Functional evidence that the self-renewal gene NANOG regulates human tumor development

Pluripotency transcription factors and cancer stem cells: small genes make a big difference

Cancer stem cells (CSCs) are thought to drive uncontrolled tumor growth, and the existence of CSCs has recently been proven by direct experimental evidence, including tracing cell lineages within a growing tumor. However, CSCs must be analyzed in additional cancer types. Cancer stem cell-like cells (CSCLCs) are a good alternative system for the study of CSCs, which hold great promise for clinical applications. OCT4, NANOG, and SOX2 are three basic transcription factors that are expressed in both CSCLCs and embryonic stem cells (ESCs). These transcription factors play critical roles in maintaining the pluripotence and self-renewal characteristics of CSCLCs and ESCs. In this review, we discuss the aberrant expression, isoforms, and pseudogenes of OCT4, NANOG, and SOX2 in the CSCLC niche, which contribute to the major differences between CSCLCs and ESCs. We also highlight an anticancer therapy that involves killing specific cancer cells directly by repressing the expression of OCT4, NANOG, or SOX2. Importantly, OCT4, NANOG, and SOX2 provide great promise for clinical applications because reducing their expression or blocking the pathways in which they function may inhibit tumor growth and turn-off the cancer “switch.” In the future, a clear understanding of transcription factor regulation will be essential for elucidating the roles of OCT4, NANOG, and SOX2 in tumorigenesis, as well as exploring their use for diagnostic and therapeutic purposes.

New insights into prostate cancer stem cells

Prostate cancer (PCa) remains one of the most prevalent malignancies affecting men in the western world. The etiology for PCa development and molecular mechanisms underlying castration-resistant progression are incompletely understood. Emerging evidence from many tumor systems has shown the existence of distinct subpopulations of stem like-cancer cells termed cancer stem cells (CSCs), which may be involved in tumor initiation, progression, metastasis and therapy resistance. Prostate cancer stem cells (PCSCs) have also been identified using different experimental strategies in distinct model systems. In this brief review, we summarize our current knowledge of normal prostate stem/progenitor cells, highlight recent progress on PCSCs, expound on the potential cell-of-origin for PCa and discuss the involvement of PCSCs in PCa progression and castration resistance. Elucidation of the phenotypic and functional properties and molecular regulation of PCSCs will help us better understand PCa biology and may lead to development of novel therapeutics targeting castration-resistant PCa cells.

Embryonic NANOG activity defines colorectal cancer stem cells and modulates through AP1- and TCF-dependent mechanisms

Embryonic NANOG (NANOG1) is considered as an important regulator of pluripotency while NANOGP8 (NANOG-pseudogene) plays a role in tumorigenesis. Herein, we show NANOG is expressed from both NANOG1 and NANOGP8 in human colorectal cancers (CRC). Enforced NANOG1-expression increases clonogenic potential and tumor formation in xenograft models, although it is expressed only in a small subpopulation of tumor cells and is colocalized with endogenous nuclear β-catenin(High) . Moreover, single NANOG1-CRCs form spherical aggregates, similar to the embryoid body of embryonic stem cells (ESCs), and express higher levels of stem-like Wnt-associated target genes. Furthermore, we show that NANOG1-expression is positively regulated by c-JUN and β-catenin/TCF4. Ectopic expression of c-Jun in murine Apc(Min/+) -ESCs results in the development of larger xenograft tumors with higher cell density compared to controls. Chromatin immunoprecipitation assays demonstrate that c-JUN binds to the NANOG1-promoter via the octamer M1 DNA element. Collectively, our data suggest that β-Catenin/TCF4 and c-JUN together drive a subpopulation of CRC tumor cells that adopt a stem-like phenotype via the NANOG1-promoter.

Sox2 is an androgen receptor-repressed gene that promotes castration-resistant prostate cancer

Despite advances in detection and therapy, castration-resistant prostate cancer continues to be a major clinical problem. The aberrant activity of stem cell pathways, and their regulation by the Androgen Receptor (AR), has the potential to provide insight into novel mechanisms and pathways to prevent and treat advanced, castrate-resistant prostate cancers. To this end, we investigated the role of the embryonic stem cell regulator Sox2 [SRY (sex determining region Y)-box 2] in normal and malignant prostate epithelial cells. In the normal prostate, Sox2 is expressed in a portion of basal epithelial cells. Prostate tumors were either Sox2-positive or Sox2-negative, with the percentage of Sox2-positive tumors increasing with Gleason Score and metastases. In the castration-resistant prostate cancer cell line CWR-R1, endogenous expression of Sox2 was repressed by AR signaling, and AR chromatin-IP shows that AR binds the enhancer element within the Sox2 promoter. Likewise, in normal prostate epithelial cells and human embryonic stem cells, increased AR signaling also decreases Sox2 expression. Resistance to the anti-androgen MDV3100 results in a marked increase in Sox2 expression within three prostate cancer cell lines, and in the castration-sensitive LAPC-4 prostate cancer cell line ectopic expression of Sox2 was sufficient to promote castration-resistant tumor formation. Loss of Sox2 expression in the castration-resistant CWR-R1 prostate cancer cell line inhibited cell growth. Up-regulation of Sox2 was not associated with increased CD133 expression but was associated with increased FGF5 (Fibroblast Growth Factor 5) expression. These data propose a model of elevated Sox2 expression due to loss of AR-mediated repression during castration, and consequent castration-resistance via mechanisms not involving induction of canonical embryonic stem cell pathways.

Stem-like cells with luminal progenitor phenotype survive castration in human prostate cancer

Castration is the standard therapy for advanced prostate cancer (PC). Although this treatment is initially effective, tumors invariably relapse as incurable, castration-resistant PC (CRPC). Adaptation of androgen-dependent PC cells to an androgen-depleted environment or selection of pre-existing, CRPC cells have been proposed as mechanisms of CRPC development. Stem cell (SC)-like PC cells have been implicated not only as tumor initiating/maintaining in PC but also as tumor-reinitiating cells in CRPC. Recently, castration-resistant cells expressing the NK3 homeobox 1 (Nkx3-1) (CARNs), the other luminal markers cytokeratin 18 (CK18) and androgen receptor (AR), and possessing SC properties, have been found in castrated mouse prostate and proposed as the cell-of-origin of CRPC. However, the human counterpart of CARNs has not been identified yet. Here, we demonstrate that in the human PC xenograft BM18, pre-existing SC-like and neuroendocrine (NE) PC cells are selected by castration and survive as totally quiescent. SC-like BM18 cells, displaying the SC markers aldehyde dehydrogenase 1A1 or NANOG, coexpress the luminal markers NKX3-1, CK18, and a low level of AR (AR(low)) but not basal or NE markers. These CR luminal SC-like cells, but not NE cells, reinitiate BM18 tumor growth after androgen replacement. The AR(low) seems to mediate directly both castration survival and tumor reinitiation. This study identifies for the first time in human PC SC-/CARN-like cells that may represent the cell-of-origin of tumor reinitiation as CRPC. This finding will be fundamental for refining the hierarchy among human PC cancer cells and may have important clinical implications.

NANOGP8: evolution of a human-specific retro-oncogene

NANOGP8 is a human (Homo sapiens) retrogene, expressed predominantly in cancer cells where its protein product is tumorigenic. It arose through retrotransposition from its parent gene, NANOG, which is expressed predominantly in embryonic stem cells. Based on identification of fixed and polymorphic variants in a genetically diverse set of human NANOG and NANOGP8 sequences, we estimated the evolutionary origin of NANOGP8 at approximately 0.9 to 2.5 million years ago, more recent than previously estimated. We also discovered that NANOGP8 arose from a derived variant allele of NANOG containing a 22-nucleotide pair deletion in the 3' UTR, which has remained polymorphic in modern humans. Evidence from our experiments indicates that NANOGP8 is fixed in modern humans even though its parent allele is polymorphic. The presence of NANOGP8-specific sequences in Neanderthal reads provided definitive evidence that NANOGP8 is also present in the Neanderthal genome. Some variants between the reference sequences of NANOG and NANOGP8 utilized in cancer research to distinguish RT-PCR products are polymorphic within NANOG or NANOGP8 and thus are not universally reliable as distinguishing features. NANOGP8 was inserted in reverse orientation into the LTR region of an SVA retroelement that arose in a human-chimpanzee-gorilla common ancestor after divergence of the orangutan ancestral lineage. Transcription factor binding sites within and beyond this LTR may promote expression of NANOGP8 in cancer cells, although current evidence is inferential. The fact that NANOGP8 is a human-specific retro-oncogene may partially explain the higher genetic predisposition for cancer in humans compared with other primates.

Nanog signaling in cancer promotes stem-like phenotype and immune evasion

Adaptation of tumor cells to the host is a major cause of cancer progression, failure of therapy, and ultimately death. Immune selection drives this adaptation in human cancer by enriching tumor cells with a cancer stem cell-like (CSC-like) phenotype that makes them resistant to CTL-mediated apoptosis; however, the mechanisms that mediate CSC maintenance and proliferation are largely unknown. Here, we report that CTL-mediated immune selection drives the evolution of tumor cells toward a CSC-like phenotype and that the CSC-like phenotype arises through the Akt signaling pathway via transcriptional induction of Tcl1a by Nanog. Furthermore, we found that hyperactivation of the Nanog/Tcl1a/Akt signaling axis was conserved across multiple types of human cancer. Inhibition of Nanog in a murine model of colon cancer rendered tumor cells susceptible to immune-mediated clearance and led to successful, long-term control of the disease. Our findings establish a firm link among immune selection, disease progression, and the development of a stem-like tumor phenotype in human cancer and implicate the Nanog/Tcl1a/Akt pathway as a central molecular target in this process.

Resveratrol depletes mitochondrial DNA and inhibition of autophagy enhances resveratrol-induced caspase activation

We recently demonstrated that resveratrol induces caspase-dependent apoptosis in multiple cancer cell types. Whether apoptosis is also regulated by other cell death mechanisms such as autophagy is not clearly defined. Here we show that inhibition of autophagy enhanced resveratrol-induced caspase activation and apoptosis. Resveratrol inhibited colony formation and cell proliferation in multiple cancer cell types. Resveratrol treatment induced accumulation of LC3-II, which is a key marker for autophagy. Pretreatment with 3-methyladenine (3-MA), an autophagy inhibitor, increased resveratrol-mediated caspase activation and cell death in breast and colon cancer cells. Inhibition of autophagy by silencing key autophagy regulators such as ATG5 and Beclin-1 enhanced resveratrol-induced caspase activation. Mechanistic analysis revealed that Beclin-1 did not interact with proapoptotic proteins Bax and Bak; however, Beclin-1 was found to interact with p53 in the cytosol and mitochondria upon resveratrol treatment. Importantly, resveratrol depleted ATPase 8 gene, and thus, reduced mitochondrial DNA (mtDNA) content, suggesting that resveratrol induces damage to mtDNA causing accumulation of dysfunctional mitochondria triggering autophagy induction. Together, our findings indicate that induction of autophagy during resveratrol-induced apoptosis is an adaptive response.

Klf4 transcription factor is expressed in the cytoplasm of prostate cancer cells

BACKGROUND

Cancer initiation and progression might be driven by small populations of cells endowed with stem cell-like properties. Here we comparatively addressed the expression of genes encoding putative stemness regulators including c-Myc, Klf4, Nanog, Oct4A and Sox2 genes in benign prostatic hyperplasia (BPH) and prostate cancer (PCA).

METHODS

Fifty-eight PCA and thirty-nine BPH tissues samples were used for gene expression analysis, as evaluated by quantitative real-time polymerase chain reaction (qRT-PCR). The expression of specific Klf4 isoforms was tested by conventional PCR. Klf4 specific antibodies were used for protein detection in a tissue microarray including 404 prostate samples.

RESULTS

Nanog, Oct4A and Sox2 genes were comparably expressed in BPH and PCA samples, whereas c-Myc and Klf4 genes were expressed to significantly higher extents in PCA than in BPH specimens. Immunohistochemical studies revealed that Klf4 protein is detectable in a large majority of epithelial prostatic cells, irrespective of malignant transformation. However, in PCA, a predominantly cytoplasmic location was observed, consistent with the expression of a differentially spliced Klf4α isoform.

CONCLUSION

Klf4 is highly expressed at gene and protein level in BPH and PCA tissues but a cytoplasmic location of the specific gene product is predominantly detectable in malignant cells. Klf4 location might be of critical relevance to steer its functions during oncogenesis.

NANOG modulates stemness in human colorectal cancer

NANOG is a stem cell transcription factor that is essential for embryonic development, reprogramming normal adult cells and malignant transformation and progression. The nearly identical retrogene NANOGP8 is expressed in multiple cancers, but generally not in normal tissues and its function is not well defined. Our postulate is that NANOGP8 directly modulates the stemness of individual human colorectal carcinoma (CRC) cells. Stemness was measured in vitro as the spherogenicity of single CRC cells in serum-free medium and the size of the side population (SP) and in vivo as tumorigenicity and experimental metastatic potential in NOD/SCID mice. We found that 80% of clinical liver metastases express a NANOG with 75% of the positive metastases containing NANOGP8 transcripts. In all, 3-62% of single cells within six CRC lines form spheroids in serum-free medium in suspension. NANOGP8 is translated into protein. The relative expression of a NANOG gene increased 8- to 122-fold during spheroid formation, more than the increase in OCT4 or SOX2 transcripts with NANOGP8 the more prevalent family member. Short hairpin RNA (shRNA) to NANOG not only inhibits spherogenicity but also reduces expression of OCT4 and SOX2, the size of the SP and tumor growth in vivo. Inhibition of NANOG gene expression is associated with inhibition of proliferation and decreased phosphorylation of G2-related cell-cycle proteins. Overexpression of NANOGP8 rescues single-cell spherogenicity when NANOG gene expression is inhibited and increases the SP in CRC. Thus, NANOGP8 can substitute for NANOG in directly promoting stemness in CRC.

A 1536-well quantitative high-throughput screen to identify compounds targeting cancer stem cells

Tumor cell subpopulations called cancer stem cells (CSCs) or tumor-initiating cells (TICs) have self-renewal potential and are thought to drive metastasis and tumor formation. Data suggest that these cells are resistant to current chemotherapy and radiation therapy treatments, leading to cancer recurrence. Therefore, finding new drugs and/or drug combinations that cause death of both the differentiated tumor cells as well as CSC populations is a critical unmet medical need. Here, we describe how cancer-derived CSCs are generated from cancer cell lines using stem cell growth media and nonadherent conditions in quantities that enable high-throughput screening (HTS). A cell growth assay in a 1536-well microplate format was developed with these CSCs and used to screen a focused collection of oncology drugs and clinical candidates to find compounds that are cytotoxic against these highly aggressive cells. A hit selection process that included potency and efficacy measurements during the primary screen allowed us to efficiently identify compounds with potent cytotoxic effects against spheroid-derived CSCs. Overall, this research demonstrates one of the first miniaturized HTS assays using CSCs. The procedures described here should enable further testing of the effect of compounds on CSCs and help determine which pathways need to be targeted to kill them.

Pseudogenes: newly discovered players in human cancer

Because they are generally noncoding and thus considered nonfunctional and unimportant, pseudogenes have long been neglected. Recent advances have established that the DNA of a pseudogene, the RNA transcribed from a pseudogene, or the protein translated from a pseudogene can have multiple, diverse functions and that these functions can affect not only their parental genes but also unrelated genes. Therefore, pseudogenes have emerged as a previously unappreciated class of sophisticated modulators of gene expression, with a multifaceted involvement in the pathogenesis of human cancer.

Epithelial cell adhesion molecule regulates tumor initiation and tumorigenesis via activating reprogramming factors and epithelial-mesenchymal transition gene expression in colon cancer

Epithelial cell adhesion molecule (EpCAM) is highly expressed in epithelial-transformed neoplasia and tumor-initiated cells (TICs), but the role that EpCAM plays in the stemness properties of TICs is still unclear. Here we show that EpCAM and reprogramming factors (c-Myc, Oct4, Nanog, and Sox2) were concomitantly elevated in TICs, which were shown to have superior self-renewal, invasiveness, and tumor-initiating abilities. Elevation of EpCAM enhanced tumorsphere formation and tumor initiation. Knockdown of EpCAM inhibited the expressions of reprogramming factors and epithelial-mesenchymal transition genes, thereby suppressing tumor initiation, self-renewal, and invasiveness. In addition, EpCAM, especially intracellular domain of EpCAM (EpICD), bound to and activated the promoter of reprogramming factors. Treatment with the inhibitor of γ-secretase (DAPT) led to the blockage of the expressions of reprogramming factors and epithelial-mesenchymal transition genes, which was accompanied by the reduction of tumor self-renewal and invasion. Furthermore, the increased release of EpEX enhanced production of EpICD and regulated the expression of reprogramming factors. Together, these findings suggest that EpCAM plays an important role in regulating cancer-initiating abilities in TICs of colon cancer. This discovery can be used in the development of new strategies for cancer therapy.

Expression of the pluripotency markers Oct3/4, Nanog and Sox2 in human breast cancer cell lines

Previous studies have demonstrated that pluripotency-associated transcription factors, such as Oct3/4, Nanog and Sox2, play a crucial role in the development and malignant progression of various types of tumors. Breast cancer is the most frequent cancer among females, being a heterogeneous disease, with distinct morphologies, metastatic behavior and therapeutic responses. The expression of Oct3/4, Nanog and Sox2 in 3 human breast cancer cell lines, MCF7, T-47D and MDA-MB-231, was determined. The expression of Oct3/4, Nanog and Sox2 mRNA was determined by reverse transcription polymerase chain reaction (RT-PCR) and protein expression was detected by immunocytohistochemistry. RT-PCR revealed that all three human breast cancer cell lines tested expressed evident Oct3/4, Nanog and Sox-2 mRNA at various levels. Higher levels of Oct3/4 were identified in MCF7 and MDA-MB-231 cells compared with T-47D cells. Higher levels of Nanog were observed in MCF7 and T-47D cells compared with MDA-MB-231 cells and the highest expression of Sox-2 was detected in MCF7 cells. The nuclear localization of Oct3/4, Nanog and Sox-2 was confirmed by immunostaining. Oct3/4, Nanog and Sox2 were expressed in human breast cancer cell lines. Further studies are required to characterize the role of Oct3/4, Nanog and Sox2 in human breast cancer.

Increased Nanog expression promotes tumor development and Cisplatin resistance in human esophageal cancer cells

BACKGROUND/AIMS

Nanog plays a key role in stem cell self-renewal and pluripotency differentiation in embryonic stem cells ( ESCs). Recently, some studies reported that abnormal expression of Nanog could be detected in several tumors, indicating that Nanog might be related to tumor development. However, studies on the correlation between Nanog expression and esophageal cancer are sparse.

METHODS

In this study, we established two esophageal cancer cell lines 9706-Nanog and 9706-shNanog which stably expressed Nanog and Nanog-short-hairpin RNA (shRNA) genes.

RESULTS

We found that Nanog expression could promote the proliferation and invasiveness of the cancer cells, and inhibit the apoptosis. We also treated 9706-Nanog, EC9706 and 9706-shNanog cell lines with cisplatin and evaluated the drug sensitivity of the three cell lines. We found that the sensitivity of cisplatin was decreased with increased expression of Nanog. The expression of MDR-1 was also increased in 9706Nanog cells.

CONCLUSIONS

Nanog may play an important role in human esophageal cancer development, and could be used as a therapeutic target in esophageal cancer treatment.

The PSA(-/lo) prostate cancer cell population harbors self-renewing long-term tumor-propagating cells that resist castration

Prostate cancer (PCa) is heterogeneous and contains both differentiated and undifferentiated tumor cells, but the relative functional contribution of these two cell populations remains unclear. Here we report distinct molecular, cellular, and tumor-propagating properties of PCa cells that express high (PSA(+)) and low (PSA(-/lo)) levels of the differentiation marker PSA. PSA(-/lo) PCa cells are quiescent and refractory to stresses including androgen deprivation, exhibit high clonogenic potential, and possess long-term tumor-propagating capacity. They preferentially express stem cell genes and can undergo asymmetric cell division to generate PSA(+) cells. Importantly, PSA(-/lo) PCa cells can initiate robust tumor development and resist androgen ablation in castrated hosts, and they harbor highly tumorigenic castration-resistant PCa cells that can be prospectively enriched using ALDH(+)CD44(+)α2β1(+) phenotype. In contrast, PSA(+) PCa cells possess more limited tumor-propagating capacity, undergo symmetric division, and are sensitive to castration. Altogether, our study suggests that PSA(-/lo) cells may represent a critical source of castration-resistant PCa cells.

Stem cell transcription factor NANOG controls cell migration and invasion via dysregulation of E-cadherin and FoxJ1 and contributes to adverse clinical outcome in ovarian cancers

Ovarian cancer is the most lethal of all gynecological malignancies, and the identification of novel prognostic and therapeutic targets for ovarian cancer is crucial. It is believed that only a small subset of cancer cells are endowed with stem cell properties, which are responsible for tumor growth, metastatic progression and recurrence. NANOG is one of the key transcription factors essential for maintaining self-renewal and pluripotency in stem cells. This study investigated the role of NANOG in ovarian carcinogenesis and showed overexpression of NANOG mRNA and protein in the nucleus of ovarian cancers compared with benign ovarian lesions. Increased nuclear NANOG expression was significantly associated with high-grade cancers, serous histological subtypes, reduced chemosensitivity, and poor overall and disease-free survival. Further analysis showed NANOG is an independent prognostic factor for overall and disease-free survival. Moreover, NANOG was highly expressed in ovarian cancer cell lines with metastasis-associated property and in clinical samples of metastatic foci. Stable knockdown of NANOG impeded ovarian cancer cell proliferation, migration and invasion, which was accompanied by an increase in mRNA expression of E-cadherin, caveolin-1, FOXO1, FOXO3a, FOXJ1 and FOXB1. Conversely, ectopic NANOG overexpression enhanced ovarian cancer cell migration and invasion along with decreased E-cadherin, caveolin-1, FOXO1, FOXO3a, FOXJ1 and FOXB1 mRNA expression. Importantly, we found Nanog-mediated cell migration and invasion involved its regulation of E-cadherin and FOXJ1. This is the first report revealing the association between NANOG expression and clinical outcome of patients with ovarian cancers, suggesting NANOG to be a potential prognostic marker and therapeutic molecular target in ovarian cancer.

Nanog regulates self-renewal of cancer stem cells through the insulin-like growth factor pathway in human hepatocellular carcinoma

Hepatocellular carcinoma (HCC) exhibits cellular heterogeneity and embryonic stem-cell-related genes are preferentially overexpressed in a fraction of cancer cells of poorly differentiated tumors. However, it is not known whether or how these cancer cells contribute to tumor initiation and progression. Here, our data showed that increased expression of pluripotency transcription factor Nanog in cancer cells correlates with a worse clinical outcome in HCC. Using the Nanog promoter as a reporter system, we could successfully isolate a small subpopulation of Nanog-positive cells. We demonstrate that Nanog-positive cells exhibited enhanced ability of self-renewal, clonogenicity, and initiation of tumors, which are consistent with crucial hallmarks in the definition of cancer stem cells (CSCs). Nanog(Pos) CSCs could differentiate into mature cancer cells in in vitro and in vivo conditions. In addition, we found that Nanog(Pos) CSCs exhibited resistance to therapeutic agents (e.g., sorafenib and cisplatin) and have a high capacity for tumor invasion and metastasis. Knock-down expression of Nanog in Nanog(Pos) CSCs could decrease self-renewal accompanied with decreased expression of stem-cell-related genes and increased expression of mature hepatocyte-related genes. Overexpression of Nanog in Nanog(Neg) cells could restore self-renewal. Furthermore, we found that insulin-like growth factor (IGF)2 and IGF receptor (IGF1R) were up-regulated in Nanog(Pos) CSCs. Knock-down expression of Nanog in Nanog(Pos) CSCs inhibited the expression of IGF1R, and overexpression of Nanog in Nanog(Neg) cells increased the expression of IGF1R. A specific inhibitor of IGF1R signaling could significantly inhibit self-renewal and Nanog expression, indicating that IGF1R signaling participated in Nanog-mediated self-renewal.

CONCLUSION

These data indicate that Nanog could be a novel biomarker for CSCs in HCC, and that Nanog could play a crucial role in maintaining the self-renewal of CSCs through the IGF1R-signaling pathway.

Dynamic regulation of cancer stem cells and clinical challenges

A small population of cancer cells referred to as cancer stem cells (CSCs) have received particular attention, as they have been revealed to acquire stem cell-like properties and become the main cause of tumor propagation, metastasis and drug resistance. The CSC theory of tumor formation was believed to follow the hierarchical model initially, and therefore many CSC-targeted therapy methods were expected to cure cancer by eradicating CSCs. However, subsequent CSC research has revealed that rather than a distinct entity, the CSC is a dynamic status that can be continually dedifferentiated from progenitor or differentiated cancer cells. Elucidation of this bidirectional transition mechanism would help perfect the CSC theory and be of great value in the development of more effective anti-cancer drugs. Here, we reviewed the mechanisms of reciprocal conversion between non-CSCs and CSCs. Moreover, several approaches of target CSCs and non-CSCs together with unbiased eradication of all cancer cells are also discussed.

Neem oil limonoids induces p53-independent apoptosis and autophagy

Azadirachta indica, commonly known as neem, has a wide range of medicinal properties. Neem extracts and its purified products have been examined for induction of apoptosis in multiple cancer cell types; however, its underlying mechanisms remain undefined. We show that neem oil (i.e., neem), which contains majority of neem limonoids including azadirachtin, induced apoptotic and autophagic cell death. Gene silencing demonstrated that caspase cascade was initiated by the activation of caspase-9, whereas caspase-8 was also activated late during neem-induced apoptosis. Pretreatment of cancer cells with pan caspase inhibitor, z-VAD inhibited activities of both initiator caspases (e.g., caspase-8 and -9) and executioner caspase-3. Neem induced the release of cytochrome c and apoptosis-inducing factor (AIF) from mitochondria, suggesting the involvement of both caspase-dependent and AIF-mediated apoptosis. p21 deficiency caused an increase in caspase activities at lower doses of neem, whereas p53 deficiency did not modulate neem-induced caspase activation. Additionally, neem treatment resulted in the accumulation of LC3-II in cancer cells, suggesting the involvement of autophagy in neem-induced cancer cell death. Low doses of autophagy inhibitors (i.e., 3-methyladenine and LY294002) did not prevent accumulation of neem-induced LC3-II in cancer cells. Silencing of ATG5 or Beclin-1 further enhanced neem-induced cell death. Phosphoinositide 3-kinase (PI3K) or autophagy inhibitors increased neem-induced caspase-3 activation and inhibition of caspases enhanced neem-induced autophagy. Together, for the first time, we demonstrate that neem induces caspase-dependent and AIF-mediated apoptosis, and autophagy in cancer cells.

MicroRNA profiling of carcinogen-induced rat colon tumors and the influence of dietary spinach

SCOPE

MicroRNA (miRNA) profiles are altered in chronic conditions such as cardiovascular disease, diabetes, neurological disorders, and cancer. A systems biology approach was used to examine, for the first time, miRNAs altered in rat colon tumors induced by 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP), a heterocyclic amine carcinogen from cooked meat.

METHODS AND RESULTS

Among the most highly dysregulated miRNAs were those belonging to the let-7 family. Subsequent computational modeling and target validation identified c-Myc and miRNA-binding proteins Lin28A/Lin28B (Lin28) as key players, along with Sox2, Nanog, and Oct-3/4. These targets of altered miRNAs in colon cancers have been implicated in tumor recurrence and reduced patient survival, in addition to their role as pluripotency factors. In parallel with these findings, the tumor-suppressive effects of dietary spinach given postinitiation correlated with elevated levels of let-7 family members and partial normalization of c-myc, Sox2, Nanog, Oct-3/4, HmgA2, Dnmt3b, and P53 expression.

CONCLUSION

We conclude that the let-7/c-Myc/Lin28 axis is dysregulated in heterocyclic amine-induced colon carcinogenesis, and that the tumor suppressive effects of dietary spinach are associated with partial normalization of this pathway.

Cancer vaccines targeting the epithelial-mesenchymal transition: tissue distribution of brachyury and other drivers of the mesenchymal-like phenotype of carcinomas

The epithelial-mesenchymal transition (EMT) is thought to be a critical step along the metastasis of carcinomas. In addition to gaining motility and invasiveness, tumor cells that undergo EMT also acquire increased resistance to many traditional cancer treatment modalities, including chemotherapy and radiation. As such, EMT has become an attractive, potentially targetable process for therapeutic interventions against tumor metastasis. The process of EMT is driven by a group of transcription factors designated as EMT transcription factors, such as Snail, Slug, Twist, and the recently identified T-box family member, Brachyury. In an attempt to determine which of these drivers of EMT is more amenable to targeted therapies and, in particular, T-cell-mediated immunotherapeutic approaches, we have examined their relative expression levels in a range of human and murine normal tissues, cancer cell lines, and human tumor biopsies. Our results demonstrated that Brachyury is a molecule with a highly restricted human tumor expression pattern. We also demonstrated that Brachyury is immunogenic and that Brachyury-specific CD8(+) T cells expanded in vitro are able to lyse Brachyury-positive tumor cells. We thus propose Brachyury as an attractive target for vaccination strategies designed to specifically target tumor cells undergoing EMT.

Nanog and Oct4 overexpression increases motility and transmigration of melanoma cells

PURPOSE

Melanoma tumors are highly heterogeneous and can undergo phenotypic modifications depending on their plasticity and the microenvironment, with shifts between proliferative and invasive states. We have shown that melanoma cells, grown as spheroids in a neural crest cell medium, polarize toward an invasive and motile phenotype, in agreement with transcriptomic modulations, including the up-regulation of Nanog and Oct4. Overexpression of these genes was shown to be associated with poor prognosis and metastatic forms of some cancers. We thus investigated implication of Nanog and Oct4, two embryonic transcription factors, in melanoma motility.

METHODS

Our team used stable transfection of Nanog or Oct4 in A375 melanoma cell line to investigate motility in a wound healing assay and a transendothelial migration assay. Using semiquantitative RT-PCR, expression of two gene panels involved either in mesenchymal motility or in amoeboid migration was studied.

RESULTS

Strongly enhanced capacities of motility and extravasation were observed with cells overexpressing Oct4 and Nanog. The A375 cell line has been described as having a mesenchymal migration type. However, in the Oct4 and Nanog transfectants, several amoeboid migration markers are strongly induced. Accordingly, amoeboid migration inhibitors decrease significantly the transmigration of Oct4- and Nanog-expressing cells through endothelial cells.

CONCLUSIONS

We propose here that Nanog and Oct4 pluripotency marker expression in melanoma cells increases the transmigration capacity of these cells through the gain of amoeboid motility, leading to higher invasiveness and aggressiveness.

Distinct microRNA expression profiles in prostate cancer stem/progenitor cells and tumor-suppressive functions of let-7

MiRNAs regulate cancer cells, but their potential effects on cancer stem/progenitor cells are still being explored. In this study, we used quantitative real-time-PCR to define miRNA expression patterns in various stem/progenitor cell populations in prostate cancer, including CD44+, CD133+, integrin α2β1+, and side population cells. We identified distinct and common patterns in these different tumorigenic cell subsets. Multiple tumor-suppressive miRNAs were downregulated coordinately in several prostate cancer stem/progenitor cell populations, namely, miR-34a, let-7b, miR-106a, and miR-141, whereas miR-301 and miR-452 were commonly overexpressed. The let-7 overexpression inhibited prostate cancer cell proliferation and clonal expansion in vitro and tumor regeneration in vivo. In addition, let-7 and miR-34a exerted differential inhibitory effects in prostate cancer cells, with miR-34a inducing G1 phase cell-cycle arrest accompanied by cell senescence and let-7 inducing G2-M phase cell-cycle arrest without senescence. Taken together, our findings define distinct miRNA expression patterns that coordinately regulate the tumorigenicity of prostate cancer cells.

Cytoplasmic NANOG-positive stromal cells promote human cervical cancer progression

Tumor development has long been known to resemble abnormal embryogenesis. The embryonic stem cell gene NANOG, a divergent homeodomain transcription factor that is independent of leukemia inhibitory factor, has been reported to be expressed in germ cells and in several tumor types. However, the short-term expression and role of NANOG in cervical cancer remain unclear. In the present study, we demonstrate that NANOG exhibits cellular shuttling behavior and increasing stromal distribution during the progression of cervical cancer. Our molecular data using RT-PCR and restriction enzyme digestion show that NANOG is mainly transcribed from the NANOG gene in cervical cancer. In addition, IHC using confocal microscopy suggests that mesenchymal stem cells (MSCs) are one type of cytoplasmic NANOG-positive cells in cervical cancer stroma. Co-culture of cervical cancer-derived MSCs with SiHa cells showed increased proliferation characteristics in vitro and enhanced tumor growth in vivo. Our results show, for the first time to our knowledge, that MSCs are a source of cytoplasmic NANOG expression in the cervical cancer stroma and that they participate in the progression of cervical cancer both in vitro and in vivo. Our study provides evidence that NANOG is a cervical cancer progression marker and also serves as a starting point for a more extensive exploration of the cellular translocation of NANOG and the multifunctionality of the stromal microenvironment.

Human Nanog pseudogene8 promotes the proliferation of gastrointestinal cancer cells

There is emerging evidence that human solid tumor cells originate from cancer stem cells (CSCs). In cancer cell lines, tumor-initiating CSCs are mainly found in the side population (SP) that has the capacity to extrude dyes such as Hoechst 33342. We found that Nanog is expressed specifically in SP cells of human gastrointestinal (GI) cancer cells. Nucleotide sequencing revealed that NanogP8 but not Nanog was expressed in GI cancer cells. Transfection of NanogP8 into GI cancer cell lines promoted cell proliferation, while its inhibition by anti-Nanog siRNA suppressed the proliferation. Immunohistochemical staining of primary GI cancer tissues revealed NanogP8 protein to be strongly expressed in 3 out of 60 cases. In these cases, NanogP8 was found especially in an infiltrative part of the tumor, in proliferating cells with Ki67 expression. These data suggest that NanogP8 is involved in GI cancer development in a fraction of patients, in whom it presumably acts by supporting CSC proliferation.

Mediators of induced pluripotency and their role in cancer cells - current scientific knowledge and future perspectives

The discovery that overexpression of the transcription factors Oct4, Sox2, Klf4 and c-Myc reprograms differentiated cells into "induced pluripotent stem cells" (iPSCs) has extended our understanding of mechanisms required to maintain stem cell pluripotency and to drive differentiation. Subsequently, additional factors have been discovered that are able to induce a pluripotent state. Recently several groups have succeeded in reprogramming cancer cells to iPSC-like induced pluripotent cancer cells by use of the method established for the generation of iPSCs. This discovery highlighted several striking similarities between pluripotent stem cells and cancer cells, in turn implying that tumorigenesis and reprogramming are partly promoted by overlapping mechanisms. Thus, research on reprogramming might help unravel the mechanisms of carcinogenesis, and vice versa. This review gives an overview of the common features of pluripotent stem cells and cancer cells and summarizes the present state of knowledge in the field of cancer cell reprogramming.

Identification of a putative nuclear export signal motif in human NANOG homeobox domain

NANOG is a homeobox-containing transcription factor that plays an important role in pluripotent stem cells and tumorigenic cells. To understand how nuclear localization of human NANOG is regulated, the NANOG sequence was examined and a leucine-rich nuclear export signal (NES) motif ((125)MQELSNILNL(134)) was found in the homeodomain (HD). To functionally validate the putative NES motif, deletion and site-directed mutants were fused to an EGFP expression vector and transfected into COS-7 cells, and the localization of the proteins was examined. While hNANOG HD exclusively localized to the nucleus, a mutant with both NLSs deleted and only the putative NES motif contained (hNANOG HD-ΔNLSs) was predominantly cytoplasmic, as observed by nucleo/cytoplasmic fractionation and Western blot analysis as well as confocal microscopy. Furthermore, site-directed mutagenesis of the putative NES motif in a partial hNANOG HD only containing either one of the two NLS motifs led to localization in the nucleus, suggesting that the NES motif may play a functional role in nuclear export. Furthermore, CRM1-specific nuclear export inhibitor LMB blocked the hNANOG potent NES-mediated export, suggesting that the leucine-rich motif may function in CRM1-mediated nuclear export of hNANOG. Collectively, a NES motif is present in the hNANOG HD and may be functionally involved in CRM1-mediated nuclear export pathway.

Twists in views on RB functions in cellular signaling, metabolism and stem cells

One-quarter of a century ago, identification of the human retinoblastoma gene (RB) loci proved Knudson's 'two-hit theory' that tumor suppressor genes exist. Since then, numerous works delineated crucial roles for the RB protein (pRB)-E2F transcription factor complex in G1-S phase transition. In addition, discovering the relationship between pRB and tissue-specific transcription factors enabled a better understanding of how cell cycle exit and terminal differentiation are coupled. Recent works provoked many exciting twists in views on pRB functions during cancer initiation and progression beyond its previously well-appreciated roles. Various mitogenic and cytostatic cellular signals appeared to modulate pRB functions and thus affect a wide variety of effector molecules. In addition, genetic studies in mice as well as other creatures incessantly force us to revise our views on pRB functions. This review will focus particularly on the roles of pRB in regulating intracellular signaling, cell metabolism, chromatin function, stem cells and cancer stem cells.

Induced pluripotent stem cell-related genes influence biological behavior and 5-fluorouracil sensitivity of colorectal cancer cells

OBJECTIVE

We aimed to perform a preliminary study of the association between induced pluripotent stem cell (iPS)-related genes and biological behavior of human colorectal cancer (CRC) cells, and the potential for developing anti-cancer drugs targeting these genes.

METHODS

We used real-time reverse transcriptase polymerase chain reaction (RT-PCR) to evaluate the transcript levels of iPS-related genes NANOG, OCT4, SOX2, C-MYC and KLF4 in CRC cell lines and cancer stem cells (CSCs)-enriched tumor spheres. NANOG was knockdowned in CRC cell line SW620 by lentiviral transduction. 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assays, plate colony formation, and a mouse xenograft model were used to evaluate alterations in biological behavior in NANOG-knockdown SW620 cells. Also, mock-knockdown and NANOG-knockdown cells were treated with 5-fluorouracil (5-FU) and survival rate was measured by MTT assay to evaluate drug sensitivity.

RESULTS

A significant difference in the transcript levels of iPS-related genes between tumor spheres and their parental bulky cells was observed. NANOG knockdown suppressed proliferation, colony formation, and in vivo tumorigenicity but increased the sensitivity to 5-FU of SW620 cells. 5-FU treatment greatly inhibited the expression of the major stemness-associated genes NANOG, OCT4, and SOX2.

CONCLUSIONS

These results collectively suggest an overlap between iPS-related genes and CSCs in CRC. Quenching a certain gene NANOG may truncate the aggressiveness of CRC cells.

Nanog increases focal adhesion kinase (FAK) promoter activity and expression and directly binds to FAK protein to be phosphorylated

Nanog and FAK were shown to be overexpressed in cancer cells. In this report, the Nanog overexpression increased FAK expression in 293, SW480, and SW620 cancer cells. Nanog binds the FAK promoter and up-regulates its activity, whereas Nanog siRNA decreases FAK promoter activity and FAK mRNA. The FAK promoter contains four Nanog-binding sites. The site-directed mutagenesis of these sites significantly decreased up-regulation of FAK promoter activity by Nanog. EMSA showed the specific binding of Nanog to each of the four sites, and binding was confirmed by ChIP assay. Nanog directly binds the FAK protein by pulldown and immunoprecipitation assays, and proteins co-localize by confocal microscopy. Nanog binds the N-terminal domain of FAK. In addition, FAK directly phosphorylates Nanog in a dose-dependent manner by in vitro kinase assay and in cancer cells in vivo. The site-directed mutagenesis of Nanog tyrosines, Y35F and Y174F, blocked phosphorylation and binding by FAK. Moreover, overexpression of wild type Nanog increased filopodia/lamellipodia formation, whereas mutant Y35F and Y174F Nanog did not. The wild type Nanog increased cell invasion that was inhibited by the FAK inhibitor and increased by FAK more significantly than with the mutants Y35F and Y174F Nanog. Down-regulation of Nanog with siRNA decreased cell growth reversed by FAK overexpression. Thus, these data demonstrate the regulation of the FAK promoter by Nanog, the direct binding of the proteins, the phosphorylation of Nanog by FAK, and the effect of FAK and Nanog cross-regulation on cancer cell morphology, invasion, and growth that plays a significant role in carcinogenesis.

Sox2 targets cyclinE, p27 and survivin to regulate androgen-independent human prostate cancer cell proliferation and apoptosis

OBJECTIVES

Sox2 is a major transcription factor and the transforming growth factor-α (TGF-α)/EGFR autocrine loop is a hallmark of prostate cancer progression. In this study, we have evaluated the effects and potential mechanisms of Sox2 on cell proliferation and apoptosis, and investigated effects of TGF-α on expression of Sox2 on androgen-independent human prostate cancer cells.

MATERIALS AND METHODS

Expression of Sox2 has been determined by RT-PCR, western blot analysis and immunocytochemistry, using RNAi and over-expression strategy to study functions of Sox2 in DU145 and PC-3 cells. Changes in level of proliferation, cell cycle and apoptosis profiles were measured by MTT, colony-forming, bromodeoxyuridine incorporation assays, cell cycle and annexin V analysis.

RESULTS

Sox2 was expressed in six human prostate cancer cell lines, and its inhibition reduced cell proliferation and induced apoptosis in DU145 cells. We have shown that knock-down of Sox2 inhibited G(1) to S phase transition concomitantly with down-regulation of cyclin E and up-regulation of p27 proteins. Conversely, over-expression of Sox2 led to the opposite effect in PC-3 cells but its inhibition induced apoptosis by down-regulation of survivin in DU145 cells. We also found that TGF-α up-regulated Sox2 and survivin protein expression via the EGFR/PI3K/AKT pathway.

CONCLUSIONS

Sox2 expression is necessary for cell proliferation and evasion of apoptosis in prostate cancer cells and TGF-α could regulate Sox2 and survivin expression by activating the EGFR/PI3K/AKT pathway.

Expression profile of embryonic stem cell-associated genes Oct4, Sox2 and Nanog in human gliomas

AIMS

To investigate whether Oct4, Sox2 and Nanog, three core regulatory factors maintaining pluripotency and self-renewal of embryonic stem cells (ESCs), are coexpressed in human gliomas, and whether their expression might be linked to carcinogenesis and the formation of cancer stem cells (CSCs).

METHODS AND RESULTS

Forty cases of human glioma were examined. The expression of Oct4, Sox2 and Nanog was analysed by immunohistochemistry, reverse transcription polymerase chain reaction and western blot. We found a positive correlation between the expression levels of Oct4, Sox2 and Nanog and tumour malignancy. Immunohistochemistry showed that Oct4 and Nanog were expressed in both the nuclei and the cytoplasm of glioma cells, whereas Sox2 was expressed only in the nuclei. Double immunofluorescence staining revealed that a majority of Oct4-positive cells coexpressed Sox2 and Nanog. More than 50% of Oct4-positive cells coexpressed the putative CSC markers CD133 and Nestin. Moreover, some cells exhibited Oct4 and Nanog immunoexpression in the cytoplasm, but the frequency of positive cells did not correlate with tumour malignancy.

CONCLUSIONS

The present findings suggest that ESC-associated pathways are activated in human gliomas and that these may be involved in glioma progression, a role that is distinct from that in ESCs.

Genetic alteration of stemness factors and p53 in mouse forestomach by chemical carcinogen-induced carcinogenesis

The expression profiles of genes normally enriched in embryonic stem (ES) cells (stemness factors) are associated with poor clinical outcome in solid tumors. However, whether such gene expression is responsible for tumor initiation and progression remains to be determined. The tumor suppressor gene p53 is known to attenuate the expression of Nanog, which is essential for maintaining stem cells in response to DNA damage. On the basis of these findings, we hypothesized that stemness factors and p53 closely correlate with each other and form a network in response to genomic damage in the early phase of carcinogenesis and in the process of tumor progression. In this study, we applied the N-methylbenzylnitrosoamine (NMBA)-induced carcinogenesis model to the mouse forestomach to clarify the role of the stemness factors, c-Myc, Klf4, Sox2, Oct3/4 and Nanog, in cancer development using p53(+/+) (n=26) and p53(+/-) (n=11) C57BL/6J mice. Thirty weeks following NMBA administration, histologically evident squamous cell carcinoma was detected in the forestomachs of p53(+/+) mice, and the percentage of p53-positive nuclei in the forestomach epithelium gradually increased during carcinogenesis. Tumor development in p53(+/-) mice occurred significantly earlier than in p53(+/+) mice. Quantitative real-time PCR analyses revealed a reduced c-Myc and Klf4 expression before evident morphological changes were observed, and an increased expression with the development of squamous cell carcinoma. Sox2 expression remained unchanged until tumor development and increased with the appearance of squamous cell carcinomas. The expression of Oct3/4 and Nanog increased at the early stages following NMBA administration, and Nanog expression in situ was not positively affected by the deficiency of p53. Findings of the present study suggested that Oct3/4 may be involved in the progression of carcinogenesis from normal epithelial cells at early stages, suggesting the potential use of Oct3/4 as a biomarker in forestomach tumor formation at early stages of chemical carcinogenesis.

Malignant germ cell-like tumors, expressing Ki-1 antigen (CD30), are revealed during in vivo differentiation of partially reprogrammed human-induced pluripotent stem cells

Because many of the genes used to produce induced pluripotent stem cells (iPSCs) from somatic cells are either outright established oncogenes, such as c-myc and Klf4, or potentially related to tumorigenesis in various cancers, both the safety and the risks of tumorigenesis linked to iPSC generation require evaluation. In this work, we generated, by lentivirus-mediated gene transfer of Oct4, Sox2, Nanog, and Lin28, two types of iPSCs from human mesenchymal stem cells and human amniotic fluid-derived cells: fully reprogrammed iPSCs with silencing of the four transgenes and partially reprogrammed iPSCs that still express one or several transgenes. We assessed the behavior of these cells during both their differentiation and proliferation using in vivo teratoma assays in nonobese diabetic mice with severe combined immunodeficiency. In contrast to fully reprogrammed iPSCs, 43% of partially reprogrammed iPSC cases (6 of 14 teratomas) generated major dysplasia and malignant tumors, with yolk sac tumors and embryonal carcinomas positive for α-fetoprotein, cytokeratin AE1/AE3, and CD30. This correlated with the expression of one or several transgenes used for the reprogramming, down-regulation of CDK 1A mRNA (p21/CDKN1A), and up-regulation of antiapoptotic Bcl-2 mRNA. Therefore, the oncogenicity of therapeutically valuable patient-specific iPSC-derived cells should be scrupulously evaluated before they are used for any clinical applications.

Ultrasensitive nanostructured immunosensor for stem and carcinoma cell pluripotency gatekeeper protein NANOG

AIMS

To develop an immunosensor for ultrasensitive detection of the NANOG protein. NANOG regulates pluripotency in stem cells and some cancer cells. This article reports the first electrochemical immunosensor for ultrasensitive detection and absolute quantification of the NANOG protein. The sensor features dense capture antibody-coated gold nanoparticle layers on a pyrolytic graphite underlayer.

MATERIALS & METHODS

Two separate multilabel detection strategies were used to achieve moderate and ultra-high sensitivity.

RESULTS

Good sensitivity was achieved for NANOG over the concentration range 0.1-160 pg/ml. The moderate-sensitivity approach gave a detection limit of 25 pg/ml, while the ultrasensitive method achieved a 250-fold lower detection limit of 0.1 pg/ml. Amounts of NANOG detected in human embryonic stem cell lysates correlated well with qualitative western blots and mRNA expression.

CONCLUSION

The electrochemical gold nanoparticle immunosensor is suitable for measuring NANOG protein expression in stem and carcinoma cell tissue lysates at very low levels.

RNA interference-mediated silencing of NANOG reduces cell proliferation and induces G0/G1 cell cycle arrest in breast cancer cells

Since the processes of normal embryogenesis and neoplasia share many of similar pathways, tumor development has been interpreted as an abnormal form of organogenesis. NANOG is a homeodomain-containing transcription factor that functions to maintain self-renewal and proliferation of embryonic stem cells (ESCs). Aberrant expression of NANOG has been observed in many types of human malignancies. However, its potential implication in tumorigenesis has not been fully clarified. In this study, we have employed small interference RNA (RNAi) technology to silence endogenous NANOG expression in breast cancer cells and successfully selected three independent clones with stably inhibited NANOG expression of MCF-7 cells. Functional analysis revealed that down-regulation of NANOG reduced cell proliferation, colony formation and migration ability of MCF-7 cells. Consistently, proliferation of breast cancer MDA-MB-231 cells was also significantly inhibited after the knockdown of NANOG expression. Interestingly, we found that the expression levels of cyclinD1 and c-myc were markedly down-regulated and the cell cycle were blocked at the G0/G1 phases after the knockdown of NANOG, while the expression of cyclinE and signal transducers and activators of transcription3 (STAT3) remained unaffected. In addition, the expression of NANOG and cyclinD1 can be rescued after the transfection of pcDNA3.1 (-)-NANOG expression vector into the three clones. Finally, our chromatin immunoprecipitation (ChIP) experiment showed that NANOG protein can bind to the promoter region of cyclinD1 and regulate cells cycle. Taken together, our findings may not only establish a molecular basis for the role of NANOG in modulating cell cycle progression of breast cancer cells but also suggest a potential target for the treatment of at least some subtypes of breast cancer.

Synergistic effect of SCF and G-CSF on stem-like properties in prostate cancer cell lines

Bone marrow metastases are formed in the late phases of prostate cancer disease. Stem cell factor (SCF) and granulocyte colony-stimulating factor (G-CSF) are present in the microenvironment of the bone marrow and play a vital role in cell biology therein. The present study was to investigate the influence of SCF and G-CSF on stem-like properties in prostate cancer cell lines. Upon stimulation with SCF or G-CSF, higher levels of CD117, ABCG2, and CD44 were observed in PC-3 and DU145 cells examined by flow cytometry. Simultaneously, the expressions of Oct3/4 and Nanog were upregulated. Moreover, quantitative real-time PCR verified that the increased Nanog under the stimulations was mostly derived from NANOGP8. In parallel with the increasing expressions of these proteins, higher colony and sphere formation efficiencies were seen in these cells in response to the cytokine stimulations. Furthermore, a synergistic effect of SCF and G-CSF on colony and sphere formations and ABCG2 expression was disclosed. Our results indicate a favorable bone marrow niche for prostate cancer cells where higher levels of cell stemness are maintained at least partly by the cytokines SCF and G-CSF.

Understanding cancer stem cell heterogeneity and plasticity

Heterogeneity is an omnipresent feature of mammalian cells in vitro and in vivo. It has been recently realized that even mouse and human embryonic stem cells under the best culture conditions are heterogeneous containing pluripotent as well as partially committed cells. Somatic stem cells in adult organs are also heterogeneous, containing many subpopulations of self-renewing cells with distinct regenerative capacity. The differentiated progeny of adult stem cells also retain significant developmental plasticity that can be induced by a wide variety of experimental approaches. Like normal stem cells, recent data suggest that cancer stem cells (CSCs) similarly display significant phenotypic and functional heterogeneity, and that the CSC progeny can manifest diverse plasticity. Here, I discuss CSC heterogeneity and plasticity in the context of tumor development and progression, and by comparing with normal stem cell development. Appreciation of cancer cell plasticity entails a revision to the earlier concept that only the tumorigenic subset in the tumor needs to be targeted. By understanding the interrelationship between CSCs and their differentiated progeny, we can hope to develop better therapeutic regimens that can prevent the emergence of tumor cell variants that are able to found a new tumor and distant metastases.

CD24(+) liver tumor-initiating cells drive self-renewal and tumor initiation through STAT3-mediated NANOG regulation

Tumor-initiating cells (T-ICs) are a subpopulation of chemoresistant tumor cells that have been shown to cause tumor recurrence upon chemotherapy. Identification of T-ICs and their related pathways are therefore priorities for the development of new therapeutic paradigms. We established chemoresistant hepatocellular carcinoma (HCC) xenograft tumors in immunocompromised mice in which an enriched T-IC population was capable of tumor initiation and self-renewal. With this model, we found CD24 to be upregulated in residual chemoresistant tumors when compared with bulk tumor upon cisplatin treatment. CD24(+) HCC cells were found to be critical for the maintenance, self-renewal, differentiation, and metastasis of tumors and to significantly impact patients' clinical outcome. With a lentiviral-based knockdown approach, CD24 was found to be a functional liver T-IC marker that drives T-IC genesis through STAT3-mediated NANOG regulation. Our findings point to a CD24 cascade in liver T-ICs that may provide an attractive therapeutic target for HCC patients.

Homeobox genes in obsessive-compulsive disorder

BACKGROUND

Despite evidence that obsessive-compulsive disorder (OCD) is a familial neuropsychiatric condition, progress aimed at identifying genetic determinants of the disorder has been slow. The OCD Collaborative Genetics Study (OCGS) has identified several OCD susceptibility loci through linkage analysis.

METHODS

In this study we investigate two regions on chromosomes 15q and 1q by first refining the linkage region using additional short tandem repeat polymorphic (STRP) markers. We then performed association analysis on single nucleotide polymorphisms (SNP) genotyped (markers placed every 2-4 kb) in the linkage regions in the OCGS sample of 376 rigorously phenotyped affected families.

RESULTS

Three SNPs are most strongly associated with OCD: rs11854486 (P = 0.00005 [0.046 after adjustment for multiple tests]; genetic relative risk (GRR) = 11.1 homozygous and 1.6 heterozygous) and rs4625687 [P = 0.00007 (after adjustment = 0.06); GRR = 2.4] on 15q; and rs4387163 (P = 0.0002 (after adjustment = 0.08); GRR = 1.97) on 1q. The first SNP is adjacent to NANOGP8, the second SNP is in MEIS2, and the third is 150 kb between PBX1 and LMX1A.

CONCLUSIONS

All the genes implicated by association signals are homeobox genes and are intimately involved in neurodevelopment. PBX1 and MEIS2 exert their effects by the formation of a heterodimeric complex, which is involved in development of the striatum, a brain region involved in the pathophysiology of OCD. NANOGP8 is a retrogene of NANOG, a homeobox transcription factor known to be involved in regulation of neuronal development. These findings need replication; but support the hypothesis that genes involved in striatal development are implicated in the pathogenesis of OCD.

Prostate cancer cell lines under hypoxia exhibit greater stem-like properties

Hypoxia is an important environmental change in many cancers. Hypoxic niches can be occupied by cancer stem/progenitor-like cells that are associated with tumor progression and resistance to radiotherapy and chemotherapy. However, it has not yet been fully elucidated how hypoxia influences the stem-like properties of prostate cancer cells. In this report, we investigated the effects of hypoxia on human prostate cancer cell lines, PC-3 and DU145. In comparison to normoxia (20% O₂), 7% O₂ induced higher expressions of HIF-1α and HIF-2α, which were associated with upregulation of Oct3/4 and Nanog; 1% O₂ induced even greater levels of these factors. The upregulated NANOG mRNA expression in hypoxia was confirmed to be predominantly retrogene NANOGP8. Similar growth rates were observed for cells cultivated under hypoxic and normoxic conditions for 48 hours; however, the colony formation assay revealed that 48 hours of hypoxic pretreatment resulted in the formation of more colonies. Treatment with 1% O₂ also extended the G₀/G₁ stage, resulting in more side population cells, and induced CD44 and ABCG2 expressions. Hypoxia also increased the number of cells positive for ABCG2 expression, which were predominantly found to be CD44^bright cells. Correspondingly, the sorted CD44^bright cells expressed higher levels of ABCG2, Oct3/4, and Nanog than CD44^dim cells, and hypoxic pretreatment significantly increased the expressions of these factors. CD44^bright cells under normoxia formed significantly more colonies and spheres compared with the CD44^dim cells, and hypoxic pretreatment even increased this effect. Our data indicate that prostate cancer cells under hypoxia possess greater stem-like properties.

3-O-methylfunicone, from Penicillium pinophilum, is a selective inhibitor of breast cancer stem cells

OBJECTIVES

Cancer stem cells make up a subpopulation of cells within tumours that drive tumour initiation, growth and recurrence. They are resistant to many current types of cancer treatment, causing failure of such therapeutic approaches, including chemotherapy and radiotherapy. In the study described here, anti-proliferative effects of 3-O-methylfunicone (OMF), a metabolite from Penicillium pinophilum, were investigated on human breast cancer MCF-7 cells and cancer stem cells selected as mammospheres derived from MCF-7s.

MATERIALS AND METHODS

Stemness markers were analysed on isolated mammospheres showing positive expression of CD24, CD29, CD44, CD133, CD184 and CD338. Cell proliferation and apoptosis were analysed by flow cytometry and RT-PCR. Cell colony formation assays were performed to evaluate colony formation of mammospheres.

RESULTS AND CONCLUSION

OMF treatment affected both MCF-7 and mammosphere growth, inducing apoptosis. In addition, OMF strongly reduced stemness markers and survivin, hTERT and Nanog-1 gene expression. Growth of colonies in soft-agar was significantly affected by OMF treatment, too. Lastly, we tested ability of MCF-7 cells to form mammospheres after treatment with OMF or cisplatin, demonstrating that OMF treatment resulted in drastic reduction in number of mammospheres. These results introduce OMF as an effective molecule in suppressing breast cancer stem cells.

Differential expression of nanog1 and nanogp8 in colon cancer cells

Nanog, a homeodomain transcription factor, is an essential regulator for promotion of self-renewal of embryonic stem cells and inhibition of their differentiation. It has been demonstrated that nanog1 as well as nanogp8, a retrogene of nanog1, is preferentially expressed in advanced stages of several types of cancer, suggesting their involvement during cancer progression. Here, we investigated the expression of Nanog in well-characterized colon cancer cell lines. Expression of Nanog was detectable in 5 (HCT116, HT29, RKO, SW48, SW620) out of seven cell lines examined. RNA expression analyses of nanog1 and nanogp8 indicated that, while nanog1 was a major form in SW620 as well as in teratoma cells Tera-2, nanogp8 was preferentially expressed in HT29 and HCT116. In accordance with this, shRNA-mediated knockdown of nanog1 caused the reduction of Nanog in SW620 but not in HT29. Inhibition of Nanog in SW620 cells negatively affected cell proliferation and tumor formation in mouse xenograft. Biochemical subcellular fractionation and immunostaining analyses revealed predominant localization of Nanog in cytoplasm in SW620 and HT29, while it was mainly localized in nucleus in Tera-2. Our data indicate that nanog1 and nanogp8 are differentially expressed in colon cancer cells, and suggest that their expression contributes to proliferation of colon cancer cells.

Snail1 induces epithelial-to-mesenchymal transition and tumor initiating stem cell characteristics

Background

Tumor initiating stem-like cells (TISCs) are a subset of neoplastic cells that possess distinct survival mechanisms and self-renewal characteristics crucial for tumor maintenance and propagation. The induction of epithelial-mesenchymal-transition (EMT) by TGFβ has been recently linked to the acquisition of TISC characteristics in breast cancer. In HCC, a TISC and EMT phenotype correlates with a worse prognosis. In this work, our aim is to elucidate the underlying mechanism by which cells acquire tumor initiating characteristics after EMT.

Methods

Gene and protein expression assays and Nanog-promoter luciferase reporter were utilized in epithelial and mesenchymal phenotype liver cancer cell lines. EMT was analyzed with migration/invasion assays. TISC characteristics were analyzed with tumor-sphere self-renewal and chemotherapy resistance assays. In vivo tumor assay was performed to investigate the role of Snail1 in tumor initiation.

Conclusion

TGFβ induced EMT in epithelial cells through the up-regulation of Snail1 in Smad-dependent signaling. Mesenchymal liver cancer post-EMT demonstrates TISC characteristics such as tumor-sphere formation but are not resistant to cytotoxic therapy. The inhibition of Snail1 in mesenchymal cells results in decreased Nanog promoter luciferase activity and loss of self-renewal characteristics in vitro. These changes confirm the direct role of Snail1 in some TISC traits. In vivo, the down-regulation of Snail1 reduced tumor growth but was not sufficient to eliminate tumor initiation. In summary, TGFβ induces EMT and TISC characteristics through Snail1 and Nanog up-regulation. In mesenchymal cells post-EMT, Snail1 directly regulates Nanog expression, and loss of Snail1 regulates tumor growth without affecting tumor initiation.

Drug-tolerant cancer cells show reduced tumor-initiating capacity: depletion of CD44 cells and evidence for epigenetic mechanisms

Cancer stem cells (CSCs) possess high tumor-initiating capacity and have been reported to be resistant to therapeutics. Vice versa, therapy-resistant cancer cells seem to manifest CSC phenotypes and properties. It has been generally assumed that drug-resistant cancer cells may all be CSCs although the generality of this assumption is unknown. Here, we chronically treated Du145 prostate cancer cells with etoposide, paclitaxel and some experimental drugs (i.e., staurosporine and 2 paclitaxel analogs), which led to populations of drug-tolerant cells (DTCs). Surprisingly, these DTCs, when implanted either subcutaneously or orthotopically into NOD/SCID mice, exhibited much reduced tumorigenicity or were even non-tumorigenic. Drug-tolerant DLD1 colon cancer cells selected by a similar chronic selection protocol also displayed reduced tumorigenicity whereas drug-tolerant UC14 bladder cancer cells demonstrated either increased or decreased tumor-regenerating capacity. Drug-tolerant Du145 cells demonstrated low proliferative and clonogenic potential and were virtually devoid of CD44⁺ cells. Prospective knockdown of CD44 in Du145 cells inhibited cell proliferation and tumor regeneration, whereas restoration of CD44 expression in drug-tolerant Du145 cells increased cell proliferation and partially increased tumorigenicity. Interestingly, drug-tolerant Du145 cells showed both increases and decreases in many “stemness” genes. Finally, evidence was provided that chronic drug exposure generated DTCs via epigenetic mechanisms involving molecules such as CD44 and KDM5A. Our results thus reveal that 1) not all DTCs are necessarily CSCs; 2) conventional chemotherapeutic drugs such as taxol and etoposide may directly target CD44⁺ tumor-initiating cells; and 3) DTCs generated via chronic drug selection involve epigenetic mechanisms.

Hypoxia-dependent inhibition of tumor cell susceptibility to CTL-mediated lysis involves NANOG induction in target cells

Hypoxia is a major feature of the solid tumor microenvironment and is known to be associated with tumor progression and poor clinical outcome. Recently, we reported that hypoxia protects human non-small cell lung tumor cells from specific lysis by stabilizing hypoxia-inducible factor-1α and inducing STAT3 phosphorylation. In this study, we show that NANOG, a transcription factor associated with stem cell self renewal, is a new mediator of hypoxia-induced resistance to specific lysis. Our data indicate that under hypoxic conditions, NANOG is induced at both transcriptional and translational levels. Knockdown of the NANOG gene in hypoxic tumor cells is able to significantly attenuate hypoxia-induced tumor resistance to CTL-dependent killing. Such knockdown correlates with an increase of target cell death and an inhibition of hypoxia-induced delay of DNA replication in these cells. Interestingly, NANOG depletion results in inhibition of STAT3 phosphorylation and nuclear translocation. To our knowledge, this study is the first to show that hypoxia-induced NANOG plays a critical role in tumor cell response to hypoxia and promotes tumor cell resistance to Ag-specific lysis.

Inhibition of sonic hedgehog pathway and pluripotency maintaining factors regulate human pancreatic cancer stem cell characteristics

Activation of the sonic hedgehog (SHh) pathway is required for the growth of numerous tissues and organs and recent evidence indicates that this pathway is often recruited to stimulate growth of cancer stem cells (CSCs) and to orchestrate the reprogramming of cancer cells via epithelial mesenchymal transition (EMT). The objectives of this study were to examine the molecular mechanisms by which (-)-epigallocatechin-3-gallate (EGCG), an active compound in green tea, inhibits self-renewal capacity of pancreatic CSCs and synergizes with quercetin, a major polyphenol and flavonoid commonly detected in many fruits and vegetables. Our data demonstrated that EGCG inhibited the expression of pluripotency maintaining transcription factors (Nanog, c-Myc and Oct-4) and self-renewal capacity of pancreatic CSCs. Inhibition of Nanog by shRNA enhanced the inhibitory effects of EGCG on self-renewal capacity of CSCs. EGCG inhibited cell proliferation and induced apoptosis by inhibiting the expression of Bcl-2 and XIAP and activating caspase-3. Interestingly, EGCG also inhibited the components of SHh pathway (smoothened, patched, Gli1 and Gli2) and Gli transcriptional activity. Furthermore, EGCG inhibited EMT by inhibiting the expression of Snail, Slug and ZEB1, and TCF/LEF transcriptional activity, which correlated with significantly reduced CSC's migration and invasion, suggesting the blockade of signaling involved in early metastasis. Furthermore, combination of quercetin with EGCG had synergistic inhibitory effects on self-renewal capacity of CSCs through attenuation of TCF/LEF and Gli activities. Since aberrant SHh signaling occurs in pancreatic tumorigenesis, therapeutics that target SHh pathway may improve the outcomes of patients with pancreatic cancer by targeting CSCs.