1,720,968 research outputs found
ROLE OF POST-TRANSLATIONAL MODIFICATIONS IN MODULATING APE1 FUNCTIONS IN TUMOUR CELLS
Full text linkApurinic/apyrimidinic endonuclease 1 (APE1) is the main mammalian endonuclease involved in the repair of DNA lesions caused predominantly by oxidative and alkylating stresses through its participation in base excision repair (BER) pathway. Although APE1 was discovered for its ability to cleave and remove AP-sites and to enhance the DNA binding properties of several cancer-related transcription factors, through redox-dependent mechanisms (involving its so-called Ref-1 activity), in the latest years investigators have described new and broader functions for this DNA repair enzyme. In fact, it has been demonstrated a direct role for APE1 in the regulation of gene transcription and an unexpected role in the RNA metabolism being able to cleave damaged or site-specific RNAs. Despite different works regarding the transcriptional and post-translational mechanisms that cells used to control and to redirect APE1 to its several functions, it is still a matter of debate the role of the first 33 amino acids, a unique evolutionary N-terminus specific for the mammalian protein, that impacts, through macromolecules interaction and post-translational modifications, on controlling APE1 activities. In this work of Thesis, new acetylated lysine residues were identified in vivo and the role of acetylation sites at N-terminus (Lys 27-35) in regulating APE1 functions and subcellular localization were studied. Moreover, seventeen new interacting partners were identified. Among these, the attention was focused on APE1 and Nucleophosmin 1 (NPM1) interaction within nucleoli and nucleoplasm. NPM1 is a nucleolar protein, mainly involved in ribosome biogenesis, stress responses and genome maintenance. Growing body of evidences emphasizes a role for NPM1 in DNA repair field, but its exact role(s) has not been identified yet. Interestedly, patients with acute myeloid leukemias (AMLs), characterized by the expression of a mutated form of NPM1 (NPM1c+), causative for its aberrant cytoplasmic localization, represent better responders to chemotherapy and for favorable overall survival. At present, the molecular reasons underneath the role for NPM1 in tumorigenesis of solid tumors and in AMLs are still lacking. In this framework, a clear contribution of NPM1 in DNA repair control, through the functional regulation of the APE1 endonuclease activity in BER pathway, its subcellular localization and stability has been demonstrated in vivo. In this light, the positive clinical impact of NPM1c+ in chemotherapeutic response might be related to the potential interference with the functions of NPM1 interacting partners, once delocalized in the cytoplasm. An intriguing mechanism for explaining also the biological effects of APE1 genetic variants, considered in this work of Thesis, supported by the observation that the majority of the polymorphisms presents an altered complex network of interactions, protein stability and stress response, affecting the APE1 functional status.
Our findings provide a glimpse into the role of the nucleolus and NPM1 in controlling APE1 functions, suggesting a critical role for the intricate network of APE1 interacting partners, especially NPM1, and post-translational modifications in BER in vivo that might be important for explaining the APE1 dysregulation seen in different types of tumors
APE1 polymorphic variants cause persistent genomic stress and affect cancer cell proliferation
Full text linkApurinic/apyrimidinic endonuclease 1 (APE1) is the main mammalian AP-endonuclease responsible for the repair of endogenous DNA damage through the base excision repair (BER) pathway. Molecular epidemiological studies have identified several genetic variants associated with human diseases, but a well-defined functional connection between mutations in APE1 and disease development is lacking. In order to understand the biological consequences of APE1 genetic mutations, we examined the molecular and cellular consequences of the selective expression of four non-synonymous APE1 variants (L104R, R237C, D148E and D283G) in human cells. We found that D283G, L104R and R237C variants have reduced endonuclease activity and impaired ability to associate with XRCC1 and DNA polymerase β, which are enzymes acting downstream of APE1 in the BER pathway. Complementation experiments performed in cells, where endogenous APE1 had been silenced by shRNA, showed that the expression of these variants resulted in increased phosphorylation of histone H2Ax and augmented levels of poly(ADP-ribosyl)ated (PAR) proteins. Persistent activation of DNA damage response markers was accompanied by growth defects likely due to combined apoptotic and autophagic processes. These phenotypes were observed in the absence of exogenous stressors, suggesting that chronic replication stress elicited by the BER defect may lead to a chronic activation of the DNA damage response. Hence, our data reinforce the concept that non-synonymous APE1 variants present in the human population may act as cancer susceptibility alleles
Nucleophosmin modulates stability, activity, and nucleolar accumulation of base excision repair proteins
No full textNucleophosmin (NPM1) is a multifunctional protein that controls cell growth and genome stability via a mechanism that involves nucleolar-cytoplasmic shuttling. It is clear that NPM1 also contributes to the DNA damage response, yet its exact function is po
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
Erratum: Functional regulation of the Apurinic/apyrimidinic endonuclease APE1 by Nucleophosmin (NPM1): Impact on tumor biology
No full textNucleophosmin 1 (NPM1) is a nucleolar protein involved in ribosome biogenesis, stress responses, and maintaining genome stability. One third of acute myeloid leukemias (AMLs) are associated with aberrant localization of Nucleophosmin 1 (NPM1c+) to the cytoplasm. This mutation is critical during leukemogenesis and constitutes a good prognostic factor for chemotherapy. At present, there is no clear molecular basis for the role of NPM1 in DNA repair and the tumorigenic process. We found that the nuclear Apurinic/apyrimidinic endonuclease APE1, a core enzyme in base excision repair (BER) of DNA lesions, specifically interacts with NPM1 within nucleoli and the nucleoplasm. Cytoplasmic accumulation of APE1 is associated with cancers including, as we show, NPM1c+ AML. Here, we show that NPM1 stimulates APE1 BER activity in cells. We provide evidence that expression of the NPM1c+ variant causes cytoplasmic accumulation of APE1 in: i) a heterologous cell system (HeLa cells); ii) the myeloid cell line OCI/AML3 stably expressing NPM1c+; and iii) primary lymphoblasts of NPM1c+ AML patients. Consistent with impaired APE1 localization, OCI/AML3 cells and blasts of AML patients have impaired BER activity. Cytoplasmic APE1 in NPM1c+ myeloid cells is truncated due to proteolysis. Thus, the good prognostic response of NPM1c+ AML to chemotherapy may result from the cytoplasmic relocalization of APE1 and the consequent BER deficiency. NPM1 thus plays an indirect but significant role in BER in vivo that may also be important for NPM1c+ tumorigenesis
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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