PAC learning of probability distributions over a discrete domain

AbstractWe investigate learning of classes of distributions over a discrete domain in a PAC context. We introduce two paradigms of PAC learning, namely absolute PAC learning, which is independent of the representation of the class of hypotheses, and PAC learning wrt the indexes, which heavily depends on such representations. We characterize non-computable learnability in both contexts. Then we investigate efficient learning strategies which are simulated by a polynomial-time Turing machine. One strategy is the frequentist one. According to this strategy, the learner conjectures a hypothesis which is as close as possible to the distribution given by the frequency relative to the examples. We characterize the classes of distributions which are absolutely PAC learnable by means of this strategy, and we relate frequentist learning wrt the indexes to the NP=RP problem. Finally, we present another strategy for learning wrt the indexes, namely learning by tests

Takotsubo cardiomyopathy and neurogenic stunned myocardium: similar albeit different

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Pancreatic cancer spheres are more than just aggregates of stem marker-positive cells

Pancreatic cancer stem-like cells are described by membrane expression of CD24, CD44 and ESA (epithelial-specific antigen) and their capacity to grow as spheres in a serum-free medium containing well-defined growth factors. The capacity of a panel of four pancreatic cancer cell lines (PANC-1, CFPAC-1, PancTu-1 and PSN-1) to form spheres was tested. All cell lines with the exception of PancTu-1 developed spheres. Phenotypically, the sphere-growing cells showed an increased in vitro invasion capability. Both gene and protein expressions of markers of metastases [CXCR4 (CXC chemokine receptor 4), OPN (osteopontin) and CD44v6] and components of active hedgehog pathway signalling were assessed. Spheres clearly demonstrated increased expression of the above-mentioned markers when compared with their adherent counterpart. With the aim of identifying a minimum set of markers able to separate cells that have the capacity to form spheres from those incapable of forming spheres, a PCA (principal component analysis) of the multidimensional dataset was performed. Although PCA of the ‘accepted’ stemness genes was unable to separate sphere-forming from sphere-incapable cell lines, the addition of the ‘aggressiveness’ marker CD44v6 allowed a clear differentiation. Moreover, inoculation of the spheres and the adherent cells in vivo confirmed the superior aggressiveness (proliferation and metastasis) of the spheres over the adherent cells. In conclusion, the present study suggests that the sphere-growing cell population is not only composed of cells displaying classical stem membrane markers but also needs CD44v6-positive cells to successfully form spheres. Our results also emphasize the potential therapeutic importance of pathways such as CXCR4 and hedgehog for pancreatic cancer treatment

A chemogenomic screening identifies CK2 as a target for pro-senescence therapy in PTEN-deficient tumours

Enhancement of cellular senescence in tumours triggers a stable cell growth arrest and activation of an antitumour immune response that can be exploited for cancer therapy. Currently, there are only a limited number of targeted therapies that act by increasing senescence in cancers, but the majority of them are not selective and also target healthy cells. Here we developed a chemogenomic screening to identify compounds that enhance senescence in PTEN-deficient cells without affecting normal cells. By using this approach, we identified casein kinase 2 (CK2) as a pro-senescent target. Mechanistically, we show that Pten loss increases CK2 levels by activating STAT3. CK2 upregulation in Pten null tumours affects the stability of Pml, an essential regulator of senescence. However, CK2 inhibition stabilizes Pml levels enhancing senescence in Pten null tumours. Taken together, our screening strategy has identified a novel STAT3-CK2-PML network that can be targeted for pro-senescence therapy for cancer

A potent and selective Sirtuin 1 inhibitor alleviates pathology in multiple animal and cell models of Huntington's disease

Protein acetylation, which is central to transcriptional control as well as other cellular processes, is disrupted in Huntington's disease (HD). Treatments that restore global acetylation levels, such as inhibiting histone deacetylases (HDACs), are effective in suppressing HD pathology in model organisms. However, agents that selectively target the disease-relevant HDACs have not been available. SirT1 (Sir2 in Drosophila melanogaster) deacetylates histones and other proteins including transcription factors. Genetically reducing, but not eliminating, Sir2 has been shown to suppress HD pathology in model organisms. To date, small molecule inhibitors of sirtuins have exhibited low potency and unattractive pharmacological and biopharmaceutical properties. Here, we show that highly selective pharmacological inhibition of Drosophila Sir2 and mammalian SirT1 using the novel inhibitor selisistat (selisistat; 6-chloro-2,3,4,9-tetrahydro-1H-carbazole-1-carboxamide) can suppress HD pathology caused by mutant huntingtin exon 1 fragments in Drosophila, mammalian cells and mice. We have validated Sir2 as the in vivo target of selisistat by showing that genetic elimination of Sir2 eradicates the effect of this inhibitor in Drosophila. The specificity of selisistat is shown by its effect on recombinant sirtuins in mammalian cells. Reduction of HD pathology by selisistat in Drosophila, mammalian cells and mouse models of HD suggests that this inhibitor has potential as an effective therapeutic treatment for human disease and may also serve as a tool to better understand the downstream pathways of SirT1/Sir2 that may be critical for H

A potent and selective Sirtuin 1 inhibitor alleviates pathology in multiple animal and cell models of Huntington's disease

Protein acetylation, which is central to transcriptional control as well as other cellular processes, is disrupted in Huntington's disease (HD). Treatments that restore global acetylation levels, such as inhibiting histone deacetylases (HDACs), are effective in suppressing HD pathology in model organisms. However, agents that selectively target the disease-relevant HDACs have not been available. SirT1 (Sir2 in Drosophila melanogaster) deacetylates histones and other proteins including transcription factors. Genetically reducing, but not eliminating, Sir2 has been shown to suppress HD pathology in model organisms. To date, small molecule inhibitors of sirtuins have exhibited low potency and unattractive pharmacological and biopharmaceutical properties. Here, we show that highly selective pharmacological inhibition of Drosophila Sir2 and mammalian SirT1 using the novel inhibitor selisistat (selisistat; 6-chloro-2,3,4,9-tetrahydro-1H-carbazole-1-carboxamide) can suppress HD pathology caused by mutant huntingtin exon 1 fragments in Drosophila, mammalian cells and mice. We have validated Sir2 as the in vivo target of selisistat by showing that genetic elimination of Sir2 eradicates the effect of this inhibitor in Drosophila. The specificity of selisistat is shown by its effect on recombinant sirtuins in mammalian cells. Reduction of HD pathology by selisistat in Drosophila, mammalian cells and mouse models of HD suggests that this inhibitor has potential as an effective therapeutic treatment for human disease and may also serve as a tool to better understand the downstream pathways of SirT1/Sir2 that may be critical for HD

A922 Sequential measurement of 1 hour creatinine clearance (1-CRCL) in critically ill patients at risk of acute kidney injury (AKI)

Meeting abstrac