Protein arginine N-methyltransferase 5 in colorectal carcinoma: Insights into mechanisms of pathogenesis and therapeutic strategies

Targeting non-histone methylation in gastrointestinal cancers: From biology to clinic

Gastrointestinal (GI) cancers, encompassing a range of malignancies within the digestive tract, present significant challenges in both diagnosis and treatment, reflecting a dire need for innovative therapeutic strategies. This article delves into the profound influence of non-histone methylation on the pathogenesis and evolution of gastrointestinal (GI) cancers. Non-histone proteins, undergoing methylation by enzymes such as Protein Arginine Methyltransferases (PRMTs) and Lysine Methyltransferases (KMTs), play pivotal roles in cellular signaling, metabolism, chromatin remodeling, and other processes crucial for cancer development. This review illuminates the complex mechanisms by which non-histone methylation affects key aspects of tumor biology, including oncogenesis, growth, proliferation, invasion, migration, metabolic reprogramming, and immune escape in GI malignancies. Highlighting recent discoveries, this work underscores the importance of non-histone methylation in cancer biology and its potential as a target for innovative therapeutic strategies aimed at improving outcomes for patients with GI cancers.

Targeting PRMT5 enhances the radiosensitivity of tumor cells grown in vitro and in vivo

PRMT5 is a widely expressed arginine methyltransferase that regulates processes involved in tumor cell proliferation and survival. In the study described here, we investigated whether PRMT5 provides a target for tumor radiosensitization. Knockdown of PRMT5 using siRNA enhanced the radiosensitivity of a panel of cell lines corresponding to tumor types typically treated with radiotherapy. To extend these studies to an experimental therapeutic setting, the PRMT5 inhibitor LLY-283 was used. Exposure of the tumor cell lines to LLY-283 decreased PRMT5 activity and enhanced their radiosensitivity. This increase in radiosensitivity was accompanied by an inhibition of DNA double-strand break repair as determined by γH2AX foci and neutral comet analyses. For a normal fibroblast cell line, although LLY-283 reduced PRMT5 activity, it had no effect on their radiosensitivity. Transcriptome analysis of U251 cells showed that LLY-283 treatment reduced the expression of genes and altered the mRNA splicing pattern of genes involved in the DNA damage response. Subcutaneous xenografts were then used to evaluate the in vivo response to LLY-283 and radiation. Treatment of mice with LLY-283 decreased tumor PRMT5 activity and significantly enhanced the radiation-induced growth delay. These results suggest that PRMT5 is a tumor selective target for radiosensitization.

PRMT5 Mediated HIF1α Signaling and Ras-Related Nuclear Protein as Promising Biomarker in Hepatocellular Carcinoma

Protein arginine N-methyltransferase 5 (PRMT5) has been identified as a potential therapeutic target for various cancer types. However, its role in regulating the hepatocellular carcinoma (HCC) transcriptome remains poorly understood. In this study, publicly available databases were employed to investigate PRMT5 expression, its correlation with overall survival, targeted pathways, and genes of interest in HCC. Additionally, we utilized in-house generated NGS data to explore PRMT5 expression in dysplastic nodules compared to hepatocellular carcinoma. Our findings revealed that PRMT5 is significantly overexpressed in HCC compared to normal liver, and elevated expression correlates with poor overall survival. To gain insights into the mechanism driving PRMT5 overexpression in HCC, we analyzed promoter CpG islands and methylation status in HCC compared to normal tissues. Pathway analysis of PRMT5 knockdown in the HCC cells revealed a connection between PRMT5 expression and genes related to the HIF1α pathway. Additionally, by filtering PRMT5-correlated genes within the HIF1α pathway and selecting up/downregulated genes in HCC patients, we identified Ras-related nuclear protein (RAN) as a target associated with overall survival. For the first time, we report that PRMT5 is implicated in the regulation of HIF1A and RAN genes, suggesting the potential prognostic utility of PRMT5 in HCC.

Genetic Alterations of NF-κB and Its Regulators: A Rich Platform to Advance Colorectal Cancer Diagnosis and Treatment

Colorectal cancer (CRC) is the third leading cause of cancer mortality in the United States, with an estimated 52,000 deaths in 2023. Though significant progress has been made in both diagnosis and treatment of CRC in recent years, genetic heterogeneity of CRC-the culprit for possible CRC relapse and drug resistance, is still an insurmountable challenge. Thus, developing more effective therapeutics to overcome this challenge in new CRC treatment strategies is imperative. Genetic and epigenetic changes are well recognized to be responsible for the stepwise development of CRC malignancy. In this review, we focus on detailed genetic alteration information about the nuclear factor (NF)-κB signaling, including both NF-κB family members, and their regulators, such as protein arginine methyltransferase 5 (PRMT5), and outer dynein arm docking complex subunit 2 (ODAD2, also named armadillo repeat-containing 4, ARMC4), etc., in CRC patients. Moreover, we provide deep insight into different CRC research models, with a particular focus on patient-derived xenografts (PDX) and organoid models, and their potential applications in CRC research. Genetic alterations on NF-κB signaling components are estimated to be more than 50% of the overall genetic changes identified in CRC patients collected by cBioportal for Cancer Genomics; thus, emphasizing its paramount importance in CRC progression. Consequently, various genetic alterations on NF-κB signaling may hold great promise for novel therapeutic development in CRC. Future endeavors may focus on utilizing CRC models (e.g., PDX or organoids, or isogenic human embryonic stem cell (hESC)-derived colonic cells, or human pluripotent stem cells (hPSC)-derived colonic organoids, etc.) to further uncover the underpinning mechanism of these genetic alterations in NF-κB signaling in CRC progression. Moreover, establishing platforms for drug discovery in dishes, and developing Biobanks, etc., may further pave the way for the development of innovative personalized medicine to treat CRC in the future.

Targeting Arginine Methyltransferase PRMT5 for Cancer Therapy: Updated Progress and Novel Strategies

As a predominant type II protein arginine methyltransferase, PRMT5 plays critical roles in various normal cellular processes by catalyzing the mono- and symmetrical dimethylation of a wide range of histone and nonhistone substrates. Clinical studies have revealed that high expression of PRMT5 is observed in different solid tumors and hematological malignancies and is closely associated with cancer initiation and progression. Accordingly, PRMT5 is becoming a promising anticancer target and has received great attention in both the pharmaceutical industry and the academic community. In this Perspective, we comprehensively summarize recent advances in the development of first-generation PRMT5 enzymatic inhibitors and highlight novel strategies targeting PRMT5 in the past 5 years. We also discuss the challenges and opportunities of PRMT5 inhibition, with the aim of shedding light on future PRMT5 drug discovery.

Protein Arginine Methyltransferase 5 (PRMT5) Mutations in Cancer Cells

Arginine methylation is a form of posttranslational modification that regulates many cellular functions such as development, DNA damage repair, inflammatory response, splicing, and signal transduction, among others. Protein arginine methyltransferase 5 (PRMT5) is one of nine identified methyltransferases, and it can methylate both histone and non-histone targets. It has pleiotropic functions, including recruitment of repair machinery to a chromosomal DNA double strand break (DSB) and coordinating the interplay between repair and checkpoint activation. Thus, PRMT5 has been actively studied as a cancer treatment target, and small molecule inhibitors of its enzymatic activity have already been developed. In this report, we analyzed all reported PRMT5 mutations appearing in cancer cells using data from the Catalogue of Somatic Mutations in Cancers (COSMIC). Our goal is to classify mutations as either drivers or passengers to understand which ones are likely to promote cellular transformation. Using gold standard artificial intelligence algorithms, we uncovered several key driver mutations in the active site of the enzyme (D306H, L315P, and N318K). In silico protein modeling shows that these mutations may affect the affinity of PRMT5 for S-adenosylmethionine (SAM), which is required as a methyl donor. Electrostatic analysis of the enzyme active site shows that one of these mutations creates a tunnel in the vicinity of the SAM binding site, which may allow interfering molecules to enter the enzyme active site and decrease its activity. We also identified several non-coding mutations that appear to affect PRMT5 splicing. Our analyses provide insights into the role of PRMT5 mutations in cancer cells. Additionally, since PRMT5 single molecule inhibitors have already been developed, this work may uncover future directions in how mutations can affect targeted inhibition.

Mechanistic aspects of reversible methylation modifications of arginine and lysine of nuclear histones and their roles in human colon cancer

Developmental proceedings and maintenance of cellular homeostasis are regulated by the precise orchestration of a series of epigenetic events that eventually control gene expression. DNA methylation and post-translational modifications (PTMs) of histones are well-characterized epigenetic events responsible for fine-tuning gene expression. PTMs of histones bear molecular logic of gene expression at chromosomal territory and have become a fascinating field of epigenetics. Nowadays, reversible methylation on histone arginine and lysine is gaining increasing attention as a significant PTM related to reorganizing local nucleosomal structure, chromatin dynamics, and transcriptional regulation. It is now well-accepted and reported that histone marks play crucial roles in colon cancer initiation and progression by encouraging abnormal epigenomic reprogramming. It is becoming increasingly clear that multiple PTM marks at the N-terminal tails of the core histones cross-talk with one another to intricately regulate DNA-templated biological processes such as replication, transcription, recombination, and damage repair in several malignancies, including colon cancer. These functional cross-talks provide an additional layer of message, which spatiotemporally fine-tunes the overall gene expression regulation. Nowadays, it is evident that several PTMs instigate colon cancer development. How colon cancer-specific PTM patterns or codes are generated and how they affect downstream molecular events are uncovered to some extent. Future studies would address more about epigenetic communication, and the relationship between histone modification marks to define cellular functions in depth. This chapter will comprehensively highlight the importance of histone arginine and lysine-based methylation modifications and their functional cross-talk with other histone marks from the perspective of colon cancer development.

Tadalafil increases the antitumor activity of 5-FU through inhibiting PRMT5-mediated glycolysis and cell proliferation in colorectal cancer

BACKGROUND

Protein arginine methyltransferase 5 (PRMT5) is upregulated in multiple tumors and plays a pivotal role in cancer cell proliferation. However, the role of PRMT5 in colorectal cancer remains poorly understood.

METHODS

We detected the expression level of PRMT5 and glycolytic enzymes using online databases and colorectal cancer cell lines by immunohistochemical staining, quantitative real-time polymerase chain reaction (qRT-PCR), and western blotting. And MTT and colony formation assays were conducted to investigate cell proliferation. Then, we evaluated ECAR and OCR levels using a biological energy analyzer to investigate the energy status of colorectal cancer, and the transcriptional regulation was detected by dual luciferase reporter assay and ChIP assay. Finally, the efficacy of combined treatment of tadalafil and 5-FU was verified.

RESULTS

PRMT5 was highly expressed in colorectal cancer tissues compared with their normal counterparts and correlated with poor prognosis in CRC patients. Then, we demonstrated that PRMT5 knockdown or loss of function attenuated the viability of CRC cells, while overexpression of PRMT5 promoted cell proliferation. Mechanistically, PRMT5 enhanced glycolysis through transcriptionally activating LDHA expression. In addition, the PRMT5 inhibitor, tadalafil, rendered CRC cells sensitive to antitumor agent 5-FU in vitro and in vivo.

CONCLUSIONS

Our data indicates that PRMT5 promoted colorectal cancer proliferation partially through activating glycolysis and may be a potential target for colorectal cancer therapy.

Flavokawain A is a natural inhibitor of PRMT5 in bladder cancer

BACKGROUND

Protein arginine methyltransferases (PRMTs) regulate protein biological activity by modulating arginine methylation in cancer and are increasingly recognized as potential drug targets. Inhibitors targeting PRMTs are currently in the early phases of clinical trials and more candidate drugs are needed. Flavokawain A (FKA), extracted from kava plant, has been recognized as a potential chemotherapy drug in bladder cancer (BC), but its action mechanism remains unclear.

METHODS

We first determined the role of a type II PRMT, PRMT5, in BC tissue samples and performed cytological experiments. We then utilized bioinformatics tools, including computational simulation, virtual screening, molecular docking, and energy analysis, to identify the potential use of PRMT5 inhibitors for BC treatment. In vitro and in vivo co-IP and mutation assays were performed to elucidate the molecular mechanism of PRMT5 inhibitor. Pharmacology experiments like bio-layer interferometry, CETSA, and pull-down assays were further used to provide direct evidence of the complex binding process.

RESULTS

Among PRMTs, PRMT5 was identified as a therapeutic target for BC. PRMT5 expression in BC was correlated with poor prognosis and manipulating its expression could affect cancer cell growth. Through screening and extensive experimental validation, we recognized that a natural product, FKA, was a small new inhibitor molecule for PRMT5. We noticed that the product could inhibit the action of BC, in vitro and in vivo, by inhibiting PRMT5. We further demonstrated that FKA blocks the symmetric arginine dimethylation of histone H2A and H4 by binding to Y304 and F580 of PRMT5.

CONCLUSIONS

In summary, our research strongly suggests that PRMT5 is a potential epigenetic therapeutic target in bladder cancer, and that FKA can be used as a targeted inhibitor of PRMT5 for the treatment of bladder cancer.

SMYD3 regulates gastric cancer progression and macrophage polarization through EZH2 methylation

SET and MYND domain-containing protein 3 (SMYD3), a known histone methyltransferase, was reported to regulate cancer pathogenesis. However, its role in gastric development and progression remains unclear. EZH2 methylation had been associated with cancer metastasis, but the EZH2 methylation status in gastric cancer (GC) is unknown. Here, we report that EZH2 K421 methylation was responsible for gastric cancer cell soft agar colony formation, in vivo metastasis, and macrophage polarization. Mechanically, we identified SMYD3 as the methyltransferase of EZH2 at K421 residue which accelerates EZH2 Ubiquitin proteasome degradation. Cell harboring non-methylated EZH2 mutants promotes gastric cancer cell metastasis. Taken together, our results showed that SMYD3-EZH2 axis restricts gastric cancer metastasis via integrating epigenetic signaling.