Targeting protein arginine methyltransferase 5 inhibits colorectal cancer growth by decreasing arginine methylation of eIF4E and FGFR3

Inhibition of PRMT5-mediated regulation of DKK1 sensitizes colorectal cancer cells to chemotherapy

The Dickkopf family proteins (DKKs) are strong Wnt signaling antagonists that play a significant role in colorectal cancer (CRC) development and progression. Recent work has shown that DKKs, mainly DKK1, are associated with the induction of chemoresistance in CRC and that DKK1 expression in cancer cells correlates with that of protein arginine N-methyltransferase 5 (PRMT5). This points to the presence of a regulatory loop between DKK1 and PRMT5. Herein, we addressed the question of whether PRMT5 contributes to DKK1 expression in CRC and hence CRC chemoresistance. Both in silico and in vitro approaches were used to explore the relationship between PRMT5 and different DKK members. Our data demonstrated that DKK1 expression is significantly upregulated in CRC clinical samples, KRAS-mutated CRC in particular and that the levels of DKK1 positively correlate with PRMT5 activation. Chromatin immunoprecipitation (ChIP) data indicated a possible epigenetic role of PRMT5 in regulating DKK1, possibly through the symmetric dimethylation of H3R8. Knockdown of DKK1 or treatment with the PRMT5 inhibitor CMP5 in combination with doxorubicin yielded a synergistic anti-tumor effect in KRAS mutant, but not KRAS wild-type, CRC cells. These findings suggest that PRMT5 regulates DKK1 expression in CRC and that inhibition of PRMT5 modulates DKK1 expression in such a way that reduces CRC cell growth.

Combined inhibition of MTAP and MAT2a mimics synthetic lethality in tumor models via PRMT5 inhibition

Homozygous 5'-methylthioadenosine phosphorylase (MTAP) deletions occur in approximately 15% of human cancers. Co-deletion of MTAP and methionine adenosyltransferase 2 alpha (MAT2a) induces a synthetic lethal phenotype involving protein arginine methyltransferase 5 (PRMT5) inhibition. MAT2a inhibitors are now in clinical trials for genotypic MTAP-/- cancers, however the MTAP-/- genotype represents fewer than 2% of human colorectal cancers (CRCs), limiting the utility of MAT2a inhibitors in these and other MTAP+/+ cancers. Methylthio-DADMe-immucillin-A (MTDIA) is a picomolar transition state analog inhibitor of MTAP that renders cells enzymatically MTAP-deficient to induce the MTAP-/- phenotype. Here, we demonstrate that MTDIA and MAT2a inhibitor AG-270 combination therapy mimics synthetic lethality in MTAP+/+ CRC cell lines with similar effects in mouse xenografts and without adverse histology on normal tissues. Combination treatment is synergistic with a 104-fold increase in drug potency for inhibition of CRC cell growth in culture. Combined MTDIA and AG-270 decreases S-adenosyl-L-methionine and increases 5'-methylthioadenosine in cells. The increased intracellular methylthioadenosine:S-adenosyl-L-methionine ratio inhibits PRMT5 activity, leading to cellular arrest and apoptotic cell death by causing MDM4 alternative splicing and p53 activation. Combination MTDIA and AG-270 treatment differs from direct inhibition of PRMT5 by GSK3326595 by avoiding toxicity caused by cell death in the normal gut epithelium induced by the PRMT5 inhibitor. The combination of MTAP and MAT2a inhibitors expands this synthetic lethal approach to include MTAP+/+ cancers, especially the remaining 98% of CRCs without the MTAP-/- genotype.

Post-translational modifications of lysine-specific demethylase 1

Lysine-specific demethylase 1 (LSD1) is crucial for regulating gene expression by catalyzing the demethylation of mono- and di-methylated histone H3 lysine 4 (H3K4) and lysine 9 (H3K9) and non-histone proteins through the amine oxidase activity with FAD+ as a cofactor. It interacts with several protein partners, which potentially contributes to its diverse substrate specificity. Given its pivotal role in numerous physiological and pathological conditions, the function of LSD1 is closely regulated by diverse post-translational modifications (PTMs), including phosphorylation, ubiquitination, methylation, and acetylation. In this review, we aim to provide a comprehensive understanding of the regulation and function of LSD1 following various PTMs. Specifically, we will focus on the impact of PTMs on LSD1 function in physiological and pathological contexts and discuss the potential therapeutic implications of targeting these modifications for the treatment of human diseases.

The arginine methyltransferase PRMT5 promotes mucosal defense in the intestine

PRMT5 is a type II arginine methyltransferase abundantly expressed in the colonic epithelium. It is up-regulated in inflammatory bowel disease and colorectal cancer. However, its role in mucosal defense against enteric infection has not been studied. Here, we report that Prmt5 in the murine colon is up-regulated in response to Citrobacter rodentium infection. Pathogen clearance in mice with haploinsufficient expression of Prmt5 is significantly delayed compared with wildtype littermate controls. Transcriptomic analyses further reveal that PRMT5 regulates the expression of canonical crypt goblet cell genes involved in mucus production, assembly, and anti-microbial responses via methyltransferase activity-dependent and -independent mechanisms. Together, these findings uncover PRMT5 as a novel regulator of mucosal defense and a potential therapeutic target for treating intestinal diseases.

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.

FGFR families: biological functions and therapeutic interventions in tumors

There are five fibroblast growth factor receptors (FGFRs), namely, FGFR1-FGFR5. When FGFR binds to its ligand, namely, fibroblast growth factor (FGF), it dimerizes and autophosphorylates, thereby activating several key downstream pathways that play an important role in normal physiology, such as the Ras/Raf/mitogen-activated protein kinase kinase/extracellular signal-regulated kinase, phosphoinositide 3-kinase (PI3K)/AKT, phospholipase C gamma/diacylglycerol/protein kinase c, and signal transducer and activator of transcription pathways. Furthermore, as an oncogene, FGFR genetic alterations were found in 7.1% of tumors, and these alterations include gene amplification, gene mutations, gene fusions or rearrangements. Therefore, FGFR amplification, mutations, rearrangements, or fusions are considered as potential biomarkers of FGFR therapeutic response for tyrosine kinase inhibitors (TKIs). However, it is worth noting that with increased use, resistance to TKIs inevitably develops, such as the well-known gatekeeper mutations. Thus, overcoming the development of drug resistance becomes a serious problem. This review mainly outlines the FGFR family functions, related pathways, and therapeutic agents in tumors with the aim of obtaining better outcomes for cancer patients with FGFR changes. The information provided in this review may provide additional therapeutic ideas for tumor patients with FGFR abnormalities.

A patent review of PRMT5 inhibitors to treat cancer (2018 - present)

INTRODUCTION

Protein arginine methyltransferases 5 (PRMT5) belongs to type II arginine methyltransferases. Since PRMT5 plays an essential role in mammalian cells, it can regulate various physiological functions, including cell growth and differentiation, DNA damage repair, and cell signal transduction. It is an epigenetic target with significant clinical potential and may become a powerful drug target for treating cancers and other diseases.

AREAS COVERED

This review provides an overview of small molecule inhibitors and their associated combined treatment strategies targeting PRMT5 in cancer treatment patents published since 2018, and also summarizes the progress made by several biopharmaceutical companies in the development, application, and clinical trials of small molecule PRMT5 inhibitors. The data in this review come from WIPO, UniProt, PubChem, RCSB PDB, National Cancer Institute, and so on.

EXPERT OPINION

Many PRMT5 inhibitors have been developed with good inhibitory activities, but most of them lack selectivities and are associated with adverse clinical responses. In addition, the progress was almost all based on the previously established skeleton, and more research and development of a new skeleton still needs to be done. The development of PRMT5 inhibitors with high activities and selectivities is still an essential aspect of research in recent years.

Mechanistic aspects of reversible methylation modifications of arginine and lysine of nuclear histones and their roles in human colon cancer

Developmental proceedings and maintenance of cellular homeostasis are regulated by the precise orchestration of a series of epigenetic events that eventually control gene expression. DNA methylation and post-translational modifications (PTMs) of histones are well-characterized epigenetic events responsible for fine-tuning gene expression. PTMs of histones bear molecular logic of gene expression at chromosomal territory and have become a fascinating field of epigenetics. Nowadays, reversible methylation on histone arginine and lysine is gaining increasing attention as a significant PTM related to reorganizing local nucleosomal structure, chromatin dynamics, and transcriptional regulation. It is now well-accepted and reported that histone marks play crucial roles in colon cancer initiation and progression by encouraging abnormal epigenomic reprogramming. It is becoming increasingly clear that multiple PTM marks at the N-terminal tails of the core histones cross-talk with one another to intricately regulate DNA-templated biological processes such as replication, transcription, recombination, and damage repair in several malignancies, including colon cancer. These functional cross-talks provide an additional layer of message, which spatiotemporally fine-tunes the overall gene expression regulation. Nowadays, it is evident that several PTMs instigate colon cancer development. How colon cancer-specific PTM patterns or codes are generated and how they affect downstream molecular events are uncovered to some extent. Future studies would address more about epigenetic communication, and the relationship between histone modification marks to define cellular functions in depth. This chapter will comprehensively highlight the importance of histone arginine and lysine-based methylation modifications and their functional cross-talk with other histone marks from the perspective of colon cancer development.

Type I arginine methyltransferases are intervention points to unveil the oncogenic Epstein-Barr virus to the immune system

The oncogenic Epstein-Barr virus (EBV) evades the immune system but has an Achilles heel: its genome maintenance protein EBNA1. Indeed, EBNA1 is essential for viral genome maintenance but is also highly antigenic. Hence, EBV seemingly evolved a system in which the glycine-alanine repeat (GAr) of EBNA1 limits the translation of its own mRNA to the minimal level to ensure its essential function, thereby, at the same time, minimizing immune recognition. Therefore, defining intervention points at which to interfere with GAr-based inhibition of translation is an important step to trigger an immune response against EBV-carrying cancers. The host protein nucleolin (NCL) plays a critical role in this process via a direct interaction with G-quadruplexes (G4) formed in the GAr-encoding sequence of the viral EBNA1 mRNA. Here we show that the C-terminal arginine-glycine-rich (RGG) motif of NCL is crucial for its role in GAr-based inhibition of translation by mediating interaction of NCL with G4 of EBNA1 mRNA. We also show that this interaction depends on the type I arginine methyltransferase family, notably PRMT1 and PRMT3: drugs or small interfering RNA that target these enzymes prevent efficient binding of NCL on G4 of EBNA1 mRNA and relieve GAr-based inhibition of translation and of antigen presentation. Hence, this work defines type I arginine methyltransferases as therapeutic targets to interfere with EBNA1 and EBV immune evasion.

Downregulation of PRMT5 by AMI-1 enhances therapeutic efficacy of compound kushen injection in lung carcinoma in vitro and in vivo

Protein arginine methyltransferase 5 (PRMT5) is overexpressed in lung carcinoma, which promotes tumor cell proliferation, survival, migration and invasion. Compound Kushen injection (CKI) is a mixture of natural compounds extracted from Kushen and Baituling, which are mainly used to stop in cancer pain and bleeding. Here we found that cell viability and colony formation were inhibited after the incubation of AMI-1. Meanwhile, AMI-1 suppressed cell migration, enhanced apoptosis, induced cell cycle arrest, inhibited PRMT5 expression and histone H3R8 and H4R3 symmetric di-methylation (H3R8me2s and H4R3me2s) accumulation, down-regulated the expression of eukaryotic translation initiation factor 4E (eIF4E) in lung carcinoma cells. Moreover, AMI-1 suppressed tumor growth, decreased H3R8me2s and H4R3me2s accumulation, down-regulated eIF4E expression and increased p53 expression in lung carcinoma xenografts of BALB/c nude mice. Of note, combined and CKI markedly enhanced the anticancer efficacy CKI in lung carcinoma. The above findings demonstrated that AMI-1 has established antineoplastic activity and this role may be associated with affecting the function of eIF4E via inhibiting PRMT5 activity or protein levels in lung carcinoma. This study highlights evidence of novel selective anticancer activity of AMI-1 in combination with CKI in lung carcinoma.

Ribavirin inhibits cell proliferation and metastasis and prolongs survival in soft tissue sarcomas by downregulating both protein arginine methyltransferases 1 and 5

Protein arginine methyltransferases 1 and 5 (PRMT1 and PRMT5) are frequently overexpressed in diverse types of cancers and correlate with poor prognosis, thus making these enzymes potential therapeutic targets. The aim of this study was to assess and elucidate the anti-tumour effect and epigenetic regulatory mechanism of ribavirin in soft tissue sarcomas (STS). We showed that ribavirin inhibited growth and metastasis and prolonged survival in animals bearing STS cells by downregulating the mRNA and protein levels of PRMT1/PRMT5 and attenuating the accumulation of asymmetric and symmetric di-methylation of arginine (ADMA and SDMA). Furthermore, ribavirin lowered the permeability of the peritoneum in KM mice bearing S180 ascites via decreasing the level of vascular endothelial growth factor (VEGF). Ribavirin was a potent inhibitor of cell proliferation and metastasis in STS cells through downregulation of both type I PRMT1 and type II PRMT5. Ribavirin could be used to enhance the efficacy of doxorubicin in STS allograft tumour models.

Discovery of novel PRMT5 inhibitors bearing a methylpiperazinyl moiety

Background: PRMT5 is an epigenetics-related enzyme, which plays a critical role in cancer development. Hence PRMT5 inhibition has been validated as a promising therapeutic strategy. Methods & Results: We synthesized a series of methylpiperazinyl derivatives as novel PRMT5 inhibitors that were achieved by scaffold-hopping from EPZ015666 by virtual screening followed by rational drug design. Among all compounds 43g, bearing a thiourea linker, showed antitumor activity across multiple cancer cell lines and reduced the level of symmetric arginine dimethylation of SmD3 dose-dependently. Moreover, 43g selectively inhibited PRMT5 among protein arginine methyltransferase isoforms. Further proteomics analysis revealed that 43g remarkably reduced the global arginine dimethylation level in a cellular context. Conclusion: This work provides new chemical templates for future structural optimization of PRMT5-related cancer treatments.

Identification of PRMT5 inhibitors with novel scaffold structures through virtual screening and biological evaluations

Protein arginine methyltransferase 5 (PRMT5), an important member in PRMT family, has been validated as a promising anticancer target. In this study, through the combination of virtual screening and biological experiments, we have identified two PRMT5 inhibitors with novel scaffold structures. Among them, compound Y2431 showed moderate activity with IC₅₀ value of 10.09 μM and displayed good selectivity against other methyltransferases. The molecular docking analysis and molecular dynamics (MD) simulations suggested that the compound occupied the substrate-arginine binding site. Furthermore, Y2431 exhibited anti-proliferative activity to leukemia cells by inducing cell cycle arrest. Overall, the hit compound could provide a novel scaffold for further optimization of small-molecule PRMT5 inhibitors.

Integration of Transcriptomics and Metabolomics Reveals the Antitumor Mechanism Underlying Tadalafil in Colorectal Cancer

The potential role of tadalafil, a PDE5 inhibitor, in anticancer activity and prolonged survival has been proposed. However, the systematic effects of tadalafil in colorectal cancer were not fully understood. In this study, we assessed the anti-tumor activity of tadalafil in human colorectal cancer cells. A systematic perspective of the tadalafil-induced anti-tumor mechanism was provided by the integration of transcriptomics and metabolomics. We found that differentially expressed genes (DEGs) were mainly involved in microRNAs in cancer, purine metabolism, glycosphingolipid biosynthesis, arginine biosynthesis, and amino acid metabolism. Amino acid metabolism, especially alanine, aspartate, and glutamate metabolism was the most of the differentially accumulated metabolites (DAMs) through the analysis of metabolomics. The conjoint analysis of DEGs and DAMs presented that they were also mainly involved in alanine, aspartate, and glutamate metabolism. Amino acid metabolism-related genes, GPT, GGT5, and TAT, were significantly decreased after tadalafil treatment. In particular, the disturbance of alanine, aspartate, and glutamate metabolism may be the explanation for the major mechanism resulting from tadalafil anti-tumor activity.

Proteomics of post-translational modifications in colorectal cancer: Discovery of new biomarkers

Colorectal cancer (CRC) is one of the costliest health problems and ranks second in cancer-related mortality in developed countries. With the aid of proteomics, many protein biomarkers for the diagnosis, prognosis, and precise management of CRC have been identified. Furthermore, some protein biomarkers exhibit structural diversity after modifications. Post-translational modifications (PTMs), most of which are catalyzed by a variety of enzymes, extensively increase protein diversity and are involved in many complex and dynamic cellular processes through the regulation of protein function. Accumulating evidence suggests that abnormal PTM events are associated with a variety of human diseases, such as CRC, thus highlighting the need for studying PTMs to discover both the molecular mechanisms and therapeutic targets of CRC. In this review, we begin with a brief overview of the importance of protein PTMs, discuss the general strategies for proteomic profiling of several key PTMs (including phosphorylation, acetylation, glycosylation, ubiquitination, methylation, and citrullination), shift the emphasis to describing the specific methods used for delineating the global landscapes of each of these PTMs, and summarize the recent applications of these methods to explore the potential roles of the PTMs in CRC. Finally, we discuss the current status of PTM research on CRC and provide future perspectives on how PTM regulation can play an essential role in translational medicine for early diagnosis, prognosis stratification, and therapeutic intervention in CRC.

Protein Arginine Methylation: An Emerging Modification in Cancer Immunity and Immunotherapy

In recent years, protein arginine methyltransferases (PRMTs) have emerged as new members of a gene expression regulator family in eukaryotes, and are associated with cancer pathogenesis and progression. Cancer immunotherapy has significantly improved cancer treatment in terms of overall survival and quality of life. Protein arginine methylation is an epigenetic modification function not only in transcription, RNA processing, and signal transduction cascades, but also in many cancer-immunity cycle processes. Arginine methylation is involved in the activation of anti-cancer immunity and the regulation of immunotherapy efficacy. In this review, we summarize the most up-to-date information on regulatory molecular mechanisms and different underlying arginine methylation signaling pathways in innate and adaptive immune responses during cancer. We also outline the potential of PRMT-inhibitors as effective combinatorial treatments with immunotherapy.

Inhibition of PRMT5 by market drugs as a novel cancer therapeutic avenue

Market drugs, such as Food and Drug Administration (FDA) or European Medicines Agency (EMA)-approved drugs for specific indications provide opportunities for repurposing for newer therapeutics. This potentially saves resources invested in clinical trials that verify drug safety and tolerance in humans prior to alternative indication approval. Protein arginine methyltransferase 5 (PRMT5) overexpression has been linked to promoting the tumor phenotype in several cancers, including pancreatic ductal adenocarcinoma (PDAC), colorectal cancer (CRC), and breast cancer (BC), making PRMT5 an important target for cancer therapy. Previously, we showed that PRMT5-mediated methylation of the nuclear factor (NF)-κB, partially contributes to its constitutive activation observed in cancers. In this study, we utilized an AlphaLISA-based high-throughput screening method adapted in our lab, and identified one FDA-approved drug, Candesartan cilexetil (Can, used in hypertension treatment) and one EMA-approved drug, Cloperastine hydrochloride (Clo, used in cough treatment) that had significant PRMT5-inhibitory activity, and their anti-tumor properties were validated using cancer phenotypic assays in vitro. Furthermore, PRMT5 selective inhibition of methyltransferase activity was confirmed by reduction of both NF-κB methylation and its subsequent activation upon drug treatment. Using in silico prediction, we identified critical residues on PRMT5 targeted by these drugs that may interfere with its enzymatic activity. Finally, Clo and Can treatment have exhibited marked reduction in tumor growth in vivo. Overall, we provide basis for pursuing repurposing Clo and Can as anti-PRMT5 cancer therapies. Our study offers potential safe and fast repurposing of previously unknown PRMT5 inhibitors into clinical practice.

PRMT5 in T Cells Drives Th17 Responses, Mixed Granulocytic Inflammation, and Severe Allergic Airway Inflammation

Severe asthma is characterized by steroid insensitivity and poor symptom control and is responsible for most asthma-related hospital costs. Therapeutic options remain limited, in part due to limited understanding of mechanisms driving severe asthma. Increased arginine methylation, catalyzed by protein arginine methyltransferases (PRMTs), is increased in human asthmatic lungs. In this study, we show that PRMT5 drives allergic airway inflammation in a mouse model reproducing multiple aspects of human severe asthma. We find that PRMT5 is required in CD4⁺ T cells for chronic steroid-insensitive severe lung inflammation, with selective T cell deletion of PRMT5 robustly suppressing eosinophilic and neutrophilic lung inflammation, pathology, airway remodeling, and hyperresponsiveness. Mechanistically, we observed high pulmonary sterol metabolic activity, retinoic acid-related orphan receptor γt (RORγt), and Th17 responses, with PRMT5-dependent increases in RORγt's agonist desmosterol. Our work demonstrates that T cell PRMT5 drives severe allergic lung inflammation and has potential implications for the pathogenesis and therapeutic targeting of severe asthma.

Ribavirin inhibits the growth and ascites formation of hepatocellular carcinoma through downregulation of type I CARM1 and type II PRMT5

Type I co-activator-associated arginine methyltransferase 1 (CARM1) and type II protein arginine methyltransferase 5 (PRMT5) are highly expressed in multiple cancers including liver cancer and their overexpression contributes to poor prognosis, thus making them promising therapeutic targets. Here, we evaluated anti-tumor activity of ribavirin in hepatocellular carcinoma (HCC). We found that ribavirin significantly inhibited the proliferation of HCC cells in a time- and dose-dependent manner. Furthermore, ribavirin suppressed the growth of subcutaneous and orthotopic xenograft of HCC in mice, decreased vascular endothelial growth factor (VEGF) and peritoneal permeability to reduce ascites production, and prolonged the survival of mice in HCC ascites tumor models. Mechanistically, ribavirin potently down-regulated global protein expression of CARM1 and PRMT5, and concurrently decreased accumulation of H3R17me2a and H3R8me2s/H4R3me2s. However, ribavirin did not affect the activity and mRNA levels of both CARM1 and PRMT5 in vivo and in vitro HCC cells. In addition, our ChIP results shown that ribavirin inhibited CARM1 which in turn decreased the H3R17me2a, binds to the eukaryotic translation initiation factor 4E (eIF4E) and VEGF promoter region, and reduced the relative mRNA expression level of eIF4E and VEGF in HCC cells. Our findings suggested a potential therapeutic strategy for patients with HCC through inhibition of the abnormal activation/expression of both CARM1 and PRMT5.

Protein arginine N-methyltransferase 5 in colorectal carcinoma: Insights into mechanisms of pathogenesis and therapeutic strategies

Protein arginine N-methyltransferase 5 (PRMT5) enzyme is one of the eight canonical PRMTs, classified as a type II PRMT, induces arginine monomethylation and symmetric dimethylation. PRMT5 is known to be overexpressed in multiple cancer types, including colorectal cancer (CRC), where its overexpression is associated with poor survival. Recent studies have shown that upregulation of PRMT5 induces tumor growth and metastasis in CRC. Moreover, various novel PRMT5 inhibitors tested on CRC cell lines showed promising anticancer effects. Also, it was suggested that PRMT5 could be a valid biomarker for CRC diagnosis and prognosis. Hence, a deeper understanding of PRMT5-mediated CRC carcinogenesis could provide new avenues towards developing a targeted therapy. In this study, we started with in silico analysis correlating PRMT5 expression in CRC patients as a prelude to further our investigation of its role in CRC. We then carried out a comprehensive review of the scientific literature that dealt with the role(s) of PRMT5 in CRC pathogenesis, diagnosis, and prognosis. Also, we have summarized key findings from in vitro research using various therapeutic agents and strategies directly targeting PRMT5 or disrupting its function. In conclusion, PRMT5 seems to play a significant role in the pathogenesis of CRC; therefore, its prognostic and therapeutic potential merits further investigation.

Protein Arginine Methyltransferase 5 Promotes the Migration of AML Cells by Regulating the Expression of Leukocyte Immunoglobulin-Like Receptor B4

Acute myeloid leukemia (AML) is the most common type of acute leukemia in adults with poor prognosis. Especially for AML-M5 type, due to the strong cell migration ability, the possibility of extramedullary invasion is large and widespread, which leads to poor therapeutic effect. Previous studies have found that protein arginine methyltransferase 5 (PRMT5) could promote the proliferation and differentiation of leukemic cells in AML, but its regulation on the invasive ability of AML cells remains unclear. This study was designed to explore the role of PRMT5 in regulating the invasion of AML cells and to investigate the mechanisms. Patient samples were collected for detection of PRMT5 expression level. AML cells were used for exploring the function of PRMT5. The results of clinical samples showed that the expression of PRMT5 was significantly increased in newly diagnosed and recurrent AML patients, and the expression of leukocyte immunoglobulin-like receptor B4 (LILRB4) was positively correlated with the level of PRMT5. In the cell experiment in vitro, we found that when PRMT5 was knocked down, the invasion, migration, and adhesion capacities of MV-4-11 cells and THP-1 cells were decreased, and the mRNA and protein levels of LILRB4 were also decreased. Moreover, we screened related signaling pathways and found that PRMT5 affected the expression of downstream LILRB4 by activating mTOR pathway, which in turn enhanced the invasive ability of AML cells. Taken together, PRMT5 plays an important role in the invasion of AML, which acts via regulating the expression of LILRB4. PRMT5 could act as a potential therapeutic candidate for AML.

Targeting protein arginine methyltransferase 5 in cancers: Roles, inhibitors and mechanisms

The protein arginine methyltransferase 5 (PRMT5) as the major type II arginine methyltransferase catalyzes the mono- and symmetric dimethylation of arginine residues in both histone and non-histone proteins. Recently, increasing evidence has demonstrated that PRMT5 plays an indispensable role in the occurrence and development of various human cancers by promoting the cell proliferation, invasion, and migration. It has become a promising and valuable target in the cancer epigenetic therapy. This review is to summarize the clinical significance of PRMT5 in the cancers such as lung cancer, breast cancer and colorectal cancer, and the drug discovery targeting PRMT5. Importantly, the existing PRMT5 inhibitors representing different molecular mechanisms, and their pharmacological effect, mechanism of action and biological affinity are analyzed. Clinical status, current problems and future perspective of PRMT5 inhibitors for the treatment of cancers are also discussed, all of which provides crucial help for the future discovery of PRMT5 targeted drugs for cancer treatment.

Drug resistance in colorectal cancer: An epigenetic overview

Colorectal cancer (CRC) is a leading cause of cancer-related deaths worldwide. Despite significant progress that has been made in therapies against CRC over the past decades, drug resistance is still a major limitation in CRC treatment. Numerous investigations have unequivocally shown that epigenetic regulation plays an important role in CRC drug resistance because of the high rate of epigenetic alterations in multiple genes during cancer development or drug treatment. Furthermore, the reversibility of epigenetic alterations provides novel therapeutic strategies to overcome drug resistance using small molecules, which can target non-coding RNAs or reverse histone modification and DNA methylation. In this review, we discuss epigenetic regulation in CRC drug resistance and the possible role of preventing or reversing CRC drug resistance using epigenetic therapy in CRC treatment.

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.

PRMT5 Selective Inhibitor Enhances Therapeutic Efficacy of Cisplatin in Lung Cancer Cells

As a therapeutic approach, epigenetic modifiers have the potential to enhance the efficacy of chemotherapeutic agents. Protein arginine methyltransferase 5 (PRMT5), highly expressed in lung adenocarcinoma, was identified to be involved in tumorigenesis. In the current study, we examined the potential antineoplastic activity of PRMT5 inhibitor, arginine methyltransferase inhibitor 1 (AMI-1), and cisplatin on lung adenocarcinoma. Bioinformatic analyses identified apoptosis, DNA damage, and cell cycle progression as the main PRMT5-associated functional pathways, and survival analysis linked the increased PRMT5 gene expression to worse overall survival in lung adenocarcinoma. Combined AMI-1 and cisplatin treatment significantly reduced cell viability and induced apoptosis. Cell cycle arrest in A549 and DMS 53 cells was evident after AMI-1, and was reinforced after combination treatment. Western blot analysis showed a reduction in demethylation histone 4, a PRMT5- downstream target, after treatment with AMI-1 alone or in combination with cisplatin. While the combination approach tackled lung cancer cell survival, it exhibited cytoprotective abilities on HBEpC (normal epithelial cells). The survival of normal bronchial epithelial cells was not affected by using AMI-1. This study highlights evidence of novel selective antitumor activity of AMI-1 in combination with cisplatin in lung adenocarcinoma cells.

Validation of protein arginine methyltransferase 5 (PRMT5) as a candidate therapeutic target in the spontaneous canine model of non-Hodgkin lymphoma

Non-Hodgkin lymphoma (NHL) is a heterogeneous group of blood cancers arising in lymphoid tissues that commonly effects both humans and dogs. Protein arginine methyltransferase 5 (PRMT5), an enzyme that catalyzes the symmetric di-methylation of arginine residues, is frequently overexpressed and dysregulated in both human solid and hematologic malignancies. In human lymphoma, PRMT5 is a known driver of malignant transformation and oncogenesis, however, the expression and role of PRMT5 in canine lymphoma has not been explored. To explore canine lymphoma as a useful comparison to human lymphoma while validating PRMT5 as a rational therapeutic target in both, we characterized expression patterns of PRMT5 in canine lymphoma tissue microarrays, primary lymphoid biopsies, and canine lymphoma-derived cell lines. The inhibition of PRMT5 led to growth suppression and induction of apoptosis, while selectively decreasing global marks of symmetric dimethylarginine (SDMA) and histone H4 arginine 3 symmetric dimethylation. We performed ATAC-sequencing and gene expression microarrays with pathway enrichment analysis to characterize genome-wide changes in chromatin accessibility and whole-transcriptome changes in canine lymphoma cells lines upon PRMT5 inhibition. This work validates PRMT5 as a promising therapeutic target for canine lymphoma and supports the continued use of the spontaneously occurring canine lymphoma model for the preclinical development of PRMT5 inhibitors for the treatment of human NHL.

Stochastic modulation evidences a transitory EGF-Ras-ERK MAPK activity induced by PRMT5

The extracellular signal-regulated kinase (ERK) mitogen-activated protein kinase (MAPK) pathway involves a three-step cascade of kinases that transduce signals and promote processes such as cell growth, development, and apoptosis. An aberrant response of this pathway is related to the proliferation of cell diseases and tumors. By using simulation modeling, we document that the protein arginine methyltransferase 5 (PRMT5) modulates the MAPK pathway and thus avoids an aberrant behavior. PRMT5 methylates the Raf kinase, reducing its catalytic activity and thereby, reducing the activation of ERK in time and amplitude. Two minimal computational models of the epidermal growth factor (EGF)-Ras-ERK MAPK pathway influenced by PRMT5 were proposed: a first model in which PRMT5 is activated by EGF and a second one in which PRMT5 is stimulated by the cascade response. The reported results show that PRMT5 reduces the time duration and the expression of the activated ERK in both cases, but only in the first model PRMT5 limits the EGF range that generates an ERK activation. Based on our data, we propose the protein PRMT5 as a regulatory factor to develop strategies to fight against an excessive activity of the MAPK pathway, which could be of use in chronic diseases and cancer.

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.

Ribavirin inhibits colorectal cancer growth by downregulating PRMT5 expression and H3R8me2s and H4R3me2s accumulation

Eukaryotic translation initiation factor 4E (eIF4E) and protein arginine methyltransferase 5 (PRMT5) are frequently overexpressed in colorectal cancer (CRC) tissues and associated with poor prognosis. Ribavirin, the only clinically approved drug known to target eIF4E, is an anti-viral molecule currently used in hepatitis C therapy. The potential of ribavirin to treat CRC remains largely unknown. Ribavirin treatment in CRC cell lines drastically inhibited cell proliferation and colony formation, induced S phase arrest and reduced cyclin D1, cyclin A/E and proliferating cell nuclear antigen (PCNA) levels in vitro, and suppressed tumorigenesis in mouse model of colitis-associated CRC. Mechanistically, ribavirin treatment significantly reduced PRMT5 and eIF4E protein levels and the accumulation of symmetric dimethylation of histone 3 at arginine 8 (H3R8me2s) and that of histone 4 at arginine 3 (H4R3me2s). Importantly, inhibition of PRMT5 by ribavirin resulted in promoted H3R8 methylation in eIF4E promoter region. Our results demonstrate the anti-cancer efficacy of ribavirin in CRC and suggest that the anti-cancer efficacy of ribavirin may be mediated by downregulating PRMT5 levels but not its enzymatic activity.

PRMT5 promotes colorectal cancer growth by interaction with MCM7

Protein arginine methyltransferase 5 (PRMT5) is a type of methyltransferase enzyme that can catalyse arginine methylation of histones and non‐histone proteins. Accumulating evidence indicates that PRMT5 promotes cancer development and progression. However, its function in colorectal cancer (CRC) is poorly understood. In this study, we revealed the oncogenic roles of PRMT5 in CRC. We found that PRMT5 promoted CRC cell proliferation, migration and invasion in vitro and in vivo. We identified minichromosome maintenance‐7 (MCM7) as the direct PRMT5‐binding partner. A co‐immunoprecipitation (co‐IP) assay indicated that PRMT5 physically interacted with MCM7 and that the direct binding domain was located between residues 1‐248 in MCM7. In addition, our results from analysis of 99 CRC tissues and 77 adjacent non‐cancerous tissues indicated that the PRMT5 and MCM7 expression levels were significantly higher in CRC tissues than in control tissues, which was further confirmed by bioinformatic analysis using TCGA and GEO datasets. We also found that MCM7 promoted CRC cell proliferation, migration and invasion in vitro. Furthermore, we observed that increased PRMT5 expression predicted unfavourable patient survival in CRC patients and in the subgroup of patients with a tumour size of ≤5 cm. These data suggested that PRMT5 and MCM7 might be novel potential targets for the treatment of CRC.

PRMT5 functionally associates with EZH2 to promote colorectal cancer progression through epigenetically repressing CDKN2B expression

Background: Protein arginine methyltransferase 5 (PRMT5) is a type II arginine methyltransferase that symmetrically di-methylates arginine residues on both histone and non-histone protein substrates. Accumulating evidence suggests that PRMT5 exerts its oncogenic properties in a wide spectrum of human malignancies. However, the underlying mechanisms by which PRMT5 contributes to the progression of colorectal cancer (CRC) remain to be defined.

Methods: Western blot and real-time PCR were used to analyze the expression of CDKN2B. Co-immunoprecipitation (Co-IP), immunofluorescence and GST pulldown assays were employed to investigate the interaction between PRMT5 and EZH2. Luciferase reporter and chromatin immunoprecipitation (ChIP) assays were performed to validate CDKN2B as a direct target of PRMT5/EZH2. DNA methylation status at the CpG islands of promoter region of CDKN2B gene was analyzed by bisulfite sequencing. The effect of PRMT5/EZH2 on malignant phenotypes was examined through in vitro and in vivo assays. PRMT5 and EZH2 protein expression levels in CRC tissues were analyzed by immunohistochemistry (IHC) staining.

Results: We observed that PRMT5-deficient CRC cells exhibit proliferation defects in vitro. PRMT5 was identified as a major transcriptional repressor of CDKN2B (p15^INK4b) for determining CRC progression. Mechanistically, PRMT5-mediated histone marks H4R3me2s and H3R8me2s were predominantly deposited at the promoter region of CDKN2B gene in CRC cells. Knockdown of PRMT5 in CRC cells decreased the accumulation of H4R3me2s and H3R8me2s marks and reduced the CpG methylation level of CDKN2B promoter, then re-activated CDKN2B expression. Strikingly, silencing of CDKN2B partially abrogated the proliferation defects caused by PRMT5 depletion in vitro and in vivo. Furthermore, we proved that PRMT5 interacted with Enhancer of zeste homolog 2 (EZH2), leading to enhanced EZH2 binding and H3K27me3 deposition together with decreased transcriptional output of CDKN2B gene. Importantly, we found that the combined interventions exerted a synergistic inhibitory effect of combined treatment with PRMT5i (GSK591) and EZH2i (GSK126) on the growth of CRC cells/xenografts in vitro and in vivo. Moreover, PRMT5 and EZH2 were found to be significantly elevated and associated with poor prognosis in CRC patients.

Conclusion: PRMT5 functionally associates with EZH2 to promote CRC progression through epigenetically repressing CDKN2B expression. Thus, our findings raise the possibility that combinational intervention of PRMT5 and EZH2 may be a promising strategy for CRC therapy.

PRMT5 regulates colorectal cancer cell growth and EMT via EGFR/Akt/GSK3β signaling cascades

Emerging evidence shows that type II protein arginine methyltransferase 5 (PRMT5) serves as an oncoprotein and plays a critical role in many types of human cancer. However, the precise role and function of PRMT5 in human colorectal cancer (CRC) growth and epithelial-mesenchymal transition (EMT) are still unclear, and the related molecular mechanism and signaling axis remains largely obscure. Here, we show that PRMT5 is highly expressed in CRC cell lines and tissues. Using PRMT5 stable depletion cell lines and specific inhibitor, we discover that down-regulation of PRMT5 by shRNA or inhibition of PRMT5 activity by specific inhibitor GSK591 markedly suppresses CRC cell proliferation and cell cycle progression, which is closely associated with PRMT5 enzyme activity. Moreover, PRMT5 regulates CRC cell growth and cycle progression via activation of Akt, but not through ERK1/2, PTEN, and mTOR signaling pathway. Further study shows that PRMT5 controls EMT of CRC cells by activation of EGFR/Akt/GSK3β signaling cascades. Collectively, our results reveal that PRMT5 promotes CRC cell proliferation, cell cycle progression, and EMT via regulation of EGFR/Akt/GSK3β signaling cascades. Most importantly, our findings also suggest that PRMT5 may be a potential therapeutic target for the treatment of human colorectal cancer.

Protein arginine methyltransferase 5: a potential cancer therapeutic target

BACKGROUND

PRMT5 is a type II protein arginine methyltransferase that methylates histone or non-histone proteins. Arginine methylation by PRMT5 has been implicated in gene transcription, ribosome biogenesis, RNA transport, pre-mRNA splicing and signal transduction. High expression of PRMT5 has been observed in various cancers and PRMT5 overexpression has been reported to improve cancer cell survival, proliferation, migration and metabolism and to inhibit cancer cell apoptosis. In addition, PRMT5 has been found to be required for cancer stem cell survival, self-renewal and differentiation. Several microRNAs have been shown to regulate PRMT5 expression. As PRMT5 has oncogene-like properties, several PRMT5 inhibitors have been used to explore their efficacy as potential drugs for different types of cancer, and three of them are now being tested in clinical trials.

CONCLUSIONS

In this review, we summarize current knowledge on the role of PRMT5 in cancer development and progression, including its functions and underlying mechanisms. In addition, we highlight the rapid development of PRMT5 inhibitors and summarize ongoing clinical trials for cancer therapy. By affecting both tumor cells and the tumor microenvironment, PRMT5 inhibitors may serve as effective anti-cancer agents, especially when combined with immune therapies.

Protein arginine methyltransferase 5 (PRMT5) activates WNT/β-catenin signalling in breast cancer cells via epigenetic silencing of DKK1 and DKK3

Protein arginine methyltransferase 5 (PRMT5) activity is dysregulated in many aggressive cancers and its enhanced levels are associated with increased tumour growth and survival. However, the role of PRMT5 in breast cancer remains underexplored. In this study, we show that PRMT5 is overexpressed in breast cancer cell lines, and that it promotes WNT/β-CATENIN proliferative signalling through epigenetic silencing of pathway antagonists, DKK1 and DKK3, leading to enhanced expression of c-MYC, CYCLIN D1 and SURVIVIN. Through chromatin immunoprecipitation (ChIP) studies, we found that PRMT5 binds to the promoter region of WNT antagonists, DKK1 and DKK3, and induces symmetric methylation of H3R8 and H4R3 histones. Our findings also show that PRMT5 inhibition using a specific small molecule inhibitor, compound 5 (CMP5), reduces PRMT5 recruitment as well as methylation of H3R8 and H4R3 histones in the promoter regions of DKK1 and DKK3, which consequently results in reduced expression CYCLIN D1 and SURVIVIN. Furthermore, CMP5 treatment either alone or in combination with 5-Azacytidine and Trichostatin A restored expression of DKK1 and DKK3 in TNBCs. PRMT5 inhibition also altered the growth characteristics of breast cancer cells and induced their death. Collectively, these results show that PRMT5 controls breast cancer cell growth through epigenetic silencing of WNT/β-CATENIN pathway antagonists, DKK1 and DKK3, resulting in up-regulation of WNT/β-CATENIN proliferative signalling.

Arginine Methylation in Brain Tumors: Tumor Biology and Therapeutic Strategies

Protein arginine methylation is a common post-translational modification that plays a pivotal role in cellular regulation. Protein arginine methyltransferases (PRMTs) catalyze the modification of target proteins by adding methyl groups to the guanidino nitrogen atoms of arginine residues. Protein arginine methylation takes part in epigenetic and cellular regulation and has been linked to neurodegenerative diseases, metabolic diseases, and tumor progression. Aberrant expression of PRMTs is associated with the development of brain tumors such as glioblastoma and medulloblastoma. Identifying PRMTs as plausible contributors to tumorigenesis has led to preclinical and clinical investigations of PRMT inhibitors for glioblastoma and medulloblastoma therapy. In this review, we discuss the role of arginine methylation in cancer biology and provide an update on the use of small molecule inhibitors of PRMTs to treat glioblastoma, medulloblastoma, and other cancers.

Clinicopathological and Prognostic Significance of PRMT5 in Cancers: A System Review and Meta-Analysis

PURPOSE

Since protein arginine methyltransferase 5 (PRMT5) is abnormally expressed in various tumors, in this study we aim to assess the association between PRMT5 and clinicopathological and prognostic features.

METHODS

Electronic databases including PubMed, Web of Science, Scopus, ScienceDirect, and the Cochrane Library were searched until July 25, 2021. The critical appraisal of the eligible studies was performed using the Newcastle-Ottawa Quality Assessment Scale. Pooled hazard ratios (HR) and pooled odds ratios (OR) were calculated to assess the effect. Engauge Digitizer version 12.1, STATA version 15.1, and R version 4.0.5 were used to obtain and analysis the data.

RESULTS

A total of 32 original studies covering 15,583 patients were included. In our data, it indicated that high level of PRMT5 was significantly correlated with advanced tumor stage (OR = 2.12, 95% CI: 1.22-3.70, P =.008; I2 = 80.7%) and positively correlated with poor overall survival (HR = 1.59, 95% CI: 1.46-1.73, P < .001; I2 = 50%) and progression-free survival (HR = 1.53, 95% CI: 1.24-1.88, P < .001; I2 = 0%). In addition, sub-group analysis showed that high level of PRMT5 was associated with poor overall survival for such 5 kinds of cancers as hepatocellular carcinoma, pancreatic cancer, breast cancer, gastric cancer, and lung cancer.

CONCLUSION

For the first time we found PRMT5 was pan-cancerous as a prognostic biomarker and high level of PRMT5 was associated with poor prognosis for certain cancers.

Protein Arginine Methyltransferase 5 (PRMT5) and the ERK1/2 & PI3K Pathways: A Case for PRMT5 Inhibition and Combination Therapies in Cancer

The ERK1/2 (RAS, RAF, MEK, ERK) and PI3K (PI3K, AKT, mTOR, PTEN) pathways are the chief signaling pathways for cellular proliferation, survival, and differentiation. Overactivation and hyperphosphorylation of the ERK1/2 & PI3K pathways is frequently observed in cancer and is associated with poor patient prognosis. While it is well known that genetic alterations lead to the dysregulation of the ERK1/2 & PI3K pathways, increasing evidence showcase that epigenetic alterations also play a major role in the regulation of the ERK1/2 & PI3K pathways. Protein Arginine Methyltransferase 5 (PRMT5) is a posttranslational modifier for multiple cellular processes, which is currently being tested as a therapeutic target for cancer. PRMT5 has been shown to be overexpressed in many types of cancers, as well as negatively correlated with patient survival. Numerous studies are indicating that as a posttranslational modifier, PRMT5 is extensively involved in regulating the ERK1/2 & PI3K pathways. In addition, a large number of in vitro and in vivo studies are demonstrating that PRMT5 inhibition, as well as PRMT5 and ERK1/2 & PI3K combination therapies, show significant therapeutic effects in many cancer types. In this review, we explore the vast interactions that PRMT5 has with the ERK1/2 & PI3K pathways, and we make the case for further testing of PRMT5 inhibition, as well as PRMT5 and ERK1/2 & PI3K combination therapies, for the treatment of cancer.

Protein Arginine Methyltransferase 5 Promotes pICln-Dependent Androgen Receptor Transcription in Castration-Resistant Prostate Cancer

The majority of advanced prostate cancer therapies aim to inhibit androgen receptor (AR) signaling. However, AR reactivation inevitably drives disease progression to castration-resistant prostate cancer (CRPC). Here we demonstrate that protein arginine methyltransferase 5 (PRMT5) functions as an epigenetic activator of AR transcription in CRPC, requiring cooperation with a methylosome subunit pICln. In vitro and in xenograft tumors in mice, targeting PRMT5 or pICln suppressed growth of CRPC cells. Full-length AR and AR-V7 transcription activation required both PRMT5 and pICln but not MEP50. This activation of transcription was accompanied by PRMT5-mediated symmetric dimethylation of H4R3 at the proximal AR promoter. Further, knockdown of PRMT5 abolished the binding of pICln (but not vice versa) to the AR proximal promoter region, suggesting that PRMT5 recruits pICln to the AR promoter to activate AR transcription. Differential gene expression analysis in 22Rv1 cells confirmed that PRMT5 and pICln both regulate the androgen signaling pathway. In addition, PRMT5 and pICln protein expression positively correlated with AR and AR-V7 protein expression in CRPC tissues and their expression was highly correlated at the mRNA level across multiple publicly available CRPC datasets. Our results suggest that targeting PRMT5 or pICln may be explored as a novel therapy for CRPC treatment by suppressing expression of AR and AR splice variants to circumvent AR reactivation. SIGNIFICANCE: This study provides evidence that targeting PRMT5 can eliminate expression of AR and can be explored as a novel therapeutic approach to treat metastatic hormone-naïve and castration-resistant prostate cancer.

Transcriptional regulation by methyltransferases and their role in the heart: highlighting novel emerging functionality

Methyltransferases are a superfamily of enzymes that transfer methyl groups to proteins, nucleic acids, and small molecules. Traditionally, these enzymes have been shown to carry out a specific modification (mono-, di-, or trimethylation) on a single, or limited number of, amino acid(s). The largest subgroup of this family, protein methyltransferases, target arginine and lysine side chains of histone molecules to regulate gene expression. Although there is a large number of functional studies that have been performed on individual methyltransferases describing their methylation targets and effects on biological processes, no analyses exist describing the spatial distribution across tissues or their differential expression in the diseased heart. For this review, we performed tissue profiling in protein databases of 199 confirmed or putative methyltransferases to demonstrate the unique tissue-specific expression of these individual proteins. In addition, we examined transcript data sets from human heart failure patients and murine models of heart disease to identify 40 methyltransferases in humans and 15 in mice, which are differentially regulated in the heart, although many have never been functionally interrogated. Lastly, we focused our analysis on the largest subgroup, that of protein methyltransferases, and present a newly emerging phenomenon in which 16 of these enzymes have been shown to play dual roles in regulating transcription by maintaining the ability to both activate and repress transcription through methyltransferase-dependent or -independent mechanisms. Overall, this review highlights a novel paradigm shift in our understanding of the function of histone methyltransferases and correlates their expression in heart disease.

Protein Arginine Methyltransferase 5 as a Therapeutic Target for KRAS Mutated Colorectal Cancer

Nearly 45% of colorectal cancer (CRC) patients harbor a mutation in their KRAS gene for which, despite many years of research, there are still no targeted therapies available. Protein Arginine Methyltransferase 5 (PRMT5) is a transcription regulator for multiple cellular processes that is currently being tested as a potential target in several cancer types. PRMT5 has been previously shown to be overexpressed in approximately 75% of CRC patient tumor samples, as well as negatively correlated with CRC patient survival. Here, we provide evidence that PRMT5 can act as a surrogate target for mutated KRAS in CRC. Our findings show that PRMT5 expression is upregulated, as well as positively correlated with KRAS expression, in CRC patient datasets. Moreover, our results reveal that PRMT5 is further overexpressed in KRAS mutant CRC cells when compared to KRAS wild type (WT) CRC cells at both the transcriptional and translational levels. Additionally, our data demonstrate that this further overexpression of PRMT5 in the KRAS mutant CRC cells affects an even greater degree of growth inhibition, apoptosis, and cell cycle arrest, following treatment with PRMT5 inhibitor, when compared to the KRAS WT CRC cells. Our research therefore suggests for the first time that PRMT5 and KRAS may crosstalk, and thus, PRMT5 can potentially be used as a surrogate target for mutated KRAS in CRC.

PRMT5 function and targeting in cancer

Protein methyl transferases play critical roles in numerous regulatory pathways that underlie cancer development, progression and therapy-response. Here we discuss the function of PRMT5, a member of the nine-member PRMT family, in controlling oncogenic processes including tumor intrinsic, as well as extrinsic microenvironmental signaling pathways. We discuss PRMT5 effect on histone methylation and methylation of regulatory proteins including those involved in RNA splicing, cell cycle, cell death and metabolic signaling. In all, we highlight the importance of PRMT5 regulation and function in cancer, which provide the foundation for therapeutic modalities targeting PRMT5.

Regulation of a PRMT5/NF-κB Axis by Phosphorylation of PRMT5 at Serine 15 in Colorectal Cancer

The overexpression of PRMT5 is highly correlated to poor clinical outcomes for colorectal cancer (CRC) patients. Importantly, our previous work demonstrated that PRMT5 overexpression could substantially augment activation of the nuclear factor kappa B (NF-κB) via methylation of arginine 30 (R30) on its p65 subunit, while knockdown of PRMT5 showed the opposite effect. However, the precise mechanisms governing this PRMT5/NF-κB axis are still largely unknown. Here, we report a novel finding that PRMT5 is phosphorylated on serine 15 (S15) in response to interleukin-1β (IL-1β) stimulation. Interestingly, we identified for the first time that the oncogenic kinase, PKCι could catalyze this phosphorylation event. Overexpression of the serine-to-alanine mutant of PRMT5 (S15A), in either HEK293 cells or CRC cells HT29, DLD1, and HCT116 attenuated NF-κB transactivation compared to WT-PRMT5, confirming that S15 phosphorylation is critical for the activation of NF-κB by PRMT5. Furthermore, the S15A mutant when compared to WT-PRMT5, could downregulate a subset of IL-1β-inducible NF-κB-target genes which correlated with attenuated promoter occupancy of p65 at its target genes. Additionally, the S15A mutant reduced IL-1β-induced methyltransferase activity of PRMT5 and disrupted the interaction of PRMT5 with p65. Furthermore, our data indicate that blockade of PKCι-regulated PRMT5-mediated activation of NF-κB was likely through phosphorylation of PRMT5 at S15. Finally, inhibition of PKCι or overexpression of the S15A mutant attenuated the growth, migratory, and colony-forming abilities of CRC cells compared to the WT-PRMT5. Collectively, we have identified a novel PKCι/PRMT5/NF-κB signaling axis, suggesting that pharmacological disruption of this pivotal axis could serve as the basis for new anti-cancer therapeutics.

HMGB1: an overview of its versatile roles in the pathogenesis of colorectal cancer

BACKGROUND

In recent years, the high mobility group box-1 (HMGB1) protein, a damage-associated molecular pattern (DAMP) molecule, has been found to play multifunctional roles in the pathogenesis of colorectal cancer. Although much attention has been given to the diagnostic and prognostic values of HMGB1 in colorectal cancer, the exact functional roles of the protein as well as the mechanistic pathways involved have remained poorly defined. This systematic review aims to discuss what is currently known about the roles of HMGB1 in colorectal cancer development, growth and progression, and to highlight critical areas for future investigations. To achieve this, the bibliographic databases Pubmed, Scopus, Web of Science and ScienceDirect were systematically screened for articles from inception till June 2018, which address associations of HMGB1 with colorectal cancer.

CONCLUSIONS

HMGB1 plays multiple roles in promoting the pathogenesis of colorectal cancer, despite a few contradicting studies. HMGB1 may differentially regulate disease-related processes, depending on the redox status of the protein in colorectal cancer. Binding of HMGB1 to various protein partners may alter the impact of HMGB1 on disease progression. As HMGB1 is heavily implicated in the pathogenesis of colorectal cancer, it is crucial to further improve our understanding of the functional roles of HMGB1 not only in colorectal cancer, but ultimately in all types of cancers.

Protein Expression Profiling Identifies Key Proteins and Pathways Involved in Growth Inhibitory Effects Exerted by Guggulsterone in Human Colorectal Cancer Cells

Colorectal cancer (CRC) is a leading killer cancer worldwide and one of the most common malignancies with increasing incidences of mortality. Guggulsterone (GS) is a plant sterol used for treatment of various ailments such as obesity, hyperlipidemia, diabetes, and arthritis. In the current study, anti-cancer effects of GS in human colorectal cancer cell line HCT 116 was tested, potential targets identified using mass spectrometry-based label-free shotgun proteomics approach and key pathways validated by proteome profiler antibody arrays. Comprehensive proteomic profiling identified 14 proteins as significantly dysregulated. Proteins involved in cell proliferation/migration, tumorigenesis, cell growth, metabolism, and DNA replication were downregulated while the protein with functional role in exocytosis/tumor suppression was found to be upregulated. Our study evidenced that GS treatment altered expression of Bcl-2 mediated the mitochondrial release of cytochrome c which triggered the formation of apoptosome as well as activation of caspase-3/7 leading to death of HCT 116 cells via intrinsic apoptosis pathway. GS treatment also induced expression of p53 protein while p21 expression was unaltered with no cell cycle arrest. In addition, GS was found to inhibit NF-kB signaling in colon cancer cells by quelling the expression of its regulated gene products Bcl-2, cIAP-1, and survivin.

Inhibition of DOT1L and PRMT5 promote synergistic anti-tumor activity in a human MLL leukemia model induced by CRISPR/Cas9

MLL rearrangements play a crucial role in leukemogenesis and comprise a poor prognosis. Therefore, new treatment strategies are urgently needed. We used the CRISPR/Cas9 system to generate an innovative leukemia model based on 100% pure MLL-AF4 or -AF9 rearranged cells derived from umbilical cord blood with indefinite growth in cell culture systems. Our model shared phenotypical, morphological and molecular features of patient cells faithfully mimicking the nature of the disease. Thus, it serves as a fundamental basis for pharmacological studies: inhibition of histone methyltransferase disruptor of telomeric silencing 1-like (DOT1L) is one specific therapeutic approach currently tested in clinical trials. However, success was limited by restricted response warranting further investigation of drug combinations. Recently, it has been shown that the inhibition of protein arginine methyltransferase 5 (PRMT5) exhibits anti-tumoral activity against human cell lines and in MLL mouse models. Here, we used DOT1L and PRMT5 inhibitors in our human MLL-rearranged model demonstrating dose-dependent reduced proliferation, impairment of cell cycle, increasing differentiation, apoptosis, downregulation of target genes and sensitization to chemotherapy. Strikingly, the combination of both compounds led to synergistic anti-tumoral effects. Our study provides a strong rationale for novel targeted combination therapies to improve the outcome of MLL-rearranged leukemias.

Abrogation of myofibroblast activities in metastasis and fibrosis by methyltransferase inhibition

Myofibroblasts are a population of highly contractile fibroblasts that express and require the activity of the transcription factor Snail1. Cancer-associated fibroblasts (CAFs) correlate with low survival of cancer patients when present in the stroma of primary tumors. Remarkably, the presence of myofibroblastic CAFs (which express Snail1) creates mechanical properties in the tumor microenvironment that support metastasis. However, therapeutic blockage of fibroblast activity in patients with cancer is a double-edged sword, as normal fibroblast activities often restrict tumor cell invasion. We used fibroblasts depleted of Snail1 or protein arginine methyltransferases 1 and 4 (PRMT1/-4) to identify specific epigenetic modifications induced by TGFβ/Snail1. Furthermore, we analyzed the in vivo efficiency of methyltransferase inhibitors using mouse models of wound healing and metastasis, as well as fibroblasts isolated from patients with idiopathic pulmonary fibrosis (IPF). Mechanistically, TGFβ-induced Snail1 promotes the epigenetic mark of asymmetrically dimethylated arginine. Critically, we found that inhibitors of methyltransferases prevent myofibroblast activity (but not regular fibroblast activity) in the extracellular matrix, both in cell culture and in vivo. In a mouse breast cancer model, the inhibitor sinefungin reduces both the myofibroblast activity in the tumor stroma and the metastatic burden in the lung. Two distinct inhibitors effectively blocked the exacerbated myofibroblast activity of patient-derived IPF fibroblasts. Our data reveal epigenetic regulation of myofibroblast transdifferentiation in both wound healing and in disease (fibrosis and breast cancer). Thus, methyltransferase inhibitors are good candidates as therapeutic reagents for these diseases.

Targeting PRMT5 Activity Inhibits the Malignancy of Hepatocellular Carcinoma by Promoting the Transcription of HNF4α

Background: Liver cancer stem cells (LCSCs) are responsible for the initiation, progression and chemoresistance of liver cancer. However, no agent targeting LCSC is available in the clinic to date. Here, we investigated the effects of targeting protein arginine methyltransferase 5 (PRMT5), an epigenetic regulator, on LCSCs and HCC using a novel PRMT5 inhibitor DW14800. Methods: Tumor spheroid formation culture was used to enrich LCSCs and assess their self-renewal capability. Human alpha-1-antitrypsin (A1AT) ELISA, acetylated low-density lipoprotein (ac-LDL) uptake, periodic acid-Schiff (PAS) reactions and senescence associated β-galactosidase (SA-β-gal) activity assays were performed to examine the differentiation status of HCC cells. The effects of DW14800 on HCC malignancy were assessed in HCC cell lines and on an HCC xenograft model in mice. Chromatin immunoprecipitation was applied to clarify the transcriptional regulation of HNF4α by PRMT5-mediated Histone H4 arginine-3 symmetrical dimethylation (H4R3me2s). Results: Quantitative real-time PCR revealed that the expression of PRMT5 was upregulated in LCSCs. DW14800 specifically decreased the symmetrical dimethylation of arginine residues in HCC cells. Treatment of DW14800 suppressed the self-renewal capacity of LCSCs while re-establishing hepatocyte-specific characteristics in HCC cells. DW14800 displayed antitumor effects in HCC cells in vitro and in xenograft HCC in vivo. Importantly, ChIP assay showed that PRMT5 and H4R3me2s bound to the promoter region of HNF4α gene, and DW14800 increased the expression of HNF4α via reducing the H4R3me2s levels and enhancing the transcription of HNF4α. Conclusions: Our data revealed the significance of targeting PRMT5 activity in LCSC elimination and HCC differentiation, and proposed that DW14800 may represent a promising therapeutic agent for HCC in the clinic.