PRMT1-mediated FLT3 arginine methylation promotes maintenance of FLT3-ITD+ acute myeloid leukemia

PRMT1 promotes immune escape in hepatocellular carcinoma by regulating arginine methylation modification of MYC protein

Arginine methyltransferase 1 (PRMT1) is widely recognized as an oncogene in various cancers. However, its specific role and underlying mechanisms in hepatocellular carcinoma (HCC) remain insufficiently understood. This study investigated the function of PRMT1 in HCC development and immune evasion. A comprehensive approach combining database analysis (including TCGA, The Human Protein Atlas, Kaplan-Meier Plotter, and TIMER2.0), molecular techniques (such as RT-qPCR, Western blot analysis, and co-immunoprecipitation), cell-based assays (including MTT, colony formation, transwell, and T cell killing assays), and in vivo models was employed to explore PRMT1's role in HCC. The findings revealed a marked upregulation of PRMT1 in both HCC clinical samples and cell lines. Depletion of PRMT1 inhibited cell proliferation and immune evasion while reducing cell migration and invasion. Mechanistically, PRMT1 was shown to interact with MYC, facilitating its arginine methylation and enhancing its protein stability. Moreover, re-expression of MYC significantly reversed the anti-tumour effects associated with PRMT1 depletion. In vivo experiments further corroborated these results. Collectively, PRMT1 promotes HCC progression and immune escape by mediating ADMA methylation of MYC, thereby regulating its stability and expression.

Establishment of CD34 + hematopoietic stem cell-derived xenograft model of hyperleukocytic acute myeloid leukemia

BACKGROUND

Hyperleukocytic acute myeloid leukemia (HLL) is marked by high early mortality and presents significant therapeutic challenges. Research on HLL is still in its infancy, and comprehensive development of patient-derived xenograft (PDX) models, especially CD34 + hematopoietic stem cell-derived models, remains limited.

METHODS

We evaluated the establishment of the HLL model through blood examinations, smear analysis, bone marrow biopsy, flow cytometry, and mutation analysis. Correlation between survival times in mice and patients was assessed using linear regression.

RESULTS

In the HLL PDX mouse model, leukocyte counts could reach up to 37.35^10⁹/L, and immunophenotyping revealed the presence of hCD45+, hCD15+, and hCD33 + cells in both peripheral blood (PB) and bone marrow (BM) following inoculation with PB-derived cells for the establishment of the HLL PDX model. Similar results were observed with cells derived from the patient's BM. In the CD34 + hematopoietic stem cell-derived xenograft model, extensive infiltration of CD34 + cells into the BM, liver, and spleen was observed. Additionally, human WT1 and NRAS mutations were identified in the liver, spleen, and BM of the mice. A comparative analysis of multiple experiments revealed that shorter survival times were observed in mice receiving a higher irradiation dose of 2.5 Gy and a greater number of cells derived from PB. Additionally, shorter survival times were observed in model mice injected with cells carrying NRAS, DNMT3A, FLT3, or NPM1 gene mutations. Correlation analysis indicated that the survival times of the mice were significantly associated with the survival status of the patients.

CONCLUSIONS

We successfully established a CD34 + hematopoietic stem cell-derived xenograft model of HLL, providing a valuable tool for mechanistic research, drug screening, individualized therapy, and precision medicine.

TRIAL REGISTRATION

Not application.

PRMT1 Promotes the Self-renewal of Leukemia Stem Cells by Regulating Protein Synthesis

The application of tyrosine kinase inhibitors (TKIs) has revolutionized the management of chronic myeloid leukemia (CML). However, disease relapse and progression particularly due to persistent leukemia stem cells (LSCs) remain a big challenge in the clinic. Therefore, validation of the therapeutic vulnerability in LSCs is urgently needed. This study verifies the critical role of protein arginine methyltransferase 1 (PRMT1) in the maintenance of CML LSCs. It is found that PRMT1 promotes the survival and serially plating abilities of human primary CML LSCs. Genetic deletion of Prmt1 significantly delays the leukemogenesis and impairs the self-renewal of LSCs in BCR-ABL-driven CML mice. PRMT1 regulates LSCs and leukemia development depending on its methyltransferase activity. Pharmacological inhibition of PRMT1 activity by MS023 remarkably eliminates LSCs and prolongs the survival of CML mice. Mechanistical studies reveal that PRMT1 promotes transcriptional activation of ribosomal protein L29 (RPL29) via catalyzing asymmetric dimethylation of histone H4R3 (H4R3me2a) at its gene promoter region. PRMT1 augments the global protein synthesis via RPL29 in CML LSCs. Taken together, the findings provide new evidence that histone arginine methylation modification regulates protein synthesis in LSCs and highlight PRMT1 as a valuable druggable target for patients with CML.

PRMT3 and CARM1: Emerging Epigenetic Targets in Cancer

The family of protein arginine methyltransferases (PRMTs) occupies an important position in biology, especially during the initiation and development of cancer. PRMT3 and CARM1(also known as PRMT4), being type I protein arginine methyltransferases, are key in controlling tumour progression by catalysing the mono-methylation and asymmetric di-methylation of both histone and non-histone substrates. This paper reviews the functions and potential therapeutic target value of PRMT3 and CARM1 in a variety of cancers. Studies have identified abnormal expressions of PRMT3 and CARM1 in several malignancies, closely linked to cancer progression, advancement, and resistance to treatment. Such as hepatocellular carcinoma, colorectal cancer, ovarian cancer, and endometrial cancer. These findings offer new strategies and directions for cancer treatment, especially in enhancing the effectiveness of conventional treatment methods.

PRDM16 Induces Methylation of FLT3 to Promote FLT3-ITD Signaling and Leukemia Progression

Internal tandem duplication (ITD) in the FMS-like receptor tyrosine kinase-3 (FLT3) is one of the most frequent mutations in acute myeloid leukemia (AML) and is associated with poor prognosis. FLT3-ITD mutations result in endoplasmic reticulum (ER) retention and constitutive autophosphorylation of FLT3. The PR/SET domain 16 (PRDM16) is highly expressed in patients with FLT3-ITD+ AML, suggesting it might play a role in leukemogenesis. Here, we revealed that genetic and pharmacologic suppression of PRDM16 greatly slowed the progression of FLT3-ITD-driven leukemia, sensitized leukemic cells to tyrosine kinase inhibitors, and extended the survival of leukemic mice. PRDM16 enhanced activation of oncogenic FLT3-ITD and ligand-dependent activation of wild-type FLT3 in leukemic cells. Mechanistically, PRDM16 mediated monomethylation of FLT3-ITD at lysine-614 and promoted its ER localization, resulting in enhanced FLT3 signaling in leukemia cells. Moreover, pharmacologic suppression of FLT3-ITD methylation in combination with tyrosine kinase inhibitors increased the elimination of FLT3-ITD+ AML cells. Altogether, these results suggest that PRDM16 boosts oncogenic FLT3 signaling in leukemic cells by prompting FLT3-ITD methylation. Therefore, PRDM16 may serve as a therapeutic target for AML. Significance: Monomethylation of FLT3-ITD at lysine-614 by PRDM16 induces FLT3 ER localization and enhanced signaling, which can be inhibited by targeting PRDM16 to suppress survival of FLT3-ITD+ AML cells and increase chemosensitivity.

TRIM21-mediated PRMT1 degradation attenuates colorectal cancer malignant progression

Tripartite motif-containing 21 (TRIM21) plays a crucial role in antiviral responses and autoimmune diseases. While the impact of TRIM21 on cancer has been studied in various tumors, its role in colorectal cancer (CRC) remains unclear. In this study, we found that TRIM21 expression is reduced in primary CRC tissues. Low levels of TRIM21 in CRC are associated with unfavorable clinicopathological characteristics and shorter survival. Furthermore, we demonstrate that TRIM21 suppresses the proliferation, tumorigenesis, migration, and metastasis of CRC cells by promoting the ubiquitination-mediated degradation of PRMT1. These findings suggest that TRIM21 holds potential as a valuable predictive biomarker for assessing the prognosis of CRC patients.

PRMT1-mediated BRD4 arginine methylation and phosphorylation promote partial epithelial-mesenchymal transformation and renal fibrosis

Bromodomain-containing protein 4 (BRD4) plays a vital role in fibrosis of various organs. However, the underlying mechanism of BRD4 in renal fibrosis remains unclear. To construct in vitro and in vivo models of renal fibrosis, TCMK-1 cells were subjected to TGF-β1 treatment and mice were subjected to UUO surgery and adenine induction. IP assay was used for arginine asymmetric dimethylation (ADMA) level, ubiquitination degradation of Snail, and acetylation level of Snail test. Co-IP was used to validate the interactions of BRD4, protein arginine methyltransferase-1 (PRMT1), and Snail. HE staining and Masson staining were used for morphological examination of renal tissue. BRD4 was abnormally overexpressed during renal fibrosis. TGF-β1-induced fibrosis and partial epithelial-mesenchymal transition (pEMT) could be inhibited by BRD4 silencing. PRMT1 mediated ADMA level of BRD4 to enhance BRD4 phosphorylation and its protein stability. Snail protein degradation was attenuated by BRD4 overexpression in an acetylation-dependent manner in TCMK-1 cells. Furthermore, PRMT1 inhibitor abolished BRD4 overexpression-induced fibrosis and pEMT in TGF-β1-treated TCMK-1 cells and Snail overexpression reversed BRD4 silencing-induced inhibition of fibrosis and pEMT. What's more, the reduction of BRD4 arginine methylation inhibited BRD4 phosphorylation and Snail expression to alleviate renal fibrosis in UUO surgery and adenine induction mice. Collectively, PRMT1-mediated BRD4 arginine methylation and phosphorylation promoted pEMT and renal fibrosis through regulation of Snail expression.

Anagrelide and idarubicin combination induces GSDME-mediated pyroptosis as a potential therapy for high-PDE3A acute myeloid leukemia

Acute myeloid leukemia (AML) is an invasive hematopoietic malignancy requiring novel treatment strategies. In this study, we identified phosphodiesterase 3 A (PDE3A) as a potential new target for drug repositioning in AML. PDE3A was preferentially overexpressed in AML cells than in normal cells, and high expression of PDE3A was correlated with lower event-free survival (EFS) in de novo AML patients. The PDE3A inhibitor anagrelide (ANA) profoundly suppresses the proliferation of high PDE3A-expressing AML cells while exhibiting minimal impact on those with low PDE3A expression. Moreover, synergistic effect of ANA with other chemotherapeutic drugs in high PDE3A expression AML cells was observed. The ANA-idarubicin (IDA) combination showed the most remarkable synergistic effect among all ANA-chemotherapeutic drugs commonly used in AML cell line models. Mechanistically, the synergy between ANA and IDA inhibited the survival of PDE3Ahigh AML cell lines through pyroptosis. This mechanism was initiated by GSDME cleavage triggered by caspase-3 activation. In vivo combination treatment of leukemic animals with high PDE3A expression significantly reduced leukemia burden and prolonged survival time compared with single-drug and vehicle control treatments. Our findings suggest that combined ANA and IDA treatment is an innovative and promising therapeutic strategy for AML patients with high PDE3A expression.

Targeting splicing for hematological malignancies therapy

Alterations in splicing patterns of leukemic cells have a functional impact and influence most cellular processes since aberrantly spliced isoforms can provide a proliferative advantage, enable to evade apoptosis, induce metabolic reprogramming, change cell signaling and antitumor immune response, or develop drug resistance. In this Review, we first characterize the general mechanism of mRNA processing regulation with a focus on the role of splicing factors, which are commonly mutated in blood neoplasms. Next, we provide a comprehensive summary on the current understanding of alternative splicing events, which confer resistance to targeted treatment strategies and immunotherapy. We introduce the functional consequences of mis-spliced variants (CD19-∆ex2, CD22-∆ex2, CD22-∆ex5-6, CD33-∆ex2, PIK3CD-S, BCR-ABL35INS, BIM-γ, FPGS-8PR, dCK-∆ex2-3, and SLC29A1-∆ex13) production in leukemic cells. Of therapeutic relevance, we summarize novel strategies focused on pharmacological correction of aberrant splicing, including small-molecule splicing modulators and splice-switching oligonucleotides. We also include the findings of recent preclinical investigation of the antisense strategies based on modified oligonucleotides. Finally, we discuss the potential of emerging combination therapies for the treatment of hematological disorders with disrupted splicing.

PRMT1 mediates the proliferation of Y79 retinoblastoma cells by regulating the p53/p21/CDC2/cyclin B pathway

Retinoblastoma (RB) is the most common intraocular malignancy among children and presents a certain mortality risk, especially in low- and middle-income countries. Clarifying the molecular mechanisms underlying the onset and progression of retinoblastoma is vital for devising effective cancer treatment approaches. PRMT1, a major type I PRMT, plays significant roles in cancer development. However, its expression and role in retinoblastoma are still unclear. Our research revealed a marked increase in PRMT1 levels in both retinoblastoma tissues and Y79 cells. The overexpression of PRMT1 in Y79 cells promoted their growth and cell cycle progression. Conversely, the suppression of PRMT1 hindered the growth of Y79 cells and impeded cell cycle progression. Mechanistically, PRMT1 mediated the growth of Y79 retinoblastoma cells by targeting the p53/p21/CDC2/Cyclin B pathway. Additionally, the ability of PRMT1 knockdown to suppress cell proliferation was also observed in vivo. Overall, PRMT1 could function as a potential target for therapeutic treatment in individuals with retinoblastoma.

Phase separation of PML/RARα and BRD4 coassembled microspeckles governs transcriptional dysregulation in acute promyelocytic leukemia

In acute promyelocytic leukemia (APL), the promyelocytic leukemia-retinoic acid receptor alpha (PML/RARα) fusion protein destroys PML nuclear bodies (NBs), leading to the formation of microspeckles. However, our understanding, largely learned from morphological observations, lacks insight into the mechanisms behind PML/RARα-mediated microspeckle formation and its role in APL leukemogenesis. This study presents evidence uncovering liquid-liquid phase separation (LLPS) as a key mechanism in the formation of PML/RARα-mediated microspeckles. This process is facilitated by the intrinsically disordered region containing a large portion of PML and a smaller segment of RARα. We demonstrate the coassembly of bromodomain-containing protein 4 (BRD4) within PML/RARα-mediated condensates, differing from wild-type PML-formed NBs. In the absence of PML/RARα, PML NBs and BRD4 puncta exist as two independent phases, but the presence of PML/RARα disrupts PML NBs and redistributes PML and BRD4 into a distinct phase, forming PML/RARα-assembled microspeckles. Genome-wide profiling reveals a PML/RARα-induced BRD4 redistribution across the genome, with preferential binding to super-enhancers and broad-promoters (SEBPs). Mechanistically, BRD4 is recruited by PML/RARα into nuclear condensates, facilitating BRD4 chromatin binding to exert transcriptional activation essential for APL survival. Perturbing LLPS through chemical inhibition (1, 6-hexanediol) significantly reduces chromatin co-occupancy of PML/RARα and BRD4, attenuating their target gene activation. Finally, a series of experimental validations in primary APL patient samples confirm that PML/RARα forms microspeckles through condensates, recruits BRD4 to coassemble condensates, and co-occupies SEBP regions. Our findings elucidate the biophysical, pathological, and transcriptional dynamics of PML/RARα-assembled microspeckles, underscoring the importance of BRD4 in mediating transcriptional activation that enables PML/RARα to initiate APL.

Alkynyl nicotinamides show antileukemic activity in drug-resistant acute myeloid leukemia

Activating mutations of FLT3 contribute to deregulated hematopoietic stem and progenitor cell (HSC/Ps) growth and survival in patients with acute myeloid leukemia (AML), leading to poor overall survival. AML patients treated with investigational drugs targeting mutant FLT3, including Quizartinib and Crenolanib, develop resistance to these drugs. Development of resistance is largely due to acquisition of cooccurring mutations and activation of additional survival pathways, as well as emergence of additional FLT3 mutations. Despite the high prevalence of FLT3 mutations and their clinical significance in AML, there are few targeted therapeutic options available. We have identified 2 novel nicotinamide-based FLT3 inhibitors (HSN608 and HSN748) that target FLT3 mutations at subnanomolar concentrations and are potently effective against drug-resistant secondary mutations of FLT3. These compounds show antileukemic activity against FLT3ITD in drug-resistant AML, relapsed/refractory AML, and in AML bearing a combination of epigenetic mutations of TET2 along with FLT3ITD. We demonstrate that HSN748 outperformed the FDA-approved FLT3 inhibitor Gilteritinib in terms of inhibitory activity against FLT3ITD in vivo.

circFAM193B interaction with PRMT6 regulates AML leukemia stem cells chemoresistance through altering the oxidative metabolism and lipid peroxidation

Most forms of chemotherapy for acute myeloid leukemia (AML) are often ineffective in eliminating leukemic stem cells (LSCs), as their underlying mechanisms remain unclear. Here, we have identified circFAM193B, which regulates the redox biology of LSCs and is associated with unfavorable outcomes in AML patients. In vitro and in vivo assays suggested that circFAM193B significantly inhibits LSCs chemotherapy resistance and AML progression. Knockdown circFAM193B enhances mitochondrial OXPHOS function and inhibits the accumulation of reactive oxygen species and lipid peroxidation mediated by chemotherapy, which protects AML cells from oxidative stress-induced cell death. Mechanistically, circFAM193B physically interacts with arginine methyltransferase PRMT6 catalytic domain and enhances the transcription efficiency of key lipid peroxidation factor ALOX15 by decreasing H3R2me2a modification. In summary, we have identified circFAM193B was downregulated in LSCs to promote the survival of LSC by modulating energy metabolism and the redox balance in the postchemotherapy persistence of LSC. Our studies provide a conceptual advance and biological insights regarding the drug resistance of LSCs via circRNA mediated PRMT6-deposited methylarginine signaling.

Targeting PRMT9-mediated arginine methylation suppresses cancer stem cell maintenance and elicits cGAS-mediated anticancer immunity

Current anticancer therapies cannot eliminate all cancer cells, which hijack normal arginine methylation as a means to promote their maintenance via unknown mechanisms. Here we show that targeting protein arginine N-methyltransferase 9 (PRMT9), whose activities are elevated in blasts and leukemia stem cells (LSCs) from patients with acute myeloid leukemia (AML), eliminates disease via cancer-intrinsic mechanisms and cancer-extrinsic type I interferon (IFN)-associated immunity. PRMT9 ablation in AML cells decreased the arginine methylation of regulators of RNA translation and the DNA damage response, suppressing cell survival. Notably, PRMT9 inhibition promoted DNA damage and activated cyclic GMP-AMP synthase, which underlies the type I IFN response. Genetically activating cyclic GMP-AMP synthase in AML cells blocked leukemogenesis. We also report synergy of a PRMT9 inhibitor with anti-programmed cell death protein 1 in eradicating AML. Overall, we conclude that PRMT9 functions in survival and immune evasion of both LSCs and non-LSCs; targeting PRMT9 may represent a potential anticancer strategy.

Attenuation of protein arginine dimethylation via S-nitrosylation of protein arginine methyltransferase 1

Upregulation of nitric oxide (NO) production contributes to the pathogenesis of numerous diseases via S-nitrosylation, a post-translational modification of proteins. This process occurs due to the oxidative reaction between NO and a cysteine thiol group; however, the extent of this reaction remains unknown. S-Nitrosylation of PRMT1, a major asymmetric arginine methyltransferase of histones and numerous RNA metabolic proteins, was induced by NO donor treatment. We found that nitrosative stress leads to S-nitrosylation of cysteine 119, located near the active site, and attenuates the enzymatic activity of PRMT1. Interestingly, RNA sequencing analysis revealed similarities in the changes in expression elicited by NO and PRMT1 inhibitors or knockdown. A comprehensive search for PRMT1 substrates using the proximity-dependent biotin identification method highlighted many known and new substrates, including RNA-metabolizing enzymes. To validate this result, we selected the RNA helicase DDX3 and demonstrated that arginine methylation of DDX3 is induced by PRMT1 and attenuated by NO treatment. Our results suggest the existence of a novel regulatory system associated with transcription and RNA metabolism via protein S-nitrosylation.

PRMT1 in human neoplasm: cancer biology and potential therapeutic target

Protein arginine methyltransferase 1 (PRMT1), the predominant type I protein arginine methyltransferase, plays a crucial role in normal biological functions by catalyzing the methylation of arginine side chains, specifically monomethylarginine (MMA) and asymmetric dimethylarginine (ADMA), within proteins. Recent investigations have unveiled an association between dysregulated PRMT1 expression and the initiation and progression of tumors, significantly impacting patient prognosis, attributed to PRMT1's involvement in regulating various facets of tumor cell biology, including DNA damage repair, transcriptional and translational regulation, as well as signal transduction. In this review, we present an overview of recent advancements in PRMT1 research across different tumor types, with a specific focus on its contributions to tumor cell proliferation, metastasis, invasion, and drug resistance. Additionally, we expound on the dynamic functions of PRMT1 during distinct stages of cancer progression, elucidating its unique regulatory mechanisms within the same signaling pathway and distinguishing between its promotive and inhibitory effects. Importantly, we sought to provide a comprehensive summary and analysis of recent research progress on PRMT1 in tumors, contributing to a deeper understanding of its role in tumorigenesis, development, and potential treatment strategies.

miR-1202 acts as anti-oncomiR in myeloid leukaemia by down-modulating GATA-1S expression

Transient abnormal myelopoiesis (TAM) is a Down syndrome-related pre-leukaemic condition characterized by somatic mutations in the haematopoietic transcription factor GATA-1 that result in exclusive production of its shorter isoform (GATA-1S). Given the common hallmark of altered miRNA expression profiles in haematological malignancies and the pro-leukaemic role of GATA-1S, we aimed to search for miRNAs potentially able to modulate the expression of GATA-1 isoforms. Starting from an in silico prediction of miRNA binding sites in the GATA-1 transcript, miR-1202 came into our sight as potential regulator of GATA-1 expression. Expression studies in K562 cells revealed that miR-1202 directly targets GATA-1, negatively regulates its expression, impairs GATA-1S production, reduces cell proliferation, and increases apoptosis sensitivity. Furthermore, data from TAM and myeloid leukaemia patients provided substantial support to our study by showing that miR-1202 down-modulation is accompanied by increased GATA-1 levels, with more marked effects on GATA-1S. These findings indicate that miR-1202 acts as an anti-oncomiR in myeloid cells and may impact leukaemogenesis at least in part by down-modulating GATA-1S levels.

Promising role of protein arginine methyltransferases in overcoming anti-cancer drug resistance

Drug resistance remains a major challenge in cancer treatment, necessitating the development of novel strategies to overcome it. Protein arginine methyltransferases (PRMTs) are enzymes responsible for epigenetic arginine methylation, which regulates various biological and pathological processes, as a result, they are attractive therapeutic targets for overcoming anti-cancer drug resistance. The ongoing development of small molecules targeting PRMTs has resulted in the generation of chemical probes for modulating most PRMTs and facilitated clinical treatment for the most advanced oncology targets, including PRMT1 and PRMT5. In this review, we summarize various mechanisms underlying protein arginine methylation and the roles of specific PRMTs in driving cancer drug resistance. Furthermore, we highlight the potential clinical implications of PRMT inhibitors in decreasing cancer drug resistance. PRMTs promote the formation and maintenance of drug-tolerant cells via several mechanisms, including altered drug efflux transporters, autophagy, DNA damage repair, cancer stem cell-related function, epithelial-mesenchymal transition, and disordered tumor microenvironment. Multiple preclinical and ongoing clinical trials have demonstrated that PRMT inhibitors, particularly PRMT5 inhibitors, can sensitize cancer cells to various anti-cancer drugs, including chemotherapeutic, targeted therapeutic, and immunotherapeutic agents. Combining PRMT inhibitors with existing anti-cancer strategies will be a promising approach for overcoming anti-cancer drug resistance. Furthermore, enhanced knowledge of the complex functions of arginine methylation and PRMTs in drug resistance will guide the future development of PRMT inhibitors and may help identify new clinical indications.

Blockade of de novo pyrimidine biosynthesis triggers autophagic degradation of oncoprotein FLT3-ITD in acute myeloid leukemia

The internal tandem duplication of the FMS-like tyrosine kinase 3 (FLT3-ITD) is one of the most frequent genetic alterations in acute myeloid leukemia (AML). Limited and transient clinical benefit of FLT3 kinase inhibitors (FLT3i) emphasizes the need for alternative therapeutic options for this subset of myeloid malignancies. Herein, we showed that FLT3-ITD mutant (FLT3-ITD+) AML cells were susceptible toward inhibitors of DHODH, a rate-limiting enzyme of de novo pyrimidine biosynthesis. Genetic and pharmacological blockade of DHODH triggered downregulation of FLT3-ITD protein, subsequently suppressed activation of downstream ERK and STAT5, and promoted cell death of FLT3-ITD+ AML cells. Mechanistically, DHODH blockade triggered autophagy-mediated FLT3-ITD degradation via inactivating mTOR, a potent autophagy repressor. Notably, blockade of DHODH synergized with an FDA-approved FLT3i quizartinib in significantly impairing the growth of FLT3-ITD+ AML cells and improving tumor-bearing mice survival. We further demonstrated that DHODH blockade exhibited profound anti-proliferation effect on quizartinib-resistant cells in vitro and in vivo. In summary, this study demonstrates that the induction of degradation of FLT3-ITD protein by DHODH blockade may offer a promising therapeutic strategy for AML patients harboring FLT3-ITD mutation.

PRMT1 promotes the proliferation and metastasis of gastric cancer cells by recruiting MLXIP for the transcriptional activation of the β-catenin pathway

Protein arginine methyltransferase 1 (PRMT1), a type I PRMT, is overexpressed in gastric cancer (GC) cells. To elucidate the function of PRMT1 in GC, PRMT1 expression in HGC-27 and MKN-45 cells was knocked down by short hairpin RNA (shRNA) or inhibited by PRMT1 inhibitors (AMI-1 or DCLX069), which resulted in inhibition of GC cell proliferation, migration, invasion, and tumorigenesis in vitro and in vivo. MLX-interacting protein (MLXIP) and Kinectin 1 (KTN1) were identified as PRMT1-binding proteins. PRMT1 recruited MLXIP to the promoter of β-catenin, which induced β-catenin transcription and activated the β-catenin signaling pathway, promoting GC cell migration and metastasis. Furthermore, KTN1 inhibited the K48-linked ubiquitination of PRMT1 by decreasing the interaction between TRIM48 and PRMT1. Collectively, our findings reveal a mechanism by which PRMT1 promotes cell proliferation and metastasis mediated by the β-catenin signaling pathway.

Targeting PRMT1 prevents acute and chronic graft-versus-host disease

Graft-versus-host disease (GVHD) is a common complication after allogeneic hematopoietic stem cell transplantation. Recent studies have reported that protein arginine methyltransferase 1 (PRMT1) is essential for the differentiation and proliferation of T and B cells. Therefore, it is possible that PRMT1 may play a critical role in GVHD. In this study, we observed that PRMT1 expression was upregulated in CD4+ T and B cells from chronic GVHD (cGVHD) patients and mice. However, the prophylactic use of a PRMT1 inhibitor significantly prevented cGVHD in mice by reducing the percentage of T helper (Th)17 cells, germinal center B cells, and plasma cells. The PRMT1 inhibitor also controlled acute GVHD (aGVHD) in mice by decreasing the percentage of Th17 cells. Moreover, inhibiting PRMT1 also weakened Th17 cell differentiation, B cell proliferation, and antibody production in cells from cGVHD patients. Additionally, further studies revealed that PRMT1 regulated B cell proliferation and antibody secretion by methylating isocitrate dehydrogenase 2 (IDH2). We observed asymmetric di-methylation of IDH2 by PRMT1 at arginine 353 promoted IDH2 homodimerization, which enhanced IDH2 activity, further increasing B cell proliferation and antibody production. Collectively, this study provides a rationale for the application of PRMT1 inhibitors in the prevention of aGVHD and cGVHD.

FLT3 inhibitors and novel therapeutic strategies to reverse AML resistance: An updated comprehensive review

FMS-like tyrosine kinase 3 (FLT3) mutations occur in almost 30% of acute myeloid leukemia (AML) patients. Despite the initial clinical efficacy of FLT3 inhibitors, many treated AML patients with mutated FLT3 eventually relapse. This review critically discusses the opportunities and challenges of FLT3-targeted therapies and sheds light on their drug interactions as well as potential biomarkers. Furthermore, we focus on the molecular mechanisms underlying the resistance of FLT3 internal tandem duplication (FLT3-ITD) AMLs to FLT3 inhibitors alongside novel therapeutic strategies to reverse resistance. Notably, dynamic heterogeneous patterns of clonal selection and evolution contribute to the resistance of FLT3-ITD AMLs to FLT3 inhibitors. Ongoing preclinical research and clinical trials are actively directed towards devising rational "personalized" or "patient-tailored" combinatorial therapeutic regimens to effectively treat patients with FLT3 mutated AML.

Methylation of BRD4 by PRMT1 regulates BRD4 phosphorylation and promotes ovarian cancer invasion

Bromodomain-containing protein 4 (BRD4), the major component of bromodomain and extra-terminal domain (BET) protein family, has important functions in early embryonic development and cancer development. However, the posttranslational modification of BRD4 is not well understood. Multiple approaches were used to explore the mechanism of PRMT1-mediated BRD4 methylation and to determine the biological functions of BRD4 and PRMT1 in ovarian cancer. Here we report that BRD4 is asymmetrically methylated at R179/181/183 by PRMT1, which is antagonized by the Jumonji-family demethylase, JMJD6. PRMT1 is overexpressed in ovarian cancer tissue and is a potential marker for poor prognosis in ovarian cancer patients. Silencing of PRMT1 inhibited ovarian cancer proliferation, migration, and invasion in vivo and in vitro. PRMT1-mediated BRD4 methylation was found to promote BRD4 phosphorylation. Compared to BRD4 wild-type (WT) cells, BRD4 R179/181/183K mutant-expressing cells showed reduced ovarian cancer metastasis. BRD4 arginine methylation is also associated with TGF-β signaling. Our results indicate that arginine methylation of BRD4 by PRMT1 is involved in ovarian cancer tumorigenesis. Targeting PRMT1-mediated arginine methylation may provide a novel diagnostic target and an effective therapeutic strategy for ovarian cancer treatment.

PRMT1 methylation of WTAP promotes multiple myeloma tumorigenesis by activating oxidative phosphorylation via m6A modification of NDUFS6

Epigenetic modifications play important roles during the pathogenesis of multiple myeloma (MM). Herein, we found that protein arginine methyltransferase 1 (PRMT1) was highly expressed in MM patients, which was positively correlated with MM stages. High PRMT1 expression was correlated with adverse prognosis in MM patients. We further showed that silencing PRMT1 inhibited MM proliferation and tumorigenesis in vitro and in vivo. Mechanistically, we revealed that the knockdown of PRMT1 reduced the oxidative phosphorylation (OXPHOS) of MM cells through NDUFS6 downregulation. Meanwhile, we identified that WTAP, a key component of the m6A methyltransferase complex, was methylated by PRMT1, and NDUFS6 was identified as a bona fide m6A target of WTAP. Finally, we found that the combination of PRMT1 inhibitor and bortezomib synergistically inhibited MM progression. Collectively, our results demonstrate that PRMT1 plays a crucial role during MM tumorigenesis and suggeste that PRMT1 could be a potential therapeutic target in MM.

Post-translational modifications of histones: Mechanisms, biological functions, and therapeutic targets

Histones are DNA-binding basic proteins found in chromosomes. After the histone translation, its amino tail undergoes various modifications, such as methylation, acetylation, phosphorylation, ubiquitination, malonylation, propionylation, butyrylation, crotonylation, and lactylation, which together constitute the "histone code." The relationship between their combination and biological function can be used as an important epigenetic marker. Methylation and demethylation of the same histone residue, acetylation and deacetylation, phosphorylation and dephosphorylation, and even methylation and acetylation between different histone residues cooperate or antagonize with each other, forming a complex network. Histone-modifying enzymes, which cause numerous histone codes, have become a hot topic in the research on cancer therapeutic targets. Therefore, a thorough understanding of the role of histone post-translational modifications (PTMs) in cell life activities is very important for preventing and treating human diseases. In this review, several most thoroughly studied and newly discovered histone PTMs are introduced. Furthermore, we focus on the histone-modifying enzymes with carcinogenic potential, their abnormal modification sites in various tumors, and multiple essential molecular regulation mechanism. Finally, we summarize the missing areas of the current research and point out the direction of future research. We hope to provide a comprehensive understanding and promote further research in this field.

PRMT1 inhibition promotes ferroptosis sensitivity via ACSL1 upregulation in acute myeloid leukemia

Acute myeloid leukemia (AML) is a hematological malignancy with an alarming mortality rate. The development of novel therapeutic targets or drugs for AML is urgently needed. Ferroptosis is a form of regulated cell death driven by iron-dependent lipid peroxidation. Recently, ferroptosis has emerged as a novel method for targeting cancer, including AML. Epigenetic dysregulation is a hallmark of AML, and a growing body of evidence suggests that ferroptosis is subject to epigenetic regulation. Here, we identified protein arginine methyltransferase 1 (PRMT1) as a ferroptosis regulator in AML. The type I PRMT inhibitor GSK3368715 promoted ferroptosis sensitivity in vitro and in vivo. Moreover, PRMT1-knockout cells exhibited significantly increased sensitivity to ferroptosis, suggesting that PRMT1 is the primary target of GSK3368715 in AML. Mechanistically, both GSK3368715 and PRMT1 knockout upregulated acyl-CoA synthetase long-chain family member 1 (ACSL1), which acts as a ferroptosis promoter by increasing lipid peroxidation. Knockout ACSL1 reduced the ferroptosis sensitivity of AML cells following GSK3368715 treatment. Additionally, the GSK3368715 treatment reduced the abundance of H4R3me2a, the main histone methylation modification mediated by PRMT1, in both genome-wide and ACSL1 promoter regions. Overall, our results demonstrated a previously unknown role of the PRMT1/ACSL1 axis in ferroptosis and suggested the potential value and applications of the combination of PRMT1 inhibitor and ferroptosis inducers in AML treatment.

Set Protein Is Involved in FLT3 Membrane Trafficking

The in-frame internal tandem duplication (ITD) of the FLT3 gene is an important negative prognostic factor in acute myeloid leukemia (AML). FLT3-ITD is constitutive active and partially retained in the endoplasmic reticulum (ER). Recent reports show that 3'UTRs function as scaffolds that can regulate the localization of plasma membrane proteins by recruiting the HuR-interacting protein SET to the site of translation. Therefore, we hypothesized that SET could mediate the FLT3 membrane location and that the FLT3-ITD mutation could somehow disrupt the model, impairing its membrane translocation. Immunofluorescence and immunoprecipitation assays demonstrated that SET and FLT3 co-localize and interact in FLT3-WT cells but hardly in FLT3-ITD. SET/FLT3 interaction occurs before FLT3 glycosylation. Furthermore, RNA immunoprecipitation in FLT3-WT cells confirmed that this interaction occurs through the binding of HuR to the 3'UTR of FLT3. HuR inhibition and SET nuclear retention reduced FLT3 in the membrane of FLT3-WT cells, indicating that both proteins are involved in FLT3 membrane trafficking. Interestingly, the FLT3 inhibitor midostaurin increases FLT3 in the membrane and SET/FLT3 binding. Therefore, our results show that SET is involved in the transport of FLT3-WT to the membrane; however, SET barely binds FLT3 in FLT3-ITD cells, contributing to its retention in the ER.

Adriamycin induces cardiac fibrosis in mice via PRMT5-mediated cardiac fibroblast activation

Long-term treatment with adriamycin (ADR) is associated with higher incidences of cumulative cardiotoxicity manifest as heart failure. ADR-induced cardiomyopathy is characterized by extensive fibrosis that is caused by cardiac fibroblast activation. To date, however, no specific treatment is available to alleviate ADR-induced cardiotoxicity. Protein arginine methyltransferase 5 (PRMT5), a major enzyme responsible for methylation of arginine, regulates numerous cellular processes such as cell differentiation. In the present study we investigated the role of PRMT5 in cardiac fibrosis. Mice were administered ADR (3 mg/kg, i.p., every 2 days) for 2 weeks. We showed that aberrant PRMT5 expression was largely co-localized with α-SMA-positive activated cardiac fibroblasts in ADR-injected mice and in ADR-treated cardiac fibroblasts in vitro. PRMT5-overexpression exacerbated, whereas PRMT5 knockdown alleviated ADR-induced cardiac fibrosis in vivo and TGF-β1-induced cardiac fibroblast activation in vitro. We demonstrated that PRMT5-overexpression enhanced methylated-Smad3 levels in vivo and in vitro. Pretreatment with a specific PRMT5 inhibitor EPZ015666 (5 nM) or overexpression of a catalytically inactive mutant of PRMT5, PRMT5(E444Q), reduced PRMT5-induced methylation of Smad3, thus suppressing PRMT5-mediated cardiac fibroblast activation in vitro. Furthermore, ADR activated cardiac fibroblasts was depending on autocrine TGF-β1. Taken together, our results demonstrate that PRMT5 promotes ADR-induced cardiac fibrosis via activating cardiac fibroblasts, suggesting that it may be a potential therapeutic target of ADR-caused cardiotoxicity.

Ligand-independent EphA2 contributes to chemoresistance in small-cell lung cancer by enhancing PRMT1-mediated SOX2 methylation

Chemoresistance is the crux of clinical treatment failure of small-cell lung cancer (SCLC). Cancer stem cells play a critical role in therapeutic resistance of malignant tumors. Studies have shown that the role of erythropoietin-producing hepatocellular A2 (EphA2) in tumors is complex. This study aimed to test the hypothesis that ligand-independent activation of EphA2 modulates chemoresistance by enhancing stemness in SCLC. We verified that EphA2 was activated in chemoresistance sublines in a ligand-independent manner rather than a ligand-dependent manner. Ligand-independent EphA2 enhanced the expression of stemness-associated biomarkers (CD44, Myc, and SOX2), accelerated epithelial-mesenchymal transition (EMT) and reinforced self-renewal to drive the chemoresistance of SCLC, while the P817H mutant EphA2 neutralized intrinsic function. Co-immunoprecipitation (co-IP) and GST-pull down experiments were conducted to verify that EphA2 directly interacted with PRMT1. Moreover, EphA2 increased the expression and activity of PRMT1. Whereafter, PRMT1 interacted with and methylated SOX2 to induce stemness and chemoresistance in SCLC. Pharmacological inhibition of EphA2 showed a synergistic anti-tumor effect with chemotherapy in preclinical models, including patient-derived xenograft (PDX) models. These findings highlight, for the first time, that the EphA2/PRMT1/SOX2 pathway induces chemoresistance in SCLC by promoting stemness. EphA2 is a potential therapeutic target in SCLC treatment.

Sitravatinib as a potent FLT3 inhibitor can overcome gilteritinib resistance in acute myeloid leukemia

BACKGROUND

Gilteritinib is the only drug approved as monotherapy for acute myeloid leukemia (AML) patients harboring FMS-like tyrosine kinase 3 internal tandem duplication (FLT3-ITD) mutation throughout the world. However, drug resistance inevitably develops in clinical. Sitravatinib is a multi-kinase inhibitor under evaluation in clinical trials of various solid tumors. In this study, we explored the antitumor activity of sitravatinib against FLT3-ITD and clinically-relevant drug resistance in FLT3 mutant AML.

METHODS

Growth inhibitory assays were performed in AML cell lines and BaF3 cells expressing various FLT3 mutants to evaluate the antitumor activity of sitravatinib in vitro. Immunoblotting was used to examine the activity of FLT3 and its downstream pathways. Molecular docking was performed to predict the binding sites of FLT3 to sitravatinib. The survival benefit of sitravatinib in vivo was assessed in MOLM13 xenograft mouse models and mouse models of transformed BaF3 cells harboring different FLT3 mutants. Primary patient samples and a patient-derived xenograft (PDX) model were also used to determine the efficacy of sitravatinib.

RESULTS

Sitravatinib inhibited cell proliferation, induced cell cycle arrest and apoptosis in FLT3-ITD AML cell lines. In vivo studies showed that sitravatinib exhibited a better therapeutic effect than gilteritinib in MOLM13 xenograft model and BaF3-FLT3-ITD model. Unlike gilteritinib, the predicted binding sites of sitravatinib to FLT3 did not include F691 residue. Sitravatinib displayed a potent inhibitory effect on FLT3-ITD-F691L mutation which conferred resistance to gilteritinib and all other FLT3 inhibitors available, both in vitro and in vivo. Compared with gilteritinib, sitravatinib retained effective activity against FLT3 mutation in the presence of cytokines through the more potent and steady inhibition of p-ERK and p-AKT. Furthermore, patient blasts harboring FLT3-ITD were more sensitive to sitravatinib than to gilteritinib in vitro and in the PDX model.

CONCLUSIONS

Our study reveals the potential therapeutic role of sitravatinib in FLT3 mutant AML and provides an alternative inhibitor for the treatment of AML patients who are resistant to current FLT3 inhibitors.

PRMT3 regulates the progression of invasive micropapillary carcinoma of the breast

Invasive micropapillary carcinoma (IMPC) is a special histopathological subtype of breast cancer. Clinically, IMPC exhibits a higher incidence of lymphovascular invasion and lymph node metastasis compared with that of invasive ductal carcinoma (IDC), the most common type. However, the metabolic characteristics and related mechanisms underlying malignant IMPC biological behaviors are unknown. We performed large-scale targeted metabolomics analysis on resected tumors obtained from chemotherapy-naïve IMPC (n = 25) and IDC (n = 26) patients to investigate metabolic alterations, and we integrated mass spectrometry analysis, RNA sequencing, and ChIP-sequencing data to elucidate the potential molecular mechanisms. The metabolomics revealed distinct metabolic profiles between IMPC and IDC. For IMPC patients, the metabolomic profile was characterized by significantly high levels of arginine methylation marks, and protein arginine methyltransferase 3 (PRMT3) was identified as a critical regulator that catalyzed the formation of these arginine methylation marks. Notably, overexpression of PRMT3 was an independent risk factor for poor IMPC prognosis. Furthermore, we demonstrated that PRMT3 was a key regulator of breast cancer cell proliferation and metastasis both in vitro and in vivo, and treatment with a preclinical PRMT3 inhibitor decreased the xenograft tumorigenic capacity. Mechanistically, PRMT3 regulated the endoplasmic reticulum (ER) stress signaling pathway by facilitating histone H4 arginine 3 asymmetric dimethylation (H4R3me2a), which may endow breast cancer cells with great proliferative and metastatic capacity. Our findings highlight PRMT3 importance in regulating the malignant biological behavior of IMPC and suggest that small-molecule inhibitors of PRMT3 activity might be promising breast cancer treatments.

Decoding m6A RNA methylome identifies PRMT6-regulated lipid transport promoting AML stem cell maintenance

N⁶-methyladenosine (m⁶A) is a common chemical modification for mammalian mRNA and exhibits high dynamics in various biological processes. However, dynamics of m⁶A RNA methylome during leukemogenesis remains unknown. Here, we delineate a comprehensive m⁶A landscape during acute myeloid leukemia (AML) development and identify PRMT6 as a key for maintaining AML stem cells. We observe an obvious change in m⁶A methylome during leukemogenesis and find that protein arginine methyltransferase PRMT6 and m⁶A reader IGF2BP2 maintain the function of human and murine leukemia stem cells (LSCs). Genetic deletion or pharmacological inhibition of PRMT6 damages AML development and LSC function. Mechanistically, IGF2BP2 stabilizes PRMT6 mRNA via m⁶A-mediated manner, which catalyzes H3R2me2a and suppresses lipid transporter MFSD2A expression. PRMT6 loss upregulates MFSD2A expression that increases docosahexaenoic acid levels and impairs LSC maintenance. Collectively, our findings reveal a critical role of PRMT6-MFSD2A signaling axis in AML development and provide a therapeutic strategy for targeting LSCs.

Targeted Epigenetic Interventions in Cancer with an Emphasis on Pediatric Malignancies

Over the past two decades, novel hallmarks of cancer have been described, including the altered epigenetic landscape of malignant diseases. In addition to the methylation and hyd-roxymethylation of DNA, numerous novel forms of histone modifications and nucleosome remodeling have been discovered, giving rise to a wide variety of targeted therapeutic interventions. DNA hypomethylating drugs, histone deacetylase inhibitors and agents targeting histone methylation machinery are of distinguished clinical significance. The major focus of this review is placed on targeted epigenetic interventions in the most common pediatric malignancies, including acute leukemias, brain and kidney tumors, neuroblastoma and soft tissue sarcomas. Upcoming novel challenges include specificity and potential undesirable side effects. Different epigenetic patterns of pediatric and adult cancers should be noted. Biological significance of epigenetic alterations highly depends on the tissue microenvironment and widespread interactions. An individualized treatment approach requires detailed genetic, epigenetic and metabolomic evaluation of cancer. Advances in molecular technologies and clinical translation may contribute to the development of novel pediatric anticancer treatment strategies, aiming for improved survival and better patient quality of life.

Therapeutic Targeting of FLT3 in Acute Myeloid Leukemia: Current Status and Novel Approaches

FMS-like tyrosine kinase 3 (FLT3) is mutated in approximately 30% of acute myeloid leukemia (AML) patients. The presence of FLT3-ITD (internal tandem duplication, 20-25%) mutation and, to a lesser extent, FLT3-TKD (tyrosine kinase domain, 5-10%) mutation is associated with poorer diagnosis and therapy response since the leukemic cells become hyperproliferative and resistant to apoptosis after continuous activation of FLT3 signaling. Targeting FLT3 has been the focus of many pre-clinical and clinical studies. Hence, many small-molecule FLT3 inhibitors (FLT3is) have been developed, some of which are approved such as midostaurin and gilteritinib to be used in different clinical settings, either in combination with chemotherapy or alone. However, many questions regarding the best treatment strategy remain to be answered. On the other hand, various FLT3-dependent and -independent resistance mechanisms could be evolved during FLT3i therapy which limit their clinical impact. Therefore, identifying molecular mechanisms of resistance and developing novel strategies to overcome this obstacle is a current interest in the field. In this review, recent studies of approved FLT3i and knowledge about major resistance mechanisms of clinically approved FLT3i's will be discussed together with novel treatment approaches such as designing novel FLT3i and dual FLT3i and combination strategies including approved FLT3i plus small-molecule agents targeting altered molecules in the resistant cells to abrogate resistance. Moreover, how to choose an appropriate FLT3i for the patients will be summarized based on what is currently known from available clinical data. In addition, strategies beyond FLT3i's including immunotherapeutics, small-molecule FLT3 degraders, and flavonoids will be summarized to highlight potential alternatives in FLT3-mutated AML therapy.

Protein Arginine Methyltransferases as Therapeutic Targets in Hematological Malignancies

Arginine methylation is a common post-translational modification affecting protein activity and the transcription of target genes when methylation occurs on histone tails. There are nine protein arginine methyltransferases (PRMTs) in mammals, divided into subgroups depending on the methylation they form on a molecule of arginine. During the formation and maturation of the different types of blood cells, PRMTs play a central role by controlling cell differentiation at the transcriptional level. PRMT enzymatic activity is necessary for many cellular processes in hematological malignancies, such as the activation of cell cycle and proliferation, inhibition of apoptosis, DNA repair processes, RNA splicing, and transcription by methylating histone tails' arginine. Chemical tools have been developed to inhibit the activity of PRMTs and have been tested in several models of hematological malignancies, including primary samples from patients, xenografts into immunodeficient mice, mouse models, and human cell lines. They show a significant effect by reducing cell viability and increasing the overall survival of mice. PRMT5 inhibitors have a strong therapeutic potential, as phase I clinical trials in hematological malignancies that use these molecules show promising results, thus, underlining PRMT inhibitors as useful therapeutic tools for cancer treatment in the future.

Targeting OXPHOS de novo purine synthesis as the nexus of FLT3 inhibitor-mediated synergistic antileukemic actions

Using a genome-wide CRISPR screen, we identified CDK9, DHODH, and PRMT5 as synthetic lethal partners with gilteritinib treatment in fms-like tyrosine kinase 3 (FLT3)-internal tandem duplication (ITD) acute myeloid leukemia (AML) and genetically and pharmacologically validated their roles in gilteritinib sensitivity. The presence of FLT3-ITD is associated with an increase in anaerobic glycolysis, rendering leukemia cells highly sensitive to inhibition of glycolysis. Supportive of this, our data show the enrichment of single guide RNAs targeting 28 glycolysis-related genes upon gilteritinib treatment, suggesting that switching from glycolysis to oxidative phosphorylation (OXPHOS) may represent a metabolic adaption of AML in gilteritinib resistance. CDK9i/FLT3i, DHODHi/FLT3i, and PRMT5i/FLT3i pairs mechanistically converge on OXPHOS and purine biosynthesis blockade, implying that targeting the metabolic functions of these three genes and/or proteins may represent attractive strategies to sensitize AML to gilteritinib treatment. Our findings provide the basis for maximizing therapeutic impact of FLT3-ITD inhibitors and a rationale for a clinical trial of these novel combinations.

Application of High-Efficiency Cell Expansion and High-Throughput Drug Sensitivity Screening for Leukemia Treatment

This study is to assess the clinical value of in vitro primary cell high-efficiency expansion and high-throughput drug sensitivity screening (HEHDS) system in leukemia, and we evaluated a cohort of 121 patients with acute myeloid leukemia (AML) and 27 patients with acute lymphoblastic leukemia (ALL) using HEHDS. Bone marrow aspirates were collected from patients with leukemia. Purified leukemic cancer cells were obtained, cultured, and screened with a panel of 247 FDA-approved compounds by HEHDS technology. Ninety-six patients received HEHDS-guided therapy while 52 patients who were subjected to physician directed therapy served as controls. ALL patients who received treatment guided by HEHDS showed higher rate of complete remission (CR) than that of patients in the non-HEHDS group (90.91% vs. 56.25%). Similarly, AML patients received HEHDS-guided therapy were found to have greater CR rate, when compared with patients who received physician-directed therapy (45.88% vs. 25%). There was a significantly higher rate of CR in HEHDS-guided therapy group compared to the non-HEHDS group. The application of HEHDS could be beneficial for leukemia treatment.

Prmt1 upregulated by Hdc deficiency aggravates acute myocardial infarction via NETosis

Neutrophils are mobilized and recruited to the injured heart after myocardial infarction, and neutrophil count has been clinically implicated to be associated with coronary disease severity. Histidine decarboxylase (HDC) has been implicated in regulating reactive oxidative species (ROS) and the differentiation of myeloid cells. However, the effect of HDC on neutrophils after myocardial infarction remains unclear. Here, we found that neutrophils were disorderly recruited into the ischemic injured area of the myocardium of Hdc deficiency (Hdc^−/−) mice. Moreover, Hdc deficiency led to attenuated adhesion but enhanced migration and augmented ROS/neutrophil extracellular traps (NETs) production in neutrophils. Hdc^−/− mouse-derived NETs promoted cardiomyocyte death and cardiac fibroblast proliferation/migration. Furthermore, protein arginine methyltransferase 1 (PRMT1) was increased in Hdc^−/− mouse-derived neutrophils but decreased with exogenous histamine treatment. Its expression could be rescued by blocking histamine receptor 1 (H1R), inhibiting ATP synthesis or reducing SWItch/sucrose non fermentable (SWI/SNF) chromatin remodeling complex. Accordingly, histamine or MS023 treatment could decrease ROS and NETs ex vivo, and ameliorated cardiac function and fibrosis, along with the reduced NETs in plasma in vivo. Together, our findings unveil the role of HDC in NETosis by histamine–H1R–ATP–SWI/SNF–PRMT1–ROS signaling and provide new biomarkers and targets for identifying and tuning the detrimental immune state in cardiovascular disease.

The arginine methyltransferase PRMT7 promotes extravasation of monocytes resulting in tissue injury in COPD

Extravasation of monocytes into tissue and to the site of injury is a fundamental immunological process, which requires rapid responses via post translational modifications (PTM) of proteins. Protein arginine methyltransferase 7 (PRMT7) is an epigenetic factor that has the capacity to mono-methylate histones on arginine residues. Here we show that in chronic obstructive pulmonary disease (COPD) patients, PRMT7 expression is elevated in the lung tissue and localized to the macrophages. In mouse models of COPD, lung fibrosis and skin injury, reduced expression of PRMT7 associates with decreased recruitment of monocytes to the site of injury and hence less severe symptoms. Mechanistically, activation of NF-κB/RelA in monocytes induces PRMT7 transcription and consequential mono-methylation of histones at the regulatory elements of RAP1A, which leads to increased transcription of this gene that is responsible for adhesion and migration of monocytes. Persistent monocyte-derived macrophage accumulation leads to ALOX5 over-expression and accumulation of its metabolite LTB4, which triggers expression of ACSL4 a ferroptosis promoting gene in lung epithelial cells. Conclusively, inhibition of arginine mono-methylation might offer targeted intervention in monocyte-driven inflammatory conditions that lead to extensive tissue damage if left untreated.

Guanosine primes acute myeloid leukemia for differentiation via guanine nucleotide salvage synthesis

Differentiation arrest represents a distinct hallmark of acute myeloid leukemia (AML). Identification of differentiation-induction agents that are effective across various subtypes remains an unmet challenge. GTP biosynthesis is elevated in several types of cancers, considered to support uncontrolled tumor growth. Here we report that GTP overload by supplementation of guanosine, the nucleoside precursor of GTP, poises AML cells for differentiation and growth inhibition. Transcriptome profiling of guanosine-treated AML cells reveals a myeloid differentiation pattern. Importantly, the treatment compromises leukemia progression in AML xenograft models. Mechanistically, GTP overproduction requires sequential metabolic conversions executed by the purine salvage biosynthesis pathway including the involvement of purine nucleoside phosphorylase (PNP) and hypoxanthine phosphoribosyltransferase 1 (HPRT1). Taken together, our study offers novel metabolic insights tethering GTP homeostasis to myeloid differentiation and provides an experimental basis for further clinical investigations of guanosine or guanine nucleotides in the treatment of AML patients.

PRMT1 Regulates EGFR and Wnt Signaling Pathways and Is a Promising Target for Combinatorial Treatment of Breast Cancer

Simple Summary

Patients with triple-negative breast cancer (TNBC) respond well to chemotherapy initially but are prone to relapse. Searching for new therapeutic targets, we found that PRMT1 is highly expressed in TNBC tumor samples and is essential for breast cancer cell survival. Furthermore, this study proposes that targeting PRMT1 in combination with chemotherapies could improve the survival outcome of TNBC patients.

Abstract

Identifying new therapeutic strategies for triple-negative breast cancer (TNBC) patients is a priority as these patients are highly prone to relapse after chemotherapy. Here, we found that protein arginine methyltransferase 1 (PRMT1) is highly expressed in all breast cancer subtypes. PRMT1 depletion decreases cell survival by inducing DNA damage and apoptosis in various breast cancer cell lines. Transcriptomic analysis and chromatin immunoprecipitation revealed that PRMT1 regulates the epidermal growth factor receptor (EGFR) and the Wnt signaling pathways, reported to be activated in TNBC. PRMT1 enzymatic activity is also required to stimulate the canonical Wnt pathway. Type I PRMT inhibitors decrease breast cancer cell proliferation and show anti-tumor activity in a TNBC xenograft model. These inhibitors display synergistic interactions with some chemotherapies used to treat TNBC patients as well as erlotinib, an EGFR inhibitor. Therefore, targeting PRMT1 in combination with these chemotherapies may improve existing treatments for TNBC patients.

PRMT1-mediated EZH2 methylation promotes breast cancer cell proliferation and tumorigenesis

Protein arginine methyltransferase 1 (PRMT1) is able to promote breast cancer cell proliferation. However, the detailed mechanisms of PRMT1-mediated breast cancer cell proliferation are largely unknown. In this study, we reveal that PRMT1-mediated methylation of EZH2 at the R342 site (meR342-EZH2) has a great effect on PRMT1-induced cell proliferation. We also demonstrate that meR342-EZH2 can accelerate breast cancer cell proliferation in vitro and in vivo. Further, we show that meR342-EZH2 promotes cell cycle progression by repressing P16 and P21 transcription expression. In terms of mechanism, we illustrate that meR342-EZH2 facilitates EZH2 binding with SUZ12 and PRC2 assembly by preventing AMPKα1-mediated phosphorylation of pT311-EZH2, which results in suppression of P16 and P21 transcription by enhancing EZH2 expression and H3K27me3 enrichment at P16 and P21 promoters. Finally, we validate that the expression of PRMT1 and meR342-EZH2 is negatively correlated with pT311-EZH2 expression. Our findings suggest that meR342-EZH2 may become a novel therapeutic target for the treatment of breast cancer.

Structure, Activity, and Function of PRMT1

PRMT1, the major protein arginine methyltransferase in mammals, catalyzes monomethylation and asymmetric dimethylation of arginine side chains in proteins. Initially described as a regulator of chromatin dynamics through the methylation of histone H4 at arginine 3 (H4R3), numerous non-histone substrates have since been identified. The variety of these substrates underlines the essential role played by PRMT1 in a large number of biological processes such as transcriptional regulation, signal transduction or DNA repair. This review will provide an overview of the structural, biochemical and cellular features of PRMT1. After a description of the genomic organization and protein structure of PRMT1, special consideration was given to the regulation of PRMT1 enzymatic activity. Finally, we discuss the involvement of PRMT1 in embryonic development, DNA damage repair, as well as its participation in the initiation and progression of several types of cancers.

GATM-Mediated Creatine Biosynthesis Enables Maintenance of FLT3-ITD-Mutant Acute Myeloid Leukemia

FMS-like tyrosine kinase 3 (FLT3) is one of the most frequently mutated genes in acute myeloid leukemia (AML), with the most common mutation being internal tandem duplications (ITD). The presence of FLT3-ITD in AML carries a particularly poor prognosis and renders therapeutic resistance. New druggable targets are thus needed in this disease. In this study, we demonstrate the effects of de novo creatine biosynthesis upregulation by FLT3-ITD on AML sustainability. Our data show that FLT3-ITD constitutively activates the STAT5 signaling pathway, which upregulates the expression of glycine amidinotransferase (GATM), the first rate-limiting enzyme of de novo creatine biosynthesis. Pharmacologic FLT3-ITD inhibition reduces intracellular creatinine levels through transcriptional downregulation of genes in the de novo creatine biosynthesis pathway. The same reduction can be achieved by cyclocreatine or genetic GATM knockdown with shRNA and is reflected in significant decrease of cell proliferation and moderate increase of cell apoptosis in FLT3-ITD-mutant cell lines. Those effects are at least partially mediated through the AMPK/mTOR signaling pathway. This study uncovers a previously uncharacterized role of creatine metabolic pathway in the maintenance of FLT3-ITD-mutant AML and suggests that targeting this pathway may serve as a promising therapeutic strategy for FLT3-ITD-positive AML. IMPLICATIONS: FLT3-ITD mutation in AML upregulates de novo creatine biosynthesis that we show can be suppressed to diminish the proliferation and survival of blast cells.

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.

Methylation of dual-specificity phosphatase 4 controls cell differentiation

Mitogen-activated protein kinases (MAPKs) are inactivated by dual-specificity phosphatases (DUSPs), the activities of which are tightly regulated during cell differentiation. Using knockdown screening and single-cell transcriptional analysis, we demonstrate that DUSP4 is the phosphatase that specifically inactivates p38 kinase to promote megakaryocyte (Mk) differentiation. Mechanistically, PRMT1-mediated methylation of DUSP4 triggers its ubiquitinylation by an E3 ligase HUWE1. Interestingly, the mechanistic axis of the DUSP4 degradation and p38 activation is also associated with a transcriptional signature of immune activation in Mk cells. In the context of thrombocytopenia observed in myelodysplastic syndrome (MDS), we demonstrate that high levels of p38 MAPK and PRMT1 are associated with low platelet counts and adverse prognosis, while pharmacological inhibition of p38 MAPK or PRMT1 stimulates megakaryopoiesis. These findings provide mechanistic insights into the role of the PRMT1-DUSP4-p38 axis on Mk differentiation and present a strategy for treatment of thrombocytopenia associated with MDS.

Gene Transcription as a Therapeutic Target in Leukemia

Blood malignancies often arise from undifferentiated hematopoietic stem cells or partially differentiated stem-like cells. A tight balance of multipotency and differentiation, cell division, and quiescence underlying normal hematopoiesis requires a special program governed by the transcriptional machinery. Acquisition of drug resistance by tumor cells also involves reprogramming of their transcriptional landscape. Limiting tumor cell plasticity by disabling reprogramming of the gene transcription is a promising strategy for improvement of treatment outcomes. Herein, we review the molecular mechanisms of action of transcription-targeted drugs in hematological malignancies (largely in leukemia) with particular respect to the results of clinical trials.

Splicing regulation in hematopoiesis

PURPOSE OF REVIEW

Splicing mutations are among the most recurrent genetic perturbations in hematological malignancies, highlighting an important impact of splicing regulation in hematopoietic development. However, compared to our understanding of splicing factor mutations in hematological malignancies, studies of splicing components and alternative splicing in normal hematopoiesis have been less well investigated. Here, we outline the most recent findings on splicing regulation in normal hematopoiesis and discuss the important questions in the field.

RECENT FINDINGS

Recent studies have highlighted the critical role of splicing regulation in hematopoiesis, including characterization of splicing components in normal hematopoiesis, investigation of transcriptional alterations on splicing, and identification of stage-specific alternative splicing events during hematopoietic development.

SUMMARY

These interesting findings provide insights on hematopoietic regulation at a co-transcriptional level. More high-throughput RNA ribonucleic acid (RNA) sequencing and functional genomic screens are needed to advance our knowledge of critical alternative splicing patterns in shaping hematopoiesis.

Cancer synthetic vulnerabilities to protein arginine methyltransferase inhibitors

Protein arginine methylation is an abundant post-translational modification involved in the modulation of essential cellular processes ranging from transcription, post-transcriptional RNA metabolism, and propagation of signaling cascades to the regulation of the DNA damage response. Excitingly for the field, in the past few years there have been remarkable advances in the development of molecular tools and clinical compounds able to selectively and potently inhibit protein arginine methyltransferase (PRMT) functions. In this review, we first discuss how the somatic mutations that confer advantages to cancer cells are often associated with vulnerabilities that can be exploited by PRMTs' inhibition. In a second part, we discuss strategies to uncover synthetic lethal combinations between existing therapies and PRMT inhibitors.