No description available.

No description available.

Thesis (doctoral)--University of Helsinki, 2007. / Includes bibliographical references. Also available on the World Wide Web.

Cancer est un terme qui rassemble plusieurs ensembles hétérogène de maladies et il est caractérisé par la perte de contrôle physiologique et la transformation maligne des cellules saines. Il est essentiel de comprendre le cancer de la biologie cellulaire afin d'identifier de nouveaux biomarqueurs pour le diagnostic précoce et la conception de nouvelles stratégies thérapeutiques. Reprogrammation métabolique est une caractéristique émergente de cancer, ce qui signifie que les cellules cancéreuses passent leur métabolisme de base pour répondre aux exigences accrues de la croissance et la division cellulaire. Par conséquent, explorer reprogrammant métabolique que les cellules cancéreuses subissent est une stratégie clé pour identifier de nouvelles cibles pour le traitement du cancer. Dans cette thèse, de nouvelles possibilités pour le traitement du cancer ont été explorés en analysant la reprogrammation métabolique de la tumeur. À cet égard, nous avons étudié et proposé voie des pentoses phosphates (PPP) enzymes cibles thérapeutiques putatifs contre les cancers du sein et du côlon. En outre, nous avons exploré le métabolisme de la glutamine dans les cellules du cancer du sein et les adaptations du réseau métaboliques qu'ils subissent dans le but de contourner la privation de glutamine et la déficience mitochondriale générale. Ainsi, le ciblage PPP est l'intérêt des chercheurs d'utiliser à la fois oxydantes et non oxydantes phases de cette voie métabolique comme une cible de médicament thérapeutique. Pour tester cela, nous inhibés bœuf PPP enzymes 6PGD dans les cellules cancéreuses du sein et G6PD dans les cellules du côlon.Nous avons effectué la caractérisation de la reprogrammation métabolique induite par l'inhibition de l'enzyme de bœuf PPP par l'ARN interferase (ARNi) silençage médiation, afin d'explorer le potentiel de cette enzyme comme une cible de médicament thérapeutique dans deux lignées de cellules de cancer du sein. Nous avons demontré que l'inhibition 6PGD a entraîné une diminution taux de prolifération, arrêt du cycle cellulaire et induction de l'apoptose médiée par l'activation de p53, en diminuant les capacités de formation mammosphere et le métabolisme altéré de carbone central par modulation de Warburg phenomenan et en améliorant le métabolisme de la glutamine. D'autre part, nous avons montré l'effet de l'inhibition de la G6PD sur la prolifération des cellules du cancer du côlon et du PPP est régulée par la disponibilité de la glutamine dans les cellules cancéreuses du côlon.De plus, nous avons caractérisé les adaptations métaboliques que les cellules cancéreuses du sein subissent la privation de glutamine ou lorsque les mitochondries sont fait défection. Nous avons effectué une analyse des flux métaboliques utilisant métabolomique et Fluxomique et nous avons utilisé la biologie des systèmes afin d'estimer une vision globale des modifications de flux dans différentes conditions de culture. Nous avons observé une augmentation du cycle de pyruvate avec privation glutamine, ce qui indique que le ciblage des enzymes de cette voie telle que l'enzyme malique pourrait être une approche prometteuse combinée à l'inhibition de l'enzyme de glutaminase. D'autre part, nous avons observé que mimant une hypoxie par des cellules de cancer du sein de traitement redirigée oligomycine pour augmenter la carboxylation réductrice. Considérant que l'hypoxie est une condition commune dans l'environnement de la tumeur, le ciblage mécanisme de carboxylation réductrice pourrait être une nouvelle stratégie de lutte contre le cancer. Collectivement, les résultats présentés dans cette thèse démontre l'importance du métabolisme de la prolifération des cellules cancéreuses et la survie. Ce travail met également en évidence l'importance de la biologie des systèmes se rapproche de comprendre les mécanismes moléculaires sous-jacents des maladies multifactorielles complexes afin de souligner de nouvelles cibles thérapeutiques potentielles. / Moreover, we characterized the metabolic adaptations that breast cancer cells undergo in the deprivation of glutamine or when mitochondria are defected. We conducted metabolic flux analysis using metabolomics and fluxomics approaches and we employed Systems Biology approaches in order to estimate a global view of flux alterations in different culture conditions. We observed an increased pyruvate cycle with glutamine deprivation, thus indicating that targeting the enzymes of this pathway such as malic enzyme could be a promising approach combined with inhibition of glutaminase enzyme. On the other hand, we observed that mimicking hypoxia by oligomycin treatment redirected breast cancer cells to increase reductive carboxylation. Considering that hypoxia is a common condition in the tumor environment, targeting reductive carboxylation mechanism could be a novel strategy to fight against cancer. Collectively, all the results provided in this thesis demosntrate the importance of metabolism in cancer cell proliferation and survival. This work also highlights the importance of Systems Biology approaches to comprehend the molecular mechanisms underlying complex multifactorial diseases in order to point out new potential therapeutic targets.

Les Leucémies Aigües Myéloïdes (LAM) sont des hémopathies malignes hétérogènes de mauvais pronostic qui se caractérisent par une expansion clonale de progéniteurs immatures. De nombreuses dérégulations de voies de signalisation sont retrouvées dans les cellules leucémiques et leur confèrent un avantage de prolifération et de survie. La voie de signalisation mTORC1, qui contrôle la traduction protéique, l’autophagie et plusieurs voies métaboliques, est ainsi constitutivement activée dans les cellules leucémiques. La reprogrammation métabolique notamment via « l’effet Warburg » est un phénomène bien décrit dans les cellules cancéreuses. L’augmentation de l’utilisation de la glycolyse, confère aux cellules tumorales un avantage de survie en favorisant une production rapide d’ATP et d’intermédiaires métaboliques nécessaires pour les biosynthèses de nucléotides, d’acides-aminés et de lipides. C’est donc dans ce contexte que j’ai étudié le métabolisme du glucose dans les cellules de LAM et l’implication de la voie de signalisation mTORC1 dans la dérégulation de ce métabolisme. J’ai tout d’abord identifié par une étude transcriptomique dans la lignée leucémique MOLM-14 que la signalisation mTORC1 contrôle plusieurs voies métaboliques notamment celles permettant l’utilisation du glucose. Ceci a été vérifié dans plusieurs lignées de LAM puisque l’inhibition ou la sur-activation de mTORC1 entrainent respectivement une diminution ou une augmentation de la consommation de glucose et de la production de lactate. De façon intéressante, le niveau d’activation de la voie mTORC1 détermine la sensibilité des cellules leucémiques à l’inhibition de la glycolyse. En effet, lorsque mTORC1 est activé, le blocage de la glycolyse induit de l’autophagie et l’apoptose des cellules leucémiques. A l’inverse, le blocage de mTORC1 induit une reprogrammation métabolique des cellules leucémiques qui utilisent alors principalement la phosphorylation oxydative pour produire l’ATP dont elles ont besoin. Leur survie devient alors indépendante du glucose. A l’inverse des cellules primaires de LAM, les cellules hématopoïétiques immatures normales CD34+ sont moins sensibles au blocage de la glycolyse. Le ciblage du métabolisme du glucose pourrait donc constituer une stratégie thérapeutique intéressante dans les LAM. Je me suis ensuite intéressée aux effets anti-leucémiques induits par l’inhibition de la voie des pentoses phosphates (PP) et plus particulièrement au ciblage de la G6PD (glucose-6-phosphate déshydrogénase) par le composé le 6-aminonicotinamide (6-AN). En effet, une étude de flux métabolique a permis de mettre en évidence qu’une proportion importante de glucose est dirigé vers la voie des PP, laissant suggérer que l’addiction des cellules leucémiques au glucose pourrait être liée à une utilisation augmentée de cette voie annexe. J’ai alors observé que le 6-AN induit une cytotoxicité in-vitro y compris dans les cellules primaires de patients, sans avoir d’effets sur les cellules hématopoïétiques normales et in-vivo dans un modèle de xénogreffe de la lignée MOLM-14 chez la souris NUDE. Cette étude a donc permis de montrer que l’activation constitutive de mTORC1 rend la survie des cellules de LAM dépendante de la glycolyse et crée une sensibilité spécifique à l’inhibition de la G6PD. La dérégulation de la signalisation mTORC1 étant quasi-constante dans les LAM, cibler la G6PD pourrait donc représenter une stratégie thérapeutique intéressante. / Acute Myeloid Leukemia (AML) are heterogeneous hematological diseases with poor prognosis characterized by a clonal expansion of immature progenitors. Many deregulation of signaling pathways are found in leukemic cells and give them an advantage of proliferation and survival. The MTORC1 signaling pathway, which controls protein translation, autophagy and several metabolic pathways, is constitutively activated in leukemic cells. Metabolic reprogramming in particular the "Warburg effect" is a phenomenon well described in cancer cells. High rate of glycolysis has been considered to give tumour cells advantages through rapid production of ATP and intermediates for the synthesis of nucleotides, amino acids, and lipids. In this context, I studied glucose metabolism in AML cells and the involvement of the mTORC1 signaling pathway in the deregulation of this metabolism. First, I identified by a transcriptomic analysis in the MOLM-14 cell line that mTORC1 signaling controls several metabolic pathways including those for glucose utilization. This has been verified in several AML cell lines, since inhibition or over-activation of mTORC1 respectively induces a decrease or an increase in glucose consumption and lactate production. Interestingly, the level of activation of the mTORC1 signaling pathway determines the sensitivity of AML cells to the inhibition of glycolysis. Indeed, when mTORC1 is activated, the blockade of glycolysis induces autophagy and apoptosis of leukemic cells. Conversely, blocking mTORC1 induces metabolic reprogramming of leukemic cells, which then mainly use oxidative phosphorylation to produce ATP for their needs. AML cell survival become independent of glucose. Unlike primary AML cells, survival of normal immature hematopoietic cells CD34+ is only barely affected by the blockade of glycolysis. Thus, targeting the glucose metabolism may constitute an attractive therapeutic strategy in AML. I then investigated the anti-leukemic activity induced by the inhibition of the pentose phosphate pathway (PPP) and more particularly by the specific blockade of G6PD (glucose 6-phosphate dehydrogenase) with the 6-aminonicotinamide (6- AN) compound. Indeed, a metabolic flux analysis demonstrated that a significant proportion of glucose was directed towards the PPP. This result suggested that the addiction of leukemic cells toward glucose might be related to an increased use of PPP. I then observed that the 6-AN induced in vitro cytotoxicity including in primary AML cells from patients without effect on normal immature hematopoietic cells CD34+ and in vivo in a xenograft model of MOLM-14 cell line in the NUDE mouse. This study therefore demonstrated that the constitutive activation of mTORC1 makes AML cells survival dependent on glycolysis, and creates a specific vulnerability to the inhibition of G6PD. Given that deregulation of the mTORC1 signaling pathway is almost constant in AML, targeting G6PD may therefore represent an interesting therapeutic strategy.

<p>Apoptosis is a form of programmed cellular "suicide" which is activated in response to a variety of pro-death stimuli. Apoptotic cell death is orderly and energy-dependent, and cellular constituents are packaged into membrane-bound vesicles for consumption by phagocytes. Toxic intracellular signals are never exposed to neighboring cells or to the extracellular environment, and a host inflammatory response does not occur. Apoptosis is executed by the coordinated activation of caspase family proteins. Caspase-2 is an apical protease in this family, and promotes cell death after receipt of cues from intracellular stressor signals. Caspase-2 helps to initiate apoptosis by responding to cellular death stimuli and signaling for downstream cytochrome c release and executioner caspase activation.</p><p> Several years ago our lab determined that Xenopus laevis oocyte death is partly controlled by the activation of caspase-2. In the setting of oocyte or egg extract nutrient depletion, caspase-2 was observed to be activated upstream of mitochondrial cytochrome c. In fact, caspase-2 is suppressed in response to the nutrient status of the oocyte: nutrient-replete oocytes with healthy pentose phosphate pathway flux and abundant NADPH production are able to inhibit caspase-2 via S135 phosphorylation catalyzed by calcium/calmodulin-dependent protein kinase II. Phosphorylation of caspase-2 at S135 is critical in preventing oocyte cell death, and a caspase-2 mutant unable to be phosphorylated loses its ability to respond to suppressive NADPH signals. </p><p> In this dissertation we examine the converse mechanism of metabolically-regulated caspase-2 activation in the Xenopus egg extract. We now show that caspase-2 phosphorylated at S135 binds the interactor 14-3-3 zeta, thus preventing caspase-2 dephosphorylation. Moreover, we determined that S135 dephosphorylation is catalyzed by protein phosphatase-1, which directly binds caspase-2. Although caspase-2 dephosphorylation is responsive to metabolism, neither PP1 activity nor binding is metabolically regulated. Rather, release of 14-3-3 zeta from caspase-2 is the point of metabolic control and allows for caspase-2 dephosphorylation. Accordingly, a caspase-2 mutant unable to bind 14-3-3 zeta is highly susceptible to activation. Although this mechanism was initially established in Xenopus, we now demonstrate similar control of murine caspase-2 by phosphorylation and 14-3-3 binding in mouse eggs. </p><p> In the second part of this dissertation we examine the paradigm of caspase-2 metabolic regulation in a mammalian somatic cell context. We observed that mammalian caspase-2 is a metabolically-regulated phosphoprotein in somatic cells, and that the site of regulation is caspase-2 S164. Phosphorylation at S164 appears to inhibit mammalian caspase-2 by preventing its induced proximity oligomerization, thus also preventing procaspase-2 autocatalytic processing. We further identify some of the molecular machinery involved in S164 phosphorylation and demonstrate conservation with the validated Xenopus regulators. Interestingly, we extend the findings of caspase-2 phosphorylation to a study of ovarian cancer, and show that caspase-2 S164 phosphorylation might be involved in determining cancer cell chemosensitivity. We further provide evidence that chemosensitivity can be modulated by the cellular metabolic status in a caspase-2-dependent manner. Thus, we have identified a novel phosphorylation site on mammalian caspase-2 in somatic cells, and are working further to understand the implications of caspase-2 signaling in the context of cancer cell responsiveness to chemotherapeutic treatments.</p> / Dissertation

No description available.

Circadian rhythms are self-sustained endogenous biological oscillations with a period of approximately 24 hours. These rhythms are observed widely across kingdoms and at all levels of biological scale. Recent work has shown there to be circadian variation in metabolism, both at the organismal and cellular level. It has also been posited that rhythmic production of metabolites might be essential for maintenance of circadian rhythmicity within cells, even in the absence of nascent transcription. The first portion of this thesis investigates the contribution of primary carbohydrate metabolism to cellular timekeeping, with particular emphasis on the pentose phosphate pathway. I also describe and validate a new 13C labelling technique for accurate determination of the relative flux through early primary metabolic pathways. This is accompanied by the development and optimisation of a microfluidic system for long-term perfused tissue culture, which allows for longitudinal study of metabolic flux within the same population of cells with simultaneous recording of clock gene activity. This perfused system provides several advantages over static tissue culture. The second portion considers the effects of the metabolic hormone insulin on circadian rhythmicity, both at the level of the cell and of the whole organism. It shows that administration of insulin is sufficient to shift the phase of circadian gene expression and elicits induction of clock protein PER2. Strikingly, manipulation of insulin signalling is sufficient to determine all the essential parameters of the cellular clock (phase, period and amplitude) in a dose-dependent but glucose independent fashion. Using pharmacological and genetic approaches, a molecular explanation for this effect is determined. This data suggests that insulin is a primary determinant of rhythms in peripheral tissues and is most likely a major signal for circadian entrainment to feeding in mammals, for which I now propose a mechanistic basis.

This dissertation is a compilation of published works and a manuscript that seek to understand the possible role of polyamines in the regulation of capsule in Streptococcus pneumoniae (Spn, pneumococcus). Spn remains a major health risk worldwide while the capsule is widely recognized as the principal virulence factor. Polyamines on the other hand are small hydrocarbon molecules known to regulate a number of cellular processes in bacteria. This work investigates the impact of deletion of polyamine biosynthesis gene, SP_0916 (cadA, lysine decarboxylase at the time of first and second publication), on protein expression and the capsule biosynthesis of virulent pneumococcal serotype 4 (TIGR4). We identify loss of capsular polysaccharide (CPS) in the deletion strain and based on proteomics results, we hypothesized that a shift in metabolism that favors the pentose phosphate pathway (PPP) over glycolytic pathway, that could reduce the availability of precursors for CPS had occurred. Comparison of transcriptomic and untargeted metabolomics profile of ∆SP_0916 with TIGR4 shows impaired glycolysis and Leloir pathways that provide CPS precursors, in the mutant strain. Furthermore, gene expression changes indicate possible reduction of common polyamines (cadaverine, putrescine, spermidine and spermine). Targeted metabolomics analysis confirmed reduced levels of polyamines in SP_0916. However, the result suggests that SP_0916 encodes an arginine decarboxylase, contrary to its existing annotation as a lysine decarboxylase in many bioinformatics databases. Biochemical characterization of the purified protein encoded by SP_0916 confirms that it is indeed catalyzes arginine decarboxylation, and exogenous supplementation of agmatine, the product of the reaction, successfully restores capsule biosynthesis. This study fixes an error in annotation of the TIGR4 genome and further establishes the essentiality of agmatine, a product of arginine decarboxylation as the key polyamine molecule modulating pneumococcal capsule. We later compared the impact of deletion of polyamine synthesis by gene deletion (ΔSP_0916) with chemical inhibition of synthesis using α- difluoromethylornithine (DFMO), in multiple pneumococcal serotypes. Results of this dissertation confirmed that pneumococcal pathways impacted by the disruption of polyamine biosynthesis either by gene deletion or chemical intervention are conserved and could regulate capsule synthesis.

High aerobic glycolytic capacity is correlated with poor prognosis and increased tumour aggressiveness. 6Phosphofructo-1-kinase catalyses the first irreversible step of glycolysis, and is activated by fructose-2,6-bisphosphate, a product of the kinase activity of four bifunctional isoenzymes, 6-phosphofructo-2-kinase/fructose-2,6-biphosphatase (PFK-2/FBPase-2:PFKFB1-4). These are potential anti-tumour targets, but their individual and collective role requires further investigation. This thesis had three aims; to validate the PFK-2/FBPase-2 isoenzymes as anti-cancer targets, to investigate the requirement for isoenzyme-specific targeting, and to initiate assay development, enabling future identification of novel inhibitors. A panel of cancer cell lines was examined and PFKFB3 and PFKFB4 were confirmed to be the most strongly induced isoenzymes in hypoxia, regulated by HIF-1&alpha;. Basal and hypoxic relative PFKFB3/PFKFB4 expression varied markedly, and three cell lines with varying expression ratios (MCF-7, U87, PC3) were selected for further study. siRNA knockdown of each isoenzyme individually, markedly reduced 2D and 3D cell growth. The effect of PFKFB3 knockdown was consistently more pronounced, particularly in hypoxia. Double PFKFB3/PFKFB4 knockdown was significantly less effective than PFKFB3 knockdown alone. Direct antagonism of PFKFB3 and PFKFB4 on F-2,6-BP concentration was observed, with PFKFB3 exhibiting high kinase activity, as anticipated, and PFKFB4 exhibiting high bisphosphatase activity. The degree of antagonism was dependent on the relative PFKFB3/PFKFB4 expression ratio. Extensive efforts were made to examine the wider metabolic effect of PFKFB3/PFKFB4 on flux towards glycolysis or the pentose phosphate pathway (PPP), including using metabolite, lipid droplet, ¹³C NMR and mass spectrometry assays. No significant change in metabolic flux was detected, the evidence presented therefore suggesting the impact of the antagonistic effects of the isoenzymes on [F-2,6-BP] extends beyond regulation of metabolic flux alone. This study concluded that the most effective therapeutic strategy will be one that involves a PFKFB3-specific inhibitor, preferably hypoxia-targeted. Accordingly, steps were taken to validate and optimise a robust medium-throughput assay system.