Arginine Methylation: The Coming of Age

Expression and localisation of methylthioadenosine phosphorylase (MTAP) in oral squamous cell carcinoma and their significance in epithelial-to-mesenchymal transition

Methylthioadenosine phosphorylase (MTAP) is a rate-limiting enzyme in the methionine salvage pathway, which recycles one carbon unit that is lost during polyamine synthesis back into the methionine cycle. Although MTAP deficiency has been reported in various tumours, MTAP is overexpressed and might promote oncogenesis in other cancers, including prostate and colon cancer. Currently, little is known about the MTAP status of oral squamous cell carcinoma (OSCC). In this study, we immunohistochemically examined the expression of MTAP in surgically resected oral epithelial dysplasia (OED, n=7), carcinoma in situ (CIS) (n=16), and OSCC (n=118). In the normal epithelium, MTAP was only weakly expressed in the cytoplasm of the basal layer cells. In OED, CIS, and OSCC, MTAP was uniformly expressed in the cytoplasm of the dysplastic and cancer cells. In addition to cytoplasmic MTAP expression, 45 of 118 cases (38.1%) exhibited increased nuclear expression of MTAP in the cancer cells at the invasive front. Statistical analysis showed that the concomitant nuclear and cytoplasmic expression of MTAP was associated with a high budding score (p=0.0023); poor differentiation (p=0.0044); aggressive invasion patterns (p=0.0001); and features of epithelial-to-mesenchymal transition (EMT), such as loss of E-cadherin expression (p=0.0003) and upregulated expression of vimentin (p=0.0002), slug (p=0.0002), and laminin 5 (p<0.0001). High expression of protein arginine methyltransferase 1 or 5, the functions of which are reported to be inhibited in MTAP-deficient cancer, was associated with the concomitant nuclear and cytoplasmic expression of MTAP (p<0.0001). Concomitant nuclear and cytoplasmic expression of MTAP was marginally significantly associated with worse 5-year relapse-free survival (p=0.045). These findings suggest that MTAP not only plays a role in the oncogenesis of OSCC, but that it might also make it more aggressive by inducing EMT through its activity in the methionine salvage pathway.

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.

An update on allosteric modulators as a promising strategy targeting histone methyltransferase

Histone methylation is a vital post-translational modification process in epigenetic regulation. The perturbation of histone methylation accounts for many diseases, including malignant cancers. Although achieving significant advances over past decades, orthosteric inhibitors targeting histone methyltransferases still suffer from challenges on subtype selectivity and acquired drug-resistant mutations. As an alternative, new compounds targeting the evolutionarily less conserved allosteric sites, exemplified by HKMTs and PRMTs inhibitors, offer a promising strategy to address this quandary. Herein, we highlight the allosteric sites and mechanisms in histone methyltransferases along with representative allosteric modulators, expecting to facilitate the discovery of allosteric modulators in favor of epigenetic therapy.

Discovery of a potent and dual-selective bisubstrate inhibitor for protein arginine methyltransferase 4/5

Protein arginine methyltransferases (PRMTs) have been implicated in the progression of many diseases. Understanding substrate recognition and specificity of individual PRMT would facilitate the discovery of selective inhibitors towards future drug discovery. Herein, we reported the design and synthesis of bisubstrate analogues for PRMTs that incorporate a S-adenosylmethionine (SAM) analogue moiety and a tripeptide through an alkyl substituted guanidino group. Compound AH237 is a potent and selective inhibitor for PRMT4 and PRMT5 with a half-maximal inhibition concentration (IC50) of 2.8 and 0.42 nmol/L, respectively. Computational studies provided a plausible explanation for the high potency and selectivity of AH237 for PRMT4/5 over other 40 methyltransferases. This proof-of-principle study outlines an applicable strategy to develop potent and selective bisubstrate inhibitors for PRMTs, providing valuable probes for future structural studies.

Protein music of enhanced musicality by music style guided exploration of diverse amino acid properties

Inspired by the traceable analogies between protein sequences and music notes, protein music has been composed from amino acid sequences for popularizing science and sourcing melodies. Despite the continuous development of protein-to-music algorithms, the musicality of protein music lags far behind human music. Musicality may be enhanced by fine-tuned protein-to-music mapping to the features of a specific music style. We analyzed the features of a music style (Fantasy-Impromptu style), and used the quantized musical features to guide broad exploration of diverse amino acid properties (104 properties, sequence patterns and variations) for developing a novel protein-to-music algorithm of enhanced musicality. This algorithm was applied to 18 proteins of various biological functions. The derived music pieces consistently exhibited enhanced musicality with respect to existing protein music. Music style guided exploration of diverse amino acid properties enable protein music composition of enhanced musicality, which may be further developed and applied to a wider variety of music styles.

Profiling and Validation of Live-Cell Protein Methylation with Engineered Enzymes and Methionine Analogues

Protein methyltransferases (PMTs) regulate many aspects of normal and disease processes through substrate methylation, with S-adenosyl-L-methionine (SAM) as a cofactor. It has been challenging to elucidate cellular protein lysine and arginine methylation because these modifications barely alter physical properties of target proteins and often are context dependent, transient, and substoichiometric. To reveal bona fide methylation events associated with specific PMT activities in native contexts, we developed the live-cell Bioorthogonal Profiling of Protein Methylation (lcBPPM) technology, in which the substrates of specific PMTs are labeled by engineered PMTs inside living cells, with in situ-synthesized SAM analogues as cofactors. The biorthogonality of this technology is achieved because these SAM analogue cofactors can only be processed by the engineered PMTs-and not native PMTs-to modify the substrates with distinct chemical groups. Here, we describe the latest lcBPPM protocol and its application to reveal proteome-wide methylation and validate specific methylation events. © 2021 Wiley Periodicals LLC. Basic Protocol 1: Live-cell labeling of substrates of protein methyltransferases GLP1 and PRMT1 with lcBPPM-feasible enzymes and SAM analogue precursors Support Protocol: Gram-scale synthesis of Hey-Met Basic Protocol 2: Click labeling of lcBPPM cell lysates with a biotin-azide probe Alternate Protocol: Click labeling of small-scale lcBPPM cell lysates with a TAMRA-azide dye for in-gel fluorescence visualization Basic Protocol 3: Enrichment of biotinylated lcBPPM proteome with streptavidin beads Basic Protocol 4: Proteome-wide identification of lcBPPM targets with mass spectrometry Basic Protocol 5: Validation of individual lcBPPM targets by western blot.

Interplay Among Hydrogen Sulfide, Nitric Oxide, Reactive Oxygen Species, and Mitochondrial DNA Oxidative Damage

Hydrogen sulfide (H2S), nitric oxide (NO), and reactive oxygen species (ROS) play essential signaling roles in cells by oxidative post-translational modification within suitable ranges of concentration. All of them contribute to the balance of redox and are involved in the DNA damage and repair pathways. However, the damage and repair pathways of mitochondrial DNA (mtDNA) are complicated, and the interactions among NO, H2S, ROS, and mtDNA damage are also intricate. This article summarized the current knowledge about the metabolism of H2S, NO, and ROS and their roles in maintaining redox balance and regulating the repair pathway of mtDNA damage in plants. The three reactive species may likely influence each other in their generation, elimination, and signaling actions, indicating a crosstalk relationship between them. In addition, NO and H2S are reported to be involved in epigenetic variations by participating in various cell metabolisms, including (nuclear and mitochondrial) DNA damage and repair. Nevertheless, the research on the details of NO and H2S in regulating DNA damage repair of plants is in its infancy, especially in mtDNA.

Direct, Late-Stage Mono-N-arylation of Pentamidine: Method Development, Mechanistic Insight, and Expedient Access to Novel Antiparastitics against Diamidine-Resistant Parasites

A selective mono‐N‐arylation strategy of amidines under Chan‐Lam conditions is described. During the reaction optimization phase, the isolation of a mononuclear Cu(II) complex provided unique mechanistic insight into the operation of Chan‐Lam mono‐N‐arylation. The scope of the process is demonstrated, and then applied to access the first mono‐N‐arylated analogues of pentamidine. Sub‐micromolar activity against kinetoplastid parasites was observed for several analogues with no cross‐resistance in pentamidine and diminazene‐resistant trypanosome strains and against Leishmania mexicana. A fluorescent mono‐N‐arylated pentamidine analogue revealed rapid cellular uptake, accumulating in parasite nuclei and the kinetoplasts. The DNA binding capability of the mono‐N‐arylated pentamidine series was confirmed by UV‐melt measurements using AT‐rich DNA. This work highlights the potential to use Chan‐Lam mono‐N‐arylation to develop therapeutic leads against diamidine‐resistant trypanosomiasis and leishmaniasis.

Post-translational modifications on RNA-binding proteins: accelerators, brakes, or passengers in neurodegeneration?

RNA-binding proteins (RBPs) are critical players in RNA expression and metabolism, thus, the proper regulation of this class of proteins is critical for cellular health. Regulation of RBPs often occurs through post-translational modifications (PTMs), which allow the cell to quickly and efficiently respond to cellular and environmental stimuli. PTMs have recently emerged as important regulators of RBPs implicated in neurodegenerative disorders, in particular amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). Here, we summarize how disease-associated PTMs influence the biophysical properties, molecular interactions, subcellular localization, and function of ALS/FTD-linked RBPs, such as FUS and TDP-43. We will discuss how PTMs are believed to play pathological, protective, or ambiguous roles in these neurodegenerative disorders.

Protein arginine methyltransferases and hepatocellular carcinoma: A review

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Protein arginine methylation is essential in multiple biological processes.

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The family of PRMTs is a novel regulator of liver diseases.

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Deregulation of PRMTs is correlated with HCC prognosis and clinical features.

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PRMTs play a vital role in HCC malignancy, immune responses and metabolism.

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PRMTs may represent druggable targets as novel strategies for HCC therapy.

Hepatocellular carcinoma (HCC) is one of the most frequently diagnosed cancers with a high mortality rate worldwide. The complexity of HCC initiation and progression poses a great challenge to the diagnosis and treatment. An increasing number of studies have focused on the emerging roles of protein arginine methylation in cancers, including tumor growth, invasion, metastasis, metabolism, immune responses, chemotherapy sensitivity, etc. The family of protein arginine methyltransferases (PRMTs) is the most important proteins that mediate arginine methylation. The deregulation of PRMTs’ expression and functions in cancers have been gradually unveiled, and many PRMTs inhibitors are in preclinical and clinical investigations now. This review focuses predominantly on the aberrant expression of PRMTs, underlying mechanisms, as well as their potential applications in HCC, and provide novel insights into HCC therapy.

Arginine monomethylation by PRMT7 controls MAVS-mediated antiviral innate immunity

Accurate control of innate immune responses is required to eliminate invading pathogens and simultaneously avoid autoinflammation and autoimmune diseases. Here, we demonstrate that arginine monomethylation precisely regulates the mitochondrial antiviral-signaling protein (MAVS)-mediated antiviral response. Protein arginine methyltransferase 7 (PRMT7) forms aggregates to catalyze MAVS monomethylation at arginine residue 52 (R52), attenuating its binding to TRIM31 and RIG-I, which leads to the suppression of MAVS aggregation and subsequent activation. Upon virus infection, aggregated PRMT7 is disabled in a timely manner due to automethylation at arginine residue 32 (R32), and SMURF1 is recruited to PRMT7 by MAVS to induce proteasomal degradation of PRMT7, resulting in the relief of PRMT7 suppression of MAVS activation. Therefore, we not only reveal that arginine monomethylation by PRMT7 negatively regulates MAVS-mediated antiviral signaling in vitro and in vivo but also uncover a mechanism by which PRMT7 is tightly controlled to ensure the timely activation of antiviral defense.

Control of Breast Cancer Pathogenesis by Histone Methylation and the Hairless Histone Demethylase

Breast cancer is a highly heterogeneous disease, encompassing many subtypes that have distinct origins, behaviors, and prognoses. Although traditionally seen as a genetic disease, breast cancer is now also known to involve epigenetic abnormalities. Epigenetic regulators, such as DNA methyltransferases and histone-modifying enzymes, play essential roles in gene regulation and cancer development. Dysregulation of epigenetic regulator activity has been causally linked with breast cancer pathogenesis. Hairless (HR) encodes a 130-kDa transcription factor that is essential for development and tissue homeostasis. Its role in transcription regulation is partly mediated by its interaction with multiple nuclear receptors, including thyroid hormone receptor, retinoic acid receptor-related orphan receptors, and vitamin D receptor. HR has been studied primarily in epidermal development and homeostasis. Hr-mutant mice are highly susceptible to ultraviolet- or carcinogen-induced skin tumors. Besides its putative tumor suppressor function in skin, loss of HR function has also been implicated in increased leukemia susceptibility and promotes the growth of melanoma and brain cancer cells. HR has also been demonstrated to function as a histone H3 lysine 9 demethylase. Recent genomics studies have identified HR mutations in a variety of human cancers, including breast cancer. The anticancer function and mechanism of action by HR in mammary tissue remains to be investigated. Here, we review the emerging role of HR, its histone demethylase activity and histone methylation in breast cancer development, and potential for epigenetic therapy.

PRMT1-dependent regulation of RNA metabolism and DNA damage response sustains pancreatic ductal adenocarcinoma

Pancreatic ductal adenocarcinoma (PDAC) is an aggressive cancer that has remained clinically challenging to manage. Here we employ an RNAi-based in vivo functional genomics platform to determine epigenetic vulnerabilities across a panel of patient-derived PDAC models. Through this, we identify protein arginine methyltransferase 1 (PRMT1) as a critical dependency required for PDAC maintenance. Genetic and pharmacological studies validate the role of PRMT1 in maintaining PDAC growth. Mechanistically, using proteomic and transcriptomic analyses, we demonstrate that global inhibition of asymmetric arginine methylation impairs RNA metabolism, which includes RNA splicing, alternative polyadenylation, and transcription termination. This triggers a robust downregulation of multiple pathways involved in the DNA damage response, thereby promoting genomic instability and inhibiting tumor growth. Taken together, our data support PRMT1 as a compelling target in PDAC and informs a mechanism-based translational strategy for future therapeutic development.Statement of significancePDAC is a highly lethal cancer with limited therapeutic options. This study identified and characterized PRMT1-dependent regulation of RNA metabolism and coordination of key cellular processes required for PDAC tumor growth, defining a mechanism-based translational hypothesis for PRMT1 inhibitors.

Post-Translational Modification of MRE11: Its Implication in DDR and Diseases

Maintaining genomic stability is vital for cells as well as individual organisms. The meiotic recombination-related gene MRE11 (meiotic recombination 11) is essential for preserving genomic stability through its important roles in the resection of broken DNA ends, DNA damage response (DDR), DNA double-strand breaks (DSBs) repair, and telomere maintenance. The post-translational modifications (PTMs), such as phosphorylation, ubiquitination, and methylation, regulate directly the function of MRE11 and endow MRE11 with capabilities to respond to cellular processes in promptly, precisely, and with more diversified manners. Here in this paper, we focus primarily on the PTMs of MRE11 and their roles in DNA response and repair, maintenance of genomic stability, as well as their association with diseases such as cancer.

Protein Arginine Methyltransferase (PRMT) Inhibitors-AMI-1 and SAH Are Effective in Attenuating Rhabdomyosarcoma Growth and Proliferation in Cell Cultures

Rhabdomyosarcoma (RMS) is a malignant soft tissue cancer that develops mostly in children and young adults. With regard to histopathology, four rhabdomyosarcoma types are distinguishable: embryonal, alveolar, pleomorphic and spindle/sclerosing. Currently, increased amounts of evidence indicate that not only gene mutations, but also epigenetic modifications may be involved in the development of RMS. Epigenomic changes regulate the chromatin architecture and affect the interaction between DNA strands, histones and chromatin binding proteins, thus, are able to control gene expression. The main aim of the study was to assess the role of protein arginine methyltransferases (PRMT) in the cellular biology of rhabdomyosarcoma. In the study we used two pan-inhibitors of PRMT, called AMI-1 and SAH, and evaluated their effects on proliferation and apoptosis of RMS cells. We observed that AMI-1 and SAH reduce the invasive phenotype of rhabdomyosarcoma cells by decreasing their proliferation rate, cell viability and ability to form cell colonies. In addition, microarray analysis revealed that these inhibitors attenuate the activity of the PI3K-Akt signaling pathway and affect expression of genes related to it.

A systematic survey of PRMT interactomes reveals the key roles of arginine methylation in the global control of RNA splicing and translation

Thousands of proteins undergo arginine methylation, a widespread post-translational modification catalyzed by several protein arginine methyltransferases (PRMTs). However, global understanding of their biological functions is limited due to the lack of a complete picture of the catalytic network for each PRMT. Here, we systematically identified interacting proteins for all human PRMTs and demonstrated their functional importance in mRNA splicing and translation. We demonstrated significant overlapping of interactomes of human PRMTs with the known methylarginine-containing proteins. Different PRMTs are functionally redundant with a high degree of overlap in their substrates and high similarities between their putative methylation motifs. Importantly, RNA-binding proteins involved in regulating RNA splicing and translation contain highly enriched arginine methylation regions. Moreover, inhibition of PRMTs globally alternates alternative splicing (AS) and suppresses translation. In particular, ribosomal proteins are extensively modified with methylarginine, and mutations in their methylation sites suppress ribosome assembly, translation, and eventually cell growth. Collectively, our study provides a global view of different PRMT networks and uncovers critical functions of arginine methylation in regulating mRNA splicing and translation.

Post-Translational Modifications Modulate Proteinopathies of TDP-43, FUS and hnRNP-A/B in Amyotrophic Lateral Sclerosis

It has been shown that protein low-sequence complexity domains (LCDs) induce liquid-liquid phase separation (LLPS), which is responsible for the formation of membrane-less organelles including P-granules, stress granules and Cajal bodies. Proteins harbouring LCDs are widely represented among RNA binding proteins often mutated in ALS. Indeed, LCDs predispose proteins to a prion-like behaviour due to their tendency to form amyloid-like structures typical of proteinopathies. Protein post-translational modifications (PTMs) can influence phase transition through two main events: i) destabilizing or augmenting multivalent interactions between phase-separating macromolecules; ii) recruiting or excluding other proteins and/or nucleic acids into/from the condensate. In this manuscript we summarize the existing evidence describing how PTM can modulate LLPS thus favouring or counteracting proteinopathies at the base of neurodegeneration in ALS.

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

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

Endothelial Dysfunction Driven by Hypoxia-The Influence of Oxygen Deficiency on NO Bioavailability

Cardiovascular diseases (CVDs) are the leading cause of death worldwide. The initial stage of CVDs is characterized by endothelial dysfunction, defined as the limited bioavailability of nitric oxide (NO). Thus, any factors that interfere with the synthesis or metabolism of NO in endothelial cells are involved in CVD pathogenesis. It is well established that hypoxia is both the triggering factor as well as the accompanying factor in cardiovascular disease, and diminished tissue oxygen levels have been reported to influence endothelial NO bioavailability. In endothelial cells, NO is produced by endothelial nitric oxide synthase (eNOS) from L-Arg, with tetrahydrobiopterin (BH₄) as an essential cofactor. Here, we discuss the mechanisms by which hypoxia affects NO bioavailability, including regulation of eNOS expression and activity. What is particularly important is the fact that hypoxia contributes to the depletion of cofactor BH₄ and deficiency of substrate L-Arg, and thus elicits eNOS uncoupling-a state in which the enzyme produces superoxide instead of NO. eNOS uncoupling and the resulting oxidative stress is the major driver of endothelial dysfunction and atherogenesis. Moreover, hypoxia induces impairment in mitochondrial respiration and endothelial cell activation; thus, oxidative stress and inflammation, along with the hypoxic response, contribute to the development of endothelial dysfunction.

Protein arginine methylation: from enigmatic functions to therapeutic targeting

Protein arginine methyltransferases (PRMTs) are emerging as attractive therapeutic targets. PRMTs regulate transcription, splicing, RNA biology, the DNA damage response and cell metabolism; these fundamental processes are altered in many diseases. Mechanistically understanding how these enzymes fuel and sustain cancer cells, especially in specific metabolic contexts or in the presence of certain mutations, has provided the rationale for targeting them in oncology. Ongoing inhibitor development, facilitated by structural biology, has generated tool compounds for the majority of PRMTs and enabled clinical programmes for the most advanced oncology targets, PRMT1 and PRMT5. In-depth mechanistic investigations using genetic and chemical tools continue to delineate the roles of PRMTs in regulating immune cells and cancer cells, and cardiovascular and neuronal function, and determine which pathways involving PRMTs could be synergistically targeted in combination therapies for cancer. This research is enhancing our knowledge of the complex functions of arginine methylation, will guide future clinical development and could identify new clinical indications.

Sulforaphane inhibits PRMT5 and MEP50 function to suppress the mesothelioma cancer cell phenotype

Mesothelioma is a highly aggressive cancer of the mesothelial lining that is caused by exposure to asbestos. Surgical resection followed by chemotherapy is the current treatment strategy, but this is marginally successful and leads to drug-resistant disease. We are interested in factors that maintain the aggressive mesothelioma cancer phenotype as therapy targets. Protein arginine methyltransferase 5 (PRMT5) functions in concert with the methylosome protein 50 (MEP50) cofactor to catalyze symmetric dimethylation of key arginine resides in histones 3 and 4 which modifies the chromatin environment to alter tumor suppressor and oncogene expression and enhance cancer cell survival. Our studies show that PRMT5 or MEP50 loss reduces H4R3me2s formation and that this is associated with reduced cancer cell spheroid formation, invasion, and migration. Treatment with sulforaphane (SFN), a diet-derived anticancer agent, reduces PRMT5/MEP50 level and H4R3me2s formation and suppresses the cancer phenotype. We further show that SFN treatment reduces PRMT5 and MEP50 levels and that this reduction is required for SFN suppression of the cancer phenotype. SFN treatment also reduces tumor formation which is associated with reduced PRMT5/MEP50 expression and activity. These findings suggest that SFN may be a useful mesothelioma treatment agent that operates, at least in part, via suppression of PRMT5/MEP50 function.

Prmt5 promotes vascular morphogenesis independently of its methyltransferase activity

During development, the vertebrate vasculature undergoes major growth and remodeling. While the transcriptional cascade underlying blood vessel formation starts to be better characterized, little is known concerning the role and mode of action of epigenetic enzymes during this process. Here, we explored the role of the Protein Arginine Methyl Transferase Prmt5 in blood vessel formation as well as hematopoiesis using zebrafish as a model system. Through the combination of different prmt5 loss-of-function approaches we highlighted a key role of Prmt5 in both processes. Notably, we showed that Prmt5 promotes vascular morphogenesis through the transcriptional control of ETS transcription factors and adhesion proteins in endothelial cells. Interestingly, using a catalytic dead mutant of Prmt5 and a specific drug inhibitor, we found that while Prmt5 methyltransferase activity was required for blood cell formation, it was dispensable for vessel formation. Analyses of chromatin architecture impact on reporter genes expression and chromatin immunoprecipitation experiments led us to propose that Prmt5 regulates transcription by acting as a scaffold protein that facilitates chromatin looping to promote vascular morphogenesis.

Blood vessel formation is an essential developmental process required for the survival of all vertebrates. The vascular anatomy and the mechanisms involved in vessel formation are highly conserved among vertebrates. Hence, we used zebrafish as a model, to decipher the role and the mode of action of Prmt5, an enzyme known to regulate gene expression, in vascular morphogenesis and in blood cell formation in vivo. Using different approaches, we highlighted a key role of Prmt5 during both processes. However, we found that while blood cell formation required Prmt5 enzymatic activity, vascular morphogenesis was independent on its activity. Prmt5 has been proposed as a therapeutic target in many diseases, including cancer. Yet, we show here that Prmt5 acts at least in part independently of its methyltransferase activity to regulate vascular morphogenesis. By shedding light on a mechanism of action of Prmt5 that will be insensitive to enzymatic inhibitors, our data calls forth the design of alternative drugs. In addition, this non-canonical function of Prmt5 may have a more pervasive role than previously thought in physiological conditions, i.e. during development, but also in pathological situations such as in tumor angiogenesis and certainly deserves more attention in the future.

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.

Arginine methylation of METTL14 promotes RNA N6-methyladenosine modification and endoderm differentiation of mouse embryonic stem cells

RNA N6-methyladenosine (m6A), the most abundant internal modification of mRNAs, plays key roles in human development and health. Post-translational methylation of proteins is often critical for the dynamic regulation of enzymatic activity. However, the role of methylation of the core methyltransferase METTL3/METTL14 in m6A regulation remains elusive. We find by mass spectrometry that METTL14 arginine 255 (R255) is methylated (R255me). Global mRNA m6A levels are greatly decreased in METTL14 R255K mutant mouse embryonic stem cells (mESCs). We further find that R255me greatly enhances the interaction of METTL3/METTL14 with WTAP and promotes the binding of the complex to substrate RNA. We show that protein arginine N-methyltransferases 1 (PRMT1) interacts with and methylates METTL14 at R255, and consistent with this, loss of PRMT1 reduces mRNA m6A modification globally. Lastly, we find that loss of R255me preferentially affects endoderm differentiation in mESCs. Collectively, our findings show that arginine methylation of METTL14 stabilizes the binding of the m6A methyltransferase complex to its substrate RNA, thereby promoting global m6A modification and mESC endoderm differentiation. This work highlights the crosstalk between protein methylation and RNA methylation in gene expression.

NleB2 from enteropathogenic Escherichia coli is a novel arginine-glucose transferase effector

During infection, enteropathogenic Escherichia coli (EPEC) and enterohaemorrhagic E. coli (EHEC) directly manipulate various aspects of host cell function through the translocation of type III secretion system (T3SS) effector proteins directly into the host cell. Many T3SS effector proteins are enzymes that mediate post-translational modifications of host proteins, such as the glycosyltransferase NleB1, which transfers a single N-acetylglucosamine (GlcNAc) to arginine residues, creating an Arg-GlcNAc linkage. NleB1 glycosylates death-domain containing proteins including FADD, TRADD and RIPK1 to block host cell death. The NleB1 paralogue, NleB2, is found in many EPEC and EHEC strains but to date its enzymatic activity has not been described. Using in vitro glycosylation assays combined with mass spectrometry, we found that NleB2 can utilize multiple sugar donors including UDP-glucose, UDP-GlcNAc and UDP-galactose during glycosylation of the death domain protein, RIPK1. Sugar donor competition assays demonstrated that UDP-glucose was the preferred substrate of NleB2 and peptide sequencing identified the glycosylation site within RIPK1 as Arg603, indicating that NleB2 catalyses arginine glucosylation. We also confirmed that NleB2 catalysed arginine-hexose modification of Flag-RIPK1 during infection of HEK293T cells with EPEC E2348/69. Using site-directed mutagenesis and in vitro glycosylation assays, we identified that residue Ser252 in NleB2 contributes to the specificity of this distinct catalytic activity. Substitution of Ser252 in NleB2 to Gly, or substitution of the corresponding Gly255 in NleB1 to Ser switches sugar donor preference between UDP-GlcNAc and UDP-glucose. However, this switch did not affect the ability of the NleB variants to inhibit inflammatory or cell death signalling during HeLa cell transfection or EPEC infection. NleB2 is thus the first identified bacterial Arg-glucose transferase that, similar to the NleB1 Arg-GlcNAc transferase, inhibits host protein function by arginine glycosylation.

Bacterial gut pathogens including enteropathogenic E. coli (EPEC) and enterohaemorrhagic E. coli (EHEC), manipulate host cell function by using a type III secretion system to inject ‘effector’ proteins directly into the host cell cytoplasm. We and others have shown that many of these effectors are novel enzymes, including NleB1, which transfers a single N-acetylglucosamine (GlcNAc) sugar to arginine residues, mediating Arg-GlcNAc glycosylation. Here, we found that a close homologue of NleB1 that is also present in EPEC and EHEC termed NleB2, uses a different sugar during glycosylation. We demonstrated that in contrast to NleB1, the preferred nucleotide-sugar substrate of NleB2 is UDP-glucose and we identified the amino acid residue within NleB2 that dictates this unique catalytic activity. Substitution of this residue in NleB2 and NleB1 switches the sugar donor usage of these enzymes but does not affect their ability to inhibit host cell signalling. Thus, NleB2 is the first identified bacterial arginine-glucose transferase, an activity which has previously only been described in plants and algae.

A Pan-Inhibitor for Protein Arginine Methyltransferase Family Enzymes

Protein arginine methyltransferases (PRMTs) play important roles in transcription, splicing, DNA damage repair, RNA biology, and cellular metabolism. Thus, PRMTs have been attractive targets for various diseases. In this study, we reported the design and synthesis of a potent pan-inhibitor for PRMTs that tethers a thioadenosine and various substituted guanidino groups through a propyl linker. Compound II757 exhibits a half-maximal inhibition concentration (IC50) value of 5 to 555 nM for eight tested PRMTs, with the highest inhibition for PRMT4 (IC50 = 5 nM). The kinetic study demonstrated that II757 competitively binds at the SAM binding site of PRMT1. Notably, II757 is selective for PRMTs over a panel of other methyltransferases, which can serve as a general probe for PRMTs and a lead for further optimization to increase the selectivity for individual PRMT.

PRMT5-mediated arginine methylation activates AKT kinase to govern tumorigenesis

AKT is involved in a number of key cellular processes including cell proliferation, apoptosis and metabolism. Hyperactivation of AKT is associated with many pathological conditions, particularly cancers. Emerging evidence indicates that arginine methylation is involved in modulating AKT signaling pathway. However, whether and how arginine methylation directly regulates AKT kinase activity remain unknown. Here we report that protein arginine methyltransferase 5 (PRMT5), but not other PRMTs, promotes AKT activation by catalyzing symmetric dimethylation of AKT1 at arginine 391 (R391). Mechanistically, AKT1-R391 methylation cooperates with phosphatidylinositol 3,4,5 trisphosphate (PIP3) to relieve the pleckstrin homology (PH)-in conformation, leading to AKT1 membrane translocation and subsequent activation by phosphoinositide-dependent kinase-1 (PDK1) and the mechanistic target of rapamycin complex 2 (mTORC2). As a result, deficiency in AKT1-R391 methylation significantly suppresses AKT1 kinase activity and tumorigenesis. Lastly, we show that PRMT5 inhibitor synergizes with AKT inhibitor or chemotherapeutic drugs to enhance cell death. Altogether, our study suggests that R391 methylation is an important step for AKT activation and its oncogenic function.

Chemogenomics for drug discovery: clinical molecules from open access chemical probes

In recent years chemical probes have proved valuable tools for the validation of disease-modifying targets, facilitating investigation of target function, safety, and translation. Whilst probes and drugs often differ in their properties, there is a belief that chemical probes are useful for translational studies and can accelerate the drug discovery process by providing a starting point for small molecule drugs. This review seeks to describe clinical candidates that have been inspired by, or derived from, chemical probes, and the process behind their development. By focusing primarily on examples of probes developed by the Structural Genomics Consortium, we examine a variety of epigenetic modulators along with other classes of probe.

Protein Arginine Methyltransferase 5 Promotes Esophageal Squamous Cell Carcinoma Proliferation and Metastasis via LKB1/AMPK/mTOR Signaling Pathway

Background: Esophageal squamous cell carcinoma (ESCC) is the eighth most common cancer in the world. Protein arginine methyltransferase 5 (PRMT5), an enzyme that catalyzes symmetric and asymmetric methylation on arginine residues of histone and non-histone proteins, is overexpressed in many cancers. However, whether or not PRMT5 participates in the regulation of ESCC remains largely unclear.

Methods: PRMT5 mRNA and protein expression in ESCC tissues and cell lines were examined by RT-PCR, western blotting, and immunohistochemistry assays. Cell proliferation was examined by RT-PCR, western blotting, immunohistochemistry assays, MTT, and EdU assays. Cell apoptosis and cell cycle were examined by RT-PCR, western blotting, immunohistochemistry assays, and flow cytometry. Cell migration and invasion were examined by RT-PCR, western blotting, immunohistochemistry assays, and wound-healing and transwell assays. Tumor volume, tumors, and mouse weight were measured in different groups. Lung tissues with metastatic foci, the number of nodules, and lung/total weight were measured in different groups.

Results: In the present study, the PRMT5 expression level was dramatically upregulated in ESCC clinical tissues as well as ESCC cell lines (ECA109 and KYSE150). Furthermore, knocking down PRMT5 obviously suppressed cell migration, invasion, proliferation, and cell arrest in G1 phase and promoted cell apoptosis in ESCC cells. Meanwhile, downregulating PRMT5 also increased the expression levels of Bax, caspase-3, and caspase-9, while expression levels of Bax-2, MMP-2, MMP-9, and p21 were decreased, which are members of the cyclin-dependent kinase family. Furthermore, knocking down PRMT5 could increase the expression of LKB1 and the phosphorylation (p)-AMPK expression and decrease the p-mTOR level. Additionally, overexpression of LKB1 could reveal anti-tumor effects in ESCC cell lines by inhibiting ESCC cell, migration, invasion, and proliferation and accelerating cell apoptosis. Besides, upregulating LKB1 expression could increase the levels of Bax, caspase-3, and caspase-9 and weaken the levels of Bax-2, MMP-2, and MMP-9. Moreover, knocking down PRMT5 could weaken the tumor growth and lung metastasis in vivo with upregulating the LKB1 expression and the p-AMPK level and downregulating the p-mTOR expression.

Conclusion: PRMT5 may act as a tumor-inducing agent in ESCC by modulating LKB1/AMPK/mTOR pathway signaling.

PRMT1-p53 Pathway Controls Epicardial EMT and Invasion

Epicardial cells are cardiac progenitors that give rise to the majority of cardiac fibroblasts, coronary smooth muscle cells, and pericytes during development. An integral phase of epicardial fate transition is epithelial-to-mesenchymal transition (EMT) that confers motility. We uncover an essential role for the protein arginine methyltransferase 1 (PRMT1) in epicardial invasion and differentiation. Using scRNA-seq, we show that epicardial-specific deletion of Prmt1 reduced matrix and ribosomal gene expression in epicardial-derived cell lineages. PRMT1 regulates splicing of Mdm4, which is a key controller of p53 stability. Loss of PRMT1 leads to accumulation of p53 that enhances Slug degradation and blocks EMT. During heart development, the PRMT1-p53 pathway is required for epicardial invasion and formation of epicardial-derived lineages: cardiac fibroblasts, coronary smooth muscle cells, and pericytes. Consequently, this pathway modulates ventricular morphogenesis and coronary vessel formation. Altogether, our study reveals molecular mechanisms involving the PRMT1-p53 pathway and establish its roles in heart development.

Protein arginine methyltransferases: promising targets for cancer therapy

Protein methylation, a post-translational modification (PTM), is observed in a wide variety of cell types from prokaryotes to eukaryotes. With recent and rapid advancements in epigenetic research, the importance of protein methylation has been highlighted. The methylation of histone proteins that contributes to the epigenetic histone code is not only dynamic but is also finely controlled by histone methyltransferases and demethylases, which are essential for the transcriptional regulation of genes. In addition, many nonhistone proteins are methylated, and these modifications govern a variety of cellular functions, including RNA processing, translation, signal transduction, DNA damage response, and the cell cycle. Recently, the importance of protein arginine methylation, especially in cell cycle regulation and DNA repair processes, has been noted. Since the dysregulation of protein arginine methylation is closely associated with cancer development, protein arginine methyltransferases (PRMTs) have garnered significant interest as novel targets for anticancer drug development. Indeed, several PRMT inhibitors are in phase 1/2 clinical trials. In this review, we discuss the biological functions of PRMTs in cancer and the current development status of PRMT inhibitors in cancer therapy.

PRMT6 activates cyclin D1 expression in conjunction with the transcription factor LEF1

The establishment of cell type specific gene expression by transcription factors and their epigenetic cofactors is central for cell fate decisions. Protein arginine methyltransferase 6 (PRMT6) is an epigenetic regulator of gene expression mainly through methylating arginines at histone H3. This way it influences cellular differentiation and proliferation. PRMT6 lacks DNA-binding capability but is recruited by transcription factors to regulate gene expression. However, currently only a limited number of transcription factors have been identified, which facilitate recruitment of PRMT6 to key cell cycle related target genes. Here, we show that LEF1 contributes to the recruitment of PRMT6 to the central cell cycle regulator CCND1 (Cyclin D1). We identified LEF1 as an interaction partner of PRMT6. Knockdown of LEF1 or PRMT6 reduces CCND1 expression. This is in line with our observation that knockdown of PRMT6 increases the number of cells in G1 phase of the cell cycle and decreases proliferation. These results improve the understanding of PRMT6 activity in cell cycle regulation. We expect that these insights will foster the rational development and usage of specific PRMT6 inhibitors for cancer therapy.

Eukaryote-Conserved Methylarginine Is Absent in Diplomonads and Functionally Compensated in Giardia

Methylation is a common posttranslational modification of arginine and lysine in eukaryotic proteins. Methylproteomes are best characterized for higher eukaryotes, where they are functionally expanded and evolved complex regulation. However, this is not the case for protist species evolved from the earliest eukaryotic lineages. Here, we integrated bioinformatic, proteomic, and drug-screening data sets to comprehensively explore the methylproteome of Giardia duodenalis-a deeply branching parasitic protist. We demonstrate that Giardia and related diplomonads lack arginine-methyltransferases and have remodeled conserved RGG/RG motifs targeted by these enzymes. We also provide experimental evidence for methylarginine absence in proteomes of Giardia but readily detect methyllysine. We bioinformatically infer 11 lysine-methyltransferases in Giardia, including highly diverged Su(var)3-9, Enhancer-of-zeste and Trithorax proteins with reduced domain architectures, and novel annotations demonstrating conserved methyllysine regulation of eukaryotic elongation factor 1 alpha. Using mass spectrometry, we identify more than 200 methyllysine sites in Giardia, including in species-specific gene families involved in cytoskeletal regulation, enriched in coiled-coil features. Finally, we use known methylation inhibitors to show that methylation plays key roles in replication and cyst formation in this parasite. This study highlights reduced methylation enzymes, sites, and functions early in eukaryote evolution, including absent methylarginine networks in the Diplomonadida. These results challenge the view that arginine methylation is eukaryote conserved and demonstrate that functional compensation of methylarginine was possible preceding expansion and diversification of these key networks in higher eukaryotes.

Malic enzyme 2 connects the Krebs cycle intermediate fumarate to mitochondrial biogenesis

Mitochondria have an independent genome (mtDNA) and protein synthesis machinery that coordinately activate for mitochondrial generation. Here, we report that the Krebs cycle intermediate fumarate links metabolism to mitobiogenesis through binding to malic enzyme 2 (ME2). Mechanistically, fumarate binds ME2 with two complementary consequences. First, promoting the formation of ME2 dimers, which activate deoxyuridine 5'-triphosphate nucleotidohydrolase (DUT). DUT fosters thymidine generation and an increase of mtDNA. Second, fumarate-induced ME2 dimers abrogate ME2 monomer binding to mitochondrial ribosome protein L45, freeing it for mitoribosome assembly and mtDNA-encoded protein production. Methylation of the ME2-fumarate binding site by protein arginine methyltransferase-1 inhibits fumarate signaling to constrain mitobiogenesis. Notably, acute myeloid leukemia is highly dependent on mitochondrial function and is sensitive to targeting of the fumarate-ME2 axis. Therefore, mitobiogenesis can be manipulated in normal and malignant cells through ME2, an unanticipated governor of mitochondrial biomass production that senses nutrient availability through fumarate.

PRMT5 Enables Robust STAT3 Activation via Arginine Symmetric Dimethylation of SMAD7

Protein arginine methyltransferase 5 (PRMT5) is the type II arginine methyltransferase that catalyzes the mono- and symmetrical dimethylation of protein substrates at the arginine residues. Emerging evidence reveals that PRMT5 is involved in the regulation of tumor cell proliferation and cancer development. However, the exact role of PRMT5 in human lung cancer cell proliferation and the underlying molecular mechanism remain largely elusive. Here, it is shown that PRMT5 promotes lung cancer cell proliferation through the Smad7-STAT3 axis. Depletion or inhibition of PRMT5 dramatically dampens STAT3 activation and thus suppresses the proliferation of human lung cancer cells. Furthermore, depletion of Smad7 blocks PRMT5-mediated STAT3 activation. Mechanistically, PRMT5 binds to and methylates Smad7 on Arg-57, enhances Smad7 binding to IL-6 co-receptor gp130, and consequently ensures robust STAT3 activation. The findings position PRMT5 as a critical regulator of STAT3 activation, and suggest it as a potential therapeutic target for the treatment of human lung cancer.

The Role of Protein Arginine Methylation as Post-Translational Modification on Actin Cytoskeletal Components in Neuronal Structure and Function

The brain encompasses a complex network of neurons with exceptionally elaborated morphologies of their axonal (signal-sending) and dendritic (signal-receiving) parts. De novo actin filament formation is one of the major driving and steering forces for the development and plasticity of the neuronal arbor. Actin filament assembly and dynamics thus require tight temporal and spatial control. Such control is particularly effective at the level of regulating actin nucleation-promoting factors, as these are key components for filament formation. Arginine methylation represents an important post-translational regulatory mechanism that had previously been mainly associated with controlling nuclear processes. We will review and discuss emerging evidence from inhibitor studies and loss-of-function models for protein arginine methyltransferases (PRMTs), both in cells and whole organisms, that unveil that protein arginine methylation mediated by PRMTs represents an important regulatory mechanism in neuritic arbor formation, as well as in dendritic spine induction, maturation and plasticity. Recent results furthermore demonstrated that arginine methylation regulates actin cytosolic cytoskeletal components not only as indirect targets through additional signaling cascades, but can also directly control an actin nucleation-promoting factor shaping neuronal cells—a key process for the formation of neuronal networks in vertebrate brains.

Host Epigenetic Alterations and Hepatitis B Virus-Associated Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is the most frequent primary malignancy of the liver and a leading cause of cancer-related deaths worldwide. Although much progress has been made in HCC drug development in recent years, treatment options remain limited. The major cause of HCC is chronic hepatitis B virus (HBV) infection. Despite the existence of a vaccine, more than 250 million individuals are chronically infected by HBV. Current antiviral therapies can repress viral replication but to date there is no cure for chronic hepatitis B. Of note, inhibition of viral replication reduces but does not eliminate the risk of HCC development. HBV contributes to liver carcinogenesis by direct and indirect effects. This review summarizes the current knowledge of HBV-induced host epigenetic alterations and their association with HCC, with an emphasis on the interactions between HBV proteins and the host cell epigenetic machinery leading to modulation of gene expression.

PRMT1-mediated H4R3me2a recruits SMARCA4 to promote colorectal cancer progression by enhancing EGFR signaling

BACKGROUND

Aberrant changes in epigenetic mechanisms such as histone modifications play an important role in cancer progression. PRMT1 which triggers asymmetric dimethylation of histone H4 on arginine 3 (H4R3me2a) is upregulated in human colorectal cancer (CRC) and is essential for cell proliferation. However, how this dysregulated modification might contribute to malignant transitions of CRC remains poorly understood.

METHODS

In this study, we integrated biochemical assays including protein interaction studies and chromatin immunoprecipitation (ChIP), cellular analysis including cell viability, proliferation, colony formation, and migration assays, clinical sample analysis, microarray experiments, and ChIP-Seq data to investigate the potential genomic recognition pattern of H4R3me2s in CRC cells and its effect on CRC progression.

RESULTS

We show that PRMT1 and SMARCA4, an ATPase subunit of the SWI/SNF chromatin remodeling complex, act cooperatively to promote colorectal cancer (CRC) progression. We find that SMARCA4 is a novel effector molecule of PRMT1-mediated H4R3me2a. Mechanistically, we show that H4R3me2a directly recruited SMARCA4 to promote the proliferative, colony-formative, and migratory abilities of CRC cells by enhancing EGFR signaling. We found that EGFR and TNS4 were major direct downstream transcriptional targets of PRMT1 and SMARCA4 in colon cells, and acted in a PRMT1 methyltransferase activity-dependent manner to promote CRC cell proliferation. In vivo, knockdown or inhibition of PRMT1 profoundly attenuated the growth of CRC cells in the C57BL/6 J-Apc^Min/+ CRC mice model. Importantly, elevated expression of PRMT1 or SMARCA4 in CRC patients were positively correlated with expression of EGFR and TNS4, and CRC patients had shorter overall survival. These findings reveal a critical interplay between epigenetic and transcriptional control during CRC progression, suggesting that SMARCA4 is a novel key epigenetic modulator of CRC. Our findings thus highlight PRMT1/SMARCA4 inhibition as a potential therapeutic intervention strategy for CRC.

CONCLUSION

PRMT1-mediated H4R3me2a recruits SMARCA4, which promotes colorectal cancer progression by enhancing EGFR signaling.

Huntingtin-mediated axonal transport requires arginine methylation by PRMT6

The huntingtin (HTT) protein transports various organelles, including vesicles containing neurotrophic factors, from embryonic development throughout life. To better understand how HTT mediates axonal transport and why this function is disrupted in Huntington's disease (HD), we study vesicle-associated HTT and find that it is dimethylated at a highly conserved arginine residue (R118) by the protein arginine methyltransferase 6 (PRMT6). Without R118 methylation, HTT associates less with vesicles, anterograde trafficking is diminished, and neuronal death ensues-very similar to what occurs in HD. Inhibiting PRMT6 in HD cells and neurons exacerbates mutant HTT (mHTT) toxicity and impairs axonal trafficking, whereas overexpressing PRMT6 restores axonal transport and neuronal viability, except in the presence of a methylation-defective variant of mHTT. In HD flies, overexpressing PRMT6 rescues axonal defects and eclosion. Arginine methylation thus regulates HTT-mediated vesicular transport along the axon, and increasing HTT methylation could be of therapeutic interest for HD.

PRMT5 Promotes EMT Through Regulating Akt Activity in Human Lung Cancer

The type II protein arginine methyltransferase 5 (PRMT5) has been engaged in various human cancer development and progression types. Nevertheless, few studies uncover the biological functions of PRMT5 in the epithelial-mesenchymal transition (EMT) of human lung cancer cells, and the associated molecular mechanisms and signaling cascades are entirely unknown. Here, we show that PRMT5 is the ectopic expression in human lung cancer tissues and cell lines. Further study reveals that silencing PRMT5 by lentivirus-mediated shRNA or blocking of PRMT5 by specific inhibitor GSK591 attenuates the expression levels of EMT-related markers in vivo, using the xenograft mouse model. Moreover, our results show that down-regulation of PRMT5 impairs EGFR/Akt signaling cascades in human lung cancer cells, whereas re-expression of PRMT5 recovers those changes, suggesting that PRMT5 regulates EMT probably through EGFR/Akt signaling axis. Altogether, our results demonstrate that PRMT5 serves as a critical oncogenic regulator and promotes EMT in human lung cancer cells. More importantly, our findings also suggest that PRMT5 may be a potential therapeutic candidate for the treatment of human lung cancer.

OXR1A, a Coactivator of PRMT5 Regulating Histone Arginine Methylation

Oxidation resistance gene 1 (OXR1) protects cells against oxidative stress. We find that male mice with brain-specific isoform A knockout (Oxr1A^-/-) develop fatty liver. RNA sequencing of male Oxr1A^-/- liver indicates decreased growth hormone (GH) signaling, which is known to affect liver metabolism. Indeed, Gh expression is reduced in male mice Oxr1A^-/- pituitary gland and in rat Oxr1A^-/- pituitary adenoma cell-line GH3. Oxr1A^-/- male mice show reduced fasting-blood GH levels. Pull-down and proximity ligation assays reveal that OXR1A is associated with arginine methyl transferase PRMT5. OXR1A-depleted GH3 cells show reduced symmetrical dimethylation of histone H3 arginine 2 (H3R2me2s), a product of PRMT5 catalyzed methylation, and chromatin immunoprecipitation (ChIP) of H3R2me2s shows reduced Gh promoter enrichment. Finally, we demonstrate with purified proteins that OXR1A stimulates PRMT5/MEP50-catalyzed H3R2me2s. Our data suggest that OXR1A is a coactivator of PRMT5, regulating histone arginine methylation and thereby GH production within the pituitary gland.

Sublytic C5b-9 induces glomerular mesangial cell proliferation via ERK1/2-dependent SOX9 phosphorylation and acetylation by enhancing Cyclin D1 in rat Thy-1 nephritis

Glomerular mesangial cell (GMC) proliferation is a histopathological alteration in human mesangioproliferative glomerulonephritis (MsPGN) or in animal models of MsPGN, e.g., the rat Thy-1 nephritis (Thy-1N) model. Although sublytic C5b-9 assembly on the GMC membrane can trigger cell proliferation, the mechanisms are still undefined. We found that sublytic C5b-9-induced rat GMC proliferation was driven by extracellular signal-regulated kinase 1/2 (ERK1/2), sry-related HMG-box 9 (SOX9), and Cyclin D1. Here, ERK1/2 phosphorylation was a result of the calcium influx-PKC-α-Raf-MEK1/2 axis activated by sublytic C5b-9, and Cyclin D1 gene transcription was enhanced by ERK1/2-dependent SOX9 binding to the Cyclin D1 promoter (-582 to -238 nt). In addition, ERK1/2 not only interacted with SOX9 in the cell nucleus to mediate its phosphorylation at serine residues 64 (a new site identified by mass spectrometry) and 181 (a known site), but also indirectly induced SOX9 acetylation by elevating the expression of general control non-repressed protein 5 (GCN5), which together resulted in Cyclin D1 synthesis and GMC proliferation. Moreover, our in vivo experiments confirmed that silencing these genes ameliorated the lesions of Thy-1N rats and reduced SOX9 phosphorylation, acetylation and Cyclin D1 expression. Furthermore, the renal tissue sections of MsPGN patients also showed higher phosphorylation or expression of ERK1/2, SOX9, and Cyclin D1. In summary, these findings suggest that sublytic C5b-9-induced GMC proliferation in rat Thy-1N requires SOX9 phosphorylation and acetylation via enhanced Cyclin D1 gene transcription, which may provide a new insight into human MsPGN pathogenesis.

CRISPR/Cas9 library screening uncovered methylated PKP2 as a critical driver of lung cancer radioresistance by stabilizing β-catenin

Radiation resistance is a major cause of lung cancer treatment failure. Armadillo (ARM) superfamily proteins participate in various fundamental cellular processes; however, whether ARM proteins regulate radiation resistance is not fully understood. Here, we used an unbiased CRISPR/Cas9 library screen and identified plakophilin 2 (PKP2), a member of the ARM superfamily of proteins, as a critical driver of radiation resistance in lung cancer. The PKP2 level was significantly higher after radiotherapy than before radiotherapy, and high PKP2 expression after radiotherapy predicted poor overall survival (OS) and postprogression survival (PPS). Mechanistically, mass spectrometry analysis identified that PKP2 was methylated at the arginine site and interacted with protein arginine methyltransferase 1 (PRMT1). Methylation of PKP2 by PRMT1 stabilized β-catenin by recruiting USP7, further inducing LIG4, a key DNA ligase in nonhomologous end-joining (NHEJ) repair. Concomitantly, PKP2-induced radioresistance depended on facilitating LIG4-mediated NHEJ repair in lung cancer. More strikingly, after exposure to irradiation, treatment with the PRMT1 inhibitor C-7280948 abolished PKP2-induced radioresistance, and C-7280948 is a potential radiosensitizer in lung cancer. In summary, our results demonstrate that targeting the PRMT1/PKP2/β-catenin/LIG4 pathway is an effective approach to overcome radiation resistance in lung cancer.

Whole-body arginine dimethylation is associated with all-cause mortality in adult renal transplant recipients

Arginine residues in proteins can be singly or doubly methylated post-translationally. Proteolysis of arginine-methylated proteins provides monomethyl arginine, asymmetric dimethylarginine (ADMA) and symmetric dimethylarginine (SDMA). ADMA and SDMA are considered cardiovascular risk factors, with the underlying mechanisms being not yet fully understood. SDMA lacks appreciable metabolism and is almost completely eliminated by the kidney, whereas ADMA is extensively metabolized to dimethylamine (DMA), with a minor ADMA fraction of about 10% being excreted unchanged in the urine. Urinary DMA and ADMA are useful measures of whole-body asymmetric arginine-dimethylation, while urinary SDMA serves as a whole-body measure of symmetric arginine-dimethylation. In renal transplant recipients (RTR), we previously found that higher plasma ADMA concentrations and lower urinary ADMA and SDMA concentrations were associated with a higher risk of all-cause mortality. Yet, in this RTR collective, no data were available for urinary DMA. For the present study, we additionally measured the excretion rate of DMA in 24-h collected urine samples of the RTR and of healthy kidney donors in the cohort, with the aim to quantitate whole-body asymmetric (ADMA, DMA) and symmetric (SDMA) arginine-dimethylation. We found that lower DMA excretion rates were associated with higher all-cause mortality, yet not with cardiovascular mortality. In the healthy donors, kidney donation was associated with considerable decreases in ADMA (by - 39%, P < 0.0001) and SDMA (by - 21%, P < 0.0001) excretion rates, yet there was no significant change in DMA (by - 9%, P = 0.226) excretion rate. Our results suggest that protein-arginine dimethylation is altered in RTR compared to healthy kidney donors and that it is pronouncedly shifted from symmetric to asymmetric arginine-dimethylation, with whole-body protein-arginine dimethylation being almost unaffected.

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.

Methylation multiplicity and its clinical values in cancer

Methylation at DNA, RNA and protein levels plays critical roles in many cellular processes and is associated with diverse differentiation events, physiological activities and human diseases. To aid in the diagnostic and therapeutic design for cancer treatment utilising methylation, this review provides a boutique yet comprehensive overview on methylation at different levels including the mechanisms, cross-talking and clinical implications with a particular focus on cancers. We conclude that DNA methylation is the sole type of methylation that has been largely translated into clinics and used for, mostly, early diagnosis. Translating the onco-therapeutic and prognostic values of RNA and protein methylations into clinical use deserves intensive efforts. Simultaneous examination of methylations at multiple levels or together with other forms of molecular markers represents an interesting research direction with profound clinical translational potential.

Profiling PRMT methylome reveals roles of hnRNPA1 arginine methylation in RNA splicing and cell growth

Numerous substrates have been identified for Type I and II arginine methyltransferases (PRMTs). However, the full substrate spectrum of the only type III PRMT, PRMT7, and its connection to type I and II PRMT substrates remains unknown. Here, we use mass spectrometry to reveal features of PRMT7-regulated methylation. We find that PRMT7 predominantly methylates a glycine and arginine motif; multiple PRMT7-regulated arginine methylation sites are close to phosphorylations sites; methylation sites and proximal sequences are vulnerable to cancer mutations; and methylation is enriched in proteins associated with spliceosome and RNA-related pathways. We show that PRMT4/5/7-mediated arginine methylation regulates hnRNPA1 binding to RNA and several alternative splicing events. In breast, colorectal and prostate cancer cells, PRMT4/5/7 are upregulated and associated with high levels of hnRNPA1 arginine methylation and aberrant alternative splicing. Pharmacological inhibition of PRMT4/5/7 suppresses cancer cell growth and their co-inhibition shows synergistic effects, suggesting them as targets for cancer therapy.

Arginine methyltransferases (PRMTs) are involved in the regulation of various physiological and pathological conditions. Using proteomics, the authors here profile the methylation substrates of PRMTs 4, 5 and 7 and characterize the roles of these enzymes in cancer-associated splicing regulation.

An efficient approach based on basic strong cation exchange chromatography for enriching methylated peptides with high specificity for methylproteomics analysis

Protein methylation as one of the most important post-translational modifications has been under the spotlight due to its essential role in many biological processes. Development of methods for large-scale analysis of protein methylation greatly accelerates the related researches. To date, antibody-based enrichment strategy is the most common approach for methylproteomics analysis. However, it is still lacking of a pan-specific antibody to enrich peptides or proteins carrying all kinds of lysine and arginine methylation forms. Herein, an online basic strong cation exchange chromatography was developed to enrich methylated peptides from protein digests prepared by two complementary methods, including direct multiple enzymes digestion and carboxylic amidation followed by multiple enzymes digestion. After enrichment, the majority of identifications were obtained from direct multiple enzymes digested sample. The enrichment specificity of methylated peptides was up to 28.5%, and 445 methylation forms corresponding to 376 methylation sites were identified on 194 proteins in one LC-MS/MS run using only 100 μg of digests. This method has great potential in studying protein methylation mediated biological processes.

Wnt/β-catenin signaling: Structure, assembly and endocytosis of the signalosome

Wnt/β‐catenin signaling is an ancient pathway that regulates key aspects of embryonic development, cell differentiation, proliferation, and adult stem cell homeostasis. Work from different laboratories has shed light on the molecular mechanisms underlying the Wnt pathway, including structural details of ligand–receptor interactions. One key aspect that has emerged from multiple studies is that endocytosis of the receptor complex plays a crucial role in fine‐tuning Wnt/β‐catenin signaling. Endocytosis is a key process involved in both activation as well as attenuation of Wnt signaling, but how this is regulated is still poorly understood. Importantly, recent findings show that Wnt also regulates central metabolic pathways such as the acquisition of nutrients through actin‐driven endocytic mechanisms. In this review, we propose that the Wnt pathway displays diverse characteristics that go beyond the regulation of gene expression, through a connection with the endocytic machinery.