Human SWI/SNF-associated PRMT5 methylates histone H3 arginine 8 and negatively regulates expression of ST7 and NM23 tumor suppressor genes

Evaluating epigenetic landmarks in the brain of multiple sclerosis patients: a contribution to the current debate on disease pathogenesis

The evidence suggesting a role of epigenetics in the definition of complex trait diseases is rapidly increasing. The gender prevalence of multiple sclerosis, the low level concordance in homozygous twins and the linkage to several genetic loci, suggest an epigenetic component to the definition of this demyelinating disorder. While the immune etio-pathogenetic mechanism of disease progression has been well characterized, still relatively little is known about the initial events contributing to onset and progression of the demyelinating lesion. This article addresses the challenging question of whether loss of the mechanisms of epigenetic regulation of gene expression in the myelinating cells may contribute to the pathogenesis of multiple sclerosis, by affecting the repair process and by modulating the levels of enzymes involved in neo-epitope formation. The role of altered post-translational modifications of nucleosomal histones and DNA methylation in white matter oligodendroglial cells are presented in terms of pathogenetic concepts and the relevance to therapeutic intervention is then discussed.

Cancer treatment of the future: inhibitors of histone methyltransferases

Cancer in humans is the result of a multi-step process. This process often involves the activation of oncogenes and/or the inactivation of tumor suppressor genes. These two steps arise not only due to mutations, but can also be the result of a translocation or an altered transcription rate. One important mechanism is the occurrence of epigenetic alterations like promotor methylation (which may lead to tumor suppressor silencing) or decreased histone acetylation (which can result in the downregulation of proteins involved in apoptosis). Today, histone acetylation and DNA methylation are epigenetic modifications which have been linked closely to the pathology of human cancers and inhibitors of both enzyme classes for clinical use are at hand. In contrast, other fields of epigenetics still lack of similarly thorough knowledge. This is especially true for the group of histone methyltransferases and their inhibitors. Since connections between histone methylation patterns and cancer progression have been recognized, histone methyltransferases represent promising targets for future cancer treatment.

Protein arginine methyltransferase 5 suppresses the transcription of the RB family of tumor suppressors in leukemia and lymphoma cells

The proper epigenetic modification of chromatin by protein arginine methyltransferases (PRMTs) is crucial for normal cell growth and health. The human SWI/SNF-associated PRMT5 is involved in the transcriptional repression of target genes by directly methylating H3R8 and H4R3. To further understand the impact of PRMT5-mediated histone methylation on cancer, we analyzed its expression in normal and transformed human B lymphocytes. Our findings reveal that PRMT5 protein levels are enhanced in various human lymphoid cancer cells, including transformed chronic lymphocytic leukemia (B-CLL) cell lines. PRMT5 overexpression is caused by the altered expression of the PRMT5-specific microRNAs 19a, 25, 32, 92, 92b, and 96 and results in the increased global symmetric methylation of H3R8 and H4R3. An evaluation of both epigenetic marks at PRMT5 target genes such as RB1 (p105), RBL1 (p107), and RBL2 (p130) showed that promoters H3R8 and H4R3 are hypermethylated, which in turn triggers pocket protein transcriptional repression. Furthermore, reducing PRMT5 expression in WaC3CD5 B-CLL cells abolishes H3R8 and H4R3 hypermethylation, restores RBL2 expression, and inhibits cancer cell proliferation. These results indicate that PRMT5 overexpression epigenetically alters the transcription of key tumor suppressor genes and suggest a causal role of the elevated symmetric methylation of H3R8 and H4R3 at the RBL2 promoter in transformed B-lymphocyte pathology.

Down-regulation of asymmetric arginine methylation during replicative and H2O2-induced premature senescence in WI-38 human diploid fibroblasts

Protein arginine methylation is one of the post-translational modifications which yield monomethyl and dimethyl (asymmetric or symmetric) arginines in proteins. In the present study, we investigated the status of protein arginine methylation during human diploid fibroblast senescence. When the expression of protein arginine methyltransferases (PRMTs), namely PRMT1, PRMT4, PRMT5 and PRMT6 was examined, a significant reduction was found in replicatively senescent cells as well as their catalytic activities against histone mixtures compared with the young cells. Furthermore, when the endogenous level of arginine-dimethylated proteins was determined, asymmetric modification (the product of type I PRMTs including PRMT1, PRMT4 and PRMT6) was markedly down-regulated. In contrast, both up- and down-regulations of symmetrically arginine-methylated proteins (the product of type II PRMTs including PRMT5) during replicative senescence were found. Furthermore, when young fibroblasts were induced to premature senescence by sub-cytotoxic H2O2 treatment, results similar to replicative senescence were obtained. Finally, we found that SV40-mediated immortalized WI-38 and HeLa cell lines maintained a higher level of asymmetrically modified proteins as well as type I PRMTs than young fibroblasts. These results suggest that the maintenance of asymmetric modification in the expressed target proteins of type I PRMTs might be critical for cellular proliferation.

Chemical and structural probing of the N-terminal residues encoded by FMR1 exon 15 and their effect on downstream arginine methylation

Exon 15 of the fragile X mental retardation protein gene (FMR1) is alternatively spliced into three variants. The amino acids encoded by the 5' end of the exon contain several regulatory determinants including phosphorylation sites and a potential conformational switch. Residues encoded by the 3' end of the exon specify FMRP's RGG box, an RNA binding domain that interacts with G-quartet motifs. Previous studies demonstrated that the exon 15-encoded N-terminal residues influence the extent of arginine methylation, independent of S 500 phosphorylation. In the present study we focus on the role the putative conformational switch plays in arginine methylation. Chemical and structural probing of Ex15 alternatively spliced variant proteins and several mutants leads to the following conclusions: Ex15c resides largely in a conformation that is refractory toward methylation; however, it can be methylated by supplementing extracts with recombinant PRMT1 or PRMT3. Protein modeling studies reveal that the RG-rich region is part of a three to four strand antiparallel beta-sheet, which in other RNA binding proteins functions as a platform for nucleic acid interactions. In the Ex15c variant the first strand of this sheet is truncated, and this significantly perturbs the side-chain conformations of the arginine residues in the RG-rich region. Mutating R 507 in the conformational switch to K also truncates the first strand of the beta-sheet, and corresponding decreases in in vitro methylation were found for this and R 507/R 544 and R 507/R 546 double mutants. These effects are not due to the loss of R 507 methylation as a conformational switch-containing peptide reacted under substrate excess and in methyl donor excess was not significantly methylated. Consistent with this, similar changes in beta-sheet structure and decreases in in vitro methylation were observed with a W 513-K mutant. These data support a novel model for FMRP arginine methylation and a role for conformational switch residues in arginine modification.

Post-translational modifications of nucleosomal histones in oligodendrocyte lineage cells in development and disease

The role of epigenetics in modulating gene expression in the development of organs and tissues and in disease states is becoming increasingly evident. Epigenetics refers to the several mechanisms modulating inheritable changes in gene expression that are independent of modifications of the primary DNA sequence and include post-translational modifications of nucleosomal histones, changes in DNA methylation, and the role of microRNA. This review focuses on the epigenetic regulation of gene expression in oligodendroglial lineage cells. The biological effects that post-translational modifications of critical residues in the N-terminal tails of nucleosomal histones have on oligodendroglial cells are reviewed, and the implications for disease and repair are critically discussed.

Histone modifications and chromatin dynamics: a focus on filamentous fungi

The readout of the genetic information of eukaryotic organisms is significantly regulated by modifications of DNA and chromatin proteins. Chromatin alterations induce genome-wide and local changes in gene expression and affect a variety of processes in response to internal and external signals during growth, differentiation, development, in metabolic processes, diseases, and abiotic and biotic stresses. This review aims at summarizing the roles of histone H1 and the acetylation and methylation of histones in filamentous fungi and links this knowledge to the huge body of data from other systems. Filamentous fungi show a wide range of morphologies and have developed a complex network of genes that enables them to use a great variety of substrates. This fact, together with the possibility of simple and quick genetic manipulation, highlights these organisms as model systems for the investigation of gene regulation. However, little is still known about regulation at the chromatin level in filamentous fungi. Understanding the role of chromatin in transcriptional regulation would be of utmost importance with respect to the impact of filamentous fungi in human diseases and agriculture. The synthesis of compounds (antibiotics, immunosuppressants, toxins, and compounds with adverse effects) is also likely to be regulated at the chromatin level.

Analysis of the substrate specificity of the Dim-5 histone lysine methyltransferase using peptide arrays

Histone methylation is an epigenetic mark essential for gene regulation and development. We introduce peptide SPOT synthesis to study sequence specificity of the Dim-5 histone-3 lysine-9 methyltransferase. Dim-5 recognizes R8-G12 of the H3 tail with T11 and G12 being the most important specificity determinants. Exchange of H3 tail residue S10 and T11 by E strongly reduced methylation by Dim-5, suggesting that phosphorylation of S10 or T11 may regulate the activity of Dim-5. In the Dim-5/peptide structure, E227 interacts with H3R8 and D209 with H3-S10. Mutations of E227 or D209 caused predictable changes in the substrate preference, illustrating that peptide recognition of histone methyltransferases can be altered by protein design. Comparative analyses of peptide arrays with wild-type and mutant enzymes, therefore, are well suited to investigate the target specificity of protein methyltransferases and study epigenetic crosstalk.

The protein arginine methyltransferases CARM1 and PRMT1 cooperate in gene regulation

Protein arginine methyltransferases (PRMT) have been implicated in the regulation of transcription. They are recruited to promoters via interaction with transcription factors and exert their coactivator function by methylating arginine residues in histones and other chromatin proteins. Here, we employ an unbiased approach to identify novel target genes, which are under the control of two members of the enzyme family, PRMT1 and CARM1/PRMT4 (coactivator associated arginine methyltransferase 1). By using cDNA microarray analysis, we find that the siRNA-mediated single knockdown of neither CARM1 nor PRMT1 causes significant changes in gene expression. In contrast, double knockdown of both enzymes results in the deregulated expression of a large group of genes, among them the CITED2 gene. Cytokine-stimulated expression analysis indicates that transcriptional activation of CITED2 depends on STAT5 and the coactivation of both PRMTs. ChIP analysis identifies the CITED2 gene as a direct target gene of STAT5, CARM1 and PRMT1. In reporter gene assays, we show that STAT5-mediated transcription is cooperatively enhanced by CARM1 and PRMT1. Interaction assays reveal a cytokine-induced association of STAT5 and the two PRMTs. Our data demonstrate a widespread cooperation of CARM1 and PRMT1 in gene activation as well as repression and that STAT5-dependent transcription of the CITED2 gene is a novel pathway coactivated by the two methyltransferases.

The histone-binding protein COPR5 is required for nuclear functions of the protein arginine methyltransferase PRMT5

Protein arginine methyltransferase 5 (PRMT5) targets nuclear and cytoplasmic proteins. Here, we identified a nuclear protein, called cooperator of PRMT5 (COPR5), involved in the nuclear functions of PRMT5. COPR5 tightly binds to PRMT5, both in vitro and in living cells, but not to other members of the PRMT family. PRMT5 bound to COPR5 methylates histone H4 (R3) preferentially when compared with histone H3 (R8), suggesting that COPR5 modulates the substrate specificity of nuclear PRMT5-containing complexes, at least towards histones. Markedly, recombinant COPR5 binds to the amino terminus of histone H4 and is required to recruit PRMT5 to reconstituted nucleosomes in vitro. Consistently, COPR5 depletion in cells strongly reduces PRMT5 recruitment on chromatin at the PRMT5 target gene cyclin E1 (CCNE1) in vivo. Moreover, both COPR5 depletion and overexpression affect CCNE1 promoter expression. We propose that COPR5 is an important chromatin adaptor for PRMT5 to function on a subset of its target genes.

PRMT6-mediated methylation of R2 in histone H3 antagonizes H3 K4 trimethylation

The arginine methyltransferase PRMT6 (protein arginine methyltransferase 6) has been shown recently to regulate DNA repair and gene expression. As arginine methylation of histones is an important mechanism in transcriptional regulation, we asked whether PRMT6 possesses activity toward histones. We show here that PRMT6 methylates histone H3 at R2 and histones H4/H2A at R3 in vitro. Overexpression and knockdown analysis identify PRMT6 as the major H3 R2 methyltransferase in vivo. We find that H3 R2 methylation inhibits H3 K4 trimethylation and recruitment of WDR5, a subunit of the MLL (mixed lineage leukemia) K4 methyltransferase complex, to histone H3 in vitro. Upon PRMT6 overexpression, transcription of Hox genes and Myc-dependent genes, both well-known targets of H3 K4 trimethylation, decreases. This transcriptional repression coincides with enhanced occurrence of H3 R2 methylation and PRMT6 as well as reduced levels of H3 K4 trimethylation and MLL1/WDR5 recruitment at the HoxA2 gene. Upon retinoic acid-induced transcriptional activation of HoxA2 in a cell model of neuronal differentiation, PRMT6 recruitment and H3 R2 methylation are diminished and H3 K4 trimethylation increases at the gene. Our findings identify PRMT6 as the mammalian methyltransferase for H3 R2 and establish the enzyme as a crucial negative regulator of H3 K4 trimethylation and transcriptional activation.

The LIM protein AJUBA recruits protein arginine methyltransferase 5 to mediate SNAIL-dependent transcriptional repression

The SNAIL transcription factor contains C-terminal tandem zinc finger motifs and an N-terminal SNAG repression domain. The members of the SNAIL family have recently emerged as major contributors to the processes of development and metastasis via the regulation of epithelial-mesenchymal transition events during embryonic development and tumor progression. However, the mechanisms by which SNAIL represses gene expression are largely undefined. Previously we demonstrated that the AJUBA family of LIM proteins function as corepressors for SNAIL and, as such, may serve as a platform for the assembly of chromatin-modifying factors. Here, we describe the identification of the protein arginine methyltransferase 5 (PRMT5) as an effector recruited to SNAIL through an interaction with AJUBA that functions to repress the SNAIL target gene, E-cadherin. PRMT5 binds to the non-LIM region of AJUBA and is translocated into the nucleus in a SNAIL- and AJUBA-dependent manner. The depletion of PRMT5 in p19 cells stimulates E-cadherin expression, and the SNAIL, AJUBA, and PRMT5 ternary complex can be found at the proximal promoter region of the E-cadherin gene, concomitant with increased arginine methylation of histones at the locus. Together, these data suggest that PRMT5 is an effector of SNAIL-dependent gene repression.

CARM1 regulates estrogen-stimulated breast cancer growth through up-regulation of E2F1

Estrogen receptor alpha (ER alpha) mediates breast cancer proliferation through transcriptional mechanisms involving the recruitment of specific coregulator complexes to the promoters of cell cycle genes. The coactivator-associated arginine methyltransferase CARM1 is a positive regulator of ER alpha-mediated transcriptional activation. Here, we show that CARM1 is essential for estrogen-induced cell cycle progression in the MCF-7 breast cancer cell line. CARM1 is specifically required for the estrogen-induced expression of the critical cell cycle transcriptional regulator E2F1 whereas estrogen stimulation of cyclin D1 is CARM1 independent. Upon estrogen stimulation, the E2F1 promoter is subject to CARM1-dependent dimethylation on histone H3 arginine 17 (H3R17me2) in a process that parallels the recruitment of ER alpha. Additionally, we find that the recruitment of CARM1 and subsequent histone arginine dimethylation are dependent on the presence of the oncogenic coactivator AIB1. Thus, CARM1 is a critical factor in the pathway of estrogen-stimulated breast cancer growth downstream of ER alpha and AIB1 and upstream of the cell cycle regulatory transcription factor E2F1. These studies identify CARM1 as a potential new target in the treatment of estrogen-dependent breast cancer.

Cell identity in the preimplantation mammalian embryo: an epigenetic perspective from the mouse

The early preimplantation mouse embryo is a unique system where it is possible to explore the foundations of totipotency and differentiation. Following fertilization, a single cell, the zygote, will give rise to all tissues of the organism. The first signs of differentiation in the embryo are evident at the blastocyst stage with the formation of the trophectoderm, a differentiated tissue that envelopes the inner cell mass. The question of when and how the cells start to be different from each other in the embryo is central to developmental biology: as cell fate decisions are undertaken, loss of totipotency comes about. Although the blastomeres of the preimplantation embryo are totipotent, as the embryo develops some differences appear to develop between them which are, at least partially, related to the epigenetic information of each of these cells. The hypothesis of epigenetic asymmetries acting as driver for lineage allocation is presented. Although there are now some indications that epigenetic mechanisms are involved in cell fate determination, much work is needed to discover how such mechanisms are set in play upon fertilization and how they are transmitted through cell division. These considerations are further discussed in the context of preimplantation genetic diagnosis: does it matter to the embryo which cell is used for genetic diagnosis? The exquisite complexity and richness of chromatin-regulated events in the early embryo will certainly be the subject of exciting research in the future.

Epigenetic events in mammalian germ-cell development: reprogramming and beyond

The epigenetic profile of germ cells, which is defined by modifications of DNA and chromatin, changes dynamically during their development. Many of the changes are associated with the acquisition of the capacity to support post-fertilization development. Our knowledge of this aspect has greatly increased- for example, insights into how the re-establishment of parental imprints is regulated. In addition, an emerging theme from recent studies is that epigenetic modifiers have key roles in germ-cell development itself--for example, epigenetics contributes to the gene-expression programme that is required for germ-cell development, regulation of meiosis and genomic integrity. Understanding epigenetic regulation in germ cells has implications for reproductive engineering technologies and human health.

Protein arginine methyltransferase 1 coactivates NF-kappaB-dependent gene expression synergistically with CARM1 and PARP1

Nuclear factor kappa B (NF-kappaB) plays an important role in the transcriptional regulation of genes involved in inflammation and cell survival. Transcriptional coactivators that methylate histones become increasingly important. Recently, we provided evidence that coactivator-associated arginine methyltransferase 1 (CARM1) is a transcriptional coactivator of NF-kappaB and functions as a promoter-specific regulator of NF-kappaB recruitment to chromatin. Here, we show that protein arginine methyltransferase 1 (PRMT1) synergistically coactivates NF-kappaB-dependent gene expression at the macrophage inflammatory protein 2 and human immunodeficiency virus 1 long terminal repeat promoters in concert with the transcriptional coactivators p300/CREB binding protein, CARM1, and poly(ADP-ribose) polymerase 1. PRMT1 formed a complex with poly(ADP-ribose) polymerase 1 and NF-kappaB in vivo and interacted directly with the NF-kappaB subunit p65 in vitro. The methyltransferase activity of PRMT1 appeared essential for its coactivator function in context with CARM1 and p300/CREB binding protein. These results suggest that the cooperative action between PRMT1 and CARM1 is required for NF-kappaB-dependent gene expression.

Chromatin-modifying proteins in cancer

Chromatin-modifying proteins mold the genome into areas that are accessible for transcriptional activity and areas that are transcriptionally silent. This epigenetic gene regulation allows for different transcriptional programs to be conducted in different cell types at different timepoints-despite the fact that all cells in the organism contain the same genetic information. A large amount of data gathered over the last decades has demonstrated that deregulation of chromatin-modifying proteins is etiologically involved in the development and progression of cancer. Here we discuss how epigenetic alterations influence cancer development and review known cancer-associated alterations in chromatin-modifying proteins.

Interplay between chromatin remodelers and protein arginine methyltransferases

Chromatin modifying enzymes have emerged as key regulators of all DNA based processes, which control cell growth, development, and differentiation. Recently, it has become clear that different chromatin remodeling and histone-modifying activities are involved in transcriptional activation and repression. Among the enzymes involved in regulating chromatin structure is the family of protein arginine methyltransferases (PRMTs) that specializes in methylating both histones as well as key cellular proteins. There are eleven different PRMT genes (PRMT1-11) whose biological function remains under explored. PRMTs regulate various cellular processes such as DNA repair and transcription, RNA processing, signal transduction, and nucleo-cytoplasmic localization. Like histone lysine methylation, methylation of histone arginine residues can either induce or inhibit transcription depending on the residue being modified and the type of methylation being introduced. In this review, we will focus on the latest findings and biological roles of ATP-dependent chromatin remodeling complexes and PRMT enzymes, and how their aberrant expression is linked to cancer.

Histone arginine methylation is required for vernalization-induced epigenetic silencing of FLC in winter-annual Arabidopsis thaliana

Certain plant varieties typically require prolonged exposure to the cold of winter to become competent to flower rapidly in the spring. This process is known as vernalization. In Arabidopsis thaliana, vernalization renders plants competent to flower by epigenetically silencing the strong floral repressor FLOWERING LOCUS C (FLC). As a result of vernalization, levels of lysine-9 and lysine-27 trimethylation on histone 3, modifications that are characteristic of facultative heterochromatin in plants, increase at FLC chromatin. We have identified a mutant, protein arginine methyltransferase 5 (atprmt5), that fails to flower rapidly after vernalization treatment. AtPRMT5 encodes a type II protein arginine methyltransferase (PRMT) that, in winter-annual strains, is required for epigenetic silencing of FLC and for the vernalization-mediated histone modifications characteristic of the vernalized state. Furthermore, the levels of arginine methylation of FLC chromatin increase after vernalization. Therefore, arginine methylation of FLC chromatin is part of the histone code that is required for mitotic stability of the vernalized state.

Identification and characterization of two closely related histone H4 arginine 3 methyltransferases in Arabidopsis thaliana

Arginine methylation of histone H3 and H4 plays important roles in transcriptional regulation in eukaryotes such as yeasts, fruitflies, nematode worms, fish and mammals; however, less is known in plants. In the present paper, we report the identification and characterization of two Arabidopsis thaliana protein arginine N-methyltransferases, AtPRMT1a and AtPRMT1b, which exhibit high homology with human PRMT1. Both AtPRMT1a and AtPRMT1b methylated histone H4, H2A, and myelin basic protein in vitro. Site-directed mutagenesis of the third arginine (R3) on the N-terminus of histone H4 to lysine (H4R3N) completely abolished the methylation of histone H4. When fused to GFP (green fluorescent protein), both methyltransferases localized to the cytoplasm as well as to the nucleus. Consistent with their subcellular distribution, GST (glutathione transferase) pull-down assays revealed an interaction between the two methyltransferases, suggesting that both proteins may act together in a functional unit. In addition, we demonstrated that AtFib2 (Arabidopsis thaliana fibrillarin 2), an RNA methyltransferase, is a potential substrate for AtPRMT1a and AtPRMT1b, and, furthermore, uncovered a direct interaction between the protein methyltransferase and the RNA methyltransferase. Taken together, our findings implicate AtPRMT1a and AtPRMT1b as H4-R3 protein arginine N-methyltransferases in Arabidopsis and may be involved in diverse biological processes inside and outside the nucleus.

AS1411 alters the localization of a complex containing protein arginine methyltransferase 5 and nucleolin

AS1411 is a quadruplex-forming oligonucleotide aptamer that targets nucleolin. It is currently in clinical trials as a treatment for various cancers. We have proposed that AS1411 inhibits cancer cell proliferation by affecting the activities of certain nucleolin-containing complexes. Here, we report that protein arginine methyltransferase 5 (PRMT5), an enzyme that catalyzes the formation of symmetrical dimethylarginine (sDMA), is a nucleolin-associated protein whose localization and activity are altered by AS1411. Levels of PRMT5 were found to be decreased in the nucleus of AS1411-treated DU145 human prostate cancer cells, but increased in the cytoplasm. These changes were dependent on nucleolin and were not observed in cells pretreated with nucleolin-specific small interfering RNA. Treatment with AS1411 altered levels of PRMT5 activity (assessed by sDMA levels) in accord with changes in its localization. In addition, our data indicate that nucleolin itself is a substrate for PRMT5 and that distribution of sDMA-modified nucleolin is altered by AS1411. Because histone arginine methylation by PRMT5 causes transcriptional repression, we also examined expression of selected PRMT5 target genes in AS1411-treated cells. For some genes, including cyclin E2 and tumor suppressor ST7, a significant up-regulation was noted, which corresponded with decreased PRMT5 association with the gene promoter. We conclude that nucleolin is a novel binding partner and substrate for PRMT5, and that AS1411 causes relocalization of the nucleolin-PRMT5 complex from the nucleus to the cytoplasm. Consequently, the nuclear activity of PRMT5 is decreased, leading to derepression of some PRMT5 target genes, which may contribute to the biological effects of AS1411.

Inhibition of methyltransferases results in induction of g2/m checkpoint and programmed cell death in human T-lymphotropic virus type 1-transformed cells

Human T-lymphotropic virus type 1 (HTLV-1) is the etiologic agent for adult T-cell leukemia. The HTLV-1-encoded protein Tax transactivates the viral long terminal repeat and plays a critical role in virus replication and transformation. Previous work from our laboratory demonstrated that coactivator-associated arginine methytransferase 1, a protein arginine methytransferase, was important for Tax-mediated transactivation. To further investigate the role of methyltransferases in viral transcription, we utilized adenosine-2,3-dialdehyde (AdOx), an adenosine analog and S-adenosylmethionine-dependent methyltransferase inhibitor. The addition of AdOx decreased Tax transactivation in C81, Hut102, and MT-2 cells. Unexpectedly, we found that AdOx potently inhibited the growth of HTLV-1-transformed cells. Further investigation revealed that AdOx inhibited the Tax-activated NF-kappaB pathway, resulting in reactivation of p53 and induction of p53 target genes. Analysis of the NF-kappaB pathway demonstrated that AdOx treatment resulted in degradation of the IkappaB kinase complex and inhibition of NF-kappaB through stabilization of the NF-kappaB inhibitor IkappaBalpha. Our data further demonstrated that AdOx induced G(2)/M cell cycle arrest and cell death in HTLV-1-transformed but not control lymphocytes. These studies demonstrate that protein methylation plays an important role in NF-kappaB activation and survival of HTLV-1-transformed cells.

PRMT11: a new Arabidopsis MBD7 protein partner with arginine methyltransferase activity

Plant methyl-DNA-binding proteins (MBDs), discovered by sequence homology to their animal counterparts, have not been well characterized at the physiological and functional levels. In order better to characterize the Arabidopsis AtMBD7 protein, unique in bearing three MBD domains, we used a yeast two-hybrid system to identify its partners. One of the interacting proteins we cloned is the Arabidopsis arginine methyltransferase 11 (AtPRMT11). Glutathione S-transferase pull-down and co-immunoprecipitation assays confirmed that the two proteins interact with each other and can be co-isolated. Using GFP fluorescence, we show that both AtMBD7 and AtPRMT11 are present in the nucleus. Further analyses revealed that AtPRMT11 acts as an arginine methyltransferase active on both histones and proteins of cellular extracts. The analysis of a T-DNA mutant line lacking AtPRMT11 mRNA revealed reduced levels of proteins with asymmetrically dimethylated arginines, suggesting that AtPRMT11, which is highly similar to mammalian PRMT1, is indeed a type I arginine methyltransferase. Further, AtMBD7 is a substrate for AtPRMT11, which post-translationally modifies the portion of the protein-containing C-terminal methylated DNA-binding domain. These results suggest the existence of a link between DNA methylation and arginine methylation.

Mutations in the Type II protein arginine methyltransferase AtPRMT5 result in pleiotropic developmental defects in Arabidopsis

Human PROTEIN ARGININE METHYLTRANSFERASE5 (PRMT5) encodes a type II protein arginine (Arg) methyltransferase and its homologs in animals and yeast (Saccharomyces cerevisiae and Schizosaccharomyces pombe) are known to regulate RNA processing, signal transduction, and gene expression. However, PRMT5 homologs in higher plants have not yet been reported and the biological roles of these proteins in plant development remain elusive. Here, using conventional biochemical approaches, we purified a plant histone Arg methyltransferase from cauliflower (Brassica oleracea) that was nearly identical to AtPRMT5, an Arabidopsis (Arabidopsis thaliana) homolog of human PRMT5. AtPRMT5 methylated histone H4, H2A, and myelin basic protein in vitro. Western blot using symmetric dimethyl histone H4 Arg 3-specific antibody and thin-layer chromatography analysis demonstrated that AtPRMT5 is a type II enzyme. Mutations in AtPRMT5 caused pleiotropic developmental defects, including growth retardation, dark green and curled leaves, and FlOWERING LOCUS C (FLC)-dependent delayed flowering. Therefore, the type II protein Arg methyltransferase AtPRMT5 is involved in promotion of vegetative growth and FLC-dependent flowering time regulation in Arabidopsis.

Low levels of miR-92b/96 induce PRMT5 translation and H3R8/H4R3 methylation in mantle cell lymphoma

Protein arginine methyltransferase PRMT5 interacts with human SWI/SNF complexes and methylates histones H3R8 and H4R3. To elucidate the role of PRMT5 in human cancer, we analyzed PRMT5 expression in normal human B lymphocytes and a panel of lymphoid cancer cell lines as well as mantle cell lymphoma (MCL) clinical samples. We show that PRMT5 protein levels are elevated in all cancer cells, including clinical samples examined despite its low rate of transcription and messenger RNA stability. Remarkably, polysome profiling revealed that PRMT5 mRNA is translated more efficiently in Mino and JeKo MCL cells than in normal B cells, and that decreased miR-92b and miR-96 expression augments PRMT5 translation. Consequently, global methylation of H3R8 and H4R3 is increased and is accompanied by repression of suppressor of tumorigenecity 7 (ST7) in lymphoid cancer cells. Furthermore, knockdown of PRMT5 expression reduces proliferation of transformed JeKo and Raji cells. Thus, our studies indicate that aberrant expression of PRMT5 leads to altered epigenetic modification of chromatin, which in turn impacts transcriptional performance of anti-cancer genes and growth of transformed lymphoid cells.

The new frontier in cancer research: Deciphering cancer epigenetics

Cancer has long been known to be a disease caused by alterations in the genetic blueprint of cells. In the past decade it has become apparent that epigenetic alterations also underlie the etiology of cancer. Since epigenetic changes may be more facile to reverse than genetic lesions, much research has been invested in their characterization. Success has indeed been booked in the clinic with drugs that erase DNA methylation imprints or that target histone post-translational modifications such as lysine acetylation. However, the actual consequences of current epigenetic pharmacological intervention protocols are still poorly characterized and may be rather pleiotropic in nature. The challenge we face is therefore to define the cellular enzymes responsible for epigenetic modifications at given genes under specific conditions, so as to develop pharmacological agents that target tumorigenic epigenetic lesions while eliciting minimal unwanted side effects. Application of genome-wide analytical tools has begun to provide spatio-temporally resolved data that will be crucial to achieve this goal. Finally, the molecular mode of action of epigenetic drugs may be more intricate than initially thought, involving more than DNA and histones, since it has been reported that transcription (co)factors are themselves also targeted by histone modifying enzymes.

Evolutionarily divergent type II protein arginine methyltransferase in Trypanosoma brucei

Protein arginine methylation is a posttranslational modification that impacts cellular functions, such as RNA processing, transcription, DNA repair, and signal transduction. The majority of our knowledge regarding arginine methylation derives from studies of yeast and mammals. Here, we describe a protein arginine N-methyltransferase (PRMT), TbPRMT5, from the early-branching eukaryote Trypanosoma brucei. TbPRMT5 shares the greatest sequence similarity with PRMT5 and Skb1 type II enzymes from humans and Schizosaccharomyces pombe, respectively, although it is significantly divergent at the amino acid level from its mammalian and yeast counterparts. Recombinant TbPRMT5 displays broad substrate specificity in vitro, including methylation of a mitochondrial-gene-regulatory protein, RBP16. TbPRMT5 catalyzes the formation of omega-N(G)-monomethylarginine and symmetric omega-N(G),N(G')-dimethylarginine and does not require trypanosome cofactors for this activity. These data establish that type II PRMTs evolved early in the eukaryotic lineage. In vivo, TbPRMT5 is constitutively expressed in the bloodstream form and procyclic-form (insect host) life stages of the parasite and localizes to the cytoplasm. Genetic disruption via RNA interference in procyclic-form trypanosomes indicates that TbPRMT5 is not essential for growth in this life cycle stage. TbPRMT5-TAP ectopically expressed in procyclic-form trypanosomes is present in high-molecular-weight complexes and associates with an RG domain-containing DEAD box protein related to yeast Ded1 and two kinetoplastid-specific proteins. Thus, TbPRMT5 is likely to be involved in novel methylation-regulated functions in trypanosomes, some of which may include RNA processing and/or translation.

Inhibition of the heat shock protein 90 molecular chaperone in vitro and in vivo by novel, synthetic, potent resorcinylic pyrazole/isoxazole amide analogues

Although the heat shock protein 90 (HSP90) inhibitor 17-allylamino-17-demethoxygeldanamycin (17-AAG) shows clinical promise, potential limitations encourage development of alternative chemotypes. We discovered the 3,4-diarylpyrazole resorcinol CCT018159 by high-throughput screening and used structure-based design to generate more potent pyrazole amide analogues, exemplified by VER-49009. Here, we describe the detailed biological properties of VER-49009 and the corresponding isoxazole VER-50589. X-ray crystallography showed a virtually identical HSP90 binding mode. However, the dissociation constant (K(d)) of VER-50589 was 4.5 +/- 2.2 nmol/L compared with 78.0 +/- 10.4 nmol/L for VER-49009, attributable to higher enthalpy for VER-50589 binding. A competitive binding assay gave a lower IC(50) of 21 +/- 4 nmol/L for VER-50589 compared with 47 +/- 9 nmol/L for VER-49009. Cellular uptake of VER-50589 was 4-fold greater than for VER-49009. Mean cellular antiproliferative GI(50) values for VER-50589 and VER-49009 for a human cancer cell line panel were 78 +/- 15 and 685 +/- 119 nmol/L, respectively, showing a 9-fold potency gain for the isoxazole. Unlike 17-AAG, but as with CCT018159, cellular potency of these analogues was independent of NAD(P)H:quinone oxidoreductase 1/DT-diaphorase and P-glycoprotein expression. Consistent with HSP90 inhibition, VER-50589 and VER-49009 caused induction of HSP72 and HSP27 alongside depletion of client proteins, including C-RAF, B-RAF, and survivin, and the protein arginine methyltransferase PRMT5. Both caused cell cycle arrest and apoptosis. Extent and duration of pharmacodynamic changes in an orthotopic human ovarian carcinoma model confirmed the superiority of VER-50589 over VER-49009. VER-50589 accumulated in HCT116 human colon cancer xenografts at levels above the cellular GI(50) for 24 h, resulting in 30% growth inhibition. The results indicate the therapeutic potential of the resorcinylic pyrazole/isoxazole amide analogues as HSP90 inhibitors.

2 The family of protein arginine metkyltransferases

Arginine methylation is a widespread posttranslational modification found on both nuclear and cytoplasmic proteins. The methylation of arginine residues is catalyzed by the protein arginine N-methyltransferase (PRMT) family of enzymes, of which there are at least nine members in mammals. PRMTs are evolutionarily conserved and are foundin organisms from yeast to man, but not in bacteria. Proteins that are arginine methylated are involved in a number of different cellular processes, including transcriptional regulation, RNA metabolism, and DNA damage repair. How arginine methylation impacts these cellular actions is unclear, although it is likely through the regulation of protein-protein and protein-DNA/RNA interactions. The different PRMTs display varying degrees of substrate specificity, and a certain amount of redundancy is likely to exist between different PRMT family members. Most PRMTs methylate glycine- and arginine-rich patches within their substrates. These regions have been termed GAR motifs. The complexity of the methylarginine mark is enhanced by the ability of this residue to be methylated in three different fashions on the guanidino group (with different functional consequences for each methylated state): monomethylated, symmetrically dimethylated, and asymmetrically dimethylated. This chapter outlines the biochemistry of arginine methylation, including a detailed description of the enzymes involved, the motifs methylated, and the prospects of inhibiting these enzymes with small molecules.

Methyl-CpG-binding domain (MBD) proteins in plants

Cytosine methylation is the most prevalent epigenetic modification of plant nuclear DNA, which occurs in symmetrical CpG or CpNpG as well as in non-symmetrical contexts. Intensive studies demonstrated the central role played by cytosine methylation in genome organization, gene expression and in plant growth and development. However, the way by which the methyl group is interpreted into a functional state has only recently begun to be explored with the isolation and characterization of methylated DNA binding proteins capable of binding 5-methylcytosine. These proteins belong to an evolutionary conserved protein family initially described in animals termed methyl-CpG-binding domain (MBD) proteins. Here, we highlight recent advances and present new prospects concerning plant MBD proteins and their possible role in controlling chromatin structure mediated by CpG methylation.

Gene and Protein Expression Profiling of Human Ovarian Cancer Cells Treated with the Heat Shock Protein 90 Inhibitor 17-Allylamino-17-Demethoxygeldanamycin

The promising antitumor activity of 17-allylamino-17-demethoxygeldanamycin (17AAG) results from inhibition of the molecular chaperone heat shock protein 90 (HSP90) and subsequent degradation of multiple oncogenic client proteins. Gene expression microarray and proteomic analysis were used to profile molecular changes in the A2780 human ovarian cancer cell line treated with 17AAG. Comparison of results with an inactive analogue and an alternative HSP90 inhibitor radicicol indicated that increased expression of HSP72, HSC70, HSP27, HSP47, and HSP90beta at the mRNA level were on-target effects of 17AAG. HSP27 protein levels were increased in tumor biopsies following treatment of patients with 17AAG. A group of MYC-regulated mRNAs was decreased by 17AAG. Of particular interest and novelty were changes in expression of chromatin-associated proteins. Expression of the heterochromatin protein 1 was increased, and expression of the histone acetyltransferase 1 and the histone arginine methyltransferase PRMT5 was decreased by 17AAG. PRMT5 was shown to be a novel HSP90-binding partner and potential client protein. Cellular protein acetylation was reduced by 17AAG, which was shown to have an antagonistic interaction on cell proliferation with the histone deacetylase inhibitor trichostatin A. This mRNA and protein expression analysis has provided new insights into the complex molecular pharmacology of 17AAG and suggested new genes and proteins that may be involved in response to the drug or be potential biomarkers of drug action.

Methylation regulates the intracellular protein-protein and protein-RNA interactions of FMRP

FMRP, the fragile X mental retardation protein, is an RNA-binding protein that interacts with approximately 4% of fetal brain mRNA. We have recently shown that a methyltransferase (MT) co-translationally methylates FMRP in vitro and that methylation modulates the ability of FMRP to bind mRNA. Here, we recapitulate these in vitro data in vivo, demonstrating that methylation of FMRP affects its ability to bind to FXR1P and regulate the translation of FMRP target mRNAs. Additionally, using double-label fluorescence confocal microscopy, we identified a subpopulation of FMRP-containing small cytoplasmic granules that are distinguishable from larger stress granules. Using the oxidative-stress induced accumulation of abortive pre-initiation complexes as a measure of the association of FMRP with translational components, we have demonstrated that FMRP associates with ribosomes during initiation and, more importantly, that methylation regulates this process by influencing the ratio of FMRP-homodimer-containing mRNPs to FMRP-FXR1P-heterodimer-containing mRNPs. These data suggest a vital role for methylation in normal FMRP functioning.

hCAF1, a new regulator of PRMT1-dependent arginine methylation

Protein arginine methylation is an emergent post-translational modification involved in a growing number of cellular processes, including transcriptional regulation, cell signaling, RNA processing and DNA repair. Although protein arginine methyltransferase 1 (PRMT1) is the major arginine methyltransferase in mammals, little is known about the regulation of its activity, except for the regulation induced by interaction with the antiproliferative protein BTG1 (B-cell translocation gene 1). Since the protein hCAF1 (CCR4-associated factor 1) was described to interact with BTG1, we investigated a functional link between hCAF1 and PRMT1. By co-immunoprecipitation and immunofluorescence experiments we demonstrated that endogenous hCAF1 and PRMT1 interact in vivo and colocalize in nuclear speckles, a sub-nuclear compartment enriched in small nuclear ribonucleoproteins and splicing factors. In vitro methylation assays indicated that hCAF1 is not a substrate for PRMT1-mediated methylation, but it regulates PRMT1 activity in a substrate-dependent manner. Moreover, small interfering RNA (siRNA)-mediated silencing of hCAF1 in MCF-7 cells significantly modulates the methylation of endogenous PRMT1 substrates. Finally, we demonstrated that in vitro and in the cellular context, hCAF1 regulates the methylation of Sam68 and histone H4, two PRMT1 substrates. Since hCAF1 and PRMT1 have been involved in the regulation of transcription and RNA metabolism, we speculate that hCAF1 and PRMT1 could contribute to the crosstalk between transcription and RNA processing.

Methylation: a regulator of HIV-1 replication?

Recent characterizations of methyl transferases as regulators of cellular processes have spurred investigations into how methylation events might influence the HIV-1 life cycle. Emerging evidence suggests that protein-methylation can positively and negatively regulate HIV-1 replication. How DNA- and RNA- methylation might impact HIV-1 is also discussed.

Mechanisms of ATP dependent chromatin remodeling

The inter-relationship between DNA repair and ATP dependent chromatin remodeling has begun to become very apparent with recent discoveries. ATP dependent remodeling complexes mobilize nucleosomes along DNA, promote the exchange of histones, or completely displace nucleosomes from DNA. These remodeling complexes are often categorized based on the domain organization of their catalytic subunit. The biochemical properties and structural information of several of these remodeling complexes are reviewed. The different models for how these complexes are able to mobilize nucleosomes and alter nucleosome structure are presented incorporating several recent findings. Finally the role of histone tails and their respective modifications in ATP-dependent remodeling are discussed.

Protein arginine methyltransferases: Evolution and assessment of their pharmacological and therapeutic potential

Protein arginine N-methylation is a post-translational modification whose influence on cell function is becoming widely appreciated. Protein arginine methyltransferases (PRMT) catalyze the methylation of terminal nitrogen atoms of guanidinium side chains within arginine residues of proteins. Recently, several new members of the PRMT family have been cloned and their catalytic function determined. In this report, we present a review and phylogenetic analysis of the PRMT found so far in genomes. PRMT are found in nearly all groups of eukaryotes. Many human PRMT originated early in eukaryote evolution. Homologs of PRMT1 and PRMT5 are found in nearly every eukaryote studied. The gene structure of PRMT vary: most introns appear to be inserted randomly into the open reading frame. The change in catalytic specificity of some PRMT occurred with changes in the arginine binding pocket within the active site. Because of the high degree of conservation of sequence among the family throughout evolution, creation of specific PRMT inhibitors in pathogenic organisms may be difficult, but could be very effective if developed. Furthermore, because of the intricate involvement of several PRMT in cellular physiology, their inhibition may be fraught with unwanted side effects. Nevertheless, development of pharmaceutical agents to control PRMT functions could lead to significant new targets.

Control of the DNA methylation system component MBD2 by protein arginine methylation

DNA methylation is vital for proper chromatin structure and function in mammalian cells. Genetic removal of the enzymes that catalyze DNA methylation results in defective imprinting, transposon silencing, X chromosome dosage compensation, and genome stability. This epigenetic modification is interpreted by methyl-DNA binding domain (MBD) proteins. MBD proteins respond to methylated DNA by recruiting histone deacetylases (HDAC) and other transcription repression factors to the chromatin. The MBD2 protein is dispensable for animal viability, but it is implicated in the genesis of colon tumors. Here we report that the MBD2 protein is controlled by arginine methylation. We identify the protein arginine methyltransferase enzymes that catalyze this modification and show that arginine methylation inhibits the function of MBD2. Arginine methylation of MBD2 reduces MBD2-methyl-DNA complex formation, reduces MBD2-HDAC repression complex formation, and impairs the transcription repression function of MBD2 in cells. Our report provides a molecular description of a potential regulatory mechanism for an MBD protein family member. It is the first to demonstrate that protein arginine methyltransferases participate in the DNA methylation system of chromatin control.

The protein arginine methyltransferase Prmt5 is required for myogenesis because it facilitates ATP-dependent chromatin remodeling

Skeletal muscle differentiation requires the coordinated activity of transcription factors, histone modifying enzymes, and ATP-dependent chromatin remodeling enzymes. The type II protein arginine methyltransferase Prmt5 symmetrically dimethylates histones H3 and H4 and numerous nonchromatin proteins, and prior work has implicated Prmt5 in transcriptional repression. Here we demonstrate that MyoD-induced muscle differentiation requires Prmt5. One of the first genes activated during differentiation encodes the myogenic regulator myogenin. Prmt5 and dimethylated H3R8 (histone 3 arginine 8) are localized at the myogenin promoter in differentiating cells. Modification of H3R8 required Prmt5, and reduction of Prmt5 resulted in the abrogation of promoter binding by the Brg1 ATPase-associated with the SWI/SNF chromatin remodeling enzymes and all subsequent events associated with gene activation, including increases in chromatin accessibility and stable binding by MyoD. Prmt5 and dimethylated H3R8 were also associated with the myogenin promoter in activated satellite cells isolated from muscle tissue, further demonstrating the physiological relevance of these observations. The data indicate that Prmt5 facilitates myogenesis because it is required for Brg1-dependent chromatin remodeling and gene activation at a locus essential for differentiation. We therefore conclude that a histone modifying enzyme is necessary to permit an ATP-dependent chromatin remodeling enzyme to function.

Epigenetic regulation of immune escape genes in cancer

According to the concept of immune surveillance, the appearance of a tumor indicates that it has earlier evaded host defenses and subsequently must have escaped immunity to evolve into a full-blown cancer. Tumor escape mechanisms have focused mainly on mutations of immune and apoptotic pathway genes. However, data obtained over the past few years suggest that epigenetic silencing in cancer may be as frequent a cause of gene inactivation as are mutations. Here, we discuss the evidence that tumor immune evasion is mediated by non-mutational epigenetic events involving chromatin and that epigenetics collaborates with mutations in determining tumor progression. Since epigenetic changes are potentially reversible, the relative contribution of mutations and epigenetics, to the gene defects in any given tumor, may be a factor in determining the efficacy of treatments. We review new developments in basic chromatin mechanisms and in this context describe the rationale for the current use of epigenetic agents in cancer therapy and for a novel epigenetically generated tumor vaccine model. We emphasize that epigenetic cancer treatments are currently a 'blunt-sword' and suggest future directions for designing chromatin-based programs of potential value in the diagnosis and treatment of cancer.

Role of TIF1alpha as a modulator of embryonic transcription in the mouse zygote

The first events of the development of any embryo are under maternal control until the zygotic genome becomes activated. In the mouse embryo, the major wave of transcription activation occurs at the 2-cell stage, but transcription starts already at the zygote (1-cell) stage. Very little is known about the molecules involved in this process. We show that the transcription intermediary factor 1 α (TIF1α) is involved in modulating gene expression during the first wave of transcription activation. At the onset of genome activation, TIF1α translocates from the cytoplasm into the pronuclei to sites of active transcription. These sites are enriched with the chromatin remodelers BRG-1 and SNF2H. When we ablate TIF1α through either RNA interference (RNAi) or microinjection of specific antibodies into zygotes, most of the embryos arrest their development at the 2–4-cell stage transition. The ablation of TIF1α leads to mislocalization of RNA polymerase II and the chromatin remodelers SNF2H and BRG-1. Using a chromatin immunoprecipitation cloning approach, we identify genes that are regulated by TIF1α in the zygote and find that transcription of these genes is misregulated upon TIF1α ablation. We further show that the expression of some of these genes is dependent on SNF2H and that RNAi for SNF2H compromises development, suggesting that TIF1α mediates activation of gene expression in the zygote via SNF2H. These studies indicate that TIF1α is a factor that modulates the expression of a set of genes during the first wave of genome activation in the mouse embryo.

Chromatin-modifiying enzymes are essential when the Saccharomyces cerevisiae morphogenesis checkpoint is constitutively activated

Hsl7p plays a central role in the morphogenesis checkpoint triggered when yeast bud formation is impaired and is proposed to function as an arginine methyltransferase. HSL7 is also essential in the absence of the N-terminal tails of histones H3 or H4. The requirement for H3 and H4 tails may indicate a need for their post-translational modification to bypass the morphogenesis checkpoint. In support of this, the absence of the acetyltransferases Gcn5p or Esa1p, the deacetylase Rpd3p, or the lysine-methyltransferase Set1p resulted in death or extreme sickness in hslDelta mutants. These synthetic interactions involved both the activity of the chromatin-modifying enzymes and the complexes through which they act. Newly reported silencing phenotypes of hsl7Delta mirror those previously reported for gcn5Delta and rpd3Delta, thereby strengthening their functional links. In addition, synthetic interactions and silencing phenotypes were suppressed by inactivation of the morphogenesis checkpoint, either by SWE1 deletion or by preventing Cdc28p phosphorylation. A catalytically dead Hsl7p retained wild-type interactions, implying that modification of histone H3 or H4 N termini by Gcn5p, Esa1p, Rpd3p, and Set1p, but not by Hsl7p, was needed to bypass the morphogenesis checkpoint.

Protein arginine methylation: Cellular functions and methods of analysis

During the last few years, new members of the growing family of protein arginine methyltransferases (PRMTs) have been identified and the role of arginine methylation in manifold cellular processes like signaling, RNA processing, transcription, and subcellular transport has been extensively investigated. In this review, we describe recent methods and findings that have yielded new insights into the cellular functions of arginine-methylated proteins, and we evaluate the currently used procedures for the detection and analysis of arginine methylation.

Regulation of the EBNA1 Epstein-Barr virus protein by serine phosphorylation and arginine methylation

The Epstein-Barr virus (EBV) EBNA1 protein is important for the replication and mitotic segregation of EBV genomes in latently infected cells and also activates the transcription of some of the viral latency genes. A Gly-Arg-rich region between amino acids 325 and 376 is required for both the segregation and transcriptional activation functions of EBNA1. Here we show that this region is modified by both arginine methylation and serine phosphorylation. Mutagenesis of the four potentially phosphorylated serines in this region indicated that phosphorylation of multiple serines contributes to the efficient segregation of EBV-based plasmids by EBNA1, at least in part by increasing EBNA1 binding to hEBP2. EBNA1 was also found to bind the arginine methyltransferases PRMT1 and PRMT5. Multiple arginines in the 325-376 region were methylated in vitro by PRMT1 and PRMT5, as was an N-terminal Gly-Arg-rich region between amino acids 41 and 50. EBNA1 was also shown to be methylated in vivo, predominantly in the 325-376 region. Treatment of cells with a methylation inhibitor or down-regulation of PRMT1 altered EBNA1 localization, resulting in the formation of EBNA1 rings around the nucleoli. The results indicate that EBNA1 function is influenced by both serine phosphorylation and arginine methylation.

Blimp1 associates with Prmt5 and directs histone arginine methylation in mouse germ cells

Blimp1, a transcriptional repressor, has a crucial role in the specification of primordial germ cells (PGCs) in mice at embryonic day 7.5 (E7.5). This SET-PR domain protein can form complexes with various chromatin modifiers in a context-dependent manner. Here, we show that Blimp1 has a novel interaction with Prmt5, an arginine-specific histone methyltransferase, which mediates symmetrical dimethylation of arginine 3 on histone H2A and/or H4 tails (H2A/H4R3me2s). Prmt5 has been shown to associate with Tudor, a component of germ plasm in Drosophila melanogaster. Blimp1-Prmt5 colocalization results in high levels of H2A/H4 R3 methylation in PGCs at E8.5. However, at E11.5, Blimp1-Prmt5 translocates from the nucleus to the cytoplasm, resulting in the loss of H2A/H4 R3 methylation at the time of extensive epigenetic reprogramming of germ cells. Subsequently, Dhx38, a putative target of the Blimp1-Prmt5 complex, is upregulated. Interestingly, expression of Dhx38 is also seen in pluripotent embryonic germ cells that are derived from PGCs when Blimp1 expression is lost. Our study demonstrates that Blimp1 is involved in a novel transcriptional regulatory complex in the mouse germ-cell lineage.

Chromatin control and cancer-drug discovery: realizing the promise

Recent years have seen major advances in elucidating the complexity of chromatin and its role as an epigenetic regulator of gene expression in eukaryotes. We now have a basic understanding of chromatin control and the enzymatic modifications that impart diverse regulatory cues to the functional activity of the genome. Most importantly, although research into chromatin has uncovered fascinating insights into the control of gene expression, it has also generated a large body of information that is being harnessed to develop new therapeutic modalities for treating cancer. Here, we discuss recent advances that support the contention that future generations of chromatin-modulating drugs will provide a significant group of new, mechanism-based therapeutics for cancer.

Protein arginine methylation in lymphocyte signaling

Methylation of arginine is an additional option within the repertoire of post-translational modifications that proteins utilize for their communication with other partner proteins and nucleic acids, which ultimately contributes to cellular functions. Recent studies reveal that protein arginine methylation is more common and widespread than previously thought and that it is implicated in a number of key cellular processes including signal transduction. Two recent investigations have propelled this new world of protein modification into the immunological community by showing that TCR and CD28 signaling exploit this pathway. In contrast to other protein modifications utilized in intracellular signaling, arginine methylation seems to be long-lasting, raising interesting questions as to when, where and for what reason it can be utilized in the lymphocyte differentiation processes.

The generation and recognition of histone methylation

The posttranslational modification of histone proteins via methylation has important functions in gene activation, transcriptional silencing, establishment of chromatin states, and likely many aspects of DNA metabolism. The identification of numerous effector protein domains with the capability of binding methylated histones has significantly advanced our understanding of how such histone modifications may exert their biological effects. Here, we summarize aspects of the generation of arginine and lysine methylation marks on core histones, the characterization of the protein modules that interact with them, and how histone methylation cross-talks with other modifications.