Implication de la voie ERK3/4-MK5 dans la phase G2/M du cycle cellulaire

La division cellulaire est influencée par les différents stimuli provenant de l’extérieur ou de l’intérieur de la cellule. Plusieurs réseaux enzymatiques élaborés au cours de l’évolution relayent l’information générée par ces signaux. Les modules MAP kinases sont extrêmement importants au sein de la cellule. Chez l’humain, 14 MAP kinases sont regroupées en sept voies distinctes intervenant dans le contrôle d’une myriade de processus cellulaires. ERK3/4 sont des homologues de ERK1/2 pour lesquelles on ne connaît que très peu de choses concernant leurs fonctions et régulation. Ces MAP kinases sont dites atypiques puisqu’elles ont des particularités structurales et des modes de régulation qui diffèrent des autres MAP kinases classiques. Ainsi, notre laboratoire a démontré que l’activité de ERK3 est régulée par le système ubiquitine-protéasome et qu’elle pourrait avoir un rôle à jouer dans le contrôle de la différenciation et la prolifération cellulaire. La première étude présentée décrit la régulation de ERK3 au cours du cycle cellulaire. Nous avons observé que ERK3 est hyperphosphorylée et s’accumule spécifiquement au cours de la mitose. Des analyses de spectrométrie de masse ont mené à l’identification de quatre sites de phosphorylation situés à l’extrémité du domaine C-terminal. Nous avons pu démontrer que la kinase mitotique CDK1/cycline B phosphoryle ces sites et que les phosphatases CDC14A et CDC14B les déphosphorylent. Finalement, nous démontrons que la phosphorylation mitotique de ERK3 a pour effet de la stabiliser. Au début de mes études doctorales, la kinase MK5 fut identifiée comme premier partenaire et substrat de ERK3. MK5 a très peu de fonctions connues. Des données dans la littérature suggèrent qu’elle peut moduler le cycle cellulaire dans certaines conditions. Par exemple, MK5 a récemment été identifié comme inducteur de la sénescence induite par l’oncogène Ras. Dans la deuxième étude, nous décrivons une nouvelle fonction de MK5 dans le contrôle du cycle cellulaire. Nous démontrons par des expériences de gain et perte de fonction que MK5 ralentit l’entrée en mitose suite à un arrêt de la réplication. Cette fonction est dépendante de l’activité enzymatique de MK5 qui régule indirectement l’activité de CDK1/cycline B. Finalement, nous avons identifié Cdc25A comme un nouveau substrat in vitro de MK5 dont la surexpression supprime l’effet de MK5 sur l’entrée en mitose. En conclusion, nos résultats décrivent un nouveau mécanisme de régulation de ERK3 au cours de la mitose, ainsi qu’une nouvelle fonction pour MK5 dans le contrôle de l’entrée en mitose en réponse à des stress de la réplication. Ces résultats démontrent pour la première fois l’implication de ces protéines au cours de la transition G2/M. Nos travaux établissent de nouvelles pistes d’études pour mieux comprendre les rôles encore peu définis des kinases ERK3/4-MK5.The process of cell division is largely influenced by extracellular and intracellular cues. Many enzymatic pathways refined during evolution propagate the information generated by those cues. MAP kinase modules are extremely important within the cells. Human genome encodes 14 MAP kinases genes grouped into seven distinct pathways involved in the control of many cellular processes. ERK3/4 are kinases homologous to ERK1/2. Very little is known about their regulation and molecular functions. These MAP kinases are described as being atypical based on their unique structural characteristics and mode of regulation. Our laboratory was the first to demonstrate that the activity of ERK3 is mainly regulated by the ubiquitin-proteasome system in proliferating cells. In addition, several lines of evidence suggest a role for ERK3 in the control of cell differentiation and proliferation. The first study presented herein documents the regulation of ERK3 during the cell cycle. We observed that ERK3 is hyperphosphorylated and accumulated specifically during mitosis. Mass spectrometry analyses led to the identification of four phosphorylation sites located in the C-terminal domain. We demonstrate that mitotic kinase CDK1/cyclin B phosphorylates these sites which are dephosphorylated by Cdc14A and Cdc14B phosphatases. Finally, we show that mitotic phosphorylation of ERK3 controls its stability. At the beginning of my Ph.D. training, the kinase MK5 was the first identified binding partner and substrate of ERK3. MK5 is implicated in very few cellular functions. Data suggest that under certain conditions it modulates cell cycle progression. For example, MK5 was recently identified as a tumor suppressor gene essential for ras-induced senescence. In the second study of this thesis, we describe a novel function of MK5 in cell cycle progression. Gain and loss of function experiments demonstrate that MK5 delays G2/M transition following replicative stress. This function depends on its catalytic activity to indirectly regulates CDK1/cyclin B. Finally, we identified Cdc25A as a good in vitro substrate for MK5. Interestingly, Cdc25A expression inhibits MK5-induced delay of entry into mitosis. In conclusion, our results described a novel mechanism of regulation of ERK3 during mitosis and a novel function of MK5 in the control of G2/M transition after replicative stress. These data demonstrate for the first time the relation between these kinases and the G2/M transition. Our work should contribute to a better understanding of the roles of ERK3/4-MK5 kinases

Étude du rôle de la calnexine de Schizosaccharomyces pombe dans le repliement et la sécrétion de protéines

Mémoire numérisé par la Direction des bibliothèques de l'Université de Montréal

ER stress affects processing of MHC class I-associated peptides

<p>Abstract</p> <p>Background</p> <p>Viral infection and neoplastic transformation trigger endoplasmic reticulum (ER) stress. Thus, a large proportion of the cells that must be recognized by the immune system are stressed cells. Cells respond to ER stress by launching the unfolded protein response (UPR). The UPR regulates the two key processes that control major histocompatibility complex class I (MHC I)-peptide presentation: protein synthesis and degradation. We therefore asked whether and how the UPR impinges on MHC I-peptide presentation.</p> <p>Results</p> <p>We evaluated the impact of the UPR on global MHC I expression and on presentation of the H2K^b-associated SIINFEKL peptide. EL4 cells stably transfected with vectors coding hen egg lysozyme (HEL)-SIINFEKL protein variants were stressed with palmitate or exposed to glucose deprivation. UPR decreased surface expression of MHC I but did not affect MHC I mRNA level nor the total amount of intracellular MHC I proteins. Impaired MHC I-peptide presentation was due mainly to reduced supply of peptides owing to an inhibition of overall protein synthesis. Consequently, generation of H2K^b-SIINFEKL complexes was curtailed during ER stress, illustrating how generation of MHC I peptide ligands is tightly coupled to ongoing protein synthesis. Notably, the UPR-induced decline of MHC I-peptide presentation was more severe when the protein source of peptides was localized in the cytosol than in the ER. This difference was not due to changes in the translation rates of the precursor proteins but to increased stability of the cytosolic protein during ER stress.</p> <p>Conclusion</p> <p>Our results demonstrate that ER stress impairs MHC I-peptide presentation, and that it differentially regulates expression of ER- vs. cytosol-derived peptides. Furthermore, this work illustrates how ER stress, a typical feature of infected and malignant cells, can impinge on cues for adaptive immune recognition.</p

European Union Agricultural Policy Institutions and Decision Making Processes

This note examines European Union (EU) institutions and policy making processes in relation to its agriculture and food sector. With a market comprised of 495 million people across 27 countries and a comprehensive agricultural policy accounting for the largest share of the EU budget, how the EU policy environment functions is important to Canada. Decisions are made at the supranational EU level for agriculture, fisheries, trade, and regional development, while decision-making related to other policies occurs at the individual country level or through a system of inter-governmental cooperation. Decision-making occurs in three institutions: the Commission, the Council and the Parliament. Agriculture negotiations typically begin with a text drafted by the Council. Then the Commissioner for Agriculture works with national-level farm ministers to prepare a final text. Council decisions are voted on by member states' ministers. A qualified majority of a minimum of 74% of votes must be in favour for decisions related to agriculture. Agriculture policy is the only EU policy to receive most of its funding from the EU budget. Operating agriculture policy at the supranational level allows the EU to achieve a more level playing field for farmers across the member states. Knowledge of these and other facts relating to the EU's agri-food policy institutions and their responsibilities and decision-making processes allows us to better understand and anticipate policy outcomes in the EU

L'engagement des parents de la paroisse Marie-Médiatrice de Sherbrooke dans la nouvelle catéchèse de 1ère, 2e et 3e années

Ce mémoire est basé sur des interviews faits par des étudiants de la faculté de théologie de l'Université de Sherbrooke en décembre 1966. Le but est de donner une meilleure connaissance de l'engagement des parents dans la nouvelle catéchèse en comparant les résultats obtenus aux exigences exprimées par les auteurs des nouveaux manuels et d'autres spécialistes en catéchèse. On désire aussi fournir des indications pastorales. L'enquête a porté sur des parents qui avaient un ou des enfants en 1ère, 2e,ou 3e années du cours primaire. L'introduction donne aussi des renseignements techniques: les enquêteurs, élaboration du questionnaire, parents questionnés

European Union Agricultural Policy Institutions and Decision Making Processes

This note examines European Union (EU) institutions and policy making processes in relation to its agriculture and food sector. With a market comprised of 495 million people across 27 countries and a comprehensive agricultural policy accounting for the largest share of the EU budget, how the EU policy environment functions is important to Canada. Decisions are made at the supranational EU level for agriculture, fisheries, trade, and regional development, while decision-making related to other policies occurs at the individual country level or through a system of inter-governmental cooperation. Decision-making occurs in three institutions: the Commission, the Council and the Parliament. Agriculture negotiations typically begin with a text drafted by the Council. Then the Commissioner for Agriculture works with national-level farm ministers to prepare a final text. Council decisions are voted on by member states' ministers. A qualified majority of a minimum of 74% of votes must be in favour for decisions related to agriculture. Agriculture policy is the only EU policy to receive most of its funding from the EU budget. Operating agriculture policy at the supranational level allows the EU to achieve a more level playing field for farmers across the member states. Knowledge of these and other facts relating to the EU's agri-food policy institutions and their responsibilities and decision-making processes allows us to better understand and anticipate policy outcomes in the EU.European Union, agriculture, policy, institution, legislation, Agricultural and Food Policy, Institutional and Behavioral Economics, International Relations/Trade, Political Economy,

La raison absolue et la religion de l’esprit. Penser la Religion… de Kant avec et contre Hegel

International audienc

Russia Agriculture Policy Review

In recent years, as a result of a strong demand for energy and other natural resources, Russia's economy has experienced impressive growth. Russia's re-emergence as a political and, particularly, economic power have allowed it to increase policy support to its agricultural sector. Russia's size, improving prospects, and growing policy support make developments in its agricultural sector of interest to Canada

La raison absolue et la religion de l’esprit. Penser la Religion… de Kant avec et contre Hegel

International audienc