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La formation des métastases est un processus en plusieurs étapes à travers lequel les cellules néoplasiques se détachent de la tumeur primaire pour constituer des tumeurs secondaires à distance. Les capacités à migrer et à envahir, des cellules tumorales sont cruciales dans la cascade métastatique. Selon le type cellulaire et les stimuli présents dans le microenvironnement tumoral, les cellules peuvent se déplacer collectivement ou individuellement selon un programme de migration mésenchymateuse ou amiboïde. Différentes voies de signalisation sont liées à la régulation de la motilité cellulaire. Les GTPases Rho (Rac1, Cdc42 et RhoA) contrôlent la migration en régulant la dynamique du cytosquelette d’actine, la contraction acto-myosine et les microtubules. Rac1 régule la motilité mésenchymateuse en favorisant la formation des lamellipodes via un complexe multiprotéique, le « Wave Regulatory Complex (WRC) » et RhoA contrôle la motilité amiboïde en favorisant la contraction du cytosquelette d'acto-myosine. Les protéines Ral (RalA et RalB) appartenant à une autre famille de petites G, ont été récemment impliquées dans la régulation de la migration cellulaire. RalB, à travers le complexe « Exocyst » joue un rôle essentiel dans la motilité. Dans ce travail de thèse, nous avons étudié les mécanismes moléculaires par lesquels la voie RalB/Exocyste contrôle la motilité et l'invasion cellulaire. La première partie de ce travail démontre que l’Exocyste interagit avec SH3BP1, une protéine GAP (GTPase Activating Protein) (projet 1). Nous montrons que l’interaction entre SH3BP1 et Rac1 est nécessaire à l’activité de Rac1 au front de migration. Dans le projet 2, nous montrons que l’Exocyste interagit directement avec WRC, ce qui est un élément clé de la polymérisation de l'actine. Cette interaction est nécessaire à la localisation du complexe WRC au front de migration où il contrôle la formation de protrusions membranaires. Dans de nombreux carcinomes, la transition épithélio-mésenchymateuse (EMT) joue un rôle important dans la promotion de la migration, l’invasion et la formation des métastases. Le projet 3 a permis de mieux caractériser la plasticité de migration et l’invasion des cellules cancéreuses post-EMT et d’étudier la contribution de Ral dans l'invasion des cellules post-EMT. Nous montrons qu’après l’EMT les cellules envahissent la matrice individuellement ? en utilisant la contraction du cytosquelette d'acto-myosine. Nous montrons que RalB est nécessaire à l’invasion des cellules post-EMT, et à la contractilité cellulaire. Nous proposons que le rôle de RalB dans l'invasion passe par GEF-H1 qui est une protéine GEF (Guanine Nucleotide Exchange Factor) de Rho associée à l’Exocyste. Dans la dernière partie de ce manuscrit, nous présentons le logiciel « AVeMap » que nous avons développé afin d’automatiser la quantification des paramètres de la migration cellulaire.En résumé, dans ce travail de thèse nous montrons que la voie Ral/Exocyste est un organisateur moléculaire nécessaire à l’exécution à la fois de la motilité cellulaire contrôlée par Rac1 et à la motilité contrôlée par Rho. / Metastasis is a multistep process by which cancer cells migrate away from the primary neoplastic mass to give rise to secondary tumors at distant sites. Thus, the acquisition of motility and invasive traits by tumor cells is a crucial step for metastasis to occur. Depending on the cell type and the environment, cells can move collectively keeping stable cell-cell contacts or as individual cells, which translocate by exploiting either mesenchymal or amoeboid motility programs.Different molecules and pathways have been linked to the regulation of cell motility. Rho small GTPases (Rac1, Cdc42 and RhoA) control cell migration through their actions on actin assembly, actomyosin contractility and microtubules. Rac1 drives mesenchymal-type motility by promoting lamellipodia formation via the Wave Regulator Complex (WRC). On the contrary, amoeboid motility is governed by RhoA which promotes cell movement via the generation of actomyosin contractile force. Another family of small GTPases, the Ral proteins, was recently involved in the regulation of cell migration. RalB, through the mobilization of its main effector the Exocyst complex, was shown to play an essential role in cell motility. In this work of thesis we investigated the molecular mechanisms through which RalB/Exocyst pathway controls cell motility and invasion.In the first part of this manuscript we show that Exocyst interacts with the RacGAP SH3BP1 (project 1). In mesenchymal moving cells Exocyst/SH3BP1 interaction is required to organize membrane protrusion formation by spatially regulating the activity of Rac1 at the cellular front. In addition, in project 2, we show that the Exocyst binds to the wave regulator complex (WRC), a key promoter of actin polymerization. We provide evidences for Exocyst to be involved in driving the WRC to the leading edge of motile cells, where it can stimulate actin polymerization and membrane protrusions. Reactivation of a developmental program termed epithelial-mesenchymal transition (EMT) was recently shown to promote motility, invasion and metastasis of neoplastic cells. Tumor cells undergoing EMT loose cell-cell contacts acquire a fibroblastoid phenotype and invade the surrounding tissues as individual cells. In project 3 we characterized the invasion plasticity of cancer cells after EMT and we investigated the molecular contribution of Ral to post-EMT invasion. We showed that upon EMT cells disseminate individually in a Rho-driven fashion exploiting the generation of actomyosin force to deform the extracellular matrix. We document that RalB silencing severely impairs actomyosin contractility and dissemination of post-EMT cells. We hypothesize that RalB regulates invasion by controlling the dynamics of the Rho pathway via the Exocyst-associated RhoGEF GEF-H1 in post-EMT cells. Finally, in the last part of this thesis manuscript, we present the PIV-based “AVeMap” software which has been developed to quantify in a fully automated way cell migration and its parameters (Project 4).Taken together the results presented in this thesis manuscript point out the Ral/Exocyst pathway as a key molecular organizer of the execution of both Rac1- and Rho-driven motility programs.

Blood vessels are essential for the delivery of nutrients and oxygen to tissues, as well as for the removal of waste products. Patients with tumors, wounds or diabetes all have active angiogenesis, formation and remodeling of blood vessels, a process that is initiated and manipulated by gradients of secreted signaling proteins. This thesis describes the development of new microfluidic in vitro assays where directed migration of single endothelial cells and three dimensional vascular structures can be monitored in real time. Combining these assays with live imaging microscopy we have studied the behavior of endothelial cells in gradients of proangiogenic factors as well as directed sprouting in embryonic kidneys and stem cell cultures. With the 2D assay we have quantified endothelial cell chemotaxis towards FGF2, VEGFA165 and VEGFA121 and we also demonstrate that constant levels of VEGFA165, but not of FGF2, are able to reduce chemokinesis of endothelial cells. In the 3D migration chamber we have studied directed endothelial cell sprouting in mouse embryonic kidneys and embryoid bodies in response to VEGFA gradients. In both models directed angiogenesis is detected towards increasing levels of growth factor. Using the microarray technique on differentiating embryonic stem cells we have been able to identify the gene exoc3l2 as potentially involved in angiogenesis and endothelial cell migration and we present evidence that ExoC3l2 is associated with the exocyst complex; an important regulator of cell polarity. We have also shown that siRNA mediated gene silencing of exoc3l2 results in impaired VEGFR2 phosphorylation as well as loss of directionality in response to a VEGFA gradient. / (Faculty of Medicine)

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Diss. (sammanfattning) Stockholm : Karolinska institutet, 2005. / Härtill 4 uppsatser.

Thesis (Ph.D. in Cell Biology, Stem Cells, & Development) -- University of Colorado Denver, 2008. / Typescript. Includes bibliographical references (leaves 138-155). Free to UCD Anschutz Medical Campus. Online version available via ProQuest Digital Dissertations;

Thesis (Ph.D.) -- University of Texas Southwestern Medical Center at Dallas, 2005. / Not embargoed. Vita. Bibliography: 229-249.

Le trafic membranaire est un processus universel qui est essentiel pour la fonction neuronale dans un large spectre de fonctions. De la croissance neuronale et le développement morphologique à la libération des neurotransmetteurs et la plasticité synaptique, il prend en charge l'activité neuronale et donne d'innombrables questions qui animent la recherche sur la neurobiologie d'aujourd'hui. Notamment, l’exocytose des endosomes de recyclage (ER) dans les compartiments somatodendritiques participe à la transmission synaptique et à la potentialisation synaptique à long terme (PLT). Cependant la machine moléculaire sous-tendant l’exocytose des ER reste encore méconnue. Afin d’identifier les protéines SNAREs vésiculaires (v-SNARE) impliquées dans les différentes formes d’exocytose des ER postsynaptiques, nous avons d'abord imagé les protéines VAMP neuronales fusionnées avec la pHluorine, une GFP mutée sensible au pH dans les neurones de l’hippocampe en culture. Nous avons constaté que seulement VAMP2 et VAMP4, mais pas VAMP7, rapportaient des événements d’exocytose somatodendritique dans les neurones matures. Après avoir identifié ces deux protéines candidates, nous avons utilisé la combinaison de différentes techniques de régulation négative chronique ou aiguë pour désactiver leur fonction et observer les conséquences sur l’exocytose des ER, la transmission synaptique basale ou la PLT. Nos résultats suggèrent que VAMP2 est impliqué dans une forme d’exocytose régulée importante pour la PLT, mais pas l’exocytose constitutive des récepteurs AMPA, qui stabilise la transmission basale. VAMP4 est nécessaire pour l'exocytose constitutive d'une grande partie des endosomes, mais l'implication fonctionnelle de ces endosomes doit encore être explorée, car la régulation négative de VAMP4 ne modifie pas la transmission basale. / Membrane trafficking is a universal process that is essential for neuronal function in a wide spectrum of applications. From neuronal growth and morphological development to neurotransmitter release and synaptic plasticity, it supports neuronal activity and gives countless questions that drive today’s neurobiology research. Notably, the trafficking of recycling endosomes (REs) in somatodendritic compartments participates in synaptic transmission and plasticity, such as long-term synaptic potentiation (LTP). However, the fusion machinery mediating RE exocytosis is still unclear. To identify the vesicular SNAREs (v-SNAREs) involved in different forms of postsynaptic RE exocytosis, we first imaged neuronal VAMP proteins fused with pH-sensitive pHluorin in cultured hippocampal neurons, and found that only VAMP2 and VAMP4, but not VAMP7, underwent somatodendritic exocytosis in mature neurons. After identifying these two candidate proteins, we used a combination of different downregulation techniques to chronically or acutely deactivate their function and observe consequences on REs exocytosis, basal synaptic transmission and LTP. Our results suggest that VAMP2 is involved in activity-regulated exocytosis important for LTP, but not constitutive postsynaptic AMPARs exocytosis, supporting basal transmission. VAMP4 is required for constitutive exocytosis of at least a large proportion of REs, but the functional implication of these endosomes still need to be explored, as VAMP4 downregulation did not alter basal synaptic transmission.

Increase in the cytoplasmic Ca2+ concentration ([Ca2+]i) in the β-cells triggers insulin exocytosis. Among the Ca2+ channels present in the plasma membrane, the transient receptor potential (TRP) channels receptors are currently of great interest. The mechanisms by which the extracellular adenosine diphosphate ribose (ADPr) increases the [Ca2+]i is unknown. Our aims were to study the roles of the TRP channels in the tolbutamide induced [Ca2+]i increase and to identify the surface receptor that is activated by ADPr. We used S5 cells, a highly differentiated rat insulinoma cell line, as a model for β-cells. Single cell ratiometric microfluorometry was used to measure the [Ca2+]i changes in the Fura-2 loaded cells. Tolbutamide increased [Ca2+]i in the form of oscillations. After tolbutamide increased [Ca2+]i,capsazepine, a potent blocker of the transient receptor potential vanilloid subtype 1 (TRPV1) channel was added to the β-cells, which reduced the tolbutamide-induced [Ca2+]i increase. capsazepine, N-(p-Amylcinnamoyl) anthranilic acid (ACA),  TRPM2 channel blocker, and triphenyl phosphine oxide (TPPO), TRPM5 channel blocker were tested for their effect on potassium chloride (KCl) induced [Ca2+]i response. These blockers did not inhibit the KCl induced [Ca2+]i increase.   Adenosine diphosphate ribose (ADPr) increased [Ca2+]i in the form of initial transient peak followed by an elevated plateau. Application of ADPr shortly after a prior application and washout of Adenosine diphosphate (ADP) elicited only small [Ca2+]i increase  indicating desensitization of the receptor involved. 2´deoxy-N6-methyladenosine 3´5´bis-phosphate (MRS2179), and chloro N6-methyl-(N)-methanocarba 2´deoxyadenosine 3´5´ bis-phosphate (MRS2279), two selective inhibitors of P2Y1 receptor, abolished the ADPr-induced [Ca2+]i increase. Tolbutamide closes ATP sensitive potassium (KATP) channels. Our results demonstrate that besides the closure of the KATP channels, inward cation currents carried by Ca2+through the TRPV1 channel are necessary for depolarization to the threshold for the activation of the voltage gated calcium channels (VGCC) to increase the [Ca2+]i. Our results also show that ADPr increases [Ca2+]i by activating the P2Y1 receptor.