Rapid reconstitution of ubiquitinated nucleosome using a non-denatured histone octamer ubiquitylation approach.

BACKGROUND: Histone ubiquitination modification is emerging as a critical epigenetic mechanism involved in a range of biological processes. In vitro reconstitution of ubiquitinated nucleosomes is pivotal for elucidating the influence of histone ubiquitination on chromatin dynamics. RESULTS: In this study, we introduce a Non-Denatured Histone Octamer Ubiquitylation (NDHOU) approach for generating ubiquitin or ubiquitin-like modified histone octamers. The method entails the co-expression and purification of histone octamers, followed by their chemical cross-linking to ubiquitin using 1,3-dibromoacetone. We demonstrate that nucleosomes reconstituted with these octamers display a high degree of homogeneity, rendering them highly compatible with in vitro biochemical assays. These ubiquitinated nucleosomes mimic physiological substrates in function and structure. Additionally, we have extended this method to cross-linking various histone octamers and three types of ubiquitin-like proteins. CONCLUSIONS: Overall, our findings offer an efficient strategy for producing ubiquitinated nucleosomes, advancing biochemical and biophysical studies in the field of chromatin biology.

Author Correction: G-tract RNA removes Polycomb repressive complex 2 from genes.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

G-tract RNA removes Polycomb repressive complex 2 from genes.

Polycomb repressive complex 2 (PRC2) maintains repression of cell-type-specific genes but also associates with genes ectopically in cancer. While it is currently unknown how PRC2 is removed from genes, such knowledge would be useful for the targeted reversal of deleterious PRC2 recruitment events. Here, we show that G-tract RNA specifically removes PRC2 from genes in human and mouse cells. PRC2 preferentially binds G tracts within nascent precursor mRNA (pre-mRNA), especially within predicted G-quadruplex structures. G-quadruplex RNA evicts the PRC2 catalytic core from the substrate nucleosome. In cells, PRC2 transfers from chromatin to pre-mRNA upon gene activation, and chromatin-associated G-tract RNA removes PRC2, leading to H3K27me3 depletion from genes. Targeting G-tract RNA to the tumor suppressor gene CDKN2A in malignant rhabdoid tumor cells reactivates the gene and induces senescence. These data support a model in which pre-mRNA evicts PRC2 during gene activation and provides the means to selectively remove PRC2 from specific genes.

Comment on "Structural basis of histone H3K27 trimethylation by an active polycomb repressive complex 2".

Jiao and Liu (Research Articles, 16 October 2015, aac4383) reported the crystal structure of the protein complex polycomb repressive complex 2 from Chaetomium thermophilum This landmark structure has brought invaluable insights into the activation mechanism of this essential methyltransferase. However, the analysis of the x-ray data discussed below suggests that the description of oncogenic H3K27M peptide binding to the active site is incorrect.

Identification of (R)-N-((4-Methoxy-6-methyl-2-oxo-1,2-dihydropyridin-3-yl)methyl)-2-methyl-1-(1-(1-(2,2,2-trifluoroethyl)piperidin-4-yl)ethyl)-1H-indole-3-carboxamide (CPI-1205), a Potent and Selective Inhibitor of Histone Methyltransferase EZH2, Suitable for Phase I Clinical Trials for B-Cell Lymphomas.

Polycomb repressive complex 2 (PRC2) has been shown to play a major role in transcriptional silencing in part by installing methylation marks on lysine 27 of histone 3. Dysregulation of PRC2 function correlates with certain malignancies and poor prognosis. EZH2 is the catalytic engine of the PRC2 complex and thus represents a key candidate oncology target for pharmacological intervention. Here we report the optimization of our indole-based EZH2 inhibitor series that led to the identification of CPI-1205, a highly potent (biochemical IC50 = 0.002 µM, cellular EC50 = 0.032 µM) and selective inhibitor of EZH2. This compound demonstrates robust antitumor effects in a Karpas-422 xenograft model when dosed at 160 mg/kg BID and is currently in Phase I clinical trials. Additionally, we disclose the co-crystal structure of our inhibitor series bound to the human PRC2 complex.

Structural basis of oncogenic histone H3K27M inhibition of human polycomb repressive complex 2.

Polycomb repressive complex 2 (PRC2) silences gene expression through trimethylation of K27 of histone H3 (H3K27me3) via its catalytic SET domain. A missense mutation in the substrate of PRC2, histone H3K27M, is associated with certain pediatric brain cancers and is linked to a global decrease of H3K27me3 in the affected cells thought to be mediated by inhibition of PRC2 activity. We present here the crystal structure of human PRC2 in complex with the inhibitory H3K27M peptide bound to the active site of the SET domain, with the methionine residue located in the pocket that normally accommodates the target lysine residue. The structure and binding studies suggest a mechanism for the oncogenic inhibition of H3K27M. The structure also reveals how binding of repressive marks, like H3K27me3, to the EED subunit of the complex leads to enhancement of the catalytic efficiency of the SET domain and thus the propagation of this repressive histone modification.

Jarid2 Methylation via the PRC2 Complex Regulates H3K27me3 Deposition during Cell Differentiation.

Polycomb Group (PcG) proteins maintain transcriptional repression throughout development, mostly by regulating chromatin structure. Polycomb Repressive Complex 2 (PRC2), a component of the Polycomb machinery, is responsible for the methylation of histone H3 lysine 27 (H3K27me2/3). Jarid2 was previously identified as a cofactor of PRC2, regulating PRC2 targeting to chromatin and its enzymatic activity. Deletion of Jarid2 leads to impaired orchestration of gene expression during cell lineage commitment. Here, we reveal an unexpected crosstalk between Jarid2 and PRC2, with Jarid2 being methylated by PRC2. This modification is recognized by the Eed core component of PRC2 and triggers an allosteric activation of PRC2's enzymatic activity. We show that Jarid2 methylation is important to promote PRC2 activity at a locus devoid of H3K27me3 and for the correct deposition of this mark during cell differentiation. Our results uncover a regulation loop where Jarid2 methylation fine-tunes PRC2 activity depending on the chromatin context.

Structural features of the single-stranded DNA-binding protein MoSub1 from Magnaporthe oryzae.

The well studied general transcription cofactor Sub1/PC4 has multiple functions in transcription. It plays both a negative and a positive role in transcription initiation and is involved in elongation and downstream transcription processes and as a transcription reinitiation factor. MoSub1, a Sub1/PC4 orthologue from rice blast fungus, binds the single-stranded DNA dT(12) tightly with an affinity of 186 nM. The crystal structure of MoSub1 has been solved to 1.79 Å resolution. The structure of the protein shows high similiarity to the structure of PC4 and it has a similar dimer interface and DNA-binding region to PC4, indicating that MoSub1 could bind DNA using the same motif as other proteins of the Sub1/PC4 family. There are two novel features in the MoSub1 structure: a region N-terminal to the DNA-binding domain and a C-terminal extension. The region N-terminal to the DNA-binding domain of MoSub1 turns back towards the DNA-binding site and may interact directly with DNA or the DNA-binding site. The C-terminal extension region, which is absent in PC4, may not be capable of interacting with DNA and is one possible reason for the differences between Sub1 and PC4.

Using electronic health care records for drug safety signal detection: a comparative evaluation of statistical methods.

BACKGROUND: Drug safety monitoring relies primarily on spontaneous reporting, but electronic health care record databases offer a possible alternative for the detection of adverse drug reactions (ADRs). OBJECTIVES: To evaluate the relative performance of different statistical methods for detecting drug-adverse event associations in electronic health care record data representing potential ADRs. RESEARCH DESIGN: Data from 7 databases across 3 countries in Europe comprising over 20 million subjects were used to compute the relative risk estimates for drug-event pairs using 10 different methods, including those developed for spontaneous reporting systems, cohort methods such as the longitudinal gamma poisson shrinker, and case-based methods such as case-control. The newly developed method "longitudinal evaluation of observational profiles of adverse events related to drugs" (LEOPARD) was used to remove associations likely caused by protopathic bias. Data from the different databases were combined by pooling of data, and by meta-analysis for random effects. A reference standard of known ADRs and negative controls was created to evaluate the performance of the method. MEASURES: The area under the curve of the receiver operator characteristic curve was calculated for each method, both with and without LEOPARD filtering. RESULTS: The highest area under the curve (0.83) was achieved by the combination of either longitudinal gamma poisson shrinker or case-control with LEOPARD filtering, but the performance between methods differed little. LEOPARD increased the overall performance, but flagged several known ADRs as caused by protopathic bias. CONCLUSIONS: Combinations of methods demonstrate good performance in distinguishing known ADRs from negative controls, and we assume that these could also be used to detect new drug safety signals.

Reading, writing and editing methylated lysines on histone tails: new insights from recent structural studies.

The phenotypes of different cell types are governed by their differential gene expression programmes, which are prominently influenced by epigenetic gene regulation featuring heritable chromatin states. Different epigenetic states are associated with distinctive patterns of post-translational modifications of the histone tails, which in turn influence the recruitment of chromatin-modifying effectors and local chromatin structure. Despite rapid advances in understanding how particular histone marks correlate with transcriptional output, many of the molecular details on how the maintenance and alteration of these modifications relate to fundamental processes such as replication, DNA repair, and transcription remain to be elucidated. Here, we review recent advances in the structural description of the reading, writing, and editing of two histone methylation marks with opposite functions: at histone H3 lysine 4 (H3K4)-associated with actively transcribed genes, and at histone H3 lysine 27 (H3K27)-a hallmark of silenced chromatin. These two marks are associated with trithorax and polycomb, respectively, prototypes of the genes involved in epigenetic inheritance in Drosophila. We also briefly discuss some recent examples of how the readout of particular marks is influenced by the presence of other modifications.

Role of the polycomb protein EED in the propagation of repressive histone marks.

Polycomb group proteins have an essential role in the epigenetic maintenance of repressive chromatin states. The gene-silencing activity of the Polycomb repressive complex 2 (PRC2) depends on its ability to trimethylate lysine 27 of histone H3 (H3K27) by the catalytic SET domain of the EZH2 subunit, and at least two other subunits of the complex: SUZ12 and EED. Here we show that the carboxy-terminal domain of EED specifically binds to histone tails carrying trimethyl-lysine residues associated with repressive chromatin marks, and that this leads to the allosteric activation of the methyltransferase activity of PRC2. Mutations in EED that prevent it from recognizing repressive trimethyl-lysine marks abolish the activation of PRC2 in vitro and, in Drosophila, reduce global methylation and disrupt development. These findings suggest a model for the propagation of the H3K27me3 mark that accounts for the maintenance of repressive chromatin domains and for the transmission of a histone modification from mother to daughter cells.

The differential regulation of phosphatidylinositol 4-phosphate 5-kinases and phospholipase D1 by ADP-ribosylation factors 1 and 6.

Phosphatidylinositol 4-phosphate 5-kinases [PtdIns4P5Ks] synthesise the majority of cellular phosphatidylinositol 4,5-bisphosphate [PtdIns(4,5)P(2)] and phospholipase D1 (PLD1) synthesises large amounts of phosphatidic acid (PtdOH). The activities of PtdIns4P5Ks and PLDs are thought to be coupled during cell signalling in order to support large simultaneous increases in both PtdIns(4,5)P(2) and PtdOH, since PtdOH activates PtdIns4P5Ks and PLD1 requires PtdIns(4,5)P(2) as a cofactor. However, little is known about the control of such a system. Membrane recruitment of ADP-ribosylation factors (Arfs) activates both PtdIns4P5Ks and PLDs, but it is not known if each enzyme is controlled in series by different Arfs or in parallel by a single form. We show through pull-down and vesicle sedimentation interaction assays that PtdIns4P5K activation may be facilitated by Arf-enhanced membrane association. However PtdIns4P5Ks discriminate poorly between near homogeneously myristoylated Arf1 and Arf6 although examples of all three known active isoforms (mouse alpha>beta, gamma) respond to these G-proteins. Conversely PLD1 genuinely prefers Arf1 and so the two lipid metabolising enzymes are differentially controlled. We propose that isoform selective Arf/PLD interaction and not Arf/PtdIns4P5K will be the critical trigger in the formation of distinct, optimal triples of Arf/PLDs/PtdIns4P5Ks and be the principle regulator of any coupled increases in the signalling lipids PtdIns(4,5)P(2) and PtdOH.

Regulation of p53 activity through lysine methylation.

p53 is a tumour suppressor that regulates the cellular response to genotoxic stresses. p53 is a short-lived protein and its activity is regulated mostly by stabilization via different post-translational modifications. Here we report a novel mechanism of p53 regulation through lysine methylation by Set9 methyltransferase. Set9 specifically methylates p53 at one residue within the carboxyl-terminus regulatory region. Methylated p53 is restricted to the nucleus and the modification positively affects its stability. Set9 regulates the expression of p53 target genes in a manner dependent on the p53-methylation site. The crystal structure of a ternary complex of Set9 with a p53 peptide and the cofactor product S-adenosyl-l-homocysteine (AdoHcy) provides the molecular basis for recognition of p53 by this lysine methyltransferase.

The first strain of Clostridium perfringens isolated from an avian source has an alpha-toxin with divergent structural and kinetic properties.

Clostridium perfringens alpha-toxin is a 370-residue, zinc-dependent, phospholipase C that is the key virulence determinant in gas gangrene. It is also implicated in the pathogenesis of sudden death syndrome in young animals and necrotic enteritis in chickens. Previously characterized alpha-toxins from different strains of C. perfringens are almost identical in sequence and biochemical properties. We describe the cloning, nucleotide sequencing, expression, characterization, and crystal structure of alpha-toxin from an avian strain, SWan C. perfringens (SWCP), which has a large degree of sequence variation and altered substrate specificity compared to these strains. The structure of alpha-toxin from strain CER89L43 has been previously reported in open (active site accessible to substrate) and closed (active site obscured by loop movements) conformations. The SWCP structure is in an open-form conformation, with three zinc ions in the active site. This is the first example of an open form of alpha-toxin crystallizing without the addition of divalent cations to the crystallization buffer, indicating that the protein can retain three zinc ions bound in the active site. The topology of the calcium binding site formed by residues 269, 271, 336, and 337, which is essential for membrane binding, is significantly altered in comparison with both the open and closed alpha-toxin structures. We are able to relate these structural changes to the different substrate specificity and membrane binding properties of this divergent alpha-toxin. This will provide essential information when developing an effective vaccine that will protect against C. perfringens infection in a wide range of domestic livestock.