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PROTEIN TRANSPORT --- BACTERIA

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Transmembrane Transport is an essential process in cellular homeostasis and survival. A variety of transporters are expressed in the plasma membrane, allowing cells to properly regulate the uptake and efflux of a wide range of molecules involved in cell physiology, as well as xenobiotics. Some of those transporters are even able to actively expel drugs like chemotherapeutic agents as well as antibiotics out of the cell, sometimes causing therapeutic failure. In this context, studies made on our laboratory have demonstrated the overexpression of an ATP-bindinb cassette (ABC) protein in a human PMA-activated macrophage model, namely the Breast Cancer Resistance Protein (BCRP). This efflux transporter known to play a key role in multidrug resistance phenotype associated with certain cancers is also able to transport fluoroquinolones such as ciprofloxacin. Since this antibiotic class is commonly used to treat intracellular infections and since their activity is related to their intracellular concentration, we have investigated the potential role of BCRP overexpression on the pharmacokinetics of 5 fluoroquinolones (ciprofloxacin, norfloxacin, moxifloxacin, levofloxacin, and gemifloxacin). First, we measured cellular uptake of fluoroquinolones in unstimulated as well as PMA activated THP-1 cells. The results showed a significant reduction in ciprofloxacin and norfloxacin accumulation in activated cells. Then, in order to point out the potential role of BCRP overexpression, we assessed accumulation of fluoroquinolones using novobiocin as a specific inhibitor of BCRP. These experiments showed an increase in ciprofloxacin and norfloxacin accumulation. This suggested that the decrease in cellular accumulation observed in activated THP-1 for these two fluoroquinolones is related to an active efflux mediated by BCRP Le transport transmembranaire est un processus essentiel au maintien de l’homéostasie et de la survie cellulaire. L’existence de divers transporteurs dans la membrane plasmique permet à ces dernières de réguler l’entrée et la sortie d’une grande variété de molécules jouant un rôle physiologique mais également de xénobiotiques. Certains transporteurs sont d’ailleurs capables d’effluer activement hors de la cellule divers médicaments, parmi lesquels on retrouve des agents chimiothérapeutiques ainsi que certains antibiotiques, rendant parfois la thérapie caduque. Dans ce contexte, des études réalisées au laboratoire ont conduit à la démonstration de la surexpression dans un modèle de macrophages humains activés au PMA d’une protéine appartenant à la superfamille des transporteurs ATP-Binding Cassette (ABC), la Breast Cancer Resitance Protein (BCRP). Ce transporteur d’efflux, reconnu comme jouant un rôle important dans le mécanisme de résistance multidrogue associé à certains cancers, est aussi capable de transporter certaines fluoroquinolones telles que la ciprofloxacine. Comme cette classe d’antibiotiques est couramment utilisée dans le traitement des infections à bactéries intracellulaires et que leur activité est en partie relative à la concentration intracellulaire, nous avons étudié l’éventuel impact de la surexpression de ce transporteur sur la pharmacocinétique de cinq fluoroquinolones (la ciprofloxacine, la norfloxacine, la moxifloxacine, la levofloxacine et la gemifloxacine). Dans un premier temps nous avons mesuré l’accumulation de ces fluoroquinolones dans les cellules THP-1 non stimulées et activées par le PMA.. Les résultats obtenus montrent une diminution de l’accumulation de la ciprofloxacine et la norfloxacine dans les cellules activées par le PMA. Ensuite, afin de mettre en évidence l’éventuel rôle de la surexpression de BCRP consécutive à l’activation par le PMA, un inhibiteur spécifique de BCRP, la novobiocine, a été utilisé lors des tests d’accumulation des fluoroquinolones. Ceci nous a permis de mettre en évidence une augmentation de l’accumulation de la ciprofloxacine et de la norfloxaxcine dans ces conditions. Ceci pourrait s’expliquer par l’implication de BCRP dans un efflux actif de ces molécules hors des cellules activées, contribuant à réduire leuraccumulation

Protein Transport --- Homeostasis --- ABCG2 protein, human --- Novobiocin --- Fluoroquinolones --- Ciprofloxacin --- Norfloxacin

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The C-terminus of the PDGF receptor is known for its inhibiting activity on the activation of the kinase domain. It actually contains an inhibiting PE motif and a NHERF bonding site. NHERF is an adaptor that might act as a tumor suppressor and limit PDGF receptor’s signaling.
The main goal of this work to establish the role of the C-terminus in the regulation of the activation of two chimeric proteins created by the fusion of the PDGFR receptor with other proteins, TEL/PDGFR β and FIO1L1/PDFRE α. These two proteins are involved in leukemia.
To address this issue, we performed a co-immunoprecipitation against NHERF. The experiment shows that TEL/PDGFR β is able to bind NHERF with high affinity. By creating TEL/PDGFR β mutants with a truncated C-terminus, we managed to suppress NHERF binding to the protein. The CT 29 and CT 75 mutants in which the 29 and 75 last amino acids have been deleted did not interact with NHERF. In addition the CT 75 mutants has lost the PE motif. The L1160A mutant has a much lowered affinity towards NHERF.
When trying to characterize the different mutants in terms of proliferation by thymidine incorporation or counting assay, it appears that Ba/F3 cells expressing the CT 75 mutant have much higher ability to proliferate compared to the other mutants or even the original TEL/PDGFR β protein in the absence of IL-3
To try to explain this difference, we performed a signaling assay. It seems that TEL/PDGFR β and all the mutants we have created are able to induce STATs activation when expressed. This pathways is only activated in Ba/F3 cells when stimulated with IL-3. This result has been confirmed by luciferase assay. All the different mutants were able to activate the same signaling pathway. Nevertheless, the CT 75 mutant, again, seemed to give a better activation of the signaling pathway, more particularly in the activation of the MAP kinase pathway. This might explain why cells expressing this mutant have higher proliferation rate than those expressing the other mutants or the original TEL/PDGFR β.
To conclude, TEL/PDGFR β is actually able to bind NHREF. This binding can be altered by truncation of the C-terminal end. It also appears that the C-terminus might play a role in the activation of TEL/PDGFR β; its deletion might give a proliferate advantage due to a better activation of the protein L’extrémité C-terminale du récepteur du PDGF est connue pour son action inhibitrice sur l’activation de la protéine. En effet, elle comporte un motif inhibiteur PE et un motif de liaison à NHERD, une protéine adaptatrice qui pourrait être un suppresseur de tumeurs et qui semble jouer un rôle négatif sur la signalisation du récepteur.
L’objectif principal de ce mémoire était de déterminer le rôle de celle extrémité C-terminale dans la régulation de l’activité de deux protéines chimériques issues de mutations du récepteur de PDGF, TEL/PDGFR β et FIP1L1/PDGFR α. Ces deux protéines sont impliquées dans des leucémies.
Nous avons tout d’abord montré que TEL-/PDGFR β lie NHERF avec une grande affinité. FIP1L1/PDGFR alpha semble capable de lier NHERF mais ces observations doivent être confirmées.
En créant des mutants de TEL/PDGFR β possédant une extrémité C-terminale tronquée, on parvient à diminuer voir même supprimer la liaison à NHERF. Les mutants CT 29 et CT 75, dont les 29 et les 75 derniers acides aminés sont délétés, n’interagissent pas avec NHERF. Le mutant CT75 a, en outre, perdu le motif inhibiteur PE. Le mutant L1160A présente une affinité fortement diminuée pour NHERF.
Lorsque l’on cherche à caractériser les différents mutants en terme de prolifération grâce à une incorporation de thymidine ou à un comptage des cellules, il apparaît que les cellules Ba/F3 exprimant le mutant CT 75 possèdent une plus grande capacité à proliférer que les autres mutants et que la protéine TEL/PDGFR β intacte en absence d’IL-3.
Pour essayer d’expliquer cette différence, nous avons réalisés des tests de signalisation. Il semble aussi que TEL/PDGFR β et ses mutants soient capables d’activer la voie de STAT, voie qui n’est pas activée par le récepteur du PDGF dans les Ba/F3 mais qui est activée lorsqu’elles sont stimulées à l’IL-3. Ce résultat a été confirmée par un test de luciférase. Les mutants sont capables d’activer les mêmes voies de signalisation, plus particulièrement la voie des MAP kinases. Ces données pourraient en partie expliquer l’avantage prolifératif des cellules exprimant ce mutant.
En conclusion, TEL/PDGFR β est capable de lier NHERF, Cette liaison peut être compromise par la troncature de l’extrémité C-terminale de la protéine. Il semblerait également que le motif inhibiteur PE joue un rôle ans l’activation de la protéine TEL/PDGFR β et que sa suppression conférerait un avantage prolifératif

C-terminal binding protein --- Protein Transport --- Platelet-Derived Growth Factor --- TEL-PDGFRbeta fusion protein, human --- ETS translocation variant 6 protein

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In the last few years, significant breakthroughs in transcription research expanded our appreciation for the complexity of molecular controls on gene expression in mammalian cells. In Transcription Factors: Methods and Protocols, experts in the field describe state-of-the-art approaches that investigators can use to probe critical mechanisms underlying transcription factor nuclear-cytoplasmic trafficking as well as to assess the functional impact of post-translational modifications on transcription factor function. The chapters are written by prominent scientists, many of whom developed these methods, and highlight protocols that focus on specific transcription factor family members with particular relevance to human disease. Composed in the highly successful Methods in Molecular Biology™ series format, each chapter contains a brief introduction, step-by-step methods, a list of necessary materials, and a Notes section which shares tips on troubleshooting and avoiding known pitfalls. Comprehensive and current, Transcription Factors: Methods and Protocols compiles the latest techniques for elucidating controls on transcription factor intracellular localization and activity, and consequently is unlike any other methods-based text on transcriptional regulation today. .

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"Intrinsically Disordered Proteins: Dynamics, Binding, and Function thoroughly examines and ties together the fundamental biochemical functions of intrinsically disordered proteins (IDPs) and intrinsically disordered regions (IDRs), including signaling, binding, and regulation, with the methodology for study and the associated pathways for drug design and therapeutic intervention. The role of new mechanistic, computational, and experimental approaches in IDP study are explored in depth, with methods for the characterization of IDP dynamics; models, simulations, and mechanisms of IDP and IDR binding; and biological and medical implications of IDP dynamics prominently featured. Written and edited by leading scientists in the field, this book explores groundbreaking areas such as ensemble descriptions of IDPs and IDRs, single-molecule studies of IDPs and IDRs, IDPs and IDRs in membraneless organelles, and molecular mechanisms of fibrillation of IDPs. Intrinsically Disordered Proteins provides students and researchers in biochemistry, molecular biology, and applied microbiology with a comprehensive and updated discussion of the complex dynamics of IDPs and IDRs."--

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