Protein arginine N-methyltransferase 2 plays a noncatalytic role in the histone methylation activity of PRMT1.

Protein arginine N-methyltransferases are a family of epigenetic enzymes responsible for monomethylation or dimethylation of arginine residues on histones. Dysregulation of protein arginine N-methyltransferase activity can lead to aberrant gene expression and cancer. Recent studies have shown that PRMT2 expression and histone H3 methylation at arginine 8 are correlated with disease severity in glioblastoma multiforme, hepatocellular carcinoma, and renal cell carcinoma. In this study, we explore a noncatalytic mechanistic role for PRMT2 in histone methylation by investigating interactions between PRMT2, histone peptides and proteins, and other PRMTs using analytical and enzymatic approaches. We quantify interactions between PRMT2, peptide ligands, and PRMT1 in a cofactor- and domain-dependent manner using differential scanning fluorimetry. We found that PRMT2 modulates the substrate specificity of PRMT1. Using calf thymus histones as substrates, we saw that a 10-fold excess of PRMT2 promotes PRMT1 methylation of both histone H4 and histone H2A. We found equimolar or a 10-fold excess of PRMT2 to PRMT1 can improve the catalytic efficiency of PRMT1 towards individual histone substrates H2A, H3, and H4. We further evaluated the effects of PRMT2 towards PRMT1 on unmodified histone octamers and mononucleosomes and found marginal PRMT1 activity improvements in histone octamers but significantly greater methylation of mononucleosomes in the presence of 10-fold excess of PRMT2. This work reveals the ability of PRMT2 to serve a noncatalytic role through its SH3 domain in driving site-specific histone methylation marks.

Investigating Protein Binding with the Isothermal Ligand-induced Resolubilization Assay.

Target engagement assays typically detect and quantify the direct physical interaction of a protein of interest and its ligand through stability changes upon ligand binding. Commonly used target engagement methods detect ligand-induced stability by subjecting samples to thermal or proteolytic stress. Here we describe a new variation to these approaches called Isothermal Ligand-induced Resolubilization Assay (ILIRA), which utilizes lyotropic solubility stress to measure ligand binding through changes in target protein solubility. We identified distinct buffer systems and salt concentrations that compromised protein solubility for four diverse proteins: dihydrofolate reductase (DHFR), nucleoside diphosphate-linked moiety X motif 5 (NUDT5), poly [ADP-ribose] polymerase 1 (PARP1), and protein arginine N-methyltransferase 1 (PRMT1). Ligand-induced solubility rescue was demonstrated for these proteins, suggesting that ILIRA can be used as an additional target engagement technique. Differences in ligand-induced protein solubility were assessed by Coomassie blue staining for SDS-PAGE and dot blot, as well as by NanoOrange, Thioflavin T, and Proteostat fluorescence, thus offering flexibility for readout and assay throughput.

Methylarginine efflux in nutrient-deprived yeast mitigates disruption of nitric oxide synthesis.

Protein arginine N-methyltransferases (PRMTs) have emerged as important actors in the eukaryotic stress response with implications in human disease, aging, and cell signaling. Intracellular free methylarginines contribute to cellular stress through their interaction with nitric oxide synthase (NOS). The arginine-dependent production of nitric oxide (NO), which is strongly inhibited by methylarginines, serves as a protective small molecule against oxidative stress in eukaryotic cells. NO signaling is highly conserved between higher and lower eukaryotes, although a canonical NOS homologue has yet to be identified in yeast. Since stress signaling pathways are well conserved among eukaryotes, yeast is an ideal model organism to study the implications of PRMTs and methylarginines during stress. We sought to explore the roles and fates of methylarginines in Saccharomyces cerevisiae. We starved methyltransferase-, autophagy-, and permease-related yeast knockouts by incubating them in water and monitored methylarginine production. We found that under starvation, methylarginines are expelled from yeast cells. We found that autophagy-deficient cells have an impaired ability to efflux methylarginines, which suggests that methylarginine-containing proteins are degraded via autophagy. For the first time, we determine that yeast take up methylarginines less readily than arginine, and we show that methylarginines impact yeast NO production. This study reveals that yeast circumvent a potential methylarginine toxicity by expelling them after autophagic degradation of arginine-modified proteins.

Efficacy of laparoscopic fundoplication in patients with chronic cough and gastro-oesophageal reflux.

BACKGROUND: The outcome of anti-reflux surgery in patients with suspected gastro-oesophageal reflux-induced cough is frequently uncertain. The aims of this study were to assess the efficacy of laparoscopic fundoplication for controlling cough in patients with chronic cough without asthma, who have pathologic gastro-oesophageal reflux, and to identify predictors of response. METHODS: From a prospective database of 1598 patients who have undergone laparoscopic fundoplication, 66 (4%) with proven gastro-oesophageal reflux disease (GORD) and chronic cough without asthma were studied. All patients underwent gastroscopy and 24-h pH monitoring before operation. Heartburn and regurgitation were assessed using a modified DeMeester score. Severity of cough before and after surgery was self-assessed by the patient using a visual analog scale at a minimum of 12 months post-operatively (median 43 mo; range: 14-104 mo). Patients were considered to have responded to fundoplication if they had no cough or the cough had improved by 50% or more after operation. RESULTS: Cough and heartburn/regurgitation were relieved in 61% (40/66) and 90% (44/49) of the patients, respectively. The presence of typical GORD symptoms or oesophagitis, and pH study variables did not predict the response of the cough to fundoplication. CONCLUSION: Refinement in the aetiological diagnosis of chronic cough due to GORD is necessary for improved outcome. Patients diagnosed with GORD-related chronic cough need to be counseled regarding their expectations from anti-reflux surgery.

Protein arginine N-methyltransferase activity determination with filter binding and phosphor screening (FBAPS) assay.

We developed a cost-effective assay to measure protein arginine N-methyltransferase (PRMT) activity in a medium-throughput manner by combining P81 filter binding and phosphor screening (FBAPS). Recombinantly-expressed PRMT1 and coactivator-associated arginine methyltransferase 1 (CARM1) were used to develop the FBAPS assay using GST fusions of glycine- and arginine-rich (GAR) protein and polyA binding protein 1 (PABP1(437-488)) as substrates, respectively, and radiolabelled S-adenosyl-L-[methyl-14C]-methionine as cofactor. Methylation reactions were spotted onto P81 filter paper in a dot blot apparatus and radioactive signals were measured both by phosphor imaging and liquid scintillation counting. Kinetic parameters (KM, kcat) for enzymes and substrates were determined, and IC50 values were obtained for well-characterized inhibitors. FBAPS yielded kinetic parameters with no statistically significant difference to what was obtained using liquid scintillation counting. The IC50 values obtained by the FBAPS assay for PRMT1 and CARM1 were comparable to values reported in literature. The FBAPS assay is a modification to the P81 filter binding assay with a dot blot apparatus that allows for processing of samples in a multi-well format, moderately increasing throughput. Signal detection by phosphor imaging offers an affordable and quantitative method that can be used to screen several inhibitors simultaneously against PRMT enzymes with high accuracy.

Esophageal perforations - a population-based nationwide study in Sweden with survival analysis.

BACKGROUND: Esophageal perforation is a rare and life-threatening condition with several treatment options. The aim was to assess the incidence, type of treatment and mortality of esophageal perforations in Sweden and to identify risk factors for 90-day mortality. METHOD: All patients admitted with an esophageal perforation from 2007 to 2017 were identified from the National Patient Register. Mortality was assessed by linkage with the Cause of Death Registry. We analyze the incidence and the impact of age, sex, comorbidities on mortality. RESULTS: 879 patients with esophageal perforation were identified, giving an incidence rate of 1.09 per 100,000 person-years. The median age at diagnosis was 68.8 years and 60% were men. The mortality was 26% at 90 days. Independent risk factors for death within 90 days were age (odds ratio (OR): 6.20; 95% (confidence interval) CI: 2.16-17.79 at 60-74 years and OR: 11.58; 95% CI: 4.04-33.15 at 75 years or older), peripheral vascular disease (OR: 2.92; 95% CI: 1.44-5.92) and underlying malignant disease (OR: 5.91; 95% CI: 3.86-9.03). In patients younger than 45 years, survival was lower among women than among men (at 5 years 73 and 93%, respectively). The cause of death among young women was often drug-related or suicide. CONCLUSIONS: 90-day mortality was 26%, old age, vascular disease and underlying malignant disease were risk factors.

Protein arginine methyltransferase 8 modulates mitochondrial bioenergetics and neuroinflammation after hypoxic stress.

Protein arginine methyltransferases (PRMTs) are a family of enzymes involved in gene regulation and protein/histone modifications. PRMT8 is primarily expressed in the central nervous system, specifically within the cellular membrane and synaptic vesicles. Recently, PRMT8 has been described to play key roles in neuronal signaling such as a regulator of dendritic arborization, synaptic function and maturation, and neuronal differentiation and plasticity. Here, we examined the role of PRMT8 in response to hypoxia-induced stress in brain metabolism. Our results from liquid chromatography mass spectrometry, mitochondrial oxygen consumption rate, and protein analyses indicate that PRMT8(-/-) knockout mice presented with altered membrane phospholipid composition, decreased mitochondrial stress capacity, and increased neuroinflammatory markers, such as tumor necrosis factor alpha and ionized calcium binding adaptor molecule 1 (Iba1, a specific marker for microglia/macrophage activation) after hypoxic stress. Furthermore, adenovirus-based overexpression of PRMT8 reversed the changes in membrane phospholipid composition, mitochondrial stress capacity, and neuroinflammatory markers. Together, our findings establish PRMT8 as an important regulatory component of membrane phospholipid composition, short-term memory function, mitochondrial function, and neuroinflammation in response to hypoxic stress.

The application of differential scanning fluorimetry in exploring bisubstrate binding to protein arginine N-methyltransferase 1.

Protein arginine N-methyltransferases (PRMTs) are a family of 9 enzymes that catalyze mono- or di-methylation of arginine residues using S-adenosyl-l-methionine (SAM). Arginine methylation is an important post-translational modification that can regulate the activity and structure of target proteins. Altered PRMT activity can lead to a variety of health issues including neurodevelopmental disease, autoimmune disorders, cancer, and cardiovascular disease. Thus, developing a robust mechanistic understanding of PRMT function may provide insight into these various disease states and enable the development of potential therapeutic agents. Although PRMTs have been studied for nearly two decades, a consensus regarding the mechanism of action for this class of enzymes has remained noticeably elusive. To address this shortcoming, differential scanning fluorimetry (DSF) was used to gain mechanistic insight into the order of PRMT substrate and cofactor binding. This methodology confirms that PRMT cofactor binding precedes target substrate binding and supports the use of DSF to study bisubstrate enzymatic reaction mechanisms.

Characterization of impact pile driving signals during installation of offshore wind turbine foundations.

Impact pile driving creates intense, impulsive sound that radiates into the surrounding environment. Piles driven vertically into the seabed generate an azimuthally symmetric underwater sound field whereas piles driven on an angle will generate an azimuthally dependent sound field. Measurements were made during pile driving of raked piles to secure jacket foundation structures to the seabed in waters off the northeastern coast of the U.S. at ranges between 500 m and 15 km. These measurements were analyzed to investigate variations in rise time, decay time, pulse duration, kurtosis, and sound received levels as a function of range and azimuth. Variations in the radiated sound field along opposing azimuths resulted in differences in measured sound exposure levels of up to 10 dB and greater due to the pile rake as the sound propagated in range. The raked pile configuration was modeled using an equivalent axisymmetric FEM model to describe the azimuthally dependent measured sound fields. Comparable sound level differences in the model results confirmed that the azimuthal discrepancy observed in the measured data was due to the inclination of the pile being driven relative to the receiver.

Kinetic Analysis of PRMT1 Reveals Multifactorial Processivity and a Sequential Ordered Mechanism.

Arginine methylation is a prevalent post-translational modification in eukaryotic cells. Two significant debates exist within the field: do these enzymes dimethylate their substrates in a processive or distributive manner, and do these enzymes operate using a random or sequential method of bisubstrate binding? We revealed that human protein arginine N-methyltransferase 1 (PRMT1) enzyme kinetics are dependent on substrate sequence. Further, peptides containing an Nη-hydroxyarginine generally demonstrated substrate inhibition and had improved KM values, which evoked a possible role in inhibitor design. We also revealed that the perceived degree of enzyme processivity is a function of both cofactor and enzyme concentration, suggesting that previous conclusions about PRMT sequential methyl transfer mechanisms require reassessment. Finally, we demonstrated a sequential ordered Bi-Bi kinetic mechanism for PRMT1, based on steady-state kinetic analysis. Together, our data indicate a PRMT1 mechanism of action and processivity that might also extend to other functionally and structurally conserved PRMTs.

Structural basis of arginine asymmetrical dimethylation by PRMT6.

PRMT6 is a type I protein arginine methyltransferase, generating the asymmetric dimethylarginine mark on proteins such as histone H3R2. Asymmetric dimethylation of histone H3R2 by PRMT6 acts as a repressive mark that antagonizes trimethylation of H3 lysine 4 by the MLL histone H3K4 methyltransferase. PRMT6 is overexpressed in several cancer types, including prostate, bladder and lung cancers; therefore, it is of great interest to develop potent and selective inhibitors for PRMT6. Here, we report the synthesis of a potent bisubstrate inhibitor GMS [6'-methyleneamine sinefungin, an analog of sinefungin (SNF)], and the crystal structures of human PRMT6 in complex, respectively, with S-adenosyl-L-homocysteine (SAH) and the bisubstrate inhibitor GMS that shed light on the significantly improved inhibition effect of GMS on methylation activity of PRMT6 compared with SAH and an S-adenosyl-L-methionine competitive methyltransferase inhibitor SNF. In addition, we also crystallized PRMT6 in complex with SAH and a short arginine-containing peptide. Based on the structural information here and available in the PDB database, we proposed a mechanism that can rationalize the distinctive arginine methylation product specificity of different types of arginine methyltransferases and pinpoint the structural determinant of such a specificity.

Stochastic Modeling of Behavioral Response to Anthropogenic Sounds.

The effect of anthropogenic sounds on marine wildlife is typically assessed by convolving the spatial, temporal, and spectral properties of a modeled sound field with a representation of animal distribution within the field. Both components benefit from stochastic modeling techniques based on field observations. Recent studies have also highlighted the effect of context on the probability and severity of the animal behavioral response to sound. This paper extends the stochastic approach to three modeling scenarios, including key contextual variables in aversion from a given level of sound and as a means of evaluating the effectiveness of passive acoustic monitoring.

Current Status of Development of Methods to Assess Effects of Cumulative or Aggregated Underwater Sounds on Marine Mammals.

There are no standards for assessment of the cumulative effects of underwater sound. Quantitative assessments typically consider a single source, whereas qualitative assessments may include multiple sources but rarely identify response variables. As a step toward understanding the cumulative effects of underwater sound, we assessed the aggregated sounds of multiple sources received by migrating bowhead whales (Balaena mysticetus). The quantitative method models the sound field from multiple sources and simulates movement of a population through it. The qualitative method uses experts to assess the responses of individuals and populations to sound sources and identify the potential mechanisms. These methods increase the transparency of assessments.

Arginine methylation in yeast proteins during stationary-phase growth and heat shock.

Arginine methyltransferases (RMTs) catalyze the methylation of arginine residues on proteins. We examined the effects of log-phase growth, stationary-phase growth, and heat shock on the formation of methylarginines on yeast proteins to determine if the conditions favor a particular type of methylation. Utilizing linear ion trap mass spectrometry, we identify methylarginines in wild-type and RMT deletion yeast strains using secondary product ion scans (MS(3)), and quantify the methylarginines using multiple reaction monitoring (MRM). Employing MS(3) and isotopic incorporation, we demonstrate for the first time that Nη1, Nη2-dimethylarginine (sDMA) is present on yeast proteins, and make a detailed structural determination of the fragment ions from the spectra. Nη-monomethylarginine (ηMMA), Nδ-monomethylarginine (δMMA), Nη1, Nη1-dimethylarginine (aDMA), and sDMA were detected in RMT deletion yeast using MS(3) and MRM with and without isotopic incorporation, suggesting that additional RMT enzymes remain to be discovered in yeast. The concentrations of ηMMA and δMMA decreased by half during heat shock and stationary phase compared to log-phase growth of wild-type yeast, whereas sDMA increased by as much as sevenfold and aDMA decreased by 11-fold. Therefore, upon entering stressful conditions like heat shock or stationary-phase growth, there is a net increase in sDMA and decreases in aDMA, ηMMA, and δMMA on yeast proteins.

Genome-wide analysis of esophageal adenocarcinoma yields specific copy number aberrations that correlate with prognosis.

The incidence of esophageal adenocarcinoma (EAC) has been increasing rapidly for the past 3 decades in Western (Caucasian) populations. Curative treatment is based around esophagectomy, which has a major impact on quality of life. For those suitable for treatment with curative intent, 5-year survival is ∼30%. More accurate prognostic tools are therefore needed, and copy number aberrations (CNAs) may offer the ability to act as prospective biomarkers in this regard. We performed a genome-wide examination of CNAs in 54 samples of EAC using single-nucleotide polymorphism (SNP) arrays. Our aims were to describe frequent regions of CNA, to define driver CNAs, and to identify CNAs that correlated with survival. Regions of frequent amplification included oncogenes such as EGFR, MYC, KLF12, and ERBB2, while frequently deleted regions included tumor suppressor genes such as CDKN2A/B, PTPRD, FHIT, and SMAD4. The genomic identification of significant targets in cancer (GISTIC) algorithm identified 24 regions of gain and 28 regions of loss that were likely to contain driver changes. We discovered 61 genes in five regions that, when stratified by CNA type (gain or loss), correlated with a statistically significant difference in survival. Pathway analysis of the genes residing in both the GISTIC and prognostic regions showed they were significantly enriched for cancer-related networks. Finally, we discovered that copy-neutral loss of heterozygosity is a frequent mechanism of CNA in genes currently targetable by chemotherapy, potentially leading to under-reporting of cases suitable for such treatment.

Protein arginine N-methyltransferase substrate preferences for different nη-substituted arginyl peptides.

Protein arginine N-methyltransferases (PRMTs) catalyze methyl-group transfer from S-adenosyl-L-methionine onto arginine residues in proteins. In this study, modifications were introduced at the guanidine moiety of a peptidyl arginine residue to investigate how changes to the PRMT substrate can modulate enzyme activity. We found that peptides bearing Nη-hydroxy or Nη-amino substituted arginine showed higher apparent kcat values than for the monomethylated substrate when using PRMT1, whereas this catalytic preference was not observed for PRMT4 and PRMT6. Methylation by compromised PRMT1 variants E153Q and D51N further supports the finding that the N-hydroxy substitution facilitates methyl transfer by tuning the reactivity of the guanidine moiety. In contrast, Nη-nitro and Nη-canavanine substituted substrates inhibit PRMT activity. These findings demonstrate that methylation of these PRMT substrates is dependent on the nature of the modification at the guanidine moiety.

Whistle source levels of free-ranging bottlenose dolphins and Atlantic spotted dolphins in the Gulf of Mexico.

Whistles of bottlenose dolphins (Tursiops truncatus) and Atlantic spotted dolphins (Stenella frontalis) in the eastern Gulf of Mexico were recorded and measured with a calibrated towed hydrophone array. Surveys encountered groups of both bottlenose (N = 10) and spotted dolphins (N = 5). Analysis of those data produced 1695 bottlenose dolphin whistles and 1273 spotted dolphin whistles with a high signal-to-noise ratio. Whistle frequency metrics were lower in bottlenose than spotted dolphins, while whistle duration was longer in spotted dolphins, data that may help inform automatic classification algorithms. Source levels were estimated by determining the range and bearing of an individual dolphin from the array and then adding the predicted transmission loss to the calculated received level. The median bottlenose dolphin source level was 138 dB re 1µPa at 1 m with a range of 114-163 dB re 1µPa at 1 m. The median spotted dolphin source level was 138 dB re 1µPa at 1 m with a range of 115-163 dB re 1µPa at 1 m. These source level measurements, in conjunction with estimates of vocalization rates and transmission loss models, can be used to improve passive acoustically determined dolphin abundance estimates in the Gulf of Mexico.

Achieving a textbook outcome in patients undergoing gastric resections in a low incidence, high-volume Australian Upper GI unit.

BACKGROUND: Textbook outcome (TBO) has been proposed as a composite measure of quality in esophagogastric surgery, and achieving a TBO has been associated with improved overall survival (OS). The Dutch Upper Gastrointestinal Cancer Audit group determined their TBO rate for gastrectomy to be 32.1%, using 10 parameters. Our study aimed to assess the TBO rate in patients who had a gastrectomy for cancer in an Australian Upper GI unit, allowing for comparisons with international specialist centers. METHODS: Retrospective analysis of a prospectively maintained database of patients who had a gastrectomy for cancer performed by the surgeons in a single Australian center between 2013 and 2018. Postoperative complications were analyzed using Clavien-Dindo (CD) ≥2 and CD ≥3 definitions. Baseline factors and their association with TBO were analyzed using multivariable logistical regression. The association between TBO and survival rates was determined by Cox proportional hazards regression analysis. RESULTS: In 136 patients, 84 (62%) achieved a TBO when complications were graded as CD ≥2. Greatest negative impact on TBO was the complication rate, lymph node yield, and length of stay. Patients more likely to achieve a TBO were younger, with an increased body mass index and absence of underlying respiratory disease. A nonsignificant trend toward improved OS was seen when TBO was achieved. CONCLUSION: Our TBO rate compares favorably with published data from high-volume centers. Assessment of a unit's TBO may provide a stronger evaluation of quality when assessing where complex surgery should be performed within Australia.

Structure, Function, and Activity of Small Molecule and Peptide Inhibitors of Protein Arginine Methyltransferase 1.

Protein arginine N-methyltransferases (PRMT) are a family of S-adenosyl-l-methionine (SAM)-dependent enzymes that transfer methyl-groups to the ω-N of arginyl residues in proteins. PRMTs are involved in regulating gene expression, RNA splicing, and other activities. PRMT1 is responsible for most cellular arginine methylation, and its dysregulation is involved in many cancers. Accordingly, many groups have targeted PRMT1 using small molecules and peptide inhibitors. In this Perspective, we discuss the structure and function of selected peptide and small molecule inhibitors of PRMT1. We examine inhibitors that target the substrate arginyl peptide, SAM, or both binding sites, and the type of inhibition that results. Small molecules, and peptides that are bisubstrate, and/or PRMT transition state mimic inhibitors as well as inhibitors that alkylate PRMTs will be discussed. We define a structure-activity relationship for the aromatic/heteroaromatic N-methylethylenediamine inhibitors of PRMT1 and review current progress of PRMT1 inhibitors in clinical trials.