EZHIP constrains Polycomb Repressive Complex 2 activity in germ cells

Epigenomic Reprogramming as a Driver of Malignant Glioma

Malignant gliomas are central nervous system tumors and remain among the most treatment-resistant cancers. Exome sequencing has revealed significant heterogeneity and important insights into the molecular pathogenesis of gliomas. Mutations in chromatin modifiers-proteins that shape the epigenomic landscape through remodeling and regulation of post-translational modifications on chromatin-are very frequent and often define specific glioma subtypes. This suggests that epigenomic reprogramming may be a fundamental driver of glioma. Here, we describe the key chromatin regulatory pathways disrupted in gliomas, delineating their physiological function and our current understanding of how their dysregulation may contribute to gliomagenesis.

Post-translational modifications of PRC2: signals directing its activity

Polycomb repressive complex 2 (PRC2) is a chromatin-modifying enzyme that catalyses the methylation of histone H3 at lysine 27 (H3K27me1/2/3). This complex maintains gene transcriptional repression and plays an essential role in the maintenance of cellular identity as well as normal organismal development. The activity of PRC2, including its genomic targeting and catalytic activity, is controlled by various signals. Recent studies have revealed that these signals involve cis chromatin features, PRC2 facultative subunits and post-translational modifications (PTMs) of PRC2 subunits. Overall, these findings have provided insight into the biochemical signals directing PRC2 function, although many mysteries remain.

The epigenomics of sarcoma

Epigenetic regulation is critical to physiological control of development, cell fate, cell proliferation, genomic integrity and, fundamentally, transcriptional regulation. This epigenetic control occurs at multiple levels including through DNA methylation, histone modification, nucleosome remodelling and modulation of the 3D chromatin structure. Alterations in genes that encode chromatin regulators are common among mesenchymal neoplasms, a collection of more than 160 tumour types including over 60 malignant variants (sarcomas) that have unique and varied genetic, biological and clinical characteristics. Herein, we review those sarcomas in which chromatin pathway alterations drive disease biology. Specifically, we emphasize examples of dysregulation of each level of epigenetic control though mechanisms that include alterations in metabolic enzymes that regulate DNA methylation and histone post-translational modifications, mutations in histone genes, subunit loss or fusions in chromatin remodelling and modifying complexes, and disruption of higher-order chromatin structure. Epigenetic mechanisms of tumorigenesis have been implicated in mesenchymal tumours ranging from chondroblastoma and giant cell tumour of bone to chondrosarcoma, malignant peripheral nerve sheath tumour, synovial sarcoma, epithelioid sarcoma and Ewing sarcoma - all diseases that present in a younger patient population than most cancers. Finally, we review current and potential future approaches for the development of sarcoma therapies based on this emerging understanding of chromatin dysregulation.

Polycomb and Trithorax Group Proteins: The Long Road from Mutations in Drosophila to Use in Medicine

Polycomb group (PcG) and Trithorax group (TrxG) proteins are evolutionarily conserved factors responsible for the repression and activation of the transcription of multiple genes in Drosophila and mammals. Disruption of the PcG/TrxG expression is associated with many pathological conditions, including cancer, which makes them suitable targets for diagnosis and therapy in medicine. In this review, we focus on the major PcG and TrxG complexes, the mechanisms of PcG/TrxG action, and their recruitment to chromatin. We discuss the alterations associated with the dysfunction of a number of factors of these groups in oncology and the current strategies used to develop drugs based on small-molecule inhibitors.

A benzimidazole inhibitor attenuates sterile inflammation induced in a model of systemic autoinflammation in female mice

Sterile stimuli can trigger inflammatory responses, and in some cases can lead to a variety of acute or chronic diseases. In this study, we hypothesize that a benzimidazole inhibitor may be used as a therapeutic in the treatment of sterile inflammation. In vitro, this inhibitor blocks TLR signalling and inflammatory responses. The benzimidazole inhibitor does not prevent mouse macrophage activation after stimulation with 2,6,10,14-tetramethylpentadecane (TMPD, also known as pristane), a hydrocarbon oil that mimics features of sterile inflammation when injected in vivo. However, C57BL/6J female mice treated with the benzimidazole inhibitor exhibited a significant reduction of pristane-dependent induction of splenocyte number and weight. Conversely, no significant difference was observed in males. Using mass spectrometry, we found that the urine of pristane-injected mice contained increased levels of putative markers for several inflammatory diseases, which were reduced by the benzimidazole inhibitor. To study the mechanism, we showed that pristane-injected mice had increased cell free DNA in serum, which was not impacted by inhibitor treatment. However, chemokine release (e.g. MCP-1, RANTES and TARC) was significantly reduced in inhibitor-treated mice. Thus, the benzimidazole inhibitor might be used as a new drug to block the recruitment of immune cells during sterile inflammatory diseases in humans.

Into Thin Air: Hypoxia Drives Metabolic and Epigenomic Deregulation of Lethal Pediatric Ependymoma

Posterior fossa type A (PFA) ependymoma is a lethal pediatric brain tumor proposed to be driven solely by epigenetic deregulation. Michealraj et al. (2020) demonstrate that hypoxia reprograms PFA metabolism and, subsequently, the epigenome toward H3K27 hypomethylation, mirroring transcriptional and metabolic signatures of gliogenic progenitors involved in embryonal hindbrain development.

Heterochromatin Morphodynamics in Late Oogenesis and Early Embryogenesis of Mammals

During the period of oocyte growth, chromatin undergoes global rearrangements at both morphological and molecular levels. An intriguing feature of oogenesis in some mammalian species is the formation of a heterochromatin ring-shaped structure, called the karyosphere or surrounded "nucleolus", which is associated with the periphery of the nucleolus-like bodies (NLBs). Morphologically similar heterochromatin structures also form around the nucleolus-precursor bodies (NPBs) in zygotes and persist for several first cleavage divisions in blastomeres. Despite recent progress in our understanding the regulation of gene silencing/expression during early mammalian development, as well as the molecular mechanisms that underlie chromatin condensation and heterochromatin structure, the biological significance of the karyosphere and its counterparts in early embryos is still elusive. We pay attention to both the changes of heterochromatin morphology and to the molecular mechanisms that can affect the configuration and functional activity of chromatin. We briefly discuss how DNA methylation, post-translational histone modifications, alternative histone variants, and some chromatin-associated non-histone proteins may be involved in the formation of peculiar heterochromatin structures intimately associated with NLBs and NPBs, the unique nuclear bodies of oocytes and early embryos.

Characterization of SETD3 methyltransferase-mediated protein methionine methylation

Most characterized protein methylation events encompass arginine and lysine N-methylation, and only a few cases of protein methionine thiomethylation have been reported. Newly discovered oncohistone mutations include lysine-to-methionine substitutions at positions 27 and 36 of histone H3.3. In these instances, the methionine substitution localizes to the active-site pocket of the corresponding histone lysine methyltransferase, thereby inhibiting the respective transmethylation activity. SET domain-containing 3 (SETD3) is a protein (i.e. actin) histidine methyltransferase. Here, we generated an actin variant in which the histidine target of SETD3 was substituted with methionine. As for previously characterized histone SET domain proteins, the methionine substitution substantially (76-fold) increased binding affinity for SETD3 and inhibited SETD3 activity on histidine. Unexpectedly, SETD3 was active on the substituted methionine, generating S-methylmethionine in the context of actin peptide. The ternary structure of SETD3 in complex with the methionine-containing actin peptide at 1.9 Å resolution revealed that the hydrophobic thioether side chain is packed by the aromatic rings of Tyr³¹² and Trp²⁷³, as well as the hydrocarbon side chain of Ile³¹⁰ Our results suggest that placing methionine properly in the active site-within close proximity to and in line with the incoming methyl group of SAM-would allow some SET domain proteins to selectively methylate methionine in proteins.

The enigma of DNA methylation in the mammalian oocyte

The mammalian genome experiences profound setting and resetting of epigenetic patterns during the life-course. This is understood best for DNA methylation: the specification of germ cells, gametogenesis, and early embryo development are characterised by phases of widespread erasure and rewriting of methylation. While mitigating against intergenerational transmission of epigenetic information, these processes must also ensure correct genomic imprinting that depends on faithful and long-term memory of gamete-derived methylation states in the next generation. This underscores the importance of understanding the mechanisms of methylation programming in the germline. De novo methylation in the oocyte is of particular interest because of its intimate association with transcription, which results in a bimodal methylome unique amongst mammalian cells. Moreover, this methylation landscape is entirely set up in a non-dividing cell, making the oocyte a fascinating model system in which to explore mechanistic determinants of methylation. Here, we summarise current knowledge on the oocyte DNA methylome and how it is established, focussing on recent insights from knockout models in the mouse that explore the interplay between methylation and chromatin states. We also highlight some remaining paradoxes and enigmas, in particular the involvement of non-nuclear factors for correct de novo methylation.

The growing role of epigenetics in childhood cancers

PURPOSE OF REVIEW

Altered epigenetics is central to oncogenesis in many pediatric cancers. Aberrant epigenetic states are induced by mutations in histones or epigenetic regulatory genes, aberrant expression of genes regulating chromatin complexes, altered DNA methylation patterns, or dysregulated expression of noncoding RNAs. Developmental contexts of dysregulated epigenetic states are equally important for initiation and progression of many childhood cancers. As an improved understanding of disease-specific roles and molecular consequences of epigenetic alterations in oncogenesis is emerging, targeting these mechanisms of disease in childhood cancers is increasingly becoming important.

RECENT FINDINGS

In addition to disease-causing epigenetic events, DNA methylation patterns and specific oncohistone mutations are being utilized for the diagnosis of pediatric central nervous system (CNS) and solid tumors. These discoveries have improved the classification of poorly differentiated tumors and laid the foundation for future improved clinical management. On the therapeutic side, the first therapies targeting epigenetic alterations have recently entered clinical trials. Current clinical trials include pharmacological inhibition of histone and DNA modifiers in aggressive types of pediatric cancer.

SUMMARY

Targeting novel epigenetic vulnerabilities, either by themselves, or coupled with targeting altered transcriptional states, developmental cell states or immunomodulation will result in innovative approaches for treating deadly pediatric cancers.

Invited Review: Emerging functions of histone H3 mutations in paediatric diffuse high-grade gliomas

Paediatric diffuse high-grade gliomas (pHGG) are rare, but deadly tumours. The discovery of recurrent mutations in the tail of histone H3, changing lysine 27 to methionine, or glycine 34 to arginine or valine, has illuminated a critical role for epigenetic dysregulation in the aetiology of childhood gliomas and opened new avenues of exploration that have resulted in numerous advances for the field. In this review, we describe the current models of H3K27M mutant cancer that are available to the research community and the insights they have provided on tumour biology and the epigenetic and transcriptional effects of histone mutations. We also review the current understanding of the H3G34R/V mutation and the therapeutic outlook for the treatment of pHGG.

Exploiting the dynamic properties of Pt on ceria for low-temperature CO oxidation

Low-temperature redispersion leads to an intermediate Pt monolayer arrangement, very active for CO oxidation.

PRC2 functions in development and congenital disorders

Polycomb repressive complex 2 (PRC2) is a conserved chromatin regulator that is responsible for the methylation of histone H3 lysine 27 (H3K27). PRC2 is essential for normal development and its loss of function thus results in a range of developmental phenotypes. Here, we review the latest advances in our understanding of mammalian PRC2 activity and present an updated summary of the phenotypes associated with its loss of function in mice. We then discuss recent studies that have highlighted regulatory interplay between the modifications laid down by PRC2 and other chromatin modifiers, including NSD1 and DNMT3A. Finally, we propose a model in which the dysregulation of these modifications at intergenic regions is a shared molecular feature of genetically distinct but highly phenotypically similar overgrowth syndromes in humans.