1,720,963 research outputs found
Role of mithocondrial Ca2+ uptake in breast cancer cell migration and invasiveness
Full text linkMitochondrial Ca2+ uptake regulates cellular energetic by triggering ATP synthesis. At the same time, Ca2+mit acts as key controller of both cell metabolism and fate. Indeed, a decrease in ATP production elicits autophagy induction, while Ca2+ overload causes organelle dysfunction and release of caspase cofactors. Several pathological conditions, including tumor formation and progression, are directly related to mitochondrial dysfunctions, and reprogramming of mitochondrial metabolism is now considered as an emerging hallmark of cancer. Indeed, even in the presence of oxygen, cancer cells limit their energy supply largely to glycolysis, leading to the so called “aerobic glycolysis” phenotype. Of note, the dependence on glycolytic fueling is further potentiated by hypoxia, a condition that characterizes most tumor microenvironments. Indeed, in response to oxygen deprivation, the hypoxia-indicible-factor-1α (HIF-1α) is stabilized and, consequently, transcription of glucose transporters and glycolysis-related enzymes is induced. In addition, several hereditary tumors have been associated with mutations in key mitochondrial enzymes showing that, in specific settings, an altered mitochondrial metabolism represents a primary trigger for cancer progression.
Consistent with these observations, among the most aggressive human breast tumors, triple-negative-breast-cancers (TNBC), a clinically heterogeneous category of breast tumors that lack expression of estrogen, progesterone and HER2 receptors, show profound metabolic alterations with impaired mitochondrial oxidative.
Our preliminary observations suggested that, in contrast to pre-malignant cells, TNBC metastatic cells accumulate high [Ca2+] into the mitochondrial matrix upon agonist stimulation. These elevate Ca2+mit transients might be essential for metastatic progression, while sensitize premalignant cells to apoptotic stimuli. Accordingly, we hypothesized alternative roles of mitochondrial Ca2+, distinct from mitochondrial energy production and control of cell death, possibly involved in the metastatic progression of these highly malignant breast tumors.
The molecular characterization of the Mitochondrial Calcium Uniporter (MCU), the highly selective channel responsible for Ca2+mit entry into the matrix, opened the chance to modulate mitochondrial function by modifying MCU channel’s activity.
We demonstrated that both pharmacological and genetic inhibition of MCU causes a significant decline in TNBC metastatic cell motility and invasiveness.
Thus, we investigated how Ca2+mit uptake contributes to mitochondrial Reactive-Oxygen-Species (mROS) production, thus playing a crucial role in the regulation of ROS-dependent cascades. Indeed, ROS molecules are considered fundamental molecular effectors for cancer progression, by eliciting metabolic adaptations and in vivo metastasis formation. Coherently, we observed that antioxidant treatments reduce significantly MDA-MB-231 cell migration. Moreover, in the absence of MCU, production of mROS is significantly reduced, suggesting that mROS might play a crucial role in cell malignancy regulation by Ca2+mit uptake. In addition, MCU silencing inhibits hypoxia-inducible factor 1α (HIF-1α) transcription, thus impairing the expression of HIF-target genes involved in metastasis progression, possibly in a ROS-dependent manner. Of note, rescue of HIF-1α expression restores migration of MCU-silenced TNBC cells.
Our results highlight a crucial role of MCU in the control of TNBC metastatic potential and indicate that mitochondrial Ca2+ uptake could represent a novel therapeutic target for clinical intervention.Il flusso di Ca2+ mitocondriale (Ca2+mit) è il principale regolatore della bioenergetica cellulare, grazie al fatto che stimola la produzione di ATP. Allo stesso tempo, il Ca2+mit gioca un ruolo chiave nella regolazione sia del metabolismo sia della morte cellulare. Infatti, una diminuita produzione di ATP porta all’attivazione del processo autofagico (per compensare la mancanza di nutrienti) mentre un accumulo elevato di Ca2+ nel mitocondrio porta inevitabilmente ad una disfunzione dell’organello, seguita dall’attivazione caspasica e quindi dalla morte cellulare . Molte patologie, tra cui la formazione e crescita tumorale, sono direttamente correlabili con le disfunzioni mitocondriali. Inoltre, il reprogramming del metabolismo mitocondriale è ora considerato un aspetto chiave nella patogenesi del cancro. Infatti, anche in presenza di ossigeno, le cellule tumorali limitano gran parte del loro supporto energetico alla glicolisi, raggiungendo lo stato energetico denominato “glicolisi aerobica”. Vale la pena evidenziare che la dipendenza energetica da un regime glicolitico può venir ulteriormente rafforzata in ipossia, condizione che contraddistingue la maggior parte dei microambienti tumorali. Infatti, in risposta alla carenza di ossigeno, il fattore trascrizionale HIF-1α viene stabilizzato e, di conseguenza, viene indotta la trascrizione di proteine di trasporto del glucosio e di enzimi coinvolti direttamente nel metabolismo glicolitico. Inoltre, molti tumori ereditari sono stati associati a mutazioni a carico di enzimi mitocondriali, dimostrando in questo modo che, in particolari condizioni, un’alterazione del metabolismo mitocondriale può esser considerata fattore eziologico per lo sviluppo del tumore.
A supporto di queste considerazioni, il tumore mammario metastatico triplo negativo, una delle più aggressive ed eterogenee classi di tumori caratterizzata dalla mancata espressione dei recettori estrogenici, progestinici ed HER2, mostra una profonda alterazione metabolica con ridotta attività ossidativa mitocondriale.
I nostri risultati preliminari suggeriscono che, al contrario delle cellule pre-maligne, le metastatiche triplo negative riescono ad accumulare, dopo stimolazione, alte [Ca2+] all’interno della matrice mitocondriale. Transienti di Ca2+mit così elevati possono risultare addirittura essenziali per la progressione metastatica, mentre in cellule pre-maligne sensibilizzano alla morte cellulare. Di conseguenza, abbiamo ipotizzato ruoli alternativi per il Ca2+mit, possibilmente coinvolti nello sviluppo metastatico, che fossero diversi da quelli di produzione energetica mitocondriale e di controllo dell’apoptosi.
La caratterizzazione molecolare dell’Uniporto Mitocondriale del Calcio (dall’inglese MCU), canale selettivo per il Ca2+ che ne regola l’ingresso all’interno della matrice, ha aperto la possibilità di modulare la funzione mitocondriale modificando l’attività del canale MCU.
Così, si è deciso di investigare come l’ingresso di Ca2+mit contribuisca alla produzione mitocondriale di specie radicaliche dell’ossigeno (ROS), giocando in questo modo un ruolo cruciale nella regolazione di tutti i meccanismi di segnale ROS-dipendenti: i ROS sono considerati dei critici effettori molecolari della progressione tumorale, promuovendo l’adattamento metabolico e la formazione di metastasi in vivo. Di conseguenza, si è osservato che trattamenti antiossidanti riducono significativamente la migrazione delle cellule tumorali triple negative MDA-MB-231. Inoltre, è stato verificato che, in assenza di MCU, la produzione di ROS è significativamente ridotta, suggerendo così che i ROS mitocondriali giocano un ruolo cruciale nella regolazione della malignità tumorale mediata dal Ca2+mit. In aggiunta, è stato dimostrato che il silenziamento di MCU inibisce significativamente la trascrizione del fattore di trascrizione HIF-1α, riducendo di conseguenza l’espressione dei geni da lui regolati, soprattutto di quelli coinvolti nella progressione metastatica e possibilmente con un meccanismo ROS-dipendente. Da notare, a tal proposito, che la ri-espressione di HIF-1α ripristina completamente la capacità di migrazione nelle cellule in cui MCU è silenziato.
In conclusione, i nostri risultati mettono in luce un ruolo cruciale di MCU nel controllo del potenziale metastatico del tumore mammario triplo negativo ed indicano che il flusso mitocondriale di Ca2+ può rappresentare un nuovo bersaglio terapeutico per un innovativo approccio clinico
Ca(2+) Measurements in Mammalian Cells with Aequorin-based Probes
No full textAequorin is a Ca(2+) sensitive photoprotein suitable to measure intracellular Ca(2+) transients in mammalian cells. Thanks to recombinant cDNAs expression, aequorin can be specifically targeted to various subcellular compartments, thus allowing an accurate measurement of Ca(2+) uptake and release of different intracellular organelles. Here, we describe how to use this probe to measure cytosolic Ca(2+) levels and mitochondrial Ca(2+) uptake in mammalian cells
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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