanoma cells to UV radiation through the activation of Fas/caspase-8 pathway.

MicroRNAs (miRNAs) are small non-coding RNA molecules that regulate the expression of mRNA targets, and are aberrantly expressed in several cancers, including breast cancer. Using a transgenic mouse model of mammary tumorigenesis (MTB-IGFIR), a miRNA array was previously performed in our lab to study the expression level of various miRNAs in mammary tumours compared to wild-type mammary tissue. Next, the expression of a number of the differentially expressed miRNAs was confirmed and manipulated in a tumour cell line (RM11A) generated from a MTB-IGFIR mammary tumour. Synthetic miRNA precursors and inhibitors were then used to overexpress and knockdown, respectively, the levels of five miRNAs: miR-31, miR-183, miR-200c, miR-210, and miR-378. Upon optimization of miRNA overexpression and downregulation in RM11A cells, this study tested the effects of these miRNAs on cellular growth, survival, or invasiveness in vitro. Compared to negative controls, overexpression of all five miRNAs was associated with a significant decrease in cellular invasion, while only the overexpression of miR-31 had a significant effect on proliferation. No significant effects were found on cell survival. Our results implicate these five miRNAs in different aspects of mammary tumorigenesis, as well as having a tissue specific role in RM11A cells.

Small intestinal neuroendocrine tumours (SI-NETs) are rare, hormone producing and proliferate slowly. Patients usually display metastases at time of diagnosis, the tumours are difficult to cure, and the disease course is unpredictable. The gene expression pattern was investigated in paper I, with emphasis on aggressive disease and tumour progression. Expression microarrays were performed on 42 tumours. Unsupervised hierarchal clustering revealed three clusters that were correlated to clinical features, and expression changes from primary tumour to metastasis. Eight novel genes, ACTG2, GREM2, REG3A, TUSC2, RUNX1, TGFBR2, TPH1 and CDH6 may be of importance for tumour progression. In paper II, expression of ACTG2 was detected in a fraction of SI-NETs, but not in normal enterochromaffin cells. Inhibition of histone methyltransferase and transfection of miR-145 induced expression and no effect was seen after DNA methylation or selective EZH2 inhibition in vitro. miR-145 expression was reduced in metastases compared to primary tumours. Overexpression of ACTG2 inhibited cell growth, and inducing ACTG2 may have therapeutic effects. TCEB3C (Elongin A3) is located on chromosome 18 and is imprinted in some tissues. In paper III a reduced protein expression was detected. The gene was epigenetically repressed by both DNA and histone methylation in a tumour tissue specific context. The expression was also induced in primary cell cultures after DNA demethylation and pyrosequencing revealed promoter region hypermethylation. Overexpression of TCEB3C inhibited cell growth by 50%, suggesting TCEB3C to be a tumour suppressor gene. In paper IV, 69 biomarkers were analysed in blood serum using multiplex proximity ligation assay. Nineteen markers displayed different levels between patients and controls. In an extended cohort, ELISA analysis showed elevated serum levels of Mindin, DcR3 and TFF3 in patients and protein expression in tumour cells. High levels of DcR3 and TFF3 were associated with poor survival, and DcR3 may be a marker for liver metastases. Mindin, DcR3, and TFF3 are potential novel diagnostic biomarkers for SI-NETs.

Research Doctorate - Doctor of Philosophy (PhD) / Reversible protein phosphorylation plays a central role in the regulation of intracellular signalling, and is controlled by the opposing activities of protein kinases and phosphatases. Deregulation of these mechanisms can result in increased proliferation and enhanced survival, which is a hallmark feature of malignant transformation. For example, over 90% of chronic myeloid leukaemia (CML) patients express the BCR/ABL oncoprotein, which exhibits unrestrained tyrosine kinase activity. In addition, activating mutations within the receptor tyrosine kinase, c-KIT, contribute to the pathogenesis of gastrointestinal stromal tumours (GIST), systemic mastocytosis, acute myeloid leukaemia (AML), testicular seminoma and melanoma. The advent of small molecule tyrosine kinase inhibitors, such as imatinib, has revolutionised the treatment of malignancies driven by these oncogenic kinases. However, a proportion of patients are either unresponsive or develop resistance, and as such, relapse and disease progression is a major clinical problem. In order to improve the treatment outcome for these patients, a greater understanding of the signalling pathways regulated downstream of BCR/ABL and c-KIT is required. The data presented in this thesis indicates that oncogenic BCR/ABL and mutant c-KIT both require inhibition of the tumour suppressor, protein phosphatase 2A (PP2A), to induce tumourigenesis. PP2A is a large family of serine/threonine phosphatases that provide the fine control on signalling pathways by governing the rate and duration of phosphorylation. The heterotrimeric PP2A enzyme is comprised of a structural subunit (PP2A Aα and Aβ), a catalytic subunit (PP2Acα and cβ) and a regulatory subunit, which consists of three unrelated families: B55 (α, β, γ, δ), B56 (α, β, γ, δ, ε) and B" (PR72/130 / PR70/48). Binding of the regulatory subunit to the core PP2A AC dimer directs both the substrate specificity and cellular localisation of the enzyme. The combinatorial assembly of these individual components permits the formation of distinct complexes which have been implicated in numerous cellular functions such as proliferation, survival and mitosis. In particular, important roles for PP2A in various aspects of malignant transformation are beginning to emerge. Recent work demonstrates that PP2A is functionally inactivated by BCR/ABL in myeloid progenitor cells. Using the mouse myeloid progenitor cell line, FDC-P1, these observations were confirmed in the current study. Detailed investigation into the underlying mechanisms have demonstrated for the first time that active BCR/ABL increases the expression of the PP2A structural and certain regulatory subunits. This alters the PP2A holoenzyme composition and results in the abundance of complexes containing B55α and B56α. Consequently, B56γ, a known tumour suppressive subunit, appears to be simultaneously displaced. To investigate which subunits are functionally important for BCR/ABL-mediated leukaemogenesis, individual PP2A subunits were targeted with shRNA sequences in WT BCR/ABL FDC-P1 cells. Subsequent evaluation identified B56α as a key player which facilitates the leukaemic phenotype. In accordance with an increase in PP2A activity, knockdown of B56α significantly inhibited the cellular growth and reduced the clonogenic potential of BCR/ABL⁺ myeloid progenitors. Furthermore, suppression of the B56δ subunit in WT BCR/ABL FDC-P1 cells appears to delay progression through the cell cycle. Together, these findings provide new insights into the biology of PP2A and begin to define the precise mechanisms by which BCR/ABL induces leukaemogenesis via PP2A in CML. Investigation of the regulation of PP2A was also extended to the oncogenic tyrosine kinase, c-KIT. Using FDC-P1 cells expressing imatinib-sensitive (V560G) or –resistant (D816V) mutant c-KIT, this work demonstrates for the first time that constitutive activation of c-KIT impairs the activity of PP2A, and this is essential for tumourigenesis. Pharmacological reactivation of PP2A with FTY720 significantly reduced the proliferation, impaired the clonogenic potential and induced apoptosis of oncogenic c-KIT cells, whilst having no effect on empty vector controls or WT c-KIT cells stimulated with stem cell factor (SCF). These cytotoxic effects of FTY720 are mediated, in part, by the rapid dephosphorylation, and hence inactivation, of oncogenic c-KIT receptors. These promising in vitro findings were translated into an in vivo model, where the daily administration of FTY720 significantly delayed the growth of mutant c-KIT⁺ tumours. Furthermore, FTY720 markedly prevented the infiltration of D816V c-KIT tumour cells into secondary lymphoid organs, such as the spleen and bone marrow. As a result, the survival of FTY720-treated mice was significantly prolonged compared to saline-treated controls. Overall, this body of work greatly enhances our understanding of PP2A function and identifies the complex mechanisms of PP2A regulation by the oncogenic tyrosine kinases, BCR/ABL and c-KIT. Taken together, the data suggests that inhibition of PP2A may represent a general mechanism employed by constitutively active kinases to facilitate tumour growth. As such, this work supports the future application of PP2A-activating agents in a broad range of human malignancies.

Together, colorectal (CRC) and bladder cancer (BlCa) are responsible for a large percentage of cancer related morbidity and mortality in Western society. A dramatic reduction in patient survival occurs as these cancers progress towards invasive and metastatic disease, from a five year survival rate of about 90% for localised disease to approximately 5-10% for advanced disease involving distant metastasis. A greater understanding of disease progression will lead to enhanced screening, diagnostic and treatment strategies, in turn providing an improved prognosis for the patient. The purpose of this study was to expand the current molecular knowledge of CRC and BlCa by elucidating the role of Mxi1 mutations and MTSS1 expression in CRC and BlCa respectively, and to examine the diagnostic potential of these genes. The Mxi1 coding region for 41 tumours, collected by the South Western Sydney Colorectal Cancer Tumour Bank from 2000-2001, was screened for mutations using Dideoxy Fingerprinting (ddF) and sequencing. Sequence alterations were detected in 34% of tumours. Three different polymorphisms and three mutations were detected. One mutation could possibly affect the tumour suppressor function of Mxi1. The presence of a gene mutation did not correlate to any clinical characteristics and is therefore not a suitable diagnostic marker. Microsatellite instability (MSI) status however, significantly correlated with tumour grade. Expression levels of MTSS1 and an associated gene, MTSS2, were examined in 16 BlCa cell lines, 9 clonally-derived BlCa sublines, and 30 transitional cell carcinomas (TCCs) collected by the Heinrich-Heine University from 1993-2000. Variable gene expression was observed in BlCa cell lines and tumour samples. No significant correlation of MTSS expression and invasive ability was observed for the cell lines or tumour samples. Further studies eliminated promoter methylation and p53 functional status as mechanisms involved in MTSS1 and MTSS2 down-regulation. Functional studies performed on stable MTSS1-expressing BlCa lines found that although migration was increased, cells displayed reduced anchorage-independent growth. The invasive ability of these cells was unchanged confirming that expression does not correlate with invasive ability. These data support the role of MTSS1 as a tumour suppressor and not as a metastasis suppressor gene. Although MTSS1 may not be useful in predicting more invasive disease, its role as a tumour suppressor in cancer may be useful.

Together, colorectal (CRC) and bladder cancer (BlCa) are responsible for a large percentage of cancer related morbidity and mortality in Western society. A dramatic reduction in patient survival occurs as these cancers progress towards invasive and metastatic disease, from a five year survival rate of about 90% for localised disease to approximately 5-10% for advanced disease involving distant metastasis. A greater understanding of disease progression will lead to enhanced screening, diagnostic and treatment strategies, in turn providing an improved prognosis for the patient. The purpose of this study was to expand the current molecular knowledge of CRC and BlCa by elucidating the role of Mxi1 mutations and MTSS1 expression in CRC and BlCa respectively, and to examine the diagnostic potential of these genes. The Mxi1 coding region for 41 tumours, collected by the South Western Sydney Colorectal Cancer Tumour Bank from 2000-2001, was screened for mutations using Dideoxy Fingerprinting (ddF) and sequencing. Sequence alterations were detected in 34% of tumours. Three different polymorphisms and three mutations were detected. One mutation could possibly affect the tumour suppressor function of Mxi1. The presence of a gene mutation did not correlate to any clinical characteristics and is therefore not a suitable diagnostic marker. Microsatellite instability (MSI) status however, significantly correlated with tumour grade. Expression levels of MTSS1 and an associated gene, MTSS2, were examined in 16 BlCa cell lines, 9 clonally-derived BlCa sublines, and 30 transitional cell carcinomas (TCCs) collected by the Heinrich-Heine University from 1993-2000. Variable gene expression was observed in BlCa cell lines and tumour samples. No significant correlation of MTSS expression and invasive ability was observed for the cell lines or tumour samples. Further studies eliminated promoter methylation and p53 functional status as mechanisms involved in MTSS1 and MTSS2 down-regulation. Functional studies performed on stable MTSS1-expressing BlCa lines found that although migration was increased, cells displayed reduced anchorage-independent growth. The invasive ability of these cells was unchanged confirming that expression does not correlate with invasive ability. These data support the role of MTSS1 as a tumour suppressor and not as a metastasis suppressor gene. Although MTSS1 may not be useful in predicting more invasive disease, its role as a tumour suppressor in cancer may be useful.

Together, colorectal (CRC) and bladder cancer (BlCa) are responsible for a large percentage of cancer related morbidity and mortality in Western society. A dramatic reduction in patient survival occurs as these cancers progress towards invasive and metastatic disease, from a five year survival rate of about 90% for localised disease to approximately 5-10% for advanced disease involving distant metastasis. A greater understanding of disease progression will lead to enhanced screening, diagnostic and treatment strategies, in turn providing an improved prognosis for the patient. The purpose of this study was to expand the current molecular knowledge of CRC and BlCa by elucidating the role of Mxi1 mutations and MTSS1 expression in CRC and BlCa respectively, and to examine the diagnostic potential of these genes. The Mxi1 coding region for 41 tumours, collected by the South Western Sydney Colorectal Cancer Tumour Bank from 2000-2001, was screened for mutations using Dideoxy Fingerprinting (ddF) and sequencing. Sequence alterations were detected in 34% of tumours. Three different polymorphisms and three mutations were detected. One mutation could possibly affect the tumour suppressor function of Mxi1. The presence of a gene mutation did not correlate to any clinical characteristics and is therefore not a suitable diagnostic marker. Microsatellite instability (MSI) status however, significantly correlated with tumour grade. Expression levels of MTSS1 and an associated gene, MTSS2, were examined in 16 BlCa cell lines, 9 clonally-derived BlCa sublines, and 30 transitional cell carcinomas (TCCs) collected by the Heinrich-Heine University from 1993-2000. Variable gene expression was observed in BlCa cell lines and tumour samples. No significant correlation of MTSS expression and invasive ability was observed for the cell lines or tumour samples. Further studies eliminated promoter methylation and p53 functional status as mechanisms involved in MTSS1 and MTSS2 down-regulation. Functional studies performed on stable MTSS1-expressing BlCa lines found that although migration was increased, cells displayed reduced anchorage-independent growth. The invasive ability of these cells was unchanged confirming that expression does not correlate with invasive ability. These data support the role of MTSS1 as a tumour suppressor and not as a metastasis suppressor gene. Although MTSS1 may not be useful in predicting more invasive disease, its role as a tumour suppressor in cancer may be useful.

No description available.