Cellular signaling in normal and cancerous stem cells

Clinical significance of PNO1 as a novel biomarker and therapeutic target of hepatocellular carcinoma

The RNA-binding protein PNO1 plays an essential role in ribosome biogenesis. Recent studies have shown that it is involved in tumorigenesis; however, its role in hepatocellular carcinoma (HCC) is not well understood. The purpose of this study was to examine whether PNO1 can be used as a biomarker of HCC and also examine the therapeutic potential of PNO1 knockout for the treatment of HCC. PNO1 expression was upregulated in HCC and associated with poor prognosis. PNO1 expression was positively associated with tumour stage, lymph node metastasis and poor survival. PNO1 expression was significantly higher in HCC compared to that in fibrolamellar carcinoma or normal tissues. Furthermore, HCC tissues with mutant Tp53 expressed higher PNO1 than those with wild-type Tp53. PNO1 knockout suppressed cell viability, colony formation and EMT of HCC cells. Since activation of Notch signalling pathway promotes HCC, we measured the effects of PNO1 knockout on the components of Notch pathway and its targets. PNO1 knockout suppressed Notch signalling by modulating the expression of Notch ligands and their receptors, and downstream targets. PNO1 knockout also inhibited genes involved in surface adhesion, cell cycle, inflammation and chemotaxis. PNO1 knockout also inhibited colony and spheroid formation, cell migration and invasion, and markers of stem cells, pluripotency and EMT in CSCs. Overall, our data suggest that PNO1 can be used as a diagnostic and prognostic biomarker of HCC, and knockout of PNO1 by CRISPR/Cas9 can be beneficial for the management of HCC by targeting CSCs.

Inhibition of ribosome assembly factor PNO1 by CRISPR/Cas9 technique suppresses lung adenocarcinoma and Notch pathway: Clinical application

Growth is crucially controlled by the functional ribosomes available in cells. To meet the enhanced energy demand, cancer cells re-wire and increase their ribosome biogenesis. The RNA-binding protein PNO1, a ribosome assembly factor, plays an essential role in ribosome biogenesis. The purpose of this study was to examine whether PNO1 can be used as a biomarker for lung adenocarcinoma and also examine the molecular mechanisms by which PNO1 knockdown by CRISPR/Cas9 inhibited growth and epithelial-mesenchymal transition (EMT). The expression of PNO1 was significantly higher in lung adenocarcinoma compared to normal lung tissues. PNO1 expression in lung adenocarcinoma patients increased with stage, nodal metastasis, and smoking. Lung adenocarcinoma tissues from males expressed higher PNO1 than those from females. Furthermore, lung adenocarcinoma tissues with mutant Tp53 expressed higher PNO1 than those with wild-type Tp53, suggesting the influence of Tp53 status on PNO1 expression. PNO1 knockdown inhibited cell viability, colony formation, and EMT, and induced apoptosis. Since dysregulated signalling through the Notch receptors promotes lung adenocarcinoma, we measured the effects of PNO1 inhibition on the Notch pathway. PNO1 knockdown inhibited Notch signalling by suppressing the expression of Notch receptors, their ligands, and downstream targets. PNO1 knockdown also suppressed CCND1, p21, PTGS-2, IL-1α, IL-8, and CXCL-8 genes. Overall, our data suggest that PNO1 can be used as a diagnostic biomarker, and also can be an attractive therapeutic target for the treatment of lung adenocarcinoma.

Chromatin regulators in retinoblastoma: Biological roles and therapeutic applications

Retinoblastoma (RB) is a pediatric ocular tumor mostly occurring due to the biallelic loss of RB1 gene in the developing retina. Early studies of genomic aberrations in RB have provided a valuable insight into how RB can progress following the tumor-initiating RB1 mutations and have established a notion that inactivation of RB1 gene is critical to initiate RB but this causative genetic lesion alone is not sufficient for malignant progression. With the advent of high-throughput sequencing technologies, we now have access to the comprehensive genomic and epigenetic landscape of RB and have come to appreciate that RB tumorigenesis requires both genetic and epigenetic alterations that might be directly or indirectly driven by RB1 loss. This integrative perspective on RB tumorigenesis has inspired research efforts to better understand the types and functions of epigenetic mechanisms contributing to RB development, leading to the identification of multiple epigenetic regulators misregulated in RB in recent years. A complete understanding of the intricate network of genetic and epigenetic factors in modulation of gene expression during RB tumorigenesis remains a major challenge but would be crucial to translate these findings into therapeutic interventions. In this review, we will provide an overview of chromatin regulators identified to be misregulated in human RB among the numerous epigenetic factors implicated in RB development. For a subset of these chromatin regulators, recent findings on their functions in RB development and potential therapeutic applications are discussed.

miR-125a is upregulated in cancer stem-like cells derived from TW01 and is responsible for maintaining stemness by inhibiting p53

microRNA (miR)-125a and miR-125b were demonstrated to translationally and transcriptionally inhibit the mRNA level of p53 following the induction of chemo-reagents in our previous report. As a small subpopulation of nasopharyngeal carcinoma (NPC), cancer stem-like cells (CSCs) function critically in multi-malignant behaviors, including tumorigenesis and metastasis; however, the expression pattern and regulatory role of miR-125a, miR-125b and p53 in CSCs derived from NPC remain unclear. In order to investigate the potential regulatory role of miR-125 on p53, firstly CSCs was isolated from TW01 by culturing in serum-free medium. The stemness of isolated CSCs was examined via self-renewal capacity and side population assays. Following this, the miR-125a, miR-125b and p53 mRNA levels were evaluated via reverse-transcription quantitative polymerase chain reaction. Following the transfections of wild-type p53 or p53 without DNA binding activity (p53-mutR^248Q) into TW01 or CSCs, Chromatin Immunoprecipitation (ChIP), and cell cycle analyses using flow cytometry or Cell Counting Kit-8 assays were performed. Notably, it was determined that miR-125a was significantly upregulated in CSCs derived from TW01, but not miR-125b, and the mRNA and protein levels of p53 were downregulated. The transfection of p53 significantly decreased the cell viability and stopped cell cycle at the G₀/G₁ phases in TW01 and CSCs. The ChIP assay confirmed that the ectopic expression of wild-type p53 transcriptionally regulates its downstream gene, p21, but not B-cell lymphoma 2 nor Sco2. Taken together, the results of the present study indicated that p53 regulates CSCs via its DNA binding activity and potentially, in CSCs, miR-125a regulates the expression of p53, maintaining stemness.

High LIFr expression stimulates melanoma cell migration and is associated with unfavorable prognosis in melanoma

Increased or decreased expression of LIF receptor (LIFr) has been reported in several human cancers, including skin cancer, but its role in melanoma is unknown. In this study, we investigated the expression pattern of LIFr in melanoma and assessed its prognostic value. Using tissue microarrays consisting of 441 melanomas and 96 nevi, we found that no normal nevi showed high LIFr expression. LIFr staining was significantly increased in primary melanoma compared to dysplastic nevi (P = 0.0003) and further increased in metastatic melanoma (P = 0.0000). Kaplan–Meier survival curve and univariate Cox regression analyses showed that increased expression of LIFr was correlated with poorer 5-year patient survival (overall survival, P = 0.0000; disease-specific survival, P = 0.0000). Multivariate Cox regression analyses indicated that increased LIFr expression was an independent prognostic marker for primary melanoma (P = 0.036). LIFr knockdown inhibited melanoma cell migration in wound healing assays and reduced stress fiber formation. LIFr knockdown correlated with STAT3 suppression, but not YAP, suggesting that LIFr activation might stimulate melanoma cell migration through the STAT3 pathway. Our data indicate that strong LIFr expression identifies potentially highly malignant melanocytic lesions at an early stage and LIFr may be a potential target for the development of early intervention therapeutics.

Regulatory Roles of Dclk1 in Epithelial Mesenchymal Transition and Cancer Stem Cells

The identification of functionally relevant subpopulations of therapy-resistant cancer cells is a challenge. These cells, intrinsically resistant to conventional therapy, can cause recurrence. Evidence has suggested that therapy-resistant cancer cells are likely epithelial–mesenchymal transition (EMT) cells and/or stem-like cells called cancer stem cells (CSCs). EMT, a normal embryological process that converts epithelial cells into mesenchymal cells, is frequently activated during cancer development and progression. CSCs are a small subpopulation of cancer cells within a tumor mass that have the ability to self-renew and maintain tumor-initiating capacity by giving rise to heterogeneous lineages of cancer cells that comprise the whole tumor. Although the origin of CSCs and EMT cells remains to be fully explored, a growing body of evidence has indicated that the biology of EMT and CSCs is strongly linked. Doublecortin-like kinase 1 (DCLK1), a cancer stem cell marker, is functionally involved in maintaining cancer stemness and the process of EMT important for cancer initiation, cancer metastasis, and secondary tumor formation. Therefore, targeting these cells may provide new strategies to overcome tumor heterogeneity, therapeutic resistance, and cancer relapse. In this review, we will provide a potential mechanistic link between EMT induction and the emergence of CSCs for the origin and progression of cancer. We will highlight the functional activity of DCLK1 in supporting EMT and cancer cell self-renewal, which will lead us to a better understanding of DCLK1 expression in cancer development and progression, and help us to develop targeted therapies for effective cancer treatment.

Control of AC133/CD133 and impact on human hematopoietic progenitor cells through nucleolin

AC133 is a prominent surface marker of CD34+ and CD34- hematopoietic stem/progenitor cell (HSPC) subsets. AC133+ HSPCs contain high progenitor cell activity and are capable of hematopoietic reconstitution. Furthermore, AC133 is used for prospective isolation of tumor-initiating cells in several hematological malignancies. Nucleolin is a multifunctional factor of growing and cancer cells, which is aberrantly active in certain hematological neoplasms, and serves as a candidate molecular target for cancer therapy. Nucleolin is involved in gene transcription and RNA metabolism and is prevalently expressed in HSPCs, as opposed to differentiated hematopoietic tissue. The present study dissects nucleolin-mediated activation of surface AC133 and its cognate gene CD133, via specific interaction of nucleolin with the tissue-dependent CD133 promoter P1, as a mechanism that crucially contributes to AC133 expression in CD34+ HSPCs. In mobilized peripheral blood (MPB)-derived HSPCs, nucleolin elevates colony-forming unit (CFU) frequencies and enriches granulocyte-macrophage CFUs. Furthermore, nucleolin amplifies long-term culture-initiating cells and also promotes long-term, cytokine-dependent maintenance of hematopoietic progenitor cells. Active β-catenin, active Akt and Bcl-2 levels in MPB-derived HSPCs are nucleolin-dependent, and effects of nucleolin on these cells partially rely on β-catenin activity. The study provides new insights into molecular network relevant to stem/progenitor cells in normal and malignant hematopoiesis.

BMI-1, a promising therapeutic target for human cancer

BMI-1 oncogene is a member of the polycomb-group gene family and a transcriptional repressor. Overexpression of BMI-1 has been identified in various human cancer tissues and is known to be involved in cancer cell proliferation, cell invasion, distant metastasis, chemosensitivity and patient survival. Accumulating evidence has revealed that BMI-1 is also involved in the regulation of self-renewal, differentiation and tumor initiation of cancer stem cells (CSCs). However, the molecular mechanisms underlying these biological processes remain unclear. The present review summarized the function of BMI-1 in different human cancer types and CSCs, and discussed the signaling pathways in which BMI-1 is potentially involved. In conclusion, BMI-1 may represent a promising target for the prevention and therapy of various cancer types.

Increased level of nucleolin confers to aggressive tumor progression and poor prognosis in patients with hepatocellular carcinoma after hepatectomy

BACKGROUND

Nucleolin, as a multifunctional protein, has been demonstrated to play an oncogenic role in human hepatocellular carcinoma (HCC). The aim of this study was to investigate the expression pattern of nucleolin in HCC and determine its correlation with tumor progression and prognosis.

METHODS

Nucleolin expression at both mRNA and protein levels in HCC and adjacent nonneoplastic tissues were respectively detected by quantitative real time polymerase chain reaction (Q-PCR), immunohistochemistry and western blotting.

RESULTS

Nucleolin expression, at both mRNA and protein levels, was significantly higher in HCC tissues than in the adjacent nonneoplastic tissues (both P<0.001). In addition, the elevated nucleolin expression was markedly correlated with advanced tumor stage (P=0.001), high tumor grade (P=0.02) and serum AFP level (P=0.008). Moreover, HCC patients with high nucleolin expression had shorter 5-year disease-free survival and shorter 5-year overall survival than those with low expression (both P<0.001). Furthermore, the Cox proportional hazards model showed that nucleolin expression was an independent poor prognostic factor for both 5-year disease-free survival (hazards ratio [HR]=3.696, 95% confidence interval [CI] = 1.662-8.138, P=0.01) and 5-year overall survival (HR=3.872, CI=1.681-8.392, P=0.01) in HCC.

CONCLUSION

These results showed that the markedly and consistently increasing expression of nucleolin may be associated with aggressive characteristics of HCC, and implied that nucleolin expression may serve as a promising biochemical marker for predicting the clinical outcome of patients with this malignancy.

VIRTUAL SLIDES

The virtual slide(s) for this article can be found here: http://www.diagnosticpathology.diagnomx.eu/vs/13000_2014_175.

Glioma spheroids obtained via ultrasonic aspiration are viable and express stem cell markers: a new tissue resource for glioma research

BACKGROUND

Ultrasonic aspirators allow safe, rapid, and accurate removal of brain tumors. However, the tissue fragments removed are used surprisingly little in research.

OBJECTIVE

To investigate whether such tissue fragments could be cultured as organotypic multicellular spheroids because access to biopsy tissue is often limited.

METHODS

Tissue fragments obtained by ultrasonic aspiration from 10 glioblastomas and tumor biopsy tissue from 7 of these tumors were cultured in serum-containing and serum-free medium. On culturing, the fragments formed spheroids, which were prepared for histology. Two glioblastoma cell lines from ultrasonic fragments and biopsy tissue were established as well.

RESULTS

Hematoxylin and eosin staining showed viable glioma spheroids obtained from both ultrasonic and biopsy tissue in both types of medium. Endothelial growth factor receptor and PTEN/chromosome 10 status was found to be preserved in most spheroids (7-8 of 10 tumors), together with the level of glial fibrillary acidic protein, von Willebrand factor, and Ki-67. The levels of stem cell markers CD133, Bmi-1, nestin, and Sox2 also were preserved. The ultrasonic spheroids had higher levels of glial fibrillary acidic protein and von Willebrand factor and lower levels of Bmi-1, nestin, Sox2, and Olig2 compared with conventional biopsy spheroids. For both types of spheroids, the stem cell medium seemed to favor expression of stem cell markers. The established cell lines were capable of both spheroid formation at clonal density and tumor formation in vivo.

CONCLUSION

Viable organotypic and proliferating spheroids were easily obtained from ultrasonic tissue fragments. The preservation of markers and the establishment of cell lines with tumor-initiating cell properties suggest ultrasonic spheroids as a new tissue resource for glioma research.

Overexpression of nucleolin and different expression sites both related to the prognosis of gastric cancer

The aim of this study was to investigate the expression of nucleolin in tumorous tissues and corresponding non-malignant tissues in gastric cancer (GC), and the correlation of different expression sites with clinicopathologic parameters and prognosis. Immunohistochemistry was used for detecting the expression levels of nucleolin in GC tissues and corresponding non-malignant tissues from 124 gastrectomy specimens with stage I-III. Staining results were correlated with clinicopathologic features and survival. Both GC tissues and corresponding non-malignant tissues showed nucleolar staining for nucleolin. Nucleolin expression was higher in GC tissues than in non-malignant tissues. Among the 124 GCs, 85 (68.5%) were nucleolin-high. No significant correlation between nucleolin expression and other clinicopathologic parameters was found. The Cox univariate analysis indicated that both cytoplasmic staining and nucleolar staining of nucleolin expression correlated with patients' prognosis (log-rank, p < 0.0001; p = 0.0075, respectively). It was concluded in the study that nucleolin was overexpressed in GCs. A high level of nucleolar expression of nucleolin was an independent prognostic marker for better survival while high cytoplasmic staining was closely associated with worse prognosis for GC patients.

Bmi1 is required for tumorigenesis in a mouse model of intestinal cancer

The epigenetic regulator BMI1 is upregulated progressively in a wide variety of human tumors including colorectal cancer. In this study, we assessed the requirement for Bmi1 in intestinal tumorigenesis using an autochthonous mouse model in which Apc was conditionally ablated in the intestinal epithelium. Germline mutation of Bmi1 significantly reduced both the number and size of small intestinal adenomas arising in this model, and it acted in a dose-dependent manner. Moreover, in contrast to wild-type controls, Bmi1(-/-) mice showed no increase in median tumor size, and a dramatic decrease in tumor number, between 3 and 4 months of age. Thus, Bmi1 is required for both progression and maintenance of small intestinal adenomas. Importantly, Bmi1 deficiency did not disrupt oncogenic events arising from Apc inactivation. Instead, the Arf tumor suppressor, a known target of Bmi1 epigenetic silencing, was upregulated in Bmi1 mutant tumors. This was accompanied by significant upregulation of p53, which was confirmed by sequencing to be wild-type, and also elevated apoptosis within the smallest Bmi1(-/-) adenomas. By crossing Arf into this cancer model, we showed that Arf is required for the induction of both p53 and apoptosis, and it is a key determinant of the ability of Bmi1 deficiency to suppress intestinal tumorigenesis. Finally, a conditional Bmi1 mutant strain was generated and used to determine the consequences of deleting Bmi1 specifically within the intestinal epithelium. Strikingly, intestinal-specific Bmi1 deletion suppressed small intestinal adenomas in a manner that was indistinguishable from germline Bmi1 deletion. Thus, we conclude that Bmi1 deficiency impairs the progression and maintenance of small intestinal tumors in a cell autonomous and highly Arf-dependent manner.

IL-1β promotes stemness and invasiveness of colon cancer cells through Zeb1 activation

BACKGROUND

IL-1β is a pleiotropic pro-inflammatory cytokine and its up-regulation is closely associated with various cancers including gastrointestinal tumors. However, it remains unclear how IL-1β may contribute to the initiation and development of these inflammation-associated cancers. Here we investigated the role of IL-1β in colon cancer stem cell (CSC) development.

METHODS

Using self-renewal assay, soft-agar assay, invasion assay, real-time PCR analysis, immunoblot assay and shRNA knockdown, we determined the effects of IL-1β on cancer stem cell development and epithelial-mesenchymal transition (EMT) in human primary colon cancer cells and colon cancer cell line HCT-116.

RESULTS

We found that IL-1β can increase sphere-forming capability of colon cancer cells in serum-free medium. IL-1β-induced spheres displayed an up-regulation of stemness factor genes (Bmi1 and Nestin) and increased drug resistance, hallmarks of CSCs. Importantly, expression of EMT activator Zeb1 was increased in IL-1β-induced spheres, indicating that there might be a close association between EMT and IL-1β-induced CSC self-renewal. Indeed, IL-1β treatment led to EMT of colon cancer cells with loss of E-cadherin, up-regulation of Zeb1, and gain of the mesenchymal phenotype. Furthermore, shRNA-mediated knockdown of Zeb1 in HCT-116 cells reversed IL-1β-induced EMT and stem cell formation.

CONCLUSION

Our findings indicate that IL-1β may promote colon tumor growth and invasion through activation of CSC self-renewal and EMT, and Zeb1 plays a critical role in these two processes. Thus, IL-1β and Zeb1 might be new therapeutic targets against colon cancer stem cells.

Cancer stem cells: potential target for bioactive food components

Cancer stem cells often have phenotypic and functional characteristics similar to normal stem cells including the properties of self-renewal and differentiation. Recent findings suggest that uncontrolled self-renewal may explain cancer relapses and may represent a critical target for cancer prevention. It is conceivable that the loss of regulatory molecules resulting from inappropriate consumption of specific foods and their constituents may foster the aberrant self-renewal of cancer stem cells. In fact, increasing evidence points to the network delivering signals for self-renewal from extracellular compartments to the nucleus including changes in stem cell environments, inducible expression of microRNAs, hyperplastic nuclear chromatin structures, and the on/off of differentiation process as possible sites of action for bioactive food components. Diverse dietary constituents such as vitamins A and D, genistein, (-)-epigallocatechin-3-gallate (EGCG), sulforaphane, curcumin, piperine, theanine and choline have been shown to modify self-renewal properties of cancer stem cells. The ability of these bioactive food components to influence the balance between proliferative and quiescent cells by regulating critical feedback molecules in the network including dickkopf 1 (DKK-1), secreted frizzled-related protein 2 (sFRP2), B cell-specific Moloney murine leukemia virus integration site 1 (Bmi-1) and cyclin-dependent kinase 6 (CDK6) may account for their biological response. Overall, the response to food components does not appear to be tissue or organ specific, suggesting there may be common cellular mechanisms. Unquestionably, additional studies are needed to clarify the physiological role of these dietary components in preventing the resistance of tumor cells to traditional drugs and cancer recurrence.

Therapeutic targeting of the p53 pathway in cancer stem cells

INTRODUCTION

Cancer stem cells (CSCs) are a high profile drug target for cancer therapeutics due to their indispensable role in cancer progression, maintenance and therapeutic resistance. Restoring wild-type (WT) p53 function is an attractive new therapeutic approach for the treatment of cancer due to the well-described powerful tumor suppressor function of p53. As emerging evidence intimately links p53 and stem cell biology, this approach also provides an opportunity to target CSCs.

AREAS COVERED

This review covers the therapeutic approaches to restore the function of WT p53, cancer and normal stem cell biology in relation to p53 and the downstream effects of p53 on CSCs.

EXPERT OPINION

The restoration of WT p53 function by targeting p53 directly, its interacting proteins or its family members holds promise as a new class of cancer therapies. This review examines the impact that such therapies may have on normal and CSCs based on the current evidence linking p53 signaling with these populations.

Bmi-1 induces radioresistance in MCF-7 mammary carcinoma cells

Bmi-1, a member of the polycomb family, it is involved in self renewal of stem cells and functions as an oncogene in many malignant human cancer types. Recent studies have demonstrated that Bmi-1 is a predictive factor for poor patient prognosis. However, the underlying mechanisms of radioresistance mediated by Bmi-1 are poorly understood. In this study, the dose-survival relationship was analyzed using a clonogenic survival assay and combined radiation treatment with Bmi-1 overexpression or silencing. DNA double-strand break (DSB) and repair was assessed by immunofluorescence staining of γH2AX foci. In addition, mitochondrial membrane potential was detected between Bmi-1 knockdown and control MCF-7 cells after irradiation. Apoptosis and cell cycle were evaluated by flow cytometry. We found that exposure of MCF-7 cells overexpressing Bmi-1 to ionizing radiation resulted in dramatically enhanced survival relative to control cells, whereas cells with silenced Bmi-1 showed markedly reduced survival. Bmi-1 inhibition significantly increased DSBs and decreased DSB repair. Furthermore, Bmi-1 knockdown induced loss of mitochondrial membrane potential and enhanced apoptosis by up-regulating p53, p21, Bax expression and down-regulating p-AKT and Bcl-2 expression. These results indicate that Bmi-1 may play an important role in radiosensitivity, and the suppression of its expression might be a potential therapeutic target for breast cancer.

Targeting surface nucleolin with multivalent HB-19 and related Nucant pseudopeptides results in distinct inhibitory mechanisms depending on the malignant tumor cell type

BACKGROUND

Nucleolin expressed at the cell surface is a binding protein for a variety of ligands implicated in tumorigenesis and angiogenesis. By using a specific antagonist that binds the C-terminal RGG domain of nucleolin, the HB-19 pseudopeptide, we recently reported that targeting surface nucleolin with HB-19 suppresses progression of established human breast tumor cells in the athymic nude mice, and delays development of spontaneous melanoma in the RET transgenic mice.

METHODS

By the capacity of HB-19 to bind stably surface nucleolin, we purified and identified nucleolin partners at the cell surface. HB-19 and related multivalent Nucant pseudopeptides, that present pentavalently or hexavalently the tripeptide Lysψ(CH2N)-Pro-Arg, were then used to show that targeting surface nucleolin results in distinct inhibitory mechanisms on breast, prostate, colon carcinoma and leukemia cells.

RESULTS

Surface nucleolin exists in a 500-kDa protein complex including several other proteins, which we identified by microsequencing as two Wnt related proteins, Ku86 autoantigen, signal recognition particle subunits SRP68/72, the receptor for complement component gC1q-R, and ribosomal proteins S4/S6. Interestingly, some of the surface-nucleolin associated proteins are implicated in cell signaling, tumor cell adhesion, migration, invasion, cell death, autoimmunity, and bacterial infections. Surface nucleolin in the 500-kDa complex is highly stable. Surface nucleolin antagonists, HB-19 and related multivalent Nucant pseudopeptides, exert distinct inhibitory mechanisms depending on the malignant tumor cell type. For example, in epithelial tumor cells they inhibit cell adhesion or spreading and induce reversion of the malignant phenotype (BMC cancer 2010, 10:325) while in leukemia cells they trigger a rapid cell death associated with DNA fragmentation. The fact that these pseudopeptides do not cause cell death in epithelial tumor cells indicates that cell death in leukemia cells is triggered by a specific signaling mechanism, rather than nonspecific cellular injury.

CONCLUSIONS

Our results suggest that targeting surface nucleolin could change the organization of the 500-kDa complex to interfere with the proper functioning of surface nucleolin and the associated proteins, and thus lead to distinct inhibitory mechanisms. Consequently, HB-19 and related Nucant pseudopeptides provide novel therapeutic opportunities in treatment of a wide variety of cancers and related malignancies.

Rb and nucleolin antagonize in controlling human CD34 gene expression

Retinoblastoma protein (Rb) controls cell proliferation, differentiation, survival and gene expression and it has a central role in the signaling network that provides a cell cycle checkpoint in the G1 phase of the cell cycle. Studies in mice have shown that Rb regulates interactions between hematopoietic stem cells and their bone marrow microenvironment and it acts as a critical regulator of hematopoietic stem and progenitor cells under stress. In human hematopoiesis, the CD34 protein is expressed on a subset of progenitor cells capable of self-renewal, multilineage differentiation, and hematopoietic reconstitution, and CD34 has a role in the differentiation of hematopoietic cells. Here we find that, in CD34-positive hematopoietic cells, Rb controls the human CD34 promoter region by antagonizing the CD34 promoter factor nucleolin to provide a mechanism that links expression of endogenous CD34 to cell cycle progression. Our study suggests a direct involvement of Rb in the transcriptional program of human CD34-positive hematopoietic stem/progenitor cells, thus providing further insights into the molecular network relevant to the features of these cells.

Regulatory mechanisms of tumor suppressor P16(INK4A) and their relevance to cancer

P16(INK4A) (also known as P16 and MTS1), a protein consisting exclusively of four ankyrin repeats, is recognized as a tumor suppressor mainly because of the prevalence of genetic inactivation of the p16(INK4A) (or CDKN2A) gene in virtually all types of human cancers. However, it has also been shown that an elevated level of expression (upregulation) of P16 is involved in cellular senescence, aging, and cancer progression, indicating that the regulation of P16 is critical for its function. Here, we discuss the regulatory mechanisms of P16 function at the DNA level, the transcription level, and the posttranscriptional level, as well as their implications for the structure-function relationship of P16 and for human cancers.

Naturally occurring, tumor-specific, therapeutic proteins

The emerging approach to cancer treatment known as targeted therapies offers hope in improving the treatment of therapy-resistant cancers. Recent understanding of the molecular pathogenesis of cancer has led to the development of targeted novel drugs such as monoclonal antibodies, small molecule inhibitors, mimetics, antisense and small interference RNA-based strategies, among others. These compounds act on specific targets that are believed to contribute to the development and progression of cancers and resistance of tumors to conventional therapies. Delivered individually or combined with chemo- and/or radiotherapy, such novel drugs have produced significant responses in certain types of cancer. Among the most successful novel compounds are those which target tyrosine kinases (imatinib, trastuzumab, sinutinib, cetuximab). However, these compounds can cause severe side-effects as they inhibit pathways such as epidermal growth factor receptor (EGFR) or platelet-derived growth factor receptor, which are also important for normal functions in non-transformed cells. Recently, a number of proteins have been identified which show a remarkable tumor-specific cytotoxic activity. This toxicity is independent of tumor type or specific genetic changes such as p53, pRB or EGFR aberrations. These tumor-specific killer proteins are either derived from common human and animal viruses such as E1A, E4ORF4 and VP3 (apoptin) or of cellular origin, such as TRAIL (tumor necrosis factor-related apoptosis-inducing ligand) and MDA-7 (melanoma differentiation associated-7). This review aims to present a current overview of a selection of these proteins with preferential toxicity among cancer cells and will provide an insight into the possible mechanism of action, tumor specificity and their potential as novel tumor-specific cancer therapeutics.

Suppression of tumorigenicity of rhabdoid tumor derived G401 cells by the multivalent HB-19 pseudopeptide that targets surface nucleolin

Several studies have indicated that the cell-surface expressed nucleolin is implicated in tumorigenesis and angiogenesis, and represents an important target for cancer therapy. Here we show that treatment of rhabdoid tumor derived G401 cells with a nucleolin antagonist, the HB-19 pseudopeptide, could restore contact inhibition, impair anchorage-independent growth, and suppress tumor development in nude mice. G401 cells grow without contact inhibition, which is an in vitro characteristic property of malignant tumor cells. At concentrations of HB-19 that does not affect cell viability and multiplication index, there is restoration of contact inhibition thus suggesting that HB-19 treatment causes reversion of the malignant phenotype. Accordingly, HB-19 pretreated G401 cells lose the capacity to form colonies in soft agar. When assayed for tumorigenicity in nude mice, only 50% of mice injected with HB-19 pretreated G401 cells developed tumors with the mean tumor weight of 0.32 g, compared to 100% of mice injected with control G401 cells with the mean tumor weight of 2.36 g. Interestingly, the restoration of contact inhibition in HB-19 treated G401 cells is concomitant with marked reduction of transcripts coding the Wilms' tumor 1 gene, matrix metalloproteinase-2, epithelial isoform of CD44, and vascular endothelial growth factor, whereas no apparent modification is detected for transcripts coding the proto-oncogene c-Myc, anti-apoptotic Bcl-2, pro-apoptotic Bax, tissue inhibitor of metalloproteinase TIMP-1, angiogenesis inhibitor TSP-1, and growth factor Midkine. These findings indicate that the molecular mechanism of action of HB-19 on such highly malignant rhabdoid tumor cells is associated with a selective inhibitory effect on the expression of genes implicated in tumorigenesis and angiogenesis.

Cancer stem cells and cancer therapy

Cancer stem cells (CSCs) are a subpopulation of tumour cells that possess the stem cell properties of self-renewal and differentiation. Stem cells might be the target cells responsible for malignant transformation, and tumour formation may be a disorder of stem cell self-renewal pathway. Epigenetic alterations and mutations of genes involved in signal transmissions may promote the formation of CSCs. These cells have been identified in many solid tumours including breast, brain, lung, prostate, testis, ovary, colon, skin, liver, and also in acute myeloid leukaemia. The CSC theory clarifies not only the issue of tumour initiation, development, metastasis and relapse, but also the ineffectiveness of conventional cancer therapies. Treatments directed against the bulk of the cancer cells may produce striking responses but they are unlikely to result in long-term remissions if the rare CSCs are not targeted. In this review, we consider the properties of CSCs and possible strategies for controlling the viability and tumourigenecity of these cells, including therapeutic models for selective elimination of CSCs and induction of their proper differentiation.

Surface expressed nucleolin is constantly induced in tumor cells to mediate calcium-dependent ligand internalization

BACKGROUND

Nucleolin is one of the major proteins of the nucleolus, but it is also expressed on the cell surface where is serves as a binding protein for variety of ligands implicated in tumorigenesis and angiogenesis. Emerging evidence suggests that the cell-surface expressed nucleolin is a strategic target for an effective and nontoxic cancer therapy.

METHODOLOGY/PRINCIPAL FINDINGS

By monitoring the expression of nucleolin mRNA, and by measuring the level of nucleolin protein recovered from the surface and nucleus of cells, here we show that the presence of nucleolin at the cell surface is dependent on the constant induction of nucleolin mRNA. Indeed, inhibitors of RNA transcription or translation block expression of surface nucleolin while no apparent effect is observed on the level of nucleolin in the nucleus. The estimated half-life of surface nucleolin is less than one hour, whereas that of nuclear nucleolin is more than 8 hours. Nucleolin mRNA induction is reduced markedly in normal fibroblasts that reach confluence, while it occurs continuously even in post-confluent epithelial tumor cells consistent with their capacity to proliferate without contact inhibition. Interestingly, cold and heat shock induce nucleolin mRNA concomitantly to enhanced mRNA expression of the heat shock protein 70, thus suggesting that surface nucleolin induction also occurs in response to an environmental insult. At the cell surface, one of the main functions of nucleolin is to shuttle specific extracellular ligands by an active transport mechanism, which we show here to be calcium dependent.

CONCLUSION/SIGNIFICANCE

Our results demonstrate that the expression of surface nucleolin is an early metabolic event coupled with tumor cell proliferation and stress response. The fact that surface nucleolin is constantly and abundantly expressed on the surface of tumor cells, makes them a preferential target for the inhibitory action of anticancer agents that target surface nucleolin.

Aberrant expression of regulators of cell-fate found in eutopic endometrium is found in matched ectopic endometrium among women and in a baboon model of endometriosis

BACKGROUND

We have recently shown that women with endometriosis express an increased amount of telomerase and nucleolin, with concomitant loss of γ-H2AX in eutopic endometrium. To further examine these selected factors that regulate cell fate, in the pathogenesis of endometriosis, we studied the expression of telomerase, nucleolin, proliferating cell nuclear antigen and γ-H2AX in ectopic endometriotic deposits from women, and in matched eutopic and ectopic endometrial tissue from a baboon model of endometriosis.

METHODS

Ectopic active peritoneal endometriotic lesions were collected from seven symptomatic women. Endometriosis was induced in six baboons by intra-peritoneal autologous inoculation of menstrual endometrium. Eutopic and matched ectopic endometrial tissues were collected prior to and 6, 12 and 15 months after the induction of endometriosis as previously described. Eutopic endometrium was also obtained from eight healthy fertile control baboons. Immunohistochemistry was performed as previously described, and telomerase activity was confirmed using the telomeric repeat amplification protocol assay.

RESULTS

All active human endometriotic lesions expressed the proliferative markers but showed weak or absent staining for γ-H2AX. A similar expression pattern of these markers was seen in the ectopic lesions of the baboons with induced disease. In these baboons, the eutopic endometrium also showed intense immunoreactivity for all proliferative markers 6-12 months after induction with a parallel loss of γ-H2AX. The opposite staining pattern was seen in eutopic endometrium of healthy animals and in pre-induction endometrium of animals with induced disease.

CONCLUSIONS

Endometriotic lesions have excess proliferative potential; in baboons, these were present within 12 months of the initiation of the disease. In eutopic tissue, these changes appear to be induced by the development of endometriosis.

Interleukins, laminin and Epstein - Barr virus latent membrane protein 1 (EBV LMP1) promote metastatic phenotype in nasopharyngeal carcinoma

Background

Nasopharyngeal carcinoma (NPC) is a type of neoplasm that is highly prevalent in East Asia and Africa with Epstein-Barr virus (EBV), genetic, and dietary factors implicated as possible aetiologic factors. Previous studies suggested the association of certain cytokines with the invasion and metastatic properties of NPC. The present study examined the roles of EBV latent membrane protein-1 (LMP1), interleukin-6 (IL-6), interleukin-10 (IL-10), transforming growth factor-beta 1 (TGF-β1) and laminin in the regulation of matrix-metalloproteinases (MMPs) and vascular endothelial growth factor (VEGF) in NPC. The effects of these factors on bmi-1, an oncogene, and ngx6, a tumour suppressor gene, were also investigated.

Methods

TW01 cells expressing LMP1 (TW01-LMP1) were established via transfection with the B95.8 EBV LMP1 gene. Both TW01 and TW01-LMP1 cells were treated with 100 pg/ml IL-6, 1000 pg/ml IL-10 and 100 pg/ml TGF-β1, separately and also in combination at their respective concentration for 48 hours. Treated cells were subjected to laminin adherence assay. The cells were also cultured with and without laminin and assayed for MMP-3, MMP-9 and VEGF production using enzyme-linked immunosorbent assay (ELISA). The cellular apoptotic property was analysed using caspase-3 apoptosis assay. The expression of bmi-1 and ngx6 gene was investigated using real time reverse transcriptase polymerase chain reaction.

Results

LMP1 was found to reduce the adherence of NPC cells towards laminin (p < 0.05) as compared to control. Treatment with IL-6 at 100 pg/ml enhanced the production of MMP-9 in both TW01 and TW01-LMP1 cells (p < 0.05). When cultured on laminin, the levels of MMP-3 and VEGF were significantly increased (p < 0.05) in TW01-LMP1 cells. TW01-LMP1 cells had relatively greater resistance to apoptosis as compared to TW01 cells (p < 0.05). Laminin, IL-6 and LMP1 were found to up-regulate the expression of bmi-1 and suppressed the expression of ngx6.

Conclusions

We conclude that IL-6 reduced cell adherence towards laminin and increased MMP-9 production in NPC cells. Our data suggested that EBV LMP1 was able to confer resistance of apoptosis and increased MMP-9 production in NPC cells. When cultured on laminin, TW01 cells expressing the EBV LMP1 (TW0-LMP1) that were treated with IL-6 at 100 pg/ml displayed increased MMP-9 production, up-regulation of bmi-1 oncogene expression and down-regulation of ngx6 tumour suppressor gene expression. These findings implicate the roles of EBV LMP1, laminin and IL-6 in the promotion of invasion and metastasis in NPC.

Identification and characterization of Bmi-1-responding element within the human p16 promoter

Bmi-1, the first functionally identified polycomb gene family member, plays critical roles in cell cycle regulation, cell immortalization, and cell senescence. Bmi-1 is involved in the development and progression of carcinomas and is a potent target for cancer therapy. One important pathway regulated by Bmi-1 is that involving two cyclin-dependent kinase inhibitors, p16(Ink4a) and p19(Arf), as Bmi-1 represses the INK4a locus on which they are encoded. A close correlation between the up-regulation of Bmi-1 and down-regulation of p16 has been demonstrated in various tumors; however, how Bmi-1 regulates p16 expression is not clear. In this study, we revealed that Bmi-1 regulates the expression of p16 by binding directly to the Bmi-1-responding element (BRE) within the p16 promoter. The BRE resided at bp -821 to -732 upstream of the p16 ATG codon. BRE alone was sufficient to allow Bmi-1-mediated regulation of the CMV promoter. Bmi-1 typically functions by forming a complex with Ring2; however, regulation of p16 was independent of Ring2. Chromatin immunoprecipitation sequencing of Bmi-1-precipitated chromatin DNA revealed that 1536 genes were targeted by Bmi-1, including genes involved in tissue-specific differentiation, cell cycle, and apoptosis. By analyzing the binding sequences of these genes, we found two highly conserved Bmi-1-binding motifs, which were required for Bmi-1-mediated p16 promoter regulation. Taken together, our results revealed the molecular mechanism of Bmi-1-mediated regulation of the p16 gene, thus providing further insights into the functions of Bmi-1 as well as a sensitive high-throughput platform with which to screen Bmi-1-targeted small molecules for cancer therapy.

Expression of Lgr5 in human colorectal carcinogenesis and its potential correlation with beta-catenin

BACKGROUNDS AND AIMS

Lgr5 is a member of the G protein receptor super-family and was shown recently to be a stem cell marker for cells with intestinal differentiation. Its over-expression has been demonstrated in hepatocellular, basal cell carcinoma, and ovarian cancers but the underlying mechanisms are poorly understood. The aim of this study was to investigate if Lgr5 over-expression was correlated with human colorectal carcinogenesis and its potential correlation with beta-catenin.

METHODS

The study was carried out on a tissue microarray that consisted of 102 colorectal carcinomas (CRC; M:F = 55:47), 18 colon adenoma, and 12 colon normal mucosa cases. Immunostains were performed with the standard EnVision method with primary antibodies against Lgr5, beta-catenin, and p53 antigens. Immunoreactivity of neoplastic cells to each antibody was double-blindly semi-quantified by two pathologists and the data were analyzed with the Chi-square and Spearman rank correlation tests. Subsequently, expression of Lgr5 in tissue sections of tumor centre and invasive margins of 21 cases of CRC certified to be immunoreactive of Lgr5 in TMA were evaluated and possible differences of Lgr5 expression between them were analyzed.

RESULTS

Lgr5 immunoreactivity was observed only in single cells in the base of normal colon mucosal crypts but high in 28% (five out of 18) adenomas, and significantly higher in 54% (55/102, p = 0.016) CRC cases. In normal mucosa, adenoma, and CRC, beta-catenin expression was seen in 25% (three out of 12), 27% (five out of 18), and 81% (83/102) cases, respectively, in contrast to 0, 0, and 40% (41/102) for p53 expression, respectively. In CRC, Lgr5 expression was more intense in women than men (p < 0.0001), and positively correlated with beta-catenin expression (p < 0.001), but not with patients' ages, tumor sizes, nodal status, TNM stages, and p53 expression. Different expression of Lgr5 between tumor centre and invasive margins was not found (p > 0.05).

CONCLUSIONS

The results suggest that up-regulation of Lgr5 expression, especially in female patients, may play an important role in colorectal carcinogenesis, probably through the WNT/beta-catenin pathway, but not involve the progression of the CRC.

Polycomb group protein gene silencing, non-coding RNA, stem cells, and cancer

Epigenetic programming is an important facet of biology, controlling gene expression patterns and the choice between developmental pathways. The Polycomb group proteins (PcGs) silence gene expression, allowing cells to both acquire and maintain identity. PcG silencing is important for stemness, X chromosome inactivation (XCI), genomic imprinting, and the abnormally silenced genes in cancers. Stem and cancer cells commonly share gene expression patterns, regulatory mechanisms, and signalling pathways. Many microRNA species have oncogenic or tumor suppressor activity, and disruptions in these networks are common in cancer; however, long non-coding (nc)RNA species are also important. Many of these directly guide PcG deposition and gene silencing at the HOX locus, during XCI, and in examples of genomic imprinting. Since inappropriate HOX expression and loss of genomic imprinting are hallmarks of cancer, disruption of long ncRNA-mediated PcG silencing likely has a role in oncogenesis. Aberrant silencing of coding and non-coding loci is critical for both the genesis and progression of cancers. In addition, PcGs are commonly abnormally overexpressed years prior to cancer pathology, making early PcG targeted therapy an option to reverse tumor formation, someday replacing the blunt instrument of eradication in the cancer therapy arsenal.

Proteins selectively killing tumor cells

All human cells have a genetic program that upon activation will cause cell death, named apoptosis. Cancer cells can grow due to unbalances in proliferation, cell cycle regulation and their apoptosis machinery: genomic mutations resulting in non-functional pro-apoptosis proteins or over-expression of anti-apoptosis proteins form the basis of tumor formation. Surprisingly, lessons learned from viruses show that cancer cannot be regarded simply as the opposite of apoptosis. For instance, adenovirus can only transform cells when both its anti- and pro-apoptotic proteins are produced. Oncolytic viruses are known to replicate selectively in tumor cells resulting in cell death. Proteins derived from viruses, i.e. chicken anemia virus (CAV)-derived apoptosis-inducing protein (apoptin), adenovirus early region 4 open reading frame (E4orf4) and parvovirus-H1 derived non-structural protein 1 (NS1), the human alpha-lactalbumin made lethal to tumor cells (HAMLET), which is present in human milk or the human cytokines melanoma differentiation-associated gene-7 (mda-7) and tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) have all the ability to induce tumor-selective apoptosis. The tumor-selective apoptosis-inducing proteins seem to interact with transforming survival processes, which can become redirected by these proteins into cell death. Transformation-related processes have been identified, which seem to be crucial for the tumor-selectively killing activity of these proteins. For instance, the transformation-related protein phosphatase 2A (PP2A) plays a role in the induction of tumor-selective apoptosis. The proteins mda-7, TRAIL and HAMLET are already successfully tested in first clinical trials. Proteins harboring tumor-selective apoptosis characteristics represent, therefore, a therapeutic potential and a tool for unraveling tumor-related processes. Fundamental molecular and (pre)clinical therapeutic studies of the various tumor-selective apoptosis-inducing proteins apoptin, E4orf4, HAMLET, mda-7, NS1, TRAIL and related proteins will be discussed.

Bmi-1, stem cells and cancer

Bmi-1, a polycomb gene family member, plays an important role in cell cycle regulation, cell immortalization, and cell senescence. Recently, numerous studies have demonstrated that Bmi-1 is involved in the regulation of self-renewal and differentiation of stem cells. However, the molecular mechanism underlying this biological process remains largely unclear. In the present review, we summarized the function of Bmi-1 as a transcriptional regulator of gene expression, with particular reference to stem cells.

Targeting stem cells-clinical implications for cancer therapy

Cancer stem cells (CSC), also called tumor initiating cells (TIC), are considered to be the origin of replicating malignant tumor cells in a variety of human cancers. Their presence in the tumor may herald malignancy potential, mediate resistance to conventional chemotherapy or radiotherapy, and confer poor survival outcomes. Thus, CSC may serve as critical cellular targets for treatment. The ability to therapeutically target CSC hinges upon identifying their unique cell surface markers and the underlying survival signaling pathways. While accumulating evidence suggests cell-surface antigens (such as CD44, CD133) as CSC markers for several tumor tissues, emerging clinical needs exist for the identification of new markers to completely separate CSC from normal stem cells. Recent studies have demonstrated the critical role of the tumor suppressor PTEN/PI3 kinase pathway in regulating TIC in leukemia, brain, and intestinal tissues. The successful eradication of tumors by therapies targeting CSC will require an in-depth understanding of the molecular mechanisms governing CSC self renewal, differentiation, and escape from conventional therapy. Here we review recent progress from brain tumor and intestinal stem cell research with a focus on the PTEN-Akt-Wnt pathway, and how the components of CSC pathways may serve as biomarkers for diagnosis, prognosis, and therapeutics.

Sustained replication in endometrium of women with endometriosis occurs without evoking a DNA damage response

BACKGROUND

To test our hypothesis that eutopic secretory phase endometrium from women with endometriosis is similar to proliferative phase endometrium from fertile women without endometriosis, we explored the expression of regulators of cell fate across the menstrual cycle.

METHODS

Endometrial biopsies were taken from 73 women, comprising 38 women with surgically diagnosed active peritoneal endometriosis (Group 1) and 35 fertile women without endometriosis (Group 2). Nucleolin, proliferating cell nuclear antigen (PCNA), telomerase and histone gamma-H2AX expression was evaluated by immunohistochemistry and mean telomere length (TL) by quantitative PCR.

RESULTS

We have immunolocalized nucleolin and gamma-H2AX in the benign premenopausal endometrium for the first time. All markers were present in the proliferative phase endometrium of all women. In Group 2, during the secretory phase, proliferative markers declined with a paradoxical increase in stromal gamma-H2AX. Women in Group 1, however, showed a persistent immunoreactivity for the proliferative markers, while the staining for gamma-H2AX decreased in secretory endometrium (P < 0.05). This difference between groups was significant in both stroma and glands for nucleolin (P < 0.0001), PCNA (P < 0.01) and gamma-H2AX (P < 0.05) in the secretory phase. We showed a positive correlation between mean TL and nucleolin expression (glandular r = 0.37, P = 0.002; stromal r = 0.4, P = 0.001), telomerase immunoreactivity (glandular r = 0.33, P = 0.009; stromal r = 0.4, P = 0.001) and glandular PCNA (r = 0.35, P = 0.004), whereas a negative correlation was seen between mean TL and gamma-H2AX (r = -0.28, P = 0.04).

CONCLUSIONS

These findings demonstrate that the state of replication seen in secretory phase endometrium from women with active peritoneal endometriosis is not a simple extension of the proliferative phase.

Multifactorial analysis of predictors of outcome in pediatric intracranial ependymoma

Pediatric ependymomas are enigmatic tumors, and their clinical management remains one of the more difficult in pediatric oncology. The identification of biological correlates of outcome and therapeutic targets remains a significant challenge in this disease. We therefore analyzed a panel of potential biological markers to determine optimal prognostic markers. We constructed a tissue microarray from 97 intracranial tumors from 74 patients (WHO grade II-III) and analyzed the candidate markers nucleolin, telomerase catalytic subunit (hTERT; antibody clone 44F12), survivin, Ki-67, and members of the receptor tyrosine kinase I (RTK-I) family by immunohistochemistry. Telomerase activity was determined using the in vitro-based telomere repeat amplification protocol assay, and telomere length was measured using the telomere restriction fragment assay. Primary tumors with low versus high nucleolin protein expression had a 5-year event-free survival of 74%+/-13% and 31%+/-7%, respectively. Multivariate analysis identified low nucleolin expression to be independently associated with a more favorable prognosis (hazard ratio=6.25; 95% confidence interval, 1.6-24.2; p=0.008). Ki-67 and survivin correlated with histological grade but not with outcome. Immunohistochemical detection of the RTK-I family did not correlate with grade or outcome. Telomerase activity was evident in 19 of 22 primary tumors, with telomere lengthening and/or maintenance occurring in five of seven recurrent cases. Low nucleolin expression was the single most important biological predictor of outcome in pediatric intracranial ependymoma. Furthermore, telomerase reactivation and maintenance of telomeric repeats appear necessary for childhood ependymoma progression. These findings require corroboration in a clinical trial setting.

New hope for cancer treatment: exploring the distinction between normal adult stem cells and cancer stem cells

For decades, intensive studies have attempted to identify the mechanisms underlying malignant tumor growth. Despite significant progress, most therapeutic approaches fail to eliminate all tumor cells. The remaining tumor cells often result in recurrence and metastasis. Recently, the idea of a cancer stem cell was proposed to explain of the origin of cancer cells. According to this hypothesis, a small fraction of tumor cells have the capacity for self-renewal, with unlimited slow proliferation potential. They are often resistant to chemotherapy and radiation and thus are responsible for continuously supplying new cancer cells, which themselves may have a limited life span. In recent years, accumulating experimental evidence supports this hypothesis and provides new possibilities to conquer cancer. This review will focus on the distinction between normal adult stem cells and cancer stem cells and identifies possible key targets for effective therapies of cancer.