Apoptosis is a type of cell death with a specific morphology and molecular program, which is essential for the development of the nervous system. However, inappropriate cell death has been implicated in several neurodegenerative diseases. The Bcl-2 protein family is a class of proteins, which can regulate the cell death program in either a positive (pro-apoptotic family members) or a negative (anti-apoptotic family members) way. This thesis further elucidates the role of Bcl-2 family members in the nervous system. Special focus has been put on the anti-apoptotic family member Bcl-w, whose function in the nervous system was previously unknown, and the pro-apoptotic family member Bad which serves as a link between growth factor signalling and apoptosis. Bcl-w mRNA was found to be upregulated during rat brain development suggesting increasing importance of Bcl-w with age in the nervous system. In contrast, mRNA levels encoding the anti-apoptotic protein Bcl-x were downregulated during development. Bcl-w was also found to have an anti-apoptotic function in neurons, rescuing sympathetic neurons from cell death after nerve growth factor deprivation. To further elucidate the mechanism by which Bcl-w exerts its function, we screened a yeast two-hybrid library for proteins interacting with Bcl-w. Two of the isolated positive clones encoded the pro-apoptotic protein Bad and a novel splice variant of Bad with a different carboxyterminal sequence. Both isoforms of Bad induced cell death in sympathetic neurons, which could be counteracted by Bcl-w, indicating that Bcl-w and Bad can interact both physically and functionally. Further studies on the genomic structure of the Bad gene suggested the presence of an additional splice variant, not expressing the first exon. Immunohistochemical analysis indicates that the isoform(s) not expressing the first exon is more widely expressed in adult rat brain than the known forms. Finally, we show that high cell density can enhance survival of cerebellar granule neurons and that bcl-2 and bcl-x mRNA levels are upregulated in high density cultures.

Apoptosis is a genetically regulated cell death program, which shows distinct morphological characteristics. It takes place during neuronal development and in some neurodegenerative diseases. During apoptosis, the intracellular proteins are degraded by various caspases, cysteine aspartases, which are regulated by pro- and anti-apoptotic signals. This thesis elucidates the role of anti-apoptotic proteins in nerve cell survival and neurodegeneration. Studies have focused on Bcl-2 family members and Inhibitor of Apoptosis Proteins (IAP). XIAP and RIAP-2 are IAP proteins, which are expressed by neurons in the central nervous system. Kainic acid, a glutamate receptor agonist that induces seizures, increased XIAP immunoreactivity in rat hippocampus, whereas RIAP-2 expression in the same time decreased in degenerating neurons. Both XIAP and RIAP-2 were absent in dying neurons indicating that these proteins have a protective role in kainic acid induced neurodegeneration. NAIP, another IAP family member, was shown to interact with the calcium binding protein Hippocalcin using the yeast two-hybrid system and immunoprecipitation experiments. Hippocalcin-NAIP interaction increased motoneuron survival in caspase-3 independent and dependent manners. The anti-apoptotic Bcl-2 proteins, Bcl-2 and Bcl-x, were studied using cultured neurons and human neuronal progenitor cells. In the progenitor cells, Bcl-2 overexpression enhanced cell survival and induced downregulation of Caspase-2 (ICH-1) and caspase-3 (YAMA/CPP32). These results suggest a novel mechanism for the action of Bcl-2. Estrogen was shown to inhibit death of cultured dorsal root ganglion neurons (DRG) after nerve growth factor withdrawal. The hormone increased the levels of Bcl-x, which may explain the known neuroprotective function of estrogen.

Type 1 diabetes is a multifactorial disease resulting from the selective destruction of insulin-producing β-cells within the pancreatic islets of Langerhans. The mechanisms of β-cell death are not fully understood but cytokines are important mediators of this process. In the present study we found that the combination of IL-1β, TNF-α and IFN-γ induced a nitric oxide-dependent disruption of the mitochondrial membrane potential in rat insulin-producing RINm5F-cells, which seems to be a necessary event for both RINm5F-cell apoptosis and necrosis. The antiapoptotic protein Bcl-2 was able to prevent cellular death in RINm5F cells, most probably by counteracting the mitochondrial permeability transition. These results pointed out the potential of such antiapoptotic genes as gene therapy tools, to allow enhanced resistance against autoimmune destruction of β-cells in type 1 diabetes. For this purpose we used a progesterone-antagonist (RU 486)-inducible gene transfer system to achieve an efficient and controlled Bcl-2 overexpression in primary rat β-cells. However, in our experience, prolonged in vitro culture revealed adenoviral-induced islet cell necrosis, a process that was not prevented by Bcl-2 overexpression. Moreover, we observed that specific adenoviral genotypes correlate with differential induction of necrosis in both human and rat pancreatic islet cells. Although human islet cells showed an increased resistance in terms of viral concentrations required for the induction of cell-toxicity, our results showed that they were unable to build up an efficient antiviral response following infection and that their survival was dependent on the exogenous addition of α-interferon. In conclusion, adenoviral techniques for overexpression of antiapoptotic proteins in insulin-producing cells may provide useful tools against β-cell directed autoimmune destruction. However, understanding the specific interactions of the viral gene products with cellular proteins and how they are involved in β-cell death regulation is fundamental for an efficient and safe application of gene therapy approaches to type 1 diabetes.

Mast cells are long-lived effector cells of importance for both acute and chronic inflammations. Mast cells can be activated in many different ways, leading to the release of inflammatory mediators. In contrast to most other inflammatory cells, activated mast cells have the capacity to recover, regranulate and thereby be activated again. In this thesis I have investigated the mechanisms involved in regulating activation-induced mast cell survival. We have found that cross-linking of FcεRI-bound IgE with an antigen (IgER-CL) induces a survival program in mast cells. Upon IgER-CL, mouse and human mast cells upregulate the pro-survival Bcl-2 family gene A1/Bfl-1. A1-/- mast cells degranulate upon FcεRI activation but they cannot recover most likely due to the lack of A1. Sensitized and provoked A1-/- mice exhibit lower amounts of mast cells compared to littermate controls. In contrast to mast cells, no Bfl-1 expression or survival promotion can be detected in basophils after IgER-CL. Another mast cell secretagogue, an adenosine receptor agonist, neither promoted upregulation of A1 nor survival. Although it is well established that mast cell survival is dependent on stem cell factor (SCF), it has not been described how this process is regulated. We have found that SCF promotes survival through Akt-mediated inhibition of the forkhead transcription factor FOXO3a and its transcriptional target Bim, a BH3-only pro-apoptotic protein. SCF-treatment prevents upregulation of Bim protein expression and leads to an upregulation of Bim phosphorylation through PI3-kinase and MEK-dependent pathways. Overexpression of FOXO3a causes an upregulation of Bim and induces mast cell apoptosis, even in the presence of SCF. Taken together, the work in this thesis demonstrates that A1/Bfl-1 and Bim play key roles in mast cell survival. These findings might be of importance in understanding the mechanisms of mast cell longevity and hence for possible new therapeutics used for mast cell-associated inflammations.

Upon activation mast cells release numerous proinflammatory mediators. With this feature, mast cells play an important role in host defense against pathogens, and are involved in tissue remodeling and wound healing. However, in cases of excessive inflammation the effects of mast cells are detrimental. This is observed in allergy, asthma, rheumatoid arthritis, atherosclerosis, certain types of heart failure, and in several other chronic destructive inflammations. Mast cell numbers are typically increased at inflammatory sites. There they act both directly, as effector cells, and in a regulatory manner, secreting agents that recruit and activate other immune cells. The studies presented here investigated mechanisms regulating mast cell numbers at sites of inflammation, focusing on cell migration and regulation of survival/apoptosis. We report that SCF-induced mast cell migration requires p38 MAP kinase activity. Moreover, we found that SCF-mediated mast cell survival is regulated through downregulation of the proapoptotic Bcl-2 family member Bim, as well as through phoshorylation of Bim. SCF seems to control Bim protein levels via FOXO transcription factors, and to induce phosphorylation of Bim via the Mek/Erk and the PI3-kinase/Akt signaling pathways. Furthermore, mast cell death triggered by deprivation of SCF and/or IL-3 involves the Bim protein, as demonstrated using bim-/- mast cells. Additional studies revealed that IgE-receptor activation, which occurs in allergy, promotes both prosurvival and proapoptotic signaling events. This includes upregulation of Bim and the prosurvival Bcl-XL and A1, as well as phosphorylation of Akt, FOXO factors, GSK-3β, IκB-α, Bad, and Bim. The simultaneous stimulation of prosurvival and proapoptotic signaling events could be a way to fine-tune the fate of mast cells after IgE-receptor activation and degranulation. The new insights about mechanisms involved in mast cell migration and regulation of survival/apoptosis might prove useful for future efforts to design new drugs to be used for mast cell-associated diseases.

MicroARN (miARN) ont récemment émergé comme un acteur central du gène réseau de régulation impliqués dans la prise du destin cellulaire. L'apoptose, un actif processus, par lequel des cellules déclenchent leur auto-destruction en réponse à un signal, peut être contrôlé par les miARN. Il a également été impliqué dans une variété de maladies humaines, comme les maladies du cœur, et a été pensé comme une cible pour le traitement de la maladie. Tanshinone IIA (TIIA), un monomère de phenanthrenequinones utilisé pour traiter maladies cardiovasculaires, est connu pour exercer des effets cardioprotecteurs de l'infarctus du myocarde en ciblant l'apoptose par le renforcement de Bcl-2 expression. Pour explorer les liens potentiels entre le miARN et l'action anti-apoptotique de TIIA, nous étudié l'implication possible des miARN. Nous avons constaté que l'expression de tous les trois membres de la famille miR-34, miR-34a, miR-34b et miR-34c ont été fortement régulée à la hausse après l'exposition soit à la doxorubicine, un agent endommageant l'ADN ou de pro-oxydant H2O2 pendant 24 heures. Cette régulation à la hausse causé significativement la mort cellulaire par apoptose, comme déterminé par fragmentation de l'ADN, et les effets ont été renversés par les ARNs antisens de ces miARN. Le prétraitement des cellules avec TIIA avant l'incubation avec la doxorubicine ou H2O2 a empêché surexpression de miR-34 et a réduit des apoptose. Nous avons ensuite établi BCL2L2, API5 et TCL1, en plus de BCL2, comme les gènes nouveaux cibles pour miR-34. Nous avons également élucidé que la répression des ces gènes par MiR-34 explique l'effet proapoptotique dans les cardiomyocytes. Ce que la régulation positive de ces gènes par TIIA realisée par la répression de l'expression de miR-34 est probable le mécanisme moléculaire de son effet bénéfique contre ischémique lésions cardiaques. / MiRNAs (miRNAs) have recently emerged as a central player of gene regulatory network involved in decision of cell fate. Apoptosis, an active process that leads to cell death, has been shown to be controlled by miRNAs. It has also been implicated in a variety of human disease, such as heart disease, and established as a target process for disease therapy. Tanshinone IIA (TIIA), a monomer of phenanthrenequinones used to treat cardiovascular diseases, is known to exert cardioprotective effects in myocardial infarction by targeting apoptosis through enhancing Bcl-2 expression. To explore the potential link between miRNAs and the anti-apoptotic action of TIIA, we studied the possible involvement of miRNAs. We found that expression of all three members of the miR-34 family, miR-34a, miR-34b and miR-34c that have been known to mediate the apoptotic effect of p53 in cancer cells, were robustly upregulated after exposure to either the DNA-damaging agent doxorubicin or pro-oxidant H2O2 for 24 hr in cultured neonatal rat ventricular myocytes. This upregulation caused significant apoptotic cell death, as determined by DNA fragmentation, and the effects were reversed by the antisense to these miRNAs. Pretreatment of cells with TIIA prior to incubation with doxorubicin or H2O2 prevented upregulation of miR-34 and reduced apoptosis. We then established BCL2L2, API5 and TCL1, in addition to BCL2, as the novel target genes for miR-34. We further unraveled that repression of these genes by miR-34 accounts for its proapoptotic effect in cardiomyocytes whereas upregulation of these genes by TIIA through downregulating miR-34 is likely the molecular mechanism for its beneficial effect against ischemic myocardial injuries.

Thèse numérisée par la Division de la gestion de documents et des archives de l'Université de Montréal

Les leucémies aiguës myéloblastiques (LAM) sont des maladies hématopoïétiques caractérisées par une prolifération incontrôlée de précurseurs myéloïdes bloqués à divers stades de différenciation. Le pronostic des LAM reste sombre à cause de la résistance aux traitements et des rechutes après rémission. En conséquence, des thérapies moins intensives et mieux tolérées doivent être développées ; ceci nécessite le développement de stratégies combinatoires associant des molécules avec des modes d'action différents pour augmenter l'efficacité des traitements. Plusieurs approches sont en cours d'étude préclinique et clinique [inhibiteurs des voies de signalisation PI3K/Akt/mTOR, anticorps monoclonaux couplés à une drogue (Mylotarg®), inhibiteurs du protéasome (bortezomib)...] Des travaux récents ont relancé l'intérêt de l'étude des molécules d'origine naturelle pour le traitement des cancers. Ainsi, l'acide flavone-8-acétique (FAA) a suscité de nombreux espoirs au vu de son action sur les tumeurs greffées chez la souris ; il s'est néanmoins révélé inactif chez l'homme du fait d'une métabolisation différente de celle de la souris. L'objectif de ma thèse a été d'étudier les effets d'anticorps monoclonaux dirigés contre l'antigène tumoral CD13 (aminopeptidase-N) et de deux dérivés de FAA, la 2',3-Dinitroflavone-8-acétique (DNFAA ; inhibiteur de l'activité enzymatique de CD13) et la 3,3'-Diamino-4'-méthoxyflavone (DD1) dans les LAM. Mon étude a montré que DNFAA n'affecte ni la prolifération ni la survie des cellules de LAM (lignées et cellules primaires). Cependant, le traitement de ces cellules par les anticorps anti-CD13, (MY7, SJ1D1, WM15 ; reconnaissant ou non le site enzymatique) induit l'apoptose en activant les voies extrinsèque et intrinsèque. Dans la voie intrinsèque, les anti-CD13 régulent négativement l'expression des protéines anti-apoptotiques Bcl-2 et Mcl-1 et positivement l'expression de la protéine pro-apoptotique Bax. De plus, l'activation de la voie PI3K/Akt apparaît associée au processus apoptotique. Mon étude sur les effets du 3,3'-Diamino-4'-méthoxyflavone dans les cellules de LAM montre une induction d'apoptose résultant de la convergence de l'inhibition du protéasome et de l'activation des voies extrinsèque et intrinsèque. Les cibles de DD1 sont le protéasome, la kinase p70S6K (kinase en aval de mTOR), et les protéines pro-apoptotiques Bad et Bax. De plus, j'ai mis en évidence la dégradation de p70S6K sous l'action de la caspase 3, par le traitement avec DD1, nouvelle propriété partagée par DD1 et le bortezomib. En conclusion, mon travail a permis de mettre en évidence les capacités à induire in vitro des voies d'apoptose déficientes dans les cellules de LAM, d'anticorps monoclonaux anti-CD13 et de la flavone originale, 3,3'-Diamino-4'-methoxyflavone, en tant que nouvel inhibiteur du protéasome. Les propriétés de ces agents pro-apoptotiques méritent d'être analysées de façon plus approfondie.

La formation de cancers est liée à des dérèglements de la progression du cycle cellulaire ou de l'apoptose. L'identification des acteurs cellulaires mis en jeu dans la maladie et l'élucidation des mécanismes responsables de ces dysfonctionnements sont à la base de nouveaux traitements anticancéreux. Ainsi, en vue du développement de thérapies ciblées, les kinases Pim et les protéines anti-apoptotiques de la famille des Bcl-2, surexprimées dans de nombreux types de cancers et associées à des phénomènes de chimiorésistance, constituent des cibles pertinentes. Les kinases Pim (Pim-1,-2 et -3) sont une famille de sérine / thréonine kinases qui jouent un rôle fondamental dans les processus de survie, de prolifération ou de différenciation cellulaire. Bien qu'elles possèdent un substrat commun avec les autres protéines kinases, l'ATP, des différences structurales permettent de les différencier et de les inhiber sélectivement. En tenant compte de ces spécificités, nous nous sommes intéressés à la synthèse de nouveaux inhibiteurs sélectifs des kinases Pim, compétitifs de l'ATP. Parmi les autres agents impliqués dans la formation de tumeurs, les protéines de la famille des Bcl-2, responsables du phénomène d'apoptose ou mort cellulaire programmée, font l'objet d'un domaine d'étude récent. Elles se classent en deux familles selon leur fonction : les protéines pro-apoptotiques et les protéines anti-apoptotiques dont la surexpression est observée dans de nombreux cancers. Nous avons poursuivi l'étude de relations structure-activité initiée au laboratoire à partir de trimères d'alkoxyquinoléines, inhibiteurs micromolaires des protéines anti-apoptotiques Bcl-2 et Bcl-xL, en préparant de nouveaux analogues.

<p>Hematopoiesis is the continual process of blood cell generation that primarily occurs in the bone marrow of adult animals. Hematologic neoplasms can also occur in the bone marrow and often result from dysregulation of signal transduction pathways. One example is the activation of the Ras oncogene, which has been linked to a variety of different cancers, including hematologic neoplasms. Ras is located proximal to the cell membrane and can activate many downstream effector pathways, thus it is difficult to determine which downstream pathway is mediating oncogenic Ras function. My thesis work focused on the effect of inappropriate activation of MEK/ERK, a downstream Ras effector pathway, in the hematopoietic system.</p><p>Using a retroviral transduction system, we expressed a constitutively active form of MEK1 in hematopoietic stem cells (HSCs). Mice transplanted with HSCs expressing active MEK developed a lethal myelodysplastic syndrome/myeloproliferative disease (MDS/MPN) characterized by the expansion of granulocytes/macrophages (GM) at the expense of lymphoid cell development. Transplantation of active MEK-induced MDS/MPNs into naïve mice did not result in further disease, suggesting that the MDS/MPN is not a frank leukemia.</p><p>Bcl-2 is an anti-apoptotic molecule that has been shown to play a role in leukemia development and maintenance. Coupling expression of active MEK and Bcl-2 resulted in MDS/MPNs that were phenotypically identical and had very similar disease onset compared to active MEK-induced MDS/MPNs. However, transplantation of Bcl-2/active MEK-induced MDS/MPNs did not result in a myeloid disease; rather, it resulted in the development of T-acute lymphoblastic leukemia (T-ALL) that was marked by activated Notch signaling. </p><p>These results led us to conclude that activation of MEK/ERK was sufficient to cause a pre-leukemic myeloid disease; however, additional oncogenic factors, such as Bcl-2 and Notch, were necessary for frank leukemia development. Moreover, additional oncogenic factors can alter the disease phenotype and disease course. Future analysis of the interplay between oncogenic factors will help shed light on disease development and aid in the development of more effective cancer treatments.</p> / Dissertation