Downregulation of Ezh2 expression by RNA interference induces cell cycle arrest in the G0/G1 phase and apoptosis in U87 human glioma cells

EZH2: The roles in targeted therapy and mechanisms of resistance in breast cancer

Drug resistance presents a formidable challenge in the realm of breast cancer therapy. Accumulating evidence suggests that enhancer of zeste homolog 2 (EZH2), a component of the polycomb repressive complex 2 (PRC2), may serve as a key regulator in controlling drug resistance. EZH2 overexpression has been observed in breast cancer and many other malignancies, showing a strong correlation with poor outcomes. This review aims to summarize the mechanisms by which EZH2 regulates drug resistance, with a specific focus on breast cancer, in order to provide a comprehensive understanding of the underlying molecular processes. Additionally, we will discuss the current strategies and outcomes of targeting EZH2 using both single agents and combination therapies, with the goal of offering improved guidance for the clinical treatment of breast cancer patients who have developed drug resistance.

EZH2-regulated PARP-1 Expression is a Likely Mechanism for the Chemoresistance of Gliomas to Temozolomide

BACKGROUND

Chemoresistance in gliomas accounts for the major cause of tumor progress and recurrence during comprehensive treatment with alkylating agents including temozolomide (TMZ). The oncogenic role of Enhancer of zeste homolog 2 (EZH2) has been identified in many solid malignancies including gliomas, though the accurate effect of EZH2 on chemotherapy resistance of gliomas has been elusive.

OBJECTIVE

To elucidate the role of EHZ2 on TMZ resistance of gliomas and the molecular mechanisms.

METHODS

Immunohistochemistry (IHC) and Reverse transcription-quantitative (RT-q) PCR, and western blot assay were performed for expressional analysis. Cell Counting Kit-8 (CCK-8) assay was applied to determine the TMZ sensitivity. EZH2-silencing lentivirus was generated for mechanic study.

RESULTS

EZH2 was overexpressed in gliomas both at the transcriptional and protein levels. EZH2 level in glioma cell lines was positively correlated with resistance to TMZ, represented by the 50% inhibition rate (IC50). Moreover, there was increased TMZ sensitivity in EZH2-inhibited glioma cells than in the control cells. Furthermore, we determined that PARP1 was a common molecule among the downregulated DNA repair proteins in both U251 and U87 glioma cell lines after EZH2 inhibition. Specifically, we observed a spontaneous increase of PARP1 expression with TMZ treatment and interestingly, the increase of PARP1 could be also reduced by EZH2 inhibition in the glioma cells. Finally, combined treatment with lentivirus-induced EZH2 inhibition and a PARP1 inhibitor dramatically enhanced TMZ cytotoxicity compared with either one alone.

CONCLUSION

EZH2-PARP-1 signaling axis is possibly responsible for the chemoresistance of gliomas to TMZ. Simultaneously inhibiting these two genes may improve the outcome of TMZ chemotherapy.

GSK343, an Inhibitor of Enhancer of Zeste Homolog 2, Reduces Glioblastoma Progression through Inflammatory Process Modulation: Focus on Canonical and Non-Canonical NF-κB/IκBα Pathways

Glioblastoma (GB) is a tumor of the central nervous system characterized by high proliferation and invasiveness. The standard treatment for GB includes radiotherapy and chemotherapy; however, new therapies are needed. Particular attention was given to the role of histone methyltransferase enhancer of zeste-homolog-2 (EZH2) in GB. Recently, several EZH2-inhibitors have been developed, particularly GSK343 is well-known to regulate apoptosis and autophagy processes; however, its abilities to modulate canonical/non-canonical NF-κB/IκBα pathways or an immune response in GB have not yet been investigated. Therefore, this study investigated for the first time the effect of GSK343 on canonical/non-canonical NF-κB/IκBα pathways and the immune response, by an in vitro, in vivo and ex vivo model of GB. In vitro results demonstrated that GSK343 treatments 1, 10 and 25 μM significantly reduced GB cell viability, showing the modulation of canonical/non-canonical NF-κB/IκBα pathway activation. In vivo GSK343 reduced subcutaneous tumor mass, regulating canonical/non-canonical NF-κB/IκBα pathway activation and the levels of reactive oxygen species (ROS), malondialdehyde (MDA), and superoxide dismutase (SOD). Ex vivo results confirmed the anti-proliferative effect of GSK343 and also demonstrated its ability to regulate immune response through CXCL9, CXCL10 and CXCL11 expression in GB. Thus, GSK343 could represent a therapeutic strategy to counteract GB progression, thanks to its ability to modulate canonical/non-canonical NF-κB/IκBα pathways and immune response.

The Pivotal Immunoregulatory Functions of Microglia and Macrophages in Glioma Pathogenesis and Therapy

Gliomas are mixed solid tumors composed of both neoplastic and nonneoplastic cells. In glioma microenvironment, the most common nonneoplastic and infiltrating cells are macrophages and microglia. Microglia are the exact phagocytes of the central nervous system, whereas macrophages are myeloid immune cells that are depicted with ardent phagocytosis. Microglia are heterogeneously located in almost all nonoverlapping sections of the brain as well as the spinal cord, while macrophages are derived from circulating monocytes. Microglia and macrophages utilize a variety of receptors for the detection of molecules, particles, and cells that they engulf. Both microglia and peripheral macrophages interact directly with vessels both in the periphery of and within the tumor. In glioma milieu, normal human astrocytes, glioma cells, and microglia all exhibited the ability of phagocytosing glioma cells and precisely apoptotic tumor cells. Also, microglia and macrophages are robustly triggered by the glioma via the expression of chemoattractants such as monocyte chemoattractant protein, stromal-derived factor-1, and macrophage-colony stimulating factor. Glioma-associated microglia and/or macrophages positively correlated with glioma invasiveness, immunosuppression, and patients' poor outcome, making these cells a suitable target for immunotherapeutic schemes.

EZH2 as a new therapeutic target in brain tumors: Molecular landscape, therapeutic targeting and future prospects

Brain tumors are responsible for high mortality and morbidity worldwide. The brain tumor treatment depends on identification of molecular pathways involved in progression and malignancy. Enhancer of zeste homolog 2 (EZH2) has obtained much attention in recent years in field of cancer therapy due to its aberrant expression and capacity in modulating expression of genes by binding to their promoter and affecting methylation status. The present review focuses on EZH2 signaling in brain tumors including glioma, glioblastoma, astrocytoma, ependymomas, medulloblastoma and brain rhabdoid tumors. EZH2 signaling mainly participates in increasing proliferation and invasion of cancer cells. However, in medulloblastoma, EZH2 demonstrates tumor-suppressor activity. Furthermore, EZH2 can regulate response of brain tumors to chemotherapy and radiotherapy. Various molecular pathways can function as upstream mediators of EZH2 in brain tumors including lncRNAs and miRNAs. Owing to its enzymatic activity, EZH2 can bind to promoter of target genes to induce methylation and affects their expression. EZH2 can be considered as an independent prognostic factor in brain tumors that its upregulation provides undesirable prognosis. Both anti-tumor agents and gene therapies such as siRNA have been developed for targeting EZH2 in cancer therapy.

Mitochondria and Their Relationship with Common Genetic Abnormalities in Hematologic Malignancies

Hematologic malignancies are known to be associated with numerous cytogenetic and molecular genetic changes. In addition to morphology, immunophenotype, cytochemistry and clinical characteristics, these genetic alterations are typically required to diagnose myeloid, lymphoid, and plasma cell neoplasms. According to the current World Health Organization (WHO) Classification of Tumors of Hematopoietic and Lymphoid Tissues, numerous genetic changes are highlighted, often defining a distinct subtype of a disease, or providing prognostic information. This review highlights how these molecular changes can alter mitochondrial bioenergetics, cell death pathways, mitochondrial dynamics and potentially be related to mitochondrial genetic changes. A better understanding of these processes emphasizes potential novel therapies.

The Pivotal Immunomodulatory and Anti-Inflammatory Effect of Histone-Lysine N-Methyltransferase in the Glioma Microenvironment: Its Biomarker and Therapy Potentials

Enhancer of zeste homolog 2 (EZH2) is a histone-lysine N-methyltransferase that encrypts a member of the Polycomb group (PcG) family. EZH2 forms a repressive chromatin structure which eventually participates in regulating the development as well as lineage propagation of stem cells and glioma progression. Posttranslational modifications are distinct approaches for the adjusted modification of EZH2 in the development of cancer. The amino acid succession of EZH2 protein makes it appropriate for covalent modifications, like phosphorylation, acetylation, O-GlcNAcylation, methylation, ubiquitination, and sumoylation. The glioma microenvironment is a dynamic component that comprises, besides glioma cells and glioma stem cells, a complex network that comprises diverse cell types like endothelial cells, astrocytes, and microglia as well as stromal components, soluble factors, and the extracellular membrane. EZH2 is well recognized as an essential modulator of cell invasion as well as metastasis in glioma. EZH2 oversecretion was implicated in the malfunction of several fundamental signaling pathways like Wnt/β-catenin signaling, Ras and NF-κB signaling, PI3K/AKT signaling, β-adrenergic receptor signaling, and bone morphogenetic protein as well as NOTCH signaling pathways. EZH2 was more secreted in glioblastoma multiforme than in low-grade gliomas as well as extremely secreted in U251 and U87 human glioma cells. Thus, the blockade of EZH2 expression in glioma could be of therapeutic value for patients with glioma. The suppression of EZH2 gene secretion was capable of reversing temozolomide resistance in patients with glioma. EZH2 is a promising therapeutic as well as prognostic biomarker for the treatment of glioma.

EZH2-Inhibited MicroRNA-454-3p Promotes M2 Macrophage Polarization in Glioma

Glioma is a primary intracranial tumor with high incidence and mortality. The oncogenic role of EZH2 has been reported in glioma. EZH2 inhibited microRNA-454-3p (miR-454-3p) by binding to its promoter in chondrosarcoma cells. Therefore, our study aimed to identify whether EZH2 regulated M2 macrophage polarization in glioma via miR-454-3p. Clinical samples of different grades of glioma and glioma cells were collected and immunohistochemistry and RT-qPCR demonstrated that EZH2 was highly expressed in glioma tissues. Expression of EZH2 was positively correlated with the degree of M2 macrophage polarization in glioma tissues. EZH2 was silenced by lentivirus in glioma cells, which were subsequently co-cultured with macrophages to evaluate its effect on macrophage polarization. miR-454-3p, a down-regulated miR in glioma, was found to be increased after silencing of EZH2. Furthermore, MethPrimer analysis showed that EZH2 silencing inhibited the DNA methylation level of miR-454-3p. Additionally, MS-PCR, dual-luciferase reporter, RIP and RNA pull down assays revealed that miR-454-3p promoted PTEN expression by inhibiting m⁶A modification through binding to the enzyme YTHDF2. Either inhibition of miR-454-3p or PTEN resulted in promotion of M2 macrophage polarization. Collectively, histone methyltransferase EZH2 inhibited miR-454-3p through methylation modification and promoted m⁶A modification of PTEN to induce glioma M2 macrophage polarization.

EZH2 is essential for spindle assembly regulation and chromosomal integrity during porcine oocyte meiotic maturation†

Enhancer of zeste homolog 2 (EZH2) has been extensively investigated to participate in diverse biological processes, including carcinogenesis, the cell cycle, X-chromosome inactivation, and early embryonic development. However, the functions of this protein during mammalian oocyte meiotic maturation remain largely unexplored. Here, combined with RNA-Seq, we provided evidence that EZH2 is essential for oocyte meiotic maturation in pigs. First, EZH2 protein expression increased with oocyte progression from GV to MII stage. Second, the siRNA-mediated depletion of EZH2 led to accelerated GVBD and early occurrence of the first polar body extrusion. Third, EZH2 knockdown resulted in defective spindle assembly, abnormal SAC activity, and unstable K-MT attachment, which was concomitant with the increased rate of aneuploidy. Finally, EZH2 silencing exacerbated oxidative stress by increasing ROS levels and disrupting the distribution of active mitochondria in porcine oocytes. Furthermore, parthenogenetic embryonic development was impaired following the depletion of EZH2 at GV stage. Taken together, we concluded that EZH2 is necessary for porcine oocyte meiotic progression through regulating spindle organization, maintaining chromosomal integrity, and mitochondrial function.

Targeting post-translational histone modifying enzymes in glioblastoma

Glioblastoma (GBM) is the most common primary brain tumor in adults, and the most lethal form of glioma, characterized by variable histopathology, aggressiveness and poor clinical outcome and prognosis. GBMs constitute a challenge for oncologists because of their molecular heterogeneity, extensive invasion, and tendency to relapse. Glioma cells demonstrate a variety of deregulated genomic pathways and extensive interplay with epigenetic alterations. Epigenetic modifications have emerged as essential players in GBM research, with biomarker potential for tumor classification and prognosis and for drug targeting. Histone posttranslational modifications (PTMs) are crucial regulators of chromatin architecture and gene expression, playing a pivotal role in malignant transformation, tumor development and progression. Alteration in the expression of genes coding for lysine and arginine methyltransferases (G9a, SUV39H1 and SETDB1) and acetyltransferases and deacetylases (KAT6A, SIRT2, SIRT7, HDAC4, 6, 9) contribute to GBM pathogenesis. In addition, proteins of the sumoylation pathway are upregulated in GBM cell lines, including E1 (SAE1), E2 (Ubc9) components, and a SUMO-specific protease (SENP1). Preclinical and clinical studies are currently in progress targeting epigenetic enzymes in gliomas, including a new generation of histone deacetylase (HDAC), protein arginine methyltransferase (PRMT) and bromodomain (BRD) inhibitors. Herein, we provide an update on recent advances in glioma epigenetic research, focusing on the role of histone modifications and the use of epigenetic therapy as a valid treatment option for glioblastoma.

Antihistamine Drug Ebastine Inhibits Cancer Growth by Targeting Polycomb Group Protein EZH2

Enhancer of zester homolog 2 (EZH2), a histone lysine methyltransferase and the catalytic component of polycomb repressive complex 2, has been extensively investigated as a chromatin regulator and a transcriptional suppressor by methylating H3 at lysine 27 (H3K27). EZH2 is upregulated or mutated in most cancers, and its expression levels are negatively associated with clinical outcomes. However, the current developed small-molecule inhibitors targeting EZH2 enzymatic activities could not inhibit the growth and progression of solid tumors. Here, we discovered an antihistamine drug, ebastine, as a novel EZH2 inhibitor by targeting EZH2 transcription and subsequently downregulating EZH2 protein level and H3K27 trimethylation in multiple cancer cell lines at concentrations below 10 μmol/L. The inhibition of EZH2 by ebastine further impaired the progression, migration, and invasiveness of these cancer cells. Overexpression of Ezh2 wild-type and its mutant, H689A (lacking methyltransferase activity), rescued the neoplastic properties of these cancer cells after ebastine treatment, suggesting that EZH2 targeted by ebastine is independent of its enzymatic function. Next-generation RNA-sequencing analysis also revealed that C4-2 cells treated with 8 μmol/L ebastine showed a gene profiling pattern similar to EZH2-knockdown C4-2 cells, which was distinctively different from cells treated with GSK126, an EZH2 enzyme inhibitor. In addition, ebastine treatment effectively reduced tumor growth and progression, and enhanced progression-free survival in triple-negative breast cancer and drug-resistant castration-resistant prostate cancer patient-derived xenograft mice. Our data demonstrated that ebastine is a novel, safe, and potent anticancer agent for patients with advanced cancer by targeting the oncoprotein EZH2.

Critical role of HOX transcript antisense intergenic RNA (HOTAIR) in gliomas

Despite extensive research, gliomas are associated with high morbidity and mortality, mainly attributed to the rapid growth rate, excessive invasiveness, and molecular heterogeneity, as well as regenerative potential of cancer stem cells. Therefore, elucidation of the underlying molecular mechanisms and the identification of potential molecular diagnostic and prognostic biomarkers are of paramount importance. HOX transcript antisense intergenic RNA (HOTAIR) is a well-studied long noncoding RNA, playing an emerging role in tumorigenesis of several human cancers. A growing amount of preclinical and clinical evidence highlights the pro-oncogenic role of HOTAIR in gliomas, mainly attributed to the enhancement of proliferation and migration, as well as inhibition of apoptosis. In vitro and in vivo studies demonstrate that HOTAIR modulates the activity of specific transcription factors, such as MXI1, E2F1, ATF5, and ASCL1, and regulates the expression of cell cycle-associated genes along with related signaling pathways, like the Wnt/β-catenin axis. Moreover, it can interact with specific miRNAs, including miR-326, miR-141, miR-148b-3p, miR-15b, and miR-126-5p. Of importance, HOTAIR has been demonstrated to enhance angiogenesis and affect the permeability of the blood-tumor barrier, thus modulating the efficacy of chemotherapeutic agents. Herein, we provide evidence on the functional role of HOTAIR in gliomas and discuss the benefits of its targeting as a novel approach toward glioma treatment.

Ribophorin II is upregulated in myelodysplastic syndromes and prevents apoptosis and cell cycle progression

IMPACT STATEMENT

This study explored the role of ribophorin II (RPN2) in myelodysplastic syndromes (MDSs) cell proliferation and growth and revealed that RPN2 knockdown suppressed OCI-AML3 cell growth and proliferation and triggered cell cycle arrest and elicited apoptosis in OCI-AML3 cells. In addition, it shed light on the etiology of RPN2's role in MDS cell proliferation that RPN2 can negatively impact enhancer of zeste homolog-2 (EZH2) expression, which in turn is able to modulate the cell cycle location and death in OCI-AML3 cells. Hence, RPN2 expression could be a latent predictor of prognosis in patients with MDS.

Nanocrystallized Oleanolic Acid Better Inhibits Proliferation, Migration and Invasion in Intracranial Glioma via Caspase-3 Pathway

Glioma associates with high malignancy and poor prognosis for traditional treatment. Oleanolic acid (OA) has been confirmed to have an inhibitory effect on different kinds of tumors, while accompanying with low efficiency because of its large molecular mass and low solubility. Nanoliposome is an appropriate drug delivery system that can compensate for the limitations of traditional insoluble drugs, involving improvement of their solubility, stability and lipophilicity. In the present study, we comprised of OA covered with nanoliposomes, named OA^nano, to observe antitumor effects on U87 glioma cells. The results showed that OA^nano raised the solubility and oil-water partition coefficient. OA^nano suppressed proliferation of U87 glioma cells, and also had an anticancer effect on U87 glioma cells, which was found to be higher than that of OA. Moreover, treatment with OA^nano induced apoptosis and degraded migration ability by caspase-3 pathway. In conclusion, our results demonstrated that OA covered with nanoliposomes led to enhanced anticancer effects by suppressing proliferation, migration and invasion abilities. The findings may provide a reliable reference for development of new anti-cancer drugs.

EZH2 deletion promotes spermatogonial differentiation and apoptosis

Spermatogenesis is crucial for male fertility and is therefore tightly controlled by a variety of epigenetic regulators. However, the function of enhancer of zeste homolog 2 (EZH2) in spermatogenesis and the molecular mechanisms underlying its activity remain poorly defined. Here, we demonstrate that deleting EZH2 promoted spermatogonial differentiation and apoptosis. EZH2 is expressed in spermatogonia, spermatocytes and round and elongated spermatids from stage 9 to 11 but not in leptotene and zygotene spermatocytes. Knocking down Ezh2 in vitro using a lentivirus impaired self-renewal in spermatogonial stem cells (SSC_s), and the conditional knockout of Ezh2 in spermatogonial progenitors promoted precocious spermatogonial differentiation. EZH2 functions to balance self-renewal and differentiation in spermatogonia by suppressing NEUROG3 and KIT via a direct interaction that is independent of its histone methyltransferase activity. Moreover, deleting Ezh2 enhanced the activation of CASP3 in spermatids, resulting in reduced spermatozoa production. Collectively, these data demonstrate that EZH2 plays a nonclassical role in the regulation of spermatogonial differentiation and apoptosis in murine spermatogenesis.

Functional and therapeutic significance of EZH2 in urological cancers

The enhancer of zeste homolog 2 (EZH2) is a core subunit of the polycomb repressor complex 2 (PRC2), which is overexpressed in numerous cancers and mutated in several others. Notably, EZH2 acts not only a critical epigenetic repressor through its role in histone methylation, it is also an activator of gene expression, acting through multiple signaling pathways in distinct cancer types. Increasing evidence suggests that EZH2 is an oncogene and is central to initiation, growth and progression of urological cancers. In this review, we highlight the critical role of EZH2 as a master regulator of tumorigenesis in the prostate, bladder and the kidney through epigenetic control of transcription as well as a modulation of various critical signaling pathways. We also discuss the promise and challenges for EZH2 inhibitors as future anticancer therapeutics, some of which are currently in clinical trials.

EZH2 suppression in glioblastoma shifts microglia toward M1 phenotype in tumor microenvironment

BACKGROUND

Glioblastoma multiforme (GBM) induces tumor immunosuppression through interacting with tumor-infiltrating microglia or macrophages (TAMs) with an unclear pathogenesis. Enhancer of zeste homolog 2 (EZH2) is abundant in GBM samples and cell lines and is involved in GBM proliferation, cell cycle, and invasion, whereas its association with innate immune response is not yet reported. Herein, the aim of this study was to investigate the role of EZH2 in GBM immune.

METHODS

Co-culturing models of human/murine GBM cells with PBMC-derived macrophages/primary microglia were employed. EZH2 mRNAs and function were suppressed by siEZH2 and DZNep. Real-time PCR and flow cytometry were used to determine levels of microglia/macrophages markers. The fluorescence-labeled latex beads and flow cytometry were utilized to evaluate phagocytic abilities of microglia. CCK8 assay was performed to assess microglia proliferation.

RESULTS

EZH2 inhibition led to significant reduction of TGFβ1-3 and IL10 and elevation of IL1β and IL6 in human and murine GBM cells. More importantly, EZH2 suppression in GBM cells resulted in significant increase of M1 markers (TNFα and iNOS) and decrease of a pool of M2 markers in murine microglia. The proportion of CD206⁺ cells was decreased in PBMC-derived macrophages as co-incubated with EZH2-inhibited GBM cells. Functional researches showed that phagocytic capacities of microglia were significantly ameliorated after EZH2 inhibition in co-culturing GBM cells and microglia proliferation was declined after addition of TGFβ2 antibodies to co-incubated GBM cells with EZH2 inhibition. Besides, we found that EZH2 suppression in GBM cells enhanced co-culturing microglia engulfment through activation of iNOS.

CONCLUSIONS

Our data demonstrates that EZH2 participates in GBM-induced immune deficient and EZH2 suppression in GBM can remodel microglia immune functions, which is beneficial for understanding GBM pathogenesis and suggests potential targets for therapeutic approaches.

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.

Long Noncoding RNAs Regulate Cell Growth, Proliferation, and Apoptosis

The revolutionary findings in nonprotein-coding part of human genome analysis have revealed a large number of RNA transcripts longer than 200 nucleotides that lack coding protein function, termed long noncoding RNAs (lncRNAs). Recently, accumulating shreds of evidence suggest that lncRNAs are widely distributed in human genome and deeply involved in cellular activities such as cell growth, proliferation, and apoptosis. Generally, lncRNAs regulate cell behaviors by targeting cell cycle-associated cyclins, cyclin-dependent kinases (CDKs), and/or CDK inhibitors. Specifically, lncRNAs serve as scaffolds or guides for chromatin-modifying complexes and act as signals in response to DNA damage. In addition, lncRNAs function as protein decoys and microRNA decoys, as well as interveners in cell division by modulating oncogenes and/or tumor suppressors. In this review, we mainly focus on the current understanding of the molecular mechanisms, how lncRNAs influence cellular processes and cancer progression. Finally, we also prospect the limitations of lncRNAs in cell behaviors and the novel roles of lncRNAs in epigenetic regulations.

Long non-coding RNA HOTAIR promotes glioblastoma cell cycle progression in an EZH2 dependent manner

The long non-coding RNA Hox transcript antisense intergenic RNA (HOTAIR) was recently implicated in breast cancer metastasis and is predictive of poor prognosis in colorectal and pancreatic cancers. We recently discovered that HOTAIR is a cell cycle-related lncRNA in human glioma, and its expression is closely associated with glioma staging and poor prognosis. Although lysine specific demethylase 1 (LSD1) and polycomb repressive complex 2 (PRC2) have been demonstrated to be functional targets of HOTAIR, how HOTAIR regulates glioma cell cycle progression remains largely unknown. In this study, we found that EZH2 (predominant PRC2 complex component) inhibition blocked cell cycle progression in glioma cells, consistent with the effects elicited by HOTAIR siRNA. However, the inhibition of LSD1 did not affect cell cycle progression in glioma cells. These results suggest that HOTAIR might regulate cell cycle progression through EZH2. Our intracranial mice model also revealed delayed tumor growth in HOTAIR siRNA- and EZH2 inhibitor-treated groups. Moreover, in HOTAIR knock-down cell lines, the expression of the PRC2-binding domain of HOTAIR (5′ domain) but not of the LSD1-binding domain of HOTAIR (3′ domain) resulted in accelerated cell cycle progression. In conclusion, HOTAIR promotes cell cycle progression in glioma as a result of the binding of its 5′ domain to the PRC2 complex.

Modulation of EZH2 Expression by MEK-ERK or PI3K-AKT Signaling in Lung Cancer Is Dictated by Different KRAS Oncogene Mutations

EZH2 overexpression promotes cancer by increasing histone methylation to silence tumor suppressor genes, but how EZH2 levels become elevated in cancer is not understood. In this study, we investigated the mechanisms by which EZH2 expression is regulated in non-small cell lung carcinoma cells by oncogenic KRAS. In cells harboring KRAS(G12C) and KRAS(G12D) mutations, EZH2 expression was modulated by MEK-ERK and PI3K/AKT signaling, respectively. Accordingly, MEK-ERK depletion decreased EZH2 expression in cells harboring the KRAS(G12C) mutation, whereas PI3K/AKT depletion decreased EZH2 expression, EZH2 phosphorylation, and STAT3 activity in KRAS(G12D)-mutant cell lines. Combined inhibition of EZH2 and MEK-ERK or PI3K/AKT increased the sensitivity of cells with specific KRAS mutations to MEK-ERK and PI3K/AKT-targeted therapies. Our work defines EZH2 as a downstream effector of KRAS signaling and offers a rationale for combining EZH2 inhibitory strategies with MEK-ERK- or PI3K/AKT-targeted therapies to treat lung cancer patients, as stratified into distinct treatment groups based on specific KRAS mutations.

Functional roles of enhancer of zeste homolog 2 in gliomas

Gliomas are the most common and lethal type of primary malignant brain tumor. Due to the infiltrative nature and high resistance to standard first line treatment with combinations of radiation and chemotherapy, the prognosis of patient is very poor. Recently, accumulated evidence suggests that enhancer of zeste homolog 2 (EZH2) serves as an oncogene and is involved in multiple glioma cell processes, including cell cycle, invasion, glioma stem cell maintenance, drug and radiotherapy resistance and so on. In this review, we will focus on updating current knowledge of EZH2 in gliomas. Moreover, the regulation of EZH2 by microRNAs and long non-coding RNAs and the therapeutic strategies targeting EZH2 for gliomas will also be discussed.

Retinoic acid‑incorporated glycol chitosan nanoparticles inhibit the expression of Ezh2 in U118 and U138 human glioma cells

At present, one of the most life threatening types of adult brain tumor is glioblastoma multiforme (GBM). The molecular mechanism underlying the progression of GBM remains to be fully elucidated. The modern method of clinical treatment has only improved the average survival rates of a newly diagnosed patients with GBM by ~15 months. Therefore, the discovery of novel molecules, which are involved in glioma inhibition is required. In the present study, U118 and U138 human glioma cells were transfected with all-trans retinoic acid (RA)-incorporated glycol chitosan (GC) nanoparticles. An MTT assay was used for the analysis of cell proliferation and flow cytometric analysis and ssDNA detection assays were performed for the determination of induction of cell apoptosis. Cell cycle distribution was analyzed by flow cytometry. Exposure of the U118 and U138 human glioma cells to the RA-incorporated GC nanoparticles for 24 h resulted in a concentration-dependent inhibition of cell proliferation. Among the range of experimental RA concentrations, the minimum effective treatment concentration was 10 µM, with a half maximal inhibitory concentration of 25 µM. The results also demonstrated that RA transfection resulted in the inhibition of cell proliferation, inhibition of the expression of Ezh2, and apoptosis through the mitochondrial signaling pathway by a decrease in membrane potential, the release of cytochrome c, and cell cycle arrest in the G₀/G₁ phase.

Deregulation of histone-modifying enzymes and chromatin structure modifiers contributes to glioma development

The epigenetic landscape is deregulated in cancer due to aberrant activation or inactivation of enzymes maintaining and modifying the epigenome. Histone modifications and global aberrations at the histone level may result in distorted patterns of gene expression, and malfunction of proteins that regulate chromatin modification and remodeling. Recent whole genome studies demonstrated that histones and chaperone proteins harbor mutations that may result in gross alterations of the epigenome leading to genome instability. Glioma development is a multistep process, involving genetic and epigenetic alterations. This review summarizes newly identified mechanisms affecting expression/functions of histone-modifying enzymes and chromatin modifiers in gliomas. We discuss recent approaches to overcome epigenetic alterations with histone-modifying enzyme inhibitors and their prospects for glioma therapy.

MicroRNA-144 suppresses tumorigenesis and tumor progression of astrocytoma by targeting EZH2

Our previous study demonstrated that enhancer of zeste homolog 2 (EZH2) overexpression may be associated with aggressive tumor progression and poor prognosis in human astrocytoma. The aim of this study was to investigate the underlying mechanisms of EZH2 on astrocytoma tumorigenesis. An online program miRWalk (http://www.umm.uni-heidelberg.de/apps/zmf/mirwalk/) was used to predict possible microRNAs (miRNAs) that might target EZH2 messenger RNA (mRNA). Then the functions of the miRNA-EZH2 mRNA axis in astrocytoma cell proliferation, invasion, and migration were also assessed. We further evaluated the clinical value of the miRNA-EZH2 mRNA axis in astrocytomas. As a result, we identified EZH2 as a target gene of miR-144. In addition, forced expression of miR-144 suppressed astrocytoma cell proliferation, invasion, and migration by down-regulating EZH2. Moreover, miR-144 down-regulation and EZH2 mRNA up-regulation were both significantly associated with advanced World Health Organization grades and low Karnofsky performance status score of astrocytoma patients. Importantly, survival analysis identified the combined expression of miR-144 and EZH2 (miR-144/EZH2) as an independent prognostic factor for overall survival in astrocytoma patients. In conclusion, miR-144 may function as a tumor suppressor by regulating EZH2 expression, and miR-144/EZH2 expression may be a highly sensitive marker for the prognosis in astrocytoma patients.

Alterations in enhancer of zeste homolog 2, matrix metalloproteinase-2 and tissue inhibitor of metalloproteinase-2 expression are associated with ex vivo and in vitro bone metastasis in renal cell carcinoma

Renal cell carcinoma (RCC) has a high potential for bone metastasis; however, the molecular mechanisms underlying this metastasis have remained to be elucidated. The present study aimed to explore the expression levels of enhancer of zeste homolog 2 (EZH2), matrix metalloproteinase-2 (MMP2) and tissue inhibitor of metalloproteinase-2 (TIMP2) as determinants of RCC-associated bone metastasis. Their expression was evaluated in a newly generated RCC cell subline that has a high potential for bone metastasis, in tissue specimens from metastasized bone tissues from patients with RCC and in RCC tissues without metastasis. A total of 25 RCC tissue specimens without metastasis and 13 RCC tissue specimens with bone metastasis were acquired for immunohistochemical analysis of EZH2, MMP2 and TIMP2 protein expression. The expression levels of EZH2, MMP2 and TIMP2 mRNA and protein were analyzed in the ACHN and ACHN-BO5 cell lines using western blot and reverse transcription polymerase chain reaction (PCR) analyses. Methylation-specific PCR was also used to analyze TIMP2 promoter methylation. EZH2 and MMP2 proteins were found to be expressed at higher levels in tissues from patients where RCC had metastasized to the bone as compared with those in RCC patients without metastasis, whereas there was no significant difference in the expression of TIMP2 protein between the two tissues. Furthermore, the expression of EZH2 protein was correlated with MMP2 expression, but there was no significant correlation between the expression of EZH2 and TIMP2 proteins. The in vitro results using cell lines confirmed the ex vivo findings, indicating that the expression levels of EZH2 and MMP2 protein and mRNA were higher in ACHN-BO5 cells than those in ACHN cells. By contrast, TIMP2 protein and mRNA expression levels were lower in ACHN-BO5 cells than those in the parental ACHN cells. The TIMP2 promoter was highly methylated in ACHN-BO5 cells compared with that in ACHN cells. Upregulation of EZH2, MMP2 and TIMP2 expression was correlated with metastasis of RCC to bone tissues ex vivo and in vitro. Further studies are required in order to elucidate the mechanism underlying the altered expression of these genes.

PCI-24781 down-regulates EZH2 expression and then promotes glioma apoptosis by suppressing the PIK3K/Akt/mTOR pathway

PCI-24781 is a novel histone deacetylase inhibitor that inhibits tumor proliferation and promotes cell apoptosis. However, it is unclear whether PCI-24781 inhibits Enhancer of Zeste 2 (EZH2) expression in malignant gliomas. In this work, three glioma cell lines were incubated with various concentrations of PCI-24781 (0, 0.25, 0.5, 1, 2.5 and 5 μM) and analyzed for cell proliferation by the MTS [3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium] assay and colony formation, and cell cycle and apoptosis were assessed by flow cytometry. The expression of EZH2 and apoptosis-related proteins was assessed by western blotting. Malignant glioma cells were also transfected with EZH2 siRNA to examine how PCI-24781 suppresses tumor cells. EZH2 was highly expressed in the three glioma cell lines. Incubation with PCI-24781 reduced cell proliferation and increased cell apoptosis by down-regulating EZH2 in a concentration-dependent manner. These effects were simulated by EZH2 siRNA. In addition, PCI-24781 or EZH2 siRNA accelerated cell apoptosis by down-regulating the expression of AKT, mTOR, p70 ribosomal protein S6 kinase (p70s6k), glycogen synthase kinase 3A and B (GSK3a/b) and eukaryotic initiation factor 4E binding protein 1 (4E-BP1). These data suggest that PCI-24781 may be a promising therapeutic agent for treating gliomas by down-regulating EZH2 which promotes cell apoptosis by suppressing the phosphatidylinositol 3-kinase (PI3K)/Akt/mammalian target of the rapamycin (mTOR) pathway.

Epigenetic modification in gliomas: role of the histone methyltransferase EZH2

INTRODUCTION

Gliomas are characterized by increased anaplasia, malignization, proliferation and invasion. They exhibit high resistance to standard treatment with combinations of radiotherapy and chemotherapy. They are currently the most common primary malignancy tumors in the brain that is related to a high mortality rate. Recently, increasing evidence suggests that EZH2 is involved in a number of glioma cell processes, including proliferation, apoptosis, invasion and angiogenesis.

AREAS COVERED

In this review, we emphasize the role of EZH2 in gliomas. We also address that EZH2 interacting with DNA methylation mediates transcriptional repression of specific genes in gliomas, and the regulation of EZH2 by microRNAs in gliomas.

EXPERT OPINION

Although the exact role of EZH2 in gliomas has not been fully elucidated, to understand the role of EZH2 proteins in epigenetic modification will provide valuable insights into the causes of gliomas, and pave the way to the potential future applications of EZH2 in the treatment of gliomas.

Inhibition enhancer of zeste homologue 2 promotes senescence and apoptosis induced by doxorubicin in p53 mutant gastric cancer cells

OBJECTIVES

Enhancer of zeste homologue 2 (EZH2) is crucially involved in epigenetic silencing by acting as a histone methyltransferase. Although EZH2 is overexpressed in many cancers and is involved in malignant cell proliferation and invasion, the role of EZH2 in senescence induced by DNA damage has up to now remained largely unknown. In this study, we sought to explore the outcome of EZH2 depletion along with exposure of doxorubicin (DOX), and related mechanisms, in gastric cancer cells.

MATERIALS AND METHODS

Here, senescence induced by DNA damage was achieved in gastric cancer cells by DOX treatment. EZH2 was downregulated by transfection with siRNA or treated with (-)-epigallocatechin-3-gallate, a targeted inhibitor. Senescence-associated β galactosidase (SA-β-gal) and formation of senescence-associated heterochromatin foci were used to identify cell senescence. To investigate effects of EZH2 depletion on the cell cycle, apoptosis and proliferation, flow cytometry and MTT analysis were employed. Changes in p53-p21 axis activation were detected by Western blotting.

RESULTS

We found that cell proliferative arrest caused by DOX could be promoted by EZH2 depletion. Mechanistically, EZH2 depletion not only worked in coordination with DNA damage during the progression of cell senescence but also promoted apoptosis in p53 mutant cells. However, it had no cooperative relationship with DOX in p53 wild-type cells.

CONCLUSIONS

These data help unravel a crucial role for EZH2 in senescence and apoptosis in gastric cancer cells and that p53 genomic status was associated with different cell responses to EZH2 silencing.

Combined aberrant expression of Bmi1 and EZH2 is predictive of poor prognosis in glioma patients

BACKGROUND AND OBJECTIVES

Bmi1 and EZH2 are involved in tumorigenesis of gliomas. However, clinicopathologic significance of their expression in gliomas is unknown; especially, the prognostic value of combined expression of Bmi1 and EZH2 has not been explored.

METHODS

Bmi1 and EZH2 expression in human gliomas and nonneoplastic brain tissues was measured by immunohistochemistry.

RESULTS

Both Bmi1 and EZH2 expressions in glioma tissues were significantly higher than those in corresponding nonneoplastic brain tissues (both P<0.001). Additionally, the upregulations of Bmi1 and EZH2 proteins were both significantly associated with advanced WHO grades (both P<0.001) and low KPS (P=0.008 and 0.01, respectively). Moreover, the overall survival of patients with high Bmi1 protein expression (P=0.006) or high EZH2 protein expression (P=0.01) was obviously lower than those with low expressions. More interestingly, glioma patients with combined overexpression of Bmi1 and EZH2 proteins had the shortest overall survival (P<0.001). Furthermore, multivariate analysis showed that Bmi1n expression (P=0.02), EZH2 expression (P=0.03), and combined expression of Bmi1 and EZH2 (P=0.008), were all independent prognostic factors for overall survival in glioma patients.

CONCLUSIONS

Our data suggest for the first time that the combination of Bmi1 and EZH2 overexpression may be a highly sensitive marker for the prognosis in glioma patients.

Evaluation of histone 3 lysine 27 trimethylation (H3K27me3) and enhancer of Zest 2 (EZH2) in pediatric glial and glioneuronal tumors shows decreased H3K27me3 in H3F3A K27M mutant glioblastomas

H3F3A mutations are seen in ∼30% of pediatric glioblastoma (GBMs) and involve either the lysine residue at position 27 (K27M) or glycine at position 34 (G34R/V). Sixteen genes encode histone H3, each variant differing in only a few amino acids. Therefore, how mutations in a single H3 gene contribute to carcinogenesis is unknown. H3F3A K27M mutations are predicted to alter methylation of H3K27. H3K27me3 is a repressive mark critical to stem cell maintenance and is mediated by EZH2, a member of the polycomb-group (PcG) family. We evaluated H3K27me3 and EZH2 expression using immunohistochemistry in 76 pediatric brain tumors. H3K27me3 was lowered/absent in tumor cells but preserved in endothelial cells and infiltrating lymphocytes in six out of 20 GBMs. H3K27me3 showed strong immunoreactivity in all other tumor subtypes. Sequencing of GBMs showed H3F3A K27M mutations in all six cases with lowered/absent H3K27me3. EZH2 expression was high in GBMs, but absent/focal in other tumors. However, no significant differences in EZH2 expression were observed between H3F3A K27M mutant and wild type GBMs, suggesting that EZH2 mediated trimethylation of H3K27 is inhibited in GBM harboring K27M mutations. Our results indicate that H3F3A K27M mutant GBMs show decreased H3K27me3 that may be of both diagnostic and biological relevance.