Protein arginine methyltransferase 5 accelerates tumor growth by arginine methylation of the tumor suppressor programmed cell death 4

The role of Pdcd4 in tumour suppression and protein translation

Programmed cell death 4 (Pdcd4), a tumour suppressor, is frequently down-regulated in various types of cancer. Pdcd4 has been demonstrated to efficiently suppress tumour promotion, progression and proliferation. The biochemical function of Pdcd4 is a protein translation inhibitor. Although the fact that Pdcd4 inhibits protein translation has been known for more than a decade, the mechanism by which Pdcd4 controls tumorigenesis through translational regulation of its target genes is still not fully understood. Recent studies show that Pdcd4 inhibits translation of stress-activated-protein kinase interacting protein 1 to suppress tumour invasion, depicting a picture of how Pdcd4 inhibits tumorigenesis through translational inhibition. Thus, understanding the mechanism of how Pdcd4 attenuates tumorigenesis by translational control should provide a new strategy for combating cancer.

The LINC01138 drives malignancies via activating arginine methyltransferase 5 in hepatocellular carcinoma

Recurrent chromosomal aberrations have led to the discovery of oncogenes or tumour suppressors involved in carcinogenesis. Here we characterized an oncogenic long intergenic non-coding RNA in the frequent DNA-gain regions in hepatocellular carcinoma (HCC), LINC01138 (long intergenic non-coding RNA located on 1q21.2). The LINC01138 locus is frequently amplified in HCC; the LINC01138 transcript is stabilized by insulin like growth factor-2 mRNA-binding proteins 1/3 (IGF2BP1/IGF2BP3) and is associated with the malignant features and poor outcomes of HCC patients. LINC01138 acts as an oncogenic driver that promotes cell proliferation, tumorigenicity, tumour invasion and metastasis by physically interacting with arginine methyltransferase 5 (PRMT5) and enhancing its protein stability by blocking ubiquitin/proteasome-dependent degradation in HCC. The discovery of LINC01138, a promising prognostic indicator, provides insight into the molecular pathogenesis of HCC, and the LINC01138/PRMT5 axis is an ideal therapeutic target for HCC treatment.

Protein arginine methyltransferase 5 promotes lung cancer metastasis via the epigenetic regulation of miR-99 family/FGFR3 signaling

Protein arginine methyltransferase 5 (PRMT5) functions as a tumor initiator to regulate several cancer progressions, such as proliferation and apoptosis, by catalyzing the symmetrical dimethylation (me2s) of arginine residues within targeted molecules. However, the exact role of PRMT5-mediated metastasis in lung cancer is not fully understood. Here, we illustrated its potential effects in lung cancer metastasis in vivo and vitro. PRMT5 was frequently overexpressed in lung tumors, and its expression was positively related to tumor stages, lymphatic metastasis and poor outcome. In this model, PRMT5 repressed the transcription of the miR-99 family by symmetrical dimethylation of histone H4R3, which increased FGFR3 expression and in turn activated Erk1/2 and Akt, leading to cell growth and metastasis in lung cancer. Furthermore, loss of PRMT5 exerted anti-metastasis effects on lung cancer progression by blocking histone-modification of miR-99 family. Overall, this study provides new insights into the PRMT5/miR-99 family/FGFR3 axis in regulating lung cancer progression and identifies PRMT5 as a promising prognostic biomarker and therapeutic target.

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.

Targeting protein arginine methyltransferase 5 in disease

PRMT5 catalyzes the mono- and symmetric dimethylation of the arginine N-guanidine group of a wide variety of target proteins including histones, transcriptional elongation factors, kinases and tumor suppressors by utilizing the essential co-factor S-adenosylmethionine as methyl source. PRMT5 overexpression has been linked to the progression of various diseases, including cancer, and is oftentimes associated with a poor prognosis. Therefore, PRMT5 is promoted as a valuable target for drug discovery approaches and was a subject matter in recent endeavors aiming for the development of specific PRMT5 inhibitors. This review will embrace the significance of PRMT5 as therapeutic target with respect to its molecular interdependencies in disease states as well as its implication in drug development approaches.

Arginine methyltransferase inhibitor 1 inhibits gastric cancer by downregulating eIF4E and targeting PRMT5

Arginine methylation is carried out by protein arginine methyltransferase (PRMTs) family. Arginine methyltransferase inhibitor 1 (AMI-1) is mainly used to inhibit type I PRMT activity in vitro. However, the effects of AMI-1 on type II PRMT5 activity and gastric cancer (GC) remain unclear. In this study, we provided the first evidence that AMI-1 significantly inhibited GC cell proliferation and migration while induced GC cell apoptosis, and reduced the expression of PRMT5, eukaryotic translation initiation factor 4E (eIF4E), symmetric dimethylation of histone 3 (H3R8me2s) and histone 4 (H4R3me2s). In addition, AMI-1 inhibited tumor growth, downregulated eIF4E, H4R3me2s and H3R8me2s expression in mice xenografts model of GC. Collectively, our results suggest that AMI-1 inhibits GC by downregulating eIF4E and targeting type II PRMT5.

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.

Inhibitors of Protein Methyltransferases and Demethylases

Post-translational modifications of histones by protein methyltransferases (PMTs) and histone demethylases (KDMs) play an important role in the regulation of gene expression and transcription and are implicated in cancer and many other diseases. Many of these enzymes also target various nonhistone proteins impacting numerous crucial biological pathways. Given their key biological functions and implications in human diseases, there has been a growing interest in assessing these enzymes as potential therapeutic targets. Consequently, discovering and developing inhibitors of these enzymes has become a very active and fast-growing research area over the past decade. In this review, we cover the discovery, characterization, and biological application of inhibitors of PMTs and KDMs with emphasis on key advancements in the field. We also discuss challenges, opportunities, and future directions in this emerging, exciting research field.

Protein arginine methyltransferase 5 functions as an epigenetic activator of the androgen receptor to promote prostate cancer cell growth

Protein arginine methyltransferase 5 (PRMT5) is an emerging epigenetic enzyme that mainly represses transcription of target genes via symmetric dimethylation of arginine residues on histones H4R3, H3R8 and H2AR3. Accumulating evidence suggests that PRMT5 may function as an oncogene to drive cancer cell growth by epigenetic inactivation of several tumor suppressors. Here, we provide evidence that PRMT5 promotes prostate cancer cell growth by epigenetically activating transcription of the androgen receptor (AR) in prostate cancer cells. Knockdown of PRMT5 or inhibition of PRMT5 by a specific inhibitor reduces the expression of AR and suppresses the growth of multiple AR-positive, but not AR-negative, prostate cancer cells. Significantly, knockdown of PRMT5 in AR-positive LNCaP cells completely suppresses the growth of xenograft tumors in mice. Molecular analysis reveals that PRMT5 binds to the proximal promoter region of the AR gene and contributes mainly to the enriched symmetric dimethylation of H4R3 in the same region. Mechanistically, PRMT5 is recruited to the AR promoter by its interaction with Sp1, the major transcription factor responsible for AR transcription, and forms a complex with Brg1, an ATP-dependent chromatin remodeler, on the proximal promoter region of the AR gene. Furthermore, PRMT5 expression in prostate cancer tissues is significantly higher than that in benign prostatic hyperplasia tissues, and PRMT5 expression correlates positively with AR expression at both the protein and mRNA levels. Taken together, our results identify PRMT5 as a novel epigenetic activator of AR in prostate cancer. Given that inhibiting AR transcriptional activity or androgen synthesis remains the major mechanism of action for most existing anti-androgen agents, our findings also raise an interesting possibility that targeting PRMT5 may represent a novel approach for prostate cancer treatment by eliminating AR expression.

PRMT5-Selective Inhibitors Suppress Inflammatory T Cell Responses and Experimental Autoimmune Encephalomyelitis

In the autoimmune disease multiple sclerosis and its animal model, experimental autoimmune encephalomyelitis (EAE), expansion of pathogenic, myelin-specific Th1 cell populations drives active disease; selectively targeting this process may be the basis for a new therapeutic approach. Previous studies have hinted at a role for protein arginine methylation in immune responses, including T cell-mediated autoimmunity and EAE. However, a conclusive role for the protein arginine methyltransferase (PRMT) enzymes that catalyze these reactions has been lacking. PRMT5 is the main PRMT responsible for symmetric dimethylation of arginine residues of histones and other proteins. PRMT5 drives embryonic development and cancer, but its role in T cells, if any, has not been investigated. In this article, we show that PRMT5 is an important modulator of CD4⁺ T cell expansion. PRMT5 was transiently upregulated during maximal proliferation of mouse and human memory Th cells. PRMT5 expression was regulated upstream by the NF-κB pathway, and it promoted IL-2 production and proliferation. Blocking PRMT5 with novel, highly selective small molecule PRMT5 inhibitors severely blunted memory Th expansion, with preferential suppression of Th1 cells over Th2 cells. In vivo, PRMT5 blockade efficiently suppressed recall T cell responses and reduced inflammation in delayed-type hypersensitivity and clinical disease in EAE mouse models. These data implicate PRMT5 in the regulation of adaptive memory Th cell responses and suggest that PRMT5 inhibitors may be a novel therapeutic approach for T cell-mediated inflammatory disease.

Discovery and optimization of selective inhibitors of protein arginine methyltransferase 5 by docking-based virtual screening

A series of highly selective and potent inhibitors against PRMT5 have been achieved using virtual screening and medicinal chemistry approaches.

Role of protein arginine methyltransferase 5 in inflammation and migration of fibroblast-like synoviocytes in rheumatoid arthritis

To probe the role of protein arginine methyltransferase 5 (PRMT5) in regulating inflammation, cell proliferation, migration and invasion of fibroblast‐like synoviocytes (FLSs) from patients with rheumatoid arthritis (RA). FLSs were separated from synovial tissues (STs) from patients with RA and osteoarthritis (OA). An inhibitor of PRMT5 (EPZ015666) and short interference RNA (siRNA) against PRMT5 were used to inhibit PRMT5 expression. The standard of protein was measured by Western blot or immunofluorescence. The excretion and genetic expression of inflammatory factors were, respectively, estimated by enzyme‐linked immunosorbent assay (ELISA) and real‐time polymerase chain reaction (PCR). Migration and invasion in vitro were detected by Boyden chamber assay. FLSs proliferation was detected by BrdU incorporation. Increased PRMT5 was discovered in STs and FLSs from patients with RA. In RA FLSs, the level of PRMT5 was up‐regulated by stimulation with IL‐1β and TNF‐α. Inhibition of PRMT5 by EPZ015666 and siRNA‐mediated knockdown reduced IL‐6 and IL‐8 production, and proliferation of RA FLSs. In addition, inhibition of PRMT5 decreased in vitro migration and invasion of RA FLSs. Furthermore, EPZ015666 restrained the phosphorylation of IκB kinaseβ and IκBα, as well as nucleus transsituation of p65 as well as AKT in FLSs. PRMT5 regulated the production of inflammatory factors, cell proliferation, migration and invasion of RA FLS, which was mediated by the NF‐κB and AKT pathways. Our data suggested that targeting PRMT5 to prevent synovial inflammation and destruction might be a promising therapy for RA.

Dysregulation of histone methyltransferases in breast cancer - Opportunities for new targeted therapies?

Histone methyltransferases (HMTs) catalyze the methylation of lysine and arginine residues on histone tails and non-histone targets. These important post-translational modifications are exquisitely regulated and affect chromatin compaction and transcriptional programs leading to diverse biological outcomes. There is accumulating evidence that genetic alterations of several HMTs impinge on oncogenic or tumor-suppressor functions and influence both cancer initiation and progression. HMTs therefore represent an opportunity for therapeutic targeting in those patients with tumors in which HMTs are dysregulated, to reverse the histone marks and transcriptional programs associated with aggressive tumor behavior. In this review, we describe the known histone methyltransferases and their emerging roles in breast cancer tumorigenesis.

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

Protein arginine methyltransferases (PRMTs) plays critical roles in cancer. PRMT5 has been implicated in several types of tumors. However, the role of PRMT5 in cancer development remains to be fully elucidated. Here, we provide evidence that PRMT5 is overexpressed in colorectal cancer (CRC) cells and patient-derived primary tumors, correlated with increased cell growth and decreased overall patient survival. Arginine methyltransferase inhibitor 1 (AMI-1)strongly inhibited tumor growth, increased the ratio of Bax/Bcl-2, and induced apoptosis in mouse CRC xenograt model. AMI-1 also induced apoptosis and decreased the migratory activity in several CRC cells. In CRC xenografts AMI-1 significantly decreased symmetric dimethylation of histone 4 (H4R3me2s), a histone mark of type II PRMT5, but not the expression of H4R3me2a, a histone mark of type I PRMTs. These results suggest that the inhibition of PRMT5 contributes to the antitumor efficacy of AMI-1. Chromatin immunoprecipitation (ChIP) identified FGFR3 and eIF4E as two key genes regulated by PRMT5. PRMT5 knockdown reduced the levels of H4R3me2s and H3R8me2s methylation on FGFR3 and eIF4E promoters, leading to decreased expressions of FGFR3 and eIF4E. Collectively, our findings provide new evidence that PRMT5 plays an important role in CRC pathogenesis through epigenetically regulating arginine methylation of oncogenes such as eIF4E and FGFR3.

Aflatoxin B1 induced upregulation of protein arginine methyltransferase 5 in human cell lines

The exposure of naturally occurring mycotoxins affects human health and play a vital role in cancer initiation and progression. Aflatoxin B1 is a difuranocoumarin mycotoxin, classified as a group I carcinogen. The present study was conducted to assess the effect of aflatoxin B1 on epigenetic regulatory proteins. The protein arginine methyltransferase 5 expression was induced upon aflatoxin B1 treatment in a dose and time dependent manner. Further global arginine methylation was also increased in the same manner. This is the first report showing the induction of epigenetic regulatory protein, protein arginine methyltransferase 5 upon aflatoxin B1 treatment. Further study is required to establish the detailed pathway of PRMT5 induction.

Relation between microRNAs and Apoptosis in Hepatocellular Carcinoma

AIM:

To determine the relation between serum microRNAs and apoptotic markers as regards development of HCC to understand the underlying mechanism of HCV related hepatocarcinogenesis.

PATIENTS AND METHODS:

A total of 65 serum samples (25 samples from controls, 20 samples from hepatitis and 20 samples from HCC patients) were collected for miRNAs (mir 21, mir 199-a, and mir 155) detection. Human Programmed cell death protein-4 (PDCD-4) and Human Cytochrome-C (CYT-C) were determined.

RESULTS:

miRNAs 21 and 155 were over expressed in sera of patients with HCC compared to patients with chronic hepatitis (p < 0.0001). While serum means values of miR 199a was significantly decreased among HCC group patients when compared to patients with chronic hepatitis (p < 0.0001). The serum levels of PCDC4 and CYTC were increased in patients with HCC when compared to chronic hepatitis patients. They were also increased in patients with chronic hepatitis when compared to controls (p < 0.05, significant). There was direct correlations between apoptotic markers and oncomirs miRNAs 21 and 155 while apoptotic markers were inversely correlated with miRNA 199-a.

CONCLUSION:

Both microRNAs and apoptotic markers have roles in HCC pathogenesis. It seems that oncogenic microRNAs induce liver carcinogenesis in HCV patients irrespective of suppression of apoptosis.

Small Molecule Inhibitors of Protein Arginine Methyltransferases

INTRODUCTION

Arginine methylation is an abundant posttranslational modification occurring in mammalian cells and catalyzed by protein arginine methyltransferases (PRMTs). Misregulation and aberrant expression of PRMTs are associated with various disease states, notably cancer. PRMTs are prominent therapeutic targets in drug discovery.

AREAS COVERED

The authors provide an updated review of the research on the development of chemical modulators for PRMTs. Great efforts are seen in screening and designing potent and selective PRMT inhibitors, and a number of micromolar and submicromolar inhibitors have been obtained for key PRMT enzymes such as PRMT1, CARM1, and PRMT5. The authors provide a focus on their chemical structures, mechanism of action, and pharmacological activities. Pros and cons of each type of inhibitors are also discussed.

EXPERT OPINION

Several key challenging issues exist in PRMT inhibitor discovery. Structural mechanisms of many PRMT inhibitors remain unclear. There lacks consistency in potency data due to divergence of assay methods and conditions. Physiologically relevant cellular assays are warranted. Substantial engagements are needed to investigate pharmacodynamics and pharmacokinetics of the new PRMT inhibitors in pertinent disease models. Discovery and evaluation of potent, isoform-selective, cell-permeable and in vivo-active PRMT modulators will continue to be an active arena of research in years ahead.

Structure and Property Guided Design in the Identification of PRMT5 Tool Compound EPZ015666

The recent publication of a potent and selective inhibitor of protein methyltransferase 5 (PRMT5) provides the scientific community with in vivo-active tool compound EPZ015666 (GSK3235025) to probe the underlying pharmacology of this key enzyme. Herein, we report the design and optimization strategies employed on an initial hit compound with poor in vitro clearance to yield in vivo tool compound EPZ015666 and an additional potent in vitro tool molecule EPZ015866 (GSK3203591).

Arginine Methylation of SREBP1a via PRMT5 Promotes De Novo Lipogenesis and Tumor Growth

Dysregulation of the sterol regulatory element-binding transcription factors sterol regulatory element-binding protein (SREBP) and SREBF activates de novo lipogenesis to high levels in cancer cells, a critical event in driving malignant growth. In this study, we identified an important posttranslational mechanism by which SREBP1a is regulated during metabolic reprogramming in cancer cells. Mass spectrometry revealed protein arginine methyltransferase 5 (PRMT5) as a binding partner of SREBP1a that symmetrically dimethylated it on R321, thereby promoting transcriptional activity. Furthermore, PRMT5-induced methylation prevented phosphorylation of SREBP1a on S430 by GSK3β, leading to its disassociation from Fbw7 (FBXW7) and its evasion from degradation through the ubiquitin-proteasome pathway. Consequently, methylation-stabilized SREBP1a increased de novo lipogenesis and accelerated the growth of cancer cells in vivo and in vitro. Clinically, R321 symmetric dimethylation status was associated with malignant progression of human hepatocellular carcinoma, where it served as an independent risk factor of poor prognosis. By showing how PRMT5-induced methylation of SREBP1a triggers hyperactivation of lipid biosynthesis, a key event in tumorigenesis, our findings suggest a new generalized strategy to selectively attack tumor metabolism.

The E3 ubiquitin ligase CHIP mediates ubiquitination and proteasomal degradation of PRMT5

Protein arginine methyltransferase 5 (PRMT5) is an important member of the protein arginine methyltransferase family that regulates many cellular processes through epigenetic control of target gene expression. Because of its overexpression in a number of human cancers and its essential role in cell proliferation, transformation, and cell cycle progression, PRMT5 has been recently proposed to function as an oncoprotein in cancer cells. However, how its expression is regulated in cancer cells remains largely unknown. We have previously demonstrated that the transcription of PRMT5 can be negatively regulated by the PKC/c-Fos signaling pathway through modulating the transcription factor NF-Y in prostate cancer cells. In the present study, we demonstrated that PRMT5 undergoes polyubiquitination, possibly through multiple lysine residues. We also identified carboxyl terminus of heat shock cognate 70-interacting protein (CHIP), an important chaperone-dependent E3 ubiquitin ligase that couples protein folding/refolding to protein degradation, as an interacting protein of PRMT5 via mass spectrometry. Their interaction was further verified by co-immuoprecipitation, GST pull-down, and bimolecular fluorescence complementation (BiFC) assay. In addition, we provided evidence that the CHIP/chaperone system is essential for the negative regulation of PRMT5 expression via K48-linked ubiquitin-dependent proteasomal degradation. Given that down-regulation of CHIP and overexpression of PRMT5 have been observed in several human cancers, our finding suggests that down-regulation of CHIP may be one of the mechanisms underlying PRMT5 overexpression in these cancers.

Targeting protein arginine methyltransferase 5 inhibits human hepatocellular carcinoma growth via the downregulation of beta-catenin

BACKGROUND

Protein arginine methyltransferase 5 (PRMT5), a type II PRMT, is highly expressed in some tumors, but its role in hepatocellular carcinoma (HCC) is still unknown.

METHODS

PRMT5 level in HCC specimens was determined by immunohistochemical staining and the association with clinicopathologic features was evaluated. PRMT5 was inhibited by AMI-1 (a small molecule inhibitor of PRMTs) or small interference RNA (siRNA). The proliferation of HCC cells was tested by Cell Counting Kit-8, cell migration was evaluated by Transwell assay and cell cycle and apoptosis were analyzed by flow cytometry. The effect of AMI-1 on HCC in vivo was examined by mouse xenograft model.

RESULTS

PRMT5 expression was markedly upregulated in HCC tissues, and correlated inversely with overall patient survival. Knockdown of PRMT5 significantly reduced the proliferation of HCC cells, but did not affect the growth of normal liver cells. Furthermore, β-catenin was identified as a target of PRMT5. Silencing PRMT5 significantly down-regulated the expression of β-catenin and the downstream effector Cyclin D1 in HCC cells. AMI-1 strongly inhibited HCC growth in vivo, increased the ratio of Bax/Bcl-2, and led to apoptosis and loss of migratory activity in several HCC cells. Meanwhile, AMI-1 decreased the expression levels of symmetric dimethylation of H4 (H4R3me2s), a histone mark of PRMT5.

CONCLUSIONS

PRMT5 plays an important role in HCC. PRMT5 may be a promising target for HCC therapy.

High nuclear expression of protein arginine methyltransferase-5 is a potentially useful marker to estimate submucosal invasion in endoscopically resected early colorectal carcinoma

Protein arginine methyltransferase-5 (PRMT5), a major type II arginine methyltransferase, is an important epigenetic modifier with oncogene-like properties because of its ability to repress the expression of tumor suppressor genes. We determined the correlations between PRMT5 expression or its cellular localization and malignant progression, with special reference to invasiveness, in colorectal adenomas and early colorectal carcinomas (CRCs). We performed immunohistochemical detection of PRMT5 in 108 endoscopically resected tissue samples (6 adenomas with low-grade dysplasia, 34 adenomas with high-grade dysplasia, 30 intramucosal carcinomas, and 38 submucosal invasive carcinomas). Early CRC (55 of 68, 80.9%) showed more frequent nuclear expression of PRMT5 than adenoma (15 of 40, 37.5%) (P < 0.001). Furthermore, high (strong staining in ≥ 50% of nuclei) nuclear expression of PRMT5 was more common in submucosal invasive carcinoma (21 of 38, 55.3%) than in intramucosal carcinoma (9 of 30, 30.0%) (P = 0.037). In conclusion, our data suggests that high nuclear expression of PRMT5 is a potentially useful marker for estimating submucosal invasion of early CRC in endoscopically resected specimens.

Late Cornified Envelope Group I, a novel target of p53, regulates PRMT5 activity

p53 is one of the most important tumor suppressor genes involved in human carcinogenesis. Although downstream targets of p53 and their biologic functions in cancer cells have been extensively investigated, it is still far from the full understanding. Here, we demonstrate that Late Cornified Envelope Group I (LCE1) genes, which are located in the LCE gene clusters encoding multiple well-conserved stratum-corneum proteins, are novel downstream targets of p53. Exogenous p53 overexpression using an adenoviral vector system significantly enhanced the expression of LCE1 cluster genes. We also observed induction of LCE1 expressions by DNA damage, which was caused by treatment with adriamycin or UV irradiation in a wild-type p53-dependent manner. Concordantly, the induction of LCE1 by DNA damage was significantly attenuated by the knockdown of p53. Among predicted p53-binding sites within the LCE1 gene cluster, we confirmed one site to be a p53-enhancer sequence by reporter assays. Furthermore, we identified LCE1 to interact with protein arginine methyltransferase 5 (PRMT5). Knockdown of LCE1 by specific small interfering RNAs significantly increased the symmetric dimethylation of histone H3 arginine 8, a substrate of PRMT5, and overexpression of LCE1F remarkably decreased its methylation level. Our data suggest that LCE1 is a novel p53 downstream target that can be directly transactivated by p53 and is likely to have tumor suppressor functions through modulation of the PRMT5 activity.

Differential expression, distinct localization and opposite effect on Golgi structure and cell differentiation by a novel splice variant of human PRMT5

Alternative splicing contributes greatly to the proteomic diversity of metazoans. Protein arginine methyltransferase 5 (PRMT5) methylates arginines of Golgi components and other factors exerting diverse effects on cell growth/differentiation, but the underlying molecular basis for its subcellular distribution and diverse roles has not been fully understood. Here we show the detailed properties of an evolutionarily emerged splice variant of human PRMT5 (PRMT5S) that is distinct from the original isoform (PRMT5L). The isoforms are differentially expressed among mammalian cells and tissues. The PRMT5S is distributed all over the cell but PRMT5L mainly colocalizes with Giantin, a Golgi marker. PRMT5 knockdown led to an enlarged Giantin pattern, which was prevented by the expression of either isoform. Rescuing PRMT5S also increased the percentage of cells with an interphase Giantin pattern compacted at one end of the nucleus, consistent with its cell cycle-arresting effect, while rescuing PRMT5L increased that of the mitotic Giantin patterns of dynamically fragmented structures. Moreover, the isoforms are differentially expressed during neuronal or dendritic cell differentiation, and their ectopic expression showed an opposite effect on dendritic cell differentiation. Furthermore, besides their differential regulation of gene expression, both isoforms also similarly regulate over a thousand genes particularly those involved in apoptosis and differentiation. Taking these properties together, we propose that their differential expression and subcellular localization contribute to spatial and temporal regulation of arginine methylation and gene expression to exert different effects. The novel PRMT5S likely contributes to the observed diverse effects of PRMT5 in cells.

The PRMT5 arginine methyltransferase: many roles in development, cancer and beyond

Post-translational arginine methylation is responsible for regulation of many biological processes. The protein arginine methyltransferase 5 (PRMT5, also known as Hsl7, Jbp1, Skb1, Capsuleen, or Dart5) is the major enzyme responsible for mono- and symmetric dimethylation of arginine. An expanding literature demonstrates its critical biological function in a wide range of cellular processes. Histone and other protein methylation by PRMT5 regulate genome organization, transcription, stem cells, primordial germ cells, differentiation, the cell cycle, and spliceosome assembly. Metazoan PRMT5 is found in complex with the WD-repeat protein MEP50 (also known as Wdr77, androgen receptor coactivator p44, or Valois). PRMT5 also directly associates with a range of other protein factors, including pICln, Menin, CoPR5 and RioK1 that may alter its subcellular localization and protein substrate selection. Protein substrate and PRMT5-MEP50 post-translation modifications induce crosstalk to regulate PRMT5 activity. Crystal structures of C. elegans PRMT5 and human and frog PRMT5-MEP50 complexes provide substantial insight into the mechanisms of substrate recognition and procession to dimethylation. Enzymological studies of PRMT5 have uncovered compelling insights essential for future development of specific PRMT5 inhibitors. In addition, newly accumulating evidence implicates PRMT5 and MEP50 expression levels and their methyltransferase activity in cancer tumorigenesis, and, significantly, as markers of poor clinical outcome, marking them as potential oncogenes. Here, we review the substantial new literature on PRMT5 and its partners to highlight the significance of understanding this essential enzyme in health and disease.

Role of JMJD6 in Breast Tumourigenesis

Background

Protein arginine methylation is a common post translational modification that regulates protein properties. This modification is carried out by a family of nine arginine methyltransferases (PRMTs). Arginine methylation has already been linked to tumourigenesis as overexpression of these enzymes was associated with various cancers, notably in breast cancers. Since the Jumonji Domain Containing 6 protein (JMJD6) possesses an arginine demethylase activity able to remove the methyl mark, we wanted to assess its potential role in breast tumourigenesis.

Methods

The expression of the protein by tissue microarray immunohistochemical staining was performed on a cohort of 133 breast tumours. Using cell lines stably overexpressing or knocked down for JMJD6, we evaluated its role on cell proliferation, cell migration, colony formation and mice tumour xenografts.

Results

The analysis of JMJD6 expression in a cohort of breast tumour samples indicates that JMJD6 was highly expressed in aggressive breast tumours. Moreover, high expression of JMJD6 was associated with poor disease-free survival of patients in this cohort. JMJD6 silencing in breast tumoural cells promotes certain characteristics of tumourigenesis including proliferation, migration in vitro, and tumour growth in vivo. These effects are dependent on its demethylase activity as an enzymatic dead mutant lost these properties.

Conclusions

Although JMJD6 displays anti-tumoral properties in cell lines, its expression in breast tumours may be a marker of poor prognosis, suggesting that its function could be altered in breast cancer.

A selective inhibitor of PRMT5 with in vivo and in vitro potency in MCL models

Protein arginine methyltransferase-5 (PRMT5) is reported to have a role in diverse cellular processes, including tumorigenesis, and its overexpression is observed in cell lines and primary patient samples derived from lymphomas, particularly mantle cell lymphoma (MCL). Here we describe the identification and characterization of a potent and selective inhibitor of PRMT5 with antiproliferative effects in both in vitro and in vivo models of MCL. EPZ015666 (GSK3235025) is an orally available inhibitor of PRMT5 enzymatic activity in biochemical assays with a half-maximal inhibitory concentration (IC50) of 22 nM and broad selectivity against a panel of other histone methyltransferases. Treatment of MCL cell lines with EPZ015666 led to inhibition of SmD3 methylation and cell death, with IC50 values in the nanomolar range. Oral dosing with EPZ015666 demonstrated dose-dependent antitumor activity in multiple MCL xenograft models. EPZ015666 represents a validated chemical probe for further study of PRMT5 biology and arginine methylation in cancer and other diseases.

Evolutionary emergence of a novel splice variant with an opposite effect on the cell cycle

Alternative splicing contributes greatly to the diversification of mammalian proteomes, but the molecular basis for the evolutionary emergence of splice variants remains poorly understood. We have recently found a novel class of splicing regulatory elements between the polypyrimidine tract (Py) and 3' AG (REPA) at intron ends in many human genes, including the multifunctional PRMT5 (for protein arginine methyltransferase 5) gene. The PRMT5 element is comprised of two G tracts that arise in most mammals and accompany significant exon skipping in human transcripts. The G tracts inhibit splicing by recruiting heterogeneous nuclear ribonucleoprotein (hnRNP) H and F (H/F) to reduce U2AF65 binding to the Py, causing exon skipping. The resulting novel shorter variant PRMT5S exhibits a histone H4R3 methylation effect similar to that seen with the original longer PRMT5L isoform but exhibits a distinct localization and preferential control of critical genes for cell cycle arrest at interphase in comparison to PRMT5L. This report thus provides a molecular mechanism for the evolutionary emergence of a novel splice variant with an opposite function in a fundamental cell process. The presence of REPA elements in a large group of genes implies their wider impact on different cellular processes for increased protein diversity in humans.

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

In this study, we examined protein arginine methyltransferase 5 (PRMT5) and tumor necrosis factor receptor-associated 4 (TRAF4) expression in breast cancer to find the interaction mechanism between the two. We examined TRAF4 and PRMT5 expression by immunohistochemistry and found that their expression is positively correlated in breast cancer. Besides, PRMT5 expression was significantly associated with histological type and tumor size (p < 0.05). PRMT5 nuclear expression was significantly associated with HER2 expression (p < 0.05). PRMT5 and TRAF4 were both overexpressed in breast cancer tissues and cells, and we found that PRMT5 binds to the zinc finger structures in TRAF4 by coimmunoprecipitation and Western blotting. We also tested the potential regulatory effect between TRAF4 and PRMT5. TRAF4 upregulated PRMT5 expression, which occurred predominantly in the nucleus, on which TRAF4 promotion of cell proliferation in breast cancer is mainly dependent. PRMT5 may play an important role in activation of the NF-κB signaling pathway.

Post-transcriptional regulation of programmed cell death 4 (PDCD4) mRNA by the RNA-binding proteins human antigen R (HuR) and T-cell intracellular antigen 1 (TIA1)

Post-transcriptional processing of mRNA transcripts plays a critical role in establishing the gene expression profile of a cell. Such processing events are mediated by a host of factors, including RNA-binding proteins and microRNAs. A number of critical cellular pathways are subject to regulation at multiple levels that allow fine-tuning of key biological responses. Programmed cell death 4 (PDCD4) is a tumor suppressor and an important modulator of mRNA translation that is regulated by a number of mechanisms, most notably as a target of the oncomiR, miR-21. Here, we provide evidence for post-transcriptional regulation of PDCD4 by the RNA-binding proteins, HuR and TIA1. Complementary approaches reveal binding of both HuR and TIA1 to the PDCD4 transcript. Consistent with a model where RNA-binding proteins modulate the PDCD4 transcript, knockdown of HuR and/or TIA1 results in a significant decrease in steady-state PDCD4 mRNA and protein levels. However, fractionation experiments suggest that the mode of regulation of the PDCD4 transcript likely differs in the cytoplasm and the nucleus as the pool of PDCD4 mRNA present in the cytoplasm is more stable than the nuclear pool of PDCD4 transcript. We observe a competitive mode of binding between HuR and TIA1 on the PDCD4 transcript in the cytoplasm, suggesting that these two factors dynamically interact with one another as well as the PDCD4 transcript to maintain tight control of PDCD4 levels. Overall, this study reveals an additional set of regulatory interactions that modulate the expression of PDCD4, a key pro-apoptotic factor, and also reveals new insights into how HuR and TIA1 functions are integrated to achieve such regulation.

Protein arginine methyltransferase 5 catalyzes substrate dimethylation in a distributive fashion

Protein arginine methyltransferase 5 (PRMT5) is a histone-modifying enzyme whose activity is aberrantly upregulated in various cancers and thereby contributes to a progrowth phenotype. Indeed, knockdown of PRMT5 leads to growth arrest and apoptosis, suggesting that inhibitors targeting this enzyme may have therapeutic utility in oncology. To aid the development of inhibitors targeting PRMT5, we initiated mechanistic studies geared to understand how PRMT5 selectively catalyzes the symmetric dimethylation of its substrates. Toward that end, we characterized the regiospecificity and processivity of bacterially expressed Caenorhabditis elegans PRMT5 (cPRMT5), insect cell-expressed human PRMT5 (hPRMT5), and human PRMT5 complexed with methylosome protein 50 (MEP50), i.e., the PRMT5·MEP50 complex. Our studies confirm that arginine 3 is the only site of methylation in both histone H4 and H4 tail peptide analogues and that sites distal to the site of methylation promote the efficient symmetric dimethylation of PRMT5 substrates by increasing the affinity of the monomethylated substrate for the enzyme. Additionally, we show for the first time that both cPRMT5 and the hPRMT5·MEP50 complex catalyze substrate dimethylation in a distributive manner, which is assisted by long-range interactions. Finally, our data confirm that MEP50 plays a key role in substrate recognition and activates PRMT5 activity by increasing its affinity for protein substrates. In total, our results suggest that it may be possible to allosterically inhibit PRMT5 by targeting binding pockets outside the active site.

Protein arginine methyltransferase 5 is a key regulator of the MYCN oncoprotein in neuroblastoma cells

Approximately half of poor prognosis neuroblastomas (NBs) are characterized by pathognomonic MYCN gene amplification and MYCN over-expression. Here we present data showing that short-interfering RNA mediated depletion of the protein arginine methyltransferase 5 (PRMT5) in cell-lines representative of NBs with MYCN gene amplification leads to greatly impaired growth and apoptosis. Growth suppression is not apparent in the MYCN-negative SH-SY5Y NB cell-line, or in two immortalized human fibroblast cell-lines. Immunoblotting of NB cell-lines shows that high PRMT5 expression is strongly associated with MYCN-amplification (P < 0.004, Mann-Whitney U-test) and immunohistochemical analysis of primary NBs reveals that whilst PRMT5 protein is ubiquitously expressed in the cytoplasm of most cells, MYCN-amplified tumours exhibit pronounced nuclear PRMT5 staining. PRMT5 knockdown in MYCN-overexpressing cells, including the SHEP-21N cell-line with inducible MYCN expression leads to a dramatic decrease in MYCN protein and MYCN-associated cell-death in SHEP-21N cells. Quantitative gene expression analysis and cycloheximide chase experiments suggest that PRMT5 regulates MYCN at a post-transcriptional level. Reciprocal co-immunoprecipitation experiments demonstrated that endogenous PRMT5 and MYCN interact in both SK-N-BE(2)C and NGP cell lines. By using liquid chromatography - tandem mass spectrometry (LC-MS/MS) analysis of immunoprecipitated MYCN protein, we identified several potential sites of arginine dimethylation on the MYCN protein. Together our studies implicate PRMT5 in a novel mode of MYCN post-translational regulation and suggest PRMT5 plays a major role in NB tumorigenesis. Small-molecule inhibitors of PRMT5 may therefore represent a novel therapeutic strategy for neuroblastoma and other cancers driven by the MYCN oncogene.

Transcriptional activation of PRMT5 by NF-Y is required for cell growth and negatively regulated by the PKC/c-Fos signaling in prostate cancer cells

Protein arginine methyltransferase 5 (PRMT5) symmetrically methylates arginine residues of histones and non-histone protein substrates and regulates a variety of cellular processes through epigenetic control of target gene expression or post-translational modification of signaling molecules. Recent evidence suggests that PRMT5 may function as an oncogene and its overexpression contributes to the development and progression of several human cancers. However, the mechanism underlying the regulation of PRMT5 expression in cancer cells remains largely unknown. In the present study, we have mapped the proximal promoter of PRMT5 to the -240bp region and identified nuclear transcription factor Y (NF-Y) as a critical transcription factor that binds to the two inverted CCAAT boxes and regulates PRMT5 expression in multiple cancer cell lines. Further, we present evidence that loss of PRMT5 is responsible for cell growth inhibition induced by knockdown of NF-YA, a subunit of NF-Y that forms a heterotrimeric complex with NF-YB and NF-YC for function. Significantly, we have found that activation of protein kinase C (PKC) by phorbol 12-myristate 13-acetate (PMA) in LNCaP prostate cancer cells down-regulates the expression of NF-YA and PRMT5 at the transcription level in a c-Fos-dependent manner. Given that down-regulation of several PKC isozymes is implicated in the development and progression of several human cancers, our findings suggest that the PKC-c-Fos-NF-Y signaling pathway may be responsible for PRMT5 overexpression in a subset of human cancer patients.

PRMT5 is essential for the eIF4E-mediated 5'-cap dependent translation

It is becoming clear that PRMT5 plays essential roles in cell cycle progression, survival, and responses to external stresses. However, the precise mechanisms underlying such roles of PRMT5 have not been clearly understood. Previously, we have demonstrated that PRMT5 participates in cellular adaptation to hypoxia by ensuring 5'-cap dependent translation of HIF-1α. Given that c-Myc and cyclin D1 expressions are also tightly regulated in 5'-cap dependent manner, we here tested the possibility that PRMT5 promotes cell proliferation by increasing de novo syntheses of the oncoproteins. c-Myc and cyclin D1 were found to be noticeably downregulated by PRMT5 knock-down. A RNA immunoprecipitation analysis, which can identify RNA-protein interactions, showed that PRMT5 is required for the interaction among eIF4E and 5'-UTRs of HIF-1α, c-Myc and cyclin D1 mRNAs. In addition, PRMT5 knock-down inhibited cell proliferation by inducing cell cycle arrest at the G1 phase. More importantly, ectopic expression of eIF4E significantly rescued the cell cycle progression and cell proliferation even in PRMT5-deficeint condition. Based on these results, we propose that PRMT5 determines cell fate by regulating 5'-cap dependent translation of proteins essential for proliferation and survival.

An evolutionarily conserved interaction of tumor suppressor protein Pdcd4 with the poly(A)-binding protein contributes to translation suppression by Pdcd4

The tumor suppressor protein programmed cell death 4 (Pdcd4) has been implicated in the translational regulation of specific mRNAs, however, the identities of the natural Pdcd4 target mRNAs and the mechanisms by which Pdcd4 affects their translation are not well understood. Pdcd4 binds to the eukaryotic translation initiation factor eIF4A and inhibits its helicase activity, which has suggested that Pdcd4 suppresses translation initiation of mRNAs containing structured 5′-untranslated regions. Recent work has revealed a second inhibitory mechanism, which is eIF4A-independent and involves direct RNA-binding of Pdcd4 to the target mRNAs. We have now identified the poly(A)-binding protein (PABP) as a novel direct interaction partner of Pdcd4. The ability to interact with PABP is shared between human and Drosophila Pdcd4, indicating that it has been highly conserved during evolution. Mutants of Pdcd4 that have lost the ability to interact with PABP fail to stably associate with ribosomal complexes in sucrose density gradients and to suppress translation, as exemplified by c-myb mRNA. Overall, our work identifies PABP as a novel functionally relevant Pdcd4 interaction partner that contributes to the regulation of translation by Pdcd4.

Enhanced arginine methylation of programmed cell death 4 protein during nutrient deprivation promotes tumor cell viability

The role of programmed cell death 4 (PDCD4) in tumor biology is context-dependent. PDCD4 is described as a tumor suppressor, but its coexpression with protein arginine methyltransferase 5 (PRMT5) promotes accelerated tumor growth. Here, we report that PDCD4 is methylated during nutrient deprivation. Methylation occurs because of increased stability of PDCD4 protein as well as increased activity of PRMT5 toward PDCD4. During nutrient deprivation, levels of methylated PDCD4 promote cell viability, which is dependent on an enhanced interaction with eIF4A. Upon recovery from nutrient deprivation, levels of methylated PDCD4 are regulated by phosphorylation, which controls both the localization and stability of methylated PDCD4. This study reveals that, in response to particular environmental cues, the role of PDCD4 is up-regulated and is advantageous for cell viability. These findings suggest that the methylated form of PDCD4 promotes tumor viability during nutrient deprivation, ultimately allowing the tumor to grow more aggressively.

Expression of PRMT5 correlates with malignant grade in gliomas and plays a pivotal role in tumor growth in vitro

Protein arginine methyltransferase 5 (PRMT5) catalyzes the formation of ω-NG,N'G-symmetric dimethylarginine residues on histones as well as other proteins. These modifications play an important role in cell differentiation and tumor cell growth. However, the role of PRMT5 in human glioma cells has not been characterized. In this study, we assessed protein expression profiles of PRMT5 in control brain, WHO grade II astrocytomas, anaplastic astrocytomas, and glioblastoma multiforme (GBM) by immunohistochemistry. PRMT5 was low in glial cells in control brain tissues and low grade astrocytomas. Its expression increased in parallel with malignant progression, and was highly expressed in GBM. Knockdown of PRMT5 by small hairpin RNA caused alterations of p-ERK1/2 and significantly repressed the clonogenic potential and viability of glioma cells. These findings indicate that PRMT5 is a marker of malignant progression in glioma tumors and plays a pivotal role in tumor growth.

Expression of PRMT5 in lung adenocarcinoma and its significance in epithelial-mesenchymal transition

Although protein arginine methyltransferase 5 (PRMT5) has been implicated in various cancers, its expression pattern in lung adenocarcinoma cell lines and tissues has not been elucidated enough. In this study, microarray analysis of 40 non-small-cell lung carcinoma cell lines showed that PRMT5 was a candidate histone methyltransferase gene that correlated with epithelial-mesenchymal transition. Immunocytochemical analysis of these cell lines indicated that the expression of PRMT5 was localized to the cytoplasm of E-cadherin-low and vimentin-high cell lines, whereas it was predominant in the nucleus and faint in the cytoplasm of E-cadherin-high and vimentin-low cell lines. Immunohistochemical analysis of lung adenocarcinoma cases (n = 130) revealed that the expression of PRMT5 was high in the cytoplasm of 47 cases (36%) and the nuclei of 34 cases (26%). The marked cytoplasmic expression of PRMT5 was frequently observed in high-grade subtypes (1 of 17 low grade, 21 of 81 intermediate grade, and 25 of 32 high grade; P < .0001) such as solid adenocarcinoma with the low expression of thyroid transcription factor 1 (the master regulator of lung) and low expression of cytokeratin 7 and E-cadherin (2 markers for bronchial epithelial differentiation), whereas the high nuclear expression of PRMT5 was frequently noted in adenocarcinoma in situ, a low-grade subtype (6 of 17 low grade, 25 of 81 intermediate grade, and 3 of 32 high grade; P = .0444). The cytoplasmic expression of PRMT5 correlated with a poor prognosis (P = .0089). We herein highlighted the importance of PRMT5 expression, especially its cytoplasmic expression, in the process of epithelial-mesenchymal transition and loss of the bronchial epithelial phenotype of lung adenocarcinoma.

Cellular localization of protein arginine methyltransferase-5 correlates with grade of lung tumors

Background

Protein arginine methyltransferase-5 (PRMT5) is a chromatin-modifying enzyme capable of methylating histone and non-histone proteins, and is involved in a wide range of cellular processes that range from transcriptional regulation to organelle biosynthesis. As such, its overexpression has been linked to tumor suppressor gene silencing, enhanced tumor cell growth and survival.

Material and methods

Quantitative real-time polymerase chain reaction, Western immunoblot and immunohistochemistry were used to characterize PRMT5 expression in lung cancer cell lines and human tumors. Clinicopathological findings of tissue microarray based samples from 229 patients with non-small cell lung carcinomas (NSCLC) and 133 cases with pulmonary neuroendocrine tumors (NET) were analyzed with regard to nuclear and cytoplasmic PRMT5 expression.

Results

There was statistically significant difference in PRMT5 messenger RNA expression between tumors and nonneoplastic lung tissues. Immunoblot experiments showed abundant expression of PRMT5 and its symmetric methylation mark H4R3 in lung carcinoma but not in non-neoplastic human pulmonary alveolar and bronchial epithelial cell lines. More than two thirds of lung tumors expressed PRMT5. High levels of cytoplasmic PRMT5 were detected in 20.5% of NSCLC and in 16.5% of NET; high levels of nuclear PRMT5 were detected in 38.0% of NSCLC and 24.0% of NET. Cytoplasmic PRMT5 was associated with high grade in both NSCLC and pulmonary NET while nuclear PRMT5 was more frequent in carcinoid tumors (p < 0.05).

Conclusion

The observed findings support the role of PRMT5 in lung tumorigenesis and reflect its functional dichotomy in cellular compartments.

Virtual slide

The virtual slides for this article can be found here: http://www.diagnosticpathology.diagnomx.eu/vs/1611895162102528

Protein arginine methylation of non-histone proteins and its role in diseases

Protein arginine methyltransferases (PRMTs) are a family of enzymes that can methylate arginine residues on histones and other proteins. PRMTs play a crucial role in influencing various cellular functions, including cellular development and tumorigenesis. Arginine methylation by PRMTs is found on both nuclear and cytoplasmic proteins. Recently, there is increasing evidence regarding post-translational modifications of non-histone proteins by PRMTs, illustrating the previously unknown importance of PRMTs in the regulation of various cellular functions by post-translational modifications. In this review, we present the recent developments in the regulation of non-histone proteins by PRMTs.