1,720,959 research outputs found
Role of RAD51 overexpession on activation of the Fanconi complex after DNA damage
No full textZiel dieser Arbeit war, den Einfluss der Überexpression von RAD51 – dem zentralen Protein der homologen Rekombination – auf die funktionelle Aktivierung der nachfolgenden Signalkaskade der DNA-Reparatur zu überprüfen. Dies wurde anhand der Phosphorylierung von ATM, ATR und FANCD2 nach Schadensinduktion mittels Bestrahlung beziehungsweise Behandlung mit Mitomycin C und Wasserstoffperoxid untersucht. In einer vorangegangenen Arbeit wurde bereits gezeigt, dass eine Überexpression von RAD51, nicht – wie erwartet – zu einer Resistenzbildung nach vergleichbarer Schadensinduktion führte (Parplys et al., 2015). Eine mögliche Ursache hierfür könnte die veränderte Synthese bzw. Aktivierung von Sensoren der DNA-Reparatur, wie z.B. ATM, ATR oder FANCD2, oder eine fehlerhafte Beladung des Chromatins mit RAD51 sein. In der vorgelegten Arbeit wurde der Einfluss der RAD51 Überexpression auf die Aktivierung der intrazellulären Signalkaskaden, vermittelt durch ATM und ATR, untersucht.
In den methodischen Vorarbeiten wurde zunächst der optimale Zeitpunkt für die maximale Aktivierung der Proteine ATM, ATR und FANCD2 nach Schadensinduktion untersucht. Für ATM wurde eine sehr frühe Aktivierung, nach 2-8h nach Bestrahlung, analog dazu für H2O2 ebenfalls nach 1-4h, und keine Aktivierung durch MMC beobachtet. Für die Aktivierung von ATR zeigte sich dagegen ein vollständig anderes Bild, mit einer schnellen und persistierenden Aktivierung von 0.5 bis 24h nach MMC, 24h für Bestrahlung und keine auffällige Aktivierung nach H2O2. Für FANCD2 zeigte sich im Wesentlichen nur eine Aktvierung durch Behandlung mit MMC. Basierend auf diesen Ergebnissen erfolgte in den weiteren Experimenten zum Einfluss der RAD51 Überexpression auf die Aktivierung der Signalkaskade die Extraktion bei Bestrahlung nach 8h, bei MMC nach 24 h und bei H2O2 nach 4h.
Bezogen auf die Aktivierung von ATM zeigte sich eine verminderte Aktivierung nach Bestrahlung unter RAD51 Überexpression und eine leicht erhöhte Aktivierung nach MMC und Wasserstoffperoxid. Bezüglich ATR war auffällig, dass die Expression von ATR selbst anstieg, die Aktivierung allerdings vergleichbar oder eher geringer im Vergleich zu den Kontrollzellen ausfiel. Die Aktivierung von FANCD2 war nach Behandlung mit H2O2 deutlich erhöht in Zellen mit RAD51 Überexpression. Diese beobachteten Unterschiede zeigten sich ebenfalls im zellulären Überleben nach Behandlung mit den verschiedenen Agenzien. So zeigte sich keine Veränderung in der zellulären Strahlenempfindlichkeit nach Bestrahlung bei Überexpression von RAD51, aber eine deutliche Sensitivierung nach Behandlung mit MMC und H2O2.
Die Arbeit zeigte damit erstmalig, dass die RAD51 Überexpression zu einer Störung der intrazellulären Signalkaskade auf der Ebene von ATR und FANCD2 führt, während die Aktivierung von ATM weitestgehend unverändert bleibt. Dies drückt sich auch auf der Ebene des zellulären Überlebens aus, mit einer Sensitivität gegenüber Agenzien, die insbesondere zur Schädigung in der S-Phase führen. Diese Ergebnisse deuten darauf hin, dass sich die Überexpression von RAD51 insbesondere bei der Reparatur von Schäden, welche die aktive Replikation stören, auswirkt – entweder durch fehlerhafte Signalgebung, oder verminderte DNA Reparaturprozesse. Diese Beobachtungen sind insbesondere für Tumorentitäten von Bedeutung, für die bereits eine Überexpression von RAD51 beobachtet wurde. Möglich wäre, dass diese Tumore deutlich empfindlicher auf DNA-DNA vernetzende Agenzien, wie Cisplatin, sowie Topoisomerase I hemmende Agenzien wie Camptothecin, aber auch neue Inhibitoren wie PARP1 reagieren könnten und damit das Outcome dieser Patienten maßgeblich verbessert werden könnte.The aim of this study was to investigate the effect of RAD51 overexpression on the activation of DNA-repair proteins. RAD51 is the central protein in the homologous recombination pathway of the DNA repair mechanism. The effect of RAD51 overexpression was analysed by investigating the phosphorylation of ATM, ATR and FANCD2 after irradiation, treatment with MMC and H2O2.
In a previous study, no influence of RAD51 overexpression on cellular resistance after comparable DNA damage was observed (Parplys et al., 2015). The reason could be a modified synthesis or activation of the sensors of DNA repair, for example ATM, ATR or FANCD2, or an inaccurate loading of RAD51 onto DNA. In our study, the influence of RAD 51 overexpression on the activation of intracellular pathways mediated by ATM and ATR was investigated.
In ancillary methodological studies, the time point of the maximum activation of the proteins ATM, ATR and FANCD2 after DNA damage was established. An early activation of ATM after irradiation (2-8h) and after treatment with H2O2 (1-4h), as well as no activation after treatment with MMC were detected. In contrast, the activation of ATR was fast and persistent after treatment with MMC (0,5-24h) and after irradiation (24h), and not detectable after treatment with H2O2. Only activation after treatment with MMC was observed for FANCD2, essentially. Based on these results, the protein extraction was performed 8h after irradiation, 24h after treatment with MMC and 4h after treatment with H2O2.
In RAD51 overexpression, we observed reduced activation of ATM after irradiation and slightly elevated activation of ATM after MMC and H2O2. With regard to ATR, an increased expression of the ATR protein was noticed, while its activation remained similar or slightly reduced in RAD51 overexpression compared to control cells. Furthermore, the activation of FANCD2 after exposure to H2O2 was substantially elevated in cells with RAD51 overexpression.
Similar findings were also observed in cellular survival after treatment with the various substances. In detail, no difference in cellular survival was noticed in RAD51 overexpression after irradiation, in contrast to a substantially reduced cellular survival after treatment with MMC and H2O2.
In conclusion, to the best of our knowledge, this work showed for the first time that RAD51 overexpression leads to dysfunction of the intracellular signalling cascade at the level of ATR and FANCD2, while the activation of ATM remains largely intact. This results in augmented sensitivity towards substances acting during the S-phase, which also impacts cellular survival. Our results indicate that RAD51 overexpression particularly impacts the repair of DNA damage disturbing active replication. This may be caused by dysfunctional signalling or disturbed response to DNA damage.
Our observations are of particular relevance for tumours with known overexpression of RAD51. Possibly such tumours would react much more sensitively towards DNA crosslinking agents such as Cisplatin, as well as towards topomerase-I-inhibitors (e.g., Camptothecin), and novel inhibitors such as PARP1. Thus, the outcomes of patients suffering from such neoplasms could potentially be improved significantly
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
Optical Coherence Tomography Angiography (OCTA) Captures Early Micro-Vascular Remodeling in Non-Melanoma Skin Cancer During Superficial Radiotherapy: A Proof-of-Concept Study
Full text linkBackground/Objectives: This proof-of-concept study evaluated whether optical coherence tomography angiography (OCTA) can non-invasively capture micro-vascular alterations in non-melanoma skin cancer (NMSC) lesions during and after superficial orthovoltage radiotherapy (RT) using radiomics and vascular features analysis. Methods: Eight patients (13 NMSC lesions) received 36–50 Gy in 6–20 fractions. High-resolution swept-source OCTA volumes (1.1 × 10 × 10 mm3) were acquired from each lesion at three time points: pre-RT, immediately post-RT, and three months post-RT. Additionally, healthy skin baseline was scanned. After artifact suppression and region-of-interest cropping, (i) first-order and texture radiomics and (ii) skeleton-based vascular features were extracted. Selected features after LASSO (least absolute shrinkage and selection operator) were explored with principal-component analysis. An XGBoost model was trained to classify time points with 100 bootstrap out-of-bag validations. Kruskal–Wallis tests with Benjamini–Hochberg correction assessed longitudinal changes in the 20 most influential features. Results: Sixty-one OCTA volumes were analyzable. LASSO retained 47 of 103 features. The first two principal components explained 63% of the variance, revealing a visible drift of lesions from pre- to three-month post-RT clusters. XGBoost achieved a macro-averaged AUC of 0.68 ± 0.07. Six features (3 texture, 2 first order, 1 vascular) changed significantly across time points (adjusted p < 0.05), indicating dose-dependent reductions in signal heterogeneity and micro-vascular complexity as early as treatment completion, which deepened by three months. Conclusions: OCTA-derived radiomic and vascular signatures tracked RT-induced micro-vascular remodeling in NMSC. The approach is entirely non-invasive, label-free, and feasible at the point of care. As an exploratory proof-of-concept, this study helps to refine scanning and analysis protocols and generates knowledge to support future integration of OCTA into adaptive skin-cancer radiotherapy workflows
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
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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