The bromodomain: a chromatin browser?

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Gcn5 histone acetyltransferase is present in the mitoplasts

In Saccharomyces cerevisiae the Lysine-acetyltransferase Gcn5 (KAT2) is part of the SAGA complex and is responsible for histone acetylation widely or at specific lysines. In this paper we report that GCN5 deletion differently affects the growth of two strains. The defective mitochondrial phenotype is related to a marked decrease in mtDNA content, which also involves the deletion of specific regions of the molecule. We also show that in wild-type mitochondria the Gcn5 protein is present in the mitoplasts, suggesting a new mitochondrial function independent from the SAGA complex and possibly a new function for this protein connecting epigenetics and metabolism

Ty1 extrachromosomal circular copies in Saccharomyces cerevisiae

AbstractThe eukaryotic transposable element Ty1 is present in about 20–30 integrated copies per yeast aploid genome, variably localized in different strains. Here, we report the presence in yeast of circular extrachromosomal molecules homologous to Ty1, 6 kilobases in size (the same as integrated copies) present in about 1 circular copy/250–300 cells. This finding shows another analogy between eurkaryotic-transposable elements and the pro-viral integrative form of retroviruses

Epigenetic Factors and Mitochondrial Biology in Yeast: A New Paradigm for the Study of Cancer Metabolism?

Bidirectional cross-talk between nuclear and mitochondrial DNA is fundamental for cell homeostasis. Epigenetic mechanisms regulate the inter-organelle communication between nucleus and mitochondria. Recent research highlights not only the retrograde activation of nuclear gene transcription in case of mitochondria dysfunction, but also the role of post-translational modifications of mitochondrial proteins in respiratory metabolism. Here we discuss some aspects and novel findings in Saccharomyces cerevisiae. In yeast, KAT-Gcn5 and DUB-Ubp8 have a role in respiration and are localized, as single proteins, into mitochondria. These findings, beside the canonical and widely known nuclear activity of SAGA complex in chromatin regulation, provide novel clues on promising aspects linking evolutionary conserved epigenetic factors to the re-programmed metabolism of cancer cells

Role of yUbp8 in Mitochondria and Hypoxia Entangles the Finding of Human Ortholog Usp22 in the Glioblastoma Pseudo-Palisade Microlayer

KAT Gcn5 and DUB Ubp8 are required for respiration and mitochondria functions in budding yeast, and in this study we show that loss of respiratory activity is acquired over time. Interestingly, we show that absence of Ubp8 allows cells to grow in hypoxic conditions with altered mitophagy. Comparatively, the aggressive glioblastoma (GBM) multiforme tumor shows survival mechanisms able to overcome hypoxia in the brain. Starting from yeast and our findings on the role of Ubp8 in hypoxia, we extended our analysis to the human ortholog and signature cancer gene Usp22 in glioblastoma tumor specimens. Here we demonstrate that Usp22 is localized and overexpressed in the pseudo-palisade tissue around the necrotic area of the tumor. In addition, Usp22 colocalizes with the mitophagy marker Parkin, indicating a link with mitochondria function in GBM. Collectively, this evidence suggests that altered expression of Usp22 might provide a way for tumor cells to survive in hypoxic conditions, allowing the escape of cells from the necrotic area toward vascularized tissues. Collectively, our experimental data suggest a model for a possible mechanism of uncontrolled proliferation and invasion in glioblastoma

Physical association of the WC-1 photoreceptor and the histone acetyltransferase NGF-1 is requifed for blue light signal transduction in Neurospora crassa

In Neurospora crassa and other filamentous fungi, light-dependent–specific phenomena are regulated by transcription factors WC-1 and WC-2. In addition to its transcriptional activity, WC-1 is able to directly sense light stimuli through a LOV sensor domain. Its location in the nucleus and heterodimerization with WC-2, together with the presence of a zinc-finger DNA-binding domain and an environmental sensor domain, all resemble the functional evolutionary architecture adopted by vertebrate nuclear receptors (NRs). Here we describe a scenario in which WC-1 represents a functional orthologue of NRs and acts through association with the chromatin-modifying coactivator NGF-1, which encodes a homologue of the yeast Gcn5p acetyltransferase. To support this view, we show a direct association between WC-1 and NGF-1 that depends on a WC-1 region containing a conserved functional LXXLL motif, a signature previously described as being an exclusive feature of NR/coactivator interaction. Our data suggest that a WC-1/NGF-1 complex is preassembled in the dark on light-inducible promoters and that, after exposure to light stimulation, NGF-1–associated HAT activity leads to histone H3 acetylation and transcriptional activation. Finally, we provide evidence for a NGF-1–independent acetylated form of WC-1. Overall our data indicate that Neurospora and higher eukaryotes share a common mechanism for the signal transduction of environmental stimuli

A novel Gcn5p inhibitor represses cell growth, gene transcription and histone acetylation in budding yeast

Histone acetyltransferases are key chromatin regulators responsible for transcriptional activation and cell cycle progression. We propose a simple yeast-based assay to determine the specificity and targets of novel Gcn5p inhibitors. Here, we report the finding of a novel, small molecule, MC1626, which is able to inhibit yeast cell growth, Gcn5p-dependent gene transcription and acetylation of the histone H3 N-terminal tail in vivo. Because HATs misregulation is invariably associated with human diseases, the identification of MC1626 as a novel cell-permeable Gcn5p inhibitor suggests that it may be a very useful starting tool for the further development of new molecules to be applied to expression profiling of genes regulated by histone H3 acetylation. In addition, our results demonstrate that MC1626 is a Gcn5p-dependent yeast growth inhibitor

Gcn5p Plays an Important Role in Centromere Kinetochore Function in Budding Yeast▿

We report that the histone acetyltransferase Gcn5p is involved in cell cycle progression, whereas its absence induces several mitotic defects, including inefficient nuclear division, chromosome loss, delayed G2 progression, and spindle elongation. The fidelity of chromosome segregation is finely regulated by the close interplay between the centromere and the kinetochore, a protein complex hierarchically assembled in the centromeric DNA region, while disruption of GCN5 in mutants of inner components results in sick phenotype. These synthetic interactions involving the ADA complex lay the genetic basis for the critical role of Gcn5p in kinetochore assembly and function. We found that Gcn5p is, in fact, physically linked to the centromere, where it affects the structure of the variant centromeric nucleosome. Our findings offer a key insight into a Gcn5p-dependent epigenetic regulation at centromere/kinetochore in mitosis

Chemogenomic profiling of the cellular effects associated with histone H3 acetylation impairment by a quinoline-derived compound

We report the results of a chemogenomic profiling aimed to explore the mode of action of a quinolic analogue of the p300 histone acetyltransferase (HAT) inhibitor anacardic acid, named MC1626. This compound reduced histone H3 acetylation in a dose-dependent manner and the HATs Gcn5 and Rtt109, which specifically target H3 lysines, were the only ones that caused chemical-genetic synthetic sickness with MC1626 when mutated. Deletion of specific Gcn5 (e.g., Ada1) and Rtt109 (e.g., Asf1) multiprotein complex components also enhanced MC1626 sensitivity. In addition to N-terminal H3 lysines, MC1626 inhibits H3K56 acetylation, a histone modification that, in yeast, is exclusively supported by Rtt109 and indirectly influences DNA integrity. Several DNA repair mutants were found to be sensitive to MC1626. Functional links between histone acetylation impairment by MC1626 and mitochondrion as well as cytoskeleton functionality were also revealed, thus extending the range of non-nuclear processes that are influenced by histone acetylation. (C) 2010 Elsevier Inc. All rights reserved