Increased expression of the EZH2 polycomb group gene in BMI-1-positive neoplastic cells during bronchial carcinogenesis

Metabolic reprogramming driven by EZH2 inhibition depends on cell-matrix interactions

EZH2 (Enhancer of Zeste Homolog 2), a subunit of Polycomb Repressive Complex 2 (PRC2), catalyzes the trimethylation of histone H3 at lysine 27 (H3K27me3), which represses expression of genes. It also has PRC2-independent functions, including transcriptional coactivation of oncogenes, and is frequently overexpressed in lung cancers. Clinically, EZH2 inhibition can be achieved with the FDA-approved drug EPZ-6438 (tazemetostat). To realize the full potential of EZH2 blockade, it is critical to understand how cell-cell/cell-matrix interactions present in 3D tissue and cell culture systems influences this blockade in terms of growth-related metabolic functions. Here, we show that EZH2 suppression reduced growth of human lung adenocarcinoma A549 cells in 2D cultures but stimulated growth in 3D cultures. To understand the metabolic underpinnings, we employed [13C6]-glucose stable isotope-resolved metabolomics to determine the effect of EZH2 suppression on metabolic networks in 2D versus 3D A549 cultures. The Krebs cycle, neoribogenesis, γ-aminobutyrate metabolism, and salvage synthesis of purine nucleotides were activated by EZH2 suppression in 3D spheroids but not in 2D cells, consistent with the growth effect. Using simultaneous 2H7-glucose + 13C5,15N2-Gln tracers and EPZ-6438 inhibition of H3 trimethylation, we delineated the effects on the Krebs cycle, γ-aminobutyrate metabolism, gluconeogenesis, and purine salvage to be PRC2-dependent. Furthermore, the growth/metabolic effects differed for mouse Matrigel versus self-produced A549 extracellular matrix. Thus, our findings highlight the importance of the presence and nature of extracellular matrix in studying the function of EZH2 and its inhibitors in cancer cells for modeling the in vivo outcomes.

Polycomb repressor complex: Its function in human cancer and therapeutic target strategy

The Polycomb Repressor Complex (PRC) plays a pivotal role in gene regulation during development and disease, with dysregulation contributing significantly to various human cancers. The intricate interplay between PRC and cellular signaling pathways sheds light on cancer complexity. PRC presents promising therapeutic opportunities, with inhibitors undergoing rigorous evaluation in preclinical and clinical studies. In this review, we emphasize the critical role of PRC complex in gene regulation, particularly PcG proteins mediated chromatin compaction through phase separation. We also highlight the pathological implications of PRC complex dysregulation in various tumors, elucidating underlying mechanisms driving cancer progression. The burgeoning field of therapeutic strategies targeting PRC complexes, notably EZH2 inhibitors, has advanced significantly. However, we explore the need for combination therapies to enhance PRC targeted treatments efficacy, providing a glimpse into the future of cancer therapeutics.

Roles of BMI1 in the Initiation, Progression, and Treatment of Hepatocellular Carcinoma

Liver cancer has high rates of morbidity and mortality, and its treatment is a global health challenge. Hepatocellular carcinoma (HCC) accounts for 90% of all primary liver cancer cases. B-lymphoma Mo-MLV insertion region 1 (BMI1) has been identified as a proto-oncogene, which contributes to the initiation and progression of many malignant tumors. BMI1 expression is upregulated in HCC, and it influences the occurrence and development of HCC by various mechanisms, such as the INK4a/ARF locus, NF-κB signaling pathway, and PTEN/PI3K/AKT signaling pathway. In addition, the expression of BMI1 is related to prognosis and recurrence of HCC. Hence, there is clear evidence that BMI1 is a novel and valid therapeutic target for HCC. Accordingly, the development of therapeutic strategies targeting BMI1 has been a focus of recent research, providing new directions for HCC treatment. This review summarizes the role of BMI1 in the occurrence and treatment of HCC, which will provide a basis for using BMI1 as a potential target for the development of therapeutic strategies for HCC.

Dynamics of methylated cell-free DNA in the urine of non-small cell lung cancer patients

High levels of methylated DNA in urine represent an emerging biomarker for non-small cell lung cancer (NSCLC) detection and are the subject of ongoing research. This study aimed to investigate the circadian variation of urinary cell-free DNA (cfDNA) abundance and methylation levels of cancer-associated genes in NSCLC patients. In this prospective study of 23 metastatic NSCLC patients with active disease, patients were asked to collect six urine samples during the morning, afternoon, and evening of two subsequent days. Urinary cfDNA concentrations and methylation levels of CDO1, SOX17, and TAC1 were measured at each time point. Circadian variation and between- and within-subject variability were assessed using linear mixed models. Variability was estimated using the Intraclass Correlation Coefficient (ICC), representing reproducibility. No clear circadian patterns could be recognized for cfDNA concentrations or methylation levels across the different sampling time points. Significantly lower cfDNA concentrations were found in males (p=0.034). For cfDNA levels, the between- and within-subject variability were comparable, rendering an ICC of 0.49. For the methylation markers, ICCs varied considerably, ranging from 0.14 to 0.74. Test reproducibility could be improved by collecting multiple samples per patient. In conclusion, there is no preferred collection time for NSCLC detection in urine using methylation markers, but single measurements should be interpreted carefully, and serial sampling may increase test performance. This study contributes to the limited understanding of cfDNA dynamics in urine and the continued interest in urine-based liquid biopsies for cancer diagnostics.

Methyltransferases in the Pathogenesis of Keratinocyte Cancers

Recent evidence suggests that the disruption of gene expression by alterations in DNA, RNA, and histone methylation may be critical contributors to the pathogenesis of keratinocyte cancers (KCs), made up of basal cell carcinoma (BCC) and cutaneous squamous cell carcinoma (cSCC), which collectively outnumber all other human cancers combined. While it is clear that methylation modifiers are frequently dysregulated in KCs, the underlying molecular and mechanistic changes are only beginning to be understood. Intriguingly, it has recently emerged that there is extensive cross-talk amongst these distinct methylation processes. Here, we summarize and synthesize the latest findings in this space and highlight how these discoveries may uncover novel therapeutic approaches for these ubiquitous cancers.

The Role of Polycomb Group Protein BMI1 in DNA Repair and Genomic Stability

The polycomb group (PcG) proteins are a class of transcriptional repressors that mediate gene silencing through histone post-translational modifications. They are involved in the maintenance of stem cell self-renewal and proliferation, processes that are often dysregulated in cancer. Apart from their canonical functions in epigenetic gene silencing, several studies have uncovered a function for PcG proteins in DNA damage signaling and repair. In particular, members of the poly-comb group complexes (PRC) 1 and 2 have been shown to recruit to sites of DNA damage and mediate DNA double-strand break repair. Here, we review current understanding of the PRCs and their roles in cancer development. We then focus on the PRC1 member BMI1, discussing the current state of knowledge of its role in DNA repair and genome integrity, and outline how it can be targeted pharmacologically.

Chromatin remodeling by the histone methyltransferase EZH2 drives lung pre-malignancy and is a target for cancer prevention

Background

Trimethylation of lysine 27 and dimethylation of lysine 9 of histone-H3 catalyzed by the histone methyltransferases EZH2 and G9a impede gene transcription in cancer. Our human bronchial epithelial (HBEC) pre-malignancy model studied the role of these histone modifications in transformation. Tobacco carcinogen transformed HBEC lines were characterized for cytosine DNA methylation, transcriptome reprogramming, and the effect of inhibiting EZH2 and G9a on the transformed phenotype. The effects of targeting EZH2 and G9a on lung cancer prevention was assessed in the A/J mouse lung tumor model.

Results

Carcinogen exposure induced transformation and DNA methylation of 12–96 genes in the four HBEC transformed (T) lines that was perpetuated in malignant tumors. In contrast, 506 unmethylated genes showed reduced expression in one or more HBECTs with many becoming methylated in tumors. ChIP-on-chip for HBEC2T identified 327 and 143 genes enriched for H3K27me3 and H3K9me2. Treatment of HBEC2T and HBEC13T with DZNep, a lysine methyltransferase inhibitor depleted EZH2, reversed transformation, and induced transcriptional reprogramming. The EZH2 small molecule inhibitor EPZ6438 also affected transformation and expression in HBEC2T, while a G9a inhibitor, UNC0642 was ineffective. Genetic knock down of EZH2 dramatically reduced carcinogen-induced transformation of HBEC2. Only DZNep treatment prevented progression of hyperplasia to adenomas in the NNK mouse lung tumor model through reducing EZH2 and affecting the expression of genes regulating cell growth and invasion.

Conclusion

These studies demonstrate a critical role for EZH2 catalyzed histone modifications for premalignancy and its potential as a target for chemoprevention of lung carcinogenesis.

Prognostic Value of EZH2 in Non-Small-Cell Lung Cancers: A Meta-Analysis and Bioinformatics Analysis

Background

The prognosis of non-small-cell lung cancer (NSCLC) has not been significantly improved. In the past several years, research on epigenetics is in full swing. There is a focus on the gene EZH2; however, its role as a predictor of the prognosis of NSCLC is in the debate.

Objective

To clarify if the expression level of EZH2 can influence the prognosis of NSCLC and explain its prognostic value.

Methods

We have systematically searched PubMed, Web of Science, and Cochrane library, screened relevant articles, and conducted a meta-analysis on the expression level of EZH2 in NSCLC. We collected the hazard ratio (HR) and the 95% confidence interval (CI) and used STATA 12.0 to calculate the combined result of EZH2 overall survival. In addition, we conducted subgroup analyses, a sensitivity analysis, and a funnel plot to test the reliability of the results. We further validated these meta-analysis results using the Kaplan-Meier plotter database and The Cancer Genome Atlas (TCGA) database. In addition, we have investigated the correlation between EZH2 expression and EGFR expression, KRAS expression, BRAF expression, and smoking in TCGA database to further explore the mechanism behind the influence of high EZH2 expression on lung cancer prognosis.

Results

13 studies including 2180 participants were included in the meta-analysis. We found that high expression of EZH2 indicates a poor prognosis of NSCLC (HR = 1.65 and 95% CI 1.16-2.35; p ≤ 0.001). Subgroup analyses showed high heterogeneity in stages I-IV (I ² = 85.1% and p ≤ 0.001) and stages I-III (I ² = 66.9% and p = 0.029) but not in stage I (I ² = 0.00% and p = 0.589). In the Kaplan-Meier plotter database, there was a high expression in 963 cases and low expression in 964 cases (HR = 1.31 and 95% CI 1.15-1.48; p < 0.05). Further analysis found that the high expression of EZH2 was statistically significant in lung adenocarcinoma (HR = 1.27and 95% CI 1.01-1.6; p = 0.045), but not in lung squamous cell carcinoma (HR = 1.03 and 95% CI 0.81-1.3; p = 0.820). The results of the TCGA database showed that the expression of EZH2 in normal tissues was lower than that in lung cancer tissues (p < 0.05). Smoking was associated with high expression of EZH2 (p < 0.001). EZH2 was also highly expressed in lung cancers with positive KRAS expression, and the correlation was positive in lung adenocarcinoma (r = 0.3129 and p < 0.001). The correlation was also positive in lung squamous cell carcinoma (r = 0.3567 and p < 0.001). EZH2 expression was positively correlated with BRAF expression (r = 0.2397 and p < 0.001), especially in lung squamous cell carcinoma (r = 0.3662 and p < 0.001). In lung squamous cell carcinoma, a positive yet weak correlation was observed between EZH2 expression and EGFR expression (r = 0.1122 and p < 0.001).

Conclusions

The high expression of EZH2 indicates a poor prognosis of NSCLC, which may be related to tumor stage or cancer type. EZH2 may be an independent prognostic factor for NSCLC. EZH2 high expression or its synergistic action with KRAS and BRAF mutations affects the prognosis of non-small-cell lung cancer.

Identification and Expression Pattern of EZH2 in Pig Developing Fetuses

The proper methylation status of histones is essential for appropriate cell lineage and organogenesis. EZH2, a methyltransferase catalyzing H3K27me3, has been abundantly studied in human and mouse embryonic development. The pig is an increasing important animal model for molecular study and pharmaceutical research. However, the transcript variant and temporal expression pattern of EZH2 in the middle and late porcine fetus are still unknown. Here, we identified the coding sequence of the EZH2 gene and characterized its expression pattern in fetal tissues of Duroc pigs at 65- and 90-day postcoitus (dpc). Our results showed that the coding sequence of EZH2 was 2241 bp, encoding 746 amino acids. There were 9 amino acid insertions and an amino acid substitution in this transcript compared with the validated reference sequence in NCBI. EZH2 was ubiquitously expressed in the fetal tissues of two time points with different expression levels. These results validated a different transcript in pigs and characterized its expression profile in fetal tissues of different gestation stages, which indicated that EZH2 played important roles during porcine embryonic development.

EZH2 overexpression dampens tumor-suppressive signals via an EGR1 silencer to drive breast tumorigenesis

The mechanism underlying EZH2 overexpression in breast cancer and its involvement in tumorigenesis remain poorly understood. In this study, we developed an approach to systematically identify the trans-acting factors regulating the EZH2 expression, and identified more than 20 such factors. We revealed reciprocal regulation of early growth response 1 (EGR1) and EZH2: EGR1 activates the expression of EZH2, and EZH2 represses EGR1 expression. Using CRISPR-mediated genome/epigenome editing, we demonstrated that EHZ2 represses EGR1 expression through a silencer downstream of the EGR1 gene. Deletion of the EGR1 silencer resulted in reduced cell growth, invasion, tumorigenicity of breast cancer cells, and extensive changes in gene expression, such as upregulation of GADD45, DDIT3, and RND1; and downregulation of genes encoding cholesterol biosynthesis pathway enzymes. We hypothesize that EZH2/PRC2 acts as a "brake" for EGR1 expression by targeting the EGR1 silencer, and EZH2 overexpression dampens tumor-suppressive signals mediated by EGR1 to drive breast tumorigenesis.

BMI-1 expression increases in oral leukoplakias and correlates with cell proliferation

Oral leukoplakia (OL) is a white lesion of an indeterminate risk not related to any excluded (other) known diseases or disorders that carry no increased risk for cancer. Many biological markers have been used in an attempt to predict malignant transformation; however, no reliable markers have been established so far.

Depletion of histone methyltransferase KMT9 inhibits lung cancer cell proliferation by inducing non-apoptotic cell death

Background

Lung cancer is the leading cause of cancer related death worldwide. Over the past 15 years no major improvement of survival rates could be accomplished. The recently discovered histone methyltransferase KMT9 that acts as epigenetic regulator of prostate tumor growth has now raised hopes of enabling new cancer therapies. In this study, we aimed to identify the function of KMT9 in lung cancer.

Methods

We unraveled the KMT9 transcriptome and proteome in A549 lung adenocarcinoma cells using RNA-Seq and mass spectrometry and linked them with functional cell culture, real-time proliferation and flow cytometry assays.

Results

We show that KMT9α and -β subunits of KMT9 are expressed in lung cancer tissue and cell lines. Importantly, high levels of KMT9α correlate with poor patient survival. We identified 460 genes that are deregulated at the RNA and protein level upon knock-down of KMT9α in A549 cells. These genes cluster with proliferation, cell cycle and cell death gene sets as well as with subcellular organelles in gene ontology analysis. Knock-down of KMT9α inhibits lung cancer cell proliferation and induces non-apoptotic cell death in A549 cells.

Conclusions

The novel histone methyltransferase KMT9 is crucial for proliferation and survival of lung cancer cells harboring various mutations. Small molecule inhibitors targeting KMT9 therefore should be further examined as potential milestones in modern epigenetic lung cancer therapy.

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.

Evaluation of the expression of Bmi-1 stem cell marker in sinonasal melanomas and its correlation with the expression of cell cycle proteins

Background

Sinonasal melanomas (SNM) are aggressive neoplasms, which present distinct clinicopathological and molecular aspects when compared to cutaneous melanomas (CM). B-cell-specific moloney murine leukemia virus integration site-1 (Bmi-1) is a stem cell marker involved in the regulation of the cell cycle and has been found to be expressed in 70% of CM and 100% of benign nevi. Regarding the cell cycle, Bmi-1 is known to be an upstream repressor of p16, which is a tumor suppressor encoded by the INK4a/Arf locus. Considering this, the aim of this study is to evaluate the immunohistochemical expression of Bmi-1 in a series of SNM and its correlation with the expression of cell cycle proteins (p16 and Ki-67, a nuclear antigen of proliferating cells).

Methods

In 16 cases of SNM, nuclear expression of Bmi-1 and nuclear and cytoplasmic of p16 was classified as: absent, low (> 5 to < 50% of cells) and high (≥50%). Ki-67 proliferation index was represented by the ratio positive cells/ total cells.

Results

Histologically, all cases presented varying amount of necrosis and 75% contained undifferentiated cells. Bmi-1 was detected in 6 cases (37.5%) with high level of expression in 2; p16 expression was seen in 10 cases (62.5%) with high level in 7. The frequency of p16 expression did not differ significantly between tumors with or without Bmi-1 expression. Ki-67 index ranged from 8 to 22%. Neither Bmi-1 nor p16 expression showed correlation with Ki-67 index. Bmi-1 negative tumors presented more extensive necrosis (71.4%); no association between Bmi-1 expression and undifferentiated phenotype was observed.

Conclusions

In our SNM series, low immunohistochemical expression of Bmi-1 was a common phenomenon favoring the hypothesis that mucosal melanoma possibly presents molecular pathways different from the cutaneous counterpart. In SNM, Bmi-1 and p16 expression levels did not correlate with each other or with the cell proliferative index.

An immunohistochemical panel consisting of EZH2, C-KIT, and CD205 is useful for distinguishing thymic squamous cell carcinoma from type B3 thymoma

Type B3 thymoma and thymic squamous cell carcinoma (SqCC) often cause a diagnostic problem due to their histological similarities. The aim of this study is to identify EZH2 as a novel and powerful biomarker that can effectively distinguish thymic SqCC from type B3 thymoma, and find optimal combinations among 11 markers. A total of 53 patients, comprising 26 with type B3 thymoma and 27 with thymic SqCC, were allocated to the discovery or validation cohorts, and immunohistochemical staining was performed and analyzed. The expression level of each marker was scored, and receiver-operator characteristic curve analysis was performed to evaluate their diagnostic accuracies. This analysis identified EZH2, C-KIT, and CD205 as useful markers for distinguishing thymic SqCC, and a combined panel approach using them further improved diagnostic accuracy in both the discovery and validation cohorts. In the combined cohorts analysis, EZH2 was the single best marker with 88.9% sensitivity and 100% specificity [area under the curve (AUC) = 0.967]. The sensitivity and specificity were 85.2% and 100% (AUC = 0.962) for C-KIT, and 100% and 73.1% (AUC = 0.844) for CD205. The combined panel had the highest sensitivity and specificity at 96.3% and 100%, which was significantly or marginally higher than those of EZH2, C-KIT, and CD205 alone (P = 0.071, 0.034, and 0.005, respectively). The present findings indicate that EZH2 is useful as a novel diagnostic marker for distinguishing thymic SqCC and that the panel approach can be used as an effective differential diagnostic tool in daily practice.

Lung cancer epigenetics: From knowledge to applications

Lung cancer is the leading cause of cancer-related mortality worldwide. Advances in our understanding of the genomics of lung cancer have led to substantial progress in the treatment of specific molecular subsets. Immunotherapy also emerges as a major breakthrough in lung cancer treatment. However, challenges remain as a consensual approach for early lung cancer detection remains elusive while primary or secondary drug resistance eventually leads to treatment failure in all patients with advanced disease. Furthermore, a large portion of patients are still treated with conventional chemotherapy that is only modestly effective. The last two decades have seen exponential developments in the epigenetic understanding of lung cancer. Epigenetic alterations in DNA methylation, non-coding RNA expression, chromatin modeling and post transcriptional regulators are key events in each step of lung cancer pathogenesis. Here, we review the central role epigenetic disruptions play in lung cancer carcinogenesis and the acquisition of cancerous phenotype and aggressive behavior as well as in the resistance to therapy. Epigenetic disruptions could represent reliable biomarkers for lung cancer risk assessment, early diagnosis, prognosis stratification, molecular classification and prediction of treatment efficacy. The therapeutic potential of epigenetics targeted drugs in combination with chemotherapy, targeted therapy and/or immunotherapy is currently being intensively investigated. We suggest that integration of tissue-derived or circulating epigenetic biomarkers and epidrugs in clinical trial design will translate epigenetic knowledge of lung cancer into the clinic and improve lung cancer patient outcomes.

Expression and survival significance of B-cell-specific Moloney murine leukemia virus integration site 1 and matrix metalloproteinase-9 in non-small-cell lung cancer

One of the main challenges in lung cancer research is identifying patients at high risk of progression and metastasis following surgical resection. In the present study, the prognostic significance of B-cell-specific Moloney murine leukemia virus integration site 1 (BMI1) and matrix metalloproteinase-9 (MMP9) in non-small-cell lung cancer (NSCLC) was evaluated. BMI1 and MMP9 expression in tumors from 132 surgical NSCLC patients [squamous cell carcinoma (SCC), n=79; and adenocarcinoma (AD), n=53] was evaluated by immunohistochemistry. The clinical significance was determined using multivariate Cox regression analysis, Kaplan-Meier curves and the log-rank test. High BMI1 expression was more frequent in SCC compared with that in AD (P=0.015). Comparisons between the expression of BMI1 and that of other known biological markers revealed that the expression of BMI1 was correlated with that of MMP9 (χ²=4.241, P=0.039) in SCC. Although an association was not identified between high BMI1 expression and overall survival (OS) in NSCLC or AD, high BMI1 expression was an unfavorable predictor of survival in SCC according to the survival curves (P=0.038). In addition, combined high BMI1 and MMP9 expression levels were significantly correlated with SCC nodal/distant metastasis (χ²=6.392, P=0.014). Multivariate Cox proportional model analysis demonstrated that this combined marker was an independent prognostic indicator of OS in SCC (P=0.025; hazard ratio = 12.963; 95% confidence interval: 1.142–7.637). Therefore, this study demonstrated that combined BMI1 and MMP9 expression may be used as a marker for the progression and metastasis of SCC. These results may aid in the elucidation of the potential mechanism underlying the involvement of BMI1 and MMP9 in tissue-specific SCC progression.

Quantitative Histone Mass Spectrometry Identifies Elevated Histone H3 Lysine 27 (Lys27) Trimethylation in Melanoma

Normal cell growth is characterized by a regulated epigenetic program that drives cellular activities such as gene transcription, DNA replication, and DNA damage repair. Perturbation of this epigenetic program can lead to events such as mis-regulation of gene transcription and diseases such as cancer. To begin to understand the epigenetic program correlated to the development of melanoma, we performed a novel quantitative mass spectrometric analysis of histone post-translational modifications mis-regulated in melanoma cell culture as well as patient tumors. Aggressive melanoma cell lines as well as metastatic melanoma were found to have elevated histone H3 Lys(27) trimethylation (H3K27me3) accompanied by overexpressed methyltransferase EZH2 that adds the specific modification. The altered epigenetic program that led to elevated H3K27me3 in melanoma cell culture was found to directly silence transcription of the tumor suppressor genes RUNX3 and E-cadherin. The EZH2-mediated silencing of RUNX3 and E-cadherin transcription was also validated in advanced stage human melanoma tissues. This is the first study focusing on the detailed epigenetic mechanisms leading to EZH2-mediated silencing of RUNX3 and E-cadherin tumor suppressors in melanoma. This study underscores the utility of using high resolution mass spectrometry to identify mis-regulated epigenetic programs in diseases such as cancer, which could ultimately lead to the identification of biological markers for diagnostic and prognostic applications.

Potential roles of EZH2, Bmi-1 and miR-203 in cell proliferation and invasion in hepatocellular carcinoma cell line Hep3B

AIM: To investigate the potential roles of enhancer of zeste homolog2 (EZH2), Bmi-1 and miR-203 in cell proliferation and invasion in hepatocellular carcinoma (HCC) cell line Hep3B.

METHODS: A total of 73 patients who underwent surgical resection at Fuzong Clinical Medical College of Fujian Medical University were enrolled in this study. Hep3B cells were cultivated in RPMI 1640 medium supplemented with 10% fetal bovine serum at 37 °C. Vectors that containing cDNA of the EZH2 gene or miR-203 targeted shRNA plasmid were constructed, and then transfected into Hep3B cells. The mRNA expression of miR-203, EZH2, and Bmi-1 was analyzed using quantitative real-time polymerase chain reaction analysis, and the protein levels of EZH2 and Bmi-1 were detected by Western blot analysis. Effect of EZH2 or miR-203 on cell proliferation was observed by methyl thiazolyl tetrazolium assay, and cell apoptosis was assessed using flow cytometry. Besides, effect of EZH2 or miR-203 on tumor cell invasion was detected using Transwell assay.

RESULTS: The mRNA levels of EZH2 and Bmi-1 in HCC tissues and in Hep3B cells were significantly higher compared with those in normal samples (P < 0.01), while miR-203 level was significantly lower in HCC tissues (P < 0.01). Hep3B cells transfected with EZH2-shRNA or miR-203-shRNA showed lower expression levels of EZH2 and Bmi-1 (P < 0.05). Compared with controls, Hep3B cells transfected with EZH2-shRNA had relative slow cell proliferation, indicating that low expression of EZH2 and Bmi-1 and overexpression of miR-203 could inhibit Hep3B cell proliferation (P < 0.05). The average apoptosis rate of Hep3B cells transfected with EZH2-shRNA vector was about 18.631%, while that of Hep3B cells transfected with shRNA vector was about 5.33%, suggesting that EZH2 was down-regulated by transfecting with EZH2-shRNA, and the down-regulated EZH2 contributed to the cell apoptosis. Low expression of EZH2 and Bmi-1 and overexpression of miR-203 could reduce Hep3B cell invasion (P < 0.05).

CONCLUSION: Our study suggests that EZH2 and Bmi-1 are up-regulated while miR-203 is down-regulated in Hep3B cells. MiR-203 may contribute to the metastasis and enhance apoptosis of HCC cells by regulating EZH2 and Bmi-1. Our study may provide a theoretical basis for metastasis of HCC and targeted therapy of HCC.

Characterization and pharmacologic targeting of EZH2, a fetal retinal protein and epigenetic regulator, in human retinoblastoma

Retinoblastoma (RB) is the most common primary intraocular cancer in children, and the third most common cancer overall in infants. No molecular-targeted therapy for this lethal tumor exists. Since the tumor suppressor RB1, whose genetic inactivation underlies RB, is upstream of the epigenetic regulator EZH2, a pharmacologic target for many solid tumors, we reasoned that EZH2 might regulate human RB tumorigenesis. Histologic and immunohistochemical analyses were performed using an EZH2 antibody in sections from 43 samples of primary, formalin-fixed, paraffin-embedded human RB tissue, cryopreserved mouse retina, and in whole cell lysates from human RB cell lines (Y79 and WERI-Rb1), primary human fetal retinal pigment epithelium (RPE) and fetal and adult retina, mouse retina and embryonic stem (ES) cells. Although enriched during fetal human retinal development, EZH2 protein was not present in the normal postnatal retina. However, EZH2 was detected in all 43 analyzed human RB specimens, indicating that EZH2 is a fetal protein expressed in postnatal human RB. EZH2 expression marked single RB cell invasion into the optic nerve, a site of invasion whose involvement may influence the decision for systemic chemotherapy. To assess the role of EZH2 in RB cell survival, human RB and primary RPE cells were treated with two EZH2 inhibitors (EZH2i), GSK126 and SAH-EZH2 (SAH). EZH2i impaired intracellular adenosine triphosphate (ATP) production, an indicator of cell viability, in a time and dose-dependent manner, but did not affect primary human fetal RPE. Thus, aberrant expression of a histone methyltransferase protein is a feature of human RB. This is the first time this mechanism has been implicated for an eye, adnexal, or orbital tumor. The specificity of EZH2i toward human RB cells, but not RPE, warrants further in vivo testing in animal models of RB, especially those EZH2i currently in clinical trials for solid tumors and lymphoma.

The Bmi-1 helix-turn and ring finger domains are required for Bmi-1 antagonism of (-) epigallocatechin-3-gallate suppression of skin cancer cell survival

The Bmi-1 Polycomb group (PcG) protein is an important epigenetic regulator of chromatin status. Elevated Bmi-1 expression is observed in skin cancer and contributes to cancer cell survival. (-) Epigallocatechin-3-gallate (EGCG), an important green tea-derived cancer prevention agent, reduces Bmi-1 level resulting in reduced skin cancer cell survival. This is associated with increased p21(Cip1) and p27(Kip1) expression, reduced cyclin, and cyclin dependent kinase expression, and increased cleavage of apoptotic markers. These EGCG-dependent changes are attenuated by vector-mediated maintenance of Bmi-1 expression. In the present study, we identify Bmi-1 functional domains that are required for this response. Bmi-1 expression reverses the EGCG-dependent reduction in SCC-13 cell survival, but Bmi-1 mutants lacking the helix-turn-helix-turn-helix-turn (Bmi-1ΔHT) or ring finger (Bmi-1ΔRF) domains do not reverse the EGCG impact. The reduction in Ring1B ubiquitin ligase activity, observed in the presence of mutant Bmi-1, is associated with reduced ability of these mutants to interact with and activate Ring1B ubiquitin ligase, the major ligase responsible for the ubiquitination of histone H2A during chromatin condensation. This results in less chromatin condensation leading to increased tumor suppressor gene expression and reduced cell survival; thereby making the cells more susceptible to the anti-survival action of EGCG. We further show that these mutants act in a dominant-negative manner to inhibit the action of endogenous Bmi-1. Our results suggest that the HT and RF domains are required for Bmi-1 ability to maintain skin cancer cell survival in response to cancer preventive agents.

The Stem Cell Marker Bmi-1 Is Sensitive in Identifying Early Lesions of Carcinoma ex Pleomorphic Adenoma

In the present study, we evaluated and described the sensitivity of the stem cell marker B cell-specific moloney murine leukemia virus integration site 1 (Bmi-1) in identifying early lesions of carcinoma ex pleomorphic adenoma (CXPA). While invasive CXPAs are tumors with a prominent and easily recognizable malignant component, the identification of early carcinomatous changes in PA remains a diagnostic challenge due to the lack of objective morphological criteria. The immunohistochemical expression of Bmi-1 was assessed in both adenomatous and carcinomatous components of 9 CXPA cases at an early phase of histological progression (6 intracapsular and 3 minimally invasive) grouped according to the cellular differentiation as luminal (7 cases) or myoepithelial (2 cases). A selective nuclear expression of Bmi-1 was found exclusively in the malignant component of 8 cases (6 luminal type and 2 myoepithelial type), including intraductal carcinoma areas, except for 1 case in which scarce cells of the remnant PA were positive. Thus, Bmi-1 is expressed from the earliest morphologically detectable stages of PA malignant transformation. When faced with atypical features in PA, evaluation of Bmi-1 expression can provide more objective criteria for identification and diagnosis of early lesions of CXPA. This is applied to carcinomas with luminal or myoepithelial differentiation.

Prognostic significance of histone methyltransferase enhancer of zeste homolog 2 in patients with cervical squamous cell carcinoma

Histone methyltransferase enhancer of zeste homolog 2 (EZH2) has been reported to be associated with certain malignant phenotypes in cervical cancer. However, clinicopathological parameters and clinical outcomes of EZH2 in cervical cancer, particularly in cervical squamous cell carcinoma (CSCC) remain largely unknown. The retrospective cohort comprising of 117 consecutive patients with CSCC was incorporated into a tissue microarray which also included 23 paired normal tissues. Immunohistochemical analysis was performed to evaluate the correlation between EZH2 expression and clinicopathological implications. Aberrant overexpression of EZH2 was frequently observed in CSCCs as compared with adjacent normal tissues (P=0.0005). Expression of EZH2 is associated with poor tumor differentiation grade (P=0.020) and lymphovascular invasion (P=0.012). Univariate analysis revealed that the patients with CSCC whose tumors exhibited higher EZH2 levels had inferior overall survival (OS) compared to those whose tumors expressed lower EZH2 (log rank P=0.004). In the multivariate analysis, EZH2 expression was an independent predictor of OS (hazard ratio = 1.836, 95% confidence interval: 1.090-2.993, P=0.022). EZH2 overexpression is common in the development of CSCC and is a promising prognostic predictor for patients with CSCC.

Survival of skin cancer stem cells requires the Ezh2 polycomb group protein

Polycomb group proteins, including Ezh2, are important candidate stem cell maintenance proteins in epidermal squamous cell carcinoma. We previously showed that epidermal cancer stem cells (ECS cells) represent a minority of cells in tumors, are highly enriched in Ezh2 and drive aggressive tumor formation. We now show that Ezh2 is required for ECS cell survival, migration, invasion and tumor formation and that this is associated with increased histone H3 trimethylation on lysine 27, a mark of Ezh2 action. We also show that Ezh2 knockdown or treatment with Ezh2 inhibitors, GSK126 or EPZ-6438, reduces Ezh2 level and activity, leading to reduced ECS cell spheroid formation, migration, invasion and tumor growth. These studies indicate that epidermal squamous cell carcinoma cells contain a subpopulation of cancer stem (tumor-initiating) cells that are enriched in Ezh2, that Ezh2 is required for optimal ECS cell survival and tumor formation and that treatment with Ezh2 inhibitors may be a strategy for reducing ECS cell survival and suppressing tumor formation.

Bmi-1 expression modulates non-small cell lung cancer progression

Previous studies indicate that the role of B lymphoma Mo-MLV insertion region 1 homolog (Bmi-1) is responsible for multiple cancer progression. However, Bmi-1 in controlling gene expression in non-small cell lung cancer (NSCLC) development is not well explored. Here we report that the Bmi-1 level is highly increased in primary NSCLC tissues compared to matched adjacent non-cancerous tissues and required for lung tumor growth in xenograft model. Furthermore, we also demonstrate that Bmi-1 level is lower in matched involved lymph node cancerous tissues than the respective primary NSCLC tissues. We find that Bmi-1 does not affect cell cycle and apoptosis in lung cancer cell lines as it does not affect the expression of p16/p19, Pten, AKT and P-AKT. Mechanistic analyses note that reduction of Bmi-1 expression inversely regulates invasion and metastasis of NSCLC cells in vitro and in vivo, followed by induction of epithelial-mesenchymal transition (EMT). Using genome microarray assays, we find that RNAi-mediated silence of Bmi-1 modulates some important molecular genetics or signaling pathways, potentially associated with NSCLC development. Taken together, our findings disclose for the first time that Bmi-1 level accumulates strongly in early stage and then declines in late stage, which is potentially important for NSCLC cell invasion and metastasis during progression.

EZH2 as a potential target in cancer therapy

Over the last several years, dysregulation of epigenetic mechanisms including DNA and histone methylation has been recognized as a hallmark of cancer. Alterations of epigenetic regulators themselves, including the histone lysine methyltransferase EZH2, have been reported in numerous cancer types. With the discovery of small molecule inhibitors of EZH2, we can now begin to evaluate EZH2 as a therapeutic target in cancer. This article will provide an overview of the dysregulation of EZH2 in cancer, possible mechanisms for inhibition of EZH2 activity, and the preclinical activity of currently available EZH2 inhibitors.

Epigenetics of lung cancer

Lung cancer is the leading cause of cancer-related mortality in the United States. Epigenetic alterations, including DNA methylation, histone modifications, and noncoding RNA expression, have been reported widely in the literature to play a major role in the genesis of lung cancer. The goal of this review is to summarize the common epigenetic changes associated with lung cancer to give some clarity to its etiology, and to provide an overview of the potential translational applications of these changes, including applications for early detection, diagnosis, prognostication, and therapeutics.

Prognostic value of COX-2, P53, and EZH-2 evaluated by quantitative image analysis in premalignant and malignant breast lesions

BACKGROUND

Cytological differential diagnosis of atypical hyperplasia and well differentiated breast carcinoma may be challenging, because sometimes there is an overlap between the cytomorphological features of these lesions. The aim of the study was to investigate COX-2, EZH-2, p53 expression in carcinomas and the gray zone of breast cytology categories of atypical hyperplastic lesions with regard to biological behavior of the tumor.

METHODS

FNA speciments from 100 patients with breast hyperplastic lesions and cancer were investigated by immunocytochemistry and a quantitative analysis for COX-2, p53, and EZH-2.

RESULTS

Extent of staining for COX-2 correlated with percentage of positive for EZH-2 (P < 0.0001) and p53 nuclei (P < 0.001). The intensity of COX-2 was lower in the carcinoma group (118.57 ± 12.43) than in the hyperplastic (127.16 ± 11.71) group (P = 0.006). On the contrary the mean value of staining extent was greater in the adenocarcinoma cases (15.96 ± 13.03) than in hyperplastic (4.04 ± 1.94) cases (P < 0.0001). The percentage of EZH-2 and p53 positive cells correlated with the histological type of the lesions (P = 0.001 and P = 0.011, respectively). There was also a statistically significant relation between tumor size and expression of COX-2 (P = 0.007) and EZH-2 (P = 0.010).

CONCLUSION

Our study showed that the expression of COX-2, EZH-2, and p53 as determined by immunocytochemistry at quantitative level may be a predictor for distinguishing cytologically atypical hyperplastic from malignant breast lesions and may be regarded as potential prognostic factor in breast cancer patients.

The clinicopathological significance of epithelial mesenchymal transition associated protein expression in head and neck squamous cell carcinoma

Background

Epithelial mesenchymal transition (EMT) has an important role in invasion and metastasis of tumor cells. The purpose of this study was to evaluate the roles of EMT-associated proteins on progression and metastasis as a prognostic/predictive factor in curatively-resected (R0) head and neck squamous cell carcinoma (HNSCC).

Methods

A total of 118 patients who received curative surgery for HNSCC at Inha University Hospital between January 1996 and December 2011 were included. We used protein immunohistochemistry to evaluate the expression of E-cadherin, vimentin, and EZH2 on tissue microarrays. Also, we reviewed all medical records and analyzed the relationship between the expression of EMT-associated proteins and prognosis.

Results

The E-cadherin-negative group showed more moderate/poor differentiation of cancer cell type than the higher E-cadherin-expressing group (p=.016) and high EZH2 expression was significantly correlated with nodal metastasis (p=.012). Our results demonstrate a significant association between high expression of EZH2 and vimentin and presence of distant progression (p=.026). However, expression of E-cadherin, vimentin, and EZH2 was not significantly associated with overall survival.

Conclusions

These findings suggest that an EMT-associated protein expression profile is correlated with aggressiveness of disease and prognosis, and could be a useful marker for determination of additional treatment in curatively-resected HNSCC patients.

EZH2 protein expression associates with the early pathogenesis, tumor progression, and prognosis of non-small cell lung carcinoma

PURPOSE

Enhancer of zeste homolog 2 (EZH2) promotes carcinogenesis by epigenetically silencing tumor suppressor genes. We studied EZH2 expression by immunohistochemistry in a large series of non-small cell lung carcinomas (NSCLC) in association with tumor characteristics and patient outcomes.

EXPERIMENTAL DESIGN

EZH2 immunohistochemistry expression was analyzed in 265 normal and premalignant bronchial epithelia, 541 primary NSCLCs [221 squamous cell carcinomas (SCC) and 320 adenocarcinomas] and 36 NSCLCs with paired brain metastases. An independent set of 91 adenocarcinomas was also examined. EZH2 expression was statistically correlated with clinico-pathological information, and EGFR/KRAS mutation status.

RESULTS

EZH2 expression was significantly (P < 0.0001) higher in SCCs compared with adenocarcinomas and in brain metastasis relative to matched primary tumors (P = 0.0013). EZH2 expression was significantly (P < 0.0001) elevated in bronchial preneoplastic lesions with increasing severity. In adenocarcinomas, higher EZH2 expression significantly correlated with younger age, cigarette smoking, and higher TNM stage (P = 0.02 to P < 0.0001). Higher EZH2 expression in adenocarcinoma was associated with worse recurrence-free survival (RFS; P = 0.025; HR = 1.54) and overall survival (OS; P = 0.0002; HR = 1.96). Furthermore, lung adenocarcinomas with low EZH2 levels and high expression of the lineage-specific transcription factor, TTF-1, exhibited significantly improved RFS (P = 0.009; HR = 0.51) and OS (P = 0.0011; HR = 0.45), which was confirmed in the independent set of 91 adenocarcinomas.

CONCLUSION

In lung, EZH2 expression is involved in early pathogenesis of SCC and correlates with a more aggressive tumor behavior of adenocarcinoma. When EZH2 and TTF-1 expressions are considered together, they serve as a prognostic marker in patients with surgically resected lung adenocarcinomas.

Pre-clinical studies of epigenetic therapies targeting histone modifiers in lung cancer

Treatment options for lung cancer patients have been generally limited to standard therapies or targeted interventions which involve a small number of known mutations. Although the targeted therapies are initially successful, they most often result in drug resistance, relapse, and mortality. We now know that the complexity of lung cancer comes not only from genomic changes, but also from aberrant epigenetic regulatory events. Epigenetic therapies have shown promise as single agents in the treatment of hematological malignancies but have yet to meet this expectation in solid tumors thus fostering researchers to pursue new approaches in the development and use of epigenetic interventions. Here, we review some recent pre-clinical findings involving the use of drugs targeting histone modifying enzymes both as single agents and as co-therapies against lung cancer. A greater understanding of the impact of these epigenetic compounds in lung cancer signaling is needed and further evaluation in vivo is warranted in several cases based on the pre-clinical activity of a subset of compounds discussed in this review, including drugs co-targeting HDACs and EGF receptor, targeting Brd4 and targeting Jumonji histone demethylases.

Genomic deregulation of the E2F/Rb pathway leads to activation of the oncogene EZH2 in small cell lung cancer

Small cell lung cancer (SCLC) is a highly aggressive lung neoplasm with extremely poor clinical outcomes and no approved targeted treatments. To elucidate the mechanisms responsible for driving the SCLC phenotype in hopes of revealing novel therapeutic targets, we studied copy number and methylation profiles of SCLC. We found disruption of the E2F/Rb pathway was a prominent feature deregulated in 96% of the SCLC samples investigated and was strongly associated with increased expression of EZH2, an oncogene and core member of the polycomb repressive complex 2 (PRC2). Through its catalytic role in the PRC2 complex, EZH2 normally functions to epigenetically silence genes during development, however, it aberrantly silences genes in human cancers. We provide evidence to support that EZH2 is functionally active in SCLC tumours, exerts pro-tumourigenic functions in vitro, and is associated with aberrant methylation profiles of PRC2 target genes indicative of a “stem-cell like” hypermethylator profile in SCLC tumours. Furthermore, lentiviral-mediated knockdown of EZH2 demonstrated a significant reduction in the growth of SCLC cell lines, suggesting EZH2 has a key role in driving SCLC biology. In conclusion, our data confirm the role of EZH2 as a critical oncogene in SCLC, and lend support to the prioritization of EZH2 as a potential therapeutic target in clinical disease.

Gene silencing and Polycomb group proteins: an overview of their structure, mechanisms and phylogenetics

DNA methylation, histone modifications, and chromatin configuration are crucially important in the regulation of gene expression. Among these epigenetic mechanisms, silencing the expression of certain genes depending on developmental stage and tissue specificity is a key repressive system in genome programming. Polycomb (Pc) proteins play roles in gene silencing through different mechanisms. These proteins act in complexes and govern the histone methylation profiles of a large number of genes that regulate various cellular pathways. This review focuses on two main Pc complexes, Pc repressive complexes 1 and 2, and their phylogenetic relationship, structures, and function. The dynamic roles of these complexes in silencing will be discussed herein, with a focus on the recruitment of Pc complexes to target genes and the key factors involved in their recruitment.

The Histone Methyltransferase EZH2 Mediates Tumor Progression on the Chick Chorioallantoic Membrane Assay, a Novel Model of Head and Neck Squamous Cell Carcinoma

Current in vivo models for head and neck squamous cell carcinoma (HNSCC) have limitations in simulating some essential tumorigenic phenotypes, such as invasion. Most mouse models of human HNSCC are inadequate because tumor cells are injected directly into the connective tissue, thereby bypassing the basement membrane of the surface epithelium, the first barrier to invasion. In this manuscript, we establish the chick chorioallantoic membrane (CAM) assay as an in vivomodel of human HNSCC tumor progression. Using the CAM model of HNSCC, we investigated the role of enhancer of zeste homolog 2 (EZH2), a histone methyltransferase, in multiple aspects of HNSCC tumor progression. We found that knockdown of EZH2 reduced tumor size, angiogenesis, invasion, and metastasis of tumors produced by grafting human HNSCC cells onto the CAM. In addition, we demonstrate that EZH2 expression mediates a mesenchymal phenotype in HNSCC cell lines and mouse tumors. These findings demonstrate the advantages of the newly proposed CAM model of human HNSCC and highlight the emerging role of EZH2 in HSNCC tumor progression.

EZH2 promotes malignant behaviors via cell cycle dysregulation and its mRNA level associates with prognosis of patient with non-small cell lung cancer

BACKGROUND

Epigenetic silencing is a common mechanism to inactivate tumor suppressor genes during carcinogenesis. Enhancer of Zeste 2 (EZH2) is the histone methyltransferase subunit in polycomb repressive complex 2 which mediates transcriptional repression through histone methylation. EZH2 overexpression has been linked to aggressive phenotypes of certain cancers. However, the mechanism that EZH2 played in promoting malignancy in non-small cell lung cancer (NSCLC) remains unclear. In addition, the correlation of EZH2 overexpression and the prognosis of NSCLC patients in non-Asian cohort need to be determined.

METHODOLOGY/PRINCIPAL FINDINGS

Up-regulation of EZH2 was found in NSCLC cells compared with normal human bronchial epithelial cells by western blot assay. Upon EZH2 knockdown using small interfering RNA (siRNA), the proliferation, anchorage-independent growth and invasion of NSCLC cells were remarkably suppressed with profound induction of G1 arrest. Furthermore, the expression of cyclin D1 was notably reduced whereas p15(INK4B), p21(Waf1/Cip1) and p27(Kip1) were increased in NSCLC cells after EZH2-siRNA delivery. To determine whether EZH2 expression contributes to disease progression in patients with NSCLC, Taqman quantitative real-time RT-PCR was used to measure the expression of EZH2 in paired tumor and normal samples. Univariate analysis revealed that patients with NSCLC whose tumors had a higher EZH2 expression had significantly inferior overall, disease-specific, and disease-free survivals compared to those whose tumors expressed lower EZH2 (P = 0.005, P = 0.001 and P = 0.003, respectively). In multivariate analysis, EZH2 expression was an independent predictor of disease-free survival (hazard ratio = 0.450, 95% CI: 0.270 to 0.750, P = 0.002).

CONCLUSIONS/SIGNIFICANCE

Our results demonstrate that EZH2 overexpression is critical for NSCLC progression. EZH2 mRNA levels may serve as a prognostic predictor for patients with NSCLC.

Immunohistochemical analysis of polycomb group protein expression in advanced gastric cancer

The polycomb group proteins have recently captured the attention of cancer biologists. enhancer of zeste homologue 2 (EZH2) and B lymphoma Mo-MLV insertion region 1 homolog (BMI-1) are the best-characterized polycomb group proteins; their deregulation contributes to the development of many malignancies including gastric cancers. H3 trimethylation at lysine 27 and DNA methylase DNA methyltransferase 3B proteins are associated with the recruitment of polycomb group proteins. Overexpression of polycomb group proteins is associated with poor prognoses in some types of cancers but with favorable prognoses in others. In the present study, we investigated the expression of the polycomb group proteins EZH2 and BMI-1 and the associated proteins H3 trimethylation at lysine 27 and DNA methyltransferase 3B in advanced gastric cancers. Based on immunohistochemical detection, we evaluated the clinical relevance of these proteins in 178 cases of advanced gastric cancers that were managed with radical surgery and adjuvant systemic chemotherapy. BMI-1, enhancer of zeste homologue 2, H3 trimethylation at lysine 27, and DNA methyltransferase 3B proteins were overexpressed in the nuclei of gastric carcinoma compared with adjacent nonneoplastic gastric parenchyma. The high-level expression of BMI-1, enhancer of zeste homologue 2, H3 trimethylation at lysine 27, and DNA methyltransferase 3B proteins were frequently noted in advanced gastric cancer tissues (70.8%, 92.1%, 58.4%, and 64.6% of cases, respectively) and well intercorrelated in expression (P < .05). The expression level of BMI-1, enhancer of zeste homologue 2, and DNA methyltransferase 3B showed correlation with sex, gross type, and histologic type of the tumor among clinicopathologic variables. In terms of patient survival, low-level expression of enhancer of zeste homologue 2 was associated with cancer-related death (P = .018) and shorter overall survival (P = .005). Low-level expression of enhancer of zeste homologue 2 may represent a negative prognostic marker (P = .005) and indicate high risk in patients with advanced gastric cancer after surgery and adjuvant chemotherapy.

A proteasome inhibitor-stimulated Nrf1 protein-dependent compensatory increase in proteasome subunit gene expression reduces polycomb group protein level

The polycomb group (PcG) proteins, Bmi-1 and Ezh2, are important epigenetic regulators that enhance skin cancer cell survival. We recently showed that Bmi-1 and Ezh2 protein level is reduced by treatment with the dietary chemopreventive agents, sulforaphane and green tea polyphenol, and that this reduction involves ubiquitination of Bmi-1 and Ezh2, suggesting a key role of the proteasome. In the present study, we observe a surprising outcome that Bmi-1 and Ezh2 levels are reduced by treatment with the proteasome inhibitor, MG132. We show that this is associated with a compensatory increase in the level of mRNA encoding proteasome protein subunits in response to MG132 treatment and an increase in proteasome activity. The increase in proteasome subunit level is associated with increased Nrf1 and Nrf2 level. Moreover, knockdown of Nrf1 attenuates the MG132-dependent increase in proteasome subunit expression and restores Bmi-1 and Ezh2 expression. The MG132-dependent loss of Bmi-1 and Ezh2 is associated with reduced cell proliferation, accumulation of cells in G(2), and increased apoptosis. These effects are attenuated by forced expression of Bmi-1, suggesting that PcG proteins, consistent with a prosurvival action, may antagonize the action of MG132. These studies describe a compensatory Nrf1-dependent, and to a lesser extent Nrf2-dependent, increase in proteasome subunit level in proteasome inhibitor-treated cells and confirm that PcG protein levels are regulated by proteasome activity.

Quantitative analysis of EZH2 expression and its correlations with lung cancer patients' clinical pathological characteristics

INTRODUCTION

Elevated Enhancer of Zeste Homologue 2 (EZH2) expression is involved in many human malignancies through epigenetically silencing related genes. However, the study of the EZH2 protein expression in lung cancer remains at the qualitative or semi-quantitative level. The present study is to elucidate the roles of EZH2 in the progression and metastasis of different subtypes of lung cancer at quantitative level.

MATERIALS AND METHODS

Lung carcinoma tissue microarray was constructed containing 32 normal adult lung tissues, 113 lung carcinomas and 57 lymph-node metastases. EZH2 protein expression was detected by immunohistochemistry and assessed quantitatively with Leica Q500MC image analysis system. Positive unit (PU) value was used to evaluate the protein expression intensity of positive cells from systematically selected fields under the microscope.

RESULTS

Elevated Enhancer of Zeste Homologue 2 PU in lung carcinomas was significantly greater than that in normal lung tissues (p = 0.001). Increased EZH2 expression was correlated with histological subtypes, differentiation, TNM stage, and lymph-node metastases (p < 0.05). EZH2 PU of primary lung carcinomas was smaller than that of lymph-node metastasis (p = 0.002). EZH2 PU was not associated with patients' gender, age, smoking status, tumor location, and tumor size (p > 0.05).

CONCLUSIONS

Elevated Enhancer of Zeste Homologue 2 PU is increased with the development of lung cancer. EZH2 may play an important role in the progression and metastasis of lung cancer.

Co-expression of Bmi1 and EZH2 as an independent poor prognostic factor in esophageal squamous cell carcinoma

Bmi1 polycomb ring finger oncogene (Bmi1) and the enhancer of zeste homolog 2 (EZH2) are members of polycomb repressive complex (PRC) 1 and PRC2, respectively. PRC1 represses tumor suppressor genes such as p16INK4a and p14ARF in a PRC2-dependent manner. There have been few studies on Bmi1 or EZH2 expression in esophageal squamous cell carcinoma (ESCC). We investigated Bmi1 and EZH2 expression in 164 cases of ESCCs using immunohistochemistry, and evaluated the correlation with clinicopathologic features and their prognostic significance. Bmi1 and EZH2 were more highly expressed in tumor than in adjacent normal tissue (p<0.001). High expression of Bmi1 or EZH2 alone was not correlated with any clinicopathologic parameter and did not influence the prognosis. However, the group with high expression of both Bmi1 and EZH2 showed the poorest prognosis in overall survival (p=0.027) and disease-free survival (p=0.007). Also, it was an independent prognostic factor in overall survival (p=0.047). High expression of both Bmi1 and EZH2, not each alone, is an independent poor prognostic factor in ESCCs, supporting the repression of tumor suppressor gene by Bmi1 in an EZH2-dependent manner. This result suggests that both Bmi1 and EZH2, not each alone, could be potent candidates of new target therapy in ESCCs.

MicroRNA-26a regulates tumorigenic properties of EZH2 in human lung carcinoma cells

MicroRNAs (miRNAs) are a class of 21-23 nucleotide RNA molecules that play critical roles in the regulation of various cancers, including human lung cancer. Among them, miR-26a has been identified as a tumor-related regulator in several cancers, but its pathophysiologic properties and correlation with the development of human lung cancer remain unclear. In this study, it was determined that miR-26a expression is clearly down-regulated in human lung cancer tissues relative to normal tissues. Meanwhile, the overexpression of miR-26a in the A549 human lung cancer cell line dramatically inhibited cell proliferation, blocked G1/S phase transition, induced apoptosis, and inhibited cell metastasis and invasion in vitro. In contrast, a miR-26a inhibitor was used to transfect A549 cells, and the inhibition of endogenous miR-26a promoted cell metastasis and invasion. In addition, miR-26a expression inhibited the expression of enhancer of zeste homolog 2 (EZH2) and transactivated downstream target genes, including disabled homolog 2 (Drosophila) interacting protein gene (DAB2IP) and human Runt-related transcription factor 3 (RUNX3), which suggests that EZH2 is a potential target of miR-26a as previously reported. In conclusion, miR-26a plays an important role as an anti-oncogene in the molecular mechanism of human lung cancer and could potentially be used for the treatment of lung cancer.

Polycomb genes and cancer: time for clinical application?

Polycomb group genes (PcGs) are epigenetic effectors, essential for stem cell self-renewal and pluripotency. Two main Polycomb repressive complexes (PRC1, PRC2) mediate gene silencing through histone post-translational modifications. PcGs have been the focus of investigation in cancer research. Many cancer types show an over-expression of PcGs, predicting poor prognosis, metastasis and chemoresistance. Genetic polymorphisms of EZH2 (a PRC2 component) are significantly associated to lung cancer risk. Recently, 3-Deazaneplanocin A (DZNeP) was identified as an efficient inhibitor of PRC2 activity. DZNeP impairs cancer stem cell self-renewal and tumorigenicity. Despite the well-established role of PcGs in cancer stem cell biology, few studies dissected the clinical significance of these genes. In this paper, we explore PcGs as predictive and prognostic factors in oncology, with particular emphasis on what they can add to current biomarkers. We also propose a model for the rational development of DZNeP-based anticancer regimens and suggest the therapeutic applications of this drug.

Epigenetic factors in cancer development: polycomb group proteins

The role of chromatin-modifying factors in cancer biology emerged exponentially in the last 10 years, and increased attention has been focused on Polycomb group (PcG) proteins and their enzymatic activities. PcG proteins are repressive chromatin modifiers required for proliferation and development. The frequent deregulation of PcG activities in human tumors has direct oncogenic effects and results, essential for cancer cell proliferation. Here we will review the recent findings regarding PcG proteins in prospective tumor development, focusing on the molecular mechanisms that deregulate PcG expression in different tumors, at the downstream pathways to PcG expression (that contribute to cancer development) and at the mechanisms that regulate PcG recruitment to specific targets. Finally, we will speculate on the benefit of PcG inhibition for cancer treatment, reviewing potential pharmacological strategies.

EZH2 promotes malignant phenotypes and is a predictor of oral cancer development in patients with oral leukoplakia

Oral leukoplakia (OL) is the most common premalignancy in the oral cavity. A small proportion of OLs progresses to oral squamous cell carcinoma (OSCC). To assess OSCC risk of OLs, we investigated the role of the transcriptional repressor enhancer of zeste homolog 2 (EZH2) in oral tumorigenesis and its clinical implication as an OSCC risk predictor. Immunohistochemistry was used to measure EZH2 expression in OLs from 76 patients, including 37 who later developed OSCC and 39 who did not. EZH2 expression was associated with clinicopathologic parameters and clinical outcomes. To determine the biological role of EZH2 in OL, EZH2 level was reduced using EZH2 siRNAs in Leuk-1 cells, its impact on cell cycle, anchorage-dependent/independent growth, and invasion was assessed. We observed strong EZH2 expression in 34 (45%), moderate expression in 26 (34%), and weak/no expression in 16 (21%) of the OLs. The higher EZH2 levels were strongly associated with dysplasia (P < 0.001) and OSCC development (P < 0.0001). Multivariate analysis indicated that EZH2 expression was the only independent factor for OSCC development (P < 0.0001). At 5 years after diagnosis, 80% of patients whose OLs expressed strong EZH2 developed OSCC whereas only 24% patients with moderate and none with weak/no EZH2 expression did so (P < 0.0001). In Leuk-1 cells, EZH2 downregulation resulted in G(1) arrest; decreased invasion capability, decreased anchorage-independent growth; downregulation of cyclin D1 and upregulation of p15(INK4B). Our data suggest that EZH2 plays an important role in OL malignant transformation and may be a biomarker in predicting OSCC development in patients with OLs.

Enhancer of zeste homolog 2 expression is associated with tumor cell proliferation and invasion in cervical cancer

INTRODUCTION

Enhancer of zeste homolog 2 (EZH2) has been reported to be associated with biological malignancy in several cancers. High expression of EZH2 is associated with tumor cell proliferation, invasion and metastasis and has important clinicopathologic significance. However, little is known about the function and mechanisms of EZH2 in cervical cancer.

METHODS

This study was conducted to investigate the clinical value of EZH2 expression in cervical cancer and the association between EZH2 and possible downstream proteins using EZH2-targeted interfering RNA.

RESULTS

EZH2 expression rate was significantly greater in cervical cancer tissue than in normal cervical tissue both in mRNA and protein level. High EZH2 expression was significantly associated with differentiation, depth and lymphatic invasion. EZH2 gene RNAi resulted in inhibition of cell growth, cell cycle arrest and decreased ability of invasion in C33A cells. PCNA and MMP-2 expressions were downregulated, whereas p21 was upregulated after inhibition of EZH2.

CONCLUSIONS

High EZH2 expression may be associated with tumor cell proliferation and invasion in cervical cancer, and that EZH2 may be one of the candidates for new molecular therapeutic targets for the treatment of cervical cancer.

The expression pattern of polycomb group protein Ezh2 during mouse embryogenesis

The Polycomb group (PcG) family proteins are required for the stability of homeotic selector genes and other genes related to the regulation of mammalian development through their roles in the modulation of chromatin domains. Among them, the mammalian enhancer zeste homologue 2 (Ezh2) contributes to the transcriptional repression of these genes. Previous studies tracked the Ezh2 expression at cDNA and mRNA levels during mouse development. However, little information is known about the expression patterns of Ezh2 at the protein levels. In this study, the embryos (E6.5-E18.5) obtained through timed matings of strain Kunming mice were inserted into paraffin blocks. Tissue microarrays were constructed and followed by subsequent immunohistochemical staining. The positive cells were identified and scored based on both the percentage of stained cells and their staining intensities. Ezh2 protein expression was found throughout the embryonic tissues including the nerves, intestine epithelial, liver, pancreas, renal tubule, and lungs. Its expression level was higher at early embryonic developmental stages. However, the nerve fibers and myocardium showed weak or no immunostaining reactivities. Ezh2 protein was moderately expressed in the nuclei of renal tubule epithelial cells at E14.5. In contrast, it was weakly expressed in the fetal kidneys at E18.5 and the protein was localized in the cytoplasm of the renal tubule epithelial cells. Our data confirmed that Ezh2 protein was expressed in mouse embryos and its expression exhibited tissue specificity and dependence on the stages of embryo development. thus providing new information helpful for understanding the possible roles of Ezh2 in embryogenesis.

Increased risk for distant metastasis in patients with familial early-stage breast cancer and high EZH2 expression

The identification of women with early-stage breast cancer who will develop distant metastasis may improve clinical management. The transcriptional regulator Enhancer of Zeste-2 (EZH2) is overexpressed in invasive breast carcinoma compared with benign breast tissues, with maximal expression in breast cancer metastasis. In this article, our purpose was to investigate the performance of EZH2 protein detection as a predictor of metastasis in women with early-stage breast cancer, which is unknown. We developed a cohort of 480 women with stage I-IIA breast cancer diagnosed between 1996 and 2002 and recorded detailed sociodemographic, clinical, and pathological information. Tumors were histologically characterized and arrayed in tissue microarrays containing 1,443 samples. The nuclear EZH2 expression was investigated by immunohistochemistry and was scored as 1-2 (negative and weak) or 3-4 (moderate and strong) using a validated scoring schema. Scores 1-2 were considered low EZH2; scores 3-4 were considered high EZH2. In this study, we found that after a median follow up of 9 years (range 0.04-14.5 years) 46 of 480 patients (9.6%) developed distant metastasis. High EZH2 was associated with larger size, high histological grade, negative hormone receptors, and first degree family history of breast and/or ovarian carcinoma. While EZH2 could not predict survival in the entire cohort, high EZH2 was a predictor of disease-specific survival in patients with early-stage disease and first degree family history (log rank P value 0.05). Importantly, in this group of patients, high EZH2 was an independent predictor of distant metastasis up to 15 years after primary carcinoma diagnosis (hazard ratio 6.58, 95% CI: 1.40-30.89, P = 0.016) providing survival information above and beyond currently used prognosticators. In conclusion, EZH2 may be a useful biomarker of long-term metastatic risk in women with familial early-stage breast cancer, and warrant further validation studies.