Inhibition of protein arginine methyltransferase 3 activity selectively impairs liver X receptor-driven transcription of hepatic lipogenic genes in vivo

LXR Agonist T0901317's Hepatic Impact Overrules Its Atheroprotective Action in Macrophages, Driving Early Atherogenesis in Chow-Diet-Fed Male Apolipoprotein E Knockout Mice

Preclinical studies regarding the potential of liver X receptor (LXR) agonists to inhibit macrophage foam cell formation and the development of atherosclerotic lesions are generally executed in mice fed with Western-type diets enriched in cholesterol and fat. Here, we investigated whether LXR agonism remains anti-atherogenic under dietary conditions with a low basal hepatic lipogenesis rate. Hereto, atherosclerosis-susceptible male apolipoprotein E knockout mice were fed a low-fat diet with or without 10 mg/kg/day LXR agonist T0901317 supplementation for 8 weeks. Importantly, T0901317 significantly stimulated atherosclerosis susceptibility, despite an associated increase in the macrophage gene expression levels of cholesterol efflux transporters ABCA1 and ABCG1. The pro-atherogenic effect of T0901317 coincided with exacerbated hypercholesterolemia, hypertriglyceridemia, and a significant rise in hepatic triglyceride stores and macrophage numbers. Furthermore, T0901317-treated mice exhibited elevated plasma MCP-1 levels and monocytosis. In conclusion, these findings highlight that the pro-atherogenic hepatic effects of LXR agonism are dominant over the anti-atherogenic effects in macrophages in determining the overall atherosclerosis outcome under low-fat diet feeding conditions. A low-fat diet experimental setting, as compared to the commonly used high-fat-diet-based preclinical setup, thus appears more sensitive in uncovering the potential relevance of the off-target liver effects of novel anti-atherogenic therapeutic approaches that target macrophage LXR.

Combination of mangiferin and T0901317 targeting autophagy promotes cholesterol efflux from macrophage foam cell in atherosclerosis

BACKGROUND

The synthetic liver X receptor ligand (LXR) T0901317 (T0) has been reported to attenuate atherosclerosis (AS) without hyperglyceridemia due to innovative drug combination or nano-sized drug delivery. Given the key roles of mangiferin (MGF) in lipid metabolism and atherogenesis, it is critical to investigate progression of atherosclerotic lesion after combined treatment of MGF and T0.

METHODS

Atherosclerotic plaque formation and hepatic lipid accumulation were compared in Apoe-/- mice among T0 and/or MGF treatment. The in vitro functions of MGF and T0 were analyzed by Oil-red O staining, cholesterol efflux assay, transmission electron microscopy and western blot analyses with or without acetylated low density lipoprotein.

RESULTS

The combination therapy are effective regulators for atherosclerotic plaque formation in Apoe-/- mice, due to upregulation of ABCA1 and ABCG1 induced by LXR activation. Subsequently, we identified autophagy promoted by MGF and T0 treatment establishes a positive feedback loop that increases cholesterol efflux, resulted from LXRα activation. Under atherogenic conditions, the autophagy inhibitor CQ abolished the enhancement effect on cholesterol outflow of MGF and T0. Mechanically, MGF and T0 promotes LXRα and mTOR/AMPK signaling cascade in macrophage, and promotes AMPK signaling cascade in hepatocyte, leading to lipid metabolic homeostasis.

CONCLUSIONS

Altogether, our findings reveal that MGF and T0 engages in AS therapy without side effects by activating AMPK-dependent autophagy to promote macrophage cholesterol efflux, and MGF might serve as a natural compound to assist T0 in AS via targeting autophagy.

Protein arginine methyltransferase 3: A crucial regulator in metabolic reprogramming and gene expression in cancers

Post-translational modification (PTM) of proteins increases proteome diversity, which is critical for maintaining cellular homeostasis. The importance of protein methylation in the regulation of diverse biological processes has been highlighted in the past decades. Methylation of the arginine residue on proteins is catalyzed by members of the protein arginine methyltransferase (PRMT) family. PRMTs play indispensable roles in various pathways that regulate cancer development, progression, and drug response. In this review, we discuss the role of PRMT3, a member of the PRMT family, in controlling oncogenic processes. Additionally, the effects of PRMT3 on the methylation of regulatory proteins involved in transcription, post-transcriptional control, ribosomal maturation, translation, biological synthesis, and metabolic signaling are summarized. Moreover, recent progresses in the development of PRMT3 inhibitors are introduced. Overall, this review highlights the importance of PRMT3 in tumorigenesis and discusses the underlying mechanisms by which PRMT3 modulates cellular metabolism and gene expression. These results also provide a molecular basis for therapeutic modalities by targeting PRMT3.

PRMT3 drives glioblastoma progression by enhancing HIF1A and glycolytic metabolism

Glioblastoma (GBM) is the most common and aggressive primary brain tumor, but the mechanisms underlying tumor growth and progression remain unclear. The protein arginine methyltransferases (PRMTs) regulate a variety of biological processes, however, their roles in GBM growth and progression are not fully understood. In this study, our functional analysis of gene expression networks revealed that among the PRMT family expression of PRMT3 was most significantly enriched in both GBM and low-grade gliomas. Higher PRMT3 expression predicted poorer overall survival rate in patients with gliomas. Knockdown of PRMT3 markedly reduced the proliferation and migration of GBM cell lines and patient-derived glioblastoma stem cells (GSC) in cell culture, while its over-expression increased the proliferative capacity of GSC cells by promoting cell cycle progression. Consistently, stable PRMT3 knockdown strongly inhibited tumor growth in xenograft mouse models, along with a significant decrease in cell proliferation as well as an increase in apoptosis. We further found that PRMT3 reprogrammed metabolic pathways to promote GSC growth via increasing glycolysis and its critical transcriptional regulator HIF1α. In addition, pharmacological inhibition of PRMT3 with a PRMT3-specific inhibitor SGC707 impaired the growth of GBM cells. Thus, our study demonstrates that PRMT3 promotes GBM progression by enhancing HIF1A-mediated glycolysis and metabolic rewiring, presenting a point of metabolic vulnerability for therapeutic targeting in malignant gliomas.

PRMT3 inhibitor SGC707 reduces triglyceride levels and induces pruritus in Western-type diet-fed LDL receptor knockout mice

Protein arginine methyltransferase 3 (PRMT3) is a co-activator of liver X receptor capable of selectively modulating hepatic triglyceride synthesis. Here we investigated whether pharmacological PRMT3 inhibition can diminish the hepatic steatosis extent and lower plasma lipid levels and atherosclerosis susceptibility. Hereto, male hyperlipidemic low-density lipoprotein receptor knockout mice were fed an atherogenic Western-type diet and injected 3 times per week intraperitoneally with PRMT3 inhibitor SGC707 or solvent control. Three weeks into the study, SGC707-treated mice developed severe pruritus and scratching-associated skin lesions, leading to early study termination. SGC707-treated mice exhibited 50% lower liver triglyceride stores as well as 32% lower plasma triglyceride levels. Atherosclerotic lesions were virtually absent in all experimental mice. Plasma metabolite analysis revealed that levels of taurine-conjugated bile acids were ~ threefold increased (P < 0.001) in response to SGC707 treatment, which was paralleled by systemically higher bile acid receptor TGR5 signalling. In conclusion, we have shown that SGC707 treatment reduces hepatic steatosis and plasma triglyceride levels and induces pruritus in Western-type diet-fed LDL receptor knockout mice. These findings suggest that pharmacological PRMT3 inhibition can serve as therapeutic approach to treat non-alcoholic fatty liver disease and dyslipidemia/atherosclerosis, when unwanted effects on cholesterol and bile acid metabolism can be effectively tackled.

Protein arginine methyltransferase 3 promotes glycolysis and hepatocellular carcinoma growth by enhancing arginine methylation of lactate dehydrogenase A

BACKGROUND

Protein arginine methylation has emerged a pivotal role in cancer progression. However, the role of protein arginine methyltransferase 3 (PRMT3) in hepatocellular carcinoma (HCC) remains unknown.

METHODS

The expression pattern of PRMT3 in HCC was analysed using quantitative real-time-polymerase chain reaction (qRT-PCR), Western blotting and immunohistochemistry assays. Loss- and gain-of-function experiments were carried out to determine the oncogenic role of PRMT3 in HCC. Glucose consumption and lactate production assays, seahorse bioscience, mass spectrometry, co-immunoprecipitation, metabonomic analysis and site-specific mutation experiments were used to explore the underlying molecular mechanisms. Furthermore, a xenograft mouse model was established to investigate the effects of PRMT3 and its inhibitor, SGC707, treatment on tumour growth in vivo.

RESULTS

The expression of PRMT3 was significantly upregulated in HCC, with high expression of which correlated with poor prognosis. PRMT3 knockdown led to the decrease in proliferation, glycolysis of HCC cells and tumour growth, whilst its overexpression showed opposite results. The catalytic activity of PRMT3 was important in mediating these biological processes. Mechanistically, our data showed that PRMT3 interacted with and mediated asymmetric dimethylarginine (ADMA) modification of lactate dehydrogenase A (LDHA) at arginine 112 (R112). Compared with LDHA-wild-type (LDHA-WT) cells, LDHA-R112K-mutant-expressing HCC cells exhibited a decrease in lactate dehydrogenase (LDH) activity, HCC cell glycolysis and proliferation. Furthermore, the administration of SGC707, a selective inhibitor of PRMT3, disrupted the PRMT3-mediated LDHA methylation and abolished PRMT3-induced HCC glycolysis and tumour growth.

CONCLUSIONS

Our results suggested a novel oncogenic role of PRMT3 in HCC, and it could be a promising therapeutic target for HCC by linking post-translational modification and cancer metabolism.

Protein arginine methyltransferases and hepatocellular carcinoma: A review

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Protein arginine methylation is essential in multiple biological processes.

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The family of PRMTs is a novel regulator of liver diseases.

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Deregulation of PRMTs is correlated with HCC prognosis and clinical features.

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PRMTs play a vital role in HCC malignancy, immune responses and metabolism.

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PRMTs may represent druggable targets as novel strategies for HCC therapy.

Hepatocellular carcinoma (HCC) is one of the most frequently diagnosed cancers with a high mortality rate worldwide. The complexity of HCC initiation and progression poses a great challenge to the diagnosis and treatment. An increasing number of studies have focused on the emerging roles of protein arginine methylation in cancers, including tumor growth, invasion, metastasis, metabolism, immune responses, chemotherapy sensitivity, etc. The family of protein arginine methyltransferases (PRMTs) is the most important proteins that mediate arginine methylation. The deregulation of PRMTs’ expression and functions in cancers have been gradually unveiled, and many PRMTs inhibitors are in preclinical and clinical investigations now. This review focuses predominantly on the aberrant expression of PRMTs, underlying mechanisms, as well as their potential applications in HCC, and provide novel insights into HCC therapy.

Protein arginine methylation: from enigmatic functions to therapeutic targeting

Protein arginine methyltransferases (PRMTs) are emerging as attractive therapeutic targets. PRMTs regulate transcription, splicing, RNA biology, the DNA damage response and cell metabolism; these fundamental processes are altered in many diseases. Mechanistically understanding how these enzymes fuel and sustain cancer cells, especially in specific metabolic contexts or in the presence of certain mutations, has provided the rationale for targeting them in oncology. Ongoing inhibitor development, facilitated by structural biology, has generated tool compounds for the majority of PRMTs and enabled clinical programmes for the most advanced oncology targets, PRMT1 and PRMT5. In-depth mechanistic investigations using genetic and chemical tools continue to delineate the roles of PRMTs in regulating immune cells and cancer cells, and cardiovascular and neuronal function, and determine which pathways involving PRMTs could be synergistically targeted in combination therapies for cancer. This research is enhancing our knowledge of the complex functions of arginine methylation, will guide future clinical development and could identify new clinical indications.

Arginine Methylation in Brain Tumors: Tumor Biology and Therapeutic Strategies

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

Peptidic transition state analogues as PRMT inhibitors

Protein arginine N-methyltransferases (PRMTs) methylate arginine residues in target proteins using the ubiquitous methyl donor S-adenosyl-l-methionine (AdoMet) as a cofactor. PRMTs play important roles in both healthy and disease states and as such inhibition of PRMTs has gained increasing interest. A primary challenge in the development of PRMT inhibitors is achieving specificity for the PRMT of interest as the active sites are highly conserved for all nine members of the PRMT family. Notably, PRMTs show very little redundancy in vivo due to their specific sets of protein substrates. However, relatively little is known about the interactions of PRMTs with their protein substrates that drive this substrate specificity. We here describe the extended application of a methodology recently developed in our group for the production of peptide-based transition state mimicking PRMT inhibitors. Using this approach, an adenosine moiety, mimicking that of the AdoMet cofactor, is covalently linked to the guanidine side chain of a target arginine residue contained in a peptidic fragment derived from a PRMT substrate protein. Using this approach, histone H4 tail peptide-based transition state mimics were synthesized wherein the adenosine group was linked to the Arg3 residue. H4R3 is a substrate for multiple PRMTs, including PRMT1 and PRMT6. The inhibition results obtained with these new H4-based transition state mimics show low micromolar IC₅₀ values against PRMT1 and PRMT6, indicating that the methodology is applicable to the broader family of PRMTs.

Asymmetrical methyltransferase PRMT3 regulates human mesenchymal stem cell osteogenesis via miR-3648

Histone arginine methylation, which is catalyzed by protein arginine methyltransferases (PRMTs), plays a key regulatory role in various biological processes. Several PRMTs are involved in skeletal development; however, their role in the osteogenic differentiation of mesenchymal stem cells (MSCs) is not completely clear. In this study, we aimed to elucidate the function of PRMT3, a type-I PRMT that catalyzes the formation of ω-mono- or asymmetric dimethyl arginine, in MSCs osteogenesis. We found that PRMT3 promoted MSCs osteogenic commitment and bone remodeling. PRMT3 activated the expression of miR-3648 by enhancing histone H4 arginine 3 asymmetric dimethylation (H4R3me2a) levels at promoter region of the gene. Overexpression of miR-3648 rescued impaired osteogenesis in PRMT3-deficient cells. Moreover, administration of Prmt3 shRNA or a chemical inhibitor of PRMT3 (SGC707) caused an osteopenia phenotype in mice. These results indicate that PRMT3 is a potential therapeutic target for the treatment of bone regeneration and osteopenia disorders.

Inhibition of PRMT3 activity reduces hepatic steatosis without altering atherosclerosis susceptibility in apoE knockout mice

The nuclear receptor liver X receptor (LXR) impacts on cholesterol metabolism as well as hepatic lipogenesis via transcriptional regulation. It is proposed that inhibition of the protein arginine methyltransferase 3 (PRMT3) uncouples these two transcriptional pathways in vivo by acting as a specific lipogenic coactivator of LXR. Here we validated the hypothesis that treatment with the allosteric PRMT3 inhibitor SGC707 will diminish the hepatic steatosis extent, while leaving global cholesterol metabolism, important in cholesterol-driven pathologies like atherosclerosis, untouched. For this purpose, 12-week old hyperlipidemic apolipoprotein E knockout mice were fed a Western-type diet for six weeks to induce both hepatic steatosis and atherosclerosis. The mice received 3 intraperitoneal injections with SGC707 or solvent control per week. Mice chronically treated with SGC707 developed less severe hepatic steatosis as exemplified by the 51% reduced (P < 0.05) liver triglyceride levels. In contrast, the extent of in vivo macrophage foam cell formation and aortic root atherosclerosis was not affected by SGC707 treatment. Interestingly, SGC707-treated mice gained 94% less body weight (P < 0.05), which was paralleled by changes in white adipose tissue morphology, i.e. reduction in adipocyte size and browning. In conclusion, we have shown that through PRMT3 inhibitor treatment specific functions of LXR involved in respectively the development of fatty liver disease and atherosclerosis can be uncoupled, resulting in an overall diminished hepatic steatosis extent without a negative impact on atherosclerosis susceptibility. As such, our studies highlight that PRMT3 inhibition may constitute a novel therapeutic approach to limit the development of fatty liver disease in humans.

Inhibition of protein arginine methyltransferase 3 activity selectively impairs liver X receptor-driven transcription of hepatic lipogenic genes in vivo

BACKGROUND AND PURPOSE

Agonists for the liver X receptor (LXR) are considered promising therapeutic moieties in cholesterol-driven diseases by promoting cellular cholesterol efflux pathways. However, current clinical application of these agents is hampered by concomitant LXR-induced activation of a lipogenic transcriptional network, leading to hepatic steatosis. Recent studies have suggested that protein arginine methyltransferase 3 (PRMT3) may act as a selective co-activator of LXR activity. Here, we verified the hypothesis that PRMT3 inhibition selectively disrupts the ability of LXR to stimulate lipogenesis while maintaining its capacity to modulate macrophage cholesterol homeostasis.

EXPERIMENTAL APPROACH

A combination of the LXR agonist T0901317 and palm oil was administered to C57BL/6 mice to maximally stimulate LXR and PRMT3 activity. PRMT3 activity was inhibited using the allosteric inhibitor SGC707.

KEY RESULTS

Treatment with SGC707 did not negatively influence the T0901317/palm oil-induced up-regulation of the cholesterol efflux ATP-binding cassette transporter genes, ABCA1 and ABCG1, in peritoneal cells. In contrast, SGC707 treatment was associated with a significant decrease in the hepatic expression of the lipogenic gene fatty acid synthase (-64%). A similar trend was observed for stearoyl-coenzyme A desaturase and acetyl CoA carboxylase expression (-43%; -56%). This obstruction of lipogenic gene transcription coincided with a significant 2.3-fold decrease in liver triglyceride content as compared with the T0901317 and palm oil-treated control group.

CONCLUSION AND IMPLICATIONS

We showed that inhibition of PRMT3 activity by SGC707 treatment selectively impairs LXR-driven transcription of hepatic lipogenic genes, while the positive effect of LXR stimulation on macrophage cholesterol efflux pathways is maintained.