Cross-talk between the H3K36me3 and H4K16ac histone epigenetic marks in DNA double-strand break repair

Epigenetic modifications in Parkinson's disease: A critical review

Parkinson's Disease (PD) is a progressive neurodegenerative disorder expected to increase by over 50% by 2030 due to increasing life expectancy. The disease's hallmarks include slow movement, tremors, and postural instability. Impaired protein processing is a major factor in the pathophysiology of PD, leading to the buildup of aberrant protein aggregates, particularly misfolded α-synuclein, also known as Lewy bodies. These Lewy bodies lead to inflammation and further death of dopaminergic neurons, leading to imbalances in excitatory and inhibitory neurotransmitters, causing excessive uncontrollable movements called dyskinesias. It was previously suggested that a complex interplay involving hereditary and environmental variables causes the specific death of neurons in PD; however, the exact mechanism of the association involving the two primary modifiers is yet unknown. An increasing amount of research points to the involvement of epigenetics in the onset and course of several neurological conditions, such as PD. DNA methylation, post-modifications of histones, and non-coding RNAs are the primary examples of epigenetic alterations, that is defined as alterations to the expression of genes and functioning without modifications in DNA sequence. Epigenetic modifications play a significant role in the development of PD, with genes such as Parkin, PTEN-induced kinase 1 (PINK1), DJ1, Leucine-Rich Repeat Kinase 2 (LRRK2), and alpha-synuclein associated with the disease. The aberrant epigenetic changes implicated in the pathophysiology of PD and their impact on the design of novel therapeutic approaches are the primary focus of this review.

Targeting bromodomian-containing protein 8 (BRD8): An advanced tool to interrogate BRD8

Epigenetic modifications play crucial roles in physiological processes, including cell differentiation, proliferation, and death. Bromodomain/Brd-containing proteins (BCPs) regulate abnormal gene expression in various diseases by recognizing the lysine-ε-N-acetylated residues (KAc) or by acting as transcriptional co-activators. Small molecule inhibitors targeting BCPs offer an attractive strategy for modulating aberrant gene expression. Besides the extensive research on the bromodomain and extra-terminal (BET) domain family proteins, the non-BET proteins have gained increasing attention. Bromodomain containing protein 8 (BRD8), a reader of KAc and co-activator of nuclear receptors (NRs), plays a key role in various cancers. This review provides a comprehensive analysis of the structure, disease-related functions, and inhibitor development of BRD8. Opportunities and challenges for future studies targeting BRD8 in disease treatment are discussed.

Methylation of histone H3 lysine 36 is a barrier for therapeutic interventions of head and neck squamous cell carcinoma

Approximately 20% of head and neck squamous cell carcinomas (HNSCCs) exhibit reduced methylation on lysine 36 of histone H3 (H3K36me) due to mutations in histone methylase NSD1 or a lysine-to-methionine mutation in histone H3 (H3K36M). Whether such alterations of H3K36me can be exploited for therapeutic interventions is still unknown. Here, we show that HNSCC models expressing H3K36M can be divided into two groups: those that display aberrant accumulation of H3K27me3 and those that maintain steady levels of H3K27me3. The former group exhibits reduced proliferation, genome instability, and heightened sensitivity to genotoxic agents like PARP1/2 inhibitors. Conversely, H3K36M HNSCC models with constant H3K27me3 levels lack these characteristics unless H3K27me3 is elevated by DNA hypomethylating agents or inhibiting H3K27me3 demethylases KDM6A/B. Mechanistically, H3K36M reduces H3K36me by directly impeding the activities of the histone methyltransferase NSD3 and the histone demethylase LSD2. Notably, aberrant H3K27me3 levels induced by H3K36M expression are not a bona fide epigenetic mark because they require continuous expression of H3K36M to be inherited. Moreover, increased sensitivity to PARP1/2 inhibitors in H3K36M HNSCC models depends solely on elevated H3K27me3 levels and diminishing BRCA1- and FANCD2-dependent DNA repair. Finally, a PARP1/2 inhibitor alone reduces tumor burden in a H3K36M HNSCC xenograft model with elevated H3K27me3, whereas in a model with consistent H3K27me3, a combination of PARP1/2 inhibitors and agents that up-regulate H3K27me3 proves to be successful. These findings underscore the crucial balance between H3K36 and H3K27 methylation in maintaining genome instability, offering new therapeutic options for patients with H3K36me-deficient tumors.

Inducible Expression of the Restriction Enzyme Uncovered Genome-Wide Distribution and Dynamic Behavior of Histones H4K16ac and H2A.Z at DNA Double-Strand Breaks in Arabidopsis

DNA double-strand breaks (DSBs) are among the most serious types of DNA damage, causing mutations and chromosomal rearrangements. In eukaryotes, DSBs are immediately repaired in coordination with chromatin remodeling for the deposition of DSB-related histone modifications and variants. To elucidate the details of DSB-dependent chromatin remodeling throughout the genome, artificial DSBs need to be reproducibly induced at various genomic loci. Recently, a comprehensive method for elucidating chromatin remodeling at multiple DSB loci via chemically induced expression of a restriction enzyme was developed in mammals. However, this DSB induction system is unsuitable for investigating chromatin remodeling during and after DSB repair, and such an approach has not been performed in plants. Here, we established a transgenic Arabidopsis plant harboring a restriction enzyme gene Sbf I driven by a heat-inducible promoter. Using this transgenic line, we performed chromatin immunoprecipitation followed by deep sequencing (ChIP-seq) of histones H4K16ac and H2A.Z and investigated the dynamics of these histone marks around the endogenous 623 Sbf I recognition sites. We also precisely quantified DSB efficiency at all cleavage sites using the DNA resequencing data obtained by the ChIP-seq procedure. From the results, Sbf I-induced DSBs were detected at 360 loci, which induced the transient deposition of H4K16ac and H2A.Z around these regions. Interestingly, we also observed the co-localization of H4K16ac and H2A.Z at some DSB loci. Overall, DSB-dependent chromatin remodeling was found to be highly conserved between plants and animals. These findings provide new insights into chromatin remodeling that occurs in response to DSBs in Arabidopsis.

Exploring the Molecular Underpinnings of Cancer-Causing Oncohistone Mutants Using Yeast as a Model

Understanding the molecular basis of cancer initiation and progression is critical in developing effective treatment strategies. Recently, mutations in genes encoding histone proteins that drive oncogenesis have been identified, converting these essential proteins into "oncohistones". Understanding how oncohistone mutants, which are commonly single missense mutations, subvert the normal function of histones to drive oncogenesis requires defining the functional consequences of such changes. Histones genes are present in multiple copies in the human genome with 15 genes encoding histone H3 isoforms, the histone for which the majority of oncohistone variants have been analyzed thus far. With so many wildtype histone proteins being expressed simultaneously within the oncohistone, it can be difficult to decipher the precise mechanistic consequences of the mutant protein. In contrast to humans, budding and fission yeast contain only two or three histone H3 genes, respectively. Furthermore, yeast histones share ~90% sequence identity with human H3 protein. Its genetic simplicity and evolutionary conservation make yeast an excellent model for characterizing oncohistones. The power of genetic approaches can also be exploited in yeast models to define cellular signaling pathways that could serve as actionable therapeutic targets. In this review, we focus on the value of yeast models to serve as a discovery tool that can provide mechanistic insights and inform subsequent translational studies in humans.

Methylation of histone H3 lysine 36 is a barrier for therapeutic interventions of head and neck squamous cell carcinoma

Approximately 20% of head and neck squamous cell carcinomas (HNSCC) exhibit reduced methylation on lysine 36 of histone H3 (H3K36me) due to mutations in histone methylase NSD1 or a lysine-to-methionine mutation in histone H3 (H3K36M). Whether such alterations of H3K36me can be exploited for therapeutic interventions is still unknown. Here, we show that HNSCC models expressing H3K36M can be divided into two groups: those that display aberrant accumulation of H3K27me3 and those that maintain steady levels of H3K27me3. The first group shows decreased proliferation, genome instability, and increased sensitivity to genotoxic agents, such as PARP1/2 inhibitors. In contrast, the H3K36M HNSCC models with steady H3K27me3 levels do not exhibit these characteristics unless H3K27me3 levels are elevated, either by DNA hypomethylating agents or by inhibiting the H3K27me3 demethylases KDM6A/B. Mechanistically, we found that H3K36M reduces H3K36me by directly impeding the activities of the histone methyltransferase NSD3 and the histone demethylase LSD2. Notably, we found that aberrant H3K27me3 levels induced by H3K36M expression is not a bona fide epigenetic mark in HNSCC since it requires continuous expression of H3K36M to be inherited. Moreover, increased sensitivity of H3K36M HNSCC models to PARP1/2 inhibitors solely depends on the increased H3K27me3 levels. Indeed, aberrantly high H3K27me3 levels decrease BRCA1 and FANCD2-dependent DNA repair, resulting in higher sensitivity to DNA breaks and replication stress. Finally, in support of our in vitro findings, a PARP1/2 inhibitor alone reduce tumor burden in a H3K36M HNSCC xenograft model with elevated H3K27me3, whereas in a H3K36M HNSCC xenograft model with consistent H3K27me3 levels, a combination of PARP1/2 inhibitors and agents that upregulate H3K27me3 proves to be successful. In conclusion, our findings underscore a delicate balance between H3K36 and H3K27 methylation, essential for maintaining genome stability. This equilibrium presents promising therapeutic opportunities for patients with H3K36me-deficient tumors.

Targeted Profiling of Epitranscriptomic Reader, Writer, and Eraser Proteins Regulated by H3K36me3

Trimethylation of lysine 36 on histone H3 (H3K36me3), an epigenetic mark associated with actively transcribed genes, plays an important role in multiple cellular processes, including transcription elongation, DNA methylation, DNA repair, etc. Aberrant expression and mutations of the main methyltransferase for H3K36me3, i.e., SET domain-containing 2 (SETD2), were shown to be associated with various cancers. Here, we performed targeted profiling of 154 epitranscriptomic reader, writer, and eraser (RWE) proteins using a scheduled liquid chromatography-parallel-reaction monitoring (LC-PRM) method coupled with the use of stable isotope-labeled (SIL) peptides as internal standards to investigate how H3K36me3 modulates the chromatin occupancies of epitranscriptomic RWE proteins. Our results showed consistent changes in chromatin occupancies of RWE proteins upon losses of H3K36me3 and H4K16ac and a role of H3K36me3 in recruiting METTL3 to chromatin following induction of DNA double-strand breaks. In addition, protein-protein interaction network and Kaplan-Meier survival analyses revealed the importance of METTL14 and TRMT11 in kidney cancer. Taken together, our work unveiled cross-talks between histone epigenetic marks (i.e., H3K36me3 and H4K16ac) and epitranscriptomic RWE proteins and uncovered the potential roles of these RWE proteins in H3K36me3-mediated biological processes.

Inhibition of Histone H3K18 Acetylation-Dependent Antioxidant Pathways Involved in Arsenic-Induced Liver Injury in Rats and the Protective Effect of Rosa roxburghii Tratt Juice

Arsenic is a common environmental toxicant. Long-term arsenic exposure can induce various types of liver injury, but the underlying mechanism remains unclear, so effective prevention and treatment measures are unknown. This study aims to explore the mechanism of arsenic-induced rat liver injury based on the histone H3K18 acetylation-dependent antioxidant pathway and to identify the role of a medicinal and edible resource, Rosa roxburghii Tratt juice, in combating it. Hepatic steatosis and inflammatory cell infiltration were observed in rats exposed to different doses of NaAsO₂ using histopathological measurement. Increased 8-OHdG and MDA in liver tissue corroborated hepatic oxidative damage. We further found that a reduction in H3K18ac in the liver showed a dose-response relationship, with an increase in the NaAsO₂ treatment dose, and it was remarkably associated with increased 8-OHdG and MDA. The results of ChIP-qPCR identified that the decreased enrichment of H3K18ac in promoters of the Hspa1a and Hspb8 genes culminated in the inhibition of the genes' expression, which was found to be involved in the aggravation of hepatic oxidative damage induced by arsenic. Notably, Rosa roxburghii Tratt juice was found to reduce 8-OHdG and MDA in the liver, thereby alleviating the histopathological lesions induced by arsenic, which was modulated by recovering the H3K18ac-dependent transcriptional activation of the Hspa1a and Hspb8 genes. Taken together, we provide a novel epigenetics insight into clarifying the mechanism of arsenic-induced liver injury and its rescue by Rosa roxburghii Tratt juice.

PBRM1, SETD2 and BAP1 - the trinity of 3p in clear cell renal cell carcinoma

Biallelic inactivation of the tumour suppressor gene Von Hippel-Lindau (VHL) occurs in the vast majority of clear cell renal cell carcinoma (ccRCC) instances, disrupting cellular oxygen-sensing mechanisms to yield a state of persistent pseudo-hypoxia, defined as a continued hypoxic response despite the presence of adequate oxygen levels. However, loss of VHL alone is often insufficient to drive oncogenesis. Results from genomic studies have shown that co-deletions of VHL with one (or more) of three genes encoding proteins involved in chromatin modification and remodelling, polybromo-1 gene (PBRM1), BRCA1-associated protein 1 (BAP1) and SET domain-containing 2 (SETD2), are common and important co-drivers of tumorigenesis. These genes are all located near VHL on chromosome 3p and are often altered following cytogenetic rearrangements that lead to 3p loss and precede the establishment of ccRCC. These three proteins have multiple roles in the regulation of crucial cancer-related pathways, including protection of genomic stability, antagonism of polycomb group (PcG) complexes to maintain a permissive transcriptional landscape in physiological conditions, and regulation of genes that mediate responses to immune checkpoint inhibitor therapy. An improved understanding of these mechanisms will bring new insights regarding cellular drivers of ccRCC growth and therapy response and, ultimately, will support the development of novel translational therapeutics.

The Implication of Topoisomerase II Inhibitors in Synthetic Lethality for Cancer Therapy

DNA topoisomerase II (Top2) is essential for all eukaryotic cells in the regulation of DNA topology through the generation of temporary double-strand breaks. Cancer cells acquire enhanced Top2 functions to cope with the stress generated by transcription and DNA replication during rapid cell division since cancer driver genes such as Myc and EZH2 hijack Top2 in order to realize their oncogenic transcriptomes for cell growth and tumor progression. Inhibitors of Top2 are therefore designed to target Top2 to trap it on DNA, subsequently causing protein-linked DNA breaks, a halt to the cell cycle, and ultimately cell death. Despite the effectiveness of these inhibitors, cancer cells can develop resistance to them, thereby limiting their therapeutic utility. To maximize the therapeutic potential of Top2 inhibitors, combination therapies to co-target Top2 with DNA damage repair (DDR) machinery and oncogenic pathways have been proposed to induce synthetic lethality for more thorough tumor suppression. In this review, we will discuss the mode of action of Top2 inhibitors and their potential applications in cancer treatments.

The role of histone H3K36me3 writers, readers and erasers in maintaining genome stability

Histone Post-Translational Modifications (PTMs) play fundamental roles in mediating DNA-related processes such as transcription, replication and repair. The histone mark H3K36me3 and its associated methyltransferase SETD2 (Set2 in yeast) are archetypical in this regard, performing critical roles in each of these DNA transactions. Here, we present an overview of H3K36me3 regulation and the roles of its writers, readers and erasers in maintaining genome stability through facilitating DNA double-strand break (DSB) repair, checkpoint signalling and replication stress responses. Further, we consider how loss of SETD2 and H3K36me3, frequently observed in a number of different cancer types, can be specifically targeted in the clinic through exploiting loss of particular genome stability functions.

Targeting Histone Epigenetic Modifications and DNA Damage Responses in Synthetic Lethality Strategies in Cancer?

Synthetic lethality strategies are likely to be integrated in effective and specific cancer treatments. These strategies combine different specific targets, either in similar or cooperating pathways. Chromatin remodeling underlies, directly or indirectly, all processes of tumor biology. In this context, the combined targeting of proteins associated with different aspects of chromatin remodeling can be exploited to find new alternative targets or to improve treatment for specific individual tumors or patients. There are two major types of proteins, epigenetic modifiers of histones and nuclear or chromatin kinases, all of which are druggable targets. Among epigenetic enzymes, there are four major families: histones acetylases, deacetylases, methylases and demethylases. All these enzymes are druggable. Among chromatin kinases are those associated with DNA damage responses, such as Aurora A/B, Haspin, ATM, ATR, DNA-PK and VRK1-a nucleosomal histone kinase. All these proteins converge on the dynamic regulation chromatin organization, and its functions condition the tumor cell viability. Therefore, the combined targeting of these epigenetic enzymes, in synthetic lethality strategies, can sensitize tumor cells to toxic DNA-damage-based treatments, reducing their toxicity and the selective pressure for tumor resistance and increasing their immunogenicity, which will lead to an improvement in disease-free survival and quality of life.

SETD2 Haploinsufficiency Enhances Germinal Center-Associated AICDA Somatic Hypermutation to Drive B-cell Lymphomagenesis

SETD2 is the sole histone methyltransferase responsible for H3K36me3, with roles in splicing, transcription initiation, and DNA damage response. Homozygous disruption of SETD2 yields a tumor suppressor effect in various cancers. However, SETD2 mutation is typically heterozygous in diffuse large B-cell lymphomas. Here we show that heterozygous Setd2 deficiency results in germinal center (GC) hyperplasia and increased competitive fitness, with reduced DNA damage checkpoint activity and apoptosis, resulting in accelerated lymphomagenesis. Impaired DNA damage sensing in Setd2-haploinsufficient germinal center B (GCB) and lymphoma cells associated with increased AICDA-induced somatic hypermutation, complex structural variants, and increased translocations including those activating MYC. DNA damage was selectively increased on the nontemplate strand, and H3K36me3 loss was associated with greater RNAPII processivity and mutational burden, suggesting that SETD2-mediated H3K36me3 is required for proper sensing of cytosine deamination. Hence, Setd2 haploinsufficiency delineates a novel GCB context-specific oncogenic pathway involving defective epigenetic surveillance of AICDA-mediated effects on transcribed genes.

SIGNIFICANCE

Our findings define a B cell-specific oncogenic effect of SETD2 heterozygous mutation, which unleashes AICDA mutagenesis of nontemplate strand DNA in the GC reaction, resulting in lymphomas with heavy mutational burden. GC-derived lymphomas did not tolerate SETD2 homozygous deletion, pointing to a novel context-specific therapeutic vulnerability. This article is highlighted in the In This Issue feature, p. 1599.

SETD2: from chromatin modifier to multipronged regulator of the genome and beyond

Histone modifying enzymes play critical roles in many key cellular processes and are appealing proteins for targeting by small molecules in disease. However, while the functions of histone modifying enzymes are often linked to epigenetic regulation of the genome, an emerging theme is that these enzymes often also act by non-catalytic and/or non-epigenetic mechanisms. SETD2 (Set2 in yeast) is best known for associating with the transcription machinery and methylating histone H3 on lysine 36 (H3K36) during transcription. This well-characterized molecular function of SETD2 plays a role in fine-tuning transcription, maintaining chromatin integrity, and mRNA processing. Here we give an overview of the various molecular functions and mechanisms of regulation of H3K36 methylation by Set2/SETD2. These fundamental insights are important to understand SETD2’s role in disease, most notably in cancer in which SETD2 is frequently inactivated. SETD2 also methylates non-histone substrates such as α-tubulin which may promote genome stability and contribute to the tumor-suppressor function of SETD2. Thus, to understand its role in disease, it is important to understand and dissect the multiple roles of SETD2 within the cell. In this review we discuss how histone methylation by Set2/SETD2 has led the way in connecting histone modifications in active regions of the genome to chromatin functions and how SETD2 is leading the way to showing that we also have to look beyond histones to truly understand the physiological role of an ‘epigenetic’ writer enzyme in normal cells and in disease.

Transcriptional Repression of Ferritin Light Chain Increases Ferroptosis Sensitivity in Lung Adenocarcinoma

Ferroptosis is an iron- and lipid peroxidation-dependent form of regulated cell death. The release of labile iron is one of the important factors affecting sensitivity to ferroptosis. Yes-associated protein (YAP) controls intracellular iron levels by affecting the transcription of ferritin heavy chain (FTH) and transferrin receptor (TFRC). However, whether YAP regulates iron metabolism through other target genes remains unknown. Here, we observed that the system Xc^– inhibitor erastin inhibited the binding of the WW domain and PSY motif between YAP and transcription factor CP2 (TFCP2), and then suppressed the transcription of ferritin light chain (FTL) simultaneously mediated by YAP, TFCP2 and forkhead box A1 (FOXA1). Furthermore, inhibition of FTL expression abrogated ferroptosis-resistance in cells with sustained YAP expression. Unlike FTH, which exhibited first an increase and then a decrease in transcription, FTL transcription continued to decline after the addition of erastin, and a decrease in lysine acetyltransferase 5 (KAT5)-dependent acetylation of FTL was also observed. In lung adenocarcinoma (LUAD) tissues, lipid peroxidation and labile iron decreased, while YAP, TFCP2 and FTL increased compared to their adjacent normal tissues, and the lipid peroxidation marker 4-hydroxynonenal (4-HNE) was negatively correlated with the level of FTL or the degree of LUAD malignancy, but LUAD tissues with lower levels of 4-HNE showed a higher sensitivity to ferroptosis. In conclusion, the findings from this study indicated that the suppression of FTL transcription through the inhibition of the YAP-TFCP2-KAT5 complex could be another mechanism for elevating ferroptosis sensitivity and inducing cell death, and ferroptotic therapy is more likely to achieve better results in LUAD patients with a lower degree of lipid peroxidation.

Role of histone acetyltransferases MOF and Tip60 in genome stability

The accurate repair of DNA damage specifically the chromosomal double-strand breaks (DSBs) arising from exposure to physical or chemical agents, such as ionizing radiation (IR) and radiomimetic drugs is critical in maintaining genomic integrity. The DNA DSB response and repair is facilitated by hierarchical signaling networks that orchestrate chromatin structural changes specifically histone modifications which impact cell-cycle checkpoints through enzymatic activities to repair the broken DNA ends. Various histone posttranslational modifications such as phosphorylation, acetylation, methylation and ubiquitylation have been shown to play a role in DNA damage repair. Recent studies have provided important insights into the role of histone-specific modifications in sensing DNA damage and facilitating the DNA repair. Histone modifications have been shown to determine the pathway choice for repair of DNA DSBs. This review will summarize the role of important histone acetyltransferases MOF and Tip60 mediated acetylation in repair of DNA DSBs in eukaryotic cells.

H3K36 trimethylation-mediated biological functions in cancer

Histone modification is an important form of epigenetic regulation. Thereinto, histone methylation is a critical determination of chromatin states, participating in multiple cellular processes. As a conserved histone methylation mark, histone 3 lysine 36 trimethylation (H3K36me3) can mediate multiple transcriptional-related events, such as the regulation of transcriptional activity, transcription elongation, pre-mRNA alternative splicing, and RNA m⁶A methylation. Additionally, H3K36me3 also contributes to DNA damage repair. Given the crucial function of H3K36me3 in genome regulation, the roles of H3K36me3 and its sole methyltransferase SETD2 in pathogenesis, especially malignancies, have been emphasized in many studies, and it is conceivable that disruption of histone methylation regulatory network composed of "writer", "eraser", "reader", and the mutation of H3K36me3 codes have the capacity of powerfully modulating cancer initiation and development. Here we review H3K36me3-mediated biological processes and summarize the latest findings regarding its role in cancers. We highlight the significance of epigenetic combination therapies in cancers.

Effects of small-molecule compounds on fibroblast properties in golden snub-nosed monkey (Rhinopithecus roxellana)

BACKGROUND

Golden snub-nosed monkey (Rhinopithecus roxellana) is an endangered primate species, whose molecular material for conservation purposes has not yet been maintained. Although small-molecule compounds (SMCs) have been reported to improve induced pluripotent stem cells (iPSCs), their efficiency in the interspecies-transferred nucleus is still unknown.

METHODS

We thus used the fibroblasts from the golden snub-nosed monkey treated with SMC as donor cells, injected into the enucleated oocytes of goats, to test such efficiency. Gene expression profiles in the cell-constructed embryos with and without SMCs were compared by qPCR.

RESULTS

The results show that cell morphology undergoes remarkable changes (volume is smaller than normal cells, and many black spots in the cytoplasm were found); pluripotent genes (Oct4, Sox2, and Nanog) significantly increased with SMC treatment.

CONCLUSIONS

This study demonstrates that SMCs alter the properties of donor cells and promote the expression of pluripotent genes in hybrid embryos.

Structural Studies Provide New Insights into the Role of Lysine Acetylation on Substrate Recognition by CARM1 and Inform the Design of Potent Peptidomimetic Inhibitors

The dynamic interplay of post‐translational modifications (PTMs) in chromatin provides a communication system for the regulation of gene expression. An increasing number of studies have highlighted the role that such crosstalk between PTMs plays in chromatin recognition. In this study, (bio)chemical and structural approaches were applied to specifically probe the impact of acetylation of Lys¹⁸ in the histone H3 tail peptide on peptide recognition by the protein methyltransferase coactivator‐associated arginine methyltransferase 1 (CARM1). Peptidomimetics that recapitulate the transition state of protein arginine N‐methyltransferases, were designed based on the H3 peptide wherein the target Arg¹⁷ was flanked by either a free or an acetylated lysine. Structural studies with these peptidomimetics and the catalytic domain of CARM1 provide new insights into the binding of the H3 peptide within the enzyme active site. While the co‐crystal structures reveal that lysine acetylation results in minor conformational differences for both CARM1 and the H3 peptide, acetylation of Lys¹⁸ does lead to additional interactions (Van der Waals and hydrogen bonding) and likely reduces the cost of desolvation upon binding, resulting in increased affinity. Informed by these findings a series of smaller peptidomimetics were also prepared and found to maintain potent and selective CARM1 inhibition. These findings provide new insights both into the mechanism of crosstalk between arginine methylation and lysine acetylation as well as towards the development of peptidomimetic CARM1 inhibitors.

Lysine Methyltransferase Inhibitors Impair H4K20me2 and 53BP1 Foci in Response to DNA Damage in Sarcomas, a Synthetic Lethality Strategy

Background

Chromatin is dynamically remodeled to adapt to all DNA-related processes, including DNA damage responses (DDR). This adaptation requires DNA and histone epigenetic modifications, which are mediated by several types of enzymes; among them are lysine methyltransferases (KMTs).

Methods

KMT inhibitors, chaetocin and tazemetostat (TZM), were used to study their role in the DDR induced by ionizing radiation or doxorubicin in two human sarcoma cells lines. The effect of these KMT inhibitors was tested by the analysis of chromatin epigenetic modifications, H4K16ac and H4K20me2. DDR was monitored by the formation of γH2AX, MDC1, NBS1 and 53BP1 foci, and the induction of apoptosis.

Results

Chaetocin and tazemetostat treatments caused a significant increase of H4K16 acetylation, associated with chromatin relaxation, and increased DNA damage, detected by the labeling of free DNA-ends. These inhibitors significantly reduced H4K20 dimethylation levels in response to DNA damage and impaired the recruitment of 53BP1, but not of MDC1 and NBS1, at DNA damaged sites. This modification of epigenetic marks prevents DNA repair by the NHEJ pathway and leads to cell death.

Conclusion

KMT inhibitors could function as sensitizers to DNA damage-based therapies and be used in novel synthetic lethality strategies for sarcoma treatment.

H3K36me3 and PSIP1/LEDGF associate with several DNA repair proteins, suggesting their role in efficient DNA repair at actively transcribing loci

Background: Trimethylation at histone H3 at lysine 36 (H3K36me3) is associated with expressed gene bodies and recruit proteins implicated in transcription, splicing and DNA repair. PC4 and SF2 interacting protein (PSIP1/LEDGF) is a transcriptional coactivator, possesses an H3K36me3 reader PWWP domain. Alternatively spliced isoforms of PSIP1 binds to H3K36me3 and suggested to function as adaptor proteins to recruit transcriptional modulators, splicing factors and proteins that promote homology-directed repair (HDR), to H3K36me3 chromatin. Methods: We performed chromatin immunoprecipitation of H3K36me3 followed by quantitative mass spectrometry (qMS) to identify proteins associated with H3K36 trimethylated chromatin in mouse embryonic stem cells (mESCs). We also performed stable isotope labelling with amino acids in cell culture (SILAC) followed by qMS for a longer isoform of PSIP1 (PSIP/p75) and MOF/KAT8 in mESCs and mouse embryonic fibroblasts ( MEFs). Furthermore, immunoprecipitation followed by western blotting was performed to validate the qMS data. DNA damage in PSIP1 knockout MEFs was assayed by a comet assay. Results: Proteomic analysis shows the association of proteins involved in transcriptional elongation, RNA processing and DNA repair with H3K36me3 chromatin. Furthermore, we show DNA repair proteins like PARP1, gamma H2A.X, XRCC1, DNA ligase 3, SPT16, Topoisomerases and BAZ1B are predominant interacting partners of PSIP /p75. We further validated the association of PSIP/p75 with PARP1, hnRNPU and gamma H2A.X  and also demonstrated accumulation of damaged DNA in PSIP1 knockout MEFs. Conclusions: In contrast to the previously demonstrated role of H3K36me3 and PSIP/p75 in promoting homology-directed repair (HDR), our data support a wider role of H3K36me3 and PSIP1 in maintaining the genome integrity by recruiting proteins involved in DNA damage response pathways to the actively transcribed loci.

H3K36me3 and PSIP1/LEDGF associate with several DNA repair proteins, suggesting their role in efficient DNA repair at actively transcribing loci

Background: Trimethylation at histone H3 at lysine 36 (H3K36me3) is associated with expressed gene bodies and recruit proteins implicated in transcription, splicing and DNA repair. PC4 and SF2 interacting protein (PSIP1/LEDGF) is a transcriptional coactivator, possesses an H3K36me3 reader PWWP domain. Alternatively spliced isoforms of PSIP1 binds to H3K36me3 and suggested to function as adaptor proteins to recruit transcriptional modulators, splicing factors and proteins that promote homology-directed repair (HDR), to H3K36me3 chromatin. Methods: We performed chromatin immunoprecipitation of H3K36me3 followed by quantitative mass spectrometry (qMS) to identify proteins associated with H3K36 trimethylated chromatin in mouse embryonic stem cells (mESCs). We also performed stable isotope labelling with amino acids in cell culture (SILAC) followed by qMS for a longer isoform of PSIP1 (PSIP/p75) and MOF/KAT8 in mESCs and mouse embryonic fibroblasts ( MEFs). Furthermore, immunoprecipitation followed by western blotting was performed to validate the qMS data. DNA damage in PSIP1 knockout MEFs was assayed by a comet assay. Results: Proteomic analysis shows the association of proteins involved in transcriptional elongation, RNA processing and DNA repair with H3K36me3 chromatin. Furthermore, we show DNA repair proteins like PARP1, gamma H2A.X, XRCC1, DNA ligase 3, SPT16, Topoisomerases and BAZ1B are predominant interacting partners of PSIP /p75. We further validated the association of PSIP/p75 with PARP1, hnRNPU and gamma H2A.X  and also demonstrated accumulation of damaged DNA in PSIP1 knockout MEFs. Conclusions: In contrast to the previously demonstrated role of H3K36me3 and PSIP/p75 in promoting homology-directed repair (HDR), our data support a wider role of H3K36me3 and PSIP1 in maintaining the genome integrity by recruiting proteins involved in DNA damage response pathways to the actively transcribed loci.

LEDGF/p75 Is Required for an Efficient DNA Damage Response

Lens epithelium-derived growth factor splice variant of 75 kDa (LEDGF/p75) plays an important role in cancer, but its DNA-damage repair (DDR)-related implications are still not completely understood. Different LEDGF model cell lines were generated: a complete knock-out of LEDGF (KO) and re-expression of LEDGF/p75 or LEDGF/p52 using CRISPR/Cas9 technology. Their proliferation and migration capacity as well as their chemosensitivity were determined, which was followed by investigation of the DDR signaling pathways by Western blot and immunofluorescence. LEDGF-deficient cells exhibited a decreased proliferation and migration as well as an increased sensitivity toward etoposide. Moreover, LEDGF-depleted cells showed a significant reduction in the recruitment of downstream DDR-related proteins such as replication protein A 32 kDa subunit (RPA32) after exposure to etoposide. The re-expression of LEDGF/p75 rescued all knock-out effects. Surprisingly, untreated LEDGF KO cells showed an increased amount of DNA fragmentation combined with an increased formation of γH2AX and BRCA1. In contrast, the protein levels of ubiquitin-conjugating enzyme UBC13 and nuclear proteasome activator PA28γ were substantially reduced upon LEDGF KO. This study provides for the first time an insight that LEDGF is not only involved in the recruitment of CtIP but has also an effect on the ubiquitin-dependent regulation of DDR signaling molecules and highlights the role of LEDGF/p75 in homology-directed DNA repair.

Two Functionally Redundant FK506-Binding Proteins Regulate Multidrug Resistance Gene Expression and Govern Azole Antifungal Resistance

Increasing resistance to antifungal therapy is an impediment to the effective treatment of fungal infections. Candida glabrata is an opportunistic human fungal pathogen that is inherently less susceptible to cost-effective azole antifungals. Gain-of-function mutations in the Zn-finger pleiotropic drug resistance transcriptional activator-encoding gene CgPDR1 are the most prevalent causes of azole resistance in clinical settings. CgPDR1 is also transcriptionally activated upon azole exposure; however, factors governing CgPDR1 gene expression are not yet fully understood. Here, we have uncovered a novel role for two FK506-binding proteins, CgFpr3 and CgFpr4, in the regulation of the CgPDR1 regulon. We show that CgFpr3 and CgFpr4 possess a peptidyl-prolyl isomerase domain and act redundantly to control CgPDR1 expression, as a Cgfpr3Δ4Δ mutant displayed elevated expression of the CgPDR1 gene along with overexpression of its target genes, CgCDR1, CgCDR2, and CgSNQ2, which code for ATP-binding cassette multidrug transporters. Furthermore, CgFpr3 and CgFpr4 are required for the maintenance of histone H3 and H4 protein levels, and fluconazole exposure leads to elevated H3 and H4 protein levels. Consistent with the role of histone proteins in azole resistance, disruption of genes coding for the histone demethylase CgRph1 and the histone H3K36-specific methyltransferase CgSet2 leads to increased and decreased susceptibility to fluconazole, respectively, with the Cgrph1Δ mutant displaying significantly lower basal expression levels of the CgPDR1 and CgCDR1 genes. These data underscore a hitherto unknown role of histone methylation in modulating the most common azole antifungal resistance mechanism. Altogether, our findings establish a link between CgFpr-mediated histone homeostasis and CgPDR1 gene expression and implicate CgFpr in the virulence of C. glabrata.

H3K36 methylation reprograms gene expression to drive early gametocyte development in Plasmodium falciparum

Background

The Plasmodium sexual gametocyte stages are the only transmissible form of the malaria parasite and are thus responsible for the continued transmission of the disease. Gametocytes undergo extensive functional and morphological changes from commitment to maturity, directed by an equally extensive control program. However, the processes that drive the differentiation and development of the gametocyte post-commitment, remain largely unexplored. A previous study reported enrichment of H3K36 di- and tri-methylated (H3K36me2&3) histones in early-stage gametocytes. Using chromatin immunoprecipitation followed by high-throughput sequencing, we identify a stage-specific association between these repressive histone modifications and transcriptional reprogramming that define a stage II gametocyte transition point.

Results

Here, we show that H3K36me2 and H3K36me3 from stage II gametocytes are associated with repression of genes involved in asexual proliferation and sexual commitment, indicating that H3K36me2&3-mediated repression of such genes is essential to the transition from early gametocyte differentiation to intermediate development. Importantly, we show that the gene encoding the transcription factor AP2-G as commitment master regulator is enriched with H3K36me2&3 and actively repressed in stage II gametocytes, providing the first evidence of ap2-g gene repression in post-commitment gametocytes. Lastly, we associate the enhanced potency of the pan-selective Jumonji inhibitor JIB-04 in gametocytes with the inhibition of histone demethylation including H3K36me2&3 and a disruption of normal transcriptional programs.

Conclusions

Taken together, our results provide the first description of an association between global gene expression reprogramming and histone post-translational modifications during P. falciparum early sexual development. The stage II gametocyte-specific abundance of H3K36me2&3 manifests predominantly as an independent regulatory mechanism targeted towards genes that are repressed post-commitment. H3K36me2&3-associated repression of genes is therefore involved in key transcriptional shifts that accompany the transition from early gametocyte differentiation to intermediate development.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13072-021-00393-9.

Clear cell renal cell carcinoma ontogeny and mechanisms of lethality

The molecular features that define clear cell renal cell carcinoma (ccRCC) initiation and progression are being increasingly defined. The TRACERx Renal studies and others that have described the interaction between tumour genomics and remodelling of the tumour microenvironment provide important new insights into the molecular drivers underlying ccRCC ontogeny and progression. Our understanding of common genomic and chromosomal copy number abnormalities in ccRCC, including chromosome 3p loss, provides a mechanistic framework with which to organize these abnormalities into those that drive tumour initiation events, those that drive tumour progression and those that confer lethality. Truncal mutations in ccRCC, including those in VHL, SET2, PBRM1 and BAP1, may engender genomic instability and promote defects in DNA repair pathways. The molecular features that arise from these defects enable categorization of ccRCC into clinically and therapeutically relevant subtypes. Consideration of the interaction of these subtypes with the tumour microenvironment reveals that specific mutations seem to modulate immune cell populations in ccRCC tumours. These findings present opportunities for disease prevention, early detection, prognostication and treatment.

Schizosaccharomyces pombe KAT5 contributes to resection and repair of a DNA double-strand break

Chromatin remodeling is essential for effective repair of a DNA double-strand break (DSB). KAT5 (Schizosaccharomyces pombe Mst1, human TIP60) is a MYST family histone acetyltransferase conserved from yeast to humans that coordinates various DNA damage response activities at a DNA DSB, including histone remodeling and activation of the DNA damage checkpoint. In S. pombe, mutations in mst1+ causes sensitivity to DNA damaging drugs. Here we show that Mst1 is recruited to DSBs. Mutation of mst1+ disrupts recruitment of repair proteins and delays resection. These defects are partially rescued by deletion of pku70, which has been previously shown to antagonize repair by homologous recombination (HR). These phenotypes of mst1 are similar to pht1-4KR, a nonacetylatable form of histone variant H2A.Z, which has been proposed to affect resection. Our data suggest that Mst1 functions to direct repair of DSBs toward HR pathways by modulating resection at the DSB.

Combinations of histone post-translational modifications

Histones are essential proteins that package the eukaryotic genome into its physiological state of nucleosomes, chromatin, and chromosomes. Post-translational modifications (PTMs) of histones are crucial to both the dynamic and persistent regulation of the genome. Histone PTMs store and convey complex signals about the state of the genome. This is often achieved by multiple variable PTM sites, occupied or unoccupied, on the same histone molecule or nucleosome functioning in concert. These mechanisms are supported by the structures of ‘readers’ that transduce the signal from the presence or absence of PTMs in specific cellular contexts. We provide background on PTMs and their complexes, review the known combinatorial function of PTMs, and assess the value and limitations of common approaches to measure combinatorial PTMs. This review serves as both a reference and a path forward to investigate combinatorial PTM functions, discover new synergies, and gather additional evidence supporting that combinations of histone PTMs are the central currency of chromatin-mediated regulation of the genome.

VRK1 Phosphorylates Tip60/KAT5 and Is Required for H4K16 Acetylation in Response to DNA Damage

Dynamic remodeling of chromatin requires acetylation and methylation of histones, frequently affecting the same lysine residue. These alternative epigenetic modifications require the coordination of enzymes, writers and erasers, mediating them such as acetylases and deacetylases. In cells in G0/G1, DNA damage induced by doxorubicin causes an increase in histone H4K16ac, a marker of chromatin relaxation. In this context, we studied the role that VRK1, a chromatin kinase activated by DNA damage, plays in this early step. VRK1 depletion or MG149, a Tip60/KAT5 inhibitor, cause a loss of H4K16ac. DNA damage induces the phosphorylation of Tip60 mediated by VRK1 in the chromatin fraction. VRK1 directly interacts with and phosphorylates Tip60. Furthermore, the phosphorylation of Tip60 induced by doxorubicin is lost by depletion of VRK1 in both ATM +/+ and ATM-/- cells. Kinase-active VRK1, but not kinase-dead VRK1, rescues Tip60 phosphorylation induced by DNA damage independently of ATM. The Tip60 phosphorylation by VRK1 is necessary for the activating acetylation of ATM, and subsequent ATM autophosphorylation, and both are lost by VRK1 depletion. These results support that the VRK1 chromatin kinase is an upstream regulator of the initial acetylation of histones, and an early step in DNA damage responses (DDR).

Changes in γH2AX and H4K16ac levels are involved in the biochemical response to a competitive soccer match in adolescent players

The aim of this study was to examine novel putative markers of the response to the competitive soccer match in adolescent players, such as changes in global levels of γH2AX and H4K16ac in the chromatin of peripheral mononuclear blood cells (PMBCs) and a Fourier-transform infrared spectroscopy (FTIR)-based biochemical fingerprint of serum. These characteristics were examined with reference to the physiological and metabolic aspects of this response. Immediately post-match we noticed: (1) a systemic inflammatory response, manifesting as peaks in leukocyte count and changes in concentrations of IL-6, TNFα, and cortisol; (2) a peak in plasma lactate; (3) onset of oxidative stress, manifesting as a decline in GSH/GSSG; (4) onset of muscle injury, reflected in an increase in CK activity. Twenty-four hours post-match the decrease in GSH/GSSG was accompanied by accumulation of MDA and 8-OHdG, macromolecule oxidation end-products, and an increase in CK activity. No changes in SOD1 or GPX1 levels were found. Repeated measures correlation revealed several associations between the investigated biomarkers. The FTIR analysis revealed that the match had the greatest impact on serum lipid profile immediately post-game. In turn, increases in γH2AX and H4K16ac levels at 24 h post-match indicated activation of a DNA repair pathway.

Epigenetic effects of low-level sodium arsenite exposure on human liver HepaRG cells

Chronic exposure to inorganic arsenic is associated with a variety of adverse health effects, including lung, bladder, kidney, and liver cancer. Several mechanisms have been proposed for arsenic-induced tumorigenesis; however, insufficient knowledge and many unanswered questions remain to explain the integrated molecular pathogenesis of arsenic carcinogenicity. In the present study, using non-tumorigenic human liver HepaRG cells, we investigated epigenetic alterations upon prolonged exposure to a noncytotoxic concentration of sodium arsenite (NaAsO₂). We demonstrate that continuous exposure of HepaRG cells to 1 µM sodium arsenite (NaAsO₂) for 14 days resulted in substantial cytosine DNA demethylation and hypermethylation across the genome, among which the claudin 14 (CLDN14) gene was hypermethylated and the most down-regulated gene. Another important finding was a profound loss of histone H3 lysine 36 (H3K36) trimethylation, which was accompanied by increased damage to genomic DNA and an elevated de novo mutation frequency. These results demonstrate that continuous exposure of HepaRG cells to a noncytotoxic concentration of NaAsO₂ results in substantial epigenetic abnormalities accompanied by several carcinogenesis-related events, including induction of epithelial-to-mesenchymal transition, damage to DNA, inhibition of DNA repair genes, and induction of de novo mutations. Importantly, this study highlights the intimate mechanistic link and interplay between two fundamental cancer-associated events, epigenetic and genetic alterations, in arsenic-associated carcinogenesis.

The Chromatin Response to Double-Strand DNA Breaks and Their Repair

Cellular DNA is constantly being damaged by numerous internal and external mutagenic factors. Probably the most severe type of insults DNA could suffer are the double-strand DNA breaks (DSBs). They sever both DNA strands and compromise genomic stability, causing deleterious chromosomal aberrations that are implicated in numerous maladies, including cancer. Not surprisingly, cells have evolved several DSB repair pathways encompassing hundreds of different DNA repair proteins to cope with this challenge. In eukaryotic cells, DSB repair is fulfilled in the immensely complex environment of the chromatin. The chromatin is not just a passive background that accommodates the multitude of DNA repair proteins, but it is a highly dynamic and active participant in the repair process. Chromatin alterations, such as changing patterns of histone modifications shaped by numerous histone-modifying enzymes and chromatin remodeling, are pivotal for proficient DSB repair. Dynamic chromatin changes ensure accessibility to the damaged region, recruit DNA repair proteins, and regulate their association and activity, contributing to DSB repair pathway choice and coordination. Given the paramount importance of DSB repair in tumorigenesis and cancer progression, DSB repair has turned into an attractive target for the development of novel anticancer therapies, some of which have already entered the clinic.

Remodeling the epigenome and (epi)cytoskeleton: a new paradigm for co-regulation by methylation

The epigenome determines heritable patterns of gene expression in the absence of changes in DNA sequence. The result is programming of different cellular-, tissue- and organ-specific phenotypes from a single organismic genome. Epigenetic marks that comprise the epigenome (e.g. methylation) are placed upon or removed from chromatin (histones and DNA) to direct the activity of effectors that regulate gene expression and chromatin structure. Recently, the cytoskeleton has been identified as a second target for the cell's epigenetic machinery. Several epigenetic 'readers, writers and erasers' that remodel chromatin have been discovered to also remodel the cytoskeleton, regulating structure and function of microtubules and actin filaments. This points to an emerging paradigm for dual-function remodelers with 'chromatocytoskeletal' activity that can integrate cytoplasmic and nuclear functions. For example, the SET domain-containing 2 methyltransferase (SETD2) has chromatocytoskeletal activity, methylating both histones and microtubules. The SETD2 methyl mark on chromatin is required for efficient DNA repair, and its microtubule methyl mark is required for proper chromosome segregation during mitosis. This unexpected convergence of SETD2 activity on histones and microtubules to maintain genomic stability suggests the intriguing possibility of an expanded role in the cell for chromatocytoskeletal proteins that read, write and erase methyl marks on the cytoskeleton as well as chromatin. Coordinated use of methyl marks to remodel both the epigenome and the (epi)cytoskeleton opens the possibility for integrated regulation (which we refer to as 'epiregulation') of other higher-level functions, such as muscle contraction or learning and memory, and could even have evolutionary implications.

An Interplay Between MRTF-A and the Histone Acetyltransferase TIP60 Mediates Hypoxia-Reoxygenation Induced iNOS Transcription in Macrophages

Cardiac ischemia-reperfusion injury (IRI) represents a major pathophysiological event associated with permanent loss of heart function. Several inter-dependent processes contribute to cardiac IRI that include accumulation of reactive oxygen species (ROS), aberrant inflammatory response, and depletion of energy supply. Inducible nitric oxide synthase (iNOS) is a pro-inflammatory mediator and a major catalyst of ROS generation. In the present study we investigated the epigenetic mechanism whereby iNOS transcription is up-regulated in macrophages in the context of cardiac IRI. We report that germline deletion or systemic inhibition of myocardin-related transcription factor A (MRTF-A) in mice attenuated up-regulation of iNOS following cardiac IRI in the heart. In cultured macrophages, depletion or inhibition of MRTF-A suppressed iNOS induction by hypoxia-reoxygenation (HR). In contrast, MRTF-A over-expression potentiated activation of the iNOS promoter by HR. MRTF-A directly binds to the iNOS promoter in response to HR stimulation. MRTF-A binding to the iNOS promoter was synonymous with active histone modifications including trimethylated H3K4, acetylated H3K9, H3K27, and H4K16. Further analysis revealed that MRTF-A interacted with H4K16 acetyltransferase TIP60 to synergistically activate iNOS transcription. TIP60 depletion or inhibition achieved equivalent effects as MRTF-A depletion/inhibition in terms of iNOS repression. Of interest, TIP60 appeared to form a crosstalk with the H3K4 trimethyltransferase complex to promote iNOS trans-activation. In conclusion, we data suggest that the MRTF-A-TIP60 axis may play a critical role in iNOS transcription in macrophages and as such be considered as a potential target for the intervention of cardiac IRI.

Bioinformatics analysis of the network of histone H3 lysine 9 trimethylation in acute myeloid leukaemia

Changes in histone H3 lysine 9 trimethylation (H3K9me3) may be related to the development of drug-resistant acute myeloid leukaemia (AML); insights into the network of H3K9me3 may improve patient prognosis. Patient data were derived from the Gene Expression Omnibus (GEO) database and data from AML cells treated with chidamide, a novel benzamide chemical class of histone deacetylase inhibitor (HDACi), in vitro were derived from ChIP-seq. Patients and AML cell data were analysed using GEO2R, GOseq, KOBAS, the STRING database and Cytoscape 3.5.1. We identified several genes related to the upregulation or downregulation of H3K9me3 in AML patients; some of these genes were related to apoptosis, autophagy, and the pathway of cell longevity. AML cells treated with chidamide in vitro showed the same gene changes. The protein interactions in the network did not have significantly more interactions than expected, suggesting the need for more research to identify these interactions. One compelling result from the protein interaction study was that sirtuin 1 (SIRT1) may have an indirect interaction with lysine-specific demethylase 4A (KDM4A). These results help explain alterations of H3K9me3 in AML that may direct further studies aimed at improving patient prognosis. These results may also provide a basis for chidamide as a treatment strategy for AML patients in the future.

H3K36me3, message from chromatin to DNA damage repair

Histone marks control many cellular processes including DNA damage repair. This review will focus primarily on the active histone mark H3K36me3 in the regulation of DNA damage repair and the maintenance of genomic stability after DNA damage. There are diverse clues showing H3K36me3 participates in DNA damage response by directly recruiting DNA repair machinery to set the chromatin at a “ready” status, leading to a quick response upon damage. Reduced H3K36me3 is associated with low DNA repair efficiency. This review will also place a main emphasis on the H3K36me3-mediated DNA damage repair in the tumorigenesis of the newly found oncohistone mutant tumors. Gaining an understanding of different aspects of H3K36me3 in DNA damage repair, especially in cancers, would share the knowledge of chromatin and DNA repair to serve to the drug discovery and patient care.

Understanding the mechanistic insight of arsenic exposure and decoding the histone cipher

BACKGROUND

The study of heritable epigenetic changes in arsenic exposure has intensified over the last decade. Groundwater arsenic contamination causes a great threat to humans and, to date, no accurate measure has been formulated for remediation. The fascinating possibilities of epi-therapeutics identify the need for an in-depth mechanistic understanding of the epigenetic landscape.

OBJECTIVE

In this comprehensive review, we have set to analyze major studies pertaining to histone post-translational modifications in arsenic-mediated disease development and carcinogenesis during last ten years (2008-2018).

RESULTS

The role of the specific histone marks in arsenic toxicity has been detailed. A comprehensive list that includes major arsenic-induced histone modifications identified for the last 10 years has been documented and details of different states of arsenic, organisms, exposure type, study platform, and findings were provided. An arsenic signature panel was suggested to help in early prognosis. An attempt has been made to identify the grey areas of research.

PROSPECTS

Future prospective multi-target analyses of the inter-molecular crosstalk among different histone marks are needed to be explored further in order to understand the mechanism of arsenic toxicity and carcinogenicity and to confirm the suitability of these epi-marks as prognostic markers.

Does genome surveillance explain the global discrepancy between binding and effect of chromatin factors?

Knocking out a chromatin factor often does not alter the transcription of its binding targets. What explains the observed disconnect between binding and effect? We hypothesize that this discrepancy could be associated with the role of chromatin factors in maintaining genetic and epigenetic integrity at promoters, and not necessarily with transcription. Through re-analysis of published datasets, we present several lines of evidence that support our hypothesis and deflate the popular assumptions. We also tested the hypothesis through mutation accumulation assays on yeast knockouts of chromatin factors. Altogether, the proposed hypothesis presents a simple explanation for the global discord between chromatin factor binding and effect. Future work in this direction might fortify the hypothesis and elucidate the underlying mechanisms.

Histone Deacetylase (HDAC) Gene Family in Allotetraploid Cotton and Its Diploid Progenitors: In Silico Identification, Molecular Characterization, and Gene Expression Analysis under Multiple Abiotic Stresses, DNA Damage and Phytohormone Treatments

Histone deacetylases (HDACs) play a significant role in a plant’s development and response to various environmental stimuli by regulating the gene transcription. However, HDACs remain unidentified in cotton. In this study, a total of 29 HDACs were identified in allotetraploid Gossypium hirsutum, while 15 and 13 HDACs were identified in Gossypium arboretum and Gossypium raimondii, respectively. Gossypium HDACs were classified into three groups (reduced potassium dependency 3 (RPD3)/HDA1, HD2-like, and Sir2-like (SRT) based on their sequences, and Gossypium HDACs within each subgroup shared a similar gene structure, conserved catalytic domains and motifs. Further analysis revealed that Gossypium HDACs were under a strong purifying selection and were unevenly distributed on their chromosomes. Gene expression data revealed that G. hirsutumHDACs were differentially expressed in various vegetative and reproductive tissues, as well as at different developmental stages of cotton fiber. Furthermore, some G. hirsutum HDACs were co-localized with quantitative trait loci (QTLs) and single-nucleotide polymorphism (SNPs) of fiber-related traits, indicating their function in fiber-related traits. We also showed that G. hirsutum HDACs were differentially regulated in response to plant hormones (abscisic acid (ABA) and auxin), DNA damage agent (methyl methanesulfonate (MMS)), and abiotic stresses (cold, salt, heavy metals and drought), indicating the functional diversity and specification of HDACs in response to developmental and environmental cues. In brief, our results provide fundamental information regarding G.hirsutumHDACs and highlight their potential functions in cotton growth, fiber development and stress adaptations, which will be helpful for devising innovative strategies for the improvement of cotton fiber and stress tolerance.

A CRISPR/Cas9 screen identifies the histone demethylase MINA53 as a novel HIV-1 latency-promoting gene (LPG)

Although combination antiretroviral therapy is potent to block active replication of HIV-1 in AIDS patients, HIV-1 persists as transcriptionally inactive proviruses in infected cells. These HIV-1 latent reservoirs remain a major obstacle for clearance of HIV-1. Investigation of host factors regulating HIV-1 latency is critical for developing novel antiretroviral reagents to eliminate HIV-1 latent reservoirs. From our recently accomplished CRISPR/Cas9 sgRNA screens, we identified that the histone demethylase, MINA53, is potentially a novel HIV-1 latency-promoting gene (LPG). We next validated MINA53’s function in maintenance of HIV-1 latency by depleting MINA53 using the alternative RNAi approach. We further identified that in vitro MINA53 preferentially demethylates the histone substrate, H3K36me3 and that in cells MINA53 depletion by RNAi also increases the local level of H3K36me3 at LTR. The effort to map the downstream effectors unraveled that H3K36me3 has the cross-talk with another epigenetic mark H4K16ac, mediated by KAT8 that recognizes the methylated H3K36 and acetylated H4K16. Removing the MINA53-mediated latency mechanisms could benefit the reversal of post-integrated latent HIV-1 proviruses for purging of reservoir cells. We further demonstrated that a pan jumonji histone demethylase inhibitor, JIB-04, inhibits MINA53-mediated demethylation of H3K36me3, and JIB-04 synergizes with other latency-reversing agents (LRAs) to reactivate latent HIV-1.

Comparative Genome-wide Analysis and Expression Profiling of Histone Acetyltransferase (HAT) Gene Family in Response to Hormonal Applications, Metal and Abiotic Stresses in Cotton

Post-translational modifications are involved in regulating diverse developmental processes. Histone acetyltransferases (HATs) play vital roles in the regulation of chromation structure and activate the gene transcription implicated in various cellular processes. However, HATs in cotton, as well as their regulation in response to developmental and environmental cues, remain unidentified. In this study, 9 HATs were identified from Gossypium raimondi and Gossypium arboretum, while 18 HATs were identified from Gossypium hirsutum. Based on their amino acid sequences, Gossypium HATs were divided into three groups: CPB, GNAT, and TAF_II250. Almost all the HATs within each subgroup share similar gene structure and conserved motifs. Gossypium HATs are unevenly distributed on the chromosomes, and duplication analysis suggests that Gossypium HATs are under strong purifying selection. Gene expression analysis showed that Gossypium HATs were differentially expressed in various vegetative tissues and at different stages of fiber development. Furthermore, all the HATs were differentially regulated in response to various stresses (salt, drought, cold, heavy metal and DNA damage) and hormones (abscisic acid (ABA) and auxin (NAA)). Finally, co-localization of HAT genes with reported quantitative trait loci (QTL) of fiber development were reported. Altogether, these results highlight the functional diversification of HATs in cotton growth and fiber development, as well as in response to different environmental cues. This study enhances our understanding of function of histone acetylation in cotton growth, fiber development, and stress adaptation, which will eventually lead to the long-term improvement of stress tolerance and fiber quality in cotton.

Epigenetic modifiers: activities in renal cell carcinoma

Renal cell carcinomas (RCCs) are a diverse set of malignancies that have recently been shown to harbour mutations in a number of chromatin modifier genes - including PBRM1, SETD2, BAP1, KDM5C, KDM6A, and MLL2 - through high-throughput sequencing efforts. Current research focuses on understanding the biological activities that chromatin modifiers employ to suppress tumorigenesis and on developing clinical approaches that take advantage of this knowledge. Unsurprisingly, several common themes unify the functions of these epigenetic modifiers, particularly regulation of histone post-translational modifications and nucleosome organization. Furthermore, chromatin modifiers also govern processes crucial for DNA repair and maintenance of genomic integrity as well as the regulation of splicing and other key processes. Many chromatin modifiers have additional non-canonical roles in cytoskeletal regulation, which further contribute to genomic stability, expanding the repertoire of functions that might be essential in tumorigenesis. Our understanding of how mutations in chromatin modifiers contribute to tumorigenesis in RCC is improving but remains an area of intense investigation. Importantly, elucidating the activities of chromatin modifiers offers intriguing opportunities for the development of new therapeutic interventions in RCC.

Chromatin Remodeling and Epigenetic Regulation in Plant DNA Damage Repair

DNA damage response (DDR) in eukaryotic cells is initiated in the chromatin context. DNA damage and repair depend on or have influence on the chromatin dynamics associated with genome stability. Epigenetic modifiers, such as chromatin remodelers, histone modifiers, DNA (de-)methylation enzymes, and noncoding RNAs regulate DDR signaling and DNA repair by affecting chromatin dynamics. In recent years, significant progress has been made in the understanding of plant DDR and DNA repair. SUPPRESSOR OF GAMMA RESPONSE1, RETINOBLASTOMA RELATED1 (RBR1)/E2FA, and NAC103 have been proven to be key players in the mediation of DDR signaling in plants, while plant-specific chromatin remodelers, such as DECREASED DNA METHYLATION1, contribute to chromatin dynamics for DNA repair. There is accumulating evidence that plant epigenetic modifiers are involved in DDR and DNA repair. In this review, I examine how DDR and DNA repair machineries are concertedly regulated in Arabidopsis thaliana by a variety of epigenetic modifiers directing chromatin remodeling and epigenetic modification. This review will aid in updating our knowledge on DDR and DNA repair in plants.

The impact of histone post-translational modifications in neurodegenerative diseases

Every year, neurodegenerative disorders take more than 5000 lives in the US alone. Cures have not yet been found for many of the multitude of neuropathies. The majority of amyotrophic lateral sclerosis (ALS), frontotemporal dementia (FTD) and Parkinson's disease (PD) cases have no known genetic basis. Thus, it is evident that contemporary genetic approaches have failed to explain the etiology or etiologies of ALS/FTD and PD. Recent investigations have explored the potential role of epigenetic mechanisms in disease development. Epigenetics comprises heritable changes in gene utilization that are not derived from changes in the genome. A main epigenetic mechanism involves the post-translational modification of histones. Increased knowledge of the epigenomic landscape of neurodegenerative diseases would not only further our understanding of the disease pathologies, but also lead to the development of treatments able to halt their progress. Here, we review recent advances on the association of histone post-translational modifications with ALS, FTD, PD and several ataxias.

H3K9me3, H3K36me3, and H4K20me3 Expression Correlates with Patient Outcome in Esophageal Squamous Cell Carcinoma as Epigenetic Markers

BACKGROUND

Histone methylation, as an essential pattern of posttranslational modifications, contributes to multiple cancer-related biological processes. Dysregulation of histone methylation is now considered a biomarker for cancer prognosis.

AIMS

This study investigated and evaluated the potential role of four histone lysine trimethylation markers as biomarkers for esophageal squamous cell carcinoma (ESCC) prognosis.

METHODS

Tissue arrays were made from 135 paraffin-embedded ESCC samples and examined for histone markers by immunohistochemistry, and 10 pairs of cancer and noncancerous mucosa tissues from ESCC patients were investigated with Western blot. Chi-squared test, Kaplan-Meier analysis with log-rank test, and Cox proportional hazard trend analyses were performed to assess the prognostic values of the markers.

RESULTS

Histone 3 lysine 4 trimethylation (H3K4me3), histone 3 lysine 9 trimethylation (H3K9me3), and histone 4 lysine 20 trimethylation (H4K20me3), but not histone 3 lysine 36 trimethylation (H3K36me3), showed stronger immunostaining signals in tumor tissues than in the corresponding adjacent non-neoplastic mucosa tissues. The expression patterns of H3K36me3, H3K9me3, and H4K20me3 correlated with tumor infiltrating depth, lymph node involvement, and pTNM stage. Low-scoring H3K9me3 and H4K20me3 predicted better prognosis, while H3K36me3 manifested the opposite trend. Poor prognosis occurred in ESCC patients with expression patterns of high levels of H3K9me3, high levels of H4K20me3, and low levels of H3K36me3 expression.

CONCLUSIONS

H3K9me3, H4K20me3, and H3K36me3 showed a close relationship with clinical features and were considered independent risk factors for survival of ESCC patients. The combination of H3K9me3, H4K20me3, and H3K36me3 expression, rather than the expression of a single histone marker, is believed to further enhance evaluations of ESCC prognosis and management.

Understanding histone H3 lysine 36 methylation and its deregulation in disease

Methylation of histone H3 lysine 36 (H3K36) plays crucial roles in the partitioning of chromatin to distinctive domains and the regulation of a wide range of biological processes. Trimethylation of H3K36 (H3K36me3) demarcates body regions of the actively transcribed genes, providing signals for modulating transcription fidelity, mRNA splicing and DNA damage repair; and di-methylation of H3K36 (H3K36me2) spreads out within large intragenic regions, regulating distribution of histone H3 lysine 27 trimethylation (H3K27me3) and possibly DNA methylation. These H3K36 methylation-mediated events are biologically crucial and controlled by different classes of proteins responsible for either 'writing', 'reading' or 'erasing' of H3K36 methylation marks. Deregulation of H3K36 methylation and related regulatory factors leads to pathogenesis of disease such as developmental syndrome and cancer. Additionally, recurrent mutations of H3K36 and surrounding histone residues are detected in human tumors, further highlighting the importance of H3K36 in biology and medicine. This review will elaborate on current advances in understanding H3K36 methylation and related molecular players during various chromatin-templated cellular processes, their crosstalks with other chromatin factors, as well as their deregulations in the diseased contexts.

Inverse dose-rate effect of ionising radiation on residual 53BP1 foci in the eye lens

The influence of dose rate on radiation cataractogenesis has yet to be extensively studied. One recent epidemiological investigation suggested that protracted radiation exposure increases radiation-induced cataract risk: cumulative doses of radiation mostly <100 mGy received by US radiologic technologists over 5 years were associated with an increased excess hazard ratio for cataract development. However, there are few mechanistic studies to support and explain such observations. Low-dose radiation-induced DNA damage in the epithelial cells of the eye lens (LECs) has been proposed as a possible contributor to cataract formation and thus visual impairment. Here, 53BP1 foci was used as a marker of DNA damage. Unexpectedly, the number of 53BP1 foci that persisted in the mouse lens samples after γ-radiation exposure increased with decreasing dose-rate at 4 and 24 h. The C57BL/6 mice were exposed to 0.5, 1 and 2 Gy ƴ-radiation at 0.063 and 0.3 Gy/min and also 0.5 Gy at 0.014 Gy/min. This contrasts the data we obtained for peripheral blood lymphocytes collected from the same animal groups, which showed the expected reduction of residual 53BP1 foci with reducing dose-rate. These findings highlight the likely importance of dose-rate in low-dose cataract formation and, furthermore, represent the first evidence that LECs process radiation damage differently to blood lymphocytes.