[Show abstract][Hide abstract] ABSTRACT: Improving our understanding of the role of chromatin regulators in the initiation, development, and suppression of cancer and other devastating diseases is critical, as they are integral players in regulating DNA integrity and gene expression. Developing small molecule inhibitors for this target class with cellular activity is a crucial step toward elucidating their specific functions. We specifically targeted the DNA damage response protein, 53BP1, which uses its tandem tudor domain to recognize histone H4 dimethylated on lysine 20 (H4K20me2), a modification induced by double-strand DNA breaks. Through a cross-screening approach we identified UNC2170 (1) as a micromolar ligand of 53BP1, which demonstrates at least 17-fold selectivity for 53BP1 as compared to other methyl-lysine (Kme) binding proteins tested. Structural studies revealed that the tert-butyl amine of UNC2170 anchors the compound in the methyl-lysine (Kme) binding pocket of 53BP1, making it competitive with endogenous Kme substrates. X-ray crystallography also demonstrated that UNC2170 binds at the interface of two tudor domains of a 53BP1 dimer. Importantly, this compound functions as a 53BP1 antagonist in cellular lysates and shows cellular activity by suppressing class switch recombination, a process which requires a functional 53BP1 tudor domain. These results demonstrate that UNC2170 is a functionally active, fragment-like ligand for 53BP1.
ACS Chemical Biology 01/2015; 10(4). DOI:10.1021/cb500956g · 5.36 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: To identify the genetic cause of axonal hereditary motor and sensory neuropathy (HMSN2) with infrequent giant axons.
We studied 11 members of a previously described HMSN2 family with infrequent giant axons and variable cardiomyopathy. Whole-exome sequencing (WES) was performed on 2 affected persons and 1 unaffected person. Sanger sequencing was utilized to confirm the identified novel variant tracking with the affected status. Linkage analysis and haplotype mapping were obtained to confirm the causal nature of the identified variant. Cotransfection of HEK293 cells and co-immunoprecipitation assay were performed to assess the impact of the identified mutant protein in the implicated ubiquitin ligase pathway.
Giant axons with neurofilament accumulations were found in 3 affected persons who had undergone nerve biopsy evaluations. Six novel variants were identified by WES, but only DCAF8 p.R317C tracked with affected status within the family. Linkage and haplotype analysis using microsatellite markers supported this variant as causal. The mutation is within the DCAF8 WD repeat region critical for its binding to DDB1. Functional analysis shows DCAF8 p.R317C reduces the association of DCAF8 and DDB1, which is important in Cul4-ubiquitin E3 function.
Our results indicate that DCAF8 p.R317C mutation is responsible for this specific variety of HMSN2 with infrequent giant axons and mild cardiomyopathy. This mutation results in decreased DDB1-DCAF8 association, leading to an E3 ubiquitin ligase defect that is likely associated with neurofilament degradation.
[Show abstract][Hide abstract] ABSTRACT: The pathogenic sequelae of BRCA1 mutation in human and mouse cells are mitigated by concomitant deletion of 53BP1, which binds histone H4 dimethylated at Lys20 (H4K20me2) to promote nonhomologous end joining, suggesting that a balance between BRCA1 and 53BP1 regulates DNA double strand-break (DSB) repair mechanism choice. Here we document that acetylation is a key determinant of this balance. TIP60 acetyltransferase deficiency reduced BRCA1 at DSB chromatin with commensurate increases in 53BP1, whereas HDAC inhibition yielded the opposite effect. TIP60-dependent H4 acetylation diminished 53BP1 binding to H4K20me2 in part through disruption of a salt bridge between H4K16 and Glu1551 in the 53BP1 Tudor domain. Moreover, TIP60 deficiency impaired homologous recombination and conferred sensitivity to PARP inhibition in a 53BP1-dependent manner. These findings demonstrate that acetylation in cis to H4K20me2 regulates relative BRCA1 and 53BP1 DSB chromatin occupancy to direct DNA repair mechanism.
[Show abstract][Hide abstract] ABSTRACT: BACKGROUND: Mutations in DNA methyltransferase 1 (DNMT1) have been identified in 2 autosomal dominant syndromes: 1) hereditary sensory autonomic neuropathy with dementia and hearing loss (HSAN1E); and 2) cerebellar ataxia, deafness, and narcolepsy. Both syndromes have mutations in targeting sequence (TS) domain (exons 20-21), which is important in mediating DNA substrate binding to the DNMT1 catalytic domain. Frontal lobe hypometabolism has been documented in an HSAN1E family, but memory loss has been the primary cognitive complaint. The chromosomal location of the DNMT1 gene at 19p13.2 has been linked to familial late-onset Alzheimer disease. METHODS: We sequenced 41 exons of DNMT1 and their flanking regions in 1) 2 kindreds with HSAN1E; 2) 48 patients with HSAN1 alone without dementia and hearing loss; and 3) 5 probands of familial frontotemporal dementia (FTD) kindreds. We also sequenced exon 20 and 21 in 364 autopsy-confirmed late-onset Alzheimer disease cases. RESULTS: Mutations in DNMT1 were specific to 2 HSAN1E kindreds with dementia and hearing loss (no narcolepsy). One family carried previously identified mutation Tyr495Cys; the other carried a novel Tyr495His, both in the TS domain. The symptoms of these patients include prominent personality, psychiatric manifestations, and seizures in one and the onset time is later than the previously reported cases. CONCLUSION: Clinicians should consider DNMT1 mutations in patients presenting with FTD or primary memory decline who also have sensory neuropathy and hearing loss. Amino acid Tyr495 is a hot spot for HSAN1E, distinct from exon 21 mutations associated with narcolepsy.
[Show abstract][Hide abstract] ABSTRACT: Downstream regulatory element antagonistic modulator (DREAM/KChIP3), a neuronal EF-hand protein, modulates pain, potassium channel activity and binds presenilin 1. Using affinity capture of neuronal proteins by immobilized DREAM/KChIP3 in the presence and absence of calcium (Ca(2+)), followed by mass spectroscopic identification of interacting proteins, we demonstrate that in the presence of Ca(2+), DREAM/KChIP3 interacts with the EF-hand protein, calmodulin (CaM). The interaction of DREAM/KChIP3 with CaM does not occur in the absence of Ca(2+). In the absence of Ca(2+), DREAM/KChIP3 binds the EF-hand protein, calcineurin subunit-B. Ca(2+)-bound DREAM/KChIP3 binds CaM with a dissociation constant of ≈3 μM as assessed by changes in DREAM/KChIP3 intrinsic protein fluorescence in the presence of CaM. Two-dimensional (1)H-(15)N heteronuclear single quantum coherence spectra reveal changes in chemical shifts and line broadening upon the addition of CaM to (15)N DREAM/KChIP3. The amino-terminal portion of DREAM/KChIP3 is required for its binding to CaM since a construct of DREAM/KChIP3 lacking the first 94 amino terminal residues fails to bind CaM as assessed by fluorescence spectroscopy. The addition of Ca(2+)-bound DREAM/KChIP3 increases the activation of CN by calcium CaM. A DREAM/KChIP3 mutant incapable of binding Ca(2+) also stimulates calmodulin-dependent CN activity. The shortened form of DREAM/KChIP3 lacking the NH(2)-terminal amino acids fails to activate CN in the presence of calcium CaM. Our data demonstrate the interaction of DREAM/KChIP3 with the important EF-hand protein, CaM, and show that the interaction alters CN activity.
[Show abstract][Hide abstract] ABSTRACT: Tyr142, the C-terminal amino acid of histone variant H2A.X is phosphorylated by WSTF (Williams-Beuren syndrome transcription factor), a component of the WICH complex (WSTF-ISWI chromatin-remodeling complex), under basal conditions in the cell. In response to DNA double-strand breaks (DSBs), H2A.X is instantaneously phosphorylated at Ser139 by the kinases ATM and ATR and is progressively dephosphorylated at Tyr142 by the Eya1 and Eya3 tyrosine phosphatases, resulting in a temporal switch from a postulated diphosphorylated (pSer139, pTyr142) to monophosphorylated (pSer139) H2A.X state. How mediator proteins interpret these two signals remains a question of fundamental interest. We provide structural, biochemical, and cellular evidence that Microcephalin (MCPH1), an early DNA damage response protein, can read both modifications via its tandem BRCA1 C-terminal (BRCT) domains, thereby emerging as a versatile sensor of H2A.X phosphorylation marks. We show that MCPH1 recruitment to sites of DNA damage is linked to both states of H2A.X.
Proceedings of the National Academy of Sciences 08/2012; 109(36):14381-6. DOI:10.1073/pnas.1212366109 · 9.81 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: PHF20 is a multidomain protein and subunit of a lysine acetyltransferase complex that acetylates histone H4 and p53 but whose function is unclear. Using biochemical, biophysical and cellular approaches, we determined that PHF20 is a direct regulator of p53. A Tudor domain in PHF20 recognized p53 dimethylated at Lys370 or Lys382 and a homodimeric form of this Tudor domain could associate with the two dimethylated sites on p53 with enhanced affinity, indicating a multivalent interaction. Association with PHF20 promotes stabilization and activation of p53 by diminishing Mdm2-mediated p53 ubiquitylation and degradation. PHF20 contributes to upregulation of p53 in response to DNA damage, and ectopic expression of PHF20 in different cell lines leads to phenotypic changes that are hallmarks of p53 activation. Overall our work establishes that PHF20 functions as an effector of p53 methylation that stabilizes and activates p53.
[Show abstract][Hide abstract] ABSTRACT: The LOTUS or OST-HTH domain is a recently discovered motif of about 80 amino acids and is found in several germline-specific proteins including the Tudor domain-containing proteins TDRD5 and TDRD7, which are important for germ cell development. The LOTUS domain is an RNA binding domain but its exact function is unknown. Here, we report the 1H, 13C and 15N resonance assignments for the three LOTUS domains present in mouse TDRD7. These assignments will allow three-dimensional structure determination of the LOTUS domains and mapping of their interaction with RNA, steps toward deciphering the function of TDRD7.
[Show abstract][Hide abstract] ABSTRACT: Dynamic variations in the structure of chromatin influence virtually all DNA-related processes in eukaryotes and are controlled in part by post-translational modifications of histones. One such modification, the acetylation of lysine 56 (H3K56ac) in the amino-terminal α-helix (αN) of histone H3, has been implicated in the regulation of nucleosome assembly during DNA replication and repair, and nucleosome disassembly during gene transcription. In Saccharomyces cerevisiae, the histone chaperone Rtt106 contributes to the deposition of newly synthesized H3K56ac-carrying H3-H4 complex on replicating DNA, but it is unclear how Rtt106 binds H3-H4 and specifically recognizes H3K56ac as there is no apparent acetylated lysine reader domain in Rtt106. Here, we show that two domains of Rtt106 are involved in a combinatorial recognition of H3-H4. An N-terminal domain homodimerizes and interacts with H3-H4 independently of acetylation while a double pleckstrin-homology (PH) domain binds the K56-containing region of H3. Affinity is markedly enhanced upon acetylation of K56, an effect that is probably due to increased conformational entropy of the αN helix of H3. Our data support a mode of interaction where the N-terminal homodimeric domain of Rtt106 intercalates between the two H3-H4 components of the (H3-H4)(2) tetramer while two double PH domains in the Rtt106 dimer interact with each of the two H3K56ac sites in (H3-H4)(2). We show that the Rtt106-(H3-H4)(2) interaction is important for gene silencing and the DNA damage response.
[Show abstract][Hide abstract] ABSTRACT: In response to DNA damage, cells initiate complex signalling cascades leading to growth arrest and DNA repair. The recruitment of 53BP1 to damaged sites requires the activation of the ubiquitination cascade controlled by the E3 ubiquitin ligases RNF8 and RNF168, and methylation of histone H4 on lysine 20. However, molecular events that regulate the accessibility of methylated histones, to allow the recruitment of 53BP1 to DNA breaks, are unclear. Here, we show that like 53BP1, the JMJD2A (also known as KDM4A) tandem tudor domain binds dimethylated histone H4K20; however, JMJD2A is degraded by the proteasome following the DNA damage in an RNF8-dependent manner. We demonstrate that JMJD2A is ubiquitinated by RNF8 and RNF168. Moreover, ectopic expression of JMJD2A abrogates 53BP1 recruitment to DNA damage sites, indicating a role in antagonizing 53BP1 for methylated histone marks. The combined knockdown of JMJD2A and JMJD2B significantly rescued the ability of RNF8- and RNF168-deficient cells to form 53BP1 foci. We propose that the RNF8-dependent degradation of JMJD2A regulates DNA repair by controlling the recruitment of 53BP1 at DNA damage sites.
The EMBO Journal 02/2012; 31(8):1865-78. DOI:10.1038/emboj.2012.47 · 10.75 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The yeast histone chaperone Rtt106 is involved in de novo assembly of newly synthesized histones into nucleosomes during DNA replication and plays a role in regulating heterochromatin silencing and maintaining genomic integrity. The interaction of Rtt106 with H3-H4 is modulated by acetylation of H3 lysine 56 catalyzed by the lysine acetyltransferase Rtt109. Using affinity purification strategies, we demonstrate that Rtt106 interacts with (H3-H4)(2) heterotetramers in vivo. In addition, we show that Rtt106 undergoes homo-oligomerization in vivo and in vitro, and mutations in the N-terminal homodimeric domain of Rtt106 that affect formation of Rtt106 oligomers compromise the function of Rtt106 in transcriptional silencing and response to genotoxic stress and the ability of Rtt106 to bind (H3-H4)(2). These results indicate that Rtt106 deposits H3-H4 heterotetramers onto DNA and provide the first description of a H3-H4 chaperone binding to (H3-H4)(2) heterotetramers in vivo.
[Show abstract][Hide abstract] ABSTRACT: Microcephalin (MCPH1), the first gene identified as causative for primary recessive autosomal microcephaly, is aberrantly expressed in autism-like disorders and human malignancy of breast and ovarian origin. MCPH1, the encoded protein product, has been implicated in various cellular processes including the DNA damage checkpoint, DNA repair, and transcription. Although our understanding of the cellular context in which MCPH1 operates continues to develop, a structural understanding of the C-terminal tandem BRCT domains of MCPH1 remains unexplored. Here, we identify cell division cycle protein 27 (Cdc27), a component of the anaphase-promoting complex (APC/C), as a novel interacting partner of MCPH1. We provide in vitro and in vivo evidence that the C-terminal tandem BRCT domains of MCPH1 (C-BRCTs) bind Cdc27 in a phosphorylation-dependent manner. To characterize this interaction further, we determined the structure of MCPH1 C-BRCTs in complex with a phosphorylated Cdc27 peptide (pCdc27) using x-ray crystallography. Based on this structure, we identified single amino acid mutations targeted at the binding interface that disrupted the MCPH1-pCdc27 interaction. Collectively, our data define the biochemical, structural, and cellular determinants of the novel interaction between MCPH1 and Cdc27 and suggest that this interaction may occur within the larger context of MCPH1-APC/C.
[Show abstract][Hide abstract] ABSTRACT: The SAGA (Spt-Ada-Gcn5 acetyltransferase) complex is an important chromatin modifying complex that can both acetylate and deubiquitinate histones. Sgf29 is a novel component of the SAGA complex. Here, we report the crystal structures of the tandem Tudor domains of Saccharomyces cerevisiae and human Sgf29 and their complexes with H3K4me2 and H3K4me3 peptides, respectively, and show that Sgf29 selectively binds H3K4me2/3 marks. Our crystal structures reveal that Sgf29 harbours unique tandem Tudor domains in its C-terminus. The tandem Tudor domains in Sgf29 tightly pack against each other face-to-face with each Tudor domain harbouring a negatively charged pocket accommodating the first residue alanine and methylated K4 residue of histone H3, respectively. The H3A1 and K4me3 binding pockets and the limited binding cleft length between these two binding pockets are the structural determinants in conferring the ability of Sgf29 to selectively recognize H3K4me2/3. Our in vitro and in vivo functional assays show that Sgf29 recognizes methylated H3K4 to recruit the SAGA complex to its targets sites and mediates histone H3 acetylation, underscoring the importance of Sgf29 in gene regulation.
The EMBO Journal 06/2011; 30(14):2829-42. DOI:10.1038/emboj.2011.193 · 10.75 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: DNA methyltransferase 1 (DNMT1) is crucial for maintenance of methylation, gene regulation and chromatin stability. DNA mismatch repair, cell cycle regulation in post-mitotic neurons and neurogenesis are influenced by DNA methylation. Here we show that mutations in DNMT1 cause both central and peripheral neurodegeneration in one form of hereditary sensory and autonomic neuropathy with dementia and hearing loss. Exome sequencing led to the identification of DNMT1 mutation c.1484A>G (p.Tyr495Cys) in two American kindreds and one Japanese kindred and a triple nucleotide change, c.1470-1472TCC>ATA (p.Asp490Glu-Pro491Tyr), in one European kindred. All mutations are within the targeting-sequence domain of DNMT1. These mutations cause premature degradation of mutant proteins, reduced methyltransferase activity and impaired heterochromatin binding during the G2 cell cycle phase leading to global hypomethylation and site-specific hypermethylation. Our study shows that DNMT1 mutations cause the aberrant methylation implicated in complex pathogenesis. The discovered DNMT1 mutations provide a new framework for the study of neurodegenerative diseases.
[Show abstract][Hide abstract] ABSTRACT: The histone chaperone Vps75 presents the remarkable property of stimulating the Rtt109-dependent acetylation of several histone H3 lysine residues within (H3-H4)(2) tetramers. To investigate this activation mechanism, we determined x-ray structures of full-length Vps75 in complex with full-length Rtt109 in two crystal forms. Both structures show similar asymmetric assemblies of a Vps75 dimer bound to an Rtt109 monomer. In the Vps75-Rtt109 complexes, the catalytic site of Rtt109 is confined to an enclosed space that can accommodate the N-terminal tail of histone H3 in (H3-H4)(2). Investigation of Vps75-Rtt109-(H3-H4)(2) and Vps75-(H3-H4)(2) complexes by NMR spectroscopy-probed hydrogen/deuterium exchange suggests that Vps75 guides histone H3 in the catalytic enclosure. These findings clarify the basis for the enhanced acetylation of histone H3 tail residues by Vps75-Rtt109.
[Show abstract][Hide abstract] ABSTRACT: Cells have evolved mutagenic bypass mechanisms that prevent stalling of the replication machinery at DNA lesions. This process, translesion DNA synthesis (TLS), involves switching from high-fidelity DNA polymerases to specialized DNA polymerases that replicate through a variety of DNA lesions. In eukaryotes, polymerase switching during TLS is regulated by the DNA damage-triggered monoubiquitylation of PCNA. How the switch operates is unknown, but all TLS polymerases of the so-called Y-family possess PCNA and ubiquitin-binding domains that are important for their function. To gain insight into the structural mechanisms underlying the regulation of TLS by ubiquitylation, we have probed the interaction of ubiquitin with a conserved ubiquitin-binding motif (UBM2) of Y-family polymerase Polι. Using NMR spectroscopy, we have determined the structure of a complex of human Polι UBM2 and ubiquitin, revealing a novel ubiquitin recognition fold consisting of two α-helices separated by a central trans-proline residue conserved in all UBMs. We show that, different from the majority of ubiquitin complexes characterized to date, ubiquitin residue Ile44 only plays a modest role in the association of ubiquitin with Polι UBM2. Instead, binding of UBM2 is centered on the recognition of Leu8 in ubiquitin, which is essential for the interaction.