PRMT1-mediated methylation of the microprocessor-associated proteins regulates microRNA biogenesis

Regulation of protein arginine methyltransferase in osteoporosis: a narrative review

Osteoporosis (OP), a systemic bone disease characterised by increased bone fragility and susceptibility to fracture, is mainly caused by a decline in bone mineral density (BMD) and quality caused by an imbalance between bone formation and resorption. Protein arginine methyltransferases (PRMTs) are epigenetic factors and post-translational modification (PTM) enzymes participating in various biological processes, including mRNA splicing, DNA damage repair, transcriptional regulation, and cell signalling. They act by catalysing the transfer and modification of arginine residues and, thus, have become therapeutic targets for OP. In-depth studies have found that these enzymes also play key roles in bone matrix protein metabolism, skeletal cell proliferation and differentiation, and signal pathway regulation to regulate bone formation, bone resorption balance, or both and jointly maintain bone health and stability. However, the expression changes and mechanisms of action of multiple members of the PRMT family differ in OP. Therefore, this paper discusses the biological functions, mechanisms of action, and influencing factors of PRMTs in OP, which is expected to provide a new understanding of the pathogenesis of OP. Furthermore, we present theoretical support for the development of more precise and effective treatment strategies as well as for further study of the molecular mechanisms of PRMTs.

A three-layer perspective on miRNA regulation in β cell inflammation

MicroRNAs (miRNAs) are noncoding RNA molecules that regulate gene expression post-transcriptionally and influence numerous biological processes. Aberrant miRNA expression is linked to diseases such as diabetes mellitus; indeed, miRNAs regulate pancreatic islet inflammation in both type 1 (T1D) and type 2 diabetes (T2D). Traditionally, miRNA research has focused on canonical sequences and offers a two-layer view - from expression to function. However, advances in RNA sequencing have revealed miRNA variants, called isomiRs, that arise from alternative processing or modifications of canonical sequences. This introduces a three-layer view - from expression, through sequence modifications, to function. We discuss the potential link between cellular stresses and isomiR biogenesis, and how this association could improve our knowledge of islet inflammation and dysfunction.

Paraspeckle-independent co-transcriptional regulation of nuclear microRNA biogenesis by SFPQ

MicroRNAs (miRNAs) play crucial roles in physiological functions and disease, but the regulation of their nuclear biogenesis remains poorly understood. Here, BioID on Drosha, the catalytic subunit of the microprocessor complex, reveals its proximity to splicing factor proline- and glutamine (Q)-rich (SFPQ), a multifunctional RNA-binding protein (RBP) involved in forming paraspeckle nuclear condensates. SFPQ depletion impacts both primary and mature miRNA expression, while other paraspeckle proteins (PSPs) or the paraspeckle scaffolding RNA NEAT1 do not, indicating a paraspeckle-independent role. Comprehensive transcriptomic analyses show that SFPQ loss broadly affects RNAs and miRNA host gene (HG) expression, influencing both their transcription and the stability of their products. Notably, SFPQ protects the oncogenic miR-17∼92 polycistron from degradation by the nuclear exosome targeting (NEXT)-exosome complex and is tightly linked with its overexpression across a broad variety of cancers. Our findings reveal a dual role for SFPQ in regulating miRNA HG transcription and stability, as well as its significance in cancers.

ETD-Based Proteomic Profiling Improves Arginine Methylation Identification and Reveals Novel PRMT5 Substrates

Protein arginine methylations are important post-translational modifications (PTMs) in eukaryotes, regulating many biological processes. However, traditional collision-based mass spectrometry methods inevitably cause neutral losses of methylarginines, preventing the deep mining of biologically important sites. Herein we developed an optimized mass spectrometry workflow based on electron-transfer dissociation (ETD) with supplemental activation for proteomic profiling of arginine methylation in human cells. Using symmetric dimethylarginine (sDMA) as an example, we show that the ETD-based optimized workflow significantly improved the identification and site localization of sDMA. Quantitative proteomics identified 138 novel sDMA sites as potential PRMT5 substrates in HeLa cells. Further biochemical studies on SERBP1, a newly identified PRMT5 substrate, confirmed the coexistence of sDMA and asymmetric dimethylarginine in the central RGG/RG motif, and loss of either methylation caused increased the recruitment of SERBP1 to stress granules under oxidative stress. Overall, our optimized workflow not only enabled the identification and localization of extensive, nonoverlapping sDMA sites in human cells but also revealed novel PRMT5 substrates whose sDMA may play potentially important biological functions.

Targeting PRMT1-mediated SRSF1 methylation to suppress oncogenic exon inclusion events and breast tumorigenesis

PRMT1 plays a vital role in breast tumorigenesis; however, the underlying molecular mechanisms remain incompletely understood. Herein, we show that PRMT1 plays a critical role in RNA alternative splicing, with a preference for exon inclusion. PRMT1 methylome profiling identifies that PRMT1 methylates the splicing factor SRSF1, which is critical for SRSF1 phosphorylation, SRSF1 binding with RNA, and exon inclusion. In breast tumors, PRMT1 overexpression is associated with increased SRSF1 arginine methylation and aberrant exon inclusion, which are critical for breast cancer cell growth. In addition, we identify a selective PRMT1 inhibitor, iPRMT1, which potently inhibits PRMT1-mediated SRSF1 methylation, exon inclusion, and breast cancer cell growth. Combination treatment with iPRMT1 and inhibitors targeting SRSF1 phosphorylation exhibits an additive effect of suppressing breast cancer cell growth. In conclusion, our study dissects a mechanism underlying PRMT1-mediated RNA alternative splicing. Thus, PRMT1 has great potential as a therapeutic target in breast cancer treatment.

Hydrophobic Derivatization Strategy Facilitates Comprehensive Profiling of Protein Methylation

Protein methylation is receiving more and more attention due to its essential role in diverse biological processes. Large-scale analysis of protein methylation requires the efficient identification of methylated peptides at the proteome level; unfortunately, a significant number of methylated peptides are highly hydrophilic and hardly retained during reversed-phase chromatography, making it difficult to be identified by conventional approaches. Herein, we report the development of a novel strategy by combining hydrophobic derivatization and high pH strong cation exchange enrichment, which significantly expands the identification coverage of the methylproteome. Noteworthily, the total number of identified methylated short peptides was improved by more than 2-fold. By this strategy, we identified 492 methylation sites from NCI-H460 cells compared to only 356 sites identified in native forms. The identification of methylation sites before and after derivatization was highly complementary. Approximately 2-fold the methylation sites were obtained by combining the results identified in both approaches (native and derivatized) as compared with the only analysis in native forms. Therefore, this novel chemical derivatization strategy is a promising approach for the comprehensive identification of protein methylation by improving the identification of methylated short peptides.

Photoreactive Probe-Based Strategy Enables the Specific Identification of the Transient Substrates of Methyltransferase at the Proteome Scale

To decipher the biological function of protein arginine methyltransferases (PRMTs), the identification of their substrate proteins is crucial. However, this is not a trivial task as the stable and strong interacting proteins always prevail over the weak and transient substrate proteins. Herein, we report the development of a novel photoreactive probe-based strategy to identify the substrate proteins of methyltransferases. By applying it to PRMT1, we demonstrate that this strategy can effectively distinguish substrate proteins from other interacting proteins and allows the identification of highly confident substrate proteins. Noteworthily, we found for the first time that hypomethylation of proteins is a prerequisite for efficient capturing of substrate proteins. This study describes the development of a robust chemical proteomics tool for profiling the transient substrates and can be adapted for broad biomedical applications.

Prognostic and immunotherapeutic predictive value of interleukin enhancer-binding factor 3 in hepatocellular carcinoma: Integrated bioinformatics and experimental analysis

Interleukin enhancer-binding factor 3 (ILF3) as an RNA-binding protein that plays a critical role in the process of cancer and antiviral responses. However, no researcher has focused on the pan-cancer analysis of ILF3, and the effect of ILF3 on tumor immunity is still largely unclear. This study synthetically analyzed the relationship between the expression of ILF3 across various cancers and prognosis, microsatellite instability (MSI), tumor mutational burden (TMB), tumor immune cell infiltration, and common immune checkpoint molecules by multiple bioinformatics databases. Experimentally, we detected the mRNA abundance of ILF3 and immune checkpoint molecules in liver hepatocellular carcinoma (LIHC) tissues. The functions of ILF3 on hepatocellular carcinoma (HCC) cells were verified by western blot assay and cytotoxicity assay. We found that ILF3 was aberrantly expressed and associated with the prognosis in several types of tumors. The ILF3 expression was significantly correlated with infiltrating levels of immune cells and immune molecules in certain cancers, particularly in LIHC. Detection of clinical liver cancer tissues confirmed the positive correlation between ILF3 and immune checkpoint molecules, including programmed cell death 1 (PD-1), programmed cell death ligand 1 (PD-L1), cytotoxic T lymphocyte-associated antigen 4 (CTLA4), lymphocyte-activation gene 3 (LAG3), and T cell immunoglobulin domain and mucin domain-3 (TIM3). Furthermore, reduced PD-L1 and increased sensitivity of HCC cells to T cells cytotoxicity were found in ILF3-knockdown cells. This work suggested ILF3 may be used as a prognostic marker for various tumors to predict the response to immunotherapy.

Arginine attenuates chronic mountain sickness in rats via microRNA-144-5p

Hypobaric hypoxia is an environmental stress leading to high-altitude pulmonary hypertension. While high-altitude pulmonary hypertension has been linked to high hematocrit findings (chronic mountain sickness; CMS). The present study is designed to investigate the effect of arginine (ARG) on hypobaric hypoxia-induced CMS of rats. Hypobaric hypoxia resulted in lower body weight, decreased appetite, increased pulmonary artery pressure, and deteriorated lung tissue damage in rats. Red blood cells (RBC), hemoglobin, hematocrit, mean corpuscular volume, and mean corpuscular hemoglobin values and blood viscosity were increased in rats, which were alleviated by ARG. microRNA (miRNA) microarray analysis was used to filter differentially expressed miRNAs after ARG in rats. miR-144-5p was reduced under hypobaric hypoxia and upregulated by ARG. miR-144-5p silencing aggravated the erythrocytosis and hyperviscosity in rats, and also accentuated tissue damage and excessive accumulation of RBC. The role of miR-144-5p in rats with CMS was achieved by blocking erythropoietin (EPO)/erythropoietin receptor (EPOR). In conclusion, ARG alleviated CMS symptoms in rodents exposed to hypobaric hypoxia by decreasing EPO/EPOR via miR-144-5p.

Heavy Methyl SILAC Metabolic Labeling of Human Cell Lines for High-Confidence Identification of R/K-Methylated Peptides by High-Resolution Mass Spectrometry

Protein methylation is a widespread post-translational modification (PTM) involved in several important biological processes including, but not limited to, RNA splicing, signal transduction, translation, and DNA repair. Liquid chromatography-tandem mass spectrometry (LC-MS/MS) is considered today the most versatile and accurate technique to profile PTMs with high precision and proteome-wide depth; however, the identification of protein methylations by MS is still prone to high false discovery rates. In this chapter, we describe the heavy methyl SILAC metabolic labeling strategy that allows high-confidence identification of in vivo methyl-peptides by MS-based proteomics. We provide a general protocol that covers the steps of heavy methyl labeling of cultured cells, protein sample preparation, LC-MS/MS analysis, and downstream computational analysis of the acquired MS data.

Proximity-dependent biotinylation technologies for mapping RNA-protein interactions in live cells

Proximity ligation technologies are extremely powerful tools for unveiling RNA-protein interactions occurring at different stages in living cells. These approaches mainly rely on the inducible activity of enzymes (biotin ligases or peroxidases) that promiscuously biotinylate macromolecules within a 20 nm range. These enzymes can be either fused to an RNA binding protein or tethered to any RNA of interest and expressed in living cells to biotinylate the amino acids and nucleic acids of binding partners in proximity. The biotinylated molecules can then be easily affinity purified under denaturing conditions and analyzed by mass spectrometry or next generation sequencing. These approaches have been widely used in recent years, providing a potent instrument to map the molecular interactions of specific RNA-binding proteins as well as RNA transcripts occurring in mammalian cells. In addition, they permit the identification of transient interactions as well as interactions among low expressed molecules that are often missed by standard affinity purification strategies. This review will provide a brief overview of the currently available proximity ligation methods, highlighting both their strengths and shortcomings. Furthermore, it will bring further insights to the way these technologies could be further used to characterize post-transcriptional modifications that are known to regulate RNA-protein interactions.

ProMetheusDB: An In-Depth Analysis of the High-Quality Human Methyl-proteome

Protein arginine (R) methylation is a post-translational modification involved in various biological processes, such as RNA splicing, DNA repair, immune response, signal transduction, and tumor development. Although several advancements were made in the study of this modification by mass spectrometry, researchers still face the problem of a high false discovery rate. We present a dataset of high-quality methylations obtained from several different heavy methyl stable isotope labeling with amino acids in cell culture experiments analyzed with a machine learning–based tool and show that this model allows for improved high-confidence identification of real methyl-peptides. Overall, our results are consistent with the notion that protein R methylation modulates protein–RNA interactions and suggest a role in rewiring protein–protein interactions, for which we provide experimental evidence for a representative case (i.e., NONO [non-POU domain–containing octamer-binding protein]–paraspeckle component 1 [PSPC1]). Upon intersecting our R-methyl-sites dataset with the PhosphoSitePlus phosphorylation dataset, we observed that R methylation correlates differently with S/T-Y phosphorylation in response to various stimuli. Finally, we explored the application of heavy methyl stable isotope labeling with amino acids in cell culture to identify unconventional methylated residues and successfully identified novel histone methylation marks on serine 28 and threonine 32 of H3. The database generated, named ProMetheusDB, is freely accessible at https://bioserver.ieo.it/shiny/app/prometheusdb.

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hmSEEKER 2.0 identifies methyl-peptides from hmSILAC data through machine learning.

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Arginine methylation plays a role in modulating protein–protein interactions.

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Arginine methylations occur more frequently in proximity of phosphorylation sites.

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hmSEEKER 2.0 was used to identify methylations occurring on nonstandard amino acids.

The protective effect of NF-κB signaling pathway inhibitor PDTC on mice with chronic atrophic gastritis

OBJECTIVE

To understand the protective effect of NF-κB signaling pathway inhibitor pyrrolidinedithiocarbamate (PDTC) on mice with chronic atrophic gastritis (CAG).

METHODS

Helicobacter pylori (H. pylori) infection combined with high-salt diet was used to construct the CAG mouse model, and 100 or 200 mg/kg/day PDTC was intragastrically treated for 8 weeks. Then, hematoxylin and eosin (HE) and Alcian blue-periodic acid-Schiff (AB-PAS) staining were used to observe the pathology of gastric mucosa, while immunohistochemistry, quantitative real-time polymerase chain reaction (qRT-PCR), enzyme-linked immuno sorbent assay (ELISA) and western blotting were determined to detect the expression of related molecules.

RESULTS

The nuclear content of NF-κB p65 in the gastric mucosa of the CAG mice was increased accompanying by the structural disorder of the gastric mucosal epithelium, inflammatory cell infiltration, intestinal metaplasia, and increased MUC2 expression, but the symptoms were alleviated after PDTC treatment. In addition, the expressions of TNF-α, IL-1β, IL-6 and COX2 in the gastric mucosa and serum of CAG mice were higher than those control mice, which were reduced in CAG mice treated with either 100 or 200 mg/kg PDTC. Furthermore, 100 mg/kg and 200 mg/kg PDTC treatments reduced the serum PGE₂ in CAG mice with the decreased PCNA and Ki-67 expression in gastric mucosa. The therapeutic effect of 200 mg/kg PDTC was significantly better than that of 100 mg/kg PDTC.

CONCLUSION

PDTC inhibited inflammation and the excessive proliferation of gastric mucosal epithelial cells, thereby exerting a potential therapeutic effect on CAG.

Systematic Analysis of the Impact of R-Methylation on RBPs-RNA Interactions: A Proteomic Approach

RNA binding proteins (RBPs) bind RNAs through specific RNA-binding domains, generating multi-molecular complexes known as ribonucleoproteins (RNPs). Various post-translational modifications (PTMs) have been described to regulate RBP structure, subcellular localization, and interactions with other proteins or RNAs. Recent proteome-wide experiments showed that RBPs are the most representative group within the class of arginine (R)-methylated proteins. Moreover, emerging evidence suggests that this modification plays a role in the regulation of RBP-RNA interactions. Nevertheless, a systematic analysis of how changes in protein-R-methylation can affect globally RBPs-RNA interactions is still missing. We describe here a quantitative proteomics approach to profile global changes of RBP-RNA interactions upon the modulation of type I and II protein arginine methyltransferases (PRMTs). By coupling the recently described Orthogonal Organic Phase Separation (OOPS) strategy with the Stable Isotope Labelling with Amino acids in Cell culture (SILAC) and pharmacological modulation of PRMTs, we profiled RNA-protein interaction dynamics in dependence of protein-R-methylation. Data are available via ProteomeXchange with identifier PXD024601.

SPINT1-AS1 Drives Cervical Cancer Progression via Repressing miR-214 Biogenesis

Accumulating evidences have revealed the dysregulated expressions and critical roles of non-coding RNAs in various malignancies, including cervical cancer. Nevertheless, our knowledge about the vast majority of non-coding RNAs is still lacking. Here we identified long non-coding RNA (lncRNA) SPINT1-AS1 as a novel cervical cancer-associated lncRNA. SPINT1-AS1 was increased in cervical cancer and correlated with advanced stage and poor prognosis. SPINT1-AS1 was a direct downstream target of miR-214, a well-known tumor suppressive microRNA (miRNA) in cervical cancer. Intriguingly, SPINT1-AS1 was also found to repress miR-214 biogenesis via binding DNM3OS, the primary transcript of miR-214. The interaction between SPINT1-AS1 and DNM3OS repressed the binding of DROSHA and DGCR8 to DNM3OS, blocked DNM3OS cleavage, and therefore repressed mature miR-214 biogenesis. The expression of SPINT1-AS1 was significantly negatively correlated with miR-214 in cervical cancer tissues, supporting the reciprocal repression between SPINT1-AS1 and miR-214 in vivo. Through downregulating mature miR-214 level, SPINT1-AS1 upregulated the expression of β-catenin, a target of miR-214. Thus, SPINT1-AS1 further activated Wnt/β-catenin signaling in cervical cancer. Functionally, SPINT1-AS1 drove cervical cancer cellular proliferation, migration, and invasion in vitro, and also tumorigenesis in vivo. Deletion of the region mediating the interaction between SPINT1-AS1 and DNM3OS, overexpression of miR-214, and inhibition of Wnt/β-catenin signaling all reversed the roles of SPINT1-AS1 in cervical cancer. Collectively, these findings identified SPINT1-AS1 as a novel cervical cancer-associated oncogenic lncRNA which represses miR-214 biogenesis and activates Wnt/β-catenin signaling, highlighting its potential as prognostic biomarker and therapeutic target for cervical cancer.

The lncRNA HOTAIR regulates autophagy and affects lipopolysaccharide-induced acute lung injury through the miR-17-5p/ATG2/ATG7/ATG16 axis

Long non‐coding ribonucleic acids (lncRNAs) play critical roles in acute lung injury (ALI). We aimed to explore the involvement of lncRNA HOX transcript antisense intergenic ribonucleic acid (HOTAIR) in regulating autophagy in lipopolysaccharide (LPS)‐induced ALI. We obtained 1289 differentially expressed lncRNAs or messenger RNAs (mRNAs) via microarray analysis. HOTAIR was significantly upregulated in the LPS stimulation experimental group. HOTAIR knockdown (si‐HOTAIR) promoted cell proliferation in LPS‐stimulated A549 and BEAS‐2B cells, suppressing the protein expression of autophagy marker light chain 3B and Beclin‐1. Inhibition of HOTAIR suppressed LPS‐induced cell autophagy, apoptosis and arrested cells in the G0/G1 phase prior to S phase entry. Further, si‐HOTAIR alleviated LPS‐induced lung injury in vivo. We predicted the micro‐ribonucleic acid miR‐17‐5p to target HOTAIR and confirmed this via RNA pull‐down and dual luciferase reporter assays. miR‐17‐5p inhibitor treatment reversed the HOTAIR‐mediated effects on autophagy, apoptosis, cell proliferation and cell cycle. Finally, we predicted autophagy‐related genes (ATGs) ATG2, ATG7 and ATG16 as targets of miR‐17‐5p, which reversed their HOTAIR‐mediated protein upregulation in LPS‐stimulated A549 and BEAS‐2B cells. Taken together, our results indicate that HOTAIR regulated apoptosis, the cell cycle, proliferation and autophagy through the miR‐17‐5p/ATG2/ATG7/ATG16 axis, thus driving LPS‐induced ALI.

Curcumin inhibits the viability, migration and invasion of papillary thyroid cancer cells by regulating the miR-301a-3p/STAT3 axis

Thyroid cancer is one of the most common malignant tumors, and the mortality rate associated with thyroid cancer has been increasing annually. Curcumin has been reported to exert an antitumor effect on papillary thyroid cancer (PTC), and the identification of additional mechanisms underlying the anticancer effect of curcumin on PTC requires further investigation. The present study aimed to explore the effects of curcumin on the viability, migration and invasion of PTC cells. TPC-1 cells were incubated with different concentrations of curcumin, and then, cell viability, migration and invasion, and wound healing were examined by CCK-8, Transwell and wound healing assays, respectively. Subsequently, microRNA (miR)-301a-3p mimics, miR-301a-3p inhibitors and signal transducer and activator of transcription (STAT)3 overexpression vector were transfected into TPC-1 cells, and cell viability, migration, and invasion were reassessed in these transfected cells. Matrix metallopeptidase (MMP)-2, MMP-9, epithelial-mesenchymal transition (EMT)-related markers, and Janus kinase (JAK)/STAT signaling pathway components were assessed by western blot analysis. Curcumin significantly inhibited cell viability, migration and invasion and downregulated MMP-2, MMP-9 and EMT marker expression. Additionally, curcumin decreased STAT3 expression by upregulating miR-301a-3p expression, and the inhibition of miR-301a-3p and the overexpression of STAT3 reversed the effects of curcumin on cell viability, migration and invasion, and MMP-2, MMP-9 and EMT marker expression in TPC-1 cells. Furthermore, curcumin suppressed the JAK/STAT signaling pathway through the miR-301a-3p/STAT3 axis. The data of the present study indicated that curcumin could inhibit the viability, migration and invasion of TPC-1 cells by regulating the miR-301a-3p/STAT3 axis. These findings may provide a possible strategy for the clinical treatment of PTC.

Arginine methylation: the promise of a 'silver bullet' for brain tumours?

Despite intense research efforts, our pharmaceutical repertoire against high-grade brain tumours has not been able to increase patient survival for a decade and life expectancy remains at less than 16 months after diagnosis, on average. Inhibitors of protein arginine methyltransferases (PRMTs) have been developed and investigated over the past 15 years and have now entered oncology clinical trials, including for brain tumours. This review collates recent advances in the understanding of the role of PRMTs and arginine methylation in brain tumours. We provide an up-to-date literature review on the mechanisms for PRMT regulation. These include endogenous modulators such as alternative splicing, miRNA, post-translational modifications and PRMT-protein interactions, and synthetic inhibitors. We discuss the relevance of PRMTs in brain tumours with a particular focus on PRMT1, -2, -5 and -8. Finally, we include a future perspective where we discuss possible routes for further research on arginine methylation and on the use of PRMT inhibitors in the context of brain tumours.

Biochemical and Computational Approaches for the Large-Scale Analysis of Protein Arginine Methylation by Mass Spectrometry

The absence of efficient mass spectrometry-based approaches for the large-scale analysis of protein arginine methylation has hindered the understanding of its biological role, beyond the transcriptional regulation occurring through histone modification. In the last decade, however, several technological advances of both the biochemical methods for methylated polypeptide enrichment and the computational pipelines for MS data analysis have considerably boosted this research field, generating novel insights about the extent and role of this post-translational modification. Here, we offer an overview of state-of-the-art approaches for the high-confidence identification and accurate quantification of protein arginine methylation by high-resolution mass spectrometry methods, which comprise the development of both biochemical and bioinformatics methods. The further optimization and systematic application of these analytical solutions will lead to ground-breaking discoveries on the role of protein methylation in biological processes.

PRMT1 Modulates Processing of Asthma-Related Primary MicroRNAs (Pri-miRNAs) into Mature miRNAs in Lung Epithelial Cells

Protein arginine methyltransferase-1 (PRMT1) is an important epigenetic regulator of cell function and contributes to inflammation and remodeling in asthma in a cell type-specific manner. Disease-specific expression patterns of microRNAs (miRNA) are associated with chronic inflammatory lung diseases, including asthma. The de novo synthesis of miRNA depends on the transcription of primary miRNA (pri-miRNA) transcript. This study assessed the role of PRMT1 on pri-miRNA to mature miRNA process in lung epithelial cells. Human airway epithelial cells, BEAS-2B, were transfected with the PRMT1 expression plasmid pcDNA3.1-PRMT1 for 48 h. Expression profiles of miRNA were determined by small RNA deep sequencing. Comparing these miRNAs with datasets of microarrays from five asthma patients (Gene Expression Omnibus dataset), 12 miRNAs were identified that related to PRMT1 overexpression and to asthma. The overexpression or knockdown of PRMT1 modulated the expression of the asthma-related miRNAs and their pri-miRNAs. Coimmunoprecipitation showed that PRMT1 formed a complex with STAT1 or RUNX1 and thus acted as a coactivator, stimulating the transcription of pri-miRNAs. Stimulation with TGF-β1 promoted the interaction of PRMT1 with STAT1 or RUNX1, thereby upregulating the transcription of two miRNAs: let-7i and miR-423. Subsequent chromatin immunoprecipitation assays revealed that the binding of the PRMT1/STAT1 or PRMT1/RUNX1 coactivators to primary let-7i (pri-let-7i) and primary miR (pri-miR) 423 promoter was critical for pri-let-7i and pri-miR-423 transcription. This study describes a novel role of PRMT1 as a coactivator for STAT1 or RUNX1, which is essential for the transcription of pri-let-7i and pri-miR-423 in epithelial cells and might be relevant to epithelium dysfunction in asthma.

MicroRNAs Responding to Space Radiation

High-energy and high-atom-number (HZE) space radiation poses an inevitable potential threat to astronauts on deep space exploration missions. Compared with low-LET radiation, high-energy and high-LET radiation in space is more efficient in inducing clustered DNA damage with more serious biological consequences, such as carcinogenesis, central nervous system injury and degenerative disease. Space radiation also causes epigenetic changes in addition to inducing damage at the DNA level. Considering the important roles of microRNAs in the regulation of biological responses of radiation, we systematically reviewed both expression profiling and functional studies relating to microRNAs responding to space radiation as well as to space compound environment. Finally, the directions for improvement of the research related to microRNAs responding to space radiation are proposed. A better understanding of the functions and underlying mechanisms of the microRNAs responding to space radiation is of significance to both space radiation risk assessment and therapy development for lesions caused by space radiation.

Pharmacological inhibition of PRMT7 links arginine monomethylation to the cellular stress response

Protein arginine methyltransferases (PRMTs) regulate diverse biological processes and are increasingly being recognized for their potential as drug targets. Here we report the discovery of a potent, selective, and cell-active chemical probe for PRMT7. SGC3027 is a cell permeable prodrug, which in cells is converted to SGC8158, a potent, SAM-competitive PRMT7 inhibitor. Inhibition or knockout of cellular PRMT7 results in drastically reduced levels of arginine monomethylated HSP70 family stress-associated proteins. Structural and biochemical analyses reveal that PRMT7-driven in vitro methylation of HSP70 at R469 requires an ATP-bound, open conformation of HSP70. In cells, SGC3027 inhibits methylation of both constitutive and inducible forms of HSP70, and leads to decreased tolerance for perturbations of proteostasis including heat shock and proteasome inhibitors. These results demonstrate a role for PRMT7 and arginine methylation in stress response.

Protein arginine methyltransferases (PRMTs) are increasingly recognized as potential therapeutic targets but PRMT7 remains an understudied member of this enzyme family. Here, the authors develop a chemical probe for PRMT7 and apply it to elucidate the role of PRMT7 in the cellular stress response.