Yin Yang 1-mediated epigenetic silencing of tumour-suppressive microRNAs activates nuclear factor-κB in hepatocellular carcinoma

The YY1-CPT1C signaling axis modulates the proliferation and metabolism of pancreatic tumor cells under hypoxia

Carnitine palmitoyltransferase 1C (CPT1C) is an enzyme that regulates tumor cell proliferation and metabolism by modulating mitochondrial function and lipid metabolism. Hypoxia, commonly observed in solid tumors, promotes the proliferation and progression of pancreatic cancer by regulating the metabolic reprogramming of tumor cells. So far, the metabolic regulation of hypoxic tumor cells by CPT1C and the upstream mechanisms of CPT1C remain poorly understood. Yin Yang 1 (YY1) is a crucial oncogene for pancreatic tumorigenesis and acts as a transcription factor that is involved in multiple metabolic processes. This study aimed to elucidate the relationship between YY1 and CPT1C under hypoxic conditions and explore their roles in hypoxia-induced proliferation and metabolic alterations of tumor cells. The results showed enhancements in the proliferation and metabolism of PANC-1 cells under hypoxia, as evidenced by increased cell growth, cellular ATP levels, up-regulation of mitochondrial membrane potential, and decreased lipid content. Interestingly, knockdown of YY1 or CPT1C inhibited hypoxia-induced rapid cell proliferation and vigorous cell metabolism. Importantly, for the first time, we reported that YY1 directly activated the transcription of CPT1C and clarified that CPT1C was a novel target gene of YY1. Moreover, the YY1 and CPT1C were found to synergistically regulate the proliferation and metabolism of hypoxic cells through transfection with YY1 siRNA to CRISPR/Cas9-CPT1C knockout PANC-1 cells. Taken together, these results indicated that the YY1-CPT1C axis could be a new target for the intervention of pancreatic cancer proliferation and metabolism.

Exploiting gender-based biomarkers and drug targets: advancing personalized therapeutic strategies in hepatocellular carcinoma

This review systematically examines gender differences in hepatocellular carcinoma (HCC), identifying the influence of sex hormones, genetic variance, and environmental factors on the disease's epidemiology and treatment outcomes. Recognizing the liver as a sexually dimorphic organ, we highlight how gender-specific risk factors, such as alcohol consumption and obesity, contribute differently to hepatocarcinogenesis in men and women. We explore molecular mechanisms, including the differential expression of androgen and estrogen receptors, which mediate diverse pathways in tumor biology such as cell proliferation, apoptosis, and DNA repair. Our analysis underscores the critical need for gender-specific research in liver cancer, from molecular studies to clinical trials, to improve diagnostic accuracy and therapeutic effectiveness. By incorporating a gender perspective into all facets of liver cancer research, we advocate for a more precise and personalized approach to cancer treatment that acknowledges gender as a significant factor in both the progression of HCC and its response to treatment. This review aims to foster a deeper understanding of the biological and molecular bases of gender differences in HCC and to promote the development of tailored interventions that enhance outcomes for all patients.

Synthetic BZLF1-targeted transcriptional activator for efficient lytic induction therapy against EBV-associated epithelial cancers

The unique virus-cell interaction in Epstein-Barr virus (EBV)-associated malignancies implies targeting the viral latent-lytic switch is a promising therapeutic strategy. However, the lack of specific and efficient therapeutic agents to induce lytic cycle in these cancers is a major challenge facing clinical implementation. We develop a synthetic transcriptional activator that specifically activates endogenous BZLF1 and efficiently induces lytic reactivation in EBV-positive cancer cells. A lipid nanoparticle encapsulating nucleoside-modified mRNA which encodes a BZLF1-specific transcriptional activator (mTZ3-LNP) is synthesized for EBV-targeted therapy. Compared with conventional chemical inducers, mTZ3-LNP more efficiently activates EBV lytic gene expression in EBV-associated epithelial cancers. Here we show the potency and safety of treatment with mTZ3-LNP to suppress tumor growth in EBV-positive cancer models. The combination of mTZ3-LNP and ganciclovir yields highly selective cytotoxic effects of mRNA-based lytic induction therapy against EBV-positive tumor cells, indicating the potential of mRNA nanomedicine in the treatment of EBV-associated epithelial cancers.

Epigenetic regulation of enhancer of zeste homolog 2 (EZH2) -Yin Yang 1 (YY1) axis in cancer

In accordance with the World Health Organization, cancer is the second leading cause of death in patients. In recent years, the number of cancer patients has been growing, and the occurrence of cancer in people is becoming more common, primarily due to lifestyle factors. Yin Yang 1 (YY1) is a transcription factor that is widespread throughout. It is a zinc finger protein, falling under the GLI-Kruppel class. YY1 is known to regulate transcriptional activation and repression of various genes associated with different cellular processes such as DNA repair, autophagy, cell survival and apoptosis, and cell division. Meanwhile, EZH2 is a histone-lysine N-methyltransferase enzyme encoded by gene 7 in humans. Its main function involves catalyzing the addition of methyl groups to histone H3 at lysine 27 (H3K27me3), and it is involved in regulating CD8 + T cell fate and function. It is a subunit of a Polycomb repressor complex 2 (PRC2). The EZH2 gene encodes for an enzyme that is involved in histone methylation and transcriptional repression. It adds methyl groups to lysine 27 on histone H3 (H3K27me3) with the help of the cofactor S-adenosyl-L-methionine. In addition to its role in epigenetic regulation, EZH2 also acts as a regulator of CD8+ T cell fate and function. EZH2 has been implicated in T Cell Receptor (TCR) signaling via the regulation of actin polymerization. In fact, EZH2 is involved in numerous signaling pathways that lead to tumorigenesis. EZH2 is mutated in cancer and shows overexpression. Due to its mutation and overexpression, the cells that help combat cancer are suppressed and carcinogenicity is promoted. The association of EZH2 and YY1 poses an intriguing mechanism in relation to cancer.

Dysregulated microRNAs as a biomarker for diagnosis and prognosis of hepatitis B virus-associated hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is a malignancy with a high incidence and fatality rate worldwide. Hepatitis B virus (HBV) infection is one of the most important risk factors for its occurrence and development. Early detection of HBV-associated HCC (HBV-HCC) can improve clinical decision-making and patient outcomes. Biomarkers are extremely helpful, not only for early diagnosis, but also for the development of therapeutics. MicroRNAs (miRNAs), a subset of non-coding RNAs approximately 22 nucleotides in length, have increasingly attracted scientists' attention due to their potential utility as biomarkers for cancer detection and therapy. HBV profoundly impacts the expression of miRNAs potentially involved in the development of hepatocarcinogenesis. In this review, we summarize the current progress on the role of miRNAs in the diagnosis and treatment of HBV-HCC. From a molecular standpoint, we discuss the mechanism by which HBV regulates miRNAs and investigate the exact effect of miRNAs on the promotion of HCC. In the near future, miRNA-based diagnostic, prognostic, and therapeutic applications will make their way into the clinical routine.

Targeting Transcription Factor YY1 for Cancer Treatment: Current Strategies and Future Directions

Cancer represents a significant and persistent global health burden, with its impact underscored by its prevalence and devastating consequences. Whereas numerous oncogenes could contribute to cancer development, a group of transcription factors (TFs) are overactive in the majority of tumors. Targeting these TFs may also combat the downstream oncogenes activated by the TFs, making them attractive potential targets for effective antitumor therapeutic strategy. One such TF is yin yang 1 (YY1), which plays crucial roles in the development and progression of various tumors. In preclinical studies, YY1 inhibition has shown efficacy in inhibiting tumor growth, promoting apoptosis, and sensitizing tumor cells to chemotherapy. Recent studies have also revealed the potential of combining YY1 inhibition with immunotherapy for enhanced antitumor effects. However, clinical translation of YY1-targeted therapy still faces challenges in drug specificity and delivery. This review provides an overview of YY1 biology, its role in tumor development and progression, as well as the strategies explored for YY1-targeted therapy, with a focus on their clinical implications, including those using small molecule inhibitors, RNA interference, and gene editing techniques. Finally, we discuss the challenges and current limitations of targeting YY1 and the need for further research in this area.

Depletion of enhancer zeste homolog 2 (EZH2) directs transcription factors associated with T cell differentiation through epigenetic regulation of Yin Yang 1(YY1) in combating non-small cell lung cancer (NSCLC)

Non-Small Cell Lung Cancer (NSCLC) is the leading cause of death in all countries alike. In the current study, we have found out that Histone H3Lys4trimethylation is abnormal on YY1 in CD4⁺T Helper (T_H) cells of NSCLC patients which is evident by Histone H3Lys27 trimethylation mediated via EZH2. We investigated the status of Yin Yang 1 (YY1) and the involvement of certain transcription factors that lead to tumorigenesis after depleting endogenous EZH2 in vitro by CRISPR/Cas9 in the CD4⁺T_H1-or-T_H2-polarized cells isolated initially as CD4⁺T_H0 cells from the PBMC of the control subjects and patients suffering from NSCLC. After depletion of endogenous EZH2, RT-qPCR based mRNA expression analysis showed that there was an increase in the expression of T_H1 specific genes and a decrease in the expression of T_H2 specific genes in NSCLC patients CD4⁺T_H cells. We can conclude that this group of NSCLC patients may have the tendency at least in vitro to elucidate adaptive/protective immunity through the depletion of endogenous EZH2 along with the reduction in the expression of YY1. Moreover, depletion of EZH2 not only suppressed the CD4⁺CD25⁺FOXP3⁺Regulatory T cells (Treg) but also it aided the generation of CD8⁺Cytotoxic T Lymphocytes (CTL) which were involved in killing of the NSCLC cells. Thus the transcription factors involved in EZH2 mediated T cell differentiation linked to malignancies offers us an appealing avenue of targeted therapeutic intervention for NSCLC.

Comprehensive Analysis of the Expression and Prognosis for Lipid Metabolism-Related Genes in Hepatocellular Carcinoma

Hao DingBackground  This study aimed to screen potential key genes associated with lipid metabolism and to evaluate their expressions and prognosis values in hepatocellular carcinoma (HCC). Methods  Data sets GSE6764, GSE14520, and GSE112790 were used to identify the common differentially expressed genes (DEGs). Protein-protein interaction (PPI) network was constructed by STRING database. Hub genes in PPI network were identified and subjected to functional enrichment analysis to screen lipid metabolism-related genes. The expressions of selected genes and their associations with prognosis were analyzed using UALCAN, The Human Protein Atlas, and Kaplan-Meier plotter databases. The transcriptional factor (TF)-gene regulatory network was constructed using NetworkAnalyst. Results  A total of 331 common DEGs including 106 upregulated and 225 downregulated genes were identified. PPI network analysis showed that 76 genes with high degrees were identified as hub genes, among which 14 genes were lipid metabolism-related genes. PON1, CYP2C9, and SPP1 were found to be the independent prognostic markers. Key TFs with close interactions with these prognostic genes, including HINFP, SRF, YY1, and NR3C1, were identified from the TF-gene regulatory network. Conclusion  This study presented evidence for the prognostic capabilities of lipid metabolism-related genes in HCC, and newly identified HINFP and NR3C1 as potential biomarkers for HCC.

Super-Enhancers, Phase-Separated Condensates, and 3D Genome Organization in Cancer

3D chromatin organization plays an important role in transcription regulation and gene expression. The 3D genome is highly maintained by several architectural proteins, such as CTCF, Yin Yang 1, and cohesin complex. This structural organization brings regulatory DNA elements in close proximity to their target promoters. In this review, we discuss the 3D chromatin organization of super-enhancers and their relationship to phase-separated condensates. Super-enhancers are large clusters of DNA elements. They can physically contact with their target promoters by chromatin looping during transcription. Multiple transcription factors can bind to enhancer and promoter sequences and recruit a complex array of transcriptional co-activators and RNA polymerase II to effect transcriptional activation. Phase-separated condensates of transcription factors and transcriptional co-activators have been implicated in assembling the transcription machinery at particular enhancers. Cancer cells can hijack super-enhancers to drive oncogenic transcription to promote cell survival and proliferation. These dysregulated transcriptional programs can cause cancer cells to become highly dependent on transcriptional regulators, such as Mediator and BRD4. Moreover, the expression of oncogenes that are driven by super-enhancers is sensitive to transcriptional perturbation and often occurs in phase-separated condensates, supporting therapeutic rationales of targeting SE components, 3D genome organization, or dysregulated condensates in cancer.

The Mechanism Underlying the ncRNA Dysregulation Pattern in Hepatocellular Carcinoma and Its Tumor Microenvironment

HCC is one of the most common malignant tumors and has an extremely poor prognosis. Accumulating studies have shown that noncoding RNA (ncRNA) plays an important role in hepatocellular carcinoma (HCC) development. However, the details of the related mechanisms remain unclear. The heterogeneity of the tumor microenvironment (TME) calls for ample research with deep molecular characterization, with the hope of developing novel biomarkers to improve prognosis, diagnosis and treatment. ncRNAs, particularly microRNAs (miRNAs), long noncoding RNAs (lncRNAs), and circular RNAs (circRNAs), have been found to be correlated with HCC neogenesis and progression. In this review, we summarized the aberrant epigenetic and genetic alterations caused by dysregulated ncRNAs and the functional mechanism of classical ncRNAs in the regulation of gene expression. In addition, we focused on the role of ncRNAs in the TME in the regulation of tumor cell proliferation, invasion, migration, immune cell infiltration and functional activation. This may provide a foundation for the development of promising potential prognostic/predictive biomarkers and novel therapies for HCC patients.

YY1 Oligomerization Is Regulated by Its OPB Domain and Competes with Its Regulation of Oncoproteins

Simple Summary

YY1 regulates various cancer-related genes and activates key oncoproteins. In this study, we discovered that the oncoprotein binding (OPB) domain of YY1 is both necessary and stimulatory to its oligomerization. The hydrophobic residues, especially F219, in the OPB are essential to YY1 intermolecular interaction. Strikingly, the mutations of the hydrophobic residues showed better ability than wild-type YY1 in promote breast cancer cell proliferation and migration. Our further study revealed that YY1 proteins with mutated hydrophobic residues in the OPB domain showed improved binding affinity to EZH2. Overall, our data support the model of a mutually exclusive process between oligomerization of YY1 and its regulation of the oncoproteins EZH2, AKT and MDM2.

Abstract

Yin Yang 1 (YY1) plays an oncogenic role through regulating the expression of various cancer-related genes and activating key oncoproteins. Previous research reported that YY1 protein formed dimers or oligomers without definite biological implications. In this study, we first demonstrated the oncoprotein binding (OPB) and zinc finger (ZF) domains of YY1 as the regions involved in its intermolecular interactions. ZFs are well-known for protein dimerization, so we focused on the OPB domain. After mutating three hydrophobic residues in the OPB to alanines, we discovered that YY1(F219A) and YY1(3A), three residues simultaneously replaced by alanines, were defective of intermolecular interaction. Meanwhile, the OPB peptide could robustly facilitate YY1 protein oligomerization. When expressed in breast cancer cells with concurrent endogenous YY1 knockdown, YY1(F219A) and (3A) mutants showed better capacity than wt in promoting cell proliferation and migration, while their interactions with EZH2, AKT and MDM2 showed differential alterations, especially with improved EZH2 binding affinity. Our study revealed a crucial role of the OPB domain in facilitating YY1 oligomerization and suggested a mutually exclusive regulation between YY1-mediated enhancer formation and its activities in promoting oncoproteins.

Probing Synergistic Targets by Natural Compounds for Hepatocellular Carcinoma

Background

Designing combination drugs for malignant cancers has been restricted due to the scarcity of synergy-medicated targets, while some natural compounds have demonstrated potential to enhance anticancer effects.

Methods

We here explored the feasibility of probing synergy-mediated targets by Berberine (BER) and Evodiamine (EVO) in hepatocellular carcinoma (HCC). Using the genomics-derived HCC signaling networks of compound treatment, NF-κB and c-JUN were inferred as key responding elements with transcriptional activity coinhibited during the synergistic cytotoxicity induction in BEL-7402 cells. Then, selective coinhibitors of NF-κB and c-JUN were tested demonstrating similar synergistic antiproliferation activity.

Results

Consistent with in vivo experiments of zebrafish, coinhibitors were found to significantly reduce tumor growth by 79% and metastasis by 96% compared to blank control, accompanied by anti-angiogenic activity. In an analysis of 365 HCC individuals, the low expression group showed significantly lower malignancies and better prognosis, with the median survival time increased from 67 to 213%, compared to the rest of the groups.

Conclusion

Together, NF-κB and c-JUN were identified as promising synergistic inducers in developing anti-HCC therapies. Also, our method may provide a feasible strategy to explore new targeting space from natural compounds, opening opportunities for the rational design of combinational formulations in combatting malignant cancers.

Acinetobacter baumannii up-regulates LncRNA-GAS5 and promotes the degradation of STX17 by blocking the activation of YY1

Acinetobacter baumanniitriggers autophagy, affects the degradation of autophagy, and causes severe inflammatory injury. LncRNA growth arrest-specific transcript 5 (LncRNA-GAS5) and Yin and Yang 1 (YY1) are known to play an important role in the regulation of autophagy, however, the precise role of LncRNA-GAS5 and YY1 in the damage to autophagy caused by Acinetobacter baumanniiremains unclear. The aim of this study was to investigate the role of LncRNA-GAS5 and YY1 in the regulation of autophagy induced by Acinetobacter baumannii. We found that LncRNA-GAS5 was up-regulated following infection with Acinetobacter baumannii, thus resulting in the degradation of STX17, autophagy disorders, and the aggravated replication of Acinetobacter baumannii. We also analyzed the mechanism of interaction between LncRNA-GAS5 and YY1 and found that YY1 regulated its expression in a negative manner by binding to the promoter of LncRNA-GAS5. LncRNA-GAS5 and YY1 had opposite effects on the expression of STX17, this process maintained the stable expression of STX17. Following Acinetobacter baumannii infection, YY1 was down regulated and then separated from the binding region of LncRNA-GAS5, thus resulting in the activation of LncRNA-GAS5 transcription and reduction in STX17 protein expression. Finally, we infected LncRNA-GAS5 knockdown mice with Acinetobacter baumannii, the expression levels of IFN-β in the lungs increased significantly, this alleviated lung injury. In conclusion, our work demonstrated the mechanism by which Acinetobacter baumannii infection can cause the degradation of STX17. We also demonstrated that LncRNA-GAS5 may be a potential therapeutic target for the treatment of lung injury induced by Acinetobacter baumannii.

Multifaceted regulation of hepatic lipid metabolism by YY1

This study shows that YY1 regulates hepatic lipid metabolism by directly or indirectly regulating the expression of several key upstream transcription factors and their coactivators.

Recent studies suggested that dysregulated YY1 plays a pivotal role in many liver diseases. To obtain a detailed view of genes and pathways regulated by YY1 in the liver, we carried out RNA sequencing in HepG2 cells after YY1 knockdown. A rigid set of 2,081 differentially expressed genes was identified by comparing the YY1-knockdown samples (n = 8) with the control samples (n = 14). YY1 knockdown significantly decreased the expression of several key transcription factors and their coactivators in lipid metabolism. This is illustrated by YY1 regulating PPARA expression through binding to its promoter and enhancer regions. Our study further suggest that down-regulation of the key transcription factors together with YY1 knockdown significantly decreased the cooperation between YY1 and these transcription factors at various regulatory regions, which are important in regulating the expression of genes in hepatic lipid metabolism. This was supported by the finding that the expression of SCD and ELOVL6, encoding key enzymes in lipogenesis, were regulated by the cooperation between YY1 and PPARA/RXRA complex over their promoters.

Hedgehog Signaling: Implications in Cancers and Viral Infections

The hedgehog (SHH) signaling pathway is primarily involved in embryonic gut development, smooth muscle differentiation, cell proliferation, adult tissue homeostasis, tissue repair following injury, and tissue polarity during the development of vertebrate and invertebrate organisms. GLIoma-associated oncogene homolog (GLI) family of zinc-finger transcription factors and smoothened (SMO) are the signal transducers of the SHH pathway. Both SHH ligand-dependent and independent mechanisms activate GLI proteins. Various transcriptional mechanisms, posttranslational modifications (phosphorylation, ubiquitination, proteolytic processing, SUMOylation, and acetylation), and nuclear-cytoplasmic shuttling control the activity of SHH signaling pathway proteins. The dysregulated SHH pathway is associated with bone and soft tissue sarcomas, GLIomas, medulloblastomas, leukemias, and tumors of breast, lung, skin, prostate, brain, gastric, and pancreas. While extensively studied in development and sarcomas, GLI family proteins play an essential role in many host-pathogen interactions, including bacterial and viral infections and their associated cancers. Viruses hijack host GLI family transcription factors and their downstream signaling cascades to enhance the viral gene transcription required for replication and pathogenesis. In this review, we discuss a distinct role(s) of GLI proteins in the process of tumorigenesis and host-pathogen interactions in the context of viral infection-associated malignancies and cancers due to other causes. Here, we emphasize the potential of the Hedgehog (HH) pathway targeting as a potential anti-cancer therapeutic approach, which in the future could also be tested in infection-associated fatalities.

Hepigenetics: A Review of Epigenetic Modulators and Potential Therapies in Hepatocellular Carcinoma

Hepatocellular carcinoma is the fifth most common cancer worldwide and the second most lethal, following lung cancer. Currently applied therapeutic practices rely on surgical resection, chemotherapy and radiotherapy, or a combination thereof. These treatment options are associated with extreme adversities, and risk/benefit ratios do not always work in patients' favor. Anomalies of the epigenome lie at the epicenter of aberrant molecular mechanisms by which the disease develops and progresses. Modulation of these anomalous events poses a promising prospect for alternative treatment options, with an abundance of felicitous results reported in recent years. Herein, the most recent epigenetic modulators in hepatocellular carcinoma are recapitulated on.

miR-34a-5p suppresses the invasion and metastasis of liver cancer by targeting the transcription factor YY1 to mediate MYCT1 upregulation

BACKGROUND

In recent years, microRNAs (miRNAs) are reported to act as molecular biomarkers for cancer diagnosis, treatment, and prognosis (including liver cancer) and to be involved in the development and progression of cancer and other physiological and pathological changes. However, the role of miR-34a-5p in liver cancer is still largely unknown.

METHODS

In our study, the expression of miR-34a-5p in liver cancer tissues and HCC cell lines was detected by qRT-PCR. The CCK-8, scratch wound-healing motility and Transwell assays were used to evaluate the effect on cell proliferation, migration and invasion. The expression of YY1, E-cadherin, N-cadherin and vimentin was analysed by western blotting. The dual luciferase assay was performed to confirm whether YY1 is a target of miR-34a-5p. The combination of YY1 and MYCT1 was detected by chromatin immunoprecipitation (ChIP) assay.

RESULTS

The results showed that miR-34a-5p was downregulated in liver cancer tissues and HCC cell lines. Overexpression of miR-34a-5p inhibited the proliferation, migration and invasion of liver cancer cells. YY1 was a direct target of miR-34a-5p, and the expression of YY1 could reverse the influence of miR-34a-5p on the proliferation, migration and invasion of liver cancer cells. YY1 inhibited MYCT1 expression by directly binding to its promoter region, and knockdown of MYCT1 reversed the influence of miR-34a-5p on the proliferation, migration and invasion of liver cancer cells.

CONCLUSION

Our results suggest that miR-34a-5p could inhibit the invasion and metastasis of hepatoma cells by targeting YY1-mediated MYCT1 transcriptional repression.

The role of histone methylation in the development of digestive cancers: a potential direction for cancer management

Digestive cancers are the leading cause of cancer-related death worldwide and have high risks of morbidity and mortality. Histone methylation, which is mediated mainly by lysine methyltransferases, lysine demethylases, and protein arginine methyltransferases, has emerged as an essential mechanism regulating pathological processes in digestive cancers. Under certain conditions, aberrant expression of these modifiers leads to abnormal histone methylation or demethylation in the corresponding cancer-related genes, which contributes to different processes and phenotypes, such as carcinogenesis, proliferation, metabolic reprogramming, epithelial–mesenchymal transition, invasion, and migration, during digestive cancer development. In this review, we focus on the association between histone methylation regulation and the development of digestive cancers, including gastric cancer, liver cancer, pancreatic cancer, and colorectal cancer, as well as on its clinical application prospects, aiming to provide a new perspective on the management of digestive cancers.

Epigenetic Silencing of miR-9 Promotes Migration and Invasion by EZH2 in Glioblastoma Cells

Glioblastoma (GBM) is the most common primary brain tumor in adults. Tumor invasion is the major reason for treatment failure and poor prognosis in GBM. Inhibiting migration and invasion has become an important therapeutic strategy for GBM treatment. Enhancer of zeste homolog 2 (EZH2) and C-X-C motif chemokine receptor 4 (CXCR4) have been determined to have important roles in the occurrence and development of tumors, but the specific relationship between EZH2 and CXCR4 expression in GBM is less well characterized. In this study, we report that EZH2 and CXCR4 were overexpressed in glioma patients. Furthermore, elevated EZH2 and CXCR4 were correlated with shorter disease-free survival. In three human GBM cell lines, EZH2 modulated the expression of miR-9, which directly targeted the oncogenic signaling of CXCR4 in GBM. The ectopic expression of miR-9 dramatically inhibited the migratory capacity of GBM cells in vitro. Taken together, our results indicate that miR-9, functioning as a tumor-suppressive miRNA in GBM, is suppressed through epigenetic silencing by EZH2. Thus, miR-9 may be an attractive target for therapeutic intervention in GBM.

HOXD3 was negatively regulated by YY1 recruiting HDAC1 to suppress progression of hepatocellular carcinoma cells via ITGA2 pathway

Objectives

HOXD3 is associated with progression of multiple types of cancer. This study aimed to identify the association of YY1 with HOXD3‐ITGA2 axis in the progression of hepatocellular carcinoma.

Materials and Methods

Bioinformatics assay was used to identify the effect of YY1, HOXD3 and ITGA2 expression in HCC tissues. The function of YY1 and HOXD3 in HCCs was determined by qRT‐PCR, MTT, apoptosis, Western blotting, colony formation, immunohistochemistry, and wound‐healing and transwell invasion assays. The relationship between YY1 and HOXD3 or HOXD3 and ITGA2 was explored by RNA‐Seq, ChIP‐PCR, dual luciferase reports and Pearson's assays. The interactions between YY1 and HDAC1 were determined by immunofluorescence microscopy and Co‐IP.

Results

Herein, we showed that the expression of YY1, HOXD3 and ITGA2 associated with the histologic and pathologic stages of HCC. Moreover, YY1, recruiting HDAC1, can directly target HOXD3 to regulate progression of HCCs. The relationship between YY1 and HOXD3 was unknown until uncovered by our present investigation. Furthermore, HOXD3 bound to promoter region of ITGA2 and up‐regulated the expression, thus activating the ERK1/2 signalling and inducing HCCs proliferation, metastasis and migration in the vitro and vivo.

Conclusions

Therefore, HOXD3, a target of YY1, facilitates HCC progression via activation of the ERK1/2 signalling by promoting ITGA2. This finding provides a new whole way to HCC therapy by serving YY1‐HOXD3‐ITGA2 regulatory axis as a potential therapeutic target for HCC therapy.

Molecular interplay between linc01134 and YY1 dictates hepatocellular carcinoma progression

Background

Revealing the mechanical role of long non-coding RNAs (lncRNAs) in tumorigenesis can contribute to novel therapeutic target for cancers. The regulatory role of linc01134 in hepatocellular carcinoma (HCC) has not been studied yet.

Materials and methods

qRT-PCR and western blot were conducted to measure relevant RNA and protein expressions. CCK-8, colony formation, EdU, flow cytometry, wound-healing, transwell assays and xenograft experiments were performed to determine the role of linc01134 in HCC. ChIP and luciferase reporter assays were performed to analyze the effects of Yin Yang-1 (YY1) on linc01134 transcription activity. Relevant mechanical experiments were performed to verify interaction between relative genes.

Results

YY1 enhanced linc01134 transcription by interacting with linc01134 promoter. Knockdown of linc01134 inhibited proliferation, migration and epithelial-mesenchymal transition (EMT), yet promoting apoptosis in HCC cells. Mechanically, linc01134 acted as miR-324-5p sponge and interacted with insulin-like growth factor 2 mRNA binding protein 1 (IGF2BP1) to increase the stability of YY1 mRNA expression. Up-regulated YY1 continuously stimulated linc01134 expression by enhancing linc01134 promoter activity, forming a positive feedback loop.

Conclusion

Linc01134/miR-324-5p/IGF2BP1/YY1 feedback loop mediates HCC progression, which possibly provide prognosis and treatment target of HCC.

The biological implications of Yin Yang 1 in the hallmarks of cancer

Tumorigenesis is a multistep process characterized by the acquisition of genetic and epigenetic alterations. During the course of malignancy development, tumor cells acquire several features that allow them to survive and adapt to the stress-related conditions of the tumor microenvironment. These properties, which are known as hallmarks of cancer, include uncontrolled cell proliferation, metabolic reprogramming, tumor angiogenesis, metastasis, and immune system evasion. Zinc-finger protein Yin Yang 1 (YY1) regulates numerous genes involved in cell death, cell cycle, cellular metabolism, and inflammatory response. YY1 is highly expressed in many cancers, whereby it is associated with cell proliferation, survival, and metabolic reprogramming. Furthermore, recent studies also have demonstrated the important role of YY1-related non-coding RNAs in acquiring cancer-specific characteristics. Therefore, these YY1-related non-coding RNAs are also crucial for YY1-mediated tumorigenesis. Herein, we summarize recent progress with respect to YY1 and its biological implications in the context of hallmarks of cancer.

Long noncoding RNA HOTAIR promotes medulloblastoma growth, migration and invasion by sponging miR-1/miR-206 and targeting YY1

PURPOSE

Long non-coding RNA (LncRNA) HOX transcript antisense RNA (HOTAIR) and Yin Yang 1 (YY1) are reported to be involved in tumorigenesis. However, the effect and molecular mechanism of HOTAIR on YY1 expression remains poorly understood. The study aimed to investigate the functions and molecular mechanism of LncRNA HOTAIR in medulloblastoma progression.

METHODS

qPCR was performed to detect HOTAIR and YY1 mRNA in tissues and cells, as well as that of miR-1 and miR-206 expression levels. Western blot assay was used to test YY1 and EMT-related biomarkers' protein levels. Cell proliferation was tested with CCK-8 assay and colony formation assay. Migration and invasion abilities were tested with Transwell migration and invasion assays. Tumor growth was tested with an in vivo animal study. Cell apoptosis was tested with an Annexin V-FITC/PI kit. Luciferase assay was used to test the luciferase intensity of YY1 and HOTAIR. RNA pull down assay was used to detect the combination between HOTAIR and miR-1/miR-206.

RESULTS

In this study, we found that HOTAIR and YY1 were up-regulated in medulloblastoma tissues and cell lines, and HOTAIR increased YY1 expression. The molecular mechanism demonstrated that HOTAIR negatively regulated miR-1 and miR-206 expression, which can directly target YY1 in medulloblastoma cells. Moreover, HOTAIR increased YY1 expression through binding to miR-1 and miR-206. The functional experiments showed that HOTAIR knockdown suppressed medulloblastoma cell proliferation, tumor growth, migration and invasion, and promoted cell apoptosis via the modulation of the miR-1/miR-206-YY1 axis, as well as epithelial to mesenchymal transition (EMT).

CONCLUSION

These data indicate that HOTAIR promotes medulloblastoma progression via acting as a competing endogenous RNA (ceRNA) to regulate YY1 expression through binding to miR-1 and miR-206.

In silico identification of EP400 and TIA1 as critical transcription factors involved in human hepatocellular carcinoma relapse

Hepatocellular carcinoma (HCC) is the second leading cause of cancer-associated mortality worldwide. Transcription factors (TFs) are crucial proteins that regulate gene expression during cancer progression; however, the roles of TFs in HCC relapse remain unclear. To identify the TFs that drive HCC relapse, the present study constructed co-expression network and identified the Tan module the most relevant to HCC relapse. Numerous hub TFs (highly connected) were subsequently obtained from the Tan module according to the intra-module connectivity and the protein-protein interaction network connectivity. Next, E1A-binding protein p400 (EP400) and TIA1 cytotoxic granule associated RNA binding protein (TIA1) were identified as hub TFs differentially connected between the relapsed and non-relapsed subnetworks. In addition, zinc finger protein 143 (ZNF143) and Yin Yang 1 (YY1) were also identified by using the plugin iRegulon in Cytoscape as master upstream regulatory elements, which could potentially regulate expression of the genes and TFs of the Tan module, respectively. The Kaplan-Meier (KM) curves obtained from KMplot and Gene Expression Profiling Interactive Analysis tools confirmed that the high expression of EP400 and TIA1 were significantly associated with shorter relapse-free survival and disease-free survival of patients with HCC. Furthermore, the KM curves from the UALCAN database demonstrated that high EP400 expression significantly reduced the overall survival of patients with HCC. EP400 and TIA1 may therefore serve as potential prognostic and therapeutic biomarkers.

The Two Sides of YY1 in Cancer: A Friend and a Foe

Yin Yang 1 (YY1), a dual function transcription factor, is known to regulate transcriptional activation and repression of many genes associated with multiple cellular processes including cellular differentiation, DNA repair, autophagy, cell survival vs. apoptosis, and cell division. Owing to its role in processes that upon deregulation are linked to malignant transformation, YY1 has been implicated as a major driver of many cancers. While a large body of evidence supports the role of YY1 as a tumor promoter, recent reports indicated that YY1 also functions as a tumor suppressor. The mechanism by which YY1 brings out opposing outcome in tumor growth vs. suppression is not completely clear and some of the recent reports have provided significant insight into this. Likewise, the mechanism by which YY1 functions both as a transcriptional activator and repressor is not completely clear. It is likely that the proteins with which YY1 interacts might determine its function as an activator or repressor of transcription as well as its role as a tumor suppressor or promoter. Hence, a collection of YY1-protein interactions in the context of different cancers would help us gain an insight into how YY1 promotes or suppresses cancers. This review focuses on the YY1 interacting partners and its target genes in different cancer models. Finally, we discuss the possibility of therapeutically targeting the YY1 in cancers where it functions as a tumor promoter.

Yin Yang 1 facilitates hepatocellular carcinoma cell lipid metabolism and tumor progression by inhibiting PGC-1β-induced fatty acid oxidation

Lipid accumulation is a driving force in tumor development, as it provides tumor cells with both energy and the building blocks of phospholipids for construction of cell membranes. Aberrant homeostasis of lipid metabolism has been observed in various tumors; however, the molecular mechanism has not been fully elucidated.

Methods: Yin yang 1 (YY1) expression in hepatocellular carcinoma (HCC) was analyzed using clinical specimens, and its roles in HCC in lipid metabolism were examined using gain- and loss-of function experiments. The mechanism of YY1 regulation on peroxisome proliferator-activated receptor gamma coactivator-1β (PGC-1β) and its downstream genes medium-chain acyl-CoA dehydrogenase (MCAD) and long-chain acyl-CoA dehydrogenase (LCAD) were investigated using molecular biology and biochemical methods. The role of YY1/ PGC-1β axis in hepatocarcinogenesis was studied using xenograft experiment.

Results: This study showed that YY1 suppresses fatty acid β-oxidation, leading to increase of cellular triglyceride level and lipid accumulation in HCC cells, and subsequently induction of the tumorigenesis potential of HCC cells. Molecular mechanistic study revealed that YY1 blocks the expression of PGC-1β, an activator of fatty acid β-oxidation, by directly binding to its promoter; and thus downregulates PGC-1β/MCAD and PGC1-β/LCAD axis. Importantly, we revealed that YY1 inhibition on PGC-1β occurs irrespective of the expression of hypoxia-inducible factor-1α (HIF1-α), enabling it to promote lipid accumulation under both normoxic and hypoxic conditions.

Conclusion: Our study reveals the critical role of YY1/PGC-1β axis in HCC cell lipid metabolism, providing novel insight into the molecular mechanisms associated with tumor cell lipid metabolism, and a new perspective regarding the function of YY1 in tumor progression. Thus, our study provides evidences regarding the potential of YY1 as a target for lipid metabolism-based anti-tumor therapy.

YY1 inhibits the migration and invasion of pancreatic ductal adenocarcinoma by downregulating the FER/STAT3/MMP2 signaling pathway

Pancreatic ductal adenocarcinoma (PDAC) has a poor prognosis and a high mortality rate. The transcription factor YY1 acts as an inhibitor of many types of tumors. We found that YY1 knockdown promoted the invasion and migration of PANC-1 and BxPC-3 cells; FER knockdown partially restored the promotion of pancreatic cancer caused by YY1 knockdown. In vivo experiments yielded the same results. According to luciferase reporter gene, electrophoretic mobility shift (EMSA) and chromatin immunoprecipitation (ChIP) assays, YY1 directly binds to the FER promoter region. Moreover, higher level FER expression results in a worse TNM stage and prognosis for patients with PDAC. Furthermore, by downregulating FER, YY1 inhibits the formation of the STAT3-MMP2 complex, thereby suppressing expression of MMP2 and ultimately inhibiting the migration and invasion of pancreatic cancer. Our study demonstrates that the YY1/FER/STAT3/MMP2 axis is associated with the progression of pancreatic cancer and may provide a new therapeutic target for the treatment of pancreatic cancer.

Loss of tumor suppressor IGFBP4 drives epigenetic reprogramming in hepatic carcinogenesis

Genomic sequencing of hepatocellular carcinoma (HCC) uncovers a paucity of actionable mutations, underscoring the necessity to exploit epigenetic vulnerabilities for therapeutics. In HCC, EZH2-mediated H3K27me3 represents a major oncogenic chromatin modification, but how it modulates the therapeutic vulnerability of signaling pathways remains unknown. Here, we show EZH2 acts antagonistically to AKT signaling in maintaining H3K27 methylome through epigenetic silencing of IGFBP4. ChIP-seq revealed enrichment of Ezh2/H3K27me3 at silenced loci in HBx-transgenic mouse-derived HCCs, including Igfbp4 whose down-regulation significantly correlated with EZH2 overexpression and poor survivals of HCC patients. Functional characterizations demonstrated potent growth- and invasion-suppressive functions of IGFBP4, which was associated with transcriptomic alterations leading to deregulation of multiple signaling pathways. Mechanistically, IGFBP4 stimulated AKT/EZH2 phosphorylation to abrogate H3K27me3-mediated silencing, forming a reciprocal feedback loop that suppressed core transcription factor networks (FOXA1/HNF1A/HNF4A/KLF9/NR1H4) for normal liver homeostasis. Consequently, the in vivo tumorigenicity of IGFBP4-silenced HCC cells was vulnerable to pharmacological inhibition of EZH2, but not AKT. Our study unveils chromatin regulation of a novel liver tumor suppressor IGFBP4, which constitutes an AKT-EZH2 reciprocal loop in driving H3K27me3-mediated epigenetic reprogramming. Defining the aberrant chromatin landscape of HCC sheds light into the mechanistic basis of effective EZH2-targeted inhibition.

Oncometabolites in cancer aggressiveness and tumour repopulation

Tumour repopulation is recognized as a crucial event in tumour relapse where therapy-sensitive dying cancer cells influence the tumour microenvironment to sustain therapy-resistant cancer cell growth. Recent studies highlight the role of the oncometabolites succinate, fumarate, and 2-hydroxyglutarate in the aggressiveness of cancer cells and in the worsening of the patient's clinical outcome. These oncometabolites can be produced and secreted by cancer and/or surrounding cells, modifying the tumour microenvironment and sustaining an invasive neoplastic phenotype. In this review, we report recent findings concerning the role in cancer development of succinate, fumarate, and 2-hydroxyglutarate and the regulation of their related enzymes succinate dehydrogenase, fumarate hydratase, and isocitrate dehydrogenase. We propose that oncometabolites are crucially involved in tumour repopulation. The study of the mechanisms underlying the relationship between oncometabolites and tumour repopulation is fundamental for identifying efficient anti-cancer therapeutic strategies and novel serum biomarkers in order to overcome cancer relapse.

Aberrant enhancer hypomethylation contributes to hepatic carcinogenesis through global transcriptional reprogramming

Hepatocellular carcinomas (HCC) exhibit distinct promoter hypermethylation patterns, but the epigenetic regulation and function of transcriptional enhancers remain unclear. Here, our affinity- and bisulfite-based whole-genome sequencing analyses reveal global enhancer hypomethylation in human HCCs. Integrative epigenomic characterization further pinpoints a recurrent hypomethylated enhancer of CCAAT/enhancer-binding protein-beta (C/EBPβ) which correlates with C/EBPβ over-expression and poorer prognosis of patients. Demethylation of C/EBPβ enhancer reactivates a self-reinforcing enhancer-target loop via direct transcriptional up-regulation of enhancer RNA. Conversely, deletion of this enhancer via CRISPR/Cas9 reduces C/EBPβ expression and its genome-wide co-occupancy with BRD4 at H3K27ac-marked enhancers and super-enhancers, leading to drastic suppression of driver oncogenes and HCC tumorigenicity. Hepatitis B X protein transgenic mouse model of HCC recapitulates this paradigm, as C/ebpβ enhancer hypomethylation associates with oncogenic activation in early tumorigenesis. These results support a causal link between aberrant enhancer hypomethylation and C/EBPβ over-expression, thereby contributing to hepatocarcinogenesis through global transcriptional reprogramming.

There are distinct hypermethylation patterns in gene promoters in hepatocellular carcinomas (HCCs). Here, the authors show that the enhancer of C/EBPβ is recurrently hypomethylated in human HCCs, recapitulating this in a transgenic murine model and linking aberrant enhancer hypomethylation to hepatocarcinogenesis.

Down-regulation of miR-9 promotes epithelial mesenchymal transition via regulating anoctamin-1 (ANO1) in CRC cells

MicroRNA-9 (miR-9) has been reported to play a suppressive or promoting role according to cancer type. In this study, we investigated the effects of anoctamin-1 (ANO1) and miR-9 on colorectal cancer (CRC) cell proliferation, migration, and invasion and determined the underlying molecular mechanisms. Thirty-two paired CRC tissues and adjacent normal tissues were analyzed for ANO1 expression using quantitative real-time PCR (qRT-PCR). HCT116 cells were transiently transfected with miR-9 mimic, miR-9 inhibitor, or si-ANO1. Cell proliferation was determined by MTT, and flow cytometric analysis, while cell migration and invasion were assayed by trans-well migration and invasion assay in HCT116 cells. ANO1 was validated as a target of miR-9 using luciferase reporter assay and bioinformatics algorithms. We found that ANO1 expression was up-regulated in CRC tissues compared with adjacent normal tissues. ANO1 expression was associated with advanced tumor stage and lymph node metastasis, and there was an inverse relationship between miR-9 and ANO1 mRNA expression in CRC specimens, but no significant difference was found between miR-9 and ANO1 expression. ANO1 is a direct target of miR-9, and overexpression of miR-9 suppressed both mRNA and protein expression of ANO1 and inhibited cell proliferation, migration, and invasion of HCT116 cells. We also showed that overexpression of miR-9 suppressed expression of p-AKT, cyclin D1, and p-ERK in HCT116 cells. We conclude that miR-9 inhibits CRC cell proliferation, migration, and invasion by directly targeting ANO1, and miR-9/ANO1 could be a potential therapeutic target for CRC.

YY1 promotes HDAC1 expression and decreases sensitivity of hepatocellular carcinoma cells to HDAC inhibitor

YY1 is a DNA-binding transcription factor and reported to be involved in cancer progression. Histone deacetylase inhibitor (HDACi) could inhibit proliferation and promote apoptosis of Hepatocellular carcinoma (HCC) cells. However, it is unclear about the roles of YY1 in the sensitivity of HCC cells to HDACi. In this study, firstly, we identified two drug-response profiles to HDACi in HCC cell lines, while our results showed that HDAC1 expression was positively correlated with YY1 in HCC cell lines and primary tumor tissues. Secondly, YY1 decreased the sensitivity of HCC cells to HDACi in vitro and in vivo. Furthermore, we found that YY1 promoted HDAC1 expression by binding to its promoter, while HDAC1 in turn up-regulated the expression of YY1. In conclusion, our results showed that YY1 could reduce the sensitivity of HCC cells to HDACi and might be a potential therapeutic target in HCC.

Computational characterization of chromatin domain boundary-associated genomic elements

Topologically associated domains (TADs) are 3D genomic structures with high internal interactions that play important roles in genome compaction and gene regulation. Their genomic locations and their association with CCCTC-binding factor (CTCF)-binding sites and transcription start sites (TSSs) were recently reported. However, the relationship between TADs and other genomic elements has not been systematically evaluated. This was addressed in the present study, with a focus on the enrichment of these genomic elements and their ability to predict the TAD boundary region. We found that consensus CTCF-binding sites were strongly associated with TAD boundaries as well as with the transcription factors (TFs) Zinc finger protein (ZNF)143 and Yin Yang (YY)1. TAD boundary-associated genomic elements include DNase I-hypersensitive sites, H3K36 trimethylation, TSSs, RNA polymerase II, and TFs such as Specificity protein 1, ZNF274 and SIX homeobox 5. Computational modeling with these genomic elements suggests that they have distinct roles in TAD boundary formation. We propose a structural model of TAD boundaries based on these findings that provides a basis for studying the mechanism of chromatin structure formation and gene regulation.

Diagnostic and prognostic relevance of CP2c and YY1 expression in hepatocellular carcinoma

Recent studies have demonstrated an oncogenic role of the transcription factor (TF) CP2c in hepatocellular carcinoma (HCC) based on a strong correlation between CP2c expression, tumor grade, and aggressiveness. We recently found that CP2c directly interacts with another TF, YY1, which is also overexpressed in multiple cancers, including HCC. To evaluate if these proteins are co-regulated in carcinogenesis, we analyzed the expression of CP2c and YY1 in HCC (n = 136) tissues and examined the correlation between their expression and clinicopathological characteristics of HCC. Receiver operating characteristic analysis exhibited the validity of CP2c and nuclear YY1 expression as a diagnostic factor in HCC tissues. High expression of CP2c was significantly correlated with patient age, and higher histological grade, American Joint Committee on Cancer (AJCC) stage, and small and large vessel invasion in HCC tissues, whereas high expression of nuclear YY1 was significantly associated with higher AJCC stage and small vessel invasion. In univariate and multivariate analyses, high expression of CP2c was significantly correlated with disease free survival (DFS), indicating that CP2c expression is an independent prognostic factor for DFS in HCC patients. Patients with high expression of both CP2c and nuclear YY1 usually had a shorter median survival time and worse DFS prognosis than other patients, suggesting that combined detection of CP2c and nuclear YY1 is a useful prognostic marker in HCC patients.

Upregulation of miR-146a by YY1 depletion correlates with delayed progression of prostate cancer

Previously published studies explained that the excessive expression of miR-146a influences the prostate cancer (PCa) cells in terms of apoptosis, progression, and viability. Although miR-146a acts as a tumor suppressor, current knowledge on the molecular mechanisms that controls its expression in PCa is limited. In this study, gene set enrichment analysis (GSEA) showed negatively enriched expression of miR-146a target gene sets and positively enriched expression of gene sets suppressed by the enhancer of zeste homolog 2 (EZH2) after YY1 depletion in PCa cells. The current results demonstrated that the miR-146a levels in PCa tissues with high Gleason scores (>7) are significantly lower than those in PCa tissues with low Gleason scores (≤7), which were initially observed in the clinical specimens. An inverse relationship between YY1 and miR-146a expression was also observed. Experiments indicated the decrease in cell viability, proliferation, and promoting apoptosis after YY1 depletion, while through inhibiting miR-146a could alleviate the negative effect brought by YY1 depletion. We detected the reversed adjustment of YY1 to accommodate miR-146a transcriptions. On the basis of YY1 depletion, we determined that the expression of miR-146a increased after EZH2 knockdown. We validated the combination of YY1 and its interaction with EZH2 at the miR-146a promoter binding site, thereby prohibiting the transcriptional activity of miR-146a in PCa cells. Our results suggested that YY1 depletion repressed PCa cell viability and proliferation and induced apoptosis at least in a miR-146a-assisted manner.

Epigenetic Activation of Wnt/β-Catenin Signaling in NAFLD-Associated Hepatocarcinogenesis

Non-alcoholic fatty liver disease (NAFLD), characterized by fat accumulation in liver, is closely associated with central obesity, over-nutrition and other features of metabolic syndrome, which elevate the risk of developing hepatocellular carcinoma (HCC). The Wnt/β-catenin signaling pathway plays a significant role in the physiology and pathology of liver. Up to half of HCC patients have activation of Wnt/β-catenin signaling. However, the mutation frequencies of CTNNB1 (encoding β-catenin protein) or other antagonists targeting Wnt/β-catenin signaling are low in HCC patients, suggesting that genetic mutations are not the major factor driving abnormal β-catenin activities in HCC. Emerging evidence has demonstrated that obesity-induced metabolic pathways can deregulate chromatin modifiers such as histone deacetylase 8 to trigger undesired global epigenetic changes, thereby modifying gene expression program which contributes to oncogenic signaling. This review focuses on the aberrant epigenetic activation of Wnt/β-catenin in the development of NAFLD-associated HCC. A deeper understanding of the molecular mechanisms underlying such deregulation may shed light on the identification of novel druggable epigenetic targets for the prevention and/or treatment of HCC in obese and diabetic patients.

Polycomb repressive complex's evolutionary conserved function: the role of EZH2 status and cellular background

When assembled in multiprotein polycomb repressive complexes (PRCs), highly evolutionary conserved polycomb group (PcG) proteins epigenetically control gene activity. Although the composition of PRCs may vary considerably, it is well established that the embryonic ectoderm development (EED) 1, suppressor of zeste (SUZ) 12, and methyltransferase enhancer of zeste (EZH2)-containing complex, PRC2, which is abundant in highly proliferative cells (including cancer cells), establishes a repressive methylation mark on histone 3 (H3K27me3). From the perspective of molecular cancer pathogenesis, this effect, when directed towards a promoter of tumor suppressor genes, represents pro-tumorigenic effect. This mode of action was shown in several cancer models. However, EZH2 function extends beyond this scenario. The highly specific cellular background, related to the origin of cell and numerous external stimuli during a given time-window, may be the trigger for EZH2 interaction with other proteins, not necessarily histones. This is particularly relevant for cancer. This review provides a critical overview of the evolutional importance of PRC and discusses several important aspects of EZH2 functioning within PRC. The review also deals with mutational studies on EZH2. Due to the existence of several protein (and messenger RNA (mRNA)) isoforms, these mutations were stratified, using the protein sequence which is considered canonical. This approach showed that there is an urgent need for the uniformed positioning of currently known EZH2 mutations (somatic-in tumors, as well as germline mutations in the Weaver's syndrome). Finally, we discuss EZH2 function with respect to amount of trimethylated H3K27, in a specific cellular milieu, through presenting the most recent data related to EZH2-H3K27m3 relationship in cancer. All these points are significant in considering EZH2 as a therapeutic target.