EZH2 inhibition enhances the efficacy of an EGFR inhibitor in suppressing colon cancer cells

Research progress on pharmacological effects and bioavailability of berberine

Berberine (BBR), a benzylisoquinoline alkaloid obtained from natural medicines such as coptidis rhizoma, has a wide range of pharmacological activities such as protecting the nervous system, protecting the cardiovascular system, anti-inflammatory, antidiabetic, antihyperlipidemic, antitumor, antibacterial, and antidiarrheal. However, factors such as poor solubility, low permeability, P-glycoprotein (P-gp) efflux, and hepatic-intestinal metabolism result in BBR having a low bioavailability (< 1%), which restricts its application in clinical settings. Therefore, improving its bioavailability is a prerequisite for its clinical applications. This review summarizes the various pharmacological effects of BBR and analyzes the main reasons for its poor bioavailability. It introduces methods to improve the bioavailability of BBR through the use of absorption enhancers and P-gp inhibitors, structural modification of BBR, and preparation of BBR salts and cocrystals as well as the development of new formulations and focuses on the bioavailability study of the new formulations of BBR. The research of BBR was also prospected in order to provide reference for the further research of BBR.

Morphological Changes Induced by TKS4 Deficiency Can Be Reversed by EZH2 Inhibition in Colorectal Carcinoma Cells

BACKGROUND

The scaffold protein tyrosine kinase substrate 4 (TKS4) undergoes tyrosine phosphorylation by the epidermal growth factor receptor (EGFR) pathway via Src kinase. The TKS4 deficiency in humans is responsible for the manifestation of a genetic disorder known as Frank-Ter Haar syndrome (FTHS). Based on our earlier investigation, the absence of TKS4 triggers migration, invasion, and epithelial-mesenchymal transition (EMT)-like phenomena while concurrently suppressing cell proliferation in HCT116 colorectal carcinoma cells. This indicates that TKS4 may play a unique role in the progression of cancer. In this study, we demonstrated that the enhancer of zeste homolog 2 (EZH2) and the histone methyltransferase of polycomb repressive complex 2 (PRC2) are involved in the migration, invasion, and EMT-like changes in TKS4-deficient cells (KO). EZH2 is responsible for the maintenance of the trimethylated lysine 27 on histone H3 (H3K27me3).

METHODS

We performed transcriptome sequencing, chromatin immunoprecipitation, protein and RNA quantitative studies, cell mobility, invasion, and proliferation studies combined with/without the EZH2 activity inhibitor 3-deazanoplanocine (DZNep).

RESULTS

We detected an elevation of global H3K27me3 levels in the TKS4 KO cells, which could be reduced with treatment with DZNep, an EZH2 inhibitor. Inhibition of EZH2 activity reversed the phenotypic effects of the knockout of TKS4, reducing the migration speed and wound healing capacity of the cells as well as decreasing the invasion capacity, while the decrease in cell proliferation became stronger. In addition, inhibition of EZH2 activity also reversed most epithelial and mesenchymal markers. We investigated the wider impact of TKS4 deletion on the gene expression profile of colorectal cancer cells using transcriptome sequencing of wild-type and TKS4 knockout cells, particularly before and after treatment with DZNep. Additionally, we observed changes in the expression of several protein-coding genes and long non-coding RNAs that showed a recovery in expression levels following EZH2 inhibition.

CONCLUSIONS

Our results indicate that the removal of TKS4 causes a notable disruption in the gene expression pattern, leading to the disruption of several signal transduction pathways. Inhibiting the activity of EZH2 can restore most of these transcriptomics and phenotypic effects in colorectal carcinoma cells.

FGFR4 and EZH2 inhibitors synergistically induce hepatocellular carcinoma apoptosis via repressing YAP signaling

BACKGROUND

Hepatocellular carcinoma (HCC) is one of the most common and lethal cancers worldwide, but current treatment options remain limited and cause serious life-threatening side effects. Aberrant FGFR4 signaling has been validated as an oncogenic driver of HCC, and EZH2, the catalytic subunit of the PRC2 complex, is a potential factor that contributes to acquired drug resistance in many tumors, including HCC. However, the functional relationship between these two carcinogenic factors, especially their significance for HCC treatment, remains unclear. In this study, we systematically evaluated the feasibility of a combination therapy targeting FGFR4 and EZH2 for HCC.

METHODS

RNA sequencing data of patients with Liver hepatocellular carcinoma (LIHC) from The Cancer Genome Atlas (TCGA) were analyzed to determine FGFR4 and EZH2 expression and their interaction with prognosis. Moreover, the HCC cell lines, zebrafish/mouse HCC xenografts and zebrafish HCC primary tumors were treated with FGFR4 inhibitor (Roblitinib) and/or EZH2 inhibitor (CPI-169) and then subjected to cell proliferation, viability, apoptosis, and tumor growth analyses to evaluate the feasibility of combination therapy for HCC both in vitro and in vivo. Furthermore, RNA-Seq was performed in combination with ChIP-Seq data analysis to investigate the critical mechanism underlying the combination treatment with Roblitinib and CPI-169.

RESULTS

EZH2 accumulated through the non-canonical NF-kB signaling in response to FGFR4 inhibitor treatment, and the elevated EZH2 levels led to the antagonism of HCC against Roblitinib (FGFR4 inhibitor). Notably, knockdown of EZH2 sensitized HCC cells to Roblitinib, while the combination treatment of Roblitinib and CPI-169 (EZH2 inhibitor) synergistically induced the HCC cell apoptosis in vitro and suppressed the zebrafish/mouse HCC xenografts and zebrafish HCC primary tumors development in vivo. Moreover, Roblitinib and CPI-169 synergistically inhibited HCC development via repressing YAP signaling.

CONCLUSIONS

Collectively, our study highlighted the potential of the therapeutic combination of FGFR4 and EZH2 inhibitors, which would provide new references for the further development of clinical treatment strategies for HCC.

Novel insights into histone lysine methyltransferases in cancer therapy: From epigenetic regulation to selective drugs

The reversible and precise temporal and spatial regulation of histone lysine methyltransferases (KMTs) is essential for epigenome homeostasis. The dysregulation of KMTs is associated with tumor initiation, metastasis, chemoresistance, invasiveness, and the immune microenvironment. Therapeutically, their promising effects are being evaluated in diversified preclinical and clinical trials, demonstrating encouraging outcomes in multiple malignancies. In this review, we have updated recent understandings of KMTs' functions and the development of their targeted inhibitors. First, we provide an updated overview of the regulatory roles of several KMT activities in oncogenesis, tumor suppression, and immune regulation. In addition, we summarize the current targeting strategies in different cancer types and multiple ongoing clinical trials of combination therapies with KMT inhibitors. In summary, we endeavor to depict the regulation of KMT-mediated epigenetic landscape and provide potential epigenetic targets in the treatment of cancers.

Epidermal Growth Factor Receptor Inhibitor Treatment Timing does not Impact Survival in Stage 4 Colon Cancer Treatment: A Retrospective Study

Introduction

Colon cancer impacts the lives of Kansans and those across the United States. Epidermal growth factor receptor (EGFR) inhibitors, such as panitumumab and cetuximab, have gained popularity as first-line treatment for stage 4 colon cancer despite their toxicities and have been used by clinicians in later lines of therapy. EGFR inhibitors have been proven to be an efficacious first-line treatment for stage 4 colon cancer, but no study has investigated outcomes comparing EGFR inhibitors as first-line treatment to its use as second- or third-line treatment. This study investigated EGFR inhibitor therapy estimated overall survival when used as first-, second-, and third-line treatment for stage 4 colon cancer.

Methods

A retrospective review was done for patients with stage 4 colon cancer who underwent EGFR inhibitor treatment at a large academic center from November 2007 to August 2021. The patients were stratified into five groups by the line in which they received the EGFR inhibitor treatment. A log-rank test was used to analyze the groups, and the median survival for each group was determined.

Results

A total of 68 patients were reviewed; 18 received first-line, 23 received second-line, 18 received third-line, 6 received fourth-line, and 3 received sixth-line treatment with an EGFR inhibitor. Fourth- and sixth-line therapies were excluded due to small patient size. There was no significant difference in estimated survival time between any of the lines. Median survival of the therapies was found.

Conclusions

There was no statistical difference in survival between the first-, second-, or third-line groups, which may provide justification for its use as a second- or third-line therapy.

Activation of FXR and inhibition of EZH2 synergistically inhibit colorectal cancer through cooperatively accelerating FXR nuclear location and upregulating CDX2 expression

Our previous study indicated that colon cancer cells varied in sensitivity to pharmacological farnesoid X receptor (FXR) activation. Herein, we explore the regulatory mechanism of FXR in colorectal cancer (CRC) development and aim to design effective strategies of combined treatment based on the regulatory axis. We found that the expression of FXR was negatively correlated with enhancer of zeste homolog 2 (EZH2) in colon cancer tissues. EZH2 transcriptionally suppressed FXR via H3K27me3. The combination of FXR agonist OCA plus EZH2 inhibitor GSK126 acted in a synergistic manner across four colon cancer cells, efficiently inhibiting clonogenic growth and invasion in vitro, retarding tumor growth in vivo, preventing the G0/G1 to S phase transition, and inducing caspase-dependent apoptosis. Benign control cells FHC were growth-arrested without apoptosis induction, but retained long-term proliferation and invasion capacity. Mechanistically, the drug combination dramatically accelerated FXR nuclear location and cooperatively upregulated caudal-related homeobox transcription factor 2 (CDX2) expression. The depletion of CDX2 antagonized the synergistic effects of the drug combination on tumor inhibition. In conclusion, our study demonstrated histone modification-mediated FXR silencing by EZH2 in colorectal tumorigenesis, which offers useful evidence for the clinical use of FXR agonists combined with EZH2 inhibitors in combating CRC.

Palmitate-Triggered COX2/PGE2-Related Hyperinflammation in Dual-Stressed PdL Fibroblasts Is Mediated by Repressive H3K27 Trimethylation

The interrelationships between periodontal disease, obesity-related hyperlipidemia and mechanical forces and their modulating effects on the epigenetic profile of periodontal ligament (PdL) cells are assumed to be remarkably complex. The PdL serves as a connective tissue between teeth and alveolar bone and is involved in pathogen defense and the inflammatory responses to mechanical stimuli occurring during tooth movement. Altered inflammatory signaling could promote root resorption and tooth loss. Hyperinflammatory COX2/PGE2 signaling was reported for human PdL fibroblasts (HPdLFs) concomitantly stressed with Porphyromonas gingivalis lipopolysaccharides and compressive force after exposure to palmitic acid (PA). The aim of this study was to investigate the extent to which this was modulated by global and gene-specific changes in histone modifications. The expression of key epigenetic players and global H3Kac and H3K27me3 levels were quantitatively evaluated in dual-stressed HPdLFs exposed to PA, revealing a minor force-related reduction in repressive H3K27me3. UNC1999-induced H3K27me3 inhibition reversed the hyperinflammatory responses of dual-stressed PA cultures characterized by increased COX2 expression, PGE2 secretion and THP1 adhesion. The reduced expression of the gene encoding the anti-inflammatory cytokine IL-10 and the increased presence of H3K27me3 at its promoter-associated sites were reversed by inhibitor treatment. Thus, the data highlight an important epigenetic interplay between the different stimuli to which the PdL is exposed.

Development of a UPLC-MS/MS method for determination of a dual EZH1/2 inhibitor UNC1999 in rat plasma

Aim: We aimed to establish and validate a simple and sensitive UPLC-MS/MS method for the determination of UNC1999, a dual inhibitor against EZH1 and EZH2 in plasma samples. Materials & methods: UNC1999 in rat plasma was processed with protein precipitation method and then separated on a C₁₈ column and detected under positive ionization mode. The method presented good linearity over the range of 1.0-2000 ng/ml with good accuracy and precision. UNC1999 was absorbed slowly and achieved a maximum concentration of 118.8 ± 12.0 ng/ml 1.5 h after oral administration. Conclusion: The method provides a favorable character in selectivity, linearity, accuracy, precision, recovery, matrix effects and stabilities and was suitable for describing the pharmacokinetic profile of UNC1999.

Drug resistance in colorectal cancer: An epigenetic overview

Colorectal cancer (CRC) is a leading cause of cancer-related deaths worldwide. Despite significant progress that has been made in therapies against CRC over the past decades, drug resistance is still a major limitation in CRC treatment. Numerous investigations have unequivocally shown that epigenetic regulation plays an important role in CRC drug resistance because of the high rate of epigenetic alterations in multiple genes during cancer development or drug treatment. Furthermore, the reversibility of epigenetic alterations provides novel therapeutic strategies to overcome drug resistance using small molecules, which can target non-coding RNAs or reverse histone modification and DNA methylation. In this review, we discuss epigenetic regulation in CRC drug resistance and the possible role of preventing or reversing CRC drug resistance using epigenetic therapy in CRC treatment.

Histone Modifying Enzymes as Targets for Therapeutic Intervention in Oesophageal Adenocarcinoma

Oesophageal adenocarcinoma (OAC) has a dismal prognosis, where curable disease occurs in less than 40% of patients, and many of those with incurable disease survive for less than a year from diagnosis. Despite the widespread use of systematic chemotherapy in OAC treatment, many patients receive no benefit. New treatments are urgently needed for OAC patients. There is an emerging interest in epigenetic regulators in cancer pathogenesis, which are now translating into novel cancer therapeutic strategies. Histone-modifying enzymes (HMEs) are key epigenetic regulators responsible for dynamic covalent histone modifications that play roles in both normal and dysregulated cellular processes including tumorigenesis. Several HME inhibitors are in clinical use for haematological malignancies and sarcomas, with numerous on-going clinical trials for their use in solid tumours. This review discusses the current literature surrounding HMEs in OAC pathogenesis and their potential use in targeted therapies for this disease.

Targeting Autophagy-Related Epigenetic Regulators for Cancer Drug Discovery

Existing evidence has demonstrated that epigenetic modifications (including DNA methylation, histone modifications, and microRNAs), which are associated with the occurrence and development of tumors, can directly or indirectly regulate autophagy. In particular, nuclear events induced by several epigenetic regulators can regulate the autophagic process and expression levels of tumor-associated genes, thereby promoting tumor progression. Tumor-associated microRNAs, including oncogenic and tumor-suppressive microRNAs, are of great significance to autophagy during tumor progression. Targeting autophagy with emerging epigenetic drugs is expected to be a promising therapeutic strategy for human tumors. From this perspective, we aim to summarize the role of epigenetic modification in the autophagic process and the underlying molecular mechanisms of tumorigenesis. Furthermore, the regulatory efficacy of epigenetic drugs on the autophagic process in tumors is also summarized. This perspective may provide a theoretical basis for the combined treatment of epigenetic drugs/autophagy mediators in tumors.

miR-1253, a novel tumor suppressor gene in colon cancer, is associated with poor patients prognosis

MiR-1253 has been reported to play vital roles in a variety of cancers. However, its function in the progression and prognosis of colon cancer remains unclear. Here, the clinical significance and biological function of miR-1253 in the development of colon cancer was investigated. The expression of miR-1253 was identified in colon cancer tissues and cell lines by qRT-PCR. The prognostic value of miR-1253 was evaluated by Kaplan-Meier and Cox regression analysis. The roles of miR-1253 in regulating cell proliferation, migration, and invasion of colon cancer were evaluated in vitro by CCK8 and Transwell assay. It was found that miR-1253 was significantly downregulated in colon cancer tissues and cell lines (P < 0.001). The downregulation of miR-1253 was associated with the TNM stage (P = 0.007) and lymph node metastasis (P = 0.037) of patients. MiR-1253 (HR factor = 2.564, 95% CI = 1.077-6.107, P = 0.033) and TNM stage (HR factor = 2.899, 95% CI = 1.024-8.205, P = 0.045) were identified as independent factors that can predict the prognosis of patients. Functionally, miR-1253 acts as a tumor suppressor that inhibited cell proliferation, migration, and invasion of colon cancer through targeting EZH2. MiR-1253 was identified as a prognostic biomarker and a tumor suppressor of colon cancer.

The Effect of EZH2 Inhibition through DZNep on Epithelial-Mesenchymal Transition Mechanism

Although the molecular pathogenesis of hepatocellular carcinoma (HCC) is uncertain, it is known that the epithelial-mesenchymal transition (EMT) mechanism and epigenetic changes have an important role. This study was focused on evaluating the relationship of 3-Deazaneplanocin A (DZNep) with the EMT mechanism, which is a histone methyltransferase inhibitor on HCC and is also known as an enhancer of zeste homolog 2 (EZH2) inhibitor. Cell viability of HepG2 cells (HCC cell line) assessed for DZNep over 72 hours with 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. Additionally, colony-forming assay, apoptosis assay, RNA isolation, cDNA synthesis, and real-time PCR (RT-PCR) were performed to see the effect of DZNep on HepG2 cells. DZNep reduced cell proliferation for 72 hours, also significantly reduced colony formation in addition it increased the total apoptosis. DZNep on EZH2, E-cadherin, N-cadherin, and Vimentin (Vim) gene expressions was given different results by either decreasing or increasing the expressions. In this study, we observed a positive effect of DZNep on apoptosis and TIMP3 expression level and decreased colony formation. However, it gave complicated results with the level of gene expression E-cadherin and TIMP2, increase the level of Vim and MMP2 expression. Therefore, we think that further studies are necessary to clarify the role of DZNep.

Downregulation of histone-lysine N-methyltransferase EZH2 inhibits cell viability and enhances chemosensitivity in lung cancer cells

Histone-lysine N-methyltransferase EZH2 (EZH2) is the principle component of the polycomb repressive complex 2 (PRC2)/embryonic ectoderm development protein-EZH2 complex, which promotes tumorigenesis by repressing transcription of tumor suppressor genes. EZH2 is considered a key marker in several types of cancer, such as colorectal and prostate cancer. However, the molecular mechanisms and clinical value of EZH2 in lung cancer have not yet been fully investigated. The aim of the present study was to investigate the functions of EZH2 in lung cancer progression and to determine whether treatment with an EZH2 inhibitor enhanced the chemosensitivity of lung cancer cells to cisplatin (CDDP). At the logarithmic growth phase, A549 cells were treated with a small interfering (si)RNA-EZH2, and cell viability was detected using an MTT assay. The degree of apoptosis and cell cycle were detected using flow cytometry. Cell migration and invasion were detected via wound healing and Transwell Matrigel assays. According to information from the Gene Expression Omnibus database, the results of the present study demonstrated that EZH2 was upregulated in lung cancer. Furthermore, overexpression of EZH2 was associated with poor patient prognosis, while EZH2 knockdown inhibited cell viability and migration, and enhanced apoptosis and chemosensitivity in a lung cancer cell line. EZH2 knockdown and treatment of A549 cells using EZH2 inhibitor elevated the inhibitory effects of CDDP on cell viability and apoptosis. Western blot and reverse transcription-quantitative PCR analyses were performed to assess the expression levels of relative protein and mRNA, respectively, in A549 cells treated with siRNA-EZH2 or with CDDP. Overall, the results of the present study demonstrated that high EZH2 expression was associated with poor prognosis, accompanied with a potential impairment of migration and viability in lung cancer cells. These findings suggest that EZH2 may act as a candidate molecular target for gene therapy, and treatment with EZH2 inhibitor may be used to increase chemosensitivity to CDDP agents in lung cancer.

CYP27B1 Downregulation: A New Molecular Mechanism Regulating EZH2 in Ovarian Cancer Tumorigenicity

Background

Ovarian cancer has the highest mortality rate among gynecologic cancers, and most patients are diagnosed in advanced stages. Enhancer of zeste homolog 2 (EZH2) is a major tumor marker and an effective therapeutic target for ovarian cancer, but the underlying molecular mechanism remains unclear. The present study investigated the biological effects of EZH2 knockout in SKOV3 cells in vitro and in vivo and explored the molecular mechanism by integrated analysis of messenger RNA sequencing (mRNA-seq) and chromatin immunoprecipitation sequencing (ChIP-seq) data.

Methods

The CRISPR/Cas9 system was used to establish EZH2 knockout SKOV3 cells. Protein expression was evaluated by Western blotting. The effect of EZH2 on ovarian cancer was evaluated in vitro with MTT, wound healing, Transwell, and apoptosis assays and in vivo with a xenograft model. mRNA-seq and ChIP-seq were performed to explore the molecular mechanism underlying the biological function of EZH2. Immunohistochemical staining (IHC) of tissue arrays was used to analyze the correlations among EZH2 and CYP27B1 expressions and prognosis.

Results

We obtained three EZH2 knockout subclones. EZH2 knockout SKOV3 cells exhibited significantly suppressed proliferation, migration, and invasion and a significantly increased apoptosis rate. The subcutaneous tumor formation rate decreased from 100 to 0% in the EZH2 knockout group. Integrated analysis of the mRNA-seq and ChIP-seq data identified 1,455 significantly upregulated genes with matching downregulated trimethylation of histone H3 lysine 27 (H3K27me3) methylation binding sites in 1b11H cells compared to SKOV3 cells. The set of downregulated genes in EZH2 knockout cells was highly enriched in genes regulating the activation of steroid biosynthesis; the top-ranked hub gene was CYP27B1. The EZH2 and CYP27B1 expression levels showed a statistically significant inverse correlation, which was also associated with unfavorable prognosis. The in vitro experiment demonstrated that CYP27B1 can suppress the proliferation, migration, and invasion of ovarian cancer cells. Moreover, the levels of AKT and p-AKT were significantly increased, whereas STAT3 was downregulated, in 1b11H cells compared to SKOV3 cells. Moreover, STAT3 and AKT overexpression was observed in 1b11H siRNA for CYP27B1 (siCYP27B1) cells.

Conclusion

EZH2 plays an important role in promoting cell proliferation, migration, and invasion in ovarian cancer by regulating the core steroid biosynthesis gene via H3K27me3 methylation. Moreover, CYP27B1, the steroid biosynthesis hub gene, might be a novel therapeutic target for ovarian cancer.

Long non-coding RNA CASC9 promotes gefitinib resistance in NSCLC by epigenetic repression of DUSP1

Resistance to epidermal growth factor receptor tyrosine kinase inhibitors (EGFR-TKIs), such as gefitinib, has greatly affected clinical outcomes in non-small cell lung cancer (NSCLC) patients. The long noncoding RNAs (lncRNAs) are known to regulate tumorigenesis and cancer progression, but their contributions to NSCLC gefitinib resistance remain poorly understood. In this study, by analyzing the differentially expressed lncRNAs in gefitinib-resistant cells and gefitinib-sensitive cells in the National Institute of Health GEO dataset, we found that lncRNA CASC9 expression was upregulated, and this was also verified in resistant tissues. Gain and loss of function studies showed that CASC9 inhibition restored gefitinib sensitivity both in vitro and in vivo, whereas CASC9 overexpression promoted gefitinib resistance. Mechanistically, CASC9 repressed the tumor suppressor DUSP1 by recruiting histone methyltransferase EZH2, thereby increasing the resistance to gefitinib. Furthermore, ectopic expression of DUSP1 increased gefitinib sensitivity by inactivating the ERK pathway. Our results highlight the essential role of CASC9 in gefitinib resistance, suggesting that the CASC9/EZH2/DUSP1 axis might be a novel target for overcoming EGFR-TKI resistance in NSCLC.

Menin-mediated Repression of Glycolysis in Combination with Autophagy Protects Colon Cancer Against Small-molecule EGFR Inhibitors

Menin serves both tumor suppressor and promoter roles in a highly tumor-specific manner. In colorectal cancer, menin is overexpressed and plays a critical role in regulating transcription of SKP2, and combined treatment with a menin inhibitor and small-molecule EGFR inhibitor (EGFRi) leads to synergistic killing of colorectal cancer cells. However, the full spectrum of menin function in colorectal cancer remains uncertain. Herein, we demonstrate that menin inhibition increases glycolysis in colorectal cancer cells. This menin inhibitor-induced increase in glycolysis occurs in an mTOR-independent manner and enhances the sensitivity of colorectal cancer cells to EGFRis. In addition, we show that EGFRis induce autophagy in colorectal cancer cells, which is important for cell survival in the setting of combined treatment with an EGFRi and menin inhibitor. Inhibition of autophagy with chloroquine further sensitizes colorectal cancers to treatment with the combination of an EGFRi and menin inhibitor. Together, these findings uncover a novel role for menin in colorectal cancer as a repressor of glycolysis and demonstrate that menin inhibitor-induced increases in glycolysis sensitize colorectal cancer cells to EGFRis. In addition, these findings illustrate the importance of autophagy as a protective mechanism against EGFRis, especially in the presence of menin inhibition. Ultimately, these data open the possibility of using menin-mediated regulation of glycolysis to potentially improve treatment modalities for colorectal cancer.

EZH2: a novel target for cancer treatment

Enhancer of zeste homolog 2 (EZH2) is enzymatic catalytic subunit of polycomb repressive complex 2 (PRC2) that can alter downstream target genes expression by trimethylation of Lys-27 in histone 3 (H3K27me3). EZH2 could also regulate gene expression in ways besides H3K27me3. Functions of EZH2 in cells proliferation, apoptosis, and senescence have been identified. Its important roles in the pathophysiology of cancer are now widely concerned. Therefore, targeting EZH2 for cancer therapy is a hot research topic now and different types of EZH2 inhibitors have been developed. In this review, we summarize the structure and action modes of EZH2, focusing on up-to-date findings regarding the role of EZH2 in cancer initiation, progression, metastasis, metabolism, drug resistance, and immunity regulation. Furtherly, we highlight the advance of targeting EZH2 therapies in experiments and clinical studies.

Diosgenin and GSK126 Produce Synergistic Effects on Epithelial-Mesenchymal Transition in Gastric Cancer Cells by Mediating EZH2 via the Rho/ROCK Signaling Pathway

Background

Diosgenin, a natural steroidal saponin isolated from Trigonella foenum-graecum, has been reported to exert anti-cancer effects. Inhibitors of enhancer of zeste homology 2 (EZH2) have been widely used in treatment of cancers. However, the effects of combined treatment with diosgenin and an EZH2 inhibitor on gastric cancer (GC) cells, and the mechanism for those effects are not fully understood.

Methods

AGS and SGC-7901 gastric cancer cells were treated with diosgenin (0 to 8 μM), followed by treatment with either diosgenin or an EZH2 inhibitor, GSK126 alone. Afterwards, an EZH2 overexpression plasmid and Rho inhibitor, GSK429286A was involved in cells. Cell proliferation, cell cycle distribution, and cell apoptosis, migration, and invasion were examined by CCK-8 assays, flow cytometry, and transwell assays. Western blotting was performed to detect the relative levels of protein expression.

Results

Treatment with diosgenin alone caused a dose-dependent decrease in the cell viability, and combined treatment with an EZH2 inhibitor plus GSK126 caused a further significant decrease. A further analysis revealed that treatment with either diosgenin or GSK126 alone induced significant increases in G0/G1 cell cycle arrest and apoptosis, and combined treatment with both agents induced further increases in those parameters. In addition, combined treatment with diosgenin and GSK126 synergistically induced even stronger effects on impaired cell proliferation, G0/G1 phase arrest, and cell apoptosis when compared to treatment with either diosgenin or GSK126 treatment alone. At the molecular level, we demonstrated that inhibition of Rho/ROCK signaling by combined treatment with diosgenin and GSK126 could downregulate the expression of epithelial–mesenchymal transition (EMT)-related molecules. We also found that EZH2 overexpression reversed the anti-tumor effect of diosgenin by inducing cell survival, blocking G1-phase arrest, and promoted EMT. While, these biological properties were further reversed by GSK429286A.

Conclusion

Collectively, combined treatment with diosgenin and GSK126 produced even more significant effects on GC cell inhibition by targeting EZH2 via Rho/ROCK signaling-mediated EMT, which might be a therapeutic strategy for improving the poor therapeutic outcomes obtained with GSK126 monotherapy.

Focused screening reveals functional effects of microRNAs differentially expressed in colorectal cancer

BACKGROUND

Colorectal cancer (CRC) is still a leading cause of death worldwide. Recent studies have pointed to an important role of microRNAs in carcinogenesis. Several microRNAs are described as aberrantly expressed in CRC tissues and in the serum of patients. However, functional outcomes of microRNA aberrant expression still need to be explored at the cellular level. Here, we aimed to investigate the effects of microRNAs aberrantly expressed in CRC samples in the proliferation and cell death of a CRC cell line.

METHODS

We transfected 31 microRNA mimics into HCT116 cells. Total number of live propidium iodide negative (PI-) and dead (PI+) cells were measured 4 days post-transfection by using a high content screening (HCS) approach. HCS was further used to evaluate apoptosis (via Annexin V and PI staining), and to discern between intrinsic and extrinsic apoptotic pathways, by detecting cleaved Caspase 9 and 8, respectively. To reveal mRNA targets and potentially involved mechanisms, we performed microarray gene expression and functional pathway enrichment analysis. Quantitative PCR and western blot were used to validate potential mRNA targets.

RESULTS

Twenty microRNAs altered the proliferation of HCT116 cells in comparison to control. miR-22-3p, miR-24-3p, and miR-101-3p significantly repressed cell proliferation and induced cell death. Interestingly, all anti-proliferative microRNAs in our study had been previously described as poorly expressed in the CRC samples. Predicted miR-101-3p targets that were also downregulated by in our microarray were enriched for genes associated with Wnt and cancer pathways, including MCL-1, a member of the BCL-2 family, involved in apoptosis. Interestingly, miR-101-3p preferentially downregulated the long anti-apoptotic MCL-1 L isoform, and reduced cell survival specifically by activating the intrinsic apoptosis pathway. Moreover, miR-101-3p also downregulated IL6ST, STAT3A/B, and MYC mRNA levels, genes associated with stemness properties of CRC cells.

CONCLUSIONS

microRNAs upregulated in CRC tend to induce proliferation in vitro, whereas microRNAs poorly expressed in CRC halt proliferation and induce cell death. We provide novel evidence linking preferential inhibition of the anti-apoptotic MCL-1 L isoform by miR-101-3p and consequent activation of the intrinsic apoptotic pathway as potential mechanisms for its antitumoral activity, likely due to the inhibition of the IL-6/JAK/STAT signaling pathway.

Epigenetic Control of Autophagy in Cancer Cells: A Key Process for Cancer-Related Phenotypes

Although autophagy is a well-known and extensively described cell pathway, numerous studies have been recently interested in studying the importance of its regulation at different molecular levels, including the translational and post-translational levels. Therefore, this review focuses on the links between autophagy and epigenetics in cancer and summarizes the. following: (i) how ATG genes are regulated by epigenetics, including DNA methylation and post-translational histone modifications; (ii) how epidrugs are able to modulate autophagy in cancer and to alter cancer-related phenotypes (proliferation, migration, invasion, tumorigenesis, etc.) and; (iii) how epigenetic enzymes can also regulate autophagy at the protein level. One noteable observation was that researchers most often reported conclusions about the regulation of the autophagy flux, following the use of epidrugs, based only on the analysis of LC3B-II form in treated cells. However, it is now widely accepted that an increase in LC3B-II form could be the consequence of an induction of the autophagy flux, as well as a block in the autophagosome-lysosome fusion. Therefore, in our review, all the published results describing a link between epidrugs and autophagy were systematically reanalyzed to determine whether autophagy flux was indeed increased, or inhibited, following the use of these potentially new interesting treatments targeting the autophagy process. Altogether, these recent data strongly support the idea that the determination of autophagy status could be crucial for future anticancer therapies. Indeed, the use of a combination of epidrugs and autophagy inhibitors could be beneficial for some cancer patients, whereas, in other cases, an increase of autophagy, which is frequently observed following the use of epidrugs, could lead to increased autophagy cell death.

Histone Lysine Methylation Dynamics Control EGFR DNA Copy-Number Amplification

Acquired chromosomal DNA copy gains are a feature of many tumors; however, the mechanisms that underpin oncogene amplification are poorly understood. Recent studies have begun to uncover the importance of epigenetic states and histone lysine methyltransferases (KMT) and demethylases (KDM) in regulating transient site-specific DNA copy-number gains (TSSG). In this study, we reveal a critical interplay between a myriad of lysine methyltransferases and demethylases in modulating H3K4/9/27 methylation balance to control extrachromosomal amplification of the EGFR oncogene. This study further establishes that cellular signals (hypoxia and EGF) are able to directly promote EGFR amplification through modulation of the enzymes controlling EGFR copy gains. Moreover, we demonstrate that chemical inhibitors targeting specific KMTs and KDMs are able to promote or block extrachromosomal EGFR amplification, which identifies potential therapeutic strategies for controlling EGFR copy-number heterogeneity in cancer, and, in turn, drug response. SIGNIFICANCE: This study identifies a network of epigenetic factors and cellular signals that directly control EGFR DNA amplification. We demonstrate that chemical inhibitors targeting enzymes controlling this amplification can be used to rheostat EGFR copy number, which uncovers therapeutic opportunities for controlling EGFR DNA amplification heterogeneity and the associated drug response.This article is highlighted in the In This Issue feature, p. 161.

Histone Modifications and their Role in Colorectal Cancer (Review)

The development of colorectal cancer is a complex and multistep process mediated by a variety of factors including the dysregulation of genetic and epigenetic under the influence of microenvironment. It is evident that epigenetics that affects gene activity and expression has been recognized as a critical role in the carcinogenesis. Aside from DNA methylation, miRNA level, and genomic imprinting, histone modification is increasingly recognized as an essential mechanism underlying the occurrence and development of colorectal cancer. Aberrant regulation of histone modification like acetylation, methylation and phosphorylation levels on specific residues is implicated in a wide spectrum of cancers, including colorectal cancer. In addition, as this process is reversible and accompanied by a plethora of deregulated enzymes, inhibiting those histone-modifying enzymes activity and regulating its level has been thought of as a potential path for tumor therapy. This review provides insight into the basic information of histone modification and its application in the colorectal cancer treatment, thereby offering new potential targets for treatment of colorectal cancer.

Pyrazole-based inhibitors of enhancer of zeste homologue 2 induce apoptosis and autophagy in cancer cells

Novel pyrazole-based EZH2 inhibitors have been prepared through a molecular pruning approach from known inhibitors bearing a bicyclic moiety as a central scaffold. The hit compound 1o (N-((4,6-dimethyl-2-oxo-1,2-dihydropyridin-3-yl)methyl)-5-methyl-1-phenyl-1H-pyrazole-4-carboxamide) showed low micromolar EZH2/PRC2 inhibition and high selectivity towards a panel of other methyltransferases. Moreover, 1o displayed cell growth arrest in breast MDA-MB231, leukaemia K562, and neuroblastoma SK-N-BE cancer cells joined to reduction of H3K27me3 levels and induction of apoptosis and autophagy.This article is part of a discussion meeting issue 'Frontiers in epigenetic chemical biology'.

Histone Methyltransferase EZH2: A Therapeutic Target for Ovarian Cancer

Ovarian cancer is the fifth leading cause of cancer-related deaths in females in the United States. There were an estimated 22,440 new cases and 14,080 deaths due to ovarian cancer in 2017. Most patients present with advanced-stage disease, revealing the urgent need for new therapeutic strategies targeting pathways of tumorigenesis and chemotherapy resistance. While multiple genomic changes contribute to the progression of this aggressive disease, it has become increasingly evident that epigenetic events play a pivotal role in ovarian cancer development. One of the well-studied epigenetic modifiers, the histone methyltransferase EZH2, is a member of polycomb repressive complex 2 (PRC2) and is commonly involved in transcriptional repression. EZH2 is the enzymatic catalytic subunit of the PRC2 complex that can alter gene expression by trimethylating lysine 27 on histone 3 (H3K27). In ovarian cancer, EZH2 is commonly overexpressed and therefore potentially serves as an effective therapeutic target. Multiple small-molecule inhibitors are being developed to target EZH2, which are now in clinical trials. Thus, in this review, we highlight the progress made in EZH2-related research in ovarian cancer and discuss the potential utility of targeting EZH2 with available small-molecule inhibitors for ovarian cancer. Mol Cancer Ther; 17(3); 591-602. ©2018 AACR.

A Natural Isoquinoline Alkaloid With Antitumor Activity: Studies of the Biological Activities of Berberine

Coptis, a traditional medicinal plant, has been used widely in the field of traditional Chinese medicine for many years. More recently, the chemical composition and bioactivity of Coptis have been studied worldwide. Berberine is a main component of Rhizoma Coptidis. Modern medicine has confirmed that berberine has pharmacological activities, such as anti-inflammatory, analgesic, antimicrobial, hypolipidemic, and blood pressure-lowering effects. Importantly, the active ingredient of berberine has clear inhibitory effects on various cancers, including colorectal cancer, lung cancer, ovarian cancer, prostate cancer, liver cancer, and cervical cancer. Cancer, ranked as one of the world’s five major incurable diseases by WHO, is a serious threat to the quality of human life. Here, we try to outline how berberine exerts antitumor effects through the regulation of different molecular pathways. In addition, the berberine-mediated regulation of epigenetic mechanisms that may be associated with the prevention of malignant tumors is described. Thus, this review provides a theoretical basis for the biological functions of berberine and its further use in the clinical treatment of cancer.

Inhibition of EZH2 and EGFR produces a synergistic effect on cell apoptosis by increasing autophagy in gastric cancer cells

Background

Numerous reports have shown that a combination of two or more drugs leads to better cancer treatment. Inhibitors of zeste homology 2 and epidermal growth factor receptor have been widely used in cancer treatments. However, the mechanisms of the combined use of these two drugs remain elusive.

Methods

Sulforhodamine B assays and Alexa Fluor^®-488 Annexin V/Dead Cell Apoptosis Kit were used to detect the cell proliferation and cell apoptosis in vitro, respectively. Western blotting analysis was used to detect the relative protein expression, and xenografted tumor was generated in nude mice to evaluate the effect in vivo.

Results

Treatment with either Gefitinib ranging from 0 to 12.5 µM or GSK126 ranging from 0 to 8.3 µM caused a dose-dependent decrease in the cell survival fraction, and the combination of Gefitinib at 12.5 µM and GSK126 at 8.3 µM caused further significant decrease. The combination indexes were 0.061, 0.591, 0.713, and 0.371 for MGC803, A549, PC-3, and MDB-MA-231, respectively. In MGC803 cells, the combination of GSK126 and Gefitinib synergistically induced cell apoptosis (56.2%), which was markedly higher as compared to either drug alone (7.6% and 10.6%, P<0.05). Treatment with either Gefitinib or GSK126 alone induced a significant increase in cell apoptosis in LC3-II and p-ULK, whereas the combination of the two induced a further increase. Pretreatment with an autophagy inhibitor, 3-methyladenine, prevented the apoptosis induced by the combined use of Gefitinib and GSK126. In addition, the combined use of Gefitinib and GSK126 also inhibited the activation of mammalian target of rapamycin signaling pathway. Furthermore, the combined use of GSK126 and Gefitinib synergistically inhibited xenografted tumor proliferation.

Conclusion

The combined use of GSK126 and Gefitinib exerts a synergic effect on tumor growth inhibition both in vitro and in vivo through inducing autophagy and promoting apoptosis. Therefore, GSK126 and Gefitinib in combination may be considered as a potential strategy in treating solid tumor clinically.

Epigenetic Regulation of Autophagy: A Path to the Control of Autoimmunity

Autoimmune diseases are a significant cause of debilitation and mortality globally and are in need of cost-effective therapeutics. Autophagy is a cellular pathway that facilitates immune modulation involved in both pathogen control and autoimmunity. Regulation is multifactorial and includes a number of epigenetic pathways which can involve modification of DNA-binding histones to induce autophagy-related mRNA synthesis or microRNA and decapping-associated mRNA degradation which results in autophagy suppression. Appreciation of epigenetic-based pathways involved in autophagy and autoimmunity may facilitate application of a burgeoning group of epigenetic pharmaceuticals to these important diseases.

Protective effects of resveratrol against mancozeb induced apoptosis damage in mouse oocytes

Mancozeb, a mixture of ethylene-bis-dithiocarbamate manganese and zinc salts, is one of the most widely used fungicides in agriculture. Mancozeb could lead to mitochondria dysfunction, cellular anti-oxidation enzymes depletion and apoptotic pathways activation. Previous studies indicated the exposure of mancozeb through mother would lead to irregular estrous cycles, decreased progesterone levels, reduced litter sizes, and more frequent delivery of dead fetuses. In this study, we investigated mancozeb inducing reproductive toxicity, especially focusing on its apoptotic effect and epigenetic modifications. We also showed that resveratrol, a kind of phytoalexin found in peanuts and grapes, can alleviate mancozeb's adverse effects, such as declined fertility, decreased ovary weight and primary follicles. Besides, mancozeb treated oocytes displayed suboptimal developmental competence and this can also be improved by treatment of resveratrol. More detailed investigation of these processes revealed that mancozeb increased reactive oxygen species, causing cell apoptosis and abnormal epigenetic modifications, and resveratrol can block these cytotoxic changes. Collectively, our results showed that resveratrol can alleviate mancozeb induced infertility and this was mainly through the correction of apoptotic tendency and the abnormity of cellular epigenetic modification.

Small molecule epigenetic screen identifies novel EZH2 and HDAC inhibitors that target glioblastoma brain tumor-initiating cells

Glioblastoma (GBM) is the most lethal and aggressive adult brain tumor, requiring the development of efficacious therapeutics. Towards this goal, we screened five genetically distinct patient-derived brain-tumor initiating cell lines (BTIC) with a unique collection of small molecule epigenetic modulators from the Structural Genomics Consortium (SGC). We identified multiple hits that inhibited the growth of BTICs in vitro, and further evaluated the therapeutic potential of EZH2 and HDAC inhibitors due to the high relevance of these targets for GBM. We found that the novel SAM-competitive EZH2 inhibitor UNC1999 exhibited low micromolar cytotoxicity in vitro on a diverse collection of BTIC lines, synergized with dexamethasone (DEX) and suppressed tumor growth in vivo in combination with DEX. In addition, a unique brain-penetrant class I HDAC inhibitor exhibited cytotoxicity in vitro on a panel of BTIC lines and extended survival in combination with TMZ in an orthotopic BTIC model in vivo. Finally, a combination of EZH2 and HDAC inhibitors demonstrated synergy in vitro by augmenting apoptosis and increasing DNA damage. Our findings identify key epigenetic modulators in GBM that regulate BTIC growth and survival and highlight promising combination therapies.

Citrullination/Methylation Crosstalk on Histone H3 Regulates ER-Target Gene Transcription

Posttranslational modifications of histone tails are a key contributor to epigenetic regulation. Histone H3 Arg26 and Lys27 are both modified by multiple enzymes, and their modifications have profound effects on gene expression. Citrullination of H3R26 by PAD2 and methylation of H3K27 by PRC2 have opposing downstream impacts on gene regulation; H3R26 citrullination activates gene expression, and H3K27 methylation represses gene expression. Both of these modifications are drivers of a variety of cancers, and their writer enzymes, PAD2 and EZH2, are the targets of drug therapies. After biochemical and cell-based analysis of these modifications, a negative crosstalk interaction is observed. Methylation of H3K27 slows citrullination of H3R26 30-fold, whereas citrullination of H3R26 slows methylation 30,000-fold. Examination of the mechanism of this crosstalk interaction uncovered a change in structure of the histone tail upon citrullination which prevents methylation by the PRC2 complex. This mechanism of crosstalk is reiterated in cell lines using knockdowns and inhibitors of both enzymes. Based our data, we propose a model in which, after H3 Cit26 formation, H3K27 demethylases are recruited to the chromatin to activate transcription. In total, our studies support the existence of crosstalk between citrullination of H3R26 and methylation of H3K27.

Initial testing (stage 1) of tazemetostat (EPZ-6438), a novel EZH2 inhibitor, by the Pediatric Preclinical Testing Program

BACKGROUND

Tazemetostat (EPZ-6438) is a selective inhibitor of the histone methyltransferase EZH2 and currently in clinical development for non-Hodgkin lymphoma and genetically defined tumors.

PROCEDURES

Tazemetostat was tested against the Pediatric Preclinical Testing Program (PPTP) solid tumor xenografts using a dose of 400 mg/kg administered twice daily by oral gavage for 28 days. H3K27me3:H3 ratios were determined in control and treated tumors.

RESULTS

Tazemetostat induced significant differences in event-free survival (EFS) distribution compared with control in nine of 30 (30%) of the xenografts studied. Significant differences in EFS distribution were observed in five of seven (71%) rhabdoid tumor xenograft lines compared with four of 23 (17%) nonrhabdoid xenograft lines (chi-square [χ² ] test P = 0.006). Tazemetostat induced tumor growth inhibition meeting criteria for intermediate and high EFS treated-to-control (T/C) activity in two of 25 (8%) and one of 25 (4%) xenografts, respectively. Intermediate and high activity for the EFS T/C metric was observed exclusively among rhabdoid tumor xenografts (three of five rhabdoid tumor vs 0 of 22 nonrhabdoid tumors (χ² test P < 0.001). One rhabdoid tumor xenograft (G401) showed stable disease. For one rhabdoid tumor (G401), delayed tumor regression to tazemetostat was noted following 1 week of tumor growth. Tazemetostat induced significant reduction of H3K27me3 levels in the majority of tumors compared with controls.

CONCLUSIONS

Tazemetostat demonstrated significant antitumor activity in rhabdoid tumor models but showed no consistent activity against any other histology. Tazemetostat reduced H3K27me3 levels irrespective of tumor response. Further preclinical testing to evaluate tazemetostat in combination with other anticancer agents is warranted.

Epigenetic treatment of pancreatic cancer: is there a therapeutic perspective on the horizon?

Pancreatic ductal adenocarcinoma (PDAC) constitutes one of the most aggressive malignancies with a 5-year survival rate of <7%. Due to growing incidence, late diagnosis and insufficient treatment options, PDAC is predicted to soon become one of the leading causes of cancer-related death. Although intensified cytostatic combinations, particularly gemcitabine plus nab-paclitaxel and the folinic acid, fluorouracil, irinotecan, oxaliplatin (FOLFIRINOX) protocol, provide some improvement in efficacy and survival compared with gemcitabine alone, a breakthrough in the treatment of metastatic pancreatic cancer remains out of sight. Nevertheless, recent translational research activities propose that either modulation of the immune response or pharmacological targeting of epigenetic modifications alone, or in combination with chemotherapy, might open highly powerful therapeutic avenues in GI cancer entities, including pancreatic cancer. Deregulation of key epigenetic factors and chromatin-modifying proteins, particularly those responsible for the addition, removal or recognition of post-translational histone modifications, are frequently found in human pancreatic cancer and hence constitute particularly exciting treatment opportunities. This review summarises both current clinical trial activities and discovery programmes initiated throughout the biopharma landscape, and critically discusses the chances, hurdles and limitations of epigenetic-based therapy in future PDAC treatment.

Role of the EZH2 histone methyltransferase as a therapeutic target in cancer

Besides being a genetic disease, cancer is also an epigenetic disease. The histone methyltransferase EZH2 is the catalytic subunit of PRC2, a highly conserved protein complex that regulates gene expression by methylating lysine 27 on histone H3. Given its role in tumorigenesis and its prognostic value in several tumor types, this protein appears a relevant therapeutic target. This review focuses on the preclinical and preliminary clinical results of studies investigating EZH2 inhibitors in human malignancies. These emerging data suggest that EZH2 inhibitors represent a very promising class of drugs, which will probably have a major impact on improving outcome and reducing toxicity for patients with indolent and aggressive B-cell lymphomas and other specific solid tumors.

Epigenetic and Immune Regulation of Colorectal Cancer Stem Cells

Colorectal cancer stem cells (CSCs) were initially considered to be a subset of undifferentiated tumor cells with well-defined phenotypic and molecular markers. However, emerging evidence indicates instead that colorectal CSCs are heterogeneous subsets of tumor cells that are continuously reshaped by the dynamic interactions between genetic, epigenetic, and immune factors in the tumor microenvironment. Thus, the colorectal CSC phenotypes and responsiveness to therapy may not only be a tumor cell-intrinsic feature, but also depend on tumor-extrinsic microenvironmental factors. Furthermore, emerging evidence also implicates colorectal CSCs in potential immune evasion. Therefore, understanding how colorectal CSC-intrinsic mechanisms cooperate with the extrinsic microenvironmental factors to dynamically shape colorectal CSC resistance to chemotherapy and immunotherapy holds great promise for development of targeted CSC therapies of advanced human CRC.

Mutation spectra of histone methyltransferases with canonical SET domains and EZH2-targeted therapy

Germline mutations in canonical SET-methyltransferases have been identified in autism and intellectual disability syndromes and gain-of-function somatic alterations in EZH2, MLL3, NSD1, WHSC1 (NSD2) and WHSC1L1 (NSD3) in cancer. EZH2 interacts with AR, ERα, β-catenin, FOXP3, NF-κB, PRC2, REST and SNAI2, resulting in context-dependent transcriptional activation and repression. Pharmacological EZH2 inhibitors are currently in clinical trials for the treatment of B-cell lymphomas and solid tumors. EZH2 inhibitors might also be applicable in the treatment of SWI/SNF-mutant cancers, reflecting the reciprocal expression of and functional overlap between EZH2 and SMARCA4. Because of the risks for autoimmune diseases, cognitive impairment, cardiomyopathy and myelodysplastic syndrome, EZH2 inhibitors should be utilized for cancer treatment in patients receiving long-term surveillance but not for cancer chemoprevention.

Polycomb Group (PcG) Proteins and Human Cancers: Multifaceted Functions and Therapeutic Implications

Polycomb group (PcG) proteins are transcriptional repressors that regulate several crucial developmental and physiological processes in the cell. More recently, they have been found to play important roles in human carcinogenesis and cancer development and progression. The deregulation and dysfunction of PcG proteins often lead to blocking or inappropriate activation of developmental pathways, enhancing cellular proliferation, inhibiting apoptosis, and increasing the cancer stem cell population. Genetic and molecular investigations of PcG proteins have long been focused on their PcG functions. However, PcG proteins have recently been shown to exert non-classical-Pc-functions, contributing to the regulation of diverse cellular functions. We and others have demonstrated that PcG proteins regulate the expression and function of several oncogenes and tumor suppressor genes in a PcG-independent manner, and PcG proteins are associated with the survival of patients with cancer. In this review, we summarize the recent advances in the research on PcG proteins, including both the Pc-repressive and non-classical-Pc-functions. We specifically focus on the mechanisms by which PcG proteins play roles in cancer initiation, development, and progression. Finally, we discuss the potential value of PcG proteins as molecular biomarkers for the diagnosis and prognosis of cancer, and as molecular targets for cancer therapy.