RESUMO
Histone H3 arginine 2 (H3R2) is post-translationally modified in three different states by "writers" of the protein arginine methyltransferase (PRMT) family. H3R2 methylarginine isoforms include PRMT5-catalyzed monomethylation (me1) and symmetric dimethylation (me2s) and PRMT6-catalyzed me1 and asymmetric dimethylation (me2a). WD-40 repeat-containing protein 5 (WDR5) is an epigenetic "reader" protein that interacts with H3R2. Previous studies suggested that H3R2me2s specified a high-affinity interaction with WDR5. However, our prior biological data prompted the hypothesis that WDR5 may also interact with H3R2me1. Here, using highly accurate quantitative binding analysis combined with high-resolution crystal structures of WDR5 in complex with unmodified (me0) and me1/me2s l-arginine amino acids and in complex with the H3R2me1 peptide, we provide a rigorous biochemical study and address long-standing discrepancies of this important biological interaction. Despite modest structural differences at the binding interface, our study supports an interaction model regulated by a binary arginine methylation switch: H3R2me2a prevents interaction with WDR5, whereas H3R2me0, -me1, and -me2s are equally permissive.
Assuntos
Arginina/metabolismo , Histonas/metabolismo , Peptídeos e Proteínas de Sinalização Intracelular/metabolismo , Arginina/análise , Cristalografia por Raios X , Histonas/química , Humanos , Peptídeos e Proteínas de Sinalização Intracelular/química , Metilação , Modelos Moleculares , Ligação Proteica , Conformação Proteica , Mapas de Interação de ProteínasRESUMO
Protein post-translational modifications (PTMs) have long been a topic of intensive investigation. Covalent additions to the 20 genetically encoded amino acids can alter protein interactions and can even change enzymatic function. In eukarya, PTMs can amplify both the complexity and functional paradigms of the cellular environment. Therefore, PTMs have been of substantial research interest, both for understanding fundamental mechanisms and to provide insight into drug design. Indeed, targeting proteins involved in writing, reading, and erasing PTMs important for human pathologies are some of the most fruitful avenues of drug discovery. In this multi-author review, we explore exciting new work on lysine and arginine methylation, molecular and structural understanding of some of the lysine and arginine methyltransferases (KMTs and PRMTs, respectively), novel insights into nucleic acid methylation, and how the enzymes responsible for writing these PTMs and readers responsible for recognizing these PTMs could be drugged. Here, we introduce the background and the topics covered in this issue.
Assuntos
Processamento de Proteína Pós-Traducional , Arginina/metabolismo , Histona-Lisina N-Metiltransferase/metabolismo , Histonas/metabolismo , Humanos , Lisina/metabolismo , Metilação , Proteína-Arginina N-Metiltransferases/metabolismoRESUMO
Arginine methylation is a ubiquitous post-translational modification. Three predominant types of arginine-guanidino methylation occur in Eukarya: mono (Rme1/MMA), symmetric (Rme2s/SDMA), and asymmetric (Rme2a/ADMA). Arginine methylation frequently occurs at sites of protein-protein and protein-nucleic acid interactions, providing specificity for binding partners and stabilization of important biological interactions in diverse cellular processes. Each methylarginine isoform-catalyzed by members of the protein arginine methyltransferase family, Type I (PRMT1-4,6,8) and Type II (PRMT5,9)-has unique downstream consequences. Methylarginines are found in ordered domains, domains of low complexity, and in intrinsically disordered regions of proteins-the latter two of which are intimately connected with biological liquid-liquid phase separation. This review highlights discoveries illuminating how arginine methylation affects genome integrity, gene transcription, mRNA splicing and mRNP biology, protein translation and stability, and phase separation. As more proteins and processes are found to be regulated by arginine methylation, its importance for understanding cellular physiology will continue to grow.
Assuntos
Arginina/metabolismo , Proteína-Arginina N-Metiltransferases/metabolismo , Actinas/metabolismo , Cromatina/metabolismo , Reparo do DNA , Histonas/metabolismo , Humanos , Metilação , Splicing de RNA , Ribonucleoproteínas/metabolismoRESUMO
The protein arginine methyltransferase PRMT5 is complexed with the WD repeat protein MEP50 (also known as Wdr77 or androgen coactivator p44) in vertebrates in a tetramer of heterodimers. MEP50 is hypothesized to be required for protein substrate recruitment to the catalytic domain of PRMT5. Here we demonstrate that the cross-dimer MEP50 is paired with its cognate PRMT5 molecule to promote histone methylation. We employed qualitative methylation assays and a novel ultrasensitive continuous assay to measure enzyme kinetics. We demonstrate that neither full-length human PRMT5 nor the Xenopus laevis PRMT5 catalytic domain has appreciable protein methyltransferase activity. We show that histones H4 and H3 bind PRMT5-MEP50 more efficiently compared with histone H2A(1-20) and H4(1-20) peptides. Histone binding is mediated through histone fold interactions as determined by competition experiments and by high density histone peptide array interaction studies. Nucleosomes are not a substrate for PRMT5-MEP50, consistent with the primary mode of interaction via the histone fold of H3-H4, obscured by DNA in the nucleosome. Mutation of a conserved arginine (Arg-42) on the MEP50 insertion loop impaired the PRMT5-MEP50 enzymatic efficiency by increasing its histone substrate Km, comparable with that of Caenorhabditis elegans PRMT5. We show that PRMT5-MEP50 prefers unmethylated substrates, consistent with a distributive model for dimethylation and suggesting discrete biological roles for mono- and dimethylarginine-modified proteins. We propose a model in which MEP50 and PRMT5 simultaneously engage the protein substrate, orienting its targeted arginine to the catalytic site.
Assuntos
Proteínas Adaptadoras de Transdução de Sinal/química , Histonas/química , Estrutura Terciária de Proteína , Proteína-Arginina N-Metiltransferases/química , Proteínas Adaptadoras de Transdução de Sinal/genética , Proteínas Adaptadoras de Transdução de Sinal/metabolismo , Algoritmos , Animais , Caenorhabditis elegans/química , Caenorhabditis elegans/genética , Caenorhabditis elegans/metabolismo , Proteínas de Caenorhabditis elegans/genética , Proteínas de Caenorhabditis elegans/metabolismo , Domínio Catalítico , Proteínas Cromossômicas não Histona/química , Proteínas Cromossômicas não Histona/genética , Proteínas Cromossômicas não Histona/metabolismo , Histonas/genética , Histonas/metabolismo , Humanos , Cinética , Metilação , Modelos Moleculares , Mutação , Ligação Proteica , Multimerização Proteica , Proteína-Arginina N-Metiltransferases/genética , Proteína-Arginina N-Metiltransferases/metabolismo , Proteínas de Xenopus/química , Proteínas de Xenopus/genética , Proteínas de Xenopus/metabolismo , Xenopus laevis/genética , Xenopus laevis/metabolismoRESUMO
Post-translational arginine methylation is responsible for regulation of many biological processes. The protein arginine methyltransferase 5 (PRMT5, also known as Hsl7, Jbp1, Skb1, Capsuleen, or Dart5) is the major enzyme responsible for mono- and symmetric dimethylation of arginine. An expanding literature demonstrates its critical biological function in a wide range of cellular processes. Histone and other protein methylation by PRMT5 regulate genome organization, transcription, stem cells, primordial germ cells, differentiation, the cell cycle, and spliceosome assembly. Metazoan PRMT5 is found in complex with the WD-repeat protein MEP50 (also known as Wdr77, androgen receptor coactivator p44, or Valois). PRMT5 also directly associates with a range of other protein factors, including pICln, Menin, CoPR5 and RioK1 that may alter its subcellular localization and protein substrate selection. Protein substrate and PRMT5-MEP50 post-translation modifications induce crosstalk to regulate PRMT5 activity. Crystal structures of C. elegans PRMT5 and human and frog PRMT5-MEP50 complexes provide substantial insight into the mechanisms of substrate recognition and procession to dimethylation. Enzymological studies of PRMT5 have uncovered compelling insights essential for future development of specific PRMT5 inhibitors. In addition, newly accumulating evidence implicates PRMT5 and MEP50 expression levels and their methyltransferase activity in cancer tumorigenesis, and, significantly, as markers of poor clinical outcome, marking them as potential oncogenes. Here, we review the substantial new literature on PRMT5 and its partners to highlight the significance of understanding this essential enzyme in health and disease.
Assuntos
Proteínas Adaptadoras de Transdução de Sinal/metabolismo , Complexos Multiproteicos/metabolismo , Proteína-Arginina N-Metiltransferases/metabolismo , Arginina/metabolismo , Domínio Catalítico , Diferenciação Celular/genética , Regulação da Expressão Gênica/genética , Histonas/metabolismo , Humanos , Metilação , Complexos Multiproteicos/ultraestrutura , Neoplasias , Ligação Proteica , Processamento de Proteína Pós-Traducional/genética , Estrutura Quaternária de Proteína , Proteína-Arginina N-Metiltransferases/genéticaRESUMO
DNA double-stranded breaks present a serious challenge for eukaryotic cells. The inability to repair breaks leads to genomic instability, carcinogenesis and cell death. During the double-strand break response, mammalian chromatin undergoes reorganization demarcated by H2A.X Ser 139 phosphorylation (gamma-H2A.X). However, the regulation of gamma-H2A.X phosphorylation and its precise role in chromatin remodelling during the repair process remain unclear. Here we report a new regulatory mechanism mediated by WSTF (Williams-Beuren syndrome transcription factor, also known as BAZ1B)-a component of the WICH complex (WSTF-ISWI ATP-dependent chromatin-remodelling complex). We show that WSTF has intrinsic tyrosine kinase activity by means of a domain that shares no sequence homology to any known kinase fold. We show that WSTF phosphorylates Tyr 142 of H2A.X, and that WSTF activity has an important role in regulating several events that are critical for the DNA damage response. Our work demonstrates a new mechanism that regulates the DNA damage response and expands our knowledge of domains that contain intrinsic tyrosine kinase activity.
Assuntos
Dano ao DNA , Histonas/metabolismo , Proteínas Tirosina Quinases/metabolismo , Fatores de Transcrição/metabolismo , Adenosina Trifosfatases/metabolismo , Animais , Montagem e Desmontagem da Cromatina , Proteínas Cromossômicas não Histona/metabolismo , Histonas/genética , Humanos , Camundongos , Células NIH 3T3 , Nucleossomos/metabolismo , Fosforilação , Fosfotirosina/metabolismo , Estrutura Terciária de Proteína , Fatores de Transcrição/química , Fatores de Transcrição/deficiência , Fatores de Transcrição/genéticaRESUMO
Histone chaperones-structurally diverse, non-catalytic proteins enriched with acidic intrinsically disordered regions (IDRs)-protect histones from spurious nucleic acid interactions and guide their deposition into and out of nucleosomes. Despite their conservation and ubiquity, the function of the chaperone acidic IDRs remains unclear. Here, we show that the Xenopus laevis Npm2 and Nap1 acidic IDRs are substrates for TTLL4 (Tubulin Tyrosine Ligase Like 4)-catalyzed post-translational glutamate-glutamylation. We demonstrate that to bind, stabilize, and deposit histones into nucleosomes, chaperone acidic IDRs function as DNA mimetics. Our biochemical, computational, and biophysical studies reveal that glutamylation of these chaperone polyelectrolyte acidic stretches functions to enhance DNA electrostatic mimicry, promoting the binding and stabilization of H2A/H2B heterodimers and facilitating nucleosome assembly. This discovery provides insights into both the previously unclear function of the acidic IDRs and the regulatory role of post-translational modifications in chromatin dynamics.
RESUMO
Protein Arginine Methyltransferase 5 (PRMT5) regulates RNA splicing and transcription by symmetric dimethylation of arginine residues (Rme2s/SDMA) in many RNA binding proteins. However, the mechanism by which PRMT5 couples splicing to transcriptional output is unknown. Here, we demonstrate that a major function of PRMT5 activity is to promote chromatin escape of a novel, large class of mRNAs that we term Genomically Retained Incompletely Processed Polyadenylated Transcripts (GRIPPs). Using nascent and total transcriptomics, spike-in controlled fractionated cell transcriptomics, and total and fractionated cell proteomics, we show that PRMT5 inhibition and knockdown of the PRMT5 SNRP (Sm protein) adapter protein pICln (CLNS1A) -but not type I PRMT inhibition-leads to gross detention of mRNA, SNRPB, and SNRPD3 proteins on chromatin. Compared to most transcripts, these chromatin-trapped polyadenylated RNA transcripts have more introns, are spliced slower, and are enriched in detained introns. Using a combination of PRMT5 inhibition and inducible isogenic wildtype and arginine-mutant SNRPB, we show that arginine methylation of these snRNPs is critical for mediating their homeostatic chromatin and RNA interactions. Overall, we conclude that a major role for PRMT5 is in controlling transcript processing and splicing completion to promote chromatin escape and subsequent nuclear export.
RESUMO
The role of splicing dysregulation in cancer is underscored by splicing factor mutations; however, its impact in the absence of such rare mutations is poorly understood. To reveal complex patient subtypes and putative regulators of pathogenic splicing in Acute Myeloid Leukemia (AML), we developed a new approach called OncoSplice. Among diverse new subtypes, OncoSplice identified a biphasic poor prognosis signature that partially phenocopies U2AF1-mutant splicing, impacting thousands of genes in over 40% of adult and pediatric AML cases. U2AF1-like splicing co-opted a healthy circadian splicing program, was stable over time and induced a leukemia stem cell (LSC) program. Pharmacological inhibition of the implicated U2AF1-like splicing regulator, PRMT5, rescued leukemia mis-splicing and inhibited leukemic cell growth. Genetic deletion of IRAK4, a common target of U2AF1-like and PRMT5 treated cells, blocked leukemia development in xenograft models and induced differentiation. These analyses reveal a new prognostic alternative-splicing mechanism in malignancy, independent of splicing-factor mutations.
RESUMO
Histone chaperones-structurally diverse, non-catalytic proteins enriched with acidic intrinsically disordered regions (IDRs)-protect histones from spurious nucleic acid interactions and guide their deposition into and out of nucleosomes. Despite their conservation and ubiquity, the function of the chaperone acidic IDRs remains unclear. Here, we show that the Xenopus laevis Npm2 and Nap1 acidic IDRs are substrates for TTLL4 (Tubulin Tyrosine Ligase Like 4)-catalyzed post-translational glutamate-glutamylation. We demonstrate that, to bind, stabilize, and deposit histones into nucleosomes, chaperone acidic IDRs function as DNA mimetics. Our biochemical, computational, and biophysical studies reveal that glutamylation of these chaperone polyelectrolyte acidic stretches functions to enhance DNA electrostatic mimicry, promoting the binding and stabilization of H2A/H2B heterodimers and facilitating nucleosome assembly. This discovery provides insights into both the previously unclear function of the acidic IDRs and the regulatory role of post-translational modifications in chromatin dynamics.
RESUMO
Histone proteins carry information contained in post-translational modifications. Eukaryotic cells utilize this histone code to regulate the usage of the underlying DNA. In the maturing oocytes and eggs of the frog Xenopus laevis, histones are synthesized in bulk in preparation for deposition during the rapid early developmental cell cycles. During this key developmental time frame, embryonic pluripotent chromatin is established. In the egg, non-chromatin-bound histones are complexed with storage chaperone proteins, including nucleoplasmin. Here we describe the identification and characterization of a complex of the protein arginine methyltransferase 5 (Prmt5) and the methylosome protein 50 (Mep50) isolated from Xenopus eggs that specifically methylates predeposition histones H2A/H2A.X-F and H4 and the histone chaperone nucleoplasmin on a conserved motif (GRGXK). We demonstrate that nucleoplasmin (Npm), an exceedingly abundant maternally deposited protein, is a potent substrate for Prmt5-Mep50 and is monomethylated and symmetrically dimethylated at Arg-187. Furthermore, Npm modulates Prmt5-Mep50 activity directed toward histones, consistent with a regulatory role for Npm in vivo. We show that H2A and nucleoplasmin methylation appears late in oogenesis and is most abundant in the laid egg. We hypothesize that these very abundant arginine methylations are constrained to pre-mid blastula transition events in the embryo and therefore may be involved in the global transcriptional repression found in this developmental time frame.
Assuntos
Proteínas Cromossômicas não Histona/metabolismo , Regulação da Expressão Gênica no Desenvolvimento , Histonas/química , Proteína-Arginina N-Metiltransferases/metabolismo , Proteínas de Xenopus/metabolismo , Animais , Arginina/química , Arginina/metabolismo , Baculoviridae/genética , Núcleo Celular/metabolismo , Cromatina/metabolismo , Clonagem Molecular , Vetores Genéticos , Espectrometria de Massas/métodos , Metilação , Chaperonas Moleculares/metabolismo , Nucleoplasminas/metabolismo , Xenopus laevisRESUMO
Histone H2A.X is an H2A variant present in multicellular organisms that is specifically phosphorylated on the serine in the C-terminal consensus sequence, canonically "SQEY," in response to DNA damage. We have recently shown the significance of phosphorylation of the penultimate tyrosine for maintenance and processing of the DNA damage response in mammalian cells. Here, we report the identification of distinct H2A.X variants in the eggs and early embryos of the frog Xenopus laevis that contain a C-terminal SQEF, among other changes; we have denoted these proteins as "H2A.X-F." H2A.X-F is present only in late-staged oocytes, eggs, and premidblastula transition embryos and is not present in somatic cells. Similar unannotated isoforms were identified in other rapidly developing aquatic species, such as Xenopus tropicalis, goldfish, and zebrafish, and in Arabidopsis and chickpea. Furthermore, we demonstrate by mass spectrometry and phospho-specific antibodies that H2A.X-F is phosphorylated in the absence of exogenous DNA damage, in both actively dividing, unperturbed embryos and cell-free egg extract in the absence and presence of DNA damage and S-phase checkpoint conditions. We propose that this isoform may be involved in modulating the cellular response to the rapid early cell cycles in externally developing species.
Assuntos
Embrião não Mamífero/química , Histonas/análise , Óvulo/química , Xenopus laevis/embriologia , Sequência de Aminoácidos , Animais , Dano ao DNA , Replicação do DNA , Histonas/química , Histonas/fisiologia , Dados de Sequência Molecular , Fosforilação , Isoformas de Proteínas , Fase S , Espectrometria de Massas em TandemRESUMO
Protein arginine methyltransferases (PRMTs) are required for the regulation of RNA processing factors. Type I PRMT enzymes catalyze mono- and asymmetric dimethylation; Type II enzymes catalyze mono- and symmetric dimethylation. To understand the specific mechanisms of PRMT activity in splicing regulation, we inhibited Type I and II PRMTs and probed their transcriptomic consequences. Using the newly developed Splicing Kinetics and Transcript Elongation Rates by Sequencing (SKaTER-seq) method, analysis of co-transcriptional splicing demonstrated that PRMT inhibition resulted in altered splicing rates. Surprisingly, co-transcriptional splicing kinetics did not correlate with final changes in splicing of polyadenylated RNA. This was particularly true for retained introns (RI). By using actinomycin D to inhibit ongoing transcription, we determined that PRMTs post-transcriptionally regulate RI. Subsequent proteomic analysis of both PRMT-inhibited chromatin and chromatin-associated polyadenylated RNA identified altered binding of many proteins, including the Type I substrate, CHTOP, and the Type II substrate, SmB. Targeted mutagenesis of all methylarginine sites in SmD3, SmB, and SmD1 recapitulated splicing changes seen with Type II PRMT inhibition, without disrupting snRNP assembly. Similarly, mutagenesis of all methylarginine sites in CHTOP recapitulated the splicing changes seen with Type I PRMT inhibition. Examination of subcellular fractions further revealed that RI were enriched in the nucleoplasm and chromatin. Taken together, these data demonstrate that, through Sm and CHTOP arginine methylation, PRMTs regulate the post-transcriptional processing of nuclear, detained introns.
Assuntos
Regulação da Expressão Gênica , Íntrons/genética , Proteínas Nucleares/genética , Proteína-Arginina N-Metiltransferases/genética , Fatores de Transcrição/genética , Proteínas Centrais de snRNP/genética , Linhagem Celular , Humanos , Metilação , Proteínas Nucleares/metabolismo , Proteína-Arginina N-Metiltransferases/metabolismo , Fatores de Transcrição/metabolismo , Proteínas Centrais de snRNP/metabolismoRESUMO
Timing of DNA replication initiation is dependent on S-phase-promoting kinase (SPK) activity at discrete origins and the simultaneous function of many replicons. DNA damage prevents origin firing through the ATM- and ATR-dependent inhibition of Cdk2 and Cdc7 SPKs. Here, we establish that modulation of ATM- and ATR-signalling pathways controls origin firing in the absence of DNA damage. Inhibition of ATM and ATR with caffeine or specific neutralizing antibodies, or upregulation of Cdk2 or Cdc7, promoted rapid and synchronous origin firing; conversely, inhibition of Cdc25A slowed DNA replication. Cdk2 was in equilibrium between active and inactive states, and the concentration of replication protein A (RPA)-bound single-stranded DNA (ssDNA) correlated with Chk1 activation and inhibition of origin firing. Furthermore, ATM was transiently activated during ongoing replication. We propose that ATR and ATM regulate SPK activity through a feedback mechanism originating at active replicons. Our observations establish that ATM- and ATR-signalling pathways operate during an unperturbed cell cycle to regulate initiation and progression of DNA synthesis, and are therefore poised to halt replication in the presence of DNA damage.
Assuntos
Proteínas de Ciclo Celular/metabolismo , Período de Replicação do DNA/genética , Retroalimentação Fisiológica/genética , Proteínas Serina-Treonina Quinases/metabolismo , Transdução de Sinais/genética , Proteínas de Xenopus , Animais , Anticorpos/farmacologia , Proteínas Mutadas de Ataxia Telangiectasia , Quinases relacionadas a CDC2 e CDC28/genética , Quinases relacionadas a CDC2 e CDC28/metabolismo , Cafeína/farmacologia , Proteínas de Ciclo Celular/antagonistas & inibidores , Proteínas de Ciclo Celular/genética , Extratos Celulares , Sistema Livre de Células , Quinase 1 do Ponto de Checagem , Quinase 2 Dependente de Ciclina , Dano ao DNA/genética , Período de Replicação do DNA/efeitos dos fármacos , DNA de Cadeia Simples/genética , DNA de Cadeia Simples/metabolismo , Proteínas de Ligação a DNA/genética , Proteínas de Ligação a DNA/metabolismo , Feminino , Humanos , Oócitos , Proteínas Quinases/genética , Proteínas Quinases/metabolismo , Proteínas Serina-Treonina Quinases/antagonistas & inibidores , Proteínas Serina-Treonina Quinases/genética , Proteína de Replicação A , Proteínas Supressoras de Tumor , Xenopus laevis , Fosfatases cdc25/antagonistas & inibidores , Fosfatases cdc25/genética , Fosfatases cdc25/metabolismoRESUMO
Histones are the major protein components of chromatin, the physiological form of the genome in all eukaryotic cells. Chromatin is the substrate of information-directed biological processes, such as gene regulation and transcription, replication, and mitosis. A long-standing experimental model system to study many of these processes is the extract made from the eggs of the anuran Xenopus laevis. Since work in recent years has solidified the importance of post-translational modification of histones in directing biological processes, the study of histones in a biochemically dissectible model such as Xenopus is crucial for the understanding of their biological significance. Here we present a rationale and methods for isolating and studying histones and chromatin in different Xenopus egg and oocyte extracts. In particular, we present protocols for the preparation of: cell-free egg and oocyte extract; nucleoplasmic extract ("NPE"); biochemical purification of maternally-deposited, stored histones in the oocyte and the egg; assembly of pronuclei in egg extract and the isolation of pronuclear chromatin and histones; and an extract chromatin assembly assay. We also demonstrate aspects of the variability of the system to be mindful of when working with extract and the importance of proper laboratory temperature in preparing quality extracts. We expect that these methods will be of use in promoting further understanding of embryonic chromatin in a unique experimental system.
Assuntos
Cromatina/metabolismo , Histonas/fisiologia , Oócitos/metabolismo , Xenopus laevis/metabolismo , Animais , Núcleo Celular/metabolismo , Sistema Livre de Células , Citoplasma/metabolismo , DNA/metabolismo , Biologia do Desenvolvimento/métodos , Feminino , Histonas/metabolismo , Mitose , Modelos Biológicos , Plasmídeos/metabolismo , Processamento de Proteína Pós-TraducionalRESUMO
Protein arginine methyltransferases (PRMTs) catalyze the post-translational monomethylation (Rme1), asymmetric (Rme2a), or symmetric (Rme2s) dimethylation of arginine. To determine the cellular consequences of type I (Rme2a) and II (Rme2s) PRMTs, we developed and integrated multiple approaches. First, we determined total cellular dimethylarginine levels, revealing that Rme2s was â¼3% of total Rme2 and that this percentage was dependent upon cell type and PRMT inhibition status. Second, we quantitatively characterized in vitro substrates of the major enzymes and expanded upon PRMT substrate recognition motifs. We also compiled our data with publicly available methylarginine-modified residues into a comprehensive database. Third, we inhibited type I and II PRMTs and performed proteomic and transcriptomic analyses to reveal their phenotypic consequences. These experiments revealed both overlapping and independent PRMT substrates and cellular functions. Overall, this study expands upon PRMT substrate diversity, the arginine methylome, and the complex interplay of type I and II PRMTs.
RESUMO
Chromatin is the complex assembly of nucleic acids and proteins that makes up the physiological form of the eukaryotic genome. The nucleosome is the fundamental repeating unit of chromatin, and is composed of â¼147â bp of DNA wrapped around a histone octamer formed by two copies of each core histone: H2A, H2B, H3 and H4. Prior to nucleosome assembly, and during histone eviction, histones are typically assembled into soluble H2A/H2B dimers and H3/H4 dimers and tetramers. A multitude of factors interact with soluble histone dimers and tetramers, including chaperones, importins, histone-modifying enzymes and chromatin-remodeling enzymes. It is still unclear how many of these proteins recognize soluble histones; therefore, there is a need for new structural tools to study non-nucleosomal histones. Here, a single-chain, tailless Xenopus H2A/H2B dimer was created by directly fusing the C-terminus of H2B to the N-terminus of H2A. It is shown that this construct (termed scH2BH2A) is readily expressed in bacteria and can be purified under non-denaturing conditions. A 1.31â Å resolution crystal structure of scH2BH2A shows that it adopts a conformation that is nearly identical to that of nucleosomal H2A/H2B. This new tool is likely to facilitate future structural studies of many H2A/H2B-interacting proteins.
Assuntos
Histonas/química , Xenopus/metabolismo , Animais , Cristalografia por Raios X , Dimerização , Escherichia coli/metabolismo , Histonas/isolamento & purificação , Ligação de Hidrogênio , Conformação Proteica , Proteínas Recombinantes/genética , Proteínas Recombinantes/isolamento & purificação , Proteínas Recombinantes/metabolismo , Eletricidade EstáticaRESUMO
Xenopus laevis development is marked by accelerated cell division solely supported by the proteins maternally deposited in the egg. Oocytes mature to eggs with concomitant transcriptional silencing. The unique maternal chromatin state contributing to this silencing and subsequent zygotic activation is likely established by histone posttranslational modifications and histone variants. Therefore, tools for understanding the nature and function of maternal and embryonic histones are essential to deciphering mechanisms of regulation of development, chromatin assembly, and transcription. Here we describe protocols for isolating pronuclear sperm chromatin from Xenopus egg extracts and hydroxyapatite-based histone purification from this chromatin. The histones purified through this method can be directly assembled into chromatin through in vitro assembly reactions, providing a unique opportunity to biochemically dissect the effect of histone variants, histone modifications, and other factors in chromatin replication and assembly. We also describe how to isolate chromatin from staged embryos and analyze the proteins to reveal dynamic developmental histone modifications. Finally, we present protocols to measure chromatin assembly in extracts, including supercoiling and micrococcal nuclease assays. Using these approaches, analysis of maternal and zygotic histone posttranslational modifications concomitant with cell-cycle and developmental transitions can be tested.
Assuntos
Cromatina/isolamento & purificação , Misturas Complexas/isolamento & purificação , Embrião não Mamífero/química , Histocitoquímica/métodos , Histonas/isolamento & purificação , Xenopus laevis , Zigoto/química , Animais , Feminino , Masculino , Espermatozoides/químicaRESUMO
The Retinoid inducible nuclear factor (Rinf), also known as CXXC5, is a nuclear protein, but its functions in the context of the chromatin are poorly defined. We find that in mouse embryonic stem cells (mESCs), Rinf binds to the chromatin and is enriched at promoters and enhancers of Tet1, Tet2, and pluripotency genes. The Rinf-bound regions show significant overlapping occupancy of pluripotency factors Nanog, Oct4, and Sox2, as well as Tet1 and Tet2. We found that Rinf forms a complex with Nanog, Oct4, Tet1, and Tet2 and facilitates their proper recruitment to regulatory regions of pluripotency and Tet genes in ESCs to positively regulate their transcription. Rinf deficiency in ESCs reduces expression of Rinf target genes, including several pluripotency factors and Tet enzymes, and causes aberrant differentiation. Together, our findings establish Rinf as a regulator of the pluripotency network genes and Tet enzymes in ESCs.