The p68 protein, an archetypical member of the DEAD box family of RNA helicases, exhibits both ATPase and RNA helicase dependent/independent activities. To date the p68 protein has been implicated in most parts of RNA metabolism including ribosome biogenesis, transcription, RNA decay, miRNA processing and pre-mRNA processing. Alterations in both expression and functional activity of p68 have been linked to carcinogenesis, with p68 exhibiting both tumour suppressive and oncogenic properties, highlighting the extremely contextual nature of p68. Recently, p68 has been shown to be required for transcriptional co-activation of the p53 tumour suppressor, permitting the recruitment of p53 to selective p53-responsive promoters. In addition, p68 was shown to be required for p21 induction through both the recruitment of p53 and RNA pol II to the p21 promoter in response to DNA damage: Specifically, p68 was shown to be essential for the p53 dependent induction of the p21 mediated G1/S cell cycle arrest under DNA damage conditions. Here I show the pre-mRNA processing function of p68 is also required to facilitate splicing of the p21 pre-RNA under basal and DNA damage conditions, an effect found to be p53-independent. Importantly, the p68 protein is not the only product of the DDX5 gene. DDX5 also gives rise to a long non-coding RNA species identified through retention of intron 11. Here I also present, through siRNA knockdown studies and analysis of the expression of the DDX5 lncRNA, p68 and p21 proteins in breast cancer tissue, that these gene products may differentially regulate p21 levels and that the DDX5 gene may exhibit multiple mechanisms to control p21 expression. In addition, through Pulse SILAC proteomics and western blot validation I have identified a number of potential targets of the DDX5 lncRNA and miRNA species encoded within intron 11.

Despite our understanding of the role of the survival motor neuron protein (SMN) in cytoplasmic small ribonucleoproteins (snRNP) assembly, it is unclear how loss of this protein causes motor neuron degeneration in Spinal Muscular Atrophy (SMA). It could be explained by defects in functions that are specific to tissues most affected in SMA. In neurons, SMN localizes to neuronal RNA granules, RNA-containing foci in axons. They regulate many aspects of mRNA fate which include transport along neurites, mRNA stability, and mRNA translation. Most recently, our work provided evidence for SMN’s role in mRNA translation. Specifically, we demonstrated that SMN associates with polyribosomes and may repress translation of specific mRNA targets. Our group demonstrated that SMA-causing mutations within the Tudor domain of SMN completely abolished this activity. This indicates the potential significance of this novel SMN function in the SMA pathology. To further investigate SMN’s function in regulating translation, our group performed a proteomic screen on polysome-containing sucrose gradient fractions. We identified and validated novel interacting partners for SMN that may act as co-factors to regulate translation. DDX5 (an RNA helicase) is an unexpected novel interacting partner as it is known for its role in micro-RNA processing. Moreover, we observe that FMRP, a recognized protein in translational complexes, is required for the presence of SMN and DDX5 in polysomal fractions. With these latest findings, we updated our model of the molecular mechanism by which SMN regulates translation. This work provides more insights on how SMN regulates translation, a newly uncovered role for SMN in motor neurons. Identification of the molecular targets that are misregulated due to loss of this function may reveal new information on the pathogenesis of SMA.

La progression tumorale, qui conduit à la formation de métastases, est le résultat de profondes modifications des différents niveaux de régulation de l'expression des gènes comme la transcription ou l'épissage alternatif. Au cours de ma thèse, j'ai étudié le rôle de DDX5 et DDX17, deux ARN hélicases qui, au cours de la progression tumorale, sont impliquées dans la régulation transcriptionnelle, l'épissage alternatif et la biogénèse des microARNs. Pour cela, j'ai utilisé deux modèles de progression tumorale : le modèle murin 4T1, composé de cellules cancéreuses qui présentent des propriétés métastatiques différentes, et les cellules humaines MCF10A qui, après traitement au TGF-beta, sont capables de réaliser la transition épithélio-mésenchymateuse, un processus de trans-différenciation qui contribue à la formation des métastases. Dans le modèle 4T1, j'ai montré que Ddx17 et Ddx5 contribuent à l'invasivité des cellules tumorales en contrôlant des programmes transcriptionnels et d'épissage alternatif. Plus précisément, j'ai démontré que Ddx5 et Ddx17 favorisent l'agressivité des cellules cancéreuses en régulant l'épissage des variants de l'histone macroH2A1 qui, à leur tour, contrôlent l'expression de gènes impliqués dans la progression tumorale. Dans le modèle MCF10A où la transition épithélio-mésenchymateuse peut être induite sous TGF-beta, j'ai montré que DDX5 et DDX17 orchestrent dynamiquement des programmes transcriptionnels et d'épissage. Le travail effectué pendant ma thèse met en évidence l'importance des ARN hélicases DDX5 et DDX17 comme régulateurs clés de la progression tumorale, et souligne le rôle de l'épissage alternatif lors de la progression tumorale. De plus, ce travail met l'accent sur l'importance d'intégrer les différents niveaux de régulation de l'expression des gènes (transcription, épissage, microARN) pour une compréhension globale de la progression tumorale / Tumor progression leading to the formation of metastases result from deep modifications of gene expression programs at several levels, including transcription and splicing. During my PhD, I investigated the role in tumor progression of DDX5 and DDX17, two highly related multifunctional DEAD box RNA helicases that are involved in transcription and splicing as well as in microRNA biogenesis. For this purpose, I used two breast cancer models of tumor progression : the 4T1 mouse model composed of cancer cells that exhibit different metastatic properties and MCF10a human cells that undergo epithelial-to-mesenchymal transition upon Tgf-beta treatment, a trans-differentiation process contributes to metastasis formation. In the 4T1 mouse model, I showed that Ddx17 and Ddx5 contribute to tumor-cell invasiveness by controlling both transcriptional and splicing programs. More specifically, I demonstrated that Ddx5 and Ddx17 promote cancer cells aggressiveness by regulating the splicing of the macroH2A1 histone which in turn impacts on the expression of genes implicated in tumor cell invasiveness. In the Tgf-beta induced epithelial-to-mesenchymal trans-differentiation model, I showed that DDX5 and DDX17 dynamically orchestrate transcription, microRNA and splicing programs. The work performed during my PhD highlights the importance of DDX5 and DDX17 RNA helicases as key regulators of tumor progression in breast cancer, and also underlines the role of alternative splicing during tumor progression. Furthermore, this work emphasizes the importance of integrating the different layers of the gene expression process (transcription, splicing, microRNA) for a comprehensive understanding of tumor progression

La voie de signalisation NF-kB (nuclear factor kB) régule la transcription de gènes impliqués dans la réponse immune et l’inflammation. L’activation chronique de cette voie est fréquemment retrouvée associée à des désordres inflammatoires et des cancers. Les impacts fonctionnels de l’activation de la voie NF-kB ont été jusqu’à présent étudiés à l’échelle des promoteurs. Néanmoins, les études récentes de la distribution chromatinienne de NF-kB indiquent que la sous-unité NF-kB RelA se localise majoritairement dans les régions intragéniques, incluant des exons et des introns, où ses fonctions restent inconnues. Mes travaux ont consisté à adresser cette question dans le contexte de l’infection par le virus HTLV-1, un activateur chronique de la voie NF-kB, responsable de la leucémie T de l’adulte. Mes données montrent que l’activation de la voie NF-kB par l’oncogène viral Tax de HTLV-1 s’accompagne de modifications de l’épissage alternatif d’exons riches en GC qui coïncident avec le recrutement chromatinien de RelA à proximité de ces exons régulés. Les analyses intégratives des profils d’épissage et du remodelage de la chromatine, combinées à des essais de ciblage expérimental de la chromatine (TALE), démontrent que la fixation intragénique de RelA permet de recruter le régulateur d'épissage DDX17 pour moduler l’épissage alternatif de l’exon via son activité hélicase. Ces données révèlent que, outre ses fonctions transcriptionnelles, le facteur NF-kB RelA agit comme une ancre chromatinienne pour le facteur d’épissage DDX17 et fournit une spécificité de régulation d’épissage alternatif. Ces données revisitent nos connaissances des mécanismes physiopathologiques des maladies associées à HTLV-1 ainsi que d'autres désordres reliés à l’activation chronique de la voie NF-kB / The NF-kB (nuclear factor kB) signaling pathway regulates gene transcription of genes involved in immune response and inflammation. Chronic activation of NF-kB frequently associated with inflammatory disorders and cancer. The functional impacts of NF-kB have long been studied at the promoter level. Nevertheless, recent studies of the chromatin distribution of RelA indicate that this NF-kB subunit is predominantly localized in intragenic regions, including exons and introns, where its functions remain unknown. My work has addressed this question in the context of HTLV-1 infection, which is a constitutive activator of NF-kB, and the causative agent of the Adult T-cell Leukemia. The results show that the activation of NF-kB by the viral oncoprotein Tax results in changes in alternative splicing regulations of GC-rich exons that coincide with the chromatin recruitment of RelA in the vicinity of these exons. Integrative analysis of RNA splicing and chromatin occupancy, combined with experimental chromatin tethering assays (TALE) demonstrate that the intragenic binding of RelA leads to the recruitment of the splicing regulator DDX17, which modulates the inclusion rate of exon thanks to its helicase activity. Altogether, these data reveal that, besides its transcriptional role, NF-kB RelA acts as a chromatin anchor for the splicing factor DDX17 and provides alternative splicing specificity. These data revisit our knowledge of the physiopathologic mechanisms of HTLV-1 associated diseases , as well as other disorders related to the chronic activation of the NF-kB pathway

<div>G-quadruplexes (G4s) are non-canonical secondary structures formed in single-stranded guanine-rich nucleic acid sequences, such as those found in oncogene promoters and telomeres. <i>MYC</i>, one of the most critical oncogenes, has a DNA G4 (MycG4) in its proximal promoter region that functions as a transcriptional silencer. MycG4 is very stable and the pathological activation of <i>MYC</i> requires its active unfolding. However, it remains unclear what drives MycG4 unfolding in cancer cells. We have studied the interactions of DDX5 with the MycG4 at both molecular and cellular levels and discovered that DDX5 actively unfolds the MycG4 and is involved in the <i>MYC</i> gene transcriptional regulation, which is described in the first part of this dissertation. DDX5 is extremely proficient at unfolding the MycG4 and ATP hydrolysis is not directly coupled to the G4-unfolding of DDX5. In cancer cells, DDX5 is enriched at the <i>MYC</i> promoter and activates <i>MYC</i> transcription. G4-interactive small molecules inhibit the DDX5 interaction with the <i>MYC</i> promoter and DDX5-mediated <i>MYC</i> activation. The second part of this dissertation describes the study of interactions of indenoisoquinoline anticancer drugs with MycG4. The MycG4 transcriptional silencer is a very attractive therapeutic target. Compounds that bind and stabilize the MycG4 have been shown to repress <i>MYC</i> gene transcription and are antitumorigenic. Indenoisoquinolines are human topoisomerase I inhibitors in clinical testing. However, some indenoisoquinolines with potent anticancer activity do not exhibit strong topoisomerase I inhibition, suggesting a separate mechanism of action. Our studies show that indenoisoquinolines strongly bind and stabilize MycG4 and lower <i>MYC</i> levels in cancer cells. Moreover, the analysis of indenoisoquinoline analogues for their <i>MYC</i> inhibitory activity, topoisomerase I inhibitory activity, and anticancer activity reveals a synergistic effect of <i>MYC</i> inhibition and topoisomerase I inhibition on anticancer activity. Besides the MycG4, human telomeric G4s are also attractive targets for anticancer drugs due to their ability to inhibit telomere extension in cancer cells. The last part of this dissertation reviews two recent solution structural studies on small molecule complexes with the hybrid-2 telomeric G4 and the hybrid-1 telomeric G4. Structural information of those complexes can advance the design of telomeric G4-interactive small molecules in the cancer therapeutic areas.</div>

This PhD research relates to the design, fabrication, characterization, and optimization of on-chip electrochemical microelectrode arrays (MEAs) for measurement of transient concentrations and gradients, focusing on fast transients and physiological applications. In particular, this work presents the determination of kinetic mechanisms taking place at an active interface (either physiological or non-physiological) in contact with a liquid phase using the MEA device to simultaneously estimate the concentration and gradient of the analyte of interest at the surface of the active interface. The design approach of the MEA device and the corresponding measurement methodology to acquire reliable concentration information is discussed. The ability of the MEA device to measure fast (i.e., in sub-second time scale) transient gradients is demonstrated experimentally using a controllable diffusion-reaction system which mimics the consumption of hydrogen peroxide by a 2D cell culture. The proposed MEA device and measurement methodology meet effectively most of the requirements for physiological applications and as a demonstration of this, two physiological applications are presented. In one application, the MEA device was tailored to measure the hydrogen peroxide uptake rate of human astrocytes and glioblastoma multiforme cells in 2D cell culture as a function of hydrogen peroxide concentration at the cell surface; the results allowed to quantitatively determine the uptake kinetics mechanisms which are well-described by linear and Michaelis-Menten expressions, in agreement with the literature. In the other application, further customization of the MEA device was realized to study the glucose uptake kinetics of human bronchial epithelial and small cell lung cancer cells, these latter with and without DDX5 gene knockdown; the results allowed to distinguish mechanistic differences in the glucose uptake kinetics among the three cell lines. These results were complemented with measurements of glycolytic and respiration rates to obtain a bigger picture of the glucose metabolism of the three cell lines. Finally, additional applications, both physiological and non-physiological, are proposed for the developed MEA device.