Checkpoint inhibition of the APC/C in HeLa cells is mediated by a complex of BUBR1, BUB3, CDC20, and MAD2

The mitotic checkpoint prevents cells with unaligned chromosomes from prematurely exiting mitosis by inhibiting the anaphase-promoting complex/cyclosome (APC/C) from targeting key proteins for ubiquitin-mediated proteolysis. We have examined the mechanism by which the checkpoint inhibits the APC/C by purifying an APC/C inhibitory factor from HeLa cells. We call this factor the mitotic checkpoint complex (MCC) as it consists of hBUBR1, hBUB3, CDC20, and MAD2 checkpoint proteins in near equal stoichiometry. MCC inhibitory activity is 3,000-fold greater than that of recombinant MAD2, which has also been shown to inhibit APC/C in vitro. Surprisingly, MCC is not generated from kinetochores, as it is also present and active in interphase cells. However, only APC/C isolated from mitotic cells was sensitive to inhibition by MCC. We found that the majority of the APC/C in mitotic lysates is associated with the MCC, and this likely contributes to the lag in ubiquitin ligase activity. Importantly, chromosomes can suppress the reactivation of APC/C. Chromosomes did not affect the inhibitory activity of MCC or the stimulatory activity of CDC20. We propose that the preformed interphase pool of MCC allows for rapid inhibition of APC/C when cells enter mitosis. Unattached kinetochores then target the APC/C for sustained inhibition by the MCC

Modeling Dual Pathways for the Metazoan Spindle Assembly Checkpoint

Using computational modelling, we investigate mechanisms of signal transduction focusing on the spindle assembly checkpoint where a single unattached kinetochore is able to signal to prevent cell cycle progression. This inhibitory signal switches off rapidly once spindle microtubules have attached to all kinetochores. This requirement tightly constrains the possible mechanisms. Here we investigate two possible mechanisms for spindle checkpoint operation in metazoan cells, both supported by recent experiments. The first involves the free diffusion and sequestration of cell-cycle regulators. This mechanism is severely constrained both by experimental fluorescence recovery data and also by the large volumes involved in open mitosis in metazoan cells. Using a simple mathematical analysis and computer simulation, we find that this mechanism can generate the inhibition found in experiment but likely requires a two stage signal amplification cascade. The second mechanism involves spatial gradients of a short-lived inhibitory signal that propagates first by diffusion but then primarily via active transport along spindle microtubules. We propose that both mechanisms may be operative in the metazoan spindle assembly checkpoint, with either able to trigger anaphase onset even without support from the other pathway.Comment: 9 pages, 2 figure

Lecturas filosóficas de la posición política e ideológica de Batman

Although the characters (super heroes) of comic book fictions and other audiovisual products such as movies, cartoons and video games, among others, are designed -in theory- for a young audience, this does not mean that they are neutral or devoid of a defined political and ideological position that is susceptible to philosophical study, in order to reveal their essence, characteristic attributes and, in short, their true being. Considering that the impact of these characters of Anglo-Saxon popular culture has been significant in global social representations in general, the aim of the article was to carry out a philosophical re-reading of Batman's political and ideological position. Methodologically speaking, semiotic hermeneutics and Socratic maieutics were employed to reveal the crucial aspects of the discourse of Gotham's main superhero. Everything allows concluding that, in his being and doing, the so-called "bat-man" is an anarchist, in the predominant form of Anglo-Saxon type anarcho-capitalism, who distrusts the capacity of the institutions of justice of his fictional world to defeat crime and to create, in addition, true spaces of justice in the intersubjective relations of the community.Aunque los personajes (super héroes) de las ficciones propias de los comics y otros productos audiovisuales como el cine, las caricaturas y los videojuegos, entre otros, están diseñados –en teoría– para un público joven, no significa con esto que sean neutrales o que estén desprovistos de una definida posición política e ideológica que sea susceptible al estudio filosófico, para revelar su esencia, atributos característicos y, en suma, su ser verdadero. Considerando que el impacto de estos personajes propios de la cultura popular anglosajona ha sigo significativo en las representaciones sociales globales en general, el objetivo del articulo consistió en efectuar una relectura filosófica de la posición política e ideológica de Batman. Metodológicamente hablando, se empleó la hermenéutica semiótica para revelar los aspectos cruciales del discurso del principal super héroe de Ciudad Gótica. Todo permite concluir que, en su ser y hacer, el llamado “hombre murciélago” es un anarquista, en la forma predominante del anarcocapitalismo de tipo anglosajón, que desconfía de la capacidad de las instituciones de justicia de su mundo ficcional para vencer el crimen y crear, además, espacios verdaderos de justicia en las relaciones intersubjetivas de la comunidad

A tumor suppressor role of the Bub3 spindle checkpoint protein after apoptosis inhibition.

Most solid tumors contain aneuploid cells, indicating that the mitotic checkpoint is permissive to the proliferation of chromosomally aberrant cells. However, mutated or altered expression of mitotic checkpoint genes accounts for a minor proportion of human tumors. We describe a Drosophila melanogaster tumorigenesis model derived from knocking down spindle assembly checkpoint (SAC) genes and preventing apoptosis in wing imaginal discs. Bub3-deficient tumors that were also deficient in apoptosis displayed neoplastic growth, chromosomal aneuploidy, and high proliferative potential after transplantation into adult flies. Inducing aneuploidy by knocking down CENP-E and preventing apoptosis does not induce tumorigenesis, indicating that aneuploidy is not sufficient for hyperplasia. In this system, the aneuploidy caused by a deficient SAC is not driving tumorigenesis because preventing Bub3 from binding to the kinetochore does not cause hyperproliferation. Our data suggest that Bub3 has a nonkinetochore-dependent function that is consistent with its role as a tumor suppressor

A cross-sectional study of the association between ventilation of gas stoves and chronic respiratory illness in U.S. children enrolled in NHANESIII

BACKGROUND: Gas stoves emit pollutants that are respiratory irritants. U.S. children under age 6 who live in homes where gas stoves are used for cooking or heating have an increased risk of asthma, wheeze and reduced lung function. Yet few studies have examined whether using ventilation when operating gas stoves is associated with a decrease in the prevalence of respiratory illnesses in this population. METHODS: The Third National Health and Nutrition Examination Survey was used to identify U.S. children aged 2–16 years with information on respiratory outcomes (asthma, wheeze, and bronchitis) who lived in homes where gas stoves were used in the previous 12 months and whose parents provided information on ventilation. Logistic regression models evaluated the association between prevalent respiratory outcomes and ventilation in homes that used gas stoves for cooking and/or heating. Linear regression models assessed the association between spirometry measurements and ventilation use in children aged 8–16 years. RESULTS: The adjusted odds of asthma (Odds Ratio [OR] = 0.64; 95% confidence intervals [CI]: 0.43, 0.97), wheeze (OR = 0.60, 95% CI: 0.42, 0.86), and bronchitis (OR = 0.60, 95% CI: 0.37, 0.95) were lower among children whose parents reported using ventilation compared to children whose parents reported not using ventilation when operating gas stoves. One-second forced expiratory volume (FEV₁) and FEV₁/FVC ratio was also higher in girls who lived in households that used gas stoves with ventilation compared to households that used gas stoves without ventilation. CONCLUSIONS: In homes that used gas stoves, children whose parents reported using ventilation when operating their stove had higher lung function and lower odds of asthma, wheeze, and bronchitis compared to homes that never used ventilation or did not have ventilation available after adjusting for other risk factors. Additional research on the efficacy of ventilation as an intervention for ameliorating respiratory symptoms in children with asthma is warranted.Keywords: Spirometry, NHANES, Wheeze, Gas stoves, Ventilation, Bronchitis, Asthma, Childre

How cyclin A destruction escapes the spindle assembly checkpoint

Cyclin A outcompetes inhibitory spindle assembly checkpoint proteins for binding to the APC/C ubiquitin ligase coactivator Cdc20 to promote its self-destruction even when the checkpoint is active (see also a paper from van Zon et al., in this issue)