Multiplexed profiling facilitates robust m6A quantification at site, gene and sample resolution.

N6-methyladenosine (m6A) is the most prevalent modification of messenger RNA in mammals. To interrogate its functions and dynamics, there is a critical need to quantify m6A at three levels: site, gene and sample. Current approaches address these needs in a limited manner. Here we develop m6A-seq2, relying on multiplexed m6A-immunoprecipitation of barcoded and pooled samples. m6A-seq2 allows a big increase in throughput while reducing technical variability, requirements of input material and cost. m6A-seq2 is furthermore uniquely capable of providing sample-level relative quantitations of m6A, serving as an orthogonal alternative to mass spectrometry-based approaches. Finally, we develop a computational approach for gene-level quantitation of m6A. We demonstrate that using this metric, roughly 30% of the variability in RNA half life in mouse embryonic stem cells can be explained, establishing m6A as a main driver of RNA stability. m6A-seq2 thus provides an experimental and analytic framework for dissecting m6A-mediated regulation at three different levels.

Recruitment of the Mammalian Histone-modifying EMSY Complex to Target Genes Is Regulated by ZNF131.

Recent work from others and us revealed interactions between the Sin3/HDAC complex, the H3K4me3 demethylase KDM5A, GATAD1, and EMSY. Here, we characterize the EMSY/KDM5A/SIN3B complex in detail by quantitative interaction proteomics and ChIP-sequencing. We identify a novel substoichiometric interactor of the complex, transcription factor ZNF131, which recruits EMSY to a large number of active, H3K4me3 marked promoters. Interestingly, using an EMSY knock-out line and subsequent rescue experiments, we show that EMSY is in most cases positively correlated with transcriptional activity of its target genes and stimulates cell proliferation. Finally, by immunohistochemical staining of primary breast tissue microarrays we find that EMSY/KDM5A/SIN3B complex subunits are frequently overexpressed in primary breast cancer cases in a correlative manner. Taken together, these data open venues for exploring the possibility that sporadic breast cancer patients with EMSY amplification might benefit from epigenetic combination therapy targeting both the KDM5A demethylase and histone deacetylases.

A phospho/methyl switch at histone H3 regulates TFIID association with mitotic chromosomes.

Histone methylation patterns are correlated with eukaryotic gene transcription. High-affinity binding of the plant homeodomain (PHD) of TFIID subunit TAF3 to trimethylated lysine-4 of histone H3 (H3K4me3) is involved in promoter recruitment of this basal transcription factor. Here, we show that for transcription activation the PHD of TAF3 can be replaced by PHDs of other high-affinity H3K4me3 binders. Interestingly, H3K4me3 binding of TFIID and the TAF3-PHD is decreased by phosphorylation of the adjacent threonine residue (H3T3), which coincides with mitotic inhibition of transcription. Ectopic expression of the H3T3 kinase haspin repressed TAF3-mediated transcription of endogenous and of reporter genes and decreased TFIID association with chromatin. Conversely, immunofluorescence and live-cell microscopy studies showed an increased association of TFIID with mitotic chromosomes upon haspin knockdown. Based on our observations, we propose that a histone H3 phospho-methyl switch regulates TFIID-mediated transcription during mitotic progression of the cell cycle.

Histone lysine methylation and demethylation pathways in cancer.

The genetic changes leading to the development of human cancer are accompanied by alterations in the structure and modification status of chromatin, which represent powerful regulatory mechanisms for gene expression and genome stability. These epigenetic alterations have sparked interest into deciphering the regulatory pathways and function of post-translational modifications of histones during the initiation and progression of cancer. In this review we describe and summarize the current knowledge of several histone lysine methyltransferase and demethylase pathways relevant to cancer. Mechanistic insight into histone modifications will pave the way for the development and therapeutic application of "epidrugs" in cancer.

N6-methyladenosine (m6A) reader Pho92 is recruited co-transcriptionally and couples translation to mRNA decay to promote meiotic fitness in yeast.

N6- methyladenosine (m6A) RNA modification impacts mRNA fate primarily via reader proteins, which dictate processes in development, stress, and disease. Yet little is known about m6A function in Saccharomyces cerevisiae, which occurs solely during early meiosis. Here, we perform a multifaceted analysis of the m6A reader protein Pho92/Mrb1. Cross-linking immunoprecipitation analysis reveals that Pho92 associates with the 3'end of meiotic mRNAs in both an m6A-dependent and independent manner. Within cells, Pho92 transitions from the nucleus to the cytoplasm, and associates with translating ribosomes. In the nucleus Pho92 associates with target loci through its interaction with transcriptional elongator Paf1C. Functionally, we show that Pho92 promotes and links protein synthesis to mRNA decay. As such, the Pho92-mediated m6A-mRNA decay is contingent on active translation and the CCR4-NOT complex. We propose that the m6A reader Pho92 is loaded co-transcriptionally to facilitate protein synthesis and subsequent decay of m6A modified transcripts, and thereby promotes meiosis.

Identification of a novel inhibitor of coactivator-associated arginine methyltransferase 1 (CARM1)-mediated methylation of histone H3 Arg-17.

Methylation of the arginine residues of histones by methyltransferases has important consequences for chromatin structure and gene regulation; however, the molecular mechanism(s) of methyltransferase regulation is still unclear, as is the biological significance of methylation at particular arginine residues. Here, we report a novel specific inhibitor of coactivator-associated arginine methyltransferase 1 (CARM1; also known as PRMT4) that selectively inhibits methylation at arginine 17 of histone H3 (H3R17). Remarkably, this plant-derived inhibitor, called TBBD (ellagic acid), binds to the substrate (histone) preferentially at the signature motif, "KAPRK," where the proline residue (Pro-16) plays a critical role for interaction and subsequent enzyme inhibition. In a promoter-specific context, inhibition of H3R17 methylation represses expression of p21, a p53-responsive gene, thus implicating a possible role for H3 Arg-17 methylation in tumor suppressor function. These data establish TBBD as a novel specific inhibitor of arginine methylation and demonstrate substrate sequence-directed inhibition of enzyme activity by a small molecule and its physiological consequence.

Chromatin modifications (acetylation/ deacetylation/ methylation) as new targets for HIV therapy.

Human immunodeficiency virus (HIV) is one of the most deadly threats to the human race. Though the developed countries have been able to control the epidemic by utilizing the discovery of very expensive diagnostics, the situation is dangerously alarming in developing and underdeveloped countries. However, development of highly active anti- retroviral drugs has improved the survival and quality of life, but prolonged treatment results in viral load rebound to pretherapy levels. Recent advances in our understanding of eukaryotic and genome- integrated viral gene expression showed that regulation of chromatin function is closely linked to the multiplication of HIV. Therefore, a new therapeutic approach has been initiated targeting the chromatin-modifying enzymes mainly histone acetyltransferases and deacetylases which may lead to a better and economical anti- HIV combinatorial therapeutics. In this review, we have discussed the mechanisms of HIV gene expression in the chromatin context and its potentiality to be exploited as new therapeutic target.

Implications of small molecule activators and inhibitors of histone acetyltransferases in chromatin therapy.

Histone acetylation is a diagnostic feature of transcriptionally active chromatin. The group of enzymes, histone acetyltransferases (HATs), involved in this crucial step of gene regulation, covalently modifies the N-terminal lysine residues of histones by the addition of an acetyl group from acetyl coenzyme A. Dysfunction of these enzymes is often associated with several diseases, ranging from neurodegenerative disorders to cancer. These enzymes thus are potential new targets for therapeutics. We have discovered few small molecule compounds, which target HATs and either activate or inhibit the enzyme potently. These compounds would be useful as biological switching molecules for probing into the role of HATs in gene regulation and cell cycle and may be useful as new chemical entities for the development of new drugs.

The multiple endocrine neoplasia type 1 (MEN1) tumor suppressor regulates peroxisome proliferator-activated receptor gamma-dependent adipocyte differentiation.

Menin, the product of the MEN1 (multiple endocrine neoplasia type 1) tumor suppressor gene, is involved in activation of gene transcription as part of an MLL1 (mixed-lineage leukemia 1)/MLL2 (KMT2A/B)-containing protein complex which harbors methyltransferase activity for lysine 4 of histone H3 (H3K4). As MEN1 patients frequently develop lipomas and peroxisome proliferator-activated receptor gamma (PPARgamma) is expressed in several MEN1-related tumor types, we investigated regulation of PPARgamma activity by menin. We found that menin is required for adipocyte differentiation of murine 3T3-L1 cells and PPARgamma-expressing mouse embryonic fibroblasts. Menin augments PPARgamma target gene expression through recruitment of H3K4 methyltransferase activity. Menin interacts directly with the activation function 2 transcription activation domain of PPARgamma in a ligand-independent fashion. Ligand-dependent coactivation, however, is dependent on the LXXLL motif of menin and the intact helix 12 of PPARgamma. We propose that menin is an important factor in PPARgamma-mediated adipogenesis and that loss of PPARgamma function may contribute to lipoma development in MEN1 patients.

Regulation of vitamin D receptor function in MEN1-related parathyroid adenomas.

Multiple endocrine neoplasia type 1 (MEN1) is a heriditary syndrome characterised by the occurrence of parathyroid, gastroenteropancreatic and pituitary tumours. The MEN1 gene product, menin, co-activates gene transcription by recruiting histone methyltransferases for lysine 4 of histone H3 (H3K4). We investigated whether in MEN1 tumours global changes in H3K4 trimethylation (H3K4me3) occur or whether alterations in gene expression can be observed. By immunohistochemistry we found that global levels of H3K4me3 are not affected in MEN1-related parathyroid adenomas. Menin can interact directly with the vitamin D receptor (VDR) and enhance the transcriptional activity of VDR. Messenger RNA levels of VDR target genes CYP24 and KLK6 were significantly lower in MEN1 parathyroid adenomas compared to normal tissue. Thus, aberrant gene expression in MEN1 tumours is not caused by lower global H3K4me3, but rather by specific effects on genes that are regulated by menin-interacting proteins, such as VDR.

Selective anchoring of TFIID to nucleosomes by trimethylation of histone H3 lysine 4.

Trimethylation of histone H3 at lysine 4 (H3K4me3) is regarded as a hallmark of active human promoters, but it remains unclear how this posttranslational modification links to transcriptional activation. Using a stable isotope labeling by amino acids in cell culture (SILAC)-based proteomic screening we show that the basal transcription factor TFIID directly binds to the H3K4me3 mark via the plant homeodomain (PHD) finger of TAF3. Selective loss of H3K4me3 reduces transcription from and TFIID binding to a subset of promoters in vivo. Equilibrium binding assays and competition experiments show that the TAF3 PHD finger is highly selective for H3K4me3. In transient assays, TAF3 can act as a transcriptional coactivator in a PHD finger-dependent manner. Interestingly, asymmetric dimethylation of H3R2 selectively inhibits TFIID binding to H3K4me3, whereas acetylation of H3K9 and H3K14 potentiates TFIID interaction. Our experiments reveal crosstalk between histone modifications and the transcription factor TFIID. This has important implications for regulation of RNA polymerase II-mediated transcription in higher eukaryotes.

Polyisoprenylated benzophenone, garcinol, a natural histone acetyltransferase inhibitor, represses chromatin transcription and alters global gene expression.

Histone acetylation is a diagnostic feature of transcriptionally active genes. The proper recruitment and function of histone acetyltransferases (HATs) and deacetylases (HDACs) are key regulatory steps for gene expression and cell cycle. Functional defects of either of these enzymes may lead to several diseases, including cancer. HATs and HDACs thus are potential therapeutic targets. Here we report that garcinol, a polyisoprenylated benzophenone derivative from Garcinia indica fruit rind, is a potent inhibitor of histone acetyltransferases p300 (IC50 approximately 7 microm) and PCAF (IC50 approximately 5 microm) both in vitro and in vivo. The kinetic analysis shows that it is a mixed type of inhibitor with an increased affinity for PCAF compared with p300. HAT activity-dependent chromatin transcription was strongly inhibited by garcinol, whereas transcription from DNA template was not affected. Furthermore, it was found to be a potent inducer of apoptosis, and it alters (predominantly down-regulates) the global gene expression in HeLa cells.

Curcumin, a novel p300/CREB-binding protein-specific inhibitor of acetyltransferase, represses the acetylation of histone/nonhistone proteins and histone acetyltransferase-dependent chromatin transcription.

Acetylation of histones and non-histone proteins is an important post-translational modification involved in the regulation of gene expression in eukaryotes and all viral DNA that integrates into the human genome (e.g. the human immunodeficiency virus). Dysfunction of histone acetyltransferases (HATs) is often associated with the manifestation of several diseases. In this respect, HATs are the new potential targets for the design of therapeutics. In this study, we report that curcumin (diferuloylmethane), a major curcumanoid in the spice turmeric, is a specific inhibitor of the p300/CREB-binding protein (CBP) HAT activity but not of p300/CBP-associated factor, in vitro and in vivo. Furthermore, curcumin could also inhibit the p300-mediated acetylation of p53 in vivo. It specifically represses the p300/CBP HAT activity-dependent transcriptional activation from chromatin but not a DNA template. It is significant that curcumin could inhibit the acetylation of HIV-Tat protein in vitro by p300 as well as proliferation of the virus, as revealed by the repression in syncytia formation upon curcumin treatment in SupT1 cells. Thus, non-toxic curcumin, which targets p300/CBP, may serve as a lead compound in combinatorial HIV therapeutics.