Both DNA methylation and post-translational histone modifications contribute to gene silencing, but the mechanistic relationship between these epigenetic marks is unclear. Mutations in two Arabidopsis genes, the KRYPTONITE (KYP) histone H3 lysine 9 (H3K9) methyltransferase and the CHROMOMETHYLASE3 (CMT3) DNA methyltransferase, cause a reduction of CNG DNA methylation, suggesting that H3K9 methylation controls CNG DNA methylation. Here we show that the chromodomain of CMT3 can directly interact with the N-terminal tail of histone H3, but only when it is simultaneously methylated at both the H3K9 and H3K27 positions. Furthermore, using chromatin immunoprecipitation analysis and immunohistolocalization experiments, we found that H3K27 methylation colocalizes with H3K9 methylation at CMT3-controlled loci. The H3K27 methylation present at heterochromatin was not affected by mutations in KYP or in several Arabidopsis PcG related genes including the Enhancer of Zeste homologs, suggesting that a novel pathway controls heterochromatic H3K27 methylation. Our results suggest a model in which H3K9 methylation by KYP, and H3K27 methylation by an unknown enzyme provide a combinatorial histone code for the recruitment of CMT3 to silent loci.

Posttranslational modifications of histones such as methylation, acetylation, and phosphorylation regulate chromatin structure and gene expression. Here we show that protein kinase C-related kinase 1 (PRK1) phosphorylates histone H3 at threonine 11 (H3T11) upon ligand-dependent recruitment to androgen receptor (AR) target genes. PRK1 is pivotal to AR function since PRK1 knockdown or inhibition impedes AR-dependent transcription. Blocking PRK1 function abrogates androgen-induced H3T11 phosphorylation, and inhibits androgen-induced demethylation of histone H3. Moreover, serine 5-phosphorylated RNA polymerase II is no longer observed at AR target promoters. Phosphorylation of H3T11 by PRK1 accelerates demethylation by the Jumonji C (JmjC) domain-containing protein JMJD2C. Thus, phosphorylation of H3T11 by PRK1 establishes a novel chromatin mark for gene activation, identifying PRK1 as a gatekeeper of ARdependent transcription. Importantly, levels of PRK1 and phosphorylated H3T11 correlate with Gleason scores of prostate carcinomas. Finally, inhibition of PRK1 blocks AR-induced tumour cell proliferation, making PRK1 a promising therapeutic target. Keywords PRK1; androgen receptor; histone phosphorylation; prostate cancerThe N-terminal tails of histones are subject to a plethora of posttranslational modifications such as methylation, acetylation, and phosphorylation by specific chromatin-modifying enzymes1. During gene expression, these modifications influence chromatin structure to facilitate the assembly of the RNA polymerase II transcription machinery1 , 2. Androgen receptor (AR)-dependent gene expression is characterized by changes in chromatin

Summary Haspin phosphorylates histone H3 at Thr-3 (H3T3ph) during mitosis [1, 2], providing a chromatin binding site for the chromosomal passenger complex (CPC) at centromeres to regulate chromosome segregation [3–5]. H3T3ph becomes increasingly focused at inner centromeres during prometaphase [1, 2], but little is known about how its level or location and the consequent chromosomal localization of the CPC are regulated. In addition, CPC binding to Shugoshin proteins contributes to centromeric Aurora B localization [5, 6]. Recruitment of the Shugoshins to centromeres requires the phosphorylation of Histone H2A at T120 (H2AT120ph) by the kinetochore kinase Bub1 [7], but the molecular basis for the collaboration of this pathway with H3T3ph has been unclear. Here, we show that Aurora B phosphorylates Haspin to promote generation of H3T3ph, and that Aurora B kinase activity is required for normal chromosomal localization of the CPC, indicating an intimate linkage between Aurora B and Haspin functions in mitosis. We propose that Aurora B activity triggers a CPC-Haspin-H3T3ph feedback loop that promotes generation of H3T3ph on chromatin. We also provide evidence that the Bub1-Shugoshin-CPC pathway supplies a signal that boosts the CPC-Haspin-H3T3ph feedback loop specifically at centromeres to produce the well-known accumulation of the CPC in these regions.

The protein kinase haspin/Gsg2 plays an important role in mitosis, where it specifically phosphorylates Thr-3 in histone H3 (H3T3). Its protein sequence is only weakly homologous to other protein kinases and lacks the highly conserved motifs normally required for kinase activity. Here we report structures of human haspin in complex with ATP and the inhibitor iodotubercidin. These structures reveal a constitutively active kinase conformation, stabilized by haspin-specific inserts. Haspin also has a highly atypical activation segment well adapted for specific recognition of the basic histone tail. Despite the lack of a DFG motif, ATP binding to haspin is similar to that in classical kinases; however, the ATP ␥-phosphate forms hydrogen bonds with the conserved catalytic loop residues Asp-649 and His-651, and a His651Ala haspin mutant is inactive, suggesting a direct role for the catalytic loop in ATP recognition. Enzyme kinetic data show that haspin phosphorylates substrate peptides through a rapid equilibrium random mechanism. A detailed analysis of histone modifications in the neighborhood of H3T3 reveals that increasing methylation at Lys-4 (H3K4) strongly decreases substrate recognition, suggesting a key role of H3K4 methylation in the regulation of haspin activity.ATP binding ͉ histone modification ͉ phosphorylation mechanism ͉ germ cell-specific gene 2 (Gsg2) ͉ mitosis E ukaryotic protein kinases (ePKs) constitute a large group of enzymes that regulate a vast diversity of cellular processes. Kinase activity depends on a number of highly conserved sequence motifs required for ATP/Mg 2ϩ binding and catalysis. About 10% of human ePKs lack one or more essential catalytic motifs and have been initially classified as inactive pseudokinases (1). However, a number of such proteins are active kinases, including haspin [haploid germ cell-specific nuclear protein kinase, encoded by Germ cell-specific gene 2 (Gsg2)]. Haspin lacks both the conserved ATP/Mg 2ϩ binding motif Asp-Phe-Gly (DFG), which is replaced by Asp-Tyr-Thr (DYT), and the Ala-Pro-Glu (APE) motif usually found at the C terminus of the activation segment (2). In addition, haspin shares only weak sequence homology with ePKs and contains a highly divergent kinase domain with several unique inserts (2, 3). Haspin mRNA is abundant in testis and also present in somatic cells (4, 5), and orthologues are found throughout eukaryotic phyla (2). Ectopically expressed haspin localizes to the nucleus in interphase and to the chromosomes in mitosis (4, 6), while depletion of haspin leads to premature chromatid separation, failure of chromosome alignment, and a block in mitosis in a prometaphase-like state (6, 7).Haspin autophosphorylates in vitro (4, 6, 8) and phosphorylates its only currently known substrate, histone H3, at threonine-3 (H3T3ph) both in vitro and in cells (6). H3T3 phosphorylation occurs specifically during mitosis and is particularly prominent at inner centromere regions (6, 7, 9). Recently, H3T3ph has been suggested to relieve an inhibitory effect of ...

Tauopathies are neurodegenerative diseases characterized by aberrant forms of tau protein accumulation leading to neuronal death in focal brain areas. Positron emission tomography (PET) tracers that bind to pathological tau are used in diagnosis, but there are no current therapies to eliminate these tau species. We employed targeted protein degradation technology to convert a tau PET-probe into a functional degrader of pathogenic tau. The hetero-bifunctional molecule QC-01–175 was designed to engage both tau and Cereblon (CRBN), a substrate-receptor for the E3-ubiquitin ligase CRL4CRBN, to trigger tau ubiquitination and proteasomal degradation. QC-01–175 effected clearance of tau in frontotemporal dementia (FTD) patient-derived neuronal cell models, with minimal effect on tau from neurons of healthy controls, indicating specificity for disease-relevant forms. QC-01–175 also rescued stress vulnerability in FTD neurons, phenocopying CRISPR-mediated MAPT-knockout. This work demonstrates that aberrant tau in FTD patient-derived neurons is amenable to targeted degradation, representing an important advance for therapeutics.

Lysine-specific murine histone H3 methyltransferase, G9a, was expressed and purified in a baculovirus expression system. The primary structure of the recombinant enzyme is identical to the native enzyme. Enzymatic activity was favorable at alkaline conditions (>pH 8) and low salt concentration and virtually unchanged between 25 and 42°C. Purified G9a was used for substrate specificity and steady-state kinetic analysis with peptides representing un-or dimethylated lysine 9 histone H3 tails with native lysine 4 or with lysine 4 changed to alanine (K4AK9). In vitro methylation of the H3 tail peptide resulted in trimethylation of Lys-9 and the reaction is processive. The turnover number (k cat ) for methylation was 88 and 32 h ؊1 on the wild type and K4AK9 histone H3 tail, respectively. The Michaelis constants for wild type and K4AK9 (K m pep ) were 0.9 and 1.0 M and for S-adenosyl-L-methionine (K m AdoMet ) were 1.8 and 0.6 M, respectively. Comparable kinetic constants were obtained for recombinant histone H3. The conversion of K4AK9 di-to trimethyl-lysine was 7-fold slower than methyl group addition to unmethylated peptide. Preincubation studies showed that G9a-AdoMet and G9a-peptide complexes are catalytically active. Initial velocity data with peptide and S-adenosyl-L-methionine (AdoMet) and product inhibition studies with S-adenosyl-L-homocysteine were performed to assess the kinetic mechanism of the reaction. Double reciprocal plots and preincubation studies revealed S-adenosyl-L-homocysteine as a competitive inhibitor to AdoMet and mixed inhibitor to peptide. Trimethylated peptides acted as a competitive inhibitor to substrate peptide and mixed inhibitor to AdoMet suggesting a random mechanism in a Bi Bi reaction for recombinant G9a where either substrate can bind first to the enzyme, and either product can release first.Histones participate in packaging of eukaryotic DNA. Amino-terminal tails of histones are exposed in packed chromatin and are thus amenable to various post-translational modifications. Histone H3 methylation in mammals is implicated in epigenetic gene regulation (1). Other post-translational modifications namely, acetylation and phosphorylation of histone H3 and H4 N-terminal tails are also documented (2, 3). Histone tail modifications are involved in transcriptional activation or repression of chromatin. Generally, acetylated histones mark transcriptionally active chromatin and hypoacetylated chromatin are silent. Furthermore, histone methylation can be a marker for transcriptionally active or inactive segments of the genome (4). Methylation of histone H3 lysine 9 (H3-K9) is a hallmark of silent chromatin and is globally distributed throughout the heterochromatic regions, such as centromeres and telomeres (5). In the inactivated X chromosome of mammals (6) and transcriptionally silent genes in cancer cells frequent H3-K9 methylation is observed (7).Links between histone methylation and DNA methylation are emerging and have been demonstrated in Neurospora crassa and in plants. Experimental ev...

Haspin inhibitors reveal that Aurora B at centromeres is required for metaphase chromosome alignment and spindle checkpoint signaling.

Methylation of lysine residues on histones participates in transcriptional gene regulation. Lysine 9 methylation of histone H3 is a transcriptional repression signal, mediated by a family of SET domain containing AdoMet-dependent enzymes. G9a methyltransferase is a euchromatic histone H3 lysine 9 methyltransferase. Here, G9a is shown to methylate other cellular proteins, apart from histone H3, including automethylation of K239 residue. Automethylation of G9a did not impair or activate the enzymatic activity in vitro. The automethylation motif of G9a flanking target K239 (ARKT) has similarity with histone H3 lysine 9 regions (ARKS), and is identical to amino acids residues in EuHMT (ARKT) and mAM (ARKT). Under steady-state kinetic assay conditions, full-length G9a methylates peptides representing ARKS/T motif of H3, G9a, mAM and EuHMT efficiently. Automethylation of G9a at ARKT motif creates a binding site for HP1 class of protein and mutation of lysine in the motif impairs this binding. In COS-7 cells GFP fusion of the wild-type G9a co-localized with HP1α and HP1γ isoforms whereas the G9a mutant with K239A displayed poor co-localization. Thus, apart from transcriptional repression and regulatory roles of lysine methylation, the non-histone protein methylation may create binding sites for cellular protein–protein interactions.