S-Adenosyl-L-methionine-competitive inhibitors of the histone methyltransferase EZH2 induce autophagy and enhance drug sensitivity in cancer cells

EZH2-mediated development of therapeutic resistance in cancer

Enhancer of zeste homolog 2 (EZH2) regulates gene expression and plays a definite role in cell proliferation, apoptosis, and senescence. Overexpression of EZH2 has been found in various human malignancies, including prostate, breast, and ovarian cancers, and is associated with increased metastasis and poor prognosis. EZH2 catalyzes trimethylation of lysine 27 of histone H3 (H3K27me3) as a canonical role in a PRC2-dependent manner. This mechanism silences various tumor suppressor genes through EZH2-mediated histone lysine methyltransferase activity. As a non-canonical role, EZH2 partners with other signaling molecules to undergo post-translational modification to orchestrate its function as a co-activator playing a critical role in cancer progression. Dysregulation of EZH2 has also been associated with therapeutic resistance in cancer cells. Given the role of EZH2 in promoting carcinogenesis and therapy resistance, both canonical and non-canonical EZH2 inhibitors have been used to combat multiple cancer types. Moreover, combining EZH2 inhibitors with other therapeutic modalities have shown to enhance the therapeutic efficacy and overcome potential resistance mechanisms in these cancerous cells. Therefore, targeting EZH2 through canonical and non-canonical modes appears to be a promising therapeutic strategy to enhance efficacy and overcome resistance in multiple cancers.

EZH2 as a potential therapeutic target for gastrointestinal cancers

Gastrointestinal (GI) cancers continue to be a major cause of mortality and morbidity globally. Understanding the molecular pathways associated with cancer progression and severity is essential for creating effective cancer treatments. In cancer research, there is a notable emphasis on Enhancer of zeste homolog 2 (EZH2), a key player in gene expression influenced by its irregular expression and capacity to attach to promoters and alter methylation status. This review explores the impact of EZH2 signaling on various GI cancers, such as colorectal, gastric, pancreatic, hepatocellular, esophageal, and cholangiocarcinoma. The primary function of EZH2 signaling is to facilitate the accelerated progression of cancer cells. Additionally, EZH2 has the capacity to modulate the reaction of GI cancers to chemotherapy and radiotherapy. Numerous pathways, including long non-coding RNAs and microRNAs, serve as upstream regulators of EZH2 in these types of cancer. EZH2's enzymatic activity enables it to attach to target gene promoters, resulting in methylation that modifies their expression. EZH2 could be considered as an independent prognostic factor, with increased expression correlating with a worse disease prognosis. Additionally, a range of gene therapies including small interfering RNA, and anti-tumor agents are being explored to target EZH2 for cancer treatment. This comprehensive review underscores the current insights into EZH2 signaling in gastrointestinal cancers and examines the prospect of therapies targeting EZH2 to enhance patient outcomes.

FBP1 knockdown decreases ovarian cancer formation and cisplatin resistance through EZH2-mediated H3K27me3

Worldwide, ovarian cancer (OC) is the seventh common cancer and the second most common cause of cancer death in women. Due to high rates of relapse, there is an urgent need for the identification of new targets for OC treatment. The far-upstream element binding protein 1 (FBP1) and enhancer of zeste homolog 2 (EZH2) are emerging proto-oncogenes that regulate cell proliferation and metastasis. In the present study, Oncomine data analysis demonstrated that FBP1 was closely associated with the development of OC, and The Cancer Genome Atlas (TCGA) data analysis indicated that there was a positive correlation between FBP1 and EZH2 in ovarian tissues. Moreover, we found that FBP1 knockdown suppressed tumor formation in nude mice and cisplatin resistance of OC cells, but the role of FBP1 in the cisplatin resistance of OC cells remained unclear. In addition, we verified physical binding between FBP1 and EZH2 in OC cells, and we demonstrated that FBP1 knockdown enhanced cisplatin cytotoxicity in OC cells and down-regulated EZH2 expression and trimethylation of H3K27. These results suggested that FBP1 increases cisplatin resistance of OC cells by up-regulating EZH2/H3K27me3. Thus, FBP1 is a prospective novel target for the development of OC treatment.

Mechanisms of Polycomb group protein function in cancer

Cancer arises from a multitude of disorders resulting in loss of differentiation and a stem cell-like phenotype characterized by uncontrolled growth. Polycomb Group (PcG) proteins are members of multiprotein complexes that are highly conserved throughout evolution. Historically, they have been described as essential for maintaining epigenetic cellular memory by locking homeotic genes in a transcriptionally repressed state. What was initially thought to be a function restricted to a few target genes, subsequently turned out to be of much broader relevance, since the main role of PcG complexes is to ensure a dynamically choregraphed spatio-temporal regulation of their numerous target genes during development. Their ability to modify chromatin landscapes and refine the expression of master genes controlling major switches in cellular decisions under physiological conditions is often misregulated in tumors. Surprisingly, their functional implication in the initiation and progression of cancer may be either dependent on Polycomb complexes, or specific for a subunit that acts independently of other PcG members. In this review, we describe how misregulated Polycomb proteins play a pleiotropic role in cancer by altering a broad spectrum of biological processes such as the proliferation-differentiation balance, metabolism and the immune response, all of which are crucial in tumor progression. We also illustrate how interfering with PcG functions can provide a powerful strategy to counter tumor progression.

Genome-Wide Analysis of H3K27me3 in Porcine Embryonic Muscle Development

The trimethylation of histone H3 lysine 27 (H3K27me3) is one of the most important chromatin modifications, which is generally presented as a repressive mark in various biological processes. However, the dynamic and global-scale distribution of H3K27me3 during porcine embryonic muscle development remains unclear. Here, our study provided a comprehensive genome-wide view of H3K27me3 and analyzed the matching transcriptome in the skeletal muscles on days 33, 65, and 90 post-coitus from Duroc fetuses. Transcriptome analysis identified 4,124 differentially expressed genes (DEGs) and revealed the key transcriptional properties in three stages. We found that the global H3K27me3 levels continually increased during embryonic development, and the H3K27me3 level was negatively correlated with gene expression. The loss of H3K27me3 in the promoter was associated with the transcriptional activation of 856 DEGs in various processes, including skeletal muscle development, calcium signaling, and multiple metabolic pathways. We also identified for the first time that H3K27me3 could enrich in the promoter of genes, such as DES, MYL1, TNNC1, and KLF5, to negatively regulate gene expression in porcine satellite cells (PSCs). The loss of H3K27me3 could promote muscle cell differentiation. Taken together, this study provided the first genome-wide landscape of H3K27me3 in porcine embryonic muscle development. It revealed the complex and broad function of H3K27me3 in the regulation of embryonic muscle development from skeletal muscle morphogenesis to myofiber maturation.

Targeting Autophagy-Related Epigenetic Regulators for Cancer Drug Discovery

Existing evidence has demonstrated that epigenetic modifications (including DNA methylation, histone modifications, and microRNAs), which are associated with the occurrence and development of tumors, can directly or indirectly regulate autophagy. In particular, nuclear events induced by several epigenetic regulators can regulate the autophagic process and expression levels of tumor-associated genes, thereby promoting tumor progression. Tumor-associated microRNAs, including oncogenic and tumor-suppressive microRNAs, are of great significance to autophagy during tumor progression. Targeting autophagy with emerging epigenetic drugs is expected to be a promising therapeutic strategy for human tumors. From this perspective, we aim to summarize the role of epigenetic modification in the autophagic process and the underlying molecular mechanisms of tumorigenesis. Furthermore, the regulatory efficacy of epigenetic drugs on the autophagic process in tumors is also summarized. This perspective may provide a theoretical basis for the combined treatment of epigenetic drugs/autophagy mediators in tumors.

Regulation of autophagy by protein methylation and acetylation in cancer

Autophagy is a highly conserved mechanism responsible for cellular homeostasis and integrity in a variety of physiological conditions. Materials targeted for degradation are directed to autophagosomes and autolysosomes, where they are broken down into their base components. Aberrant regulation of autophagy is significantly associated with various cancers and neurodegenerative diseases. Recently, accumulating evidence has revealed that the coordinated regulation of histone and non-histone protein modification is associated with autophagy. In this review, we highlight the recent progress that has been made in elucidating the molecular basis of protein methylation and acetylation associated with autophagy at the transcriptional and posttranslational levels. Furthermore, we discuss the importance of describing causality between protein methylation/acetylation and autophagy regulation as compelling therapeutic opportunities in cancer pathogenesis and progression.

EZH2 Promotes Extracellular Matrix Degradation via Nuclear Factor-κB (NF-κB) and p38 Signaling Pathways in Pulpitis

Pulpitis is a complicated chronic inflammatory process which can be in a dynamic balance between damage and repair. The extracellular matrix plays an important regulatory role in wound healing and tissue repair. The aim of this study was to explore the role of the epigenetic mark, enhancer of zeste homolog 2 (EZH2) on the degradation of extracellular matrix during pulpitis. Quantitative polymerase chain reaction was used to assess the expression of matrix metalloproteinases (MMPs) and type I collagen in human dental pulp cells (HDPCs) upon EZH2 and EI1 (EZH2 inhibitor) stimulation. The mechanism of EZH2 affecting extracellular matrix was explored through quantitative polymerase chain reaction and Western blot. A rat model of dental pulp inflammation was established, and the expression of type I collagen in dental pulp under EZH2 stimulation was detected by immunohistochemical staining. EZH2 upregulated the expression of MMP-1, MMP-3, MMP-8, and MMP-10 and decreased the production of type I collagen in HDPCs, while EI1 had the opposite effect. EZH2 activated the nuclear factor-kappa B (NF-κB) and p38 signaling pathways in HDPCs, the inhibition of which reversed the induction of MMPs and the suppression of type I collagen. EZH2 can downregulate the type I collagen levels in an experimental model of dental pulpitis in rats. EZH2 promotes extracellular matrix degradation via nuclear factor-κB (NF-κB) and P38 signaling pathways in pulpitis. EZH2 can decrease the type I collagen levels in vivo and in vitro.

Full methylation of H3K27 by PRC2 is dispensable for initial embryoid body formation but required to maintain differentiated cell identity

Polycomb repressive complex 2 (PRC2) catalyzes methylation of histone H3 on lysine 27 and is required for normal development of complex eukaryotes. The nature of that requirement is not clear. H3K27me3 is associated with repressed genes, but the modification is not sufficient to induce repression and, in some instances, is not required. We blocked full methylation of H3K27 with both a small molecule inhibitor, GSK343, and by introducing a point mutation into EZH2, the catalytic subunit of PRC2, in the mouse CJ7 cell line. Cells with substantively decreased H3K27 methylation differentiate into embryoid bodies, which contrasts with EZH2 null cells. PRC2 targets had varied requirements for H3K27me3, with a subset that maintained normal levels of repression in the absence of methylation. The primary cellular phenotype of blocked H3K27 methylation was an inability of altered cells to maintain a differentiated state when challenged. This phenotype was determined by H3K27 methylation in embryonic stem cells through the first 4 days of differentiation. Full H3K27 methylation therefore was not necessary for formation of differentiated cell states during embryoid body formation but was required to maintain a stable differentiated state.

Under hypoxic conditions, MSCs affect the expression and methylation level of survival-related genes in ALL independent of apoptosis pathways in vitro

Mesenchymal stem cells (MSCs) are one of the most prominent cells in the bone marrow. MSCs can affect acute lymphocytic leukemia (ALL) cells under hypoxic conditions. With this aim, we used MOLT-4 cells as simulators of ALL cells cocultured with bone marrow mesenchymal stem cells (BMMSCs) under hypoxic conditions in vitro. Then, mRNA and protein expression of the MAT2A, PDK1, and HK2 genes were evaluated by real-time PCR and Western blot which was also followed by apoptosis measurement by a flow-cytometric method. Next, the methylation status of the target genes was investigated by MS-qPCR. Additionally, candidate gene expressions were examined after treatment with rapamycin using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. We found that the mRNA expression of the candidate genes was augmented under the hypoxic condition in which MAT2A was upregulated in cocultured cells compared to MOLT-4, while HK2 and PDK1 were downregulated. Moreover, we found an association between gene expression and promoter methylation levels of target genes. Besides, expressions of the candidate genes were decreased, while their methylation levels were promoted following treatment with rapamycin. Our results suggest an important role for the BMMSC in regulating the methylation of genes involved in cell survival in hypoxia conditions; however, we found no evidence to prove the MSCs' effect on directing malignant lymphoblastic cells to apoptosis.

Inhibition of Histone Methyltransferase EZH2 Suppresses Endometriotic Vesicle Development in a Rat Model of Endometriosis

Endometriosis is a painful gynecological disease with no cure and limited therapeutic options. It has been hypothesized that epigenetic drugs can be used as a nonhormonal treatment for endometriosis. This study was conducted to study the efficacy of an inhibitor of the histone methyltransferase EZH2 using an established rat model of endometriosis. We hypothesized that treatment will block or reduce the number of endometriotic vesicles in this model. We conducted a preclinical drug study in female rats with experimental endometriosis (uterine tissue transplanted next to the intestinal mesentery) or control sham (sutures only). Rats with endometriosis or sham surgery received either treatment with EZH2 inhibitor (5 mg/kg or 10 mg/kg) or vehicle (0.1%, 67% DMSO) every other day during 4 weeks. After treatment completion, the number, area, volume, and weight of vesicles were evaluated. RT [2] Profiler Arrays for neuropathic and inflammation, epithelial to mesenchymal transition, inflammatory response, and autoimmunity pathways were used to examine gene expression changes in the vesicles that developed. Treatment with EZH2 inhibitor (10 mg/kg) suppressed the development of vesicles, by significantly decreasing the total vesicle number, area, volume, and weight. In addition, EZH2 inhibition significantly increased the expression of CACNA1B and FKBP1A genes, involved in pain and proliferation, respectively. EZH2 inhibition suppresses the growth of vesicles without apparent detrimental effects to other organs. Treatment with this epigenetic inhibitor leads to upregulation of a limited number of genes related to endometriosis-relevant pathways. In conclusion, these data support follow-up studies to evaluate its potential as a therapeutic approach for endometriosis.

Epigenetic Control of Autophagy in Cancer Cells: A Key Process for Cancer-Related Phenotypes

Although autophagy is a well-known and extensively described cell pathway, numerous studies have been recently interested in studying the importance of its regulation at different molecular levels, including the translational and post-translational levels. Therefore, this review focuses on the links between autophagy and epigenetics in cancer and summarizes the. following: (i) how ATG genes are regulated by epigenetics, including DNA methylation and post-translational histone modifications; (ii) how epidrugs are able to modulate autophagy in cancer and to alter cancer-related phenotypes (proliferation, migration, invasion, tumorigenesis, etc.) and; (iii) how epigenetic enzymes can also regulate autophagy at the protein level. One noteable observation was that researchers most often reported conclusions about the regulation of the autophagy flux, following the use of epidrugs, based only on the analysis of LC3B-II form in treated cells. However, it is now widely accepted that an increase in LC3B-II form could be the consequence of an induction of the autophagy flux, as well as a block in the autophagosome-lysosome fusion. Therefore, in our review, all the published results describing a link between epidrugs and autophagy were systematically reanalyzed to determine whether autophagy flux was indeed increased, or inhibited, following the use of these potentially new interesting treatments targeting the autophagy process. Altogether, these recent data strongly support the idea that the determination of autophagy status could be crucial for future anticancer therapies. Indeed, the use of a combination of epidrugs and autophagy inhibitors could be beneficial for some cancer patients, whereas, in other cases, an increase of autophagy, which is frequently observed following the use of epidrugs, could lead to increased autophagy cell death.

GSK343 induces programmed cell death through the inhibition of EZH2 and FBP1 in osteosarcoma cells

Enhancer of zeste homolog 2 (EZH2) is an important member of the epigenetic regulatory factor polycomb group proteins (PcG) and is abnormally expressed in a wide variety of tumors, including osteosarcoma. Scientists consider EZH2 as an attractive target for the treatment of osteosarcoma and have found many potential EZH inhibitors, such as GlaxoSmithKline 343 (GSK343). It has been reported that GSK343 can be used as an inhibitor in different types of cancer. This study demonstrated that GSK343 not only induced apoptosis by increasing cleaved Casp-3 and poly ADP-ribose polymerase (PARP) expression, but also induced autophagic cell death by inhibiting p62 expression. Apoptosis and autophagic cell death induced by GSK343 were confirmed by the high expression of cleaved caspase-3, LC3-II and transmission electron microscopy. GSK343 inhibited the expression of EZH2 and c-Myc. Additionally, GSK343 inhibited the expression of FUSE binding protein 1 (FBP1), which was identified by its regulatory effects on c-Myc expression. Since c-Myc is a common target of EZH2 and FBP1, and GSK343 inhibited the expression of these proliferation-promoting proteins, a mutual regulatory mechanism between EZH2 and FBP1 was proposed. The knockdown of EZH2 suppressed the expression of FBP1; similarly, the knockdown of FBP1 suppressed the expression of EZH2. These results suggest the mutual regulatory association between EZH2 and FBP1. The knockdown of either EZH2 or FBP1 accelerated the sensitivity of osteosarcoma cells to GSK343. Based on these results, this study clarified that GSK343, an EZH2 inhibitor, may have potential for use in the treatment of osteosarcoma. The underlying mechanisms of the effects of GSK343 are partly mediated by its inhibitory activity against c-Myc and its regulators (EZH2 and FBP1).

Effects of histone methyltransferase inhibition in endometriosis

Although the histone methyltransferase EZH2 and its product H3K27me3 are well studied in cancer, little is known about their role and potential as therapeutic targets in endometriosis. We have previously reported that endometriotic lesions are characterized by global enrichment of H3K27me3. Therefore, we aimed to (1) characterize the expression levels of EZH2 in endometriotic tissues; (2) assess H3K27me3 enrichment in candidate genes promoter regions; and (3) determine if pharmacological inhibition of EZH2 impacts migration, proliferation, and invasion of endometriotic cells. Immunohistochemistry of an endometriosis-focused tissue microarray was used to assess the EZH2 protein levels in tissues. Chromatin immunoprecipitation-qPCR was conducted to assess enrichment of H3K27me3 in candidate gene promoter regions in tissues. Immunofluorescence was performed to assess the effect of an EZH2-specific pharmacological inhibitor on H3K27me3 global enrichment in cell lines. To measure effects of the inhibitor in migration, proliferation, and invasion in vitro we used Scratch, BrdU, and Matrigel assays, respectively. Endometriotic lesions had significantly higher EZH2α nuclear immunostaining levels compared to eutopic endometrium from patients (glands, stroma) and controls (glands). H3K27me3 was enriched within promoter regions of candidate genes in some but not all of the endometriotic lesions. Inhibition of EZH2 reduced H3K27me3 levels in the endometriotic cells specifically, and also reduced migration, proliferation but not invasion of endometriotic epithelial cells (12Z). These findings support future preclinical studies to determine in vivo efficacy of EZH2 inhibitors as promising nonhormonal treatments for endometriosis, still an incurable gynecological disease.

p38α/S1P/SREBP2 activation by the SAM-competitive EZH2 inhibitor GSK343 limits its anticancer activity but creates a druggable vulnerability in hepatocellular carcinoma

Enhancer of zeste homolog 2 (EZH2) mediates epigenetic gene silencing via tri-methylation of histone H3 lysine 27 (H3K27-me3). Increased expression of EZH2 is frequently detected in various cancers including hepatocellular carcinoma (HCC), which is associated with the silencing of tumor suppressor genes. S-adenosyl-L-methionine (SAM)-competitive EZH2 inhibitors fall into the major category of EZH2 inhibitors for cancer therapy. In this study, microarray analyses found that induction of genes related to cholesterol homeostasis is a common effect of SAM-competitive EZH2 inhibitors in cancer cells. As a representative, GSK343 induced lipid accumulation which promoted cancer cell survival. GSK343 selectively activated sterol regulatory element-binding protein 2 (SREBP2), but not SREBP1, in HCC cells. Inhibition of SREBP2 by siRNA reduced cell viability and enhanced the anticancer effect of GSK343. Cancer genomics analysis indicated that SREBP2 upregulation was associated with the poor overall survival of HCC patients. Mechanistically, GSK343-induced SREBP2 activation was unrelated to its original ability to compete with SAM and inhibit EZH2 activity. Instead, GSK343 activated SREBP2 in p38α- and site-1 protease (S1P)-dependent manners. Inhibition of p38α and S1P by SB-202190 and PF-429242, respectively, enhanced the in vitro anticancer activity of GSK343, thereby creating a vulnerability for treating HCC.

GSK343 induces autophagy and downregulates the AKT/mTOR signaling pathway in pancreatic cancer cells

Pancreatic cancer is a common malignancy that has a poor prognosis and limited therapeutic options. Enhancer of zeste homolog 2 (EZH2) serves a key role in the progression of different types of cancers. The effect of GSK343 (a competitive inhibitor of EZH2) on pancreatic cancer cells was assessed in the present study. Cell viability was evaluated using MTT and cell counting kit-8 assays in AsPC-1 and PANC-1 cells. Flow cytometry and an EdU assay were also performed to assess the effects of GSK343 on cell proliferation, apoptosis and the cell cycle. The induction of autophagy and associated molecular mechanisms were studied using fluorescence microscopy and western blot analysis. The results demonstrated that GSK343 inhibited cell viability in a dose- and time-dependent manner. Furthermore, GSK343 suppressed cell proliferation, promoted apoptosis and blocked cell cycle progression at the G1-phase. Furthermore, GSK343 induced autophagy in pancreatic cancer via the AKT/mTOR signaling pathway. In conclusion, GSK343 exhibited an anti-cancer effect on pancreatic cancer cells, downregulating the AKT/mTOR signaling pathway.

Pyrazole-based inhibitors of enhancer of zeste homologue 2 induce apoptosis and autophagy in cancer cells

Novel pyrazole-based EZH2 inhibitors have been prepared through a molecular pruning approach from known inhibitors bearing a bicyclic moiety as a central scaffold. The hit compound 1o (N-((4,6-dimethyl-2-oxo-1,2-dihydropyridin-3-yl)methyl)-5-methyl-1-phenyl-1H-pyrazole-4-carboxamide) showed low micromolar EZH2/PRC2 inhibition and high selectivity towards a panel of other methyltransferases. Moreover, 1o displayed cell growth arrest in breast MDA-MB231, leukaemia K562, and neuroblastoma SK-N-BE cancer cells joined to reduction of H3K27me3 levels and induction of apoptosis and autophagy.This article is part of a discussion meeting issue 'Frontiers in epigenetic chemical biology'.

H3K27me3 is an epigenetic barrier while KDM6A overexpression improves nuclear reprogramming efficiency

Aberrant epigenetic reprogramming is a major factor of developmental failure of cloned embryos. Histone H3 lysine 27 trimethylation (H3K27me3), a histone mark for transcriptional repression, plays important roles in mammalian embryonic development and induced pluripotent stem cell (iPSC) generation. The global loss of H3K27me3 marks may facilitate iPSC generation in mice and humans. However, the H3K27me3 level and its role in bovine somatic cell nuclear transfer (SCNT) reprogramming remain poorly understood. Here, we show that SCNT embryos exhibit global H3K27me3 hypermethylation from the 2- to 8-cell stage and that its removal by ectopically expressed H3K27me3 lysine demethylase (KDM)6A greatly improves nuclear reprogramming efficiency. In contrast, H3K27me3 reduction by H3K27me3 methylase enhancer of zeste 2 polycomb repressive complex knockdown or donor cell treatment with the enhancer of zeste 2 polycomb repressive complex-selective inhibitor GSK343 suppressed blastocyst formation by SCNT embryos. KDM6A overexpression enhanced the transcription of genes involved in cell adhesion and cellular metabolism and X-linked genes. Furthermore, we identified methyl-CpG-binding domain protein 3-like 2, which was reactivated by KDM6A, as a factor that is required for effective reprogramming in bovines. These results show that H3K27me3 functions as an epigenetic barrier and that KDM6A overexpression improves SCNT efficiency by facilitating transcriptional reprogramming.-Zhou, C., Wang, Y., Zhang, J., Su, J., An, Q., Liu, X., Zhang, M., Wang, Y., Liu, J., Zhang, Y. H3K27me3 is an epigenetic barrier while KDM6A overexpression improves nuclear reprogramming efficiency.

Limitations of current in vitro models for testing the clinical potential of epigenetic inhibitors for treatment of pediatric ependymoma

Background

Epigenetic modifications have been shown to play an important role in the classification and pathogenesis of the pediatric brain tumor ependymoma, suggesting they are a potential therapeutic target.

Results

Agents targeting epigenetic modifications inhibited the growth and induced the death of ependymoma cells with variable efficiency. However, this was often not at clinically achievable doses. Additionally, DNA methylation profiling revealed a lack of similarity to primary ependymomas suggesting alterations were induced during culture. Toxicity to fetal neural stem cells was also seen at similar drug concentrations

Conclusions

Agents targeting epigenetic modifications were able to inhibit the growth and induced the death of ependymoma cells grown in vitro. However, many agents were only active at high doses, outside clinical ranges, and also resulted in toxicity to normal brain cells. The lack of similarity in DNA methylation profiles between cultured cells and primary ependymomas questions the validity of using in vitro cultured cells for pre-clinical analysis of agents targeting epigenetic mechanisms and suggests further investigation using models that are more appropriate should be undertaken before agents are taken forward for clinical testing.

Materials and Methods

The effects of agents targeting epigenetic modifications on the growth and death of a panel of ependymoma cell lines was investigated, as well as toxicity to normal fetal neural stem cells. The ependymoma cell lines were characterized using DNA methylation profiling.

Histone methyl-transferases and demethylases in the autophagy regulatory network: the emerging role of KDM1A/LSD1 demethylase

Macroautophagy/autophagy is a physiological mechanism that is essential for the maintenance of cellular homeostasis and stress adaptation. Defective autophagy is associated with many human diseases, including cancer and neurodegenerative disorders. The emerging implication of epigenetic events in the control of the autophagic process opens new avenues of investigation and offers the opportunity to develop novel therapeutic strategies in diseases associated with dysfunctional autophagy-lysosomal pathways. Accumulating evidence reveals that several methyltransferases and demethylases are essential regulators of autophagy, and recent studies have led to the identification of the lysine demethylase KDM1A/LSD1 as a promising drug target. KDM1A/LSD1 modulates autophagy at multiple levels, participating in the transcriptional control of several downstream effectors. This review summarizes our current understanding of the role of KDM1A/LSD1 in the autophagy regulatory network.

Epigenetics of Mucus Hypersecretion in Chronic Respiratory Diseases

Asthma, chronic obstructive pulmonary disease, and cystic fibrosis are three chronic pulmonary diseases that affect an estimated 420 million individuals across the globe. A key factor contributing to each of these conditions is mucus hypersecretion. Although management of these diseases is vastly studied, researchers have only begun to scratch the surface of the mechanisms contributing to mucus hypersecretion. Epigenetic regulation of mucus hypersecretion, other than microRNA post-translational modification, is even more scarcely researched. Detailed study of epigenetic mechanisms, such as DNA methylation and histone modification, could not only help to better the understanding of these respiratory conditions but also reveal new treatments for them. Because mucus hypersecretion is such a complex event, there are innumerable genes involved in the process, which are beyond the scope of a single review. Therefore, the purpose of this review is to narrow the focus and summarize specific epigenetic research that has been conducted on a few aspects of mucus hypersecretion in asthma, chronic obstructive pulmonary disease, cystic fibrosis, and some cancers. Specifically, this review emphasizes the contribution of DNA methylation and histone modification of particular genes involved in mucus hypersecretion to identify possible targets for the development of future therapies for these conditions. Elucidating the role of epigenetics in these respiratory diseases may provide a breath of fresh air to millions of affected individuals around the world.

The therapeutic properties of resminostat for hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is the most common form of primary liver cancer with increases in new cases being reported annually. Histopathologists have identified hepatic steatosis as a characteristic of a broad range of chronic liver diseases that are associated with the onset and development of HCC. In this context, epigenetic modifications may serve as precancerous factors predisposing normal cells to the initiation of carcinogenesis. This study demonstrated that hepatic tumorigenesis and differentiated adipocytes may modulate both global histone deacetylase (HDAC) expression and specific class I HDAC genes in the tumour microenvironment. The novel class I HDAC inhibitor Resminostat was shown to reduce the proliferation of HCC cells along with its specificity in targeting class I HDACs and oncogenes. The combined effect of Resminostat with several pharmaceutical agents such as Sorafenib, Cisplatin and Doxorubicin was also demonstrated. The inhibition of heat shock protein 90 (HSP90) has been demonstrated as a potential therapeutic option for HCC. In line with this, the specific HSP90 inhibitor 17-(allylamino)-17-demethoxygeldanamycin (17-AAG) was selected and it was found that the combination of Resminostat and 17-AAG may provide a “smart” clinical strategy for HCC patients by targeting cellular communication within the tumour microenvironment. This study provides an insight into the use of Resminostat as an epigenetic based therapeutic for HCC along with other pharmaceutical options, in particular by targeting the cell-to-cell communication that occurs between hepatoma and adipocytes.

miR-101-3p induces autophagy in endometrial carcinoma cells by targeting EZH2

OBJECTIVE

This study aimed to investigate the effect of miR-101-3p on autophagy in endometrial carcinoma (EC) cells and the connection between miR-101-3p and EZH2.

METHODS

The expression levels of miRNAs were analyzed by microarray. The expression level of autophagy related proteins was measured by western blot. The mRNA expression level of beclin-1 was determined by qRT-PCR. Autophagy in EC cells was traced by GFP-LC3 fusion protein and observed by fluorescence microscopy. The number of autophagic vacuoles was determined by transmission electron microscopy (TEM). A luciferase reporter assay was utilized to assess the target relationship between miR-101-3p and EZH2.

RESULTS

The expression level of miR-101-3p in EC tissues was lower than in normal tissues. miR-101-3p upregulated the expression levels of the autophagy-related proteins LC3-II and beclin-1 in EC cells in a time- and dose-dependent manner. Overexpression of miR-101-3p and silencing of EZH2 both promoted autophagy in EC cells. Luciferase reporter assays verified that miR-101-3p inhibited EZH2 expression by binding to its 3'-UTR region.

CONCLUSION

miR-101-3p promoted autophagy in EC cells by downregulating the expression of EZH2, and it induced autophagy in EC cells by suppressing EZH2 expression. Inhibition of miR-101-3p could reduce its autophagy induction effect on EC cells.

Small molecule epigenetic screen identifies novel EZH2 and HDAC inhibitors that target glioblastoma brain tumor-initiating cells

Glioblastoma (GBM) is the most lethal and aggressive adult brain tumor, requiring the development of efficacious therapeutics. Towards this goal, we screened five genetically distinct patient-derived brain-tumor initiating cell lines (BTIC) with a unique collection of small molecule epigenetic modulators from the Structural Genomics Consortium (SGC). We identified multiple hits that inhibited the growth of BTICs in vitro, and further evaluated the therapeutic potential of EZH2 and HDAC inhibitors due to the high relevance of these targets for GBM. We found that the novel SAM-competitive EZH2 inhibitor UNC1999 exhibited low micromolar cytotoxicity in vitro on a diverse collection of BTIC lines, synergized with dexamethasone (DEX) and suppressed tumor growth in vivo in combination with DEX. In addition, a unique brain-penetrant class I HDAC inhibitor exhibited cytotoxicity in vitro on a panel of BTIC lines and extended survival in combination with TMZ in an orthotopic BTIC model in vivo. Finally, a combination of EZH2 and HDAC inhibitors demonstrated synergy in vitro by augmenting apoptosis and increasing DNA damage. Our findings identify key epigenetic modulators in GBM that regulate BTIC growth and survival and highlight promising combination therapies.

The polycomb group protein EZH2 induces epithelial-mesenchymal transition and pluripotent phenotype of gastric cancer cells by binding to PTEN promoter

BACKGROUND

The influences of oncogenic Ezh2 on the progression and prognosis of gastric cancer (GC) and the underlying mechanisms are still poorly understood. Here, we aimed at investigating clinicopathological significance of Ezh2 in GC and the mechanisms underlying its function in GC development.

METHODS

The expression level of Ezh2 was determined by qRT-PCR, immunoblot, and immunohistochemistry analysis in 156 pairs of GC tissues and adjacent normal gastric mucosa tissues. The biological functions of Ezh2 were assessed by in vitro and in vivo functional experiments. Chromatin immunoprecipitation (ChIP), luciferase, and Western blotting analyses were utilized to identify the relationship between Ezh2 and the PTEN/Akt signaling.

RESULTS

The expression of Ezh2 was higher in gastric cancer tissues in comparison with para-nontumorous epithelium. High expression of Ezh2 was associated with more aggressive biological behavior and poor prognosis in GC. In vitro studies indicated that Ezh2 promoted GC cells' proliferation and clonogenicity. Besides, Ezh2 led to the acquisition of epithelial-mesenchymal transition (EMT) phenotype of GC cells and enhanced GC cell migration and invasion capacity. In particular, Ezh2 strengthened sphere-forming capacity of GC cells, indicating its role in the enrichment of GC stem cells. Furthermore, we found that PTEN/Akt signaling contributed to the effects of Ezh2 on cancer stem cells (CSC) and EMT phenotype in GC cells, and blocking PTEN signaling significantly rescued the effects of Ezh2.

CONCLUSIONS

Taken together, Ezh2 has a central role in regulating diverse aspects of the pathogenesis of GC in part by involving PTEN/Akt signaling, indicating that it could be an independent prognostic factor and potential therapeutic target.

Autophagy and Hallmarks of Cancer

Autophagy is a catabolic program that is responsible for the degradation of dysfunctional or unnecessary proteins and organelles to maintain cellular homeostasis. Mechanistically, it involves the formation of double-membrane autophagosomes that sequester cytoplasmic material and deliver it to lysosomes for degradation. Eventually, the material is recycled back to the cytoplasm. Abnormalities of autophagy often lead to human diseases, such as neurodegeneration and cancer. In the case of cancer, increasing evidence has revealed the paradoxical roles of autophagy in both tumor inhibition and tumor promotion. Here, we summarize the context-dependent role of autophagy and its complicated molecular mechanisms in the hallmarks of cancer. Moreover, we discuss how therapeutics targeting autophagy can counter malignant transformation and tumor progression. Overall, the findings of studies discussed here shed new light on exploiting the complicated mechanisms of the autophagic machinery and relevant small-molecule modulators as potential antitumor agents to improve therapeutic outcomes.

(-)-Epigallocatechin-3-gallate and EZH2 inhibitor GSK343 have similar inhibitory effects and mechanisms of action on colorectal cancer cells

Epigallocatechin-3-gallate (EGCG) is a type of catechin. It exhibits excellent antioxidant effects and anti-tumour activities for cancer chemoprevention. The mechanism of anti-tumour effects of EGCG on different cancers has been studied for the past few decades, but remains controversial. To investigate the potential role that EGCG may play in the epigenetic regulation of colorectal cancer (CRC) cell line, we integrated bioinformatics analysis with experimental validation. We found that levels of the enhancer of zeste homologue 2 (EZH2) were significantly higher in CRC tissues compared to normal adjacent tissues, based on the Genomic Data Commons (GDC) data portal. Different human CRC cell lines exhibited differing expression of levels of the EZH2 protein. In RKO cells, EGCG and the EZH2 inhibitor GSK343 exhibited similar inhibitory efficacy on the proliferation, invasion and migration abilities of the cells, and suppressed protein expression of trimethylated lysine 27 on histone H3 (H3K27me3), which may be caused by the loss of the enzymatic function of EZH2. EGCG and GSK343 were found to have a synergistic effect on the growth of RKO cells in lower concentrations. EZH2-correlated genes were enriched in the cell cycle pathway, the top-ranking up-regulated pathway in tumour tissues, based on pathway analyses using the Kyoto Encyclopedia of Genes and Genomes (KEGG) and Gene Set Enrichment Analysis (GSEA). In accord with this, we confirmed that EGCG and GSK343 could both significantly arrest the G0/G1 phase in RKO cell cycle, suggesting EGCG and EZH2 inhibitor share a common mechanism of action in RKO cells.

The EZH2 inhibitor GSK343 suppresses cancer stem-like phenotypes and reverses mesenchymal transition in glioma cells

Enhancer of zeste homolog 2 (EZH2) is the catalytic unit of polycomb repressive complex 2 (PRC2) which epigenetically silences many genes involved in tumor-suppressive mechanisms via the trimethylation of lysine 27 of histone H3 (H3K27me3). We recently found that overexpression of EZH2 was associated with poor outcome of glioblastoma (GBM). In this study, we examined the antitumor effects of the EZH2 inhibitor GSK343 on glioma cells in vitro and in vivo. The proliferation and cell cycle of glioma cells was measured. Wound healing assay and transwell invasion assay were performed to evaluate the capacity of migration and invasion of glioma cells. Western blot, qPCR, immunoprecipitation and fluorescent staining were used to test the levels of EZH2 and associated proteins. Spheroid formation assay and clonogenic assays were conducted to assess the stemness of glioma stem cells. Finally, the effect of GSK343 was measured through a nude mice model with intracranially xenotransplanted glioma. We found that GSK343 reduced proliferation, attenuated cell motility and reversed epithelial-mesenchymal transition in U87 and LN229 glioma cells. GSK343 also suppressed the stemness of cell lines and patient derived glioma stem cells. Further, GSK343 inhibited histone H3K27 methylation and upregulated the expression of EZH2 target genes thereby regulating the levels of markers involved in epithelial-mesenchymal transition and stemness. Taken together, our results indicate that GSK343 could be a potential drug against glioblastoma.

Polycomb Repressor Complex 2 in Genomic Instability and Cancer

Polycomb repressor complexes PRC1 and PRC2 regulate chromatin compaction and gene expression, and are widely recognized for their fundamental contributions to developmental processes. Herein, we summarize the existing evidence and molecular mechanisms linking PRC-mediated epigenetic aberrations to genomic instability and malignancy, with a particular focus on the role of deregulated PRC2 in tumor suppressor gene expression, the DNA damage response, and the fidelity of DNA replication. We also discuss some of the recent advances in the development of pharmacological and dietary interventions affecting PRC2, which point to promising applications for the prevention and management of human malignancies.

Downregulation of Enhancer of Zeste Homolog 2 (EZH2) is essential for the Induction of Autophagy and Apoptosis in Colorectal Cancer Cells

Increasing evidence indicates that elevated expression of enhancer of zeste homolog 2 gene (EZH2) in many human malignant tumors acts a significant role in the oncogenic process. However, the underlying molecular mechanism is still unclarified. It is evident that apoptosis and autophagy of tumor cells is crucial for the tumorigenesis and progression of cancer, however, the exact role of EZH2 plays in apoptosis and autophagy has not been fully elucidated in colorectal cancer (CRC). Our previous study found that the expression level of EZH2 was higher in CRC tumor tissues than in the paired normal tissues using immunohistochemical analysis. We also recently found that the autophagy-related gene-related protein Ambra1 plays an important role in the autophagy pathway in CRC cells. In this study, mRNA and protein expression of EZH2 in four CRC cell lines were tested at first and RKO and HCT116 cells showed the highest levels among them. Here we transfected with EZH2-shRNA, or added DZNep (an EZH2 inhibitor) to RKO and HCT116 cells in order to detect the effect of EZH2 on autophagy via determining the change of the protein expression of LC3 and Ambra1. The outcome indicated an obvious decrease of autophagy level in cells transfected with EZH2-shRNA or DZNep. We also found the apoptotic rate of cells was elevated significantly after downregulation of EZH2. In addition, compared to control group, CRC cells transfected with EZH2-shRNA or added DZNep revealed a significantly increased G1 cell cycle rate and an obvious decrease in the G2 cell cycle rate. Further analysis showed that knockdown of EZH2 induced cell-cycle arrest in CRC cells. Meanwhile, downregulation of EZH2 in CRC cells induces autophagy and apoptosis. Taken together, our results suggest that EZH2 plays a critical role in autophagy and apoptosis in the progression of CRC, which potentially facilitates the development of an ideal strategy for combating colorectal cancer.

EZH2 inhibitors transcriptionally upregulate cytotoxic autophagy and cytoprotective unfolded protein response in human colorectal cancer cells

Enhancer of zeste homolog 2 (EZH2) has been emerged as novel anticancer target. Various EZH2 small-molecule inhibitors have been developed in recent years. A major class of EZH2 inhibitors are S-adenosyl-L-methionine (SAM)-competitive inhibitors, such as EPZ005687, EI1, GSK126, UNC1999 and GSK343. Autophagy, a physiological process of self-digestion, is involved in the turnover of proteins or intracellular organelles. It can serve as cytoprotective or cytotoxic function in cancer. Our previous study has found that UNC1999 and GSK343 are potent autophagy inducers. In this study, the underlying molecular mechanisms were further investigated. Our results showed that UNC1999 and GSK343 transcriptionally upregulated autophagy of human colorectal cancer (CRC) cells through inducing LC3B gene expression. Besides, UNC1999/GSK343-induced autophagy was partially dependent on ATG7 but independent to EZH2 inhibition. Microarray and PCR array analyses identified that UNC1999 and GSK343 also induced endoplasmic reticulum (ER) stress and unfolded protein response (UPR). UNC1999/GSK343-induced ER stress/UPR contributed to the survival of cancer cells, which was opposite to UNC1999/GSK343-induced autophagy that promoted cell death.

Enhancer of Zeste Homolog 2 and Histone Deacetylase 9c Regulate Age-Dependent Mesenchymal Stem Cell Differentiation into Osteoblasts and Adipocytes

Mesenchymal stem cells (MSCs) are multipotent precursors that can undergo multilineage differentiation, including osteogenesis and adipogenesis, which are two mutually exclusive events. Previously, we demonstrated that enhancer of zeste homolog 2 (EZH2), the catalytic component of the Polycomb-repressive complex 2, mediates epigenetic silencing of histone deacetylase 9c (HDAC9c) in adipocytes but not in osteoblasts and that HDAC9c accelerates osteogenesis while attenuating adipogenesis of MSCs through inactivation of peroxisome proliferator-activated receptor gamma 2 activity. Importantly, disrupting the balance between adipogenesis and osteogenesis can lead to age-associated bone loss (osteoporosis) and obesity. Here, we investigated the relationship between age, and osteogenic and adipogenic differentiation potential of MSCs by comparing EZH2 and HDAC9c expression in osteoblasts and adipocytes of both human and mice origins to determine whether the EZH2-HDAC9c axis regulates age-associated osteoporosis and obesity. Our findings indicated that a decline in HDAC9c expression over time was accompanied by increased EZH2 expression and suggested that a therapeutic intervention for age-associated osteoporosis and obesity may be feasible by targeting the EZH2-HDAC9c axis. Stem Cells 2016;34:2183-2193.

Fuse-binding protein 1 is a target of the EZH2 inhibitor GSK343, in osteosarcoma cells

Osteosarcoma is the primary cancer of leaf tissue and is regarded as a differentiation disease caused by genetic and epigenetic changes which interrupt the osteoblast differentiation from mesenchymal stem cells. Because of its high malignancy degree and rapid development, the morbidity and mortality are high. The enhancer of zeste homolog 2 (EZH2) is a catalytic subunit of polycomb repressive complex 2 (PRC2) and has been demonstrated to be involved in a variety of biological processes, such as cell proliferation and program cell death. EZH2 impairs gene expression by catalyzing the tri-methylation of histone H3 lysine 27 (H3K27me3) which controls gene transcription epigenetically. It is reported that EZH2 expression is higher in osteosarcoma than in osteoblastoma and the highest expression of EZH2 is found in osteosarcoma with metastasis. In the past few years, several potent inhibitors of EZH2 have been discovered, and GSK343 is one of them. In this study, we found that GSK343 inhibited osteosarcoma cell viability, restrained cell cycle transition and promoted programmed cell death. GSK343 not only inhibited the expression of EZH2 and its target, c-Myc and H3K27me3, but it also inhibited fuse binding protein 1 (FBP1) expression, another c-Myc regulator. Furthermore, we found that FBP1 physically interacts with EZH2. Based on these results, we believe that GSK343 is a potential molecule for osteosarcoma clinical treatment. Other than the inhibition on EZH2-c-Myc signal pathway, we postulate that the inhibition on FBP1-c-Myc signal pathway is another potential underlying mechanism with which GSK343 inhibits osteosarcoma cell viability.

Selective inhibition of EZH2 by ZLD1039 blocks H3K27 methylation and leads to potent anti-tumor activity in breast cancer

Enhancer of zeste homolog 2 (EZH2) is a candidate oncogenic driver due to its prevalent overexpression and aberrant repression of tumor suppressor genes in diverse cancers. Therefore, blocking EZH2 enzyme activity may present a valid therapeutic strategy for the treatment of cancers with EZH2 overexpression including breast cancers. Here, we described ZLD1039 a potent, highly selective, and orally bioavailable small molecule inhibitor of EZH2, which inhibited breast tumor growth and metastasis. ZLD1039 considerably inhibited EZH2 methyltransferase activity with nanomolar potency, decreased global histone-3 lysine-27 (H3K27) methylation, and reactivated silenced tumor suppressors connected to increased survival of patients with breast cancer. Comparable to conditional silencing of EZH2, its inhibition by ZLD1039 decreased cell proliferation, cell cycle arrest, and induced apoptosis. Comparably, treatment of xenograft-bearing mice with ZLD1039 led to tumor growth regression and metastasis inhibition. These data confirmed the dependency of breast cancer progression on EZH2 activity and the usefulness of ZLD1039 as a promising treatment for breast cancer.

Functional Role of G9a Histone Methyltransferase in Cancer

Post-translational modifications of DNA and histones are epigenetic mechanisms, which affect the chromatin structure, ultimately leading to gene expression changes. A number of different epigenetic enzymes are actively involved in the addition or the removal of various covalent modifications, which include acetylation, methylation, phosphorylation, ubiquitination, and sumoylation. Deregulation of these processes is a hallmark of cancer. For instance, G9a, a histone methyltransferase responsible for histone H3 lysine 9 (H3K9) mono- and dimethylation, has been observed to be upregulated in different types of cancer and its overexpression has been associated with poor prognosis. Key roles played by these enzymes in various diseases have led to the hypothesis that these molecules represent valuable targets for future therapies. Several small molecule inhibitors have been developed to specifically block the epigenetic activity of these enzymes, representing promising therapeutic tools in the treatment of human malignancies, such as cancer. In this review, the role of one of these epigenetic enzymes, G9a, is discussed, focusing on its functional role in regulating gene expression as well as its implications in cancer initiation and progression. We also discuss important findings from recent studies using epigenetic inhibitors in cell systems in vitro as well as experimental tumor growth and metastasis assays in vivo.

Polycomb Group (PcG) Proteins and Human Cancers: Multifaceted Functions and Therapeutic Implications

Polycomb group (PcG) proteins are transcriptional repressors that regulate several crucial developmental and physiological processes in the cell. More recently, they have been found to play important roles in human carcinogenesis and cancer development and progression. The deregulation and dysfunction of PcG proteins often lead to blocking or inappropriate activation of developmental pathways, enhancing cellular proliferation, inhibiting apoptosis, and increasing the cancer stem cell population. Genetic and molecular investigations of PcG proteins have long been focused on their PcG functions. However, PcG proteins have recently been shown to exert non-classical-Pc-functions, contributing to the regulation of diverse cellular functions. We and others have demonstrated that PcG proteins regulate the expression and function of several oncogenes and tumor suppressor genes in a PcG-independent manner, and PcG proteins are associated with the survival of patients with cancer. In this review, we summarize the recent advances in the research on PcG proteins, including both the Pc-repressive and non-classical-Pc-functions. We specifically focus on the mechanisms by which PcG proteins play roles in cancer initiation, development, and progression. Finally, we discuss the potential value of PcG proteins as molecular biomarkers for the diagnosis and prognosis of cancer, and as molecular targets for cancer therapy.