Proper protein arginine methylation by protein arginine methyltransferase 1 (PRMT1) is critical for maintaining cellular health, while dysregulation is often associated with disease. How the activity of PRMT1 is regulated is therefore paramount, but is not clearly understood. Several studies have observed higher order oligomeric species of PRMT1, but it is unclear if these exist at physiological concentrations and there is confusion in the literature about how oligomerization affects activity. We therefore sought to determine which oligomeric species of PRMT1 are physiologically relevant, and quantitatively correlate activity with specific oligomer forms. Through quantitative western blotting, we determined that concentrations of PRMT1 available in a variety of human cell lines are in the sub-micromolar to low micromolar range. Isothermal spectral shift binding data were modeled to a monomer/dimer/tetramer equilibrium with an EC50 for tetramer dissociation of ~20 nM. A combination of sedimentation velocity and Native polyacrylamide gel electrophoresis experiments directly confirmed that the major oligomeric species of PRMT1 at physiological concentrations would be dimers and tetramers. Surprisingly, the methyltransferase activity of a dimeric PRMT1 variant is similar to wild type, tetrameric PRMT1 with some purified substrates, but dimer and tetramer forms of PRMT1 show differences in catalytic efficiencies and substrate specificity for other substrates. Our results define an oligomerization paradigm for PRMT1, show that the biophysical characteristics of PRMT1 are poised to support a monomer/dimer/tetramer equilibrium in vivo, and suggest that the oligomeric state of PRMT1 could be used to regulate substrate specificity.

UNASSIGNED: Protein arginine methyltransferase (PRMT) family members have important roles in cancer processes. However, its functions in the regulation of cancer immunotherapy of hepatocellular carcinoma (HCC) are incompletely understood. This study aimed to investigate the roles of PRMT1 in HCC.
UNASSIGNED: Single-cell RNA sequencing (scRNA-seq) and clinicopathological data were obtained and used to explore the diagnostic and prognostic value, cellular functions and roles in immune microenvironment regulation of PRMT1 in HCC. The functions of PRMT1 were explored using Kyoto Encyclopedia of Genes and Genomes (KEGG) and Gene Ontology (GO), as well as gene set enrichment analysis (GSEA). TIMER and CIBERSORT were used to analyze the relationships between PRMT1 expression and immune cell infiltration. The STRING database was used to construct a protein-protein interaction (PPI) network.
UNASSIGNED: PRMT1 was aberrantly expressed in HCC, which high expression was associated with tumor progression, worse overall survival (OS) and disease-free survival (DFS) of patients with HCC. PRMT1 was also associated with immune cell infiltration. Moreover, it was specifically expressed in immune cells, including exhausted CD8 T cells, B cells, and mono/macro cells in patients with immunotherapy. The expression of immune checkpoints was significantly increased in the high-PRMT1 expression groups of HCC patients. Regarding biological mechanisms, cell viability, migration and invasion, and the expression of genes related to fatty acid metabolism were suppressed in PRMT1 knockdown HCC cells. Moreover, genes co-expressed with PRMT1 were involved in the fatty acid metabolic process and enriched in fatty and drug-induced liver disease.
UNASSIGNED: Taken together, these results indicate that PRMT1 might exert its oncogenic effects via immune microenvironment regulation and fatty acid metabolism in HCC. Our finding will provide a foundation for further studies and indicate a potential clinical therapeutic target for liver cancer.

Protein arginine methyltransferase (PRMT)-mediated arginine methylation is an important post-transcriptional modification that regulates various cellular processes including epigenetic gene regulation, genome stability maintenance, RNA metabolism, and stress-responsive signal transduction. The varying substrates and biological functions of arginine methylation in cancer and neurological diseases have been extensively discussed, providing a rationale for targeting PRMTs in clinical applications. An increasing number of studies have demonstrated an interplay between arginine methylation and viral infections. PRMTs have been found to methylate and regulate several host cell proteins and different functional types of viral proteins, such as viral capsids, mRNA exporters, transcription factors, and latency regulators. This modulation affects their activity, subcellular localization, protein-nucleic acid and protein-protein interactions, ultimately impacting their roles in various virus-associated processes. In this review, we discuss the classification, structure, and regulation of PRMTs and their pleiotropic biological functions through the methylation of histones and non-histones. Additionally, we summarize the broad spectrum of PRMT substrates and explore their intricate effects on various viral infection processes and antiviral innate immunity. Thus, comprehending the regulation of arginine methylation provides a critical foundation for understanding the pathogenesis of viral diseases and uncovering opportunities for antiviral therapy.

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.

HCC is a major contributor to cancer-related mortality worldwide. Curative treatments are available for a minority of patients diagnosed at early stages; however, only a few multikinase inhibitors are available and are marginally effective in advanced cases, highlighting the need for novel therapeutic targets. One potential target is the protein arginine methyltransferase, which catalyzes various forms of arginine methylation and is often overexpressed in various cancers. However, the diverse expression patterns and clinical values of PRMTs in HCC remain unclear. In the present study, we evaluated the transcriptional expression of PRMTs in HCC cohorts using publicly available datasets. Our results revealed a significant association between PRMTs and prognosis in HCC patients with diverse clinical characteristics and backgrounds. This highlights the promising potential of PRMTs as prognostic biomarkers in patients with HCC. In particular, single-cell RNA (scRNA) sequencing analysis coupled with another human cohort study highlighted the pivotal role of PRMT1 in HCC progression, particularly in the context of Tex. Translating these findings into specific therapeutic decisions may address the unmet therapeutic needs of patients with HCC.

Skeletal muscle plays a key role in systemic energy homeostasis besides its contractile function, but what links these functions is poorly defined. Protein Arginine Methyl Transferase 5 (PRMT5) is a well-known oncoprotein but also expressed in healthy tissues with unclear physiological functions. As adult muscles express high levels of Prmt5, we generated skeletal muscle-specific Prmt5 knockout (Prmt5MKO ) mice. We observe reduced muscle mass, oxidative capacity, force production, and exercise performance in Prmt5MKO mice. The motor deficiency is associated with scarce lipid droplets in myofibers due to defects in lipid biosynthesis and accelerated degradation. Specifically, PRMT5 deletion reduces dimethylation and stability of Sterol Regulatory Element-Binding Transcription Factor 1a (SREBP1a), a master regulator of de novo lipogenesis. Moreover, Prmt5MKO impairs the repressive H4R3 symmetric dimethylation at the Pnpla2 promoter, elevating the level of its encoded protein ATGL, the rate-limiting enzyme catalyzing lipolysis. Accordingly, skeletal muscle-specific double knockout of Pnpla2 and Prmt5 normalizes muscle mass and function. Together, our findings delineate a physiological function of PRMT5 in linking lipid metabolism to contractile function of myofibers.

Mild traumatic brain injury (TBI) comprises the largest percentage of TBI-related injuries, with pathophysiological and functional deficits that persist in a subset of TBI patients. In our three-hit paradigm of repetitive and mild traumatic brain injury (rmTBI), we observed neurovascular uncoupling via decreased red blood cell velocity, microvessel diameter, and leukocyte rolling velocity 3 days post-rmTBI via intra-vital two-photon laser scanning microscopy. Furthermore, our data suggest increased blood-brain barrier (BBB) permeability (leakage), with corresponding decrease in junctional protein expression post-rmTBI. Mitochondrial oxygen consumption rates (measured via Seahorse XFe24) were also altered 3 days post-rmTBI, along with disrupted mitochondrial dynamics of fission and fusion. Overall, these pathophysiological findings correlated with decreased protein arginine methyltransferase 7 (PRMT7) protein levels and activity post-rmTBI. Here, we increased PRMT7 levels in vivo to assess the role of the neurovasculature and mitochondria post-rmTBI. In vivo overexpression of PRMT7 using a neuronal specific AAV vector led to restoration of neurovascular coupling, prevented BBB leakage, and promoted mitochondrial respiration, altogether to suggest a protective and functional role of PRMT7 in rmTBI.

Mild traumatic brain injury affects the largest proportion of individuals in the United States and world-wide. Pre-clinical studies of repetitive and mild traumatic brain injury (rmTBI) have been limited in their ability to recapitulate human pathology (i.e. diffuse rotational injury). We used the closed-head impact model of engineered rotation acceleration (CHIMERA) to simulate rotational injury observed in patients and to study the pathological outcomes post-rmTBI using C57BL/6J mice. Enhanced cytokine production was observed in both the cortex and hippocampus to suggest neuroinflammation. Furthermore, microglia were assessed via enhanced iba1 protein levels and morphological changes using immunofluorescence. In addition, LC/MS analyses revealed excess glutamate production, as well as diffuse axonal injury via Bielschowsky\'s silver stain kit. Moreover, the heterogeneous nature of rmTBI has made it challenging to identify drug therapies that address rmTBI, therefore we sought to identify novel targets in the concurrent rmTBI pathology. The pathophysiological findings correlated with a time-dependent decrease in protein arginine methyltransferase 7 (PRMT7) protein expression and activity post-rmTBI along with dysregulation of PRMT upstream mediators s-adenosylmethionine and methionine adenosyltransferase 2 (MAT2) in vivo. In addition, inhibition of the upstream mediator MAT2A using the HT22 hippocampal neuronal cell line suggest a mechanistic role for PRMT7 via MAT2A in vitro. Collectively, we have identified PRMT7 as a novel target in rmTBI pathology in vivo and a mechanistic link between PRMT7 and upstream mediator MAT2A in vitro.

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.

Alzheimer\'s disease (AD) is the leading cause of mortality, disability, and long-term care burden in the United States, with women comprising the majority of AD diagnoses. While AD-related dementia is associated with tau and amyloid beta accumulation, concurrent derangements in cerebral blood flow have been observed alongside these proteinopathies in humans and rodent models. The homeostatic production of nitric oxide synthases (NOS) becomes uncoupled in AD which leads to decreased NO-mediated vasodilation and oxidative stress via the production of peroxynitrite (ONOO-∙) superoxide species. Here, we investigate the role of the novel protein arginine methyltransferase 4 (PRMT4) enzyme function and its downstream product asymmetric dimethyl arginine (ADMA) as it relates to NOS dysregulation and cerebral blood flow in AD. ADMA (type-1 PRMT product) has been shown to bind NOS as a noncanonic ligand causing enzymatic dysfunction. Our results from RT-qPCR and protein analyses suggest that aged (9-12 months) female mice bearing tau- and amyloid beta-producing transgenic mutations (3xTg-AD) express higher levels of PRMT4 in the hippocampus when compared to age- and sex-matched C57BL6/J mice. In addition, we performed studies to quantify the expression and activity of different NOS isoforms. Furthermore, laser speckle contrast imaging analysis was indicative that 3xTg-AD mice have dysfunctional NOS activity, resulting in reduced production of NO metabolites, enhanced production of free-radical ONOO-, and decreased cerebral blood flow. Notably, the aforementioned phenomena can be reversed via pharmacologic PRMT4 inhibition. Together, these findings implicate the potential importance of PRMT4 signaling in the pathogenesis of Alzheimer\'s-related cerebrovascular derangement.