Oct4 is expressed in human gliomas and promotes colony formation in glioma cells

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.

Oct-3/4 promotes migration and invasion of glioblastoma cells

As a result of increased glioblastoma migration and invasion into normal brain parenchyma, treatment of local tumor recurrence following initial treatment in glioblastoma patients remains challenging. Recent studies have demonstrated increased Oct-3/4 expression, a self-renewal regulator in stem cells, in glioblastomas. However, little is known regarding the influence of Oct-3/4 in glioblastoma cell invasiveness. The present study established Oct-3/4-overexpressing glioblastoma cells, which were prepared from human glioblastoma patients, to assess migration, invasion, and mRNA expression profiles of integrins and matrix metalloproteinases (MMPs). Compared with control cells, Oct-3/4 expressing-glioblastoma cells exhibited increased migration and invasion in wound healing and Matrigel invasion assays. Oct-3/4 overexpression resulted in upregulated FAK and c-Src expression, which mediate integrin signals. Vinculin accumulated along the leading edges of Oct-3/4 expressing-glioblastoma cells and associated with membrane ruffles during cell migration. Oct-3/4 expressing-cells exhibited increased MMP-13 mRNA expression and MMP-13 knockdown by shRNA suppressed cell invasion into Matrigel and organotypic brain slices. These results suggested that Oct-3/4 enhanced degradation of surrounding extracellular matrix by increasing MMP-13 expression and altering integrin signaling. Therefore, Oct-3/4 might contribute to tumor promoting activity in glioblastomas.

Stemness of the CT-2A Immunocompetent Mouse Brain Tumor Model: Characterization In Vitro

Evidence has pointed to brain tumor stem cells (BTSC) as culprits behind human high-grade glioma (hHGG) resistance to standard therapy. Pre-clinical rodent models are the mainstay for testing of new therapeutic strategies. The typical model involves the intracranial injection of human glioma cells into immunocompromised hosts, hindering the evaluation of tumor-host responses and resulting in non-infiltrative tumors. The CT-2A model is an immunocompetent mouse model with potential to overcome these disadvantages. In this study, we confirmed the highly infiltrative nature of intracranial CT-2A tumors and optimized reproducible injection parameters. We then generated neurospheres and established, for the first time, the stemness of this model. CT-2A expression of the BTSC marker, CD133, increased from 2% in monolayer cells to 31% in fully-formed neurospheres. Investigation of three stem cell markers (Oct4, Nanog and Nestin) revealed a distinct stemness signature with monolayer cells expressing Oct4 and Nestin (no Nanog), and neurospheres expressing all three. Additionally, CT-2A cells were more proliferative and invasive than U87 cells, while CT-2A neurospheres were significantly more proliferative and invasive than either monolayer cells in vitro. Taken together, our results show that this model is a valuable tool for pre-clinical testing of novel therapeutics against hHGG and also affords the opportunity for investigation of BTSC in an immunocompetent setting.

Coexpression of stemness factors Oct4 and Nanog predict liver resection

BACKGROUND

Oct4 and Nanog are two major transcription factors related to the stem cell self-renewal and differentiation. The aim of this study was to evaluate the correlation between these two stemness markers with recurrence, metastasis, and prognosis of hepatocellular carcinoma (HCC).

METHODS

Expression of Oct4 and Nanog was evaluated by immunohistochemistry in a random cohort of 228 HCC patients (cohort A), predominantly hepatitis B related, and validated in another independent cohort of 95 patients (cohort B). Survival analysis was performed by univariate and multivariate analyses. Oct4 and Nanog expression levels in 5 HCC cell lines with different metastatic potential were detected by Western blot assay and quantitative real-time PCR assay.

RESULTS

In tissue microarrays, coexpression of Oct4 and Nanog was dramatically associated with big tumor size (P = .001) and vascular invasion (P = .02) and was an independent predictor of postoperative recurrence (hazard ratio [HR] = 1.57, 95 % confidence interval [95 % CI] 1.21-2.04, P = .01) and poor prognosis (HR = 2.20, 95 % CI 1.71-2.88, P < .001). This association was further validated in patients in cohort B. Importantly, this correlation remained significant in patients with early-stage HCC or alpha-fetoprotein (AFP) negative HCC. In addition, expression of Oct4 and Nanog increased in a concordant manner with the increase of metastatic potential in human HCC cell lines.

CONCLUSIONS

Coexpression of stemness markers Oct4 and Nanog in HCC indicated the aggressive tumor behaviors and predicted a worse clinical outcome, which may be a useful biomarker to identify patients at high risk of postoperative recurrence.

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.

Stable expression of FoxA1 promotes pluripotent P19 embryonal carcinoma cells to be neural stem-like cells

FoxA1 belongs to the fork head/winged-helix transcription factor family and participates in stimulating neuronal differentiation of pluripotent stem cells at early stages. To explore the biological roles of FoxA1 during this process, the stable expression of a GFP-FoxA1 fusion protein was established in P19 pluripotent embryonal carcinoma cells. Although they still express pluripotency-related transcription factors such as Oct4, Nanog, and Sox2, the generated P19 GFPFoxA1 cells exhibited a decreased activity of alkaline phosphatase and an increased expression of SSEA-3 compared with P19 cells. Elevated levels of nestin expression and prominin-1+ populations were observed in P19 GFPFoxA1 cells, implicating that the stable expression of FoxA1 promoted P19 cells to gain partial characteristics of neural stem cells. Furthermore, the promoter of nestin was confirmed to be bound and activated by FoxA1 directly. The expression of neuron-specific marker tubulin betaIII also existed in P19 GFPFoxA1 cells. P19 GFPFoxA1 cells showed an earlier onset of differentiation during RA-induced neuronal differentiation, evidenced by a more rapid change on the Nanog decrease and the tubulin betaIII increase. Thus, overexpression of FoxA1 alone may promote pluripotent P19 cells to become neural stem-like cells.

Inhibition of cancer stem cell-like properties and reduced chemoradioresistance of glioblastoma using microRNA145 with cationic polyurethane-short branch PEI

Glioblastomas (GBMs) are the most common primary brain tumors with poor prognosis. CD133 has been considered a putative marker of cancer stem cells (CSCs) in malignant cancers, including GBMs. MicroRNAs (miRNAs), highly conserved small RNA molecules, may target oncogenes and have potential as a therapeutic strategy against cancer. However, the role of miRNAs in GBM-associated CSCs remains mostly unclear. In this study, our miRNA/mRNA-microarray and RT-PCR analysis showed that the expression of miR145 (a tumor-suppressive miRNA) is inversely correlated with the levels of Oct4 and Sox2 in GBM-CD133(+) cells and malignant glioma specimens. We demonstrated that miR145 negatively regulates GBM tumorigenesis by targeting Oct4 and Sox2 in GBM-CD133(+). Using polyurethane-short branch polyethylenimine (PU-PEI) as a therapeutic-delivery vehicle, PU-PEI-mediated miR145 delivery to GBM-CD133(+) significantly inhibited their tumorigenic and CSC-like abilities and facilitated their differentiation into CD133(-)-non-CSCs. Furthermore, PU-PEI-miR145-treated GBM-CD133(+) effectively suppressed the expression of drug-resistance and anti-apoptotic genes and increased the sensitivity of the cells to radiation and temozolomide. Finally, the in vivo delivery of PU-PEI-miR145 alone significantly suppressed tumorigenesis with stemness, and synergistically improved the survival rate when used in combination with radiotherapy and temozolomide in orthotopic GBM-CD133(+)-transplanted immunocompromised mice. Therefore, PU-PEI-miR145 is a novel therapeutic approach for malignant brain tumors.

Glioma-initiating cells retain their tumorigenicity through integration of the Sox axis and Oct4 protein

Although the concept of cancer stem cells or cancer-initiating cells had created a new paradigm for the treatment of malignant tumors, it remains unclear how cancer-initiating cells can be eradicated. We have previously reported that the transforming growth factor-β (TGF-β)-Sox4-Sox2 pathway is essential for glioma-initiating cells to retain their stemness, and inhibition of TGF-β signaling may lead to differentiation of glioma-initiating cells (Ikushima, H., Todo, T., Ino, Y., Takahashi, M., Miyazawa, K., and Miyazono, K. (2009) Cell Stem Cell 5, 504-514). Here we demonstrate that Oct4 plays essential roles in retention of the stemness properties of glioma-initiating cells through positive regulation of Sox2 expression. We also show that, in glioma-initiating cells, Oct4 is associated with Sox4 and that Oct4-Sox4 complexes cooperatively activate the enhancer activity of the SOX2 gene. In contrast, in fetal neural progenitor cells, Sox2 expression is enhanced by transcriptional complex containing Sox2 protein itself, and this self-reinforcing loop of Sox2 appears to be disrupted in glioma-initiating cells, suggesting that Sox2 expression in glioma-initiating cells is differently regulated from that in neural progenitor cells. Our findings reveal differences between glioma-initiating cells and fetal neural progenitor cells and may open the way to depriving glioma-initiating cells of tumorigenic activity without affecting normal tissues.

Prognostic value of OCT4 in primary intracranial germinoma: a single institute analysis of 31 cases

OCT4 expresses variably in primary intracranial germinomas. In this study, we tested our hypothesis that such variation of OCT4 is predictive of outcome in primary intracranial germinomas. Thirty-one histologically identified CNS germinoma patients were enrolled in our study. We collected medical data, immunohistochemically evaluated the OCT4 expression level, and followed up all patients from April 2001 to May 2010. We found that 7 of the 31 patients expressed OCT4 weakly, 11 expressed OCT4 moderately, and 13 expressed OCT4 strongly. No significant correlation between the OCT4 expression level and clinicopathological characteristics was observed. WV-CS combined treatment modality showed a better 5-year progression-free survival (PFS) rate than other treatment modalities and a low expression level of OCT4 showed a significantly better 5-year PFS. In both the WV-CS combined treatment modality and other treatments modality group, patients received a better 5-year PFS and had a lower level of OCT4 expression. As a result, we suggest OCT4 as a probable prognostic marker for intracranial germinoma.

Identification of a SOX2-dependent subset of tumor- and sphere-forming glioblastoma cells with a distinct tyrosine kinase inhibitor sensitivity profile

Putative cancer stem cells have been identified in glioblastomas and are associated with radio- and chemo-resistance. Further knowledge about these cells is thus highly warranted for the development of better glioblastoma therapies.

Gene expression analyses of 11 high-grade glioma cultures identified 2 subsets, designated type A and type B cultures. The type A cultures displayed high expression of CXCR4, SOX2, EAAT1, and GFAP and low expression of CNP, PDGFRB, CXCL12, and extracellular matrix proteins. Clinical significance of the 2 types was indicated by the expression of type A– and type B–defining genes in different clinical glioblastoma samples. Classification of glioblastomas with type A– and type B–defining genes generated 2 groups of tumors composed predominantly of the classical, neural, and/or proneural subsets and the mesenchymal subset, respectively. Furthermore, tumors with EGFR mutations were enriched in the group of type A samples. Type A cultures possessed a higher capacity to form xenograft tumors and neurospheres and displayed low or no sensitivity to monotreatment with PDGF- and IGF-1–receptor inhibitors but were efficiently growth inhibited by combination treatment with low doses of these 2 inhibitors. Furthermore, siRNA-induced downregulation of SOX2 reduced sphere formation of type A cultures, decreased expression of type A–defining genes, and conferred sensitivity to monotreatment with PDGF- and IGF-1–receptor inhibitors.

The present study thus describes a tumor- and neurosphere-forming SOX2-dependent subset of glioblastoma cultures characterized by a gene expression signature similar to that of the recently described classical, proneural, and/or neural subsets of glioblastoma. The findings that resistance to PDGF- and IGF-1–receptor inhibitors is related to SOX2 expression and can be overcome by combination treatment should be considered in ongoing efforts to develop novel stem cell–targeting therapies.

Downregulation of GRIM-19 promotes growth and migration of human glioma cells

It has become increasingly clear that there are notable parallels between normal development and tumorigenesis. Glioma is a classic model that links between tumorigenesis and development. We evaluated the expression of GRIM-19, a novel gene essential for normal development, in various grades of gliomas and several human glioma cell lines. We showed that GRIM-19 mRNA and protein expression were markedly lower in gliomas than in control brain tissues and negatively correlated with the malignancy of gliomas. Downregulation of GRIM-19 in glioma cells significantly enhanced cell proliferation and migration, whereas overexpression of GRIM-19 showed the opposite effects. We also showed that the activation of signal transducer and activator of transcription 3 (STAT3) and the expression of many STAT3-dependent genes were regulated by the expression of GRIM-19. In addition, GRIM-19 exerted its role probably through the non-STAT3 signaling pathway. Collectively, our data suggest that most gliomas expressed GRIM-19 at low levels, which may play a major role in tumorigenesis in the brain.

HESRG: a novel biomarker for intracranial germinoma and embryonal carcinoma

The novel stem cell-related gene, HESRG, was first identified by our group, and its expression pattern in human tumors remains unknown. In this study, we used RT-PCR to systematically investigate the expression of HESRG in various types of intracranial tumors and found that HESRG was expressed only in germinoma and embryonal carcinoma, but hardly at all in other types of brain tumors. Real-time PCR results further confirmed this expression pattern. Subsequently, we tested 134 intracranial non-germ cell tumors and 64 intracranial germ cell tumors by immunohistochemistry. Our results showed that HESRG was expressed strongly and diffusively in the nuclei of tumor cells in intracranial germinoma and embryonal carcinoma as well as in human embryonic stem cells. No positive staining signal was observed in any other type of intracranial tumors. In germinomas, 25 of 31 showed intensive (3+) expression, four cases showed moderate (2+) immunostaining and the remaining 2 cases showed weak (1+) immunostaining. In embryonal carcinoma, 6 of 9 showed intensive (3+) immunostaining and 3 of 9 showed moderate (2+) immunostaining. These results suggest that HESRG is a novel, sensitive and specific biomarker for intracranial germinoma and embryonal carcinoma.

Extracellular ATP reduces tumor sphere growth and cancer stem cell population in glioblastoma cells

Glioblastoma is the most aggressive tumor in the CNS and is characterized by having a cancer stem cell (CSC) subpopulation essential for tumor survival. The purinergic system plays an important role in glioma growth, since adenosine triphosphate (ATP) can induce proliferation of glioma cells, and alteration in extracellular ATP degradation by the use of exogenous nucleotidases dramatically alters the size of gliomas in rats. The aim of this work was to characterize the effect of the purinergic system on glioma CSCs. Human U87 glioma cultures presented tumor spheres that express the markers of glioma cancer stem cells CD133, Oct-4, and Nanog. Messenger RNA of several purinergic receptors were differently expressed in spheres when compared to a cell monolayer not containing spheres. Treatment of human gliomas U87 or U343 as well as rat C6 gliomas with 100 μM of ATP reduced the number of tumor spheres when grown in neural stem cell medium supplemented with epidermal growth factor and basic fibroblast growth factor. Moreover, ATP caused a decline in the number of spheres observed in culture in a dose-dependent manner. ATP also reduces the expression of Nanog, as determined by flow cytometry, as well as CD133 and Oct-4, as analyzed by flow cytometry and RT-PCR in U87 cells. The differential expression of purinergic receptor in tumor spheres when compared to adherent cells and the effect of ATP in reducing tumor spheres suggest that the purinergic system affects CSC biology and that ATP may be a potential agonist for differentiation therapy.

Differential expression of Oct4 in HPV-positive and HPV-negative cervical cancer cells is not regulated by DNA methyltransferase 3A

The colony-forming ability of cervical cancer is affected by many factors. Oct4, an important transcription factor, is highly expressed in several tumors and promotes the colony-forming ability of cancer cells. Thus, it is considered a potential target for the treatment of cancer. However, we know little about the expression level of Oct4 and its epigenetic regulatory mechanism in cervical cancer cells. In this study, we are the first to observe that human papillomavirus (HPV)-positive cervical cancer cell lines (HeLa, Caski) have a stronger colony-forming ability than HPV-negative cervical cancer cell lines (C-33A). Moreover, the expression level of Oct4 in both HeLa and Caski cells was also higher than that in C-33A cells. We then confirmed that there was a negative correlation between the expression of Oct4 and DNMT3A in these three types of cervical cancer cells, whereas DNA methyltransferase 1 and 3B had no differences among the cell lines. However, after DNA methylation in both key regulatory regions of the Oct4 gene and the genomic levels were analyzed, we found that DNA methyltransferase 3A could neither regulate the expression of Oct4 nor affect the whole level of genomic DNA methylation. These results suggest three points: (1) Oct4 might be treated as a new target for the treatment of cervical cancer, (2) we could not inhibit the expression of Oct4 by DNA demethylation, and (3) HPV virus might initiate cervical carcinogenesis by upregulation of Oct4 expression.

Activation of neural and pluripotent stem cell signatures correlates with increased malignancy in human glioma

The presence of stem cell characteristics in glioma cells raises the possibility that mechanisms promoting the maintenance and self-renewal of tissue specific stem cells have a similar function in tumor cells. Here we characterized human gliomas of various malignancy grades for the expression of stem cell regulatory proteins. We show that cells in high grade glioma co-express an array of markers defining neural stem cells (NSCs) and that these proteins can fulfill similar functions in tumor cells as in NSCs. However, in contrast to NSCs glioma cells co-express neural proteins together with pluripotent stem cell markers, including the transcription factors Oct4, Sox2, Nanog and Klf4. In line with this finding, in high grade gliomas mesodermal- and endodermal-specific transcription factors were detected together with neural proteins, a combination of lineage markers not normally present in the central nervous system. Persistent presence of pluripotent stem cell traits could only be detected in solid tumors, and observations based on in vitro studies and xenograft transplantations in mice imply that this presence is dependent on the combined activity of intrinsic and extrinsic regulatory cues. Together these results demonstrate a general deregulated expression of neural and pluripotent stem cell traits in malignant human gliomas, and indicate that stem cell regulatory factors may provide significant targets for therapeutic strategies.

Expression of OCT4 pseudogenes in human tumours: lessons from glioma and breast carcinoma

The POU family transcription factor OCT4 is required for maintaining the pluripotency of embryonic stem cells and for generating induced pluripotent stem cells. Although OCT4 is clearly shown to be expressed in some pluripotent germ cell tumours, its expression in human somatic tumours remains controversial. Some studies have shown that OCT4 is expressed in adult stem cells, somatic cancers and, further, cancer stem cells, while other studies failed to make such an observation. It is thus important to ascertain whether OCT4 is expressed in human somatic tumours. By using RT-PCR and sequencing analysis, three OCT4 pseudogenes, viz. OCT4-pg1, OCT4-pg3 and OCT4-pg4 but excluding the OCT4 gene, were found to be expressed in two types of human solid tumours, glioma and breast carcinoma, from which cancer stem cells had earlier been isolated. The protein expression of these pseudogenes was further demonstrated by immunochemistry and western blotting. Along with this, it was shown that OCT4 pseudogenes lacked OCT4-like activities. The expression of OCT4 splicing variant and various pseudogenes at both the mRNA and protein levels in human somatic tumours might call into question the reliability of the results regarding OCT4 expression and function in tumourigenesis. Hence, in investigations of OCT4 expression in cancers and stem cells, different approaches with appropriate controls would be desirable to exclude possibility of false-positive results.

Novel Perspectives on p53 Function in Neural Stem Cells and Brain Tumors

Malignant glioma is the most common brain tumor in adults and is associated with a very poor prognosis. Mutations in the p53 tumor suppressor gene are frequently detected in gliomas. p53 is well-known for its ability to induce cell cycle arrest, apoptosis, senescence, or differentiation following cellular stress. That the guardian of the genome also controls stem cell self-renewal and suppresses pluripotency adds a novel level of complexity to p53. Exactly how p53 works in order to prevent malignant transformation of cells in the central nervous system remains unclear, and despite being one of the most studied proteins, there is a need to acquire further knowledge about p53 in neural stem cells. Importantly, the characterization of glioma cells with stem-like properties, also known as brain tumor stem cells, has opened up for the development of novel targeted therapies. Here, we give an overview of what is currently known about p53 in brain tumors and neural stem cells. Specifically, we review the literature regarding transformation of adult neural stem cells and, we discuss how the loss of p53 and deregulation of growth factor signaling pathways, such as increased PDGF signaling, lead to brain tumor development. Reactivation of p53 in brain tumor stem cell populations in combination with current treatments for glioma should be further explored and may become a viable future therapeutic approach.

OCT4B1, a novel spliced variant of OCT4, is highly expressed in gastric cancer and acts as an antiapoptotic factor

The octamer-binding transcription factor 4 (OCT4) is involved in regulating pluripotency and self-renewal maintenance of embryonic stem cells. Recently, misexpression of OCT4 has been also reported in some adult stem as well as cancer cells; a finding which is still controversial. In addition to the previously described spliced variants of the gene (e.g., OCT4A and OCT4B), we have recently identified a novel variant of the gene, designated as OCT4-B1. In this study, we investigated a potential expression and function of OCT4B1 in a series of gastric cancer tissues and a gastric adenocarcinoma cell line, AGS. Using the Taqman real-time PCR approach, we have detected the expression of OCT4B1 in tumors with no or much lower expression in marginal samples of the same patients (p < 0.002). We have also analyzed the effects of OCT4B1 knock-down in AGS cell line treated with specific siRNA directed toward OCT4B1. Our data revealed that interfering with the expression of OCT4B1 caused profound changes in the morphology and cell cycle distribution of the cells. Furthermore, down-regulation of OCT4B1 significantly elevated the relative activity of caspase-3/caspase-7 and the rate of apoptosis in the cells (more than 30%). All together, our findings suggest that OCT4B1 has a potential role in tumorigenesis of gastric cancer and candidates the variant as a new tumor marker with potential value in diagnosis and treatment of gastric cancer.

A role for the Werner syndrome protein in epigenetic inactivation of the pluripotency factor Oct4

Werner syndrome (WS) is an autosomal recessive disorder, the hallmarks of which are premature aging and early onset of neoplastic diseases (Orren, 2006; Bohr, 2008). The gene, whose mutation underlies the WS phenotype, is called WRN. The protein encoded by the WRN gene, WRNp, has DNA helicase activity (Gray et al., 1997; Orren, 2006; Bohr, 2008; Opresko, 2008). Extensive evidence suggests that WRNp plays a role in DNA replication and DNA repair (Chen et al., 2003; Hickson, 2003; Orren, 2006; Turaga et al., 2007; Bohr, 2008). However, WRNp function is not yet fully understood. In this study, we show that WRNp is involved in de novo DNA methylation of the promoter of the Oct4 gene, which encodes a crucial stem cell transcription factor. We demonstrate that WRNp localizes to the Oct4 promoter during retinoic acid-induced differentiation of human pluripotent cells and associates with the de novo methyltransferase Dnmt3b in the chromatin of differentiating pluripotent cells. Depletion of WRNp does not affect demethylation of lysine 4 of the histone H3 at the Oct4 promoter, nor methylation of lysine 9 of H3, but it blocks the recruitment of Dnmt3b to the promoter and results in the reduced methylation of CpG sites within the Oct4 promoter. The lack of DNA methylation was associated with continued, albeit greatly reduced, Oct4 expression in WRN-deficient, retinoic acid-treated cells, which resulted in attenuated differentiation. The presented results reveal a novel function of WRNp and demonstrate that WRNp controls a key step in pluripotent stem cell differentiation.

Beta1,4-galactosyltransferase V regulates self-renewal of glioma-initiating cell

Glioma results from unregulated expansion of a self-renewing glioma-initiating cell population. The regulatory pathways which are essential for sustaining the self-renewal of glioma-initiating cells remain largely unknown. Cell surface N-linked oligosaccharides play functional roles in determining cell fate and are associated with glioma malignancy. Previously, we have reported that beta1,4-galactosyltransferase V (beta1,4GalT V) effectively galactosylates the GlcNAcbeta1-->6Man arm of the highly branched N-glycans and positively regulates glioma cell growth. Here, we show that decreasing the expression of beta1,4GalT V by RNA interference in glioma cells attenuated the formation of polylactosamine and inhibited the ability of tumor formation in vivo. Down-regulation of beta1,4GalT V depleted CD133-positive cells in glioma xenograft, and inhibited the self-renewal capacity and the tumorigenic potential of glioma-initiating cells. These data reveal a critical role of beta1,4GalT V in the self-renewal and tumorigenicity of glioma-initiating cells, and indicate that manipulating beta1,4GalT V expression may have therapeutic potential for the treatment of malignant glioma.

Upregulation of Oct-4 isoforms in pulmonary artery smooth muscle cells from patients with pulmonary arterial hypertension

Oct-4 is a transcription factor considered to be one of the defining pluripotency markers in embryonic stem cells. Its expression has also been demonstrated in adult stem cells, tumorigenic cells, and, most recently and controversially, in somatic cells. Oct-4 pseudogenes also contribute to carcinogenesis. Oct-4 may be involved in the excessive proliferation of pulmonary arterial smooth muscle cells (PASMC) in patients with idiopathic pulmonary arterial hypertension (IPAH), contributing to the pathogenesis of IPAH. In this study, we show that Oct-4 isoforms are upregulated in IPAH-PASMC. Human embryonic stem cells (H9 line) and human PASMC from normotensive subjects were used throughout the investigation as positive and negative controls. In addition to significant upregulation of Oct-4 in a population of IPAH-PASMC, HIF-2alpha, a hypoxia-inducible transcription factor that has been shown to bind to the Oct-4 promoter and induces its expression and transcriptional activity, was also increased. Interestingly, a substantial upregulation of Oct-4 isoforms and HIF-2alpha was also observed in normal PASMC exposed to chronic hypoxia. In conclusion, the data suggest that both Oct-4 isoforms are upregulated and potentially have a significant role in the development of vascular abnormalities associated with the pathogenesis of IPAH and in pulmonary hypertension triggered by chronic hypoxia.

Primary brain tumors, neural stem cell, and brain tumor cancer cells: where is the link?

The discovery of brain tumor-derived cells (BTSC) with the properties of stem cells has led to the formulation of the hypothesis that neural stem cells could be the cell of origin of primary brain tumors (PBT). In this review we present the most common molecular changes in PBT, define the criteria of identification of BTSC and discuss the similarities between the characteristics of these cells and those of the endogenous population of neural stem cells (NPCs) residing in germinal areas of the adult brain. Finally, we propose possible mechanisms of cancer initiation and progression and suggest a model of tumor initiation that includes intrinsic changes of resident NSC and potential changes in the microenvironment defining the niche where the NSC reside.

Cancer stem cell genomics: the quest for early markers of malignant progression

Biologically distinct populations of neoplastic stem cells have been identified in a variety of human cancers, in which they are associated with the initial steps of tumorigenesis. The intrinsic properties of self-renewal, clonogenicity and multipotency, along with a longer half-life within the body, may render normal adult stem cells more prone to accumulate genetic mutations leading to neoplastic transformation, as predicted by the cancer stem cell hypothesis. Tumor formation is also associated with the pluripotency of embryonic stem cells and may be induced as a consequence of complete dedifferentiation of mature cells, as recently reported for induced pluripotent stem cells. The tumor-initiating cell phenotype may result from genetic alterations affecting the expression of critical genes regulating typical stem cell processes such as self-renewal and pluripotency, in addition to genes determining stem cell senescence or longevity. Detailed genome-wide analysis of cancer stem cells and respective normal counterparts will help elucidate the cellular and molecular nature of tumors, providing fundamental information about the initial steps toward malignant transformation. Devising ways of detecting such genetic and epigenetic alterations and cell populations displaying them would allow medical interventions at the early phases of cancer development, thereby improving the chances of favorable clinical outcomes.

The hypoxic microenvironment maintains glioblastoma stem cells and promotes reprogramming towards a cancer stem cell phenotype

Glioblastomas are highly lethal cancers that contain cellular hierarchies with self-renewing cancer stem cells that can propagate tumors in secondary transplant assays. The potential significance of cancer stem cells in cancer biology has been demonstrated by studies showing contributions to therapeutic resistance, angiogenesis and tumor dispersal. We recently reported that physiologic oxygen levels differentially induce hypoxia inducible factor-2alpha (HIF2alpha) levels in cancer stem cells. HIF1alpha functioned in proliferation and survival of all cancer cells but also was activated in normal neural progenitors suggesting a potentially restricted therapeutic index while HIF2alpha was essential in only in cancer stem cells and was not expressed by normal neural progenitors demonstrating HIF2alpha is a cancer stem cell specific target. We now extend these studies to examine the role of hypoxia in regulating tumor cell plasticity. We find that hypoxia promotes the self-renewal capability of the stem and non-stem population as well as promoting a more stem-like phenotype in the non-stem population with increased neurosphere formation as well as upregulation of important stem cell factors, such as OCT4, NANOG and c-MYC. The importance of HIF2alpha was further supported as forced expression of non-degradable HIF2alpha induced a cancer stem cell marker and augmented the tumorigenic potential of the non-stem population. This novel finding may indicate a specific role of HIF2alpha in promoting glioma tumorigenesis. The unexpected plasticity of the non-stem glioma population and the stem-like phenotype emphasizes the importance of developing therapeutic strategies targeting the microenvironmental influence on the tumor in addition to cancer stem cells.

Cancer stem cells in brain tumor biology

Tumors are aberrant organ systems containing a complex interplay between the neoplastic compartment and recruited vascular, inflammatory, and stromal elements. Furthermore, most cancers display a hierarchy of differentiation states within the tumor cell population. Molecular signals that drive tumor formation and maintenance commonly overlap with those involved in normal development and wound responses--two processes in which normal stem cells function. It is therefore not surprising that cancers invoke stem cell programs that promote tumor malignancy. Stem-cell-like cancer cells (or cancer stem cells) need not be derived from normal stem cells but may be subjected to evolutionary pressures that select for the capacity to self-renew extensively or differentiate depending on conditions. Current cancer model systems may not fully recapitulate the cellular complexity of cancers, perhaps partially explaining the lack of power of these models in predicting clinical outcomes. New methods are enabling researchers to identify and characterize cancer stem cells. Our laboratory focuses on the roles of brain tumor stem cells in clinically relevant tumor biology, including therapeutic resistance, angiogenesis, and invasion/metastasis. We hope that these studies will translate into improved diagnostic, prognostic, and therapeutic approaches for these lethal cancers.

Turning cancer stem cells inside out: an exploration of glioma stem cell signaling pathways

Tumors are complex collections of heterogeneous cells with recruited vasculature, inflammatory cells, and stromal elements. Neoplastic cells frequently display a hierarchy in differentiation status. Recent studies suggest that brain tumors have a limited population of neoplastic cells called cancer stem cells with the capacity for sustained self-renewal and tumor propagation. Brain tumor stem cells contribute to therapeutic resistance and tumor angiogenesis. In this minireview, we summarize recent data regarding critical signaling pathways involved in brain tumor stem cell biology and discuss how targeting these molecules may contribute to the development of novel anti-glioma therapies.