NF-κB/mTOR/MYC Axis Drives PRMT5 Protein Induction After T Cell Activation via Transcriptional and Non-transcriptional Mechanisms

Disease Aggravation With Age in an Experimental Model of Multiple Sclerosis: Role of Immunosenescence

The onset of multiple sclerosis (MS) in older individuals correlates with a higher risk of developing primary progressive MS, faster progression to secondary progressive MS, and increased disability accumulation. This phenomenon can be related to age-related changes in the immune system: with age, the immune system undergoes a process called immunosenescence, characterized by a decline in the function of both the innate and adaptive immune responses. This decline can lead to a decreased ability to control inflammation and repair damaged tissue. Additionally, older individuals often experience a shift toward a more pro-inflammatory state, known as inflammaging, which can exacerbate the progression of neurodegenerative diseases like MS. Therefore, age-related alterations in the immune system could be responsible for the difference in the phenotype of MS observed in older and younger patients. In this study, we investigated the effects of age on the immunopathogenesis of experimental autoimmune encephalomyelitis (EAE). Our findings indicate that EAE is more severe in aged mice due to a more inflammatory and neurodegenerative environment in the central nervous system. Age-related changes predominantly affect adaptive immunity, characterized by altered T cell ratios, a pro-inflammatory Th1 response, increased regulatory T cells, exhaustion of T cells, altered B cell antigen presentation, and reduced NK cell maturation and cytotoxicity. Transcriptomic analysis reveals that fewer pathways and transcription factors are activated with age in EAE. These findings allow us to identify potential therapeutic targets specific to elderly MS patients and work on their development in the future.

PRMT5 Promotes T follicular helper Cell Differentiation and Germinal Center Responses during Influenza Virus Infection

Protein arginine methyltransferases (PRMTs) modify diverse protein targets and regulate numerous cellular processes; yet, their contributions to individual effector T cell responses during infections are incompletely understood. In this study, we identify PRMT5 as a critical regulator of CD4+ T follicular helper cell (Tfh) responses during influenza virus infection in mice. Conditional PRMT5 deletion in murine T cells results in an almost complete ablation of both Tfh and T follicular regulatory populations and, consequently, reduced B cell activation and influenza-specific Ab production. Supporting a potential mechanism, we observe elevated surface expression of IL-2Rα on non-T regulatory effector PRMT5-deficient T cells. Notably, IL-2 signaling is known to negatively impact Tfh differentiation. Collectively, our findings identify PRMT5 as a prominent regulator of Tfh programming, with potential causal links to IL-2 signaling.

MYC: there is more to it than cancer

MYC is a pleiotropic transcription factor involved in multiple cellular processes. While its mechanism of action and targets are not completely elucidated, it has a fundamental role in cellular proliferation, differentiation, metabolism, ribogenesis, and bone and vascular development. Over 4 decades of research and some 10,000 publications linking it to tumorigenesis (by searching PubMed for "MYC oncogene") have led to MYC becoming a most-wanted target for the treatment of cancer, where many of MYC's physiological functions become co-opted for tumour initiation and maintenance. In this context, an abundance of reviews describes strategies for potentially targeting MYC in the oncology field. However, its multiple roles in different aspects of cellular biology suggest that it may also play a role in many additional diseases, and other publications are indeed linking MYC to pathologies beyond cancer. Here, we review these physiological functions and the current literature linking MYC to non-oncological diseases. The intense efforts towards developing MYC inhibitors as a cancer therapy will potentially have huge implications for the treatment of other diseases. In addition, with a complementary approach, we discuss some diseases and conditions where MYC appears to play a protective role and hence its increased expression or activation could be therapeutic.

Weighted gene co-expression network analysis revealed T cell differentiation associated with the age-related phenotypes in COVID-19 patients

The risk of severe condition caused by Corona Virus Disease 2019 (COVID-19) increases with age. However, the underlying mechanisms have not been clearly understood. The dataset GSE157103 was used to perform weighted gene co-expression network analysis on 100 COVID-19 patients in our analysis. Through weighted gene co-expression network analysis, we identified a key module which was significantly related with age. This age-related module could predict Intensive Care Unit status and mechanical-ventilation usage, and enriched with positive regulation of T cell receptor signaling pathway biological progress. Moreover, 10 hub genes were identified as crucial gene of the age-related module. Protein-protein interaction network and transcription factors-gene interactions were established. Lastly, independent data sets and RT-qPCR were used to validate the key module and hub genes. Our conclusion revealed that key genes were associated with the age-related phenotypes in COVID-19 patients, and it would be beneficial for clinical doctors to develop reasonable therapeutic strategies in elderly COVID-19 patients.

PRMT5 inhibition induces pro-inflammatory macrophage polarization and increased hepatic triglyceride levels without affecting atherosclerosis in mice

Protein arginine methyltransferase 5 (PRMT5) controls inflammation and metabolism through modulation of histone methylation and gene transcription. Given the important role of inflammation and metabolism in atherosclerotic cardiovascular disease, here we examined the role of PRMT5 in atherosclerosis using the specific PRMT5 inhibitor GSK3326595. Cultured thioglycollate-elicited peritoneal macrophages were exposed to GSK3326595 or DMSO control and stimulated with either 1 ng/mL LPS or 100 ng/mL interferon-gamma for 24 h. Furthermore, male low-density lipoprotein (LDL) receptor knockout mice were fed an atherogenic Western-type diet and injected intraperitoneally 3×/week with a low dose of 5 mg/kg GSK3326595 or solvent control for 9 weeks. In vitro, GSK3326595 primed peritoneal macrophages to interferon-gamma-induced M1 polarization, as evidenced by an increased M1/M2 gene marker ratio. In contrast, no difference was found in the protein expression of iNOS (M1 marker) and ARG1 (M2 marker) in peritoneal macrophages of GSK3326595-treated mice. Also no change in the T cell activation state or the susceptibility to atherosclerosis was detected. However, chronic GSK3326595 treatment did activate genes involved in hepatic fatty acid acquisition, i.e. SREBF1, FASN, and CD36 (+59%, +124%, and +67%, respectively; p < 0.05) and significantly increased hepatic triglyceride levels (+50%; p < 0.05). PRMT5 inhibition by low-dose GSK3326595 treatment does not affect the inflammatory state or atherosclerosis susceptibility of Western-type diet-fed LDL receptor knockout mice, while it induces hepatic triglyceride accumulation. Severe side effects in liver, i.e. development of non-alcoholic fatty liver disease, should thus be taken into account upon chronic treatment with this PRMT5 inhibitor.

Inhibition of the Protein Arginine Methyltransferase PRMT5 in High-Risk Multiple Myeloma as a Novel Treatment Approach

Multiple myeloma (MM) is an incurable clonal plasma cell malignancy. Subsets of patients have high-risk features linked with dismal outcome. Therefore, the need for effective therapeutic options remains high. Here, we used bio-informatic tools to identify novel targets involved in DNA repair and epigenetics and which are associated with high-risk myeloma. The prognostic significance of the target genes was analyzed using publicly available gene expression data of MM patients (TT2/3 and HM cohorts). Hence, protein arginine methyltransferase 5 (PRMT5) was identified as a promising target. Druggability was assessed in OPM2, JJN3, AMO1 and XG7 human myeloma cell lines using the PRMT5-inhibitor EPZ015938. EPZ015938 strongly reduced the total symmetric-dimethyl arginine levels in all cell lines and lead to decreased cellular growth, supported by cell line dependent changes in cell cycle distribution. At later time points, apoptosis occurred, as evidenced by increased AnnexinV-positivity and cleavage of PARP and caspases. Transcriptome analysis revealed a role for PRMT5 in regulating alternative splicing, nonsense-mediated decay, DNA repair and PI3K/mTOR-signaling, irrespective of the cell line type. PRMT5 inhibition reduced the expression of upstream DNA repair kinases ATM and ATR, which may in part explain our observation that EPZ015938 and the DNA-alkylating agent, melphalan, have combinatory effects. Of interest, using a low-dose of mTOR-inhibitor, we observed that cell viability was partially rescued from the effects of EPZ015938, indicating a role for mTOR-related pathways in the anti-myeloma activity of EPZ015938. Moreover, PRMT5 was shown to be involved in splicing regulation of MMSET and SLAMF7, known genes of importance in MM disease. As such, we broaden the understanding of the exact role of PRMT5 in MM disease and further underline its use as a possible therapeutic target.

PRMT5 critically mediates TMAO-induced inflammatory response in vascular smooth muscle cells

A high plasma level of the choline-derived metabolite trimethylamine N-oxide (TMAO) is closely related to the development of cardiovascular disease. However, the underlying mechanism remains unclear. In the present study, we demonstrated that a positive correlation of protein arginine methyltransferase 5 (PRMT5) expression and TMAO-induced vascular inflammation, with upregulated vascular cell adhesion molecule-1 (VCAM-1) expression in primary rat and human vascular smooth muscle cells (VSMC) in vitro. Knockdown of PRMT5 suppressed VCAM-1 expression and the adhesion of primary bone marrow-derived macrophages to TMAO-stimulated VSMC. VSMC-specific PRMT5 knockout inhibited vascular inflammation with decreased expression of VCAM-1 in mice. We further identified that PRMT5 promoted VCAM-1 expression via symmetrical demethylation of Nuclear factor-κB p65 on arginine 30 (R30). Finally, we found that TMAO markedly induced the expression of nicotinamide adenine dinucleotide phosphate oxidase 4 (Nox4) and production of reactive oxygen species, which contributed to PRMT5 expression and subsequent VCAM-1 expression. Collectively, our data provide novel evidence to establish a Nox4-PRMT5-VCAM-1 in mediating TMAO-induced VSMC inflammation. PRMT5 may be a potential target for the treatment of TMAO-induced vascular diseases.

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.

Activation of TLR4 induces inflammatory muscle injury via mTOR and NF-κB pathways in experimental autoimmune myositis mice

Idiopathic inflammatory myopathy (IIM) is an autoimmune disease that invades skeletal muscle; however, the etiology of IIM is still poorly understood. Toll-like receptor (TLR) 4 has been widely reported to take part in the autoimmune inflammation of IIMs. The mammalian target of rapamycin, mTOR, is a key central substance which mediates immune responses and metabolic changes, and also has been confirmed to be involved in the pathogenesis of IIMs. However, the interconnectedness between TLR4 and mTOR in IIM inflammation has not been fully elucidated. We hypothesized that TLR4 may play an important role in IIM inflammatory muscle injury by regulating mTOR. Mice were divided into four groups: a normal control group, IIM animal model (experimental autoimmune myositis, EAM) group, TAK242 intervention group and rapamycin (RAPA) intervention group. The results of EAM mice showed that TLR4, mTOR, nuclear factor-kappa B (NF-κB) and inflammatory factors interleukin-17A (IL-17A) and interferon γ (IFN-γ) mRNA levels were significantly upregulated. These factors were positively correlated with the degree of muscle inflammatory injury. When EAM mice were given the antagonist TAK242 to inhibit the TLR4 pathway, the results demonstrated that both mTOR and NF-κB were downregulated in the muscle of the mice. Muscle staining showed that the inflammatory injury was alleviated and the EAM mouse muscle strength was improved. Then, RAPA was used to inhibit the mTOR pathway, and the inflammatory factors IL-17A and IFN-γ were downregulated in EAM mouse muscle and serum. Consistently, muscle inflammatory injury was significantly reduced, and muscle strength was significantly improved. Our results suggest that TLR4 may regulate inflammatory muscle injury in EAM by activating the mTOR and NF-κB pathways, which provides both an experimental complement for the pathological mechanism of IIM and an encouraging target for the selection of effective treatments.

PRMT5 Deficiency Enforces the Transcriptional and Epigenetic Programs of Klrg1+CD8+ Terminal Effector T Cells and Promotes Cancer Development

Protein arginine methyltransferase 5 (PRMT5) participates in the symmetric dimethylation of arginine residues of proteins and contributes to a wide range of biological processes. However, how PRMT5 affects the transcriptional and epigenetic programs involved in the establishment and maintenance of T cell subset differentiation and roles in antitumor immunity is still incompletely understood. In this study, using single-cell RNA and chromatin immunoprecipitation sequencing, we found that mouse T cell-specific deletion of PRMT5 had greater effects on CD8⁺ than CD4⁺ T cell development, enforcing CD8⁺ T cell differentiation into Klrg1⁺ terminal effector cells. Mechanistically, T cell deficiency of PRMT5 activated Prdm1 by decreasing H4R3me2s and H3R8me2s deposition on its loci, which promoted the differentiation of Klrg1⁺CD8⁺ T cells. Furthermore, effector CD8⁺ T cells that transited to memory precursor cells were decreased in PRMT5-deficient T cells, thus causing dramatic CD8⁺ T cell death. In addition, in a mouse lung cancer cell line-transplanted tumor mouse model, the percentage of CD8⁺ T cells from T cell-specific deletion of PRMT5 mice was dramatically lost, but CD8⁺Foxp3⁺ and CD8⁺PDL1⁺ regulatory T cells were increased compared with the control group, thus accelerating tumor progression. We further verified these results in a mouse colon cancer cell line-transplanted tumor mouse model. Our study validated the importance of targeting PRMT5 in tumor treatment, because PRMT5 deficiency enforced Klrg1⁺ terminal CD8⁺ T cell development and eliminated antitumor activity.

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.

PRMT5: An Emerging Target for Pancreatic Adenocarcinoma

Simple Summary

The burden of pancreatic ductal adenocarcinoma (PDAC) increases with rising incidence, yet 5-year overall survival remains poor at 17%. Routine comprehensive genomic profiling of PDAC only finds 2.5% of patients who may benefit and receive matched targeted therapy. Protein arginine methyltransferase 5 (PRMT5) as an anti-cancer target has gained significant interest in recent years and high levels of PRMT5 protein are associated with worse survival outcomes across multiple cancer types. Inhibition of PRMT5 in pre-clinical models can lead to cancer growth inhibition. However, PRMT5 is involved in multiple cellular processes, thus determining its mechanism of action is challenging. While past reviews on PRMT5 have focused on its role in diverse cellular processes and past research studies have focused mainly on haematological malignancies and glioblastoma, this review provides an overview of the possible biological mechanisms of action of PRMT5 inhibition and its potential as a treatment in pancreatic cancer.

Abstract

The overall survival of pancreatic ductal adenocarcinoma (PDAC) remains poor and its incidence is rising. Targetable mutations in PDAC are rare, thus novel therapeutic approaches are needed. Protein arginine methyltransferase 5 (PRMT5) overexpression is associated with worse survival and inhibition of PRMT5 results in decreased cancer growth across multiple cancers, including PDAC. Emerging evidence also suggests that altered RNA processing is a driver in PDAC tumorigenesis and creates a partial dependency on this process. PRMT5 inhibition induces altered splicing and this vulnerability can be exploited as a novel therapeutic approach. Three possible biological pathways underpinning the action of PRMT5 inhibitors are discussed; c-Myc regulation appears central to its action in the PDAC setting. Whilst homozygous MTAP deletion and symmetrical dimethylation levels are associated with increased sensitivity to PRMT5 inhibition, neither measure robustly predicts its growth inhibitory response. The immunomodulatory effect of PRMT5 inhibitors on the tumour microenvironment will also be discussed, based on emerging evidence that PDAC stroma has a significant bearing on disease behaviour and response to therapy. Lastly, with the above caveats in mind, current knowledge gaps and the implications and rationales for PRMT5 inhibitor development in PDAC will be explored.

FKBP4 integrates FKBP4/Hsp90/IKK with FKBP4/Hsp70/RelA complex to promote lung adenocarcinoma progression via IKK/NF-κB signaling

FKBP4 belongs to the family of immunophilins, which serve as a regulator for steroid receptor activity. Thus, FKBP4 has been recognized to play a critical role in several hormone-dependent cancers, including breast and prostate cancer. However, there is still no research to address the role of FKBP4 on lung adenocarcinoma (LUAD) progression. We found that FKBP4 expression was elevated in LUAD samples and predicted significantly shorter overall survival based on TCGA and our cohort of LUAD patients. Furthermore, FKBP4 robustly increased the proliferation, metastasis, and invasion of LUAD in vitro and vivo. Mechanistic studies revealed the interaction between FKBP4 and IKK kinase complex. We found that FKBP4 potentiated IKK kinase activity by interacting with Hsp90 and IKK subunits and promoting Hsp90/IKK association. Also, FKBP4 promotes the binding of IKKγ to IKKβ, which supported the facilitation role in IKK complex assembly. We further identified that FKBP4 TPR domains are essential for FKBP4/IKK interaction since its association with Hsp90 is required. In addition, FKBP4 PPIase domains are involved in FKBP4/IKKγ interaction. Interestingly, the association between FKBP4 and Hsp70/RelA favors the transport of RelA toward the nucleus. Collectively, FKBP4 integrates FKBP4/Hsp90/IKK with FKBP4/Hsp70/RelA complex to potentiate the transcriptional activity and nuclear translocation of NF-κB, thereby promoting LUAD progression. Our findings suggest that FKBP4 may function as a prognostic biomarker of LUAD and provide a newly mechanistic insight into modulating IKK/NF-κB signaling.

PRMT5 Promotes Cyclin E1 and Cell Cycle Progression in CD4 Th1 Cells and Correlates With EAE Severity

Multiple Sclerosis (MS) is a debilitating central nervous system disorder associated with inflammatory T cells. Activation and expansion of inflammatory T cells is thought to be behind MS relapses and influence disease severity. Protein arginine N-methyltransferase 5 (PRMT5) is a T cell activation-induced enzyme that symmetrically dimethylates proteins and promotes T cell proliferation. However, the mechanism behind PRMT5-mediated control of T cell proliferation and whether PRMT5 contributes to diseases severity is unclear. Here, we evaluated the role of PRMT5 on cyclin/cdk pairs and cell cycle progression, as well as PRMT5's link to disease severity in an animal model of relapsing-remitting MS. Treatment of T helper 1 (mTh1) cells with the selective PRMT5 inhibitor, HLCL65, arrested activation-induced T cell proliferation at the G1 stage of the cell cycle, suggesting PRMT5 promotes cell cycle progression in CD4+ T cells. The Cyclin E1/Cdk2 pair promoting G1/S progression was also decreased after PRMT5 inhibition, as was the phosphorylation of retinoblastoma. In the SJL mouse relapsing-remitting model of MS, the highest PRMT5 expression in central nervous system-infiltrating cells corresponded to peak and relapse timepoints. PRMT5 expression also positively correlated with increasing CD4 Th cell composition, disease severity and Cyclin E1 expression. These data indicate that PRMT5 promotes G1/S cell cycle progression and suggest that this effect influences disease severity and/or progression in the animal model of MS. Modulating PRMT5 levels may be useful for controlling T cell expansion in T cell-mediated diseases including MS.

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.

Upregulation of MTOR, RPS6KB1, and EIF4EBP1 in the whole blood samples of Iranian patients with multiple sclerosis compared to healthy controls

Various genetic and epigenetic mechanisms have been suggested to play roles as the underlying pathophysiology of Multiple Sclerosis (MS). Changes in different parts of the mTOR signaling pathway are among the potential suggested mechanisms based on the specific roles of this pathway in CNS. MTOR, RPS6KB1, and EIFEBP1 genes are among important genes in the mTOR pathway, responsible for the proper function of acting proteins in this signaling pathway. This study aimed to investigate the relative expression levels of these genes in the blood samples of relapsing-remitting MS (RRMS) patients compared to healthy controls. In this case-control study blood samples were collected from 30 newly diagnosed RRMS patients and 30 age and sex-matched healthy controls. mRNA level of MTOR, RPS6KB1, and EIFEBP1 genes were assessed using Real-Time PCR. The expression of MTOR, RPS6KB1, and EIF4EBP1 genes was up regulated in MS patients compared to healthy controls (p < 0.001 for all mentioned genes). Considering gender differences, expression of the mentioned genes was increased among female patients (all P < 0.001). However, no statistically significant changes were observed among male patients. Based on the receiver operating characteristic, MTOR gene had the highest diagnostic value followed by EIF4EBP1 and RPS6KB1 genes in differentiating RRMS patients from controls. In conclusion, we found the simultaneous upregulation of MTOR, RPS6KB1, and EIF4EBP1 genes among RRMS patients. MTOR showed to have the highest diagnostic value compared to other 2 genes in differentiating RRMS patients. Further studies evaluating the importance of these findings from pharmacological and prognostic perspectives are necessary.

Protein Arginine Methyltransferase 5 in T Lymphocyte Biology

Protein arginine methyltransferase 5 (PRMT5) is the major methyltransferase (MT) catalyzing symmetric dimethylation (SDM). PRMT5 regulates developmental, homeostatic and disease processes in vertebrates and invertebrates, and a carcinogenic role has been observed in mammals. Recently, tools generated for PRMT5 loss of function have allowed researchers to demonstrate essential roles for PRMT5 in mouse and human lymphocyte biology. PRMT5 modulates CD4⁺ and CD8⁺ T cell development in the thymus, peripheral homeostasis, and differentiation into CD4⁺ helper T lymphocyte (Th)17 cell phenotypes. Here, we provide a timely review of the milestones leading to our current understanding of PRMT5 in T cell biology, discuss current tools to modify PRMT5 expression/activity, and highlight mechanistic pathways.

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.

Protein arginine methyltransferase 5 promotes cholesterol biosynthesis-mediated Th17 responses and autoimmunity

Protein arginine methyltransferase 5 (PRMT5) catalyzes symmetric dimethylation (SDM) of arginine, a posttranslational modification involved in oncogenesis and embryonic development. However, the role and mechanisms by which PRMT5 modulates Th cell polarization and autoimmune disease have not yet been elucidated. Here, we found that PRMT5 promoted SREBP1 SDM and the induction of cholesterol biosynthetic pathway enzymes that produce retinoid-related orphan receptor (ROR) agonists that activate RORγt. Specific loss of PRMT5 in the CD4+ Th cell compartment suppressed Th17 differentiation and protected mice from developing experimental autoimmune encephalomyelitis (EAE). We also found that PRMT5 controlled thymic and peripheral homeostasis in the CD4+ Th cell life cycle and invariant NK (iNK) T cell development and CD8+ T cell maintenance. This work demonstrates that PRMT5 expression in recently activated T cells is necessary for the cholesterol biosynthesis metabolic gene expression program that generates RORγt agonistic activity and promotes Th17 differentiation and EAE. These results point to Th PRMT5 and its downstream cholesterol biosynthesis pathway as promising therapeutic targets in Th17-mediated diseases.