Epigenetic regulation of cancer stem cells in liver cancer: current concepts and clinical implications

Interplay among extracellular vesicles, cancer stemness and immune regulation in driving hepatocellular carcinoma progression

The intricate interplay among extracellular vesicles, cancer stemness properties, and the immune system significantly impacts hepatocellular carcinoma (HCC) progression, treatment response, and patient prognosis. Extracellular vesicles (EVs), which are membrane-bound structures, play a pivotal role in conveying proteins, lipids, and nucleic acids between cells, thereby serving as essential mediators of intercellular communication. Since a lot of current research focuses on small extracellular vesicles (sEVs), with diameters ranging from 30 nm to 200 nm, this review emphasizes the role of sEVs in the context of interactions between HCC stemness-bearing cells and the immune cells. sEVs offer promising opportunities for the clinical application of innovative diagnostic and prognostic biomarkers in HCC. By specifically targeting sEVs, novel therapeutics aimed at cancer stemness can be developed. Ongoing investigations into the roles of sEVs in cancer stemness and immune regulation in HCC will broaden our understanding and ultimately pave the way for groundbreaking therapeutic interventions.

Artificial and Natural Sweeteners Biased T1R2/T1R3 Taste Receptors Transactivate Glycosylated Receptors on Cancer Cells to Induce Epithelial-Mesenchymal Transition of Metastatic Phenotype

Understanding the role of biased taste T1R2/T1R3 G protein-coupled receptors (GPCR) agonists on glycosylated receptor signaling may provide insights into the opposing effects mediated by artificial and natural sweeteners, particularly in cancer and metastasis. Sweetener-taste GPCRs can be activated by several active states involving either biased agonism, functional selectivity, or ligand-directed signaling. However, there are increasing arrays of sweetener ligands with different degrees of allosteric biased modulation that can vary dramatically in binding- and signaling-specific manners. Here, emerging evidence proposes the involvement of taste GPCRs in a biased GPCR signaling crosstalk involving matrix metalloproteinase-9 (MMP-9) and neuraminidase-1 (Neu-1) activating glycosylated receptors by modifying sialic acids. The findings revealed that most natural and artificial sweeteners significantly activate Neu-1 sialidase in a dose-dependent fashion in RAW-Blue and PANC-1 cells. To confirm this biased GPCR signaling crosstalk, BIM-23127 (neuromedin B receptor inhibitor, MMP-9i (specific MMP-9 inhibitor), and oseltamivir phosphate (specific Neu-1 inhibitor) significantly block sweetener agonist-induced Neu-1 sialidase activity. To assess the effect of artificial and natural sweeteners on the key survival pathways critical for pancreatic cancer progression, we analyzed the expression of epithelial-mesenchymal markers, CD24, ADLH-1, E-cadherin, and N-cadherin in PANC-1 cells, and assess the cellular migration invasiveness in a scratch wound closure assay, and the tunneling nanotubes (TNTs) in staging the migratory intercellular communication. The artificial and natural sweeteners induced metastatic phenotype of PANC-1 pancreatic cancer cells to promote migratory intercellular communication and invasion. The sweeteners also induced the downstream NFκB activation using the secretory alkaline phosphatase (SEAP) assay. These findings elucidate a novel taste T1R2/T1R3 GPCR functional selectivity of a signaling platform in which sweeteners activate downstream signaling, contributing to tumorigenesis and metastasis via a proposed NFκB-induced epigenetic reprogramming modeling.

Functional Selectivity of Cannabinoid Type 1 G Protein-Coupled Receptor Agonists in Transactivating Glycosylated Receptors on Cancer Cells to Induce Epithelial-Mesenchymal Transition Metastatic Phenotype

Understanding the role of biased G protein-coupled receptor (GPCR) agonism in receptor signaling may provide novel insights into the opposing effects mediated by cannabinoids, particularly in cancer and cancer metastasis. GPCRs can have more than one active state, a phenomenon called either 'biased agonism', 'functional selectivity', or 'ligand-directed signaling'. However, there are increasing arrays of cannabinoid allosteric ligands with different degrees of modulation, called 'biased modulation', that can vary dramatically in a probe- and pathway-specific manner, not from simple differences in orthosteric ligand efficacy or stimulus-response coupling. Here, emerging evidence proposes the involvement of CB1 GPCRs in a novel biased GPCR signaling paradigm involving the crosstalk between neuraminidase-1 (Neu-1) and matrix metalloproteinase-9 (MMP-9) in the activation of glycosylated receptors through the modification of the receptor glycosylation state. The study findings highlighted the role of CB1 agonists AM-404, Aravnil, and Olvanil in significantly inducing Neu-1 sialidase activity in a dose-dependent fashion in RAW-Blue, PANC-1, and SW-620 cells. This approach was further substantiated by findings that the neuromedin B receptor inhibitor, BIM-23127, MMP-9 inhibitor, MMP9i, and Neu-1 inhibitor, oseltamivir phosphate, could specifically block CB1 agonist-induced Neu-1 sialidase activity. Additionally, we found that CB1 receptors exist in a multimeric receptor complex with Neu-1 in naïve, unstimulated RAW-Blue, PANC-1, and SW-620 cells. This complex implies a molecular link that regulates the interaction and signaling mechanism among these molecules present on the cell surface. Moreover, the study results demonstrate that CB1 agonists induce NFκB-dependent secretory alkaline phosphatase (SEAP) activity in influencing the expression of epithelial-mesenchymal markers, E-cadherin, and vimentin in SW-620 cells, albeit the impact on E-cadherin expression is less pronounced compared to vimentin. In essence, this innovative research begins to elucidate an entirely new molecular mechanism involving a GPCR signaling paradigm in which cannabinoids, as epigenetic stimuli, may traverse to influence gene expression and contribute to cancer and cancer metastasis.

TrkB inhibition of DJ-1 degradation promotes the growth and maintenance of cancer stem cell characteristics in hepatocellular carcinoma

Although TrkB may be associated with the pathogenesis of various cancer by upregulation, how upregulation of TrkB led to tumor progression in hepatocellular carcinoma (HCC) and the signaling mechanisms by which TrkB induces motility, invasion, metastasis, drug resistance, and acquisition of self-renewal traits has remained unclear. Here, we demonstrated that TrkB was significantly upregulated in highly metastatic HCC cells and HCC patients. Also, the increased TrkB levels were significantly correlated with tumor stages and poor survival of HCC patients. Furthermore, the upregulated TrkB expression enhances the metastatic ability of HCC cells through reduced anoikis sensitivity, induced migration, and colony formation. Most strikingly, TrkB markedly enhances the activation of STAT3 by preventing DJ-1 degradation through the formation of the TrkB/DJ-1 complex. This signaling mechanism is responsible for triggering cellular traits of highly aggressive HCC. The activation of the EMT program of HCC via increasing DJ-1 stability by TrkB induces the gain of cancer stem cell states and chemoresistance via the upregulation of stem cells cell markers and ABC transporters. Also, TrkB-mediated inhibition of DJ-1 degradation promotes tumor formation and metastasizes to other organs in vivo. Our observations illustrate that TrkB is a prognostic and therapeutic targeting in promoting aggressiveness and metastasis of HCC.

SMYD3 induces sorafenib resistance by activating SMAD2/3-mediated epithelial-mesenchymal transition in hepatocellular carcinoma

Drug resistance prominently hampers the effects of systemic therapy of sorafenib to hepatocellular carcinoma (HCC). Epigenetics have critical regulatory roles in drug resistance. However, the contributions of histone methylatransferase SET and MYND domain containing 3 (SMYD3) to sorafenib resistance in HCC remain largely unknown. Here, using our established sorafenib-resistant HCC cell and xenograft models, we found SMYD3 was markedly elevated in sorafenib-resistant tumors and cells. Functionally, loss- and gain-of-function studies showed that SMYD3 promoted the migration, invasion, metastasis and stemness of sorafenib-resistant HCC cells. Mechanistically, SMYD3 is required for SMAD2/3-mediated epithelial-mesenchymal transition (EMT) in sorafenib-resistant HCC cells by interacting with SMAD2/3 and epigenetically promoting the expression of SOX4, ZEB1, SNAIL1 and MMP9 genes. In summary, our data demonstrate that targeting SMYD3 is an effective approach to overcome sorafenib resistance in HCC.

Activated Carbon nanoparticles Loaded with Metformin for Effective Against Hepatocellular Cancer Stem Cells

Introduction

Hepatocellular cancer stem cells (CSCs) play crucial roles in hepatocellular cancer initiation, development, relapse, and metastasis. Therefore, eradication of this cell population is a primary objective in hepatocellular cancer therapy. We prepared a nanodrug delivery system with activated carbon nanoparticles (ACNP) as carriers and metformin (MET) as drug (ACNP-MET), which was able to selectively eliminate hepatocellular CSCs and thereby increase the effects of MET on hepatocellular cancers.

Methods

ACNP were prepared by ball milling and deposition in distilled water. Suspension of ACNP and MET was mixed and the best ratio of ACNP and MET was determined based on the isothermal adsorption formula. Hepatocellular CSCs were identified as CD133⁺ cells and cultured in serum-free medium. We investigated the effects of ACNP-MET on hepatocellular CSCs, including the inhibitory effects, the targeting efficiency, self-renewal capacity, and the sphere-forming capacity of hepatocellular CSCs. Next, we evaluated the therapeutic efficacy of ACNP-MET by using in vivo relapsed tumor models of hepatocellular CSCs.

Results

The ACNP have a similar size, a regular spherical shape and a smooth surface. The optimal ratio for adsorption was MET: ACNP=1:4. ACNP-MET could target and inhibit the proliferation of CD133⁺ population and decrease mammosphere formation and renewal of CD133⁺ population in vitro and in vivo.

Conclusion

These results not only suggest that nanodrug delivery system increased the effects of MET, but also shed light on the mechanisms of the therapeutic effects of MET and ACNP-MET on hepatocellular cancers. ACNP, as a good nano-carrier, could strengthen the effect of MET by carrying drugs to the micro-environment of hepatocellular CSCs.

Hepatic interferon regulatory factor 8 expression suppresses hepatocellular carcinoma progression and enhances the response to anti-programmed cell death protein-1 therapy

BACKGROUND AND AIMS

Therapeutic blockade of the programmed cell death protein-1 (PD-1) immune checkpoint pathways has resulted in significant reactivation of T cell-mediated antitumor immunity and is a promising clinical anticancer treatment modality in several tumor types, but the durable response rate remains relatively low (15%-20%) in most patients with HCC for unknown reasons. Evidence reveals that the interferon signaling pathway plays a critical role in modulating the efficacy and sensitivity of anti-PD-1 therapy against multiple tumor types, but the mechanisms are unclear.

APPROACH AND RESULTS

Using Kaplan-Meier survival analysis based on HCC databases, we found that deceased expression of interferon regulatory factor (IRF) 8 in HCC, among all the nine IRF members that regulate interferon signals, was associated with poor prognosis of patients with HCC. Moreover, gene set enrichment analysis identified the interferon-gamma and PD-1 signaling signatures as the top suppressed pathways in patients with IRF8-low HCC. Contrarily, overexpression of IRF8 in HCC cells significantly enhanced antitumor effects in immune-competent mice, modulating infiltration of tumor-associated macrophages (TAMs) and T cell exhaustion in tumor microenvironment. We further demonstrated that IRF8 regulated recruitment of TAMs by inhibiting the expression of chemokine (C-C motif) ligand 20 (CCL20). Mechanically, IRF8-mediated repression of c-fos transcription resulted in decreased expression of CCL20, rather than directly bound to CCL20 promoter region. Importantly, adeno-associated virus 8-mediated hepatic IRF8 rescue significantly suppressed HCC progression and enhanced the response to anti-PD-1 therapy.

CONCLUSIONS

This work identified IRF8 as an important prognostic biomarker in patients with HCC that predicted the response and sensitivity to anti-PD-1 therapy and uncovered it as a therapeutic target for enhancing the efficacy of immune therapy.

miR-3168 promotes hepatocellular carcinoma progression via downregulating p53

Hepatocellular carcinoma (HCC) is a highly malignant disease with poor prognosis, which is partly due to the presence of liver cancer stem cells (CSCs). CSCs participate in tumor recurrence, metastasis, and chemoresistance. However, the mechanisms underlying liver CSC regulation are unknown. In this study, we found that miR-3168 expression is increased in HCC and that it predicts poor prognosis. Functional assays showed that miR-3168 promotes HCC cells' proliferation and facilitates liver CSC self-renewal and tumorigenicity. Mechanistically, bioinformatics and the luciferase reporter assay demonstrated that miR-3168 targets the 3'UTR of the p53 mRNA. MiR-3168 expression was negatively correlated with p53 mRNA in HCC tissue samples. Rescue assays demonstrated that p53 knockdown abrogates the discrepancies in proliferation, self-renewal, and tumorigenicity between miR-3168 knockdown HCC cells and control HCC cells. Furthermore, miR-3168 expression was negatively correlated with p53 in HCC tissues. The combined HCC panels exhibited a worse prognostic value for HCC patients than any of these components alone. Moreover, miR-3168 expression was increased in cisplatin-resistant HCC cells and patient-derived xenografts. Clinical cohort analysis revealed that HCC patients with low miR-3168 levels have a superior survival rate when treated with postoperative transcatheter arterial chemoembolization compared with that of patients with high miR-3168 levels. In conclusion, our study uncovered a novel mechanism of liver CSC regulation and provided a potential therapeutic target for liver CSCs.

Dysregulated FOXM1 signaling in the regulation of cancer stem cells

Since the introduction of the cancer stem cell (CSC) paradigm, significant advances have been made in understanding the functional and biological plasticity of these elusive components in malignancies. Endowed with self-renewing abilities and multilineage differentiation potential, CSCs have emerged as cellular drivers of virtually all facets of tumor biology, including metastasis, tumor recurrence/relapse, and drug resistance. The functional and biological characteristics of CSCs, such as self-renewal, cell fate decisions, survival, proliferation, and differentiation are regulated by an array of extracellular factors, signaling pathways, and pluripotent transcriptional factors. Besides the well-characterized regulatory role of transcription factors OCT4, SOX2, NANOG, KLF4, and MYC in CSCs, evidence for the central role of Forkhead box transcription factor FOXM1 in the establishment, maintenance, and functions of CSCs is accumulating. Conventionally identified as a master regulator of the cell cycle, a comprehensive understanding of this molecule has revealed its multifarious oncogenic potential and uncovered its role in angiogenesis, invasion, migration, self-renewal, and drug resistance. This review compiles the large body of literature that has accumulated in recent years that provides evidence for the mechanisms by which FOXM1 expression promotes stemness in glioblastoma, breast, colon, ovarian, lung, hepatic, and pancreatic carcinomas. We have also compiled the data showing the association of stem cell mediators with FOXM1 using TCGA mRNA expression data. Further, the prognostic importance of FOXM1 and other stem cell markers is presented. The delineation of FOXM1-mediated regulation of CSCs can aid in the development of molecularly targeted pharmacological approaches directed at the selective eradication of CSCs in several human malignancies.

TrkC-mediated inhibition of DJ-1 degradation is essential for direct regulation of pathogenesis of hepatocellular carcinoma

None of the previous studies has systematically explored how upregulation of TrkC plays a central role in the pathogenesis of hepatocellular carcinoma (HCC) by regulating the underlying mechanisms that promote invasion and metastasis. In this report, we demonstrated the possible association between upregulation of TrkC and acquisition of cancer stem cells traits or chemoresistance in HCC. We show that upregulation of TrkC is closely associated with the survival and progression of HCC in vivo and in vitro. Most strikingly, activation of STAT3 by TrkC-mediated inhibition of DJ-1 degradation significantly enhances the efficacy of invasion and metastasis during the progression of HCC cells. Acquiring the traits of cancer stem cells (CSCs) by TrkC/DJ-1/STAT3 signaling pathway leads to the induction of chemoresistance via upregulation of ABC transporters and anti-apoptotic genes. Also, activating the epithelial-mesenchymal transition (EMT) program by inducing EMT-transcription factor (TF)s by TrkC/DJ-1/STAT3 signaling pathway is the direct cause of multiple tumor malignancies of HCC. Thus, understanding the mechanisms by which acquisition of anticancer drug resistance by TrkC-mediated inhibition of DJ-1 degradation can help enhance the efficacy of anticancer therapies.

In Vivo and In Vitro Models of Hepatocellular Carcinoma: Current Strategies for Translational Modeling

Hepatocellular carcinoma (HCC) is the sixth most common cancer worldwide and the third leading cause of cancer-related death globally. HCC is a complex multistep disease and usually emerges in the setting of chronic liver diseases. The molecular pathogenesis of HCC varies according to the etiology, mainly caused by chronic hepatitis B and C virus infections, chronic alcohol consumption, aflatoxin-contaminated food, and non-alcoholic fatty liver disease associated with metabolic syndrome or diabetes mellitus. The establishment of HCC models has become essential for both basic and translational research to improve our understanding of the pathophysiology and unravel new molecular drivers of this disease. The ideal model should recapitulate key events observed during hepatocarcinogenesis and HCC progression in view of establishing effective diagnostic and therapeutic strategies to be translated into clinical practice. Despite considerable efforts currently devoted to liver cancer research, only a few anti-HCC drugs are available, and patient prognosis and survival are still poor. The present paper provides a state-of-the-art overview of in vivo and in vitro models used for translational modeling of HCC with a specific focus on their key molecular hallmarks.

DNA Methylation of TGFβ Target Genes: Epigenetic Control of TGFβ Functional Duality in Liver Cancer

Transforming growth factor beta (TGFβ) plays a key role in liver carcinogenesis. However, its action is complex, since TGFβ exhibits tumor-suppressive or oncogenic properties, depending on the tumor stage. At an early stage TGFβ exhibits cytostatic features, but at a later stage it promotes cell growth and metastasis, as a potent inducer of epithelial to mesenchymal transition (EMT). Here, we evaluated DNA methylation as a possible molecular mechanism switching TGFβ activity toward tumor progression in hepatocellular carcinoma (HCC). We report that decitabine, a demethylating agent already used in the clinic for the treatment of several cancers, greatly impairs the transcriptional response of SNU449 HCC cells to TGFβ. Importantly, decitabine was shown to induce the expression of EMT-related transcription factors (e.g., SNAI1/2, ZEB1/2). We also report that the promoter of SNAI1 was hypomethylated in poor-prognosis human HCC, i.e., associated with high grade, high AFP level, metastasis and recurrence. Altogether, the data highlight an epigenetic control of several effectors of the TGFβ pathway in human HCC possibly involved in switching its action toward EMT and tumor progression. Thus, we conclude that epidrugs should be carefully evaluated for the treatment of HCC, as they may activate tumor promoting pathways.

Emerging Regulatory Mechanisms Involved in Liver Cancer Stem Cell Properties in Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is the predominant form of primary liver cancer and one of the leading causes of cancer-related deaths worldwide. A growing body of evidence supports the hypothesis that HCC is driven by a population of cells called liver cancer stem cells (LCSCs). LCSCs have been proposed to contribute to malignant HCC progression, including promoting tumor occurrence and growth, mediating tumor metastasis, and treatment resistance, but the regulatory mechanism of LCSCs in HCC remains unclear. Understanding the signaling pathways responsible for LCSC maintenance and survival may provide opportunities to improve patient outcomes. Here, we review the current literature about the origin of LCSCs and the niche composition, describe the current evidence of signaling pathways that mediate LCSC stemness, then highlight several mechanisms that modulate LCSC properties in HCC progression, and finally, summarize the new developments in therapeutic strategies targeting LCSCs markers and regulatory pathways.

GASC1 promotes hepatocellular carcinoma progression by inhibiting the degradation of ROCK2

Hepatocellular carcinoma (HCC) is a devastating malignancy without targeted therapeutic options. Our results indicated that the histone demethylase GASC1 signature is associated with later tumor stage and poorer survival in HCC patients. GASC1 depletion led to diminished HCC proliferation and tumor growth. A distinct heterogeneity in GASC1 levels was observed among HCC cell populations, predicting their inherent high or low tumor-initiating capacity. Mechanistically, GASC1 is involved in the regulation of several components of the Rho-GTPase signaling pathway including its downstream target ROCK2. GASC1 demethylase activity ensured the transcriptional repression of FBXO42, a ROCK2 protein-ubiquitin ligase, thereby inhibiting ROCK2 degradation via K63-linked poly-ubiquitination. Treatment with the GASC1 inhibitor SD70 impaired the growth of both HCC cell lines and xenografts in mice, sensitizing them to standard-of-care chemotherapy. This work identifies GASC1 as a malignant-cell-selective target in HCC, and GASC1-specific therapeutics represent promising candidates for new treatment options to control this malignancy.

Silencing CDCA8 Suppresses Hepatocellular Carcinoma Growth and Stemness via Restoration of ATF3 Tumor Suppressor and Inactivation of AKT/β-Catenin Signaling

Simple Summary

Although the overexpression of CDCA8 is frequently observed in hepatocellular carcinoma (HCC) tissues, the functions of CDCA8 during HCC development remain to be clarified. The aim of our study was to investigate if targeting CDCA8 could affect liver tumor phenotypes in vitro and in vivo and to identify underlying molecular mechanisms to exert its therapeutic effect. We found that silencing of CDCA8 by siRNA inhibits the growth of parental cancer cell culture and mice tumors and suppresses stemness of CD133⁺ cancer stem cell population through the common responses of the upregulation of the tumor suppressive ATF3/GADD34 functional pathway and inactivation of the Akt/β–catenin signaling axis. These findings suggest CDCA8 as a novel therapeutic target for both primary HCC treatment and the prevention of metastasis or recurrence providing mode of action performed by a CDCA8 inhibitor.

Abstract

Big data analysis has revealed the upregulation of cell division cycle associated 8 (CDCA8) in human hepatocellular carcinoma (HCC) and its poorer survival outcome. However, the functions of CDCA8 during HCC development remain unknown. Here, we demonstrate in vitro that CDCA8 silencing inhibits HCC cell growth and long-term colony formation and migration through the accumulation of the G2/M phase cell population. Conversely, CDCA8 overexpression increases the ability to undergo long-term colony formation and migration. RNA sequencing and bioinformatic analysis revealed that CDCA8 knockdown led to the same directional regulation in 50 genes (25 down- and 25 upregulated). It was affirmed based on protein levels that CDCA8 silencing downregulates the levels of cyclin B1 and p-cdc2 and explains how it could induce G2/M arrest. The same condition increased the protein levels of tumor-suppressive ATF3 and GADD34 and inactivated AKT/β–catenin signaling, which plays an important role in cell growth and stemness, reflecting a reduction in sphere-forming capacity. Importantly, it was demonstrated that the extent of CDCA8 expression is much greater in CD133⁺ cancer stem cells than in CD133⁻ cancer cells, and that CDCA8 knockdown decreases levels of CD133, p-Akt and β-catenin and increases levels of ATF3 and GADD34 in the CD133⁺ cancer stem cell (CSC) population. These molecular changes led to the inhibition of cell growth and sphere formation in the CD133⁺ cell population. Targeting CDCA8 also effectively suppressed tumor growth in a murine xenograft model, showing consistent molecular alterations in tumors injected with CDCA8siRNA. Taken together, these findings indicate that silencing CDCA8 suppresses HCC growth and stemness via restoring the ATF3 tumor suppressor and inactivating oncogenic AKT/β–catenin signaling, and that targeting CDCA8 may be the next molecular strategy for both primary HCC treatment and the prevention of metastasis or recurrence.

Epigenetic targeting of cancer stem cells by polyphenols (cancer stem cells targeting)

Epigenetic alterations are one of the main factors that disrupt the expression of genes and consequently, they have an important role in the carcinogenicity and the progression of different cancers. Cancer stem cells (CSCs) are accountable for the recurrence, metastasis, and therapeutic failure of cancer. The noticeable and specific pathways in CSCs can be organized by epigenetic mechanisms such as DNA methylation, chromatin remodeling, regulatory RNAs, among others. Since epigenetics modifications can be changed and reversed, it is a possible tool for cancer control and treatment. Epigenetic therapies against CSCs are emerging as a very new strategy with a good future expectation to treat cancer patients. Phenolic compounds are a vast group of substances with anticarcinogenic functions, antiinflammatory, and antioxidative activities. It seems these characteristics are related to neutralizing CSCs development, their microenvironment, and metabolism through epigenetic mechanisms. In the current work, the types of epigenetic changes known in these cells are introduced. In addition, some studies about the use of polyphenols acting through a variety of epigenetic mechanisms to counteract these cells will be reviewed. The reported results seem to indicate that the use of these phenolic compounds may be useful for CSCs defeat.

Cancer Stem Cell Functions in Hepatocellular Carcinoma and Comprehensive Therapeutic Strategies

Hepatocellular carcinoma (HCC) is a significant cause of cancer-related mortality owing to resistance to traditional treatments and tumor recurrence after therapy, which leads to poor therapeutic outcomes. Cancer stem cells (CSC) are a small subset of tumor cells with the capability to influence self-renewal, differentiation, and tumorigenesis. A number of surface markers for liver cancer stem cell (LCSC) subpopulations (EpCAM, CD133, CD44, CD13, CD90, OV-6, CD47, and side populations) in HCC have been identified. LCSCs play critical roles in regulating HCC stemness, self-renewal, tumorigenicity, metastasis, recurrence, and therapeutic resistance via genetic mutations, epigenetic disruption, signaling pathway dysregulation, or alterations microenvironment. Accumulating studies have shown that biomarkers for LCSCs contribute to diagnosis and prognosis prediction of HCC, supporting their utility in clinical management and development of therapeutic strategies. Preclinical and clinical analyses of therapeutic approaches for HCC using small molecule inhibitors, oncolytic measles viruses, and anti-surface marker antibodies have demonstrated selective, efficient, and safe targeting of LCSC populations. The current review focuses on recent reports on the influence of LCSCs on HCC stemness, tumorigenesis, and multiple drug resistance (MDR), along with LCSC-targeted therapeutic strategies for HCC.

Inhibition of EZH2 Attenuates Sorafenib Resistance by Targeting NOTCH1 Activation-Dependent Liver Cancer Stem Cells via NOTCH1-Related MicroRNAs in Hepatocellular Carcinoma

Acquired resistance and intrinsic to sorafenib therapy represents a major hurdle in improving the management of advanced hepatocellular carcinoma (HCC), which has been recently shown to be associated with the emergence of liver cancer stem cells (CSCs). However, it remains largely unknown whether and how histone posttranslational modifications, especially H3K27me3, are causally linked to the maintenance of self-renewal ability in sorafenib-resistant HCC. Here, we found that NOTCH1 signaling was activated in sorafenib-resistant HCC cells and NOTCH1 activation conferred hepatoma cells sorafenib resistance through enhanced self-renewal and tumorigenecity. Besides, the overexpression of EZH2 was required for the emergence of cancer stem cells following prolonged sorafenib treatment. As such, modulating EZH2 expression or activity suppressed activation of NOTCH1 pathway by elevating the expression of NOTCH1-related microRNAs, hsa-miR-21-5p and has-miR-26a-1-5p, via H3K27me3, and consequently weakened self-renewal ability and tumorigenecity and restored the anti-tumor effects of sorafenib. Overall, our results highlight the role of EZH2/NICD1 axis, and also suggest that EZH2 and NOTCH1 pathway are rational targets for therapeutic intervention in sorafenib-resistant HCC.

Genetic alterations and expression of PTEN and its relationship with cancer stem cell markers to investigate pathogenesis and to evaluate prognosis in hepatocellular carcinoma

Aims

To investigate molecular alteration and expression of phosphatase and tensin homolog deleted on chromosome 10 (PTEN) gene in hepatocellular carcinoma (HCC), and to evaluate the correlation between PTEN and cancer stem cell (CSC) markers and the prognostic value of these markers.

Methods

We evaluated changes of PTEN and CSC markers (CD133, epithelial cell adhesion molecule (EpCAM) and CK19) in 183 resection specimens by immunohistochemistry (IHC) and detected PTEN and phosphoinositide-3-kinase catalytic-alpha (PIK3CA) gene by fluorescence in situ hybridisation (FISH) in some specimens.

Results

PTEN and CD133, EpCAM and CK19 in 183 resection specimens were studied by IHC, and PTEN and PIK3CA genes were detected by FISH. PTEN expression was reduced in 92 HCC tissues (50.3%). There were 16 HCCs with PTEN deletion (51.6%). Comparison between PTEN IHC and FISH showed that the analysis was highly concordant (54/59, 91.5%). There were 19 HCCs with PIK3CA amplification. Deletion of PTEN was positively correlated with amplification of PIK3CA. Positive expression of CD133, EpCAM and CK19 was correlated with steatosis, moderate to poor differentiation, and so on. Reduction of PTEN expression was negatively correlated with positive expression of CD133, EpCAM and CK19. Reduced expression of PTEN (p=0.028) was an independent predictor for HCC recurrence and overall survival in HCC. PTEN−/CD133+ group had shorter OS and RFS time.

Conclusions

PTEN plays a key role in hepatocarcinogenesis and reduction of PTEN expression is related to increased expression of CD133, EpCAM and CK19, which is a useful tool to evaluate HCC prognosis and recurrence.

A Potential Antitumor Effect of Dendritic Cells Fused with Cancer Stem Cells in Hepatocellular Carcinoma

HCC stem cells were reported as posttreatment residual tumor cells that play a pivotal role in tumor relapse. Fusing dendritic cells (DCs) with tumor cells represents an ideal approach to effectively activate the antitumor immunity in vivo. DC/HCC stem cell vaccine provides a potential strategy to generate polyclonal immune response to multiple tumor stem cell antigens including those yet to be unidentified. To assess the potential capacity of DC/HCC stem cell vaccines against HCC, CD90⁺HepG2 cells were sorted from the HCC cell line HepG2. DC and CD90⁺HepG2 and DC and HepG2 fused cells were induced by polyethylene glycol (PEG). The influence of fusion cells on proliferation and immunological function transformation of lymphocytes was assessed by FCM and ELISA assay, respectively. The cytotoxicity assay of specific fusion cell-induced CTLs against HepG2 was conducted by CytoTox 96 Non-Radioactive Cytotoxicity Assay kit in vitro. At last, the prevention of HCC formation in vivo was described in a mouse model. The results of FCM analysis showed that the proportion of CD90⁺HepG2 cells in the spheral CD90⁺HepG2 enriched by suspension sphere culture was ranging from 98.7% to 99.5%, and 57.1% CD90⁺HepG2/DC fused cells were successfully constructed. The fusion cells expressed a higher level of costimulatory molecules CD80, CD83, CD86, and MHC-I and MHC-II molecules HLA-ABC and HLA-DR than did immature DCs (P < 0.05). And the functional analysis of fusion cell-induced CTLs also illustrated that CD90⁺HepG2/DC fusion cells showed a greater capacity to activate proliferation of lymphocytes in vitro (P < 0.05). The CD90⁺HepG2/DC-activated CTLs had a specific killing ability against CD90⁺HepG2 cells in vivo. These results suggested that CD90⁺HepG2/DC fusion cells could efficiently stimulate T lymphocytes to generate specific CTLs targeting CD90⁺HepG2 cells. It might be a promising strategy of immunotherapy for HCC.

Cancer stem cells in hepatocellular carcinoma: an overview and promising therapeutic strategies

The poor clinical outcome of hepatocellular carcinoma (HCC) patients is ascribed to the resistance of HCC cells to traditional treatments and tumor recurrence after curative therapies. Cancer stem cells (CSCs) have been identified as a small subset of cancer cells which have high capacity for self-renewal, differentiation and tumorigenesis. Recent advances in the field of liver CSCs (LCSCs) have enabled the identification of CSC surface markers and the isolation of CSC subpopulations from HCC cells. Given their central role in cancer initiation, metastasis, recurrence and therapeutic resistance, LCSCs constitute a therapeutic opportunity to achieve cure and prevent relapse of HCC. Thus, it is necessary to develop therapeutic strategies to selectively and efficiently target LCSCs. Small molecular inhibitors targeting the core stemness signaling pathways have been actively pursued and evaluated in preclinical and clinical studies. Other alternative therapeutic strategies include targeting LCSC surface markers, interrupting the CSC microenvironment, and altering the epigenetic state. In this review, we summarize the properties of CSCs in HCC and discuss novel therapeutic strategies that can be used to target LCSCs.

Oncogenic Signaling Induced by HCV Infection

The liver is frequently exposed to toxins, metabolites, and oxidative stress, which can challenge organ function and genomic stability. Liver regeneration is therefore a highly regulated process involving several sequential signaling events. It is thus not surprising that individual oncogenic mutations in hepatocytes do not necessarily lead to cancer and that the genetic profiles of hepatocellular carcinomas (HCCs) are highly heterogeneous. Long-term infection with hepatitis C virus (HCV) creates an oncogenic environment by a combination of viral protein expression, persistent liver inflammation, oxidative stress, and chronically deregulated signaling events that cumulate as a tipping point for genetic stability. Although novel direct-acting antivirals (DAA)-based treatments efficiently eradicate HCV, the associated HCC risk cannot be fully eliminated by viral cure in patients with advanced liver disease. This suggests that HCV may persistently deregulate signaling pathways beyond viral cure and thereby continue to perturb cancer-relevant gene function. In this review, we summarize the current knowledge about oncogenic signaling pathways derailed by chronic HCV infection. This will not only help to understand the mechanisms of hepatocarcinogenesis but will also highlight potential chemopreventive strategies to help patients with a high-risk profile of developing HCC.

Osteopontin alters DNA methylation through up-regulating DNMT1 and sensitizes CD133+/CD44+ cancer stem cells to 5 azacytidine in hepatocellular carcinoma

BACKGROUND

In hepatocellular carcinoma (HCC), CD133+/CD44+ cells are one subgroup with high stemness and responsible for metastatic relapse and resistance to treatment. Our previous studies have demonstrated that osteopontin (OPN) plays critical roles in HCC metastasis. We further investigated the molecular mechanism underlying the role of OPN in regulating the stemness of HCC epigenetically and explored possible targeting strategy.

METHODS

CD133+/CD44+ subgroup sorting from HCC cell lines and HCC tissues was used to investigate the effects of OPN knockdown on stemness. iTRAQ and MedIP-sequencing were applied to detect the protein profile and epigenetic modification of CD133+/CD44+ subgroup with or without OPN knockdown. The antitumor effects of 5 Azacytidine were examined in cultured HCC cells and patient derived xenograft (PDX) models.

RESULTS

OPN was accumulated in CD133+/CD44+ subgroup of HCC cells. Knocking down OPN significantly inhibited the sphere formation and stemness-related genes expression, and delayed tumor initiation of CD133+/CD44+ subgroup of HCC cells. Employing MedIP-sequencing, dot blot and iTRAQ analyses of CD133+/CD44+ SCR and CD133+/CD44+ shOPN cells, we found that OPN knockdown leaded to reduction in DNA methylation with particular enrichment in CGI. Meanwhile, DNA (cytosine-5)-methyltransferase 1 (DNMT1), the main methylation maintainer, was downregulated via proteomics analysis, which mediated OPN altering DNA methylation. Furthermore, DNMT1 upregulation could partially rescue the properties of CD133+/CD44+ shOPN cells. Both in vitro and in vivo assays showed that CD133+/CD44+ cells with high OPN levels were more sensitive to DNA methylation inhibitor, 5 Azacytidine (5 Aza). The above findings were validated in HCC primary cells, a more clinically relevant model.

CONCLUSIONS

OPN induces methylome reprogramming to enhance the stemness of CD133+/CD44+ subgroup and provides the therapeutic benefits to DNMT1 targeting treatment in HCC.

Downregulation of Cancer Stemness by Novel Diterpenoid Ovatodiolide Inhibits Hepatic Cancer Stem Cell-Like Traits by Repressing Wnt/[Formula: see text]-Catenin Signaling

The hierarchical tumor propagation or cancer stem cells (CSCs) model of carcinogenesis postulates that like physiologic adult stem cell (ASC), the CSCs positioned at the apex of any tumor population form the crux of tumor evolution with a constitutive regenerative capacity and differentiation potential. The propagation and recurrence of the characteristically heterogeneous and therapy-resistant hepatocellular carcinoma (HCC), adds to accumulating evidence to support this CSCs model. Based on the multi-etiologic basis of HCC formation which among others, focuses on the disruption of the canonical Wnt signaling pathway, this study evaluated the role of cembrane-type phytochemical, Ovatodiolide, in the modulation of the Wnt/[Formula: see text]-catenin pathway, and its subsequent effect on liver CSCs' activities. Our fluorescence-activated cell sorting (FACS) and quantitative RT-PCR analyses of side population (SP) indicated that CD133+ cells were [Formula: see text]-catenin-overexpressing, more aggressive, and resistant to the conventional anticancer agents, Cisplatin and Doxorubicin, when compared to [Formula: see text]-catenin-downregulated group. We demonstrated that marked upregulation of [Formula: see text]-catenin and its downstream targets effectively enhanced hepatosphere formation, with an associated induction of CD133, OCT4 and Sox2 expression and also caused an significant enhancement of HCC proliferation. However, treatment with Ovatodiolide induced downregulation of [Formula: see text]-catenin and its downstream effector genes, abolished hepatosphere formation and reversed the [Formula: see text]-catenin-associated enhancement of HCC growth. In summary, we demonstrated for the first time that Ovatodiolide suppressed the canonical Wnt signaling pathway, and inhibited the generation of liver CSCs; Thus, projecting Ovatodiolide as a putatively effective therapeutic agent for anti-HCC target therapy.

Induction of cancer cell stemness by depletion of macrohistone H2A1 in hepatocellular carcinoma

Hepatocellular carcinomas (HCC) contain a subpopulation of cancer stem cells (CSCs), which exhibit stem cell-like features and are responsible for tumor relapse, metastasis, and chemoresistance. The development of effective treatments for HCC will depend on a molecular-level understanding of the specific pathways driving CSC emergence and stemness. MacroH2A1 is a variant of the histone H2A and an epigenetic regulator of stem-cell function, where it promotes differentiation and, conversely, acts as a barrier to somatic-cell reprogramming. Here, we focused on the role played by the histone variant macroH2A1 as a potential epigenetic factor promoting CSC differentiation. In human HCC sections we uncovered a significant correlation between low frequencies of macroH2A1 staining and advanced, aggressive HCC subtypes with poorly differentiated tumor phenotypes. Using HCC cell lines, we found that short hairpin RNA-mediated macroH2A1 knockdown induces acquisition of CSC-like features, including the growth of significantly larger and less differentiated tumors when injected into nude mice. MacroH2A1-depleted HCC cells also exhibited reduced proliferation, resistance to chemotherapeutic agents, and stem-like metabolic changes consistent with enhanced hypoxic responses and increased glycolysis. The loss of macroH2A1 increased expression of a panel of stemness-associated genes and drove hyperactivation of the nuclear factor kappa B p65 pathway. Blocking phosphorylation of nuclear factor kappa B p65 on Ser536 inhibited the emergence of CSC-like features in HCC cells knocked down for macroH2A1. Conclusion: The absence of histone variant macroH2A1 confers a CSC-like phenotype to HCC cells in vitro and in vivo that depends on Ser536 phosphorylation of nuclear factor kappa B p65; this pathway may hold valuable targets for the development of CSC-focused treatments for HCC. (Hepatology 2018;67:636-650).

Sporadic PCDH18 somatic mutations in EpCAM-positive hepatocellular carcinoma

Background

The relationship between specific genome alterations and hepatocellular carcinoma (HCC) cancer stem cells (CSCs) remains unclear. In this study, we evaluated the relationship between somatic mutations and epithelial cell adhesion molecule positive (EpCAM⁺) CSCs.

Methods

Two patient-derived HCC samples (HCC1 and HCC2) were sorted by EpCAM expression and analyzed by whole exome sequence. We measured PCDH18 expression level in eight HCC cell lines as well as HCC1 and HCC2 by real-time quantitative RT-PCR. We validated the identified gene mutations in 57 paired of HCC and matched non-cancerous liver tissues by Sanger sequence.

Results

Whole exome sequencing on the sorted EpCAM⁺ and EpCAM⁻ HCC1 and HCC2 cells revealed 19,263 nonsynonymous mutations in the cording region. We selected mutations that potentially impair the function of the encoded protein. Ultimately, 60 mutations including 13 novel nonsense and frameshift mutations were identified. Among them, PCDH18 mutation was more frequently detected in sorted EpCAM⁺ cells than in EpCAM⁻ cells in HCC1 by whole exome sequences. However, we could not confirm the difference of PCDH18 mutation frequency between sorted EpCAM⁺ and EpCAM⁻ cells by Sanger sequencing, indicating that PCDH18 mutation could not explain intracellular heterogeneity. In contrast, we found novel PCDH18 mutations, including c.2556_2557delTG, c.1474C>G, c.2337A>G, and c.2976G>T, were detected in HCC1 and 3/57 (5.3%) additional HCC surgical specimens. All four HCCs with PCDH18 mutations were EpCAM-positive, suggesting that PCDH18 somatic mutations might explain the intertumor heterogeneity of HCCs in terms of the expression status of EpCAM. Furthermore, EpCAM-positive cell lines (Huh1, Huh7, HepG2, and Hep3B) had lower PCDH18 expression than EpCAM-negative cell lines (PLC/PRL/5, HLE, HLF, and SK-Hep-1), and PCDH18 knockdown in HCC2 cells slightly enhanced cell proliferation.

Conclusions

Our data suggest that PCDH18 is functionally suppressed in a subset of EpCAM-positive HCCs through somatic mutations, and may play a role in the development of EpCAM-positive HCCs.

Electronic supplementary material

The online version of this article (doi:10.1186/s12935-017-0467-x) contains supplementary material, which is available to authorized users.

ZEB1 confers stem cell-like properties in breast cancer by targeting neurogenin-3

Cancer stem cells (CSCs) are a subpopulation of cancer cells believed to be implicated in cancer initiation, progression, and recurrence. Here, we report that ectopic expression of zinc finger E-box binding homeobox 1 protein (ZEB1) results in the acquisition of CSC properties by breast cancer cells, leading to tumor initiation and progression in vitro and in vivo. The neurogenin 3 gene (Ngn3) is a bona fide target of ZEB1, and its repression is a key factor contributing to ZEB1-induced cancer cell stemness. ZEB1 suppressed Ngn3 transcription by forming a ZEB1/DNA methyltransferase (DNMT)3B/histone deacetylase 1 (HDAC1) complex on the Ngn3 promoter, leading to promoter hypermethylation and gene silencing. The rescue of Ngn3 expression attenuated ZEB1-induced cancer stemness and symmetric CSC division. Immunohistological analysis of human breast cancer specimens revealed a strong inverse relationship between ZEB1 and NGN3 protein expression. Thus, our findings suggest ZEB1-mediated silencing of Ngn3 is required for breast tumor initiation and maintenance. Targeted therapies against the ZEB1/Ngn3 axis may be highly valuable for the prevention and treatment of breast cancer.

DNMT1 Regulates Epithelial-Mesenchymal Transition and Cancer Stem Cells, Which Promotes Prostate Cancer Metastasis

Cancer metastasis is a multistep process associated with the induction of an epithelial-mesenchymal transition (EMT) and cancer stem cells (CSCs). Although significant progress has been made in understanding the molecular mechanisms regulating EMT and the CSC phenotype, little is known of how these processes are regulated by epigenetics. Here we demonstrate that reduced expression of DNA methyltransferase 1 (DNMT1) plays an important role in the induction of EMT and the CSC phenotype by prostate cancer (PCa) cells, with enhanced tumorigenesis and metastasis. First, we observed that reduction of DNMT1 by 5-azacitidine (5-Aza) promotes EMT induction as well as CSCs and sphere formation in vitro. Reduced expression of DNMT1 significantly increased PCa migratory potential. We showed that the increase of EMT and CSC activities by reduction of DNMT1 is associated with the increase of protein kinase C. Furthermore, we confirmed that silencing DNMT1 is correlated with enhancement of the induction of EMT and the CSC phenotype in PCa cells. Additionally, chromatin immunoprecipitation assay reveals that reduction of DNMT1 promotes the suppression of H3K9me3 and H3K27me3 on the Zeb2 and KLF4 promoter region in PCa cells. Critically, we found in an animal model that significant tumor growth and more disseminated tumor cells in most osseous tissues were observed following injection of 5-Aza pretreated-PCa cells compared with vehicle-pretreated PCa cells. Our results suggest that epigenetic alteration of histone demethylation regulated by reduction of DNMT1 may control induction of EMT and the CSC phenotype, which facilitates tumorigenesis in PCa cells and has important therapeutic implications in targeting epigenetic regulation.

Systems approach to characterize the metabolism of liver cancer stem cells expressing CD133

Liver cancer stem cells (LCSCs) have attracted attention because they cause therapeutic resistance in hepatocellular carcinoma (HCC). Understanding the metabolism of LCSCs can be a key to developing therapeutic strategy, but metabolic characteristics have not yet been studied. Here, we systematically analyzed and compared the global metabolic phenotype between LCSCs and non-LCSCs using transcriptome and metabolome data. We also reconstructed genome-scale metabolic models (GEMs) for LCSC and non-LCSC to comparatively examine differences in their metabolism at genome-scale. We demonstrated that LCSCs exhibited an increased proliferation rate through enhancing glycolysis compared with non-LCSCs. We also confirmed that MYC, a central point of regulation in cancer metabolism, was significantly up-regulated in LCSCs compared with non-LCSCs. Moreover, LCSCs tend to have less active fatty acid oxidation. In this study, the metabolic characteristics of LCSCs were identified using integrative systems analysis, and these characteristics could be potential cures for the resistance of liver cancer cells to anticancer treatments.

Tumor-Initiating Cells: a criTICal review of isolation approaches and new challenges in targeting strategies

Most cancers contain a subpopulation of highly tumorigenic cells, known as cancer stem cells (CSCs) or tumor-initiating cells (TICs). Targeting TICs may be essential to achieve cure, because of their self-renewal and tumorigenic properties as well as their resistance to conventional therapies. Despite significant advances in TIC biology, their isolation and identification remain largely disputed and incompletely established. In this review, we discuss the latest developments in isolation and culturing approaches of TICs, with focus on colorectal cancer (CRC). We feature recent findings on TIC-relevant signaling pathways and the metabolic identity of TICs, as well as their current clinical implications. Lastly, we highlight the influence of inter- and intra-tumoral heterogeneity on TIC function and targeting approaches.

Associations of components of PTEN/AKT/mTOR pathway with cancer stem cell markers and prognostic value of these biomarkers in hepatocellular carcinoma

AIM

We aimed to investigate the associations between components of the phosphatase and tensin homolog deleted on chromosome 10/protein kinase B/mammalian target of rapamycin (PTEN/AKT/mTOR) pathway and liver cancer stem cell (LCSC) markers, including CD133, CD90, CD44, and epithelial cell adhesion molecule (EpCAM), and to further evaluate the predictive values of these biomarkers for recurrence and survival in hepatocellular carcinoma (HCC).

METHOD

Protein expressions and mRNA levels of PTEN and LCSC markers were determined in 110 HCC tissues and 98 adjacent non-tumor tissues. Protein expressions of phosphorylated AKT (p-AKT) and phosphorylated mTOR (p-mTOR) were detected to evaluate the activation of the PTEN/AKT/mTOR pathway by using immunohistochemistry. Prognostic significance was analyzed by univariate and multivariate analysis.

RESULTS

Loss of PTEN expression was negatively correlated with positive expression of CD133, CD90, and EpCAM (P < 0.05). Positive expression of p-AKT and p-mTOR were positively associated with positive expression for CD133, CD90, and EpCAM (P < 0.05). By univariate and multivariate analysis, a higher level of α-fetoprotein, loss of PTEN expression, and CD133-positive, p-AKT-positive, p-mTOR-positive, and EpCAM-positive signals were predictors for HCC recurrence, whereas advanced TNM stage, loss of PTEN expression, and positive expression of p-AKT, p-mTOR, and CD133 were predictors for survival. Patients with PTEN^- /CD133⁺ or PTEN^- /EpCAM⁺ HCC had shorter recurrence-free survival and overall survival times.

CONCLUSION

The PTEN/AKT/mTOR pathway might play a crucial role in driving recurrence and influencing prognosis in HCC. There could be a potential repressive relationship between components of the PTEN/AKT/mTOR pathway and LCSCs. The combination of PTEN with CD133 or EpCAM expression may serve as a screening tool to monitor recurrence and predict prognosis.

DLL4 overexpression increases gastric cancer stem/progenitor cell self-renewal ability and correlates with poor clinical outcome via Notch-1 signaling pathway activation

Gastric cancer is one of the most common malignant diseases, and poses a serious threat to the quality of human life. Gastric cancer stem/progenitor cells (GCSPCs) have critical effects on tumor formation, affecting specific features of self‐renewal and differentiation and playing a critical role in metastasis. The Notch‐1 pathway is crucially important to GCSPCs and is regulated by DLL4. In this study, DLL4 and Nestin levels were measured in 383 gastric cancer tissue samples by immunohistochemistry, and the clinico‐pathological features of patients assessed. After DLL4 silencing in selected gastric cancer cell lines, the expression of GCSPC markers and colony formation ability were analyzed and the self‐renewal and differentiation capacities of the cells were evaluated. The relationship between DLL4 levels and Notch‐1 signaling pathway effector amounts was assessed via Western blotting and immunofluorescence. Finally, the tumor formation ability of the gastric cancer cells was evaluated with different levels of DLL4 and multiple cell densities in vivo. Our results indicate that DLL4 expression is associated with TNM stage and cancer metastasis, with high amounts of DLL4 leading to poor outcome. DLL4 silencing inhibited the self‐renewal ability of GCSPCs and increased their multidifferentiation capacity, resulting in reduced GCSPC ratios. DLL4 knockdown also blocked the Notch‐1 pathway, weakening invasion ability and resistance to 5‐FU chemotherapy. In vivo, DLL4 silencing inhibited the tumor formation ability of GCSPCs. In conclusion, DLL4 affects GCSPC stemness, altering their pathological behavior. DLL4 silencing inhibits GCSPC metastatic potential both in vitro and in vivo by impeding Notch‐1 signaling pathway activation, indicating that DLL4 may be a new potential therapeutic target.

B-cell-specific Moloney murine leukemia virus integration site 1: potential stratification factor and therapeutic target for epithelial ovarian cancer

Epithelial ovarian cancer, a vexing challenge for clinical management, still lacks biomarkers for early diagnosis, precise stratification, and prognostic evaluation of patients. B-cell-specific Moloney murine leukemia virus integration site 1 (BMI1), a member of the polycomb group of proteins, engages in diverse cellular processes, including proliferation, differentiation, senescence, and stem cell renewal. In addition, BMI1, as a cancer stem-cell marker, participates in tumorigenesis through various pathways. Rewardingly, recent studies have also revealed a relationship between BMI1 expression and the clinical grade/stage, therapy response, and survival outcome in a majority of human malignancies, including epithelial ovarian cancer. Therefore, BMI1 might serve as a potential stratification factor and treatment target for epithelial ovarian cancer, pending evidence from further investigations.

An Integrated Analysis of the Genome-Wide Profiles of DNA Methylation and mRNA Expression Defining the Side Population of a Human Malignant Mesothelioma Cell Line

Intratumoral heterogeneity is a hallmark of all cancers and functions as the major barrier against effective cancer therapy. In contrast to genetic mutations, the role of epigenetic modifications in the generation and maintenance of heterogeneous cancer cells remains largely undetermined. This study was performed to evaluate the epigenetic mechanisms involved in the tumor cell heterogeneity using side population (SP) and non-SP cells isolated from a human malignant mesothelioma (HMM) cell line. The subpopulations of cancer cells were analyzed by methylated DNA immunoprecipitation combined with high-throughput sequencing (MeDIP-seq) and RNA-seq methodology. The RNA-seq data were analyzed with the MeDIP-seq data in an integrated way to identify the epigenetically modified genes that defined the SP. Concomitant changes in mRNA expression and DNA methylation were found in 122 genes, including 118 down-regulated genes with hypermethylation and 4 up-regulated genes with hypomethylation. Gene ontology revealed that a large portion of the genes belonged to the groups of biological processes such as stem cell maintenance, stem cell development, stem cell differentiation, and the negative regulation of the developmental process. Among these genes, BNC1, RPS6KA3, TWSG1 and DUSP15 contained aberrant methylation in the CpG islands of the promoter region, indicating that the genes regulated by DNA methylation characterized a distinct subpopulation of HMM cells. The present study provided valuable information to shed light on the epigenetic contributions to the generation and maintenance of tumor cell heterogeneity.

DDX3 Represses Stemness by Epigenetically Modulating Tumor-suppressive miRNAs in Hepatocellular Carcinoma

Studies indicate that the presence of cancer stem cells (CSCs) is responsible for poor prognosis of hepatocellular carcinoma (HCC) patients. In this study, the functional role of DDX3 in regulation of hepatic CSCs was investigated. Our results demonstrated that reduced DDX3 expression was not only inversely associated with tumor grade, but also predicted poor prognosis of HCC patients. Knockdown of DDX3 in HCC cell line HepG2 induced stemness gene signature followed by occurrence of self-renewal, chemoreisistance, EMT, migration as well as CSC expansion, and most importantly, DDX3 knockdown promotes tumorigenesis. Moreover, we found positive correlations between DDX3 level and expressions of tumor-suppressive miR-200b, miR-200c, miR-122 and miR-145, but not miR-10b and miR-519a, implying their involvement in DDX3 knockdown-induced CSC phenotypes. In addition, DDX3 reduction promoted up-regulation of DNA methyltransferase 3A (DNMT3A), while neither DNMT3B nor DNMT1 expression was affected. Enriched DNMT3A binding along with hypermethylation on promoters of these tumor-suppressive miRNAs reflected their transcriptional repressions in DDX3-knockdown cells. Furthermore, individual restoration of these tumor-suppressive miRNAs represses DDX3 knockdown-induced CSC phenotypes. In conclusion, our study suggested that DDX3 prevents generation of CSCs through epigenetically regulating a subset of tumor-suppressive miRNAs expressions, which strengthens tumor suppressor role of DDX3 in HCC.

TWIST1 and BMI1 in Cancer Metastasis and Chemoresistance

Purpose Increasing evidences revealed that cancer cells with the characteristics of epithelial-mesenchymal transition (EMT) or cancer stem cells (CSC) have high ability of progression, invasion, metastasis and chemoresistance. TWIST1 and BMI1 are crucial transcription factors required for EMT and CSC. Both TWIST1 and BMI1 are up-regulated in various cancers and have a positive correlation with poor prognosis. Although recent results showed that the two molecules function in promoting cancer metastasis and chemoresistance respectively, the correlation of TWIST1 and BMI1 is not well understood. Methods In this review, we summarize recent advance in cancer research focus on TWIST1 and BMI1 in cancer metastasis and chemoresistance, and emphasize the possible link between EMT and CSC. Results Further investigation of TWIST1 and BMI1 cooperately promote CSC proliferation due to EMT-associated effect will help to understand the mechanism of tumor cells metastasis and chemoresistance. Conclusions TWIST1 and BMI1 in cancer cells will be effective targets for treating chemoresistant metastatic lesions.

Molecular pathogenesis of hepatocellular carcinoma and impact of therapeutic advances

Hepatocellular carcinoma (HCC) is a leading cause of cancer mortality and has an increasing incidence worldwide. HCC can be induced by multiple etiologies, is influenced by many risk factors, and has a complex pathogenesis. Furthermore, HCCs exhibit substantial heterogeneity, which compounds the difficulties in developing effective therapies against this highly lethal cancer. With advances in cancer biology and molecular and genetic profiling, a number of different mechanisms involved in the development and progression of HCC have been identified. Despite the advances in this area, the molecular pathogenesis of hepatocellular carcinoma is still not completely understood. This review aims to elaborate our current understanding of the most relevant genetic alterations and molecular pathways involved in the development and progression of HCC, and anticipate the potential impact of future advances on therapeutic drug development.

Long noncoding RNA DANCR increases stemness features of hepatocellular carcinoma by derepression of CTNNB1

Tumor cells with stemness (stem-cell) features contribute to initiation and progression of hepatocellular carcinoma (HCC), but involvement of long noncoding RNAs (lncRNAs) remains largely unclear. Genome-wide analyses were applied to identify tumor-associated lncRNA-DANCR. DANCR expression level and prognostic values of DANCR were assayed in two HCC cohorts (China and Korea, n = 135 and 223). Artificial modulation of DANCR (down- and overexpression) was done to explore the role of DANCR in tumorigenesis and colonization, and tumor-bearing mice were used to determine therapeutic effects. We found that lncRNA-DANCR is overexpressed in stem-like HCC cells, and this can serve as a prognostic biomarker for HCC patients. Experiments showed that DANCR markedly increased stemness features of HCC cells to promote tumorigenesis and intra-/extrahepatic tumor colonization. Conversely, DANCR knockdown attenuated the stem-cell properties and in vivo interference with DANCR action led to decreased tumor cell vitality, tumor shrinkage, and improved mouse survival. Additionally, we found that the role of DANCR relied largely on an association with, and regulation of, CTNNB1. Association of DANCR with CTNNB1 blocked the repressing effect of microRNA (miR)-214, miR-320a, and miR-199a on CTNNB1. This observation was confirmed in vivo, suggesting a novel mechanism of tumorigenesis involving lncRNAs, messenger RNAs, and microRNAs.

CONCLUSIONS

These studies reveal a significance and mechanism of DANCR action in increasing stemness features and offer a potential prognostic marker and a therapeutic target for HCC.

Immunohistochemical Expression and Clinical Significance of Suggested Stem Cell Markers in Hepatocellular Carcinoma

Background:

Increasing evidence has shown that tumor initiation and growth are nourished by a small subpopulation of cancer stem cells (CSCs) within the tumor mass. CSCs are posited to be responsible for tumor maintenance, growth, distant metastasis, and relapse after curative operation. We examined the expression of CSC markers in paraffin-embedded tissue sections of hepatocellular carcinoma (HCC) and correlated the results with clinicopathologic characteristics.

Methods:

Immunohistochemical staining for the markers believed to be expressed in the CSCs, including epithelial cell adhesion molecule (EpCAM), keratin 19 (K19), CD133, and CD56, was performed in 82 HCC specimens.

Results:

EpCAM expression was observed in 56% of the HCCs (46/82) and K19 in 6% (5/82). EpCAM expression in HCC significantly correlated with elevated α-fetoprotein level, microvessel invasion of tumor cells, and high histologic grade. In addition, EpCAM expression significantly correlated with K19 expression. The overall survival and relapsefree survival rates in patients with EpCAM-expressing HCC were relatively lower than those in patients with EpCAM-negative HCC. All but two of the 82 HCCs were negative for CD133 and CD56, respectively.

Conclusions:

Our results suggest that HCCs expressing EpCAM are associated with unfavorable prognostic factors and have a more aggressive clinical course than those not expressing EpCAM. Further, the expression of either CD133 or CD56 in paraffin-embedded HCC tissues appears to be rare.

Model of fibrolamellar hepatocellular carcinomas reveals striking enrichment in cancer stem cells

The aetiology of human fibrolamellar hepatocellular carcinomas (hFL-HCCs), cancers occurring increasingly in children to young adults, is poorly understood. We present a transplantable tumour line, maintained in immune-compromised mice, and validate it as a bona fide model of hFL-HCCs by multiple methods. RNA-seq analysis confirms the presence of a fusion transcript (DNAJB1-PRKACA) characteristic of hFL-HCC tumours. The hFL-HCC tumour line is highly enriched for cancer stem cells as indicated by limited dilution tumourigenicity assays, spheroid formation and flow cytometry. Immunohistochemistry on the hFL-HCC model, with parallel studies on 27 primary hFL-HCC tumours, provides robust evidence for expression of endodermal stem cell traits. Transcriptomic analyses of the tumour line and of multiple, normal hepatic lineage stages reveal a gene signature for hFL-HCCs closely resembling that of biliary tree stem cells—newly discovered precursors for liver and pancreas. This model offers unprecedented opportunities to investigate mechanisms underlying hFL-HCCs pathogenesis and potential therapies.

With no cell lines available, investigating the aetiology of human fibrolamellar hepatocellular carcinomas (hFL-HCCs) has proved problematic. Here, Oikawa et al. establish a model of hFL-HCCs as a transplantable tumour line maintained in immune-compromised mice, which proves rich in cancer stem cells.

Curcumin effectively inhibits oncogenic NF-κB signaling and restrains stemness features in liver cancer

BACKGROUND & AIMS

The cancer stem cells (CSCs) have important therapeutic implications for multi-resistant cancers including hepatocellular carcinoma (HCC). Among the key pathways frequently activated in liver CSCs is NF-κB signaling.

METHODS

We evaluated the CSCs-depleting potential of NF-κB inhibition in liver cancer achieved by the IKK inhibitor curcumin, RNAi and specific peptide SN50. The effects on CSCs were assessed by analysis of side population (SP), sphere formation and tumorigenicity. Molecular changes were determined by RT-qPCR, global gene expression microarray, EMSA, and Western blotting.

RESULTS

HCC cell lines exposed to curcumin exhibited differential responses to curcumin and were classified as sensitive and resistant. In sensitive lines, curcumin-mediated induction of cell death was directly related to the extent of NF-κB inhibition. The treatment also led to a selective CSC-depletion as evidenced by a reduced SP size, decreased sphere formation, down-regulation of CSC markers and suppressed tumorigenicity. Similarly, NF-κB inhibition by SN50 and siRNA against p65 suppressed tumor cell growth. In contrast, curcumin-resistant cells displayed a paradoxical increase in proliferation and expression of CSC markers. Mechanistically, an important component of the CSC-depleting activity of curcumin could be attributed to a NF-κB-mediated HDAC inhibition. Co-administration of the class I/II HDAC inhibitor trichostatine sensitized resistant cells to curcumin. Further, integration of a predictive signature of curcumin sensitivity with human HCC database indicated that HCCs with poor prognosis and progenitor features are most likely to benefit from NF-κB inhibition.

CONCLUSIONS

These results demonstrate that blocking NF-κB can specifically target CSC populations and suggest a potential for combined inhibition of NF-κB and HDAC signaling for treatment of liver cancer patients with poor prognosis.

Expression of cancer stem cell biomarkers as a tool for a correct therapeutic approach to hepatocellular carcinoma

Liver cancer is the fifth most commonly diagnosed malignancy and the second most frequent cause of cancer death in men worldwide. Amongst liver cancers, hepatocellular carcinoma (HCC) represents the major histological subtype and it is one of the most common malignant human tumors worldwide. Research into the molecular biology of hepatocarcinogenesis has identified several biomarkers, which could provide additional informations in order to better understand the biology of HCC. A large number of biomarkers have been shown to have potential predictive significance and a wide variety of molecular markers have been proven to be excellent diagnostic tools for HCC but it is difficult to characterize HCC with a single biomarker. Thus, signatures of a combination of biomarkers may be more valuable for the diagnosis, staging and prognosis of HCC. Specifically, a correlation of HCC-CSCs phenotype to specific hepatic cancer subtypes and to specific clinical and pathological features has not yet been reported in human liver tumors. In this view we will first discuss the possible sources of liver stem cells and their relation with liver cancer development and we will secondly focus on the prognostic significance of clinical and pathological features of HCC.

Pathogenesis and prognosis of hepatocellular carcinoma at the cellular and molecular levels

Different approaches predict the outcome for patients with hepatocellular carcinoma (HCC). The expression of biliary-hepatic progenitor cell markers generally correlates with poor prognosis. This article focuses on the pathogenesis of HCC, how differentiation or dedifferentiation leads to a phenotype switch, and heterogeneity in the same tumor. A tumor cell decides its fate based on a complex interplay of signaling pathways. Interaction with the microenvironment decides whether it will invade, proliferate, or enter survival mode. Several signaling pathways contribute to stemness features, reflecting a small chemoresistant subpopulation of the tumor that expresses biliary-hepatic progenitor cell markers.

Epithelial cell adhesion molecule-positive human hepatic neoplastic cells: development of combined hepatocellular-cholangiocarcinoma in mice

BACKGROUND AND AIM

Human combined hepatocellular-cholangiocarcinoma (CHC) expresses several hepatic stem/progenitor cell (HSPC) markers, suggesting this neoplasm originates from HSPCs. We examined the significance of HSPC marker in CHC using a human CHC cell line.

METHODS

We used a human CHC cell line (KMCH-1) previously established in our laboratory. The original tumor was classified as CHC, showing areas of typical hepatocellular carcinoma (HCC) and cholangiocarcinoma (ChC). We examined the expression of HSPC markers and hepatocyte markers in KMCH-1 by flow cytometry (FCM) and quantitative real-time polymerase chain reaction. EpCAM(+) and EpCAM(-) KMCH-1 cells were isolated. Subsequently, their morphological features, HSPC marker expression, and biological characteristics were examined in vitro and in vivo.

RESULTS

FCM showed expression of EpCAM, K7, K19, and ABCG2 in KMCH-1, with various degrees. EpCAM(+) cells expressed K19 mRNA, but did not express α-fetoprotein (AFP). In contrast, EpCAM(-) cells expressed AFP mRNA, but did not express K19. EpCAM(+) cells produced both EpCAM(+) and EpCAM(-) cells, but EpCAM(-) cells produced only EpCAM(-) cells in vitro. EpCAM(+) cells showed higher tumorigenicity and formed larger tumors than EpCAM(-) cells. Inoculation of EpCAM(+) and EpCAM(-) cells produced both ChC and HCC-like component and HCC-like component only, respectively.

CONCLUSION

It is speculated that some CHCs may originate from EpCAM(+) neoplastic cells, and that these cells may affect malignant behavior and progression in such CHCs.

Cancer stem cells in primary liver cancers: pathological concepts and imaging findings

There is accumulating evidence that cancer stem cells (CSCs) play an integral role in the initiation of hepatocarcinogenesis and the maintaining of tumor growth. Liver CSCs derived from hepatic stem/progenitor cells have the potential to differentiate into either hepatocytes or cholangiocytes. Primary liver cancers originating from CSCs constitute a heterogeneous histopathologic spectrum, including hepatocellular carcinoma, combined hepatocellular-cholangiocarcinoma, and intrahepatic cholangiocarcinoma with various radiologic manifestations. In this article, we reviewed the recent concepts of CSCs in the development of primary liver cancers, focusing on their pathological and radiological findings. Awareness of the pathological concepts and imaging findings of primary liver cancers with features of CSCs is critical for accurate diagnosis, prediction of outcome, and appropriate treatment options for patients.

Evidence for epithelial-mesenchymal transition in cancer stem-like cells derived from carcinoma cell lines of the cervix uteri

The cancer stem cell (CSC) paradigm is one possible way to understand the genesis of cancer, and cervical cancer in particular. We quantified and enriched ALDH1(+) cells within cervical cancer cell lines and subsequently characterized their phenotypical and functional properties like invasion capacity and epithelial-mesenchymal transition (EMT). ALDH1 expression in spheroid-derived cells (SDC) and the parental monolayer-derived cell (MDC) line was compared by flow-cytometry. Invasion capability was evaluated by Matrigel assay and expression of EMT-related genes Twist 1, Twist 2, Snail 1, Snail 2, Vimentin and E-cadherin by real-time PCR. ALDH1 expression was significantly higher in SDC. ALDH1(+) cells showed increased colony-formation. SDC expressed lower levels of E-cadherin and elevated levels of Twist 1, Twist 2, Snail 1, Snail 2 and Vimentin compared to MDC. Cervical cancer cell lines harbor potential CSC, characterized by ALDH1 expression as well as properties like invasiveness, colony-forming ability, and EMT. CSC can be enriched by anchorage-independent culture techniques, which may be important for the investigation of their contribution to therapy resistance, tumor recurrence and metastasis.