1,720,972 research outputs found
Ruolo anti-apoptotico della tirosin-chinasi Lyn nella leucemia linfatica cronica a cellule B
Get PDFB-chronic lymphocytic leukemia (B-CLL) is the commonest leukemia in the Western world and is characterized by the clonal expansion of small CD5+ B lymphocytes in the pheripheral blood, bone marrow and lymphoid organs, due to defective apoptosis. One of the crucial factors for the survival of B-CLL cells is the anomalous activity of a few enzymes such as the lipide kinase PI3K, the Ser/Thr kinase PKC and the tyrosine-kinases Syk and Lyn. My research focus was Src family kinase Lyn, which is overexpressed, constitutively active and delocalized in the cytosol within an aberrant multiprotein complex, in association with the molecular chaperone Hsp90, which in turn accounts for the high level of tyrosine-phosphorylation, ultimately contributing to the cancer phenotype of B-CLL cells.
The aim of my PhD work was to identify Lyn’s cytosolic substrates potentially involved in the apoptosis resistance mechanisms observed in leukemia cells.
Using biochemical and biomolecular methods as well as a bioinformatics approach, two potential substrates of Lyn were identified, namely the cysteine protease caspase-8 and the protein phosphatase-2A (PP2A).
Firstly, we established that in B-CLL, the inactive zymogen of caspase-8, procaspase-8, is phosphorylated at Tyr380 by the cytosolic pool of Lyn, which brings about its inhibition and its structural rearrangements in a dymeric cytosolic form. The phosphorylation of Tyr380 of caspase-8 is abolished by the use of both the Lyn inhibitor dasatinib and the Hsp90 inhibitor geldanamycin, the latter of which also leads to the disassembly of the aberrant cytosolic complex and the drop in the Lyn’s cytosolic activity, resulting in the caspase-dependent apoptosis.
Secondly, we verified that Lyn negatively affects the activity of one of the key factors in the modulation of cell survival signals, PP2A. Phosphorylation of the catalytic subunit of PP2A at Tyr307 causes inhibition of the phosphatase activity not only per se but also strengthening the interaction of PP2A with its cellular inhibitor SET, which is also overexpressed in B-CLL cells. As a result, PP2A is stably preserved in an inhibited form, which contributes to the persistence of prosurvival signals, in particular those mediated by the serine/threonine kinase Akt. Moreover, to identify new compounds able to activate PP2A in order to contrast survival signals in B-CLL, we tested fingolimod (FTY720), which is already known as a PP2A activator, currently in use in the treatment of multiple sclerosis and recently emerging as a pro-apoptotic factor in different types of cancer cells. Notably, the mechanism of action consists in the ability of fingolimod to bind to SET and hence remove this cellular inhibitor of PP2A from its catalytic subunit. Since this drug is used as an immunosuppressive agent, by virtue of its provoking the degradation of the sphingosine-1-phosphate receptor, and shows cardiovascular side effects, it might prove unsuitable in a more complex therapeutic strategy. Therefore, fingolimod structural analogues which could not interfere with the sphingosine receptors, but could still destabilize the PP2A/SET complex were designed and synthesized. One of these compounds, MP07-66, showed an effectiveness similar to fingolimod, as to both the ability to disrupting the PP2A/SET complex and inhibit the protein kinase Akt, this latter being vital in preserving the survival signals. This compound also was able to induce apoptosis in leukemia cells, which effect was further enhanced by the combination with dasatinib by a synergistic mechanism, further confirming the role of phosphorylation in the stability of PP2A/SET.
In conclusion, this work identifies PP2A and Caspase 8 as substrates of the cytosolic aberrant activity of Lyn, confirming the key role of this tyrosine kinase in supporting multiple anti-apoptotic signals in the B-CLL. The molecular mechanisms of apoptosis resistance here identified may be potential targets in the development of new therapies for clinical use
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Pathophysiological implications of mitochondrial oxidative stress mediated by mitochondriotropic agents and polyamines: The role of tyrosine phosphorylation
No full textMitochondria, once merely considered as the "powerhouse" of cells, as they generate more than 90 % of cellular ATP, are now known to play a central role in many metabolic processes, including oxidative stress and apoptosis. More than 40 known human diseases are the result of excessive production of reactive oxygen species (ROS), bioenergetic collapse and dysregulated apoptosis. Mitochondria are the main source of ROS in cells, due to the activity of the respiratory chain. In normal physiological conditions, ROS generation is limited by the anti-oxidant enzymatic systems in mitochondria. However, disregulation of the activity of these enzymes or interaction of respiratory complexes with mitochondriotropic agents may lead to a rise in ROS concentrations, resulting in oxidative stress, mitochondrial permeability transition (MPT) induction and triggering of the apoptotic pathway. ROS concentration is also increased by the activity of amine oxidases located inside and outside mitochondria, with oxidation of biogenic amines and polyamines. However, it should also be recalled that, depending on its concentration, the polyamine spermine can also protect against stress caused by ROS scavenging. In higher organisms, cell signaling pathways are the main regulators in energy production, since they act at the level of mitochondrial oxidative phosphorylation and participate in the induction of the MPT. Thus, respiratory complexes, ATP synthase and transition pore components are the targets of tyrosine kinases and phosphatases. Increased ROS may also regulate the tyrosine phosphorylation of target proteins by activating Src kinases or phosphatases, preventing or inducing a number of pathological states
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
- …
