Les travaux antérieurs du laboratoire ont montré que la Reptine, une AAA+ ATPase, est surexprimée dans le carcinome hépatocellulaire où elle est nécessaire à la prolifération et la survie cellulaire. Il est connu que la Reptine joue un rôle crucial dans la stabilité de la kinase mTOR, mais son rôle physiopathologique in vivo reste inconnu. Les objectifs de ma thèse étaient d’étudier le rôle de la Reptine dans le métabolisme et la régénération hépatique grâce à un nouveau modèle murin d’invalidation hépato-spécifique de la Reptine (Reptin LKO). Nous avons montré que la Reptine régule la stabilité de la protéine mTOR in vivo, via son activité ATPase. De manière inattendue, la délétion ou l’inhibition pharmacologique de la Reptine induisent une inhibition de l’activité mTORC1 et une augmentation de l’activité mTORC2, associées à une inhibition de la lipogenèse et de la production de glucose hépatique. La délétion de la Reptine supprime complètement les phénotypes pathologiques associés au syndrome métabolique induit par un régime riche en graisses. Ainsi, l’inhibition de l’ATPase Reptine pourrait représenter une nouvelle stratégie thérapeutique pour le syndrome métabolique. Dans le modèle Reptin LKO, nous avons observé une perte progressive de l’invalidation de la Reptine associée à un phénomène de régénération hépatique. Nos résultats préliminaires suggèrent que la Reptine est nécessaire à la survie des hépatocytes et est requise pour la prolifération des hépatocytes durant la régénération hépatique après hépatectomie partielle. Pour conclure, l’ensemble de nos résultats suggèrent que la Reptine joue un rôle crucial dans l’homéostasie glucido-lipidique du foie, ainsi que dans la prolifération et la survie des hépatocytes. / Previous studies of the laboratory have shown that Reptin, an AAA+ ATPase, is overexpressed in hepatocellular carcinoma where it is necessary for proliferation and cell survival. It is known that Reptin plays a critical role in the stabilization of the mTOR kinase, but its pathophysiological role in vivo remains unknown. The objectives of my thesis were to study the role of Reptin in liver metabolism and regeneration using a new hepato-specific Reptin knock-out murine model (Reptin LKO). We have shown that hepatic Reptin maintains mTOR protein level in vivo through its ATPase activity. Unexpectedly, loss or pharmacological inhibition of Reptin induces an inhibition of mTORC1 activity and an increase of mTORC2 activity, associated with inhibition of lipogenesis and hepatic glucose production. The deletion of Reptin completely rescued pathological phenotypes associated with the metabolic syndrome induced by a high fat diet. Thus, inhibition of Reptin ATPase could represent a new therapeutic perspective for the metabolic syndrome. In Reptin LKO model, we have observed a progressive loss of Reptin invalidation associated with a liver regeneration phenomenon. Our preliminary data suggest that Reptin is necessary for hepatocyte survival and is required for hepatocyte proliferation during liver regeneration after partial hepatectomy. To conclude, altogether our results suggest that Reptin plays a crucial role in glucose and lipid metabolism in the liver, and in hepatocyte proliferation and survival.

No description available.

Les cancers du sein sont une pathologie complexe et très hétérogène qui peut-être divisée en plusieurs sous-types selon leurs caractéristiques biologiques. Parmi ces sous-types, les cancers dits “triple négatifs” (TN) sont caractérisés par un marquage immunohistochimique négatif pour les récepteurs à l’oestrogène et à la progestérone et ne présentent pas de surexpression de HER2. Ces tumeurs très agressives représentent 10 à 20% des cancers du sein et sont actuellement traitées par chimiothérapie classique contrairement aux tumeurs non-TN qui bénéficient de thérapies ciblées (traitements hormono-dépendants, anticorps neutralisants). Un taux élevé de rechute et de métastases dans les cinq ans après diagnostic est observé chez les patientes TN, en lien avec le développement de résistances à la chimiothérapie. De ce fait, la compréhension des mécanismes moléculaires impliqués dans ce processus est importante pour le développement de meilleures thérapies. Les études précédemment menées par notre équipe sur le récepteur de mort CD95 et son ligand, le CD95L, ont mis en évidence leur fonction pro-oncongénique dans les cancers TNs. En effet, en comparaison aux patientes non-TNs, les patientes TNs présentent un taux plus élevé de CD95L (cl-CD95L) dans leur sérum, ce qui est associé à un mauvais pronostic. De plus, in vivo, le cl-CD95L promeut la dissémination métastatique des cellules TNs à travers la formation d’un complexe appelé MISC (Motility-Inducing Signalling Complex) et l’induction de la voie non-apoptotique PI3K/Akt/mTOR. Bien que ces nouvelles données enrichissent notre compréhension du processus oncogénique des cancers TNs, beaucoup reste à faire pour le développement de nouvelles thérapies ciblées. Deux axes de recherche ont été abordés durant mes travaux de thèse. Le premier axe s’inscrit dans la continuité des résultats précédemment obtenus par l’équipe et a consisté à développer de nouveaux inhibiteurs pour bloquer le processus de migration induit par le récepteur de mort. Le second axe propose de définir comment les acteurs majeurs de la machinerie apoptotique, et plus particulièrement les protéines anti-apoptotiques Bcl-2 et BclxL, contribuent à promouvoir la dissémination métastatique des cellules cancéreuses mammaires. Nos travaux ont mis en évidence que l’inhibition de ces membres de la famille Bcl-2, par l’utilisation de BH3 mimétiques, pourrait s’avérer être une stratégie thérapeutique originale pour prévenir la dissémination de métastases chez les patientes TNs. / Breast cancer represents a complex and heterogeneous pathology that can be divided in many subtypes according to biological characteristics. Among them, triple negative breast cancers (TNBCs) are characterized by a negative immunohistochemical staining for estrogen (ER) and progesterone (PR) receptors, and without overexpression of the human epidermal growth factor-2 (HER2). TNBCs represent 10 to 20% of breast cancers and are currently treated by chemotherapy contrary to non-TNBCs, which receive targeted therapies such as hormone therapy or neutralizing antibodies. Compared to non-TNBC, higher rates of relapse and metastasis are observed within five years after diagnosis due to the development of chemotherapy resistance. Therefore, identification of molecular mechanisms implicated in this process is crucial to develop improved therapies. Recent studies carried out by our group on the death receptor CD95 and its ligand CD95L highlighted their pro-oncogenic function in TNBCs. Indeed, in comparison to non-TNBC patients, TNBC patients present higher levels of the naturally cleaved CD95L (cl-CD95L), which is correlated with poor prognosis. Furthermore, cl-CD95L promotes in vivo metastatic dissemination of TNBC cells through the formation of the Motility-Inducing Signalling Complex (MISC) and the induction of the non-apoptotic signaling pathway PI3K/Akt/mTOR. Unless, these new findings increase our understanding of the oncogenic process in TNBC tumours, many things remain to be done to develop new targeted therapies. During my thesis, two lines of research were investigated. The first one, in agreement with previous results obtained by our team, consisted in the development of new inhibitors able to block the migration process induced by the death receptor. The second one was to define how the main actors of the apoptotic machinery, especially anti-apoptotic Bcl-2 and BclxL proteins, promote metastatic dissemination of breast cancer cells. Our work revealed that inhibiting these Bcl-2 family members using BH3-mimetics may turn out to be an original therapeutic strategy to prevent metastatic dissemination in TNBC patients.

La tumorigenèse est un processus multi-étapes, constituée d'altérations génétiques qui conduisent à la transformation maligne des cellules humaines normales. Au cours de cette transformation maligne, l’activité de différentes voies oncogéniques est augmentée. Les voies de signalisation mTORC1 et Notch1 sont des voies oncogéniques bien connues qui jouent un rôle central dans la régulation de la croissance et du métabolisme cellulaires. Les traitements anti-mTORC1 et Notch1 sont approuvées en tant que thérapies anticancéreuses pour plusieurs types de tumeurs. Néanmoins, les cellules cancéreuses développent des résistances à ces inhibiteurs induisant un nombre important de rechute et donc d’échec de ces traitements. Ainsi, le but principal de ce travail est d'étudier l'inhibition des voies de signalisation mTORC1 et Notch1 dans les cellules cancéreuses afin de concevoir de nouvelles stratégies thérapeutiques anticancéreuses. En premier lieu, nous avons décrit une nouvelle classe d'inhibiteurs de mTORC1 qui présente une cytotoxicité spécifique vis-à-vis des cellules cancéreuses. Nous avons démontré que l’ICSN3250, un analogue de l'halituline marine cytotoxique, inhibe mTORC1 et induit la mort cellulaire. Le mécanisme moléculaire de cette inhibition est basé sur le déplacement de l'acide phosphatidique, un lipide activateur du complexe mTORC1, du domaine FRB de la protéine mTOR. Dans un deuxième temps, nous avons étudié le lien entre le métabolisme de la glutamine et la signalisation de Notch1 dans la leucémie lymphoblastique aiguë à lymphocytes T (T-ALL). Les changements métaboliques dans les cellules cancéreuses sont nécessaires à une prolifération cellulaire rapide et la croissance tumorale. Nous avons généré une lignée de cellule T-ALL dont la voie de signalisation Notch1 est constitutivement active et analysé les conséquences de cette activation sur le métabolisme de la glutamine. En effet, en absence de glutamine, l’activation de Notch1 induit la mort cellulaire par apoptose en perturbant l'accumulation de la glutamine synthétase, une enzyme qui permet la production de glutamine. Ce travail de thèse a donc permis de décrire de nouvelles stratégies pour cibler les voies mTORC1 et Notch1 dans le cancer. De futures investigations seront nécessaires pour étudier leur efficacité dans les thérapies anti-cancéreuses. / Tumorigenesis is a multistep process, consisting of genetic alterations that drive the malignant transformation of normal human cells. During this transformation, different oncogenic pathways are upregulated. mTORC1 and Notch1 signaling are well-known oncogenic pathways which play a central role in the regulation of cell growth and metabolism. Anti-mTORC1 and Notch1 therapies are approved as cancer treatments for several types of tumor but there are still developed resistances and relapse diseases. Thus, the main aim of this work is to study the inhibition of mTORC1 and Notch1 signaling pathway in cancer cells in order to design new therapeutic anti-cancer strategies. In the first place, we reported new class of mTORC1 inhibitors which has cytotoxicity specifically towards cancer cells. We demonstrated that ICSN3250, an analogue of the cytotoxic marine alkaloid halitulin, inhibited mTORC1 and induced cell death. The molecular mechanism of this inhibition is based on the displacement of the lipid phosphatidic acid, an activator of mTORC1 complex, from the FRB domain of mTOR protein. At the second stage, we have studied the connection between glutamine metabolism and Notch1 signaling in T-cell acute lymphoblastic leukemia (TALL). Metabolic changes in cancer cells are advantageous for rapid cell proliferation and tumor growth. We have generated Notch1-driven T-ALL cells and analyzed the consequences of Notch1 activation on glutamine metabolism. Indeed, under glutamine withdrawal, Notch1 upregulation induced apoptotic cell death by disrupting the accumulation of glutamine synthetase, a glutamine producing-enzyme. Overall, this thesis work allowed to describe new strategies to target mTORC1 and Notch1 pathways in cancer, which need future investigations to study their efficacy in therapies.

O propósito do presente estudo foi verificar os efeitos do overtraining (OT) nas proteínas relacionadas com a via de sinalização da mammalian target of the rapamycin complex 1 (mTORC1), no conteúdo proteico de sterol regulatory element binding protein-1 (SREBP-1) e nas características morfológicas do fígado de camundongos C57BL/6. Os animais foram divididos em grupo controle (CT), overtraining em declive (OTR/down), overtraining em aclive (OTR/up) e overtraining sem inclinação (OTR). Teste do rotarod, incremental, exaustivo e força de preensão foram utilizados para avaliação de performance. Após 36 horas o teste de força de preensão, os fígados foram removidos e utilizados para immunoblotting ou análises histológicas. A fosforilação da proteína kinase B (pAkt; Ser473), mammalian target of the rapamycin (pmTOR; Ser2448), 70-kDa ribosomal protein S6 kinase 1 (pS6K1; Thr389) e da AMP-activated protein kinase (pAMPK; Thr172) foram significativamente maiores no grupo OTR/down quando comparado com os grupos CT e OTR. A fosforilação da 4E-binding protein-1 (p4E-BP1; Thr37/46) foi significativamente maior no grupo OTR/down quando comparado com o grupo CT. Os níveis proteicos de sterol regulatory element binding protein- 1 (SREBP-1; p125 precursor) foram significativamente maiores nos grupos OTR/down e OTR/up quando comparados com o grupo CT. Enquanto o grupo OTR/down apresentou sinais de esteatose com inchaço celular acompanhado de inflamação aguda, os grupos OTR/up e OTR demonstraram evidências de injúria hepática, com a presença de núcleos picnóticos, hepatócitos em balão e vacúolos citoplasmáticos. Conclui-se que o protocolo de OTR/down aumenta a modulação da via de sinalização da mTOR e induz a sinais de esteatose hepática. / The purpose of this study was to verify the effects of overtraining (OT) on the proteins related to the mammalian target of the rapamycin complex 1 (mTORC1) signaling pathway, the protein content of the sterol regulatory element binding protein-1 (SREBP-1) and the morphological characteristics in the livers of C57BL/6 mice. Rodents were divided into control (CT), overtrained by downhill running (OTR/down), overtrained by uphill running (OTR/up) and overtrained by running without inclination (OTR) groups. Rotarod, incremental load, exhaustive and grip force tests were used to evaluate performance. Thirty-six hours after the grip force test, the livers were removed and used for immunoblotting or histological analysis. The phosphorylation of the protein kinase B (pAkt; Ser473), mammalian target of the rapamycin (pmTOR; Ser2448), 70-kDa ribosomal protein S6 kinase 1 (pS6K1; Thr389) and AMP-activated protein kinase (pAMPK; Thr172) were significantly higher in the OTR/down group when compared to the CT and OTR groups. The phosphorylation of the 4Ebinding protein-1 (p4E-BP1; Thr37/46) was significantly higher in the OTR/down group when compared to the CT group. The protein levels of the sterol regulatory element binding protein-1 (SREBP-1; p125 precursor) were significantly higher in the OTR/down and OTR/up groups when compared to the CT group. While the OTR/down group presented signs of steatosis with cell swelling accompanied by acute inflammation, the OTR/up and OTR groups demonstrated evidences of injury in liver, with the presence of pyknotic nuclei, ballooned hepatocytes and cytoplasmic vacuoles. In conclusion, the OTR/down protocol up-modulated the mTOR signaling pathway and induced signs of hepatic steatosis.

A pesquisa de substâncias bioativas apresenta diversas etapas de grande complexidade técnico-científica e envolve uma atividade multidisciplinar. No estudo de antineoplásicos, dentre outros candidatos a fármacos, a determinação do perfil de atividade biológica é um ponto essencial para a determinação da potência, toxidez e o índice de seletividade. Neste projeto, os ensaios in vitro de compostos inibidores de catepsinas serão realizados usando células de câncer de próstata resistentes à quimioterapia (DU 145 e PC-3). Os estudos envolverão análises fenotípicas da resposta celular para determinar a viabilidade e o tipo de perturbação do ciclo celular utilizando técnicas colorimétricas e citometria de fluxo, juntamente com o estudo de sinalização celular PI3K-Akt-mTOR. Os testes de atividade citotóxica serão realizados com as células de fibroblasto de camundongo (Balb-c 3T3). Os resultados levarão a caracterização do tipo de resposta biológica e também da citotoxidez das substâncias de interesse. / The search for bioactive substances leads to molecules that need to be qualified throughout many complex steps, involving multidisciplinary activities. For antineoplastic molecules, among other classes of candidate drugs, the determination of the biological activity is the core of the whole process with the aim of determining the potency, toxicity and the selectivity index. In this project, in vitro cell-based bioassays of cathepsin inhibitors are going to be performed using prostate cancer cells resistant to chemotherapy (DU 145 and PC-3). Phenotypic studies are going to be used as end-points to observe the cell viability and the perturbation of the cell cycle by means of colorimetric, flow cytometry, coupled with the study of PI3K-Akt-mTOR signaling pathway. Cytotoxic assays are going to be performed in mouse fibroblasts (Balb-c 3T3). As a result, the biological outcome and the cytotoxic profile of the compounds of interest will be addressed.

A inibição de mTOR com rapamicina exacerba a intolerância glicose associada a obesidade, um efeito que pode estar associado ao desenvolvimento de processo pró-inflamatório no tecido adiposo. O tratamento de camundongos com rapamicina exacerbou a intolerância a glicose e inflamação do tecido adiposo induzida por dieta hiperlipídica. In vitro, a inibição dos complexos 1 e 2 da mTOR com rapamicina e torina induziu polarização espontânea de macrófagos para o fenótipo M1 e aumentou a atividade fagocítica de macrófagos M0. Camundongos com ativação constitutiva de mTORC1 exclusivamente em células mielóides foram protegidos do ganho de peso, adiposidade, intolerância a glicose e a insulina induzidos pela ingestão de dieta hiperlipídica e apresentaram um aumento da polarização de macrófagos para o fenótipo M2. Em conjunto, nossos dados indicam que a atividade do complexo 1 da mTOR atenua o desenvolvimento da inflamação do tecido adiposo associada a obesidade por um mecanismo que envolve a polarização de macrófagos para o fenótipo M2. / Pharmacological mTOR inhibition with rapamycin exacerbates the glucose intolerance associated with obesity, such an effect that may be associated to the development of inflammatory process in adipose tissue. Rapamycin treatment exacerbates the glucose intolerance and adipose tissue inflammation induced by high fat diet feeding. In vitro, inhibition of mTOR complexes 1 and 2 with rapamycin and torin induced spontaneous macrophage polarization into a pro-inflammatory M1 phenotype and increased M0 macrophage phagocytosis. Mice with constitutive activation of mTOR complex 1 in myeloid cells were protected from body weight gain, fat accretion, glucose and insulin tolerance induced by the intake of high fat diet and displayed a significant increase in macrophage polarization to a M2 phenotype. Altogether, our findings indicate that the activity of mTOR complex 1 attenuates the development of adipose tissue inflammation induced by high fat feeding, through a mechanism that involves a higher polarization of macrophages to anti-inflammatory M2 phenotype.

As solid tumor types, breast and prostate cancer are rivalled only by lung cancer in their propensity to metastasize to bone in the later stages of disease. At advanced stages of disease, approximately 80% of breast and 90% of prostate cancer patients will present with bone metastases. Bone metastases are often a painful conclusion to the lives of these patients, resulting in bone pain, hypercalcemia, pathological fractures and spinal cord compression. The culmination of these comorbidities considerably reduces a patient’s quality of life and prolonged survival. Hormone depletion is used as a first line of treatment in the majority of cases, negatively regulating bone health due to increased bone resorption by osteoclasts and decreased bone formation by osteoblasts. Not only is bone integrity undermined, but this action of increased bone turnover is beneficial for the colonization of metastasizing cells which co-opt and enhance the same mechanisms to establish and maintain their own growth. This is termed ‘the vicious cycle’ of osteolytic bone metastasis. Current research approaches aim to identify bone-targeted therapies which not only inhibit tumor growth but concurrently protect bone. In this study, Dickkopf-1 (DKK-1), mechanistic target of rapamycin (mTOR) and p38 mitogen-activated kinases (p38 MAPK) are presented as novel targets. Pro-tumor roles have been described for all and clinical trials are currently investigating their efficacy in different cancer types. In normal bone biology DKK-1 is an inhibitor of the canonical Wnt signaling pathway which promotes osteoblastogenesis while mTOR signaling is a promoter of osteoclastogenesis. P38 MAPK inhibitors have been shown to regulate DKK-1 expression and bone destruction in preclinical models of multiple myeloma. The aims of this current study were to 1) investigate the role of DKK-1 in the biology of osteotropic breast cancer, 2) to assess the potential bone protective effects of mTOR inhibition by everolimus in the context of osteotropic cancers and 3) to test the hypothesis that p38 MAPK is a regulator of DKK-1 expression in prostate cancer, potentially supporting an osteolytic phenotype by impairing osteoblastogenesis. In aim 1, analysis of a breast cancer tissue microarray demonstrated that DKK-1 expression was elevated in advanced and invasive tumor stages. Strikingly, positive DKK-1 expression correlated with a significantly reduced survival rate only in estrogen receptor-negative (ER-) breast cancer patients compared to patients with tumors which were negative for DKK-1 expression. In MDA-MB-231 breast cancer xenograft models, neutralization of secreted DKK-1 by treating mice with the monoclonal DKK-1 antibody BHQ880 or knocking out the expression of DKK-1 in MDA-MB-231 cells using CRISPR-Cas9 mediated gene editing, resulted in reduced tumor growth and burden by ≥ 50% (p < 0.05). In aim 2, the mTOR inhibitor everolimus is presented as an anti-tumor and bone-protective agent. The anti-tumor effects of everolimus were confirmed in two subcutaneous tumor models and a model of breast cancer bone metastasis, were tumor burden in the bone was reduced by 45.4% (p < 0.01). Bone loss induced by a hormone-deprived environment in ovariectomized mice was prevented with everolimus treatment as was bone destruction in the metastasis model. In more detail, it could be shown that everolimus maintained osteoblast function while specifically inhibiting osteoclast function. In aim 3, p38 MAPK is presented as a regulator of DKK-1 in prostate cancer. While the activation of p38 MAPK upregulated DKK-1, inhibition of p38 MAPK using small molecule inhibitors and siRNAs inhibited DKK-1 expression. Furthermore, assessment of different p38 MAPK isoforms revealed MAPK11 as the most effective regulator of DKK-1 and inhibition of DKK-1 by interfering with p38 MAPK signaling was sufficient to prevent the inhibitory effects of prostate cancer-derived DKK-1 on osteoblastogenesis in vitro. This study has assessed multiple targets and their concurrent roles in cancer and bone cell biology. Specifically, DKK-1 has been proven to be a tumor promoter in ER- breast cancer and can be targeted therapeutically to inhibit tumor growth. MTOR inhibition by everolimus has been shown to be an effective mono-therapy in ER- breast cancer, inhibiting the growth of subcutaneous tumor and bone metastases and preventing bone loss induced by estrogen ablation. This further supports its use in postmenopausal women with breast cancer who are predisposed to developing osteoporosis and bone metastases. It also supports the use of everolimus in hormone receptor-negative or triple receptor-negative breast cancer, for which it has not yet been approved. A clear link has been made between p38 MAPK signaling and DKK-1 expression in prostate cancer and its consequent regulation of osteoblastogenesis. A future focus on the inhibition of a specific MAPK isoform, MAPK11 in particular, may help in translating these encouraging in vitro results into promising pre-clinical trials in vivo. As a whole, these investigations provide a foundation for further research and could be valuable for the design of future clinical trials, leading to improvements in the treatment and prognosis of osteolytic bone metastases.

La sclérose tubéreuse complexe (TSC) est une maladie génétique caractérisée par une croissance des hamartomes dans différents organes y compris le cerveau, les reins, les poumons, la peau et le cœur. Ces lésions sont des sources de morbidité et de mortalité chez les patients TSC, car ils peuvent provoquerl’ épilepsie, l’autisme, le retard de développement et l’insuffisance rénale et pulmonaire. Les causes connues de TSC sont la perte de la fonction et les mutations des gènes TSC1 et TSC2. La majorité des lésions TSC contient plusieurs types cellulaires de la lignée mésenchymateuse, comme dans le cas des angiomyolipomes, l’lymphangioleiomyomatose et les angiofibromes. Un type unique de cellules épithélioïdes périvasculaires nommé (PEC) est constamment présent dans les lésions de TSC mésenchymateuses, comme angiomyolipomes et lymphangioleiomyomatose, basant sur les caractérisations morphologiques et l'expression des marqueurs communs mélanocytaires et myogéniques. Par conséquent, ces lésions sont officiellement classées, ainsi que d'autres tumeurs, comme PEComes. Leur origine cellulaire et les mécanismes moléculaires impliqués dans la pathologie restent à élucider. Ici, nous avons généré un modèle souris mosaïque TSC1 knockout qui développe des lésions rénales mésenchymateuses récapitulant périvasculaire épithélioïde cellules tumorales humaines (Pecoma) observés chez les patients TSC. Nous avons identifié YAP, le co-activateur transcriptionnel de la voie Hippo, a été régulée d'une manière mTOR-dépendante dans les lésions rénales de notre TSC1 knockout souris et les échantillons de l’angiomyolipome humaines. L'inhibition de YAP avec des outils génétiques ou pharmacologiques atténue considérablement la prolifération et la survie des cellules nulles TSC1 in vivo et in vitro. En outre, l’accumulation de YAP dans les cellules déficientes TSC1 / TSC2 pourra être dû à la dégradation de la protéine altéré par le système de l’autophagosome / lysosome. Ainsi, la régulation de YAP par mTOR et l'autophagie est un nouveau mécanisme de contrôle de la croissance, l'activité de YAP correspondant à la disponibilité des éléments nutritifs dans les conditions de croissance permissives. Il pourra servir comme une cible thérapeutique potentielle pour TSC et d'autres maladies avec une activité de mTOR dérégulée. / The Tuberous Sclerosis Complex (TSC) is a genetic disease characterized by growth of hamartomas in different organs including brain, kidney, lung, skin, and heart. These lesions are sources of morbidity and mortality in patients with TSC, as they may cause intractable epilepsy, autism, developmental delay, renal and pulmonary failure. Known causes of TSC are loss of function mutations in TSC1 and TSC2 genes. The majority of TSC lesions contain multiple cell types of the mesenchymal lineage, as in the case of angiomyolipomas, lymphangioleiomyomatosis and angiofibromas. A unique cell type named perivascular epithelioid cell (PEC) is constantly present in mesenchymal TSC lesions, such as angiomyolipomas and lymphangioleiomyomatosis, basing on morphological features and the common expression of melanocytic and myogenic markers. Therefore, these lesions are officially classified, along with other tumors, as PEComas. Their cell of origin and the molecular mechanisms underlying their pathogenesis remain poorly defined. Here we generated a novel mosaic Tsc1 knockout mouse model which develop renal mesenchymal lesions recapitulating human Perivascular Epithelioid Cell tumor (PEComa) observed in TSC patients. We identified YAP, the transcriptional coactivator of Hippo pathway, was upregulated in both renal lesions of TSC mouse model and human angiomyolipoma samples in a mTOR-dependent manner. Inhibition of YAP with genetic or pharmacological tools greatly attenuates the proliferation and survival of Tsc1 null cells in vivo and in vitro. Futhermore, we found YAP accumulation in TSC1/TSC2 deficient cells is due to impaired degradation of the protein through the autophagosome/lysosome system. Thus the regulation of YAP by mTOR and autophagy is a novel mechanism of growth control, matching YAP activity with nutrient availability under growth permissive conditions. It may serve as a potential therapeutical target for TSC and other diseases with dysregulated mTOR activity.

Dans les leucémies aiguës myéloïdes (LAM), l’activation anormale de nombreuses voies de signalisation intracellulaires favorise la croissance et la survie des cellules tumorales. L’amélioration des connaissances biologiques de ces pathologies hétérogènes, dont le pronostic est réservé, devrait permettre le développement de thérapies ciblées. La kinase oncogénique mTOR est présente au sein de deux complexes, parmi lesquels mTORC1, activé constitutivement dans la majorité des blastes primaires de patients porteurs de LAM, qui contrôle la synthèse protéique, et mTORC2 activé constitutivement dans 50% des LAM. Les inhibiteurs allostériques de mTORC1 (la rapamycine et ses dérivés) n’inhibent pas la phosphorylation du répresseur traductionnel 4E-BP1, ne diminuent pas la traduction et induisent peu d’apoptose in vitro dans les LAM. Utilisés en monothérapie, leur effet est décevant. De plus ces inhibiteurs n’agissent pas sur le complexe mTORC2. J’ai étudié l’effet d’un inhibiteur catalytique de mTOR, l’AZD8055, actif sur les deux complexes. In vitro, l’AZD8055 inhibe efficacement la signalisation en aval de mTORC1 et de mTORC2, dont les sites de phosphorylation de 4E-BP1 résistants à la rapamycine, ainsi que la synthèse protéique. Il diminue la prolifération, bloque le cycle cellulaire en phase G0G1 et induit une apoptose caspase-dépendante dans les blastes primaires de LAM. Il diminue également la clonogénicité des progéniteurs leucémiques, sans affecter celle des cellules CD34+ normales. Dans un modèle murin de xéno-transplantation, l’AZD8055 inhibe la croissance tumorale et améliore la survie des souris traitées. Je me suis également intéressée à la régulation de l’activité de mTORC1 par les acides aminés. Dans les cellules de mammifères, l’activation de mTORC1 nécessite la présence de glutamine et de leucine qui agissent en coopération via deux transporteurs membranaires, SLC1A5 et SLC7A5/SLC3A2. J’ai montré que la privation en glutamine, obtenue par l’activité glutaminase de la drogue L-asparaginase ou par l’utilisation de milieux de culture spécifiques dépourvus sélectivement en acides aminés, inhibe l’activation de mTORC1 et induit de l’apoptose dans diverses lignées leucémiques et dans les blastes primaires de LAM. La L-asparaginase inhibe la synthèse protéique et ses effets fonctionnels sont liés à son activité glutaminase. J’ai pu également constater une augmentation de l’expression protéique de la glutamine synthase induite par la Lasparaginase, dont l’inhibition majore l’apoptose induite par la L-asparaginase dans certaines lignées leucémiques. J’ai également étudié l’effet de l’inhibition spécifique par un shARN inductible du transporteur SLC1A5, qui permet l’import de glutamine. L’inhibition de SLC1A5 bloque la réactivation de mTORC1 par l’association leucine/glutamine après privation et induit de l’apoptose dans la lignée leucémique MOLM14. Cette inhibition diminue la croissance tumorale dans un modèle de xénogreffe / Acute myeloid leukaemias (AML) are heterogeneous diseases associated with poor prognosis. In AML, aberrant activation of many signaling pathways enhances proliferation and survival of leukemic blast cells. Understanding the mechanisms underlying survival of tumoral cells should allow the development of targeted therapies. The oncogenic kinase mTOR belongs to two distinct multimeric complexes. MTORC1 that controls protein translation, is constitutively activated in most of primary blast cells at AML diagnosis, while mTORC2 is constitutively activated in about half of AML samples. In AML, some phosphorylation events of the translational repressor 4E-BP1, are resistant to allosteric inhibitors of mTORC1 including rapamycin and its analogs. These first generation inhibitors of mTORC1 have only few effects on AML and do not induce significant apoptosis in vitro. I have tested a second generation mTOR kinase inhibitor active on both mTORC1 and mTORC2 complexes. In vitro, AZD8055 blocked mTORC1 and mTORC2 signaling, including 4E-BP1 rapamycin resistant phosphorylation events and protein synthesis. This compound decreased AML blast cells proliferation and cell cycle progression, reduced the clonogenic growth of leukemic progenitors and induced caspase-dependant apoptosis in leukemic cells but not in normal immature CD34+ cells. Finally, AZD8055 reduced tumor growth and improved survival in xenografted mouse model. In the second part of this work, I have studied the regulation of mTORC1 by amino acids in AML. In mammalian cells, activation of mTORC1 requires the presence of glutamine and leucine acting together via two membrane transporters, SLC1A5 and SLC7A5/SLC3A2. I showed that glutamine deprivation, obtained by L-asparaginase glutaminase activity or specific alpha-MEM use, inhibited mTORC1 and induced apoptosis in AML cell lines and primary AML blasts. L-asparaginase also inhibited protein synthesis and I have observed a correlation between the functional effects of L-asparaginase and its glutaminase activity. L-asparaginase induced an up-regulation of glutamine synthase (GS) protein and shRNA-induced GS inhibition increased L-asparaginase-dependant apoptosis in the MV4-11 AML cell line. I have also studied the effects of SLC1A5 inhibition with an inducible shRNA expressed in MOLM14 cells. Inhibition of this high afffinity transporter for glutamine blocked mTORC1 stimulation by leucine and glutamine after deprivation and induced apoptosis in MOLM-14 cell line. SLC1A5 inhibition reduced tumor growth and improved survival in transplanted mice