No description available.

Chemistry / Although molecules that bind DNA have the potential to modify gene expression, the reality of targeting DNA in a sequence-specific manner is still a problematic but worthwhile goal. The Iverson lab has been exploring DNA recognition through a motif known as threading polyintercalation based on connecting intercalating naphthalene diimide (NDI) units, which are molecules that insert themselves between DNA base pairs, together with peptide linkers. These polyintercalators interact with both DNA grooves by “threading” or winding through the DNA, like a snake might climb a ladder. Initially, two different bisintercalator modules with altered sequence specificities and different groove binding topologies were discovered and used to inspire the design of a hybrid NDI tetraintercalator. Surprisingly enough, this tetraintercalator bound sequence-specifically with a dissociation half-life of 16 days to its preferred 14 bp site, a record at the time it was reported for a synthetic DNA-binding molecule. The work reported here expands on the capabilities of this modular threading polyintercalation motif. Chapter 2 describes the ability of a new hybrid NDI tetraintercalator, where the bisintercalator modules are connected together in a different way compared to the previously studied tetraintercalator, to subtly discriminate between similar binding sites. Chapter 3 offers a structural understanding, through NMR analysis, for the sequence recognition abilities of this new tetraintercalator. Chapter 4 analyzes the binding abilities of an un-optimized NDI octaintercalator and proposes how to approach the second-generation design of longer polyintercalators. Chapter 5 describes the optimization of the originally designed NDI tetraintercalator by serially lengthening one of the linkers to produce a tetraintercalator with a 57 day dissociation half-life from its 14 bp sequence, a new record for a synthetic DNA-binding molecule. Using the optimized linker in the context of an NDI hexaintercalator allows for binding to a 22 bp designed site, a record for a synthetic non-nucleic acid molecule. Chapter 6 recounts a focused library screening to search for bisintercalators with new sequence specificities. These efforts have laid the groundwork to progress toward studies aimed at understanding how these molecules might function to prevent transcription in a sequence-dependent manner in vivo. / text

INTRODUÇÃO: A síndrome de Sjögren primária (SSp) é uma doença autoimune inflamatória crônica que afeta principalmente as glândulas exócrinas, levando aos sintomas de síndrome sicca. O olho seco é uma das características mais importantes dessa síndrome e um estudo recente relatou redução da atividade da DNase I em lágrimas de pacientes com olho seco de várias etiologias. Portanto, postulamos que pacientes com SSp possam ter anticorpos direcionados à DNase I. MÉTODOS: Avaliamos em um estudo de corte transversal 85 pacientes com SSp (conforme os critérios de classificação do American European Consensus Group Criteria, 2002), 50 pacientes com artrite reumatoide (AR) (American College of Rheumatology Criteria/ 1987) sem sintomas de síndrome sicca e 88 voluntários saudáveis. A reatividade IgG anti-DNase I foi detectada por ELISA utilizando a enzima de pâncreas bovino como antígeno e confirmada por Imunoblotting. RESULTADOS: A idade e sexo foram comparáveis nos três grupos (p > 0,05). A anti-DNase I foi detectada em 43,5% dos pacientes com SSp, conforme determinado por ELISA. Em contraste, essa reatividade estava ausente em todos os pacientes com AR (p= 0,0001). Comparações adicionais dos pacientes com SSp com (n= 37) e sem (n= 48) anti-DNase I revelaram que o primeiro grupo tinha níveis séricos de IgG mais altos (2293,2 ± 666,2 vs. 1483,9 ± 384,6 mg/dL, p= 0,0001) e uma frequência maior de leucopenia não induzida por drogas (43% vs. 19%, p= 0,02). A análise de regressão logística multivariada mostrou que apenas os níveis de IgG foram independentemente associados com o anti-DNase I. CONCLUSÃO: Descrevemos uma alta frequência de anticorpos anti-DNase I em pacientes com SSp associados a níveis séricos de IgG mais elevados. A falta dessa reatividade em pacientes com AR sem sintomas de sicca sugere que esse anticorpo pode ser útil no diagnóstico diferencial dessas doenças / INTRODUCTION: Primary Sjögren\'s syndrome (pSS) is a chronic inflammatory autoimmune disease that mainly affects exocrine glands. Dry eye is one of the most important features of this syndrome and a recent study reported reduced DNase I activity in tears of patients with dry eye of various etiologies. We therefore postulated that patients with pSS may have antibodies targeting DNase I. METHODS: We have evaluated in a cross-sectional study 85 pSS patients (American European Consensus Group Criteria/ 2002), 50 rheumatoid arthritis (RA) patients (American College of Rheumatology Criteria/ 1987) without sicca symptoms and 88 healthy volunteers. The IgG anti-DNase I reactivity was detected by ELISA using bovine pancreas enzyme as antigen and confirmed by Immunoblotting. RESULTS: Age/ gender were comparable in the three groups (p > 0.05). Anti-DNase I was detected in 43.5% of the pSS patients as determined by ELISA. In contrast, this reactivity was absent in all RA patients (p= 0.0001). Further comparison of pSS patients with (n= 37) and without (n= 48) anti-DNase I revealed that the former group had higher IgG serum levels (2293.2 ± 666.2 vs. 1483.9 ± 384.6 mg/dL, p= 0.0001) and a higher frequency of non-drug induced leukopenia (43% vs. 19%, p= 0.02). A multivariate logistic regression analysis identified that only IgG levels were independently associated with anti-DNase I. CONCLUSION: We describe a high frequency of anti-DNase I antibodies in pSS patients associated with higher serum IgG levels. The lack of this reactivity in RA patients without sicca symptoms suggests that this antibody may be helpful in the differential diagnosis of these diseases

Sepsis is defined as a life-threatening organ dysfunction that results in systemic activation of coagulation and inflammation in response to microbial infection. Neutrophil extracellular traps (NETs) have shown to be an important interface between innate immunity and coagulation in sepsis. The major structural components of NETs are nucleosomes (DNA-histone complexes). Although nucleosomes do not modulate coagulation, there are conditions where DNA and histones dissociate from each other in the circulation (e.g. in the presence of heparan sulfate or therapeutic heparin binding histones, or DNase digestion of DNA). In vitro, purified DNA was reported to activate coagulation, but this procoagulant activity has been questioned due to isolation methods that yield DNA that is contaminated with other procoagulant molecules. On the other hand, histones have been shown to not only activate coagulation but are cytotoxic to endothelial cells. However, their contribution to the pathogenesis of sepsis has yet to be determined in an in vivo model. Understanding the contribution of DNA, histones, and nucleosomes to the pathogenesis of sepsis may allow us to develop novel therapies that may prove targeting multiple components of NETs (i.e. DNA and histones) may be beneficial. Consequently, in this thesis, we (1) identified methods of DNA purification that produce DNA that is free of contamination and confirmed the procoagulant properties of the isolated DNA, (2) determined the harmful effects of DNA, histones, and nucleosomes cytotoxicity, coagulation, and inflammation in vitro and in vivo, (3) and then we explored the possibility of targeting both DNA and histones using a combination approach of DNase I and heparin in a mouse model of sepsis. Since heparin is administered to patients as a thromboprophylaxis and DNase I is a potential therapy in sepsis, it is important to understand any potential drug-drug interactions. / Thesis / Doctor of Philosophy (PhD) / Sepsis is a type of blood poisoning that occurs when the body has an over reactive response to an infection. This can lead to tissue damage, organ failure, and death. Sepsis is recognized as a global health priority. The death rate from sepsis is high between 15% to 30%, suggesting that an improved understanding of how sepsis leads to death may develop into new therapies. Recently, it was discovered that high levels of free-floating DNA and histones in the blood can predict death in sepsis. The DNA and histones are likely released by white blood cells in response to trying to fight off the infection. In test tubes, free-floating DNA can trigger clotting of blood. DNA often exists in blood together with histones. In test tubes, histones can kill blood vessels and make blood thicker. However, no one has confirmed that DNA and/or histones are harmful to mammals and contributes to death in sepsis. Some new studies show that getting rid of DNA with injections of DNase I minimally increases survival in mice. Other studies show that removing histones with a treatment called heparin shows a small increase in survival in mice. Heparin is also a blood thinner and decreases inflammation. No one knows if these drugs used together can improve sepsis survival. Because both drugs on their own show some survival improvement in sepsis, perhaps using them together will cure sepsis. This thesis has three objectives: (1) to confirm the clotting properties of free-floating DNA, (2) to find out if DNA and/or histones contributes to death in sepsis, and (3) if using a combination of DNase I and heparin can cure sepsis in a mouse model. Finding new therapies for sepsis can save millions of people's lives and decrease the financial burden on society and healthcare systems.

Neutrophil extracellular traps (NETs) are a link between infection and coagulation in sepsis. The major structural component of NETs is nucleosomes, consisting of DNA and histones. NETs not only act as a scaffold to trap platelets, but NET components also promote coagulation and impair fibrinolysis. Thus, removal of extracellular DNA by DNases may be a potential therapeutic strategy for sepsis. Since heparin is used for thromboprophylaxis in sepsis and may also be a potential anti-sepsis therapy, we investigated the mechanisms by which various forms of heparins modulate DNase function. There are two types of DNases in vivo: DNase I (produced by exocrine and endocrine glands) and DNase1L3 (secreted by immune cells). DNase I cleaves free DNA, whereas DNase1L3 preferentially cleaves DNA in complex with proteins such as histones. In this study, we investigated how DNase I and DNase1L3 activities are modulated by the following heparins: unfractionated heparin (UFH), enoxaparin (a low-molecular-weight heparin), Vasoflux (a low-molecular-weight, non-anticoagulant heparin), and fondaparinux (the pentasaccharide unit). Using agarose gel experiments, we showed that UFH, enoxaparin, and Vasoflux enhance the ability of DNase I to digest DNA-histone complexes (presumably by displacing DNA from histones), whereas fondaparinux does not. These findings are consistent with the KD values of the binding of heparin variants to histones, with fondaparinux having >1000-fold lower affinity for histones compared to the other heparins. Taken together, our data suggests that the ability of heparin to enhance DNase I-mediated digestion of DNA-histone complexes is size-dependent and independent of the pentasaccharide region of heparin. With respect to DNase1L3, we observed that it is able to digest histone-bound DNA, and that all heparins, except fondaparinux, inhibited DNase1L3-mediated digestion of histone-bound DNA. Next, we visualized the degradation of NETs by fluorescence microscopy. DNase I (± heparin variants) completely degraded NETs, presumably by digesting extracellular chromatin at histone-free linker regions, thereby releasing nucleosome units. DNase1L3 also degraded NETs, but not as effectively as DNase I, and was inhibited by all heparins except fondaparinux. Finally, we showed that DNase I levels are decreased and DNase1L3 levels are elevated in septic patients. Taken together, our findings demonstrate that heparin modulates the function of DNases, and that endogenous DNase levels are altered in sepsis pathophysiology. / Thesis / Master of Science (MSc) / Sepsis, a life-threatening condition due to hyperactivation of the immune system in response to infection, results in widespread inflammation and blood clotting. During sepsis, immune cells release sticky strands of DNA that block blood vessels and damage organs. Two different enzymes in the blood (DNase I and DNase1L3) can digest these DNA strands, and may represent a new class of anti-sepsis drugs. Our goal was to determine how heparins, commonly used blood thinners, alter the function of these enzymes. We found that (a) larger-sized heparins improved the activity of DNase I towards DNA-histone complexes and do not require any specific portion of heparin, (b) DNase I is more efficient than DNase1L3 in digesting DNA strands released from immune cells, and (c) levels of DNase I and DNase1L3 are altered in septic patients. Taken together, our studies provide new insights into how these enzymes function.

Les patients mucoviscidosiques sont prédisposés à une colonisation chronique de l’arbre bronchique par P. aeruginosa. Ce pathogène opportuniste se caractérise par sa capacité à adhérer à une surface et à y former un biofilm protecteur, hautement tolérant aux agents antimicrobiens. En routine, les antibiogrammes sont effectués sur des cultures bactériennes planctoniques. L’efficacité des antibiothérapies ainsi sélectionnées est donc peu probante pour l’éradication des biofilms bactériens. La réalisation d’Antibiofilmogrammes® sur des isolats cliniques mucoviscidosiques (nouvel outil évaluant la sensibilité des bactéries sessiles aux antibiotiques) a permis de mettre en évidence des phénomènes d’inhibition et d’induction de la formation du biofilm. Plus précisément, les aminosides sont capables de retarder l’adhérence bactérienne. À l’inverse, la famille des β-lactamines présente la capacité de stimuler l’adhésion précoce des micro-organismes. Ces différents effets de l’antibiothérapie générale sur le comportement microbien se vérifient par l’intermédiaire de techniques conventionnelles in vitro (Cristal Violet, traitement enzymatique à la DNase I) et cellulaires (modèle de co-culture statique cellules eucaryotes/bactéries). La pertinence clinique de l’Antibiofilmogramme® se confirme donc par sa capacité à détecter l’initiation précoce de l’adhésion bactérienne, à sélectionner les molécules l’inhibant et à écarter celles pouvant l’induire. Associée aux antibiogrammes traditionnels, son application peu permettre d’affiner les stratégies thérapeutiques pour le traitement des infections pulmonaires chroniques développées au cours de la mucoviscidose. / Cystic fibrosis (CF) patients are predisposed to chronic colonisation of the upper airways by P. aeruginosa. This opportunist pathogen is characterized by its ability to adhere to a surface and to form a protective biofilm, which is highly tolerant to antimicrobials. In routine, antibiograms are realised on planktonic bacterial cultures. The efficacy of the corresponding antimicrobial therapies appears low for the eradication of bacterial biofilms. The realisation of Antibiofilmograms® on CF clinical isolates (a new tool investigating the susceptibility of sessile bacteria to antibiotics) highlighted phenomena of biofilm formation inhibition and induction. More precisely, aminoglycosides are able to delay the bacterial adherence. Conversely, the β-lactam family shows the ability to stimulate the early adhesion of microorganisms. These different effects of antimicrobials on the bacterial behaviour are confirmed with more conventional in vitro methods (Crystal Violet, enzymatic treatment with DNase I) and a cell model (static co-culture of eukaryotic cells and bacteria). The clinical relevance of the Antibiofilmogram® is reinforced by its ability to detect the initiation of the early bacterial adhesion, to select inhibitor molecules and to avoid the inducer ones. Associated to traditional antibiograms, its application should be pertinent to optimise the CF therapies for the treatment of chronic lung infections.

Pathogenesis of enterotoxigenic Escherichia coli (ETEC) and Shigella flexneri relies predominantly on members of the AraC/XylS family of transcriptional regulators, Rns (or its homolog, CfaD) and MxiE, respectively. Rns/CfaD regulate the expression of pili, which allow the bacteria to attach to the intestinal epithelium. Better understanding of the role Rns plays in virulence was attained by expanding our knowledge of the Rns regulon, revealing that it functions as an activator of cexE, a previously uncharacterized gene. By in vitro DNase I footprinting two Rns-binding sites were identified upstream of cexEp, both of which are required for full activation of cexE. The amino terminus of CexE also contains a secretory signal peptide that is removed during translocation to the periplasm. Though the function of CexE remains unknown, these studies suggest that CexE is a novel ETEC virulence factor since it is regulated by Rns/CfaD. In Shigella flexneri, the expression of a subset of virulence genes (including, ipaH9.8 and ospE2) is dependent upon the activator MxiE and a cytoplasmic chaperone IpgC. To define the molecular mechanism of transcriptional activation by this chaperone-activator pair, an in vitro pull down assay was performed revealing that MxiE specifically interacts with IpgC in a complex. Additionally, IpgC recognizes three polypeptide regions in MxiE: within MxiE(1-46), MxiE(46-110) and MxiE(196-216). Furthermore, it seems that MxiE and IpgC regulate transcription of ipaH9.8 and ospE2 promoters differently. In the bacterium, the formation of the MxiE-IpgC complex is initially prevented because IpgC is sequestered in individual complexes with effector proteins, IpaB and IpaC. Upon contact with an eukaryotic host cell the effector proteins are secreted, thereby freeing IpgC to form a complex with MxiE and activate the expression of virulence genes. This new characterization of the role of Rns and MxiE in virulence gene regulation in ETEC and S. flexneri, respectively will give new insights into the pathogenesis of the regulators.

Le Virus de l'Hépatite B (VHB) infecte 350 millions d'individus à l'échelle mondiale. Il est responsable d'hépatites aigües pouvant évoluer vers la chronicité puis le carcinome hépatocellulaire. Le génome du VHB est constitué d'un ADN partiellement bicaténaire. De par sa nature, il pourrait être sensible à l'action de certaines nucléases cellulaires qui hydrolysent l'ADN double brin. Nous avons ainsi mis en évidence la capacité de la Désoxyribonuclase I (DNase I) à être incorporée dans les virions du VHB, ce qui permet la dégradation du génome viral et la diminution de son infectivité. La DNAse I est particulièrement surexprimée en hypoxie et pourrait contribuer à l'élimination du virus chez les individus cirrhotiques. Par ailleurs, nous avons montré que la cytidine désaminase APOBEC3DE appartenant à une famille de facteurs de restriction viraux possède un rôle proviral. En effet, son association avec APOBEC3F et APOBEC3G mène à une diminution de l'activité de ces dernières et ceci favorise la réplication du VHB. La formation d'hétérodimères APOBEC3DE/APOBEC3F et APOBEC3DE/APOBEC3G semble génèrer un encombrement stérique ne permettant pas l'encaspidation d'APOBEC3F et APOBEC3G, raison pour laquelle le génome du VHB est moins muté lorsqu'APOBEC3DE est exprimée. / Hepatitis B Virus (HBV) infects 350 millions people worldwilde. It triggers accute hepatitis that can turn into cirrhosis then hepatocellular carcinoma. HBV genome is composed of a partially double-stranded DNA.Thus, it could be targeted by some cellular nucleases that hydrolyze double-stranded DNA. We have highlighted that Deoxyribunuclease I (DNase I) can be incorporated into HBV virions and degrade its genome, leading to a loss of viral infectivity. Moreover, DNase I is upregulated under hypoxia which is a caracteristic of liver cirrhosis. DNase I could be involved in HBV elimination in cirrhotic patients. In an other study, we found that APOBECDE, a cytidine deaminase of the same family than some restriction factors, has a proviral activity. Indeed, association of APOBEC3DE with APOBEC3F or APOBEC3G leads to a loss of cytidine deaminase activity and a better viral replication. When APOBEC3DE is associated with those two proteins, APOBEC3F and APOBEC3G cannot be incorporated into HBV virions. This is the reason why HBV is more infectious when APOBEC3DE is expressed.

Glycogen phosphorylase 2 (gp-2) is a key enzyme during the development of Dictyostelium discoideum. The gp-2 enzyme breaks down glycogen into glucose monomers that are subsequently used to synthesize the terminal end products of cellular differentiation. This gene is an ideal candidate for studying the process of selective gene expression because its product figures so prominently in the development of this organism, implying a dependable control mechanism responsible for its developmentally regulated expression. I present in this thesis the identification of several putative cis-acting elements of gp-2 as revealed through footprint analysis. Due to the extreme AT-bias characteristic of Dictyostelium promoters, footprinting conditions required intensive optimization with respect to template, nonspecific competitor, source of protein extract and DNase I digestion. Using an endlabeled fragment containing seven repeated sequences (3 TA boxes [TAATTATA], 2 TAG boxes [TAAAAATGGT] and 2 C boxes [ACCCACT]), purified replication protein A and several developmental nuclear extracts were tested for DNA binding activity. Small footprints were observed on the TAG and C boxes of the promoter for both protein sources. However, using a more sensitive footprinting strategy involving multiple rounds of primer extension, larger footprints spanning the same promoter regions were detected. In both cases, the appearance of the footprints coincided with the documented transcriptional activity of the gene. It can be concluded from the data obtained that the TAG and C boxes are very likely cis-acting elements involved in the regulation of gp-2 expression. / Master of Science