Proliferative role of TRAF4 in breast cancer by upregulating PRMT5 nuclear expression

Genetically encoded fluorescent sensor to monitor intracellular arginine methylation

Arginine methylation (ArgMet), as a post-translational modification, plays crucial roles in RNA processing, transcriptional regulation, signal transduction, DNA repair, apoptosis and liquid-liquid phase separation (LLPS). Since arginine methylation is associated with cancer pathogenesis and progression, protein arginine methyltransferases have gained interest as targets for anti-cancer therapy. Despite considerable process made to elucidate (patho)physiological mechanisms regulated by arginine methylation, there remains a lack of tools to visualize arginine methylation with high spatiotemporal resolution in live cells. To address this unmet need, we generated an ArgMet-sensitive genetically encoded, Förster resonance energy transfer-(FRET) based biosensor, called GEMS, capable of quantitative real-time monitoring of ArgMet dynamics. We optimized these biosensors by using different ArgMet-binding domains, arginine-glycine-rich regions and adjusting the linkers within the biosensors to improve their performance. Using a set of mammalian cell lines and modulators, we demonstrated the applicability of GEMS for monitoring changes in arginine methylation with single-cell and temporal resolution. The GEMS can facilitate the in vitro screening to find potential protein arginine methyltransferase inhibitors and will contribute to a better understanding of the regulation of ArgMet related to differentiation, development and disease.

Phase 1 Study of JNJ-64619178, a Protein Arginine Methyltransferase 5 Inhibitor, in Advanced Solid Tumors

PURPOSE

In this first-in-human, Phase 1, open-label, multicenter study, we evaluated JNJ-64619178, a selective and potent PRMT5 inhibitor, in patients with advanced malignant solid tumors or non-Hodgkin lymphomas (NHL). The primary objective was to evaluate the safety and to identify a recommended Phase 2 dose (RP2D) of JNJ-64619178.

PATIENTS AND METHODS

Adult patients with treatment-refractory advanced solid tumors or NHL and measurable disease received escalating doses of JNJ-64619178 following two schedules (Schedule A: 14 days on/7 days off; Schedule B: every day on a 21-day cycle). Safety, pharmacokinetics (PK), pharmacodynamics (PD), and clinical activity were evaluated.

RESULTS

Ninety patients received JNJ-64619178. Thrombocytopenia was identified as the only dose-limiting toxicity. JNJ-64619178 showed dose-proportional PK and robust target engagement, as measured by plasma symmetric dimethylarginine, across all dose levels. The objective response rate was 5.6% (5 of 90). Patients with adenoid cystic carcinoma (ACC) had an ORR of 11.5% (3 of 26) and a median progression-free survival of 19.1 months.

CONCLUSIONS

JNJ-64619178 demonstrated manageable dose-dependent toxicity and preliminary evidence of antitumor activity in ACC and other tumor types. Plasma exposure was dose dependent, and target inhibition was maintained with intermittent and continuous dosing. On the basis of safety, clinical activity, PK, and PD findings, two provisional RP2Ds were selected: 1.5 mg intermittently and 1.0 mg once daily. Aside from ACC, clinical benefit was limited, and biomarkers to enrich for responsiveness to PRMT5 inhibition will be needed for further development.

TRAF Family Member 4 Promotes Cardiac Hypertrophy Through the Activation of the AKT Pathway

Background Pathological cardiac hypertrophy is a major cause of heart failure morbidity. The complex mechanism of intermolecular interactions underlying the pathogenesis of cardiac hypertrophy has led to a lack of development and application of therapeutic methods. Methods and Results Our study provides the first evidence that TRAF4, a member of the tumor necrosis factor receptor-associated factor (TRAF) family, acts as a promoter of cardiac hypertrophy. Here, Western blotting assays demonstrated that TRAF4 is upregulated in cardiac hypertrophy. Additionally, TRAF4 deletion inhibits the development of cardiac hypertrophy in a mouse model after transverse aortic constriction surgery, whereas its overexpression promotes phenylephrine stimulation-induced cardiomyocyte hypertrophy in primary neonatal rat cardiomyocytes. Mechanistically, RNA-seq analysis revealed that TRAF4 promoted the activation of the protein kinase B pathway during cardiac hypertrophy. Moreover, we found that inhibition of protein kinase B phosphorylation rescued the aggravated cardiomyocyte hypertrophic phenotypes caused by TRAF4 overexpression in phenylephrine-treated neonatal rat cardiomyocytes, suggesting that TRAF4 may regulate cardiac hypertrophy in a protein kinase B-dependent manner. Conclusions Our results revealed the regulatory function of TRAF4 in cardiac hypertrophy, which may provide new insights into developing therapeutic and preventive targets for this disease.

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.

PRMT5 promotes ovarian cancer growth through enhancing Warburg effect by methylating ENO1

Protein arginine methyltransferase 5 (PRMT5) is a major type II enzyme responsible for symmetric dimethylation of arginine (SDMA), and plays predominantly roles in human cancers, including in ovarian cancer. However, the exactly roles and underlying mechanisms of PRMT5 contributing to the progression of ovarian cancer mediated by reprogramming cell metabolism remain largely elusive. Here, we report that PRMT5 is highly expressed and correlates with poor survival in ovarian cancer. Knockdown or pharmaceutical inhibition of PRMT5 is sufficient to decrease glycolysis flux, attenuate tumor growth, and enhance the antitumor effect of Taxol. Mechanistically, we find that PRMT5 symmetrically dimethylates alpha-enolase (ENO1) at arginine 9 to promotes active ENO1 dimer formation, which increases glycolysis flux and accelerates tumor growth. Moreover, PRMT5 signals high glucose to increase the methylation modification of ENO1. Together, our data reveal a novel role of PRMT5 in promoting ovarian cancer growth by controlling glycolysis flux mediated by methylating ENO1, and highlights that PRMT5 may represent a promising therapeutic target for treating ovarian cancer.

Overexpression of TRAF4 promotes lung cancer growth and EGFR-dependent phosphorylation of ERK5

Tumor necrosis factor receptor-associated factor 4 (TRAF4) is overexpressed in a variety of carcinomas of different origins, but its role in tumorigenesis remains incompletely understood. Previous studies suggest that TRAF4 promotes epidermal growth factor receptor (EGFR) activation in non-small cell lung cancer (NSCLC). However, the downstream signaling pathway of TRAF4-mediated EGFR activation, as well as its effects on tumor cells, have not been fully elucidated. Here we report that TRAF4 overexpression is associated with increased activity of extracellular signal-regulated kinase 5 (ERK5) in NSCLC tissues. Activation of ERK5 was dependent on TRAF4-mediated EGFR activation, since inhibition of either TRAF4 or EGFR dramatically abolished phosphorylation of ERK5. Mechanistically, EGFR recruited mitogen-activated protein kinase kinase kinase 3 (MEKK3), an upstream kinase of ERK5, in a TRAF4-dependent manner. Thus, our data suggest that an EGFR-TRAF4-MEKK3-ERK5 axis promotes the proliferation of tumor cells, and this may be a potential target for therapeutic intervention of NSCLC.

Protein Arginine Methyltransferase 5 (PRMT5) Inhibitors in Oncology Clinical Trials: A review

Protein arginine methyltransferase 5 (PRMT5) inhibitors are a new class of antineoplastic agents showing promising preliminary clinical efficacy. Targeting an enzyme involved in a wide array of cellular and transcriptional pro-oncogenic processes, this class offers multifaceted tumor-suppressive effects. Partial response has been seen in adenoid cystic carcinoma from both GSK3326595 and JNJ-64619178, with four cases of stable disease seen with PRT543. Highly significant is a durable complete response in isocitrate dehydrogenase 1-mutated glioblastoma multiforme with PRT811. Both alone and in combination with existing chemotherapies and immunotherapies, this class shows promising preliminary data, particularly in cancers with splicing mutations and DNA damage repair deficiencies. Further studies are warranted, and there are clinical trials to come whose data will be telling of the efficacy of PRMT5 inhibitors in both hematologic and solid malignancies. The aim of this study is to compile available results of PRMT5 inhibitors in oncology clinical trials.

TRAF4 Inhibits the Apoptosis and Promotes the Proliferation of Breast Cancer Cells by Inhibiting the Ubiquitination of Spindle Assembly-Associated Protein Eg5

Tumor necrosis factor receptor associated factor 4 (TRAF4) is a RING domain E3 ubiquitin ligase that mediates the ubiquitination of various proteins and plays an important role in driving tumor progression. By studying the relationship between TRAF4 and Eg5, a member of the kinesin family that plays a critical role in spindle assembly, we demonstrated that TRAF4 regulated Eg5 ubiquitination and contributed to Eg5-mediated breast cancer proliferation and inhibited breast cancer apoptosis. TRAF4 and Eg5 were both highly expressed in breast cancer and their protein level was positively correlated. Relying on its Zinc fingers domain, TRAF4 interacted with Eg5 in the cytoplasm of breast cancer cells. TRAF4 was a mitosis-related protein, and by up-regulating the protein level of Eg5 TRAF4 participated in spindle assembly. Loss of TRAF4 resulted in monopolar spindles formation, but loss of function could be rescued by Eg5. Relying on its RING domain, TRAF4 up-regulated Eg5 protein levels by inhibition of Eg5 ubiquitination, thus stabilizing Eg5 protein level during mitosis. Furthermore, we found that Smurf2, a TRAF4-targeted ubiquitination substrate, mediated the regulation of Eg5 ubiquitination by TRAF4. TRAF4 inhibited the interaction between Smurf2 and Eg5, and down-regulated the protein level of Smurf2 by promoting its ubiquitination, thereby inhibited the Smurf2-catalyzed ubiquitination of Eg5 and up-regulated Eg5 protein levels. We also demonstrate that TRAF4 plays an important role in promoting cell proliferation and in inhibiting cell apoptosis induced by Eg5. In summary, our study suggests a new direction for investigating the role of TRAF4 in driving breast cancer progression.

PRMT5 Interacting Partners and Substrates in Oligodendrocyte Lineage Cells

The protein arginine methyl transferase PRMT5 is an enzyme expressed in oligodendrocyte lineage cells and responsible for the symmetric methylation of arginine residues on histone tails. Previous work from our laboratory identified PRMT5 as critical for myelination, due to its transcriptional regulation of genes involved in survival and early stages of differentiation. However, besides its nuclear localization, PRMT5 is found at high levels in the cytoplasm of several cell types, including oligodendrocyte progenitor cells (OPCs) and yet, its interacting partners in this lineage, remain elusive. By using mass spectrometry on protein eluates from extracts generated from primary oligodendrocyte lineage cells and immunoprecipitated with PRMT5 antibodies, we identified 1196 proteins as PRMT5 interacting partners. These proteins were related to molecular functions such as RNA binding, ribosomal structure, cadherin and actin binding, nucleotide and protein binding, and GTP and GTPase activity. We then investigated PRMT5 substrates using iTRAQ-based proteomics on cytosolic and nuclear protein extracts from CRISPR-PRMT5 knockdown immortalized oligodendrocyte progenitors compared to CRISPR-EGFP controls. This analysis identified a similar number of peptides in the two subcellular fractions and a total number of 57 proteins with statistically decreased symmetric methylation of arginine residues in the CRISPR-PRMT5 knockdown compared to control. Several PRMT5 substrates were in common with cancer cell lines and related to RNA processing, splicing and transcription. In addition, we detected ten oligodendrocyte lineage specific substrates, corresponding to proteins with high expression levels in neural tissue. They included: PRC2C, a proline-rich protein involved in methyl-RNA binding, HNRPD an RNA binding protein involved in regulation of RNA stability, nuclear proteins involved in transcription and other proteins related to migration and actin cytoskeleton. Together, these results highlight a cell-specific role of PRMT5 in OPC in regulating several other cellular processes, besides RNA splicing and metabolism.

The Research Progress in Physiological and Pathological Functions of TRAF4

Tumour necrosis factor receptor-associated factor 4 (TRAF4) is a member of the TRAF protein family, a cytoplasmic bridging molecule closely associated with various immune functions. The physiological processes of TRAF4 are mainly involved in embryonic development, cell polarity, cell proliferation, apoptosis, regulation of reactive oxygen species production. TRAF4 is overexpressed in a variety of tumors and regulates the formation and development of a variety of tumors. In this review, we summarize the physiological and pathological regulatory functions of TRAF4 and focus on understanding the biological processes involved in this gene, to provide a reference for further studies on the role of this gene in tumorigenesis and development.

PRMT5 disruption drives antitumor immunity in cervical cancer by reprogramming T cell-mediated response and regulating PD-L1 expression

Rationale: Protein arginine methyltransferase 5 (PRMT5) is an oncogene that promotes tumor cell proliferation, invasion and metastasis. However, the underlying mechanisms by which PRMT5 contributes to the progression of cervical cancer and especially the tumor microenvironment remain poorly understood. Methods: PRMT5 expression level was analyzed by Q-PCR, western blot, immunohistochemistry, and TCGA database. The role of PRMT5 in tumor growth was observed by transplanted tumor models, and the function of T cells in tumor microenvironment and in vitro co-culture system was investigated through flow cytometry. The transcriptional regulation of PRMT5 was analyzed using luciferase reporter and chromatin immunoprecipitation (ChIP) assay. The therapeutic effect of PRMT5 inhibitor was evaluated in a cervical cancer cell line transplanted tumor model. Results: We observed that the mRNA and protein expression levels of PRMT5 were increased in cervical cancer tissues, and the high expression of PRMT5 was associated with poor outcomes in cervical cancer patients. The absence of PRMT5 significantly inhibited tumor growth in a cervical cancer transplanted tumor model, and importantly, PRMT5 absence in tumors led to increase the number and enhance the function of tumor infiltrating T cells. Mechanistically, PRMT5 enhanced the transcription of STAT1 through symmetric dimethylation of histone H3R2 and thus promoted PD-L1 expression in cervical cancer cells. Moreover, in an in vitro co-culture system, knockdown of PRMT5 in tumor cells could directly enhance the expression of IFN-γ, TNF-α and granzyme B in T cells. These results suggested that PRMT5 promoted the development of cervical cancer by the crosstalk between tumor cells and T cells. Furthermore, the PRMT5 inhibitor EPZ015666 treatment could suppress tumor growth in a cervical cancer transplanted tumor model. Conclusion: Our results clarify a new mechanism which PRMT5 knockdown in cervical cancer cells drives an antitumor function via reprogramming T cell-mediated response and regulating PD-L1 expression. Thus, our study highlights that PRMT5 may be a potential target for cervical cancer therapy.

Protein arginine methyltransferases: promising targets for cancer therapy

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

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.

PRMT5 promotes progression of endometrioid adenocarcinoma via ERα and cell cycle signaling pathways

Protein arginine methyltransferase 5 (PRMT5) has previously been reported to be upregulated in many malignant tumors. This study investigated the significance of PRMT5 in endometrial carcinoma (EC) and explored its function in tumorigenesis. Immunohistochemistry was performed to evaluate PRMT5 expression in 62 EC and 66 endometrial hyperplasia samples. The functions of PRMT5 were investigated by cell counting kit‐8, plate colony formation, wound healing, and transwell and flow cytometry assays. Quantitative reverse transcription‐polymerase chain reaction and western blotting were used to measure the expression of PRMT5, changes in estrogen receptor α (ERα), and related functional proteins. Coimmunoprecipitation was performed to examine the interaction of PRMT5 with ERα and its coactivator steroid receptor coactivator‐1 (SRC1). Compared to endometrial hyperplasia tissue, PRMT5 was overexpressed in endometrioid adenocarcinoma (EAC) but not overexpressed in mucinous EC. The main expression pattern of PRMT5 in EAC was cytoplasmic. However, the positive cases of endometrial hyperplasia showed both cytoplasmic and nuclear positivity in the endometrial glands or were mainly positive in stromal cells. Knockdown of PRMT5 significantly inhibited the growth and migration ability of EAC cells and promoted their apoptosis by regulating cyclin D1, c‐myc, p53, and Bcl2 proteins. Furthermore, PRMT5 could form a complex with ERα and SRC1 to promote the expression of ERα. In conclusion, PRMT5 plays a significant role in the progression of EAC by interacting with ERα and impacting the cell cycle signaling pathways.

Roles of TRAFs in Ischemia-Reperfusion Injury

Tumor necrosis factor receptor-associated factor (TRAF) proteins are a family of signaling molecules that function downstream of multiple receptor signaling pathways, and they play a pivotal role in the regulation of intracellular biological progresses. These TRAF-dependent signaling pathways and physiological functions have been involved in the occurrence and progression of ischemia-reperfusion injury (IRI), which is a common pathophysiological process that occurs in a wide variety of clinical events, including ischemic shock, organ transplantation, and thrombolytic therapy, resulting in a poor prognosis and high mortality. IRI occurs in multiple organs, including liver, kidney, heart, lung, brain, intestine, and retina. In recent years, mounting compelling evidence has confirmed that the genetic alterations of TRAFs can cause subversive phenotype changes during IRI of those organs. In this review, based on current knowledge, we summarized and analyzed the regulatory effect of TRAFs on the IRI of various organs, providing clear direction and a firm theoretical basis for the development of treatment strategies to manipulate TRAF proteins or TRAF-dependent signaling pathways in IRI-related diseases.

The role of protein arginine methyltransferases in kidney diseases

The methylation of arginine residues by protein arginine methyltransferases (PRMTs) is a crucial post-translational modification for many biological processes, including DNA repair, RNA processing, and transduction of intra- and extracellular signaling. Previous studies have reported that PRMTs are extensively involved in various pathologic states, including cancer, inflammation, and oxidative stress reaction. However, the role of PRMTs has not been well described in kidney diseases. Recent studies have shown that aberrant function of PRMTs and its metabolic products-symmetric dimethylarginine (SDMA) and asymmetric dimethylarginine (ADMA)-are involved in several renal pathological processes, including renal fibrosis, acute kidney injury (AKI), diabetic nephropathy (DN), hypertension, graft rejection and renal tumors. We aim in this review to elucidate the possible roles of PRMTs in normal renal function and various kidney diseases.

Novel interaction of antioxidant-1 with TRAF4: role in inflammatory responses in endothelial cells

NADPH oxidase (NOX)-derived reactive oxygen species (ROS) and copper (Cu), an essential micronutrient, have been implicated in vascular inflammatory diseases. We reported that in proinflammatory cytokine TNF-α-stimulated endothelial cells (ECs), cytosolic Cu chaperone antioxidant-1 (Atox1) functions as a Cu-dependent transcription factor for the NOX organizer p47phox, thereby increasing ROS-dependent inflammatory gene expression. However, the role and mechanism of Atox1 nuclear translocation in inflamed ECs remain unclear. Using enface staining and nuclear fractionation, here we show that Atox1 was localized in the nucleus in inflamed aortas from ApoE^-/- mice with angiotensin II infusion on a high-fat diet, while it was found in cytosol in those from control mice. In cultured human ECs, TNF-α stimulation promoted Atox1 nuclear translocation within 15 min, which was associated with Atox1 binding to TNF-α receptor-associated factor 4 (TRAF4) in a Cu-dependent manner. TRAF4 depletion by siRNA significantly inhibited Atox1 nuclear translocation, p47phox expression, and ROS production as well as its downstream VCAM1/ICAM1 expression and monocyte adhesion to inflamed ECs, which were rescued by overexpression of nuclear targeted Atox1. Furthermore, Atox1 colocalized with TRAF4 at the nucleus in TNF-α-stimulated inflamed ECs and vessels. In summary, Cu-dependent Atox1 binding to TRAF4 plays an important role in Atox1 nuclear translocation and ROS-dependent inflammatory responses in TNF-α-stimulated ECs. Thus the Atox1-TRAF4 axis is a novel therapeutic target for vascular inflammatory disease such as atherosclerosis.

Protein arginine methyltransferase 5: A novel therapeutic target for triple-negative breast cancers

TNBC is a highly heterogeneous and aggressive breast cancer subtype associated with high relapse rates, and for which no targeted therapy yet exists. Protein arginine methyltransferase 5 (PRMT5), an enzyme which catalyzes the methylation of arginines on histone and non‐histone proteins, has recently emerged as a putative target for cancer therapy. Potent and specific PRMT5 inhibitors have been developed, but the therapeutic efficacy of PRMT5 targeting in TNBC has not yet been demonstrated. Here, we examine the expression of PRMT5 in a human breast cancer cohort obtained from the Institut Curie, and evaluate the therapeutic potential of pharmacological inhibition of PRMT5 in TNBC. We find that PRMT5 mRNA and protein are expressed at comparable levels in TNBC, luminal breast tumors, and healthy mammary tissues. However, immunohistochemistry analyses reveal that PRMT5 is differentially localized in TNBC compared to other breast cancer subtypes and to normal breast tissues. PRMT5 is heterogeneously expressed in TNBC and high PRMT5 expression correlates with poor prognosis within this breast cancer subtype. Using the small‐molecule inhibitor EPZ015666, we show that PRMT5 inhibition impairs cell proliferation in a subset of TNBC cell lines. PRMT5 inhibition triggers apoptosis, regulates cell cycle progression and decreases mammosphere formation. Furthermore, EPZ015666 administration to a patient‐derived xenograft model of TNBC significantly deters tumor progression. Finally, we reveal potentiation between EGFR and PRMT5 targeting, suggestive of a beneficial combination therapy. Our findings highlight a distinctive subcellular localization of PRMT5 in TNBC, and uphold PRMT5 targeting, alone or in combination, as a relevant treatment strategy for a subset of TNBC.

Epigenetic arginine methylation in breast cancer: emerging therapeutic strategies

Breast cancer is a heterogeneous disease, and the complexity of breast carcinogenesis is associated with epigenetic modification. There are several major classes of epigenetic enzymes that regulate chromatin activity. This review will focus on the nine mammalian protein arginine methyltransferases (PRMTs) and the dysregulation of PRMT expression and function in breast cancer. This class of enzymes catalyse the mono- and (symmetric and asymmetric) di-methylation of arginine residues on histone and non-histone target proteins. PRMT signalling (and R methylation) drives cellular proliferation, cell invasion and metastasis, targeting (i) nuclear hormone receptor signalling, (ii) tumour suppressors, (iii) TGF-β and EMT signalling and (iv) alternative splicing and DNA/chromatin stability, influencing the clinical and survival outcomes in breast cancer. Emerging reports suggest that PRMTs are also implicated in the development of drug/endocrine resistance providing another prospective avenue for the treatment of hormone resistance and associated metastasis. The complexity of PRMT signalling is further underscored by the degree of alternative splicing and the scope of variant isoforms (with distinct properties) within each PRMT family member. The evolution of PRMT inhibitors, and the ongoing clinical trials of PRMT inhibitors against a subgroup of solid cancers, coupled to the track record of lysine methyltransferases inhibitors in phase I/II clinical trials against cancer underscores the potential therapeutic utility of targeting PRMT epigenetic enzymes to improve survival outcomes in aggressive and metastatic breast cancer.

Role of protein arginine methyltransferase 5 in human cancers

Protein arginine methyltransferases (PRMTs) play important roles in protein methylation. PRMT5 is the major type II arginine methyltransferase that catalyzes the transfer of two methyl groups symmetrically to the arginine residues of either histone or non-histone proteins. In recent years, increasing evidence has shown that PRMT5, as an oncogene, plays an indispensable regulatory role in the pathological progression of several human cancers by promoting the proliferation, invasion, and migration of cancer cells. PRMT5 is overexpressed in many malignant tumors and plays an important role in the occurrence and development of cancer, which suggests that PRMT5 may become a potential biomarker or therapeutic target of cancer. This article reviews the biological function, mechanism, and clinical significance of PRMT5 in tumorigenesis.

Low expression of PRMT5 in peripheral blood may serve as a potential independent risk factor in assessments of the risk of stable CAD and AMI

Background

Protein arginine methyltransferases (PRMTs) can catalyse the methylation of arginine and participate in many important cellular reaction processes. The purpose of this research is to determine whether the expression levels of the PRMT5 gene in peripheral blood can be used as a biomarker for predicting the risk of Acute Myocardial Infarction (AMI).

Methods

In this research, peripheral blood was collected from 91 patients with AMI and 87 patients with stable coronary artery disease (CAD). Real-time fluorescent quantitative PCR was performed to measure the expression levels of the PRMT5 gene at the mRNA level, and a western blot analysis was performed to measure the expression levels of the PRMT5 gene at the protein level.

Results

The results indicate that at both the RNA and protein levels, the expression levels of the PRMT5 gene in peripheral blood from patients with AMI are significantly lower than those in peripheral blood from patients with stable CAD (Z = − 4.813, P = 0.000). The low expression of the PRMT5 gene is relevant to the Gensini score of the coronary artery (rs = − 0.205, P = 0.015) but is irrelevant to the serum level of blood lipids, level of cardiac troponin (rs = − 0.125, P = 0.413) and time intervals of occurrence (rs = − 0.146, P = 0.211). Patients who have a low PRMT5 expression in the peripheral blood are 5.472 times more likely to suffer from AMI than other patients.

Conclusion

Compared to stable CAD patients, AMI patients have a lower expression of the PRMT5 gene in their peripheral blood. Patients who have low PRMT5 gene expression in the peripheral blood are more likely to suffer from AMI than those with stable CAD. A low expression of the PRMT5 gene serves as an independent risk factor for the occurrence of AMI.

LKB1 regulates PRMT5 activity in breast cancer

Protein arginine methyltransferase 5 (PRMT5) is the main enzyme responsible for the symmetrical dimethylation of arginine residues on target proteins in both the cytoplasm and the nucleus. Though its activity has been associated with tumor progression in various cancers, the expression pattern of this oncoprotein has been scarcely studied in breast cancer. In the current work, we analyzed its expression in a large cohort of breast cancer patients, revealing higher nuclear PRMT5 levels in ERα-positive tumors and an association with prolonged disease free and overall survival. Interestingly, high PRMT5 nuclear expression was also associated with higher nuclear liver kinase B1 (LKB1), suggesting that a functional relationship may occur. Consistently, several approaches provided evidence that PRMT5 and LKB1 interact directly in the cytoplasm of mammary epithelial cells. Moreover, although PRMT5 is not able to methylate LKB1, we found that PRMT5 is a bona fade substrate for LKB1. We identified T132, 139 and 144 residues, located in the TIM-Barrel domain of PRMT5, as target sites for LKB1 phosphorylation. The point mutation of PRMT5 T139/144 to A139/144 drastically decreased its methyltransferase activity, due probably to the loss of its interaction with regulatory proteins such as MEP50, pICln and RiOK1. In addition, modulation of LKB1 expression modified PRMT5 activity, highlighting a new regulatory mechanism that could have clinical implications.

Role of the overexpression of TRAF4 in predicting the prognosis of intrahepatic cholangiocarcinoma

The incidence of intrahepatic cholangiocarcinoma (ICC) is progressively increasing worldwide, and its prognosis remains poor. Accumulating evidence has demonstrated that tumor necrosis factor receptor-associated factor 4 (TRAF4), an adaptor protein, is involved in the carcinogenesis and progression of several tumor types. However, the function of TRAF4 in predicting prognosis, and mediating migration and invasion of ICC remains to be elucidated. In the present study, immunohistochemistry, western blotting and reverse transcription-quantitative polymerase chain reaction assays were used to determine that the expression of TRAF4 at the mRNA and protein levels in ICC tissues was significantly higher compared with that in non‑tumor tissues. The overexpression of TRAF4 was positively correlated with poor differentiation, regional lymphatic metastasis, and high tumor‑node-metastasis staging. Inhibiting the expression of TRAF4 using small interfering RNA decreased the migration and invasion of ICC cells in vitro. In addition, the AKT inhibitor perifosine eliminated the effect of TRAF4 on the invasion and migration of ICC cells in vitro. Clinically, the overexpression of TRAF4 was correlated with shorter overall survival rate and elevated recurrence rate in patients with ICC. Furthermore, patients with ICC with a high expression of TRAF4 and lymphatic metastasis were closely associated with a poorer prognosis compared with the other groups. Multivariate analysis indicated that the overexpression of TRAF4 was an independent prognostic indicator for patients with ICC. It was identified that a high level of TRAF4 facilitated the invasiveness of ICC cells via the activation of AKT signaling. The overexpression of TRAF4 may be a prognostic biomarker and candidate therapeutic target for patients with ICC.

Protein arginine methylation/demethylation and cancer

Protein arginine methylation is a common post-translational modification involved in numerous cellular processes including transcription, DNA repair, mRNA splicing and signal transduction. Currently, there are nine known members of the protein arginine methyltransferase (PRMT) family, but only one arginine demethylase has been identified, namely the Jumonji domain-containing 6 (JMJD6). Although its demethylase activity was initially challenged, its dual activity as an arginine demethylase and a lysine hydroxylase is now recognized. Interestingly, a growing number of substrates for arginine methylation and demethylation play key roles in tumorigenesis. Though alterations in the sequence of these enzymes have not been identified in cancer, their overexpression is associated with various cancers, suggesting that they could constitute targets for therapeutic strategies. In this review, we present the recent knowledge of the involvement of PRMTs and JMJD6 in tumorigenesis.

PRMT5 Is a Critical Regulator of Breast Cancer Stem Cell Function via Histone Methylation and FOXP1 Expression

Breast cancer progression, treatment resistance, and relapse are thought to originate from a small population of tumor cells, breast cancer stem cells (BCSCs). Identification of factors critical for BCSC function is therefore vital for the development of therapies. Here, we identify the arginine methyltransferase PRMT5 as a key in vitro and in vivo regulator of BCSC proliferation and self-renewal and establish FOXP1, a winged helix/forkhead transcription factor, as a critical effector of PRMT5-induced BCSC function. Mechanistically, PRMT5 recruitment to the FOXP1 promoter facilitates H3R2me2s, SET1 recruitment, H3K4me3, and gene expression. Our findings are clinically significant, as PRMT5 depletion within established tumor xenografts or treatment of patient-derived BCSCs with a pre-clinical PRMT5 inhibitor substantially reduces BCSC numbers. Together, our findings highlight the importance of PRMT5 in BCSC maintenance and suggest that small-molecule inhibitors of PRMT5 or downstream targets could be an effective strategy eliminating this cancer-causing population.

Nuclear PRMT5, cyclin D1 and IL-6 are associated with poor outcome in oropharyngeal squamous cell carcinoma patients and is inversely associated with p16-status

Protein arginine methyltransferase-5 (PRMT5) plays an important role in cancer progression by repressing the expression of key tumor suppressor genes via the methylation of transcriptional factors and chromatin-associated proteins. However, very little is known about the expression and biological role of PRMT5 in head and neck cancer. In this study, we examined expression profile of PRMT5 at subcellular levels in oropharyngeal squamous cell carcinoma (OPSCC) and assessed its correlation with disease progression and patient outcome. Our results show that nuclear PRMT5 was associated with poor overall survival (p < 0.012) and these patients had 1.732 times higher hazard of death (95% CI: 1.127–2.661) as compared to patients in whom PRMT5 was not present in the nucleus of the tumors. Nuclear PRMT5 expression was inversely correlated with p16-status (p < 0.001) and was significantly higher in tumor samples from patients who smoked > 10 pack-years (p = 0.013). In addition, nuclear PRMT5 was directly correlated with cyclin D1 (p = 0.0101) and IL-6 expression (p < 0.001). In a subgroup survival analysis, nuclear PRMT5-positive/IL-6-positive group had worst survival, whereas nuclear PRMT5-negative/IL-6-negative group had the best survival. Similarly, patients with p16-negative/nuclear PRMT5-positive tumors had worse survival compared to patients with p16-positive/nuclear PRMT5-negative tumors. Our mechanistic results suggest that IL-6 promotes nuclear translocation of PRMT5. Taken together, our results demonstrate for the first time that nuclear PRMT5 expression is associated with poor clinical outcome in OPSCC patients and IL-6 plays a role in the nuclear translocation of PRMT5.

TRAF4 Regulates Migration, Invasion, and Epithelial-Mesenchymal Transition via PI3K/AKT Signaling in Hepatocellular Carcinoma

Overexpression of the tumor necrosis factor receptor-associated factor 4 (TRAF4) has been detected in many cancer types and is considered to foster tumor progression. However, the role of TRAF4 in hepatocellular carcinoma (HCC) remains elusive. In this study, we found that TRAF4 was highly expressed in HCC cell lines and HCC tissues compared with normal liver cell lines and adjacent noncancerous tissues. TRAF4 overexpression in HCC tissues was correlated with tumor quantity and vascular invasion. In vitro studies showed that TRAF4 was associated with HCC cell migration and invasion. An in vivo study verified that TRAF4 overexpression facilitated metastasis in nude mice. In addition, overexpressed TRAF4 promoted the phosphorylation of Akt and induced Slug overexpression, leading to downregulated E-cadherin and upregulated vimentin, while silencing TRAF4 moderated the phosphorylation of Akt and repressed the expression of Slug, which resulted in upregulated E-cadherin and downregulated vimentin. These effects were inversed after pretreatment of the PI3K/Akt inhibitor LY294002 or overexpression of constitutively active Akt1. Our study demonstrated that TRAF4 was involved in promoting HCC cell migration and invasion. The process was induced by the EMT through activation of the PI3K/Akt signaling pathway.

Elevated expression of protein arginine methyltransferase 5 predicts the poor prognosis of breast cancer

Protein arginine methyltransferase 5 is one of the type II protein arginine methyltransferase family members that can symmetrically dimethylate arginine residues on target proteins in both the cytoplasm and the nucleus. Protein arginine methyltransferase 5 was reported to be an oncoprotein that participates in tumor progression through both epigenetic silencing and organelle biogenesis. So far, it has been implicated in various cancers, but its expression pattern in breast cancer has not been elucidated thoroughly. We analyzed the protein arginine methyltransferase 5 expression patterns in several breast cancer samples and tissue arrays to better characterize its contribution to breast cancer. Primary breast tumors showed increased protein arginine methyltransferase 5 expression compared with adjacent normal tissues in both the fresh tissue samples and tissue arrays. Also, there was a tendency that metastatic lymph nodes demonstrated enhanced protein arginine methyltransferase 5 expression compared to primary sites. Moreover, we found a significant correlation between protein arginine methyltransferase 5 and Ki-67, with higher Ki-67 and protein arginine methyltransferase 5 expressions in primary breast tumors compared with normal breast tissues. Moreover, the Cancer Genome Atlas cohort analysis revealed that high protein arginine methyltransferase 5 messenger RNA expression was associated with an unfavorable prognosis in human epidermal growth factor receptor 2 (HER-2) positive and triple negative breast cancer patients. Finally, the roles and mechanisms of protein arginine methyltransferase 5 in the proliferation, cell cycle progression, and apoptosis of MDA-MB-231 cells were assessed using protein arginine methyltransferase 5 and shPRMT5 transfection. In conclusion, we proposed that protein arginine methyltransferase 5 is an independent prognostic biomarker for breast cancer, and targeting protein arginine methyltransferase 5 might be a promising strategy for breast cancer treatment.