Bien que très proches dans leur organisation génomique, le rétrovirus HTLV-1 est impliqué dans le développement de la leucémie à cellule T de l’adulte (ATL) alors que l’infection par HTLV-2 n’a jamais été associée à des désordres hématologiques malins. La transformation des cellules infectées par HTLV-1 a longtemps été attribuée uniquement à la protéine virale transactivatrice Tax (Tax-1). Cependant, son expression est très faible dans les cellules ATL. La protéine HBZ a été découverte en 2002. Elle est traduite à partir d'un ARNm transcrit à partir du LTR 3' d'HTLV-1 et est exprimée par les cellules infectées issues de tous les patients HTLV-1 quel que soit leur statut clinique. HBZ participe au maintien du phénotype tumoral en stimulant la prolifération des cellules leucémiques et intervient dans l'échappement du virus au système immunitaire. Des analyses in silico nous avaient permis de détecter un cadre ouvert de lecture sur le brin complémentaire de l’ARN génomique d’HTLV-2. Mon travail de thèse a consisté à amplifier et caractériser d’une part le transcrit APH-2 et d’autre part la protéine qui en est issue. Nous avons démontré dans un premier temps que la transcription d’APH-2 était initié dans le LTR 3’ et que le transcrit APH-2 était épissé et poly-adénylé. Nous avons ensuite mis en évidence l’expression d’APH-2 dans les lignées infectées par HTLV-2, ainsi que dans des cultures de lymphocytes issus de deux porteurs sains africains. La mise au point d’une technique quantitative de RT-PCR nous a permis de détecter APH-2 ex vivo chez 94% des individus d’une série de 51 porteurs sains américains. Nous avons aussi montré que l'expression de cet ARNm était proportionnelle à la charge provirale. APH-2 code une protéine de 183 acides aminés dont nous avons mis en évidence l’expression dans la lignée MO. Mes travaux ont aussi permis de démontrer le rôle inhibiteur d’APH-2 sur la transcription virale malgré l’absence d’un domaine bZip classique, ainsi que son interaction avec le facteur de transcription CREB. Par immunofluorescence, nous avons établi la localisation nucléaire d’APH-2. La protéine semble associée aux corps PML grâce à une région de six arginines comprise entre les résidus 78 et 92. Cependant, contrairement à HBZ, nous n’avons pas observé d’interactions entre APH-2 et les facteurs cJun, JunD ou le cofacteur de transcription CBP/p300. De plus nous avons observé qu’APH-2 était incapable d’induire la prolifération des lymphocytes in vitro alors qu’une lymphocytose est souvent observée chez les porteurs d’HTLV-2. Grâce à une approche comparative, mes travaux ont ainsi permis d’apporter des éléments nouveaux dans la compréhension de la différence de pathogénicité qu’il existe entre HTLV-1 et HTLV-2. / Although they are very similar in their genomic organization, the HTLV-1 retrovirus is involved in the development of adult T cell leukaemia (ATL) while HTLV-2 has not been associated to any malignant haematological disorders. The tumoral transformation of infected cells was widely associated to the viral transactivactor protein Tax (Tax-1), which modulates many cellular functions. However, its expression is slightly in ATL cells. In 2002, the HBZ protein was discovered, encoded from the 3’ LTR by the complementary strand of HTLV-1 and expressed by all HTLV-1 infected people. HBZ participates in the maintenance of the tumoral phenotype by stimulating leukemic cells proliferation and is involved in the immune system escape. We recently detected a coding region by an in silico analysis in the complementary strand of HTLV-2. My work consisted in the characterization of the APH-2 transcript, and in a second part, of the associated protein. At first, we characterized the APH-2 transcription initiation in the 3’LTR and that transcript was spliced and poly-adenylated and demonstrated that the APH-2 expression in all HTLV-2 cell lines and in short cultured lymphocytes from African healthy carriers. We used a quantitative RT-PCR on uncultured cells from 51 American HTLV-2 healthy carriers and we we detected APH-2 expression in 94% of them. We then showed that APH-2 RNA expression is correlated to the HTLV-2 proviral load. The APH-2 transcript encoded a 183 amino acid protein that was shown to be expressed in the HTLV-2 infected Mo cell line. Our work demonstrated the inhibitory functions of APH-2 in the viral transcription and its interaction with the transcriptional cofactor CREB despite the lack of a bZip domain. By an immunofluorescence approach we established the nuclear localisation of APH-2, which is in particular in the PML nuclear bodies. We demonstrated that six arginines in the 78-92 amino acids region is involved in this PML colocalization. Contrary to HBZ, we didn’t observe any interaction with between APH-2 and cJun or JunD factors nor with the transcriptional cofactor CBP/p300. Furthermore we showed that APH-2 is not involved in lymphocyte proliferation in vitro although a lymphocytosis is often observed in HTLV-2 carriers. According to this comparative approach, my work allowed us to better understand the difference of pathogenicity existing between HTLV-1 and HTLV-2.

O splicing alternativo do pré-mRNA de BCL-X produz duas isoformas de mRNAs com funções antagônicas, a pró-apoptótica BCL-XS e a anti-apoptótica BCL-XL, cujo balanço regula a homeostasia celular. Entretanto, o mecanismo que regula esse processamento ainda é desconhecido. Nesse trabalho, nós identificamos e caracterizamos um longo RNA não codificador de proteínas (lncRNA) nomeado INXS, que é transcrito a partir da fita oposta do locus genômico de BCL-X, sendo menos abundante em linhagens celulares tumorais e tecidos tumorais de pacientes quando comparados com os respectivos pares não tumorais. INXS é um RNA unspliced de 1903 nts, é transcrito pela RNA Polimerase II, possui cap 5\', está enriquecido na fração nuclear das células e se liga à proteína Sam68 do complexo modulador de splicing. O tratamento de células tumorais 786-O com cada um de três agentes indutores de apoptose aumentou a expressão endógena do INXS, levando ao aumento expressivo da proporção entre os mRNAs de BCL-XS / BCL-XL, e ativação das caspases 3, 7 e 9. Estes efeitos foram anulados na presença do knockdown do INXS. Da mesma forma, a superexpressão ectópica do INXS causou uma mudança no splicing favorecendo a isoforma BCL-XS e ativação das caspases, aumentando os níveis da proteína BCL-XS e conduzindo as células à apoptose. Utilizando um modelo in vivo, cinco injeções intra-tumorais do INXS durante 15 dias causaram uma regressão acentuada no volume dos xenotumores. Portanto, INXS é um lncRNA que induz a apoptose, sugerindo que essa molécula seja um possível alvo a ser explorado na terapia contra o câncer. / BCL-X mRNA alternative splicing generates pro-apoptotic BCL-XS or anti-apoptotic BCL-XL, whose balance regulates cell homeostasis. However, the mechanism that regulates the splice shifting is incompletely understood. Here, we identified and characterized a long noncoding RNA (lncRNA) named INXS, transcribed from the opposite genomic strand of BCL-X, that was less abundant in tumor cell lines and patient tumor tissues compared with non-tumors. INXS is an unspliced 1903 nt-long RNA, is transcribed by RNA Polymerase II, 5\'-capped, nuclear enriched and binds Sam68 splicing-modulator. The treatment of tumor cell line 786-O with each of three apoptosis-inducing agents increased endogenous INXS lncRNA, increased BCL-XS / BCL-XL mRNA ratio, and activated caspases 3, 7 and 9. These effects were abrogated in the presence of INXS knockdown. Similarly, ectopic INXS overexpression caused a shift in splicing towards BCL-XS and activation of caspases, increasing the levels of BCL-XS protein and then leading the cells to apoptosis. In a mouse xenograft model, five intra-tumor injections of INXS along 15 days caused a marked regression in tumor volume. INXS is an lncRNA that induces apoptosis, suggesting that INXS is a possible target to be explored in cancer therapies.

O gene, uma seqüência de nucleotídeos necessária para a síntese de moléculas funcionais, é transcrito e regulado por um conjunto de processos e fatores extremamente complexos. Entender o momento e o tecido em que os genes são expressos, as isoformas funcionais, as regiões controladoras e os fatores envolvidos na regulação da expressão de cada gene é um dos grandes desafios da biologia molecular moderna. Hoje, com a enorme quantidade de informações de seqüências genômicas e de transcriptomas, aliado ao desenvolvimento de métodos computacionais para agrupar e analisar estes dados em larga escala, o estudo dos fenômenos relacionados à transcrição e regulação gênica está passando por uma revolução. Por exemplo, é possível medir, concomitantemente, a expressão gênica de milhares de genes em diferentes tecidos, assim como identificar diversos fenômenos que atuam nestes genes. Neste trabalho nós desenvolvemos e aplicamos métodos computacionais no estudo de quatro temas envolvendo aspectos chave da transcrição e regulação gênica. No primeiro trabalho, nós abordamos a expressão gênica tecido-específica através do estudo dos genes expressos no cérebro e em dez regiões cerebrais de camundongo. No segundo trabalho, nós identificamos seqüências potencialmente envolvidas no controle da transcrição gênica através do estudo de motivos sobre representados na região promotora dos genes de receptores olfativos. No terceiro trabalho, analisamos o transcriptoma humano quanto a presença de eventos de retenção de intron, um tipo de splicing alternativo. No quarto trabalho, nós abordamos a complexidade do transcriptoma e a regulação da expressão gênica através do estudo de pares de genes senso-antisenso em humanos e camundongos. Em todos os trabalhos, obtivemos resultados que nos permitiram tirar conclusões específicas sobre cada fenômeno estudado e nos mostraram a importância de estudá-los através de uma abordagem em larga escala. Adicionalmente, verificamos que os nossos métodos computacionais foram eficientes e adequados para o estudo da transcrição e regulação gênica em Homo sapiens e Mus musculus. / Genes, nucleotide sequences necessary for the synthesis of functional molecules, are transcribed and regulated by extremely complex cellular and molecular processes. To understand when and in which tissues the genes are expressed, their functional isoforms, control regions and the factors involved in gene regulation is one of major challenges of modern molecular biology. Today, the availability of complete genome sequences and transcriptomes, together with the development of new computational methods allows the study of phenomena related to the transcription and gene regulation in a large scale. For example, it is possible to quantify, concomitantly, gene expression of thousands of genes in different tissues and analyze different aspects of their regulation. In this work we developed and applied computational methods to the study of four key aspects of gene transcription and regulation. In the first study, we addressed tissue specific gene expression through the study of genes that are preferentially expressed in the brain and ten different mouse brain regions. In the second study, we identified sequences that are potentially involved in the control of gene transcription through the study of motifs that are over represented in the promoter region of olfactory receptor genes. In the third study, we browsed the human for the presence of intron retention, a type of alternative splicing. In the fourth study, we addressed the transcriptoma complexity and gene expression regulation through the study of pair of sense-antisense genes in human and mouse. In all studies, our results allowed us to make specific conclusions about each phenomenon analyzed which showed us the importance of a large scale approach. In addition, we verified that our computational methods can be efficiently applied to the study of transcription and gene regulation in Homo sapiens and Mus musculus.

Currently, human norovirus is the leading cause of acute gastroenteritis and accounts for most cases of foodborne illnesses in the United States each year. Due to its tissue culture inefficiency, studies of human norovirus have been crippled for more than forty years.Tulane virus (TV) stands out as a suitable surrogate of human norovirus given its high amino acid identity with human norovirus and its well-established cell culture system. It was first isolated from rhesus macaques (Macaca mulatta) in 2008 and identified as a novel Calicivirusrepresenting a new genus, Recovirus genus (Farkas et al., 2008). However, there are still unanswered questions about its infectious cycle and the essential factors for its infection. In this study, we have obtained a TV variant (the 9-6-17 strain) that has lost the binding ability to the B-type histo-blood group antigen (HBGA), which was proposed to be the receptor of both TV and human norovirus. In the first chapter, we outline how the sequence analysis,structural biology studies, and mutagenesis studies of the 9-6-17 TV strain have shed light on the interaction with its host cell receptor. To investigate the key residues for HBGA binding, we established the full-length infectious clone of the 9-6-17 TV strain. We present a highly selective transformation of serine 367, located in the predicted HBGA binding site, into a lysine residu e. Our results advance the understanding of genetic changes in TV required for adaptation to cell culture environments. Cryo-EM is an awarding winning technique that has been the greatest scientific breakthrough in recent years. It was awarded the Nobel Prize in Chemistry in 2017. Despite the technological advances of the direct electron detector and image processing software, several major roadblocks remain for high-resolution structure determination with cryo-EM. In the later chapters, we explored the most efficient way of using VPP to enhance image contrast, how to tackle the airwater interface problem by encapsulating target protein, how to reach a higher resolution by refining high order parameters, and the helical indexing problem in real space. These technical advances would benefit the whole cryo-EM community by providing convenient tools or insights for future directions.

No description available.

No description available.

L'épissage des ARN pré-messagers est une étape essentielle pour l'expression des gènes chez les eucaryotes supérieurs. La reconnaissance des exons par la machinerie d'épissage est réalisée grâce à différents éléments cis-régulateurs incluant les séquences consensus d'épissage et les séquences auxiliaires activatrices ou inhibitrices d'épissage. Le pré-ARNm représente une nouvelle cible thérapeutique pour le traitement des maladies génétiques. L'approche du saut d'exon thérapeutique, destinée à restaurer l'expression d'une protéine totalement ou partiellement fonctionnelle en interférant avec le processus d'épissage, suscite un grand intérêt notamment pour la dystrophie musculaire de Duchenne où la modification du transcrit permettrait d'obtenir une forme modérée de la maladie, la Dystrophie musculaire de Becker. Des oligonucléotides antisens sont utilisés pour masquer les signaux d'épissage de reconnaissance d'un exon par le spliceosome, et induire son excision (ou saut) du transcrit mature. La détermination de la meilleure séquence cible des AONs est une difficulté majeure de cette approche. Pour le gène DMD, nous avons pu établir grâce à des analyses bioinformatiques et statistiques combinées avec des tests fonctionnels utilisant des minigènes rapporteurs d'épissage, que le ciblage de motifs exoniques qui fixent le facteur d'épissage SF2/ASF permettait d'obtenir la meilleure efficacité des AONs. Par ailleurs, nous avons exploré la régulation de l'épissage des pseudoexons dans le gène DMD, et notamment les mécanismes conduisant à l'inclusion de ces séquences introniques dans le transcrit mature en condition pathologique. L'étude de deux cas exceptionnels d'activation de pseudoexons associée à des remaniements introniques rares (double délétion, inversion) élargit le spectre des mutations à l'origine de ces défauts d'épissage, et illustre le rôle encore mal connu des remaniements introniques en pathologie humaine. / Splicing of pre-messenger RNAs to mature transcripts is a crucial step in eukaryotic gene expression. The recognition of exon by the splicing machinery involves different cis-regulatory elements, including the splice site motifs and auxiliary sequences, which can act by stimulating or repressing splicing. The pre-mRNA represents a new therapeutic target for the treatment of genetic diseases. Notably, the exon skipping strategy is currently one of the most promising therapeutic approaches for the Duchenne muscular dystrophy. It intends to restore the expression of a partially functional protein by interfering with the splicing process, and converts the severe DMD phenotype into the moderate form of the disease, Becker muscular Dystrophy (BMD). Antisense oligonucleotides are used to mask the splicing signals involved in exon recognition by the spliceosome to induce its skipping from the mature transcript and restore an open reading frame. The determination of the best target sequence of the AONs is one of the major hurdles to overcome. For the DMD gene, a bioinformatic and statistical analysis combined with minigenes studies allowed us to establish that targeting binding sites for the splicing factor SF2/ASF maximizes the AONs efficiency. In a second part of this work, we investigated the splicing regulation of pseudoexons in the DMD gene, in particular the mechanisms leading to the inclusion of these intronic sequences in the mature transcript in pathological conditions. The study of two exceptional cases of pseudoexons activation associated with rare intronic rearrangements (double-deletions, inversion) expands the spectrum of missplicing mutations, and demonstrates the potential role of pure intronic rearrangements in human pathology.

L'hypertension artérielle est l'une des principales causes de morbidité et de mortalité dans le monde. La compréhension des mécanismes qui sont à la base du développement de l'hypertension offrira de nouvelles perspectives pour un meilleur contrôle de l'hypertension. Nous avons précédemment montré que le niveau des protéines Giα-2 et Giα-3 est augmenté chez les rats spontanément hypertendus (SHR) avant l'apparition de l'hypertension. Le traitement avec les inhibiteurs de l’enzyme de conversion de l’Angiotensine (IEC) est associé à une diminution de l’expression des protéines Gi. De plus, l'injection intrapertoneale de la toxine de la coqueluche inactive les deux protéines Giα et empêche le développement de l'hypertension chez les SHR. Cependant, la contribution spécifique des protéines Giα-2 et Giα-3 dans le développement de l'hypertension n'est pas encore connue. Dans la présente étude, l’Anti-sens oligodésoxynucléotide (AS-ODN) de Giα-2 et Giα-3 (1mg/Kg en poids corporel) encapsulé dans des liposomes cationiques PEG / DOTAP/ DOPE ont été administrés par voie intraveineuse aux SHR pré-hypertendus âgé de trois semaines et aux Wistar Kyoto (WKY) rats de même âge. Les contrôles des WKY et SHR non traités ont été injectés avec du PBS stérile, liposomes vides ou oligomères sens. La pression artérielle (PA) a été suivie chaque semaine en utilisant la technique manchon caudal. Les rats ont été sacrifiés à l'âge de six semaines et neuf semaines. Le coeur et l'aorte ont été utilisés pour étudier l'expression des protéines Gi. Le knockdown des protéines Giα-2 par l’injection de Giα-2-AS a empêché le développement de l'hypertension à l'âge de six semaines. Par la suite, la PA a commencé à augmenter rapidement et a atteint le niveau que l'on retrouve dans les groupes témoins à l'âge de neuf semaines. D'autre part, la PA du groupe traité avec le Giα-3-AS a commencé à augmenter à l'âge de quatre semaines. Dans le groupe des SHR-Giα-3-AS, la PA a augmenté à l’âgé de six semaines, mais moins que celle de SHR-CTL. Le coeur et l'aorte obtenues des SHR Giα-2-AS et Giα-3-AS à partir de l’âgé de six semaines ont eu une diminution significative de l’expression des protéines Giα-2 et Giα-3 respectivement. Dans le groupe des WKY Giα-2-AS et Giα-3-AS l'expression des protéines Giα-2 et Giα-3 respectivement a diminué malgré l'absence de changement dans la PA par rapport aux WKY CTL. À l'âge de neuf semaines, les SHR traités avec du Giα-2-AS et Giα-3-AS avaient la même PA et expression des protéines Gi que le SHR CTL. Ces résultats suggèrent que les deux protéines Giα-2 et Giα-3 sont impliqués dans le développement de l'hypertension chez les SHR, mais le knockdown de Giα-2 et pas de Giα-3 a empêché le développement de l'hypertension. / Hypertension is one of the leading causes of morbidity and mortality in the world. Understanding the mechanisms underlying the development of hypertension will provide new insights into better control of hypertension. We have previously shown that the levels of Giα-2 and Giα-3 proteins were augmented in SHR before the onset of hypertension. Antihypertensive (ACE) inhibitor is associated with decreased Gi-proteins. In addition, intrapertoneal injection of pertussis toxin (PTX) inactivated both Giα proteins and prevented the development of hypertension in SHR. However, the specific contribution of Giα-2 and Giα-3 proteins in hypertension development is still not known. In the present study, Giα-2 and Giα-3 Antisense oligodeoxynuleotide (AS-ODN) (1 mg/Kg body weight) encapsulated in PEG/DOTAP/DOPE cationic liposomes were administrated intravenously to three-week-old pre-hypertensive SHR and their age-matched WKY while control WKY and SHR were injected with sterile PBS, empty liposomes or sense oligomer. Blood pressure (BP) was monitored weekly using tail-cuff technique. The rats were sacrificed at the age of six weeks and nine weeks. Heart and aorta were used to study Gi proteins expression. The knockdown of Giα-2 protein by Giα-2-AS injection prevented the development of hypertension up to the age of six weeks; thereafter the BP began to increase rapidly and reached the same level found in control groups at the age of nine weeks. On the other hand, the BP of the Giα-3-AS treated group began to increase at the age of four weeks. The SHR Giα-3-AS had augmented BP at six weeks but lower than that of SHR-CTL. The heart and aorta obtained from six week-old SHR Giα-2-AS and Giα-3-AS had significant decrease in Giα-2 and Giα-3 proteins expression respectively. WKY Giα-2-AS and Giα-3-AS had decreased in Giα-2 and Giα-3 protein expression respectively despite having no change in BP compared to CTL WKY. At the age of nine weeks, the SHR Giα-2-AS and Giα-3-AS had the same BP and Gi protein expression as the control SHR. These results suggest that both Giα-2 and Giα-3 proteins are implicated in the development of hypertension in SHR but the knockdown of Giα-2 not Giα-3 has prevented the development of hypertension.

Le premier membre de la famille des rétrovirus humains HTLV (Virus T-lymphotropique Humain), HTLV-1, a été découvert en 1980 et l’on estime aujourd’hui à plus de 10 millions le nombre d’individus infectés à travers le monde. Après une période de latence d’environ 40 ans, 5% des individus infectés développent des leucémies, des lymphomes adultes de lymphocytes T (ATLL) ou encore une myélopathie associée à HTLV-1/ paraparésie spastique tropicale (HAM/TSP). L’apparition de la maladie serait en grande partie orchestrée par deux protéines virales, soit Tax et HTLV-1 bZIP factor (HBZ). L’expression du génome viral se fait à partir d’un transcrit sens de pleine longueur suite à un épissage alternatif, à l’exception du gène HBZ. HBZ est produite à partir d’un transcrit antisens initié dans la séquence terminale longue répétée (LTR)’3. Elle a été décrite comme étant capable de réguler négativement la transcription virale dépendante de Tax en se dimérisant avec des facteurs de transcription cellulaires tels que CREB-2 et certains membres de la famille Jun. HBZ a aussi un pouvoir prolifératif et bien que nous ne sachions toujours pas le mécanisme moléculaire menant à l’oncogenèse par HBZ, nous savons qu’elle module une multitude de voies de transduction de signaux, dont AP-1. Nous avons récemment mis en évidence un transcrit antisens nommé Antisense Protein of HTLV-2 (APH-2) chez HTLV-2 qui n’est associé qu’à une myélopathie apparentée au HAM/TSP. Ce n’est qu’en 2005 que HTLV-3 et HTLV-4 se sont rajoutés au groupe HTLV. Cependant, aucune corrélation avec le développement d’une quelconque maladie n’a été montrée jusqu’à ce jour. Le premier volet de ce projet de doctorat avait pour objectif de détecter et caractériser les transcrits antisens produits par HTLV-3 et HTLV-4 et d’étudier les protéines traduites à partir de ces transcrits pour ainsi évaluer leurs similitudes et/ou différences avec HBZ et APH-2. Nos études de localisation cellulaire réalisées par microscopie confocale ont montré que APH-3 et APH-4 sont des protéines nucléaires, se retrouvant sous la forme de granules et, dans le cas d’APH-3, partiellement cytoplasmique. Ces granules co-localisent en partie avec HBZ. Les analyses à l’aide d’un gène rapporteur luciférase contenant le LTR 5’ de HTLV-1 ont montré que APH-3 et APH-4 peuvent aussi inhiber la transactivation du LTR 5’ par Tax. Aussi, des études faisant appel au gène rapporteur précédé d’un promoteur de collagénase (site AP-1), ont montré que ces deux protéines, contrairement à HBZ, activent la transcription dépendante de tous les membres des facteurs de transcription de la famille Jun. De plus, les mutants ont montré que le motif fermeture éclair (LZ) atypique de ces protéines est impliqué dans cette régulation. En effet, APH-3 et APH-4 modulent la voie Jun-dépendante en se dimérisant via leur LZ atypique avec la famille Jun et semblent activer la voie par un mécanisme ne faisant pas par d’un domaine activateur autonome. Dans un deuxième volet, nous avions comme objectif d’approfondir nos connaissances sur la localisation nucléolaire de HBZ. Lors de nos analyses, nous avons identifié deux nouveaux partenaires d’interaction, B23 et la nucléoline, qui semblent être associés à sa localisation nucléolaire. En effet, ces interactions sont plus fortes suivant une délétion des domaines AD et bZIP de HBZ qui dans ce cas est localisée strictement au nucléole. De plus, bien que APH-3 et APH-4 puissent se localiser aux nucléoles, HBZ est la seule protéine traduite à partir d’un transcrit antisens pouvant interagir avec B23. Finalement, ces travaux ont clairement mis en évidence que HTLV-3 et HTLV-4 permettent la production de transcrits antisens comme chez d’autres rétrovirus. Les protéines traduites à partir de ces transcrits antisens jouent d’importants rôles dans la réplication rétrovirale mais semblent avoir des fonctions différentes de celles de HBZ au niveau de la régulation de la transcription de la voie Jun. HBZ semble aussi jouer un rôle unique dans le nucléole en ciblant les protéines nucléolaires de la cellule. Ces études démontrent que les protéines produites à partir de transcrits antisens chez les rétrovirus HTLV partagent plusieurs ressemblances, mais démontrent aussi des différences. Ainsi, les APH pourraient, en tant qu’outil comparatif, aider à mieux cibler les mécanismes moléculaires importants utilisés par HBZ pour induire la pathogénèse associée à une infection par HTLV. / The first human T-cell lymphotropic virus (HTLV) family member was discovered in 1980 and it is estimated that approximately 10 million people are infected with HTLV-1 worldwide. After about 40 years, 5% of infected individuals will develop an adult T-cell leukemia/lymphoma (ATLL) while another 4% will develop HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP). It is believed that two viral proteins, Tax and HBZ, together orchestrate the oncogenic process. The viral proteins are expressed from an alternatively spliced sense transcript except for the HBZ gene. HBZ is translated from an antisense transcript initiated in the long terminal repeat (LTR)’3. This viral protein is capable of inhibiting Tax transactivation of the LTR5’ by dimerizing with cellular transcription factors such as CREB-2 and c-Jun. HBZ also has proliferating capacities and while the molecular mechanisms leading to the disease still need to be elucidated, it is well known that HBZ can modulate a multitude of signal transduction pathways like AP-1. We have recently discovered an antisense transcript termed Antisense Protein of HTLV-2 (APH-2) produced in HTLV-2. HTLV-2 is only associated to myelopathies resembling HAM/TSP. HTLV-3 and HTLV-4 were discovered in 2005 and have not been associated with any type of disease thus far. The first goal of this PhD project was hence to detect and characterize the antisense transcripts produced in HTLV-3 and HTLV-4, to study the functions of these translated proteins and to evaluate their similarities and/or differences shared with HBZ and APH-2. Our localization studies using confocal microscopy demonstrated that APH-3 and APH-4 are found in the nucleus as speckles, and for APH-3, also partially cytoplasmic. These two proteins can also partially colocalize with HBZ. Using a luciferase reporter plasmid bearing the HTLV-1 LTR5’, we demonstrated that APH-3 and APH-4 could inhibit Tax transactivation of the LTR5’. We also used a luciferase reporter plasmid bearing the collagenase promoter, which bears an AP-1 site, and demonstrated that both viral proteins could activate transcription in the presence of any of the Jun family of transcription factors. We generated several mutants and the atypical leucine zipper (LZ) found in APH-3 and APH-4 is crucial for this regulation. In fact, APH-3 and APH-4 using their atypical LZ dimerize with Jun family members and activate this pathway using a mechanism other than an autonomous activation domain. Our next goal was to investigate the significance of the HBZ nucleolar localization. During this project, we identified two new interacting partners, B23 and nucleolin, which seem to be associated with its nucleolar localization. In fact, these interactions are stronger when HBZ is deleted of its AD and bZIP domains and hence when HBZ demonstrates a stronger nucleolar distribution. Moreover, while APH-3 and APH-4 are also found in the nucleolus, HBZ is the only antisense protein able to interact with B23. Finally, this work clearly demonstrates that HTLV-3 and HTLV-4 can produce an antisense transcript alike other retroviruses. The encoded proteins play an important role in retroviral replication and seem to regulate Jun-dependant transcription differently than HBZ. HBZ also seems to have a unique role in the nucleoli by targeting specific cellular nucleolar proteins. Similarities but also differences are shared between the antisense proteins. Thus, the APH proteins represent a good comparative tool in order to better understand the molecular mechanisms involved in HTLV induced diseases.

O gene supressor tumoral RASSF1A tem sido associado com redução da proliferação celular em diversos tumores. Sua expressão é regulada por eventos epigenéticos que envolvem o complexo repressivo polycomb (PRC2), no entanto os mecanismos moleculares da modulação do recrutamento deste modificador epigenético para este locus ainda são desconhecidos. Neste trabalho identificamos e caracterizamos ANRASSF1, um RNA não codificador longo (lncRNA) intrônico unspliced, que é transcrito na fita oposta do gene RASSF1A, em várias linhagem celulares e tecidos, e se liga a PRC2. ANRASSF1 é transcrito pela RNAPII, possui cap-5´ e cauda poli-A, além de localizar-se no núcleo e possuir uma meia-vida em média quatro vezes menor comparada com outros lncRNAs ligados à PRC2. A super-expressão ectópica de ANRASSF1 reduziu os níveis de RASSF1A e aumentou a taxa de proliferação em células HeLa, enquanto seu silenciamento provocou efeito oposto. Essas mudanças nos níveis de ANRASSF1 não afetaram a abundância da isoforma RASSF1C em nenhuma das condições. A super-expressão de ANRASSF1 provocou um grande aumento tanto da ocupação de PRC2 como da marca de histona repressiva H3K27me3 especificamente na região promotora RASSF1A. Nenhum efeito da super-expressão de ANRASSF1 foi detectado na ocupação de PRC2 e na histona H3K27me3 nas regiões promotoras de RASSF1C e de outros quatro genes vizinhos, incluindo dois genes supressores tumorais bem caracterizados. Além disso, foi demonstrado que ANRASSF1 forma um híbrido de RNA/DNA e recruta SUZ12, um componente do PRC2, para o promotor de RASSF1A. Notavelmente, foi detectado pelo ensaio de RNase-ChIP que a degradação de ANRASSF1 diminui a ocupação de PRC2 neste promotor. Esses resultados demonstram um novo mecanismo de repressão epigenética do supressor tumoral RASSF1A, envolvendo um lncRNA unspliced antissenso, onde ANRASSF1 reprime seletivamente a expressão da isoforma de RASSF1 que sobrepõe o transcrito antissenso de modo local e específico. Considerando uma perspectiva mais ampla, nossos resultados sugerem que outros lncRNAs intrônicos unspliced não caracterizados no genoma humano podem contribuir para uma modulação epigenética local e específica de cada região em que os lncRNAs são transcritos. / Tumor-suppressor RASSF1A gene down-regulation has been implicated in increasing cell proliferation in several tumors. Its expression is regulated by epigenetic events involving polycomb repressive complex 2 (PRC2), however the molecular mechanisms modulating recruitment of this epigenetic modifier to the locus remain largely unknown. Here, we identify and characterize ANRASSF1, an endogenous unspliced long noncoding RNA (lncRNA) that is transcribed from the opposite strand of RASSF1 gene in several cell lines and tissues, and binds to PRC2. ANRASSF1 is transcribed by RNA Polymerase II, 5\'-capped, polyadenylated, displays nuclear localization, and has on average a four-fold shorter half-life compared to other lncRNAs that bind PRC2. ANRASSF1 ectopic overexpression decreases RASSF1A abundance and increases the proliferation rate of HeLa cells, whereas its silencing causes opposite effects. These changes in NRASSF1 levels do not affect RASSF1C isoform abundance. ANRASSF1 overexpression causes a marked increase both in PRC2 occupancy and in histone H3K27me3 repressive mark specifically at the RASSF1A promoter region. No effect of ANRASSF1 overexpression is detected on PRC2 occupancy and on histone H3K27me3 at the promoter regions of RASSF1C and of four other neighbor genes, including two well-characterized tumor suppressor genes. Additionally, we demonstrate that ANRASSF1 forms an RNA/DNA hybrid, and recruits SUZ12, a PRC2 component, to the RASSF1A promoter. Notably, depletion of ANRASSF1 disrupts SUZ12 occupancy on RASSF1A promoter as measured by RNAse-ChIP assay. Together, these results show a new mechanism of epigenetic repression of RASSF1A tumor suppressor gene involving an antisense unspliced lncRNA, in which ANRASSF1 selectively represses expression of the RASSF1 isoform overlapping the antisense transcript in a location-specific manner. In a broader perspective, our findings suggest that other non-characterized unspliced intronic lncRNAs transcribed in the human genome may contribute to a location-specific epigenetic modulation of genes.