Biochemical control of CARM1 enzymatic activity by phosphorylation

CARM1 S217 phosphorylation by CDK1 in late G2 phase facilitates mitotic entry

The coactivator-associated arginine methyltransferase 1 (CARM1) functions as an epigenetic writer, however, its role in mitosis remains poorly understood. In this study, we identified CARM1 as a novel substrate of cyclin-dependent kinase 1 (CDK1) and revealed its novel function as a scaffold that regulates CDK1 stability. During interphase, CARM1 acts as an adaptor in the Cullin-1-mediated CDK1 degradation process, limiting nuclear levels of CDK1. In late G2 phase, the CDK1/Cyclin B1 complex translocates to the nucleus, where it phosphorylates the S217 residue of CARM1. This phosphorylation not only inhibits CARM1's enzymatic activity but also facilitates its translocation to the cytoplasm, leading to the loss of its scaffolding function. Consequently, the CDK1/Cyclin B1 complex resides for longer in the nucleus and initiates mitosis. In addition, depletion or inhibition of CARM1 facilitates entry into mitosis, resulting in accelerated cell growth. Overall, our findings expand the cellular functions of CARM1 beyond its enzymatic activity.

PSMD14-mediated deubiquitination of CARM1 facilitates the proliferation and metastasis of hepatocellular carcinoma by inducing the transcriptional activation of FERMT1

Hepatocellular carcinoma (HCC) is a highly potent malignancy. The enzyme coactivator-associated arginine methyltransferase 1 (CARM1) is highly expressed in different types of cancer. However, the precise levels of expression, clinical significance, biological functions, and molecular mechanisms of CARM1 in HCC, particularly related to the downstream genes regulated by CARM1 through histone arginine methylation, remain unclear. In this study, we presented findings from the TCGA database and clinical samples, which collectively demonstrated the overexpression of CARM1 in HCC. Additionally, we found that the upregulation of CARM1 was mediated by PSMD14-induced deubiquitination. CARM1 promoted the proliferation and metastasis of HCC cells in vitro and in vivo. Mechanistic investigations further revealed that FERMT1 is a downstream gene of CARM1, and CARM1 activates the transcription of FERMT1 through the dimethylation of arginine 17 on histone 3 (H3R17me2). Additionally, administering SGC2085, a CARM1 inhibitor, effectively suppressed the malignant behaviors of HCC cells. To summarize, our findings provided strong evidence that CARM1 can serve as a key oncoprotein; thus, it holds promise as a therapeutic target for HCC.

The emerging role of CARM1 in cancer

Coactivator-associated arginine methyltransferase 1 (CARM1), pivotal for catalyzing arginine methylation of histone and non-histone proteins, plays a crucial role in developing various cancers. CARM1 was initially recognized as a transcriptional coregulator by orchestrating chromatin remodeling, transcription regulation, mRNA splicing and stability. This diverse functionality contributes to the recruitment of transcription factors that foster malignancies. Going beyond its established involvement in transcriptional control, CARM1-mediated methylation influences a spectrum of biological processes, including the cell cycle, metabolism, autophagy, redox homeostasis, and inflammation. By manipulating these physiological functions, CARM1 becomes essential in critical processes such as tumorigenesis, metastasis, and therapeutic resistance. Consequently, it emerges as a viable target for therapeutic intervention and a possible biomarker for medication response in specific cancer types. This review provides a comprehensive exploration of the various physiological functions of CARM1 in the context of cancer. Furthermore, we discuss potential CARM1-targeting pharmaceutical interventions for cancer therapy.

CARM1 phosphorylation at S595 by p38γ MAPK drives ROS-mediated cellular senescence

CARM1 is predominantly localized in the nucleus and plays a pivotal role in maintaining mitochondrial homeostasis by regulating gene expression. It suppresses mitochondrial biogenesis by downregulating PGC-1α and TFAM expression, while promoting mitochondrial fission through increased DNM1L expression. Under oxidative stress, CARM1 translocates to the cytoplasm, where it directly methylates DRP1 and accelerates mitochondrial fission, enhancing reactive oxygen species (ROS) production. Cytoplasmic localization of CARM1 is facilitated by its phosphorylation at S595 by ROS-activated p38γ MAPK, creating a positive feedback loop. Consequently, cytoplasmic CARM1 contributes to cellular senescence by altering mitochondrial dynamics and increasing ROS levels. This observation was supported by the increased cytoplasmic CARM1 levels and disrupted mitochondrial dynamics in the transformed 10T1/2 cells. Moreover, CARM1 inhibitors not only inhibit the proliferation of cancer cells but also induce apoptotic death in senescent cells. These findings highlight the potential of CARM1 inhibitors, particularly those targeting cytoplasmic functions, as novel strategies for eliminating cancer and senescent cells.

Tyrosine phosphorylation of CARM1 promotes its enzymatic activity and alters its target specificity

An important epigenetic component of tyrosine kinase signaling is the phosphorylation of histones, and epigenetic readers, writers, and erasers. Phosphorylation of protein arginine methyltransferases (PRMTs), have been shown to enhance and impair their enzymatic activity. In this study, we show that the hyperactivation of Janus kinase 2 (JAK2) by the V617F mutation phosphorylates tyrosine residues (Y149 and Y334) in coactivator-associated arginine methyltransferase 1 (CARM1), an important target in hematologic malignancies, increasing its methyltransferase activity and altering its target specificity. While non-phosphorylatable CARM1 methylates some established substrates (e.g. BAF155 and PABP1), only phospho-CARM1 methylates the RUNX1 transcription factor, on R223 and R319. Furthermore, cells expressing non-phosphorylatable CARM1 have impaired cell-cycle progression and increased apoptosis, compared to cells expressing phosphorylatable, wild-type CARM1, with reduced expression of genes associated with G2/M cell cycle progression and anti-apoptosis. The presence of the JAK2-V617F mutant kinase renders acute myeloid leukemia (AML) cells less sensitive to CARM1 inhibition, and we show that the dual targeting of JAK2 and CARM1 is more effective than monotherapy in AML cells expressing phospho-CARM1. Thus, the phosphorylation of CARM1 by hyperactivated JAK2 regulates its methyltransferase activity, helps select its substrates, and is required for the maximal proliferation of malignant myeloid cells.

Protein Arginine Methyltransferases in Pancreatic Ductal Adenocarcinoma: New Molecular Targets for Therapy

Pancreatic ductal adenocarcinoma (PDAC) is a lethal malignant disease with a low 5-year overall survival rate. It is the third-leading cause of cancer-related deaths in the United States. The lack of robust therapeutics, absence of effective biomarkers for early detection, and aggressive nature of the tumor contribute to the high mortality rate of PDAC. Notably, the outcomes of recent immunotherapy and targeted therapy against PDAC remain unsatisfactory, indicating the need for novel therapeutic strategies. One of the newly described molecular features of PDAC is the altered expression of protein arginine methyltransferases (PRMTs). PRMTs are a group of enzymes known to methylate arginine residues in both histone and non-histone proteins, thereby mediating cellular homeostasis in biological systems. Some of the PRMT enzymes are known to be overexpressed in PDAC that promotes tumor progression and chemo-resistance via regulating gene transcription, cellular metabolic processes, RNA metabolism, and epithelial mesenchymal transition (EMT). Small-molecule inhibitors of PRMTs are currently under clinical trials and can potentially become a new generation of anti-cancer drugs. This review aims to provide an overview of the current understanding of PRMTs in PDAC, focusing on their pathological roles and their potential as new therapeutic targets.

Transcriptional co-activators: emerging roles in signaling pathways and potential therapeutic targets for diseases

Specific cell states in metazoans are established by the symphony of gene expression programs that necessitate intricate synergic interactions between transcription factors and the co-activators. Deregulation of these regulatory molecules is associated with cell state transitions, which in turn is accountable for diverse maladies, including developmental disorders, metabolic disorders, and most significantly, cancer. A decade back most transcription factors, the key enablers of disease development, were historically viewed as 'undruggable'; however, in the intervening years, a wealth of literature validated that they can be targeted indirectly through transcriptional co-activators, their confederates in various physiological and molecular processes. These co-activators, along with transcription factors, have the ability to initiate and modulate transcription of diverse genes necessary for normal physiological functions, whereby, deregulation of such interactions may foster tissue-specific disease phenotype. Hence, it is essential to analyze how these co-activators modulate specific multilateral processes in coordination with other factors. The proposed review attempts to elaborate an in-depth account of the transcription co-activators, their involvement in transcription regulation, and context-specific contributions to pathophysiological conditions. This review also addresses an issue that has not been dealt with in a comprehensive manner and hopes to direct attention towards future research that will encompass patient-friendly therapeutic strategies, where drugs targeting co-activators will have enhanced benefits and reduced side effects. Additional insights into currently available therapeutic interventions and the associated constraints will eventually reveal multitudes of advanced therapeutic targets aiming for disease amelioration and good patient prognosis.

Coactivator-associated arginine methyltransferase 1: A versatile player in cell differentiation and development

Protein arginine methylation is a common post-translational modification involved in the regulation of various cellular functions. Coactivator-associated arginine methyltransferase 1 (CARM1) is a protein arginine methyltransferase that asymmetrically dimethylates histone H3 and non-histone proteins to regulate gene transcription. CARM1 has been found to play important roles in cell differentiation and development, cell cycle progression, autophagy, metabolism, pre-mRNA splicing and transportation, and DNA replication. In this review, we describe the molecular characteristics of CARM1 and summarize its roles in the regulation of cell differentiation and development in mammals.

Protein arginine methylation in viral infection and antiviral immunity

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.

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.

Functional Implications of Protein Arginine Methyltransferases (PRMTs) in Neurodegenerative Diseases

During the aging of the global population, the prevalence of neurodegenerative diseases will be continuously growing. Although each disorder is characterized by disease-specific protein accumulations, several common pathophysiological mechanisms encompassing both genetic and environmental factors have been detected. Among them, protein arginine methyltransferases (PRMTs), which catalyze the methylation of arginine of various substrates, have been revealed to regulate several cellular mechanisms, including neuronal cell survival and excitability, axonal transport, synaptic maturation, and myelination. Emerging evidence highlights their critical involvement in the pathophysiology of neurodegenerative diseases, including Alzheimer's disease (AD), Parkinson's disease (PD), frontotemporal dementia-amyotrophic lateral sclerosis (FTD-ALS) spectrum, Huntington's disease (HD), spinal muscular atrophy (SMA) and spinal and bulbar muscular atrophy (SBMA). Underlying mechanisms include the regulation of gene transcription and RNA splicing, as well as their implication in various signaling pathways related to oxidative stress responses, apoptosis, neuroinflammation, vacuole degeneration, abnormal protein accumulation and neurotransmission. The targeting of PRMTs is a therapeutic approach initially developed against various forms of cancer but currently presents a novel potential strategy for neurodegenerative diseases. In this review, we discuss the accumulating evidence on the role of PRMTs in the pathophysiology of neurodegenerative diseases, enlightening their pathogenesis and stimulating future research.

Unraveling the complexity of histone-arginine methyltransferase CARM1 in cancer: From underlying mechanisms to targeted therapeutics

Coactivator-associated arginine methyltransferase 1 (CARM1), a type I protein arginine methyltransferase (PRMT), has been widely reported to catalyze arginine methylation of histone and non-histone substrates, which is closely associated with the occurrence and progression of cancer. Recently, accumulating studies have demonstrated the oncogenic role of CARM1 in many types of human cancers. More importantly, CARM1 has been emerging as an attractive therapeutic target for discovery of new candidate anti-tumor drugs. Therefore, in this review, we summarize the molecular structure of CARM1 and its key regulatory pathways, as well as further discuss the rapid progress in better understanding of the oncogenic functions of CARM1. Moreover, we further demonstrate several representative targeted CARM1 inhibitors, especially focusing on demonstrating their designing strategies and potential therapeutic applications. Together, these inspiring findings would shed new light on elucidating the underlying mechanisms of CARM1 and provide a clue on discovery of more potent and selective CARM1 inhibitors for the future targeted cancer therapy.

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 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.

CARM1/PRMT4: Making Its Mark beyond Its Function as a Transcriptional Coactivator

Coactivator-associated arginine methyltransferase 1 (CARM1), identified 20 years ago as a coregulator of transcription, is an enzyme that catalyzes arginine methylation of proteins. Beyond its well-established involvement in the regulation of transcription, the physiological functions of CARM1 are still poorly understood. However, recent studies have revealed novel roles of CARM1 in autophagy, metabolism, paraspeckles, and early development. In addition, CARM1 is emerging as an attractive therapeutic target and a drug response biomarker for certain types of cancer. Here, we provide a comprehensive overview of the structure of CARM1 and its post-translational modifications, its various functions, apart from transcriptional coactivation, and its involvement in cancer.

The atypical protein arginine methyltrasferase of Entamoeba histolytica (EhPRMTA) is involved in cell proliferation, heat shock response and in vitro virulence

Protein arginine methylation regulates several cellular events, including epigenetics, splicing, translation, and stress response, among others. This posttranslational modification is catalyzed by protein arginine methyltransferases (PRMTs), which according to their products are classified from type I to type IV. The type I produces monomethyl arginine and asymmetric dimethyl arginine; in mammalian there are six families of this PRMT type (PRMT1, 2, 3, 4, 6, and 8). The protozoa parasite Entamoeba histolytica has four PRMTs related to type I; three of them are similar to PRMT1, but the other one does not show significant homology to be grouped in any known PRMT family, thus we called it as atypical PRMT (EhPRMTA). Here, we showed that EhPRMTA does not contain several of the canonical amino acid residues of type I PRMTs, confirming that it is an atypical PRMT. A specific antibody against EhPRMTA localized this protein in cytoplasm. The recombinant EhPRMTA displayed catalytic activity on commercial histones and the native enzyme modified its expression level during heat shock and erythrophagocytosis. Besides, the knockdown of EhPRMTA produced an increment in cell growth, and phagocytosis, but decreases cell migration and the survival of trophozoites submitted to heat shock, suggesting that this protein is involved in regulate negatively or positively these events, respectively. Thus, results suggest that this methyltransferase regulates some cellular functions related to virulence and cell surviving.

Modulating the modulators: regulation of protein arginine methyltransferases by post-translational modifications

The therapeutic potential of targeting protein arginine methyltransferases (PRMTs) is inextricably linked to their key roles in various cellular functions, including splicing, proliferation, cell cycle regulation, differentiation, and DNA damage signaling. Unsurprisingly, the development of inhibitors against these enzymes has become a rapidly expanding research area. However, effective targeting of PRMTs requires a deeper understanding of the mechanistic details behind their regulation at multiple levels, involving those mechanisms that alter their activity, interactions, and localization. Recently, post-translational modifications (PTMs) of PRMTs have emerged as another crucial aspect of this regulation. Here, we review the regulatory role of PTMs in the activity and function of PRMTs, with emphasis on the contribution of these PTMs to pathological states, such as cancer.

Translocatome: a novel resource for the analysis of protein translocation between cellular organelles

Here we present Translocatome, the first dedicated database of human translocating proteins (URL: http://translocatome.linkgroup.hu). The core of the Translocatome database is the manually curated data set of 213 human translocating proteins listing the source of their experimental validation, several details of their translocation mechanism, their local compartmentalized interactome, as well as their involvement in signalling pathways and disease development. In addition, using the well-established and widely used gradient boosting machine learning tool, XGBoost, Translocatome provides translocation probability values for 13 066 human proteins identifying 1133 and 3268 high- and low-confidence translocating proteins, respectively. The database has user-friendly search options with a UniProt autocomplete quick search and advanced search for proteins filtered by their localization, UniProt identifiers, translocation likelihood or data complexity. Download options of search results, manually curated and predicted translocating protein sets are available on its website. The update of the database is helped by its manual curation framework and connection to the previously published ComPPI compartmentalized protein–protein interaction database (http://comppi.linkgroup.hu). As shown by the application examples of merlin (NF2) and tumor protein 63 (TP63) Translocatome allows a better comprehension of protein translocation as a systems biology phenomenon and can be used as a discovery-tool in the protein translocation field.

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.

Protein arginine methyltransferases: insights into the enzyme structure and mechanism at the atomic level

Protein arginine methyltransferases (PRMTs) catalyze the methyl transfer to the arginine residues of protein substrates and are classified into three major types based on the final form of the methylated arginine. Recent studies have shown a strong correlation between PRMT expression level and the prognosis of cancer patients. Currently, crystal structures of eight PRMT members have been determined. Kinetic and structural studies have shown that all PRMTs share similar, but unique catalytic and substrate recognition mechanism. In this review, we discuss the structural similarities and differences of different PRMT members, focusing on their overall structure, S-adenosyl-L-methionine-binding pocket, substrate arginine recognition and catalytic mechanisms. Since PRMTs are valuable targets for drug discovery, we also rationally classify the known PRMT inhibitors into five classes and discuss their mechanisms of action at the atomic level.

Exercise-induced Protein Arginine Methyltransferase Expression in Skeletal Muscle

PURPOSE

This study aimed to determine protein arginine methyltransferase 1 (PRMT1), -4 (also known as coactivator-associated arginine methyltransferase 1 [CARM1]), and -5 expression and function during acute, exercise-induced skeletal muscle remodeling in vivo.

METHODS

C57BL/6 mice were assigned to one of three experimental groups: sedentary, acute bout of exercise, or acute exercise followed by 3 h of recovery. Mice in the exercise groups performed a single bout of treadmill running at 15 m·min for 90 min. Hindlimb muscles were collected, and quantitative real-time polymerase chain reaction and Western blotting were used to examine exercise-induced gene expression.

RESULTS

The PRMT gene expression and global enzyme activity were muscle-specific, generally being higher (P < 0.05) in slow, oxidative muscle, as compared with faster, more glycolytic tissue. Despite the significant activation of canonical exercise-induced signaling involving AMP-activated protein kinase and peroxisome proliferator-activated receptor γ coactivator-1α (PGC-1α), PRMT expression and activity at the whole muscle level were unchanged. However, subcellular analyses revealed a significant exercise-evoked myonuclear translocation of PRMT1 before the nuclear accumulation of PGC-1α. Acute physical activity also augmented (P < 0.05) the targeted methyltransferase activities of the PRMT in the myonuclear compartment, suggesting that PRMT-mediated histone arginine methylation is part of the early signals that drive muscle plasticity. Finally, basal PGC-1α asymmetric dimethylarginine status, as well as constitutive interactions between PGC-1α and PRMT1 or CARM1 may contribute to the exercise-induced muscle remodeling process.

CONCLUSIONS

The present study provides the first evidence that PRMT activity is selectively augmented during the initial activation of exercise-induced skeletal muscle remodeling in vivo. These data support the emergence of PRMTs as important players in the regulation of skeletal muscle plasticity.

The Dystrophin Glycoprotein Complex Regulates the Epigenetic Activation of Muscle Stem Cell Commitment

Asymmetrically dividing muscle stem cells in skeletal muscle give rise to committed cells, where the myogenic determination factor Myf5 is transcriptionally activated by Pax7. This activation is dependent on Carm1, which methylates Pax7 on multiple arginine residues, to recruit the ASH2L:MLL1/2:WDR5:RBBP5 histone methyltransferase complex to the proximal promoter of Myf5. Here, we found that Carm1 is a specific substrate of p38γ/MAPK12 and that phosphorylation of Carm1 prevents its nuclear translocation. Basal localization of the p38γ/p-Carm1 complex in muscle stem cells occurs via binding to the dystrophin-glycoprotein complex (DGC) through β1-syntrophin. In dystrophin-deficient muscle stem cells undergoing asymmetric division, p38γ/β1-syntrophin interactions are abrogated, resulting in enhanced Carm1 phosphorylation. The resulting progenitors exhibit reduced Carm1 binding to Pax7, reduced H3K4-methylation of chromatin, and reduced transcription of Myf5 and other Pax7 target genes. Therefore, our experiments suggest that dysregulation of p38γ/Carm1 results in altered epigenetic gene regulation in Duchenne muscular dystrophy.

Characterization of Protein Methyltransferases Rkm1, Rkm4, Efm4, Efm7, Set5 and Hmt1 Reveals Extensive Post-Translational Modification

Protein methylation is one of the major post-translational modifications (PTMs) in the cell. In Saccharomyces cerevisiae, over 20 protein methyltransferases (MTases) and their respective substrates have been identified. However, the way in which these MTases are modified and potentially subject to regulation remains poorly understood. Here, we investigated six overexpressed S. cerevisiae protein MTases (Rkm1, Rkm4, Efm4, Efm7, Set5 and Hmt1) to identify PTMs of potential functional relevance. We identified 48 PTM sites across the six MTases, including phosphorylation, acetylation and methylation. Forty-two sites are novel. We contextualized the PTM sites in structural models of the MTases and revealed that many fell in catalytic pockets or enzyme-substrate interfaces. These may regulate MTase activity. Finally, we compared PTMs on Hmt1 with those on its human homologs PRMT1, PRMT3, CARM1, PRMT6 and PRMT8. This revealed that several PTMs are conserved from yeast to human, whereas others are only found in Hmt1. The mass spectrometry proteomics data have been deposited to the ProteomeXchange Consortium via the PRIDE partner repository with the dataset identifier PXD006767.

Regulation of Skeletal Muscle Plasticity by Protein Arginine Methyltransferases and Their Potential Roles in Neuromuscular Disorders

Protein arginine methyltransferases (PRMTs) are a family of enzymes that catalyze the methylation of arginine residues on target proteins, thereby mediating a diverse set of intracellular functions that are indispensable for survival. Indeed, full-body knockouts of specific PRMTs are lethal and PRMT dysregulation has been implicated in the most prevalent chronic disorders, such as cancers and cardiovascular disease (CVD). PRMTs are now emerging as important mediators of skeletal muscle phenotype and plasticity. Since their first description in muscle in 2002, a number of studies employing wide varieties of experimental models support the hypothesis that PRMTs regulate multiple aspects of skeletal muscle biology, including development and regeneration, glucose metabolism, as well as oxidative metabolism. Furthermore, investigations in non-muscle cell types strongly suggest that proteins, such as peroxisome proliferator-activated receptor-γ coactivator-1α, E2F transcription factor 1, receptor interacting protein 140, and the tumor suppressor protein p53, are putative downstream targets of PRMTs that regulate muscle phenotype determination and remodeling. Recent studies demonstrating that PRMT function is dysregulated in Duchenne muscular dystrophy (DMD), spinal muscular atrophy (SMA), and amyotrophic lateral sclerosis (ALS) suggests that altering PRMT expression and/or activity may have therapeutic value for neuromuscular disorders (NMDs). This review summarizes our understanding of PRMT biology in skeletal muscle, and identifies uncharted areas that warrant further investigation in this rapidly expanding field of research.

Inhibition of coactivator-associated arginine methyltransferase 1 modulates dendritic arborization and spine maturation of cultured hippocampal neurons

An improved understanding of the molecular mechanisms in synapse formation provides insight into both learning and memory and the etiology of neurodegenerative disorders. Coactivator-associated arginine methyltransferase 1 (CARM1) is a protein methyltransferase that negatively regulates synaptic gene expression and inhibits neuronal differentiation. Despite its regulatory function in neurons, little is known about the CARM1 cellular location and its role in dendritic maturation and synapse formation. Here, we examined the effects of CARM1 inhibition on dendritic spine and synapse morphology in the rat hippocampus. CARM1 was localized in hippocampal post-synapses, with immunocytochemistry and electron microscopy revealing co-localization of CARM1 with post-synaptic density (PSD)-95 protein, a post-synaptic marker. Specific siRNA-mediated suppression of CARM1 expression resulted in precocious dendritic maturation, with increased spine width and density at sites along dendrites and induction of mushroom-type spines. These changes were accompanied by a striking increase in the cluster size and number of key synaptic proteins, including N-methyl-d-aspartate receptor subunit 2B (NR2B) and PSD-95. Similarly, pharmacological inhibition of CARM1 activity with the CARM1-specific inhibitor AMI-1 significantly increased spine width and mushroom-type spines and also increased the cluster size and number of NR2B and cluster size of PSD-95. These results suggest that CARM1 is a post-synaptic protein that plays roles in dendritic maturation and synaptic formation and that spatiotemporal regulation of CARM1 activity modulates neuronal connectivity and improves synaptic dysfunction.

Beyond transcription factors: how oncogenic signalling reshapes the epigenetic landscape

Cancer, once thought to be caused largely by genetic alterations, is now considered to be a mixed genetic and epigenetic disease. The epigenetic landscape, which is dictated by covalent DNA and histone modifications, is profoundly altered in transformed cells. These abnormalities may arise from mutations in, or altered expression of, chromatin modifiers. Recent reports on the interplay between cellular signalling pathways and chromatin modifications add another layer of complexity to the already complex regulation of the epigenome. In this Review, we discuss these new studies and how the insights they provide can contribute to a better understanding of the molecular pathogenesis of neoplasia.

Burkholderia glumae ToxA Is a Dual-Specificity Methyltransferase That Catalyzes the Last Two Steps of Toxoflavin Biosynthesis

Toxoflavin is a major virulence factor of the rice pathogen Burkholderia glumae. The tox operon of B. glumae contains five putative toxoflavin biosynthetic genes toxABCDE. ToxA is a predicted S-adenosylmethionine-dependent methyltransferase, and toxA knockouts of B. glumae are less virulent in plant infection models. In this study, we show that ToxA performs two consecutive methylations to convert the putative azapteridine intermediate, 1,6-didemethyltoxoflavin, to toxoflavin. In addition, we report a series of crystal structures of ToxA complexes that reveals the molecular basis of the dual methyltransferase activity. The results suggest sequential methylations with initial methylation at N6 of 1,6-didemethyltoxoflavin followed by methylation at N1. The two azapteridine orientations that position N6 or N1 for methylation are coplanar with a 140° rotation between them. The structure of ToxA contains a class I methyltransferase fold having an N-terminal extension that either closes over the active site or is largely disordered. The ordered conformation places Tyr7 at a position of a structurally conserved tyrosine site of unknown function in various methyltransferases. Crystal structures of ToxA-Y7F consistently show a closed active site, whereas structures of ToxA-Y7A consistently show an open active site, suggesting that the hydroxyl group of Tyr7 plays a role in opening and closing the active site during the multistep reaction.

Coactivator-Associated Arginine Methyltransferase-1 Function in Alveolar Epithelial Senescence and Elastase-Induced Emphysema Susceptibility

Chronic obstructive pulmonary disease (COPD) is characterized by an irreversible loss of lung function and is one of the most prevalent and severe diseases worldwide. A major feature of COPD is emphysema, which is the progressive loss of alveolar tissue. Coactivator-associated arginine methyltransferase-1 (CARM1) regulates histone methylation and the transcription of genes involved in senescence, proliferation, and differentiation. Complete loss of CARM1 leads to disrupted differentiation and maturation of alveolar epithelial type II (ATII) cells. We thus hypothesized that CARM1 regulates the development and progression of emphysema. To address this, we investigated the contribution of CARM1 to alveolar rarefication using the mouse model of elastase-induced emphysema in vivo and small interfering (si)RNA-mediated knockdown in ATII-like LA4 cells in vitro. We demonstrate that emphysema progression in vivo is associated with a time-dependent down-regulation of CARM1. Importantly, elastase-treated CARM1 haploinsufficient mice show significantly increased airspace enlargement (52.5 ± 9.6 μm versus 38.8 ± 5.5 μm; P < 0.01) and lung compliance (2.8 ± 0.32 μl/cm H2O versus 2.4 ± 0.4 μl/cm H2O; P < 0.04) compared with controls. The knockdown of CARM1 in LA4 cells led to decreased sirtuin 1 expression (0.034 ± 0.003 versus 0.022 ± 0.001; P < 0.05) but increased expression of p16 (0.27 ± 0.013 versus 0.31 ± 0.010; P < 0.5) and p21 (0.81 ± 0.088 versus 1.28 ± 0.063; P < 0.01) and higher β-galactosidase-positive senescent cells (50.57 ± 7.36% versus 2.21 ± 0.34%; P < 0.001) compared with scrambled siRNA. We further demonstrated that CARM1 haploinsufficiency impairs transdifferentiation and wound healing (32.18 ± 0.9512% versus 8.769 ± 1.967%; P < 0.001) of alveolar epithelial cells. Overall, these results reveal a novel function of CARM1 in regulating emphysema development and premature lung aging via alveolar senescence as well as impaired regeneration, repair, and differentiation of ATII cells.

Role of co-regulators in metabolic and transcriptional actions of thyroid hormone

Thyroid hormone (TH) controls a wide range of physiological processes through TH receptor (TR) isoforms. Classically, TRs are proposed to function as tri-iodothyronine (T3)-dependent transcription factors: on positively regulated target genes, unliganded TRs mediate transcriptional repression through recruitment of co-repressor complexes, while T3 binding leads to dismissal of co-repressors and recruitment of co-activators to activate transcription. Co-repressors and co-activators were proposed to play opposite roles in the regulation of negative T3 target genes and hypothalamic-pituitary-thyroid axis, but exact mechanisms of the negative regulation by TH have remained elusive. Important insights into the roles of co-repressors and co-activators in different physiological processes have been obtained using animal models with disrupted co-regulator function. At the same time, recent studies interrogating genome-wide TR binding have generated compelling new data regarding effects of T3, local chromatin structure, and specific response element configuration on TR recruitment and function leading to the proposal of new models of transcriptional regulation by TRs. This review discusses data obtained in various mouse models with manipulated function of nuclear receptor co-repressor (NCoR or NCOR1) and silencing mediator of retinoic acid receptor and thyroid hormone receptor (SMRT or NCOR2), and family of steroid receptor co-activators (SRCs also known as NCOAs) in the context of TH action, as well as insights into the function of co-regulators that may emerge from the genome-wide TR recruitment analysis.

The Role of Protein Arginine Methyltransferases in Inflammatory Responses

Protein arginine methyltransferases (PRMTs) mediate the methylation of a number of protein substrates of arginine residues and serve critical functions in many cellular responses, including cancer development, progression, and aggressiveness, T-lymphocyte activation, and hepatic gluconeogenesis. There are nine members of the PRMT family, which are divided into 4 types (types I–IV). Although most PRMTs do not require posttranslational modification (PTM) to be activated, fine-tuning modifications, such as interactions between cofactor proteins, subcellular compartmentalization, and regulation of RNA, via micro-RNAs, seem to be required. Inflammation is an essential defense reaction of the body to eliminate harmful stimuli, including damaged cells, irritants, or pathogens. However, chronic inflammation can eventually cause several types of diseases, including some cancers, atherosclerosis, rheumatoid arthritis, and periodontitis. Therefore, inflammation responses should be well modulated. In this review, we briefly discuss the role of PRMTs in the control of inflammation. More specifically, we review the roles of four PRMTs (CARM1, PRMT1, PRMT5, and PRMT6) in modulating inflammation responses, particularly in terms of modulating the transcriptional factors or cofactors related to inflammation. Based on the regulatory roles known so far, we propose that PRMTs should be considered one of the target molecule groups that modulate inflammatory responses.

Biochemistry and regulation of the protein arginine methyltransferases (PRMTs)

Many key cellular processes can be regulated by the seemingly simple addition of one, or two, methyl groups to arginine residues by the nine known mammalian protein arginine methyltransferases (PRMTs). The impact that arginine methylation has on cellular well-being is highlighted by the ever growing evidence linking PRMT dysregulation to disease states, which has marked the PRMTs as prominent pharmacological targets. This review is meant to orient the reader with respect to the structural features of the PRMTs that account for catalytic activity, as well as provide a framework for understanding how these enzymes are regulated. An overview of what we understand about substrate recognition and binding is provided. Control of product specificity and enzyme processivity are introduced as necessary but flexible features of the PRMTs. Precise control of PRMT activity is a critical component to eukaryotic cell health, especially given that an arginine demethylase has not been identified. We therefore conclude the review with a comprehensive discussion of how protein arginine methylation is regulated.

Regulation of Glucose Homeostasis by Glucocorticoids

Glucocorticoids are steroid hormones that regulate multiple aspects of glucose homeostasis. Glucocorticoids promote gluconeogenesis in liver, whereas in skeletal muscle and white adipose tissue they decrease glucose uptake and utilization by antagonizing insulin response. Therefore, excess glucocorticoid exposure causes hyperglycemia and insulin resistance. Glucocorticoids also regulate glycogen metabolism. In liver, glucocorticoids increase glycogen storage, whereas in skeletal muscle they play a permissive role for catecholamine-induced glycogenolysis and/or inhibit insulin-stimulated glycogen synthesis. Moreover, glucocorticoids modulate the function of pancreatic α and β cells to regulate the secretion of glucagon and insulin, two hormones that play a pivotal role in the regulation of blood glucose levels. Overall, the major glucocorticoid effect on glucose homeostasis is to preserve plasma glucose for brain during stress, as transiently raising blood glucose is important to promote maximal brain function. In this chapter we will discuss the current understanding of the mechanisms underlying different aspects of glucocorticoid-regulated mammalian glucose homeostasis.

Identification of Differential Protein Expression in Hepatocellular Carcinoma Induced Wistar Albino Rats by 2D Electrophoresis and MALDI-TOF-MS Analysis

Hepato cellular carcinoma (HCC) is a type of malignant tumor. To investigate the proteins in cancer molecular mechanism and its role in HCC, we have used proteomic tools such as 2DE and MALDI-TOF-MS. Our investigation ravels that, plasma α-fetoprotein and carcinoembryonic antigen levels were elevated in DEN induced rats and gradually decreased after the treatment with 1,3BPMU. 2DE and MALDI-TOF-MS tool offers to identify the up and down regulation of proteins in HCC. Proteomic study reveals that, five differentially expressed proteins were identified in DEN induced rats and 1,3BPMU treated rats i.e. three up regulated protein such as T kininogen, NDPKB, PRMT1 (DEN induced rats), RGS19 and PAF (1,3BPMU treated rats) in 3BPMU treated rats, activation of transcription of a single gene from multiple promoters provides flexibility in the controlled gene expression. The regulations of hepatocyte stimulating factor were slow down the proliferation of hepatic cell and uncontrolled hepatic cell growth and also molecular signals strongly argue for a patho-physiological role in liver metastasis to control the cell aggression. This indicates that, anti cancer property of 1,3BPMU can be used as potent anti cancer agent. The present study also shows the proteomic approach helps to elucidate the tumor maker as well as regulatory marker proteins in HCC.

O-GlcNAcylation of co-activator-associated arginine methyltransferase 1 regulates its protein substrate specificity

Co-activator-associated arginine methyltransferase 1 (CARM1) asymmetrically di-methylates proteins on arginine residues. CARM1 was previously known to be modified through O-linked-β-N-acetylglucosaminidation (O-GlcNAcylation). However, the site(s) of O-GlcNAcylation were not mapped and the effects of O-GlcNAcylation on biological functions of CARM1 were undetermined. In the present study, we describe the comprehensive mapping of CARM1 post-translational modification (PTM) using top-down MS. We found that all detectable recombinant CARM1 expressed in human embryonic kidney (HEK293T) cells is automethylated as we previously reported and that about 50% of this automethylated CARM1 contains a single O-linked-β-N-acetylglucosamine (O-GlcNAc) moiety [31]. The O-GlcNAc moiety was mapped by MS to four possible sites (Ser595, Ser598, Thr601 and Thr603) in the C-terminus of CARM1. Mutation of all four sites [CARM1 quadruple mutant (CARM1QM)] markedly decreased O-GlcNAcylation, but did not affect protein stability, dimerization or cellular localization of CARM1. Moreover, CARM1QM elicits similar co-activator activity as CARM1 wild-type (CARM1WT) on a few transcription factors known to be activated by CARM1. However, O-GlcNAc-depleted CARM1 generated by wheat germ agglutinin (WGA) enrichment, O-GlcNAcase (OGA) treatment and mutation of putative O-GlcNAcylation sites displays different substrate specificity from that of CARM1WT. Our findings suggest that O-GlcNAcylation of CARM1 at its C-terminus is an important determinant for CARM1 substrate specificity.

Phosphorylation of epigenetic "readers, writers and erasers": Implications for developmental reprogramming and the epigenetic basis for health and disease

Epigenetic reprogramming that occurs during critical periods of development can increase the susceptibility to many diseases in adulthood. Programming of the epigenome during development occurs via the activity of a variety of epigenetic modifiers, including "readers, writers and erasers" of histone methyl marks. Posttranslational modification of these programmers can alter their activity, resulting in global or gene-specific changes in histone methylation and gene transcription. This review summarizes what is currently known about phosphorylation of histone methyltransferases ("writers"), demethylases ("erasers") and effector proteins ("readers) that program the epigenome, and the impact of this posttranslational modification on their activity. Understanding how the activity of these epigenetic programmers is perturbed by environmental exposures via changes in phosphorylation is key to understanding mechanisms of developmental reprogramming and the epigenetic basis of health and disease.

Survey of phosphorylation near drug binding sites in the Protein Data Bank (PDB) and their effects

While it is currently estimated that 40 to 50% of eukaryotic proteins are phosphorylated, little is known about the frequency and local effects of phosphorylation near pharmaceutical inhibitor binding sites. In this study, we investigated how frequently phosphorylation may affect the binding of drug inhibitors to target proteins. We examined the 453 non-redundant structures of soluble mammalian drug target proteins bound to inhibitors currently available in the Protein Data Bank (PDB). We cross-referenced these structures with phosphorylation data available from the PhosphoSitePlus database. Three hundred twenty-two of 453 (71%) of drug targets have evidence of phosphorylation that has been validated by multiple methods or labs. For 132 of 453 (29%) of those, the phosphorylation site is within 12 Å of the small molecule-binding site, where it would likely alter small molecule binding affinity. We propose a framework for distinguishing between drug-phosphorylation site interactions that are likely to alter the efficacy of drugs versus those that are not. In addition we highlight examples of well-established drug targets, such as estrogen receptor alpha, for which phosphorylation may affect drug affinity and clinical efficacy. Our data suggest that phosphorylation may affect drug binding and efficacy for a significant fraction of drug target proteins.

PRMT4-mediated arginine methylation negatively regulates retinoblastoma tumor suppressor protein and promotes E2F-1 dissociation

The retinoblastoma protein (pRb/p105) tumor suppressor plays a pivotal role in cell cycle regulation by blockage of the G1-to-S-phase transition. pRb tumor suppressor activity is governed by a variety of posttranslational modifications, most notably phosphorylation by cyclin-dependent kinase (Cdk) complexes. Here we report a novel regulation of pRb through protein arginine methyltransferase 4 (PRMT4)-mediated arginine methylation, which parallels phosphorylation. PRMT4 specifically methylates pRb at the pRb C-terminal domain (pRb C(term)) on arginine (R) residues R775, R787, and R798 in vitro and R787 in vivo. Arginine methylation is important for efficient pRb C(term) phosphorylation, as manifested by the reduced phosphorylation of a methylation-impaired mutant, pRb (R3K). A methylmimetic form of pRb, pRb (R3F), disrupts the formation of the E2F-1/DP1-pRb complex in cells as well as in an isolated system. Finally, studies using a Gal4-E2F-1 reporter system show that pRb (R3F) expression reduces the ability of pRb to repress E2F-1 transcriptional activation, while pRb (R3K) expression further represses E2F-1 transcriptional activation relative to that for cells expressing wild-type pRb. Together, our results suggest that arginine methylation negatively regulates the tumor suppressor function of pRb during cell cycle control, in part by creating a better substrate for Cdk complex phosphorylation and disrupting the interaction of pRb with E2F-1.

Structural biology and chemistry of protein arginine methyltransferases

PRMT inhibitors can compete with cofactor, substrate, or bind at allosteric sites found in the active or inactive states.

Protein arginine methyltransferases (PRMTs), an emerging target class in drug discovery, can methylate histones and other substrates, and can be divided into three subgroups, based on the methylation pattern of the reaction product (monomethylation, symmetrical or asymmetrical dimethylation). Here, we review the growing body of structural information characterizing this protein family, including structures in complex with substrate-competitive and allosteric inhibitors. We outline structural differences between type I, II and III enzymes and propose a model underlying class-specificity. We analyze the structural plasticity and diversity of the substrate, cofactor and allosteric binding sites, and propose that the conformational dynamics of PRMTs can be exploited towards the discovery of allosteric inhibitors that would antagonize conformationally active states.

Role of PRMTs in cancer: Could minor isoforms be leaving a mark?

Protein arginine methyltransferases (PRMTs) catalyze the methylation of a variety of protein substrates, many of which have been linked to the development, progression and aggressiveness of different types of cancer. Moreover, aberrant expression of PRMTs has been observed in several cancer types. While the link between PRMTs and cancer is a relatively new area of interest, the functional implications documented thus far warrant further investigations into its therapeutic potential. However, the expression of these enzymes and the regulation of their activity in cancer are still significantly understudied. Currently there are nine main members of the PRMT family. Further, the existence of alternatively spliced isoforms for several of these family members provides an additional layer of complexity. Specifically, PRMT1, PRMT2, CARM1 and PRMT7 have been shown to have alternative isoforms and others may be currently unrealized. Our knowledge with respect to the relative expression and the specific functions of these isoforms is largely lacking and needs attention. Here we present a review of the current knowledge of the known alternative PRMT isoforms and provide a rationale for how they may impact on cancer and represent potentially useful targets for the development of novel therapeutic strategies.

Using unnatural amino acid mutagenesis to probe the regulation of PRMT1

Protein arginine methyltransferase 1 (PRMT1)-dependent methylation contributes to the onset and progression of numerous diseases (e.g., cancer, heart disease, ALS); however, the regulatory mechanisms that control PRMT1 activity are relatively unexplored. We therefore set out to decipher how phosphorylation regulates PRMT1 activity. Curated mass spectrometry data identified Tyr291, a residue adjacent to the conserved THW loop, as being phosphorylated. Natural and unnatural amino acid mutagenesis, including the incorporation of p-carboxymethyl-l-phenylalanine (pCmF) as a phosphotyrosine mimic, were used to show that Tyr291 phosphorylation alters the substrate specificity of PRMT1. Additionally, p-benzoyl-l-phenylalanine (pBpF) was incorporated at the Tyr291 position, and cross-linking experiments with K562 cell extracts identified several proteins (e.g., hnRNPA1 and hnRNP H3) that bind specifically to this site. Moreover, we also demonstrate that Tyr291 phosphorylation impairs PRMT1's ability to bind and methylate both proteins. In total, these studies demonstrate that Tyr291 phosphorylation alters both PRMT1 substrate specificity and protein-protein interactions.

Nuclear receptor coactivators: master regulators of human health and disease

Transcriptional coregulators (coactivators and corepressors) have emerged as the principal modulators of the functions of nuclear receptors and other transcription factors. During the decade since the discovery of steroid receptor coactivator-1 (SRC-1), the first authentic coregulator, more than 400 coregulators have been identified and characterized, and deciphering their function has contributed significantly to our understanding of their role in human physiology. Deregulated expression of coregulators has been implicated in diverse disease states and related pathologies. The advancement of molecular technologies has enabled us to better characterize the molecular associations of the SRC family of coactivators with other protein complexes in the context of gene regulation. These continuing discoveries not only expand our knowledge of the roles of coactivators in various human diseases but allow us to discover novel coactivator-targeting strategies for therapeutic intervention in these diseases.

Overexpression of CARM1 in breast cancer is correlated with poorly characterized clinicopathologic parameters and molecular subtypes

BACKGROUND

Coactivator-associated arginine methyltransferase 1 (CARM1) belongs to the protein arginine methyltransferase family. CARM1 has been reported to be associated with high grade tumors in breast cancer. It still remains unknown the expression pattern of CARM1 in breast cancer and its relationships with clinicopathological characteristics and molecular subtypes.

METHODS

Two hundred forty-seven invasive breast cancer cases were collected and prepared for tissue array. There were thirty-seven tumors with benign glandular epithelium adjacent to the tumors among these cases. Molecular subtype and CARM1 expression were investigated using immunohistochemistry.

RESULTS

Cell staining was observed in the cytoplasm and/or nucleus. Staining for CARM1 was significantly stronger in adenocarcinoma compared with adjacent benign epithelium. There is a significant correlation between CARM1 overexpression with young age, high grade, estrogen receptor (ER) and progesterone receptor (PR) negative, increased p53 expression, and high Ki-67 index. Our study demonstrated CARM1 overexpression was associated with an increase in the protein expression of HER2. Furthermore, our data indicated CARM1-overexpression rate were remarkably higher in HER2 subtype (69.6%), luminal B subtype (59.6%) and TN subtype (57.1%) compared with luminal A subtype (41.3%).

CONCLUSIONS

CARM1 expression was increased in invasive breast cancer. CARM1 overexpression was associated with poorly characterized clinicopathologic parameters and HER2 overexpression. There were significant differences between different molecular subtypes in their relationship to CARM1 overexpression. Our results support the value of using CARM1 in prognostic stratification of breast cancer patients and its potential therapeutic implications in targeting treatment.

VIRTUAL SLIDES

The virtual slide(s) for this article can be found here: http://www.diagnosticpathology.diagnomx.eu/vs/4116338491022965.

CARM1 automethylation is controlled at the level of alternative splicing

Co-activator-associated arginine methyltransferase 1 (CARM1) is subjected to multiple post-translational modifications. Our previous finding that automethylation of CARM1 is essential for regulation of transcription and pre-mRNA splicing prompted us to investigate how automethylation is regulated. Here, we report that automethylation is regulated by alternative splicing of CARM1 mRNA to remove exon 15, containing the automethylation site. Specifically, we find that two major alternative transcripts encoding full-length CARM1 (CARM1FL) and CARM1 with exon 15 deleted (CARM1ΔE15) exist in cells, and each transcript produces the expected protein. Further biochemical characterizations of the automethylation-defective mutant and CARM1ΔE15 reveal overlapping yet different properties. Interestingly, other arginine methylation substrates also have missing exons encompassing the site(s) of methylation, suggesting that protein arginine methylation level may, in general, be controlled by the alternative splicing mechanism. Finally, we observed differential distribution of CARM1FL and CARM1ΔE15 in epithelial and stromal cells in normal mouse mammary gland. Thus, alternative splicing not only serves as the determinant for CARM1 automethylation but also generates cell type-specific isoforms that might regulate normal ERα biology in the mammary gland.

Transcriptional regulation of the human ferritin gene by coordinated regulation of Nrf2 and protein arginine methyltransferases PRMT1 and PRMT4

Antioxidant genes such as ferritin are transcriptionally activated in oxidative stress via the antioxidant responsive element (ARE), to which nuclear factor-E2-related factor 2 (Nrf2) binds and activates transcription. Histone modification plays a cooperative and essential role in transcriptional regulation; however, its role in antioxidant gene transcription remains elusive. Arsenic exposure activated ferritin transcription via the ARE concomitant with increased methylation of histones H4Arg3 (H4R3) and H3Arg17 (H3R17). To test our hypothesis that histone H4R3 and H3R17 methylation regulates ferritin transcription, H4R3 and H3R17 protein arginine (R) methyltransferases 1 and 4 (PRMT1 and PRMT4) were investigated. Arsenic exposure of human HaCaT keratinocytes induced nuclear accumulation of PRMT1 and PRMT4, histone H4R3 and H3R17 methylation proximal to the ARE, but not to the non-ARE regions of ferritin genes. PRMT1 or PRMT4 knockdown did not block Nrf2 nuclear accumulation but inhibited Nrf2 binding to the AREs by ∼40% (P<0.05), thus diminishing ferritin transcription in HaCaT and human primary keratinocytes and fibroblasts, causing enhanced cellular susceptibility to arsenic toxicity as evidenced by 2-fold caspase 3 activation. Focused microarray further characterized several oxidative stress response genes are subject to PRMT1 or PRMT4 regulation. Collectively, PRMT1 and PRMT4 regulate the ARE and cellular antioxidant response to arsenic.

Molecular pathways: environmental estrogens activate nongenomic signaling to developmentally reprogram the epigenome

Exposure to environmental xenoestrogens is a major health concern because of the ability of these compounds to perturb estrogen receptor (ER) signaling and act as endocrine disrupting compounds (EDC). Inappropriate exposure to EDCs during development, even at low doses, can predispose individuals to an increased lifetime risk of disease, including cancer. Recent data indicate that perinatal exposure to EDCs increases cancer risk by (re)programming the epigenome via alterations in DNA and histone methylation. We and others have begun to dissect the mechanisms by which xenoestrogens disrupt the epigenetic machinery to reprogram the epigenome and induce developmental reprogramming. Our studies revealed that xenoestrogens induce nongenomic ER signaling to activate PI3K/AKT, resulting in AKT phosphorylation and inactivation of the histone methyltransferase EZH2, thus providing a direct link to disruption of the epigenome. Other epigenetic "readers, writers, and erasers" may also be targeted by nongenomic signaling, suggesting this is a central mechanism by which xenoestrogens and other EDCs disrupt the epigenome to induce developmental reprogramming. Elucidating mechanisms of developmental reprogramming of the epigenome is important for understanding how environmental exposures increase cancer risk, and provides a rationale for developing epigenetic interventions that can reverse the effects of environmental exposures to reduce cancer risk.

Emerging roles for chromatin as a signal integration and storage platform

Cells of a multicellular organism, all containing nearly identical genetic information, respond to differentiation cues in variable ways. In addition, cells are plastic, able to execute their specialized function while maintaining the ability to adapt to environmental changes. This is achieved through multiple mechanisms, including the direct regulation of chromatin-based processes in response to stimuli. How signal transduction pathways directly communicate with chromatin to change the epigenetic landscape is poorly understood. The preponderance of covalent modifications on histone tails coupled with a relatively small number of functional outputs raises the possibility that chromatin acts as a site of signal integration and storage.