EZH2 polycomb transcriptional repressor expression correlates with methylation of the APAF-1 gene in superficial transitional cell carcinoma of the bladder

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.

Functional and therapeutic significance of EZH2 in urological cancers

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

The prognostic role of epigenetic dysregulation in bladder cancer: A systematic review

BACKGROUND

Despite adequate treatment and follow-up, around one fifth of patients with localized bladder cancer will present with disease progression. Adequate prognostic biomarkers are lacking to define patients who are at risk. Mutations in chromatin remodeling genes are more frequently found in bladder cancer than in any other solid tumor. However, the prognostic relevance of epigenetic dysregulation has not been established and may offer an opportunity for biomarker discovery.

METHODS

Looking for prognostic epigenetic factors, we performed a comprehensive PubMed search using keywords such as "bladder cancer", "chromatin remodeling", "gene methylation" and "epigenetics". We only included studies reporting on the association of epigenetic markers with prognostic outcomes such as recurrence, progression or survival.

RESULTS

Of 1113 results, 87 studies met the inclusion criteria, which represented a total of 85 epigenetic markers with potential prognostic relevance. No prospective studies were identified. Seventy-three percent (64/87) of the studies involved mixed cohorts of muscle invasive and non-muscle invasive bladder cancer. Promoter methylation of genes with putative prognostic value affected cellular processes such as cell cycle, apoptosis, cell-adhesion or migration, as well as critical pathways such as MAP-kinase or Wnt. Alteration of chromatin regulatory elements suggest a prognostic relevance alterations leading to a predominantly silenced chromatin state.

CONCLUSIONS

The prognostic impact of epigenetic alterations in bladder cancer is still unclear. Prospective evaluation of methylation marks and chromatin remodeling gene alterations using consistent methods and criteria is warranted.

Apoptotic protease activating factor-1 and tumors

Apoptotic protease activating factor-1 (Apaf-1) functions as a core apoptosis factor in the mitochondrial apoptosis pathway. Apaf-1 promoter methylation and loss of heterozygosity are the main causes of cancer, and lower expression of Apaf-1 is closely related to malignant tumors. Apaf-1 expression deletion and methylation can be used as markers for deeper tumor invasion, frequent lymph node metastasis, tumor differentiation and poor prognosis. Apaf-1 can be used as a molecular target for anticancer therapy and prognosis prediction. Further research on Apaf-1 will contribute to the development of effective anti-tumor drugs. In this paper, we will review the biochemical structure and function of Apaf-1, Apaf-1 signal transduction pathway, expression of Apaf-1 in a variety of tumors, as well as its role in tumor occurrence, drug resistance and treatment.

Enhancer of zeste homolog 2 expression is associated with metastasis and adverse clinical outcome in clear cell renal cell carcinoma: a comparative study and review of the literature

CONTEXT

Enhancer of zeste homolog 2 (EZH2), a histone methyltransferase mediating chromatin condensation and epigenetic modulation, is overexpressed in various human carcinomas and is associated with adverse clinicopathologic characteristics and biologic behavior. The expression of EZH2 in renal cell carcinomas (RCCs) has not been fully characterized yet.

OBJECTIVE

To evaluate the prognostic role of EZH2 in RCC by analyzing the immunohistochemical staining pattern of the marker in relation to pathologic features and clinical outcome.

DESIGN

We correlated the immunolabeling of EZH2 with multiple clinicopathologic features, including Fuhrman nuclear grade, pathologic stage, metastatic status, and clinical outcome in 223 clear cell RCCs (CRCCs) and 21 papillary RCCs, by using tissue microarrays of primary and metastatic cases.

RESULTS

Most CRCCs (75%) showed positive EZH2 staining, with most primary tumors showing focal staining in comparison to nonfocal staining in metastatic cases. In primary tumors, EZH2 expression was associated with higher nuclear grade and lower pathologic stage. Metastatic tumors showed a higher number of positive cases (81% versus 67%) and a more diffuse and more intense pattern of staining than primary CRCCs. For the 22 locally advanced primary tumors (T3/4) and 43 metastatic RCCs, patients who experienced RCC-related deaths significantly overexpressed the marker in comparison to patients who did not experience RCC-related mortality.

CONCLUSIONS

By showing that EZH2 expression is associated with increased metastatic potential and a worse clinical outcome, this study suggests that EZH2 can serve as a prognostic biomarker for RCC, thus confirming it as a key molecule driving oncogenesis and metastasis.

Evading apoptosis in cancer

Carcinogenesis is a mechanistically complex and variable process with a plethora of underlying genetic causes. Cancer development comprises a multitude of steps that occur progressively starting with initial driver mutations leading to tumorigenesis and, ultimately, metastasis. During these transitions, cancer cells accumulate a series of genetic alterations that confer on the cells an unwarranted survival and proliferative advantage. During the course of development, however, cancer cells also encounter a physiologically ubiquitous cellular program that aims to eliminate damaged or abnormal cells: apoptosis. Thus, it is essential that cancer cells acquire instruments to circumvent programmed cell death. Here we discuss emerging evidence indicating how cancer cells adopt various strategies to override apoptosis, including amplifying the antiapoptotic machinery, downregulating the proapoptotic program, or both.

mRNA expression and hypermethylation of tumor suppressor genes apoptosis protease activating factor-1 and death-associated protein kinase in oral squamous cell carcinoma

Apoptosis protease activating factor-1 (Apaf-1) and death-associated protein kinase (DAPK) are p53 pathway-related genes that play significant roles in the activation of caspases, which are involved in mitochondrial-mediated apoptosis. The present study aimed to confirm the role of hyper-methylation of the Apaf-1 and DAPK gene promoter regions in oral squamous cell carcinoma (OSCC) and the effect of the demethylation drug, 5-aza-2'-deoxycytidine (DAC). mRNA from 53 OSCC samples, 23 normal oral mucosa samples and Tca8113 human tongue carcinoma cell lines was detected using semi-quantitative reverse transcription-polymerase chain reaction (RT-PCR). The DNA from each sample was analyzed using methylation-specific PCR (MSP). The Tca8113 cells were demethylated using DAC and the demethylation and re-expression of Apaf-1 and DAPK were analyzed. The Apaf-1 and DAPK mRNA expression index was decreased in 51 (96.23%) and 50 (94.34%) cases, respectively, in the tumor tissues. Hypermethylation of the Apaf-1 and DAPK promoter regions was detected in 46 (86.79%) and 38 (71.69%) cases, respectively. Promoter hypermethylation of the two genes correlated with a decreased mRNA expression in the tumor tissues. Subsequent to being treated with DAC, Apaf-1 and DAPK were demethylated and re-expressed in the Tca8113 cells. Apaf-1 and DAPK promoter hypermethylation may be associated with low gene expression in OSCC. Furthermore, a loss of Apaf-1 and DAPK expression may recover following demethylation. The data provide evidence that methylation exists in OSCC and may play a role in the development of this disease.

DNA methylation and apoptosis resistance in cancer cells

Apoptosis is a cell death programme primordial to cellular homeostasis efficiency. This normal cell suicide program is the result of the activation of a cascade of events in response to death stimuli. Apoptosis occurs in normal cells to maintain a balance between cell proliferation and cell death. A deregulation of this balance due to modifications in the apoptosic pathway leads to different human diseases including cancers. Apoptosis resistance is one of the most important hallmarks of cancer and some new therapeutical strategies focus on inducing cell death in cancer cells. Nevertheless, cancer cells are resistant to treatment inducing cell death because of different mechanisms, such as DNA mutations in gene coding for pro-apoptotic proteins, increased expression of anti-apoptotic proteins and/or pro-survival signals, or pro-apoptic gene silencing mediated by DNA hypermethylation. In this context, aberrant DNA methylation patterns, hypermethylation and hypomethylation of gene coding for proteins implicated in apoptotic pathways are possible causes of cancer cell resistance. This review highlights the role of DNA methylation of apoptosis-related genes in cancer cell resistance.

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.

Gene expression study related with the intrinsic pathway of apoptosis in bladder cancer by real-time PCR technique

We examined the expression of anti-apoptotic genes (XIAP and Bcl-2) and apoptotic genes (cytochrome c, caspase-9, Apaf-1) in tissue samples of patients with superficial bladder cancer. Thirty-two bladder cancer tissue samples (8 papillary urothelial neoplasm of low malignant potential, 10 low-grade, and 14 high-grade) and 8 normal bladder tissue samples from necropsy were used for the study of gene expression by real-time PCR analysis. Analysis of the expression of apoptotic gene constituents of an apoptosome demonstrated an increase in Apaf-1 expression in the three tumor grades when compared with the control (P < 0.01, P < 0.05, and P < 0.01), low expression of caspase-9 in all groups (P < 0.05), and an increase in cytochrome c expression in all tumor grades in relation to the control, although without statistically significant difference. The expression of anti-apoptotic genes revealed an increase in XIAP expression in all tumor grades in relation to the control, although without statistically significant difference, and low expression of Bcl-2 in all tumor grades and the control (P < 0.05). The results proved that there is low evidence of apoptotic activity by the intrinsic pathway, demonstrated by the low expression of caspase-9 and considerable increase in XIAP expression, which may render these genes potential therapeutic targets in bladder cancer treatment.

Bladder cancer: a simple model becomes complex

Bladder cancer is one of the most frequent malignancies in developed countries and it is also characterized by a high number of recurrences. Despite this, several authors in the past reported that only two altered molecular pathways may genetically explain all cases of bladder cancer: one involving the FGFR3 gene, and the other involving the TP53 gene. Mutations in any of these two genes are usually predictive of the malignancy final outcome. This cancer may also be further classified as low-grade tumors, which is always papillary and in most cases superficial, and high-grade tumors, not necessarily papillary and often invasive. This simple way of considering this pathology has strongly changed in the last few years, with the development of genome-wide studies on expression profiling and the discovery of small non-coding RNA affecting gene expression. An easy search in the OMIM (On-line Mendelian Inheritance in Man) database using "bladder cancer" as a query reveals that genes in some way connected to this pathology are approximately 150, and some authors report that altered gene expression (up- or down-regulation) in this disease may involve up to 500 coding sequences for low-grade tumors and up to 2300 for high-grade tumors. In many clinical cases, mutations inside the coding sequences of the above mentioned two genes were not found, but their expression changed; this indicates that also epigenetic modifications may play an important role in its development. Indeed, several reports were published about genome-wide methylation in these neoplastic tissues, and an increasing number of small non-coding RNA are either up- or down-regulated in bladder cancer, indicating that impaired gene expression may also pass through these metabolic pathways. Taken together, these data reveal that bladder cancer is far to be considered a simple model of malignancy. In the present review, we summarize recent progress in the genome-wide analysis of bladder cancer, and analyse non-genetic, genetic and epigenetic factors causing extensive gene mis-regulation in malignant cells.

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.

Methylation of the APAF-1 and DAPK-1 promoter region correlates with progression of renal cell carcinoma in North Indian population

Aberrant promoter hypermethylation of cancer associated genes occur frequently during carcinogenesis and may serve as a cancer biomarker. The aim of this study was to investigate the occurrence and relevance of promoter methylation of the tumor suppressor DAPK-1, APAF-1 () and SPARC in relation to different pathological stages and histological grades of tumor progression that might act as possible independent prognostic factor in the susceptibility towards renal cell carcinoma (RCC) in North Indian population. Three tumor suppressor gene promoters namely APAF-1, DAPK-1 and SPARC were assessed by methylation-specific PCR (MS-PCR) in 196 primarily resected renal cell tumors paired with the corresponding normal tissue samples. After genomic DNA isolation and sodium bisulfite modification, methylation levels were determined and correlated with standard clinicopathological parameters, pathological stage and Fuhrman nuclear grade of RCC. Significant differences in methylation frequency among the four subtypes of renal tumors were found for APAF-1 (p < 0.001), DAPK-1 (p < 0.001) and SPARC (p = 0.182), when compared with the corresponding normal tissue. Male subjects showed stronger association of methylation frequency of all the three genes with RCC than the female subjects. Additionally, higher frequency of APAF-1, DAPK-1 and SPARC promoter methylation were directly correlated with higher tumor stage (p (trend) < 0.001). Higher frequency of promoter methylation of APAF-1 and SPARC were also associated with higher nuclear grade (p < 0.001 and p = 0.036, respectively). This gene panel might contribute to a more optimal diagnostic coverage and information, improving preoperative assessment and therapeutic decision-making in patients harboring suspicious renal masses.

DNA hypermethylation profiles associated with glioma subtypes and EZH2 and IGFBP2 mRNA expression

We explored the associations of aberrant DNA methylation patterns in 12 candidate genes with adult glioma subtype, patient survival, and gene expression of enhancer of zeste human homolog 2 (EZH2) and insulin-like growth factor-binding protein 2 (IGFBP2). We analyzed 154 primary glioma tumors (37 astrocytoma II and III, 52 primary glioblastoma multiforme (GBM), 11 secondary GBM, 54 oligodendroglioma/oligoastrocytoma II and III) and 13 nonmalignant brain tissues for aberrant methylation with quantitative methylation-specific PCR (qMS-PCR) and for EZH2 and IGFBP2 expression with quantitative reverse transcription PCR (qRT-PCR). Global methylation was assessed by measuring long interspersed nuclear element-1 (LINE1) methylation. Unsupervised clustering analyses yielded 3 methylation patterns (classes). Class 1 (MGMT, PTEN, RASSF1A, TMS1, ZNF342, EMP3, SOCS1, RFX1) was highly methylated in 82% (75/91) of lower-grade astrocytic and oligodendroglial tumors, 73% (8/11) of secondary GBMs, and 12% (6/52) of primary GBMs. The primary GBMs in this class were early onset (median age 37 years). Class 2 (HOXA9 and SLIT2) was highly methylated in 37% (19/52) of primary GBMs. None of the 10 genes for class 3 that were differentially methylated in classes 1 and 2 were hypermethylated in 92% (12/13) of nonmalignant brain tissues and 52% (27/52) of primary GBMs. Class 1 tumors had elevated EZH2 expression but not elevated IGFBP2; class 2 tumors had both high IGFBP2 and high EZH2 expressions. The gene-specific hypermethylation class correlated with higher levels of global LINE1 methylation and longer patient survival times. These findings indicate a generalized hypermethylation phenotype in glioma linked to improved survival and low IGFBP2. DNA methylation markers are useful in characterizing distinct glioma subtypes and may hold promise for clinical applications.

EZH2 silencing by RNA interference inhibits proliferation in bladder cancer cell lines

The Enhancer of Zeste homologue2 gene (EZH2) is frequently expressed at high levels in malignant tumours, including bladder cancer. It functions as a transcriptional regulator to the maintenance of cell identity, cell cycle regulation and oncogenesis. In the study, we detected EZH2 expression in bladder cancer tissues. These results showed EZH2 high expression in bladder cancer tissue at level of transcript and protein compared with normal bladder tissue and EZH2 expression correlated positively with tumour stage and grade. Then, we used RNA interference to inhibit EZH2 expression in bladder cancer EJ cell line. Efficient downregulation of EZH2 resulted in significantly decreased cell proliferation in EJ cells and retarded transition of G(1) phase to S phase. Our data suggest that EZH2 is involved in the tumourigenesis of bladder cancer and EZH2 downregulation contributes to inhibiting malignant growth by retarding cell entrance to S phase.

Effects of 5-Aza-CdR on the proliferation of human breast cancer cell line MCF-7 and on the expression of Apaf-1 gene

Hypermethylation in the promoter region of tumor suppressor genes is a common mechanism of gene silencing, which tends to occur in cancer. The effects of 5-Aza-2'-deoxycytidine (5-Aza-CdR), a specific DNA methyltransferase inhibitor, on the cell proliferation of human breast cancer cell line MCF-7 and on the expression of Apaf-1 gene were investigated. Human MCF-7 cells were incubated with increasing concentrations of 5-Aza-CdR for 12 to 120 h. The growth inhibition rates of MCF-7 cells were detected by MTT assay. Changes of cell cycle distribution and apoptotic rates of MCF-7 cells were determined by flow cytometry. The expressions of DNA methyltransferase 3b mRNA and Apaf-1 mRNA were measured by reverse transcription polymerase chain reaction (RT-PCR). Meanwhile, the expression of Apaf-1 protein was detected by Western blotting. The results showed that 5-Aza-CdR significantly inhibited the growth of MCF-7 cells and the growth inhibition rate of MCF-7 cells was significantly enhanced with the concentration of 5-Aza-CdR and the action time. Flow cytometry indicated that 5-Aza-CdR could significantly induce G(1)/S cell cycle arrest and increase the apoptosis rate of MCF-7 cells. The mRNA and protein expressions of Apaf-1 were up-regulated in MCF-7 cells treated with 5-Aza-CdR, which was accompanied by down-regulation of DNA methyltransferase 3b mRNA. It is concluded that 5-Aza-CdR might retard the growth of tumor cells and promote the apoptosis of MCF-7 breast cancer cells by inhibiting the expression of DNA methyltransferase 3b and re-activating the Apaf-1 gene expression.