EZH2 genetic variants affect risk of gastric cancer in the Chinese Han population

Progress in research of EZH2 in digestive system tumors

EZH2 is a key member of the PcG protein family and a subunit of catalytic activity in the PRC2 complex. It has histone methylation transferase activity and plays an important role in epigenetic modification. A large number of studies have shown that it is closely related to the occurrence, development, and prognosis of various digestive system tumors and is highly expressed in tumor tissues, such as gastric cancer, liver cancer, colorectal cancer, pancreatic cancer, and gallbladder cancer. In this paper, we review the biological characteristics of EZH2d , its role in digestive system tumors, and the prospect of targeted therapy for EZH2.

Synergistic triad epistasis of epigenetic H3K27me modifier genes, EZH2, KDM6A, and KDM6B, in gastric cancer susceptibility

BACKGROUND

For an epigenetic regulation of human genome, three enzymes write or erase methylation of lysine-27 residue on histone H3 (H3K27me). This methylation is catalyzed by EZH2 (KMT6A) methyltransferase and reversed by KDM6A (UTX) or KDM6B (JMJD3) demethylase. Genetic cancer risk association has been reported on EZH2, but not on KDM6A or KDM6B yet.

METHODS

A total of 23 tag single-nucleotide polymorphisms (SNPs) of the three genes were genotyped in 2349 Korean participants, and their gastric cancer risk associations and epistases were statistically examined by comparing the SNP genotypes of 1100 gastric cancer patients and 1249 healthy controls.

RESULTS

All three genes are individually associated with gastric cancer susceptibility, as evident with the genotypes of KDM6A SNP rs5952279 (P = 0.00010) and rs144974719 (P = 0.00024), KDM6B rs78633955 (P = 0.0019) and rs11657063 (P = 0.0036), and EZH2 rs67648693 (P = 0.0028) and rs1061037 (P = 0.023). Furthermore, when odds ratio of interaction (OR_int) is calculated for all intergenic SNP pairs, synergistic epistasis is evident among the three genes. Specifically, the interaction is synergistic between EZH2 rs58579167 and KDM6A rs5952279 (OR_int = 3.2, P = 0.00066), between KDM6A rs2230018 and KDM6B rs78633955 (OR_int = 1.9, P = 0.044), and between KDM6B rs78633955 and EZH2 rs73158295 (OR_int = 1.7, P = 0.00030). These inter-SNP interactions together constitute a synergistic triad epistasis of ring-type topology.

CONCLUSIONS

All three H3K27me modifier genes are individually associated with gastric cancer susceptibility with synergistic triad interaction. Not only two enzymes with the same function (KDM6A and KDM6B), but also those with opposite functions (EZH2 versus KDM6A or KDM6B) synergistically affect H3K27me consequences such as gastric cancer susceptibility.

Identification of hub genes with prognostic values in gastric cancer by bioinformatics analysis

Background

Gastric cancer (GC) is a prevalent malignant cancer of digestive system. To identify key genes in GC, mRNA microarray GSE27342, GSE29272, and GSE33335 were downloaded from GEO database.

Methods

Differentially expressed genes (DEGs) were obtained using GEO2R. DAVID database was used to analyze function and pathways enrichment of DEGs. Protein-protein interaction (PPI) network was established by STRING and visualized by Cytoscape software. Then, the influence of hub genes on overall survival (OS) was performed by the Kaplan-Meier plotter online tool. Module analysis of the PPI network was performed using MCODE. Additionally, potential stem loop miRNAs of hub genes were predicted by miRecords and screened by TCGA dataset. Transcription factors (TFs) of hub genes were detected by NetworkAnalyst.

Results

In total, 67 DEGs were identified; upregulated DEGs were mainly enriched in biological process (BP) related to angiogenesis and extracellular matrix organization and the downregulated DEGs were mainly enriched in BP related to ion transport and response to bacterium. KEGG pathways analysis showed that the upregulated DEGs were enriched in ECM-receptor interaction and the downregulated DEGs were enriched in gastric acid secretion. A PPI network of DEGs was constructed, consisting of 43 nodes and 87 edges. Twelve genes were considered as hub genes owing to high degrees in the network. Hsa-miR-29c, hsa-miR-30c, hsa-miR-335, hsa-miR-33b, and hsa-miR-101 might play a crucial role in hub genes regulation. In addition, the transcription factors-hub genes pairs were displayed with 182 edges and 102 nodes. The high expression of 7 out of 12 hub genes was associated with worse OS, including COL4A1, VCAN, THBS2, TIMP1, COL1A2, SERPINH1, and COL6A3.

Conclusions

The miRNA and TFs regulation network of hub genes in GC may promote understanding of the molecular mechanisms underlying the development of gastric cancer and provide potential targets for GC diagnosis and treatment.

Electronic supplementary material

The online version of this article (10.1186/s12957-018-1409-3) contains supplementary material, which is available to authorized users.

Effects of four single nucleotide polymorphisms of EZH2 on cancer risk: a systematic review and meta-analysis

Background

Although the relationship between several single nucleotide polymorphisms (SNPs) of the oncogene EZH2 and cancer risk has been assessed by some case–control studies, results of subsequent studies are controversial. Sample sizes from single-center studies are also limited, thereby providing unreliable findings. Hence, we conducted a comprehensive search and meta-analysis to evaluate the associations between EZH2 SNPs and cancer risk.

Materials and methods

A comprehensive literature search for studies focusing on EZH2 SNPs and cancer risk was conducted on PubMed, Web of Science, Embase, and China National Knowledge Infrastructure online databases. Genotype data were extracted and examined through a meta-analysis, and pooled odds ratios (ORs) with 95% CIs were used to assess the corresponding associations. Sensitivity analysis, publication bias assessment, and heterogeneity test were performed using STATA 12.0.

Results

Twelve eligible studies were included in this meta-analysis. The association of 4 SNPs, namely, rs887569, rs2302427, rs3757441, and rs41277434, in the EZH2 locus with cancer risk was evaluated. Five studies (1,794 cases and 1,878 controls) indicated that rs887569 was related to a decreased cancer risk (CTTT/CC: OR =0.849, 95% CI: [0.740 to 0.973], P=0.019; TT/CCCT: OR =0.793, 95% CI: [0.654 to 0.962], P=0.019). Seven studies (2,408 cases and 2,910 controls) showed that rs2302427 was linked to a decreased cancer risk (GG/CC: OR =0.562, 95% CI: [0.400 to 0.792], P=0.001; CGGG/CC: OR =0.856, 95% CI: [0.748 to 0.980], P=0.024; GG/CCCG: OR =0.733, 95% CI: [0.571 to 0.940], P=0.015). No relationships were observed between rs3757441 or rs41277434 and cancer risk.

Conclusion

rs887569 and rs2302427 in EZH2 may be correlated with a decreased cancer risk. Although rs3757441 and rs41277434 are independent risk factors of cancer, further large-scale and functional studies are warranted to validate our findings.

Epigenetic regulation of cancer biology and anti-tumor immunity by EZH2

Polycomb group proteins regulate chromatin structure and have an important regulatory role on gene expression in various cell types. Two polycomb group complexes (Polycomb repressive complex 1 (PRC1) and 2 (PRC2)) have been identified in mammalian cells. Both PRC1 and PRC2 compact chromatin, and also catalyze histone modifications. PRC1 mediates monoubiquitination of histone H2A, whereas PRC2 catalyzes methylation of histone H3 on lysine 27. These alterations of histones can lead to altered gene expression patterns by regulating chromatin structure. Numerous studies have highlighted the role of the PRC2 catalytic component enhancer of zeste homolog 2 (EZH2) in neoplastic development and progression, and EZH2 mutations have been identified in various malignancies. Through modulating the expression of critical genes, EZH2 is actively involved in fundamental cellular processes such as cell cycle progression, cell proliferation, differentiation and apoptosis. In addition to cancer cells, EZH2 also has a decisive role in the differentiation and function of T effector and T regulatory cells. In this review we summarize the recent progress regarding the role of EZH2 in human malignancies, highlight the molecular mechanisms by which EZH2 aberrations promote the pathogenesis of cancer, and discuss the anti-tumor effects of EZH2 targeting via activating direct anti-cancer mechanisms and anti-tumor immunity.

Correlations of EZH2 and SMYD3 gene polymorphisms with breast cancer susceptibility and prognosis

The aim of the present study was to investigate the correlation of enhancer of Zeste homolog 2 (EZH2) and SET and MYND domain containing 3 (SMYD3) gene polymorphisms with breast cancer susceptibility and prognosis. A total of 712 patients with breast cancer and 783 healthy individuals were selected. Normal breast epithelial cells MCF-10A and breast cancer cells MCF-7, MDA-MB-231, T47D, and Bcap-37 were cultured. Polymerase chain reaction (PCR)-restriction fragment length polymorphism method was applied for genotyping. Reverse-transcription quantitative PCR (RT-qPCR) and Western blotting were used to examine EZH2 and SMYD3 expression in breast cancer tissues and cells. The risk factors and prognostic factors for breast cancer were estimated. The C allele of EZH2 rs12670401 (odds ratio (OR) =1.255, 95% confidence interval (95% CI): 1.085-1.452), T allele of EZH2 rs6464926 (OR =1.240, 95% CI: 1.071-1.435), and three alleles of SMYD3 variable number of tandem repeats (VNTRs) (OR =1.305, 95% CI: 1.097-1.552) could increase susceptibility to breast cancer. Combined genotypes of EZH2 rs12670401 (TC + CC) and EZH2 rs6464926 (CT + TT) were associated with breast cancer susceptibility. Breast cancer tissues had higher EZH2 and SMYD3 expression. EZH2 rs12670401, EZH2 rs6464926, age of menarche, and menopausal status were associated with breast cancer susceptibility. Patients with TT genotype of EZH2 rs12670401 or with CC genotype of EZH2 rs6464926 had higher overall survival (OS). EZH2 rs12670401, EZH2 rs6464926, and clinical staging were independent prognostic factors for breast cancer. SMYD3 VNTR polymorphism exhibited no association with susceptibility and prognosis. EZH2 rs12670401 and rs6464926 polymorphisms, EZH2 and SMYD3 expression, clinical staging, lymph node metastasis, human epidermal growth factor receptor-2 (HER2) status, and metastasis may be correlated with breast cancer susceptibility and prognosis.

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.

MicroRNA-124 inhibits proliferation and induces apoptosis by directly repressing EZH2 in gastric cancer

MicroRNA-124 (miR-124), a pivotal member of the p53 network, was found to be down-regulated in multiple types of tumors and further reported as tumor suppressor microRNA. In this study, we found that miR-124 was down-regulated in gastric cancer cell lines and specimens. Restoration of miR-124 expression inhibited the proliferation and colony formation of gastric cancer cells. EZH2 (enhancer of zeste homolog 2), which has been shown to be an important transcription factor involved in the proliferation and metastasis of tumor cells, was here confirmed to be a direct target gene of miR-124. On the other hand, silencing EZH2 also inhibits cell proliferation of gastric cancer cells. Furthermore, the treatment combining miR-124 with 5-fluorouracil (5-FU) significantly showed more efficient anti-tumor effects than single treatment of miR-124 or 5-FU, and over-expression of miR-124 suppresses the tumor growth in vivo. Our study indicate that miR-124 can suppress gastric cancer cell growth by directly targeting the EZH2 gene and sensitize the treatment effect of 5-FU. Therefore, miR-124 shows tumor-suppressive activity and may be a new and useful approach of gastric cancer therapy.

Gastrokine 1 expression in the human gastric mucosa is closely associated with the degree of gastritis and DNA methylation

Purpose

Gastrokine 1 plays an important role in gastric mucosal defense. Additionally, the Gastrokine 1-miR-185-DNMT1 axis has been shown to suppress gastric carcinogenesis through regulation of epigenetic alteration. Here, we investigated the effects of Gastrokine 1 on DNA methylation and gastritis.

Materials and Methods

Expression of Gastrokine 1, DNMT1, EZH2, and c-Myc proteins, and the presence of Helicobacter pylori CagA protein were determined in 55 non-neoplastic gastric mucosal tissue samples by western blot analysis. The CpG island methylation phenotype was also examined using six markers (p16, hMLH1, CDH1, MINT1, MINT2 and MINT31) by methylation-specific polymerase chain reaction. Histological gastritis was assessed according to the updated Sydney classification system.

Results

Reduced Gastrokine 1 expression was found in 20 of the 55 (36.4%) gastric mucosal tissue samples and was closely associated with miR-185 expression. The Gastrokine 1 expression level was inversely correlated with that of DNMT1, EZH2, and c-Myc, and closely associated with the degree of gastritis. The H. pylori CagA protein was detected in 26 of the 55 (47.3%) gastric mucosal tissues and was positively associated with the expression of DNMT1, EZH2, and c-Myc. In addition, 30 (54.5%) and 23 (41.9%) of the gastric mucosal tissues could be classified as CpG island methylation phenotype-low and CpG island methylation phenotype-high, respectively. Reduced expression of Gastrokine 1 and miR-185, and increased expression of DNMT1, EZH2, and c-Myc were detected in the CpG island methylation phenotype-high gastric mucosa.

Conclusions

Gastrokine 1 has a crucial role in gastric inflammation and DNA methylation in gastric mucosa.

Gastric cancer: epidemiologic aspects

A multifactorial and multistep model of gastric cancer (GC) is currently accepted, according to which different environmental and genetic factors are involved at different stages in the cancer process. The aim of this article is to review the most relevant information published on the relative contribution of genetic and environmental factors. Large meta-analyses confirmed the association between IL8, IL10, TNF-b, TP53 and PSCA, while genetic variation at different genes such as XPG, PLCE1, HFE, ERCC5, EZH2, DOC2, CYP19A1, ALDH2, and CDH1 have been reported to be associated with GC risk. Several microRNAs have also been associated with GC and their prognosis. Cohort studies have shown the association between GC and fruit, flavonoid, total antioxidant capacity, and green tea intake. Obesity was associated with cardia GC, heme iron intake from meat with GC risk. Several large meta-analyses have confirmed the positive association of GC with salt intake and pickled foods and the negative association with aspirin use.

DNA and histone methylation in gastric carcinogenesis

Epigenetic alterations contribute significantly to the development and progression of gastric cancer, one of the leading causes of cancer death worldwide. Epigenetics refers to the number of modifications of the chromatin structure that affect gene expression without altering the primary sequence of DNA, and these changes lead to transcriptional activation or silencing of the gene. Over the years, the study of epigenetic processes has increased, and novel therapeutic approaches that target DNA methylation and histone modifications have emerged. A greater understanding of epigenetics and the therapeutic potential of manipulating these processes is necessary for gastric cancer treatment. Here, we review recent research on the effects of aberrant DNA and histone methylation on the onset and progression of gastric tumors and the development of compounds that target enzymes that regulate the epigenome.

Association of the variant rs2243421 of human DOC-2/DAB2 interactive protein gene (hDAB2IP) with gastric cancer in the Chinese Han population

Human DOC-2/DAB2 interactive protein (hDAB2IP) gene is a novel member of the Ras GTPase-activating family and has been demonstrated to be a tumor-suppressor gene that inhibits cell survival and proliferation and induces cell apoptosis. It was reported that the expression level of hDAB2IP in gastric cancer tissue was highly correlated with tumor progression, however, whether hDAB2IP genetic variants are associated with the risk of gastric cancer remains yet unknown. In this case-control study, we conducted a genetic analysis for hDAB2IP variants in 311 patients with gastric cancer and 425 controls from the Chinese Han population. We found that the SNP rs2243421 of hDAB2IP gene with the minor allele C significantly revealed strong association with decreased gastric cancer susceptibility (P=0.007, adjusted odds ratio [OR]=0.734, 95%CI=0.586-0.919). Haplotypes rs2243421 and rs10985332 (HaploType: CC, P=0.012, aOR=0.760) and haplotypes rs2243421 and rs555996 (HaploType: CG, P=0.034, aOR=0.788) represented the decreased risk of gastric cancer, respectively. On the contrary, rs2243421 and rs555996 showed an elevated susceptibility (HaploType: TG, P=0.010, aOR=1.320). Our results for the first time provided new insight into susceptibility factors of hDAB2IP gene variants in carcinogenesis of gastric cancer.