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Publisher Correction: A reconstituted cell-free assay for the evaluation of the intrinsic activity of purified human ribosomes
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Shiga toxin 1 acting on DNA in vitro is a heat-stable enzyme not requiring proteolytic activation
No full textA reconstituted cell-free assay for the evaluation of the intrinsic activity of purified human ribosomes
No full textWe describe a cell-free translation system for evaluating the activity of ribosomes stringently purified from human cells. This system is based on in vitro reconstitution of the cellular translation machinery, in which a ribosome-free rabbit reticulocyte lysate (RRL) is reassembled with human ribosomes and in vitro-Transcribed reporter mRNAs. The protocol describes the preparation of the RRL-derived fractions, purification of ribosomes devoid of detectable nonribosomal-Associated factors, and assembly of the reactions to evaluate ribosomal translational efficiency and fidelity using appropriate reporter transcripts. The whole procedure can be completed in ∼ 2.5 d (plus 2 weeks for RRL preparation and cell expansion time). This protocol can be applied to study intrinsic functional properties (cis-Acting element-mediated translation initiation or translational fidelity) of ribosome populations from different sources (including nonhuman origin). It is therefore useful for the characterization of ribosomal function in ribosomopathies and cancer, and it will be applicable in the emerging fields of ribosome diversity and specialized ribosomes
The inhibition of lactate dehydrogenase A hinders the transcription of histone 2B gene independently from the block of aerobic glycolysis
No full textMost cancer cells use aerobic glycolysis to fuel their growth and many efforts are made to selectively block this metabolic pathway in cancer cells by inhibiting lactate dehydrogenase A (LDHA). However, LDHA is a moonlighting protein which exerts functions also in the nucleus as a factor associated to transcriptional complexes. Here we found that two small molecules which inhibit the enzymatic activity of LDHA hinder the transcription of histone 2B gene independently from the block of aerobic glycolysis. Moreover, we observed that silencing this gene reduces cell replication, hence suggesting that the inhibition of LDHA can also affect the proliferation of normal non-glycolysing dividing cells
The antibiotic polymyxin B impairs the interactions between Shiga toxins and human neutrophils
No full textHemolytic uremic syndrome (HUS) is the life-threatenig sequela of intestinal infections by Shiga toxin (Stx)-producing Escherichia coli (STEC) in children. Human neutrophils specifically bind Stx through TLR4, the receptor of LPS. The binding could be considered protective (Stx sequestration) or harmful (toxin delivery to target organs). The amount of Stx on neutrophils is in equilibrium with the amount of Stx present in the gut, and it is also related to renal and neurologic symptoms. The TLR4-mediated interaction of LPS with innate immune cells is hampered by the well-known antibiotic polymyxin B. In this study, we show that the same antibiotic impairs the binding of Stx to neutrophils, also blocking their functional effects (release of CXCL8, formation of neutrophil/platelet aggregates) involved in HUS pathogenesis. Controls for contaminating LPS in Stx-induced neutrophil responses inhibited by polymyxin B were performed. Stx interact with human neutrophils through their A chain, since these leukocytes do not express globotriaosylceramide, the specific receptor for Stx B chains. Consistently, polymyxin B blocked the enzymatic activity of Stx1, Stx2, Stx1 A chain, and the analogous plant protein gelonin, whereas the antibiotic did not show any protective effect on Stx-induced cytotoxicity in globotriaosylceramide-expressing Raji cells. Antibiotic administration is not recommended in human STEC infections during the prodromal intestinal phase, and the toxicity of polymyxin B could further discourage its therapeutic use. However, nontoxic, nonbactericidal polymyxin derivatives have been developed and might be used in animal models of STEC infection to study their efficacy in preventing the onset of HUS during the systemic blood phase of Stx
Cap-independent protein synthesis is enhanced by betaine under hypertonic conditions
No full textProtein synthesis is one of the main cellular functions inhibited during hypertonic challenge. The subsequent accumulation of the compatible osmolyte betaine during the later adaptive response allows not only recovery of translation but also its stimulation. In this paper, we show that betaine modulates translation by enhancing the formation of cap-independent 48 S pre-initiation complexes, leaving cap-dependent 48 S pre-initiation complexes basically unchanged. In the presence of betaine, CrPV IRES- and sodium-dependent neutral amino acid transporter-2 (SNAT2) 5′-UTR-driven translation is 2- and 1.5-fold stimulated in MCF7 cells, respectively. Thus, betaine could provide an advantage in translation of messengers coding for proteins implicated in the response of cells to different stressors, which are often recognized by ribosomal 40 S subunit through simplified cap-independent mechanisms
A Rapid and Sensitive Method to Measure the Functional Activity of Shiga Toxins in Human Serum
No full textShiga toxins (Stx) have a definite role in the development of hemolytic uremic syndrome in children with hemorrhagic colitis caused by pathogenic Stx-producing Escherichia coli (STEC) strains. The dramatic effects of these toxins on the microvasculature of different organs, particularly of the kidney, are well known, whereas there is no consensus on the mechanism by which Stx reach the endothelia of target organs and/or indirectly injure these body sites. We hereby describe a quick (4 h), radioactive, Raji cell-based method designed for the detection of Stx in human sera. The assay monitors the translation impairment induced by these powerful inhibitors of protein synthesis, which are identified properly by neutralizing their activity with specific monoclonal antibodies. By this method, we detected for the first time the functional activity of Stx in sera of STEC-infected patients during hemorrhagic colitis. Recent research has pointed to a dynamic process of Stx-induced renal intoxication in which concurrent and interactive steps are involved. Our rapid and specific method could be useful for studying the kinetics of Stx during the natural course of STEC infection and the interplay between Stx activity in serum and Stx presence in different blood fractions (neutrophils, monocytes, platelets, leukocyte-platelet aggregates, microvesicles, lipoproteins)
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
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