1,720,956 research outputs found
Expression of mutationally activated Gαs stimulates growth and differentiation of thyroid FRTL5 cells
No full textThe α subunit of the GTP-binding protein Gs mediates hormonal stimulation of adenylyl cyclase. Human pituitary and thyroid tumours harbour mutations of Gαs that constitutively activate the protein by inhibiting its intrinsic GTPase activity. We have investigated the mitogenic action of mutationally activated αs in thyroid FRTL5 cells, a cell line dependent upon thyroid-stimulating hormone (TSH) for both growth and differentiation. Introduction of αs carrying the substitution of glutamine-227 with leucine (Q227Lαs) by retroviral infection of FRTL5 cells resulted in the expected stimulation of membrane adenylyl cyclase activity and in increased intracellular accumulation of cAMP. Measurements of cytosolic Ca2+ levels did not detect any concomitant effect on the polyphosphoinositide-Ca2+ signalling pathway. Expression of Q227Lαs conferred to FRTL5 cells the ability to synthesize DNA in the absence of TSH, as revealed by [3H]thymidine incorporation experiments, and to proliferate independently of the mitogenic hormone, although with a rate of growth slower than that observed with TSH stimulation. The effect of Q227Lαs on cell proliferation was associated with the constitutive activation of iodide uptake. The results indicate that expression of mutationally activated Gαs is sufficient to bypass the requirement for TSH and promotes autonomous growth and activation of thyroid-specific differentiated functions in FRTL5 cells
Differential coupling of dopaminergic D2 receptors expressed in different cell types
No full textDopaminergic D2 receptors are widely regarded as typical inhibitory receptors, as they both inhibit adenylyl cyclase and decrease the cytosolic free Ca2+ concentration ([Ca2+]i) by activating K+ channels. A D2 receptor has recently been cloned (Bunzow, J. R., Van Tol, H. H. M., Grandy, D. K., Albert, P., Salon, J., Christie, M. D., Machida, C. A., Neve, K. A., and Civelli, O. (1988) Nature 336, 783-787) and expressed in two different cell lines, pituitary GH4C1 cells and Ltk- fibroblasts, where it has been shown to induce inhibition of adenylyl cyclase. We have investigated the additional effector systems coupled to this receptor. The responses observed in the two cells lines, which express similar levels of receptors (0.5-1 × 105/cell), were surprisingly different. In GH4C1 cells D2 receptors failed to affect phosphoinositide hydrolysis and induced a decrease of [Ca2+]i. This latter effect appears to be mediated by hyperpolarization, most likely due to the activation of K+ channels. In striking contrast, in Ltk- fibroblasts the D2 receptor induced a rapid stimulation of inositol(1,4,5)-trisphosphate (+73% at 15 s) followed by the other inositol phosphates, and an immediate increase of [Ca2+]i due to both Ca2+ mobilization from internal stores and influx from the extracellular medium. In both GH4C1 and Ltk- cells, the D2 receptor response was mediated by G protein(s) sensitive to pertussis toxin. The increases of inositol trisphosphate and [Ca2+]i observed in Ltk- cells required dopamine concentrations only slightly higher than those inhibiting adenylyl cyclase (EG50 = 25, 29, and 11 nM, respectively) and were comparable in magnitude to the responses induced by the endogenous stimulatory receptor agonists, thrombin and ATP. The results demonstrate that in certain cells D2 receptors are efficiently coupled to the stimulation of phosphoinositide hydrolysis. The nature of receptor responses appears therefore to depend on the specific properties not only of the receptor molecule but also of the cell type in which it is expressed
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
Activation of cyclic nucleotide phosphodiesterases in FRTL5 thyroid cells expressing a constitutively active Gsα
No full textThe expression of a constitutively activated Gsα protein in the rat thyroid cell line FRTL-5 causes an increase in the hormone-independent adenylyl cyclase activity and promotes TSH-independent growth of the cells. In spite of the constitutive activation of the adenylyl cyclase, the basal cAMP levels in these cells are only marginally increased. To define the role of phosphodiesterases (PDEs) in the genesis of this phenotype, cyclic nucleotide hydrolysis was determined in two cell lines expressing a mutated Gsα (Q227L). In these cells, the hydrolysis of both cAMP and cGMP was markedly increased in comparison with normal cells. This increase is the result of the activation of different forms of PDEs. Analysis of the cGMP hydrolysis and Ca ++/calmodulin stimulation of the PDE activity indicated that the activity of a Ca ++/calmodulin-stimulated PDE is increased in both cell lines. In addition, an increase in high-affinity, rolipram-sensitive cAMP-PDE activity was associated in both cell lines with the appearance of a 67-68 kilodalton (kDa) protein that cross-reacts with two antibodies against cAMP-PDEs. This form had the properties of ratPDE3.2/PDE4D2, a cAMP-PDE that is inducible by TSH in wild type cells. That an increase in cAMP-specific, rolipram-sensitive PDE plays a role in the phenotype induced by Q227L Gsα was confirmed by measurements of the mitogenic activity. Incubation with rolipram, which had no effect on wild type cells, caused an increase in cAMP levels and further stimulated TSH-independent proliferation in both cell lines carrying the mutation. These data demonstrate that activation of the PDE system in FRTL-5 counteracts, at least in part, the phenotype caused by an activating mutation in Gsα
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
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