PRMT7 Preserves Satellite Cell Regenerative Capacity

PRMT7 in cancer: Structure, effects, and therapeutic potentials

Protein arginine methyltransferase 7 (PRMT7), a type III methyltransferase responsible solely for arginine mono-methylation, plays a critical role in numerous physiological and pathological processes. Recent studies have highlighted its aberrant expression or mutation in various cancers, implicating it in tumorigenesis, cancer progression, and drug resistance. Consequently, PRMT7 has emerged as a promising target for cancer diagnosis and therapeutic intervention. In this review, we present an overview of the molecular structure of PRMT7, discuss its roles and mechanisms in different cancer types, and analyze the binding modes and structure-activity relationships of reported PRMT7 inhibitors. Furthermore, we identify the challenges encountered in functional exploration and drug development targeting PRMT7, propose potential solutions to these challenges, and outline future directions for the development of PRMT7 inhibitors to inform future drug discovery efforts.

Protein arginine methyltransferase 7 modulators in disease therapy: Current progress and emerged opportunity

Protein arginine methyltransferase 7 (PRMT7) is an essential epigenetic and post-translational regulator in eukaryotic organisms. Dysregulation of PRMT7 is intimately related to multiple types of human diseases, particularly cancer. In addition, PRMT7 exerts multiple effects on cellular processes such as growth, migration, invasion, apoptosis, and drug resistance in various cancers, making it as a promising target for anti-tumor therapeutics. In this review, we initially provide an overview of the structure and biological functions of PRMT7, along with its association with diseases. Subsequently, we summarized the PRMT inhibitors in clinical trials and the co-crystal structural of PRMT7 inhibitors. Moreover, we also focus on recent progress in the design and development of modulators targeting PRMT7, including isoform-selective and non-selective PRMT7 inhibitors, and the dual-target inhibitors based on PRMT7, from the perspectives of rational design, pharmacodynamics, pharmacokinetics, and the clinical status of these modulators. Finally, we also provided the challenges and prospective directions for PRMT7 targeting drug discovery in cancer therapy.

Cellular stress and epigenetic regulation in adult stem cells

Stem cells are a unique class of cells that possess the ability to differentiate and self-renew, enabling them to repair and replenish tissues. To protect and maintain the potential of stem cells, the cells and the environment surrounding these cells (stem cell niche) are highly responsive and tightly regulated. However, various stresses can affect the stem cells and their niches. These stresses are both systemic and cellular and can arise from intrinsic or extrinsic factors which would have strong implications on overall aging and certain disease states. Therefore, understanding the breadth of drivers, namely epigenetic alterations, involved in cellular stress is important for the development of interventions aimed at maintaining healthy stem cells and tissue homeostasis. In this review, we summarize published findings of epigenetic responses to replicative, oxidative, mechanical, and inflammatory stress on various types of adult stem cells.

Methylation and phosphorylation of formin homology domain proteins (Fhod1 and Fhod3) by protein arginine methyltransferase 7 (PRMT7) and Rho kinase (ROCK1)

Protein post-translational modifications (PTMs) can regulate biological processes by altering an amino acid's bulkiness, charge, and hydrogen bonding interactions. Common modifications include phosphorylation, methylation, acetylation, and ubiquitylation. Although a primary focus of studying PTMs is understanding the effects of a single amino acid modification, the possibility of additional modifications increases the complexity. For example, substrate recognition motifs for arginine methyltransferases and some serine/threonine kinases overlap, leading to potential enzymatic crosstalk. In this study we have shown that the human family of formin homology domain-containing proteins (Fhods) contain a substrate recognition motif specific for human protein arginine methyltransferase 7 (PRMT7). In particular, PRMT7 methylates two arginine residues in the diaphanous autoinhibitory domain (DAD) of the family of Fhod proteins: R1588 and/or R1590 of Fhod3 isoform 4. Additionally, we confirmed that S1589 and S1595 in the DAD domain of Fhod3 can be phosphorylated by Rho/ROCK1 kinase. Significantly, we have determined that if S1589 is phosphorylated then PRMT7 cannot subsequently methylate R1588 or R1590. In contrast, if R1588 or R1590 of Fhod3 is methylated then ROCK1 phosphorylation activity is only slightly affected. Finally, we show that the interaction of the N-terminal DID domain can also inhibit the methylation of the DAD domain. Taken together these results suggest that the family of Fhod proteins, potential in vivo substrates for PRMT7, might be regulated by a combination of methylation and phosphorylation.

Epigenetic control of skeletal muscle atrophy

Skeletal muscular atrophy is a complex disease involving a large number of gene expression regulatory networks and various biological processes. Despite extensive research on this topic, its underlying mechanisms remain elusive, and effective therapeutic approaches are yet to be established. Recent studies have shown that epigenetics play an important role in regulating skeletal muscle atrophy, influencing the expression of numerous genes associated with this condition through the addition or removal of certain chemical modifications at the molecular level. This review article comprehensively summarizes the different types of modifications to DNA, histones, RNA, and their known regulators. We also discuss how epigenetic modifications change during the process of skeletal muscle atrophy, the molecular mechanisms by which epigenetic regulatory proteins control skeletal muscle atrophy, and assess their translational potential. The role of epigenetics on muscle stem cells is also highlighted. In addition, we propose that alternative splicing interacts with epigenetic mechanisms to regulate skeletal muscle mass, offering a novel perspective that enhances our understanding of epigenetic inheritance's role and the regulatory network governing skeletal muscle atrophy. Collectively, advancements in the understanding of epigenetic mechanisms provide invaluable insights into the study of skeletal muscle atrophy. Moreover, this knowledge paves the way for identifying new avenues for the development of more effective therapeutic strategies and pharmaceutical interventions.

PRMT5-mediated homologous recombination repair is essential to maintain genomic integrity of neural progenitor cells

Maintaining genomic stability is a prerequisite for proliferating NPCs to ensure genetic fidelity. Though histone arginine methylation has been shown to play important roles in safeguarding genomic stability, the underlying mechanism during brain development is not fully understood. Protein arginine N-methyltransferase 5 (PRMT5) is a type II protein arginine methyltransferase that plays a role in transcriptional regulation. Here, we identify PRMT5 as a key regulator of DNA repair in response to double-strand breaks (DSBs) during NPC proliferation. Prmt5F/F; Emx1-Cre (cKO-Emx1) mice show a distinctive microcephaly phenotype, with partial loss of the dorsal medial cerebral cortex and complete loss of the corpus callosum and hippocampus. This phenotype is resulted from DSBs accumulation in the medial dorsal cortex followed by cell apoptosis. Both RNA sequencing and in vitro DNA repair analyses reveal that PRMT5 is required for DNA homologous recombination (HR) repair. PRMT5 specifically catalyzes H3R2me2s in proliferating NPCs in the developing mouse brain to enhance HR-related gene expression during DNA repair. Finally, overexpression of BRCA1 significantly rescues DSBs accumulation and cell apoptosis in PRMT5-deficient NSCs. Taken together, our results show that PRMT5 maintains genomic stability by regulating histone arginine methylation in proliferating NPCs.

Molecular hallmarks of ageing in amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a fatal, severely debilitating and rapidly progressing disorder affecting motor neurons in the brain, brainstem, and spinal cord. Unfortunately, there are few effective treatments, thus there remains a critical need to find novel interventions that can mitigate against its effects. Whilst the aetiology of ALS remains unclear, ageing is the major risk factor. Ageing is a slowly progressive process marked by functional decline of an organism over its lifespan. However, it remains unclear how ageing promotes the risk of ALS. At the molecular and cellular level there are specific hallmarks characteristic of normal ageing. These hallmarks are highly inter-related and overlap significantly with each other. Moreover, whilst ageing is a normal process, there are striking similarities at the molecular level between these factors and neurodegeneration in ALS. Nine ageing hallmarks were originally proposed: genomic instability, loss of telomeres, senescence, epigenetic modifications, dysregulated nutrient sensing, loss of proteostasis, mitochondrial dysfunction, stem cell exhaustion, and altered inter-cellular communication. However, these were recently (2023) expanded to include dysregulation of autophagy, inflammation and dysbiosis. Hence, given the latest updates to these hallmarks, and their close association to disease processes in ALS, a new examination of their relationship to pathophysiology is warranted. In this review, we describe possible mechanisms by which normal ageing impacts on neurodegenerative mechanisms implicated in ALS, and new therapeutic interventions that may arise from this.

PRMT5 mediates FoxO1 methylation and subcellular localization to regulate lipophagy in myogenic progenitors

Development is regulated by various factors, including protein methylation status. While PRMT5 is well known for its roles in oncogenesis by mediating symmetric di-methylation of arginine, its role in normal development remains elusive. Using Myod1Cre to drive Prmt5 knockout in embryonic myoblasts (Prmt5MKO), we dissected the role of PRMT5 in myogenesis. The Prmt5MKO mice are born normally but exhibit progressive muscle atrophy and premature death. Prmt5MKO inhibits proliferation and promotes premature differentiation of embryonic myoblasts, reducing the number and regenerative function of satellite cells in postnatal mice. Mechanistically, PRMT5 methylates and destabilizes FoxO1. Prmt5MKO increases the total FoxO1 level and promotes its cytoplasmic accumulation, leading to activation of autophagy and depletion of lipid droplets (LDs). Systemic inhibition of autophagy in Prmt5MKO mice restores LDs in myoblasts and moderately improves muscle regeneration. Together, PRMT5 is essential for muscle development and regeneration at least partially through mediating FoxO1 methylation and LD turnover.

Critical Roles of Protein Arginine Methylation in the Central Nervous System

A remarkable post-transitional modification of both histones and non-histone proteins is arginine methylation. Methylation of arginine residues is crucial for a wide range of cellular process, including signal transduction, DNA repair, gene expression, mRNA splicing, and protein interaction. Arginine methylation is modulated by arginine methyltransferases and demethylases, like protein arginine methyltransferase (PRMTs) and Jumonji C (JmjC) domain containing (JMJD) proteins. Symmetric dimethylarginine and asymmetric dimethylarginine, metabolic products of the PRMTs and JMJD proteins, can be changed by abnormal expression of these proteins. Many pathologies including cancer, inflammation and immune responses have been closely linked to aberrant arginine methylation. Currently, the majority of the literature discusses the substrate specificity and function of arginine methylation in the pathogenesis and prognosis of cancers. Numerous investigations on the roles of arginine methylation in the central nervous system (CNS) have so far been conducted. In this review, we display the biochemistry of arginine methylation and provide an overview of the regulatory mechanism of arginine methyltransferases and demethylases. We also highlight physiological functions of arginine methylation in the CNS and the significance of arginine methylation in a variety of neurological diseases such as brain cancers, neurodegenerative diseases and neurodevelopmental disorders. Furthermore, we summarize PRMT inhibitors and molecular functions of arginine methylation. Finally, we pose important questions that require further research to comprehend the roles of arginine methylation in the CNS and discover more effective targets for the treatment of neurological diseases.

Inhibition of type I PRMTs reforms muscle stem cell identity enhancing their therapeutic capacity

In skeletal muscle, muscle stem cells (MuSC) are the main cells responsible for regeneration upon injury. In diseased skeletal muscle, it would be therapeutically advantageous to replace defective MuSCs, or rejuvenate them with drugs to enhance their self-renewal and ensure long-term regenerative potential. One limitation of the replacement approach has been the inability to efficiently expand MuSCs ex vivo, while maintaining their stemness and engraftment abilities. Herein, we show that inhibition of type I protein arginine methyltransferases (PRMTs) with MS023 increases the proliferative capacity of ex vivo cultured MuSCs. Single cell RNA sequencing (scRNAseq) of ex vivo cultured MuSCs revealed the emergence of subpopulations in MS023-treated cells which are defined by elevated Pax7 expression and markers of MuSC quiescence, both features of enhanced self-renewal. Furthermore, the scRNAseq identified MS023-specific subpopulations to be metabolically altered with upregulated glycolysis and oxidative phosphorylation (OxPhos). Transplantation of MuSCs treated with MS023 had a better ability to repopulate the MuSC niche and contributed efficiently to muscle regeneration following injury. Interestingly, the preclinical mouse model of Duchenne muscular dystrophy had increased grip strength with MS023 treatment. Our findings show that inhibition of type I PRMTs increased the proliferation capabilities of MuSCs with altered cellular metabolism, while maintaining their stem-like properties such as self-renewal and engraftment potential.

PRMT7 Inhibitor SGC8158 Enhances Doxorubicin-Induced DNA Damage and Its Cytotoxicity

Protein arginine methyltransferase 7 (PRMT7) regulates various cellular responses, including gene expression, cell migration, stress responses, and stemness. In this study, we investigated the biological role of PRMT7 in cell cycle progression and DNA damage response (DDR) by inhibiting PRMT7 activity with either SGC8158 treatment or its specific siRNA transfection. Suppression of PRMT7 caused cell cycle arrest at the G₁ phase, resulting from the stabilization and subsequent accumulation of p21 protein. In addition, PRMT7 activity is closely associated with DNA repair pathways, including both homologous recombination and non-homologous end-joining. Interestingly, SGC8158, in combination with doxorubicin, led to a synergistic increase in both DNA damage and cytotoxicity in MCF7 cells. Taken together, our data demonstrate that PRMT7 is a critical modulator of cell growth and DDR, indicating that it is a promising target for cancer treatment.

From cyclins to CDKIs: Cell cycle regulation of skeletal muscle stem cell quiescence and activation

After extensive proliferation during development, the adult skeletal muscle cells remain outside the cell cycle, either as post-mitotic myofibers or as quiescent muscle stem cells (MuSCs). Despite its terminally differentiated state, adult skeletal muscle has a remarkable regeneration potential, driven by MuSCs. Upon injury, MuSC quiescence is reversed to support tissue growth and repair and it is re-established after the completion of muscle regeneration. The distinct cell cycle states and transitions observed in the different myogenic populations are orchestrated by elements of the cell cycle machinery. This consists of i) complexes of cyclins and Cyclin-Dependent Kinases (CDKs) that ensure cell cycle progression and ii) their negative regulators, the Cyclin-Dependent Kinase Inhibitors (CDKIs). In this review we discuss the roles of these factors in developmental and adult myogenesis, with a focus on CDKIs that have emerging roles in stem cell functions.

The epigenetic regulation of the germinal center response

In response to T-cell-dependent antigens, antigen-experienced B cells migrate to the center of the B-cell follicle to seed the germinal center (GC) response after cognate interactions with CD4⁺ T cells. These GC B cells eventually mature into memory and long-lived antibody-secreting plasma cells, thus generating long-lived humoral immunity. Within GC, B cells undergo somatic hypermutation of their B cell receptors (BCR) and positive selection for the emergence of high-affinity antigen-specific B-cell clones. However, this process may be dangerous, as the accumulation of aberrant mutations could result in malignant transformation of GC B cells or give rise to autoreactive B cell clones that can cause autoimmunity. Because of this, better understanding of GC development provides diagnostic and therapeutic clues to the underlying pathologic process. A productive GC response is orchestrated by multiple mechanisms. An emerging important regulator of GC reaction is epigenetic modulation, which has key transcriptional regulatory properties. In this review, we summarize the current knowledge on the biology of epigenetic mechanisms in the regulation of GC reaction and outline its importance in identification of immunotherapy decision making.

PRMT7 ablation stimulates anti-tumor immunity and sensitizes melanoma to immune checkpoint blockade

Despite the success of immune checkpoint inhibitor (ICI) therapy for cancer, resistance and relapse are frequent. Combination therapies are expected to enhance response rates and overcome this resistance. Herein, we report that combining PRMT7 inhibition with ICI therapy induces a strong anti-tumor T cell immunity and restrains tumor growth in vivo by increasing immune cell infiltration. PRMT7-deficient B16.F10 melanoma exhibits increased expression of genes in the interferon pathway, antigen presentation, and chemokine signaling. PRMT7 deficiency or inhibition with SGC3027 in B16.F10 melanoma results in reduced DNMT expression, loss of DNA methylation in the regulatory regions of endogenous retroviral elements (ERVs) causing their increased expression. PRMT7-deficient cells increase RIG-I and MDA5 expression with a reduction in the H4R3me2s repressive histone mark at their gene promoters. Our findings identify PRMT7 as a regulatory checkpoint for RIG-I, MDA5, and their ERV-double-stranded RNA (dsRNA) ligands, facilitating immune escape and anti-tumor T cell immunity to restrain tumor growth.

An enhancer variant at 16q22.1 predisposes to hepatocellular carcinoma via regulating PRMT7 expression

Most cancer causal variants are found in gene regulatory elements, e.g., enhancers. However, enhancer variants predisposing to hepatocellular carcinoma (HCC) remain unreported. Here we conduct a genome-wide survey of HCC-susceptible enhancer variants through a three-stage association study in 11,958 individuals and identify rs73613962 (T > G) within the intronic region of PRMT7 at 16q22.1 as a susceptibility locus of HCC (OR = 1.41, P = 6.02 × 10^-10). An enhancer dual-luciferase assay indicates that the rs73613962-harboring region has allele-specific enhancer activity. CRISPR-Cas9/dCas9 experiments further support the enhancer activity of this region to regulate PRMT7 expression. Mechanistically, transcription factor HNF4A binds to this enhancer region, with preference to the risk allele G, to promote PRMT7 expression. PRMT7 upregulation contributes to in vitro, in vivo, and clinical HCC-associated phenotypes, possibly by affecting the p53 signaling pathway. This concept of HCC pathogenesis may open a promising window for HCC prevention/treatment.

PRMT7 ablation in cardiomyocytes causes cardiac hypertrophy and fibrosis through β-catenin dysregulation

Angiotensin II (AngII) has potent cardiac hypertrophic effects mediated through activation of hypertrophic signaling like Wnt/β-Catenin signaling. In the current study, we examined the role of protein arginine methyltransferase 7 (PRMT7) in cardiac function. PRMT7 was greatly decreased in hypertrophic hearts chronically infused with AngII and cardiomyocytes treated with AngII. PRMT7 depletion in rat cardiomyocytes resulted in hypertrophic responses. Consistently, mice lacking PRMT7 exhibited the cardiac hypertrophy and fibrosis. PRMT7 overexpression abrogated the cellular hypertrophy elicited by AngII, while PRMT7 depletion exacerbated the hypertrophic response caused by AngII. Similar with AngII treatment, the cardiac transcriptome analysis of PRMT7-deficient hearts revealed the alteration in gene expression profile related to Wnt signaling pathway. Inhibition of PRMT7 by gene deletion or an inhibitor treatment enhanced the activity of β-catenin. PRMT7 deficiency decreases symmetric dimethylation of β-catenin. Mechanistic studies reveal that methylation of arginine residue 93 in β-catenin decreases the activity of β-catenin. Taken together, our data suggest that PRMT7 is important for normal cardiac function through suppression of β-catenin activity.

Protein Arginine Methyltransferases in Neuromuscular Function and Diseases

Neuromuscular diseases (NMDs) are characterized by progressive loss of muscle mass and strength that leads to impaired body movement. It not only severely diminishes the quality of life of the patients, but also subjects them to increased risk of secondary medical conditions such as fall-induced injuries and various chronic diseases. However, no effective treatment is currently available to prevent or reverse the disease progression. Protein arginine methyltransferases (PRMTs) are emerging as a potential therapeutic target for diverse diseases, such as cancer and cardiovascular diseases. Their expression levels are altered in the patients and molecular mechanisms underlying the association between PRMTs and the diseases are being investigated. PRMTs have been shown to regulate development, homeostasis, and regeneration of both muscle and neurons, and their association to NMDs are emerging as well. Through inhibition of PRMT activities, a few studies have reported suppression of cytotoxic phenotypes observed in NMDs. Here, we review our current understanding of PRMTs' involvement in the pathophysiology of NMDs and potential therapeutic strategies targeting PRMTs to address the unmet medical need.

Novel PRMT7 mutation in a rare case of dysmorphism and intellectual disability

Protein arginine N-methyltransferase 7 (PRMT7) encodes an arginine methyltransferase central to a number of fundamental biological processes, mutations in which result in an autosomal recessive developmental disorder characterized by short stature, brachydactyly, intellectual developmental disability and seizures (SBIDDS). To date, fewer than 15 patients with biallelic mutations in PRMT7 have been documented. Here we report brothers from a consanguineous Iraqi family presenting with a developmental disorder characterized by global developmental delay, shortened stature, facial dysmorphisms, brachydactyly, and kidney dysfunction. In both affected brothers, whole genome sequencing (WGS) identified a novel homozygous substitution in PRMT7 (ENST00000339507.5), c.1097 G > A (p.Cys366Tyr), considered to account for the majority of the phenotypic presentation. Rare compound heterozygous mutations in the dysplasia-associated perlecan-encoding HSPG2 gene (ENST00000374695.3) were also found (c.10721-2dupA, p.Ser71Asn and c.212 G > A), potentially accounting for the kidney dysfunction. In addition to expanding the known mutational spectrum of variably expressive PRMT7 mutations alongside potential digenic inheritance with HSPG2, this report underlines the diagnostic utility of a WGS-guided analysis in the detection of rare genetic disorders.

The Effects of Flavonoid Apigenin on Male Reproductive Health: Inhibition of Spermatogonial Proliferation through Downregulation of Prmt7/Akt3 Pathway

Apigenin, a common dietary flavonoid abundantly present in a variety of fruits and vegetables, has promising anticancer properties. As an effector of apigenin in myoblasts, protein arginine methyltransferase 7 (Prmt7) is required for male germ cell development. However, whether apigenin may influence male reproductive health through Prmt7 is still unclear. To this end, mouse spermatogonia were treated with different concentrations (2.5 to 50 μM) of apigenin for 48 h, which showed that apigenin could cause reduced cell proliferation in conjunction with longer S phase and G2/M phase (with concentrations of 10 and 20 μM, respectively), and increased apoptosis of spermatogonia (with concentration of 20 μM). Reduced Prmt7 expression was found in 20 μM apigenin-treated spermatogonia. Moreover, siRNA-induced Prmt7 knockdown exhibited similar influence on spermatogonia as that of apigenin treatment. In mechanistic terms, transcriptome analysis revealed 287 differentially expressed genes between Prmt7-downregulated and control spermatogonia. Furthermore, rescue experiments suggested that the effects of apigenin on spermatogonia might be mediated through the Prmt7/Akt3 pathway. Overall, our study supports that apigenin can interfere with mouse spermatogonial proliferation by way of the downregulated Prmt7/Akt3 pathway, which demonstrates that the concentration should be taken into account in future applications of apigenin for cancer therapy of men.

Cellular pathways influenced by protein arginine methylation: Implications for cancer

Arginine methylation is an influential post-translational modification occurring on histones, RNA binding proteins, and many other cellular proteins, affecting their function by altering their protein-protein and protein-nucleic acid interactions. Recently, a wealth of information has been gathered, implicating protein arginine methyltransferases (PRMTs), enzymes that deposit arginine methylation, in transcription, pre-mRNA splicing, DNA damage signaling, and immune signaling with major implications for cancer therapy, especially immunotherapy. This review summarizes this recent progress and the current state of PRMT inhibitors, some in clinical trials, as promising drug targets for cancer.

PRMT7: A Pivotal Arginine Methyltransferase in Stem Cells and Development

Protein arginine methylation is a posttranslational modification catalyzed by protein arginine methyltransferases (PRMTs), which play critical roles in many biological processes. To date, nine PRMT family members, namely, PRMT1, 2, 3, 4, 5, 6, 7, 8, and 9, have been identified in mammals. Among them, PRMT7 is a type III PRMT that can only catalyze the formation of monomethylarginine and plays pivotal roles in several kinds of stem cells. It has been reported that PRMT7 is closely associated with embryonic stem cells, induced pluripotent stem cells, muscle stem cells, and human cancer stem cells. PRMT7 deficiency or mutation led to severe developmental delay in mice and humans, which is possibly due to its crucial functions in stem cells. Here, we surveyed and summarized the studies on PRMT7 in stem cells and development in mice and humans and herein provide a discussion of the underlying molecular mechanisms. Furthermore, we also discuss the roles of PRMT7 in cancer, adipogenesis, male reproduction, cellular stress, and cellular senescence, as well as the future perspectives of PRMT7-related studies. Overall, PRMT7 mediates the proliferation and differentiation of stem cells. Deficiency or mutation of PRMT7 causes developmental delay, including defects in skeletal muscle, bone, adipose tissues, neuron, and male reproduction. A better understanding of the roles of PRMT7 in stem cells and development as well as the underlying mechanisms will provide information for the development of strategies for in-depth research of PRMT7 and stem cells as well as their applications in life sciences and medicine.

Role of Protein Arginine Methyltransferases and Inflammation in Muscle Pathophysiology

Arginine methylation mediated by protein arginine methyltransferases (PRMTs) is a post-translational modification of both histone and non-histone substrates related to diverse biological processes. PRMTs appear to be critical regulators in skeletal muscle physiology, including regeneration, metabolic homeostasis, and plasticity. Chronic inflammation is commonly associated with the decline of skeletal muscle mass and strength related to aging or chronic diseases, defined as sarcopenia. In turn, declined skeletal muscle mass and strength can exacerbate chronic inflammation. Thus, understanding the molecular regulatory pathway underlying the crosstalk between skeletal muscle function and inflammation might be essential for the intervention of muscle pathophysiology. In this review, we will address the current knowledge on the role of PRMTs in skeletal muscle physiology and pathophysiology with a specific emphasis on its relationship with inflammation.

PAX7 Balances the Cell Cycle Progression via Regulating Expression of Dnmt3b and Apobec2 in Differentiating PSCs

PAX7 transcription factor plays a crucial role in embryonic myogenesis and in adult muscles in which it secures proper function of satellite cells, including regulation of their self renewal. PAX7 downregulation is necessary for the myogenic differentiation of satellite cells induced after muscle damage, what is prerequisite step for regeneration. Using differentiating pluripotent stem cells we documented that the absence of functional PAX7 facilitates proliferation. Such action is executed by the modulation of the expression of two proteins involved in the DNA methylation, i.e., Dnmt3b and Apobec2. Increase in Dnmt3b expression led to the downregulation of the CDK inhibitors and facilitated cell cycle progression. Changes in Apobec2 expression, on the other hand, differently impacted proliferation/differentiation balance, depending on the experimental model used.

Structure and Function of Protein Arginine Methyltransferase PRMT7

PRMT7 is a member of the protein arginine methyltransferase (PRMT) family, which methylates a diverse set of substrates. Arginine methylation as a posttranslational modification regulates protein-protein and protein-nucleic acid interactions, and as such, has been implicated in various biological functions. PRMT7 is a unique, evolutionarily conserved PRMT family member that catalyzes the mono-methylation of arginine. The structural features, functional aspects, and compounds that inhibit PRMT7 are discussed here. Several studies have identified physiological substrates of PRMT7 and investigated the substrate methylation outcomes which link PRMT7 activity to the stress response and RNA biology. PRMT7-driven substrate methylation further leads to the biological outcomes of gene expression regulation, cell stemness, stress response, and cancer-associated phenotypes such as cell migration. Furthermore, organismal level phenotypes of PRMT7 deficiency have uncovered roles in muscle cell physiology, B cell biology, immunity, and brain function. This rapidly growing information on PRMT7 function indicates the critical nature of context-dependent functions of PRMT7 and necessitates further investigation of the PRMT7 interaction partners and factors that control PRMT7 expression and levels. Thus, PRMT7 is an important cellular regulator of arginine methylation in health and disease.

The role of protein arginine methyltransferase 7 in human developmentally arrested embryos cultured in vitro

Human embryos of in vitro fertilization (IVF) are often susceptible to developmental arrest, which greatly reduces the efficiency of IVF treatment. In recent years, it has been found that protein arginine methyltransferase 7 (PRMT7) plays an important role in the process of early embryonic development. However, not much is known about the relationship between PRMT7 and developmentally arrested embryos. The role of PRMT7 in developmentally arrested embryos was thus investigated in this study. Discarded human embryos from IVF were collected for experimental materials. Quantitative real-time polymerase chain reaction (qRT-PCR) and confocal analyses were used to identify PRMT7 mRNA and protein levels in early embryos at different developmental stages, as well as changes in the methylation levels of H4R3me2s. Additionally, PRMT7 was knocked down in the developmentally arrested embryos to observe the further development of these embryos. Our results demonstrated that PRMT7 mRNA and protein levels in arrested embryos were significantly increased compared with those in control embryos; meanwhile, the methylation levels of H4R3me2s in arrested embryos were also increased significantly. Knockdown of PRMT7 could rescue partially developmentally arrested embryos, and even individual developmentally arrested embryos could develop into blastocysts. In conclusion, over-expression of PRMT7 disrupts the early embryo development process, leading to early embryos developmental arrest, but these developmentally arrested defects could be partially rescued by knockdown of the PRMT7 protein.

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.

PRMT7 is involved in regulation of germ cell proliferation during embryonic stage

Arginine methylation is one of the most important post-translational modifications which is catalyzed by protein arginine methyltransferases (PRMTs). Previous studies have demonstrated that Prmt5 plays important role in germ cell development. Prmt7 is the only family member responsible for mono-methylation of arginine residue. However, whether Prmt7 is also involved in germ cell development remains unclear. In this study, we find that PRMT7 is abundantly expressed in the male germ cells during embryonic stage (from E10.5). Depletion of Prmt7 results in the defect of germ cell proliferation during embryonic stage and the number of primordial germ cells is significantly reduced in Prmt7^-/- mice at E11.5. We also find that the size of testes is reduced in Prmt7^-/- mice at P5 with reduced germ cell number and the diameter of seminiferous tubules. Further study reveals that the expression of BMPs and TGF-β singling pathway is significantly changed in germ cells of Prmt7^-/- mice at E12.5. However, no defect of testes development is observed in adult Prmt7^-/flox; Mvh-Cre mice. Collectively, this study demonstrates that Prmt7 plays roles in male germ cell proliferation during embryonic stages and it is not required for germ cell development postnatally.

Whole-genome resequencing of Dulong Chicken reveal signatures of selection

1. Dulong Chickens (DLCs) live at high altitude (~3000 m) and humidity (~90%), are endemic to the Yunnan province, and have gradually developed unique physiological characteristics, but their genetic basis is still unclear. Using the fixation index (F_ST ) approach, based on whole-genome resequencing, DLCs were analysed to uncover the genomic architecture of the population and candidate genes involved in selection during domestication. 2. A total of 469 candidate genes were obtained to be putatively under selection in DLCs. Further investigations revealed the genic footprint for local adaptation (high-altitude and high-humidity) as the genic signatures that are involved in economic traits (related to egg production). 3. Candidate genes were identified that may be associated with disease resistance, aggressiveness, small body size and positive selection of vision in DLCs. 4. These data revealed loci of selective signals that operate during selection for production at high altitude and humidity.

Fine-Tuning of GLI Activity through Arginine Methylation: Its Mechanisms and Function

The glioma-associated oncogene (GLI) family consists of GLI1, GLI2, and GLI3 in mammals. This family has important roles in development and homeostasis. To achieve these roles, the GLI family has widespread outputs. GLI activity is therefore strictly regulated at multiple levels, including via post-translational modifications for context-dependent GLI target gene expression. The protein arginine methyl transferase (PRMT) family is also associated with embryogenesis, homeostasis, and cancer mainly via epigenetic modifications. In the PRMT family, PRMT1, PRMT5, and PRMT7 reportedly regulate GLI1 and GLI2 activity. PRMT1 methylates GLI1 to upregulate its activity and target gene expression. Cytoplasmic PRMT5 methylates GLI1 and promotes GLI1 protein stabilization. Conversely, nucleic PRMT5 interacts with MENIN to suppress growth arrest-specific protein 1 expression, which assists Hedgehog ligand binding to Patched, indirectly resulting in downregulated GLI1 activity. PRMT7-mediated GLI2 methylation upregulates its activity through the dissociation of GLI2 and Suppressor of Fused. Together, PRMT1, PRMT5, and PRMT7 regulate GLI activity at multiple revels. Furthermore, the GLI and PRMT families have strong links with various cancers through cancer stem cell maintenance. Therefore, PRMT-mediated regulation of GLI activity would have important roles in cancer stem cell maintenance.

Satellite cell-specific ablation of Cdon impairs integrin activation, FGF signalling, and muscle regeneration

BACKGROUND

Perturbation in cell adhesion and growth factor signalling in satellite cells results in decreased muscle regenerative capacity. Cdon (also called Cdo) is a component of cell adhesion complexes implicated in myogenic differentiation, but its role in muscle regeneration remains to be determined.

METHODS

We generated inducible satellite cell-specific Cdon ablation in mice by utilizing a conditional Cdon allele and Pax7 ^CreERT2 . To induce Cdon ablation, mice were intraperitoneally injected with tamoxifen (tmx). Using cardiotoxin-induced muscle injury, the effect of Cdon depletion on satellite cell function was examined by histochemistry, immunostaining, and 5-ethynyl-2'-deoxyuridine (EdU) incorporation assay. Isolated myofibers or myoblasts were utilized to determine stem cell function and senescence. To determine pathways related to Cdon deletion, injured muscles were subjected to RNA sequencing analysis.

RESULTS

Satellite cell-specific Cdon ablation causes impaired muscle regeneration with fibrosis, likely attributable to decreased proliferation, and senescence, of satellite cells. Cultured Cdon-depleted myofibers exhibited 32 ± 9.6% of EdU-positive satellite cells compared with 58 ± 4.4% satellite cells in control myofibers (P < 0.05). About 32.5 ± 3.7% Cdon-ablated myoblasts were positive for senescence-associated β-galactosidase (SA-β-gal) while only 3.6 ± 0.5% of control satellite cells were positive (P < 0.001). Transcriptome analysis of muscles at post-injury Day 4 revealed alterations in genes related to mitogen-activated protein kinase signalling (P < 8.29 e^-5 ) and extracellular matrix (P < 2.65 e^-24 ). Consistent with this, Cdon-depleted tibialis anterior muscles had reduced phosphorylated extracellular signal-regulated kinase (p-ERK) protein levels and expression of ERK targets, such as Fos (0.23-fold) and Egr1 (0.31-fold), relative to mock-treated control muscles (P < 0.001). Cdon-depleted myoblasts exhibited impaired ERK activation in response to basic fibroblast growth factor. Cdon ablation resulted in decreased and/or mislocalized integrin β1 activation in satellite cells (weak or mislocalized integrin1 in tmx = 38.7 ± 1.9%, mock = 21.5 ± 6%, P < 0.05), previously linked with reduced fibroblast growth factor (FGF) responsiveness in aged satellite cells. In mechanistic studies, Cdon interacted with and regulated cell surface localization of FGFR1 and FGFR4, likely contributing to FGF responsiveness of satellite cells. Satellite cells from a progeria model, Zmpste24^-/- myofibers, showed decreased Cdon levels (Cdon-positive cells in Zmpste24^-/- = 63.3 ± 11%, wild type = 90 ± 7.7%, P < 0.05) and integrin β1 activation (weak or mislocalized integrin β1 in Zmpste24^-/- = 64 ± 6.9%, wild type = 17.4 ± 5.9%, P < 0.01).

CONCLUSIONS

Cdon deficiency in satellite cells causes impaired proliferation of satellite cells and muscle regeneration via aberrant integrin and FGFR signalling.

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.

ZNF746/PARIS overexpression induces cellular senescence through FoxO1/p21 axis activation in myoblasts

Various stresses, including oxidative stress, impair the proliferative capacity of muscle stem cells leading to declined muscle regeneration related to aging or muscle diseases. ZNF746 (PARIS) is originally identified as a substrate of E3 ligase Parkin and its accumulation is associated with Parkinson’s disease. In this study, we investigated the role of PARIS in myoblast function. PARIS is expressed in myoblasts and decreased during differentiation. PARIS overexpression decreased both proliferation and differentiation of myoblasts without inducing cell death, whereas PARIS depletion enhanced myoblast differentiation. Interestingly, high levels of PARIS in myoblasts or fibroblasts induced cellular senescence with alterations in gene expression associated with p53 signaling, inflammation, and response to oxidative stress. PARIS overexpression in myoblasts starkly enhanced oxidative stress and the treatment of an antioxidant Trolox attenuated the impaired proliferation caused by PARIS overexpression. FoxO1 and p53 proteins are elevated in PARIS-overexpressing cells leading to p21 induction and the depletion of FoxO1 or p53 reduced p21 levels induced by PARIS overexpression. Furthermore, both PARIS and FoxO1 were recruited to p21 promoter region and Trolox treatment attenuated FoxO1 recruitment. Taken together, PARIS upregulation causes oxidative stress-related FoxO1 and p53 activation leading to p21 induction and cellular senescence of myoblasts.

Decoding the relationship between ageing and amyotrophic lateral sclerosis: a cellular perspective

With an ageing population comes an inevitable increase in the prevalence of age-associated neurodegenerative diseases, such as amyotrophic lateral sclerosis (ALS), a relentlessly progressive and universally fatal disease characterized by the degeneration of upper and lower motor neurons within the brain and spinal cord. Indeed, the physiological process of ageing causes a variety of molecular and cellular phenotypes. With dysfunction at the neuromuscular junction implicated as a key pathological mechanism in ALS, and each lower motor unit cell type vulnerable to its own set of age-related phenotypes, the effects of ageing might in fact prove a prerequisite to ALS, rendering the cells susceptible to disease-specific mechanisms. Moreover, we discuss evidence for overlap between age and ALS-associated hallmarks, potentially implicating cell type-specific ageing as a key contributor to this multifactorial and complex disease. With a dearth of disease-modifying therapy currently available for ALS patients and a substantial failure in bench to bedside translation of other potential therapies, the unification of research in ageing and ALS requires high fidelity models to better recapitulate age-related human disease and will ultimately yield more reliable candidate therapeutics for patients, with the aim of enhancing healthspan and life expectancy.

Identification, expression and functional analysis of prmt7 in medaka Oryzias latipes

Arginine methylation is an important posttranslational modification and catalyzed by a family of protein arginine methyltransferases (PRMTs). PRMT7 is the type III PRMT and produces solely monomethylarginine products. PRMT7 has been found to play important roles in multiple biological processes in mammals. However, the expression pattern and function of Prmt7 remain largely unknown in fish. In this study, we characterized the medaka prmt7 gene and determined its expression pattern and function during embryogenesis and germ cell development. The results showed that the chromosomal location and gene structure of medaka prmt7 were similar to its mammalian orthologs. Comparisons of deduced amino acid sequences indicated that medaka Prmt7 was a homolog of human PRMT7 with two methyltransferase domains. Reverse transcription-polymerase chain reaction (RT-PCR) and real time RT-PCR revealed that medaka prmt7 had maternal origin with continuous and dynamical expression during embryonic development. Whole-mount in situ hybridization analysis observed that the transcripts of prmt7 were ubiquitous at morula and gastrula stage, and were later riched in the brain and otic vesicles during embryogenesis. In the adult stage, prmt7 messenger RNA was detected in all examined tissues with the high levels in the ovary and testis. The expression of prmt7 in the gonads was restricted to oocytes of the ovary and spermatids/sperm of the testis. Functional analysis showed that knockdown of medaka prmt7 did not reduce the total number of primordial germ cells (PGCs) in vivo but significantly affected PGCs distribution during embryonic development. These results indicate that prmt7 may be involved in germ cell development in medaka.

The emergence of protein arginine methyltransferases in skeletal muscle and metabolic disease

Protein arginine methyltransferases (PRMTs) are a family of enzymes that catalyze the methylation of arginine residues on target proteins and thus alter the stability, localization, or activity of the substrate. In doing so, PRMTs mediate a variety of intracellular functions that are essential for survival. Additionally, PRMT dysregulation is involved in a number of the most prevalent health disorders, including cancer and neurodegenerative and cardiovascular diseases, as well as in the aging process. Investigations of PRMT biology in skeletal muscle cells began in 2002, and since then these enzymes have emerged as regulators of skeletal muscle phenotype determination, maintenance, and remodeling. Specifically, more recent in vivo studies have revealed that PRMTs impact multiple aspects of skeletal muscle biology, including satellite cell function and phenotypic plasticity in response to exercise and disuse. Skeletal muscle plays critically important roles in regulating whole body metabolism, and recent investigations have also begun elucidating PRMT expression and function under conditions of metabolic dysfunction. The goals of this review are to 1) summarize the literature on PRMT biology in skeletal muscle with a particular emphasis on the in vivo evidence and 2) survey PRMTs in metabolic disorders, namely, obesity and type 2 diabetes mellitus. We also identify notable knowledge gaps therein and present opportunities to further expand our understanding of these enzymes so critical to health and disease.

Zebrafish prmt7 negatively regulates antiviral responses by suppressing the retinoic acid-inducible gene-I-like receptor signaling

Arginine methylation is a post-translational modification in histone and nonhistone proteins that can affect numerous cellular activities. Protein arginine methyltransferase 7 (Prmt7), a type III arginine methyltransferase, catalyzes the formation of stable monomethylarginines of histones. The role of PRMT7 in virus-induced innate immunity signaling, however, remains largely unknown. We demonstrate that zebrafish prmt7 could be inhibited by spring viremia of carp virus (SVCV) and grass carp reovirus (GCRV) infection. The overexpression of prmt7 suppresses cellular antiviral responses that are partially dependent on the arginine methyltransferase activity of prmt7. Consistently, prmt7-null zebrafish were more resistant to SVCV or GCRV infection, exhibiting enhanced expression of key antiviral genes and fewer necrotic cells in the liver and kidney upon viral infection. Furthermore, we established a zebrafish model to investigate grass carp hemorrhagic disease. Our findings suggest that by suppressing the RIG-I-like receptors signaling, zebrafish prmt7 negatively regulates antiviral responses, indicating the vital role of prmt7 and its arginine methyltransferase activity in innate immunity.

PRMTs and Arginine Methylation: Cancer's Best-Kept Secret?

Post-translational modification (PTM) of proteins is vital for increasing proteome diversity and maintaining cellular homeostasis. If the writing, reading, and removal of modifications are not controlled, cancer can develop. Arginine methylation is an understudied modification that is increasingly associated with cancer progression. Consequently protein arginine methyltransferases (PRMTs), the writers of arginine methylation, have rapidly gained interest as novel drug targets. However, for clinical success a deep mechanistic understanding of the biology of PRMTs is required. In this review we focus on advances made regarding the role of PRMTs in stem cell biology, epigenetics, splicing, immune surveillance and the DNA damage response, and highlight the rapid rise of specific inhibitors that are now in clinical trials for cancer therapy.

PRMT7 deficiency enhances adipogenesis through modulation of C/EBP-β

Obesity that is critically correlated with the initiation and development of metabolic syndrome and cardiovascular diseases has increased worldwide. Adipogenesis is coordinated through multi-steps involving adipogenic commitment, mitotic clonal expansion (MCE) and differentiation. Recently, protein arginine methyltransferase 4 (PRMT4) and PRMT5 have been implicated in modulation of adipogenesis via regulation of C/EBP-β activity or PPAR-γ2 expression. In the current study, we demonstrate a suppressive role of PRMT7 in adipogenesis. PRMT7-depleted preadipocytes or PRMT7^-/- mouse embryonic fibroblasts (MEFs) displayed increased adipogenesis while PRMT7 overexpression attenuated it. PRMT7 depletion in preadipocytes promoted MCE, an initial step of adipogenesis. Furthermore, we found that PRMT7 interacted with and methylated a key adipogenic factor C/EBP-β upon adipogenic induction and modulated the accumulation of C/EBP-β at its target sites in the PPAR-γ2 promoter. Taken together, our data suggest that PRMT7 suppresses adipogenesis through modulation of C/EBP-β activity.

Assaying epigenome functions of PRMTs and their substrates

Among the widespread and increasing number of identified post-translational modifications (PTMs), arginine methylation is catalyzed by the protein arginine methyltransferases (PRMTs) and regulates fundamental processes in cells, such as gene regulation, RNA processing, translation, and signal transduction. As epigenetic regulators, PRMTs play key roles in pluripotency, differentiation, proliferation, survival, and apoptosis, which are essential biological programs leading to development, adult homeostasis but also pathological conditions including cancer. A full understanding of the molecular mechanisms that underlie PRMT-mediated gene regulation requires the genome wide mapping of each player, i.e., PRMTs, their substrates and epigenetic marks, methyl-marks readers as well as interaction partners, in a thorough and unambiguous manner. However, despite the tremendous advances in high throughput sequencing technologies and the numerous efforts from the scientific community, the epigenomic profiling of PRMTs as well as their histone and non-histone substrates still remains a big challenge owing to obvious limitations in tools and methodologies. This review will summarize the present knowledge about the genome wide mapping of PRMTs and their substrates as well as the technical approaches currently in use. The limitations and pitfalls of the technical tools along with conventional approaches will be then discussed in detail. Finally, potential new strategies for chromatin profiling of PRMTs and histone substrates will be proposed and described.

Protein arginine methyltransferase biology in humans during acute and chronic skeletal muscle plasticity

Protein arginine methyltransferases (PRMTs) are a family of enzymes that catalyze the methylation of arginine residues on target proteins. While dysregulation of PRMTs has been documented in a number of the most prevalent diseases, our understanding of PRMT biology in human skeletal muscle is limited. This study served to address this knowledge gap by exploring PRMT expression and function in human skeletal muscle in vivo and characterizing PRMT biology in response to acute and chronic stimuli for muscle plasticity. Fourteen untrained, healthy men performed one session of sprint interval exercise (SIE) before completing four bouts of SIE per week for 6 wk as part of a sprint interval training (SIT) program. Throughout this time course, multiple muscle biopsies were collected. We found that at basal, resting conditions PRMT1, PRMT4, PRMT5, and PRMT7 were the most abundantly expressed PRMT mRNAs in human quadriceps muscle. Additionally, the broad subcellular distribution pattern of PRMTs suggests methyltransferase activity throughout human myofibers. A spectrum of PRMT-specific inductions, and decrements, in expression and activity were observed in response to acute and chronic cues for muscle plasticity. In conclusion, our findings demonstrate that PRMTs are present and active in human skeletal muscle in vivo and that there are distinct, enzyme-specific responses and adaptations in PRMT biology to acute and chronic stimuli for muscle plasticity. This work advances our understanding of this critical family of enzymes in humans.NEW & NOTEWORTHY This is the first report of protein arginine methyltransferase (PRMT) biology in human skeletal muscle in vivo. We observed that PRMT1, -4, -5, and -7 were the most abundant PRMT mRNAs in human muscle and that PRMT proteins exhibited a broad subcellular localization that included myonuclear, cytosolic, and sarcolemmal compartments. Acute exercise and chronic training evoked PRMT-specific alterations in expression and activity. This study reveals a hitherto unknown complexity to PRMT biology in human muscle.

Roles and regulation of histone methylation in animal development

Histone methylation can occur at various sites in histone proteins, primarily on lysine and arginine residues, and it can be governed by multiple positive and negative regulators, even at a single site, to either activate or repress transcription. It is now apparent that histone methylation is critical for almost all stages of development, and its proper regulation is essential for ensuring the coordinated expression of gene networks that govern pluripotency, body patterning and differentiation along appropriate lineages and organogenesis. Notably, developmental histone methylation is highly dynamic. Early embryonic systems display unique histone methylation patterns, prominently including the presence of bivalent (both gene-activating and gene-repressive) marks at lineage-specific genes that resolve to monovalent marks during differentiation, which ensures that appropriate genes are expressed in each tissue type. Studies of the effects of methylation on embryonic stem cell pluripotency and differentiation have helped to elucidate the developmental roles of histone methylation. It has been revealed that methylation and demethylation of both activating and repressive marks are essential for establishing embryonic and extra-embryonic lineages, for ensuring gene dosage compensation via genomic imprinting and for establishing body patterning via HOX gene regulation. Not surprisingly, aberrant methylation during embryogenesis can lead to defects in body patterning and in the development of specific organs. Human genetic disorders arising from mutations in histone methylation regulators have revealed their important roles in the developing skeletal and nervous systems, and they highlight the overlapping and unique roles of different patterns of methylation in ensuring proper development.

Prmt7 promotes myoblast differentiation via methylation of p38MAPK on arginine residue 70

MyoD functions as a master regulator to induce muscle-specific gene expression and myogenic differentiation. Here, we demonstrate a positive role of Protein arginine methyltransferase 7 (Prmt7) in MyoD-mediated myoblast differentiation through p38MAPK activation. Prmt7 depletion in primary or C2C12 myoblasts impairs cell cycle withdrawal and myogenic differentiation. Furthermore, Prmt7 depletion decreases the MyoD-reporter activities and the MyoD-mediated myogenic conversion of fibroblasts. Together with MyoD, Prmt7 is recruited to the Myogenin promoter region and Prmt7 depletion attenuates the recruitment of MyoD and its coactivators. The mechanistic study reveals that Prmt7 methylates p38MAPKα at the arginine residue 70, thereby promoting its activation which in turn enhances MyoD activities. The arginine residue 70 to alanine mutation in p38MAPKα impedes MyoD/E47 heterodimerization and the recruitment of Prmt7, MyoD and Baf60c to the Myogenin promoter resulting in blunted Myogenin expression. In conclusion, Prmt7 promotes MyoD-mediated myoblast differentiation through methylation of p38MAPKα at arginine residue 70.

PRMT7 methylates and suppresses GLI2 binding to SUFU thereby promoting its activation

Cellular senescence is implicated in aging or age-related diseases. Sonic hedgehog (Shh) signaling, an inducer of embryonic development, has recently been demonstrated to inhibit cellular senescence. However, the detailed mechanisms to activate Shh signaling to prevent senescence is not well understood. Here, we demonstrate that Protein arginine methyltransferase 7 (PRMT7) promotes Shh signaling via GLI2 methylation which is critical for suppression of cellular senescence. PRMT7-deficient mouse embryonic fibroblasts (MEFs) exhibited a premature cellular senescence with accompanied increase in the cell cycle inhibitors p16 and p21. PRMT7 depletion results in reduced Shh signaling activity in MEFs while PRMT7 overexpression enhances GLI2-reporter activities that are sensitive to methylation inhibition. PRMT7 interacts with and methylates GLI2 on arginine residues 225 and 227 nearby a binding region of SUFU, a negative regulator of GLI2. This methylation interferes with GLI2-SUFU binding, leading to facilitation of GLI2 nuclear accumulation and Shh signaling. Taken together, these data suggest that PRMT7 induces GLI2 methylation, reducing its binding to SUFU and increasing Shh signaling, ultimately leading to prevention of cellular senescence.

PRMT7 as a unique member of the protein arginine methyltransferase family: A review

Protein arginine methyltransferases (PRMTs) are found in a wide variety of eukaryotic organisms and can regulate gene expression, DNA repair, RNA splicing, and stem cell biology. In mammalian cells, nine genes encode a family of sequence-related enzymes; six of these PRMTs catalyze the formation of ω-asymmetric dimethyl derivatives, two catalyze ω-symmetric dimethyl derivatives, and only one (PRMT7) solely catalyzes ω-monomethylarginine formation. Purified recombinant PRMT7 displays a number of unique enzymatic properties including a substrate preference for arginine residues in R-X-R motifs with additional flanking basic amino acid residues and a temperature optimum well below 37 °C. Evidence has been presented for crosstalk between PRMT7 and PRMT5, where methylation of a histone H4 peptide at R17, a PRMT7 substrate, may activate PRMT5 for methylation of R3. Defects in muscle stem cells (satellite cells) and immune cells are found in mouse Prmt7 homozygous knockouts, while humans lacking PRMT7 are characterized by significant intellectual developmental delays, hypotonia, and facial dysmorphisms. The overexpression of the PRMT7 gene has been correlated with cancer metastasis in humans. Current research challenges include identifying cellular factors that control PRMT7 expression and activity, identifying the physiological substrates of PRMT7, and determining the effect of methylation on these substrates.

Developmental expression of three prmt genes in Xenopus

Protein arginine methyltransferases (PRMTs) are involved in many cellular processes via the arginine methylation of histone or non-histone proteins. We examined the expression patterns of prmt4, prmt7, and prmt9 during embryogenesis in Xenopus using whole-mount in situ hybridization and quantitative reverse transcription polymerase chain reaction (RT-PCR). Xenopus prmt4 and prmt7 were expressed in the neural crest, brain, and spinal cord, and also detected in the eye, branchial arches, and heart at the tailbud stage. Specific prmt9 signals were not detected in Xenopus embryos until the late tailbud stage when weak expression was observed in the branchial arches. Quantitative RT-PCR indicated that the expressions of prmt4 and prmt7 were up-regulated during the neurula stage, whereas prmt9 maintained its low expression until the late tailbud stage, consistent with the whole-mount in situ hybridization results. Thus, the developmental expression patterns of these three prmt genes in Xenopus embryos provide a basis for further functional study of such genes.

Further delineation of the phenotype caused by loss of function mutations in PRMT7

PRMT7 encodes for an arginine methyltransferase that methylates arginine residues on various protein substrates and has been shown to play a role in various developmental processes. Mutations in PRMT7 have been recently shown to be implicated in a phenotype with intellectual disability, short stature and brachydactyly, and considered to be a phenocopy of pseudohypoparathyroidism. We report a patient with short stature, psychomotor delay, hearing loss and brachydactyly, for whom whole exome sequencing detected two mutations in PRMT7 and parental segregation studies detected biallelic mutation inheritance. Few patients with biallelic PRMT7 mutations have been reported so far in the literature. We report a new patient and review all reported cases to date to delineate the clinical manifestations that may help in diagnosis this disorder, known as Short Stature, Brachydactyly, Intellectual Developmental Disability, and Seizures syndrome, allowing appropriate management and genetic counselling.

Recent advances in targeting protein arginine methyltransferase enzymes in cancer therapy

INTRODUCTION

Exploration in the field of epigenetics has revealed the diverse roles of the protein arginine methyltransferase (PRMT) family of proteins in multiple disease states. These findings have led to the development of specific inhibitors and discovery of several new classes of drugs with potential to treat both benign and malignant conditions. Areas covered: We provide an overview on the role of PRMT enzymes in healthy and malignant cells, highlighting the role of arginine methylation in specific pathways relevant to cancer pathogenesis. Additionally, we describe structure and catalytic activity of PRMT and discuss the mechanisms of action of novel small molecule inhibitors of specific members of the arginine methyltransferase family. Expert opinion: As the field of PRMT biology advances, it's becoming clear that this class of enzymes is highly relevant to maintaining normal physiologic processes as well and disease pathogenesis. We discuss the potential impact of PRMT inhibitors as a broad class of drugs, including the pleiotropic effects, off target effects the need for more detailed PRMT-centric interactomes, and finally, the potential for targeting this class of enzymes in clinical development of experimental therapeutics for cancer.