1,721,013 research outputs found
Interaction of HIV-1 Tat protein with heparin. Role of the backbone structure, sulfation, and size.
No full textHuman immunodeficiency virus type 1 (HIV-1) Tat protein is released from infected cells. Extracellular Tat enters the cell where it stimulates the transcriptional activity of HIV-long terminal repeat (LTR) and of endogenous genes. Heparin modulates the angiogenic (Albini, A., Benelli, R., Presta, M., Rusnati, M., Ziche, M., Rubartelli, A., Paglialunga, G., Bussolino, F., and Noonan, D. (1996) Oncogene 12, 289-297) and transcriptional (Mann, D. A., and Frankel, A. D. (1991) EMBO J. 10, 1733-1739) activity of extracellular Tat. Here we demonstrate that heparin binds specifically to recombinant HIV-1 Tat produced as glutathione S-transferase (GST) fusion protein and immobilized on glutathione-agarose beads. Heparin and heparan sulfate (HS), but not dermatan sulfate, chondroitin sulfates A and C, hyaluronic acid, and K5 polysaccharide, competed with 3H-labeled heparin for binding to immobilized GST-Tat and inhibited HIV-LTR transactivation induced by extracellular GST-Tat. Selective 2-O-, 6-O-, total-O-desulfation, or N-desulfation/N-acetylation dramatically reduced the capacity of heparin to bind GST-Tat. Totally-O-desulfated and 2-O-desulfated heparins also showed a reduced capacity to inhibit the transactivating activity of GST-Tat. Very low molecular weight heparins showed a significant decrease in their capacity to bind GST-Tat and to inhibit its LTR transactivating activity when compared with conventional 13.6-kDa heparin. However, when 3.0-kDa heparin was affinity chromatographed on immobilized GST-Tat to isolate binding and non-binding subfractions, the Tat-bound fraction was >/=1,000 times more potent than the unbound fraction in inhibiting the transactivating activity of GST-Tat. The results demonstrate that Tat interacts in a size-dependent manner with heparin/HS and that high affinity Tat-heparin interaction requires at least some 2-O-, 6-O-, and N-positions to be sulfated. The Tat binding activity of the glycosaminoglycans tested correlates with their capacity to affect the transactivating activity of extracellular Tat, indicating the possibility to design specific heparin/HS-like structures with Tat-antagonist activity
The basic domain in HIV-1 Tat protein as a target for polysulfonated heparin-mimicking extracellular Tat antagonists.
No full textHeparin binds extracellular HIV-1 Tat protein and modulates its HIV long terminal repeat (LTR)-transactivating activity (M. Rusnati, D. Coltrini, P. Oreste, G. Zoppetti, A. Albini, D. Noonan, F. d'Adda di Fagagna, M. Giacca, and M. Presta (1997) J. Biol. Chem. 272, 11313-11320). On this basis, the glutathione S-transferase (GST)-TatR49/52/53/55/56/57A mutant, in which six arginine residues within the basic domain of Tat were mutagenized to alanine residues, was compared with GST-Tat for its capacity to bind immobilized heparin. Dissociation of the GST-TatR49/52/53/55/56/57A.heparin complex occurred at ionic strength significantly lower than that required to dissociate the GST-Tat.heparin complex. Accordingly, heparin binds immobilized GST-Tat and GST-TatR49/52/53/55/56/57A with a dissociation constant equal to 0.3 and 1.0 microM, respectively. Also, the synthetic basic domain Tat-(41-60) competes with GST-Tat for heparin binding. Suramin inhibits [3H]heparin/Tat interaction, 125I-GST-Tat internalization, and the LTR-transactivating activity of extracellular Tat in HL3T1 cells and prevents 125I-GST-Tat binding and cell proliferation in Tat-overexpressing T53 cells. The suramin derivative 14C-PNU 145156E binds immobilized GST-Tat with a dissociation constant 5 times higher than heparin and is unable to bind GST-TatR49/52/53/55/56/57A. Although heparin was an antagonist more potent than suramin, modifications of the backbone structure in selected suramin derivatives originated Tat antagonists whose potency was close to that shown by heparin. In conclusion, suramin derivatives bind the basic domain of Tat, prevent Tat/heparin and Tat/cell surface interactions, and inhibit the biological activity of extracellular Tat. Our data demonstrate that tailored polysulfonated compounds represent potent extracellular Tat inhibitors of possible therapeutic value
Basic fibroblast growth factor: production, mitogenic response, and post-receptor signal transduction in cultured normal and transformed fetal bovine aortic endothelial cells
No full textNormal FBAE AG 7680 cells and chemically transformed FBAE GM 7373 cells were compared for their capacity to produce and to respond to bFGF. Normal FBAE cells showed higher levels of bFGF protein and of poly(A)+ bFGF mRNA than transformed GM 7373 cells, indicating that chemical transformation in FBAE cells is paralleled by a decrease of bFGF gene expression. Basic FGF induced cell proliferation in both normal and transformed FBAE cells. However, bFGF appeared to be much more potent in transformed than in normal cells. No differences in bFGF membrane receptors were observed between normal and transformed FBAE cells in terms of apparent molecular weight, number per cell, dissociation constant, and kinetic of downregulation. In respect to normal cells, however, transformed GM 7373 cells showed higher basal levels of PKC activity. This kinase is activated by bFGF and is involved in mediating the mitogenic activity of bFGF, as shown by the capacity of the PKC inhibitor H-7 to abolish the mitogenic activity of bFGF both in normal and transformed FBAE cells. Like bFGF, the PKC activators DAG and TPA exerted a stronger mitogenic activity in transformed than in normal FBAE cells. Thus, the different susceptibility of normal and transformed FBAE cells to bFGF appears to depend on differences in the post-receptor signal transduction mediated by PKC rather than on differences in bFGF receptors. The results indicate that chemical transformation causes significant modifications of bFGF physiology in FBAE cells. The relevance of these modifications to the genesis of tumors of vascular origin deserves further investigation
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
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