Le nicotinamide est un des deux constituants de la vitamine B3. C’est aussi un agent pharmacologique qui a été testé dans le traitement du HIV chez l’homme, et comme traitement contre diverses pathologies. Il présente également des capacités cytoprotectrices dans plusieurs modèles de stress cellulaire et est considéré comme un agent pharmacologique prometteur dans le traitement des maladies de dégénérescence cérébrale d’origine vasculaire. Il module la réponse innée en inhibant notamment la synthèse de molécules pro-inflammatoires. Toutefois, son influence sur la réponse adaptative n’a pas encore été analysée. <p>Le nicotinamide intervient dans la biosynthèse du NAD comme précurseur dans la voie de « sauvetage ». Le rôle du NAD comme coenzyme dans de nombreuses réactions enzymatiques du métabolisme de la cellule est bien connu. De plus, le NAD peut être dégradé par différentes enzymes impliquées dans différentes modifications post-traductionnelles de protéines (PARPs, Sirtuines et MARTs). Le nicotinamide est un produit de la dégradation du NAD mais également un inhibiteur de ces enzymes et constitue donc un outil permettant d’étudier le rôle de ces enzymes dans la transduction de signaux intracellulaires. <p>Nous avons utilisé le nicotinamide comme un inhibiteur non toxique des différentes enzymes impliquées dans les réactions d’ADP-ribosylation et étudié son effet sur l’activation des lymphocytes B. Le nicotinamide inhibe la prolifération et la différentiation de ces cellules. Il ne module pas les étapes précoces du BCR mais inhibe l’activation des MAPKs et de la kinase Akt. L’inhibition des MAPKs Erk est corrélée avec une réduction de l’expression de la cycline D2 et du marqueur d’activation CD69. L’utilisation d’un inhibiteur des PARPs ne nous a pas permis de reproduire les effets du NAm sur la voie MAPK Erk et CD69. Par contre, le MIBG, un inhibiteur des MARTs inhibe bien la surexpression du CD69 ainsi que la phosphorylation des kinases Erk. Bien que le nicotinamide soit capable d’inhiber l’expression du CD69 in vivo, nos expériences ne nous ont pas permis de moduler la réponse immune adaptative in vivo. <p>Ceci suggère dès lors que l’utilisation de fortes doses de nicotinamide comme traitement pharmacologique de certaines affections chez l’homme ne devrait pas poser de problème au niveau de la réponse adaptative. De plus, notre mise en évidence des MARTs dans le contrôle de l’activation des lymphocytes B ouvre des perspectives encourageantes pour de nouveaux traitements modulant la réponse adaptative. Cette réponse étant particulièrement impliquée dans certaines maladies auto-immunes, il est potentiellement intéressant de trouver des inhibiteurs de ces enzymes plus puissants que le nicotinamide afin de moduler la réponse immune adaptative in vivo<p> / Doctorat en sciences, Spécialisation biologie moléculaire / info:eu-repo/semantics/nonPublished

With an increased popularity for systems-based approaches in biology, a wide spectrum of techniques has been applied to the simulation and analysis of biochemical systems which involves uncertainty and stochasticity. It is particularly concerned with modelling and analysis of metabolic pathways, regulatory and signal transduction networks for understanding intra-cellular pathway behaviour. Typically, parameter estimation in ordinary differential equations(ODEs) models is used for this purpose when there is large number of molecules involved in the reaction system. However this approach is correct when the system is large enough to be deterministic in nature. But there are uncertainty involved in the system and the processes are stochastic in nature due to smaller population molecules participating in the pathway reactions. In this thesis the common theme is the study of uncertainties in the chemical kinetics of biochemical reaction systems associated with various intra-cellular pathways and channels. The study is at the mesoscale of the system, i.e., we study systems that do not have too few molecules disallowing any higher scale system level approximation nor too many where a non-stochastic (mesoscale) system approximation will be valid. In our first study we estimate the parameters in the mitogen activated protein kinase (MAPK) signal transduction pathway involved in the departure from the normal Epithelial Growth Factor(EGF) dose-dependency in prostate cancer cells. A model-based pathway analysis is performed. The pathway is mathematically modelled with 28 rate equations yielding those many ordinary differential equations(ODE) with kinetic rate constants that have been reported to take random values in the existing literature. This has led to us treating the ODE model of the pathways kinetics as a random differential equations(RDE) system in which the parameters are random variables. The most likely set of values of the kinetic rate constants obtained from fitting the RDE model into the experimental data is then used in a direct transcription based dynamic optimization method for computing the changes needed in these kinetic rate constant values for the restoration of the normal EGF dose response. It identifies the parameters, i.e., the kinetic rate constants in the RDE model, that are the most sensitive to the change in the EGF dose response behaviour in the PC3 prostate cancer cells. Biochemical pathways involving chemical kinetics equations in terms of low concen-trations of the model variables can be represented as chemical Langevin equations(CLE) as there is stochasticity involved in the processes. Most CLE systems come with the implicit constraint that the concentration state cannot be negative at any time over the sample path. Due to the inherent stiffness(especially in diffusion coefficient) of the CLE system, it has been difficult for numerical schemes to meet this positivity constraint during numerical simulations. Most available methods resort to heuristics by dropping selective noise terms from the original CLE inconsistent with the mesoscale physics involved in forming the CLE. Other methods take very small time steps thus making the simulation inefficient. In our second study we preserve positivity by using a physically consistent numerical scheme which is a modified form of fully stochastic α method for stiff stochastic differential equation. Ion channels are fundamental molecules in the nervous system that catalyse the flux of ions across the cell membrane. Single ion channel flux activity is comparable to the catalytic activity of single enzyme molecules. Saturating concentrations of substrate induce dynamic disorder in the kinetic rate processes of single enzyme molecules and consequently, develop correlative memory of the previous history of activities. Conversely, binding of substrate ion is known to alter the catalytic turnover of single ion channels. Here, we investigated the possible existence of dynamic disorder and molecular memory in single human TREK1 channel due to binding of substrate/agonist using the excised inside-out patch-clamp technique. Our results suggest that single hTREK1 channel behaves as a typical Michaelis-Menten enzyme molecule with a single high-affinity binding site for substrate K+ ion but with uncertainty in reaction rates.

Toll-like receptors (TLRs) are important receptor family of innate immunity. They enable fast recognition of infection through so called pathogen associated molecular patterns (PAMPs). In this thesis, we studied interaction of mouse polyomavirus (MPyV) with TLRs of mouse embryonic fibroblasts (MEF cells). We observed that inhibition of TLR4 signaling abolished response of MEF cells to MPyV. This suggested that TLR4 plays a role in MEF cells recognition of MPyV. To detect response of MEF cell to MPyV, we measured IL-6 production by ELISA. Next, we investigated effect of TLR4 signalization on MPyV infection. Inhibition of TLR4 signaling with CLI-095 inhibitor did not affect number of infected cells. Presence of TLR4 antagonist, LPS-RS, led to significant decrease in quantity of infected cells 20 hours post infection. Decrease in number of infected cells was also observed in presence of LPS. Viral infection was also inhibited by TLR9 antagonist ODN 2088. We also investigated role of MAP kinases in MPyV infection. We tested, whether inhibition of selected MAP kinases would affect number of infected cells. Inhibition of kinase p38 did not affect infection. On the other hand, inhibition of MEK kinase or JNK resulted in decrease of number of cells infected by MPyV.

The development of an organism and its adult homeostasis rely on regulatory mechanisms that control the underlying gene expression programs. In certain biological contexts, such as germ cell development, gene expression regulation is largely executed at the post-­‐transcriptional level. This relies on RNA-­‐binding proteins (RBPs), whose activity and expression are also heavily controlled. While the RNA-­‐binding potential of RBPs is currently of intense scrutiny, surprisingly little is known to date about the molecular mechanisms that control RNA-­‐binding proteins abundance in the context of germ cell development. This work identifies the molecular mechanisms that shape expression patterns of two evolutionarily conserved RNA-­‐binding proteins, CPB-­‐3 and GLD-­‐ 1, which belong to CPEB and STAR protein family, respectively. By focusing on their regulation in the C. elegans germ line, this work reveals an involvement of the proteasome in reducing levels of CPB-­‐3/CPEB and GLD-­‐1/STAR at the pachytene-­‐to-­‐diplotene transition during meiotic prophase I. Furthermore, it documents that CPB-­‐3 and GLD-­‐1 are targeted to proteasomal degradation by a conserved SCF ubiquitin ligase complex that utilises SEL-­‐10/Fbxw7 as a substrate recognition subunit. Importantly, destabilisation of both RBPs is likely triggered by their phosphorylation, which is regulated by the mitogen-­‐activated protein kinase, MPK-­‐1, and restricted to the meiotic timepoint of pachytene exit. Lastly, this work investigates the potential consequences of target mRNA regulation upon delayed RBP degradation. Altogether, the collected data characterise a molecular pathway of CPEB and STAR protein turnover, and suggest that MPK-­‐1 signaling may couple RBP-­‐mediated regulation of gene expression to progression through meiosis during oogenesis.

No description available.

Acute and chronic morphine administration can significantly reduce ischemia- reperfusion injury of the rat heart. However, the molecular mechanisms mediating the protective effect of morphine are not yet fully elucidated. Concurrently, there is a lack of information about the effects of the long-term action of morphine on heart tissue. Therefore, in the first part of the project, we studied the effect of long-term administration of high doses of morphine (10 mg/kg/day, 10 days) on rat heart tissue. In the second part of the project, we investigated the effect of 1 mM morphine on viability and redox state of rat cardiomyoblast cell line H9c2 that was influenced by oxidative stress elicited by exposure to 300 μM tert-butyl hydroperoxide (t-BHP). Our experiments have shown that long-term morphine administration affected neither the amount nor the affinity of myocardial β-adrenergic receptors (β-AR), but almost doubled the number of the dominant isoforms of myocardial adenylyl cyclase (AC) V/VI and led to supersensitization of AC. At the same time, proteomic analyses revealed that long-term morphine administration was associated with significant changes in the left ventricular proteome. In particular, there was an increase in the expression of heat shock proteins (HSP). Increased expression of HSP27...

La voie de signalisation Ras/mitogen-activated protein kinase (Ras/MAPK) occupe un rôle central dans la régulation de différents processus biologiques tels que la croissance, la survie mais aussi la prolifération cellulaire. En réponse à des signaux extracellulaires, cette voie de signalisation mène à l’activation des protéines ERK1/2, impliquées dans l’activation de nombreux substrats cellulaires dont les protéines kinases RSK (p90 ribosomal S6 kinase). Ces protéines kinases sont, entre autres, impliquées dans l’invasion et la migration cellulaire mais les mécanismes responsables de ces phénomènes biologiques restent inconnus à ce jour. Dans mon mémoire, je développe tout d’abord les travaux précédemment réalisés dans notre laboratoire, et identifie la protéine p120-Catenin (p120ctn), un composant majeur des jonctions adhérentes (AJ), comme un nouveau substrat de la voie Ras/MAPK. En utilisant notamment un anticorps phospho-spécificique, nous avons pu démontrer que p120ctn est phosphorylée sur la sérine 320, un nouveau site de phosphorylation, d’une manière dépendante des kinases RSK. D’autre part, nous avons trouvé que la signalisation Ras/MAPK réduit l’interaction entre les protéines p120ctn et N-cadhérine. Ainsi, nos observations suggèrent que l’activation de la voie Ras/MAPK est impliquée dans la diminution de l’adhérence entre cellules par la déstabilisation des AJ. Compte tenu du rôle primordial de la voie de signalisation Ras/MAPK dans le cancer, ce mécanisme nouvellement décrit pourrait contribuer à l’avancement des connaissances sur le développement des cancers dépendents de cette voie de signalisation. / The Ras/MAPK (mitogen-activated protein kinase) signalling pathway is vital in regulating cell growth, survival and proliferation in response to extracellular signals. Positioned downstream in the pathway, the p90 ribosomal S6 kinase (RSK) family regulates cell invasion by weakening cell-cell adhesion, but the mechanisms involved remain elusive. In this thesis, I expand upon previous work performed in our lab and identify p120ctn, a major component of adherens junctions (AJ), as a new substrate of the Ras/MAPK pathway. Using a phospho-specific antibody, we demonstrate that p120ctn is phosphorylated on a new phosphorylation site on S320 upon activation of MAPK signalling in a RSK-dependent manner. Furthermore, we show that Ras/MAPK signaling reduces p120ctn binding to N-cadherin, suggesting a new mechanism by which MAPK activity decreases cell-cell adhesion by destabilizing AJs. Finally, we designed and optimized two individual assays to be used in future experiments examining the effects of Ras/MAPK signalling on AJ function. Taken together, our data identifies RSK as a regulator of p120ctn phosphorylation, and also implicates Ras/MAPK signalling in regulating cell-cell adhesion by destabilizing AJ through p120ctn. Given the role of Ras/MAPK signalling in cancer, this new mechanism may play a role in the development and progression of Ras-driven cancers.

L'efficacité de la reproduction bovine a considérablement diminué dans les dernières décennies et cette diminution constitue un problème économique majeur. Pour mieux contrer ce problème, la physiologie des cellules stéroïdogéniques ovariennes dont les cellules de granulosa (CG) doit être mieux comprise au cours des dernières étapes de la croissance folliculaire, de l'ovulation et de la lutéinisation. En ce sens, nous avons précédemment identifié divers gènes induits dans les CG des follicules ovulatoires bovins par la LH/hCG incluant Ankyrin-repeat and SOCS-box protein 9 (ASB9). Cependant, les mécanismes d’action d’ASB9 dans les CG étaient encore indéfinis. Les objectifs de cette étude étaient d'élucider le rôle d'ASB9 dans les CG ainsi que ses effets sur ses partenaires spécifiques PAR1, TSG6 et TAOK1. Un modèle in vivo de CG provenant de follicules à différentes phases de développement: petits follicules (SF), follicules dominants (DF) et follicules ovulatoires (OF), et un modèle in vitro de CG en culture ont été utilisées. L'inhibition d’ASB9 dans les CG via CRISPR/Cas9 a montré une augmentation significative de PAR1, PCNA, CCND2 et CCNE2 et une diminution significative de TAOK1, TSG6 et CASP3. Dans le modèle in vivo, PAR1 a été différentiellement exprimé dans DF et TSG6 et TAOK1 ont été induits dans OF. L'inhibition de l'ASB9 a aussi entraîné une diminution de l'apoptose des CG et de l'activité caspase3/7. Des analyses Western blot ont démontré que l'induction d'ASB9 dans OF, après l'injection d'hCG, était concomitante avec une diminution significative des niveaux de phosphorylation de MAPK3/1 tandis que pMAPK3/1 augmentait après l'inhibition d'ASB9. Ces résultats supportent qu'ASB9 pourrait être un régulateur de l'activité et de la fonction des CG en ciblant des protéines spécifiques qui affectent la signalisation MAPK, limitant la prolifération des CG. Ces résultats contribuent à une meilleure compréhension de l’activité ovarienne et de la reproduction bovine. / The efficiency of bovine reproduction has considerably decreased in recent decades and this decrease constitutes a major economic problem. To better counter this problem, the physiology of ovarian steroidogenic cells including granulosa (CG) cells needs to be better understood during the later stages of follicular growth, ovulation and luteinization. In this sense, we have previously identified various genes induced in the CGs of bovine ovulatory follicles by LH / hCG including Ankyrin-repeat and SOCS-box protein 9 (ASB9). However, ASB9 mechanisms of action in GC were still undefined. The objectives of this study were to elucidate the role of ASB9 in CG as well as its effects on target partners PAR1, TSG6 and TAOK1, and on MAPK signaling. An in vivo model of GC from follicles at different developmental stages: small follicles (SF), dominant follicles (DF), and ovulatory follicles (OF) and an in vitro model of cultured GC along with the CRISPR/Cas9 approach to inhibit ASB9 were used. Inhibition of ASB9 in GC resulted in significant increase in PAR1, PCNA, CCND2, and CCNE2 and significant decrease in TAOK1, TNFAIP6, and CASP3 expression. From in vivo samples, PAR1 was differentially expressed in DF as compared to OF while TSG6 and TAOK1 were induced in OF. Further analyses showed an increase in GC number and a decrease in apoptosis and caspase3/7 activity following ASB9 inhibition. Western blot analyses demonstrated that ASB9 induction in OF by hCG was concomitant with a significant decrease in MAPK3/1 phosphorylation levels while pMAPK3/1 increased following ASB9 inhibition. These results provide strong evidence that ASB9 is a regulator of GC activity and function by modulating MAPK signaling pathway likely through specific binding partners such as PAR1, therefore controlling GC proliferation. These results contribute to a better understanding of ovarian activity and bovine reproduction.

Indiana University-Purdue University Indianapolis (IUPUI) / Neurofibromatosis type 1 (NF1) is a neurocutaneous disorder that affects roughly 1 in 3500 individuals. In addition to physical features (e.g., neurofibromas), developmental disorders are also common that can affect cognition, learning, attention and social function. The NF1 gene encodes neurofibromin, a GTPase activating protein (GAP)-like protein that negatively regulates Ras GTPase activation. Mutation at the NF1 locus increases the output of MAPK and PI3K signal transduction from the cellular membrane to the nucleus. Similar to humans, Nf1+/- mice show spatial learning abnormalities that are potentially correlated with increases in GABA-mediated inhibition and deficits in long-term potentiation in the hippocampus. Here, we demonstrate for the first time that Nf1+/- mice exhibit a selective loss of long-term social learning / memory and increased GABAergic inhibition in the basolateral amygdala, a critical brain region for regulating social behaviors. Next, utilizing a genetic intercross, we show that the co-deletion of p21-activated kinase type 1 (Pak1-/-), which positively regulates MAPK activation, restores Nf1+/--dependent MAPK hyperactivation in neurons cultured from the frontal cortex. We found that the co-deletion of Pak1 in Nf1+/- mice (Nf1+/- / Pak1-/-) also restores the deficits in long-term social learning / memory seen in Nf1+/- mice and normalizes the increases in GABA-mediated inhibition in the BLA, as compared to Nf1+/- mice. Together, these findings establish a role for Nf1 and Pak1 genes in the regulation of social learning in Nf1-deficient mice. Furthermore, proteomic studies identify dysregulation of F-actin and microtubule dynamics in the prefrontal cortex, and implicate proteins associated with vesicular release as well as neurite formation and outgrowth (e.g., LSAMP, STXBP1, DREB). In the BLA, disintegrin and metalloproteinase domain-containing protein 22 (ADAM22) was identified, and ADAM22 may play a role in the regulation of AMPA receptors. Finally, due to the increased co-occurrence of NF1 and autism, these findings may also have important implications for the pathology and treatment of NF1-related social deficits and some forms of autism.

<p> The ErbB2/Neu orphan receptor tyrosine kinase is amplified in 20-30% of breast and ovarian cancers and predicates poor patient prognosis. Five conserved tyrosine residues, autophosphorylated by Neu catalytic activity, "dock" adaptors and second messengers that activate discrete signalling pathways, most prominently the Ras/MAPK pathway, to regulate cell survival and proliferation. </p> <p> Genetic analysis using Drosophila provides an efficient means for identifying evolutionarily conserved signalling components. Neu and Drosophila EGFR overexpression directs Drosophila tissue development synonymously. Consistent with biochemical evidence, genetic analysis ofNeu signalling through individual pTyr revealed activating signals for 4(Yl144, YB; Y1201, YC; Y1226/7, YD; Y1253, YE) of the 5 sites. Strong Ras-dependent signalling was mediated through adaptors Grb-2 (YB) and SHC (YD). In contrast to biochemical evidence, a strong Ras component was not genetically detected for YC or YE. </p> <p> We have conducted two enhancer-suppressor screens to identify novel Ras and non-Ras requirements for YC signalling. For the first screen, a quantitative approach was designed to identify modification of an YC-specific wing notch phenotype. Thirty-two members of the Ras/MAPK signalling cassette were assessed. Sensitivity to Ras, Raf, MAPK and the Ras-related GTPase R-Ras was identified downstream ofYC. The second screen, a large-scale mutagenesis, took advantage of an YC-induced rough eye phenotype. From over 19 000 screened flies, 11 enhancers and 6 suppressors were isolated. One strong suppressor has been genetically mapped to the dual transcription factor and phosphatase eyes absent. Other promising Ras-dependent and Ras-independent modifiers await farther mapping. Results from both screens point to YC as a unique pTyr that uses both Ras-dependent and Ras-independent outputs. </p> / Thesis / Doctor of Philosophy (PhD)