Cytosine residues in mammalian DNA occur in at least three forms, cytosine (C), 5-methylcytosine (M; 5mC) and 5-hydroxymethylcytosine (H; 5hmC). During semi-conservative DNA replication, hemi-methylated (M/C) and hemi-hydroxymethylated (H/C) CpG dinucleotides are transiently generated, where only the parental strand is modified and the daughter strand contains native cytosine. Here, we explore the role of DNA methyltransferases (DNMT) and ten eleven translocation (Tet) proteins in perpetuating these states after replication, and the molecular basis of their recognition by methyl-CpG-binding domain (MBD) proteins. Using recombinant proteins and modified double-stranded deoxyoligonucleotides, we show that DNMT1 prefers a hemi-methylated (M/C) substrate (by a factor of >60) over hemi-hydroxymethylated (H/C) and unmodified (C/C) sites, whereas both DNMT3A and DNMT3B have approximately equal activity on all three substrates (C/C, M/C and H/C). Binding of MBD proteins to methylated DNA inhibited Tet1 activity, suggesting that MBD binding may also play a role in regulating the levels of 5hmC. All five MBD proteins generally have reduced binding affinity for 5hmC relative to 5mC in the fully modified context (H/M versus M/M), though their relative abilities to distinguish the two varied considerably. We further show that the deamination product of 5hmC could be excised by thymine DNA glycosylase and MBD4 glycosylases regardless of context.

We present the crystal structure of the catalytic SET domain of G9a-like protein (GLP) in complex with BIX-01294. The inhibitor is bound in the substrate peptide groove at the location where the histone H3 residues (Lys4 to Arg8) N-terminal to the target lysine would occupy. The inhibitor is positioned in place by residues specific for G9a and GLP using planar stacking contacts, polar hydrogen bonds and van der Waals interactions.

Protein lysine methylation signaling is implicated in diverse biological and disease processes. Yet the catalytic activity and substrate specificity are unknown for many human protein lysine methyltransferases (PKMTs). We screened over forty candidate PKMTs and identified SETD6 as a methyltransferase that monomethylates chromatin-associated NF-κB RelA at lysine 310 (RelAK310me1). SETD6-mediated methylation rendered RelA inert and attenuated RelA-driven transcriptional programs, including inflammatory responses in primary immune cells. RelAK310me1 was recognized by the ankryin repeat of GLP, which under basal conditions, promoted a repressed chromatin state at RelA target genes through GLP-mediated H3K9 methylation. NF-κB activation-linked phosphorylation of RelA by PKCζ at serine 311 blocked GLP binding to RelAK310me1 and relieved target gene repression. Our findings establish a new mechanism by which chromatin signaling regulates inflammation programs.

The protein lysine methyltransferase SET7 regulates DNA methyltransferase-1 (DNMT1) activity in mammalian cells by promoting degradation of DNMT1 and thus allows epigenetic changes via DNA demethylation. Here we reveal an interplay between monomethylation of DNMT1 Lys142 by SET7 and phosphorylation of DNMT1 Ser143 by AKT1 kinase. These two modifications are mutually exclusive, and structural analysis suggests that Ser143 phosphorylation interferes with Lys142 monomethylation. AKT1 kinase colocalizes and directly interacts with DNMT1 and phosphorylates Ser143. Phosphorylated DNMT1 peaks during DNA synthesis, before DNMT1 methylation. Depletion of AKT1 or overexpression of dominant-negative AKT1 increases methylated DNMT1, resulting in a decrease in DNMT1 abundance. In mammalian cells, phosphorylated DNMT1 is more stable than methylated DNMT1. These results reveal cross-talk on DNMT1, through modifications mediated by AKT1 and SET7, that affects cellular DNMT1 levels.Multiple interdependent post-translational modifications of cellular proteins allow for combinatorial repertoires of interactions. Some of these modifications, including acetylation, phosphorylation, methylation and sumoylation, might participate in cross-talk for dynamic control of cellular signaling under various physiological conditions 1 . Protein phosphorylation is involved in various cellular processes, including cell growth, development and apoptosis, and regulates essential physiological systems, such as the period of the circadian rhythm within mammalian cells, via cellular signaling pathways 2 . Protein methylation, especially on lysines, is another important reversible post-translational modification of cellular proteins; for example, histone methylation is involved in the © 2011 Nature America, Inc. All rights reserved.Correspondence should be addressed to S.P. (pradhan@neb.com). Accession codes. Protein Data Bank: The coordinates and structure factors of the SET7-DNMT1 peptide complex have been deposited with accession code 3OS5.Note: Supplementary information is available on the Nature Structural & Molecular Biology website.AUTHOR CONT RIBUTIONS P.-O.E. performed cell biology and biochemistry experiments. M.S. made constructs, tested kinetics and performed the pull-down assay. G.R.F. performed quantitative PCR. Y.C. performed SET7 purifications, MS-based methylation assays on DNMT1 peptide, mutagenesis of K142R and crystallization of SET7-DNMT1 peptide. A.K.U. purified the DNMT1 N-terminal domain and performed MS-based methylation assays on this fragment. J.R.H. performed crystallographic experiments. X.C. and S.P. organized and analyzed data and wrote the manuscript. COMPETING FINANCIAL INT ERESTSThe authors declare no competing financial interests.Reprints and permissions information is available online at http://npg.nature.com/reprintsandpermissions/. Previously, we have demonstrated that methylation of Lys142 on DNMT1 leads to DNMT1 degradation15. Adjacent to Lys142 is Ser143, a known phosphorylation site 16 . Therefore, we s...

Calcium homeostasis balances passive calcium leak and active calcium uptake. Human Bax inhibitor 1 (hBI-1) is an anti-apoptotic protein that mediates a calcium leak and is representative of highly conserved and widely distributed family, the transmembrane Bax inhibitor motif (TMBIM) proteins. Here we present crystal structures of a bacterial homolog and characterize its calcium leak activity. The structure has a seven-transmembrane-helix fold that features two triple-helix sandwiches wrapped around a central C-terminal helix. Structures obtained in closed and open conformations are reversibly inter-convertible by change of pH. A hydrogen-bonded, pKa-perturbed pair of conserved aspartate residues explains the pH dependence of this equilibrium, and biochemical studies show that pH regulates calcium influx in proteoliposomes. Homology models for hBI-1 provide insights into TMBIM-mediated calcium leak and cytoprotective activity.

Dynamic histone lysine methylation involves the activities of modifying enzymes (writers), enzymes removing modifications (erasers) and readers of the histone code. One common feature of these activities is the recognition of lysines in methylated and unmethylated states, whether they are substrates, reaction products or binding partners. We applied the concept of adding a lysine mimic to an established inhibitor (BIX-01294) of histone H3 lysine 9 methyltransferases G9a and G9a-like protein (GLP) by including a 5-aminopentyloxy moiety, which is inserted into the target lysinebinding channel and becomes methylated by GLP, albeit slowly. The compound enhanced its potency in vitro and reduced cell toxicity in vivo. We suggest that adding a lysine or methyllysine mimic should be considered in the design of small molecule inhibitors for other methyl-lysine writers, erasers and readers. Author Contributions Y.C. performed SET-domain enzyme purifications, mass spectrometry-based inhibition assays, ITC measurements, crystallization, and participated in X-ray data collection; T.G. performed compound design, chemical synthesis, and wrote the method of chemical synthesis; A.K.U. performed Jumonji demethylation assays; J.R.H. collected X-ray data, determined structures and performed structural refinements; A.S. and M.T.B. performed Fas reactivation; J.L. performed Glide docking and contributed to compound design; A.S. assisted with compound design; X.Z developed and optimized mass spectrometry-based assay; Y.S. performed cell toxicity assay; J.P.S. coordinated synthesis and modeling activities, contributed to compound design, and wrote method of molecular modeling and legend of supplementary figure S6; X.C. organized and designed the scope of the study, participated in designing compounds with T.G., and wrote the manuscript; all were involved in analyzing data and helped in revising the manuscript. PDB accession numbersThe coordinates and structure factor for human GLP catalytic domain bound with E72, E67, and E11, respectively, and AdoHcy have been deposited with accession numbers3MO5, 3MO2, and 3MO0.

DNA CpG methylation and histone H3 lysine 9 (H3K9) methylation are two major repressive epigenetic modifications, and these methylations are positively correlated with one another in chromatin. Here we show that G9a or G9a-like protein (GLP) dimethylate the amino-terminal lysine 44 (K44) of mouse Dnmt3a (equivalent to K47 of human DNMT3A) in vitro and in cells overexpressing G9a or GLP. The chromodomain of MPP8 recognizes the dimethylated Dnmt3aK44me2. MPP8 also interacts with self-methylated GLP in a methylation-dependent manner. The MPP8 chromodomain forms a dimer in solution and in crystals, suggesting that a dimeric MPP8 molecule could bridge the methylated Dnmt3a and GLP, resulting in a silencing complex of Dnmt3a–MPP8–GLP/G9a on chromatin templates. Together, these findings provide a molecular explanation, at least in part, for the co-occurrence of DNA methylation and H3K9 methylation in chromatin.

DNA methyltransferases (DNMTs) are important enzymes involved in epigenetic control of gene expression and represent valuable targets in cancer chemotherapy. A number of nucleoside DNMT inhibitors (DNMTi) have been studied in cancer, including in cancer stem cells, and two of them (azacytidine and decitabine) have been approved for treatment of myelodysplastic syndromes. However, only a few non-nucleoside DNMTi have been identified so far, and even fewer have been validated in cancer. Through a process of hit-to-lead optimization, we report here the discovery of compound 5 as a potent non-nucleoside DNMTi that is also selective toward other AdoMet-dependent protein methyltransferases. Compound 5 was potent at single-digit micromolar concentrations against a panel of cancer cells and was less toxic in peripheral blood mononuclear cells than two other compounds tested. In mouse medulloblastoma stem cells, 5 inhibited cell growth, whereas related compound 2 showed high cell differentiation. To the best of our knowledge, 2 and 5 are the first non-nucleoside DNMTi tested in a cancer stem cell line.