La Nucléophosmine (NPM1/B23) est une petite chaperonne moléculaire impliquée dans de nombreux processus cellulaires, tels que la régulation de l’expression génique ou le contrôle du cycle cellulaire. De nombreuses études rapportent une surexpression de NPM1 dans divers types de tumeurs solides incluant les cancers de la prostate, et son rôle proH prolifératif dans des lignées cellulaires tumorales d’origines variées est bien établi. La première partie de notre travail s’est attaché à évaluer le potentiel oncogénique de NPM1 dans l’épithélium prostatique in vivo. Pour cela, nous avons généré un modèle de souris transgéniques qui surexpriment NPM1 spécifiquement dans l’épithélium de la prostate. Ces animaux présentent une hyperplasie prostatique associée à une augmentation de l’index prolifératif de l’épithélium. Nos expériences révèlent que NPM1 pourrait lever la quiescence des cellules épithéliales différenciées en dérégulant l’expression de gènes clés de la régulation du cycle cellulaire, comme la Cycline E ou p27kip1. Bien que ces souris ne développent pas de lésions néoplasiques, ces données suggèrent que NPM1 participe à la carcinogenèse prostatique en association avec d’autres lésions oncogéniques. La seconde partie du travail visait à comprendre la nature des mécanismes qui supportent la surexpression de NPM1 dans les tumeurs prostatiques. Des données récentes de la littérature indiquent un enrichissement de la protéine kinase mTOR au niveau du promoteur proximal de NPM1 dans des foies de souris. Pour déterminer s’il existe un lien fonctionnel entre mTOR et NPM1, nous avons tiré parti d’un modèle de fibroblastes embryonnaires de souris invalidés pour le suppresseur de tumeur PTEN dont l’inactivation mène à une hyperactivité de mTOR. Dans ce contexte, les taux d’ARNm et de protéines NPM1 sont augmentés par rapport aux cellules sauvages. Nos résultats montrent également que mTOR contrôle l’expression de NPM1 i) en se fixant sur son promoteur et en stimulant l’expression du gène et ii) en stabilisant l’ARNm de NPM1. Nous avons confirmé le lien entre NPM1 et mTOR in vivo grâce à notre modèle de souris invalidées pour PTEN dans l’épithélium prostatique. Enfin, nous avons montré que l’expression de NPM1 est nécessaire pour transduire les effets prolifératifs de la voie PI3K/AKT/mTOR. Ces données placent donc NPM1 comme nouvel effecteur en aval de cette voie de signalisation, faisant de cette protéine une potentielle cible thérapeutique dans les tumeurs présentant une perte de PTEN. / Nucleophosmin (NPM1/B23) is a small molecular chaperone involved in a large array of cellular processes, including the regulation of gene expression and the control of the cell cycle. Several studies have reported the overexpression of NPM1 in solid tumors from various histological origin, including prostate cancer, and its proliferative impact on several human cancer cell line is being well described. The first part of our work aimed at assessing the NPM1 oncogenic properties in the prostate gland in vivo. To do so, we generated a new transgenic mouse model that overexpresses NPM1 specifically in the prostatic epithelium. These mice harbor prostatic hyperplasia associated with an increase of the ki67 proliferative index. Our molecular investigations revealed that NPM1 could be an inhibitor of the quiescent state of epithelial cells through a dysregulation of key cell-cycle controlers such as Cyclin E or p27kip1. Although these mice do not develop neoplastic lesions, our data suggest that NPM1 overexpression accelerate prostate cancer progression when associated with other oncogenic alterations. The second part of the work aimed at understanding the mechanisms underlying NPM1 overexpression in prostate tumors. The serine/threonine Kinase mTOR was recently shown to bind to the proximal promoter of NPM1 in the mouse liver. In order to characterize a fonctionnal link between NPM1 and mTOR, we took advantage of murine embryonic fibroblast (MEF) deleted for PTEN, since these cells display a constitutive mTOR activity. In such cells, NPM1 protein and mRNA levels are increased compared to wild type MEF. We also demonstrated that mTOR controls NPM1 expression i) through its binding to NPM1 promoter, thus stimulating NPM1 gene expression and ii) by stabilizing NPM1 mRNA. We have confirmed the functional link between NPM1 and mTOR in vivo in a mouse model deleted for PTEN specifically in the prostatic epithelium. Finally, we have shown that NPM1 expression is necessary for the proliferation of PTEN knock-out MEF. These data set NPM1 as a new downstream effector of the PI3K/AKT/mTOR pathway, and suggest that it could be a new potential therapeutic target in PTEN negative human prostate cancer.

Many obese individuals and type 2 diabetes mellitus (T2DM) patients have elevated levels of insulin. Hyperinsulinemia is a major cancer risk factor in T2DM individuals and activated insulin receptor (IR) has been linked to many types of cancer and poor survival. However, the mechanisms that account for the link between the hyper-active insulin signaling and cancer risk is not well understood. PTEN plays an antagonistic role in the canonical insulin signaling pathway, and is the second most commonly mutated tumour suppressor (after p53) found in human cancers. In many cancers the PTEN gene is not deleted, but instead the protein is lost. Therefore the regulation of PTEN protein in humans is of great importance. Here we hypothesized that the activated insulin signaling down-regulates PTEN. Considering that insulin signaling is highly conserved from C. elegans to human, I used C. elegans as a model and showed that DAF-2, the worm homolog of IR, is a negative regulator of DAF-18, the worm homolog of PTEN. In addition, I showed that DAF-28, the worm homolog of insulin, also negatively regulates DAF-18/PTEN. I used western blot and immunostaining to show that the protein level of DAF-18/PTEN is increased in the daf-2/IR and daf-28/insulin mutants. I further showed that daf-18/Pten is genetically epistatic to daf-2/IR in regulating neuronal development. I then employed human cell culture experiments and reported that this negative regulation is conserved in human cancer cell lines. I showed that knocking-down IR through siRNA up-regulates PTEN, and over-expressing a gain-of-function IR down-regulates PTEN. I also showed that insulin stimulation dramatically decreased PTEN and this decrease is dependent on IR. I further confirmed a physical association between IR and PTEN in both human and C. elegans, and reported that IR could phosphorylate PTEN. To provide mechanistic insight to DAF-18/PTEN regulation, I identified another protein, which is a ubiquitin ligase, that functions in insulin signaling to down-regulate DAF-18/PTEN. Additionally, I also provided evidence that insulin signaling cross talks with Eph receptor signaling. In summary, my findings will be informative for cancer biologists to study the roles of these genes in carcinogenesis. / Thesis (Ph.D, Biology) -- Queen's University, 2013-02-04 14:37:29.376

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No description available.

There will be an estimated 60,000 new cases and nearly 8000 deaths in the US this year due to malignant melanoma. People living in the US are expected to have a 1 in 71 lifetime risk of developing the disease. Activating mutations in BRAF occur in approximately 60% of melanomas and in 80% of benign melanocytic nevi. PTEN is a tumor suppressor that has been shown to be deleted or epigenetically silenced in approximately 30% of melanomas. Cdkn2a is a locus encoding 2 tumor suppressors in alternate reading frames that has been found to be mutated in up to 40% of familial melanomas and is near universally lost in human melanoma cell lines. We used these data to generate novel mouse models of metastatic melanoma involving an inducible Cre transgenic mouse (Tyr::CreER-T2). We demonstrate that Pten loss, Cdkn2a loss or Braf activation in isolation does not induce melanoma. In contrast, when Braf activation is combined with Pten loss, mice develop aggressive pigmented melanomas with 100% penetrance and a mean tumor free survival of 19.5 days. Melanocytic proliferation occurs immediately following induction with virtually no latency. Expansile metastases are observed in lymph nodes and isolated tumor cells are present in the lungs and brain. Both incipient and established melanomas are sensitive to the mTOR inhibitor rapamycin. Furthermore, mTORC1 signaling is prevented upon rapamycin treatment, but mTORC2, MAPK, and Akt signaling appear to be unaffected. Additionally, when Cdkn2a loss is combined with Braf activation, the mice develop a nevic phenotype with complete penetrance and stochastic progression to melanoma. Median melanoma free survival is 85.5 days and tumors are metastatic to lymph nodes in 100% of mice. These novel mouse models of melanoma will likely be useful in the study of the biology of metastasis, in tumor immunology, and in new models of preclinical testing.

Growth and proliferation are normal functions of cells mediated in part via receptor tyrosine kinases such as the epidermal growth factor (EGF) receptor (EGFR). The EGFR binds the extracellular signaling ligand EGF and transduces the signal into the cell. Phosphatidylinositol 3'-kinase (PI3K) responds to EGFR activation and initiates downstream signaling cascades responsible for cell cycle entry, proliferation and inhibition of apoptosis. Cell cycle arrest is required to stop cell growth and proliferation as well as allow apoptosis, if required. The phosphatase and tensin homologue deleted on chromosome ten (PTEN) directly opposes PI3K signaling since its substrate is the PI3K product phosphatidylinositol 3,4,5-trisphosphate. PI3K is a heterodimer composed of a p85 regulatory subunit and a p110 catalytic subunit. PTEN is an essential tumor suppressor protein. Absence of PTEN has been associated with several types of cancer. <p>Our laboratory has characterized new specialized functions for the p85 protein. One function discovered was the ability of p85 to enhance PTEN lipid phosphatase activity. In this thesis PTEN activity is shown to be enhanced at least 3.5 fold in vitro by an equimolar amount of p85. <p>We performed an analysis of PTEN using seven PTEN mutants. Two types of mutants were created: i) regulatory or possible regulatory phosphorylation sites were substituted to mimic both phosphorylated and non-phosphorylated states and ii) alanine substitution of basic amino acid residues. The phosphorylation sites altered were the casein kinase 2 phosphorylation sites in the regulatory domain and tyrosine 336, a proposed regulatory phosphorylation site. Three mutants involving alanine substitution for basic amino acid residues included one mutant in the PASE domain and two more mutants in the C2 domain. It was observed that GFP-PTEN translocates to the plasma membrane upon EGF stimulation. The mimic of constitutive phosphorylation of the Casein kinase 2 sites resulted in cytoplasmic localization whereas the non-phosphorylated mimic was plasma membrane localized regardless of EGFR activation status. Neutralization of positive charge in the PASE and C2 domains seriously impeded the ability of PTEN to bind to phosphorylated phosphatidylinositol lipids and abolished the ability of the protein to translocate to the plasma membrane in response to receptor activation. Located within a cluster of positively charged lysine residues in the C2 domain is a potential phosphorylation site at tyrosine 336. The phosphorylation mimic showed decreased binding to some membrane lipids compared to the non-phosphorylated mimic. The results we generated are consistent with a current model for PTEN regulation that proposes PTEN is localized to the cytoplasm in quiescent cells and dephosphorylation of the regulatory domain occurs upon EGF stimulation allowing translocation to the plasma membrane. The model proposes that dephosphorylation of the casein kinase 2 sites unmasks regions of positive charge that interact with the anionic plasma membrane. Furthermore, the results suggested that at the plasma membrane p85 interacts with PTEN to increase lipid phosphatase activity and may be involved in targeting PTEN to the activated receptor where PI3,4,5P3 lipids are being produced.

Growth and proliferation are normal functions of cells mediated in part via receptor tyrosine kinases such as the epidermal growth factor (EGF) receptor (EGFR). The EGFR binds the extracellular signaling ligand EGF and transduces the signal into the cell. Phosphatidylinositol 3'-kinase (PI3K) responds to EGFR activation and initiates downstream signaling cascades responsible for cell cycle entry, proliferation and inhibition of apoptosis. Cell cycle arrest is required to stop cell growth and proliferation as well as allow apoptosis, if required. The phosphatase and tensin homologue deleted on chromosome ten (PTEN) directly opposes PI3K signaling since its substrate is the PI3K product phosphatidylinositol 3,4,5-trisphosphate. PI3K is a heterodimer composed of a p85 regulatory subunit and a p110 catalytic subunit. PTEN is an essential tumor suppressor protein. Absence of PTEN has been associated with several types of cancer. <p>Our laboratory has characterized new specialized functions for the p85 protein. One function discovered was the ability of p85 to enhance PTEN lipid phosphatase activity. In this thesis PTEN activity is shown to be enhanced at least 3.5 fold in vitro by an equimolar amount of p85. <p>We performed an analysis of PTEN using seven PTEN mutants. Two types of mutants were created: i) regulatory or possible regulatory phosphorylation sites were substituted to mimic both phosphorylated and non-phosphorylated states and ii) alanine substitution of basic amino acid residues. The phosphorylation sites altered were the casein kinase 2 phosphorylation sites in the regulatory domain and tyrosine 336, a proposed regulatory phosphorylation site. Three mutants involving alanine substitution for basic amino acid residues included one mutant in the PASE domain and two more mutants in the C2 domain. It was observed that GFP-PTEN translocates to the plasma membrane upon EGF stimulation. The mimic of constitutive phosphorylation of the Casein kinase 2 sites resulted in cytoplasmic localization whereas the non-phosphorylated mimic was plasma membrane localized regardless of EGFR activation status. Neutralization of positive charge in the PASE and C2 domains seriously impeded the ability of PTEN to bind to phosphorylated phosphatidylinositol lipids and abolished the ability of the protein to translocate to the plasma membrane in response to receptor activation. Located within a cluster of positively charged lysine residues in the C2 domain is a potential phosphorylation site at tyrosine 336. The phosphorylation mimic showed decreased binding to some membrane lipids compared to the non-phosphorylated mimic. The results we generated are consistent with a current model for PTEN regulation that proposes PTEN is localized to the cytoplasm in quiescent cells and dephosphorylation of the regulatory domain occurs upon EGF stimulation allowing translocation to the plasma membrane. The model proposes that dephosphorylation of the casein kinase 2 sites unmasks regions of positive charge that interact with the anionic plasma membrane. Furthermore, the results suggested that at the plasma membrane p85 interacts with PTEN to increase lipid phosphatase activity and may be involved in targeting PTEN to the activated receptor where PI3,4,5P3 lipids are being produced.

Hepatocellular carcinoma (HCC) is one of the most common cancerous diseases worldwide. The annual occurrences exceed one million peoples affected. Currently, the treatment modalities for HCC include surgical resection, trans-arterial embolization (TAE) and chemotherapy. However, these modalities are not completely effective, underscoring the need for development of novel therapeutic approaches. PTEN, a tumor suppressor that antagonizes the PI3K pathway, is frequently mutated or deleted in various human cancers. Loss of PTEN occurs in 40-50% of surgical resected HCC samples and predicts poor prognosis for HCC patients, suggesting PTEN restoration may constitute a treatment alternative for HCC. Since PTEN increased ethanol-induced cytotoxicity in hepatoma cells, PTEN gene delivery may serve as an adjuvant therapy in conjunction with ethanol TAE for HCC. In the present study, we evaluated the efficacy of PTEN gene therapy and its combination with ethanol in a syngenic Novikoff hepatoma model by implantation of N1-S1 cells into livers of Sprague Dawley rats. Adenovirus encoding PTEN (Ad-PTEN) or green fluorescent protein (Ad-GFP) was generated for gene delivery studies. The optimal condition for adenovirus vectors to infect N1-S1 cells was determined at multiplicity of infection (MOI) of 100-200. Infection of N1-S1 cells with Ad-PTEN, but not Ad-GFP, increased PTEN levels and led to 40-50% inhibition of cell proliferation via cell cycle arrest. Besides, the half maximal -inhibitory concentration (IC50) for ethanol in N1-S1 cells was determined at 6%. Combination with PTEN gene delivery further augmented the cytotoxicity of ethanol in N1-S1 cells from 40% to 70% inhibition. To evaluate the prevention efficacy of PTEN gene delivery, N1-S1 cells were infected with adenovirus vectors then implanted into livers of Sprague-Dawley rats to induce Novikoff hepatoma. Injection of PBS- or Ad-GFP-treated N1-S1 cells led to large hepatoma (with an average size of 3-4 cm) with tumor incidence of 80-90%. In contrast, injection of Ad-PTEN-infected N1-S1 cells only induced one hepatoma (with size of 0.1 cm) in six rats, suggesting that pretreatment with PTEN gene delivery effectively abolished the tumorigenic potential of N1-S1 hepatoma cells in vivo. In summary, these results validate the feasibility of PTEN gene delivery as a new promising therapeutic strategy for the treatment of orthotopic hepatoma in immune-competent rats.

Hepatocellular carcinoma (HCC) is one of the most prevalent cancers worldwide. Hepatocarcinogenesis is considered a multifactorial and mulitstep process that involves the activation of oncogenes or the inactivation of tumor suppressor genes. Tumor suppressor gene PTEN (also known as MMAC or TEP1) is located on human chromosome 10q23. The 403¡Vamino acid PTEN protein encodes dual specificity protein phosphatases. Mutation of the PTEN is a common event in advanced stage of diverse human cancers. In our previous studies, immunohistochemical analysis indicated that reduced PTEN expression was found in nearly 40% of HCC specimens. Furthermore, restored PTEN expression by adenovirus gene delivery effectively inhibited the in vitro and in vivo tumorigenicity of Mahlavu cells, a human HCC cell line with PTEN inactivation. In the present study, we further characterize whether PTEN gene delivery still suppressed the oncogenic potential in HCC cell lines with functional PTEN. By expression and sequencing analysis, we identified human SK-Hep-1 cells as the hepatoma cell line with functional PTEN expression. The optimal condition for adenovirus vector to infect SK-Hep-1 cells was determined at the multiplicity of infection (MOI) of 50-100. Tough SK-Hep-1 cells were effectively transduced with exogenous PTEN gene, the enhanced PTEN expression by adenovirus gene delivery did not alter the phosphoryation extent of Akt in SK-Hep1 cells. Nevertheless, PTEN gene delivery reduced the proliferation of SK-Hep-1 cells by ~20%. In addition, the motility of PTEN-transduced SK-Hep-1 cells significantly decreased comparing to cells of control groups. Western blot analysis suggested the decreased cell motility might be attributed to the reduced phosphorylation of focal adhesion kinase (FAK) by PTEN gene delivery. Above all, PTEN gene delivery profoundly reduced the colony formation of SK-Hep-1 cells in soft-agar. However, PTEN gene delivery did not affect the secretion of matrix metallo-proteinases (MMPs) release. Animal studies will be carried out in the future to validate the present in vitro findings. In summary, PTEN gene delivery holds promise for treatment of HCC even when the hepatoma cells possess functional PTEN gene.

TBX2, a member of the T-box family of transcription factors, plays important roles in embryonic development. Aberrant expression of TBX2 is observed in many cancers, and serves as an oncogene to maintain tumor cell proliferative and malignant properties. We found that TBX2 was expressed in both embryonic myoblasts and adult proliferative satellite cells, but was quickly down regulated during muscle differentiation in mouse models, which suggests an important function of TBX2 in the early myogenesis. Using molecular and cellular biology approaches we showed that TBX2 forms complex with myogenin and MyoD, and then recruits HDAC1 to muscle-specific promoters to repress the myogenin and MyoD dependent differentiation of myoblasts. In rhabdomyosarcoma (RMS), which is typically referred to as a muscle derived cancer, we found TBX2 was over expressed in both major subtypes of RMS. The deregulated TBX2 repressed the expression of cell cycle regulators, such as p21 and p14/p19, and the tumor suppressor PTEN in RMS tumor cells. Knock down of TBX2 significantly decreased the proliferation rate of RMS cells. We also found that loss of TBX2 significantly inhibited tumorigenesis of RMS cells by decreasing cell proliferation, mobility, migration, anchorage-independent growth and xenograft formation. To determine why TBX2 was deregulated in RMS cells, we performed cellular biological experiments to understand how TBX2 is regulated by cell signaling pathways and growth factors in both normal muscle myoblasts and RMS tumor cells. In normal murine myoblasts and primary murine ARMS tumor cells TBX2 was up regulated by FGF-2 treatment, but in primary murine ERMS cells TBX2 expression showed no response to FGF-2 stimulation. In human RMS cell lines a modest up regulation of TBX2 was detected by treatment of FGF-2. RMS cells constitutively express PAX3 and PAX7 which are expressed and function in myogenic precursors, but are quickly degraded in myoblasts and during myogenesis. We found that TBX2 was a downstream target of PAX3 in RMS cells, as well as the ARMS specific fusion proteins PAX3/7-FOXO1. Our novel findings on TBX2 highlight the significant roles of TBX2 in muscle development and adult muscle regeneration, where TBX2 represses MRF activities to inhibit myogenic differentiation and promote proliferation of myoblasts. Also, our work establishes essential oncogene effects of TBX2 in driving and maintaining RMS proliferation and tumorigenesis by repressing cell cycle regulatory factors, p21 and p19/p14, and tumor suppressor of PTEN. Therefore, this work provides an exciting opportunity for development of new therapeutic treatments for TBX2 driven RMS cancer.