1,720,967 research outputs found
ANALYSIS OF BIASED SIGNALING IN THE CHEMOKINE SYSTEM
Full text linkChemokines constitute a family of almost 50 small secreted cytokines, recognized by about 20 different 7TM spanning G protein coupled receptors (GPCRs), that activating pertussis toxin sensitive G proteins induce cell migration. These receptor are abundantly expressed by leukocytes and, controlling cell migration, they dictate leukocyte positioning during homeostatic patrolling within peripheral tissues, their maintenance in bone marrow during maturation and in addition mediate their recruitment to inflamed tissues. Upon inflammation in fact a number of chemokines are produced or activated by inflammatory mediators and diffuse within the tissue, generating a chemical gradient along which leukocytes migrate to reach the center of inflammation to contain and remove the insulting factor. This system needs an extremely tight control, since its dysregulation has been demonstrated to be at the basis of different inflammatory diseases, auto-immunity and has also been linked to cancer development. In particular, in this thesis we focused our attention on two regulatory system: post-translational modifications of chemokines, mediated by enzymes specifically released upon inflammation also by immune cells, and on the activity of atypical chemokine receptors, a subfamily of chemokine receptors that despite high structural homology and similar binding properties compared to conventional chemokine receptors, are unable to drive chemotaxis but act instead as key regulators of the chemokine system activity. In detail we looked at the ability of these regulatory mechanisms to modulate chemokine signaling properties generating a biased signaling, an emerging feature of GPCR pharmacology that describes the ability of a given receptor to elicit different or even opposite functional activities depending on the ability of different agonists to stabilize different receptor’s active structural conformation, resulting in different phenotypes mediated by the same receptor. In the chemokine system biased signaling has already been described to occur on different receptors upon binding of their different ligands, therefore during our investigation on chemokine regulatory system signaling we maintained our focus on the ability of these systems to bias chemokine signaling properties in order to better understand how this regulation occurs.
To this point we assessed the ability of differently post-translationally modified chemokines to elicit signaling activities on different receptors by measuring in HEK293 cells their potential in inhibiting adenylyl cyclase, a proximal downstream signal of Gα inhibitory proteins activation, and in inducing β-arrestin recruitment to the receptors in energy transfer-based assays. We also compared signaling properties of an atypical chemokine receptor to the ones elicited by a conventional receptor analyzing the phosphoproteome modifications occurring constitutively and after stimulation with the same agonist.
Our results indicate that regulation of CXCL5 and CXCL8 chemokine activity by post-translational modifications is more prone to regulate chemokine activity modifying chemokine potency, rather than generating a bias in their signaling properties. Truncation of chemokine NH2-terminus increases both CXCL5 and CXCL8 activity, while citrullination of the most NH2-terminal arginine results in opposite effects on the two agonists since on CXCL8 increases chemokine potency, while it reduces CXCL5 activity. We investigated the properties of ACKR2 in recruiting β-arrestins, demonstrating that this receptor is able to associate both β-arrestin 1 and 2 in basal conditions while upon agonist stimulation preferentially increases its association with β-arrestin 1, resulting in a completely different agonist-induced outcome of proteome phosphorylation, compared to CCR5, in terms of kinetics, protein phosphorylation modifications, biological function of the regulated proteins and signal mediators activated. Taken together, these results indicate that chemokine system regulation is based not only on chemokine post-translational modifications that modulate chemokine potency, but also on the activity of structurally biased atypical chemokine receptors, as in the case of ACKR2 that interacts with different effectors and kinetics to generate distinct functional outcomes, compared to the conventional chemokine receptor CCR5.
In this thesis it has also been attempted to translate the investigation of chemokine signaling to a clinical intervention for inflammatory diseases. We assessed the modulation of CXCR1 signaling activity exerted by Reparixin, a leukocyte migration inhibitor that blocks cell recruitment to inflamed tissues, that binds to its target receptors in an allosteric binding site, without inhibiting chemokine binding to the receptor. In our assays performed on HEK293 cells we could not detect any inhibition of the signaling pathways assayed, possibly indicating that HEK293 cells are not the best model to assay the activity of this molecule, with the need to assess in this cellular model drug inhibitory activity on read-outs already evaluated in literature on other cell types.
In conclusion, we can say that observations described in this thesis allow to better understand chemokine system regulation, that occurs by biased signaling activity in the case of atypical chemokine receptors that by selected interaction with signaling mediators induce opposite biological outcomes compared to conventional chemokine receptors, while post-translational modifications regulate chemokines activity modulating their potency, rather than biasing their signaling properties
Overview and potential unifying themes of the atypical chemokine receptor family
No full textChemokines modulate immune responses through their ability to orchestrate the migration of target cells. Chemokines directly induce cell migration through a distinct set of 7 transmembrane domain G protein-coupled receptors but are also recognized by a small subfamily of atypical chemokine receptors, characterized by their inability to support chemotactic activity. Atypical chemokine receptors are now emerging as crucial regulatory components of chemokine networks in a wide range of physiologic and pathologic contexts. Although a new nomenclature has been approved recently to reflect their functional distinction from their conventional counterparts, a systematic view of this subfamily is still missing. This review discusses their biochemical and immunologic properties to identify potential unifying themes in this emerging family
Atypical chemokine receptors : from silence to sound
Full text linkACRs (atypical chemokine receptors) were initially referred to as 'silent' receptors on the basis of a lack of signalling and functional activities that are typically observed with conventional chemokine receptors. Although ACRs do not directly induce cell migration, they indirectly control leucocyte recruitment by shaping chemokine gradients in tissues through degradation, transcytosis or local concentration of their cognate ligands. Recent evidence also suggests that these biological activities are supported by G-protein-independent, beta-arrestin-dependent signalling events. In the present article, we review current knowledge on structural and signalling properties of ACRs that are changing our view on this entire class of receptors from silent to endogenous beta-arrestin-biased signalling receptors
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Variations on the Author
Full text link“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
Full text linkWe 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
Full text linkWe 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
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