O Trypanosoma brucei é o agente etiológico da Tripanossomíase Africana Humana. Este protozoário é um parasita extracelular que possui um único flagelo e um citoesqueleto de alta estabilidade, responsável por vários processos celulares como motilidade, morfologia, infectividade e divisão celular. Em todos os gêneros da família Trypanosomatidae foram descritas proteínas de alto peso molecular (500-3500 kDa) as quais, além do papel estrutural, podem estar envolvidas na organização e regulação do citoesqueleto e seus constituintes. Este projeto teve como objetivo caracterizar no âmbito celular, bioquímico e molecular as proteínas gigantes de T. brucei e determinar os seus papéis funcionais na biologia do parasito. A partir do isolamento do citoesqueleto de T. brucei e análise por SDS-PAGE, produzimos anticorpos contra as proteínas gigantes que serviu como ferramenta para realização de Western Blotting (WB) e imunofluorescência no estudo das propriedades moleculares destas proteínas. O sequenciamento por espectrometria de massas foi utilizado para determinação da sequência primária parcial destas proteínas e identificação dos genes em no banco de dados TriTrypDB. Aqui, mostramos que as proteínas de alta massa molecular se localizam em estruturas essenciais para a regulação do citoesqueleto como na zona de adesão flagelar (FAZ), bem como no complexo tripartido responsável pela adesão do flagelo ao cinetoplasto. A espectrometria de massas revelou 19 novas proteínas de alta massa molecular ainda não estudadas em T. brucei dentre as quais 2 foram caracterizadas funcionalmente: FAZ10 e Tb927.8.3540. Para investigar os seus papeis biológicos utilizamos o modelo de silenciamento gênico por RNA de interferência. O silenciamento da proteína FAZ10 levou ao destacamento do flagelo, ao reposicionamento incorreto dos núcleos e cinetoplastos, e mais importante ao erro na definição do local de ingressão do sulco de clivagem durante a citocinese, em formas procíclicas e sanguícolas de T. brucei. Por sua vez, a proteína Tb927.8.3540 é responsável pela estabilização do citoesqueleto de microtúbulos e formação do FAZ e flagelo. Quando ausente nas células, estas adquirem um formato esférico com a presença de um flagelo internalizado. Em ambos os casos, as células induzidas apresentam inibição da proliferação celular e o acúmulo de células multinucleadas na cultura. O estudo funcional das proteínas gigantes revelou que elas possuem um papel central na morfogênese do T. brucei, agindo diretamente na organização e formação de estruturas do citoesqueleto, na manutenção da adesão flagelar, e no direcionamento da citocinese. / Trypanosoma brucei, the causative agent of sleeping sickness or Human African Trypanosomiasis (HAT), has been used as experimental model for cellular, biochemical and molecular studies. This is an extracellular protozoan parasite that has a single flagellum and a highly stable cytoskeleton, responsible for many cellular processes such as motility, morphology, infectivity and cell division. In Trypanosomatidae family, a novel class of High Molecular Weight Proteins (HMWPs; 500-3500 kDa) has been described, which besides their structural role, may play a role in cytoskeleton organization and regulation. Trypanosomatids cytoskeletons contain abundant HMWPs, but many of their biological functions are still unclear. Here, we aimed to describe the cellular and molecular properties of these proteins, and to determine their functional roles in the parasite biology. SDS-PAGE was used to analyze T. brucei cytoskeletons. Also, the HMWP bands were injected in mouse in order to produce polyclonal antibodies, which were used as a molecular tool in Western Blotting (WB) and immunofluorescence analysis. Here we show that the high molecular weight proteins are located on essential structures for the regulation of the cytoskeleton such as the flagellar adhesion zone (FAZ) and the tripartite complex, which connects the flagellum to the kinetoplast. Detergent-extracted cytoskeletons were also analyzed by gradient SDS-PAGE and the HMWP bands were sent to mass spectrometry analysis. We able to identify 19 new high molecular weight proteins most of which are uncharacterized so far in T. brucei. Here, we report the characterization of two giant proteins: FAZ10 and Tb927.8.3540. To investigate their biological roles we used a model of gene silencing by RNA interference (RNAi). Our data showed that FAZ10 is an essential giant cytoskeletal protein in both procyclic and bloodstream parasite life cycle stages, since its depletion led to defects in cell morphogenesis, flagellum attachment and kinetoplast and nucleus positioning. More importantly, ablation of FAZ10 impaired the timing and placement of the cleavage furrow during cytokinesis, resulting in premature or asymmetrical cell division. In turn, the Tb927.8.3540 protein is responsible for the stabilization and regulation of the microtubule cytoskeleton as well as the flagellum and FAZ. In its absence, cells acquire a spherical shape together with an internalized flagellum. In both cases, the resulting phenotype results in inhibition of cell proliferation and accumulation of multinucleated cells in culture. The functional study of the giant proteins revealed that they have a central role in morphogenesis of T. brucei, acting directly on the organization and regulation of cytoskeletal structures, such as the flagellum and the FAZ.

<i>Legionella pneumophila,</i> the etiological agent of Legionnaires’ disease, replicates intracellularly in protozoan and human hosts. Successful colonization and replication of this pathogen in host cells requires the Dot/Icm type IVB secretion system, which translocates over 330 effector proteins into the host cell to modulate various cellular processes. In this study, we identified RavK (Lpg0969) as a Dot/Icm substrate that targets the host cytoskeleton and reduces actin filament abundance in mammalian cells upon ectopic expression. RavK harbors an H₉₅E_XXH₉₉ (x, any amino acid) motif associated with diverse metalloproteases, which is essential for the inhibition of yeast growth and for the induction of cell rounding in HEK293T cells. We demonstrate that the actin is the cellular target of RavK and that this effector cleaves actin at a site between residues Thr351 and Phe352. Importantly, RavK-mediated actin cleavage occurs during <i>L. pneumophila </i>infection. Cleavage by RavK abolishes the ability of actin to form polymers. Furthermore, an F352A mutation renders actin resistant to RavK-mediated cleavage; expression of the mutant in mammalian cells suppresses the cell rounding phenotype caused by RavK, further establishing that actin is the physiological substrate of RavK. Thus, <i>L. pneumophila</i> exploits components of the host cytoskeleton by multiple effectors with distinct mechanisms, highlighting the importance of modulating cellular processes governed by the actin cytoskeleton in the intracellular life cycle of this pathogen.

A moesina, uma das proteínas do complexo ERM (ezrina, radixina e moesina), está envolvida nos processos de migração e invasão tumoral, participando da dinâmica do citoesqueleto na movimentação celular associada à ativação da GTPase Rho-A. O objetivo desse estudo foi avaliar a correlação da imunoexpressão da moesina e da Rho-A em tumores odontogênicos benignos, diagnosticados no Serviço de Anatomia Patológica da Faculdade de Odontologia de Bauru (USP), no período de 1963 a 2009. Um total de 45 tumores odontogênicos benignos incluindo 7 ameloblastomas, 8 tumores odontogênicos adenomatóides, 19 tumores odontogênicos queratocísticos, 2 cistos odontogênicos ortoqueratinizantes, 1 tumor odontogênico epitelial calcificante, 2 fibromas ameloblásticos, 4 fiboodontomas ameloblásticos e 2 tumores odontogênicos císticos calcificantes, foram avaliados quanto a expressão imunohistoquímica da moesina e da Rho-A pelas células odontogênicas. A correlação entre as expressões membranosa e citoplasmática da moesina e da Rho-A pelo epitélio odontogênico nos diferentes tumores foi avaliada pelo teste de correlação de Spearman, com nível de significância de 5%. Os resultados mostraram uma forte expressão membranosa de moesina e citoplasmática de Rho-A em 66,7% e 62,2% dos tumores odontogênicos benignos, respectivamente. Houve uma correlação positiva e estatisticamente significativa entre a expressão membranosa e citoplasmática da moesina (&#x3C1;=0,000) e de Rho-A (&#x3C1;=0,048) nos tumores. Entretanto, não houve correlação entre as expressões demoesina e de Rho-A nos tumores odontogênicos benignos. Estes resultados comprovam que a moesina e a Rho-A são fortemente expressas pelo epitélio odontogênico neoplásico e, sugerem que ambas proteínas provavelmente participamdo crescimento e expansão local destes tumores odontogênicos benignos. / The moesin, one of the proteins of the ERM complex (ezrin, radixin and moesin), is involved in the migration and tumor invasion processes participating in the cytoskeleton dynamics in cell movement associated with the activation of the GTPase Rho-A. The aim of this study was to evaluate the immunoexpression orrelation of moesin and Rho-A in benign odontogenic tumors, diagnosed at the Bauru School of Dentistry Oral Pathology Biopsy Service of the University of São Paulo in the period of 1963-2009. A total of 45 benign odontogenic tumors including 7 ameloblastomas, 8 adenomatoid odontogenic tumors, 19 keratocystic odontogenic tumors, 2 orthokeratinized odontogenic cyst, 1 calcifying epithelial odontogenic tumor, 2 ameloblastic fibroma, 4 ameloblastic fibroodontoma and 2 calcifying cystic odontogenic tumors, were evaluated for immunohistochemical expression of moesin and Rho-A by odontogenic cells. The correlation between the membranous and cytoplasmic expression of moesin and Rho-A by the odontogenic epithelium in different tumors was evaluated by the Spearman correlation test, with a significance level of 5%. The results showed strong membranous expression of moesin and cytoplasmic expression of Rho-A in 66.7% and 62.2% of the benign odontogenic tumors, respectively. There was a positive and statistically significant correlation between membranous and cytoplasmic expression of moesin (&#x3C1;=0.000) and Rho-A (&#x3C1;=0.048) in the tumors. However, there was no correlation between the expression of moesin and Rho-A in benign odontogenic tumors. These results show that the moesin and Rho-A are strongly expressed by neoplastic odontogenic epithelium and suggest that both proteins probably participate in the growth and local expansion of these benign odontogenic tumors.

Actin isoform specific mutations have been identified as causes for various human diseases. These include twelve missense mutations in γ-nonmuscle actin leading to early onset autosomal dominate nonsyndromic hearing loss and twenty two missense mutations in α-smooth muscle actin leading to thoracic aortic aneurysms and dissections (TAAD). The molecular mechanisms leading to these human pathologies are mainly unknown, principally due to the inability to isolate pure mutant γ-nonmuscle actin and α-smooth muscle actin in quantities required for biochemical analysis. To begin to address these problems, I have individually expressed the human nonmuscle actin isoforms, β– and γ– nonmuscle actin, in a baculovirus expression system and characterized their biochemical properties. Surprisingly, despite a conserved amino acid difference of only 4 residues at or near the N-terminus, Ca-γ-actin exhibits slower monomeric and filamentous biochemical properties than β-actin. In the Mg-form, the difference between the two is smaller. Mixing experiments with Ca-actins reveal the two will readily co-polymerize. Calcium bound in the high affinity binding site of γ-actin may cause a selective energy barrier relative to β-actin that retards the equilibration between G– and F-monomer conformations resulting in a slower polymerizing actin with greater filament stability. This difference may be particularly important in sites such as the γ-actin-rich cochlear hair cell stereocilium where local mM calcium concentrations may exist. In hair cells γ-nonmuscle actin seems to play a central role in stereocilia maintenance. To determine how the deafness causing D51N-γ-mutant actin mutation leads to deafness, I expressed and characterized it in the γ-actin background. The D51N mutation, lethal when cloned into yeast, displayed decreased filament stability and polymerization kinetics of an actin more dynamic than γ-actin. This result suggests that the hearing effects of the γ-actin mutations on the hearing apparatus are not simply caused by an inability to polymerize. The observed increased polymerization rates and decreased filament stability may have major implications for the human disease, as the mutation may alter the ability of the γ-actin to fulfill its maintenance functions. To address the basis by which TAAD mutations cause vascular dysfunction I introduced two of the know human mutations, N115T and R116Q, into yeast actin, 86% identical to human α-smooth muscle actin. I then generated yeast strains expressing each of these mutations as the sole actin in the cell to assess their effect on actin function in vivo and in vitro. Both mutant strains exhibited reduced ability to grow under a variety of stress conditions, although the N115T cells were more severely affected. In vitro the mutations caused exhibited altered thermostability and nucleotide exchange rates indicating effects on monomer conformation with R116Q the most severely affected. The N115T actin demonstrated a biphasic elongation phase during polymerization, while R116Q actin demonstrated a markedly extended nucleation phase. Allele-specific effects were also seen on critical concentration, rate of depolymerization and filament treadmilling. R116Q filaments were hypersensitive to severing by the actin-binding protein cofilin. In contrast, N115T filaments were hyposensitive to cofilin, despite near normal binding affinities of actin for cofilin. The mutant specific effects on actin behavior suggest that individual mechanisms may contribute to TAAD. Understanding the mechanisms of actin dependent human diseases requires elucidation of the effects of the mutations on the behavior of actin per se, its regulation, and the impact on actin mediated processes within the cell. The work provided in this thesis and future studies will provide the information required to understand the pathways involved in these diseases and form innovative treatments for deafness and TAAD.

Prostaglandins (PGs) are small, lipid signaling molecules produced downstream of cyclooxygenase (COX) enzymes. PG signaling regulates many processes including pain, inflammation, fertility, cardiovascular function and disease, and cancer. One mechanism by which PG signaling exerts its function is by regulating the dynamics of the actin cytoskeleton; however, the exact mechanisms remain largely undefined. Drosophila oogenesis provides an ideal system to determine how PG signaling regulates the actin cytoskeleton. Drosophila follicles, or eggs, pass through 14 well- characterized, morphologically defined stages of development. Each developing follicle is comprised of 16 interconnected germline-derived cells (15 nurse cells and 1 oocyte) that are surrounded by a layer of somatically derived epithelial cells. During Stage 10B (S10B), the nurse cells form a cage-like network of parallel actin filament bundles that extend from the nurse cell membranes inward, toward the nurse cell nuclei. During Stage 11 (S11), the nurse cells rapidly transfer their cytoplasmic contents into the oocyte in an actomysoin-dependent contraction termed nurse cell dumping. Previous work uncovered that the Drosophila COX-like enzyme, Peroxinectin-like (Pxt), and thus PG signaling, is required to promote both actin filament bundle formation during S10B and subsequent nurse cell dumping. This finding established Drosophila oogenesis as a genetically tractable model in which to elucidate the conserved mechanisms underlying PG- dependent actin remodeling. The research presented in this dissertation focused on identifying actin-binding proteins that are regulated by PG signaling during Drosophila oogenesis. To identify these downstream effectors, we performed a dominant modifier screen to uncover factors that could suppress or enhance the ability of COX inhibitors to block nurse cell dumping in vitro. This screen revealed a number of actin-binding proteins that enhance the dumping defects caused by COX-inhibition, including the actin bundling protein, Fascin (Drosophila Singed, Sn); the actin filament elongation factor, Enabled (Ena); and the actin filament capper, Capping protein (Drosophila Capping protein alpha, Cpa, and beta, Cpb). Through a collaborative effort between Christopher Groen and myself, Fascin was shown to mediate PG-dependent cortical actin integrity and actin bundle formation during Drosophila ooogenesis. Ena and Capping protein regulate actin filament elongation through opposing actions: Ena promotes their elongation, while Capping protein binds to, or caps, the growing end of actin filaments to prevent their further elongation. However, genetic reduction of either Ena or Capping protein enhance the nurse cell dumping defects caused by COX inhibition. These findings suggest that Ena activity must be balanced to promote proper actin remodeling during S10B. Ena localization to the growing ends of actin filament bundles is reduced in pxt mutants during S10B, suggesting that PG signaling is required to promote Ena localization at this stage. Together, these data support a model in which PG signaling promotes actin remodeling during S10B, at least in part, by modulating Ena-dependent actin remodeling. While PG signaling promotes parallel actin filament bundle formation during S10B, PGs also restrict actin remodeling during Stage 9 (S9). Loss of Pxt results in early actin remodeling, including the formation of extensive actin filaments and actin aggregate structures within the posterior nurse cells of S9 follicles. Wild-type follicles exhibit similar structures at a low frequency. Ena preferentially localizes to the early actin structures observed in pxt mutants and reduced Ena levels strongly suppress early actin remodeling in pxt mutants. These data indicate that PG signaling temporally restricts actin remodeling during Drosophila oogenesis, at least in part, through negative regulation of Ena localization or activity during S9. The data presented here support a model in which PG signaling coordinates the concerted activity of a number of actin-binding proteins to regulate actin remodeling during Drosophila oogenesis. Specifically, PG signaling temporally restricts actin remodeling during S9 of Drosophila oogenesis, but promotes parallel actin filament bundle formation during S10B. PG signaling achieves this temporal regulation, at least in part, through differential regulation of Ena-dependent actin remodeling. Based on prior pharmacologic studies, we hypothesize that PGE2 is required to restrict Ena-dependent actin remodeling during S9, while PGF2Α; is required to promote Ena-dependent actin remodeling during S10B. Determining how these signaling cascades achieve differential regulation of Ena throughout Drosophila oogenesis is an important area for future investigation. As both the actin cytoskeletal machinery and PG signaling are conserved across species, the data presented here provide new and significant insights into the likely conserved mechanisms by which PG signaling regulates actin remodeling across species.

Curcumin is the yellow pigment found in the Indian spice curry. It has anti-inflammatory, ant-oxidant, anti-cancer, anti-viral, anti-bacterial and wound healing properties. It is widely used in industry for its flavor as a spice and as a coloring agent because of its brilliant yellow color. It is also used as a dye for textiles and as an additive to cosmetics. Dendritic cells (DCs) are the sentinels of the immune system and functions as the bridge between the innate and adaptive immune response. The effect of curcumin on DCs is poorly understood. A study shows curcumin prevents the immuno-stimulatory function of bone marrow-derived murine DCs, but no study examines the effects on human DCs. This study investigates the effects of curcumin on immature human DC maturation and function in response to immune stimulants lipopolysaccharide (LPS) and polyinosinic-polycytidylic acid (poly I:C). Human CD14+ monocytes isolated from the peripheral blood of donors are cultured with GM-CSF and IL-4 supplemented media to generate immature DCs. The cultures are treated with curcumin, stimulated with the above mentioned stimulants then functional assays performed. These assays include homotypic cluster formation, surface marker expression, cytokine production, chemotaxis, endocytosis, DC-induced allogeneic CD4+ T cell proliferation after mixed lymphocyte reaction, gene expression analysis and immuno-fluorescence labeling and imaging. Curcumin-induced changes in gene expression indicate the actin cytoskeleton signaling pathway is a target. Immuno-fluorescence labeling and imaging of f-actin was carried out. Curcumin reduces DC maturation in response to the stimulants used in the study. Expression of surface markers, cytokines and chemokines is reduced as well as DC-induced stimulation of allogeneic CD4+ cells after MLR. Curcumin prevents chemotaxis without affecting chemokine receptor expression and significantly reduces endocytosis in non-stimulated cells. Curcumin-treated DCs do not induce a Th1 or Th2 population in allogeneic MLR but induces a CD25+Foxp3+ regulatory cell population. Immuno-fluorescence imaging shows curcumin causes the cell to become more rounded. These data imply that curcumin inhibits f-actin polymerization and thereby prevents DC maturation and function in response to stimulation. This outlines a novel role for curcumin as an immune suppressant and shows its therapeutic potential as an anti-inflammatory agent.

Abstract not available

Thesis (Ph. D.)--University of Chicago, Dept. of Biochemistry and Molecular Biology, June 1999. / Includes bibliographical references. Also available on the Internet.

Ph.D. / Biomedical Engineering / The cardiovascular disease atherosclerosis is directly linked to the functions of the endothelium, the monolayer of endothelial cells (ECs) that line the lumen of all blood vessels. EC functions are affected by fluid shear stress (FSS), the tangential force exerted by flowing blood. In vivo FSS is determined by vascular geometry with relatively straight vessels producing high, unidirectional FSS and vessel branch points and curvatures producing low, oscillatory FSS. While these distinct FSS conditions differentially regulate EC functions, they also dramatically affect EC shape and cytoskeletal structure. High and unidirectional FSS induces EC elongation and cytoskeletal alignment, while concurrently promoting EC functions that are atheroprotective. In contrast, low and oscillatory FSS induces cobblestone-shaped ECs with randomly oriented cytoskeletal features, while simultaneously promoting EC functions that create an athero-prone vascular environment. Whether these distinct EC shapes and cytoskeletal structures influence EC functions, independent of FSS, is largely unknown. The overall hypothesis of this study is that cell shape and cytoskeletal structure regulate EC functions through mechanisms that are independent of FSS. Due to advances in surface engineering in the field of micropatterning, EC shape can be controlled independent of external forces by creating spatially localized surface cues. In this research, lanes of protein were micropatterned on glass surfaces to induce EC elongated shape in the absence of FSS. In Aim 1, micropattern-elongated EC (MPEC) shape and cytoskeletal structure were fully characterized and determined to be comparable to FSS-elongated ECs. Thus, inducing EC elongation on micropatterned lanes provides a platform for studying the functional consequences of EC shape, independent of FSS. Using this model, the following important markers of EC functions related to atherosclerosis were evaluated to determine the influence of EC shape and cytoskeletal alignment: extracellular matrix deposition (Aim 2), inflammatory function(Aim 3), and thrombotic potential (Aim 4). The results indicate that EC-elongated shape and cytoskeletal alignment participate in promoting selected EC functions that are protective against atherosclerosis, independent of FSS. Since EC shape is governed by the cytoskeleton, this data suggests that the cytoskeleton plays an active role in the regulation of EC functions that promote cardiovascular health.

Le cytosquelette dactine est une structure dynamique impliquée dans de nombreux processus biologiques tels que les mouvements cellulaires, la phagocytose ou encore la mitose. En plus de son intervention dans ces différents événements essentiels pour lhoméostasie de la cellule, de nombreuses études ont démontré quil était également capable dinfluer sur des voies de transduction notamment en modulant lactivité de protéines kinases ou de facteurs de transcription. Un facteur de transcription important est le facteur de transcription NF-κB. Ce facteur de transcription joue un rôle majeur dans la régulation de nombreux processus cellulaires tels que les réponses immunitaires innée et adaptative, la réponse inflammatoire, lapoptose et la division cellulaire. Il peut être activé en réponse à de nombreux stimuli tels que les cytokines pro-inflammatoires, les produits bactériens ou viraux ou encore suite à un stress oxydant. Malgré les différentes études démontrant que le cytosquelette dactine est capable de moduler certaines voies de signalisation et que certains stimuli capables dactiver le NF-κB, comme le LPS et le TNFα, sont également associés à des modifications du cytosquelette dactine, peu de travaux ont été réalisés afin de déterminer limpact des perturbations du cytosquelette dactine sur lactivation de cet important facteur de transcription. Ces différents arguments nous ont donc poussé à étudier le rôle des perturbations du cytosquelette dactine dans les voies dactivation du NF-κB. Ainsi, dans une première partie, nous avons étudié leffet de plusieurs agents perturbant le cytosquelette dactine [la Cytochalasine D (CytD), le Jasplakinolide (JP) et la Latrunculine B (Lat B)] sur lactivation du NF-κB. Nous avons pu mettre en évidence que ces différentes substances sont capables dinduire la voie classique dactivation du NF-κB uniquement dans des cellules myélomonocytaires. De plus, nous avons également observé que ces agents sont capables dinduire la production despèces réactives à loxygène (ROS) Dans un second temps, nous nous sommes intéressés à leffet de la CytD sur lactivation du NF-κB dans des cellules myélomonocytaires induites par le TNFα ou le LPS. Nous avons pu démontrer que la CytD promouvoit la voie classique du NF-κB dans les cellules induites par le LPS. En effet, il semblerait que la CytD agisse notamment sur cette voie en augmentant le temps de résidence du récepteur à cet inducteur, le TLR4, à la surface de la membrane plasmique. Parallèlement à ces observations, nous avons pu mettre en évidence que la CytD augmente la phosphorylation de certains résidus de la sous-unité RelA du NF-κB induite par les deux inducteurs classiques ce qui permet un meilleur recrutement de la RNA polymérase II sur le promoteur endogène de la chémokine IL-8.