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Metastasis is one of the major causes of endocrine resistance and mortality in breast cancer patients. The epithelial to mesenchymal transition (EMT) enables the metastatic spread of cancer cells. EMT-promoting transcription factors determine a continuum of different EMT states. In contrast, estrogen receptor α (ERα) contributes to the maintenance of the epithelial phenotype of breast cancer cells and is crucial for effective hormonal therapies. Determining whether and how the EMT modulates ERα signaling at early stage of EMT could drive the discovery of novel therapeutic approaches to prevent or to fight metastasis. We have discovered that during EMT initiation the expression of ZEB1 modulates ERα-mediated transcription induced by estrogen or cAMP signaling in breast cancer cells. We discovered that a cooperative interaction between ZEB1 and ERα is important for modulating tissue tropism of breast cancer cells towards bone metastasis.

The molecular chaperone TRAP1 has been studied for almost two decades, yet, the mechanistic basis underlying its function in the mitochondria still remains poorly understood. Recent studies have presented it as an inhibitor of OXPHOS and an inducer of the Warburg phenotype, but multiple reports have conflicted with this paradigm. This study seeks to reconcile previous reports in a cohesive model by proposing that TRAP1 does not necessarily down or upregulate OXPHOS, but, is actually required to maintain OXPHOS homeostasis. Using multiple CRISPR KO cell lines, real time OCR analyses with different carbon sources, metabolomics and various proteomic approaches to understand interactions, this study provides a platform to understand TRAP1 function in mitochondria. We show that TRAP1 induces a metabolic rewiring independent of its ATPase activity, requires an ATP-bound state to interact with various mitochondrial proteins and forms an oligomerized protein complex that may be the functional unit of TRAP1.

Following the identification of two new KIAA2022 variants in two subjects with non-autoimmune diabetes. In order to determine if Kiaa2022 could play a role in diabetes we performed in vitro studies in insulin-secreting INS-1E cells. Additionally, we generated Kiaa2022 knock out mice, which showed a reduced amount of proliferating β-cells. Interestingly, besides a pancreatic phenotype a variety of other phenotypes was observed in mutant and non-mutant progeny. RNAseq showed that down-regulated genes in Kiaa2022 mutant islets are associated to stress response and the disposition of epigenetic marks. We also observed an upregulation of LINE1 elements and not only in the pancreas, but also in the brain and testis. Activated LINE1 elements can cause genomic instability and genetic variation through retrotransposition into the genome. This suggests a mechanism by which genomic instability could be induced in Kiaa2022 mutant mice, which could cause phenotypic variability in all progeny.

CD47 is a ubiquitously expressed immune checkpoint receptor playing a major role in recognition of self by phagocytes. CD47 interacts with SIRPα to generate an inhibitory signal blocking phagocytosis. Tumor cells have hijacked this immunosuppressive mechanism by overexpressing CD47, which efficiently protects them against attack by the body's immune system. Targeting CD47, with a blocking monoclonal antibody (mAb), promotes tumor elimination via antibody dependent cellular phagocytosis (ADCP) and antibody dependent cellular cytotoxicity (ADCC). In several in vivo models, blocking CD47 leads to tumor elimination, inhibits the development of metastasis and promotes the development of an antitumor immunological memory. Several anti-CD47 mAb are under clinical investigation for cancer treatment. However, the development of these antibodies is confronted with several hurdles. Due to the expression of CD47 also on healthy cells, mAb based therapies lead to toxicity, including severe anemia and thrombocytopenia, as well as rapid drug elimination. As a solution, we hypothesized that using not a mAb but a bispecific Ab format (biAb) pairing a high affinity tumor associated antigen (TAA) arm with a CD47 targeting arm of lower affinity could avoid these unwanted characteristics. Such a biAb with unbalanced affinities would allow to selectively target CD47 to the tumor cells. Both anti-human and anti-mouse CD47/TAA biAb were generated using the κλ body format, a fully human biAb composed of a common IgG heavy chain and two different light chains (i.e., kappa and lambda). We exploited light chain diversity to identify the TAA and CD47 targeting arms composing the biAbs. The resulting biAbs efficiently neutralized CD47 on TAA positive tumor cells, but interacted only weakly with healthy cells. Accordingly, the biAbs were not subject to CD47- mediated drug disposition and were well tolerated in vivo. The selection of a low affinity anti- CD47 arm was also primordial for biAb anti-tumor activity in a context of CD47 ubiquitous expression. The combination of targeted CD47 neutralization and Fc effector functions afforded by the biAb format resulted in potent killing by ADCP and ADCC in vitro, and translated into a potent anti-tumor activity in both xenograft and syngeneic in vivo models. In immunocompetent mouse models, biAb-mediated blockade of CD47 lead to tumor cell phagocytosis and the development of a long term immunological memory in vivo as mice were protected from tumor rechallenge. In vitro, we demonstrated that indeed cross-priming of anti-tumor CD8+ T cells had occurred. Taken together, my work confirmed that targeting CD47 is a powerful way to engage the innate and adaptive immune system to kill cancer. Thus, dual-targeting biAbs with unbalanced affinities are an elegant means to employ this strategy effectively yet safely in patients. With a better risk to benefit ratios, the biAb approach to CD47 targeting can be envisioned as part of combination therapies, for example synergizing with cyclophosphamide or anti-PD-L1 therapies. These studies also suggest that a similar bispecific design could be exploited for the targeting of other widely expressed receptors.

T cell lymphocytes play an essential role in the adaptive immunity. They arise from the hematopoietic compartment and reach the thymus, where they achieve their development through specialized maturation and selection steps. Immune system comprises specific and complex mechanisms in the thymus and the periphery aiming at preventing the generation and the survival of self-reactive T cells that could lead to autoimmune disorders. These mechanisms are known as central and peripheral tolerance and rely on different cellular actors such as medullary thymic epithelial cells (mTECs), dendritic cells (DCs), lymph node stromal cells (LNSCs) and regulatory T and B cells. Self-reactive T cells escaping thymic central tolerance are kept in check in the periphery through specific mechanisms that include T cell anergy, T cell deletion and Treg induction. Although conventional DCs (cDCs) have been first in line in mediating peripheral tolerance, increasing evidence demonstrates the contribution of other actors such as plasmacytoid dendritic cells (pDCs) in this process. pDCs are important linkers of the innate and adaptive immunity. They are characterized by their ability to secrete pro-inflammatory cytokines and large amount of type I interferon (IFN-I) upon pathogenic infections, but also express major Histocompatibility complex (MHC) and costimulatory molecules enabling them to interact with T cells. pDCs have been involved in the control of infections, but are also important actors of peripheral tolerance. The diversity of their functions, depending on the context in which they will evolve, has associated pDCs to pro-immunogenic and tolerogenic scopes. In the lab, we are principally interested in the contribution of pDCs in Multiple sclerosis, a progressive inflammatory demyelinating disease of the central nervous system (CNS). To address the role of pDCs in MS, we performed our studies in the murine model of Experimental autoimmune encephalomyelitis (EAE). Using genetically modified mice harbouring specific abrogation of Ag-presenting function in pDCs, my co-workers previously demonstrated that myelin Ag presentation by pDCs promotes the expansion of regulatory T cells (Tregs) that inhibit encephalitogenic TH1 and TH17 cell priming in secondary lymphoid organs (SLOs). In this manuscript I report our recent findings supporting that pDCs display tolerogenic functions during the priming and the effector phase of EAE development and are able to control and dampen the disease. The first study investigates the interplays between pDCs and Tregs and shows that Ag-specific MHCII interactions with Tregs licenced tolerogenic features in steady-state pDCs by inducing their expression of the indoleamine-2,3 dioxygenase (IDO1). In EAE context, Treg-educated IDO+ pDCs are required to confer suppressive functions to Tregs which promote the inhibition of encephalitogenic T cell priming in draining LNs, resulting in attenuated EAE. In the second study, we explore the therapeutic effect of pDCs transfer in EAE mice after disease onset. We show that the transfer of immature MOG35-55 pre-loaded pDCs during EAE acute phase leads to substantial reduction of CNS inflammation and significant amelioration of disease clinical scores. We demonstrate that pDC-protection relies on the massive recruitment of endogenous immature pDCs in the inflamed spinal cord via the Chemerine/CMKLR1 axis. Endogenous pDC recruitment is required to down-modulate CNS inflammation, encephalitogenic TH1 and TH17 cell responses and EAE severity. Overall this work supports previous findings showing the importance of pDCs in the regulation of CNS autoimmunity and unravel these cells for potential use, by targeting different particular functions, in the development of future therapies to treat MS patients.

Afin de mieux comprendre les mécanismes cellulaires impliqués dans le développement du cancer de l'ovaire, nous nous sommes intéressés à la protéine GRP78. Dans les cellules cancéreuses, la GRP78 du RE est relocalisée à la surface cellulaire et participe au développement tumoral. Afin d'apporter des informations sur les mécanismes de transport de la GRP78 du RE à la membrane plasmique, nous avons investigué le rôle d'un potentiel partenaire : la protéine Par-4. Nous confirmons l'implication de Par-4 dans, 1) le transport de la GRP78 à la membrane plasmique et, 2) le développement tumoral et la réponse au taxol dans le cancer de l'ovaire. Nous avons également investigué l'implication des différents domaines de la GRP78 dans son transport à la membrane plasmique et montrons que le SBD joue un rôle important. Enfin, nous suggérons que la forme transmembranaire au niveau du RE ne serait pas l'« origine » de la forme transmembranaire à la surface cellulaire.

Systemic Lupus Erythematosus (SLE) is an autoimmune disease mainly characterized by an overactivation of autoreactive lymphocyte which leads to the production of autoantibodies recognizing self-nucleic acids. This results in the formation of excessive immune complexes that settle in several organs and lead to inflammation and functional damages such as glomerulonephritis in the kidney. In order to investigate the mechanisms involved in SLE pathology we focused our studies on B cell and monocyte implication in our model of lupus-prone mice. We explored the role of the endosomal Toll-like receptor 8 (TLR8) in development of disease in lupus-prone mice and the key molecules involved in B cell differentiation and plasma cell survival, such as APRIL and its receptors TACI and BCMA. Our researches demonstrated two interesting pathways, one which is dependent to endosomal TLR and another which implicates TACI-dependent APRIL signaling. These pathways should be further explored with the hope that a deeper understanding could help to the development of novel effective therapies to treat human SLE.

The protozoan parasite Plasmodium falciparum (Pf) has to cope with perpetual environmental stresses during its whole lifecycle. As an adaptation to this, the parasite resorts to a sophisticated system of molecular chaperones. Hsp90 is one of the most important molecular chaperones that help regulate numbers of biological processes such as signal transduction, cell cycle control, hormone signaling, transcription, heat shock response, etc. Additional evidence suggested that Hsp90 is involved in the development of the parasite and its pathogenesis during the infection. The Hsp90 inhibitor geldanamycin has been found to be effective against infection by Plasmodium yoelli in a mouse model. These results suggested that Hsp90 inhibitors may have great potential as new antimalarial agents. As most of the known antimalarials intervene during the blood-stages of the infection, the design of antimalarial drugs should maximally evade human off targets on which impact may potentially elicit toxicity. But many drug targets are actually essential proteins that are functionally and structurally conserved. This fact hinders the therapeutic exploitation of many promising drug targets. Hsp90 might be among them. Hsp90s are highly conserved between Pf and human. There are only three substitutions found in the drug-binding pocket, which account for a 92% of conservation in protein sequences. Such high degree of homology hinders the discovery of species-specific inhibitors. Is there still a chance for Hsp90 to become an antimalarial target? The work presented in this thesis is a “hunt” for selective inhibitors against PfHsp90 using structure-based drug design (SBDD). We have elaborated a strategy of SBDD based on comparative analyses of the drug-binding pocket between PfHsp90 and its human counterparts. Furthermore, we have established several in vivo and in vitro systems as tools for step-wise drug validation. The combination of the efforts allowed us to discover a lead molecule, IND31119, that inhibits exclusively PfHsp90 while bypassing its highly similar human orthologs. Our work illustrates a new trend in drug discovery that involves a highly dynamic cooperation across biology, chemistry and computer science. Our publication also represented the first report that confirmed the feasibility of designing selective inhibitors against PfHsp90. My thesis can pave the way for translational research into PfHsp90 inhibitors as new weapons in the fight against malaria.

Within skeletal muscles, myogenic stem cells - satellite cells - will proliferate and then, differentiate to build/re-build muscle fibers. In vitro, myoblasts derived from human satellite cells can be induced to differentiate after medium switch. Using this cellular model, we previously showed that one of the first steps of myoblast differentiation is a hyperpolarization of myoblasts' membrane. This change of membrane potential is followed by a calcium entry and the expression of myogenic transcription factors. More precisely, myoblast hyperpolarization relies on a potassium channel, Kir2.1 which is maintained inactive during proliferation. Here, EGF receptor, was identified as a stimulator of proliferation and an inhibitor of differentiation. EGFR expression is physiologically regulated in myoblasts and decreases during differentiation, in particular via the proteasome. Absence of EGFR results in a decrease of Kir2.1 phosphorylation, activation of this channel favoring calcium entry, expression of muscle-specific transcription factors and proteins.

Metabolic liver diseases include disorders ranging from hepatic steatosis to steatohepatitis and cirrhosis. Finally, hepatocellular carcinoma can occur as an end stage of these disorders. With obesity, the metabolic syndrome and alcohol consumption, hepatic viral infections are one of the major causes of metabolic liver disorders. Among them, hepatitis C virus (HCV) is of particular importance. The phosphatase and tensin homolog deleted on chromosome 10 (PTEN) has been reported to be downregulated in the liver of obese rats and patients having hepatic steatosis. Additionally, liver-specific PTEN knockout mice develop steatosis in the liver then evolving into steatohepatitis and hepatocellular carcinoma. In this work, we showed that PTEN protein expression is downregulated by HCV infection in patients having genotype-induced steatosis and that this downregulation can trigger lipid droplet accumulation and insulin resistance. We also established that PTEN downregulation by HCV is able to improve viral release from infected cells.

Ma thèse porte sur l'étude des interactions entre les bactéries pathogènes et l'hôte qu'elles infectent. L'utilisation de l'amibe Dictyostelium discoideum, un phagocyte professionnel, m'a permis d'analyser d'une part la pathogénicité bactérienne, et d'autre part les mécanismes par lesquels une cellule phagocytaire tue les bactéries. J'ai étudié l'évolution de la virulence bactérienne de souches cliniques de Pseudomonas aeruginosa, au cours de l'infection aiguë ou chronique. Mes résultats montrent que la virulence diminue chez environ 50% des patients atteints de mucoviscidose, mais pas chez les patients intubés, et ce indépendamment de l'apparition de mutations dans le gène lasR (un régulateur du quorum-sensing). Par mutagenèse aléatoire de D. discoideum, j'ai dévoilé l'implication de plusieurs nouveaux gènes dans les interactions amibe-bactérie. J'ai montré que la protéine Kil2 est indispensable pour tuer efficacement Klebsiella pneumoniae. Cette P-ATPase semble transporter du magnésium à l'intérieur du phagosome, ce qui active les enzymes protéolytiques responsables de l'élimination des bactéries.

Cardiovascular disease is the leading cause of morbidity and mortality in the adult population in industrialized countries. It is now well-established that immuno-inflammatory processes are involved in several cardiovascular diseases, such as atherosclerosis and myocardial infarction. Chemokines are known to trigger and direct leukocyte trafficking from the blood to inflamed tissues through the binding to their cell-surface receptors. Chemokines and there receptors are involved in multiple inflammatory diseases such as atherosclerosis, rheumatoid arthritis, multiple sclerosis or chronic obstructive pulmonary disease, as well as HIV infectious disease, making them particularly attractive therapeutic targets. In this thesis, we investigated the role of the chemokine CCL5/RANTES and its receptors in atherogenesis and myocardial reperfusion injury. Using both pharmacological and genetic approaches, we showed that inhibition of CCL5/RANTES and its receptor CCR5 could represent an attractive therapeutic strategy to decrease atherosclerosis progression and limit damages due to the reperfusion of ischemic myocardium, in mice.

Immune cells are known to infiltrate human gliomas, but their implication in immunosurveillance is controversial. Since these infiltrates have been observed only at terminal stages of glioma development, it is not defined whether immunoediting occurs in these tumors. Alternatively, defective afferent immunity may delay a potent anti-tumor response, which is then overwhelmed by the tumor outgrowth. Finally, immune cells infiltrating gliomas may have poor anti-tumor competency, or may even promote tumor growth from early stages. In this study, a transgenic mouse model of spontaneous astrocytoma (GFAP-V12HA-ras or RasB8 mice) was analyzed to address these issues. Brain-infiltrating immune cells were characterized at different stages of tumor development. In addition, this model was used to determine whether the local immune balance in spontaneous gliomas could be tilted towards effector immune responses.

The endogenous retroviral envelope glycoprotein, gp70, implicated in murine lupus nephritis is secreted by hepatocytes as an acute phase protein. To better understand the genetic basis of the expression of serum gp70, we analyzed the abundance of Xeno, PT or mPT gp70 RNAs in livers in various strains of mice. Our results demonstrated that the expression of different gp70 RNAs was remarkably heterogeneous among mouse strains and that serum gp70 production was regulated by multiple genes in physiological vs. inflammatory conditions. In addition, we observed a contribution of PT and mPT gp70s, in addition of Xeno gp70, to serum gp70. Furthermore, we observed an increased expression of intact mPT env RNA, regulated by the Sgp3 locus, in all lupus-prone mice, as compared with non-autoimmune strains of mice. Finally, we demonstrated that TLR7 played a critical role in the expression of gp70 and in the production of anti-gp70 autoantibodies. These data suggest that lupus-prone mice may possess a unique genetic mechanism responsible for the expression of mPT retroviruses, which could act as a triggering factor through activating TLR7 for the development of autoimmune responses in mice predisposed to SLE.

The steroid hormone 17β-estradiol (E2) regulates a number of developmental and physiological processes. The classical understanding of the estrogen signaling implies that the two nuclear receptors (ER), ERα and ERβ, mediate all the physiological responses of E2. ERs are transcription factors, which regulate the expression of their targets upon binding to E2. Estrogens also mediate a lot of rapid outcomes within a matter of seconds to minutes that cannot be explained by the classical understanding of estrogen signaling, which involves transcription of target genes mediated by the ERs. Whereas, many of the rapid effects of estrogen are attributed to the cytoplasmic pools of ERs, it has become clear in the recent years that there are other factors contributing to the rapid effects of estrogen and one of the emerging such factors is a G-protein coupled receptor, GPR30. MicroRNAs (miRNAs) are a new class of small non-coding RNAs, 20 to 25 nucleotides in length that regulate the expression of other genes. Upon binding the 3' untranslated region (UTR) of target mRNAs, miRNAs typically reduce their stability and/or translation. miRNAs are shown to be involved in regulating virtually every cellular process and their deregulation has been shown to contribute to many diseases. There are nearly 1,000 different miRNAs in humans, which regulate expression of thousands of other genes, reflecting that this is indeed a major layer of gene expression regulation. In my PhD, I had focused on these two different themes of estrogen signaling. In the first project, using a DNA microarray approach, we identified the target genes of the emerging new player in estrogen signaling, GPR30. In the second part, we have addressed some previously unexplained observations about the role of the 3ʼUTR of the ERα mRNA in regulating ERα levels and estrogen signaling.

L'infection chronique par le virus de l'hépatite B touche plus de 350 millions de personnes et constitue un facteur de risque majeur de l'hépatocarcinome. Dans les hépatocytes infectés, le virus synthétise la protéine régulatrice HBx dont la fonction exacte est inconnue. Son interaction avec la protéine cellulaire DDB1 est essentielle pour l'établissement de l'infection chez l'animal et son expression est associée au développement du cancer du foie durant l'infection chronique. HBx semble en effet favoriser la carcinogenèse en induisant une instabilité génétique dans les hépatocytes en division. Notre étude génétique et structurale a montré que HBx présente une structure commune à d'autres protéines virales et cellulaires se liant à DDB1 et jouant le rôle d'adaptateurs de substrats pour la DDB1-Cullin4A E3 ligase. Au travers de l'interaction avec ce complexe, HBx stimule l'expression du génome viral par un mécanisme différent de celui qui caractérise les activateurs de transcription cellulaire.

Dans ce travail, nous avons étudié comment est-ce que les contacts cellules-cellules influencent la sécrétion d'insuline des cellules β-pancréatiques. Cette étude nous a permis de mettre en évidence le double rôle des contacts intercellulaires dans la régulation de la sécrétion d'insuline puisque les cellules privées de contacts entre elles présentent une sécrétion basale trop élevée ainsi qu'une sécrétion stimulée trop faible en comparaison des cellules en contact les unes avec les autres. Nous montrons que les contacts physiques intercellulaires permettent de maintenir un niveau de calcium cytosolique stable, ce qui est indispensable pour une sécrétion basale adéquate et que, plus spécifiquement, l'engagement des molécules d'adhésion E-cadhérine entre cellules adjacentes permet d'optimiser la sécrétion d'insuline suite à une stimulation au glucose. Finalement, nous montrons que les cellules isolées restent capables de répondre au glucose une fois que leur sécrétion basale a été normalisée.

Nous avons identifié les changements transcriptionnels communs à différents stimuli qui induisent la différenciation neuronale par la technologie de puces à ADN. Les cellules NS1 a été induite par six différents stimuli. L'utilisation d'inhibiteurs sélectifs suggère que les voies de signalisation des kinases MEK et JAK sont nécessairement pour la différenciation induite par NGF ou dbcAMP, et que l'activation de PKA, PI3Kα et mTOR est indispensable pour la différenciation induite par dbcAMP, mais inhibe celle induite par NGF. Le silencing des gènes PIK2 et PVR résulte dans l'inhibition de la différenciation induite par NGF. Par contre, le silencing de Cryab accroît l'effet inducteur de différenciation du NGF. Le silencing de PIk2 ou de PVR prévient la diminution de l'expression de Cryab induite par le NGF. Par conséquent, ces deux gènes sont en amont de Cryab dans la voie de signalisation impliquée dans la différenciation neuronale induite par NGF.

La particule de reconnaissance du signal (SRP) et son récepteur (SR) assurent l'entrée des protéines dans le réticulum endoplasmique. Pour mieux comprendre le rôle de SRP dans le processus de la translocation des protéines dans les cellules de mammifères, nous avons diminué, en utilisant des RNAi, la quantité de différentes sous unités de SRP. Lorsque l'une des sous-unités est affectée, la translocation des protéines dans le RE devient défectueuse. Nous avons voulu déterminer quelles sont l'importance et les bases moléculaires de l'arrêt d'élongation. Pour cela, nous avons remplacé le SRP endogène par un SRP ayant perdu sa fonction d'arrêt d'élongation. Sans arrêt d'élongation, la translocation et la croissance sont affectées. Ces défauts sont corrigés par un ralentissement de la traduction ou une augmentation de la quantité de SR. Globalement, nos études montrent que le SRP est essentiel pour la translocation des protéines, plus particulièrement, sa fonction d'arrêt d'élongation est nécessaire au ralentissement de la traduction et permet une translocation efficace.

Like other enveloped viruses, vesicular stomatitis virus infects cells through endosomes. There, the viral envelope undergoes fusion with endosomal membranes, thereby releasing the nucleocapsid into the cytoplasm and allowing infection to proceed. Here, we report that the viral envelope fuses preferentially with the membrane of vesicles present within multivesicular endosomes. Then, these intra-endosomal vesicles (containing nucleocapsids) are transported to late endosomes, where back-fusion with the endosome limiting membrane delivers the nucleocapsid into the cytoplasm. Presumably, export of cargo proteins from within endosomes also occurs "via" back-fusion with the limiting membrane, so that they become available for subsequent transport to their final destination. We further find out that this back-fusion process is altered by cholesterol accumulation and is regulated by the ESCRT component Tsg101, the endosomal lipid lysobisphosphatidic acid under the control of Ali/Vps31p and by phosphatidylinositol-3-phosphate "via" SNX16.

La protéine Has1 est un membre des hélicases à boîte DEAD de la levure "S cerevisiae". La déplétion de cette protéine chez la levure induit une diminution de la biosynthèse des ribosomes et, en particulier, de la petite sous-unité. D'après les différentes analyses effectuées, il apparaît que la protéine Has1 est essentielle à la maturation de l'ARN pré-ribosomique (ARNpré-r). Malgré un effet prédominent sur la biogénèse de la petite sous-unité du ribosome, il apparaît clairement que Has1p est majoritairement associée aux complexes de la voie de synthèse de la grande sous-unité. Pourtant la déplétion de Has1p ne conduit qu'à peu d'effets sur cette voie de maturation. Testée in vitro, la protéine recombinante Has1 est capable d'hydrolyser l'ATP (activité ATPase) et de dénaturer de courts hétéro-duplex ARN/ADN (activité hélicase). La maturation de certains acides aminés (dans les motifs conservés) induit une diminution des activités ATPase et/ou hélicase.

La protéine HBx du virus de l'hépatite B est essentielle pour l'établissement de l'infection virale et elle est également impliquée dans le développement des hépatocarcinomes suite à une infection chronique. L'expression de HBx dans des cellules en culture provoque de multiples effets, parmi lesquels l'induction de la mort cellulaire et la stimulation de la réplication du virus. Nous montrons l'importance fonctionnelle de l'interaction entre HBx et la protéine cellulaire DDB1 pour ces deux activités qui montrent des exigences similaires relatives à l'interaction avec DDB1. HBx et DDB1 doivent interagir au moyen de leurs sites d'interaction naturels et former un complexe dans le noyau. Cependant le chemin menant à la stimulation de la réplication virale est distinct de celui menant à la mort cellulaire. La découverte que HBx effectue ces deux activités lorsque exprimé de son propre génome viral suggère qu'elles sont potentiellement relevantes pour l'infection virale et/ou la carcinogenèse.

La particule de reconnaissance du signal (SRP) joue un rôle essentiel dans le ciblage cotraductionnel des protéines membranaires et secrétées vers le réticulum endoplasmique. La particule se compose d'un ARN de 300 nucléotides et de six protéines; elle est divisée en deux domaines fonctionnellement distincts: le domaine S et le domaine Alu. La liaison de SRP aux ribosomes synthétisant une chaîne naissante contenant une séquence signal résulte en un arrêt de la traduction, désigné arrêt d'élongation. Nous avons étudié le rôle des composants du domaine Alu de SRP dans la fonction d'arrêt d'élongation par une analyse mutationnelle et confirmé le rôle de la protéine SRP14. Nous avons aussi démontré que l'affaiblissement de la formation de la conformation compacte du domaine Alu n'affecte pas l'arrêt d'élongation. Enfin nous avons démontré qu'une structure spécifique de l'ARN du domaine Alu de SRP est nécessaire à l'activité d'arrêt d'élongation.