No description available.

I evaluated the potential of isomers of the low molecular weight phosphomonoester naphthyl phosphate as general diagnostic substrates for differentiating between two families of protein phosphatases: the protein-tyrosine phosphatases [PTPs] and the dual-specificity protein phosphatases [DSPs]. Three PTPs, PTP-1B, Tc-PTPa, and PTP-H1, and three DSPs, Cdc-14, VHR, and IphP, were challenged in vitro with alpha-naphthyl phosphate and beta-naphthyl phosphate. Both the DSPs and PTPs readily hydrolyzed beta-naphthyl phosphate. As expected, the DSPs also hydrolyzed alpha-naphthyl phosphate at rates comparable to beta-naphthyl phosphate and two of the PTPs, PTP-1B and Tc-PTPa, hydrolyzed alpha-naphthyl phosphate at a rate one-tenth that of beta-naphthyl phosphate. However, PTP-H1 hydrolyzed both alpha- and beta- naphthyl phosphate at nearly equal rates. Intriguingly, when challenged with radiolabeled phosphoproteins, PTP-H1 was markedly less stringent, by a factor of 40- to 200- fold, than PTP-1B or Tc-PTPa in its selectivity for [32P]phosphotyrosyl- over [32P]phosphoseryl- proteins in vitro. The DSPs and PTPs listed above also were challenged in vitro with free phosphoserine. Each displayed little or no activity towards free phosphoserine. However, the addition of a hydrophobic "handle" to form N-(cyclohexane carboxyl)-O-phospho-L-serine produced a derivative that was hydrolyzed by IphP at rates comparable to that of the avid substrates p-nitrophenyl phosphate and beta-naphthyl phosphate. VHR also hydrolyzed N-(cyclohexane carboxyl)-O-phospho-L-serine, though at a lower rate than IphP. Cdc14 displayed little activity towards N-(cyclohexane carboxyl)-O-phospho-L-serine. The active site of VHR was mapped and amino acid residues potentially involved in binding N-(cyclohexane carboxyl)-O-phospho-L-serine were identified. The amino acid sequence of VHR was aligned with the amino acid sequences of IphP and Cdc14 to identify the nature of the corresponding residues in IphP and Cdcd14. Low molecular weight phosphomonoesters have proven to be effective in vitro indicators of protein phosphatase activity. They also have shown potential as diagnostic substrates for specific subclasses of protein phosphatases. However, neither alpha- and beta- naphthyl phosphate nor N-(cyclohexane carboxyl)-O-phospho-L-serine proved to be universal discriminatory substrates for the functional subgroups within the family of protein-tyrosine phosphatases. Indeed, the probability of identifying such a substrate would appear to be relatively low. / Master of Science

No description available.

Angiogenesis, de novo formation of blood vessels from the pre-existing vasculature, is crucial in embryo development, and in processes in the adult such as wound healing and ovulation. Angiogenesis is also involved in pathological conditions such as cancer and chronic inflammatory diseases, which are propagated by dysregulated, excess angiogenesis. On the other hand, lack of functional vessels and poor blood flow is a major problem in myocardial and peripheral ischemia. A detailed understanding of the molecular mechanisms underlying angiogenesis is of vital importance for the development of drugs to regulate angiogenesis. The aim of this thesis has been to identify genes involved in regulation of angiogenesis. We have investigated gene expression over time in endothelial cells (ECs), using different in vitro models. We show that the proteoglycan endocan is upregulated in ECs invading a fibrin matrix in response to vascular endothelial growth factor (VEGF)-A. There was increased expression of endocan in renal tumour cells and tumour vessels compared to normal renal tissues, indicating that endocan might have a role in tumour growth and tumour angiogenesis. We also show that vascular endothelial protein tyrosine phosphatase (VE-PTP) is induced in ECs during differentiation into vessel structures in a three dimensional collagen matrix. Silencing of VE-PTP disrupts vessel formation and increases the activity of VEGF receptor-2 (VEGFR-2) and downstream signalling, leading to increased EC proliferation. This presents a possible mechanism for the failure of vessel formation, as EC morphogenesis requires growth arrest of the cells. We also show that VE-PTP and VEGFR-2 are closely associated in resting ECs. VEGF-A stimulation leads to rapid loss of association, coinciding with increased phosphorylation of VEGFR-2. The function of VE-PTP in vivo was investigated using the zebrafish model. We demonstrate specific expression of a zebrafish VE-PTP orthologue (zVE-PTP) in the developing vasculature. Silencing of zVE-PTP leads to defective vessel sprouting and branching, indicating a critical role for zVE-PTP in development of the zebrafish vasculature. In conclusion, this thesis presents gene regulation during endothelial cell morphogenesis and details the expression pattern of endocan and the function of VE-PTP in regulation of VEGFR-2-driven angiogenesis.

Protein phosphorylation is a post translational modification of proteins in which a serine, a threonine or a tyrosine residue is phosphorylated by an enzyme, kinase. Phosphorylation of proteins is a reversible and very important regulatory mechanism that occurs in both prokaryotes and eukaryotes. Phosphorylation turns many protein enzymes on and off, preventing or causing many diseases such as diabetes, cancer and rheumatoid arthritis. The phosphorylation on tyrosine residues of proteins is essential for transmission of signals for cell growth, proliferation and differentiation. Protein tyrosine phosphatases (PTPs) in concert with protein tyrosine kinases (PTKs) regulate many signal transduction pathways by controlling the degree of phosphorylation of tyrosine residues within the protein. While the roles and mechanisms of protein tyrosine kinases are well documented, our present understanding of protein tyrosine phosphatases is very limited. In this regard we still have much more to learn about PTPs. Here we propose the design and synthesis of novel protein tyrosine phosphatase mimetics and their activity against tyrosine phosphatases. Chapter two describes the synthesis of 2-aminopyrimidine chlorides, sulfonamides and the sequence of reactions to make its amino acid analog. Chapter three describes the synthesis of α-aryl, α,β-epoxy carboxylates, phosphonates and their biological activity against tyrosine phosphatases. These compounds could be very helpful in significantly improving the current understandings about the roles and mechanisms of the PTPs. These proposed tyrosine phosphatase inhibitors are believed to work effectively in treating the diseases by modulating the phosphorylation in signal transductions pathways. Chapter four describes the design and the synthesis of Peptide Nucleic Acids (PNAs) both standard as well as hybrid PNAs with novel cysteine based monomers that are aimed to increase the cellular uptake by introducing positively charged or amphipathic species attached to cysteine thiol functional group.

Thesis (M.Sc.). / Written for the Dept. of Biochemistry. Title from title page of PDF (viewed 2008/12/09). Includes bibliographical references.

Orientador: Hiroshi Aoyama / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Biologia / Made available in DSpace on 2018-08-06T06:33:37Z (GMT). No. of bitstreams: 1 Sousa_RobertaReginaRuelade_M.pdf: 3257089 bytes, checksum: 29f24a432f8c0bfd7dd71af48cc7608a (MD5) Previous issue date: 2005 / Resumo: As proteínas tirosina fosfatases (PTP) (EC 3.1.3.48) são enzimas regulatórias chaves que participam na transdução de sinal e são essenciais na regulação do crescimento, diferenciação, ciclos celulares, na transcrição gênica, resposta imune e outros processos. Esta classe de enzimas, que contém cisteína no sítio ativo, pode ser inativada por agentes oxidantes. Neste trabalho, estudamos os efeitos de peróxido de hidrogênio e t-butil hidroperóxido, compostos que induzem estresse oxidativo, na atividade de uma PTP purificada de membranas de linfócitos humanos, indicativamente a CD45. A PTP foi purificada de membranas de linfócitos humanos através de cromatografias de troca iônica (DEAE Sepharose) e exclusão molecular (Sephacryl S-200). A purificação enzimática foi acompanhada por SDS-PAGE e eletroforese bidimensional. A atividade enzimática foi determinada através de incubação a 37°C por 30 min em pH 5,0 em presença de 5 mM de p-nitrofenil fosfato (pNPP) como substrato. A enzima obtida da cromatografia de exclusão molecular apresentou uma massa molecular relativa de aproximadamente 200 kDa, reconheceu mais eficientemente tirosina fosfato (cerca de 3,2 vezes) como substrato quando comparado ao pNPP, e foi inibida por inibidores específicos de PTP, tais como vanadato (40%), pervanadato (100%), p-cloromercuribenzoato (20%) and Cu2+ (95%). Ácido okadáico, um inibidor específico de serina e treonina proteína fosfatases, não afetou a atividade da PTP de membranas de linfócitos. Estes resultados de caracterização sugerem fortemente que a PTP purificada de membranas de linfócitos humanos é a CD45. Peróxido de hidrogênio e t-butil hidroperóxido inibiram a atividade dessa proteína com valores de IC50 (concentração do composto que produz 50% de inibição enzimática) de 50 µM e 16 mM, respectivamente. Glutationa reduzida (GSH) protegeu parcialmente a enzima contra estes oxidantes, porém proteções totais foram obtidas quando se adicionava 250 mM de desferoxamina ao meio de ensaio. Nossos resultados sugerem que essa proteína pode ser regulada por alteração do estado de oxidação dos grupos funcionais do sítio ativo e que esta regulação poderia fornecer um mecanismo de controle celular através de espécies reativas de oxigênio / Abstract: Protein phosphatases, that dephosphorylate proteins in residues of threonine, serine and tyrosine, are a class of enzymes that can be stressed by compounds present in oxidant or reductant environments. In particular, the protein tyrosine phosphatases (PTP) (EC 3.1.3.48) are key regulatory enzymes that participate in signal transduction and are essential for regulating cellular growth, differentiation, cell cycle, gene transcription, immune response and other processes. This class of enzymes, which contain cysteine in the active site, can be inactivated by oxidant reagents. In this work we have studied the effect of hydrogen peroxide and t-butyl hydroperoxide, compounds that induce oxidative stress, on a purified PTP (CD45) from membrane human lymphocytes. PTP was purified from human lymphocyte membranes through ion exchange (DEAE Sepharose) and molecular exclusion (Sephacryl S-200) chromatographies. The enzyme purification was followed by SDS-PAGE and 2D electrophoresis. The enzyme activity was determined by incubation at 37oC for 30 minutes at pH 5.0 in presence of 5 mM p-nitrophenylphosphate (pNPP) as substrate. The enzyme obtained from molecular exclusion chromatography had a relative molecular mass of approximately 200 kDa, recognized more efficiently tyrosine phosphate (about 3.2-fold) as substrate when compared with p-NPP, and was inhibited by specific PTP inhibitors, such as, vanadate (40%), pervanadate (100%), p-chloromercuribenzoate (20%) and Cu2+ (95%). Okadaic acid, a specific serine and threonine protein phosphatases inhibitor, did not significantly affect the lymphocyte membrane PTP activity. These characterization results strongly suggest that the membrane PTP purified from human lymphocytes was the CD45. Hydrogen peroxide and t-butyl hydroperoxide inhibited the CD45 activities with IC50 (concentration of compound that produces 50% enzyme inhibition) values of 50 µM and 16 mM, respectively. Reduced glutathione (GSH) partially protected the enzyme against these oxidations, but full protections were observed when 250 mM deferoxamine were added to the assay medium. Our results suggest that CD45 can be regulated by altering the oxidation state of active site functional groups, and that this regulation could provide a mechanism of cell control by reactive oxygen species / Mestrado / Bioquimica / Mestre em Biologia Funcional e Molecular

No description available.

Résumé : Les podocytes, cellules épithéliales rénales, sont nécessaires au maintien de la structure et de la fonction de filtration des glomérules rénaux. La dédifférenciation et l’apoptose des podocytes sont des évènements précoces de la néphropathie diabétique. Des études ont rapporté que l’insuline est nécessaire à la survie des podocytes puisque la délétion du récepteur à l’insuline dans les podocytes de souris entraîne une pathologie glomérulaire semblable à la néphropathie. D’autres études ont montré que la protéine tyrosine phosphatase Src homology-2 domain-containing phosphatase-1 (SHP-1) inhibe les voies de signalisation de l’insuline au niveau du foie et du muscle en déphosphorylant la sous-unité bêta du récepteur à l’insuline (IRβ) et la kinase Phosphatidylinositide 3-kinase (PI3K). Il a récemment été démontré que l’expression de SHP-1 est élevée dans les cortex rénaux de souris diabétiques. Nous avons donc émis l’hypothèse que l’expression de SHP-1 induite par l’hyperglycémie altère les actions de l’insuline dans les podocytes. Nous avons premièrement utilisé un modèle in vivo de souris diabétiques de type 1 (Ins2+/C96Y; Akita). Comparées aux souris contrôles (Ins2+/+), les souris Akita présentaient une apoptose élevée des podocytes ainsi qu’une perte des pédicelles. La phosphorylation de la protéine kinase B (Akt) et de Extracellular signal-regulated kinase 1/2 (ERK1/2), suite à une injection systémique d’insuline, était également significativement diminuée dans les cortex rénaux des souris Akita. Cette diminution correspondant à une résistance à l’insuline corrélait avec une augmentation de deux fois de l’expression de SHP-1 dans les glomérules. Nous avons ensuite utilisé une lignée immortalisée de podocytes murins en culture et avons observé que l’exposition à des concentrations élevées de glucose (HG; 25 mM) pendant 96 h, entraînait l’augmentation de l’expression de marqueurs apoptotiques et de l’activité enzymatique de caspase-3/7 en comparaison aux concentrations normales de glucose (NG; 5,6 mM). L’exposition en HG a augmenté l’expression de l’ARNm et protéique de SHP-1, en plus de réduire la signalisation de l’insuline dans les podocytes. La surexpression de la forme dominante-négative de SHP-1 dans les podocytes a permis de renverser les effets de HG et de restaurer les actions de l’insuline. Finalement, l’augmentation de l’expression de SHP-1, tant in vivo qu’in vitro, a été directement corrélée à son association avec IRβ et à la diminution de la phosphorylation de IRβ, Akt et ERK1/2 suite à une stimulation à l’insuline. En conclusion, nous avons montré que l’expression élevée de SHP-1 dans les glomérules cause une résistance à l’insuline et la mort des podocytes contribuant ainsi à la néphropathie diabétique. // Abstract : Podocytes are epithelial renal cells required to preserve glomerular structure and filtration. Their dedifferentiation and apoptosis are early events of diabetic nephropathy progression. Previous studies have shown that insulin action is critical for podocyte survival since deletion of its receptor lead to a glomerular pathology similar to nephropathy. It has also been demonstrated that Src homology-2 domain-containing phosphatase-1 (SHP-1), a protein tyrosine phosphatase, inhibits insulin signaling pathway in liver and muscle by dephosphorylating tyrosine residues on insulin receptor beta-subunit (IRβ) and the Phosphatidylinositide 3-kinase (PI3K). A recent study concluded that SHP-1 is elevated in kidney cortex of type 1 diabetic mice. We hypothesized that hyperglycemia-induced SHP-1 expression may affect insulin actions in podocytes. To confirm this hypothesis, we used type 1 diabetic Akita mice (Ins2+/C96Y). Compared to control littermate mice (Ins2+/+), Akita mice developed elevated podocyte foot process effacement and podocyte apoptosis. In contrast to control mice, insulin-stimulated protein kinase B (Akt) and extracellular signal-regulated kinase 1/2 (ERK1/2) phosphorylation was remarkably reduced in renal podocytes of Akita mice. This phosphorylation diminution associated to a renal insulin resistance was correlated with a two-fold increase of SHP-1 expression in the glomeruli. We then used cultured murine podocytes cell line to confirm our in vivo results. Podocytes exposed to high glucose concentration (HG; 25 mM) for 96 h exhibited high levels of apoptotic markers and caspase-3/7 enzymatic activity as compared to normal glucose concentration (NG; 5,6 mM). HG exposure raised mRNA and protein levels of SHP-1 and reduced the insulin-signaling pathway in podocytes. Overexpression of dominant-negative SHP-1 in podocytes prevented HG effects and restored insulin actions. Finally, elevated SHP-1 expression induced by high glucose levels was directly correlated to an increased association with insulin receptor-β subunit (IRβ) in vitro and in vivo. This association is therefore leading to the reduction of both IRβ phosphorylation and insulin-stimulated Akt and ERK phosphorylation. In conclusion, our results showed that high levels of SHP-1 in glomeruli cause insulin resistance and podocyte loss, thereby contributing to diabetic nephropathy.

A proteína tirosina fosfatase eta de rato (rPTPeta), é uma RPTP transmembranar do tipo classe I. A rPTP eta e seu homólogo DEP-1 provenientes, respectivamente, de ratos e de humanos, estão inibidas em células neoplásicas. Este fenótipo maligno é revertido após reconstituição exógena, o que sugere que a capacidade restauradora da rPTP eta pode ser uma ferramenta importante na terapia de alguns tipos de câncer. Portanto, o objetivo deste projeto incluiu o estudo molecular, biofísico e estrutural do domínio catalítico da rPTPeta (rPTPetaDC). Para isso, sub-clonamos no vetor pET-28a(+) o inserto que codifica para a região C-terminal da rPTPeta . Em seguida, bactérias E. coli da linhagem BL21 (DE3) foram transformadas com o plasmídeo e a proteína recombinante expressada e purificada. A His6-rPTPetaDC purificada teve a cauda de histidina subseqüentemente removida por digestão com trombina. O ponto isoelétrico de 7,3 da proteína de 41kDa foi medido experimentalmente e a sua funcionalidade acessada pelo ensaio de hidrólise do pNPP. A enzima apresentou uma atividade específica de 9nmol/min/microg a qual é compatível com as atividades específicas descritas para as RPTPu, RPTPalfa, PTPB1 e SHP2. A estrutura secundária e a estabilidade da rPTPetaDC recombinante foi analisada por dicroísmo circular e espectroscopia de fluorescência. A rPTPetaDC mostrou-se estável a 18 graus Celsius e propriamente enovelada (Santos, et al., Prot. Expr. Purif., 2005. Anexo A). A proteína foi, em seguida, submetida a diferentes condições de cristalização e a estudos estruturais em solução. Nas condições de 0,1M de MES, pH 6,5 e 20% PEG 10000 cresceram cristais que difrataram na resolução de 1,87Å. Os cristais pertencem ao grupo espacial P2(1)2(1)2(1) com parâmetros de célula unitária: a=46,46; b=63,07; c=111,64 Å, e com uma única molécula por unidade assimétrica (Matozo, et al., Acta crystallogr. F, 2006. Anexo B). A estrutura da rPTPetaDC, em solução, foi analisada usando-se a técnica de SAXS e medidas de anisotropia de fluorescência. Os dados de SAXS mostraram que a proteína, forma dímeros alongados, com Rg de 2,65nm e Dmax de 8,5nm. A conformação da rPTPetaDC analisada por modelos de homologia sugere que seu dímero está mais próxima da estrutura cristalográfica dimérica da RPTPalfa-D1. Alem disso, a caracterização da rPTPetaDC por anisotropia de fluorescência demonstrou que o Kd do dímero da rPTPetaDC é de 21,6 + 2,0uM e a variação da energia livre de Gibbs dímero-monômero é de 7,2kcal/mol (Mtozo, et al., Biophys. J., 2007. Anexo C ). / The rat protein tyrosine phosphatase eta, rPTPeta, is a transmembrane RPTP, with an intracellular portion composed of a unique catalytic region. The rPTPeta and the human homolog DEP-1 are down-regulated in rat and human neoplastic cells, respectively. However, the malignant phenotype is reverted after exogenous reconstitution of rPTPeta, suggesting that its function restoration could be an important tool for gene therapy of several types of cancer. Therefore, the objective of our project aimed on the molecular, biophysical and structural study of the catalytic domain of rPTPeta, rPTPetaDC. We began our study cloning the rPTPetaDC into PET28a(+) vector, followed by its expression in Escherichia coli, and purification. The His6-tag from the rPTPetaDC purified was subsequently removed by thrombin digestion. PhastGel IEF electrophoresis demonstrated that the isoelectric point of the 41kDa was 7.3. To assess the functionality of the rPTPetaDC we used the pNPP hydrolysis assay and observed that the enzyme has a specific activity of 9nmol/min/ug. The experimentally determined rPTPetaDC specific activity showed to be in the same range as the previously reported activities for RPTPu, RPTPalfa, PTPB1 and SHP2. The secondary structure and stability of the recombinant protein was analyzed by circular dichroism and fluorescence spectroscopy. The results demonstrated that rPTPetaDC was stable at 18 Celsius and properly folded (Santos, et al., Prot. Expr. Purif., 2005. In attachment A). Then, the purified protein was submitted to different crystallization conditions and structural studies in solution. Crystals appeared at 0.1M MES, pH 6.5 and 20% PEG 10,000 and diffracted with resolution of 1.87Å. The crystals belong to spatial group P2(1)2(1)2(1) with unit cell parameters of a=46.46, b=63.07, c=111.64Å and contained one molecule for asymmetric unit (Matozo, et al., Acta crystallog. F, 2006. In attachment B). Also, the structural of rPTPetaDC, in solution, was analyzed by SAXS and fluorescence anisotropy. SAXS data showed that the protein forms elongated dimers in solution with an Rg of 2.65nm and a Dmax of 8.5nm. The rPTPetaDC conformation in solution, studied by homology models, suggested that the rPTPetaDC dimer architecture is more closely related to the crystal structure of RPTPalfa-D1. The characterization of rPTPetaDC by fluorescence anisotropy measurements demonstrated that the Kd of the dimer is 21.6 + 2.0uM and the energy Gibbs dimer-monomer is equal to 7.2kcal/mol (Matozo, et al., Bioph. J., 2007. In attachment C).