Reversible Histone Modifications Research Articles

Reversible Histone Modifications Contribute to the Frozen and Thawed Recovery States of Wood Frog Brains.

Epigenetic regulation, notably histone post-translational modification (PTM), has emerged as a major transcriptional control of gene expression during cellular stress adaptation. In the present study, we use an acid extraction method to isolate total histone protein and investigate dynamic changes in 23 well-characterized histone methylations/acetylations in the brains of wood frogs subject to 24-h freezing and subsequent 8-h thawed recovery conditions. Our results identify four histone PTMs (H2BK5ac, H3K14ac, H3K4me3, H3K9me2) and three histone proteins (H1.0, H2B, H4) that were significantly (p < 0.05) responsive to freeze-thaw in freeze-tolerant R. sylvatica brains. Two other permissive modifications (H3R8me2a, H3K9ac) also trended downwards following freezing stress. Together, these data are strongly supportive of the proposed global transcriptional states of hypometabolic freeze tolerance and rebounded thawed recovery. Our findings shed light on the intricate interplay between epigenetic regulation, gene transcription and energy metabolism in wood frogs' adaptive response to freezing stress.

Polycomb-dependent differential chromatin compartmentalization determines gene coregulation in Arabidopsis.

In animals, distant H3K27me3-marked Polycomb targets can establish physical interactions forming repressive chromatin hubs. In plants, growing evidence suggests that H3K27me3 acts directly or indirectly to regulate chromatin interactions, although how this histone modification modulates 3D chromatin architecture remains elusive. To decipher the impact of the dynamic deposition of H3K27me3 on the Arabidopsis thaliana nuclear interactome, we combined genetics, transcriptomics, and several 3D epigenomic approaches. By analyzing mutants defective for histone H3K27 methylation or demethylation, we uncovered the crucial role of this chromatin mark in short- and previously unnoticed long-range chromatin loop formation. We found that a reduction in H3K27me3 levels led to a decrease in the interactions within Polycomb-associated repressive domains. Regions with lower H3K27me3 levels in the H3K27 methyltransferase clf mutant established new interactions with regions marked with H3K9ac, a histone modification associated with active transcription, indicating that a reduction in H3K27me3 levels induces a global reconfiguration of chromatin architecture. Altogether, our results reveal that the 3D genome organization is tightly linked to reversible histone modifications that govern chromatin interactions. Consequently, nuclear organization dynamics shapes the transcriptional reprogramming during plant development and places H3K27me3 as a key feature in the coregulation of distant genes.

Effects of soybean meal on digestive enzymes activity, expression of inflammation-related genes, and chromatin modifications in marine fish (Sparus aurata L.) larvae.

The effects of soybean meal (SBM) in early diet of Sparus aurata larvae at two developmental windows were assessed. Prolonged (beyond 14days post-hatch, dph) feeding with SBM decreased the activity of pancreatic enzymes of larvae. In the absence of SBM these larvae later resumed enzyme activities, but exhibited a significant delay in development. Larvae response to SBM involved up-regulation of extracellular matrix remodeling enzymes and pro-inflammatory cytokines, coupled with a drop in putative intestinal enzymes. Larvae receiving SBM at first feeding appear later to have lower expression of inflammation-related genes, especially those fed SBM until 14 dph. Multivariate analysis confirmed that the duration of the SBM early feeding period drives the physiology of larvae in different directions. Feeding larvae with SBM increased global histone H3 acetylation, whereas upon removal of SBM the process was reverted. A more in deep analysis revealed a dynamic interplay among several reversible histone modifications such as H3K14ac and H3K27m3. Finally, we showed that SBM feeding of larvae results in global hypomethylation that persist after SBM removal. This study is the first demonstrating an effect of diet on marine fish epigenetics. It is concluded that there are limitations for extending SBM feeding of S. aurata larvae beyond 14 dph even under co-feeding with live feed, affecting key physiological processes and normal growth. However, up to 14 dph, SBM does not affect normal development, and produces apparently lasting effects on some key enzymes, genes, and chromatin modifications.

ADP-ribosyltransferases Parp1 and Parp7 safeguard pluripotency of ES cells

Embryonic stem (ES) cells are in a dynamic equilibrium of distinct functional states, characterized by the heterogeneous expression of critical pluripotency factors and regulated by a spectrum of reversible histone modifications. Maintenance of this equilibrium is a hallmark of pluripotency. Here we find that the ADP-ribosyltransferases Parp1 and Parp7 play a critical role in safeguarding this state by occupying key pluripotency genes, notably Nanog, Pou5f1, Sox2, Stella, Tet1 and Zfp42, thereby protecting them from progressive epigenetic repression. In the absence of either Parp1 or Parp7, or upon inhibition of the ADP-ribosylating activity, ES cells exhibit a decrease in ground state pluripotency as they cannot maintain the typical heterogeneity characteristic of the metastable state. As a consequence, they display a higher propensity to differentiate. These findings place Parp1 and Parp7 at the genetic-epigenetic interface of pluripotency networks, fine-tuning the transcriptional heterogeneity and thereby determining the developmental plasticity of ES cells.

Involvement of insulin-induced reversible chromatin remodeling in altering the expression of oxidative stress-responsive genes under hyperglycemia in 3T3-L1 preadipocytes

The epigenetic control mechanisms, regulating insulin-induced oxidative stress generation, under hyperglycemic condition are yet to be elucidated. We set out to assess the role of chromatin regulatory factors in regulating the transcription of genes that are critical for mediating oxidative stress response under hyperglycemic/hyperinsulinemic condition. Our results outline a significant increase in the ROS generation accompanied by a decrease in the histone H3 acetylation, H3 Ser-10 phosphorylation, H3K4 methylation and an increase in the H3K9 methylation, after 30min of insulin treatment under hyperglycemic condition. However, after 12h of insulin treatment a reversal of these histone H3 modifications was observed which commensurate with the reduced ROS generation. Microarray data revealed that the expression of stress responsive genes (Hsp90, Hspd1, DnajC15, Hsf5 and Mapk3) decreased after12h of insulin treatment, after an initial increase at 30min. We observed the direct regulation of these stress responsive genes by reversible histone modifications under hyperglycemic/hyperinsulinemic condition at both time intervals. Further, pre-incubation with catalase attenuates these changes. To the best of our knowledge this is the first report that shows the role of reversible histone modifications in regulating oxidative stress-responsive genes under hyperglycemic condition in 3T3-L1 preadipocytes.

Epigenetic mechanisms in tumorigenesis, tumor cell heterogeneity and drug resistance

Resistance of cancer cells to chemotherapeutics and emerging targeted drugs is a devastating problem in the treatment of cancer patients. Multiple mechanisms contribute to drug resistance such as increased drug efflux, altered drug metabolism, secondary mutations in drug targets, and activation of downstream or parallel signal transduction pathways. The rapid kinetics, the reversibility of acquired drug resistance and the absence of genetic mutations suggest an epigenetic basis for drug insensitivity. Similar to the cellular variance seen in the human body, epigenetic mechanisms, through reversible histone modifications and DNA methylation patterns, generate a variety of transcriptional states resulting in a dynamic heterogeneous tumor cell population. Consequently, epigenomes favoring survival in the presence of a drug by aberrant transcription of drug transporters, DNA-repair enzymes and pro-apoptotic factors render cytotoxic and targeted drugs ineffective and allow selection of rare drug-resistant tumor cells. Recent advances in charting cancer genomes indeed strongly indicate a role for epigenetic regulators in driving cancer, which may result in the acquisition of additional (epi)genetic modifications leading to drug resistance. These observations have important clinical consequences as they provide an opportunity for "epigenetic drugs" to change reversible drug-resistance-associated epigenomes to prevent or reverse non-responsiveness to anti-cancer drugs.

PHF8 mediates histone H4 lysine 20 demethylation events involved in cell cycle progression

While reversible histone modifications are linked to an ever-expanding range of biological functions1–5, the demethylases for histone H4 lysine 20 and their potential regulatory roles remain unknown. Here, we report that the PHD and Jumonji C (JmjC) domain-containing protein, PHF8, while utilizing multiple substrates, including H3K9me1/2 and H3K27me2, also functions as an H4K20me1 demethylase. PHF8 is recruited to promoters by its PHD domain based on interaction with H3K4me2/3 and controls G1/S transition in conjunction with E2F1, HCF-1 and Set1A, at least in part, by removing the repressive H4K20me1 mark from a subset of E2F1-regulated gene promoters. Phosphorylation-dependent PHF8 dismissal from chromatin in prophase is apparently required for the accumulation of H4K20me1 during early mitosis, which might represent a component of the Condensin II loading process. Accordingly, the HEAT repeat clusters in two non-SMC Condensin II subunits, N-CAPD3 and N-CAPG2, are capable of recognizing H4K20me1, and ChIP-seq. analysis demonstrate a significant overlap of Condensin II and H4K20me1 sites in mitotic HeLa cells. Thus, the identification and characterization of the first H4K20me1 demethylase, PHF8, has revealed an intimate link between this enzyme and two distinct events in cell cycle progression.

A Major Role for the Plasmodium falciparum ApiAP2 Protein PfSIP2 in Chromosome End Biology

The heterochromatic environment and physical clustering of chromosome ends at the nuclear periphery provide a functional and structural framework for antigenic variation and evolution of subtelomeric virulence gene families in the malaria parasite Plasmodium falciparum. While recent studies assigned important roles for reversible histone modifications, silent information regulator 2 and heterochromatin protein 1 (PfHP1) in epigenetic control of variegated expression, factors involved in the recruitment and organization of subtelomeric heterochromatin remain unknown. Here, we describe the purification and characterization of PfSIP2, a member of the ApiAP2 family of putative transcription factors, as the unknown nuclear factor interacting specifically with cis-acting SPE2 motif arrays in subtelomeric domains. Interestingly, SPE2 is not bound by the full-length protein but rather by a 60kDa N-terminal domain, PfSIP2-N, which is released during schizogony. Our experimental re-definition of the SPE2/PfSIP2-N interaction highlights the strict requirement of both adjacent AP2 domains and a conserved bipartite SPE2 consensus motif for high-affinity binding. Genome-wide in silico mapping identified 777 putative binding sites, 94% of which cluster in heterochromatic domains upstream of subtelomeric var genes and in telomere-associated repeat elements. Immunofluorescence and chromatin immunoprecipitation (ChIP) assays revealed co-localization of PfSIP2-N with PfHP1 at chromosome ends. Genome-wide ChIP demonstrated the exclusive binding of PfSIP2-N to subtelomeric SPE2 landmarks in vivo but not to single chromosome-internal sites. Consistent with this specialized distribution pattern, PfSIP2-N over-expression has no effect on global gene transcription. Hence, contrary to the previously proposed role for this factor in gene activation, our results provide strong evidence for the first time for the involvement of an ApiAP2 factor in heterochromatin formation and genome integrity. These findings are highly relevant for our understanding of chromosome end biology and variegated expression in P. falciparum and other eukaryotes, and for the future analysis of the role of ApiAP2-DNA interactions in parasite biology.

Regulation of β4-integrin expression by epigenetic modifications in the mammary gland and during the epithelial-to-mesenchymal transition

The beta 4 integrin is expressed in epithelial cells, a few other cell types and in some carcinomas. Despite this restricted expression pattern and the functional importance of beta 4 integrin in epithelial and carcinoma biology, little is known about how its expression is regulated. Here, we assessed the epigenetic regulation of beta 4 integrin based on the presence of a large CpG island in the beta 4-integrin gene promoter. We separated basal (beta 4+) and luminal (beta 4-) epithelial cells from the mammary glands of K14-eGFP mice and demonstrated that the beta 4-integrin promoter is unmethylated in basal cells and methylated in luminal cells. We also observed that expression of beta 4 integrin and E-cadherin is lost during the epithelial-to-mesenchymal transition (EMT) of mammary gland cells induced by transforming growth factor beta (TGFbeta), which is coincident with de novo DNA methylation, a decrease in active histone modifications (H3K9Ac and H3K4me3) and an increase in the repressive histone modification H3K27me3. Furthermore, TGFbeta withdrawal promotes a mesenchymal-to-epithelial transition (MET) and triggers the re-expression of beta 4 integrin and E-cadherin. Intriguingly, demethylation at either promoter is not obligatory for transcriptional reactivation after TGFbeta withdrawal. However, both H3K9Ac and H3K4me3 modifications are restored during the MET, and H3K27me3 is reduced, strongly suggesting that reversible histone modifications rather than DNA demethylation are the predominant factors in reactivating expression of these genes. Our data indicate that complex epigenetic modifications contribute to the regulation of the beta 4 integrin and E-cadherin.

GlcNAcylation of a histone methyltransferase in retinoic-acid-induced granulopoiesis

The post-translational modifications of histone tails generate a 'histone code' that defines local and global chromatin states. The resultant regulation of gene function is thought to govern cell fate, proliferation and differentiation. Reversible histone modifications such as methylation are under mutual controls to organize chromosomal events. Among the histone modifications, methylation of specific lysine and arginine residues seems to be critical for chromatin configuration and control of gene expression. Methylation of histone H3 lysine 4 (H3K4) changes chromatin into a transcriptionally active state. Reversible modification of proteins by beta-N-acetylglucosamine (O-GlcNAc) in response to serum glucose levels regulates diverse cellular processes. However, the epigenetic impact of protein GlcNAcylation is unknown. Here we report that nuclear GlcNAcylation of a histone lysine methyltransferase (HKMT), MLL5, by O-GlcNAc transferase facilitates retinoic-acid-induced granulopoiesis in human HL60 promyelocytes through methylation of H3K4. MLL5 is biochemically identified in a GlcNAcylation-dependent multi-subunit complex associating with nuclear retinoic acid receptor RARalpha (also known as RARA), serving as a mono- and di-methyl transferase to H3K4. GlcNAcylation at Thr 440 in the MLL5 SET domain evokes its H3K4 HKMT activity and co-activates RARalpha in target gene promoters. Increased nuclear GlcNAcylation by means of O-GlcNAc transferase potentiates retinoic-acid-induced HL60 granulopoiesis and restores the retinoic acid response in the retinoic-acid-resistant HL60-R2 cell line. Thus, nuclear MLL5 GlcNAcylation triggers cell lineage determination of HL60 through activation of its HKMT activity.

Modulation of histone deacetylase activity by dietary isothiocyanates and allyl sulfides: Studies with sulforaphane and garlic organosulfur compounds

Histone deacetylase (HDAC) inhibitors reactivate epigenetically-silenced genes in cancer cells, triggering cell cycle arrest and apoptosis. Recent evidence suggests that dietary constituents can act as HDAC inhibitors, such as the isothiocyanates found in cruciferous vegetables and the allyl compounds present in garlic. Broccoli sprouts are a rich source of sulforaphane (SFN), an isothiocyanate that is metabolized via the mercapturic acid pathway and inhibits HDAC activity in human colon, prostate, and breast cancer cells. In mouse preclinical models, SFN inhibited HDAC activity and induced histone hyperacetylation coincident with tumor suppression. Inhibition of HDAC activity also was observed in circulating peripheral blood mononuclear cells obtained from people who consumed a single serving of broccoli sprouts. Garlic organosulfur compounds can be metabolized to allyl mercaptan (AM), a competitive HDAC inhibitor that induced rapid and sustained histone hyperacetylation in human colon cancer cells. Inhibition of HDAC activity by AM was associated with increased histone acetylation and Sp3 transcription factor binding to the promoter region of the P21WAF1 gene, resulting in elevated p21 protein expression and cell cycle arrest. Collectively, the results from these studies, and others reviewed herein, provide new insights into the relationships between reversible histone modifications, diet, and cancer chemoprevention.