Cooperativity between DNA methyltransferases in the maintenance methylation of repetitive elements

Design and Synthesis of Novel Deazapurine DNMT 1 Inhibitors with In Vivo Efficacy in DLBCL

The application of drugs to regulate abnormal epigenetic changes has become an important means of tumor treatment. In this study, we employed computer-aided design methods to develop a novel deazapurine compound targeting DNA methyltransferase 1 (DNMT1). Through screening for enzyme activity, selectivity, and cellular efficacy, we optimized three structural skeletons, ultimately yielding compound 55, exhibiting an IC50 of 2.42 μM for DNMT1. Compound 55 displayed excellent in vitro inhibitory effects on various hematological tumor and solid tumor cell lines, especially lymphoma cells, with IC50 values in the nanomolar range. In vitro studies confirmed compound 55 selectively inhibited DNMT1 and exhibited demethylation ability. In vivo mouse model validated the DNA methylation inhibition of compound 55. Compound 55 demonstrated good antitumor activity in vivo. Specifically, compound 55 combined with chidamide demonstrated a superior therapeutic effect over the first-line therapy RTX-CHOP in both the DEL and TP53 mutant DLBCL PDX tumor models.

Allele-Specific CG/CCWGG Methylation of the PSA Promoter Discriminates Aggressive, Indolent, and Benign Prostate Cell Lines and Is Involved in the Regulation of PSA Expression

Prostate-specific antigen remains a cornerstone biomarker for prostate cancer diagnosis and management. However, the molecular mechanisms regulating its expression, particularly through DNA methylation, are not fully understood. Here, we report a comprehensive analysis of allele-specific CpG and CCWGG methylation in the proximal PSA promoter across aggressive (PC3), indolent (LNCaP), benign (BPH1), and normal (HPrEpiC) prostate cell lines and provide insights into the unique methylation patterns associated with these states. Our findings reveal that PC3 cells, representing an aggressive PCa phenotype, exhibit complete biallelic methylation of the PSA promoter, leading to PSA gene silencing. Conversely, LNCaP cells display a fully unmethylated promoter with biallelic PSA expression. Interestingly, BPH1 cells display a monoallelic CG/CCWGG methylation pattern, yet fail to express PSA, suggesting imprinting defects or RNA decay mechanisms. Notably, acquisition of biallelic PSA promoter methylation status in PC3 was accompanied by upregulation of DNMT1, whereas unmethylated PSA promoter state in LNCaP was associated with downregulation of DNMT1. These findings highlight distinct methylation patterns in the PSA promoter that differentiate between aggressive, indolent, and benign prostate states. Translating this epigenetic insight into clinical diagnostics could enhance the precision of PSA-based diagnostics, addressing limitations such as false negatives in PSA testing for aggressive PCa. Further exploration of CCWGG methylation's role in imprinting and monoallelic expression is warranted, particularly in patient-derived samples.

Regulation of de novo and maintenance DNA methylation by DNA methyltransferases in postimplantation embryos

DNA methylation is mainly catalyzed by three DNA methyltransferase (DNMT) proteins in mammals. Usually DNMT1 is considered the primary DNMT for maintenance DNA methylation, whereas DNMT3A and DNMT3B function in de novo DNA methylation. Interestingly, we found DNMT3A and DNMT3B exerted maintenance and de novo DNA methylation in postimplantation mouse embryos. Together with DNMT1, they maintained DNA methylation at some pluripotent genes and lineage marker genes. Germline-derived DNA methylation at the imprinting control regions (ICRs) is stably maintained in embryos. DNMT1 maintained DNA methylation at most ICRs in postimplantation embryos. Surprisingly, DNA methylation was increased at five ICRs after implantation, and two DNMT3 proteins maintained the newly acquired DNA methylation at two of these five ICRs. Intriguingly, DNMT3A and DNMT3B maintained preexisting DNA methylation at four other ICRs, similar to what we found in embryonic stem cells before. These results suggest that DNA methylation is more dynamic than originally thought during embryogenesis including the ICRs of the imprinted regions. DNMT3A and DNMT3B exert both de novo and maintenance DNA methylation functions after implantation. They maintain large portions of newly acquired DNA methylation at variable degrees across the genome in mouse embryos, together with DNMT1. Furthermore, they contribute to maintenance of preexisting DNA methylation at a subset of ICRs as well as in the CpG islands and certain lineage marker gene. These findings may have some implications for the important roles of DNMT proteins in development and human diseases.

Using human disease mutations to understand de novo DNA methyltransferase function

DNA methylation is a repressive epigenetic mark that is pervasive in mammalian genomes. It is deposited by DNA methyltransferase enzymes (DNMTs) that are canonically classified as having de novo (DNMT3A and DNMT3B) or maintenance (DNMT1) function. Mutations in DNMT3A and DNMT3B cause rare Mendelian diseases in humans and are cancer drivers. Mammalian DNMT3 methyltransferase activity is regulated by the non-catalytic region of the proteins which contain multiple chromatin reading domains responsible for DNMT3A and DNMT3B recruitment to the genome. Characterising disease-causing missense mutations has been central in dissecting the function and regulation of DNMT3A and DNMT3B. These observations have also motivated biochemical studies that provide the molecular details as to how human DNMT3A and DNMT3B mutations drive disorders. Here, we review progress in this area highlighting recent work that has begun dissecting the function of the disordered N-terminal regions of DNMT3A and DNMT3B. These studies have elucidated that the N-terminal regions of both proteins mediate novel chromatin recruitment pathways that are central in our understanding of human disease mechanisms. We also discuss how disease mutations affect DNMT3A and DNMT3B oligomerisation, a process that is poorly understood in the context of whole proteins in cells. This dissection of de novo DNMT function using disease-causing mutations provides a paradigm of how genetics and biochemistry can synergise to drive our understanding of the mechanisms through which chromatin misregulation causes human disease.

The Role of DNMT Methyltransferases and TET Dioxygenases in the Maintenance of the DNA Methylation Level

This review deals with the functional characteristics and biological roles of enzymes participating in DNA methylation and demethylation as key factors in epigenetic regulation of gene expression. The set of enzymes that carry out such processes in human cells is limited to representatives of two families, namely DNMT (DNA methyltransferases) and TET (DNA dioxygenases). The review presents detailed information known today about each functionally important member of these families and describes the catalytic activity and roles in the mammalian body while also providing examples of dysregulation of the expression and/or activity of these enzymes in conjunction with the development of some human disorders, including cancers, neurodegenerative diseases, and developmental pathologies. By combining the up-to-date information on the dysfunction of various enzymes that control the DNA "methylome" in the human body, we hope not only to draw attention to the importance of the maintenance of a required DNA methylation level (ensuring epigenetic regulation of gene expression and normal functioning of the entire body) but also to help identify new targets for directed control over the activity of the enzymes that implement the balance between processes of DNA methylation and demethylation.

Strategies for the detection of site-specific DNA methylation and its application, opportunities and challenges in the field of electrochemical biosensors

DNA methylation is an epigenetic modification that plays a crucial role in various biological processes. Aberrant DNA methylation is closely associated with the onset of diseases, and the specific localization of methylation sites in the genome offers further insight into the connection between methylation and diseases. Currently, there are numerous methods available for site-specific methylation detection. Electrochemical biosensors have garnered significant attention due to their distinct advantages, such as rapidity, simplicity, high sensitivity, low cost, and the potential for miniaturization. In this paper, we present a systematic review of the primary sensing strategies utilized in the past decade for analyzing site-specific methylation and their applications in electrochemical sensors, from a novel perspective focusing on the localization analysis of site-specific methylation. These strategies include bisulfite treatment, restriction endonuclease treatment, other sensing strategies, and deamination without direct bisulfite treatment. We hope that this paper can offer ideas and references for establishing site-specific methylation electrochemical analysis in clinical practice.

Mechanisms of DNA Methylation Regulatory Function and Crosstalk with Histone Lysine Methylation

DNA methylation is a well-studied epigenetic modification that has key roles in regulating gene expression, maintaining genome integrity, and determining cell fate. Precisely how DNA methylation patterns are established and maintained in specific cell types at key developmental stages is still being elucidated. However, research over the last two decades has contributed to our understanding of DNA methylation regulation by other epigenetic processes. Specifically, lysine methylation on key residues of histone proteins has been shown to contribute to the allosteric regulation of DNA methyltransferase (DNMT) activities. In this review, we discuss the dynamic interplay between DNA methylation and histone lysine methylation as epigenetic regulators of genome function by synthesizing key recent studies in the field. With a focus on DNMT3 enzymes, we discuss mechanisms of DNA methylation and histone lysine methylation crosstalk in the regulation of gene expression and the maintenance of genome integrity. Further, we discuss how alterations to the balance of various sites of histone lysine methylation and DNA methylation contribute to human developmental disorders and cancers. Finally, we provide perspectives on the current direction of the field and highlight areas for continued research and development.

Tunable DNMT1 degradation reveals DNMT1/DNMT3B synergy in DNA methylation and genome organization

DNA methylation (DNAme) is a key epigenetic mark that regulates critical biological processes maintaining overall genome stability. Given its pleiotropic function, studies of DNAme dynamics are crucial, but currently available tools to interfere with DNAme have limitations and major cytotoxic side effects. Here, we present cell models that allow inducible and reversible DNAme modulation through DNMT1 depletion. By dynamically assessing whole genome and locus-specific effects of induced passive demethylation through cell divisions, we reveal a cooperative activity between DNMT1 and DNMT3B, but not of DNMT3A, to maintain and control DNAme. We show that gradual loss of DNAme is accompanied by progressive and reversible changes in heterochromatin, compartmentalization, and peripheral localization. DNA methylation loss coincides with a gradual reduction of cell fitness due to G1 arrest, with minor levels of mitotic failure. Altogether, this system allows DNMTs and DNA methylation studies with fine temporal resolution, which may help to reveal the etiologic link between DNAme dysfunction and human disease.

The molecular basis of cell memory in mammals: The epigenetic cycle

Cell memory refers to the capacity of cells to maintain their gene expression program once the initiating environmental signal has ceased. This exceptional feature is key during the formation of mammalian organisms, and it is believed to be in part mediated by epigenetic factors that can endorse cells with the landmarks required to maintain transcriptional programs upon cell duplication. Here, we review current literature analyzing the molecular basis of epigenetic memory in mammals, with a focus on the mechanisms by which transcriptionally repressive chromatin modifications such as methylation of DNA and histone H3 are propagated through mitotic cell divisions. The emerging picture suggests that cellular memory is supported by an epigenetic cycle in which reversible activities carried out by epigenetic regulators in coordination with cell cycle transition create a multiphasic system that can accommodate both maintenance of cell identity and cell differentiation in proliferating stem cell populations.

DNMT3B PWWP mutations cause hypermethylation of heterochromatin

The correct establishment of DNA methylation patterns is vital for mammalian development and is achieved by the de novo DNA methyltransferases DNMT3A and DNMT3B. DNMT3B localises to H3K36me3 at actively transcribing gene bodies via its PWWP domain. It also functions at heterochromatin through an unknown recruitment mechanism. Here, we find that knockout of DNMT3B causes loss of methylation predominantly at H3K9me3-marked heterochromatin and that DNMT3B PWWP domain mutations or deletion result in striking increases of methylation in H3K9me3-marked heterochromatin. Removal of the N-terminal region of DNMT3B affects its ability to methylate H3K9me3-marked regions. This region of DNMT3B directly interacts with HP1α and facilitates the bridging of DNMT3B with H3K9me3-marked nucleosomes in vitro. Our results suggest that DNMT3B is recruited to H3K9me3-marked heterochromatin in a PWWP-independent manner that is facilitated by the protein's N-terminal region through an interaction with a key heterochromatin protein. More generally, we suggest that DNMT3B plays a role in DNA methylation homeostasis at heterochromatin, a process which is disrupted in cancer, aging and Immunodeficiency, Centromeric Instability and Facial Anomalies (ICF) syndrome.

Large Deletions, Cleavage of the Telomeric Repeat Sequence, and Reverse Transcriptase-Mediated DNA Damage Response Associated with Long Interspersed Element-1 ORF2p Enzymatic Activities

L1 elements can cause DNA damage and genomic variation via retrotransposition and the generation of endonuclease-dependent DNA breaks. These processes require L1 ORF2p protein that contains an endonuclease domain, which cuts genomic DNA, and a reverse transcriptase domain, which synthesizes cDNA. The complete impact of L1 enzymatic activities on genome stability and cellular function remains understudied, and the spectrum of L1-induced mutations, other than L1 insertions, is mostly unknown. Using an inducible system, we demonstrate that an ORF2p containing functional reverse transcriptase is sufficient to elicit DNA damage response even in the absence of the functional endonuclease. Using a TK/Neo reporter system that captures misrepaired DNA breaks, we demonstrate that L1 expression results in large genomic deletions that lack any signatures of L1 involvement. Using an in vitro cleavage assay, we demonstrate that L1 endonuclease efficiently cuts telomeric repeat sequences. These findings support that L1 could be an unrecognized source of disease-promoting genomic deletions, telomere dysfunction, and an underappreciated source of chronic RT-mediated DNA damage response in mammalian cells. Our findings expand the spectrum of biological processes that can be triggered by functional and nonfunctional L1s, which have impactful evolutionary- and health-relevant consequences.

Antagonistic interactions safeguard mitotic propagation of genetic and epigenetic information in zebrafish

The stability of cellular phenotypes in developing organisms depends on error-free transmission of epigenetic and genetic information during mitosis. Methylation of cytosine residues in genomic DNA is a key epigenetic mark that modulates gene expression and prevents genome instability. Here, we report on a genetic test of the relationship between DNA replication and methylation in the context of the developing vertebrate organism instead of cell lines. Our analysis is based on the identification of hypomorphic alleles of dnmt1, encoding the DNA maintenance methylase Dnmt1, and pole1, encoding the catalytic subunit of leading-strand DNA polymerase epsilon holoenzyme (Pole). Homozygous dnmt1 mutants exhibit genome-wide DNA hypomethylation, whereas the pole1 mutation is associated with increased DNA methylation levels. In dnmt1/pole1 double-mutant zebrafish larvae, DNA methylation levels are restored to near normal values, associated with partial rescue of mutant-associated transcriptional changes and phenotypes. Hence, a balancing antagonism between DNA replication and maintenance methylation buffers against replicative errors contributing to the robustness of vertebrate development.

Retrotransposon life cycle and its impacts on cellular responses

Approximately 45% of the human genome is comprised of transposable elements (TEs), also known as mobile genetic elements. However, their biological function remains largely unknown. Among them, retrotransposons are particularly abundant, and some of the copies are still capable of mobilization within the genome through RNA intermediates. This review focuses on the life cycle of human retrotransposons and summarizes their regulatory mechanisms and impacts on cellular processes. Retrotransposons are generally epigenetically silenced in somatic cells, but are transcriptionally reactivated under certain conditions, such as tumorigenesis, development, stress, and ageing, potentially leading to genetic instability. We explored the dual nature of retrotransposons as genomic parasites and regulatory elements, focusing on their roles in genetic diversity and innate immunity. Furthermore, we discuss how host factors regulate retrotransposon RNA and cDNA intermediates through their binding, modification, and degradation. The interplay between retrotransposons and the host machinery provides insight into the complex regulation of retrotransposons and the potential for retrotransposon dysregulation to cause aberrant responses leading to inflammation and autoimmune diseases.

The Role of DNMT1 and C/EBPα in the Regulation of CYP11A1 Expression During Syncytialization of Human Placental Trophoblasts

Progesterone synthesized in the placenta is essential for pregnancy maintenance. CYP11A1 is a key enzyme in progesterone synthesis, and its expression increases greatly during trophoblast syncytialization. However, the underlying mechanism remains elusive. Here, we demonstrated that passive demethylation of CYP11A1 promoter accounted for the upregulation of CYP11A1 expression during syncytialization with the participation of the transcription factor C/EBPα. We found that the methylation rate of a CpG locus in the CYP11A1 promoter was significantly reduced along with decreased DNA methyltransferase 1 (DNMT1) expression and its enrichment at the CYP11A1 promoter during syncytialization. DNMT1 overexpression not only increased the methylation of this CpG locus in the CYP11A1 promoter, but also decreased CYP11A1 expression and progesterone production. In silico analysis disclosed multiple C/EBPα binding sites in both CYP11A1 and DNMT1 promoters. C/EBPα expression and its enrichments at both the DNMT1 and CYP11A1 promoters were significantly increased during syncytialization. Knocking-down C/EBPα expression increased DNMT1 while it decreased CYP11A1 expression during syncytialization. Conclusively, C/EBPα plays a dual role in the regulation of CYP11A1 during syncytialization. C/EBPα not only drives CYP11A1 expression directly, but also indirectly through downregulation of DNMT1, which leads to decreased methylation in the CpG locus of the CYP11A1 promoter, resulting in increased progesterone production during syncytialization.

Biological methylation: redefining the link between genotype and phenotype

The central dogma of molecular biology is responsible for the crucial flow of genetic information from DNA to protein through the transcription and translation process. Although the sequence of DNA is constant in all organs, the difference in protein and variation in the phenotype is mainly due to the quality and quantity of tissue-specific gene expression and methylation pattern. The term methylation has been defined and redefined by various scientists in the last fifty years. There is always huge excitement around this field because the inheritance of something is beyond its DNA sequence. Advanced gene methylation studies have redefined molecular genetics and these tools are considered de novo in alleviating challenges of animal disease and production. Recent emerging evidence has shown that the impact of DNA, RNA, and protein methylation is crucial for embryonic development, cell proliferation, cell differentiation, and phenotype production. Currently, many researchers are focusing their work on methylation to understand its significant role in expression, disease-resistant traits, productivity, and longevity. The main aim of the present review is to provide an overview of DNA, RNA, and protein methylation, current research output from different sources, methodologies, factors responsible for methylation of genes, and future prospects in animal genetics.

Human LINE-1 retrotransposons: impacts on the genome and regulation by host factors

Genome sequencing revealed that nearly half of the human genome is comprised of transposable elements. Although most of these elements have been rendered inactive due to mutations, full-length intact long interspersed element-1 (LINE-1 or L1) copies retain the ability to mobilize through RNA intermediates by a so-called "copy-and-paste" mechanism, termed retrotransposition. L1 is the only known autonomous mobile genetic element in the genome, and its retrotransposition contributes to inter- or intra-individual genetic variation within the human population. However, L1 retrotransposition also poses a threat to genome integrity due to gene disruption and chromosomal instability. Moreover, recent studies suggest that aberrant L1 expression can impact human health by causing diseases such as cancer and chronic inflammation that might lead to autoimmune disorders. To counteract these adverse effects, the host cells have evolved multiple layers of defense mechanisms at the epigenetic, RNA and protein levels. Intriguingly, several host factors have also been reported to facilitate L1 retrotransposition, suggesting that there is competition between negative and positive regulation of L1 by host factors. Here, we summarize the known host proteins that regulate L1 activity at different stages of the replication cycle and discuss how these factors modulate disease-associated phenotypes caused by L1.

Germinal center output is sustained by HELLS-dependent DNA-methylation-maintenance in B cells

HELLS/LSH (Helicase, Lymphoid Specific) is a SNF2-like chromatin remodelling protein involved in DNA methylation. Its loss-of-function in humans causes humoral immunodeficiency, called ICF4 syndrome (Immunodeficiency, Centromeric Instability, Facial anomalies). Here we show by our newly generated B-cell-specific Hells conditional knockout mouse model that HELLS plays a pivotal role in T-dependent B-cell responses. HELLS deficiency induces accelerated decay of germinal center (GC) B cells and impairs the generation of high affinity memory B cells and circulating antibodies. Mutant GC B cells undergo dramatic DNA hypomethylation and massive de-repression of evolutionary recent retrotransposons, which surprisingly does not directly affect their survival. Instead, they prematurely upregulate either memory B cell markers or the transcription factor ATF4, which is driving an mTORC1-dependent metabolic program typical of plasma cells. Treatment of wild type mice with a DNMT1-specific inhibitor phenocopies the accelerated kinetics, thus pointing towards DNA-methylation maintenance by HELLS being a crucial mechanism to fine-tune the GC transcriptional program and enable long-lasting humoral immunity.

Methylation is maintained specifically at imprinting control regions but not other DMRs associated with imprinted genes in mice bearing a mutation in the Dnmt1 intrinsically disordered domain

Differential methylation of imprinting control regions in mammals is essential for distinguishing the parental alleles from each other and regulating their expression accordingly. To ensure parent of origin-specific expression of imprinted genes and thereby normal developmental progression, the differentially methylated states that are inherited at fertilization must be stably maintained by DNA methyltransferase 1 throughout subsequent somatic cell division. Further epigenetic modifications, such as the acquisition of secondary regions of differential methylation, are dependent on the methylation status of imprinting control regions and are important for achieving the monoallelic expression of imprinted genes, but little is known about how imprinting control regions direct the acquisition and maintenance of methylation at these secondary sites. Recent analysis has identified mutations that reduce DNA methyltransferase 1 fidelity at some genomic sequences but not at others, suggesting that it may function differently at different loci. We examined the impact of the mutant DNA methyltransferase 1 P allele on methylation at imprinting control regions as well as at secondary differentially methylated regions and non-imprinted sequences. We found that while the P allele results in a major reduction in DNA methylation levels across the mouse genome, methylation is specifically maintained at imprinting control regions but not at their corresponding secondary DMRs. This result suggests that DNA methyltransferase 1 may work differently at imprinting control regions or that there is an alternate mechanism for maintaining methylation at these critical regulatory regions and that maintenance of methylation at secondary DMRs is not solely dependent on the methylation status of the ICR.

DNA strand asymmetry generated by CpG hemimethylation has opposing effects on CTCF binding

CpG methylation generally occurs on both DNA strands and is essential for mammalian development and differentiation. Until recently, hemimethylation, in which only one strand is methylated, was considered to be simply a transitory state generated during DNA synthesis. The discovery that a subset of CCCTC-binding factor (CTCF) binding sites is heritably hemimethylated suggests that hemimethylation might have an unknown biological function. Here we show that the binding of CTCF is profoundly altered by which DNA strand is methylated and by the specific CTCF binding motif. CpG methylation on the motif strand can inhibit CTCF binding by up to 7-fold, whereas methylation on the opposite strand can stimulate binding by up to 4-fold. Thus, hemimethylation can alter binding by up to 28-fold in a strand-specific manner. The mechanism for sensing methylation on the opposite strand requires two critical residues, V454 and S364, within CTCF zinc fingers 7 and 4. Similar to methylation, CpG hydroxymethylation on the motif strand can inhibit CTCF binding by up to 4-fold. However, hydroxymethylation on the opposite strand removes the stimulatory effect. Strand-specific methylation states may therefore provide a mechanism to explain the transient and dynamic nature of CTCF-mediated chromatin interactions.

Mitigating the detrimental developmental impact of early fetal alcohol exposure using a maternal methyl donor-enriched diet

Fetal alcohol exposure at any stage of pregnancy can lead to fetal alcohol spectrum disorder (FASD), a group of life-long conditions characterized by congenital malformations, as well as cognitive, behavioral, and emotional impairments. The teratogenic effects of alcohol have long been publicized; yet fetal alcohol exposure is one of the most common preventable causes of birth defects. Currently, alcohol abstinence during pregnancy is the best and only way to prevent FASD. However, alcohol consumption remains astoundingly prevalent among pregnant women; therefore, additional measures need to be made available to help protect the developing embryo before irreparable damage is done. Maternal nutritional interventions using methyl donors have been investigated as potential preventative measures to mitigate the adverse effects of fetal alcohol exposure. Here, we show that a single acute preimplantation (E2.5; 8-cell stage) fetal alcohol exposure (2 × 2.5 g/kg ethanol with a 2h interval) in mice leads to long-term FASD-like morphological phenotypes (e.g. growth restriction, brain malformations, skeletal delays) in late-gestation embryos (E18.5) and demonstrate that supplementing the maternal diet with a combination of four methyl donor nutrients, folic acid, choline, betaine, and vitamin B12, prior to conception and throughout gestation effectively reduces the incidence and severity of alcohol-induced morphological defects without altering DNA methylation status of imprinting control regions and regulation of associated imprinted genes. This study clearly supports that preimplantation embryos are vulnerable to the teratogenic effects of alcohol, emphasizes the dangers of maternal alcohol consumption during early gestation, and provides a potential proactive maternal nutritional intervention to minimize FASD progression, reinforcing the importance of adequate preconception and prenatal nutrition.

Extremely low-frequency electromagnetic field (ELF-EMF) induces alterations in epigenetic regulation in the myometrium - An in vitro study

Previous research by the authors indicated that an extremely low-frequency electromagnetic field (ELF-EMF) evokes molecular alterations in the porcine myometrium. It was hypothesized that the ELF-EMF could induce alterations in the epigenetic regulation of gene expression in the myometrium. In the current study, slices of the porcine myometrium during the peri-implantation period (n = 4) were used for further in vitro exposition to ELF-EMF (50 Hz, 8 mT, 2 h treatment duration). The study tested whether the ELF-EMF may affect: 1/the expression of DNA (cytosine-5)-methyltransferase 1 (DNMT1) and DNA (cytosine-5)-methyltransferase 3a (DNMT3a), 2/the level of genomic DNA methylation, and 3/the level of amplification of methylated and unmethylated variants of promoter regions of selected genes with altered expression in response to ELF-EMF. It was found that ELF-EMF treatment increased DNMT1, decreased DNMT3a mRNA transcript and protein abundance, and increased the level of genomic DNA methylation. The direction of alterations in the level of amplification of methylated and unmethylated variants of the promoter region of selected genes with altered expression, i.e. prodynorphin (PDYN), interleukin 15 (IL15) signal transducer and activator of transcription 5A (STAT5A), tumor necrosis factor (TNF), and between down-regulated genes were early growth response 2 (EGR2), hyaluronan and proteoglycan link protein 1 (HAPLN1), and uteroferrin associated basic protein-2 (UABP2), mostly involving the direction of changes in their transcriptional activity, which was evaluated in a previous study by the authors. Thus, ELF-EMF radiation disturbs epigenetic mechanisms, which may underlay ELF-EMF-related transcriptomic alterations in the myometrium.

Chemopreventive Activity of Ellagitannins from Acer pseudosieboldianum (Pax) Komarov Leaves on Prostate Cancer Cells

Several studies have shown that compounds from Acer pseudosieboldianum (Pax) Komarov leaves (APL) display potent anti-oxidative, anti-inflammatory, and anti-proliferative activities. Prostate cancer (PCa) is the most common cancer among older men, and DNA methylation is associated with PCa progression. This study aimed to investigate the chemopreventive activities of the compounds which were isolated from APL on prostate cancer cells and elucidate the mechanisms of these compounds in relation to DNA methylation. One novel ellagitannin [komaniin (14)] and thirteen other known compounds, including glucose derivatives [ethyl-β-D-glucopyranose (3) and (4R)-p-menth-1-ene-7,8-diol 7-O-β-D-glucopyranoside (4)], one phenylpropanoid [junipetrioloside A (5)], three phenolic acid derivatives [ellagic acid-4-β-D-xylopyranoside (1), 4-O-galloyl-quinic acid (2), and gallic acid (8)], two flavonoids [quercetin (11) and kaempferol (12)], and five hydrolysable tannins [geraniin (6), punicafolin (7), granatin B (9), 1,2,3,4,6-penta-galloyl-β-D-glucopyranoside (10), and mallotusinic acid (13)] were isolated from APL. The hydrolyzable tannins (6, 7, 9, 10, 13, and 14) showed potent anti-PCa proliferative and apoptosis-promoting activities. Among the compounds, the ellagitannins in the dehydrohexahydroxydiphenoyl (DHHDP) group (6, 9, 13, and 14), the novel compound 14 showed the most potent inhibitory activity on DNA methyltransferase (DNMT1, 3a and 3b) and glutathione S-transferase P1 methyl removing and re-expression activities. Thus, our results suggested that the ellagitannins (6, 9, 13, and 14) isolated from APL could be a promising treatment option for PCa.

Epigenetic Modification of Cytosines in Hematopoietic Differentiation and Malignant Transformation

The mammalian DNA methylation landscape is established and maintained by the combined activities of the two key epigenetic modifiers, DNA methyltransferases (DNMT) and Ten-eleven-translocation (TET) enzymes. Once DNMTs produce 5-methylcytosine (5mC), TET proteins fine-tune the DNA methylation status by consecutively oxidizing 5mC to 5-hydroxymethylcytosine (5hmC) and further oxidized derivatives. The 5mC and oxidized methylcytosines are essential for the maintenance of cellular identity and function during differentiation. Cytosine modifications with DNMT and TET enzymes exert pleiotropic effects on various aspects of hematopoiesis, including self-renewal of hematopoietic stem/progenitor cells (HSPCs), lineage determination, differentiation, and function. Under pathological conditions, these enzymes are frequently dysregulated, leading to loss of function. In particular, the loss of DNMT3A and TET2 function is conspicuous in diverse hematological disorders, including myeloid and lymphoid malignancies, and causally related to clonal hematopoiesis and malignant transformation. Here, we update recent advances in understanding how the maintenance of DNA methylation homeostasis by DNMT and TET proteins influences normal hematopoiesis and malignant transformation, highlighting the potential impact of DNMT3A and TET2 dysregulation on clonal dominance and evolution of pre-leukemic stem cells to full-blown malignancies. Clarification of the normal and pathological functions of DNA-modifying epigenetic regulators will be crucial to future innovations in epigenetic therapies for treating hematological disorders.

The phosphorylation to acetylation/methylation cascade in transcriptional regulation: how kinases regulate transcriptional activities of DNA/histone-modifying enzymes

Transcription factors directly regulate gene expression by recognizing and binding to specific DNA sequences, involving the dynamic alterations of chromatin structure and the formation of a complex with different kinds of cofactors, like DNA/histone modifying-enzymes, chromatin remodeling factors, and cell cycle factors. Despite the significance of transcription factors, it remains unclear to determine how these cofactors are regulated to cooperate with transcription factors, especially DNA/histone modifying-enzymes. It has been known that DNA/histone modifying-enzymes are regulated by post-translational modifications. And the most common and important modification is phosphorylation. Even though various DNA/histone modifying-enzymes have been classified and partly explained how phosphorylated sites of these enzymes function characteristically in recent studies. It still needs to find out the relationship between phosphorylation of these enzymes and the diseases-associated transcriptional regulation. Here this review describes how phosphorylation affects the transcription activity of these enzymes and other functions, including protein stability, subcellular localization, binding to chromatin, and interaction with other proteins.

Mechanisms of chromatin-based epigenetic inheritance

Multi-cellular organisms such as humans contain hundreds of cell types that share the same genetic information (DNA sequences), and yet have different cellular traits and functions. While how genetic information is passed through generations has been extensively characterized, it remains largely obscure how epigenetic information encoded by chromatin regulates the passage of certain traits, gene expression states and cell identity during mitotic cell divisions, and even through meiosis. In this review, we will summarize the recent advances on molecular mechanisms of epigenetic inheritance, discuss the potential impacts of epigenetic inheritance during normal development and in some disease conditions, and outline future research directions for this challenging, but exciting field.

DNA methyltransferases are complementary in maintaining DNA methylation in embryonic stem cells

ZFP57 and ZFP445 maintain genomic imprinting in mouse embryos. We found DNA methylation was lost at most examined imprinting control regions (ICRs) in mouse Zfp57 mutant ES cells, which could not be prevented by the elimination of three TET proteins. To elucidate methylation maintenance mechanisms, we generated mutant ES clones lacking three major DNA methyltransferases (DNMTs). Intriguingly, DNMT3A and DNMT3B were essential for DNA methylation at a subset of ICRs in mouse ES cells although DNMT1 maintained DNA methylation at most known ICRs. These were similarly observed after extended culture. Germline-derived DNA methylation was lost at the examined ICRs lacking DNMTs according to allelic analysis. Similar to DNMT1, DNMT3A and DNMT3B were required for maintaining DNA methylation at repeats, genic regions, and other genomic sequences. Therefore, three DNA methyltransferases play complementary roles in maintaining DNA methylation in mouse ES cells including DNA methylation at the ICRs primarily mediated through the ZFP57-dependent pathway.

•

ZFP57 maintains DNA methylation at the ICR of most imprinted regions in ES cells

•

TET proteins may not be essential for maintaining most ICR DNA methylation in ES cells

•

DNMT3 is required for the maintenance of DNA methylation at a subset of ICRs in ES cells

•

Maintenance functions of DNMT1 and DNMT3 are complementary at repeats and genic regions

The emerging role of non-coding RNAs in the epigenetic regulation of pediatric cancers

Epigenetics is a process that involves the regulation of gene expression without altering the sequence of DNA. Numerous studies have documented that epigenetic mechanisms play a critical role in cell growth, differentiation, and cancer over the past decade. The well-known epigenetic modifications are either on DNA or at the histone proteins. Although several studies have focused on regulating gene expression by non-coding RNAs, the current understanding of their biological functions in various human diseases, particularly in cancers, is inadequate. Only about two percent of DNA is involved in coding the protein-coding genes, and leaving the rest 98 percent is non-coding and the scientific community regarded as junk or noise with no known purpose. Most non-coding RNAs are derived from such junk DNA and are known to be involved in various signaling pathways involving cancer initiation, progression, and the development of therapy resistance in many human cancer types. Recent studies have suggested that non-coding RNAs, especially microRNAs, piwi-interactingRNAs, and long non-coding RNAs, play a significant role in controlling epigenetic mechanism(s), indicating the potential effect of epigenetic modulation of non-coding RNAs on cancer progression. In this review article, we briefly presented epigenetic marks' characteristics, crosstalk between epigenetic modifications and microRNAs, piwi-interactingRNAs, and long non-coding RNAs to uncover the effect on the phenotype of pediatric cancers. Further, current knowledge on understanding the RNA epigenetics will help design novel therapeutics that target epigenetic regulatory networks to benefit cancer patients in the clinic.

Dynamic changes in hepatic DNA methylation during the development of nonalcoholic fatty liver disease induced by a high-sugar diet

DNA methylation is an important epigenetic mechanism of gene expression control. The present study aimed to evaluate the temporal effect of isocaloric high-sugar diet (HSD) intake on the development of nonalcoholic fatty liver disease (NAFLD) and the role of DNA methylation in this event. Newly weaned Wistar rats were divided into eight groups and fed a standard chow diet or an HSD ad libitum for 4 weeks, 8 weeks, 15 weeks, and 18 weeks. After the experimental periods, the animals were euthanized and their livers were removed for histological analysis, gene expression of maintenance methylase (Dnmt1), de novo methylases (Dnmt3a and Dnmt3b), demethylases (Tet2 and Tet3) of DNA, and global DNA methylation. HSD intake led to the gradual development of NAFLD. HSD intake for 18 weeks was associated with downregulation of Dnmt1 expression and global DNA hypomethylation; these results were negatively correlated with more severe steatosis scores observed in these animals. The HSD consumption for 18 weeks was also associated with a decrease in Dnmt3a and Tet2 expression. Interestingly, the expression of de novo methyltransferase Dnmt3b was reduced by HSD during all experimental periods. Together, these results indicate that the downregulation of de novo DNA methylation, Dnmt3b, induced by HSD is the primary factor in the development of NAFLD. On the other hand, disease progression is associated with downregulation of maintenance DNA methylation and global DNA hypomethylation. These results suggest a link between the dynamic changes in hepatic DNA methylation and the development of NAFLD induced by an HSD intake.

Chromosome-specific retention of cancer-associated DNA hypermethylation following pharmacological inhibition of DNMT1

The DNA methylation status of the X-chromosome in cancer cells is often overlooked because of computational difficulties. Most of the CpG islands on the X-chromosome are mono-allelically methylated in normal female cells and only present as a single copy in male cells. We treated two colorectal cancer cell lines from a male (HCT116) and a female (RKO) with increasing doses of a DNA methyltransferase 1 (DNMT1)-specific inhibitor (GSK3685032/GSK5032) over several months to remove as much non-essential CpG methylation as possible. Profiling of the remaining DNA methylome revealed an unexpected, enriched retention of DNA methylation on the X-chromosome. Strikingly, the identified retained X-chromosome DNA methylation patterns accurately predicted de novo DNA hypermethylation in colon cancer patient methylomes in the TCGA COAD/READ cohort. These results suggest that a re-examination of tumors for X-linked DNA methylation changes may enable greater understanding of the importance of epigenetic silencing of cancer related genes.

A comprehensive approach for genome-wide efficiency profiling of DNA modifying enzymes

A precise understanding of DNA methylation dynamics is of great importance for a variety of biological processes including cellular reprogramming and differentiation. To date, complex integration of multiple and distinct genome-wide datasets is required to realize this task. We present GwEEP (genome-wide epigenetic efficiency profiling) a versatile approach to infer dynamic efficiencies of DNA modifying enzymes. GwEEP relies on genome-wide hairpin datasets, which are translated by a hidden Markov model into quantitative enzyme efficiencies with reported confidence around the estimates. GwEEP predicts de novo and maintenance methylation efficiencies of Dnmts and furthermore the hydroxylation efficiency of Tets. Its design also allows capturing further oxidation processes given available data. We show that GwEEP predicts accurately the epigenetic changes of ESCs following a Serum-to-2i shift and applied to Tet TKO cells confirms the hypothesized mutual interference between Dnmts and Tets.

DNA Methylation Malleability and Dysregulation in Cancer Progression: Understanding the Role of PARP1

Mammalian genomic DNA methylation represents a key epigenetic modification and its dynamic regulation that fine-tunes the gene expression of multiple pathways during development. It maintains the gene expression of one generation of cells; particularly, the mitotic inheritance of gene-expression patterns makes it the key governing mechanism of epigenetic change to the next generation of cells. Convincing evidence from recent discoveries suggests that the dynamic regulation of DNA methylation is accomplished by the enzymatic action of TET dioxygenase, which oxidizes the methyl group of cytosine and activates transcription. As a result of aberrant DNA modifications, genes are improperly activated or inhibited in the inappropriate cellular context, contributing to a plethora of inheritable diseases, including cancer. We outline recent advancements in understanding how DNA modifications contribute to tumor suppressor gene silencing or oncogenic-gene stimulation, as well as dysregulation of DNA methylation in cancer progression. In addition, we emphasize the function of PARP1 enzymatic activity or inhibition in the maintenance of DNA methylation dysregulation. In the context of cancer remediation, the impact of DNA methylation and PARP1 pharmacological inhibitors, and their relevance as a combination therapy are highlighted.

Domain Structure of the Dnmt1, Dnmt3a, and Dnmt3b DNA Methyltransferases

In mammals, three major DNA methyltransferases, Dnmt1, Dnmt3a, and Dnmt3b, have been identified. Dnmt3a and Dnmt3b are responsible for establishing DNA methylation patterns produced through their de novo-type DNA methylation activity in implantation stage embryos and during germ cell differentiation. Dnmt3-like (Dnmt3l), which is a member of the Dnmt3 family but does not possess DNA methylation activity, was reported to be indispensable for global methylation in germ cells. Once the DNA methylation patterns are established, maintenance-type DNA methyltransferase Dnmt1 faithfully propagates them to the next generation via replication. All Dnmts possess multiple domains. For instance, Dnmt3a and Dnmt3b each contain a Pro-Trp-Trp-Pro (PWWP) domain that recognizes the histone H3K36me2/3 mark, an Atrx-Dnmt3-Dnmt3l (ADD) domain that recognizes unmodified histone H3 tail, and a catalytic domain that methylates CpG sites. Dnmt1 contains an N-terminal independently folded domain (NTD) that interacts with a variety of regulatory factors, a replication foci-targeting sequence (RFTS) domain that recognizes the histone H3K9me3 mark and H3 ubiquitylation, a CXXC domain that recognizes unmodified CpG DNA, two tandem Bromo-Adjacent-homology (BAH1 and BAH2) domains that read the H4K20me3 mark with BAH1, and a catalytic domain that preferentially methylates hemimethylated CpG sites. In this chapter, the structures and functions of these domains are described.

Epigenetics and tissue immunity-Translating environmental cues into functional adaptations

There is an increasing appreciation that many innate and adaptive immune cell subsets permanently reside within non-lymphoid organs, playing a critical role in tissue homeostasis and defense. The best characterized are macrophages and tissue-resident T lymphocytes that work in concert with organ structural cells to generate appropriate immune responses and are functionally shaped by organ-specific environmental cues. The interaction of tissue epithelial, endothelial and stromal cells is also required to attract, differentiate, polarize and maintain organ immune cells in their tissue niche. All of these processes require dynamic regulation of cellular transcriptional programmes, with epigenetic mechanisms playing a critical role, including DNA methylation and post-translational histone modifications. A failure to appropriately regulate immune cell transcription inevitably results in inadequate or inappropriate immune responses and organ pathology. Here, with a focus on the mammalian kidney, an organ which generates differing regional environmental cues (including hypersalinity and hypoxia) due to its physiological functions, we will review the basic concepts of tissue immunity, discuss the technologies available to profile epigenetic modifications in tissue immune cells, including those that enable single-cell profiling, and consider how these mechanisms influence the development, phenotype, activation and function of different tissue immune cell subsets, as well as the immunological function of structural cells.

Non-Canonical Helical Structure of Nucleic Acids Containing Base-Modified Nucleotides

Chemically modified nucleobases are thought to be important for therapeutic purposes as well as diagnosing genetic diseases and have been widely involved in research fields such as molecular biology and biochemical studies. Many artificially modified nucleobases, such as methyl, halogen, and aryl modifications of purines at the C8 position and pyrimidines at the C5 position, are widely studied for their biological functions. DNA containing these modified nucleobases can form non-canonical helical structures such as Z-DNA, G-quadruplex, i-motif, and triplex. This review summarizes the synthesis of chemically modified nucleotides: (i) methylation, bromination, and arylation of purine at the C8 position and (ii) methylation, bromination, and arylation of pyrimidine at the C5 position. Additionally, we introduce the non-canonical structures of nucleic acids containing these modifications.

Impact of miRNAs expression modulation on the methylation status of breast cancer stem cell-related genes

PURPOSE

Altered miRNAs play a crucial role in the emergence of the breast cancer stem cell (BCSC) phenotype. The interplay between miRNAs and methylation enzymes has been documented. One of the most aggressive breast cancer cell lines, MDA-MB-231, has expressed much more DNMT3B than DNMT3A. This study aims to evaluate the ability of miR-203 restoration and miR-150 inhibition to regulate DNMT3B and DNMT3A to modify the methylation level of BCSC-associated genes.

METHODS

MDA-MB-231 cells were transfected with miR-203 mimic or miR-150 inhibitor or DNMT3B siRNA, and downstream analysis was performed by flow cytometry, real-time PCR and Western blotting.

RESULTS

DNMT3A and DNMT3B are regulated both by miR-203a-3p and miR-150-5p. Transfection with miR-203 mimic and miR-150 inhibitor significantly reduced the CD44+CD24- subpopulation and down-regulated the expression of CD44 mRNA by increasing promoter methylation levels. SiRNA knockdown of DNMT3B increased the CD44+CD24- subpopulation and the expression of CD44 and ALDH1A3 by decreasing methylation density. The inhibition of miR-150 down-regulated OCT3/4 and SOX2 expression without affecting methylation levels, while miR-203 restoration and miR-150 inhibition down-regulated NANOG expression by elevating the methylation level. A positive-feedback loop was found between miR-203 and its target DNMT3B, as restoring miR-203 suppressed DNMT3B, while knocking down DNMT3B up-regulated miR-203. The restoration of miR-203 and knockdown of DNMT3B decreased methylation levels and increased the expression of miR-141 and miR-200c.

CONCLUSIONS

The study concluded that miR-203 and miR-150 play a role in the regulation of genes involved in BCSC methylation, including other miRNAs, by targeting DNMT3B and DNMT3A.

Human Endogenous Retrovirus as Therapeutic Targets in Neurologic Disease

Human endogenous retroviruses (HERVs) are ancient retroviral DNA sequences established into germline. They contain regulatory elements and encoded proteins few of which may provide benefits to hosts when co-opted as cellular genes. Their tight regulation is mainly achieved by epigenetic mechanisms, which can be altered by environmental factors, e.g., viral infections, leading to HERV activation. The aberrant expression of HERVs associates with neurological diseases, such as multiple sclerosis (MS) or amyotrophic lateral sclerosis (ALS), inflammatory processes and neurodegeneration. This review summarizes the recent advances on the epigenetic mechanisms controlling HERV expression and the pathogenic effects triggered by HERV de-repression. This article ends by describing new, promising therapies, targeting HERV elements, one of which, temelimab, has completed phase II trials with encouraging results in treating MS. The information gathered here may turn helpful in the design of new strategies to unveil epigenetic failures behind HERV-triggered diseases, opening new possibilities for druggable targets and/or for extending the use of temelimab to treat other associated diseases.

Simultaneously measuring the methylation of parent and daughter strands of replicated DNA at the single-molecule level by Hammer-seq

The stable maintenance of DNA methylation patterns during mitotic cell division is crucial for cell identity. Precisely determining the maintenance kinetics and dissecting the exact contributions of relevant regulators requires a method to accurately measure parent and daughter strand DNA methylation at the same time, ideally at the single-molecule level. Recently, we developed a method referred to as Hammer-seq (hairpin-assisted mapping of methylation of replicated DNA) that fulfils the above criteria. This method integrates 5-ethynyl-2'-deoxyuridine (EdU) labeling of replicating DNA, biotin conjugation and streptavidin-based affinity purification, and whole-genome hairpin bisulfite sequencing technologies. Hammer-seq offers the unique advantage of simultaneously measuring the methylation status of parent and daughter strands within a single DNA molecule, which makes it possible to determine maintenance kinetics across various genomic regions without averaging effects from bulk measurements and to assess de novo methylation events that accompany methylation maintenance. Importantly, when combined with mutant cell lines in which mechanisms of interest are disrupted, Hammer-seq can be applied to determine the functional contributions of potential regulators to methylation maintenance, with accurate kinetics information that cannot be acquired with other currently available methods. Hammer-seq library preparation requires ~100 ug EdU-labeled genomic DNA as input (~15 million mammalian cells). The whole protocol, from pulse labeling to library construction, can be completed within 2-3 d, depending on the chasing time.

Cutting Edge: Hypoxia-Induced Ubc9 Promoter Hypermethylation Regulates IL-17 Expression in Ulcerative Colitis

Dysregulated IL-17 expression is central to the pathogenesis of several inflammatory disorders, including ulcerative colitis. We have shown earlier that SUMOylation of ROR-γt, the transcription factor for IL-17, regulates colonic inflammation. In this study, we show that the expression of Ubc9, the E2 enzyme that targets ROR-γt for SUMOylation, is significantly reduced in the colonic mucosa of ulcerative colitis patients. Mechanistically, we demonstrate that hypoxia-inducible factor 1α (HIF-1α) binds to a CpG island within the Ubc9 gene promoter, resulting in its hypermethylation and reduced Ubc9 expression. CRISPR-Cas9-mediated inhibition of HIF-1α normalized Ubc9 and attenuated IL-17 expression in Th17 cells and reduced diseases severity in Rag1 ^-/- mice upon adoptive transfer. Collectively, our study reveals a novel epigenetic mechanism of regulation of ROR-γt that could be exploited in inflammatory diseases.

Mitotic inheritance of DNA methylation: more than just copy and paste

Decades of investigation on DNA methylation have led to deeper insights into its metabolic mechanisms and biological functions. This understanding was fueled by the recent development of genome editing tools and our improved capacity for analyzing the global DNA methylome in mammalian cells. This review focuses on the maintenance of DNA methylation patterns during mitotic cell division. We discuss the latest discoveries of the mechanisms for the inheritance of DNA methylation as a stable epigenetic memory. We also highlight recent evidence showing the rapid turnover of DNA methylation as a dynamic gene regulatory mechanism. A body of work has shown that altered DNA methylomes are common features in aging and disease. We discuss the potential links between methylation maintenance mechanisms and disease-associated methylation changes.

Unravelling the Epigenome of Myelodysplastic Syndrome: Diagnosis, Prognosis, and Response to Therapy

Simple Summary

Myelodysplastic syndrome (MDS) is a type of blood cancer that mostly affects older individuals. Invasive tests to obtain bone samples are used to diagnose MDS and many patients do not respond to therapy or stop responding to therapy in the short-term. Less invasive tests to help diagnose, prognosticate, and predict response of patients is a felt need. Factors that influence gene expression without changing the DNA sequence (epigenetic modifiers) such as DNA methylation, micro-RNAs and long-coding RNAs play an important role in MDS, are potential biomarkers and may also serve as targets for therapy.

Abstract

Myelodysplastic syndrome (MDS) is a malignancy that disrupts normal blood cell production and commonly affects our ageing population. MDS patients are diagnosed using an invasive bone marrow biopsy and high-risk MDS patients are treated with hypomethylating agents (HMAs) such as decitabine and azacytidine. However, these therapies are only effective in 50% of patients, and many develop resistance to therapy, often resulting in bone marrow failure or leukemic transformation. Therefore, there is a strong need for less invasive, diagnostic tests for MDS, novel markers that can predict response to therapy and/or patient prognosis to aid treatment stratification, as well as new and effective therapeutics to enhance patient quality of life and survival. Epigenetic modifiers such as DNA methylation, long non-coding RNAs (lncRNAs) and micro-RNAs (miRNAs) are perturbed in MDS blasts and the bone marrow micro-environment, influencing disease progression and response to therapy. This review focusses on the potential utility of epigenetic modifiers in aiding diagnosis, prognosis, and predicting treatment response in MDS, and touches on the need for extensive and collaborative research using single-cell technologies and multi-omics to test the clinical utility of epigenetic markers for MDS patients in the future.

Epigenetics in modulating immune functions of stromal and immune cells in the tumor microenvironment

Epigenetic regulation of gene expression in cancer cells has been extensively studied in recent decades, resulting in the FDA approval of multiple epigenetic agents for treating different cancer types. Recent studies have revealed novel roles of epigenetic dysregulation in altering the phenotypes of immune cells and tumor-associated stromal cells, including fibroblasts and endothelial cells. As a result, epigenetic dysregulation of these cells reshapes the tumor microenvironment (TME), changing it from an antitumor environment to an immunosuppressive environment. Here, we review recent studies demonstrating how specific epigenetic mechanisms drive aspects of stromal and immune cell differentiation with implications for the development of solid tumor therapeutics, focusing on the pancreatic ductal adenocarcinoma (PDA) TME as a representative of solid tumors. Due to their unique ability to reprogram the TME into a more immunopermissive environment, epigenetic agents have great potential for sensitizing cancer immunotherapy to augment the antitumor response, as an immunopermissive TME is a prerequisite for the success of cancer immunotherapy but is often not developed with solid tumors. The idea of combining epigenetic agents with cancer immunotherapy has been tested both in preclinical settings and in multiple clinical trials. In this review, we highlight the basic biological mechanisms underlying the synergy between epigenetic therapy and immunotherapy and discuss current efforts to translate this knowledge into clinical benefits for patients.

DNA methylation dynamics during zygotic genome activation in goat

DNA methylation is a crucial element in the epigenetic regulation of mammalian embryonic development. However, the subtle changes in DNA methylation differ in species, and, little information is known regarding the dynamics of DNA methylation at the single-base resolution in goat. In the present study, we studied the DNA methylation dynamics during goat zygotic genome activation (ZGA) at global and single-base resolution using immunostaining and reduced representation bisulfite sequencing, respectively. We showed that DNA methylation was decreased both at global and single-base resolution, and the expression of TET1 was increased while DNMT1 was decreased during ZGA in goat. We identified 51058 tiles of differential methylation regions (DMRs), which were enriched in the developmental process, the regulation of developmental process, AMPK signaling pathway, mTOR signaling pathway, autophagy, and lysosome, as revealed by GO and KEGG enrichment analysis. Furthermore, we found an association between the methylation level and the expression of imprinted genes (IGF2R, PEG3, and ZFP64), maternal genes (TRIM28, SETD1A, SIN3A, and NPM2), and zygotic genes (DUXA, IGF2BP1, WT1, and ZIM3), suggesting that DNA methylation is in the tight control of ZGA in goat by regulating the expression of the critical genes. Our data will help to understand the stochastic ZGA events to achieve better development of goat embryos in vitro and provide an excellent source for further ZGA studies.

dnmt1 function is required to maintain retinal stem cells within the ciliary marginal zone of the zebrafish eye

The ciliary marginal zone (CMZ) of the zebrafish retina contains a population of actively proliferating resident stem cells, which generate retinal neurons throughout life. The maintenance methyltransferase, dnmt1, is expressed within the CMZ. Loss of dnmt1 function results in gene misregulation and cell death in a variety of developmental contexts, however, its role in retinal stem cell (RSC) maintenance is currently unknown. Here, we demonstrate that zebrafish dnmt1^s872 mutants possess severe defects in RSC maintenance within the CMZ. Using a combination of immunohistochemistry, in situ hybridization, and a transgenic reporter assay, our results demonstrate a requirement for dnmt1 activity in the regulation of RSC proliferation, gene expression and in the repression of endogenous retroelements (REs). Ultimately, cell death is elevated in the dnmt1^−/− CMZ, but in a p53-independent manner. Using a transgenic reporter for RE transposition activity, we demonstrate increased transposition in the dnmt1^−/− CMZ. Taken together our data identify a critical role for dnmt1 function in RSC maintenance in the vertebrate eye.

Kinetics and mechanisms of mitotic inheritance of DNA methylation and their roles in aging-associated methylome deterioration

Mitotic inheritance of the DNA methylome is a challenging task for the maintenance of cell identity. Whether DNA methylation pattern in different genomic contexts can all be faithfully maintained is an open question. A replication-coupled DNA methylation maintenance model was proposed decades ago, but some observations suggest that a replication-uncoupled maintenance mechanism exists. However, the capacity and the underlying molecular events of replication-uncoupled maintenance are unclear. By measuring maintenance kinetics at the single-molecule level and assessing mutant cells with perturbation of various mechanisms, we found that the kinetics of replication-coupled maintenance are governed by the UHRF1-Ligase 1 and PCNA-DNMT1 interactions, whereas nucleosome occupancy and the interaction between UHRF1 and methylated H3K9 specifically regulate replication-uncoupled maintenance. Surprisingly, replication-uncoupled maintenance is sufficiently robust to largely restore the methylome when replication-coupled maintenance is severely impaired. However, solo-WCGW sites and other CpG sites displaying aging- and cancer-associated hypomethylation exhibit low maintenance efficiency, suggesting that although quite robust, mitotic inheritance of methylation is imperfect and that this imperfection may contribute to selective hypomethylation during aging and tumorigenesis.

Genome-wide analysis in the mouse embryo reveals the importance of DNA methylation for transcription integrity

Mouse embryos acquire global DNA methylation of their genome during implantation. However the exact roles of DNA methyltransferases (DNMTs) in embryos have not been studied comprehensively. Here we systematically analyze the consequences of genetic inactivation of Dnmt1, Dnmt3a and Dnmt3b on the methylome and transcriptome of mouse embryos. We find a strict division of function between DNMT1, responsible for maintenance methylation, and DNMT3A/B, solely responsible for methylation acquisition in development. By analyzing severely hypomethylated embryos, we uncover multiple functions of DNA methylation that is used as a mechanism of repression for a panel of genes including not only imprinted and germline genes, but also lineage-committed genes and 2-cell genes. DNA methylation also suppresses multiple retrotransposons and illegitimate transcripts from cryptic promoters in transposons and gene bodies. Our work provides a thorough analysis of the roles of DNA methyltransferases and the importance of DNA methylation for transcriptome integrity in mammalian embryos.

Realgar (α-As4S4) Treats Myelodysplasic Syndromes through Reducing DNA Hypermethylation

DNA hypermethylation is an epigenetic modification that plays a critical role in the oncogenesis of myelodysplastic syndromes (MDS). Aberrant DNA methylation represses the transcription of promotors of tumor suppressor genes, inducing gene silencing. Realgar (α-As₄S₄) is a traditional medicine used for the treatment of various diseases in the ancient time. Realgar was reported to have efficacy for acute promyelocytic leukemia (APL). It has been demonstrated that realgar could efficiently reduce DNA hypermethylation of MDS. This review discusses the mechanisms of realgar on inhibiting DNA hypermethylation of MDS, as well as the species and metabolisms of arsenic in vivo.

A function of fascin1 in the colony formation of mouse embryonic stem cells

Fascin1 is known to participate in the migration of cancer cells by binding to actin filaments. Recent studies evidenced that fascin1 also modulates processes such as the tumorigenesis and maintenance of pluripotency genes in cancer stem cells. However, the function of fascin1 in embryonic stem cells remains unclear. In this article, we report that fascin1 is highly expressed and widely distributed in mouse embryonic stem cells (mESCs), which are regulated by JAK-STAT3 and β-catenin. We found that the overexpression of fascin1 impairs the formation of mESC colonies via the downregulation of intercellular adhesion molecules, and that mimicking the dephosphorylated mutation of fascin1 or inhibiting phosphorylation with Gö6983 significantly enhances colony formation. Hyperphosphorylated fascin1 can promote the maintenance of pluripotency in mESCs via nuclear localization and suppressing DNA methyltransferase expression. Our findings demonstrate a novel function of fascin1, as a vital regulator, in the colony formation and pluripotency of mESCs and provide insights into the molecular mechanisms underlying embryonic stem cell self-organization and development in vitro.