Genomic organization, physical mapping, and expression analysis of the human protein arginine methyltransferase 1 gene

Arginine methylation and respiratory disease

Arginine methylation, a vital post-translational modification, plays a pivotal role in numerous cellular functions such as signal transduction, DNA damage response and repair, regulation of gene transcription, mRNA splicing, and protein interactions. Central to this modification is the role of protein arginine methyltransferases (PRMTs), which have been increasingly recognized for their involvement in the pathogenesis of various respiratory diseases. This review begins with an exploration of the biochemical underpinnings of arginine methylation, shedding light on the intricate molecular regulatory mechanisms governed by PRMTs. It then delves into the impact of arginine methylation and the dysregulation of arginine methyltransferases in diverse pulmonary disorders. Concluding with a focus on the therapeutic potential and recent advancements in PRMT inhibitors, this article aims to offer novel perspectives and therapeutic avenues for the management and treatment of respiratory diseases.

Enhanced Transcriptional Signature and Expression of Histone-Modifying Enzymes in Salivary Gland Tumors

Salivary gland tumors (SGTs) are rare and complex neoplasms characterized by heterogenous histology and clinical behavior as well as resistance to systemic therapy. Tumor etiology is currently under elucidation and an interplay of genetic and epigenetic changes has been proposed to contribute to tumor development. In this work, we investigated epigenetic regulators and histone-modifying factors that may alter gene expression and participate in the pathogenesis of SGT neoplasms. We performed a detailed bioinformatic analysis on a publicly available RNA-seq dataset of 94 ACC tissues supplemented with clinical data and respective controls and generated a protein-protein interaction (PPI) network of chromatin and histone modification factors. A significant upregulation of TP53 and histone-modifying enzymes SUV39H1, EZH2, PRMT1, HDAC8, and KDM5B, along with the upregulation of DNA methyltransferase DNMT3A and ubiquitin ligase UHRF1 mRNA levels, as well as a downregulation of lysine acetyltransferase KAT2B levels, were detected in ACC tissues. The protein expression of p53, SUV39H1, EZH2, and HDAC8 was further validated in SGT tissues along with their functional deposition of the repressive histone marks H3K9me3 and H3K27me3, respectively. Overall, this study is the first to detect a network of interacting proteins affecting chromatin structure and histone modifications in salivary gland tumor cells, further providing mechanistic insights in the molecular profile of SGTs that confer to altered gene expression programs.

Identification of Novel Circular RNAs of the Human Protein Arginine Methyltransferase 1 (PRMT1) Gene, Expressed in Breast Cancer Cells

Circular RNAs (circRNAs) constitute a type of RNA formed through back-splicing. In breast cancer, circRNAs are implicated in tumor onset and progression. Although histone methylation by PRMT1 is largely involved in breast cancer development and metastasis, the effect of circular transcripts deriving from this gene has not been examined. In this study, total RNA was extracted from four breast cancer cell lines and reversely transcribed using random hexamer primers. Next, first- and second-round PCRs were performed using gene-specific divergent primers. Sanger sequencing followed for the determination of the sequence of each novel PRMT1 circRNA. Lastly, bioinformatics analysis was conducted to predict the functions of the novel circRNAs. In total, nine novel circRNAs were identified, comprising both complete and truncated exons of the PRMT1 gene. Interestingly, we demonstrated that the back-splice junctions consist of novel splice sites of the PRMT1 exons. Moreover, the circRNA expression pattern differed among these four breast cancer cell lines. All the novel circRNAs are predicted to act as miRNA and/or protein sponges, while five circRNAs also possess an open reading frame. In summary, we described the complete sequence of nine novel circRNAs of the PRMT1 gene, comprising distinct back-splice junctions and probably having different molecular properties.

Structure, Activity, and Function of PRMT1

PRMT1, the major protein arginine methyltransferase in mammals, catalyzes monomethylation and asymmetric dimethylation of arginine side chains in proteins. Initially described as a regulator of chromatin dynamics through the methylation of histone H4 at arginine 3 (H4R3), numerous non-histone substrates have since been identified. The variety of these substrates underlines the essential role played by PRMT1 in a large number of biological processes such as transcriptional regulation, signal transduction or DNA repair. This review will provide an overview of the structural, biochemical and cellular features of PRMT1. After a description of the genomic organization and protein structure of PRMT1, special consideration was given to the regulation of PRMT1 enzymatic activity. Finally, we discuss the involvement of PRMT1 in embryonic development, DNA damage repair, as well as its participation in the initiation and progression of several types of cancers.

Global analysis of protein arginine methylation

Quantitative information about the levels and dynamics of post-translational modifications (PTMs) is critical for an understanding of cellular functions. Protein arginine methylation (ArgMet) is an important subclass of PTMs and is involved in a plethora of (patho)physiological processes. However, because of the lack of methods for global analysis of ArgMet, the link between ArgMet levels, dynamics, and (patho)physiology remains largely unknown. We utilized the high sensitivity and robustness of nuclear magnetic resonance (NMR) spectroscopy to develop a general method for the quantification of global protein ArgMet. Our NMR-based approach enables the detection of protein ArgMet in purified proteins, cells, organoids, and mouse tissues. We demonstrate that the process of ArgMet is a highly prevalent PTM and can be modulated by small-molecule inhibitors and metabolites and changes in cancer and during aging. Thus, our approach enables us to address a wide range of biological questions related to ArgMet in health and disease.

Novel alternative splice variants of the human protein arginine methyltransferase 1 (PRMT1) gene, discovered using next-generation sequencing

Next-generation sequencing (NGS) technology is highly expected to help researchers disclose the complexity of alternative splicing and understand its association with carcinogenesis. Alternative splicing alterations are firmly associated with multiple malignancies, in terms of functional roles in malignant transformation, motility, and/or metastasis of cancer cells. One perfect example illustrating the connection between alternative splicing and cancer is the human protein arginine methyltransferase 1 (PRMT1) gene, previously cloned from members of our research group and involved in a variety of processes including transcription, DNA repair, and signal transduction. Two splice variants of PRMT1 (variants v.1 and v.2) are downregulated in breast cancer. In addition, PRMT1 v.2 promotes the survival and invasiveness of breast cancer cells, while it could serve as a biomarker of unfavorable prognosis in colon cancer patients. The aim of this study was the molecular cloning of novel alternative splice variants of PRMT1 with the use of 3' RACE coupled with NGS technology. Extensive bioinformatics and computational analysis revealed a significant number of 19 novel alternative splicing events between annotated exons of PRMT1 as well as one novel exon, resulting in the discovery of multiple PRMT1 transcripts. In order to validate the full sequence of the novel transcripts, RT-PCR was carried out with the use of variant-specific primers. As a result, 58 novel PRMT1 transcripts were identified, 34 of which are mRNAs encoding new protein isoforms, whereas the rest 24 transcripts are candidates for nonsense-mediated mRNA decay (NMD).

Novel prognostic marker PRMT1 regulates cell growth via downregulation of CDKN1A in HCC

Hepatocellular carcinoma (HCC) is a major type of liver cancer caused by the hepatitis B and C viruses, alcohol and exposure to aflatoxin. For HCC treatment, anticancer drugs have been widely used, but drug resistance in advanced HCC is an important problem, resulting in a continuous need for novel therapeutic targets. Therefore, in this study, we established a screening pipeline based on RNA-seq to screen novel therapeutic/prognostic targets in HCC and identified PRMT1 (Protein Arginine Methyltransferase 1). In the prognostic analysis, the overexpression of PRMT1 was clearly associated with poor prognosis in a number of HCC patient cohorts. Moreover, after PRMT1 knockdown, HCC cell lines exhibited cell growth and spheroid formation suppression, an increase in Sub-G1 cells by FACS analysis, and enrichment of the cell cycle pathway via functional enrichment analysis. With these results, we demonstrated that PRMT1 could be a novel prognostic marker and therapeutic target for HCC therapy.

A novel splicing isoform of protein arginine methyltransferase 1 (PRMT1) that lacks the dimerization arm and correlates with cellular malignancy

Methylation of arginine residues is an important modulator of protein function that is involved in epigenetic gene regulation, DNA damage response and RNA maturation, as well as in cellular signaling. The enzymes that catalyze this post-translational modification are called protein arginine methyltransferases (PRMTs), of which PRMT1 is the predominant enzyme. Human PRMT1 has previously been shown to occur in seven splicing isoforms, which are differentially abundant in different tissues, and have distinct substrate specificity and intracellular localization. Here we characterize a novel splicing isoform which does not affect the amino-terminus of the protein like the seven known isoforms, but rather lacks exons 8 and 9 which encode the dimerization arm of the enzyme that is essential for enzymatic activity. Consequently, the isoform does not form catalytically active oligomers with the other endogenous PRMT1 isoforms. Photobleaching experiments reveal an immobile fraction of the enzyme in the nucleus, in accordance with earlier results from our laboratory that had shown a tight association of inhibited or inactivated PRMT1 with chromatin and the nuclear scaffold. Thus, it apparently is able to bind to the same substrates as catalytically active PRMT1. This isoform is found in a variety of cell lines, but is increased in those of cancer origin or after expression of the EMT-inducing transcriptional repressor Snail1. We discuss that the novel isoform could act as a modulator of PRMT1 activity in cancer cells by acting as a competitive inhibitor that shields substrates from access to active PRMT1 oligomers.

Intricate Effects of α-Amino and Lysine Modifications on Arginine Methylation of the N-Terminal Tail of Histone H4

Chemical modifications of the DNA and nucleosomal histones tightly control the gene transcription program in eukaryotic cells. The "histone code" hypothesis proposes that the frequency, combination, and location of post-translational modifications (PTMs) of the core histones compose a complex network of epigenetic regulation. Currently, there are at least 23 different types and >450 histone PTMs that have been discovered, and the PTMs of lysine and arginine residues account for a crucial part of the histone code. Although significant progress has been achieved in recent years, the molecular basis for the histone code is far from being fully understood. In this study, we investigated how naturally occurring N-terminal acetylation and PTMs of histone H4 lysine-5 (H4K5) affect arginine-3 methylation catalyzed by both type I and type II PRMTs at the biochemical level. Our studies found that acylations of H4K5 resulted in decreased levels of arginine methylation by PRMT1, PRMT3, and PRMT8. In contrast, PRMT5 exhibits an increased rate of arginine methylation upon H4K5 acetylation, propionylation, and crotonylation, but not upon H4K5 methylation, butyrylation, or 2-hydroxyisobutyrylation. Methylation of H4K5 did not affect arginine methylation by PRMT1 or PRMT5. There was a small increase in the rate of arginine methylation by PRMT8. Strikingly, a marked increase in the rate of arginine methylation was observed for PRMT3. Finally, N-terminal acetylation reduced the rate of arginine methylation by PRMT3 but had little influence on PRMT1, -5, and -8 activity. These results together highlight the underlying mechanistic differences in substrate recognition among different PRMTs and pave the way for the elucidation of the complex interplay of histone modifications.

The BTG2-PRMT1 module limits pre-B cell expansion by regulating the CDK4-Cyclin-D3 complex

Developing pre-B cells in the bone marrow alternate between proliferation and differentiation phases. We found that protein arginine methyl transferase 1 (PRMT1) and B cell translocation gene 2 (BTG2) are critical components of the pre-B cell differentiation program. The BTG2-PRMT1 module induced a cell-cycle arrest of pre-B cells that was accompanied by re-expression of Rag1 and Rag2 and the onset of immunoglobulin light chain gene rearrangements. We found that PRMT1 methylated cyclin-dependent kinase 4 (CDK4), thereby preventing the formation of a CDK4-Cyclin-D3 complex and cell cycle progression. Moreover, BTG2 in concert with PRMT1 efficiently blocked the proliferation of BCR-ABL1-transformed pre-B cells in vitro and in vivo. Our results identify a key molecular mechanism by which the BTG2-PRMT1 module regulates pre-B cell differentiation and inhibits pre-B cell leukemogenesis.

PRMT8 demonstrates variant-specific expression in cancer cells and correlates with patient survival in breast, ovarian and gastric cancer

Recent emphasis has been placed on the role of epigenetic regulators and epigenetic marks as biomarkers for cancer diagnosis and prognosis, and as therapeutic targets for treatment. One such class of regulators is the protein arginine methyltransferase (PRMT) family. The present study examined available curated data regarding the expression and alteration of one of the least studied PRMT family members, PRMT8, in various types of cancer and cancer cell lines. Publicly available cancer data on PRMT8 expression were examined using the Human Protein Atlas and the Kaplan-Meier Plotter, and reverse transcription-polymerase chain reaction was used to screen a selection of human cell lines for variant-specific PRMT8 expression. High levels of PRMT8 expression in breast, ovarian and cervical cancer was observed. Additionally, in patients with breast and ovarian cancer, high PRMT8 expression was correlated with increased patient survival, whereas in gastric cancer, high PRMT8 expression was correlated with decreased patient survival. The present study also investigated the expression of PRMT8 variant 2, a novel transcript variant recently identified in our laboratory, in various cancer cell lines. Variant-specific expression of PRMT8 in numerous distinct cancer cell lines derived from different tissues, including the expression of the novel PRMT8 variant 2 in U87MG glioblastoma cells was demonstrated. The present study proposes the possibility of PRMT8 as a cancer biomarker, based on the high level of PRMT8 expression in various types of cancer, particularly in tissues that would not normally be expected to express PRMT8, and on the correlation of PRMT8 and patient lifespan in several cancer types. Variant-specific expression of PRMT8 in diverse cancer cell lines suggests the possibility of alternate PRMT8 isoforms to have diverse effects on cancer cell phenotypes.

PARAQUAT TOLERANCE3 Is an E3 Ligase That Switches off Activated Oxidative Response by Targeting Histone-Modifying PROTEIN METHYLTRANSFERASE4b

Oxidative stress is unavoidable for aerobic organisms. When abiotic and biotic stresses are encountered, oxidative damage could occur in cells. To avoid this damage, defense mechanisms must be timely and efficiently modulated. While the response to oxidative stress has been extensively studied in plants, little is known about how the activated response is switched off when oxidative stress is diminished. By studying Arabidopsis mutant paraquat tolerance3, we identified the genetic locus PARAQUAT TOLERANCE3 (PQT3) as a major negative regulator of oxidative stress tolerance. PQT3, encoding an E3 ubiquitin ligase, is rapidly down-regulated by oxidative stress. PQT3 has E3 ubiquitin ligase activity in ubiquitination assay. Subsequently, we identified PRMT4b as a PQT3-interacting protein. By histone methylation, PRMT4b upregulates the expression of APX1 and GPX1, encoding two key enzymes against oxidative stress. On the other hand, PRMT4b is recognized by PQT3 for targeted degradation via 26S proteasome. Therefore, we have identified PQT3 as an E3 ligase that acts as a negative regulator of activated response to oxidative stress and found that histone modification by PRMT4b at APX1 and GPX1 loci plays an important role in oxidative stress tolerance.

Oxidative stress is a major stress in plant cells when biotic and abiotic stresses are imposed. While the response to oxidative stress has been extensively studied, little is known about how the activated response is switched off when oxidative stress is diminished. By studying Arabidopsis mutant paraquat tolerance3, we identified the genetic locus PARAQUAT TOLERANCE3 (PQT3) as a major negative regulator of oxidative tolerance. PQT3 encodes an E3 ubiquitin ligase and is rapidly down-regulated by oxidative stress. Subsequently, we identified PRMT4b as a PQT3-interacting protein. PQT3 was demonstrated to recognize PRMT4b for targeted degradation via 26S proteasome. By histone methylation, PRMT4b may regulate the expression of APX1 and GPX1, encoding two key enzymes against oxidative stress. Therefore, we have identified PQT3 as an E3 ubiquitin ligase that turns off the activated response to oxidative stress. Our study provides new insights into the post-translational regulation of plant oxidative stress response and ROS signaling.

Novel Protein Arginine Methyltransferase 8 Isoform Is Essential for Cell Proliferation

Identification of molecular mechanisms that regulate cellular replicative lifespan is needed to better understand the transition between a normal and a neoplastic cell phenotype. We have previously reported that low oxygen-mediated activity of FGF2 leads to an increase in cellular lifespan and acquisition of regeneration competence in human dermal fibroblasts (iRC cells). Though cells display a more plastic developmental phenotype, they remain non-tumorigenic when injected into SCID mice (Page et al. [2009] Cloning Stem Cells 11:417-426; Page et al. [2011] Eng Part A 17:2629-2640) allowing for investigation of mechanisms that regulate increased cellular lifespan in a non-tumorigenic system. Analysis of chromatin modification enzymes by qRT-PCR revealed a 13.3-fold upregulation of the arginine methyltransferase PRMT8 in iRC cells. Increased protein expression was confirmed in both iRC and human embryonic stem cells-the first demonstration of endogenous human PRMT8 expression outside the brain. Furthermore, iRC cells express a novel PRMT8 mRNA variant. Using siRNA-mediated knockdown we demonstrated that this novel variant was required for proliferation of human dermal fibroblasts (hDFs) and grade IV glioblastomas. PRMT8 upregulation in a non-tumorigenic system may offer a potential diagnostic biomarker and a therapeutic target for cells in pre-cancerous and cancerous states. J. Cell. Biochem. 117: 2056-2066, 2016. © 2016 Wiley Periodicals, Inc.

The dual function of PRMT1 in modulating epithelial-mesenchymal transition and cellular senescence in breast cancer cells through regulation of ZEB1

Although the involvement of protein arginine methyltransferase 1 (PRMT1) in tumorigenesis has been reported, its roles in breast cancer progression and metastasis has not been elucidated. Here we identified PRMT1 as a key regulator of the epithelial-mesenchymal transition (EMT) in breast cancer. We showed that the EMT program induced by PRMT1 endowed the human mammary epithelial cells with cancer stem cell properties. Moreover, PRMT1 promoted the migratory and invasive behaviors in breast cancer cells. We also demonstrated that abrogation of PRMT1 expression in breast cancer cells abated metastasis in vivo in mouse model. In addition, knockdown of PRMT1 arrested cell growth in G1 tetraploidy and induced cellular senescence. Mechanistically, PRMT1 impacted EMT process and cellular senescence by mediating the asymmetric dimethylation of arginine 3 of histone H4 (H4R3me2as) at the ZEB1 promoter to activate its transcription, indicating the essential roles of this epigenetic control both in EMT and in senescence. Thus, we unraveled a dual function of PRMT1 in modulation of both EMT and senescence via regulating ZEB1. This finding points to the potent value of PRMT1 as a dual therapeutic target for preventing metastasis and for inhibiting cancer cell growth in malignant breast cancer patients.

Genotype polymorphisms of genes regulating nitric oxide synthesis determine long-term arteriovenous fistula patency in male hemodialysis patients

OBJECTIVES

Nitric oxide (NO) is a pivotal vasoactive substance modulating arteriovenous fistula (AVF) patency for hemodialysis (HD). Since genetic background could be the predicting factor of AVF malfunction, we aimed to investigate whether the NO-related genotype polymorphisms determine AVF survival rates.

METHODS

This is a retrospective, observational, multi-center study involving eight HD units in Taiwan, enrolled 580 patients initiating maintenance HD via AVFs. Genotype polymorphisms of NO-biosynthesis regulating enzymes (DDAH-1, DDAH-2, eNOS and PRMT1) were compared between HD patients with (n = 161) and without (n = 419) history of AVF malfunction. Subgroup analyses by gender were performed to evaluate the genetic effect in difference sexes.

RESULTS

In overall population, statistically significant associations were not found between AVF malfunction and the genetic polymorphisms. In the male subgroup (n = 313), a single nucleotide polymorphism (SNP) of PRMT1, rs10415880 (IVS9-193 A/G), showed a significant association with AVF malfunction. Male patients with AA/AG genotype had inferior AVF outcomes compared to GG genotype, regarding primary patency (70.6% vs. 40.9%, p = 0.001), assisted primary patency (81.0% vs. 58.4%, p < 0.001) and secondary patency (83.7% vs. 63.3%, p < 0.001) at a 5-year observation period. From multivariate Cox regression model, the AA/AG genotypes of PRMT1 were an independent risk factor for AVF malfunction in men (HR: 4.539, 95% CI 2.015-10.223; p < 0.001). However, such associations were not found in women.

CONCLUSIONS

rs10415880, the SNP of PRMT1 could be a novel genetic marker associated with AVF malfunction risk in male HD patients. Those with AA and AG genotypes of rs10415880 may predict a poorer long-term patency of AVF.

PRMT1-mediated methylation of the EGF receptor regulates signaling and cetuximab response

Posttranslational modifications to the intracellular domain of the EGFR are known to regulate EGFR functions; however, modifications to the extracellular domain and their effects remain relatively unexplored. Here, we determined that methylation at R198 and R200 of the EGFR extracellular domain by protein arginine methyltransferase 1 (PRMT1) enhances binding to EGF and subsequent receptor dimerization and signaling activation. In a mouse orthotopic colorectal cancer xenograft model, expression of a methylation-defective EGFR reduced tumor growth. Moreover, increased EGFR methylation sustained signaling activation and cell proliferation in the presence of the therapeutic EGFR monoclonal antibody cetuximab. In colorectal cancer patients, EGFR methylation level also correlated with a higher recurrence rate after cetuximab treatment and reduced overall survival. Together, these data indicate that R198/R200 methylation of the EGFR plays an important role in regulating EGFR functionality and resistance to cetuximab treatment.

Molecular cloning, characterization and expression analysis of the protein arginine N-methyltransferase 1 gene (As-PRMT1) from Artemia sinica

Protein arginine N-methyltransferase 1 (PRMT1) is an important epigenetic regulation factor in eukaryotic genomes. PRMT1 is involved in histone arginine loci methylation modification, changes in eukaryotic genomes' chromatin structure, and gene expression regulation. In the present paper, the full-length 1201-bp cDNA sequence of the PRMT1 homolog of Artemia sinica (As-PRMT1) was cloned for the first time. The putative As-PRMT1 protein comprises 346 amino acids with a SAM domain and a PRMT5 domain. Multiple sequence alignments revealed that the putative sequence of As-PRMT1 protein was relatively conserved across species, especially in the SAM domain. As-PRMT1 is widely expressed during embryo development of A. sinica. This is followed by a dramatic upregulation after diapause termination and then downregulation from the nauplius stage. Furthermore, As-PRMT1 transcripts are highly upregulated under conditions of high salinity and low temperature stress. These findings suggested that As-PRMT1 is a stress-related factor that might promote or inhibit the expression of certain genes, play a critical role in embryonic development and in resistance to low temperature and high salinity stress.

Virtual screening and biological evaluation of novel small molecular inhibitors against protein arginine methyltransferase 1 (PRMT1)

Protein arginine methylation is a common post-translational modification which is crucial for a variety of biological processes. Dysregulation of protein arginine methyltransferases (PRMTs) activity has been implicated in cancer and other serious diseases. Thus, small molecule inhibitors against PRMT have great potential for therapeutic development. Herein, through the combination of virtual screening and bioassays, six small molecular compounds were identified as PRMT1 inhibitors. Amongst them, the binding affinity of compounds DCLX069 and DCLX078 with PRMT1 was further validated by T1ρ and saturation transfer difference (STD) NMR experiments. Most important of all, both compounds effectively blocked cell proliferation in breast cancer, liver cancer and acute myeloid leukemia cell lines. The binding mode analysis from molecular docking simulations theoretically indicated that both inhibitors occupied the SAM binding pocket to exert the inhibitory effect. Taken together, our compounds enriched the structural scaffolds as PRMT1 inhibitors and afforded clues for further optimization.

Role of PRMTs in cancer: Could minor isoforms be leaving a mark?

Protein arginine methyltransferases (PRMTs) catalyze the methylation of a variety of protein substrates, many of which have been linked to the development, progression and aggressiveness of different types of cancer. Moreover, aberrant expression of PRMTs has been observed in several cancer types. While the link between PRMTs and cancer is a relatively new area of interest, the functional implications documented thus far warrant further investigations into its therapeutic potential. However, the expression of these enzymes and the regulation of their activity in cancer are still significantly understudied. Currently there are nine main members of the PRMT family. Further, the existence of alternatively spliced isoforms for several of these family members provides an additional layer of complexity. Specifically, PRMT1, PRMT2, CARM1 and PRMT7 have been shown to have alternative isoforms and others may be currently unrealized. Our knowledge with respect to the relative expression and the specific functions of these isoforms is largely lacking and needs attention. Here we present a review of the current knowledge of the known alternative PRMT isoforms and provide a rationale for how they may impact on cancer and represent potentially useful targets for the development of novel therapeutic strategies.

Immunoaffinity enrichment and mass spectrometry analysis of protein methylation

Protein methylation is a common posttranslational modification that mostly occurs on arginine and lysine residues. Arginine methylation has been reported to regulate RNA processing, gene transcription, DNA damage repair, protein translocation, and signal transduction. Lysine methylation is best known to regulate histone function and is involved in epigenetic regulation of gene transcription. To better study protein methylation, we have developed highly specific antibodies against monomethyl arginine; asymmetric dimethyl arginine; and monomethyl, dimethyl, and trimethyl lysine motifs. These antibodies were used to perform immunoaffinity purification of methyl peptides followed by LC-MS/MS analysis to identify and quantify arginine and lysine methylation sites in several model studies. Overall, we identified over 1000 arginine methylation sites in human cell line and mouse tissues, and ∼160 lysine methylation sites in human cell line HCT116. The number of methylation sites identified in this study exceeds those found in the literature to date. Detailed analysis of arginine-methylated proteins observed in mouse brain compared with those found in mouse embryo shows a tissue-specific distribution of arginine methylation, and extends the types of proteins that are known to be arginine methylated to include many new protein types. Many arginine-methylated proteins that we identified from the brain, including receptors, ion channels, transporters, and vesicle proteins, are involved in synaptic transmission, whereas the most abundant methylated proteins identified from mouse embryo are transcriptional regulators and RNA processing proteins.

Alternatively spliced protein arginine methyltransferase 1 isoform PRMT1v2 promotes the survival and invasiveness of breast cancer cells

Protein arginine methylation is catalyzed by protein arginine methyltransferases (PRMTs) and plays an important role in many cellular processes. Aberrant PRMT expression has been observed in several common cancer types; however, their precise contribution to the cell transformation process is not well understood. We previously reported that the PRMT1 gene generates several alternatively spliced isoforms, and our initial biochemical characterization of these isoforms revealed that they exhibit distinct substrate specificity and subcellular localization. We focus here on the PRMT1v2 isoform, which is the only predominantly cytoplasmic isoform, and we have found that its relative expression is increased in breast cancer cell lines and tumors. Specific depletion of PRMT1v2 using RNA interference caused a significant decrease in cancer cell survival due to an induction of apoptosis. Furthermore, depletion of PRMT1v2 in an aggressive cancer cell line significantly decreased cell invasion. We also demonstrate that PRMT1v2 overexpression in a non-aggressive cancer cell line was sufficient to render them more invasive. Importantly, this novel activity is specific to PRMT1v2, as overexpression of other isoforms did not enhance invasion. Moreover, this activity requires both proper subcellular localization and methylase activity. Lastly, PRMT1v2 overexpression altered cell morphology and reduced cell-cell adhesion, a phenomenon that we convincingly linked with reduced β-catenin protein expression. Overall, we demonstrate a specific role for PRMT1v2 in breast cancer cell survival and invasion, underscoring the importance of identifying and characterizing the distinct functional differences between PRMT1 isoforms.

Identification of small-molecule enhancers of arginine methylation catalyzed by coactivator-associated arginine methyltransferase 1

Arginine methylation is a common post-translational modification that is crucial in modulating gene expression at multiple critical levels. The arginine methyltransferases (PRMTs) are envisaged as promising druggable targets, but their role in physiological and pathological pathways is far from being clear due to the limited number of modulators reported to date. In this effort, enzyme activators can be invaluable tools useful as gain-of-function reagents to interrogate the biological roles in cells and in vivo of PRMTs. Yet the identification of such molecules is rarely pursued. Herein we describe a series of aryl ureido acetamido indole carboxylates (dubbed "uracandolates"), able to increase the methylation of histone (H3) or nonhistone (polyadenylate-binding protein 1, PABP1) substrates induced by coactivator-associated arginine methyltransferase 1 (CARM1), both in in vitro and cellular settings. To the best of our knowledge, this is the first report of compounds acting as CARM1 activators.

Molecular characterization, phylogenetic analysis and expression patterns of five protein arginine methyltransferase genes of channel catfish, Ictalurus punctatus (Rafinesque)

Protein arginine methylation, catalyzed by protein arginine methyltransferases (PRMT), has recently emerged as an important modification in the regulation of gene expression. In this communication, we identified and characterized the channel catfish orthologs to human PRMT 1, 3, 4 and 5, and PRMT4 like. Each PRMT nucleic acid sequence has an open reading frame (ORF) and 3'-untranslated regions. Each ORF appears to encode 361, 587 and 458 amino acid residues for PRMT1, PRMT4 and variant, respectively. The partial ORF of PRMT3 and PRMT5 encode 292 and 563 amino acids, respectively. By comparison with the human counterparts, each channel catfish PRMT also has conserved domains. For expression profile, the channel catfish PRMT1 transcript was detected by RT-PCR in spleens, anterior kidneys, livers, intestines, skin and gills of fish examined. Except in liver, the PRMT3 transcript was detected in all catfish tissues examined. However, the PRMT4 cDNA was detected in livers from all three catfish and gills from two fish, but not other tissues. This information will enable us to further elucidate PRMT functions in channel catfish.

Correlation of SRSF1 and PRMT1 expression with clinical status of pediatric acute lymphoblastic leukemia

BACKGROUND

Acute lymphoblastic leukemia (ALL) is the most frequently-occurring malignant neoplasm in children, but the pathogenesis of the disease remains unclear. In a microarray assay using samples from 100 children with ALL, SFRS1 was found to be up-regulated. Serine/arginine-rich splicing factor 1 (SRSF1, also termed SF2/ASF), encoded by the SFRS1 gene, had been shown to be a pro-oncoprotein. Our previous study indicated that SRSF1 can be methylated by protein arginine methyltransferase 1 (PRMT1) in vitro; however, the biological function of SRSF1 and PRMT1 in pediatric ALL are presently unknown.

METHODS

Matched, newly diagnosed (ND), complete remission (CR) and relapse (RE) bone marrow samples from 57 patients were collected in order to evaluate the expression patterns of SRSF1 and PRMT1. The potential oncogenic mechanism of SRSF1 and PRMT1 in leukemogenesis was also investigated.

RESULTS

We identified significant up-regulation of SRSF1 and PRMT1 in the ND samples. Importantly, the expression of SRSF1 and PRMT1 returned to normal levels after CR, but rebounded in the RE samples. Our observation that SRSF1 could predict disease relapse was of particular interest, although the expression patterns of SRSF1 and PRMT1 were independent of the cytogenetic subtypes. In pre-B-cell lines, both SRSF1 and PRMT1 expression could be efficiently attenuated by the clinical chemotherapy agents arabinoside cytosine (Ara-c) or vincristine (VCR). Moreover, SRSF1 and PRMT1 were associated with each other in leukemia cells in vivo. Knock-down of SRSF1 resulted in an increase in early apoptosis, which could be further induced by chemotherapeutics.

CONCLUSIONS

Our results indicate that SRSF1 serves as an anti-apoptotic factor and potentially contributes to leukemogenesis in pediatric ALL patients by cooperating with PRMT1.

Dapson in heterocyclic chemistry, part VIII: synthesis, molecular docking and anticancer activity of some novel sulfonylbiscompounds carrying biologically active 1,3-dihydropyridine, chromene and chromenopyridine moieties

Several new sulfonebiscompounds having a biologically active 1,2-dihydropyridine-2-one 3-19, acrylamide 20, chromene 21, 22 and chromenopyridine 23, 24 moieties were synthesized and evaluated as potential anticancer agents. The structures of the products were confirmed via elemental analyses and spectral data. The screening tests showed that many of the biscompounds obtained exhibited good anticancer activity against human breast cell line (MCF7) comparable to doxorubicin which was used as reference drug. Compounds 11, 17 and 24 showed IC50 values 35.40 μM, 29.86 μM and 30.99 μM, respectively. In order to elucidate the mechanism of action of the synthesized compounds as anticancer agents, docking on the active site of farnesyltransferase and arginine methyltransferase was also performed and good results were obtained.

Targets in epigenetics: inhibiting the methyl writers of the histone code

Growing evidence suggests that protein lysine methyltransferases (PKMTs) and protein arginine methyltransferases (PRMTs) are associated with the development of various human diseases, including cancer, inflammation, and psychiatric disorders. Given the significant role of these proteins in human disease, efforts to discover selective small-molecule inhibitors of these enzymes are quickly gaining momentum. In this review, we focus on the recent progress in the discovery of selective PKMT and PRMT inhibitors. A future perspective on developing methyltransferase inhibitors is also offered.

Carotid restenosis is associated with plasma ADMA concentrations in carotid endarterectomy patients

BACKGROUND

The aim of this work has been to study the association between plasma asymmetric dimethylarginine (ADMA) concentrations and carotid stenosis in a group of 64 patients undergoing carotid endarterectomy (CEA).

METHODS

Arginine, ADMA and symmetric dimethylarginine (SDMA) were measured using capillary electrophoresis with UV detection. An evaluation of plasma concentrations of total cysteine (tCys) and total homocysteine (tHcy) was also performed.

RESULTS

Pearson's analysis show a positive correlation between ADMA and carotid stenosis (r=0.37, p=0.003), which is also confirmed after stepwise multiple linear regression analysis. ADMA plasma concentrations were significantly associated with tHcy (r=0.40, p=0.001) and to a lesser extent, even if not significantly, with tCys (r=0.23, p=0.07).

CONCLUSIONS

Our data suggest that plasma ADMA is involved in carotid narrowing after CEA intervention. This suggests that this molecule may have an important role in the events that lead to stenosis.

The predominant protein arginine methyltransferase PRMT1 is critical for zebrafish convergence and extension during gastrulation

Protein arginine methyltransferase (PRMT)1 is the predominant type I methyltransferase in mammals. In the present study, we used zebrafish (Danio rerio) as the model system to elucidate PRMT1 expression and function during embryogenesis. Zebrafish prmt1 transcripts were detected from the zygote period to the early larva stage. Knockdown of prmt1 by antisense morpholino oligo (AMO) resulted in delayed growth, shortened body-length, curled tails and cardiac edema. PRMT1 protein level, type I protein arginine methyltransferase activity, specific asymmetric protein arginine methylation and histone H4 R3 methylation all decreased in the AMO-injected morphants. The morphants showed defective convergence and extension and the abnormalities were more severe at the posterior than the anterior parts. Cell migration defects suggested by the phenotypes were not only observed in the morphant embryos, but also in a cellular prmt1 small-interfering RNA knockdown model. Rescue of the phenotypes by co-injection of wild-type but not catalytic defective prmt1 mRNA confirmed the specificity of the AMO and the requirement of methyltransferase activity in early development. The results obtained in the present study demonstrate a direct link of early development with protein arginine methylation catalyzed by PRMT1.

Clinical evaluation of PRMT1 gene expression in breast cancer

Methylation of arginine residues has been implicated in many cellular activities like mRNA splicing, transcription regulation, signal transduction and protein-protein interactions. Protein arginine methyltransferases are the enzymes responsible for this modification in living cells. The most commonly used methyltransferase in man is protein arginine methyltransferase 1 (PRMT1). Since methylation processes appear to interfere in the emergence of several diseases, including cancer, we investigated the localisation of the protein in cancer tissue and, for the first time, the relation that possibly exists between the expression of PRMT1 gene and breast cancer progression. We used tumour specimens from 62 breast cancer patients and semi-quantitative RT-PCR to determine the expression of PRMT1 gene and was found to be associated with patient's age (p = 0.002), menopausal status (p = 0.006), tumour grade (p = 0.03), and progesterone receptor status (p = 0.001). Survival curves revealed that PRMT1-v1 status-low expression relates to longer disease-free survival (DFS; p = 0.036). To the contrary, PRMT1-v2 status is not associated neither with the clinical or pathological parameters nor with DFS (p = 0.31). PRMT1-v3 was not statistically significantly expressed in breast cancer tissue. Selected cancer and normal breast samples were stained for PRMT1. In both normal and cancerous breast tissues, staining was in the cytoplasm and only in rare cases the cell nucleus appeared stained. Present results show a potential use for this gene as a marker of unfavourable prognosis for breast cancer patients.

The protein arginine methyltransferase family: an update about function, new perspectives and the physiological role in humans

Information about the family of protein arginine methyltransferases (PRMTs) has been growing rapidly over the last few years and the emerging role of arginine methylation involved in cellular processes like signaling, RNA processing, gene transcription, and cellular transport function has been investigated. To date, 11 PRMTs gene transcripts have been identified in humans. Almost all PRMTs have been shown to have enzymatic activity and to catalyze arginine methylation. This review will summarize the overall function of human PRMTs and include novel highlights on each family member.

The PRMT1 gene expression pattern in colon cancer

The methylation of arginine has been implicated in many cellular processes, such as regulation of transcription, mRNA splicing, RNA metabolism and transport. The enzymes responsible for this modification are the protein arginine methyltransferases. The most abundant methyltransferase in human cells is protein arginine methyltransferase 1. Methylation processes appear to interfere in the emergence of several diseases, including cancer. During our study, we examined the expression pattern of protein arginine methyltransferase 1 gene in colon cancer patients. The emerging results showed that the expression of one of the gene variants is associated with statistical significant probability to clinical and histological parameters, such as nodal status and stage. This is a first attempt to acquire an insight on the possible relation of the expression pattern of protein arginine methyltransferase 1 and colon cancer progression.

Promiscuous modification of the nuclear poly(A)-binding protein by multiple protein-arginine methyltransferases does not affect the aggregation behavior

The mammalian nuclear poly(A)-binding protein, PABPN1, carries 13 asymmetrically dimethylated arginine residues in its C-terminal domain. By fractionation of cell extracts, we found that protein-arginine methyltransferases (PRMTs)-1, -3, and -6 are responsible for the modification of PABPN1. Recombinant PRMT1, -3, and -6 also methylated PABPN1. Our data suggest that these enzymes act on their own, and additional polypeptides are not involved in recognizing PABPN1 as a substrate. PRMT1 is the predominant methyltransferase acting on PABPN1. Nevertheless, PABPN1 was almost fully methylated in a Prmt1(-/-) cell line; thus, PRMT3 and -6 suffice for methylation. In contrast to PABPN1, the heterogeneous nuclear ribonucleoprotein (hnRNP) K is selectively methylated only by PRMT1. Efficient methylation of synthetic peptides derived from PABPN1 or hnRNP K suggested that PRMT1, -3, and -6 recognize their substrates by interacting with local amino acid sequences and not with additional domains of the substrates. However, the use of fusion proteins suggested that the inability of PRMT3 and -6 to modify hnRNP K is because of structural masking of the methyl-accepting amino acid sequences by neighboring domains. Mutations leading to intracellular aggregation of PABPN1 cause the disease oculopharyngeal muscular dystrophy. The C-terminal domain containing the methylated arginine residues is known to promote PAPBN1 self-association, and arginine methylation has been reported to inhibit self-association of an orthologous protein. Thus, arginine methylation might be relevant for oculopharyngeal muscular dystrophy. However, in two different types of assays we have been unable to detect any effect of arginine methylation on the aggregation of bovine PABPN1.

Alternative Splicing Yields Protein Arginine Methyltransferase 1 Isoforms with Distinct Activity, Substrate Specificity, and Subcellular Localization

PRMT1 is the predominant member of a family of protein arginine methyltransferases (PRMTs) that have been implicated in various cellular processes, including transcription, RNA processing, and signal transduction. It was previously reported that the human PRMT1 pre-mRNA was alternatively spliced to yield three isoforms with distinct N-terminal sequences. Close inspection of the genomic organization in the 5'-end of the PRMT1 gene revealed that it can produce up to seven protein isoforms, all varying in their N-terminal domain. A detailed biochemical characterization of these variants revealed that unique N-terminal sequences can influence catalytic activity as well as substrate specificity. In addition, our results uncovered the presence of a functional nuclear export sequence in PRMT1v2. Finally, we find that the relative balance of PRMT1 isoforms is altered in breast cancer.

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.

Cancer genetics of epigenetic genes

The cancer epigenome is characterised by specific DNA methylation and chromatin modification patterns. The proteins that mediate these changes are encoded by the epigenetics genes here defined as: DNA methyltransferases (DNMT), methyl-CpG-binding domain (MBD) proteins, histone acetyltransferases (HAT), histone deacetylases (HDAC), histone methyltransferases (HMT) and histone demethylases. We review the evidence that these genes can be targeted by mutations and expression changes in human cancers.

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.

Increased Protein Arginine Methylation in Chronic Hypoxia

Asymmetric dimethylarginine (ADMA) is an endogenous inhibitor of nitric oxide synthesis. ADMA is generated by catabolism of proteins containing methylated arginine residues, and its levels are correlated with endothelial dysfunction in systemic cardiovascular diseases. Arginine methylation of cellular proteins is catalyzed by protein arginine methyltransferases (PRMT). The expression and localization of PRMT in the lung has not been addressed. Here, we sought to analyze the expression of PRMT isoforms in the lung and to determine whether PRMT expression is altered during exposure to chronic hypoxia (10% oxygen). Adult mice were exposed to hypoxia for up to 3 wk, and lung tissues were harvested and processed for RT-PCR, Western blotting, immunohistochemistry, and determination of tissue ADMA levels. All PRMT isoforms investigated were detected at the mRNA and protein level in mouse lung, and were localized primarily to the bronchial and alveolar epithelium. In lungs of mice subjected to chronic hypoxia, PRMT2 mRNA and protein levels were up-regulated, whereas the expression of all other PRMT isoforms remained unchanged. This was mainly due to increased expression of PRMT2 in alveolar type II cells, which did not express detectable levels of PRMT2 under normoxic conditions. Consistent with these observations, lung ADMA levels and ADMA/l-Arginine ratios were increased under hypoxic conditions. These results demonstrate that PRMTs are expressed and functional in the lung, and that hypoxia is a potent regulator of PRMT2 expression and lung ADMA concentrations. These data suggest that structural and functional changes caused by hypoxia may be linked to ADMA metabolism.

Immune responses to DNA mismatch repair enzymes hMSH2 and hPMS1 in patients with pancreatic cancer, dermatomyositis and polymyositis

To identify tumor antigens useful for diagnosis and immunotherapy of patients with pancreatic ductal adenocarcinoma, we applied a SEREX approach with a cDNA library made from 5 pancreatic cancer cell lines and sera obtained from 8 patients with pancreatic cancer, and isolated total 32 genes, including 14 previously characterized genes and 18 genes with unknown functions. Among these isolated antigens, serum IgG antibodies for 2 isolated DNA mismatch repair enzymes, Homo sapiens mutS homolog 2 (hMSH2) and Homo sapiens postmeiotic segregation increased 1 (hPMS1), were detected in patients with pancreatic ductal adenocarcinoma and dermatomyositis (DM), and polymyositis (PM), but not in sera from healthy individuals. Immunohistochemical study demonstrated that hMSH2 and hPMS1 were over-expressed in pancreatic ductal adenocarcinoma compared to normal pancreatic ducts. These results suggested that hMSH2 and hPMS1 may be useful as CD4+ helper T cell antigens for immunotherapy of pancreatic cancer patients and that serum IgG antibodies may be useful for diagnosis of patients with pancreatic ductal adenocarcinoma and DM/PM.

Arginine methylation an emerging regulator of protein function

Arginine methylation is now coming out of the shadows of protein phosphorylation and entering the mainstream, largely due to the identification of the family of enzymes that lay down this modification. In addition, modification-specific antibodies and proteomic approaches have facilitated the identification of an array of substrates for the protein arginine methyltransferases. This review describes recent insights into the molecular processes regulated by arginine methylation in normal and diseased cells.

mRNA expression analysis of a variety of apoptosis-related genes, including the novel gene of the BCL2-family, BCL2L12, in HL-60 leukemia cells after treatment with carboplatin and doxorubicin

Apoptosis is a type of programmed cell death involved in many crucial biological processes. It represents the basic mechanism for the action of chemotherapeutic agents, such as doxorubicin and carboplatin. Both are able to cause cell death through the induction of apoptosis in the human leukemic cell line HL-60. We investigated the possible alterations in the expression of apoptosis-related genes, including the novel BCL2L12 gene, which was recently cloned in our group. The kinetics of apoptosis induction and cell toxicity was investigated by DNA laddering and by the MTT method, respectively. Total RNA was extracted and cDNA was prepared by reverse transcription. BCL2 , BAX , FAS , caspase-9, caspase-3 and BCL2L12 were amplified by PCR. Overexpression of FAS , BCL2L12 and caspase-3 was observed after treatment of HL-60 cells for 3 or 6 h with carboplatin, while their expression was decreased after a 12-h treatment, demonstrating that these genes may take part in the early stages of apoptosis. Overexpression of the same genes was also observed after 6 h of treatment with doxorubicin (concomitantly with DNA laddering). In the case of carboplatin-induced apoptosis we detected down-regulation of BAX , BCL2 and caspase-9, whereas in the case of doxorubicin, BAX and BCL2 remained at control levels and caspase-9 was increased.

SR-A1, a member of the human pre-mRNA splicing factor family, and its expression in colon cancer progression

SR (serine-arginine) proteins are essential pre-mRNA splicing factors. Several SR proteins have been characterized in humans, among them SR-A1. It has been demonstrated by members of our group that the SR-A1 gene is constitutively expressed in most of the human tissues, while its transcription is increased in breast carcinoma cell lines. Moreover, the SR-A1 gene is overexpressed in a set of ovarian tumors, suggesting that it may be involved in the pathogenesis and/or progression of ovarian cancer. Therefore, in the present study we examined the expression of the SR-A1 gene in colon cancer tissues by RT-PCR and found that it is overexpressed as compared to normal mucosa (p=0.01). The SR-A1 gene was expressed more frequently in well-differentiated tumors than those with poor differentiation. Survival curves determined by the Kaplan-Meier method and univariate analysis demonstrated that SR-A1-positivity is associated with a long survival (p=0.044). However, when entered into a Cox multivariate model adjusted for other clinicopathological features studied, SR-A1 expression status was not found to be of independent prognostic significance. To the best of our knowledge, this is the first study examining the expression of the novel gene SR-A1 in colon cancer progression.

Expression analysis of BCL2L12, a new member of apoptosis-related genes, in colon cancer

Apoptosis is an active process regulated by a variety of genes. Recently, the molecular cloning, physical mapping and expression analysis of a novel gene of the Bcl-2 family, BCL2L12, was reported. Expression analysis of the BCL2L12 gene in breast cancer confirmed an association of BCL2L12 with favorable prognosis of patients. In the present study, the expression of the BCL2L12 gene was analyzed in colon cancer by RT-PCR. Two transcripts, BCL2L12 and BCL2L12-A, were overexpressed in the cancer tissues as compared to their paired normal mucosa. An association was found between BCL2L12-A transcript expression and nodal status, as well as Dukes' stage. The BCL2L12-A transcript appears to be of importance for colon cancer since its expression is associated with disease progression.

In vivo analysis of nucleolar proteins modified by the yeast arginine methyltransferase Hmt1/Rmt1p

In this report, we have investigated the impact of arginine methylation on the Gar1, Nop1, and Nsr1 nucleolar proteins in Saccharomyces cerevisiae. Although previous reports have established that protein arginine methylation is important for nucleocytoplasmic shuttling, they have focused on the examination of heterogeneous nuclear ribonucleoproteins (hnRNPs). We have extended this analysis to several nucleolar proteins that represent a distinct functional class of arginine-methylated proteins. We first developed an in vivo assay to identify proteins methylated by the Hmt1 arginine methyltransferase. This assay is based on the fact that the Hmt1 enzyme utilizes S-Adenosyl-L-methionine as the methyl donor for protein arginine methylation. Following SDS polyacrylamide electrophoresis, 11 distinct proteins were identified as substrates for the Hmt1 methyltransferase. Hmt1p overexpression did not increase the methylation level on these proteins, suggesting they are fully methylated under the conditions examined. Three of the radiolabeled proteins were confirmed to be Gar1p, Nop1p, and Nsr1p. To monitor the cellular localization of these proteins, functional GFP fusion proteins were generated and found to be localized to the nucleolus. This localization was independent of arginine methylation. Furthermore, all three proteins examined did not export to the cytoplasm. In contrast, arginine methylation is required for the export of the nuclear RNA-binding proteins Npl3p, Hrp1p, and Nab2p. The observation that three nucleolar proteins are modified by Hmt1p but are not exported from the nucleolus implies an alternate role for arginine methylation.

Polyadenylate polymerase (PAP) and 3' end pre-mRNA processing: function, assays, and association with disease

Polyadenylate polymerase (PAP) is one of the enzymes involved in the formation of the polyadenylate tail of the 3' end of mRNA. Poly (A) tail formation is a significant component of 3' processing, a link in the chain of events, including transcription, splicing, and cleavage/polyadenylation of pre-mRNA. Transcription, capping, splicing, polyadenylation, and transport take place as coupled processes that can regulate one another. The poly(A) tail is found in almost all eukaryotic mRNA and is important in enhancing translation initiation and determining mRNA stability. Control of poly(A) tail synthesis could possibly be a key regulatory step in gene expression. PAP-specific activity values are measured by a highly sensitive assays and immunocytochemical methods. High levels of PAP activity are associated with rapidly proliferating cells, it also prevents apoptosis. Changes of PAP activity may cause a decrease in the rate of polyadenylation in the brain during epileptic seizures. Testis-specific PAP may play an important role in spermiogenesis. PAP was found to be an unfavorable prognostic factor in leukemia and breast cancer. Furthermore, measurements of PAP activity may contribute to the definition of the biological profile of tumor cells. It is crucial to know the specific target causing the elevation of serum PAP, for it to be used as a marker for disease. This review summarizes the recently accumulated knowledge on PAP including its function, assays, and association with various human diseases, and proposes future avenues for research.