Clinical significance of enhancer of zeste homolog 2 expression in colorectal cancer cases

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.

The role of non-coding RNAs in chemotherapy for gastrointestinal cancers

Gastrointestinal (GI) cancers, including colorectal, gastric, hepatic, esophageal, and pancreatic tumors, are responsible for large numbers of deaths around the world. Chemotherapy is the most common approach used to treat advanced GI cancer. However, chemoresistance has emerged as a critical challenge that prevents successful tumor elimination, leading to metastasis and recurrence. Chemoresistance mechanisms are complex, and many factors and pathways are involved. Among these factors, non-coding RNAs (ncRNAs) are critical regulators of GI tumor development and subsequently can induce resistance to chemotherapy. This occurs because ncRNAs can target multiple signaling pathways, affect downstream genes, and modulate proliferation, apoptosis, tumor cell migration, and autophagy. ncRNAs can also induce cancer stem cell features and affect the epithelial-mesenchymal transition. Thus, ncRNAs could possibly act as new targets in chemotherapy combinations to treat GI cancer and to predict treatment response.

Histone Methyltransferase EZH2: A Potential Therapeutic Target for Kidney Diseases

Enhancer of zeste homolog 2 (EZH2) is a histone-lysine N-methyltransferase enzyme that catalyzes the addition of methyl groups to histone H3 at lysine 27, leading to gene silencing. Mutation or over-expression of EZH2 has been linked to many cancers including renal carcinoma. Recent studies have shown that EZH2 expression and activity are also increased in several animal models of kidney injury, such as acute kidney injury (AKI), renal fibrosis, diabetic nephropathy, lupus nephritis (LN), and renal transplantation rejection. The pharmacological and/or genetic inhibition of EZH2 can alleviate AKI, renal fibrosis, and LN, but potentiate podocyte injury in animal models, suggesting that the functional role of EZH2 varies with renal cell type and disease model. In this article, we summarize the role of EZH2 in the pathology of renal injury and relevant mechanisms and highlight EZH2 as a potential therapeutic target for kidney diseases.

LINC00565 promotes the progression of colorectal cancer by upregulating EZH2

The present study aimed to illustrate the role of LINC00565 in aggravating colorectal cancer (CRC) by targeting enhancer of zeste homolog 2 (EZH2). The relative levels of LINC00565 and EZH2 in CRC tissues, based on their Tumor-Node-Metastasis stage and tumor size, were detected by reverse transcription-quantitative polymerase chain reaction. The diagnostic value of LINC00565 in CRC was assessed by depicting receiver operating characteristic curves. Pearson's correlation test was applied to analyze the expression correlation between LINC00565 and EZH2 in CRC tissues. The transfection efficacy of three LINC00565 small interfering RNAs was examined in CRC HCT116 and SW480 cell lines. After knockdown of LINC00565, the proliferative and migratory abilities of CRC cells were detected by Cell Counting Kit-8 and Transwell assays, respectively. The subcellular distribution of LINC00565 was analyzed, and the interaction between LINC00565 and EZH2 was determined by RNA immunoprecipitation. Finally, co-regulation of LINC00565 and EZH2 on CRC cell functions was explored by performing rescue experiments. Results showed that LINC00565 was upregulated in CRC tissues, especially in patients with stage III+IV and in those with large tumor sizes, suggesting its diagnostic value in CRC. EZH2 was also upregulated in CRC tissues, showing a positive correlation with LINC00565. LINC00565 was mainly expressed in the cytoplasm and was found to bind with EZH2. Validation was performed by overexpressing EZH2, which abolished the role of silenced LINC00565 in regulating proliferative and migratory abilities in CRC. Therefore, the upregulation of LINC00565 in CRC tissues was found to stimulate the aggravation of CRC by upregulating EZH2.

Loss of enhancer of zeste homologue 2 (EZH2) at tumor invasion front is correlated with higher aggressiveness in colorectal cancer cells

PURPOSE

Enhancer of zeste homolog 2 (EZH2) is associated with epigenetic gene silencing and aggressiveness in many tumor types. However, the prognostic impact of high EZH2 expression is controversially discussed for colorectal cancer. For this reason, we immunohistochemically analyzed EZH2 expression in 105 specimens from colon cancer patients separately for tumor center and invasion front.

METHODS

All sections from tissue microarrays were evaluated manually and digitally using Definiens Tissue Studio software (TSS). To mirror-image the EZH2 status at the tumor invasion front, we treated HCT116 colon cancer cells with the EZH2 inhibitor 3-Deazaneplanocin A (DZNep) and studied the growth of in ovo xenografts in the chorioallantoic membrane (CAM) assay.

RESULTS

We showed a significant decrease in EZH2 expression and the repressive H3K27me3 code at the tumor invasion front as supported by the TSS-constructed heatmaps. Loss of EZH2 at tumor invasion front, but not in tumor center was correlated with unfavorable prognosis and more advanced tumor stages. The observed cell cycle arrest in vitro and in vivo was associated with higher tumor aggressiveness. Xenografts formed by DZNep-treated HCT116 cells showed loosely packed tumor masses, infiltrative growth into the CAM, and high vessel density.

CONCLUSION

The differences in EZH2 expression between tumor center and invasion front as well as different scoring and cutoff values can most likely explain controversial literature data concerning the prognostic value of EZH2. Epigenetic therapies using EZH2 inhibitors have to be carefully evaluated for each specific tumor type, since alterations in cell differentiation might lead to unfavorable results.

MicroRNA-31 triggers G2/M cell cycle arrest, enhances the chemosensitivity and inhibits migration and invasion of human gastric cancer cells by downregulating the expression of zeste homolog 2 (ZH2)

Gastric cancer is the second most leading cause of cancer related mortality across the world over. Although the incidence of GC has declined to some extent but it is still the fourth highly diagnosed cancer across the world. GC generally remains undiagnosed till advanced stages due to unavailability of biomarkers and when diagnosed it becomes difficult to manage due to the lack of therapeutic targets and efficient chemotherapy. There are concrete evidences suggesting that miRNAs may prove important therapeutic targets for the treatment of devastating diseases such as cancer. The study was designed to investigate the tumor suppressive role of miR-31 via regulation of zeste homolog 2 (ZH2). It was found that miR-31 is significantly downregulated in GC cell lines. Overexpression of miR-31 causes significant (P < 0.05) decrease in the viability and colony formation via initiation of G2/M cell cycle arrest of the AGS cancer cells. Moreover, miR-31 overexpression also enhanced the chemosensitivity of miR-31 to the anticancer drug 5-fluorouracil. In silico analysis together with dual luciferase reporter assay indicated zeste homolog 2 (ZH2) to be the potential target of miR-31 in AGS cells. Investigation of ZH2 expression in GC cell lines showed it to be significantly (P < 0.05) upregulated. Nonetheless, overexpression of miR-31 in AGS cells resulted in the suppression of ZH2 expression. Additionally, silencing of ZH2 in the AGS cells also caused inhibition of AGS cell proliferation and colony formation via G2/M arrest. Moreover, overexpression of ZH2 could at least partially reverse the tumor suppressive effects of miR-31 indicating direct involvement of ZH2 in the miR-31 mediated inhibitory effects on AGS cell proliferation. Finally, miR-31 overexpression caused significant (P < 0.05) inhibition of the migration and invasion of the AGS gastric cancer cells. The overexpression of miR-31 also caused downregulation of mesenchymal markers (Vimentin and N-cadherin) and upregulation of epithelial marker (E-cadherin) protein expression was in AGS cells. It is therefore concluded that miR-31 acts as a tumor suppressor and may prove essential in the treatment of GC.

Prognostic value of histone marks H3K27me3 and H3K9me3 and modifying enzymes EZH2, SETDB1 and LSD-1 in colorectal cancer

PURPOSE

Studies on the performance of epigenetic-based biomarkers in colorectal cancer (CRC) are scarce and have shown contradictory results. Thus, we sought to examine the prognostic value of histone-modifying enzymes (EZH2, SETDB1 and LSD-1) and histone post-translational marks (H3K27me3 and H3K9me3) in CRC.

METHODS

A retrospective series of 207 CRC patients primarily submitted to surgery in a cancer center was included in this study. Clinicopathological data were retrieved. One representative paraffin block per case was selected for immunohistochemistry, including normal and CRC tissues whenever possible. The percentage of positive nuclear staining (digital image analysis) was used to classify patients into "low" and "high" expression groups for each biomarker. Correlations between immunoexpression levels, clinicopathological features and clinical outcomes [disease-specific (DSS) and disease-free (DFS) survival] were examined. Statistical significance was set at p < 0.05.

RESULTS

CRC tissues showed significantly lower expression of SETDB1 and higher expression of the remainder four biomarkers compared to normal mucosa. High EZH2 expression correlated with disease recurrence/progression, whereas low LSD1 expression and high H3K9me3 and H3K27me3 expression were associated with more advanced stage. In multivariable analysis, cases with high LSD1 expression displayed significantly better DSS and DFS (HR 0.477, 95% confidence interval: 0.247-0.923) adjusted for pathological TNM stage.

CONCLUSION

EZH2, SETDB1, LSD1, H3K9me3 and H3K27me3 expression are altered in CRC and may play a role in colorectal carcinogenesis. LSD1 immunoexpression levels independently predicted patient outcome in this cohort. Further investigations, using larger series, are warranted to confirm its potential clinical value and unravel underlying molecular mechanisms.

The expression of histone deacetylase HDAC1 correlates with the progression and prognosis of gastrointestinal malignancy

Gastrointestinal malignancy is a severe public health threat worldwide, and survival for most types of gastrointestinal cancer is very poor. Therefore, finding better cancer biomarkers to diagnose gastrointestinal malignancy and predict patient survival is essential. HDAC1 has been reported to be closely associated with several types of cancer, but the precise role of HDAC1 in gastrointestinal cancer is not clear. Recently, quite a few studies have investigated the correlation between HDAC1 expression and clinical features or prognosis in multiple types of gastrointestinal malignancies, but the results were inconsistent. In this study, we systematically reviewed the association between HDAC1 and gastrointestinal malignancy using meta-analysis methods, and 28 eligible studies were analyzed. We found that the expression level of HDAC1 in gastrointestinal malignancies, especially in colorectal cancer (OR = 10.84, 95% CI = 5.33-22.07, P< 0.00001), was higher than that in noncancerous tissue, and HDAC1 expression was closely associated with some clinical features of gastrointestinal cancer patients, such as tumor stage (OR = 1.62, 95% CI = 1.28-2.05, P < 0.0001) and tumor grade (OR = 1.75, 95% CI = 1.03-2.95, P = 0.04). In addition, we also found that patients with low HDAC1 expression showed better overall survival than those with high HDAC1 expression in gastrointestinal malignancy, especially in gastric cancer (HR = 1.88, 95% CI = 1.14-3.12, P = 0.01). Our results strongly suggest that HDAC1 may serve as a good diagnostic and prognostic marker for gastrointestinal malignancy.

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.

The role of EZH2 in overall survival of colorectal cancer: a meta-analysis

Enhancer of zeste homolog 2 (EZH2) is the catalitic subunit of polycomb repressive complex 2 and mediates gene silencing. EZH2 is overexpressed in many cancers and correlates with poor prognosis. The role of the gene EZH2 in colorectal cancer survival is uncertainly, the aim of this study is clear this relationship. Relevant literaure was searched from electronic databases. A meta-analysis was performed with elegible studies which quantitatively evaluated the relationship between EZH2 overexpression and survival of patients with colorectal cancer. Survival data were aggregated and quantitatively analyzed. We performed a meta-analysis of 8 studies (n = 1059 patients) that evaluated the correlation between EZH2 overexpression and survival in patients with colorectal cancer. Combined hazard ratios suggested that EZH2 overexpression was associated with better prognosis of overall survival (OS) HR(hazard ratio) = 0.61 95% CI (0.38-0.84) We performed bias analysis according Egger and Begg,s test and we did not find publication bias. EZH2 overexpression indicates a better prognosis for colorectal cancer.

Prognostic value of high EZH2 expression in patients with different types of cancer: a systematic review with meta-analysis

Enhancer of zeste homologue 2 (EZH2) is a potential independent mechanism for epigenetic silencing of tumor suppressor genes in cancer. We conducted an electronic search on PubMed, EMBASE, Web of Science, and Cochrane library to perform this up-to-date meta-analysis. Fifty-one studies with a total of 9444 patients were included. The prevalence of high EZH2 expression was 0.54 (95% CI: 0.47-0.61). High EZH2 expression was significantly associated with poorer prognosis [overall survival: HR 1.54 (95% CI: 1.30-1.78), P < 0.000; disease free survival: HR 1.35 (95% CI: 1.00-1.71), P < 0.000]. In breast cancer, high EZH2 expression correlated with histological types [OR: 1.53 (95CI: 1.13-2.06); P < 0.006], histological grade [OR: 1.62 (95CI: 1.35-1.95); P < 0.000], estrogen receptor (ER) negativity [OR: 2.05 (95CI: 1.67-2.52); P < 0.000], progesterone receptor (PgR) negativity [OR: 1.42 (95CI: 1.03-1.96); P = 0.034], HER-2 positivity [OR: 1.35 (95CI: 1.08-1.69); P = 0.009], and high p53 expression [OR: 1.66 (95CI: 1.07-2.59); P = 0.024]. These results suggest that high EZH2 expression may be a promising prognostic factor to different cancers. High EZH2 expression tends to correlate with pathological types, histological grade, ER negativity, PgR negativity, HER-2 positivity and p53 high expression in breast cancer.

PRC2 Epigenetically Silences Th1-Type Chemokines to Suppress Effector T-Cell Trafficking in Colon Cancer

Infiltration of tumors with effector T cells is positively associated with therapeutic efficacy and patient survival. However, the mechanisms underlying effector T-cell trafficking to the tumor microenvironment remain poorly understood in patients with colon cancer. The polycomb repressive complex 2 (PRC2) is involved in cancer progression, but the regulation of tumor immunity by epigenetic mechanisms has yet to be investigated. In this study, we examined the relationship between the repressive PRC2 machinery and effector T-cell trafficking. We found that PRC2 components and demethylase JMJD3-mediated histone H3 lysine 27 trimethylation (H3K27me3) repress the expression and subsequent production of Th1-type chemokines CXCL9 and CXCL10, mediators of effector T-cell trafficking. Moreover, the expression levels of PRC2 components, including EZH2, SUZ12, and EED, were inversely associated with those of CD4, CD8, and Th1-type chemokines in human colon cancer tissue, and this expression pattern was significantly associated with patient survival. Collectively, our findings reveal that PRC2-mediated epigenetic silencing is not only a crucial oncogenic mechanism, but also a key circuit controlling tumor immunosuppression. Therefore, targeting epigenetic programs may have significant implications for improving the efficacy of current cancer immunotherapies relying on effective T-cell-mediated immunity at the tumor site.

Th22 cells control colon tumorigenesis through STAT3 and Polycomb Repression complex 2 signaling

Th22 cells traffic to and retain in the colon cancer microenvironment, and target core stem cell genes and promote colon cancer stemness via STAT3 and H3K79me2 signaling pathway and contribute to colon carcinogenesis. However, whether Th22 cells affect colon cancer cell proliferation and apoptosis remains unknown. We studied the interaction between Th22 cells and colon cancer cells in the colon cancer microenvironment. Colon cancer proliferation was examined by flow cytometry analysis and H(3) thymidine incorporation. Cell cycle related genes were quantified by real-time PCR and Western blotting. We transfected colon cancer cells with lentiviral vector encoding specific gene shRNAs and used chromatin immunoprecipitation (ChIP) assay to determine the genetic signaling involved in interleukin (IL)-22-mediated colon cancer cell proliferation. We showed that Th22 cells released IL-22 and stimulated colon cancer proliferation. Mechanistically, IL-22 activated STAT3, and subsequently STAT3 bound to the promoter areas of the Polycomb Repression complex 2 (PRC2) components SUZ12 and EED, and stimulated the expression of PRC2. Consequently, the activated PRC2 catalyzed the promoters of the cell cycle check-point genes p16 and p21, and inhibited their expression through H3K27me3-mediated histone methylation, and ultimately caused colon cancer cell proliferation. Bioinformatics analysis revealed that the levels of IL-22 expression positively correlated with the levels of genes controlling cancer proliferation and cell cycling in colon cancer. In addition to controlling colon cancer stemness, Th22 cells support colon carcinogenesis via affecting colon cancer cell proliferation through a distinct histone modification.

Dysregulated Class I histone deacetylases are indicators of poor prognosis in multiple myeloma

Histone deacetylases (HDAC) control gene expression through their ability to acetylate proteins, thereby influencing a diverse range of cellular functions. Class I HDAC (HDAC1-3 and 8) and HDAC6 are predominantly upregulated in malignancies and their altered expression in some cancers has a significant prognostic implication. The expression and prognostic consequence of dysregulated Class I HDAC and HDAC6, key players in multiple myeloma (MM), are unknown. This study hypothesized that HDAC are dysregulated in MM and patients with high expression have significantly poorer prognostic outcomes. Quantitative PCR for 11 HDAC (Class I, II, and IV) was performed in genetically heterogeneous human myeloma cell lines (HMCL) and primary MM and compared to normal plasma cells (PC). In HMCL, HDAC1-3 and 8 (Class I), and HDAC5 and HDAC10 (Class II) were significantly upregulated compared to normal PC. In primary MM, the median expression level of all of the HDAC, except HDAC1 and HDAC11, were elevated when compared to normal PC. Patients with higher levels of HDAC1-3, HDAC4, HDAC6, and HDAC11 transcripts demonstrated a significantly shorter progression-free survival (PFS). Immunohistochemical staining for HDAC1 and HDAC6 on bone marrow trephines from a uniformly treated cohort of transplant eligible MM patients revealed that HDAC1 protein was detectable in most patients and that higher levels of MM cell HDAC1 protein expression (≥90 % versus ≤20 % MM cell positivity) correlated with both shorter PFS (P = 0 .07) and shorter overall survival (P = 0 .003). Conversely, while the majority of patients expressed HDAC6, there was no correlation between HDAC6 levels and patient outcome. Together, these results indicate that overexpression of Class I HDAC, particularly HDAC1, is associated with poor prognosis in MM.

Enhancer of zeste homolog 2 as an independent prognostic marker for cancer: a meta-analysis

Background

Novel biomarkers are of particular interest for predicting cancer prognosis. This study aimed to explore the associations between enhancer of zeste homolog 2 (EZH2) and patient survival in various cancers.

Methods

Relevant literature was retrieved from PubMed and Web of Science databases. Pooled hazard ratios (HRs), odds ratios (ORs), and 95% confidence intervals (CIs) were calculated.

Results

Forty-nine studies (8,050 patients) were included. High EZH2 expression was significantly associated with shorter overall (hazard ratio [HR] 1.74, 95% CI: 1.46–2.07), disease-free (HR 1.59, 95% CI: 1.27–1.99), metastasis-free (HR 2.19, 95% CI: 1.38–3.47), progression-free (HR 2.53, 95% CI: 1.52–4.21), cancer-specific (HR 3.13, 95% CI: 1.70–5.74), and disease-specific (HR 2.29, 95% CI: 1.56–3.35) survival, but not recurrence-free survival (HR 1.38, 95% CI: 0.93–2.06). Moreover, EZH2 expression significantly correlated with distant metastasis (OR 3.25, 95% CI: 1.07–9.87) in esophageal carcinoma; differentiation (OR 3.00, 95% CI: 1.37–6.55) in non-small cell lung cancer; TNM stage (OR 3.18, 95% CI: 2.49–4.08) in renal cell carcinoma; and histological grade (OR 4.50, 95% CI: 3.33–6.09), estrogen receptor status (OR 0.15, 95% CI: 0.11–0.20) and progesterone receptor status (OR 0.30, 95% CI: 0.23–0.39) in breast cancer.

Conclusions

Our results suggested that EZH2 might be an independent prognostic factor for multiple survival measures in different cancers.

SSX2 is a novel DNA-binding protein that antagonizes polycomb group body formation and gene repression

Polycomb group (PcG) complexes regulate cellular identity through epigenetic programming of chromatin. Here, we show that SSX2, a germline-specific protein ectopically expressed in melanoma and other types of human cancers, is a chromatin-associated protein that antagonizes BMI1 and EZH2 PcG body formation and derepresses PcG target genes. SSX2 further negatively regulates the level of the PcG-associated histone mark H3K27me3 in melanoma cells, and there is a clear inverse correlation between SSX2/3 expression and H3K27me3 in spermatogenesis. However, SSX2 does not affect the overall composition and stability of PcG complexes, and there is no direct concordance between SSX2 and BMI1/H3K27me3 presence at regulated genes. This suggests that SSX2 antagonizes PcG function through an indirect mechanism, such as modulation of chromatin structure. SSX2 binds double-stranded DNA in a sequence non-specific manner in agreement with the observed widespread association with chromatin. Our results implicate SSX2 in regulation of chromatin structure and function.

Role of EZH2 polymorphisms in esophageal squamous cell carcinoma risk in Han Chinese population

Gene single nucleotide polymorphisms play a critical role in the development of esophageal squamous cell carcinoma (ESCC). The aim of this study is to investigate the associations between EZH2 gene polymorphisms and ESCC risk. We undertook a case-control study to analyze three EZH2 polymorphisms (148505302C>T, 2110+6A>C and 626-394T>C) in an Han Chinese population, by extraction of genomic DNA from the peripheral blood of 476 patients with ESCC and 492 control participants, and performed EZH2 genotyping using DNA sequencing. The obtained results indicated that overall, no statistically significant association was observed in 148505302C>T and 2110+6A>C. However, 626-394T>C genotype was at increased risk of ESCCs (p=0.006; odds ratio (OR)=1.131, CI 95%: 1.034-1.236). Moreover, 626-394C/C genotype ESCCs were more significantly common in patients with tumor size of >5 cm than T allele ESCC and in cases of poor differentiation and lower advanced pathological stage. In conclusion, polymorphism in 626-394T>C was observed to be associated with susceptibility of ESCC. Nevertheless, further investigation with a larger sample size is needed to support our results.

Association between EZH2 polymorphisms and colorectal cancer risk in Han Chinese population

The aim of this study is to investigate the associations between EZH2 gene polymorphisms and colorectal cancer (CRC) risk. We undertook a case-control study to analyze three EZH2 polymorphisms (148505302C>T, 2110+6A>C and 626-394T>C) in an Han Chinese population, by extraction of genomic DNA from the peripheral blood of 512 patients with CRC and 546 control participants, and performed EZH2 genotyping using DNA sequencing. The obtained results indicated that overall, no statistically significant association was observed in 2,110+6A>C. Nevertheless, 148505302C>T genotype demonstrated a protective effect in CRCs (P=0.014; odds ratio (OR) 0.777, CI 95%:0.647-0.933). Furthermore, 148505302 T allele CRC was more significantly common in patients with tumor size of <4 cm than C allele CRC and in cases of good differentiation and lower advanced pathological stage. However, 626-394T>C genotype was at increased risk of CRCs (P<0.001; odds ratio (OR) 1.457, CI 95%:1.160-1.829). Moreover, 626-394C/C genotype CRCs were more significantly common in patients with tumor size of >4 cm than T allele CRC and in cases of poor differentiation and lower advanced pathological stage. In conclusion, polymorphism in 626-394T>C was observed to be associated with susceptibility of CRC. However, 148505302C>T polymorphism indicated to play a protective role in susceptibility to CRC. Nevertheless, further investigation with a larger sample size is needed to support our results.

High expression of H3K27me3 is an independent predictor of worse outcome in patients with urothelial carcinoma of bladder treated with radical cystectomy

It has been suggested that trimethylation of lysine 27 on histone H3 (H3K27me3) is a crucial epigenetic process in tumorigenesis. However, the expression pattern of H3K27me3 and its clinicopathological/prognostic significance in urothelial carcinoma of bladder (UCB) are unclear. In this study, upregulated expression of H3K27me3 protein was observed in the majority of UCBs by Western blotting. High expression of H3K27me3 was examined by IHC in 59/126 (46.8%) of UCB tissues and in 18/72 (25.0%) of normal urothelial bladder epithelial tissues (P = 0.002). High expression of H3K27me3 was associated with multifocal tumors and lymph node metastases (P < 0.05). Patients with high expression of H3K27me3 had shorter cancer-specific survival (CSS) time than patients with low expression of H3K27me3 (P < 0.001). In different subsets of UCB patients, high expression of H3K27me3 was also a prognostic indicator in patients with grade 2 and grade 3, pT1, pT2, pT3, and pN− disease (P < 0.05). Importantly, expression of H3K27me3 was an independent predictor for CSS (P < 0.001) of UCB patients treated with radical cystectomy (RC). Our data suggests that high expression of H3K27me3 is an independent molecular marker for predicting poor prognosis of UCB patients treated with RC.

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.

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.

Histone modifications as a pathogenic mechanism of colorectal tumorigenesis

Epigenetic regulation of gene expression has provided colorectal cancer (CRC) pathogenesis with an additional trait during the past decade. In particular, histone post-translational modifications set up a major component of this process dictating chromatin status and recruiting non-histone proteins in complexes formed to "handle DNA". In CRC, histone marks of aberrant acetylation and methylation levels on specific residues have been revealed, along with a plethora of deregulated enzymes that catalyze these reactions. Mutations, deletions or altered expression patterns transform the function of several histone-modifying proteins, further supporting the crucial role of epigenetic effectors in CRC oncogenesis, being closely associated to inactivation of tumor suppressor genes. Elucidation of the biochemical basis of these new tumorigenic mechanisms allows novel potential prognostic factors to come into play. Moreover, the detection of these changes even in early stages of the multistep CRC process, along with the reversible nature of these mechanisms and the technical capability to detect such alterations in cancer cells, places this group of covalent modifications as a further potential asset for clinical diagnosis or treatment of CRC. This review underlines the biochemistry of histone modifications and the potential regulatory role of histone-modifying proteins in CRC pathogenesis, to date. Furthermore, the underlying mechanisms of the emerging epigenetic interplay along with the chemical compounds that are candidates for clinical use are discussed, offering new insights for further investigation of key histone enzymes and new therapeutic targets.

An EZH2 polymorphism is associated with clinical outcome in metastatic colorectal cancer patients

BACKGROUND

Despite therapeutic innovations, metastatic colorectal cancer (mCRC) is still characterized by poor prognosis and few molecular markers predict the risk of progression. Polycomb group genes (PcGs) are epigenetic modifiers involved in tumor suppressor gene silencing. PcG member EZH2 mediates gene silencing through histone-H3 lysine-27 methylation. In colorectal cancer (CRC), EZH2 overexpression predicts shorter survival. Recently, four EZH2 single-nucleotide polymorphisms (SNPs) have been described. The present study was aimed at evaluating the correlation between EZH2 SNPs and outcome parameters in mCRC patients.

PATIENTS AND METHODS

DNA was extracted from blood samples of 110 mCRC patients treated with first-line 5-fluorouracil, folinic acid, irinotecan (FOLFIRI) and bevacizumab. Genotyping was carried out by real-time PCR. Genotype was used to predict objective response, progression-free survival (PFS) and overall survival (OS). EZH2 messenger RNA levels were evaluated on lymphocytes of a parallel cohort of 50 CRC patients.

RESULTS

One allelic variant (rs3757441 C/C versus C/T or T/T) was significantly associated with shorter PFS and OS (P < 0.01 and P < 0.05, respectively). At multivariate analysis, the same variant resulted an independent predictor of PFS and OS (P < 0.05). The C/C variant was associated with significantly higher EZH2 expression (P < 0.05).

CONCLUSION

An EZH2 SNP may be useful to predict clinical outcome in mCRC patients.

Vitamin D has wide regulatory effects on histone demethylase genes

Vitamin D from the diet or synthesized in the skin upon UV-B irradiation is converted in the organism into the active metabolite 1α,25- dihydroxyvitamin D 3 [1,25(OH) 2D 3, calcitriol], a pleiotropic hormone with wide regulatory actions. The classical model of 1,25(OH)2D3 action implies the activation of the vitamin D receptor, which binds specific DNA sequences in its target genes and modulates their transcription rate. We have recently shown that 1,25(OH) 2D 3 induces the expression of the JMJD3 gene coding for a histone demethylase that is involved in epigenetic regulation. JMJD3 mediates the effects of 1,25(OH) 2D 3 on a subset of target genes and affects the expression of ZEB1, ZEB2 and SNAI1, inducers of epithelial-mesenchymal transition. Novel data indicate that 1,25(OH) 2D 3 has an unanticipated wide regulatory action on the expression of genes coding for histone demethylases of the Jumonji C (JmjC) domain and lysine-specific demethylase (LSD) families. Moreover, JMJD3 knockdown decreases the expression of miR‑200b and miR‑200c, two microRNAs targeting ZEB1 RNA. This may explain the upregulation of this transcription factor found in JMJD3-depleted cells. Thus, 1,25(OH) 2D 3 exerts an ample regulatory effect on the expression of histone-modifying enzymes involved in epigenetic regulation that may mediate its actions on gene transcription and cell phenotype.

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.

Extra sex combs, chromatin, and cancer: exploring epigenetic regulation and tumorigenesis in Drosophila

Developmental genetic studies in Drosophila unraveled the importance of Polycomb group (PcG) and Trithorax group (TrxG) genes in controlling cellular identity. PcG and TrxG proteins form histone modifying complexes that catalyze repressive or activating histone modifications, respectively, and thus maintaining the expression status of homeotic genes. Human orthologs of PcG and TrxG genes are implicated in tumorigenesis as well as in determining the prognosis of individual cancers. Recent whole genome analyses of cancers also highlighted the importance of histone modifying proteins in controlling tumorigenesis. Comprehensive understanding of the mechanistic relationship between histone regulation and tumorigenesis holds the promise of significantly advancing our understanding and management of cancer. It is anticipated that Drosophila melanogaster, the model organism that contributed significantly to our understanding of the functional role of histone regulation in development, could also provide unique insight for our understanding of how histone dysregulation can lead to cancer. In this review, we will discuss several recent advances in this regard.

Roles of the Polycomb group proteins in stem cells and cancer

Polycomb group proteins have long been linked to the occurrence of different forms of cancer. Polycomb proteins form at least two distinct complexes, the Polycomb-repressive complexes 1 and 2 (PRC1 and PRC2). Some of the PRC complex subunits have been found to be overexpressed in a variety of different tumors. Epigenetic perturbations are likely to be the cause for transcriptional misregulation of tumor suppressor genes and of certain cell fates. It is especially critical for stem cells that their potential to self-renewal and to differentiate is tightly controlled and properly orchestrated. Misregulation of Polycomb protein levels often leads to either a block or unscheduled activation of developmental pathways, thereby enhancing the proliferation capability of a cell. The consequences of this misregulation have been linked to the establishment of cancer stem cells, which can produce tumors through a combination of increased self-renewal and the lack of complete cellular differentiation. Cancer stem cells are believed to persist within tumors and to elicit relapse and metastasis. In this review, we recapitulate the roles of Polycomb proteins in stem cell biology, and the impact their misregulation can have on cancer.

EZH2 depletion blocks the proliferation of colon cancer cells

The Enhancer of Zeste 2 (EZH2) protein has been reported to stimulate cell growth in some cancers and is therefore considered to represent an interesting new target for therapeutic intervention. Here, we investigated a possible role of EZH2 for the growth control of colon cancer cells. RNA interference (RNAi)-mediated intracellular EZH2 depletion led to cell cycle arrest of colon carcinoma cells at the G1/S transition. This was associated with a reduction of cell numbers upon transient transfection of synthetic EZH2-targeting siRNAs and with inhibition of their colony formation capacity upon stable expression of vector-borne siRNAs. We furthermore tested whether EZH2 may repress the growth-inhibitory p27 gene, as reported for pancreatic cancer. However, expression analyses of colon cancer cell lines and colon cancer biopsies did not reveal a consistent correlation between EZH2 and p27 levels. Moreover, EZH2 depletion did not re-induce p27 expression in colon cancer cells, indicating that p27 repression by EZH2 may be cell- or tissue-specific. Whole genome transcriptome analyses identified cellular genes affected by EZH2 depletion in colon cancer cell lines. They included several cancer-associated genes linked to cellular proliferation or invasion, such as Dag1, MageD1, SDC1, Timp2, and Tob1. In conclusion, our results demonstrate that EZH2 depletion blocks the growth of colon cancer cells. These findings might provide benefits for the treatment of colon cancer.

H3K27me3 protein is a promising predictive biomarker of patients' survival and chemoradioresistance in human nasopharyngeal carcinoma

Trimethylation of lysine 27 on histone H3 (H3K27me3) is an epigenetic change which plays a critical role in tumor development and/or progression. However, the molecular status of H3K27me3 and its clinicopathologic/prognostic significance in nasopharyngeal carcinoma (NPC) have not been elucidated. In this study, the methods of Western blotting and immunohistochemistry (IHC) were utilized to examine the expression of H3K27me3 protein in NPC tissues and nonneoplastic nasopharyngeal epithelial tissues. Receiver operating characteristic (ROC) curve analysis was used to determine the cutpoint for H3K27me3 high expression. High expression of H3K27me3 could be observed in 127/209 (60.8%) of NPCs and in 8/50 (16.0%) normal nasopharyngeal epithelial tissues (P < 0.001). Further correlation analysis demonstrated that high expression of H3K27me3 was positively associated with tumor later T classification, tumor metastasis, advanced clinical stage and chemoradioresistance (P < 0.05). Moreover, high expression of H3K27me3 was closely associated with NPC patient shortened survival time as evidenced by univariate and multivariate analysis (P < 0.05). Consequently, a new clinicopathologic prognostic model with three poor prognostic factors (H3K27me3 expression, distant metastasis and treatment regimen) was constructed. The model could stratify risk significantly (low, intermediate and high) for overall survival and progression-free survival (P < 0.0001). These findings provide evidence that H3K27me3 expression, as examined by IHC, has the potential to be used as an immunomarker to predict NPC chemoradiotherapy response and patient prognosis. The combined clinicopathologic prognostic model may become a useful tool for identifying NPC patients with different clinical outcomes.

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.

Gene silencing by the Polycomb group proteins and associations with cancer

Cancer not only is associated with inherited genetic sequences but also results from epigenetic changes. Thus, understanding the mechanisms underlying epigenetic modifications is important for cancer prevention, diagnosis, and therapy. There is much evidence showing that some Polycomb group (PcG) proteins are abnormally expressed in certain tumors. This review addresses biological functions and biochemical behaviors of the Polycomb repression complex proteins, including their enzymatic activities. Additionally, the potential mechanisms of PcG gene silencing by PcG and its link to cancers are summarized that will shed light on this novel area of study in cancer.

EZH2 supports ovarian carcinoma cell invasion and/or metastasis via regulation of TGF-beta1 and is a predictor of outcome in ovarian carcinoma patients

It was suggested that the enhancer of zeste homolog 2 (EZH2) gene is a putative candidate oncogene in several types of human cancer. The potential oncogenic role of EZH2 and its clinical/prognostic significance, however, in ovarian carcinoma are unclear. In this study, EZH2 expression was examined by immunohistochemistry (IHC) in cohorts of normal and tumorous ovarian tissues. High expression of EZH2 was examined in none of the normal ovaries, in 3% of the cystadenomas, in 23% of the borderline tumors and in 50% of the ovarian carcinomas, respectively. In the ovarian carcinomas, high expression of EZH2 was positively correlated with an ascending histological grade and/or advanced stage of the disease (P < 0.05). Moreover, high expression of EZH2 in ovarian carcinoma was determined to be a strong and an independent predictor of short overall survival (P < 0.05). In ovarian carcinoma HO-8910 and UACC-326 cell lines, EZH2 knockdown by RNA interference led to a G(1) phase cell cycle arrest, reduced cell growth/proliferation and inhibited cell migration and/or invasion in vitro. In addition, EZH2 knockdown was found to reduce transforming growth factor-beta1 (TGF-beta1) expression and increase E-cadherin expression either in the transcript or in the protein levels. Furthermore, a significant positive correlation between overexpression of EZH2 and TGF-beta1 in ovarian carcinoma tissues was observed (P < 0.001). These findings suggest a potential important role of EZH2 in the control of cell migration and/or invasion via the regulation of TGF-beta1 expression, and the high expression of EZH2, as detected by IHC, is an independent molecular marker for shortened survival time of patients with ovarian carcinoma.

High expression of EZH2 is associated with tumor aggressiveness and poor prognosis in patients with esophageal squamous cell carcinoma treated with definitive chemoradiotherapy

The enhancer of zeste homolog 2 (EZH2), a known repressor of gene transcription, has been reported to be associated with biological malignancy in several cancers. The potential oncogenic role of EZH2 and its clinical/prognostic significance, however, in esophageal squamous cell carcinoma (ESCC) are unclear. In this study, the methods of immunohistochemistry and fluorescence in-situ hybridization were used to examine protein expression and amplification of EZH2 in 98 pretreatment biopsy specimens of ESCC who received definitive chemoradiotherapy (CRT). High expression of EZH2 and amplification of EZH2 was found in 54.1% and 12.0% of ESCCs, respectively. High EZH2 expression was significantly correlated with increased cell proliferation (p = 0.009), high histopathological grade (p = 0.002), regional (p = 0.025) and distant lymph node metastasis (p < 0.001) and lack of clinical complete response to CRT (p = 0.028). Univariate analysis revealed that high expression of EZH2 was associated with poor metastasis-free survival (MFS) (p = 0.003), poor progression-free survival (PFS) (p = 0.001) and poor disease-specific survival (DSS) (p < 0.001). In multivariate analysis, high expression of EZH2, together with lack of clinical complete response, were evaluated as significant independent prognostic factors of MFS, PFS and DSS for patients with ESCC. These findings suggest that high expression of EZH2 correlates with tumor aggressiveness and adverse patient outcome in ESCC treated with definitive CRT. Evaluation of EZH2 expressions might be useful for predicting tumor response to CRT and prognosis for patients with ESCC.

EZH2 and STAT6 expression profiles are correlated with colorectal cancer stage and prognosis

AIM: To investigate the role of enhancer of zeste homologue 2 (EZH2) and STAT6 immunohistochemistry in the evaluation of clinical stages and prognosis of colorectal cancer (CRC).

METHODS: The expression patterns were examined by immunohistochemistry in both tumor and adjacent non-neoplastic tissues of 119 CRC patients who underwent operation during the time period from 2002 to 2004.

RESULTS: The positive rates of EZH2 and STAT6 in CRC cases were 69.7% (83 of 119) and 60.5% (72 of 119), respectively, and there was significant difference when compared with tumor adjacent non-neoplastic tissues (P < 0.05). In all CRC cases, patients with EZH2-positive, or STAT6-positive expression had lower survival rates than those with EZH2-negative or STAT6-negative expression (P = 0.002 and P = 0.005, respectively). Co-expression of EZH2 and STAT6 showed significantly higher levels in CRC cases of high clinical TNM stages (P = 0.001), and the expression of STAT6 was also correlated with lymph node metastasis and distant metastasis (P = 0.001 and P = 0.016, respectively). Multivariate analysis revealed that EZH2 expression was an independent prognostic indicator of CRC (P = 0.039).

CONCLUSION: EZH2 and STAT6 expressions have significant values in distinguishing clinical stages of CRC and predicting the prognosis of the patients.

The role of nuclear organization in cancer

The functional significance of changes in nuclear structure and organization in transformed cells remains one of the most enigmatic questions in cancer biology. In this review, we discuss relationships between nuclear organization and transcription in terms of the three-dimensional arrangement of genes in the interphase cancer nucleus and the regulatory functions of nuclear matrix proteins. We also analyse the role of nuclear topology in the generation of gene fusions. We speculate that this type of multi-layered analysis will one day provide a framework for a more comprehensive understanding of the genetic origins of cancer and the identification of new therapeutic targets.

Prognostic impact of H3K27me3 expression on locoregional progression after chemoradiotherapy in esophageal squamous cell carcinoma

Background

Trimethylation of lysine 27 on histone H3 (H3K27me3) by enhancer of zeste homolog 2 (EZH2) is an epigenetic mark that mediates gene silencing. EZH2 is overexpressed and correlates with poor prognosis in many cancers. However, the clinical implication of H3K27me3 in human malignancies has not been well established. We wished to ascertain whether a correlation exists between the expression of H3K27me3 and clinical outcome in a group of patients with esophageal squamous cell carcinoma (ESCC) treated with definitive chemoradiotherapy (CRT).

Methods

The method of immunohistochemistry (IHC) was utilized to examine the protein expression of H3K27me3 in 98 pretreatment biopsy specimens of ESCC and in 30 samples of normal esophageal mucosa. The clinical/prognostic significance of H3K27me3 expression was statistically analyzed.

Results

The expression frequency and expression levels of H3K27me3 were significantly higher in ESCCs than in normal tissues. There was a positive correlation between H3K27me3 expression and WHO grade (P = 0.016), tumor size (P = 0.019), T status (P = 0.024), locoregional progression (P = 0.009) and EZH2 expression (P = 0.036). High H3K27me3 expression was associated with poor locoregional progression-free survival (LPFS) (P = 0.010) in ESCC. Further analysis demonstrated that H3K27me3 could stratify patient outcome in T2-3 (P = 0.048), N0 (P = 0.005) and M0 (P = 0.018) stages as well as in CRT effective group (P = 0.022).

Conclusions

Our data suggests that H3K27me3 expression examined by IHC might be useful for stratifying LPFS for different subsets of ESCC patients treated with definitive CRT.

HDAC expression and clinical prognosis in human malignancies

Histone deacetylases are known to play a central role in the regulation of several cellular properties intimately interlinked with the development and progression of cancer. Consequently, a multitude of histone deacetylase (HDAC) inhibitors have been developed and are currently tested as anticancer agents in a variety of solid and hematologic malignancies. However, only recently research began to focus on the actual expression patterns of specific HDAC isoforms in neoplasias. The majority of studies investigating this issue reported an enhanced expression of class I HDAC isoforms in solid human tumours, both on mRNA and protein level, when compared to the respective tissue of origin. In most studies, class I HDAC expression was high in locally advanced, dedifferentiated, strongly proliferating tumours. In some but not all entities elevated class I HDAC expression was associated with compromised patient prognosis, however, an association of elevated class I HDAC expression with improved prognosis has also be reported for selected tumour entities. In contrast to class I isoforms, expression of class II HDACs has been found reduced in tumours and high expression of these isoforms in some entities predicted better patient outcome. Since all of these data point to a potential biological role of differences in HDAC expression in human tumours, future translational studies will focus on the question, whether HDAC expression patterns are predictive for response to treatment with histone deacetylase inhibitors.

The role of the polycomb complex in silencing alpha-globin gene expression in nonerythroid cells

Although much is known about globin gene activation in erythroid cells, relatively little is known about how these genes are silenced in nonerythroid tissues. Here we show that the human alpha- and beta-globin genes are silenced by fundamentally different mechanisms. The alpha-genes, which are surrounded by widely expressed genes in a gene dense region of the genome, are silenced very early in development via recruitment of the Polycomb (PcG) complex. By contrast, the beta-globin genes, which lie in a relatively gene-poor chromosomal region, are not bound by this complex in nonerythroid cells. The PcG complex seems to be recruited to the alpha-cluster by sequences within the CpG islands associated with their promoters; the beta-globin promoters do not lie within such islands. Chromatin associated with the alpha-globin cluster is modified by histone methylation (H3K27me3), and silencing in vivo is mediated by the localized activity of histone deacetylases (HDACs). The repressive (PcG/HDAC) machinery is removed as hematopoietic progenitors differentiate to form erythroid cells. The alpha- and beta-globin genes thus illustrate important, contrasting mechanisms by which cell-specific hematopoietic genes (and tissue-specific genes in general) may be silenced.

Roles of the EZH2 histone methyltransferase in cancer epigenetics

EZH2 is the catalytic subunit of Polycomb repressive complex 2 (PRC2), which is a highly conserved histone methyltransferase that targets lysine-27 of histone H3. This methylated H3-K27 chromatin mark is commonly associated with silencing of differentiation genes in organisms ranging from plants to flies to humans. Studies on human tumors show that EZH2 is frequently over-expressed in a wide variety of cancerous tissue types, including prostate and breast. Although the mechanistic contributions of EZH2 to cancer progression are not yet determined, functional links between EZH2-mediated histone methylation and DNA methylation suggest partnership with the gene silencing machinery implicated in tumor suppressor loss. Here we review the basic molecular biology of EZH2 and the findings that implicate EZH2 in different cancers. We also discuss EZH2 connections to other silencing enzymes, such as DNA methyltransferases and histone deacetylases, and we consider progress on deciphering mechanistic consequences of EZH2 overabundance and its potential roles in tumorigenesis. Finally, we review recent findings that link EZH2 roles in stem cells and cancer, and we consider prospects for integrating EZH2 blockade into strategies for developing epigenetic therapies.

Concise Review: Roles of Polycomb Group Proteins in Development and Disease: A Stem Cell Perspective

The acquisition and maintenance of cell fate are essential for metazoan growth and development. A strict coordination between genetic and epigenetic programs regulates cell fate determination and maintenance. Polycomb group (PcG) genes are identified as essential in these epigenetic developmental processes. These genes encode components of multimeric transcriptional repressor complexes that are crucial in maintaining cell fate. PcG proteins have also been shown to play a central role in stem cell maintenance and lineage specification. PcG proteins, together with a battery of components including sequence-specific DNA binding/accessory factors, chromatin remodeling factors, signaling pathway intermediates, noncoding small RNAs, and RNA interference machinery, generally define a dynamic cellular identity through tight regulation of specific gene expression patterns. Epigenetic modification of chromatin structure that results in expression silencing of specific genes is now emerging as an important molecular mechanism in this process. In embryonic stem (ES) cells and adult stem cells, such specific genes represent those associated with differentiation and development, and silencing of these genes in a PcG protein-dependent manner confers stemness. ES cells also contain novel chromatin motifs enriched in epigenetic modifications associated with both activation and repression of genes, suggesting that certain genes are poised for activation or repression. Interestingly, these chromatin domains are highly coincident with the promoters of developmental regulators, which are also found to be occupied by PcG proteins. The epigenetic integrity is compromised, however, by mutations or other alterations that affect the function of PcG proteins in stem cells leading to aberrant cell proliferation and tissue transformation, a hallmark of cancer. Disclosure of potential conflicts of interest is found at the end of this article.

Connections between epigenetic gene silencing and human disease

Alterations in epigenetic gene regulation are associated with human disease. Here, we discuss connections between DNA methylation and histone methylation, providing examples in which defects in these processes are linked with disease. Mutations in genes encoding DNA methyltransferases and proteins that bind methylated cytosine residues cause changes in gene expression and alterations in the patterns of DNA methylation. These changes are associated with cancer and congenital diseases due to defects in imprinting. Gene expression is also controlled through histone methylation. Altered levels of methyltransferases that modify lysine 27 of histone H3 (K27H3) and lysine 9 of histone H3 (K9H3) correlate with changes in Rb signaling and disruption of the cell cycle in cancer cells. The K27H3 mark recruits a Polycomb complex involved in regulating stem cell pluripotency, silencing of developmentally regulated genes, and controlling cancer progression. The K9H3 methyl mark recruits HP1, a structural protein that plays a role in heterochromatin formation, gene silencing, and viral latency. Cells exhibiting altered levels of HP1 are predicted to show a loss of silencing at genes regulating cancer progression. Gene silencing through K27H3 and K9H3 can involve histone deacetylation and DNA methylation, suggesting cross talk between epigenetic silencing systems through direct interactions among the various players. The reversible nature of these epigenetic modifications offers therapeutic possibilities for a wide spectrum of disease.

Cancer genetics of epigenetic genes

The cancer epigenome is characterised by specific DNA methylation and chromatin modification patterns. The proteins that mediate these changes are encoded by the epigenetics genes here defined as: DNA methyltransferases (DNMT), methyl-CpG-binding domain (MBD) proteins, histone acetyltransferases (HAT), histone deacetylases (HDAC), histone methyltransferases (HMT) and histone demethylases. We review the evidence that these genes can be targeted by mutations and expression changes in human cancers.