Crosstalk between SET7/9-dependent methylation and ARTD1-mediated ADP-ribosylation of histone H1.4

The 24-Hour Time Course of Integrated Molecular Responses to Resistance Exercise in Human Skeletal Muscle Implicates MYC as a Hypertrophic Regulator That is Sufficient for Growth

Molecular control of recovery after exercise in muscle is temporally dynamic. A time course of biopsies around resistance exercise (RE) combined with -omics is necessary to better comprehend the molecular contributions of skeletal muscle adaptation in humans. Vastus lateralis biopsies before and 30 minutes, 3-, 8-, and 24-hours after acute RE were collected. A time-point matched biopsy-only group was also included. RNA-sequencing defined the transcriptome while DNA methylomics and computational approaches complemented these data. The post-RE time course revealed: 1) DNA methylome responses at 30 minutes corresponded to upregulated genes at 3 hours, 2) a burst of translation- and transcription-initiation factor-coding transcripts occurred between 3 and 8 hours, 3) global gene expression peaked at 8 hours, 4) ribosome-related genes dominated the mRNA landscape between 8 and 24 hours, 5) methylation-regulated MYC was a highly influential transcription factor throughout the 24-hour recovery and played a primary role in ribosome-related mRNA levels between 8 and 24 hours. The influence of MYC in human muscle adaptation was strengthened by transcriptome information from acute MYC overexpression in mouse muscle. To test whether MYC was sufficient for hypertrophy, we generated a muscle fiber-specific doxycycline inducible model of pulsatile MYC induction. Periodic 48-hour pulses of MYC over 4 weeks resulted in higher muscle mass and fiber size in the soleus of adult female mice. Collectively, we present a temporally resolved resource for understanding molecular adaptations to RE in muscle and reveal MYC as a regulator of RE-induced mRNA levels and hypertrophy.

DNA hypomethylation characterizes genes encoding tissue-dominant functional proteins in liver and skeletal muscle

Each tissue has a dominant set of functional proteins required to mediate tissue-specific functions. Epigenetic modifications, transcription, and translational efficiency control tissue-dominant protein production. However, the coordination of these regulatory mechanisms to achieve such tissue-specific protein production remains unclear. Here, we analyzed the DNA methylome, transcriptome, and proteome in mouse liver and skeletal muscle. We found that DNA hypomethylation at promoter regions is globally associated with liver-dominant or skeletal muscle-dominant functional protein production within each tissue, as well as with genes encoding proteins involved in ubiquitous functions in both tissues. Thus, genes encoding liver-dominant proteins, such as those involved in glycolysis or gluconeogenesis, the urea cycle, complement and coagulation systems, enzymes of tryptophan metabolism, and cytochrome P450-related metabolism, were hypomethylated in the liver, whereas those encoding-skeletal muscle-dominant proteins, such as those involved in sarcomere organization, were hypomethylated in the skeletal muscle. Thus, DNA hypomethylation characterizes genes encoding tissue-dominant functional proteins.

Poly ADP-ribosylation of SET8 leads to aberrant H4K20 methylation in mammalian nuclear genome

In mammalian cells, SET8 mediated Histone H4 Lys 20 monomethylation (H4K20me1) has been implicated in regulating mitotic condensation, DNA replication, DNA damage response, and gene expression. Here we show SET8, the only known enzyme for H4K20me1 is post-translationally poly ADP-ribosylated by PARP1 on lysine residues. PARP1 interacts with SET8 in a cell cycle-dependent manner. Poly ADP-ribosylation on SET8 renders it catalytically compromised, and degradation via ubiquitylation pathway. Knockdown of PARP1 led to an increase of SET8 protein levels, leading to aberrant H4K20me1 and H4K20me3 domains in the genome. H4K20me1 is associated with higher gene transcription levels while the increase of H4K20me3 levels was predominant in DNA repeat elements. Hence, SET8 mediated chromatin remodeling in mammalian cells are modulated by poly ADP-ribosylation by PARP1.

ZKSCAN5 Activates VEGFC Expression by Recruiting SETD7 to Promote the Lymphangiogenesis, Tumour Growth, and Metastasis of Breast Cancer

The growth of lymphatic vessels (lymphangiogenesis) plays a pivotal role in breast cancer progression and metastasis and the immune response. Vascular endothelial growth factor C (VEGFC) has been demonstrated to accelerate cancer metastasis and modulate the immune system by enhancing lymphangiogenesis. However, it remains largely unclear how transcription factors physically regulate VEGFC expression by interacting with histone-modifying enzymes. Like many histone-modifying enzymes, SETD7 plays a key role in cell proliferation and inhibits tumour cell differentiation. In this study, we identified the role of the transcription factor zinc finger with KRAB and SCAN domains 5 (ZKSCAN5) in interacting with histone methyltransferase SETD7 and mediating VEGFC transcription and tumour lymphangiogenesis. ZKSCAN5 interacts with and recruits SETD7 to the VEGFC promoter. By regulating breast cancer-secreted VEGFC, ZKSCAN5 could induce the tube formation of lymph endothelial cells, which promotes tumour proliferation, migration, and metastasis. Clinically, the expression of ZKSCAN5 was frequently upregulated in patients with breast cancer and positively correlated with the expression of VEGFC and the number of lymphatic microvessels. ZKSCAN5 is a poor prognostic factor for patients with breast cancer. Our results characterise the role of ZKSCAN5 in regulating VEGFC transcription and predict ZKSCAN5 as a breast cancer therapeutic target.

The Role of Lysine Methyltransferase SET7/9 in Proliferation and Cell Stress Response

Lysine-specific methyltransferase 7 (KMT7) SET7/9, aka Set7, Set9, or SetD7, or KMT5 was discovered 20 years ago, yet its biological role remains rather enigmatic. In this review, we analyze the particularities of SET7/9 enzymatic activity and substrate specificity with respect to its biological importance, mostly focusing on its two well-characterized biological functions: cellular proliferation and stress response.

The regulatory landscape of the human HPF1- and ARH3-dependent ADP-ribosylome

Despite the involvement of Poly(ADP-ribose) polymerase-1 (PARP1) in many important biological pathways, the target residues of PARP1-mediated ADP-ribosylation remain ambiguous. To explicate the ADP-ribosylation regulome, we analyze human cells depleted for key regulators of PARP1 activity, histone PARylation factor 1 (HPF1) and ADP-ribosylhydrolase 3 (ARH3). Using quantitative proteomics, we characterize 1,596 ADP-ribosylation sites, displaying up to 1000-fold regulation across the investigated knockout cells. We find that HPF1 and ARH3 inversely and homogenously regulate the serine ADP-ribosylome on a proteome-wide scale with consistent adherence to lysine-serine-motifs, suggesting that targeting is independent of HPF1 and ARH3. Notably, we do not detect an HPF1-dependent target residue switch from serine to glutamate/aspartate under the investigated conditions. Our data support the notion that serine ADP-ribosylation mainly exists as mono-ADP-ribosylation in cells, and reveal a remarkable degree of histone co-modification with serine ADP-ribosylation and other post-translational modifications.

ADP-Ribosylation as Post-Translational Modification of Proteins: Use of Inhibitors in Cancer Control

Among the post-translational modifications of proteins, ADP-ribosylation has been studied for over fifty years, and a large set of functions, including DNA repair, transcription, and cell signaling, have been assigned to this post-translational modification (PTM). This review presents an update on the function of a large set of enzyme writers, the readers that are recruited by the modified targets, and the erasers that reverse the modification to the original amino acid residue, removing the covalent bonds formed. In particular, the review provides details on the involvement of the enzymes performing monoADP-ribosylation/polyADP-ribosylation (MAR/PAR) cycling in cancers. Of note, there is potential for the application of the inhibitors developed for cancer also in the therapy of non-oncological diseases such as the protection against oxidative stress, the suppression of inflammatory responses, and the treatment of neurodegenerative diseases. This field of studies is not concluded, since novel enzymes are being discovered at a rapid pace.

PARPs in lipid metabolism and related diseases

PARPs and tankyrases (TNKS) represent a family of 17 proteins. PARPs and tankyrases were originally identified as DNA repair factors, nevertheless, recent advances have shed light on their role in lipid metabolism. To date, PARP1, PARP2, PARP3, tankyrases, PARP9, PARP10, PARP14 were reported to have multi-pronged connections to lipid metabolism. The activity of PARP enzymes is fine-tuned by a set of cholesterol-based compounds as oxidized cholesterol derivatives, steroid hormones or bile acids. In turn, PARPs modulate several key processes of lipid homeostasis (lipotoxicity, fatty acid and steroid biosynthesis, lipoprotein homeostasis, fatty acid oxidation, etc.). PARPs are also cofactors of lipid-responsive nuclear receptors and transcription factors through which PARPs regulate lipid metabolism and lipid homeostasis. PARP activation often represents a disruptive signal to (lipid) metabolism, and PARP-dependent changes to lipid metabolism have pathophysiological role in the development of hyperlipidemia, obesity, alcoholic and non-alcoholic fatty liver disease, type II diabetes and its complications, atherosclerosis, cardiovascular aging and skin pathologies, just to name a few. In this synopsis we will review the evidence supporting the beneficial effects of pharmacological PARP inhibitors in these diseases/pathologies and propose repurposing PARP inhibitors already available for the treatment of various malignancies.

Proteogenomic analysis of Inhibitor of Differentiation 4 (ID4) in basal-like breast cancer

BACKGROUND

Basal-like breast cancer (BLBC) is a poorly characterised, heterogeneous disease. Patients are diagnosed with aggressive, high-grade tumours and often relapse with chemotherapy resistance. Detailed understanding of the molecular underpinnings of this disease is essential to the development of personalised therapeutic strategies. Inhibitor of differentiation 4 (ID4) is a helix-loop-helix transcriptional regulator required for mammary gland development. ID4 is overexpressed in a subset of BLBC patients, associating with a stem-like poor prognosis phenotype, and is necessary for the growth of cell line models of BLBC through unknown mechanisms.

METHODS

Here, we have defined unique molecular insights into the function of ID4 in BLBC and the related disease high-grade serous ovarian cancer (HGSOC), by combining RIME proteomic analysis, ChIP-seq mapping of genomic binding sites and RNA-seq.

RESULTS

These studies reveal novel interactions with DNA damage response proteins, in particular, mediator of DNA damage checkpoint protein 1 (MDC1). Through MDC1, ID4 interacts with other DNA repair proteins (γH2AX and BRCA1) at fragile chromatin sites. ID4 does not affect transcription at these sites, instead binding to chromatin following DNA damage. Analysis of clinical samples demonstrates that ID4 is amplified and overexpressed at a higher frequency in BRCA1-mutant BLBC compared with sporadic BLBC, providing genetic evidence for an interaction between ID4 and DNA damage repair deficiency.

CONCLUSIONS

These data link the interactions of ID4 with MDC1 to DNA damage repair in the aetiology of BLBC and HGSOC.

PARP1 Hinders Histone H2B Occupancy at the NFATc1 Promoter to Restrain Osteoclast Differentiation

Induction of nuclear factor of activated T cell cytoplasmic 1 (NFATc1) by macrophage colony-stimulating factor (M-CSF) and receptor activator of NF-κB ligand (RANKL) is essential for macrophage differentiation into osteoclasts (OCs), but the underlying mechanisms remain unclear. The ability of poly(ADP-ribose) polymerase 1 (PARP1) to poly-ADP-ribosylate NFATc1 in T cells prompted us to investigate the PARP1 and NFATc1 interaction during osteoclastogenesis. However, extensive studies failed to directly link PARP1 to NFATc1. A combination of transcriptomics and proteomics studies was then used to identify PARP1 targets under these conditions. These unbiased approaches in conjunction with site-directed mutagenesis studies revealed that PARP1 inhibited NFATc1 expression and OC formation by ADP-ribosylating histone H2B at serine 7 and decreasing the occupancy of this histone variant at the NFATc1 promoter. The anti-osteoclastogenic function of PARP1 was confirmed in vivo in several mouse models of PARP1 loss-of-function or gain-of-function, including a novel model in which PARP1 was conditionally ablated in myeloid cells. Thus, PARP1 ADP-ribosylates H2B to negatively regulate NFATc1 expression and OC differentiation. © 2019 American Society for Bone and Mineral Research.

Lysine methyltransferase SETD6 modifies histones on a glycine-lysine motif

Although central to regulating the access to genetic information, most lysine methyltransferases remain poorly characterised relative to other family of enzymes. Herein, I report new substrates for the lysine methyltransferase SETD6. Based on the SETD6-catalysed site on the histone variant H2AZ, I identified similar sequences in the canonical histones H2A, H3, and H4 that are modified by SETD6 in vitro, and putative non-histone substrates. I herein expend the repertoire of substrates for methylation by SETD6.

Biological processes and signal transduction pathways regulated by the protein methyltransferase SETD7 and their significance in cancer

Protein methyltransferases have been shown to methylate histone and non-histone proteins, leading to regulation of several biological processes that control cell homeostasis. Over the past few years, the histone-lysine N-methyltransferase SETD7 (SETD7; also known as SET7/9, KIAA1717, KMT7, SET7, SET9) has emerged as an important regulator of at least 30 non-histone proteins and a potential target for the treatment of several human diseases. This review discusses current knowledge of the structure and subcellular localization of SETD7, as well as its function as a histone and non-histone methyltransferase. This work also underlines the putative contribution of SETD7 to the regulation of gene expression, control of cell proliferation, differentiation and endoplasmic reticulum stress, which indicate that SETD7 is a candidate for novel targeted therapies with the aim of either stimulating or inhibiting its activity, depending on the cell signaling context.

Identification and Characterizations of Novel, Selective Histone Methyltransferase SET7 Inhibitors by Scaffold Hopping- and 2D-Molecular Fingerprint-Based Similarity Search

SET7, serving as the only histone methyltransferase that monomethylates 'Lys-4' of histone H3, has been proved to function as a key regulator in diverse biological processes, such as cell proliferation, transcriptional network regulation in embryonic stem cell, cell cycle control, protein stability, heart morphogenesis and development. What's more, SET7 is involved inthe pathogenesis of alopecia aerate, breast cancer, tumor and cancer progression, atherosclerosis in human carotid plaques, chronic renal diseases, diabetes, obesity, ovarian cancer, prostate cancer, hepatocellular carcinoma, and pulmonary fibrosis. Therefore, there is urgent need to develop novel SET7 inhibitors. In this paper, based on DC-S239 which has been previously reported in our group, we employed scaffold hopping- and 2D fingerprint-based similarity searches and identified DC-S285 as the new hit compound targeting SET7 (IC₅₀ = 9.3 μM). Both radioactive tracing and NMR experiments validated the interactions between DC-S285 and SET7 followed by the second-round similarity search leading to the identification ofDC-S303 with the IC₅₀ value of 1.1 μM. In cellular level, DC-S285 retarded tumor cell proliferation and showed selectivity against MCF7 (IC₅₀ = 21.4 μM), Jurkat (IC₅₀ = 2.2 μM), THP1 (IC₅₀ = 3.5 μM), U937 (IC₅₀ = 3.9 μM) cell lines. Docking calculations suggested that DC-S303 share similar binding mode with the parent compoundDC-S239. What's more, it presented good selectivity against other epigenetic targets, including SETD1B, SETD8, G9a, SMYD2 and EZH2. DC-S303 can serve as a drug-like scaffold which may need further optimization for drug development, and can be used as chemical probe to help the community to better understand the SET7 biology.

From Heterochromatin to Long Noncoding RNAs in Drosophila: Expanding the Arena of Gene Function and Regulation

Recent years have witnessed a remarkable interest in exploring the significance of pervasive noncoding transcripts in diverse eukaryotes. Classical cytogenetic studies using the Drosophila model system unraveled the perplexing attributes and "functions" of the "gene"-poor heterochromatin. Recent molecular studies in the fly model are likewise revealing the very diverse and significant roles played by long noncoding RNAs (lncRNAs) in development, gene regulation, chromatin organization, cell and nuclear architecture, etc. There has been a rapid increase in the number of identified lncRNAs, although a much larger number still remains unknown. The diversity of modes of actions and functions of the limited number of Drosophila lncRNAs, which have been examined, already reflects the profound roles of such RNAs in generating and sustaining the biological complexities of eukaryotes. Several of the known Drosophila lncRNAs originate as independent sense or antisense transcripts from promoter or intergenic, intronic, or 5'/3'-UTR regions, while many of them are independent genes that produce only lncRNAs or coding as well as noncoding RNAs. The different lncRNAs affect chromatin organization (local or large-scale pan-chromosomal), transcription, RNA processing/stability, or translation either directly through interaction with their target DNA sequences or indirectly by acting as intermediary molecules for specific regulatory proteins or may act as decoys/sinks, or storage sites for specific proteins or groups of proteins, or may provide a structural framework for the assembly of substructures in nucleus/cytoplasm. It is interesting that many of the "functions" alluded to heterochromatin in earlier cytogenetic studies appear to find correlates with the known subtle as well as far-reaching actions of the different small and long noncoding RNAs. Further studies exploiting the very rich and powerful genetic and molecular resources available for the Drosophila model are expected to unravel the mystery underlying the long reach of ncRNAs.

Epiallelic changes in known stress-responsive genes under extreme drought conditions in Brassica juncea (L.) Czern

Under severe drought conditions, Brassica juncea shows differential methylation and demethylation events, such that certain epialleles are silenced and some are activated. The plant employed avoidance strategy by delaying apoptosis through the activation of several genes. Harsh environmental conditions pose serious threat to normal growth and development of crops, sometimes leading to their death. However, plants have developed an essential mechanism of modulation of gene activities by epigenetic modifications. Brassica juncea is an important oilseed crop contributing effectively to the economy of India. In the present investigation, we studied the changes in the methylation level of various stress-responsive genes of B. juncea variety RH30 by methylation-dependent immune-precipitation-chip in response to severe drought. On the basis of changes in the number of differential methylation regions in response to drought, the promoter regions were designated as hypermethylated and hypomethylated. Gene body methylation increased in all the genes, whereas promoter methylation was dependent on the function of the gene. Overall, the genes responsible for delaying apoptosis were hypomethylated and many genes responsible for normal routine activities were hypermethylated at promoter regions, thereby suggesting that these may be suspending the activities under harsh conditions.

Epigenetic dysfunctional diseases and therapy for infection and inflammation

Even though the discovery of the term 'epigenetics' was in the 1940s, it has recently become one of the most promising and expanding fields to unravel the gene expression pattern in several diseases. The most well studied example is cancer, but other diseases like metabolic disorders, autism, or inflammation-associated diseases such as lung injury, autoimmune disease, asthma, and type-2 diabetes display aberrant gene expression and epigenetic regulation during their occurrence. The change in the epigenetic pattern of a gene may also alter gene function because of a change in the DNA status. Constant environmental pressure, lifestyle, as well as food habits are the other important parameters responsible for transgenerational inheritance of epigenetic traits. Discovery of epigenetic modifiers targeting DNA methylation and histone deacetylation enzymes could be an alternative source to treat or manipulate the pathogenesis of diseases. Particularly, the combination of epigenetic drugs such as 5-aza-2-deoxycytidine (Aza) and trichostatin A (TSA) are well studied to reduce inflammation in an acute lung injury model. It is important to understand the epigenetic machinery and the function of its components in specific diseases to develop targeted epigenetic therapy. Moreover, it is equally critical to know the specific inhibitors other than the widely used pan inhibitors in clinical trials and explore their roles in regulating specific genes in a more defined way during infection.

PARP1 orchestrates epigenetic events setting up chromatin domains

Epigenetic events include reversible modifications of DNA and histone tails driving chromatin organization and thus transcription. The epigenetic regulation is a highly integrated process underlying the plasticity of the genomic information both in the context of complex physiological and pathological processes. The global regulatory aspects of epigenetic events are largely unknown. PARylation and PARP1 are recently emerging as multi-level regulatory effectors that modulate the topology of chromatin by orchestrating very different processes. This review focuses in particular on the role of PARP1 in epigenetics, trying to build a comprehensive perspective of its involvement in the regulation of epigenetic modifications of histones and DNA, contextualizing it in the global organization of chromatin domains in the nucleus.

Whole-genome analysis of the methylome and hydroxymethylome in normal and malignant lung and liver

DNA methylation at the 5-position of cytosine (5mC) is an epigenetic modification that regulates gene expression and cellular plasticity in development and disease. The ten-eleven translocation (TET) gene family oxidizes 5mC to 5-hydroxymethylcytosine (5hmC), providing an active mechanism for DNA demethylation, and it may also provide its own regulatory function. Here we applied oxidative bisulfite sequencing to generate whole-genome DNA methylation and hydroxymethylation maps at single-base resolution in human normal liver and lung as well as paired tumor tissues. We found that 5hmC is significantly enriched in CpG island (CGI) shores while depleted in CGIs themselves, especially in active genes, which exhibit a bimodal distribution of 5hmC around CGI that corresponds to H3K4me1 modifications. Hydroxymethylation on promoters, gene bodies, and transcription termination regions (TTRs) showed strong positive correlation with gene expression within and across tissues, suggesting that 5hmC is a marker of active genes and could play a role in gene expression mediated by DNA demethylation. Comparative analysis of methylomes and hydroxymethylomes revealed that 5hmC is significantly enriched in both tissue-specific DMRs (t-DMRs) and cancer-specific DMRs (c-DMRs), and 5hmC is negatively correlated with methylation changes, especially in non-CGI-associated DMRs. These findings revealed novel reciprocity between epigenetic markers at CGI shores corresponding to differential gene expression in normal tissues and matching tumors. Overall, our study provided a comprehensive analysis of the interplay between the methylome, hydroxymethylome, and histone modifications during tumorigenesis.

Cell fate regulation by chromatin ADP-ribosylation

ADP-ribosylation is an evolutionarily conserved complex posttranslational modification that alters protein function and/or interaction. Intracellularly, it is mainly catalyzed by diphtheria toxin-like ADP-ribosyltransferases (ARTDs), which attach one or several ADP-ribose residues onto target proteins. Several specific mono- and poly-ADP-ribosylation binding modules exist; hydrolases reverse the modification. The best-characterized ARTD family member, ARTD1, regulates various DNA-associated processes. Here, we focus on the role of ARTD1-mediated chromatin ADP-ribosylation in development, differentiation, and pluripotency, and the recent development of new methodologies that will enable more insight into these processes.

PARP, transcription and chromatin modeling

Compaction mode of chromatin and chromatin highly organised structures regulate gene expression. Posttranslational modifications, histone variants and chromatin remodelers modulate the compaction, structure and therefore function of specific regions of chromatin. The generation of poly(ADP-ribose) (PAR) is emerging as one of the key signalling events on sites undergoing chromatin structure modulation. PAR is generated locally in response to stresses. These include genotoxic stress but also differentiation signals, metabolic and hormonal cues. A pictures emerges in which transient PAR formation is essential to orchestrate chromatin remodelling and transcription factors allowing the cell to adapt to alteration in its environment. This review summarizes the diverse factors of ADP-ribosylation in the adaptive regulation of chromatin structure and transcription.

Modulation of chromatin function through linker histone H1 variants

In this review, the structural aspects of linker H1 histones are presented as a background for characterization of the factors influencing their function in animal and human chromatin. The action of H1 histone variants is largely determined by dynamic alterations of their intrinsically disordered tail domains, posttranslational modifications and allelic diversification. The interdependent effects of these factors can establish dynamic histone H1 states that may affect the organization and function of chromatin regions.

SETD7 Regulates the Differentiation of Human Embryonic Stem Cells

The successful use of specialized cells in regenerative medicine requires an optimization in the differentiation protocols that are currently used. Understanding the molecular events that take place during the differentiation of human pluripotent cells is essential for the improvement of these protocols and the generation of high quality differentiated cells. In an effort to understand the molecular mechanisms that govern differentiation we identify the methyltransferase SETD7 as highly induced during the differentiation of human embryonic stem cells and differentially expressed between induced pluripotent cells and somatic cells. Knock-down of SETD7 causes differentiation defects in human embryonic stem cell including delay in both the silencing of pluripotency-related genes and the induction of differentiation genes. We show that SETD7 methylates linker histone H1 in vitro causing conformational changes in H1. These effects correlate with a decrease in the recruitment of H1 to the pluripotency genes OCT4 and NANOG during differentiation in the SETD7 knock down that might affect the proper silencing of these genes during differentiation.

Analysis of Chromatin ADP-Ribosylation at the Genome-wide Level and at Specific Loci by ADPr-ChAP

Chromatin ADP-ribosylation regulates important cellular processes. However, the exact location and magnitude of chromatin ADP-ribosylation are largely unknown. A robust and versatile method for assessing chromatin ADP-ribosylation is therefore crucial for further understanding its function. Here, we present a chromatin affinity precipitation method based on the high specificity and avidity of two well-characterized ADP-ribose binding domains to map chromatin ADP-ribosylation at the genome-wide scale and at specific loci. Our ADPr-ChAP method revealed that in cells exposed to oxidative stress, ADP-ribosylation of chromatin scales with histone density, with highest levels at heterochromatic sites and depletion at active promoters. Furthermore, in growth factor-induced adipocyte differentiation, increased chromatin ADP-ribosylation was observed at PPARγ target genes, whose expression is ADP-ribosylation dependent. In combination with deep-sequencing and conventional chromatin immunoprecipitation, the established ADPr-ChAP provides a valuable resource for the bioinformatic comparison of ADP-ribosylation with other chromatin modifications and for addressing its role in other biologically important processes.

Linker histones in hormonal gene regulation

In the present review, we summarize advances in our knowledge on the role of the histone H1 family of proteins in breast cancer cells, focusing on their response to progestins. Histone H1 plays a dual role in gene regulation by hormones, both as a structural component of chromatin and as a dynamic modulator of transcription. It contributes to hormonal regulation of the MMTV promoter by stabilizing a homogeneous nucleosome positioning, which reduces basal transcription whereas at the same time promoting progesterone receptor binding and nucleosome remodeling. These combined effects enhance hormone dependent gene transcription, which eventually requires H1 phosphorylation and displacement. Various isoforms of histone H1 have specific functions in differentiated breast cancer cells and compact nucleosomal arrays to different extents in vitro. Genome-wide studies show that histone H1 has a key role in chromatin dynamics of hormone regulated genes. A complex sequence of enzymatic events, including phosphorylation by CDK2, PARylation by PARP1 and the ATP-dependent activity of NURF, are required for H1 displacement and gene de-repression, as a prerequisite for further nucleosome remodeling. Similarly, during hormone-dependent gene repression a dedicated enzymatic mechanism controls H1 deposition at promoters by a complex containing HP1γ, LSD1 and BRG1, the ATPase of the BAF complex. Thus, a broader vision of the histone code should include histone H1, as the linker histone variants actively participate in the regulation of the chromatin structure. How modifications of the core histones tails affect H1 modifications and vice versa is one of the many questions that remains to be addressed to provide a more comprehensive view of the histone cross-talk mechanisms.

Nuclear ADP-Ribosylation and Its Role in Chromatin Plasticity, Cell Differentiation, and Epigenetics

Protein ADP-ribosylation is an ancient posttranslational modification with high biochemical complexity. It alters the function of modified proteins or provides a scaffold for the recruitment of other proteins and thus regulates several cellular processes. ADP-ribosylation is governed by ADP-ribosyltransferases and a subclass of sirtuins (writers), is sensed by proteins that contain binding modules (readers) that recognize specific parts of the ADP-ribosyl posttranslational modification, and is removed by ADP-ribosylhydrolases (erasers). The large amount of experimental data generated and technical progress made in the last decade have significantly advanced our knowledge of the function of ADP-ribosylation at the molecular level. This review summarizes the current knowledge of nuclear ADP-ribosylation reactions and their role in chromatin plasticity, cell differentiation, and epigenetics and discusses current progress and future perspectives.

A comprehensive view of the epigenetic landscape. Part II: Histone post-translational modification, nucleosome level, and chromatin regulation by ncRNAs

The complexity of the genome is regulated by epigenetic mechanisms, which act on the level of DNA, histones, and nucleosomes. Epigenetic machinery is involved in various biological processes, including embryonic development, cell differentiation, neurogenesis, and adult cell renewal. In the last few years, it has become clear that the number of players identified in the regulation of chromatin structure and function is still increasing. In addition to well-known phenomena, including DNA methylation and histone modification, new, important elements, including nucleosome mobility, histone tail clipping, and regulatory ncRNA molecules, are being discovered. The present paper provides the current state of knowledge about the role of 16 different histone post-translational modifications, nucleosome positioning, and histone tail clipping in the structure and function of chromatin. We also emphasize the significance of cross-talk among chromatin marks and ncRNAs in epigenetic control.

The role of dietary histone deacetylases (HDACs) inhibitors in health and disease

Modification of the histone proteins associated with DNA is an important process in the epigenetic regulation of DNA structure and function. There are several known modifications to histones, including methylation, acetylation, and phosphorylation, and a range of factors influence each of these. Histone deacetylases (HDACs) remove the acetyl group from lysine residues within a range of proteins, including transcription factors and histones. Whilst this means that their influence on cellular processes is more complex and far-reaching than histone modifications alone, their predominant function appears to relate to histones; through deacetylation of lysine residues they can influence expression of genes encoded by DNA linked to the histone molecule. HDAC inhibitors in turn regulate the activity of HDACs, and have been widely used as therapeutics in psychiatry and neurology, in which a number of adverse outcomes are associated with aberrant HDAC function. More recently, dietary HDAC inhibitors have been shown to have a regulatory effect similar to that of pharmacological HDAC inhibitors without the possible side-effects. Here, we discuss a number of dietary HDAC inhibitors, and how they may have therapeutic potential in the context of a whole food.

MethylSig: a whole genome DNA methylation analysis pipeline

MOTIVATION

DNA methylation plays critical roles in gene regulation and cellular specification without altering DNA sequences. The wide application of reduced representation bisulfite sequencing (RRBS) and whole genome bisulfite sequencing (bis-seq) opens the door to study DNA methylation at single CpG site resolution. One challenging question is how best to test for significant methylation differences between groups of biological samples in order to minimize false positive findings.

RESULTS

We present a statistical analysis package, methylSig, to analyse genome-wide methylation differences between samples from different treatments or disease groups. MethylSig takes into account both read coverage and biological variation by utilizing a beta-binomial approach across biological samples for a CpG site or region, and identifies relevant differences in CpG methylation. It can also incorporate local information to improve group methylation level and/or variance estimation for experiments with small sample size. A permutation study based on data from enhanced RRBS samples shows that methylSig maintains a well-calibrated type-I error when the number of samples is three or more per group. Our simulations show that methylSig has higher sensitivity compared with several alternative methods. The use of methylSig is illustrated with a comparison of different subtypes of acute leukemia and normal bone marrow samples.

AVAILABILITY

methylSig is available as an R package at http://sartorlab.ccmb.med.umich.edu/software.

SUPPLEMENTARY INFORMATION

Supplementary data are available at Bioinformatics online.

Mammalian epigenetic mechanisms

The mammalian genome is packaged into chromatin that is further compacted into three-dimensional structures consisting of distinct functional domains. The higher order structure of chromatin is in part dictated by enzymatic DNA methylation and histone modifications to establish epigenetic layers controlling gene expression and cellular functions, without altering the underlying DNA sequences. Apart from DNA and histone modifications, non-coding RNAs can also regulate the dynamics of the mammalian gene expression and various physiological functions including cell division, differentiation, and apoptosis. Aberrant epigenetic signatures are associated with abnormal developmental processes and diseases such as cancer. In this review, we will discuss the different layers of epigenetic regulation, including writer enzymes for DNA methylation, histone modifications, non-coding RNA, and chromatin conformation. We will highlight the combinatorial role of these structural and chemical modifications along with their partners in various cellular processes in mammalian cells. We will also address the cis and trans interacting "reader" proteins that recognize these modifications and "eraser" enzymes that remove these marks. Furthermore, an attempt will be made to discuss the interplay between various epigenetic writers, readers, and erasures in the establishment of mammalian epigenetic mechanisms.

Alterations of epigenetic signatures in hepatocyte nuclear factor 4α deficient mouse liver determined by improved ChIP-qPCR and (h)MeDIP-qPCR assays

Hepatocyte nuclear factor 4α (HNF4α) is a liver-enriched transcription factor essential for liver development and function. In hepatocytes, HNF4α regulates a large number of genes important for nutrient/xenobiotic metabolism and cell differentiation and proliferation. Currently, little is known about the epigenetic mechanism of gene regulation by HNF4α. In this study, the global and specific alterations at the selected gene loci of representative histone modifications and DNA methylations were investigated in Hnf4a-deficient female mouse livers using the improved MeDIP-, hMeDIP- and ChIP-qPCR assay. Hnf4a deficiency significantly increased hepatic total IPed DNA fragments for histone H3 lysine-4 dimethylation (H3K4me2), H3K4me3, H3K9me2, H3K27me3 and H3K4 acetylation, but not for H3K9me3, 5-methylcytosine,or 5-hydroxymethylcytosine. At specific gene loci, the relative enrichments of histone and DNA modifications were changed to different degree in Hnf4a-deficient mouse liver. Among the epigenetic signatures investigated, changes in H3K4me3 correlated the best with mRNA expression. Additionally, Hnf4a-deficient livers had increased mRNA expression of histone H1.2 and H3.3 as well as epigenetic modifiers Dnmt1, Tet3, Setd7, Kmt2c, Ehmt2, and Ezh2. In conclusion, the present study provides convenient improved (h)MeDIP- and ChIP-qPCR assays for epigenetic study. Hnf4a deficiency in young-adult mouse liver markedly alters histone methylation and acetylation, with fewer effects on DNA methylation and 5-hydroxymethylation. The underlying mechanism may be the induction of epigenetic enzymes responsible for the addition/removal of the epigenetic signatures, and/or the loss of HNF4αper se as a key coordinator for epigenetic modifiers.

H1 histones: current perspectives and challenges

H1 and related linker histones are important both for maintenance of higher-order chromatin structure and for the regulation of gene expression. The biology of the linker histones is complex, as they are evolutionarily variable, exist in multiple isoforms and undergo a large variety of posttranslational modifications in their long, unstructured, NH₂- and COOH-terminal tails. We review recent progress in understanding the structure, genetics and posttranslational modifications of linker histones, with an emphasis on the dynamic interactions of these proteins with DNA and transcriptional regulators. We also discuss various experimental challenges to the study of H1 and related proteins, including limitations of immunological reagents and practical difficulties in the analysis of posttranslational modifications by mass spectrometry.

Glycemic memories and the epigenetic component of diabetic nephropathy

A strong case for the deregulation of epigenetic chromatin modifications in the development and progression of various chronic complications of diabetes has emerged from recent experimental observations. Clinical trials of type 1 and type 2 diabetes patients highlight the importance of early and intensive treatment and the prolonged damage of hyperglycemia on organs such as the kidney. The functional relationship between the regulation of chromatin architecture and persistent gene expression changes conferred by prior hyperglycemia represents an important avenue of investigation for explaining diabetic nephropathy. While several studies implicate epigenetic changes at the chromatin template in the deregulated gene expression associated with diabetic nephropathy, the molecular determinants of metabolic memory in renal cells remain poorly understood. There is now strong evidence from experimental animals and cell culture of persistent glucose-driven changes in vascular endothelial gene expression that may also have relevance for the microvasculature of the kidney. Exploration of epigenetic mechanisms underlying the hyperglycemic cue mediating persistent transcriptional changes in renal cells holds novel therapeutic potential for diabetic nephropathy.

Transcriptional regulation by the Set7 lysine methyltransferase

Posttranslational histone modifications define chromatin structure and function. In recent years, a number of studies have characterized many of the enzymatic activities and diverse regulatory components required for monomethylation of histone H3 lysine 4 (H3K4me1) and the expression of specific genes. The challenge now is to understand how this specific chemical modification is written and the Set7 methyltransferase has emerged as a key regulatory enzyme mediating methylation of lysine residues of histone and non-histone proteins. In this review, we comprehensively explore the regulatory proteins modified by Set7 and highlight mechanisms of specific co-recruitment of the enzyme to activating promoters. With a focus on signaling and transcriptional control in disease we discuss recent experimental data emphasizing specific components of diverse regulatory complexes that mediate chromatin modification and reinterpretation of Set7-mediated gene expression.