Dissertations / Theses on the topic 'MET signalling'

The Receptor Tyrosine Kinase (RTK) Met influences behaviour of several cancers by controlling growth, survival and metastasis. Recently, compartmentalisation of signals generated by RTKs, due to their endocytosis / trafficking, has emerged as a major determinant of various cell functions. The aim of my project was to study oncogenic Met signalling in relation to endosomal trafficking and to determine the consequences of such spatial changes on tumour cell growth and migration in vitro and in vivo. The model studied was NIH3T3 cells stably transfected with Wild type (Wt) Met or with three distinct mutants reported in human cancers. I found that two activating mutations in the kinase domain are highly tumorigenic in vivo. Using functional assays and tumour growth experiments, I demonstrated that one mutant is highly sensitive to Met specific tyrosine kinase inhibitors (TKI) while another is resistant. Such results suggested that therapeutical approaches to these mutants should be different. Furthermore, I demonstrated a direct link between endocytosis and tumorigenicity, suggesting a major role for Met endosomal signalling in cancer progression. Using confocal microscopy and quantitative biochemical assays, I demonstrated that Met mutants displayed an increased endocytosis and recycling and a decreased degradation profile. This led to an accumulation of phosphorylated Met on endosomes that induced activation of the GTPase Rac1, loss of stress fibres and increased cell migration. Blocking endocytosis by pharmacological and genetic 4 means inhibited mutants’ anchorage independent growth and, strikingly, tumorigenesis and experimental metastasis. Interestingly, the mutant resistant to TKI inhibition was sensitive to endocytosis inhibition. Taken together, these results suggest that Met localisation constitutes a major determinant in neoplastic development, while Met activation alone is insufficient to effect this change.

Met, the receptor of Hepatocyte Growth Factor, is a receptor tyrosine kinase (RTK) overexpressed or mutated in cancer. RTKs have been increasingly recognised to signal post-endocytosis, possibly leading to unique consequences on cellular outcome due to the spatial and temporal activation of downstream signalling pathways. The objectives of my study were to investigate the role of Met “endosomal signalling” in cancer progression. I found, using four human breast cell lines, that the requirement of Met endocytosis for Met signalling as well as Met trafficking significantly vary with the cells’ aggressiveness, suggesting Met resides longer on endosomes in invasive cells. Furthermore Met endosomal localisation increases with the progression of breast cancer of human samples. Our study suggests that the endosomal location of Met is important in breast cancer progression. I used a model of Wt and two Met oncogenic mutants, M1268T and D1246N, expressed in NIH3T3 fibroblasts. I determined some mechanisms regulating the constitutive endocytosis and defect in degradation of the mutants. I established that targeting these mechanisms could be used to reduce Met mutants’ tumourigenicity. Thus impairing c-Cbl or Grb2 expression and/or binding to Met mutant or restoring Met mutant degradation through inhibiting the chaperone protein HSP90, greatly reduced the transforming capacities of the mutants in vitro and in vivo, including the D1246N that I show to be resistant to small molecule Met inhibitors.

Growth factor receptor tyrosine kinases (RTKs) are critical initiators of signal transduction pathways necessary for cell growth, differentiation, migration and survival. Many of these signals are coordinated through scaffold proteins that are phosphorylated upon their recruitment to the activated receptor complex. This provides binding sites for multiple proteins to activate and generate distinct biological responses. The amplitude and duration of a signal is regulated via dephosphorylation and degradation of target proteins. Signal regulation in this manner acts to promote the formation and disassembly of multi-protein complexes and diversify and localize signals downstream from RTKs.
The Met RTK and its ligand, hepatocyte growth factor (HGF), are positive regulators of epithelial morphogenesis, scatter, and survival. However little was known regarding the proteins responsible for attenuating Met receptor activation. In Chapter II, I demonstrated that the Met receptor was hyperphopshorylated in PTP1B-null mice in response to Fas-induced liver damage. Inhibition of Met signaling with PHA665752, removed protection from liver failure in PTP1B-null hepatocytes, demonstrating that PTP1B was a negative regulator of the Met RTK and its removal promoted cell survival against Fas-induced hepatic failure.
In response to Met receptor stimulation, the Gab1 scaffold protein is the prominent protein recruited and phosphorylated downstream from Met and is critical in mediating Met-dependent biological responses. In chapters III and IV, I identified the serine/threonine kinase Pak4 and the microtubule-bound guanine nucleotide exchange factor GEF-H1 as novel proteins recruited to Gab1 following Met receptor activation. I demonstrate that Gab1 and Pak4 synergize to enhance migration and invasion following HGF stimulation. Furthermore, the recruitment of Pak4 to Gab1 is important for its subcellular localization to lamellipodia and critical for epithelial cell dispersal and morphogenesis downstream from Met. In addition, GEF-H1 is important in focal adhesion formation and turnover and this correlates with the ability of GEF-H1 to promote epithelial migration and invasion downstream from Met.
Overall, these studies investigate molecular mechanisms regulating Met-dependent signals and demonstrate for the first time that the Met receptor is a substrate for PTP1B and identify Pak4 and GEF-H1 as key integrators of Met dependent cellular migration and invasion.
Les récepteurs tyrosine kinase aux facteurs de croissance sont des initiateurs critiques des voies de signalisation nécessaires à la croissance, la différentiation, la migration et la survie cellulaire. Beaucoup de ces signaux sont coordonnés par des protéines d'échafaudage qui sont phosphorylées au cours de leur recrutement au complexe de récepteurs activés. Ceci fournit des sites de liaison à de multiples protéines permettant l'activation et la génération de différentes réponses biologiques. L'amplitude et la durée d'un signal est régulée via la déphosphorylation et la dégradation des protéines cibles. De cette façon, la régulation du signal agit pour promouvoir la formation et le désassemblage de complexes protéiques et pour diversifier et localiser les signaux en aval des récepteurs tyrosine kinase.
Le récepteur Met et son ligand HGF (Hepatocyte Growth Factor) sont des régulateurs de la morphogenèse, la dispersion et la survie des cellules épithéliales. Toutefois, peu d'informations sont disponibles sur les protéines responsables de l'extinction des signaux issus du récepteur Met. Dans le chapitre II, je démontre que le récepteur Met est hyperphosphorylé dans les souris knock-out pour PTP1B en réponse aux dommages induits par Fas. L'inhibition par le composé PHA665752 de la signalisation par Met, relève la protection contre les crises hépatiques dans les souris KO pour PTP1B. Ceci démontre que PTP1B est un régulateur négatif de Met et son retrait permet la survie cellulaire contre les crises hépatiques induites par Fas.
En réponse à la stimulation du récepteur Met, la protéine d'échafaudage Gab1 est la plus importante des protéines recrutées et phosphorylées en aval de Met et cette protéine est critique dans la médiation des réponses biologiques dépendantes de Met. Dans les chapitres III et IV, j'ai identifié la kinase Ser/Thr Pak4 et le facteur d'échange de guanine lié aux microtubules (GEF-H1) en tant que nouvelles protéines recrutées à Gab1 suite à l'activation de Met. Je démontre que Gab1 et Pak4 agissent de façon synergique pour promouvoir la migration et l'invasion suite à la stimulation par HGF. De plus, le recrutement de Pak4 à Gab1 est important pour sa localisation cellulaire dans les lamellipodes et est critique pour la dispersion et la morphogenèse des cellules épithéliales en aval de Met. En outre, GEF-H1 est important pour la formation et le roulement des points d'adhésion focaux ce qui est en corrélation avec la capacité de GEF-H1 de promouvoir la migration et l'invasion épithéliale en aval de Met.
Ces études ont pour but d'investiguer les mécanismes moléculaires régulant les signaux dépendants de Met et démontrent pour la première fois que le récepteur Met est un substrat pour PTP1B. Finalement, Pak4 et GEF-H1 sont identifiés comme des intégrateurs clés de la migration et l'invasion cellulaire dépendante de Met.

Activation of the Met receptor tyrosine kinase by its ligand, Hepatocyte Growth Factor (HGF), leads to mitogenesis, cell motility, morphogenesis, and angiogenesis. Mutational analysis has demonstrated the requirement of a single tyrosine within the carboxy-terminus (Y1356) of the Met receptor for the recruitment and activation of all Met-dependent signalling pathways and for the transformation of fibroblasts by the Tpr-Met oncogene. The selective abolishment of Grb2 from the Tpr-Met oncoprotein, by generating an asparagine to histidine mutation two amino acids downstream from Y1356 (N1358H), led to a reduction in Tpr-Met-mediated transformation of fibroblasts. Moreover, Met receptor studies demonstrate that while a Grb2 binding site is not required for epithelial cell motility, it is critical for the formation of branching tubules when cells are suspended in a collagen matrix. This suggests that Grb2-dependent pathways are involved in the organization and polarization of epithelial cells following Met receptor stimulation.
Grb2 associated molecules, Gab1 and Cbl, are highly phosphorylated following stimulation of the Met receptor. Moreover, signaling pathways associated with Gab1 are critical for branching tubulogenesis in epithelial cells. Expression of a constitutively active version of Cbl, 70z-Cbl, results in an epithelial-mesenchymal transition, leading to the breakdown of cellular junctions and reorganization of the actin cytoskeleton. The amino-terminal SH2 domain is the minimal region required to induce morphological changes, which may be mediated through its interaction with the Met receptor, and/or an unidentified protein of 150 kDa.

Receptor tyrosine kinases (RTKs) are transmembrane cellular receptors that respond to growth factor stimulation and promote cellular proliferation in normal biological processes, such embryogenesis and wound healing. RTK activation and signalling are tightly regulated processes; their dysregulation promotes unrestrained cellular proliferation and is associated with cancer initiation and progression. As such, RTKs are targets of many therapeutic strategies for the treatment of cancer. However, despite initial success, both innate and acquired resistance hinders the efficacy of many of these inhibitors. Active signalling by the Met RTK plays a role in melanomas, osteosarcomas, breast carcinomas, gliomas, non-small cell lung cancers (NSCLC), and cancers of the gastro-intestinal (GI) tract. Multiple mechanisms of Met oncogenic activation have been identified, including autocrine/paracrine stimulation, Met overexpression, genomic amplification, point mutation and alternative splicing. Inhibitors of Met are currently in all phases of clinical trials for multiple tumour types, thus there exists a need to better understand the mechanisms through which Met promotes tumourigenesis, and how cells respond to Met inhibitors, and how resistance can occur.In my thesis, I establish that in four different MET-amplified gastric cancer cells there is a Met-dependent loss of its negative regulator, the E3 ligase, Cbl. I utilized structure-function analysis to demonstrate that this loss of Cbl levels requires Met kinase activity, Cbl E3 ligase activity, and recruitment of Cbl to Met. Where Met is active, Cbl is recruited and subsequently ubiquitinated, and degraded through the proteasome. I also observed that EGFR, which is also negatively regulated by Cbl, is less efficiently degraded upon stimulation in the presence of active Met and low Cbl levels. Thus, I demonstrate that Met-driven Cbl loss not only promotes dysregulation of Met, but of other Cbl target proteins as well.As much of what is known with respect to Met signalling has been identified in the context of activation by its ligand, hepatocyte growth factor (HGF), I investigated the Met-dependent pathways and transcriptional program in gastric cancer cells where Met is chronically active via amplification. I observed that activation of the Ras/Mek/Erk, PI3K/AKT and STAT3 pathways all require Met kinase activity, with STAT3 signalling required for Met-dependent cell proliferation. Interestingly, upon treatment with Met inhibitor, Erk becomes reactivated at later time points (16-24h) in 2/4 cell lines tested. This correlated with loss of Erk negative regulators, DUSP4 and DUSP6, upon Met inhibition. Dual inhibition of Met and Mek decreased cell viability as compared to inhibition of either alone. Hence loss of Erk negative regulators upon Met inhibition, allows for reactivated Erk to promote cell survival and may contribute to innate resistance to targeted Met therapeutics. Next, I established Met inhibitor-resistant cells and utilized gene and protein expression arrays to identify the mechanisms of resistance. I observed that resistant cells were still MET-amplified, but Met kinase activity remained inhibited. Met-independent cell proliferation is, in part, mediated by Erk signalling. Further, I also provide evidence that cell survival signals, in the presence of Met inhibition, may be mediated by a mesenchymal-to-epithelial transition. Altogether, the reactivation of Erk signalling under conditions of innate and acquired resistance to Met inhibitors suggests that combinatorial therapy targeting both Met and Mek may lead to better efficacy and response.
Les récepteurs à activité kinase (RTK) sont des protéines transmembranaires situées à la surface des cellules qui, une fois activés par des facteurs de croissance, induisent la prolifération cellulaire durant des processus biologiques normaux. La signalisation par les RTKs est un processus devant être hautement régulé étant donné qu'une signalisation aberrante des RTKs induit une prolifération cellulaire incontrôlée typique au développement et à la progression de tumeurs. Les RTKs constituent donc une cible thérapeutique de choix pour le traitement du cancer et plusieurs inhibiteurs de RTKs sont maintenant utilisés en clinique. Par contre, malgré des résultats initiaux prometteurs, il appert que de multiples tumeurs développent des mécanismes de résistance aux inhibiteurs de RTKs. Le RTK Met joue un rôle important dans de multiples cancers. Plusieurs mécanismes d'activation oncogénique du récepteur Met ont été identifiés. Des inhibiteurs de Met sont présentement testés en essais cliniques pour le traitements du cancers. Il est donc essentiel de mieux comprendre comment le RTK Met promeut la formation de tumeurs, comment les cellules cancéreuses répondent aux traitements ainsi que les mécanismes de développement de résistance aux inhibiteurs. Dans cette thèse, j'établis que dans des lignées de cellules cancéreuses gastriques où le gène MET est amplifié, il y a une perte de la protéine ligase E3 Cbl qui est un inhibiteur de Met. À l'aide d'une analyse structurelle et fonctionnelle, je démontre que cette perte de Cbl requière l'activité kinase de Met, l'activité ligase de Cbl et le recrutement de Cbl à Met. L'activation de Met mène au recrutement de Cbl, à son ubiquitination et sa dégradation via le protéasome. J'ai observé que le RTK EGFR, qui est aussi régulé négativement par Cbl, est moins efficacement dégradé suite à sa stimulation en présence d'un récepteur Met actif et de bas niveaux de Cbl. Ainsi, je démontre que la perte de Cbl suite à l'activation de Met mène à la dérégulation de Met, ainsi que d'autres cibles de Cbl.Étant donné que la majorité de ce qui est connu concernant la signalisation en aval de Met a été étudiée dans le contexte de l'activation du RTK par son ligand, le facteur de croissance hépatocytaire HGF, j'ai décidé d'étudier les signaux et programmes de transcription activés en aval de Met quand le récepteur est activé de manière chronique, suite à son amplification. J'ai observé que l'activation des voies de signalisation Erk, AKT et STAT3 requièrent toutes l'activité kinase Met, la signalisation par STAT3 contribuant à la prolifération cellulaire. Curieusement, suite au traitement des cellules cancéreuses avec un inhibiteur de Met, Erk devient réactivé à des temps subséquents (16-24h) dans deux des quatre lignées cellulaires analysées. Ceci corrobore avec la perte des régulateurs négatifs de Erk, DUSP4 et DUSP6, suite à l'inhibition de Met. L'inhibition combinée de Met et Mek diminue la viabilité cellulaire comparée à l'inhibition de Met ou Mek seulement. Par conséquent, la perte des régulateurs négatifs d'Erk suite à l'inhibition de Met permet la réactivation d'Erk et la survie des cellules, et peut contribuer à la résistance innée de certaines cellules cancéreuses aux inhibiteurs de Met.Suite à ces résultats, j'ai établi des lignées cellulaires résistantes à un inhibiteur de Met et analysé l'expression des gènes et protéines à l'aide de matrices pour identifier les mécanismes de résistances. J'ai observé que le gène MET est toujours amplifié dans les cellules résistantes, mais que l'activité kinase reste inhibée en présence de l'inhibiteur. La prolifération cellulaire indépendante de Met est en partie assurée par Erk. Sur la base de ces résultats, la réactivation de la voie de signalisation Erk dans des conditions de résistance innée ou acquise aux inhibiteurs de Met implique qu'une thérapie combinatoire ciblant Met et Mek puisse être plus efficace que les monothérapies.

Le cancer de la prostate (PCa) est le deuxième cancer le plus courant chez les hommes au niveau mondial. Le suppresseur de la signalisation des cytokines 1 (SOCS1) est considéré comme un suppresseur de tumeur en raison de la fréquente répression épigénétique de ce gène dans de nombreux cancers. Il a été reporté que SOCS1 inhibait l’activation de STAT3 induite par l’IL-6, ainsi que les cyclines et les kinases dépendantes des cyclines dans les cellules malignes de la prostate. D’autre part, il a été montré que SOCS1 n’était pas essentiel lors du contrôle de la signalisation de l’IL-6 dans les hépatocytes dépourvus de cette protéine, cependant elle est essentielle pour atténuer la signalisation du facteur de croissance des hépatocytes (HGF) via son récepteur MET. MET est un récepteur de tyrosine kinases qui est surexprimé dans le PCa agressif et métastatique. Notre hypothèse de recherche propose que la répression de SOCS1 par méthylation du promoteur et la dérégulation de l’expression de MET et de sa signalisation, sont des mécanismes pathogéniques liés au développement et à la progression du PCa. Nous avons généré des lignées de cellules PC3 et DU145 stables exprimant SOCS1. Les cellules ont été stimulées avec HGF et l’activation des voies de signalisation a été évaluée par immunobuvardage. Des essais in vitro de migration, de prolifération et d’invasion ont été effectués en présence de HGF. Des gènes de transition épithélio-mésenchymateuse ont été évalués par PCR quantitatif en présence ou non du facteur de croissance. Les cellules du PCa transfectées ou pas avec SOCS1 ont été inoculées dans des souris NOD SCID gamma de façon sous-cutanée ou orthoptique afin d’évaluer respectivement la croissance tumorale et la formation de métastases. Les tumeurs reséquées ont été analysées histologiquement et biochimiquement. Nos résultats montrent que SOCS1 atténue l'activation de MET induite par HGF et la phosphorylation d’ERK dans les cellules PC3, ainsi que la phosphorylation d’ERK et d’AKT dans les cellules DU145. SOCS1 inhibe également la prolifération cellulaire induite par HGF, ainsi que la migration et l’invasion in vitro. De plus, SOCS1 réduit l’expression des gènes de transition épithélio-mésenchymateuse impliqués dans la dégradation des composants de la matrice extracellulaire dans les cellules DU145 mais pas dans les cellules PC3. La surexpression de SOCS1 a stimulé l’augmentation de déposition de collagène, in vivo. Les tumeurs formées par les cellules exprimant SOCS1 étaient de taille significativement plus petites avec une réduction de la prolifération comparé aux tumeurs provenant des cellules contrôles. En outre, SOCS1 a inhibé la formation de métastases à distance dans un modèle orthotopique. En conclusion, nous suggérons que SOCS1 est un suppresseur de tumeur indispensable de la prostate, et qu’au moins une partie de sa fonction a lieu via la régulation négative de la signalisation du récepteur MET.
Abstract : Prostate cancer (PCa) is the second most common cancer among men worldwide. Suppressor of cytokine signaling 1 (SOCS1) is considered a tumor suppressor due to frequent epigenetic repression of the SOCS1 gene in several human malignancies. Inactivation of SOCS1 also occurs in PCa by gene methylation and micro-RNA-mediated repression. SOCS1 has been reported to inhibit IL-6-induced STAT3 activation and down-regulates cyclins and cyclin-dependent kinases in PCa cells. It has been shown that SOCS1 is not required to control IL-6 signaling in SOCS1-deficient hepatocytes, but is essential to attenuate hepatocyte growth factor (HGF) signaling via its receptor MET. This protein is a receptor tyrosine kinase (RTK), overexpressed in aggressive and metastatic PCa. Thus we hypothesized that the repression of SOCS1 via promoter methylation and deregulated MET expression and signaling are inter-related pathogenic mechanisms in PCa development and progression. We generated stable SOCS1-expressing PCa cell lines (PC3 and DU145) using lentiviral transduction followed by clonal selection via limiting dilution. Cells were stimulated with HGF and downstream signaling events were assessed by Western blot. Proliferation, migration and invasion assays were also conducted in the presence of HGF in vitro. Epithelial mesenchymal transition genes were evaluated by qPCR in the presence or absence of the growth factor. The PCa cells transfected with SOCS1 and non-transfected controls were inoculated into NOD SCID gamma mice as xenografts or as orthotopic tumors to assess tumor growth and metastasis formation, respectively. Resected tumors were further analyzed histologically and biochemically. Our results showed that SOCS1 attenuates HGF-induced MET activation and ERK phosphorylation in PC3 and DU145 PCa cell lines. SOCS1 inhibited HGF induced cell proliferation, migration and invasion in vitro. Additionally, SOCS1 decreased epithelial mesenchymal transition genes involved in the degradation of extracellular matrix components in DU145 cells but not in PC3. In vivo, SOCS1 overexpression leads to an increase of collagen deposition. Tumors formed by SOCS1 expressing cells were significantly smaller in size with reduced cell proliferation compared to tumors arising from control cells. Furthermore, SOCS1 inhibited distant metastasis formation in the orthotopic model. Overall our results suggest that SOCS1 has a tumor suppressor role in PCa evolution and part of this function is mediated by the negative regulation of MET receptor signalling and down-regulation of genes supporting migration and invasion processes such as matrix metalloproteinases.

Bacterial pathogens dramatically affect host cell transcription programs for their own profit, however the underlying mechanism in most cases remain elusive. While investigating the effects of listeria monocytogenes on histone modifications, we discovered a new transcription regulatory machanism by which the expression of genes is repressed, during infection. Upon infection by L. monocytogenes, the secret virulence factor, InlB, binds the c-Met receptor and activates signaling through PI3K/Akt. This signaling platform is necessary for causing the relocalization of the histone deacetylase, SIRT2, to the nucleus and associating to chromatin.In characterizing the mechanism governing SIRT2 nuclear relocazing during infection, our results have demonstrated that SIRT2 undergoes a post-translational modification. SIRT2 undergoes dephosphorylation at a novel N-terminal phospho-site. SIRT2 is recruiter to the transcription star sites of genes repressed during inection leading to H3K18 deacetylation and transcriptional repression.finnaly, my results demonstrate that SIRT2 is hijacked by L monocytogenes and promotes an increase in intracellular bacteria. Together, these data uncover a key role for SIRT2 mediated H3K18 deacetylation during infection and characterize a novel mechanisme imposed by a pathogenic bacteriomto reprogram the host cell.

Neutrophils form a first line of defence against infections. These short-lived, terminally differentiated cells perform many important functions, including chemotaxis, degranulation, reactive oxygen species (ROS) release and cytokine production. Whilst neutrophils are essential for host immunity, their inappropriate recruitment, activation and/or removal can contribute to excessive inflammation and host damage, as exemplified in autoimmune diseases such as rheumatoid arthritis. It is therefore essential that neutrophil function is tightly regulated. Neutrophils are activated by a range of stimuli, including immune complexes. Neutrophil functions are tightly regulated by intracellular signalling events that are induced by the ligation of cell surface receptors, for example, the binding of immune complexes to Fc receptors. Phosphoinositide 3-kinase (PI3K) and extracellular signal-regulated kinase (Erk) are key signalling intermediates that act downstream of many cell surface receptors. They are involved in the regulation of numerous biological processes in the neutrophil. Using pharmacological interventions, I analysed PI3K signalling in immune complex-stimulated human neutrophils and uncovered a previously uncharacterised, noncanonical signalling pathway, PI3K-Cdc42-Pak-Mek-Erk. This represents an unusual situation where Pak acts as the MAP3K downstream of Cdc42 in a PI3K-dependent fashion. By performing a range of functional experiments, I showed that this unconventional signalling pathway promotes apoptosis in human neutrophils by regulating the ratio between anti- and pro-apoptotic members of the Bcl-2 family proteins. No other immune complex-induced, PI3K-dependent neutrophil function tested depended on PI3K-Cdc42-Pak-Mek-Erk signalling. Mouse knock-outs of all components of this signalling pathway have been described. Immune complex-induced apoptosis was also PI3K-dependent in mouse neutrophils, but experiments performed with inhibitors showed that, in contrast to human neutrophils, this was not dependent on PI3K-Cdc42-Pak-Mek-Erk signalling. The myeloid leukaemia cell line, PLB-985 is amenable to knock-down and can be differentiated to become neutrophil-like. These cells are not notably activated by immune complexes, perhaps because they do not express the major Fcγ receptor, CD16. Since retroviral expression of CD16 in PLB985 cells did not improve their response to activation by immune complexes, I was not able to confirm my observations with human neutrophils genetically. Collectively, I showed that a novel, pro-apoptotic signalling pathway operates downstream of Fcγ receptors in the human neutrophil. The fact that this signalling pathway appears to regulate apoptosis specifically suggests uncoupling pro- and anti-inflammatory effects induced by immune complexes might be possible. This may be helpful in the design of improved therapies of autoimmune diseases such as rheumatoid arthritis, in which immune complex-driven neutrophilic inflammation contributes to disease pathogenesis and where neutrophil apoptosis is disturbed.

Tot i que es coneix l’involucrament de les cèl·lules pancreàtiques acinars en patologies exocrines (pancreatitis i càncer de pàncrees), la manca de models normals basats en cèl·lules ha limitat l’estudi de les alteracions que succeeixen en el programa de diferenciació pancreàtica. Hem demostrat prèviament que les cèl·lules mare embrionàries murines, que són pluripotents, poden adquirir un fenotip acinar in vitro. Això es va aconseguir, en part, amb una combinació de senyals que provenien del cultiu de pàncrees fetals que no era, però, específic del llinatge pancreàtic. L’objectiu d’aquest treball ha estat el de desenvolupar un protocol selectiu pel llinatge acinar basat en l’activació seqüencial de vies de senyalització que recapitulin el desenvolupament pancreàtic in vivo, a través de la formació definitiva de l’endoderm, l’especificació pancreàtica i acinar i l’expansió/diferenciació de progenitors acinars. El tractament de cossos embrionaris amb Activina A va promoure l’expressió de gens d’endoderm com està prèviament descrit. El tractament subsegüent amb àcid Retinoic, FGF10 i Ciclopamina, un inhibidor de la via de Hedgehog, va resutar en la inducció dels marcadors de progenitors pancreàtics Pdx1, Ptf1a i Cpa1 però també d’aquells expressats en el llinatge pancreàtic, que van ser reduïts amb la inhibició de BMPs. Les cèl·lules van ser a continuació cultivades en Matrigel utilitzant un sistema de cultiu en 3D en presència de fol·listatina, dexametasona i KGF comportant una inducció significativa dels nivells de mRNA i proteïna de marcadors acinars i una disminució de l’expressió dels de marcadors acinars. A més, es va veure que Amyl es secretava en el medi. Aquestes dades indiquen que l’activació selectiva del programa de diferenciació acinar en cèl·lules mare embrionàries es pot dur a terme mitjançant una inducció esgraonada de vies de senyalització involucrades en el desenvolupament pancreàtic exocrí proporcionant una eina potencial per estudiar la diferenciació pancreàtica i malalties relacionades amb el pàncrees.
Despite known involvement of pancreatic acinar cells in exocrine pathologies (pancreatitis and pancreatic cancer), the lack of normal cell-based models has limited the study of the alterations that occur in the acinar differentiation program. We have previously shown that mESC (murine embryonic stem cells), which are pluripotent, can acquire an acinar phenotype in vitro. This was achieved, in part, by a combination of signals provided by the culture of foetal pancreases which was, however, no specific for the acinar lineage. The aim of this work was to develop a protocol selective for the acinar lineage based on the sequential activation of signaling pathways that recapitulate pancreatic development in vivo, through the definitive endoderm formation, the pancreatic and acinar specification and the expansion/differentiation of acinar progenitors. Treatment of embryoid bodies with Activin A enhanced the expression of endodermal genes as previously described. Subsequent treatment with Retinoic acid, FGF10 and Cyclopamine, an inhibitor of the Hedgehog pathway, resulted in the enhancement of pancreatic progenitor markers Pdx1, Ptf1a and Cpa1 but also of those expressed in the hepatic lineage, which were reduced by BMPs inhibition. Cells were further cultured in Matrigel using a 3D culture system in the presence of follistatin, dexamethasone, and KGF leading to a significant enhancement of the mRNA and protein levels of acinar markers while decreasing the expression of endocrine ones. Moreover, active Amyl was released into the medium. These data indicate that the selective activation of the acinar differentiation program in ES cells can be achieved by stepwise induction of signaling pathways involved in pancreatic exocrine development providing a potential tool for studying pancreatic differentiation and pancreas-related diseases.

Class I PI3Ks are a family (α, β, δ and γ) of ubiquitous lipid kinases that can be activated by cell surface receptors to 3-phosphorylate PI(4,5)P2 (phosphatidylinositol(4,5)-bisphosphate) and generate the signalling lipid PI(3,4,5)P3. The PI(3,4,5)P3 signal then activates a diverse collection of effector proteins involved in regulation of cell migration, metabolism and growth. The importance of this network is evidenced by the relatively high frequency with which cancers acquire gain-of-function mutations in this pathway and huge efforts to make PI3K inhibitors to treat cancer. The canonical model describing these events suggests class I PI3Ks are activated at the plasma membrane and generate PI(3,4,5)P3 in the inner leaflet of the plasma membrane where its effectors are activated. The PI(3,4,5)P3 signal can be terminated directly, by the tumour-suppressor and PI(3,4,5)P3-3-phosphatase PTEN, or modified to a distinct PI(3,4)P2 signal, by SHIP-family 5-phosphatases. The PI(3,4)P2 is removed by INPP4-family 4-phosphatases. Published work has shown that PI(3,4,5)P3 signalling can also occur in endosomes and nuclei, however, there is very little data defining the intracellular distribution of endogenous class I PI3Ks that supports these ideas; this is as a result of technical problems such as; their very low abundance, poor antibody-based tools and artefacts generated by overexpression of PI3Ks. Past work has indicated that, in PTEN-null mouse models of prostate tumour progression, either PI3Kβ or PI3Ks α and β, have important roles. Furthermore, the cell types and mechanism involved remained unclear. Recent published work in the host laboratory had indicated that there is an unexpectedly large accumulation of PI(3,4)P2 in PTEN-null cells that might be an important part of its status as a major tumour suppressor. The explanation and prevalence of this observation was unclear but potentially a result of PTEN also acting as a PI(3,4)P2 3-phosphatase in vivo. MEFs were derived from genetically-modified mice expressing endogenous, AviTagged class I PI3K subunits and used in experiments to define the subcellular localisation of class I PI3Ks. We found that following stimulation with PDGF, class IA PI3K subunits were unexpectedly depleted from the adherent basal membrane, in contrast, p85α and p110α, but not p85β and p110β, accumulated transiently in the nucleus. Interestingly, p110β, but none of the other subunits, was constitutively localised in the nucleus. These results support the idea that class I PI3K and PI(3,4,5)P3 signalling occurs in the nucleus. In organoids derived from WT, PI3Kγ-null or PTEN-null mouse prostate, application of PI3K-selective inhibitors revealed that PI3Kα had a dominant role in generating PI(3,4,5)P3 in prostate epithelial cells. The levels of PI(3,4)P2 were also elevated substantially in PTEN-null, compared to WT prostate organoids, use of PI3K-selective inhibitors suggested that it was also generated by PI3Kα. These data were consistent with the idea that PTEN can act as a PI(3,4)P2 3-phosphatase. Surprisingly, raising the pH of the organoids medium dramatically increased accumulation of PI(3,4,5)P3 and PI(3,4)P2, although the cause of this effect was unclear, we hypothesised the pH of the local environment may influence signalling via class I PI3Ks.

Background: Very recently a gene marker panel that allows the mutational analysis of APC, CTNNB1, B-RAF and K-RAS was conceived. The aim of the present study was to use the 4-gene marker panel covering the Wnt and Ras-Raf-MEK-MAPK signalling pathways to determine the percentage of sporadic colorectal carcinomas (CRC) carrying at least one of the four above-mentioned genes in a mutated form alone and/or in combination with microsatellite instability (MSI) and to compare the sensitivity of the gene marker panel used in this study with that of gene marker panels previously reported in the scientific literature. Methods: CTNNB1 and B-RAF were screened by PCR-single-strand conformation polymorphism analysis and K-RAS gene mutations by restriction fragment length polymorphism analysis. For the mutational analysis of the APC gene mutation cluster region (codons 1243–1567) direct DNA sequencing was performed. The U.S. National Cancer Institute microsatellite panel (BAT25, BAT26, D2S123, D5S346 and D17S250) was used for MSI analysis. Results: It could be shown that about 80% of early stage CRC (UICC stages I and II) and over 90% of CRC in the UICC stage IV carried at least one mutated gene and/or showed MSI. No significant increase in the gene mutation frequencies could be determined when comparing tumours in the UICC stage I with those in UICC stage IV. Conclusions: When compared with previously published gene marker panels the 4-gene marker panel used in the present study shows an excellent performance, allowing to detect genetic alterations in 80–90% of human sporadic CRC samples analyzed.

This study focused on Corporate Community Involvement Disclosures (CCID), a theme usually disclosed under Corporate Social Responsibility Disclosures (CSRD) in annual reports. The primary aim of the research is to investigate the genuineness and raison d'être of CCID in annual reports. To do this the researcher adopted a holistic approach employing an extensive theoretical framework, which integrates Legitimacy, Stakeholder, Agency, Signalling and Semiotics theories and asking three main research questions. Firstly, what are the motivations for CCID in annual reports? Secondly, what is the information content of CCID in annual reports? And lastly, how real is CCID in annual reports? That is can CCID be read and construed as a real measure of corporate community development (CCD)? Using content analysis and a quality score index the study examined a panel dataset covering the period from 1999 to 2009. The data was collected from a sample of 803 annual reports of 73 UK companies taken from the FTSE 350 companies and cutting across all ten industries of the Industrial Classification Benchmark (ICB) Index. Generally the study is more of a quantitative study with hypotheses developed and tested with panel data regression models in order to provide answers to the three research questions. However, due to the sensitivity of the third research question, in addition to panel regression, the researcher performed a qualitative analysis of question three using semiotics. The study provided evidence to show that CCID as disclosed in annual reports have an undertone of reputation/impression management like other CSR disclosures (CSRD). The community activities reported do not seem to address the expectations of the local communities per se; rather the disclosures seemed to be targeted at a wider stakeholder group that is likely to offer immediate reward for such disclosures. Similarly result from semiotic analysis revealed that signification of reality is either doubtful or unreal for most companies sampled. The study is unique as it is the first to explore the reality of CCID as it appears in annual reports using a combination of a panel study approach and semiotics. In addition a major contribution of the study is that it explored the ways in which multiple theoretical underpinnings can inform research by developing a CCID Meta-theory model and thus provided a robust and enriched analysis and unique insights into the CCID phenomenon.

Colorectal cancer (CRC) is the third leading cause of death from cancer in North America. The KRAS gene is mutated in approximately 40-50% of all CRC, and this mutation precludes treatment with promising targeted therapeutics. c-MET is a receptor tyrosine kinase that is overexpressed in ~70% of CRCs, and expression is correlated with disease progression. We hypothesized that high c-MET plus mutant KRAS would result poor survival of CRC patients, by activating unique signalling pathways that may be targeted for therapeutic purposes. To this end, we used phosphoproteomics in a KRAS mutant cell line, and identified proteins phosphorylated on tyrosine in response to HGF stimulation, including a subset of those that contain SRC family kinase consensus motifs. Small molecule inhibitors of either SRC or c-MET reduced tyrosine phosphorylation of both proteins, indicating reciprocal signalling. We chose the c-MET target p190RhoGAP for future study, as it is often ubiquitously bound to p120RasGAP via phosphorylated tyrosine. We found that RasGAP expression is mediated in part by KRAS signalling, and that expression of RasGAP could partly rescue tumourigenicity of a CRC cell line where the mutant KRAS allele has been inactivated, indicating the requirement of both mutant KRAS and RasGAP expression in this model. We then conclude by looking at CRC patient samples to determine the role of KRAS mutation in the progression and survival of CRC. We found that both KRAS and c-MET copy number are correlated to KRAS mutation status, and that c-MET polysomy plus KRAS mutation leads to worse overall survival than KRAS mutation alone. Overall, we identified novel targets of c-MET and KRAS oncogenic signaling, and identify a population which may derive the most benefit from treatments targeting both of these lesions.

Medulloblastoma is the most common malignant paediatric brain tumour. Similar to other tumours, medulloblastoma pathogenesis involves abnormal regulation of several developmental growth pathways. As my thesis project, I studied the effects of aberrant HGF/MET signalling on medulloblastoma formation in two ways. In my first objective, I investigated the role that mutations play in activated HGF/MET signalling in medulloblastoma by searching for mutations in HGF/MET pathway genes, SPINT1, SPINT2, and MET, within primary medulloblastoma specimens. This screen identified several single nucleotide polymorphisms (SNPs) and two novel variations, one in each SPINT1 and SPINT2 genes. In my second objective, I generated a transgenic mouse model with cerebellar-specific aberrant MET signalling. These mice developed extensive cerebellar abnormalities but formed no tumours. These results indicate that mutations in the HGF/MET pathway components alone are not sufficient to initiate medulloblastoma formation and must coincide with additional genetic insults to promote tumour formation, maintenance, and progression.

Androgens are critical for the development and maintenance of adult male characteristics such as muscle mass and sexual function. Consequently, the established decline with age of serum testosterone (T) in males has major health implications. While the androgen receptor (AR) is the major mediator of genomic androgen action and is required for the development of the male phenotype, reproductive organs and the maintenance of male secondary sexual characteristics, it is the entrance of androgens into the cell that mediates the activation of the AR and the subsequent modulation of expression of androgen regulated genes. Testosterone, biologically the most important androgen in male serum, circulates either free, loosely bound to albumin or tightly bound to sex hormone binding globulin (SHBG). Each of these forms of serum T have different abilities to enter cells, and which proportion of serum T is capable of entering cells and initiating the androgen signalling cascade, thereby leading to the activation of the AR has not been precisely defined. The AR amino terminal domain (NTD) is responsible for the majority of the ability of the AR to activate genes but the relative roles of the two activation functions in the AR NTD (activation functions 1 and 5; AF1 and 5) have not been precisely defined while the role of the AF2 surface which forms in the ligand binding domain upon agonist binding is responsible for interactions with key coregulators and also with the NTD in the amino-carboxyl (N/C) interaction. Our laboratory has recently identified a region within AF5 between amino acids 500-535 to which somatic mutations in castrate resistant prostate tumour samples collocate. Due to the lack of functional information on the AF5 region and the NTD in general, the function of this region and the functional consequences of the mutations remain to be defined. The objectives of this thesis were to develop a specific mammalian cell based bioassay capable of reliable measuring T in serum and to determine the ability of this bioassay to measure a physiologically relevant fraction of T in serum. Additionally, this thesis aimed to determine the relative contributions and roles of the activation functions of the AR to overall AR transcriptional activity along with the functional consequences for AR signalling of prostate cancer mutations which have previously been identified in the AF5 region of the AR NTD. The mammalian-cell based bioassay developed in this thesis is capable of sensitively and reliably measuring serum T. However, evaluation of this bioassay utilising approximately 1000 serum samples from the Florey Adelaide Male Aging Study reveals that this bioassay measures a fraction of T in serum that most closely relates to serum T. Furthermore, this measure does not correlate more strongly with grip strength, sexual function or waist circumference than the existing immunoassay-based measures of serum T, highlighting the limitations of utilising a static mammalian cell-based androgen bioassay to measure physiological levels of serum T in males. The investigation of the roles of the activation functions in the AR in this thesis have revealed that while the AF1 domain is responsible for the majority of the transactivation activity of the AR, AF5 and AF2 govern the sensitivity and cellular response of the AR to androgens by providing protein and interdomain interaction interfaces. Furthermore, the evidence in this thesis demonstrates that the AR requires interdomain communication for sensitive AR signalling. Finally, the findings in this thesis demonstrate that the AF5 surface is required for the N/C interaction and coregulator interactions while advanced prostate cancer mutations identified within this region confer increased transactivation activity of the AR in the presence of high cellular levels of coregulators. Collectively, the findings in this thesis provide several novel insights into the mechanism of action of serum androgens and challenges several long held assumptions of androgenic action in males. These findings also delineate a mechanism of treatment failure in advanced prostate cancer, provide a novel model for the events leading to sensitive AR transactivation and contribute to the understanding of physiologically relevant levels of serum T.
Thesis (Ph.D.) -- University of Adelaide, School of Medicine, 2008